New Findings On The Function of Mitofusin 2 in The Cellular Energy Metabolism (Biology)

Mitofusin 2 is a key protein in the regulation of the physiology of mitochondria—cellular organelles that produce energy—involved in several neurodegenerative and cardiovascular diseases, as well as in cancer. Now, a study published in the journal EMBO Reports reveals that the regulation of the bioenergetic activity in the mitochondria requires mitofusin 2 to be found in the endoplasmic reticulum, a system built by a complex network of membranes in the cell cytoplasm.

The study is led by the lecturer Francesc Soriano, from the Faculty of Biology and the Institute of Neurosciences (UBNeuro) of the UB. Other co-authors of the paper are the experts Ofelia M. Martínez and Francesc Villarroya, from the Faculty of Biology and the Institute of Biomedicine (IBUB) of the UB, and Manuel Reina, from the same faculty, among others.

Mitofusin 2: A bridge between cell organelles

Mitofusin 2 (Mfn2) is a protein in the external membrane of the mitochondria with a distinguished role in several physiological processes: mitochondrial dynamics, energy metabolism, embryo development, cell death, etc. This essential protein in the morphology and function of mitochondria is involved in several pathologies related to dysfunctions in the production of mitochondrial energy. Therefore, understanding how Mfn2 regulates the mitochondrial bioenergy could serve to design new therapeutic strategies to work on neurodegenerative diseases in which the functionality of this protein is altered.

“Cells have a series of small specialized structures—cell organelles—that are not independent entities, but they interact, and this helps to regulate their function”, notes Professor Francesc Soriano, from the Department of Cell Biology, Physiology and Immunology. “Specifically, the Mfn2 has a mainly mitochondrial localization, but a small portion of the protein is also in the endoplasmic reticulum. In this location, Mfn2 interacts with the mitochondrial Mfn2 and Mfn1 proteins and establishes a bridge between both cell organelles”.

In the study, the team confirmed that the problems in the mitochondrial bioenergy in cells with Mfn2 deficiency can be solved with the expression of an artificial Mfn2 protein exclusively localized in the endoplasmic reticulum. “The bioenergetic physiology is restored in the cell, since it allows the establishing of the contacts between those two organelles, so it favors the journey of the calcium from the endoplasmic reticulum to the mitochondria that activates several enzymes involved in the generation of mitochondrial energy”.

Specifically, the team could reverse the defects in the neurite growth in neurons with Mfn2 deficiency thanks to the expression of an artificial Mfn2 protein that joins the endoplasmic reticulum and mitochondria. The study is a first proof of concept of new therapeutic strategies based on the restoration of cellular contacts between the endoplasmic reticulum and the mitochondria in the physiopathology of diseases associated with the Mfn2 protein.

Featured image: The Mfn2 has a mainly mitochondrial localization, but a small portion of the protein is also in the endoplasmic reticulum. Credit: University of Barcelona

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More information: Sergi Casellas‐Díaz et al, Mfn2 localization in the ER is necessary for its bioenergetic function and neuritic development, EMBO reports (2021). DOI: 10.15252/embr.202051954

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Provided by University of Barcelona

For The First Time, Researchers Visualize Metabolic Process at the Single-cell Level (Biology)

Understanding cellular metabolism – how a cell uses energy- could be key to treating a wide array of diseases, including vascular diseases and cancer.

While many techniques can measure these processes among tens of thousands of cells, researchers have been unable to measure them at the single-cell level.

Researchers at the University of Chicago’s Pritzker School of Molecular Engineering and Biological Sciences Division have developed a combined imaging and machine learning technique that can, for the first time, measure a metabolic process at both the cellular and sub-cellular levels.

Using a genetically encoded biosensor paired with artificial intelligence, the researchers were able to measure glycolysis, the process of turning glucose into energy, of single endothelial cells, the cells that line blood vessels.

They found that when these cells move and contract, they use more glucose, and they also found that cells uptake glucose through a previously unknown receptor. Understanding this process could lead to better treatments for cancer and vascular diseases, including COVID-19.

The research, published in Nature Metabolism, was led by Assoc. Prof. Yun Fang and co-led by Asst. Prof. Jun Huang, with former postdoctoral fellow and now Asst. Prof David Wu and biophysical sciences graduate student Devin Harrison.

“Understanding cellular metabolism is universally important,” Huang said. “By measuring single-cell metabolism, we potentially have a new way of treating a wide range of diseases.”

“This is the first time that we can visualize cellular metabolism at different temporal and spatial scales, even at the subcellular level, which could fundamentally change the language and approach for researchers to study cellular metabolism,” Fang said.

Measuring glycolysis

Endothelial cells normally provide a tight layer inside blood vessels, but they can contract, leaving gaps within this layer, when they need help from the immune system. Abnormal contraction can cause leaky blood vessels, leading to heart attack or stroke. Such contraction in blood vessels around the lungs can also cause fluid to leak in, which happens in the case of acute respiratory distress syndrome. (This often occurs in patients with severe cases of COVID-19.)

To better understand how cells metabolize energy to fuel this contraction, the researchers turned to Förster resonance energy transfer sensors–genetically encoded biosensors that can measure the amount of lactate inside cells. Lactate is the byproduct of glycolysis.

Though the researchers did not create the sensors, by pairing the sensors with machine learning algorithms, they created an even more powerful technique that allowed them to image cells, analyze the data, and parse out glycolysis reactions at the cellular and subcellular levels.

