bims-mimcad 2024-01-14 papers

bims-mimcad

Biomed News

on Mitochondrial metabolism and cardiometabolic diseases

Issue of 2024‒01‒14
twelve papers selected by
Henver Brunetta, University of Guelph

Age and dietary restriction modulate mitochondrial quality in quadriceps femoris muscle of male mice.
Systems-level analyses dissociate genetic regulators of reactive oxygen species and energy production.
TALK-1-mediated alterations of β-cell mitochondrial function and insulin secretion impair glucose homeostasis on a diabetogenic diet.
Longevity control by supersulfide-mediated mitochondrial respiration and regulation of protein quality.
Effect of skeletal muscle mitochondrial phenotype on H2O2 emission.
Breviscapine protects against pathological cardiac hypertrophy by targeting FOXO3a-mitofusin-1 mediated mitochondrial fusion.
Skeletal muscle TET3 promotes insulin resistance through destabilisation of PGC-1α.
Butyrate reduction and HDAC4 increase underlie maternal high fructose-induced metabolic dysfunction in hippocampal astrocytes in female rats.
Sex differences in mitochondrial gene expression during viral myocarditis.
NRF2 is required for neonatal mouse beta cell growth by maintaining redox balance and promoting mitochondrial biogenesis and function.
Exogenous mitochondrial transfer increases energy expenditure and attenuates adiposity gains in mice with diet-induced obesity.
Kinetic modeling of leucine-mediated signaling and protein metabolism in human skeletal muscle.

Biogerontology. 2024 Jan 06.

Age and dietary restriction modulate mitochondrial quality in quadriceps femoris muscle of male mice.

Ting-Rui Zhang, Chun-Hsien Chiang, Tzu-Chieh Hsu, Chih-Yun Wang, Ching-Yi Chen.

  Dietary restriction (DR) is a potential intervention for ameliorating ageing-related damages. Mitochondrial quality control is the key mechanism for regulating cellular functions in skeletal muscle. This study aimed to explore the effect of age and DR on the homeostasis of mitochondrial quality control in skeletal muscle. To study the effect of age on mitochondrial homeostasis, young (3 months old) male C57BL/6J mice were fed ad libitum (AL) until 7 (Young), 14 (Middle), and 19 months (Aged) of age. For the DR intervention, 60% of AL intake was given to the mice at 3 months of age until they reached 19 months of age (16 months). The quadriceps femoris muscle was collected for further analysis. Significant changes in the skeletal muscle were noticed during the transition between middle age and the elderly stages. An accumulation of collagen was observed in the muscle after middle age. Compared with the Middle muscle, Aged muscle displayed a greater expression of VDAC, and lower expressions of mitochondrial dynamic proteins and OXPHOS proteins. The DR intervention attenuated collagen content and elongated the sarcomere length in the skeletal muscle during ageing. In addition, DR adjusted the abnormalities in mitochondrial morphology in the Aged muscle. DR downregulated VDAC expression, but upregulated OPA1 and DRP1 expressions. Taken together, greater pathological changes were noticed in the skeletal muscle during ageing, especially in the transition between middle age and the elderly, whereas early-onset DR attenuated the muscular ageing via normalising partial functions of mitochondria.

Keywords:  Ageing; Dietary restriction; Mitochondrial homeostasis; Quadriceps femoris muscle

DOI:  https://doi.org/10.1007/s10522-023-10086-3
Proc Natl Acad Sci U S A. 2024 Jan 16. 121(3): e2307904121

Systems-level analyses dissociate genetic regulators of reactive oxygen species and energy production.

Neal K Bennett, Megan Lee, Adam L Orr, Ken Nakamura.

