Exercise and Esr1 Control Mitochondrial Content and Function to Regulate Adiposity

Mechanisms that underlie adipose tissue remodeling to enhance metabolic health in response to exercise training remain inadequately understood. PURPOSE: We utilized mouse genetics and human GWAS to determine the impact of exercise training on mitochondrial DNA copy number, and interrogate the relationship between Esr1 and adipose tissue health. METHODS: We performed RNAseq on adipose tissue from 100 strains of inbred mice following exercise training and determined mitochondrial content by qPCR. We performed deep phenotyping of mice harboring conditional Esr1 overexpression selectively in adipose tissue. Adipose specific Esr1 overexpression and control mice were fed a high fat diet and placed in metabolic chambers to interrogate the effects of Esr1 on whole body metabolism. RESULTS: We determined that exercise training significantly increased adipose tissue mtDNA content in mouse and man and that increased mitochondrial content correlated with reduced adiposity. Adipocyte health was associated with increased expression of transcripts involved in mitochondrial cristae formation including OPA1, Polg1, and Dnm1l. Since Esr1 is a transcription factor negatively associated with adipose tissue mass, and since deletion of Esr1 disrupts mitochondrial function and reduces expression of Polg1, OPA1, and Dnm1l, we interrogated in impact of conditional Esr1 overexpression on mitochondrial function and adipose tissue health. Adipocyte-specific Esr1 overexpression increased expression of mitochondrial gene targets, increased mtDNA copy number and mitochondrial respiration, and enhanced whole body energy expenditure of animals challenged by high fat diet feeding. Adipocyte-specific Esr1 overexpression protected mice against HFD-induced obesity. CONCLUSION: Exercise promotes remodeling of adipose tissue mitochondria and is associated with fat mass reduction. Overexpression of Esr1 drives a similar adipose tissue remodeling and weight loss as exercise training, and protects against adipose tissue weight gain in the context of overnutrition. These data suggest that exercise responsive transcripts in adipose tissue can be selectively targeted to enhance weight loss and improve metabolic health

Genetic drivers of cardiac remodeling in health and disease in female mice

SWACSM Abstract Genetic drivers of cardiac remodeling in health and disease in female mice Alexander R. Strumwasser1, Timothy M. Moore1, Zhenqi Zhou1, Lorraine P. Turcotte2, Aldons J. Lusis1, Andrea L. Hevener1 1Department of Medicine, University of California, Los Angeles 2Department of Biological Sciences, University of Southern California Hevener Laboratory; Department of Medicine; University of California Los Angeles Laboratory Category: Masters Advisor / Mentor: Hevener, Andrea L. [email protected] ABSTRACT PURPOSE: Sex differences in cardiac metabolism and cardiometabolic disease susceptibility are well documented. However, the mechanisms underlying sexual dimorphism and the role estrogens play in cardiac physiology aren’t well understood, especially in aging women when cardiometabolic disease susceptibility is heightened. The purpose of the current study was to determine key genetic drivers of healthy vs. pathogenic cardiac remodeling and determine the impact of estrogen action on cardiomyocellular function. METHODS: The UCLA Exercise Hybrid Mouse Diversity Panel (ExcHMDP), comprised of ~100 strains of inbred mice, was leveraged to interrogate genetic drivers of cardiac remodeling in response to exercise training. Female mice from the ExcHMDP remained sedentary (SED) or preformed volitional exercise (TRN) by in cage wheel running (30d). Heart samples (4 SED and 4 TRN mice per strain) harvested following a 6h fast, 30h after the last bout of exercise, were subjected to RNA sequencing. A similar analysis was performed on hearts from 91 strains of female mice treated with the cardiac remodeling drug isoproterenol (ISO). Estrogen action related to cardiac remodeling was studied in female mice with a conditional cardiac-specific deletion of estrogen receptor alpha (encoded by Esr1). Integrated informatic assessment of these transcriptomic data sets identified pathways driving healthy versus pathogenic cardiac remodeling. RESULTS: Heart weight was increased following exercise training in 85 of 100 strains studied. Cardiac enrichment analysis of differentially expressed transcripts and candidate gene identification analyses revealed 5 potential regulatory genes associated with healthy cardiac remodeling in response to exercise training. We contrasted these findings with the genetic architecture of two mouse models of cardiac hypertrophy-associated heart failure, the ISO-HMDP and cardiac-specific Esr1 knockout. Mitochondrial function and calcium homeostasis emerged as key pathways of regulation related to cardiac hypertrophy. CONCLUSION: Our studies provide important insight into the genetic architecture and key genetic drivers of cardiac remodeling in females. The goal of our research is to identify cardiac-specific transcripts and pathways that can be targeted therapeutically to preserve cardiac function during aging in women

Key Genetic Drivers of Volitional Physical Activity in the Central Nervous System