“Now we can look at and understand details within the cells, like certain areas of cells where there is an increase of glycolysis,” Fang said. “This is a key technological innovation.”

They were able to measure just how much glucose cells used when they contracted and moved, and they also found a new mechanism of glucose transport mediated by the cell’s cytoskeleton – a receptor called GLUT3 – that these cells use to uptake glucose.

Creating new treatments

Understanding how glycolysis works at the cellular level could ultimately lead to treatments that inhibit this process when beneficial – in the case of leaky blood vessels in patients with atherosclerosis, for example. It could also help patients whose immune systems are overreacting to COVID-19, for example, and need help closing the gaps within their endothelial cells around their lungs.

“If we can find a way to inhibit contraction, we could lessen the acute respiratory distress syndrome in COVID-19 patients,” Fang said.

It also has important implications in treating cancer. Endothelial migration and proliferation, driven by glycolysis, are major cellular processes involved in vascular growth, which is necessary for tumor survival and growth. Understanding just how this works could help researchers both destroy tumors and inhibit tumor growth.

It could also be useful in CAR T-cell therapy, which recruits the body’s own immune system to fight tumors. While the therapy has been lifesaving for some, many patients don’t respond to it. Since endothelial cells are important for allowing T-cells to infiltrate tumors and cellular metabolism is instrumental to T-cell functions, researchers believe that modulating cellular metabolism could help create a better immunotherapy system.

The researchers are currently testing such inhibitors to treat COVID-19-induced acute respiratory distress syndrome at Argonne National Laboratory.

“Can we ultimately reprogram cells through metabolism?” Huang said. “It’s an important question, and we need to understand just how metabolism works. There is huge potential here, and this is just the starting point.”

Other authors on the paper include Teodora Szasz, Chih-Fan Yeh, Tzu-Pin Shentu, Angelo Meliton, Ru-Ting Huang, Zhenjie Zhou, and Gökhan Mutlu.

Featured image: A new PME imaging and machine learning technique can measure glycolysis at both the cellular and sub-cellular levels, potentially leading to new methods for treating a wide array of diseases, including cancer and COVID-19. © Fang Lab at University of Chicago

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Reference: “Single-cell metabolic imaging reveals a SLC2A3-dependent glycolytic burst in motile endothelial cells,” Wu, D., Harrison, D.L., Szasz, T. et al. Nature Metabolism, May 24, 2021, https://doi.org/10.1038/s42255-021-00390-y

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Provided by University of Chicago

Targeting Abnormal Cell Metabolism Shows Promise For Treating Pediatric Brain Tumors (Medicine)

Two experimental drug approaches that target vulnerabilities in cancer cell metabolism may extend survival and enhance the effectiveness of standard chemotherapies for a highly aggressive type of pediatric brain cancer.

The findings were reported by Johns Hopkins Kimmel Cancer Center researchers in two published studies.

Medulloblastoma is the most common malignant pediatric brain tumor. A subset of patients with tumors known as Group 3 MYC-amplified medulloblastoma have an overall survival rate of less than 25%. In these patients, the cancer-promoting MYC oncogene drives cancer cell growth by altering cancer cell metabolism. Cancer cells use energy in ways that are different from normal cells, so they are potentially vulnerable to therapies that target the abnormal metabolic pathways downstream of MYC. 

In the first study, published March 22 in the Journal of Neuropathology and Experimental Neurology, pediatric oncologist and senior author Eric Raabe, M.D., Ph.D., associate professor of oncology at the Johns Hopkins University School of Medicine, focused on the metabolism altering drug DON (6-diazo-5-oxo-L-norleucine). DON is a naturally occurring compound studied in adult and pediatric cancer clinical trials since the 1980s, but it was never systematically tested against MYC-driven brain tumors.

Although DON was safe in children in early cancer clinical trials, it is not currently clinically available.

The research team, led by Barbara Slusher, Ph.D., M.A.S., director of Johns Hopkins Drug Discovery and professor of neurology at the Johns Hopkins University School of Medicine, modified DON to increase its ability to cross the blood-brain barrier, creating a DON prodrug, JHU395. In a prodrug, the chemistry is changed so that the drug is activated only in cancer cells.

“The promise of DON prodrugs is to develop a treatment that wouldn’t hurt normal cells but could be released preferentially in brain cancer cells,” says Raabe.

In one set of experiments, investigators treated human high-MYC medulloblastoma cell lines with JHU395 and with DON. They found the prodrug effectively suppressed growth and killed the cancer cells at lower concentrations compared to DON alone.

Next, mice bearing implanted human medulloblastoma tumors were treated with JHU395. The researchers found the treatment led to selective killing of the MYC-driven cancer cells, while normal brain cells were spared. Furthermore, JHU395 treatment significantly extended survival. Treated mice lived nearly twice as long as mice given placebo.

“JHU395 is equally effective as DON at a lower dose because it has better penetration of the brain cancer cells,” Raabe says. “Coming up with a new therapy with potentially reduced side effects means we can combine drugs for better patient survival, which is what this is all about.”

In a second study, published online Feb. 8 in Cancer Letters, Raabe and colleagues at three other cancer research institutions targeted the mammalian rapamycin complexes involved in cell metabolism. The protein mTOR signals cancer cells to grow, invade healthy tissue and resist therapy. 