  Respiratory chain dysfunction can decrease ATP and increase reactive oxygen species (ROS) levels. Despite the importance of these metabolic parameters to a wide range of cellular functions and disease, we lack an integrated understanding of how they are differentially regulated. To address this question, we adapted a CRISPRi- and FACS-based platform to compare the effects of respiratory gene knockdown on ROS to their effects on ATP. Focusing on genes whose knockdown is known to decrease mitochondria-derived ATP, we showed that knockdown of genes in specific respiratory chain complexes (I, III, and CoQ10 biosynthesis) increased ROS, whereas knockdown of other low ATP hits either had no impact (mitochondrial ribosomal proteins) or actually decreased ROS (complex IV). Moreover, although shifting metabolic conditions profoundly altered mitochondria-derived ATP levels, it had little impact on mitochondrial or cytosolic ROS. In addition, knockdown of a subset of complex I subunits-including NDUFA8, NDUFB4, and NDUFS8-decreased complex I activity, mitochondria-derived ATP, and supercomplex level, but knockdown of these genes had differential effects on ROS. Conversely, we found an essential role for ether lipids in the dynamic regulation of mitochondrial ROS levels independent of ATP. Thus, our results identify specific metabolic regulators of cellular ATP and ROS balance that may help dissect the roles of these processes in disease and identify therapeutic strategies to independently target energy failure and oxidative stress.

Keywords:  ATP; CRISPRi; ROS; metabolism; mitochondria

DOI:  https://doi.org/10.1073/pnas.2307904121
Cell Rep. 2024 Jan 10. pii: S2211-1247(24)00001-9. [Epub ahead of print]43(1): 113673

TALK-1-mediated alterations of β-cell mitochondrial function and insulin secretion impair glucose homeostasis on a diabetogenic diet.

Sarah M Graff, Arya Y Nakhe, Prasanna K Dadi, Matthew T Dickerson, Jordyn R Dobson, Karolina E Zaborska, Chloe E Ibsen, Regan B Butterworth, Nicholas C Vierra, David A Jacobson.

  Mitochondrial Ca2+ ([Ca2+]m) homeostasis is critical for β-cell function and becomes disrupted during the pathogenesis of diabetes. [Ca2+]m uptake is dependent on elevations in cytoplasmic Ca2+ ([Ca2+]c) and endoplasmic reticulum Ca2+ ([Ca2+]ER) release, both of which are regulated by the two-pore domain K+ channel TALK-1. Here, utilizing a novel β-cell TALK-1-knockout (β-TALK-1-KO) mouse model, we found that TALK-1 limited β-cell [Ca2+]m accumulation and ATP production. However, following exposure to a high-fat diet (HFD), ATP-linked respiration, glucose-stimulated oxygen consumption rate, and glucose-stimulated insulin secretion (GSIS) were increased in control but not TALK1-KO mice. Although β-TALK-1-KO animals showed similar GSIS before and after HFD treatment, these mice were protected from HFD-induced glucose intolerance. Collectively, these data identify that TALK-1 channel control of β-cell function reduces [Ca2+]m and suggest that metabolic remodeling in diabetes drives dysglycemia.

Keywords:  CP: Cell biology; CP: Metabolism; K2P; TALK-1; calcium handling; diabetes; endoplasmic reticulum; insulin secretion; metabolism; mitochondria; pancreatic β-cell; two-pore-domain potassium channel

DOI:  https://doi.org/10.1016/j.celrep.2024.113673
Redox Biol. 2024 Jan 03. pii: S2213-2317(23)00419-6. [Epub ahead of print]69 103018

Longevity control by supersulfide-mediated mitochondrial respiration and regulation of protein quality.

Akira Nishimura, Sunghyeon Yoon, Tetsuro Matsunaga, Tomoaki Ida, Minkyung Jung, Seiryo Ogata, Masanobu Morita, Jun Yoshitake, Yuka Unno, Uladzimir Barayeu, Tsuyoshi Takata, Hiroshi Takagi, Hozumi Motohashi, Albert van der Vliet, Takaaki Akaike.

  Supersulfides, which are defined as sulfur species with catenated sulfur atoms, are increasingly being investigated in biology. We recently identified pyridoxal phosphate (PLP)-dependent biosynthesis of cysteine persulfide (CysSSH) and related supersulfides by cysteinyl-tRNA synthetase (CARS). Here, we investigated the physiological role of CysSSH in budding yeast (Saccharomyces cerevisiae) by generating a PLP-binding site mutation K109A in CRS1 (the yeast ortholog of CARS), which decreased the synthesis of CysSSH and related supersulfides and also led to reduced chronological aging, effects that were associated with an increased endoplasmic reticulum stress response and impaired mitochondrial bioenergetics. Reduced chronological aging in the K109A mutant could be rescued by using exogenous supersulfide donors. Our findings indicate important roles for CARS in the production and metabolism of supersulfides-to mediate mitochondrial function and to regulate longevity.

