Sex and depot differences in adipocyte insulin sensitivity and glucose metabolism

Sex-dependent adipose glucose partitioning by the mitochondrial pyruvate carrier

Objective

The mitochondrial pyruvate carrier (MPC) occupies a critical node in intermediary metabolism, prompting interest in its utility as a therapeutic target for the treatment of obesity and cardiometabolic disease. Dysregulated nutrient metabolism in adipose tissue is a prominent feature of obesity pathophysiology, yet the functional role of adipose MPC has not been explored. We investigated whether the MPC shapes the adaptation of adipose tissue to dietary stress in female and male mice.

Methods

The impact of pharmacological and genetic disruption of the MPC on mitochondrial pathways of triglyceride assembly (lipogenesis and glyceroneogenesis) was assessed in 3T3L1 adipocytes and murine adipose explants, combined with analyses of adipose MPC expression in metabolically compromised humans. Whole-body and adipose-specific glucose metabolism were subsequently investigated in male and female mice lacking adipocyte MPC1 (Mpc1AD-/-) and fed either standard chow, high-fat western style, or high-sucrose lipid restricted diets for 24 weeks, using a combination of radiolabeled tracers and GC/MS metabolomics.

Results

Treatment with UK5099 or siMPC1 impaired the synthesis of lipids and glycerol-3-phosphate from pyruvate and blunted triglyceride accumulation in 3T3L1 adipocytes, whilst MPC expression in human adipose tissue was negatively correlated with indices of whole-body and adipose tissue metabolic dysfunction. Mature adipose explants from Mpc1AD-/- mice were intrinsically incapable of incorporating pyruvate into triglycerides. In vivo, MPC deletion restricted the incorporation of circulating glucose into adipose triglycerides, but only in female mice fed a zero fat diet, and this associated with sex-specific reductions in tricarboxylic acid cycle pool sizes and compensatory transcriptional changes in lipogenic and glycerol metabolism pathways. However, whole-body adiposity and metabolic health were preserved in Mpc1AD-/- mice regardless of sex, even under conditions of zero dietary fat.

Conclusion

These findings highlight the greater capacity for mitochondrially driven triglyceride assembly in adipose from female versus male mice and expose a reliance upon MPC-gated metabolism for glucose partitioning in female adipose under conditions of dietary lipid restriction.

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.

In vivo techniques for assessment of insulin sensitivity and glucose metabolism

Metabolic tests are vital to determine in vivo insulin sensitivity and glucose metabolism in preclinical models, usually rodents. Such tests include glucose tolerance tests, insulin tolerance tests, and glucose clamps. Although these tests are not standardized, there are general guidelines for their completion and analysis that are constantly being refined. In this review, we describe metabolic tests in rodents as well as factors to consider when designing and performing these tests.

Consideration of sex as a biological variable in diabetes research across twenty years

BACKGROUND

Sex differences exist in the risk of developing type 1 and type 2 diabetes, and in the risk of developing diabetes-associated complications. Sex differences in glucose homeostasis, islet and β cell biology, and peripheral insulin sensitivity have also been reported. Yet, we lack detailed information on the mechanisms underlying these differences, preventing the development of sex-informed therapeutic strategies for persons living with diabetes. To chart a path toward greater inclusion of biological sex as a variable in diabetes research, we first need a detailed assessment of common practices in the field.

METHODS

We developed a scoring system to evaluate the inclusion of biological sex in manuscripts published in Diabetes, a journal published by the American Diabetes Association. We chose Diabetes as this journal focuses solely on diabetes and diabetes-related research, and includes manuscripts that use both clinical and biomedical approaches. We scored papers published across 3 years within a 20-year period (1999, 2009, 2019), a timeframe that spans the introduction of funding agency and journal policies designed to improve the consideration of biological sex as a variable.

RESULTS

Our analysis showed fewer than 15% of papers used sex-based analysis in even one figure across all study years, a trend that was reproduced across journal-defined categories of diabetes research (e.g., islet studies, signal transduction). Single-sex studies accounted for approximately 40% of all manuscripts, of which > 87% used male subjects only. While we observed a modest increase in the overall inclusion of sex as a biological variable during our study period, our data highlight significant opportunities for improvement in diabetes research practices. We also present data supporting a positive role for journal policies in promoting better consideration of biological sex in diabetes research.

CONCLUSIONS

Our analysis provides significant insight into common practices in diabetes research related to the consideration of biological sex as a variable. Based on our analysis we recommend ways that diabetes researchers can improve inclusion of biological sex as a variable. In the long term, improved practices will reveal sex-specific mechanisms underlying diabetes risk and complications, generating knowledge to enable the development of sex-informed prevention and treatment strategies.

CD248 promotes insulin resistance by binding to the insulin receptor and dampening its insulin-induced autophosphorylation

BACKGROUND

In spite of new treatments, the incidence of type 2 diabetes (T2D) and its morbidities continue to rise. The key feature of T2D is resistance of adipose tissue and other organs to insulin. Approaches to overcome insulin resistance are limited due to a poor understanding of the mechanisms and inaccessibility of drugs to relevant intracellular targets. We previously showed in mice and humans that CD248, a pre/adipocyte cell surface glycoprotein, acts as an adipose tissue sensor that mediates the transition from healthy to unhealthy adipose, thus promoting insulin resistance.

METHODS

Molecular mechanisms by which CD248 regulates insulin signaling were explored using in vivo insulin clamp studies and biochemical analyses of cells/tissues from CD248 knockout (KO) and wild-type (WT) mice with diet-induced insulin resistance. Findings were validated with human adipose tissue specimens.

FINDINGS

Genetic deletion of CD248 in mice, overcame diet-induced insulin resistance with improvements in glucose uptake and lipolysis in white adipose tissue depots, effects paralleled by increased adipose/adipocyte GLUT4, phosphorylated AKT and GSK3β, and reduced ATGL. The insulin resistance of the WT mice could be attributed to direct interaction of the extracellular domains of CD248 and the insulin receptor (IR), with CD248 acting to block insulin binding to the IR. This resulted in dampened insulin-mediated autophosphorylation of the IR, with reduced downstream signaling/activation of intracellular events necessary for glucose and lipid homeostasis.

INTERPRETATION

Our discovery of a cell-surface CD248-IR complex that is accessible to pharmacologic intervention, opens research avenues toward development of new agents to prevent/reverse insulin resistance.

FUNDING

Funded by Canadian Institutes of Health Research (CIHR), Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundations for Innovation (CFI), the Swedish Diabetes Foundation, Family Ernfors Foundation and Novo Nordisk Foundation.

Sperm chromatin accessibility's involvement in the intergenerational effects of stress hormone receptor activation

Dexamethasone is a stress hormone receptor agonist used widely in clinics. We and others previously showed that paternal administration of dexamethasone in mice affects the phenotype of their offspring. The substrate of intergenerational transmission of environmentally induced effects often involves changes in sperm RNA, yet other epigenetic modifications in the germline can be affected and are also plausible candidates. First, we tested the involvement of altered sperm RNAs in the transmission of dexamethasone induced phenotypes across generations. We did this by injecting sperm RNA into naïve fertilized oocytes, before performing metabolic and behavioral phenotyping of the offspring. We observed phenotypic changes in discordance with those found in offspring generated by in vitro fertilization using sperm from dexamethasone exposed males. Second, we investigated the effect of dexamethasone on chromatin accessibility using ATAC sequencing and found significant changes at specific genomic features and gene regulatory loci. Employing q-RT-PCR, we show altered expression of a gene in the tissue of offspring affected by accessibility changes in sperm. Third, we establish a correlation between specific DNA modifications and stress hormone receptor activity as a likely contributing factor influencing sperm accessibility. Finally, we independently investigated this dependency by genetically reducing thymine-DNA glycosylase levels and observing concomitant changes at the level of chromatin accessibility and stress hormone receptor activity.

Dietary intervention in adult rats exposed to a high-sugar diet early in life permanently impairs sperm quality

Childhood obesity predicts the presence of adult obesity. Obesity is associated with poor sperm quality. We hypothesized that exposure to a high-sugar diet (HSD) in early life would cause permanent histomorphology damage to the testes, resulting in reduced sperm quality in adult life. Wistar rats (aged 21days) were divided into four groups (n=6). In the first experiment, the rats received tap water (control) and a 30% sucrose diet for two months (S30). In the second experiment, the control and 30% sucrose diets were fed for two months, followed by replacement with tap water for two months (IS30). Eating and drinking were monitored. Animals were then euthanized, visceral and gonadal fat tissue and testes were collected, and epididymal spermatozoa were excised. Testicular samples were used for morphological description by H&E staining and for quantifying triacylglycerol content, caspase activity, and oxidative stress. Serum testosterone concentration was evaluated. Spermatozoa were used to assess sperm quality. Our results show that sperm quality was impaired by consuming HSD and could not be restored by dietary intervention. HSD feeding induced hyperplasia of visceral adipose tissue, increased testicular weight, and serum testosterone levels. The dietary intervention increased visceral adipose tissue, serum, and testicular triacylglycerol levels and normalized serum testosterone levels. Overall, the HSD diet caused permanent changes in seminiferous tubule cross-sectional area, caspase activity, oxidative stress, and sperm quality. Therefore, a high-sugar diet in early life causes permanent damage to sperm quality in adulthood.