Previous research showed that, in addition to high MYC expression, aggressive pediatric medulloblastoma tumors have high-level mTOR expression, pointing investigators toward mTOR inhibitors as having possible therapeutic value. A bioinformatics drug screen identified TAK228 (also known as sapanisertib), a brain-penetrating mTORC1/2 kinase inhibitor as a potentially effective agent for children, Raabe says.

Researchers found that TAK228 inhibited mTORC1/2, suppressed tumor cell growth up to 75% and effectively killed MYC-driven human medulloblastoma cancer cells.

Next, investigators focused on measuring the abnormal metabolism of MYC-driven medulloblastoma. In cancer, elevated glutathione is one means by which tumor cells become resistant to chemotherapy. Glutathione specifically allows cells to block the effect of chemotherapy drugs containing platinum, such as cisplatin and carboplatin. These platinum-containing drugs are some of the major components of medulloblastoma therapy. In human medulloblastoma tumors grown in mice, Raabe and colleagues found that the tumor cells have more glutathione than normal brain cells. Using the excess glutathione may be one way these cancer cells resist chemotherapy.

The researchers found that the TAK228 mTOR inhibitor disrupted and decreased glutathione synthesis in cancer cells. When they treated mice that had high-MYC medulloblastoma brain tumors with a combination of TAK228 and carboplatin, the combination effectively killed tumor cells and extended survival more than either drug used alone. Mice treated with combination therapy lived nearly twice as long as control mice. Of the combination-treated mice, 20% were considered very long survivors, living nearly 80 days after the start of the experiment, while all control mice died from their tumor within 25 days.

“By targeting the mTOR pathway, TAK228 overcame a key resistance mechanism that cancer cells have to traditional chemotherapy,” Raabe says. “These MYC-driven cancers make a lot of glutathione — they’re growing so fast they need a lot of it. TAK228 reduces the amount they can make, and that makes them vulnerable to the chemotherapy.”

“This is valuable pre-clinical data for future trials in children of combination mTOR inhibitor with traditional chemotherapy, which could ultimately change outcomes for children who will be diagnosed with MYC-driven medulloblastoma,” he adds.

Co-authors of the Journal of Neuropathology and Experimental Neurology study are Khoa Pham, Micah Maxwell, Heather Sweeney, Jesse Alt, Rana Rais, Charles Eberhart and Barbara Slusher.

The work was supported by the National Institutes of Health’s National Institute of Neurological Disorders and Stroke (1R01NS103927) and National Cancer Institute (R01 R01CA229451), the Spencer Grace Foundation, the Ace for the Cure Foundation, the Giant Food Pediatric Cancer Research Fund and a National Cancer Institute core grant to the Sidney Kimmel Comprehensive Cancer Center.

Other researchers participating in the Cancer Letters study are Rachael Maynard, Brad Poore, Allison Hanaford, Khoa Pham, Madison James, Jesse Alt, Youngran Park, Barbara Slusher and Charles Eberhart from Johns Hopkins, Pablo Tamayo and Jill Mesirov from the University of California San Diego, and Tenley Archer and Scott Pomeroy from the Broad Institute of the Massachusetts Institute of Technology, Harvard University and the Harvard Medical School.

Funding was provided by Alex’s Lemonade Stand Foundation for Childhood Cancer, the Spencer Grace Foundation, the Ace for the Cure Foundation, the Giant Food Pediatric Cancer Research Fund, the National Institutes of Health (U24CA220341, U01CA217885, U24CA194107, U54CA209891 and U01 CA184898) and a National Cancer Institute support grant to the Sidney Kimmel Comprehensive Cancer Center at Johns Hopkins.

Featured image: High-power microscope view showing human MYC-amplified medulloblastoma ( large, pale blue cells at bottom) growing in the mouse cerebellum. Normal brain is shown at top (pink colored connections between brain cells and small, dark blue brain cells). The tumor cells are pressing into and disrupting the normal brain © Khoa Pham, M.D.

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References: (1) Maynard RE, Poore B, Hanaford AR, Pham K, James M, Alt J, Park Y, Slusher BS, Tamayo P, Mesirov J, Archer TC, Pomeroy SL, Eberhart CG, Raabe EH. TORC1/2 kinase inhibition depletes glutathione and synergizes with carboplatin to suppress the growth of MYC-driven medulloblastoma. Cancer Lett. 2021 Apr 28;504:137-145. doi: 10.1016/j.canlet.2021.02.001. (2) Khoa Pham, MD, Micah J Maxwell, MD, PhD, Heather Sweeney, Jesse Alt, BS, Rana Rais, PhD, Charles G Eberhart, MD, PhD, Barbara S Slusher, PhD, Eric H Raabe, MD, PhD, Novel Glutamine Antagonist JHU395 Suppresses MYC-Driven Medulloblastoma Growth and Induces Apoptosis, Journal of Neuropathology & Experimental Neurology, Volume 80, Issue 4, April 2021, Pages 336–344, https://doi.org/10.1093/jnen/nlab018

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Provided by Johns Hopkins Medicine

New Immune Evasion Mechanism Achieved by FTO-mediated Regulation of Glycolytic Metabolism (Biology)

CD8⁺ T cells are the key immune cells to recognize and eliminate tumor cells, but their functions are usually inhibited by the immunosuppressive tumor microenvironment. Previous studies have shown that tumor cells utilize diverse epigenetic mechanisms to evade T cell-mediated immune surveillance.

