Sexual dimorphism and the multi-omic response to exercise training in rat subcutaneous white adipose tissue.

Subcutaneous white adipose tissue (scWAT) is a dynamic storage and secretory organ that regulates systemic homeostasis, yet the impact of endurance exercise training (ExT) and sex on its molecular landscape is not fully established. Utilizing an integrative multi-omics approach, and leveraging data generated by the Molecular Transducers of Physical Activity Consortium (MoTrPAC), we show profound sexual dimorphism in the scWAT of sedentary rats and in the dynamic response of this tissue to ExT. Specifically, the scWAT of sedentary females displays -omic signatures related to insulin signaling and adipogenesis, whereas the scWAT of sedentary males is enriched in terms related to aerobic metabolism. These sex-specific -omic signatures are preserved or amplified with ExT. Integration of multi-omic analyses with phenotypic measures identifies molecular hubs predicted to drive sexually distinct responses to training. Overall, this study underscores the powerful impact of sex on adipose tissue biology and provides a rich resource to investigate the scWAT response to ExT.

The mitochondrial multi-omic response to exercise training across rat tissues.

Mitochondria have diverse functions critical to whole-body metabolic homeostasis. Endurance training alters mitochondrial activity, but systematic characterization of these adaptations is lacking. Here, the Molecular Transducers of Physical Activity Consortium mapped the temporal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats trained for 1, 2, 4, or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart, and skeletal muscle. The colon showed non-linear response dynamics, whereas mitochondrial pathways were downregulated in brown adipose and adrenal tissues. Protein acetylation increased in the liver, with a shift in lipid metabolism, whereas oxidative proteins increased in striated muscles. Exercise-upregulated networks were downregulated in human diabetes and cirrhosis. Knockdown of the central network protein 17-beta-hydroxysteroid dehydrogenase 10 (HSD17B10) elevated oxygen consumption, indicative of metabolic stress. We provide a multi-omic, multi-tissue, temporal atlas of the mitochondrial response to exercise training and identify candidates linked to mitochondrial dysfunction.

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.

Leveraging inter-individual transcriptional correlation structure to infer discrete signaling mechanisms across metabolic tissues.

Inter-organ communication is a vital process to maintain physiologic homeostasis, and its dysregulation contributes to many human diseases. Given that circulating bioactive factors are stable in serum, occur naturally, and are easily assayed from blood, they present obvious focal molecules for therapeutic intervention and biomarker development. Recently, studies have shown that secreted proteins mediating inter-tissue signaling could be identified by 'brute force' surveys of all genes within RNA-sequencing measures across tissues within a population. Expanding on this intuition, we reasoned that parallel strategies could be used to understand how individual genes mediate signaling across metabolic tissues through correlative analyses of gene variation between individuals. Thus, comparison of quantitative levels of gene expression relationships between organs in a population could aid in understanding cross-organ signaling. Here, we surveyed gene-gene correlation structure across 18 metabolic tissues in 310 human individuals and 7 tissues in 103 diverse strains of mice fed a normal chow or high-fat/high-sucrose (HFHS) diet. Variation of genes such as FGF21, ADIPOQ, GCG, and IL6 showed enrichments which recapitulate experimental observations. Further, similar analyses were applied to explore both within-tissue signaling mechanisms (liver PCSK9) and genes encoding enzymes producing metabolites (adipose PNPLA2), where inter-individual correlation structure aligned with known roles for these critical metabolic pathways. Examination of sex hormone receptor correlations in mice highlighted the difference of tissue-specific variation in relationships with metabolic traits. We refer to this resource as gene-derived correlations across tissues (GD-CAT) where all tools and data are built into a web portal enabling users to perform these analyses without a single line of code (gdcat.org). This resource enables querying of any gene in any tissue to find correlated patterns of genes, cell types, pathways, and network architectures across metabolic organs.

Conserved multi-tissue transcriptomic adaptations to exercise training in humans and mice.

Physical activity is associated with beneficial adaptations in human and rodent metabolism. We studied over 50 complex traits before and after exercise intervention in middle-aged men and a panel of 100 diverse strains of female mice. Candidate gene analyses in three brain regions, muscle, liver, heart, and adipose tissue of mice indicate genetic drivers of clinically relevant traits, including volitional exercise volume, muscle metabolism, adiposity, and hepatic lipids. Although ∼33% of genes differentially expressed in skeletal muscle following the exercise intervention are similar in mice and humans independent of BMI, responsiveness of adipose tissue to exercise-stimulated weight loss appears controlled by species and underlying genotype. We leveraged genetic diversity to generate prediction models of metabolic trait responsiveness to volitional activity offering a framework for advancing personalized exercise prescription. The human and mouse data are publicly available via a user-friendly Web-based application to enhance data mining and hypothesis development.