Adipocyte traits limiting cellular insulin responsiveness and glucose transport

Adipocyte dysfunction is a hallmark of systemic insulin resistance. Insulin-responsive glucose transporter 4 (GLUT4) is downregulated in the insulin resistant state, and cellular insulin responsiveness varies depending on fat depot origin and degree of adipose expansion. Here, we have resolved factors limiting cellular insulin responsiveness, by examining adipocyte function and traits related to glucose transport at the cellular level. Subcutaneous (inguinal) and visceral (epididymal) adipocytes were isolated from C57BL/6J mice fed either chow or high-fat diet. Cell size was determined using coulter counter method, glucose uptake and cytosolic volume were assessed using glucose tracer assays. Total and GLUT4 protein content expressions were determined by Western blot. We found that basal glucose uptake per cell was preserved independent of diet or fat depot origin. Insulin-stimulated glucose uptake per cell was sustained in visceral adipocytes but decreased with adipose expansion in subcutaneous adipocytes. In parallel, the cytosolic space and total protein increased proportionally to total cellular volumetric expansion in visceral, but not in subcutaneous, adipocytes, whereas GLUT4 content decreased exclusively in expanding subcutaneous adipocytes. Together, these data support the existence of distinct phenotypic adipocyte traits that could limit cellular insulin responsiveness. Potentially, these characteristics account for fat depot-specific differences related to glucose transport capacity.NEW & NOTEWORTHY This work illustrates that adipocyte characteristics related to fat depot origin rather than adipocyte size per se limit cellular insulin responsiveness and glucose uptake in male C57BL/6J mice. These findings contribute to the overall understanding of factors limiting adipocyte function and how adipose progression affects insulin response and glucose transport capacity differently in diverse fat depots. Future studies examining whether the proposed characteristics hold true in adipocytes derived from female mice or human origin are needed.

Deficiency of histone variant macroH2A1.1 is associated with sexually dimorphic obesity in mice

Obesity has a major socio-economic health impact. There are profound sex differences in adipose tissue deposition and obesity-related conditions. The underlying mechanisms driving sexual dimorphism in obesity and its associated metabolic disorders remain unclear. Histone variant macroH2A1.1 is a candidate epigenetic mechanism linking environmental and dietary factors to obesity. Here, we used a mouse model genetically depleted of macroH2A1.1 to investigate its potential epigenetic role in sex dimorphic obesity, metabolic disturbances and gut dysbiosis. Whole body macroH2A1 knockout (KO) mice, generated with the Cre/loxP technology, and their control littermates were fed a high fat diet containing 60% of energy derived from fat. The diet was administered for three months starting from 10 to 12 weeks of age. We evaluated the progression in body weight, the food intake, and the tolerance to glucose by means of a glucose tolerance test. Gut microbiota composition, visceral adipose and liver tissue morphology were assessed. In addition, adipogenic gene expression patterns were evaluated in the visceral adipose tissue. Female KO mice for macroH2A1.1 had a more pronounced weight gain induced by high fat diet compared to their littermates, while the increase in body weight in male mice was similar in the two genotypes. Food intake was generally increased upon KO and decreased by high fat diet in both sexes, with the exception of KO females fed a high fat diet that displayed the same food intake of their littermates. In glucose tolerance tests, glucose levels were significantly elevated upon high fat diet in female KO compared to a standard diet, while this effect was absent in male KO. There were no differences in hepatic histology. Upon a high fat diet, in female adipocyte cross-sectional area was larger in KO compared to littermates: activation of proadipogenic genes (ACACB, AGT, ANGPT2, FASN, RETN, SLC2A4) and downregulation of antiadipogenic genes (AXIN1, E2F1, EGR2, JUN, SIRT1, SIRT2, UCP1, CCND1, CDKN1A, CDKN1B, EGR2) was detected. Gut microbiota profiling showed increase in Firmicutes and a decrease in Bacteroidetes in females, but not males, macroH2A1.1 KO mice. MacroH2A1.1 KO mice display sexual dimorphism in high fat diet-induced obesity and in gut dysbiosis, and may represent a useful model to investigate epigenetic and metabolic differences associated to the development of obesity-associated pathological conditions in males and females.

Metabolic control by AMPK in white adipose tissue

White adipose tissue (WAT) plays an important role in the integration of whole-body metabolism by storing fat and mobilizing triacylglycerol when needed. The released free fatty acids can then be oxidized by other tissues to provide ATP. AMP-activated protein kinase (AMPK) is a key regulator of metabolic pathways, and can be targeted by a new generation of direct, small-molecule activators. AMPK activation in WAT inhibits insulin-stimulated lipogenesis and in some situations also inhibits insulin-stimulated glucose uptake, but AMPK-induced inhibition of β-adrenergic agonist-stimulated lipolysis might need to be re-evaluated in vivo. The lack of dramatic effects of AMPK activation on basal metabolism in WAT could be advantageous when treating type 2 diabetes with pharmacological pan-AMPK activators.

Synergism of mechanisms underlying early-stage changes in retina function in male hyperglycemic db/db mice in the absence and presence of chemically-induced dyslipidemia

The study was designed to quantify retina function in a spontaneous mutation mouse model of diabetes, in which sustained dyslipidemia was induced chemically. The goal of the study was to identify if dyslipidemia in the presence of hyperglycemia resulted in either a synergistic, or a merely additive, exacerbation of retinal and visual dysfunctions in diabetes. Two cohorts of mice, male C57BL/6 and C57BL/KsJ-db/db mice were divided into two groups each. One group of each strain received the triblock copolymer, poloxamer 407 (P-407), administered by intraperitoneal injection ("WT P-407" and "db/db P-407" groups) with saline as a control in the remaining two groups ("WT" and "db/db" groups). Blood glucose, total cholesterol (TC) and total triglyceride (TG) levels were quantified using enzyme-based colorimetric assays. Retina function was measured using electroretinography (ERG) and visual acuity was determined by behaviorally assessing parameters of the optomotor reflex. TC and TG levels were normal in both saline controls (WT) and db/db mice but were significantly elevated in the WT P-407 group (p < 0.01 for TC; p < 0.001 for TG), while levels of the same lipids were further elevated in the db/db P-407 group when compared to the WT P-407 group levels (p < 0.001 for both TC and TG). Behavioral assessment of the optomotor reflex indicated reduced visual acuity for the db/db P-407 group when compared to either the WT P-407 or the db/db groups (p < 0.001, p < 0.0001). ERG measurements of scotopic retina function showed a significant decline in the scotopic b-wave amplitude of the WT P-407 animals (p < 0.01) and a further reduction for the db/db P-407 group when compared to controls (p < 0.0001). Very significant, strong correlations between scotopic b-wave amplitude and implicit time to TC (r =  - 0.8376, p =  < 0.0001 and r = 0.7069, p = 0.0022, respectively) and TG levels (r =  - 0.8554, p =  < 0.0001 and r = 0.7150, p = 0.0019, respectively) were found. Dyslipidemia in the presence of hyperglycemia synergistically exacerbated the severity of retinal dysfunction in diabetes. P-407 administration significantly elevated plasma TC and TG levels in male wild-type (WT) and diabetic mice (db/db), but the resulting hyperlipidemia was more significantly pronounced in the diabetic mice. While elevated plasma lipid and blood glucose levels were individually correlated with a decline in retinal function, the combination of both exacerbated retinal dysfunction. This model of combined hyperglycemia and dyslipidemia can be used to dissect individual contributions of features of the metabolic syndrome to the pathogenesis of retinal dysfunction in diabetes.