As a dynamic and reversible modification of the epitranscriptome, m⁶A modification affects the RNA stability and translation processes, playing an important role in the occurrence and progress of tumors. However, how m⁶A modifications participate in regulating the tumor immune microenvironment and regulating T cell-mediated immune surveillance is still unclear.

In a study published in Cell Metabolism, a team led by Prof. HAN Dali from Beijing Institute of Genomics of the Chinese Academy of Sciences (China National Center for Bioinformation), Prof. XU Michelle Meng from Tsinghua University, and Prof. YANG Caiguang from Shanghai Institute of Materia Medica of the Chinese Academy of Sciences, revealed that the m⁶A demethylase FTO could enhance the glycolytic metabolism of tumor cells through epitranscriptomic regulation, thereby inhibiting T cell activation and promoting immune evasion.

The researchers found that knocking down the m⁶A demethylase FTO in various solid tumors can inhibit tumor growth in mice and increase the proportion of tumor-infiltrating antigen-specific CD8⁺ T cells, and showed that knocking down FTO in tumors leads to faster activation of CD8⁺ T cells, promoting their antitumor capability.

Through integrated analysis of multidimensional omics sequencing data, including RNA-seq, MeRIP-seq (m⁶A-seq), ATAC-seq, ChIP-seq, they found that FTO can specifically remove the m⁶A modification on mRNA transcripts of multiple bZIP family transcription factors, thus facilitating their mRNA stability. These bZIP family transcription factors can promote the expression of glycolytic genes and enhance the glycolytic activity of tumor cells, which in turn inhibits the activation of CD8⁺ T cells.

Besides, the researchers used the small molecule inhibitor Dac51 that targets FTO to further verify the mechanism of FTO in regulating glycolysis metabolism and escaping immune surveillance.

They conducted PD-L1 blockade and Dac51 treatment in tumor-bearing mice model, and found that both can effectively inhibit tumor growth in mice, while the combination of PD-L1 and Dac51 can greatly improve the therapeutic effect. Also, they found that Dac51 treatment can also effectively enhance the antitumor immune response of T cells in patient-derived organoid model, suggesting the possibility of Dac51 in clinical applications.

This study uncovers that RNA epitranscriptome can be operating as an additional layer of genetic regulation for immune evasion, which would facilitate the discovery of a new class of potentially vulnerable epitranscriptomic immunotherapy targets.

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Reference: Yi Liu, Guanghao Liang, Hongjiao Xu et al., “Tumors exploit FTO-mediated regulation of glycolytic metabolism to evade immune surveillance”, Cell Metabolism, 2021 DOI: https://doi.org/10.1016/j.cmet.2021.04.001

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Provided by Chinese Academy of Sciences

Groundbreaking Research into White-Rot Fungi Proves Its Value in Carbon Sequestration from Lignin (Biology)

A foundational study conducted by scientists at the National Renewable Energy Laboratory (NREL) shows for the first time that white-rot fungi are able to use carbon captured from lignin as a carbon source.

The research confirms a hypothesis from Davinia Salvachúa Rodriguez, the senior author of a newly published paper. Until now, scientists were unsure whether white-rot fungi—the most efficient lignin-degrading organisms in nature—actually consume the products generated from breaking down lignin.

“What we have demonstrated here is that white-rot fungi can actually utilize lignin-derived aromatic compounds as a carbon source, which means they can eat them and utilize them to grow,” Salvachúa said. “That is another strategy for carbon sequestration in nature and has not been reported before.”

The paper, “Intracellular pathways for lignin catabolism in white-rot fungi,” appears in the journal Proceedings of the National Academy of Sciences. Her co-authors from NREL are Carlos del Cerro, Erika Erickson, Tao Dong, Kelsey Ramirez, Venkataramanan Subramanian, Rui Katahira, Jeffrey Linger, Wei Xiong, and Michael Himmel. Other co-authors are from the Environmental Molecular Sciences Laboratory at Pacific Northwest National Laboratory and the Joint Genome Institute at Lawrence Berkeley National Laboratory.

Salvachúa, a research scientist in NREL’s Renewable Resources and Enabling Sciences Center, has spent more than a decade studying white-rot fungi. Last year, the Department of Energy’s Office of Science awarded her a prestigious $2.5 million grant as part of the Early Career Research Program to further her work.

White-rot fungi evolved to degrade lignin, which Salvachúa calls “the most recalcitrant biopolymer on Earth.” Lignin helps make the plant’s cell walls more rigid. Other parts of the plant, such as cellulose, are also recalcitrant but can be fully depolymerized to single monomeric species for use as a biofuel and biochemical precursors, for example. But the intractability of lignin and the lack of an efficient method to deconstruct and convert lignin to monomeric compounds hampers the viability of plant-based biorefineries.

Salvachúa’s work forms the foundation of a new research area based on lignin being broken down by white-rot fungi, which could be further exploited to simultaneously convert the biopolymer into value-added compounds.

The researchers examined two species of white-rot fungi: Trametes versicolor and Gelatoporia subvermispora. Through the use of genomic analysis, isotopic labeling, and systems biology approaches, the researchers determined the ability of these organisms to incorporate carbon from lignin-derived aromatic compounds into central metabolism and were able to map out the potential aromatic catabolic pathways for that conversion process. Further, in vitro enzyme analyses enable validation of some of the proposed steps. The researchers also highlight that this work is just the beginning of a broad area towards discovering new enzymes and pathways and better understanding carbon flux in these organisms.

