Characterization of the skeletal muscle arginine methylome in health and disease reveals remodeling in amyotrophic lateral sclerosis

Arginine methylation is a protein posttranslational modification important for the development of skeletal muscle mass and function. Despite this, our understanding of the regulation of arginine methylation under settings of health and disease remains largely undefined. Here, we investigated the regulation of arginine methylation in skeletal muscles in response to exercise and hypertrophic growth, and in diseases involving metabolic dysfunction and atrophy. We report a limited regulation of arginine methylation under physiological settings that promote muscle health, such as during growth and acute exercise, nor in disease models of insulin resistance. In contrast, we saw a significant remodeling of asymmetric dimethylation in models of atrophy characterized by the loss of innervation, including in muscle biopsies from patients with myotrophic lateral sclerosis (ALS). Mass spectrometry-based quantification of the proteome and asymmetric arginine dimethylome of skeletal muscle from individuals with ALS revealed the largest compendium of protein changes with the identification of 793 regulated proteins, and novel site-specific changes in asymmetric dimethyl arginine (aDMA) of key sarcomeric and cytoskeletal proteins. Finally, we show that in vivo overexpression of PRMT1 and aDMA resulted in increased fatigue resistance and functional recovery in mice. Our study provides evidence for asymmetric dimethylation as a regulator of muscle pathophysiology and presents a valuable proteomics resource and rationale for numerous methylated and nonmethylated proteins, including PRMT1, to be pursued for therapeutic development in ALS.

ACSM1 and ACSM3 regulate fatty acid metabolism to support prostate cancer growth and constrain ferroptosis

Solid tumors are highly reliant on lipids for energy, growth, and survival. In prostate cancer, the activity of the androgen receptor (AR) is associated with reprogramming of lipid metabolic processes. Here, we identified acyl-CoA synthetase medium chain family members 1 and 3 (ACSM1 and ACSM3) as AR-regulated mediators of prostate cancer metabolism and growth. ACSM1 and ACSM3 were upregulated in prostate tumors compared to non-malignant tissues and other cancer types. Both enzymes enhanced proliferation and protected prostate cancer cells from death in vitro, while silencing ACSM3 led to reduced tumor growth in an orthotopic xenograft model. ACSM1 and ACSM3 were major regulators of the prostate cancer lipidome and enhanced energy production via fatty acid oxidation. Metabolic dysregulation caused by loss of ACSM1/3 led to mitochondrial oxidative stress, lipid peroxidation and cell death by ferroptosis. Conversely, elevated ACSM1/3 activity enabled prostate cancer cells to survive toxic levels of medium chain fatty acids and promoted resistance to ferroptosis-inducing drugs and AR antagonists. Collectively, this study reveals a tumor-promoting function for medium chain acyl-CoA synthetases and positions ACSM1 and ACSM3 as key players in prostate cancer progression and therapy resistance.

Two regulatory T cell populations in the visceral adipose tissue shape systemic metabolism

Visceral adipose tissue (VAT) is an energy store and endocrine organ critical for metabolic homeostasis. Regulatory T (Treg) cells restrain inflammation to preserve VAT homeostasis and glucose tolerance. Here, we show that the VAT harbors two distinct Treg cell populations: prototypical serum stimulation 2-positive (ST2+) Treg cells that are enriched in males and a previously uncharacterized population of C-X-C motif chemokine receptor 3-positive (CXCR3+) Treg cells that are enriched in females. We show that the transcription factors GATA-binding protein 3 and peroxisome proliferator-activated receptor-γ, together with the cytokine interleukin-33, promote the differentiation of ST2+ VAT Treg cells but repress CXCR3+ Treg cells. Conversely, the differentiation of CXCR3+ Treg cells is mediated by the cytokine interferon-γ and the transcription factor T-bet, which also antagonize ST2+ Treg cells. Finally, we demonstrate that ST2+ Treg cells preserve glucose homeostasis, whereas CXCR3+ Treg cells restrain inflammation in lean VAT and prevent glucose intolerance under high-fat diet conditions. Overall, this study defines two molecularly and developmentally distinct VAT Treg cell types with unique context- and sex-specific functions.

Fetuin B in white adipose tissue induces inflammation and is associated with peripheral insulin resistance in mice and humans

OBJECTIVE

Fetuin B is a steatosis-responsive hepatokine that causes glucose intolerance in mice, but the underlying mechanisms remain incompletely described. This study aimed to elucidate the mechanisms of action of fetuin B by investigating its putative effects on white adipose tissue metabolism.