Transcriptome and secretome profiling of sensory neurons reveals sex differences in pathways relevant to insulin sensing and insulin secretion

Sensory neurons in the dorsal root ganglia (DRG) convey somatosensory and metabolic cues to the central nervous system and release substances from stimulated terminal endings in peripheral organs. Sex-biased variations driven by the sex chromosome complement (XX and XY) have been implicated in the sensory-islet crosstalk. However, the molecular underpinnings of these male-female differences are not known. Here, we aim to characterize the molecular repertoire and the secretome profile of the lower thoracic spinal sensory neurons and to identify molecules with sex-biased insulin sensing- and/or insulin secretion-modulating activity that are encoded independently of circulating gonadal sex hormones. We used transcriptomics and proteomics to uncover differentially expressed genes and secreted molecules in lower thoracic T5-12 DRG sensory neurons derived from sexually immature 3-week-old male and female C57BL/6J mice. Comparative transcriptome and proteome analyses revealed differential gene expression and protein secretion in DRG neurons in males and females. The transcriptome analysis identified, among others, higher insulin signaling/sensing capabilities in female DRG neurons; secretome screening uncovered several sex-specific candidate molecules with potential regulatory functions in pancreatic β cells. Together, these data suggest a putative role of sensory interoception of insulin in the DRG-islet crosstalk with implications in sensory feedback loops in the regulation of β-cell activity in a sex-biased manner. Finally, we provide a valuable resource of molecular and secretory targets that can be leveraged for understanding insulin interoception and insulin secretion and inform the development of novel studies/approaches to fathom the role of the sensory-islet axis in the regulation of energy balance in males and females.

Adiponectin: A "Friendly adipokine" in Diabetic Retinopathy?

PURPOSE

Adiponectin has also been associated with diabetic retinopathy, a diabetic microvascular complication. However, the mechanism of action of adiponectin in retinopathy is still under investigation. This review summarizes emerging evidence on the association with diabetic retinopathy in type 2 diabetes.

METHODS

We reviwed papers from 2004 to 2022 and included studies related to retinopathy and its association with blood and intraocular adiponectin in type 2 diabetes.

RESULTS

Most of the studies analyzed in this review suggested an association between the diabetic retinopathy progression and intraocular, serum, or plasma adiponectin levels. Increased levels of adiponectin contributed to the development of the disease in diabetic patients. In a minority of studies, it was indicated an inversely proportional relationship between adiponectin concentration and diabetic retinopathy severity.

CONCLUSION

The high levels of adiponectin in diabetic patients may be related to the decrease in renal clearance. Under this situation, if the predominant isoform is globular adiponectin, this may explain the retinopathy progression, considering a pro-inflammatory response induced by this isoform. However, the actions of adiponectin in diabetic retinopathy pathophysiology are still controversial.

Role of glucose in daily torpor of Djungarian hamsters (Phodopus sungorus): challenge of continuous in vivo blood glucose measurements

Djungarian hamsters use daily torpor to save energy during winter. This metabolic downstate is part of their acclimatization strategy in response to short photoperiod and expressed spontaneously without energy challenges. During acute energy shortage, torpor incidence, depth, and duration can be modulated. Torpor induction might rely on glucose availability as acute metabolic energy source. To investigate this, the present study provides the first continuous in vivo blood glucose measurements of spontaneous daily torpor in short photoperiod-acclimated and fasting-induced torpor in long photoperiod-acclimated Djungarian hamsters. Glucose levels were almost identical in both photoperiods and showed a decrease during resting phase. Further decreases appeared during spontaneous daily torpor entrance, parallel with metabolic rate but before body temperature, while respiratory exchange rates were rising. During arousal, blood glucose tended to increase, and pretorpor values were reached at torpor termination. Although food-restricted hamsters underwent a considerable energetic challenge, blood glucose levels remained stable during the resting phase regardless of torpor expression. The activity phase preceding a torpor bout did not reveal changes in blood glucose that might be used as torpor predictor. Djungarian hamsters show a robust, circadian rhythm in blood glucose irrespective of season and maintain appropriate levels throughout complex acclimation processes including metabolic downstates. Although these measurements could not reveal blood glucose as proximate torpor induction factor, they provide new information about glucose availability during torpor. Technical innovations like in vivo microdialysis and in vitro transcriptome or proteome analyses may help to uncover the connection between torpor expression and glucose metabolism.

The metabolic effects of resumption of a high fat diet after weight loss are sex dependent in mice

Dietary restriction is a frequent strategy for weight loss, but adherence is difficult and returning to poor dietary habits can result in more weight gain than that previously lost. How weight loss due to unrestricted intake of a healthy diet affects the response to resumption of poor dietary habits is less studied. Moreover, whether this response differs between the sexes and if the insulin-like growth factor (IGF) system, sex dependent and involved in metabolic control, participates is unknown. Mice received rodent chow (6% Kcal from fat) or a high-fat diet (HFD, 62% Kcal from fat) for 4 months, chow for 3 months plus 1 month of HFD, or HFD for 2 months, chow for 1 month then HFD for 1 month. Males and females gained weight on HFD and lost weight when returned to chow at different rates (p < 0.001), but weight gain after resumption of HFD intake was not affected by previous weight loss in either sex. Glucose metabolism was more affected by HFD, as well as the re-exposure to HFD after weight loss, in males. This was associated with increases in hypothalamic mRNA levels of IGF2 (p < 0.01) and IGF binding protein (IGFBP) 2 (p < 0.05), factors involved in glucose metabolism, again only in males. Likewise, IGF2 increased IGFBP2 mRNA levels only in hypothalamic astrocytes from males (p < 0.05). In conclusion, the metabolic responses to dietary changes were less severe and more delayed in females and the IGF system might be involved in some of the sex specific observations.

TNIK is a conserved regulator of glucose and lipid metabolism in obesity

Obesity and type 2 diabetes (T2D) are growing health challenges with unmet treatment needs. Traf2- and NCK-interacting protein kinase (TNIK) is a recently identified obesity- and T2D-associated gene with unknown functions. We show that TNIK governs lipid and glucose homeostasis in Drosophila and mice. Loss of the Drosophila ortholog of TNIK, misshapen, altered the metabolite profiles and impaired de novo lipogenesis in high sugar-fed larvae. Tnik knockout mice exhibited hyperlocomotor activity and were protected against diet-induced fat expansion, insulin resistance, and hepatic steatosis. The improved lipid profile of Tnik knockout mice was accompanied by enhanced skeletal muscle and adipose tissue insulin-stimulated glucose uptake and glucose and lipid handling. Using the T2D Knowledge Portal and the UK Biobank, we observed associations of TNIK variants with blood glucose, HbA1c, body mass index, body fat percentage, and feeding behavior. These results define an untapped paradigm of TNIK-controlled glucose and lipid metabolism.

Maternal High-Fat Diet Results in Long-Term Sex-Specific Alterations to Metabolic and Gut Microbial Diurnal Oscillations in Adult Offspring

SCOPE

Circadian rhythms profoundly impact metabolism and the gut microbiota. A maternal high-fat diet (HFD) exerts effects on the metabolic syndrome of adult offspring in a sex-specific manner, the underlying mechanisms, however, remain unclear.

METHODS AND RESULTS

Female mice are fed an HFD and raise their offspring on a standard chow diet until 24 weeks. The glucose tolerance, insulin sensitivity, and diurnal rhythms of serum metabolic profiles are assessed in male and female adult offspring. Simultaneously, 16S rRNA is applied to characterize gut microbiota diurnal rhythms. The study finds that maternal HFD tends to deteriorate glucose tolerance and impairs insulin sensitivity in male offspring, but not female offspring, which can be associated with the circadian alterations of serum metabolic profiles in male offspring. As expected, maternal HFD sex-specifically alters diurnal rhythms of the gut microbiota, which exhibits putative associations with metabolic profiles in males.

CONCLUSIONS

The present study identifies the critical role of gut microbiota diurnal rhythms in triggering sex-biased metabolic diurnal rhythms in response to maternal HFD, at least in part. As early life may be a critical window for preventing metabolic diseases, these findings provide the basis for developing chronobiology applications targeting the gut microbiota to combat early metabolic alterations, especially in males.

Associations of serum aminotransferase and the risk of all-cause and cause-specific mortality in Chinese type 2 diabetes: a community-based cohort study

OBJECTIVE

Investigating the associations of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) with all-cause, cardiovascular disease (CVD) and cancer mortality in a large cohort of community-dwelling patients with type 2 diabetes mellitus (T2DM).

DESIGN

Community-based prospective cohort study conducted between 2013 and 2014.

SETTING

44 selected townships in Changshu and Huai'an City, Jiangsu province, China.

PARTICIPANTS

20340 participants with T2DM were recruited in Jiangsu province, China.

METHODS

We use Cox proportional hazard models to estimate the HR and 95% CIs of associations of serum ALT and AST levels with all-cause and cause-specific mortality. Restricted cubic splines were used to explore the dose-response relationships between ALT and AST levels with mortality.