Keywords:  Cysteinyl-tRNA synthetase; ER stress; Longevity; Mitochondrial energy metabolism; Supersulfides

DOI:  https://doi.org/10.1016/j.redox.2023.103018
Comp Biochem Physiol B Biochem Mol Biol. 2024 Jan 06. pii: S1096-4959(24)00007-1. [Epub ahead of print]271 110940

Effect of skeletal muscle mitochondrial phenotype on H2O2 emission.

Collins Kamunde, Yashodya Wijayakulathilake, Chidozie Okoye, Nirmala Chinnappareddy, Zahra Kalvani, Pius Tetteh, Michael van den Heuvel, Ravinder Sappal, Don Stevens.

  Reactive oxygen species (ROS) are a key output of the skeletal muscle mitochondrial information processing system both at rest and during exercise. In skeletal muscle, mitochondrial ROS release depends on multiple factors; however, fiber-type specific differences remain ambiguous in part owing to the use of mitochondria from mammalian muscle that consist of mixed fibers. To elucidate fiber-type specific differences, we used mitochondria isolated from rainbow trout (Oncorhynchus mykiss) red and white skeletal muscles that consist of spatially distinct essentially pure red and white fibers. We first characterized the assay conditions for measuring ROS production (as H2O2) in isolated fish red and white skeletal muscle mitochondria (RMM and WMM) and thereafter compared the rates of emission during oxidation of different substrates and the responses to mitochondrial electron transport system (ETS) pharmacological modulators. Our results showed that H2O2 emission rates by RMM and WMM can be quantified using the same protein concentration and composition of the Amplex UltraRed-horseradish peroxidase (AUR-HRP) detection system. For both RMM and WMM, protein normalized H2O2 emission rates were highest at the lowest protein concentration tested and decreased exponentially thereafter. However, the absolute values of H2O2 emission rates depended on the calibration curves used to convert fluorescent signals to H2O2 while the trends depended on the normalization strategy. We found substantial qualitative and quantitative differences between RMM and WMM in the H2O2 emission rates depending on the substrates being oxidized and their concentrations. Similarly, pharmacological modulators of the ETS altered the magnitudes and trends of the H2O2 emission differently in RMM and WMM. While comparable concentrations of substrates elicited maximal albeit quantitively different emission rates in RMM and WMM, different concentrations of pharmacological ETS modulators may be required for maximal H2O2 emission rates depending on muscle fiber-type. Taken together, our study suggests that biochemical differences exist in RMM compared with WMM that alter substrate oxidation and responses to ETS modulators resulting in fiber-type specific mitochondrial H2O2 emission rates.

Keywords:  Assay conditions; H(2)O(2) emission; Mitochondria; Muscle fiber type

DOI:  https://doi.org/10.1016/j.cbpb.2024.110940
Free Radic Biol Med. 2024 Jan 06. pii: S0891-5849(24)00007-8. [Epub ahead of print]

Breviscapine protects against pathological cardiac hypertrophy by targeting FOXO3a-mitofusin-1 mediated mitochondrial fusion.

Xiaobing Lin, Ming-Zhou Fei, An-Xian Huang, Liu Yang, Ze-Jie Zeng, Wen Gao.

  Forkhead box O3a (FOXO3a)-mediated mitochondrial dysfunction plays a pivotal effect on cardiac hypertrophy and heart failure (HF). However, the role and underlying mechanisms of FOXO3a, regulated by breviscapine (BRE), on mitochondrial function in HF therapy remain unclear. This study reveals that BRE-induced nuclear translocation of FOXO3a facilitates mitofusin-1 (MFN-1)-dependent mitochondrial fusion in cardiac hypertrophy and HF. BRE effectively promotes cardiac function and ameliorates cardiac remodeling in pressure overload-induced mice. In addition, BRE mitigates phenylephrine (PE)-induced cardiac hypertrophy in cardiomyocytes and fibrosis remodeling in fibroblasts by inhibiting ROS production and promoting mitochondrial fusion, respectively. Transcriptomics analysis underscores the close association between the FOXO pathway and the protective effect of BRE against HF, with FOXO3a emerging as a potential target of BRE. BRE potentiates the nuclear translocation of FOXO3a by attenuating its phosphorylation, other than its acetylation in cardiac hypertrophy. Mechanistically, over-expression of FOXO3a significantly inhibits cardiac hypertrophy and mitochondrial injury by promoting MFN-1-mediated mitochondrial fusion. Furthermore, BRE demonstrates its ability to substantially curb cardiac hypertrophy, reduce mitochondrial ROS production, and enhance MFN-1-mediated mitochondrial fusion through a FOXO3a-dependent mechanism. In conclusion, nuclear FOXO3a translocation induced by BRE presents a successful therapeutic avenue for addressing cardiac hypertrophy and HF through promoting MFN-1-dependent mitochondrial fusion.