The mitochondrial multi-omic response to exercise training across tissues.

Mitochondria are adaptable organelles with diverse cellular functions critical to whole-body metabolic homeostasis. While chronic endurance exercise training is known to alter mitochondrial activity, these adaptations have not yet been systematically characterized. Here, the Molecular Transducers of Physical Activity Consortium (MoTrPAC) mapped the longitudinal, multi-omic changes in mitochondrial analytes across 19 tissues in male and female rats endurance trained for 1, 2, 4 or 8 weeks. Training elicited substantial changes in the adrenal gland, brown adipose, colon, heart and skeletal muscle, while we detected mild responses in the brain, lung, small intestine and testes. The colon response was characterized by non-linear dynamics that resulted in upregulation of mitochondrial function that was more prominent in females. Brown adipose and adrenal tissues were characterized by substantial downregulation of mitochondrial pathways. Training induced a previously unrecognized robust upregulation of mitochondrial protein abundance and acetylation in the liver, and a concomitant shift in lipid metabolism. The striated muscles demonstrated a highly coordinated response to increase oxidative capacity, with the majority of changes occurring in protein abundance and post-translational modifications. We identified exercise upregulated networks that are downregulated in human type 2 diabetes and liver cirrhosis. In both cases HSD17B10, a central dehydrogenase in multiple metabolic pathways and mitochondrial tRNA maturation, was the main hub. In summary, we provide a multi-omic, cross-tissue atlas of the mitochondrial response to training and identify candidates for prevention of disease-associated mitochondrial dysfunction.

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.

Genetic variation of putative myokine signaling is dominated by biological sex and sex hormones.

Skeletal muscle plays an integral role in coordinating physiological homeostasis, where signaling to other tissues via myokines allows for coordination of complex processes. Here, we aimed to leverage natural genetic correlation structure of gene expression both within and across tissues to understand how muscle interacts with metabolic tissues. Specifically, we performed a survey of genetic correlations focused on myokine gene regulation, muscle cell composition, cross-tissue signaling, and interactions with genetic sex in humans. While expression levels of a majority of myokines and cell proportions within skeletal muscle showed little relative differences between males and females, nearly all significant cross-tissue enrichments operated in a sex-specific or hormone-dependent fashion; in particular, with estradiol. These sex- and hormone-specific effects were consistent across key metabolic tissues: liver, pancreas, hypothalamus, intestine, heart, visceral, and subcutaneous adipose tissue. To characterize the role of estradiol receptor signaling on myokine expression, we generated male and female mice which lack estrogen receptor α specifically in skeletal muscle (MERKO) and integrated with human data. These analyses highlighted potential mechanisms of sex-dependent myokine signaling conserved between species, such as myostatin enriched for divergent substrate utilization pathways between sexes. Several other putative sex-dependent mechanisms of myokine signaling were uncovered, such as muscle-derived tumor necrosis factor alpha (TNFA) enriched for stronger inflammatory signaling in females compared to males and GPX3 as a male-specific link between glycolytic fiber abundance and hepatic inflammation. Collectively, we provide a population genetics framework for inferring muscle signaling to metabolic tissues in humans. We further highlight sex and estradiol receptor signaling as critical variables when assaying myokine functions and how changes in cell composition are predicted to impact other metabolic organs.

The muscles that are responsible for voluntary movements such as exercise are called skeletal muscles. These muscles secrete proteins called myokines, which play roles in a variety of processes by interacting with other tissues. Essentially, myokines allow skeletal muscles to communicate with organs such as the kidneys, the liver or the brain, which is essential for the body to keep its metabolic balance. Some of the process myokines are involved include inflammation, cancer, the changes brought about by exercise, and even cognition. Despite the clear relevance of myokines to so many physiological outcomes, the way these proteins are regulated and their effects are not well understood. Genetic sex ­ specified by sex chromosomes in mammals ­ contributes to critical aspects of physiology. Specifically, many of the metabolic traits impacted by myokines show striking differences arising from hormonal or genetic interactions depending on the genetic sex of the subject being studied. It is therefore important to consider genetic sex when studying the effects of myokines on the body. Velez, Van et al. wanted to gain a better understanding of how skeletal muscles interact with metabolic tissues such as pancreas, liver and brain, taking genetic sex into consideration. To do this they surveyed human datasets for the correlations between the activity of genes that code for myokines, the composition of muscle cells, the signaling between muscles and metabolic tissues and genetic sex. Their results showed that, genetic sex and sex hormones predicted most of the effects of skeletal muscle on other tissues. For example, myokines from muscle were predicted to be more impactful on liver or pancreas, depending on whether individuals were male or female, respectively. The results of Velez, Van et al. illustrate the importance of considering the effects of genetic sex and sexual hormones when studying metabolism. In the future, these results will allow other researchers to design sex-specific experiments to be able to gather more accurate information about the mechanisms of myokine signaling.