METHODS

First, fetuin B gene and protein expression was measured in multiple organs in mice and in cultured adipocytes. Next, the authors performed a hyperinsulinemic-euglycemic clamp in mice and in humans to examine the link between white adipose tissue fetuin B content and indices of insulin sensitivity. Finally, the effect of fetuin B on inflammation was investigated in cultured adipocytes by quantitative polymerase chain reaction and full RNA sequencing.

RESULTS

This study demonstrated in adipocytes and mice that fetuin B was produced and secreted by the liver and taken up by adipocytes and adipose tissue. There was a strong negative correlation between white adipose tissue fetuin B content and peripheral insulin sensitivity in mice and in humans. RNA sequencing and polymerase chain reaction analysis revealed that fetuin B induced an inflammatory response in adipocytes.

CONCLUSIONS

Fetuin B content in white adipose tissue strongly associated with peripheral insulin resistance in mice and humans. Furthermore, fetuin B induced a proinflammatory response in adipocytes, which might drive peripheral insulin resistance.

Liver-derived extracellular vesicles improve whole-body glycaemic control via inter-organ communication

Small extracellular vesicles (EVs) are signalling messengers that regulate inter-tissue communication through delivery of their molecular cargo. Here, we show that liver-derived EVs are acute regulators of whole-body glycaemic control in mice. Liver EV secretion into the circulation is increased in response to hyperglycaemia, resulting in increased glucose effectiveness and insulin secretion through direct inter-organ EV signalling to skeletal muscle and the pancreas, respectively. This acute blood glucose lowering effect occurs in healthy and obese mice with non-alcoholic fatty liver disease, despite marked remodelling of the liver-derived EV proteome in obese mice. The EV-mediated blood glucose lowering effects were recapitulated by administration of liver EVs derived from humans with or without progressive non-alcoholic fatty liver disease, suggesting broad functional conservation of liver EV signalling and potential therapeutic utility. Taken together, this work reveals a mechanism whereby liver EVs act on peripheral tissues via endocrine signalling to restore euglycaemia in the postprandial state.

Mitochondria- and NOX4-dependent antioxidant defense mitigates progression to nonalcoholic steatohepatitis in obesity

Nonalcoholic fatty liver disease (NAFLD) is prevalent in the majority of individuals with obesity, but in a subset of these individuals, it progresses to nonalcoholic steatohepatitis (0NASH) and fibrosis. The mechanisms that prevent NASH and fibrosis in the majority of patients with NAFLD remain unclear. Here, we report that NAD(P)H oxidase 4 (NOX4) and nuclear factor erythroid 2-related factor 2 (NFE2L2) were elevated in hepatocytes early in disease progression to prevent NASH and fibrosis. Mitochondria-derived ROS activated NFE2L2 to induce the expression of NOX4, which in turn generated H2O2 to exacerbate the NFE2L2 antioxidant defense response. The deletion or inhibition of NOX4 in hepatocytes decreased ROS and attenuated antioxidant defense to promote mitochondrial oxidative stress, damage proteins and lipids, diminish insulin signaling, and promote cell death upon oxidant challenge. Hepatocyte NOX4 deletion in high-fat diet-fed obese mice, which otherwise develop steatosis, but not NASH, resulted in hepatic oxidative damage, inflammation, and T cell recruitment to drive NASH and fibrosis, whereas NOX4 overexpression tempered the development of NASH and fibrosis in mice fed a NASH-promoting diet. Thus, mitochondria- and NOX4-derived ROS function in concert to drive a NFE2L2 antioxidant defense response to attenuate oxidative liver damage and progression to NASH and fibrosis in obesity.

Intestinal-specific Hdac3 deletion increases susceptibility to colitis and small intestinal tumor development in mice fed a high-fat diet