Keywords:  Breviscapine; Forkhead box O3a; Heart failure; Mitochondrial fusion; Mitofusin-1; Myocardial remodelling

DOI:  https://doi.org/10.1016/j.freeradbiomed.2024.01.007
Diabetologia. 2024 Jan 13.

Skeletal muscle TET3 promotes insulin resistance through destabilisation of PGC-1α.

Beibei Liu, Di Xie, Xinmei Huang, Sungho Jin, Yangyang Dai, Xiaoli Sun, Da Li, Anton M Bennett, Sabrina Diano, Yingqun Huang.

  AIM/HYPOTHESIS: The peroxisome proliferator-activated receptor-γ coactivator α (PGC-1α) plays a critical role in the maintenance of glucose, lipid and energy homeostasis by orchestrating metabolic programs in multiple tissues in response to environmental cues. In skeletal muscles, PGC-1α dysregulation has been associated with insulin resistance and type 2 diabetes but the underlying mechanisms have remained elusive. This research aims to understand the role of TET3, a member of the ten-eleven translocation (TET) family dioxygenases, in PGC-1α dysregulation in skeletal muscles in obesity and diabetes.METHODS: TET expression levels in skeletal muscles were analysed in humans with or without type 2 diabetes, as well as in mouse models of high-fat diet (HFD)-induced or genetically induced (ob/ob) obesity/diabetes. Muscle-specific Tet3 knockout (mKD) mice were generated to study TET3's role in muscle insulin sensitivity. Genome-wide expression profiling (RNA-seq) of muscle tissues from wild-type (WT) and mKD mice was performed to mine deeper insights into TET3-mediated regulation of muscle insulin sensitivity. The correlation between PGC-1α and TET3 expression levels was investigated using muscle tissues and in vitro-derived myotubes. PGC-1α phosphorylation and degradation were analysed using in vitro assays.
RESULTS: TET3 expression was elevated in skeletal muscles of humans with type 2 diabetes and in HFD-fed and ob/ob mice compared with healthy controls. mKD mice exhibited enhanced glucose tolerance, insulin sensitivity and resilience to HFD-induced insulin resistance. Pathway analysis of RNA-seq identified 'Mitochondrial Function' and 'PPARα Pathway' to be among the top biological processes regulated by TET3. We observed higher PGC-1α levels (~25%) in muscles of mKD mice vs WT mice, and lower PGC-1α protein levels (~25-60%) in HFD-fed or ob/ob mice compared with their control counterparts. In human and murine myotubes, increased PGC-1α levels following TET3 knockdown contributed to improved mitochondrial respiration and insulin sensitivity. TET3 formed a complex with PGC-1α and interfered with its phosphorylation, leading to its destabilisation.
CONCLUSIONS/INTERPRETATION: Our results demonstrate an essential role for TET3 in the regulation of skeletal muscle insulin sensitivity and suggest that TET3 may be used as a potential therapeutic target for the metabolic syndrome.
DATA AVAILABILITY: Sequences are available from the Gene Expression Omnibus ( https://www.ncbi.nlm.nih.gov/geo/ ) with accession number of GSE224042.

Keywords:  Diabetes; Insulin resistance; Mitochondria; Obesity; PGC-1α; Skeletal muscle; TET3

DOI:  https://doi.org/10.1007/s00125-023-06073-5
J Nutr Biochem. 2024 Jan 08. pii: S0955-2863(24)00005-6. [Epub ahead of print] 109571

Butyrate reduction and HDAC4 increase underlie maternal high fructose-induced metabolic dysfunction in hippocampal astrocytes in female rats.