Lignin accounts for about 30% of the organic carbon in the biosphere. Concerns about the changing climate have sparked a growing interest in the issue of carbon cycling, in which carbon is absorbed by natural reservoirs—such as plants—from the atmosphere and later decomposed and returned to the atmosphere or other natural reservoirs. Because more carbon is stored in the soil than in the atmosphere or plants, white-rot fungi are now positioned as key players in the sequestration of lignin-derived carbon in soils.

Scientists have demonstrated the ability of some bacterial strains to break down lignin as well, but not as effectively as white-rot fungi. Salvachúa said bacteria are easier to work with than fungi because they grow more quickly, and many are genetically tractable, contrary to white-rot fungi. “With fungi, one experiment can be up to two months,” she said. “We try to be very careful when we plan an experiment because that’s a long time. That’s six experiments a year if you need results to move forward. With bacteria, you can do one per week.”

The Department of Energy’s Office of Science, Biological and Environmental Research program, funded a portion of the research, with other funding coming from the Laboratory Directed Research and Development program at NREL.

NREL is the U.S. Department of Energy’s primary national laboratory for renewable energy and energy efficiency research and development. NREL is operated for the Energy Department by the Alliance for Sustainable Energy, LLC.

Featured image: Davinia Salvachúa Rodriguez holds a petri dish containing white-rot fungi. She is the senior author of a study showing that white-rot fungi consume and use the products generated from breaking down lignin, a pathway for sequestering carbon in nature. Photo by Werner Slocum, NREL

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Reference: Carlos del Cerro, Erika Erickson, Tao Dong, Allison R. Wong, Elizabeth K. Eder, Samuel O. Purvine, Hugh D. Mitchell, Karl K. Weitz, Lye Meng Markillie, Meagan C. Burnet, David W. Hoyt, Rosalie K. Chu, Jan-Fang Cheng, Kelsey J. Ramirez, Rui Katahira, Wei Xiong, Michael E. Himmel, Venkataramanan Subramanian, Jeffrey G. Linger, Davinia Salvachúa, “Intracellular pathways for lignin catabolism in white-rot fungi”, Proceedings of the National Academy of Sciences Mar 2021, 118 (9) e2017381118; DOI: 10.1073/pnas.2017381118

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Provided by NREL

Cell Replacement by the Numbers (Biology)

Mapping cellular turnover sheds light on the balance between renewal and stability in our bodies

One of the earliest thought experiments in history asked whether the ship commanded by the legendary king Theseus could have its old timber replaced, piece by piece, and still remain the same ship. At some point would it actually be a new ship? Our bodies are something like Theseus’ ship, steadily turning over cells so that as we age, we can say that few of the original “planks” are left. In our bodies, some cells never get replaced, while others are exchanged on practically a daily basis. What does the overall picture of cell replacement look like? For biomedical research, that is more than a philosophical question, as it touches on numerous processes in the body, from metabolic health to cancer.

Prof. Ron Milo and research student Ron Sender of the Weizmann Institute of Science’s Plant and Environmental Sciences Department went about this issue using a biological census method developed in Milo’s group. Of the 30 trillion cells in an adult body, Milo and Sender first selected a number of the most prevalent, representative types, with red blood cells and the epithelial cells lining the intestinal tract at the high end of the turnover scale, the non-renewable brain cells and cardiac cells at the other extreme. Then, using the available statistics for each, they created comparative maps to show, at a glance, how many types, and how much of each type of the cells in the body die and get replaced over time – by numbers as well as by weight.

Roughly every 80 days our bodies produce a number of new cells roughly equal to the total number in the body

In the final tally, around 330 billion cells die and roughly the same number of new ones are born every day. By numbers, red and white blood cells – which live between one day and several months – are by far the largest portion, accounting for some 90%, of that turnover. Blood cells are quite light, so by mass, the daily total comes out to something a bit less than a hundred grams. Thus roughly every 80 days our bodies produce a number of new cells roughly equal to the total number in the body. However, in terms of mass, we create our weight in new cells every year and a half (not seven, as some have suggested).

When the cells are compared by the overall weight of cells that get turned over, blood cells still come out on top, but less so. Gut epithelial cells, which are much larger than blood cells, are a fair second, accounting for about 12% by numbers but 40%, by weight, and getting replaced, on average, every few days. By mass, fat cells and skin cells trail far behind, each accounting for around 4% of the total daily turnover, with lung cells making up only half a percent.

Because blood cells are light, they account for only around half of the mass © Weizmann Institute of Science

And the researchers did not forget another component of our body mass: The few hundred grams of gut bacteria we carry with us have an extremely high replacement rate of around 100 grams a day.

“These maps can now provide a baseline for a healthy adult,” says Milo. “We can, in the future, use them to explore, on the one hand, how the ratios change during growth and development and, on the other, how the balance between life and death in cell turnover is upset in cancer and many other diseases. In the future we might be able to develop diagnostic tests for determining unhealthy levels of turnover in certain cell types that could provide early signs of disease, or apply the findings to answering questions concerning the ways that cancer upsets this balance

”Our study gives a fresh quantitative perspective on the classic question of the ‘Theseus ship’ of the body, showing you can learn a lot by paying close attention to the numbers. Our body is both new and the same in a way we can now quantify, undergoing constant change through the process of cell turnover and yet keeping the same ratios of cells that preserve the same basic form and function.”