High-fat (HF) diets (HFDs) and inflammation are risk factors for colon cancer; however, the underlying mechanisms remain to be fully elucidated. The transcriptional corepressor HDAC3 has recently emerged as a key regulator of intestinal epithelial responses to diet and inflammation with intestinal-specific Hdac3 deletion (Hdac3IKO) in mice increasing fatty acid oxidation genes and the rate of fatty acid oxidation in enterocytes. Hdac3IKO mice are also predisposed to experimentally induced colitis; however, whether this is driven by the intestinal metabolic reprogramming and whether this predisposes these mice to intestinal tumorigenesis is unknown. Herein, we examined the effects of intestinal-specific Hdac3 deletion on colitis-associated intestinal tumorigenesis in mice fed a standard (STD) or HFD. Hdac3IKO mice were highly prone to experimentally induced colitis, which was further enhanced by an HFD. Hdac3 deletion also accelerated intestinal tumor development, specifically when fed an HFD and most notably in the small intestine where lipid absorption is maximal. Expression of proteins involved in fatty acid metabolism and oxidation (SCD1, EHHADH) were elevated in the small intestine of Hdac3IKO mice fed an HFD, and these mice displayed increased levels of lipid peroxidation, DNA damage, and apoptosis in their villi, as well as extensive expansion of the stem cell and progenitor cell compartment. These findings reveal a novel role for Hdac3 in suppressing colitis and intestinal tumorigenesis, particularly in the context of consumption of an HFD, and reveal a potential mechanism by which HFDs may increase intestinal tumorigenesis by increasing fatty acid oxidation, DNA damage, and intestinal epithelial cell turnover.NEW & NOTEWORTHY We reveal a novel role for the transcriptional corepressor Hdac3 in suppressing colitis and intestinal tumorigenesis, particularly in the context of consumption of an HFD, and reveal a potential mechanism by which HFDs may increase intestinal tumorigenesis by increasing fatty acid oxidation, DNA damage, and intestinal epithelial cell turnover. We also identify a unique mouse model for investigating the complex interplay between diet, metabolic reprogramming, and tumor predisposition in the intestinal epithelium.

Exercise training induces depot-specific remodeling of protein secretion in skeletal muscle and adipose tissue of obese male mice

Acute exercise induces changes in circulating proteins, which are known to alter metabolism and systemic energy balance. Skeletal muscle is a primary contributor to changes in the plasma proteome with acute exercise. An important consideration when assessing the endocrine function of muscle is the presence of different fiber types, which show distinct functional and metabolic properties and likely secrete different proteins. Similarly, adipokines are important regulators of systemic metabolism and have been shown to differ between depots. Given the health-promoting effects of exercise, we proposed that understanding depot-specific remodeling of protein secretion in muscle and adipose tissue would provide new insights into intertissue communication and uncover novel regulators of energy homeostasis. Here, we examined the effect of endurance exercise training on protein secretion from fast-twitch extensor digitorum longus (EDL) and slow-twitch soleus muscle and visceral and subcutaneous adipose tissue. High-fat diet-fed mice were exercise trained for 6 wk, whereas a Control group remained sedentary. Secreted proteins from excised EDL and soleus muscle, inguinal, and epididymal adipose tissues were detected using mass spectrometry. We detected 575 and 784 secreted proteins from EDL and soleus muscle and 738 and 920 proteins from inguinal and epididymal adipose tissue, respectively. Of these, 331 proteins were secreted from all tissues, whereas secretion of many other proteins was tissue and depot specific. Exercise training led to substantial remodeling of protein secretion from EDL, whereas soleus showed only minor changes. Myokines released exclusively from EDL or soleus were associated with glycogen metabolism and cellular stress response, respectively. Adipokine secretion was completely refractory to exercise regulation in both adipose depots. This study provides an in-depth resource of protein secretion from muscle and adipose tissue, and its regulation following exercise training, and identifies distinct depot-specific secretion patterns that are related to the metabolic properties of the tissue of origin.NEW & NOTEWORTHY The present study examines the effects of exercise training on protein secretion from fast-twitch and slow-twitch muscle as well as visceral and subcutaneous adipose tissue of obese mice. Although exercise training leads to substantial remodeling of protein secretion from fast-twitch muscle, adipose tissue is completely refractory to exercise regulation.

Mouse strain-dependent variation in metabolic associated fatty liver disease (MAFLD): a comprehensive resource tool for pre-clinical studies