RESULTS

ALT and AST levels were inversely associated with CVD mortality, compared with the lowest quintile (Q1), the multivariable HRs of the highest quintile (Q5) was 0.82 (95% CI: 0.66 to 1.01, p for trend=0.022) and 0.78 (95% CI: 0.63 to 0.96, p for trend=0.022), respectively. Furthermore, the HRs for ALT levels in all-cause mortality were 0.90 (95% CI: 0.79 to 1.01, p for trend=0.018), and the HRs for AST levels in cancer mortality were 1.29 (95% CI: 1.02 to 1.63, p for trend=0.023). Stronger inverse effects of ALT and AST levels on all-cause mortality were observed in the older subgroup and in those with dyslipidaemia (all p for interaction <0.05). Further analysis based on gender showed that the associations between serum aminotransferases and the mortality risk were more significant in women and substantially attenuated in men.

CONCLUSION

Our findings suggested patients with T2DM with lower levels of ALT and AST had an increased risk of CVD mortality, which needs confirmation in future clinical trials.

Involvement of a serotonin/GLP-1 circuit in adolescent isolation-induced diabetes

In 2020, stay-at-home orders were implemented to stem the spread of SARS-CoV-2 worldwide. Social isolation can be particularly harmful to children and adolescents-during the pandemic, the prevalence of obesity increased by ∼37% in persons aged 2-19. Obesity is often comorbid with type 2 diabetes, which was not assessed in this human pandemic cohort. Here, we investigated whether male mice isolated throughout adolescence develop type 2 diabetes in a manner consistent with human obesity-induced diabetes, and explored neural changes that may underlie such an interaction. We find that isolating C57BL/6J mice throughout adolescence is sufficient to induce type 2 diabetes. We observed fasted hyperglycemia, diminished glucose clearance in response to an insulin tolerance test, decreased insulin signaling in skeletal muscle, decreased insulin staining of pancreatic islets, increased nociception, and diminished plasma cortisol levels compared to group-housed control mice. Using Promethion metabolic phenotyping chambers, we observed dysregulation of sleep and eating behaviors, as well as a time-dependent shift in respiratory exchange ratio of the adolescent-isolation mice. We profiled changes in neural gene transcription from several brain areas and found that a neural circuit between serotonin-producing and GLP-1-producing neurons is affected by this isolation paradigm. Overall, spatial transcription data suggest decreased serotonin neuron activity (via decreased GLP-1-mediated excitation) and increased GLP-1 neuron activity (via decreased serotonin-mediated inhibition). This circuit may represent an intersectional target to further investigate the relationship between social isolation and type 2 diabetes, as well as a pharmacologically-relevant circuit to explore the effects of serotonin and GLP-1 receptor agonists.

Article Highlights

Isolating C57BL/6J mice throughout adolescence is sufficient to induce type 2 diabetes, presenting with fasted hyperglycemia.Adolescent-isolation mice have deficits in insulin responsiveness, impaired peripheral insulin signaling, and decreased pancreatic insulin production.Transcriptional changes across the brain include the endocannabinoid, serotonin, and GLP-1 neurotransmitters and associated receptors. The neural serotonin/GLP-1 circuit may represent an intersectional target to further investigate the relationship between social isolation and type 2 diabetes. Serotonin-producing neurons of adolescent-isolation mice produce fewer transcripts for the GLP-1 receptor, and GLP-1 neurons produce fewer transcripts for the 5-HT 1A serotonin receptor.

Mustn1 ablation in skeletal muscle results in increased glucose tolerance concomitant with upregulated GLUT expression in male mice

Glucose homeostasis is closely regulated to maintain energy requirements of vital organs and skeletal muscle plays a crucial role in this process. Mustn1 is expressed during embryonic and postnatal skeletal muscle development and its function has been implicated in myogenic differentiation and myofusion. Whether Mustn1 plays a role in glucose homeostasis in anyway remains largely unknown. As such, we deleted Mustn1 in skeletal muscle using a conditional knockout (KO) mouse approach. KO mice did not reveal any specific gross phenotypic alterations in skeletal muscle. However, intraperitoneal glucose tolerance testing (IPGTT) revealed that 2-month-old male KO mice had significantly lower glycemia than their littermate wild type (WT) controls. These findings coincided with mRNA changes in genes known to be involved in glucose metabolism, tolerance, and insulin sensitivity; 2-month-old male KO mice had significantly higher expression of GLUT1 and GLUT10 transporters, MUP-1 while OSTN expression was lower. These differences in glycemia and gene expression were statistically insignificant after 4 months. Identical experiments in female KO and WT control mice did not indicate any differences at any age. Our results suggest a link between Mustn1 expression and glucose homeostasis during a restricted period of skeletal muscle development/maturation. While this is an observational study, Mustn1's relationship to glucose homeostasis appears to be more complex with a possible connection to other key proteins such as GLUTs, MUP-1, and OSTN. Additionally, our data indicate temporal and sex differences. Lastly, our findings strengthen the notion that Mustn1 plays a role in the metabolic capacity of skeletal muscle.

G-protein coupled receptor 19 (GPR19) knockout mice display sex-dependent metabolic dysfunction

G-protein coupled receptors (GPCRs) mediate signal transduction from the cellular surface to intracellular metabolic pathways. While the function of many GPCRs has been delineated previously, a significant number require further characterization to elucidate their cellular function. G-protein coupled receptor 19 (GPR19) is a poorly characterized class A GPCR which has been implicated in the regulation of circadian rhythm, tumor metastasis, and mitochondrial homeostasis. In this report, we use a novel knockout (KO) mouse model to examine the role of GPR19 in whole-body metabolic regulation. We show that loss of GPR19 promotes increased energy expenditure and decreased activity in both male and female mice. However, only male GPR19 KO mice display glucose intolerance in response to a high fat diet. Loss of GPR19 expression in male mice, but not female mice, resulted in diet-induced hepatomegaly, which was associated with decreased expression of key fatty acid oxidation genes in male GPR19 KO livers. Overall, our data suggest that loss of GPR19 impacts whole-body energy metabolism in diet-induced obese mice in a sex-dependent manner.

Sex differences in glycolipidic disorders after exposure to maternal hyperglycemia during early development

PURPOSE

The aim of this review was to summarize sex differences in glycolipid metabolic phenotypes of human and animal models after exposure to maternal hyperglycemia and overview the underlying mechanisms, providing a new perspective on the maternal hyperglycemia-triggered risk of glycolipidic disorders in offspring.

METHODS

A comprehensive literature search within PubMed was performed. Selected publications related to studies on offspring exposed to maternal hyperglycemia investigating the sex differences of glycolipid metabolism were reviewed.

RESULTS

Maternal hyperglycemia increases the risk of glycolipid metabolic disorders in offspring, such as obesity, glucose intolerance and diabetes. Whether with or without intervention, metabolic phenotypes have been shown to exhibit sex differences between male and female offspring in response to maternal hyperglycemia, which may be related to gonadal hormones, organic intrinsic differences, placenta, and epigenetic modifications.

CONCLUSION

Sex may play a role in the different incidences and pathogenesis of abnormal glycolipid metabolism. More studies investigating both sexes are needed to understand how and why environmental conditions in early life affect long-term health between male and female individuals.

Pericytes modulate islet immune cells and insulin secretion through Interleukin-33 production in mice

Introduction

Immune cells were recently shown to support β-cells and insulin secretion. However, little is known about how islet immune cells are regulated to maintain glucose homeostasis. Administration of various cytokines, including Interleukin-33 (IL-33), was shown to influence β-cell function. However, the role of endogenous, locally produced IL-33 in pancreatic function remains unknown. Here, we show that IL-33, produced by pancreatic pericytes, is required for glucose homeostasis.

Methods

To characterize pancreatic IL-33 production, we employed gene expression, flow cytometry, and immunofluorescence analyses. To define the role of this cytokine, we employed transgenic mouse systems to delete the Il33 gene selectively in pancreatic pericytes, in combination with the administration of recombinant IL-33. Glucose response was measured in vivo and in vitro, and morphometric and molecular analyses were used to measure β-cell mass and gene expression. Immune cells were analyzed by flow cytometry.

Resuts

Our results show that pericytes are the primary source of IL-33 in the pancreas. Mice lacking pericytic IL-33 were glucose intolerant due to impaired insulin secretion. Selective loss of pericytic IL-33 was further associated with reduced T and dendritic cell numbers in the islets and lower retinoic acid production by islet macrophages.

Discussion

Our study demonstrates the importance of local, pericytic IL-33 production for glucose regulation. Additionally, it proposes that pericytes regulate islet immune cells to support β-cell function in an IL-33-dependent manner. Our study reveals an intricate cellular network within the islet niche.

Tissue-Specific Sex Difference in Mouse Eye and Brain Metabolome Under Fed and Fasted States

Purpose

Visual physiology and various ocular diseases demonstrate sexual dimorphisms; however, how sex influences metabolism in different eye tissues remains undetermined. This study aims to address common and tissue-specific sex differences in metabolism in the retina, RPE, lens, and brain under fed and fasted conditions.