Video: Design: Itai Raveh | Animation: Oleg Fedorkov

Prof. Ron Milo is Head of the Mary and Tom Beck – Canadian Center for Alternative Energy Research; his research is also supported by the Zuckerman STEM Leadership Program; the Larson Charitable Foundation New Scientist Fund; the Ben B. and Joyce E. Eisenberg Foundation; the Yotam Project; the Ullmann Family Foundation; Dana and Yossie Hollander; Sonia T. Marschak; and the European Research Council. Prof. Milo is the incumbent of the Charles and Louise Gartner Professorial Chair.

Featured image: By numbers, blood cells make up 90% of those replaced each day © Weizmann Institute of Science

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Reference: Sender, R., Milo, R. The distribution of cellular turnover in the human body. Nat Med 27, 45–48 (2021). https://www.nature.com/articles/s41591-020-01182-9 https://doi.org/10.1038/s41591-020-01182-9

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Provided by Weizmann Institute of Science

Discovery Illuminates How Thyroid Hormone ‘Dims’ Metabolism (Biology)

Basic biology finding could lead to new treatments for obesity, diabetes and related disorders

It has been known for some time that the thyroid gland is a strong regulator of the body’s metabolism, making it key to many health conditions. But the molecular details of how thyroid hormone acts on cells in the body have never been fully understood. Now researchers at the Perelman School of Medicine at the University of Pennsylvania have taken a big step toward the resolution of this mystery by showing that it doesn’t operate as a straight on/off switch, but more like a dimmer.

Biologists have known that, in cells where thyroid hormone acts to regulate metabolism, it operates in the cell nucleus, increasing the activity of some genes and decreasing the activity of others. The details of how the hormone controls gene activity have been mostly unknown, due to technical hurdles that have made it difficult to study them. The Penn Medicine researchers, who report their discovery today in Genes and Development, were able to overcome many of these technical hurdles to provide a much clearer picture of thyroid hormone’s basic mechanisms of action — in the process overturning other prominent models of these mechanisms.

“We were able in this study to show that thyroid hormone doesn’t just turn things on or off, as the canonical model suggests, but instead more subtly shifts the balance between the repression and enhancement of gene activity,” said principal investigator Mitchell Lazar, MD, PhD, Ware professor of Diabetes and Metabolic Diseases, and the director of the Institute for Diabetes, Obesity and Metabolism, at Penn Medicine. “Yet, as people with hypothyroidism know, the lack of thyroid hormone can have profound effects on the body.”

Diseases of the thyroid gland, including hypothyroidism, hyperthyroidism, and goiter, have been described for as long as there have been doctors. The thyroid-produced molecule thyroxine, the chemical precursor to the main active form of thyroid hormone, was identified in 1914.

Endocrinologists also have long recognized that thyroid hormone is an essential metabolism-enhancing regulator whose insufficiency can lead not only to obvious thyroid diseases but also to weight gain and related metabolic problems including diabetes, high cholesterol, and fatty liver disease. Thus, the hormone’s mechanism of action, if understood, could be a drug target of enormous value for medicine.

But although scientists have known for almost 40 years that thyroid hormone acts in the cell nucleus to control gene activity by binding itself to special proteins called thyroid hormone receptors, how it all works has remained an enigma — largely because the interactions of thyroid hormone and its receptors have been difficult to study. Among other challenges, the receptors normally are produced in relatively tiny quantities in cells, and scientists have lacked a good way to mark their binding sites on DNA — and to see how these binding sites differ when thyroid hormone is present.

In the new study, for which Yehuda Shabtai, PhD, a postdoctoral researcher in the Lazar lab, served as lead author, the researchers developed a mouse model in which a special tag was added to TRβ, the main thyroid hormone receptor in the liver — where some of thyroid hormone’s most important metabolic effects occur. The researchers used this tag for marking the thousands of locations on DNA where TRβ binds, both in a condition when thyroid hormone was present and could bind to TRβ and also when the hormone was largely absent. With these and other experiments, the team provided strong evidence that thyroid hormone works with TRβ in an unexpectedly subtle way.

When it binds to a given site on coiled DNA in the nucleus, TRβ will enhance or repress the activity of a nearby gene or genes. To achieve this, it forms complexes with other proteins called co-activators and co-repressors. The researchers showed when thyroid hormone is bound to TRβ, it can shift the balance of these associated co-regulator proteins in favor of more gene activation at some sites, and more gene repression at others. This is in contrast to prior models of thyroid hormone / TRβ function in which thyroid hormone has a more absolute, switch-like effect on gene activity.

The researchers acknowledge that more work needs to be done to elucidate why thyroid hormone’s binding to TRβ lowers gene activity at some sites on DNA, and increases gene activity at other sites. But they see the new findings as a significant advance in understanding a basic process in biology — a process that future medicines may be able to target precisely to treat a variety of metabolic diseases.

Co-authors on this study include Yehuda Shabtai, Nagaswaroop Nagaraj, Kirill Batmanov, Young-Wook Cho, Yuxia Guan, Chunjie Jiang, Jarrett Remsberg, Douglas Forrest, and Mitchell Lazar.

Their work was supported by the National Institute of Diabetes and Digestive and Kidney Diseases (DK43806, DK19525) and the Cox Institute for Medical Research.

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This science news is confirmed by us from Frank Otto, Penn Medicine

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Provided by Penn Medicine

Today’s Stem Cell Special: Small Intestine on a Plate! (Biology)

A team of scientists from Japan have found success in growing small intestinal cells, akin to those found in the human body, from human-induced pluripotent stem cells. The scientists used a procedure they previously developed on embryonic stem cells for this discovery. They claim that the grown cells can be used for laboratory studies focusing on human small intestinal drug transport and metabolism.