ABCB10 exports mitochondrial biliverdin, driving metabolic maladaptation in obesity.

Although the role of hydrophilic antioxidants in the development of hepatic insulin resistance and nonalcoholic fatty liver disease has been well studied, the role of lipophilic antioxidants remains poorly characterized. A known lipophilic hydrogen peroxide scavenger is bilirubin, which can be oxidized to biliverdin and then reduced back to bilirubin by cytosolic biliverdin reductase. Oxidation of bilirubin to biliverdin inside mitochondria must be followed by the export of biliverdin to the cytosol, where biliverdin is reduced back to bilirubin. Thus, the putative mitochondrial exporter of biliverdin is expected to be a major determinant of bilirubin regeneration and intracellular hydrogen peroxide scavenging. Here, we identified ABCB10 as a mitochondrial biliverdin exporter. ABCB10 reconstituted into liposomes transported biliverdin, and ABCB10 deletion caused accumulation of biliverdin inside mitochondria. Obesity with insulin resistance up-regulated hepatic ABCB10 expression in mice and elevated cytosolic and mitochondrial bilirubin content in an ABCB10-dependent manner. Revealing a maladaptive role of ABCB10-driven bilirubin synthesis, hepatic ABCB10 deletion protected diet-induced obese mice from steatosis and hyperglycemia, improving insulin-mediated suppression of glucose production and decreasing lipogenic SREBP-1c expression. Protection was concurrent with enhanced mitochondrial function and increased inactivation of PTP1B, a phosphatase disrupting insulin signaling and elevating SREBP-1c expression. Restoration of cellular bilirubin content in ABCB10 KO hepatocytes reversed the improvements in mitochondrial function and PTP1B inactivation, demonstrating that bilirubin was the maladaptive effector linked to ABCB10 function. Thus, we identified a fundamental transport process that amplifies intracellular bilirubin redox actions, which can exacerbate insulin resistance and steatosis in obesity.

A pro-diabetogenic mtDNA polymorphism in the mitochondrial-derived peptide, MOTS-c.

Type 2 Diabetes (T2D) is an emerging public health problem in Asia. Although ethnic specific mtDNA polymorphisms have been shown to contribute to T2D risk, the functional effects of the mtDNA polymorphisms and the therapeutic potential of mitochondrial-derived peptides at the mtDNA polymorphisms are underexplored. Here, we showed an Asian-specific mitochondrial DNA variation m.1382A>C (rs111033358) leads to a K14Q amino acid replacement in MOTS-c, an insulin sensitizing mitochondrial-derived peptide. Meta-analysis of three cohorts (n = 27,527, J-MICC, MEC, and TMM) show that males but not females with the C-allele exhibit a higher prevalence of T2D. In J-MICC, only males with the C-allele in the lowest tertile of physical activity increased their prevalence of T2D, demonstrating a kinesio-genomic interaction. High-fat fed, male mice injected with MOTS-c showed reduced weight and improved glucose tolerance, but not K14Q-MOTS-c treated mice. Like the human data, female mice were unaffected. Mechanistically, K14Q-MOTS-c leads to diminished insulin-sensitization in vitro. Thus, the m.1382A>C polymorphism is associated with susceptibility to T2D in men, possibly interacting with exercise, and contributing to the risk of T2D in sedentary males by reducing the activity of MOTS-c.

ERα in the Control of Mitochondrial Function and Metabolic Health.

Decrements in metabolic health elevate disease risk, including type 2 diabetes, heart disease, and certain cancers. Thus, treatment strategies to combat metabolic dysfunction are needed. Reduced ESR1 (estrogen receptor, ERα) expression is observed in muscle from women, men, and animals presenting clinical features of the metabolic syndrome. Human studies of natural expression of ESR1 in metabolic tissues show that muscle expression of ESR1 is positively correlated with markers of metabolic health, including insulin sensitivity. Herein, we highlight the important impact of ERα on mitochondrial form and function and present how these actions of the receptor govern metabolic homeostasis. Studies identifying ERα-regulated pathways for disease prevention will lay the foundation for the design of novel therapeutics to improve the health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.