Methods

After ad libitum fed or being deprived of food for 18 hours, mouse eye tissues (retina, RPE/choroid, and lens), brain, and plasma were harvested for targeted metabolomics. The data were analyzed with both partial least squares-discriminant analysis and volcano plot analysis.

Results

Among 133 metabolites that cover major metabolic pathways, we found 9 to 45 metabolites that are sex different in different tissues under the fed state and 6 to 18 metabolites under the fasted state. Among these sex-different metabolites, 33 were changed in 2 or more tissues, and 64 were tissue specific. Pantothenic acid, hypotaurine, and 4-hydroxyproline were the top commonly changed metabolites. The lens and the retina had the most tissue-specific, sex-different metabolites enriched in the metabolism of amino acid, nucleotide, lipids, and tricarboxylic acid cycle. The lens and the brain had more similar sex-different metabolites than other ocular tissues. The female RPE and female brain were more sensitive to fasting with more decreased metabolites in amino acid metabolism, tricarboxylic acid cycles, and glycolysis. The plasma had the fewest sex-different metabolites, with very few overlapping changes with tissues.

Conclusions

Sex has a strong influence on eye and brain metabolism in tissue-specific and metabolic state-specific manners. Our findings may implicate the sexual dimorphisms in eye physiology and susceptibility to ocular diseases.

Estrogens in Adipose Tissue Physiology and Obesity-Related Dysfunction

Menopause-related decline in estrogen levels is accompanied by a change in adipose tissue distribution from a gynoid to an android and an increased prevalence of obesity in women. These unfavorable phenomena can be partially restored by hormone replacement therapy, suggesting a significant role for estrogen in the regulation of adipocytes' function. Indeed, preclinical studies proved the involvement of these hormones in adipose tissue development, metabolism, and inflammatory activity. However, the relationship between estrogen and obesity is bidirectional. On the one hand-their deficiency leads to excessive fat accumulation and impairs adipocyte function, on the other-adipose tissue of obese individuals is characterized by altered expression of estrogen receptors and key enzymes involved in their synthesis. This narrative review aims to summarize the role of estrogen in adipose tissue development, physiology, and in obesity-related dysfunction. Firstly, the estrogen classification, synthesis, and modes of action are presented. Next, their role in regulating adipogenesis and adipose tissue activity in health and the course of obesity is described. Finally, the potential therapeutic applications of estrogen and its derivates in obesity treatment are discussed.

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 and sex on its molecular landscape has not been fully established. Utilizing an integrative multi-omics approach with data generated by the Molecular Transducers of Physical Activity Consortium (MoTrPAC), we identified profound sexual dimorphism in the dynamic response of rat scWAT to endurance exercise training. Despite similar cardiorespiratory improvements, only male rats reduced whole-body adiposity, scWAT adipocyte size, and total scWAT triglyceride abundance with training. Multi-omic analyses of adipose tissue integrated with phenotypic measures identified sex-specific training responses including enrichment of mTOR signaling in females, while males displayed enhanced mitochondrial ribosome biogenesis and oxidative metabolism. Overall, this study reinforces our understanding that sex impacts scWAT biology and provides a rich resource to interrogate responses of scWAT to endurance training.

Sex differences in islet stress responses support female β cell resilience

OBJECTIVE

Pancreatic β cells play a key role in maintaining glucose homeostasis; dysfunction of this critical cell type causes type 2 diabetes (T2D). Emerging evidence points to sex differences in β cells, but few studies have examined male-female differences in β cell stress responses and resilience across multiple contexts, including diabetes. Here, we address the need for high-quality information on sex differences in β cell and islet gene expression and function using both human and rodent samples.

METHODS

In humans, we compared β cell gene expression and insulin secretion in donors with T2D to non-diabetic donors in both males and females. In mice, we generated a well-powered islet RNAseq dataset from 20-week-old male and female siblings with similar insulin sensitivity. Our unbiased gene expression analysis pointed to a sex difference in the endoplasmic reticulum (ER) stress response. Based on this analysis, we hypothesized female islets would be more resilient to ER stress than male islets. To test this, we subjected islets isolated from age-matched male and female mice to thapsigargin treatment and monitored protein synthesis, cell death, and β cell insulin production and secretion. Transcriptomic and proteomic analyses were used to characterize sex differences in islet responses to ER stress.

RESULTS

Our single-cell analysis of human β cells revealed sex-specific changes to gene expression and function in T2D, correlating with more robust insulin secretion in human islets isolated from female donors with T2D compared to male donors with T2D. In mice, RNA sequencing revealed differential enrichment of unfolded protein response pathway-associated genes, where female islets showed higher expression of genes linked with protein synthesis, folding, and processing. This differential expression was physiologically significant, as islets isolated from female mice were more resilient to ER stress induction with thapsigargin. Specifically, female islets showed a greater ability to maintain glucose-stimulated insulin production and secretion during ER stress compared with males.

CONCLUSIONS

Our data demonstrate sex differences in β cell gene expression in both humans and mice, and that female β cells show a greater ability to maintain glucose-stimulated insulin secretion across multiple physiological and pathological contexts.

Adipocyte Metabolism and Health after the Menopause: The Role of Exercise

Postmenopausal women represent an important target population in need of preventative cardiometabolic approaches. The loss of estrogen following the menopause eliminates protections against metabolic dysfunction, largely due to its role in the health and function of adipose tissue. In addition, some studies associate the menopause with reduced physical activity, which could potentially exacerbate the deleterious cardiometabolic risk profile accompanying the menopause. Meanwhile, exercise has adipocyte-specific effects that may alleviate the adverse impact of estrogen loss through the menopausal transition period and beyond. Exercise thus remains the best therapeutic agent available to mitigate menopause-associated metabolic dysfunction and represents a vital behavioral strategy to prevent and alleviate health decline in this population.

Gender Differences in Cardiovascular Health: Hormonal Effects on Cardiovascular Risk and Management

Cardiovascular disease is the number one cause of death worldwide both in men and women. Significant differences however exist in the age of onset, type of cardiovascular disease (CVD), and treatment response among the genders. These differences are due to both gender societal effects and biological differences from the influence of the hormonal and metabolic milieu in the two sexes.Estrogens are the main female hormone. They impact signaling in almost every body organ and thus affect cardiovascular risk factors. These result in differential expression of CVD. The differential effect of treatment modalities is only recently being evaluated.Research is ongoing regarding the pathophysiology of these differences. Our current level of knowledge is described in this chapter.

Streptozotocin as a tool for induction of rat models of diabetes: a practical guide

Streptozotocin (STZ) is the most used diabetogenic chemical for creating rat models of type 1 and type 2 diabetes. Despite ~60 years of using STZ in animal diabetes research, some prevailing views about STZ preparation and use are not supported by evidence. Here, we provide practical guides for using STZ to induce diabetes in rats. Susceptibility to the diabetogenic effect of STZ is inversely related to age, and males are more susceptible to STZ than females. Wistar and Sprague-Dawley rats, the most commonly-used rat strains, are sensitive to STZ, but some strains (e.g., Wistar-Kyoto rats) are less sensitive. STZ is mostly injected intravenously or intraperitoneally, but its intravenous injection produces more stable hyperglycemia. Despite the prevailing view, no fasting is necessary before STZ injection, and injection of its anomer-equilibrated solutions (i.e., more than 2 hours of dissolving) is recommended. Mortality following the injection of diabetogenic doses of STZ is due to severe hypoglycemia (during the first 24 h) or severe hyperglycemia (24 h after the injection and onwards). Some measures to prevent hypoglycemia-related mortality in rats include providing access to food soon after the injection, administration of glucose/sucrose solutions during the first 24-48 h after the injection, administration of STZ to fed animals, and using anomer-equilibrated solutions of STZ. Hyperglycemia-related mortality following injection of high doses of STZ can be overcome with insulin administration. In conclusion, STZ is a valuable chemical for inducing diabetes in rats, but some practical guides should be considered to perform well-conducted and ethical studies.

Prodromal Glutamatergic Modulation with Riluzole Impacts Glucose Homeostasis and Spatial Cognition in Alzheimer's Disease Mice

BACKGROUND

Prior research supports a strong link between Alzheimer's disease (AD) and metabolic dysfunction that involves a multi-directional interaction between glucose, glutamatergic homeostasis, and amyloid pathology. Elevated soluble amyloid-β (Aβ) is an early biomarker for AD-associated cognitive decline that contributes to concurrent glutamatergic and metabolic dyshomeostasis in humans and male transgenic AD mice. Yet, it remains unclear how primary time-sensitive targeting of hippocampal glutamatergic activity may impact glucose regulation in an amyloidogenic mouse model. Previous studies have illustrated increased glucose uptake and metabolism using a neuroprotective glutamate modulator (riluzole), supporting the link between glucose and glutamatergic homeostasis.