Enterocytes, which line the epithelium of the small intestine, are the sites of absorption and metabolism of most orally consumed medications. For this reason, studies on the absorption of novel oral drugs rely on in vitro or animal models to accurately recreate the environment of the small intestine. Currently, scientists widely use the human colon cancer cell line Caco-2 as a model of the intestinal epithelium. However, this has its drawbacks: Caco-2 cells have been derived from the colon; therefore, they more closely resemble the colon than the small intestine. For example, these cells do not express cytochrome P450 3A4 (CYP3A4), a protein critical for drug metabolism that is abundantly expressed in the small intestine. Moreover, Caco-2 cells tend to show high cell-line to cell-line variations.

To tackle these problems, scientists from the Tokyo Institute of Technology, The University of Tokyo, Kanto Chemical Co. Inc., Shionogi & Co., Ltd. and Shionogi TechnoAdvance Research Co., Ltd., developed novel enterocyte-like cells from human-induced pluripotent stem cells (hiPSCs), which can differentiate into any type of cell when provided with right growth factors.

By modifying a procedure that they previously used on human embryonic stem cells, the scientists initially grew cells that resemble the early stages of small intestine cells, called intestinal progenitor cells. Then, they cultured these progenitor cells on a collagen vitrigel membrane (CVM). Further, they treated the progenitor cells with a maturation medium containing 6-bromoindirubin-3′-oxime, dimethyl sulfoxide, dexamethasone, and activated vitamin D3. Their efforts resulted in the development of enterocyte-like cells that closely resembled actual enterocytes, expressing efflux transporter proteins regulating drug absorption as well as CYP3A4, which Caco-2 cells lack. Dr. Nobuaki Shiraki, Associate Professor at Tokyo Institute of Technology, and one of the corresponding authors of this study, adds, “We established an efficient culture procedure for generating enterocyte-like cells from hiPSCs by culturing the hiPSC-derived endoderm or intestine progenitor cells on CVM.”

The scientists claim that these first-of-their-kind enterocyte-like cells can be used as an in vitro model of the small intestine for evaluating the intestinal absorption of drugs in humans. Elaborating on the advantages of using these cells for future studies, Dr. Shoen Kume, Professor at Tokyo Institute of Technology, and co-corresponding author of this study, comments, “The hiPSC-derived enterocyte-like cells established in this study could be used for the quantitative prediction of the intestinal absorption of drugs in humans under special occasions such as alteration of the functions of transporters/metabolic enzymes by drug-drug interactions as well as normal conditions.”

Indeed, let us hope that the hiPSC-derived enterocyte-like cells would aid breakthrough research in future pharmacokinetic studies!

Featured image: Human-induced pluripotent stem cells derived enterocyte-like cells exhibit P-gp- and BCRP-mediated efflux and cytochrome P450 (CYP3A4)-mediated metabolism. We concluded that hiPS cell-derived enterocyte-like cells can be used as a model for the evaluation of drug transport and metabolism studies in the human small intestine. © Tokyo Tech

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Reference: Shinpei Yoshida, Takayuki Honjo, Keita Iino, Ryunosuke Ishibe, Sylvia Leo, Tomoka Shimada, Teruhiko Watanabe, Masaya Ishikawa, Kazuya Maeda, Hiroyuki Kusuhara, Nobuaki Shiraki and Shoen Kume, “Generation of human-induced pluripotent stem cell-derived functional enterocyte-like cells for pharmacokinetic studies“, Stem Cell Reports, 2021. DOI :10.1016/j.stemcr.2020.12.017

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Provided by Tokyo Institute of Technology

Hormones in the Brain May Explain How Exercise Improves Metabolism (Biology)

During moderate exercise, the brain’s hypothalamus – the region controlling metabolism – releases a hormone linked to obesity resistance, according to research in mice.

A mitochondrial hormone expressed by cells deep in the brain appears to play a role in improving metabolism and fighting off obesity, according to a new study in mice.

A collaboration between the USC Leonard Davis School of Gerontology and researchers in South Korea has shown how moderate exercise prompts cells in the hypothalamus, the small region within the brain that controls metabolism, to release a hormone called MOTS-c. MOTS-c is a small protein that is encoded in cells’ smaller mitochondrial genome, rather than the larger collection of genes in the nucleus, said Changhan David Lee, assistant professor of gerontology at the USC Leonard Davis School and co-senior author of the new study.

Mitochondria, while more commonly known as the energy-producing parts of cells, have in recent years been found to play much bigger roles in health and aging by providing instructions for cellular processes.  Subsequent studies by Lee and his colleagues have shown how mitochondrial-encoded MOTS-c interacts with the nuclear genome and regulates cellular metabolism and stress responses.

Stress as a balancing act

The new study also illustrates how stress in the mitochondria can promote healthy metabolism – when kept in careful balance.

Existing research has shown how low-grade stress in mitochondria can promote health and longevity, a phenomenon termed mitohormesis, Lee said. Essentially, while high levels of a stressor such as a toxin can cause major harm, a small amount of a stressor may actually strengthen healthy mitochondrial function.

“As [philosopher Friedrich] Nietzsche once said, ‘That which does not kill us makes us stronger,'” Lee remarked.