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.

Estrogen receptor α controls metabolism in white and brown adipocytes by regulating Polg1 and mitochondrial remodeling.

Obesity is heightened during aging, and although the estrogen receptor α (ERα) has been implicated in the prevention of obesity, its molecular actions in adipocytes remain inadequately understood. Here, we show that adipose tissue ESR1/Esr1 expression inversely associated with adiposity and positively associated with genes involved in mitochondrial metabolism and markers of metabolic health in 700 Finnish men and 100 strains of inbred mice from the UCLA Hybrid Mouse Diversity Panel. To determine the anti-obesity actions of ERα in fat, we selectively deleted Esr1 from white and brown adipocytes in mice. In white adipose tissue, Esr1 controlled oxidative metabolism by restraining the targeted elimination of mitochondria via the E3 ubiquitin ligase parkin. mtDNA content was elevated, and adipose tissue mass was reduced in adipose-selective parkin knockout mice. In brown fat centrally involved in body temperature maintenance, Esr1 was requisite for both mitochondrial remodeling by dynamin-related protein 1 (Drp1) and uncoupled respiration thermogenesis by uncoupled protein 1 (Ucp1). In both white and brown fat of female mice and adipocytes in culture, mitochondrial dysfunction in the context of Esr1 deletion was paralleled by a reduction in the expression of the mtDNA polymerase γ subunit Polg1 We identified Polg1 as an ERα target gene by showing that ERα binds the Polg1 promoter to control its expression in 3T3L1 adipocytes. These findings support strategies leveraging ERα action on mitochondrial function in adipocytes to combat obesity and metabolic dysfunction.

The Impact of Skeletal Muscle ERα on Mitochondrial Function and Metabolic Health.

The incidence of chronic disease is elevated in women after menopause. Increased expression of ESR1 (the gene that encodes the estrogen receptor alpha, ERα) in muscle is highly associated with metabolic health and insulin sensitivity. Moreover, reduced muscle expression levels of ESR1 are observed in women, men, and animals presenting clinical features of the metabolic syndrome (MetSyn). Considering that metabolic dysfunction elevates chronic disease risk, including type 2 diabetes, heart disease, and certain cancers, treatment strategies to combat metabolic dysfunction and associated pathologies are desperately needed. This review will provide published work supporting a critical and protective role for skeletal muscle ERα in the regulation of mitochondrial function, metabolic homeostasis, and insulin action. We will provide evidence that muscle-selective targeting of ERα may be effective for the preservation of mitochondrial and metabolic health. Collectively published findings support a compelling role for ERα in the control of muscle metabolism via its regulation of mitochondrial function and quality control. Studies identifying ERα-regulated pathways essential for disease prevention will lay the important foundation for the design of novel therapeutics to improve metabolic health of women while limiting secondary complications that have historically plagued traditional hormone replacement interventions.

The E3 ligase MARCH5 is a PPARγ target gene that regulates mitochondria and metabolism in adipocytes.

Mitochondrial dynamics refers to the constant remodeling of mitochondrial populations by multiple cellular pathways that help maintain mitochondrial health and function. Disruptions in mitochondrial dynamics often lead to mitochondrial dysfunction, which is frequently associated with disease in rodents and humans. Consistent with this, obesity is associated with reduced mitochondrial function in white adipose tissue, partly via alterations in mitochondrial dynamics. Several proteins, including the E3 ubiquitin ligase membrane-associated RING-CH-type finger 5 (MARCH5), are known to regulate mitochondrial dynamics; however, the role of these proteins in adipocytes has been poorly studied. Here, we show that MARCH5 is regulated by peroxisome proliferator-activated receptor-γ (PPARγ) during adipogenesis and is correlated with fat mass across a panel of genetically diverse mouse strains, in ob/ob mice, and in humans. Furthermore, manipulation of MARCH5 expression in vitro and in vivo alters mitochondrial function, affects cellular metabolism, and leads to differential regulation of several metabolic genes. Thus our data demonstrate an association between mitochondrial dynamics and metabolism that defines MARCH5 as a critical link between these interconnected pathways.

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.

New mitochondrial DNA synthesis enables NLRP3 inflammasome activation.