Previous studies suggest that physical activity is driven by the Central Nervous System (CNS). PURPOSE: We determined the central genetic drivers of volitional activity in the CNS and identified several molecular mechanisms promoting improvements in metabolism as a consequence of daily exercise. METHODS: Leveraging genetic diversity, we studied 100 strains of sedentary (SED) and exercise-trained (TRN; in cage running wheels) animals of the UCLA hybrid mouse diversity panel (HMDP). Candidate gene identification analysis and single-cell RNA sequencing in three brain regions (hypothalamus, hippocampus, and striatum) were performed. Differential gene analysis was conducted between a cohort of exercise-trained and sedentary C57BL/6J mice using the same exercise training protocol as employed for the exercise HMDP. RESULTS: The hypothalamus contained the highest number of candidate genes associated with volitional activity (n=81), followed by the striatum (n=56), and the hippocampus (n=41), with many driver transcripts being shared among all three brain regions. Seventeen distinct cell populations were identified within the hypothalamus, and significant differences in cell-specific transcripts were identified in TRN vs SED mice (FDRHumanin, was significantly increased in nearly all cell types. CONCLUSION: Volitional activity appears significantly controlled by the genetic architecture of the hypothalamus, striatum, and hippocampus brain regions. Transcript signatures within the various cell types of these brain regions were altered following 30 days of exercise training. Our findings show that the gene encoding the mitochondrial peptide Humanin is exercise responsive, induced by exercise training in all three brain regions examined, and is a likely mediator of exercise-induced neuroprotection

Effect of voluntary exercise upon the metabolic syndrome and gut microbiome composition in mice

The metabolic syndrome is a cluster of conditions that increase an individual's risk of developing diseases. Being physically active throughout life is known to reduce the prevalence and onset of some aspects of the metabolic syndrome. Furthermore, previous studies have demonstrated that an individual's gut microbiome composition has a large influence on several aspects of the metabolic syndrome. However, the mechanism(s) by which physical activity may improve metabolic health are not well understood. We sought to determine if endurance exercise is sufficient to prevent or ameliorate the development of the metabolic syndrome and its associated diseases. We also analyzed the impact of physical activity under metabolic syndrome progression upon the gut microbiome composition. Utilizing whole-body low-density lipoprotein receptor (LDLR) knockout mice on a "Western Diet," we show that long-term exercise acts favorably upon glucose tolerance, adiposity, and liver lipids. Exercise increased mitochondrial abundance in skeletal muscle but did not reduce liver fibrosis, aortic lesion area, or plasma lipids. Lastly, we observed several changes in gut bacteria and their novel associations with metabolic parameters of clinical importance. Altogether, our results indicate that exercise can ameliorate some aspects of the metabolic syndrome progression and alter the gut microbiome composition

Mitochondrial Dysfunction Is an Early Consequence of Partial or Complete Dystrophin Loss in mdx Mice

Duchenne muscular dystrophy (DMD) is characterized by rapid wasting of skeletal muscle. Mitochondrial dysfunction is a well-known pathological feature of DMD. However, whether mitochondrial dysfunction occurs before muscle fiber damage in DMD pathology is not well known. Furthermore, the impact upon heterozygous female mdx carriers (mdx/+), who display dystrophin mosaicism, has received little attention. We hypothesized that dystrophin deletion leads to mitochondrial dysfunction, and that this may occur before myofiber necrosis. As a secondary complication to mitochondrial dysfunction, we also hypothesized metabolic abnormalities prior to the onset of muscle damage. In this study, we detected aberrant mitochondrial morphology, reduced cristae number, and large mitochondrial vacuoles from both male and female mdx mice prior to the onset of muscle damage. Furthermore, we systematically characterized mitochondria during disease progression starting before the onset of muscle damage, noting additional changes in mitochondrial DNA copy number and regulators of mitochondrial size. We further detected mild metabolic and mitochondrial impairments in female mdx carrier mice that were exacerbated with high-fat diet feeding. Lastly, inhibition of the strong autophagic program observed in adolescent mdx male mice via administration of the autophagy inhibitor leupeptin did not improve skeletal muscle pathology. These results are in line with previous data and suggest that before the onset of myofiber necrosis, mitochondrial and metabolic abnormalities are present within the mdx mouse

Parkin regulates adiposity by coordinating mitophagy with mitochondrial biogenesis in white adipocytes.

Parkin, an E3 ubiquitin ligase, plays an essential role in mitochondrial quality control. However, the mechanisms by which Parkin connects mitochondrial homeostasis with cellular metabolism in adipose tissue remain unclear. Here, we demonstrate that Park2 gene (encodes Parkin) deletion specifically from adipose tissue protects mice against high-fat diet and aging-induced obesity. Despite a mild reduction in mitophagy, mitochondrial DNA content and mitochondrial function are increased in Park2 deficient white adipocytes. Moreover, Park2 gene deletion elevates mitochondrial biogenesis by increasing Pgc1α protein stability through mitochondrial superoxide-activated NAD(P)H quinone dehydrogenase 1 (Nqo1). Both in vitro and in vivo studies show that Nqo1 overexpression elevates Pgc1α protein level and mitochondrial DNA content and enhances mitochondrial activity in mouse and human adipocytes. Taken together, our findings indicate that Parkin regulates mitochondrial homeostasis by balancing mitophagy and Pgc1α-mediated mitochondrial biogenesis in white adipocytes, suggesting a potential therapeutic target in adipocytes to combat obesity and obesity-associated disorders