Assistant Professor Changhan David Lee © USC Leonard Davis

To examine the effects of mitochondrial stress on metabolism, Lee and colleagues examined mice that were bred to be either partially or completely deficient in a single gene within a specific type of brain cell, hypothalamic proopiomelanocortin (POMC) neurons. The missing gene, Crif1, controls how cells use proteins encoded by mitochondria.

The mice that were homodeficient in Crif1 – meaning that they had no copies of the Crif1 gene at all – experienced severe mitochondrial stress and showed indicators of metabolic problems when they reached adulthood, including weight gain and reduced energy expenditure. In addition, the mice missing Crif1 entirely also had insulin resistance and high blood sugar, much like type 2 diabetes in humans.

However, the mice that were heterodeficient in the Crif1 gene – they could partially express the gene, but not as much as normal mice – experienced mild mitochondrial stress and protection against obesity or insulin resistance. When fed a high-fat diet, the mice missing part of their Crif1 function gained less weight than normal mice on the same diet, even though the former ate more calories. Further study of the mice revealed that their affected neurons expressed both more MOTS-c as well as more beta-endorphin (β-END), a pain-suppressing molecule typically released during exercise.

The mice with mild mitochondrial stress in POMC neurons may have avoided obesity due to the fat tissues within their bodies changing. The researchers noticed that the Crif1 heterodeficient mice display more thermogenesis – the ability to generate heat – and further examination of the fat cells revealed increased amounts of brown fat cells.

Brown fat appears brown because of the presence of more mitochondria versus white fat. In babies, who don’t yet have the ability to shiver to keep their bodies warm, their larger proportion of brown fat consumes sugar and white fat to generate energy and produce heat. Scientists are interested in the effects of “browning” fat, or turning white fat into brown fat, as a possible way to address obesity in adults, who typically retain only small pockets of brown fat.

MOTS-c treatment, exercise each give similar benefits

In later experiments, the researchers were able to mimic these changes, including increases in brown fat and thermogenesis, in normal mice by directly administering MOTS-c to the brain.

Tellingly, the same benefits also arose after mice engaged in moderate exercise. The study’s findings indicate that the process of balancing mild mitochondrial stress may be a key part of why exercise improves metabolism. The process appears to be mediated by MOTS-c, adding to the body of research supporting the hormone’s metabolic involvement.

“Our brain is a control center for a lot of physiological functions,” Lee said. “This is a new mechanism of exercise physiology that may provide new venues for future therapeutic development of exercise-mimetics.”

Lee and Pinchas Cohen, professor of gerontology, medicine and biological sciences and dean of the USC Leonard Davis School, first described MOTS-c in 2015, along with its role in restoring insulin sensitivity and counteracting diet-induced and age-dependent insulin resistance – effects commonly associated with exercising. In a separate paper published January 20 in Nature Communication, Lee, Cohen, and colleagues demonstrated that MOTS-c levels increase upon exercise in humans and, when given to mice, can double the running capacity of young and old animals. These studies raise the possibility of developing drugs to provide the health benefits of exercise to frail or disabled individuals who cannot safely exercise.

The current study indicates that the mitochondrial hormone is not just acting locally within muscle tissues but arising from the brain’s headquarters for metabolism, Lee said.

“The question is, ‘upon exercise, do mitochondria communicate to your command center, or do they bypass that and talk straight to the target (peripheral) organs?'” Lee said of the research surrounding MOTS-c’s role in exercise and metabolism. “We’re showing that it could be both.”

“Mitohormesis in hypothalamic POMC neurons mediates regular exercise-induced high-turnover metabolism” first appeared online in Cell Metabolism on Feb. 2, 2021. Lee’s co-corresponding authors included Minho Shong of Chungnam National University in Daejeon, Korea, and Min-Seon Kim of the University of Ulsan College of Medicine in Seoul. The study’s first authors were Gil Myoung Kang, Se Hee Min, and Chan Hee Lee of the University of Ulsan College of Medicine. Other coauthors included Ji Ye Kim, Hyo Sun Lim, Jae Woo Park, Sung Jun Kim, Chae Beom Park, Hong Dugu, Jong Han Choi, Won Hee Jang, Se Eun Park, and Kyung-Gon Kim of the University of Ulsan College of Medicine; Saet-Byel Jung of Chungnam National University; Young Min Cho of the Seoul National University College of Medicine; Jae Geun Kim of Incheon National University, Korea; Cheol Soo Choi of Gachon University in Inchon, Korea; and Young-Bum Kim of Beth Israel Deaconess Medical Center and Harvard Medical School.

This study was supported by grants from the National Research Foundation of Korea (NRF), funded by the Ministry of Science and ICT of Korea (2017R1A2B3007123, 2020R1A2C3004843, 2017R1E1A1A01075126), the Asan Institute for Life Sciences (18-326, 2019-IP0855-1), and the National Institutes of Health (R01AG052558 and R01GM136837 to Changhan David Lee and R01DK123002 to Young-Bum Kim). Lee is a consultant and shareholder of CohBar Inc. CohBar is developing analogues of mitochondrial peptides, including of MOTS-c, for metabolic diseases of aging.

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Reference: Gil Myoung Kang, Se Hee Min, Chan Hee Lee, Changhan Lee et al., “Mitohormesis in Hypothalamic POMC Neurons Mediates Regular Exercise-Induced High-Turnover Metabolism”, Cell metabolism, 33(2), pp. 334-349, 2021. https://doi.org/10.1016/j.cmet.2021.01.003

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Provided by University of Southern California