OBJECTIVE

We hypothesized that targeting early glutamatergic hyperexcitation through riluzole treatment could aid in attenuating co-occurring metabolic and amyloidogenic pathologies with the intent of ameliorating cognitive decline.

METHODS

We conducted an early intervention study in male and female transgenic (AβPP/PS1) and knock-in (APPNL - F/NL - F) AD mice to assess the on- and off-treatment effects of prodromal glutamatergic modulation (2-6 months of age) on glucose homeostasis and spatial cognition through riluzole treatment.

RESULTS

Results indicated a sex- and genotype-specific effect on glucose homeostasis and spatial cognition with riluzole intervention that evolved with disease progression and time since treatment.

CONCLUSION

These findings support the interconnected nature of glucose and glutamatergic homeostasis with amyloid pathology and petition for further investigation into the targeting of this relationship to improve cognitive performance.

The insulin signaling pathway a century after its discovery: Sexual dimorphism in insulin signaling

Since practically a century ago, the insulin pathway was discovered in both vertebrates and invertebrates, implying an evolutionarily ancient origin. After a century of research, it is now clear that the insulin signal transduction pathway is a critical, flexible and pleiotropic pathway, evolving into multiple anabolic functions besides glucose homeostasis. It regulates paramount aspects of organismal well-being like growth, longevity, intermediate metabolism, and reproduction. Part of this diversification has been attained by duplications and divergence of both ligands and receptors riding on a common general signal transduction system. One of the aspects that is strikingly different is its usage in reproduction, particularly in male versus female development and fertility within the same species. This review highlights sexual divergence in metabolism and reproductive tract differences, the occurrence of sexually "exaggerated" traits, and sex size differences that are due to the sexes' differential activity/response to the insulin signaling pathway.

Sex Differences in Glucose Homeostasis

Sexual dimorphism has been demonstrated to have an effect on various physiological functions. In this regard, researchers have investigated its impact on glucose homeostasis in both preclinical and clinical studies. Sex differences mainly arise from physiological factors such as sex hormones, body fat and muscle distribution, and sex chromosomes. The sexual dimorphism has also been studied in the context of diabetes. Reflecting the prevalence of the disease among the population, studies focusing on the sex difference in type 1 diabetes (T1D) are not common as the ones in type 2 diabetes (T2D). T1D is reported as the only major specific autoimmune disease that exhibits a male predominance. Clinical studies have demonstrated that impaired fasting glucose is more frequent in men whereas women more commonly exhibit impaired glucose tolerance. Understanding the sex difference in glucose homeostasis becomes more attractive when focusing on the findings that highlight sexual dimorphism on the efficacy or adverse effect profile of antidiabetic medications. Thus, in this chapter, we aimed to discuss the impact of sex on the glucose homeostasis both in health and in diabetes.

Altered Adipocyte Cell Size Distribution Prior to Weight Loss in the R6/2 Model of Huntington's Disease

BACKGROUND

Metabolic alterations contribute to disease onset and prognosis of Huntington's disease (HD). Weight loss in the R6/2 mouse model of HD is a consistent feature, with onset in mid-to-late stage of disease.

OBJECTIVE

In the present study, we aimed to investigate molecular and functional changes in white adipose tissue (WAT) that occur at weight loss in R6/2 mice. We further elaborated on the effect of leptin-deficiency and early obesity in R6/2 mice.

METHODS

We performed analyses at 12 weeks of age; a time point that coincides with the start of weight loss in our R6/2 mouse colony. Gonadal (visceral) and inguinal (subcutaneous) WAT depot weights were monitored, as well as adipocyte size distribution. Response to isoprenaline-stimulated glycerol release and insulin-stimulated glucose uptake in adipocytes from gonadal WAT was assessed.

RESULTS

In R6/2 mice, WAT depot weights were comparable to wildtype (WT) mice, and the response to insulin and isoprenaline in gonadal adipocytes was unaltered. Leptin-deficient R6/2 mice exhibited distinct changes compared to leptin-deficient WT mice. At 12 weeks, female leptin-deficient R6/2 mice had reduced body weight accompanied by an increased proportion of smaller adipocytes, while in contrast; male mice displayed a shift towards larger adipocyte sizes without a significant body weight reduction at this timepoint.

CONCLUSIONS

We here show that there are early sex-specific changes in adipocyte cell size distribution in WAT of R6/2 mice and leptin-deficient R6/2 mice.

Diet supplemented with olive cake as a model of circular economy: Metabolic and endocrine responses of beef cattle

Introduction

Integrating by-products into livestock diet represents a great opportunity for implementing the concept of circular economy while reducing feed costs. Olive cake (OC) is considered an agro-industrial waste, but the high content of valuable metabolites makes it a promising feed integration. Therefore, this study investigated the effect of OC integration in beef cattle diet on different blood parameters.

Methods

Forty-eight young growing fattening Limousines-−24 bulls (body weight 350 ± 15 kg) and 24 heifers (280 ± 10 kg)—, aged 240 ± 20 days, were randomly allocated to 1 of 3 dietary treatments: concentrate at 0% (Control group: CTR), 10% (Low-olive cake group: L-OC), or 15% (High-olive cake group: H-OC) of OC inclusion. Blood samples and body weights were collected before administrating the supplemented diet (0 d), at the end of the stocker growing phase (56 d), and at the end of the fattening (147 d). After being slaughtered, animal carcasses were weighted. A linear regression model was fitted for each blood parameter with the 0 d as covariate and diet, time, sex, diet × time, and diet × sex as fixed effects.

Results

In males, body weight was highest in CTR, but carcass weight was similar in all the groups. All the blood parameters were within physiological ranges, independently from the animal diet. CTR group showed the highest alanine aminotransferase (ALT, P = 0.0027) and creatine kinase (P = 0.0119), whereas total bilirubin (P = 0.0023) was higher in H-OC than in CTR. Moreover, ALT was highest in CTR at 56 d, becoming similar in all the groups at 147 d (P = 0.0280). Instead, the increase observed in total cholesterol from 56 to 147 d was lower in H-OC compared with CTR and L-OC (P = 0.0451). A significant effect of diet × sex interaction was observed on triglycerides, urea, liver enzymes, and insulin. These data support the OC inclusion of up to 15% of the concentrate with no detrimental effect on beef cattle metabolic status.

Discussion

In conclusion, OC can be considered as a component in beef diet giving an opportunity to improve agriculture sustainability.

A modest change in housing temperature alters whole body energy expenditure and adipocyte thermogenic capacity in mice

Typical vivarium temperatures (20-26°C) induce facultative thermogenesis in mice, a process attributable in part to uncoupling protein-1 (UCP1). The impact of modest changes in housing temperature on whole body and adipose tissue energetics in mice remains unclear. Here, we determined the effects of transitioning mice from 24°C to 30°C on total energy expenditure and adipose tissue protein signatures. C57BL/6J mice were housed at 24°C for 2 wk and then either remained at 24°C (n = 16/group, 8M/8F) or were transitioned to 30°C (n = 16/group, 8M/8F) for 4 wk. Total energy expenditure and its components were determined by indirect calorimetry. Interscapular brown adipose tissue (iBAT) and inguinal white adipose tissue (iWAT) proteins were quantified by Western blot and quantitative proteomics. Transitioning from 24°C to 30°C reduced total energy expenditure in both male (-25%) and female (-16%) mice, which was attributable to lower basal energy expenditure in males (-36%) and females (-40%). Total iBAT UCP1 protein content was 50% lower at 30°C compared with 24°C, whereas iWAT UCP1 protein content was similar between conditions. iBAT UCP1 protein content remained 20-fold greater than iWAT at 30°C. In iBAT and iWAT, 183 and 41 proteins were differentially expressed between 24°C and 30°C, respectively. iWAT proteins (257) differentially expressed between sexes at 30°C were not differentially expressed at 24°C. Thus, 30°C housing lowers total energy expenditure of mice when compared with an ambient temperature (24°C) that falls within the National Research Council's guidelines for housing laboratory mice. Lower iBAT UCP1 content accompanied chronic housing at 30°C. Furthermore, housing temperature influences sexual dimorphism in the iWAT proteome. These data have implications regarding the optimization of preclinical models of human disease.NEW & NOTEWORTHY Housing mice at 30°C reduced the basal and total energy expenditure compared with 24°C, which was accompanied by a reduction in brown adipose tissue UCP1 content. Proteomic profiling demonstrated the brown adipose tissue and white adipose tissue proteomes were largely influenced by housing temperature and sex, respectively. Therefore, 30°C housing revealed sexual dimorphism in the white adipose tissue proteome that was largely absent in animals housed at 24°C.