Drp1 controls complex II assembly and skeletal muscle metabolism by Sdhaf2 action on mitochondria

The dynamin-related guanosine triphosphatase, Drp1 (encoded by Dnm1l), plays a central role in mitochondrial fission and is requisite for numerous cellular processes; however, its role in muscle metabolism remains unclear. Here, we show that, among human tissues, the highest number of gene correlations with DNM1L is in skeletal muscle. Knockdown of Drp1 (Drp1-KD) promoted mitochondrial hyperfusion in the muscle of male mice. Reduced fatty acid oxidation and impaired insulin action along with increased muscle succinate was observed in Drp1-KD muscle. Muscle Drp1-KD reduced complex II assembly and activity as a consequence of diminished mitochondrial translocation of succinate dehydrogenase assembly factor 2 (Sdhaf2). Restoration of Sdhaf2 normalized complex II activity, lipid oxidation, and insulin action in Drp1-KD myocytes. Drp1 is critical in maintaining mitochondrial complex II assembly, lipid oxidation, and insulin sensitivity, suggesting a mechanistic link between mitochondrial morphology and skeletal muscle metabolism, which is clinically relevant in combatting metabolic-related diseases

The impact of exercise on mitochondrial dynamics and the role of Drp1 in exercise performance and training adaptations in skeletal muscle

Objective Mitochondria are organelles primarily responsible for energy production, and recent evidence indicates that alterations in size, shape, location, and quantity occur in response to fluctuations in energy supply and demand. We tested the impact of acute and chronic exercise on mitochondrial dynamics signaling and determined the impact of the mitochondrial fission regulator Dynamin related protein (Drp)1 on exercise performance and muscle adaptations to training. Methods Wildtype and muscle-specific Drp1 heterozygote (mDrp1+/−) mice, as well as dysglycemic (DG) and healthy normoglycemic men (control) performed acute and chronic exercise. The Hybrid Mouse Diversity Panel, including 100 murine strains of recombinant inbred mice, was used to identify muscle Dnm1L (encodes Drp1)-gene relationships. Results Endurance exercise impacted all aspects of the mitochondrial life cycle, i.e. fission-fusion, biogenesis, and mitophagy. Dnm1L gene expression and Drp1Ser616 phosphorylation were markedly increased by acute exercise and declined to baseline during post-exercise recovery. Dnm1L expression was strongly associated with transcripts known to regulate mitochondrial metabolism and adaptations to exercise. Exercise increased the expression of DNM1L in skeletal muscle of healthy control and DG subjects, despite a 15% ↓(P = 0.01) in muscle DNM1L expression in DG at baseline. To interrogate the role of Dnm1L further, we exercise trained male mDrp1+/− mice and found that Drp1 deficiency reduced muscle endurance and running performance, and altered muscle adaptations in response to exercise training. Conclusion Our findings highlight the importance of mitochondrial dynamics, specifically Drp1 signaling, in the regulation of exercise performance and adaptations to endurance exercise training

Age-induced mitochondrial DNA point mutations are inadequate to alter metabolic homeostasis in response to nutrient challenge.

Mitochondrial dysfunction is frequently associated with impairment in metabolic homeostasis and insulin action, and is thought to underlie cellular aging. However, it is unclear whether mitochondrial dysfunction is a cause or consequence of insulin resistance in humans. To determine the impact of intrinsic mitochondrial dysfunction on metabolism and insulin action, we performed comprehensive metabolic phenotyping of the polymerase gamma (PolG) D257A "mutator" mouse, a model known to accumulate supraphysiological mitochondrial DNA (mtDNA) point mutations. We utilized the heterozygous PolG mutator mouse (PolG+/mut ) because it accumulates mtDNA point mutations ~ 500-fold > wild-type mice (WT), but fails to develop an overt progeria phenotype, unlike PolGmut/mut animals. To determine whether mtDNA point mutations induce metabolic dysfunction, we examined male PolG+/mut mice at 6 and 12 months of age during normal chow feeding, after 24-hr starvation, and following high-fat diet (HFD) feeding. No marked differences were observed in glucose homeostasis, adiposity, protein/gene markers of metabolism, or oxygen consumption in muscle between WT and PolG+/mut mice during any of the conditions or ages studied. However, proteomic analyses performed on isolated mitochondria from 12-month-old PolG+/mut mouse muscle revealed alterations in the expression of mitochondrial ribosomal proteins, electron transport chain components, and oxidative stress-related factors compared with WT. These findings suggest that mtDNA point mutations at levels observed in mammalian aging are insufficient to disrupt metabolic homeostasis and insulin action in male mice