Kay L H Wu, Wen-Chung Liu, Chih-Wei Wu, Mu-Hui Fu, Hsiu-Mei Huang, You-Lin Tain, Chih-Kuang Liang, Chun-Ying Hung, I-Chun Chen, Pi-Lien Hung, Yu-Ju Lin, Hajime Hirase.

  Maternal nutrient intake influences the health of the offspring via microenvironmental systems in digestion and absorption. Maternal high fructose diet (HFD) impairs hippocampus-dependent memory in adult female rat offspring. However, the underlying mechanisms remain largely unclear. Maternal HFD causes microbiota dysbiosis. In this study, we find that the plasma level of butyrate, a major metabolite of microbiota, is significantly decreased in the adult female maternal HFD offspring. In these rats, GPR43, a butyrate receptor was downregulated in the hippocampus. Moreover, the expressions of mitochondrial transcription factor A (TFAM), and peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α) were downregulated in the hippocampus. The decreases of these functional proteins were reversed by fructooligosaccharides (FOS, a probiotic) treatment in adulthood. Astrocytes are critical for energy metabolism in the brain. Primary astrocyte culture from female maternal HFD offspring indicated that GPR43 and the mitochondrial biogenesis were significantly suppressed, which was reversed by supplemental butyrate incubation. The oxygen consumption rate (OCR) was reduced in the HFD group and rescued by butyrate. Intriguingly, the nuclear histone deacetylase 4 (HDAC4) was enhanced in the HFD group, suggesting an inhibitory role of butyrate on histone deacetylase activity. Inhibition of HDAC4 effectively restored the OCR, bioenergetics, and biogenesis of mitochondria. Together, these results suggested that the impaired butyrate signaling by maternal HFD could underlie the reduced mitochondrial functions in the hippocampus via HDAC4-mediated epigenetic changes. ONE SENTENCE SUMMARY: Maternal HFD compromises astrocytic mitochondrial function via HDAC4-mediated epigenetic modifications that concomitantly occur with decreased levels of butyrate and GPR43 expression.

Keywords:  GPR43; HDAC4; Maternal high fructose diet; bioenergetics; butyrate; mitochondrial biogenesis

DOI:  https://doi.org/10.1016/j.jnutbio.2024.109571
Res Sq. 2023 Dec 19. pii: rs.3.rs-3716881. [Epub ahead of print]

Sex differences in mitochondrial gene expression during viral myocarditis.

Damian Di Florio, David Gorelov, Elizabeth McCabe, Danielle Beetler, Katie Shapiro, Katelyn Bruno, Isha Chekuri, Angita Jain, Emily Whelan, Gary Salomon, Sami Khatib, Natalie Bonvie-Hill, Presley Giresi, Varsini Balamurugan, Gabriel Weigel, Jessica Fliess, Ashley Darakjian, Brandy Edenfield, Christian Kocsis, Christopher McLeod, Leslie Cooper, Etienne Audet-Walsh, Michael Coronado, Jon Sin, DeLisa Fairweather.

Background Myocarditis is an inflammation of the heart muscle most often caused by an immune response to viral infections. Sex differences in the immune response during myocarditis have been well described but upstream mechanisms in the heart that might influence sex differences in disease are not completely understood. Methods Male and female BALB/c wild type mice received an intraperitoneal injection of heart-passaged coxsackievirus B3 (CVB3) or vehicle control. Bulk-tissue RNA-sequencing was conducted to better understand sex differences in CVB3 myocarditis. We performed enrichment analysis to understand sex differences in the transcriptional landscape of myocarditis and identify candidate transcription factors that might drive sex differences in myocarditis. Results The hearts of male and female mice with myocarditis were significantly enriched for pathways related to an innate and adaptive immune response compared to uninfected controls. When comparing females to males with myocarditis, males were enriched for inflammatory pathways and gene changes that suggested worse mitochondrial transcriptional support (e.g., mitochondrial electron transport genes). In contrast, females were enriched for pathways related to mitochondrial respiration and bioenergetics, which were confirmed by higher transcript levels of master regulators of mitochondrial function including peroxisome proliferator-activated receptor gamma coactivator 1 (PGC1α), nuclear respiratory factor 1 (NRF1) and estrogen-related receptor alpha (ERRα). TRANSFAC analysis identified ERRa as a transcription factor that may mediate sex differences in mitochondrial function during myocarditis. Conclusions Master regulators of mitochondrial function were elevated in females with myocarditis compared to males and may promote sex differences in mitochondrial respiratory transcript expression during viral myocarditis resulting in less severe myocarditis in females following viral infection.