Trends in the prevalence of metabolically healthy and unhealthy obesity in the US adult population: analysis of eight NHANES cross-sectional survey cycles, 1999-2014

OBJECTIVE

To exam the time trend of the prevalence of metabolically healthy obesity (MHO) in the US adult population.

DESIGN

Eight cross-sectional survey cycles.

SETTING

National Health and Nutrition Examination Survey (NHANES), 1999-2014.

PARTICIPANTS

16 459 NHANES participants aged 20 years and older.

PRIMARY OUTCOME MEASURE

MHO was defined as central obesity (waist circumference ≥102 cm for men and ≥88 cm for women) without any of the following conditions: elevated levels of blood pressure (≥130/85 mm Hg), glucose (≥100 mg/dL) and triglycerides (≥150 mm/dL); reduced levels of high-density lipoprotein cholesterol (<40 mg/dL for men and <50 mg/dL for women) or any medication use for high cholesterol, hypertension or diabetes.

RESULTS

The prevalence of central obesity significantly increased from 45.2% in 1999-2000 to 56.7% in 2013-2014 (p=0.003). Over the same period, MHO prevalence among those with central obesity only slightly and non-significantly increased from 11.0% to 15.7% (p=0.38). However, MHO prevalence among women increased significantly (p=0.04) from 7.1% to 13.7%. Female gender, a younger age, being Hispanic and non-Hispanic black and high education (some college or above) were significantly (p<0.05) associated with higher prevalence of MHO.

CONCLUSIONS

While the prevalence of central obesity in the US population has increased since 1999, the prevalence of MHO among those who are centrally obese remained fairly stable.

RAGE displays sex-specific differences in obesity-induced adipose tissue insulin resistance

Background

The receptor for advanced glycation end products (RAGE) plays an important role in obesity-associated insulin sensitivity. We have also previously reported that RAGE deficiency improved insulin resistance in obesity-induced adipose tissue. The current study was aimed to elucidate the sex-specific mechanism of RAGE deficiency in adipose tissue metabolic regulation and systemic glucose homeostasis.

Methods

RAGE-deficient (RAGE^−/−) mice were fed a high-fat diet (HFD) and subjected to glucose and insulin tolerance tests. Subcutaneous adipose tissue (sAT) was collected, and macrophage polarization was assessed by quantitative real-time PCR. Immunoblotting was performed to evaluate the insulin signaling in adipose tissues.

Results

Under HFD feeding conditions, body weight and adipocyte size of female RAGE deficient (RAGE^−/−) were markedly lower than that of male mice. Female RAGE^−/− mice showed significantly improved glucose and insulin tolerance compared to male RAGE^−/− mice, accompanied with increased M2 macrophages polarization. Expressions of genes involved in anti-oxidant and browning were up-regulated in adipose tissues of female RAGE^−/− mice. Moreover, insulin-induced AKT phosphorylation was significantly elevated in adipose tissue in female RAGE^−/− mice compared to male RAGE^−/− mice.

Conclusions

Our findings suggest that RAGE-mediated adipose tissue insulin resistance is sex-specific, which is associated with different expression of genes involved in anti-oxidant and browning and insulin-induced AKT phosphorylation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13293-022-00476-6.

Female RAGE^−/− mice showed significantly improved glucose and insulin tolerance compared to male RAGE^−/− mice.

Female RAGE deficiency promotes M2 macrophage polarization in adipose tissues.

Female RAGE deficiency prevents oxidative stress in adipose tissues.

Female RAGE deficiency protects insulin-AKT signaling in adipose tissues.

Of mice and men: Pinpointing species differences in adipose tissue biology

The prevalence of obesity and metabolic diseases continues to rise, which has led to an increased interest in studying adipose tissue to elucidate underlying disease mechanisms. The use of genetic mouse models has been critical for understanding the role of specific genes for adipose tissue function and the tissue’s impact on other organs. However, mouse adipose tissue displays key differences to human fat, which has led, in some cases, to the emergence of some confounding concepts in the adipose field. Such differences include the depot-specific characteristics of visceral and subcutaneous fat, and divergences in thermogenic fat phenotype between the species. Adipose tissue characteristics may therefore not always be directly compared between species, which is important to consider when setting up new studies or interpreting results. This mini review outlines our current knowledge about the cell biological differences between human and mouse adipocytes and fat depots, highlighting some examples where inadequate knowledge of species-specific differences can lead to confounding results, and presenting plausible anatomic explanations that may underlie the differences. The article thus provides critical insights and guidance for researchers working primarily with only human or mouse fat tissue, and may contribute to new ideas or concepts in the important and evolving field of adipose biology.

The female syndecan-4−/− heart has smaller cardiomyocytes, augmented insulin/pSer473-Akt/pSer9-GSK-3β signaling, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels

Background: In cardiac muscle, the ubiquitously expressed proteoglycan syndecan-4 is involved in the hypertrophic response to pressure overload. Protein kinase Akt signaling, which is known to regulate hypertrophy, has been found to be reduced in the cardiac muscle of exercised male syndecan-4−/− mice. In contrast, we have recently found that pSer473-Akt signaling is elevated in the skeletal muscle (tibialis anterior, TA) of female syndecan-4−/− mice. To determine if the differences seen in Akt signaling are sex specific, we have presently investigated Akt signaling in the cardiac muscle of sedentary and exercised female syndecan-4−/− mice. To get deeper insight into the female syndecan-4−/− heart, alterations in cardiomyocyte size, a wide variety of different extracellular matrix components, well-known syndecan-4 binding partners and associated signaling pathways have also been investigated.

Methods: Left ventricles (LVs) from sedentary and exercise trained female syndecan-4−/− and WT mice were analyzed by immunoblotting and real-time PCR. Cardiomyocyte size and phosphorylated Ser473-Akt were analyzed in isolated adult cardiomyocytes from female syndecan-4−/− and WT mice by confocal imaging. LV and skeletal muscle (TA) from sedentary male syndecan-4−/− and WT mice were immunoblotted with Akt antibodies for comparison. Glucose levels were measured by a glucometer, and fasting blood serum insulin and C-peptide levels were measured by ELISA.

Results: Compared to female WT hearts, sedentary female syndecan-4−/− LV cardiomyocytes were smaller and hearts had higher levels of pSer473-Akt and its downstream target pSer9-GSK-3β. The pSer473-Akt inhibitory phosphatase PHLPP1/SCOP was lowered, which may be in response to the elevated serum insulin levels found in the female syndecan-4−/− mice. We also observed lowered levels of pThr308-Akt/Akt and GLUT4 in the female syndecan-4−/− heart and an increased LRP6 level after exercise. Otherwise, few alterations were found. The pThr308-Akt and pSer473-Akt levels were unaltered in the cardiac and skeletal muscles of sedentary male syndecan-4−/− mice.

Conclusion: Our data indicate smaller cardiomyocytes, an elevated insulin/pSer473-Akt/pSer9-GSK-3β signaling pathway, and lowered SCOP, pThr308-Akt/Akt and GLUT4 levels in the female syndecan-4−/− heart. In contrast, cardiomyocyte size, and Akt signaling were unaltered in both cardiac and skeletal muscles from male syndecan-4−/− mice, suggesting important sex differences.

Association of the triglyceride-glucose index with weight-adjusted appendicular lean mass in Chinese adolescents aged 12-18 years old

There is no study exploring the association between triglyceride-glucose (TyG) index and skeletal muscle mass in Chinese adolescents. Therefore, the objective of this study is to explore the association between TyG index and appendicular lean mass (ALM) in Chinese adolescents. In this study, 1336 adolescents (805 boys, 60.25%) aged 12-18 years in China were randomly selected through a stratified cluster sampling. According to the tertiles of TyG index, we separated all participants into three groups, and LM was measured by Bioelectrical Impedance Analysis. The TyG index was negatively related to ALM/weight in Chinese adolescents whether stratified by gender (boys: β = - 0.293; girls: β = - 0.195; all P < 0.001). After adjusting for age and BMI, a significant correlation between the TyG index and ALM/weight was observed only in boys (β = - 0.169, P = 0.001). The highest TyG index tertile was significantly associated with low ALM/weight after adjusting for all covariates in the full sample (OR = 3.04, 95% CI 1.12-8.26, P = 0.029) and boys (OR = 4.68, 95% CI 1.22-17.95, P = 0.025) only in overweight/obese group. Our findings suggested elevated levels of TyG index may be a risk factor of low ALM/weight in Chinese adolescents, especially in boys.