Dysregulated NLRP3 inflammasome activity results in uncontrolled inflammation, which underlies many chronic diseases. Although mitochondrial damage is needed for the assembly and activation of the NLRP3 inflammasome, it is unclear how macrophages are able to respond to structurally diverse inflammasome-activating stimuli. Here we show that the synthesis of mitochondrial DNA (mtDNA), induced after the engagement of Toll-like receptors, is crucial for NLRP3 signalling. Toll-like receptors signal via the MyD88 and TRIF adaptors to trigger IRF1-dependent transcription of CMPK2, a rate-limiting enzyme that supplies deoxyribonucleotides for mtDNA synthesis. CMPK2-dependent mtDNA synthesis is necessary for the production of oxidized mtDNA fragments after exposure to NLRP3 activators. Cytosolic oxidized mtDNA associates with the NLRP3 inflammasome complex and is required for its activation. The dependence on CMPK2 catalytic activity provides opportunities for more effective control of NLRP3 inflammasome-associated diseases.

The impact of ERα action on muscle metabolism and insulin sensitivity - Strong enough for a man, made for a woman.

BACKGROUND: The incidence of chronic disease is elevated in women after menopause. Natural variation in muscle expression of the estrogen receptor (ER)α is inversely associated with plasma insulin and adiposity. Moreover, reduced muscle ERα expression levels are observed in women and animals presenting clinical features of the metabolic syndrome (MetSyn). Considering that metabolic dysfunction impacts nearly a quarter of the U.S. adult population and elevates chronic disease risk including type 2 diabetes, heart disease, and certain cancers, treatment strategies to combat metabolic dysfunction and associated pathologies are desperately needed. SCOPE OF THE REVIEW: This review will provide evidence supporting a critical and protective role for skeletal muscle ERα in the regulation of metabolic homeostasis and insulin sensitivity, and propose novel ERα targets involved in the maintenance of metabolic health. MAJOR CONCLUSIONS: Studies identifying ERα-regulated pathways essential for disease prevention will lay the important foundation for the rational design of novel therapeutics to improve the metabolic health of women while limiting secondary complications that have plagued traditional hormone replacement interventions.

Genetic, dietary, and sex-specific regulation of hepatic ceramides and the relationship between hepatic ceramides and IR.

Elevated hepatic ceramide levels have been implicated in both insulin resistance (IR) and hepatic steatosis. To understand the factors contributing to hepatic ceramide levels in mice of both sexes, we have quantitated ceramides in a reference population of mice, the Hybrid Mouse Diversity Panel that has been previously characterized for a variety of metabolic syndrome traits. We observed significant positive correlations between Cer(d18:1/16:0) and IR/hepatic steatosis, consistent with previous findings, although the relationship broke down between sexes, as females were less insulin resistant, but had higher Cer(d18:1/16:0) levels than males. The sex difference was due in part to testosterone-mediated repression of ceramide synthase 6. One ceramide species, Cer(d18:1/20:0), was present at higher levels in males and was associated with IR only in males. Clear evidence of gene-by-sex and gene-by-diet interactions was observed, including sex-specific genome-wide association study results. Thus, our studies show clear differences in how hepatic ceramides are regulated between the sexes, which again suggests that the physiological roles of certain hepatic ceramides differ between the sexes.

Estrogen receptor α protects pancreatic ß-cells from apoptosis by preserving mitochondrial function and suppressing endoplasmic reticulum stress.

Estrogen receptor α (ERα) action plays an important role in pancreatic ß-cell function and survival; thus, it is considered a potential therapeutic target for the treatment of type 2 diabetes in women. However, the mechanisms underlying the protective effects of ERα remain unclear. Because ERα regulates mitochondrial metabolism in other cell types, we hypothesized that ERα may act to preserve insulin secretion and promote ß-cell survival by regulating mitochondrial-endoplasmic reticulum (EndoRetic) function. We tested this hypothesis using pancreatic islet-specific ERα knockout (PERαKO) mice and Min6 ß-cells in culture with Esr1 knockdown (KD). We found that Esr1-KD promoted reactive oxygen species production that associated with reduced fission/fusion dynamics and impaired mitophagy. Electron microscopy showed mitochondrial enlargement and a pro-fusion phenotype. Mitochondrial cristae and endoplasmic reticulum were dilated in Esr1-KD compared with ERα replete Min6 ß-cells. Increased expression of Oma1 and Chop was paralleled by increased oxygen consumption and apoptosis susceptibility in ERα-KD cells. In contrast, ERα overexpression and ligand activation reduced both Chop and Oma1 expression, likely by ERα binding to consensus estrogen-response element sites in the Oma1 and Chop promoters. Together, our findings suggest that ERα promotes ß-cell survival and insulin secretion through maintenance of mitochondrial fission/fusion-mitophagy dynamics and EndoRetic function, in part by Oma1 and Chop repression.