DOI: https://doi.org/10.21203/rs.3.rs-3716881/v1
Diabetologia. 2024 Jan 11.

NRF2 is required for neonatal mouse beta cell growth by maintaining redox balance and promoting mitochondrial biogenesis and function.

Sharon Baumel-Alterzon, Liora S Katz, Luca Lambertini, Isabelle Tse, Fatema Heidery, Adolfo Garcia-Ocaña, Donald K Scott.

  AIMS/HYPOTHESIS: All forms of diabetes result from insufficient functional beta cell mass. Due to the relatively limited expression of several antioxidant enzymes, beta cells are highly vulnerable to pathological levels of reactive oxygen species (ROS), which can lead to the reduction of functional beta cell mass. During early postnatal ages, both human and rodent beta cells go through a burst of proliferation that quickly declines with age. The exact mechanisms that account for neonatal beta cell proliferation are understudied but mitochondrial release of moderated ROS levels has been suggested as one of the main drivers. We previously showed that, apart from its conventional role in protecting beta cells from oxidative stress, the nuclear factor erythroid 2-related factor 2 (NRF2) is also essential for beta cell proliferation. We therefore hypothesised that NRF2, which is activated by ROS, plays an essential role in beta cell proliferation at early postnatal ages.METHODS: Beta cell NRF2 levels and beta cell proliferation were measured in pancreatic sections from non-diabetic human cadaveric donors at different postnatal ages, childhood and adulthood. Pancreatic sections from 1-, 7-, 14- and 28-day-old beta cell-specific Nrf2 (also known as Nfe2l2)-knockout mice (βNrf2KO) or control (Nrf2lox/lox) mice were assessed for beta cell NRF2 levels, beta cell proliferation, beta cell oxidative stress, beta cell death, nuclear beta cell pancreatic duodenal homeobox protein 1 (PDX1) levels and beta cell mass. Seven-day-old βNrf2KO and Nrf2lox/lox mice were injected daily with N-acetylcysteine (NAC) or saline (154 mmol/l NaCl) to explore the potential contribution of oxidative stress to the phenotypes seen in βNrf2KO mice at early postnatal ages. RNA-seq was performed on 7-day-old βNrf2KO and Nrf2lox/lox mice to investigate the mechanisms by which NRF2 stimulates beta cell proliferation at early postnatal ages. Mitochondrial biogenesis and function were determined using dispersed islets from 7-day-old βNrf2KO and Nrf2lox/lox mice by measuring MitoTracker intensity, mtDNA/gDNA ratio and ATP/ADP ratio. To study the effect of neonatal beta cell-specific Nrf2 deletion on glucose homeostasis in adulthood, blood glucose, plasma insulin and insulin secretion were determined and a GTT was performed on 3-month-old βNrf2KO and Nrf2lox/lox mice fed on regular diet (RD) or high-fat diet (HFD).
RESULTS: The expression of the master antioxidant regulator NRF2 was increased at early postnatal ages in both human (1 day to 19 months old, 31%) and mouse (7 days old, 57%) beta cells, and gradually declined with age (8% in adult humans, 3.77% in adult mice). A significant correlation (R2=0.568; p=0.001) was found between beta cell proliferation and NRF2 levels in human beta cells. Seven-day-old βNrf2KO mice showed reduced beta cell proliferation (by 65%), beta cell nuclear PDX1 levels (by 23%) and beta cell mass (by 67%), and increased beta cell oxidative stress (threefold) and beta cell death compared with Nrf2lox/lox control mice. NAC injections increased beta cell proliferation in 7-day-old βNrf2KO mice (3.4-fold) compared with saline-injected βNrf2KO mice. Interestingly, RNA-seq of islets isolated from 7-day-old βNrf2KO mice revealed reduced expression of mitochondrial RNA genes and genes involved in the electron transport chain. Islets isolated from 7-day old βNrf2KO mice presented reduced MitoTracker intensity (by 47%), mtDNA/gDNA ratio (by 75%) and ATP/ADP ratio (by 68%) compared with islets from Nrf2lox/lox littermates. Lastly, HFD-fed 3-month-old βNrf2KO male mice displayed a significant reduction in beta cell mass (by 35%), a mild increase in non-fasting blood glucose (1.2-fold), decreased plasma insulin (by 14%), and reduced glucose tolerance (1.3-fold) compared with HFD-fed Nrf2lox/lox mice.
CONCLUSIONS/INTERPRETATION: Our study highlights NRF2 as an essential transcription factor for maintaining neonatal redox balance, mitochondrial biogenesis and function and beta cell growth, and for preserving functional beta cell mass in adulthood under metabolic stress.
DATA AVAILABILITY: Sequencing data are available in the NCBI Gene Expression Omnibus, accession number GSE242718 ( https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE242718 ).