The Regulation of Adipose Tissue Health by Estrogens

Obesity and its' associated metabolic diseases such as type 2 diabetes and cardiometabolic disorders are significant health problems confronting many countries. A major driver for developing obesity and metabolic dysfunction is the uncontrolled expansion of white adipose tissue (WAT). Specifically, the pathophysiological expansion of visceral WAT is often associated with metabolic dysfunction due to changes in adipokine secretion profiles, reduced vascularization, increased fibrosis, and enrichment of pro-inflammatory immune cells. A critical determinate of body fat distribution and WAT health is the sex steroid estrogen. The bioavailability of estrogen appears to favor metabolically healthy subcutaneous fat over visceral fat growth while protecting against changes in metabolic dysfunction. Our review will focus on the role of estrogen on body fat partitioning, WAT homeostasis, adipogenesis, adipocyte progenitor cell (APC) function, and thermogenesis to control WAT health and systemic metabolism.

Multiomics reveals persistence of obesity-associated immune cell phenotypes in adipose tissue during weight loss and weight regain in mice

Within adipose tissue (AT), immune cells and parenchymal cells closely interact creating a complex microenvironment. In obesity, immune cell derived inflammation contributes to insulin resistance and glucose intolerance. Diet-induced weight loss improves glucose tolerance; however, weight regain further exacerbates the impairment in glucose homeostasis observed with obesity. To interrogate the immunometabolic adaptations that occur in AT during murine weight loss and weight regain, we utilized cellular indexing of transcriptomes and epitopes by sequencing (CITEseq) in male mice. Obesity-induced imprinting of AT immune cells persisted through weight-loss and progressively worsened with weight regain, ultimately leading to impaired recovery of type 2 regulatory cells, activation of antigen presenting cells, T cell exhaustion, and enhanced lipid handling in macrophages in weight cycled mice. This work provides critical groundwork for understanding the immunological causes of weight cycling-accelerated metabolic disease. For further discovery, we provide an open-access web portal of diet-induced AT immune cell imprinting: https://hastylab.shinyapps.io/MAIseq .

Non-alcoholic fatty liver disease: a multi-system disease influenced by ageing and sex, and affected by adipose tissue and intestinal function

In recent years, a wealth of factors are associated with increased risk of developing non-alcoholic fatty liver disease (NAFLD) and NAFLD is now thought to increase the risk of multiple extra-hepatic diseases. The aim of this review is first to focus on the role of ageing and sex as key, poorly understood risk factors in the development and progression of NAFLD. Secondly, we aim to discuss the roles of white adipose tissue (WAT) and intestinal dysfunction, as producers of extra-hepatic factors known to further contribute to the pathogenesis of NAFLD. Finally, we aim to summarise the role of NAFLD as a multi-system disease affecting other organ systems beyond the liver. Both increased age and male sex increase the risk of NAFLD and this may be partly driven by alterations in the distribution and function of WAT. Similarly, changes in gut microbiota composition and intestinal function with ageing and chronic overnutrition are likely to contribute to the development of NAFLD both directly (i.e. by affecting hepatic function) and indirectly via exacerbating WAT dysfunction. Consequently, the presence of NAFLD significantly increases the risk of various extra-hepatic diseases including CVD, type 2 diabetes mellitus, chronic kidney disease and certain extra-hepatic cancers. Thus changes in WAT and intestinal function with ageing and chronic overnutrition contribute to the development of NAFLD – a multi-system disease that subsequently contributes to the development of other chronic cardiometabolic diseases.

Role of Estrogen and Its Receptors in Adipose Tissue Glucose Metabolism in Pre- and Postmenopausal Women

CONTEXT

Reduced estrogen levels in postmenopausal women predispose them to metabolic side effects, including insulin resistance and type 2 diabetes; however, the cellular mechanisms are not well understood.

OBJECTIVE

This work aimed to study the expression of estrogen receptors in adipose tissue from pre- and postmenopausal women and the effects of estradiol (E2) on glucose uptake of adipocytes.

METHODS

Subcutaneous (SAT) and visceral adipose tissue (VAT) obtained from pre- and postmenopausal women (19-51 and 46-75 years old, respectively) were used to measure gene expression of ESR1 and ESR2. SAT tissue was incubated with E2, and glucose uptake and estrogen receptor levels were measured. Polymorphisms in ESR1 and ESR2 were addressed in public databases to identify single nucleotide polymorphisms associated with metabolic traits.

RESULTS

ESR2 expression was lower in pre- vs postmenopausal women, corresponding to lower ESR1:ESR2 gene expression ratio in postmenopausal women. In premenopausal women, the expression of ESR1 was higher in VAT than in SAT. In both pre- and postmenopausal women, ESR2 expression was lower in VAT than in SAT. In late, but not pre- or early postmenopausal women, E2 reduced glucose uptake and GLUT4 protein and increased expression of ESR2. ESR1 polymorphisms were associated with weight, body fat distribution, and total cholesterol, and ESR2 polymorphisms were associated with total cholesterol and triglyceride levels and with body fat percentage.

CONCLUSION

E2 inhibits glucose utilization in human adipocytes in late postmenopausal women. Changes in glucose utilization over time since menopause may be explained by a lower ESR1:ESR2 ratio. This can have clinical implications on the timing of estrogen treatment in postmenopausal women.

A low-sugar diet enhances Drosophila body size in males and females via sex-specific mechanisms

In Drosophila, changes to dietary protein elicit different body size responses between the sexes. Whether these differential body size effects extend to other macronutrients remains unclear. Here, we show that lowering dietary sugar (0S diet) enhanced body size in male and female larvae. Despite an equivalent phenotypic effect between the sexes, we detected sex-specific changes to signalling pathways, transcription and whole-body glycogen and protein. In males, the low-sugar diet augmented insulin/insulin-like growth factor signalling pathway (IIS) activity by increasing insulin sensitivity, where increased IIS was required for male metabolic and body size responses in 0S. In females reared on low sugar, IIS activity and insulin sensitivity were unaffected, and IIS function did not fully account for metabolic and body size responses. Instead, we identified a female-biased requirement for the Target of rapamycin pathway in regulating metabolic and body size responses. Together, our data suggest the mechanisms underlying the low-sugar-induced increase in body size are not fully shared between the sexes, highlighting the importance of including males and females in larval studies even when similar phenotypic outcomes are observed.

Enrichment of the exocytosis protein STX4 in skeletal muscle remediates peripheral insulin resistance and alters mitochondrial dynamics via Drp1

Mitochondrial dysfunction is implicated in skeletal muscle insulin resistance. Syntaxin 4 (STX4) levels are reduced in human diabetic skeletal muscle, and global transgenic enrichment of STX4 expression improves insulin sensitivity in mice. Here, we show that transgenic skeletal muscle-specific STX4 enrichment (skmSTX4tg) in mice reverses established insulin resistance and improves mitochondrial function in the context of diabetogenic stress. Specifically, skmSTX4tg reversed insulin resistance caused by high-fat diet (HFD) without altering body weight or food consumption. Electron microscopy of wild-type mouse muscle revealed STX4 localisation at or proximal to the mitochondrial membrane. STX4 enrichment prevented HFD-induced mitochondrial fragmentation and dysfunction through a mechanism involving STX4-Drp1 interaction and elevated AMPK-mediated phosphorylation at Drp1 S637, which favors fusion. Our findings challenge the dogma that STX4 acts solely at the plasma membrane, revealing that STX4 localises at/proximal to and regulates the function of mitochondria in muscle. These results establish skeletal muscle STX4 enrichment as a candidate therapeutic strategy to reverse peripheral insulin resistance.

Adipose Tissue Inflammation and Cardiovascular Disease: An Update

PURPOSE OF REVIEW

The obesity epidemic is on the rise, and while it is well known that obesity is associated with an increase in cardiovascular risk factors such as type 2 diabetes mellitus, hypertension, and obstructive sleep apnea, recent data has highlighted that the degree and type of fat distribution may play a bigger role in the pathogenesis of cardiovascular disease (CVD) than body mass index (BMI) alone. We aim to review updated data on adipose tissue inflammation and distribution and CVD.

RECENT FINDINGS

We review the pathophysiology of inflammation secondary to adipose tissue, the association of obesity-related adipokines and CVD, and the differences and significance of brown versus white adipose tissue. We delve into the clinical manifestations of obesity-related inflammation in CVD. We discuss the available data on heterogeneity of adipose tissue-related inflammation with a focus on subcutaneous versus visceral adipose tissue, the differential pathophysiology, and clinical CVD manifestations of adipose tissue across sex, race, and ethnicity. Finally, we present the available data on lifestyle modification, medical, and surgical therapeutics on reduction of obesity-related inflammation. Obesity leads to a state of chronic inflammation which significantly increases the risk for CVD. More research is needed to develop non-invasive VAT quantification indices such as risk calculators which include variables such as sex, age, race, ethnicity, and VAT concentration, along with other well-known CVD risk factors in order to comprehensively determine risk of CVD in obese patients. Finally, pre-clinical biomarkers such as pro-inflammatory adipokines should be validated to estimate risk of CVD in obese patients.