Keywords:  Beta cell death; Beta cell proliferation; Diabetes; Mitochondria; NRF2; Neonatal development; Oxidative stress; Redox balance

DOI:  https://doi.org/10.1007/s00125-023-06071-7
bioRxiv. 2023 Dec 23. pii: 2023.12.23.573206. [Epub ahead of print]

Exogenous mitochondrial transfer increases energy expenditure and attenuates adiposity gains in mice with diet-induced obesity.

Maria Namwanje, Soumi Mazumdar, Amanda Stayton, Prisha S Patel, Christine Watkins, Catrina White, Chester Brown, James D Eason, Khyobeni Mozhui, Cem Kuscu, Navjot Pabla, Erin J Stephenson, Amandeep Bajwa.

Obesity is associated with chronic multi-system bioenergetic stress that may be improved by increasing the number of healthy mitochondria available across organ systems. However, treatments capable of increasing mitochondrial content are generally limited to endurance exercise training paradigms, which are not always sustainable long-term, let alone feasible for many patients with obesity. Recent studies have shown that local transfer of exogenous mitochondria from healthy donor tissues can improve bioenergetic outcomes and alleviate the effects of tissue injury in recipients with organ specific disease. Thus, the aim of this project was to determine the feasibility of systemic mitochondrial transfer for improving energy balance regulation in the setting of diet-induced obesity. We found that transplantation of mitochondria from lean mice into mice with diet-induced obesity attenuated adiposity gains by increasing energy expenditure and promoting the mobilization and oxidation of lipids. Additionally, mice that received exogenous mitochondria demonstrated improved glucose uptake, greater insulin responsiveness, and complete reversal of hepatic steatosis. These changes were, in part, driven by adaptations occurring in white adipose tissue. Together, these findings are proof-of-principle that mitochondrial transplantation is an effective therapeutic strategy for limiting the deleterious metabolic effects of diet-induced obesity in mice.

DOI: https://doi.org/10.1101/2023.12.23.573206
iScience. 2024 Jan 19. 27(1): 108634

Kinetic modeling of leucine-mediated signaling and protein metabolism in human skeletal muscle.

Taylor J McColl, David C Clarke.

  Skeletal muscle protein levels are governed by the relative rates of muscle protein synthesis (MPS) and breakdown (MPB). The mechanisms controlling these rates are complex, and their integrated behaviors are challenging to study through experiments alone. The purpose of this study was to develop and analyze a kinetic model of leucine-mediated mTOR signaling and protein metabolism in the skeletal muscle of young adults. Our model amalgamates published cellular-level models of the IRS1-PI3K-Akt-mTORC1 signaling system and of skeletal-muscle leucine kinetics with physiological-level models of leucine digestion and transport and insulin dynamics. The model satisfactorily predicts experimental data from diverse leucine feeding protocols. Model analysis revealed that total levels of p70S6K are a primary determinant of MPS, insulin signaling substantially affects muscle net protein balance via its effects on MPB, and p70S6K-mediated feedback of mTORC1 signaling reduces MPS in a dose-dependent manner.

Keywords:  Biological sciences; Protein

DOI:  https://doi.org/10.1016/j.isci.2023.108634