Non-alcoholic steatohepatitis (NASH), characterized as the joint presence of steatosis, hepatocellular ballooning and lobular inflammation, and liver fibrosis are strong contributors to liver-related and overall mortality. Despite the high global prevalence of NASH and the substantial healthcare burden, there are currently no FDA-approved therapies for preventing or reversing NASH and/or liver fibrosis. Importantly, despite nearly 200 pharmacotherapies in different phases of pre-clinical and clinical assessment, most therapeutic approaches that succeed from pre-clinical rodent models to the clinical stage fail in subsequent Phase I-III trials. In this respect, one major weakness is the lack of adequate mouse models of NASH that also show metabolic comorbidities commonly observed in NASH patients, including obesity, type 2 diabetes and dyslipidaemia. This study provides an in-depth comparison of NASH pathology and deep metabolic profiling in eight common inbred mouse strains (A/J, BALB/c, C3H/HeJ, C57BL/6J, CBA/CaH, DBA/2J, FVB/N and NOD/ShiLtJ) fed a western-style diet enriched in fat, sucrose, fructose and cholesterol for eight months. Combined analysis of histopathology and hepatic lipid metabolism, as well as measures of obesity, glycaemic control and insulin sensitivity, dyslipidaemia, adipose tissue lipolysis, systemic inflammation and whole-body energy metabolism points to the FVB/N mouse strain as the most adequate diet-induced mouse model for the recapitulation of metabolic (dysfunction) associated fatty liver disease (MAFLD) and NASH. With efforts in the pharmaceutical industry now focussed on developing multi-faceted therapies; that is, therapies that improve NASH and/or liver fibrosis, and concomitantly treat other metabolic comorbidities, this mouse model is ideally suited for such pre-clinical use.

Investigating dual inhibition of ACC and CD36 for the treatment of nonalcoholic fatty liver disease in mice

Nonalcoholic fatty liver disease (NAFLD) is the most common chronic liver disease worldwide. Dysregulation in hepatic lipid metabolism, including increased fatty acid uptake and de novo lipogenesis (DNL), is a hallmark of NAFLD. Here, we investigated dual inhibition of the fatty acid transporter fatty acid translocase (FAT/CD36), and acetyl-CoA carboxylase (ACC), the rate-limiting enzyme in DNL, for the treatment of NAFLD in mice. Mice with hepatic CD36 deletion (Cd36^LKO) and wild-type littermates were fed a high-fat diet for 12 wk and treated daily with either oral administration of an ACC inhibitor (GS-834356, Gilead Sciences; ACCi) or vehicle for 8 wk. Neither CD36 deletion or ACC inhibition impacted body composition, energy expenditure, or glucose tolerance. Cd36^LKO mice had elevated fasting plasma insulin, suggesting mild insulin resistance. Whole body fatty acid oxidation was significantly decreased in Cd36^LKO mice. Liver triglyceride content was significantly reduced in mice treated with ACCi; however, CD36 deletion caused an unexpected increase in liver triglycerides. This was associated with upregulation of genes and proteins of DNL, including ACC, and decreased liver triglyceride secretion ex vivo. Overall, these data confirm the therapeutic utility of ACC inhibition for steatosis resolution but indicate that inhibition of CD36 is not an effective treatment for NAFLD in mice.NEW & NOTEWORTHY Dysregulation of hepatic lipid metabolism is a hallmark of nonalcoholic fatty liver disease. Here, we show that dual inhibition of the de novo lipogenesis enzyme, ACC, and hepatic deletion of the fatty acid transporter, CD36, was ineffective for the treatment of NAFLD in mice. This was due to a paradoxical increase in liver triglycerides with CD36 deletion resulting from decreased hepatic triglyceride secretion and increased lipogenic gene expression.

Metabolic effects of lipectomy and of adipose tissue transplantation

OBJECTIVE

The goal of this study was to review the metabolic effects of fat transplantation.

METHODS

Fat (adipose tissue [AT]) transplantation has been performed extensively for many years in the cosmetic reconstruction industry. However, not all fats are equal. White, brown, and beige AT differ in energy storage and use. Brown and beige AT consume glucose and lipids for thermogenesis and, theoretically, may provide greater metabolic benefit in transplantation. Here, the authors review the metabolic effects of AT transplantation.

RESULTS

Removal of subcutaneous human AT does not have beneficial metabolic effects. Most studies find no benefit from visceral AT transplantation and some studies report harmful effects. In contrast, transplantation of inguinal or subcutaneous AT in mice has positive effects. Brown AT transplant studies have variable results depending on the model but most show benefit.

CONCLUSIONS

Many technical improvements have optimized fat grafting and transplantation in cosmetic surgery. Transplantation of subcutaneous AT has the potential for significant metabolic benefits, although there are few studies in humans or using human AT. Brown AT transplantation is beneficial but not readily feasible in humans thus ex vivo "beiging" may be a useful strategy. AT transplantation may provide clinical benefits in metabolic disorders, especially in the setting of lipodystrophy.

Liver-Secreted Hexosaminidase A Regulates Insulin-Like Growth Factor Signalling and Glucose Transport in Skeletal Muscle

Non-alcoholic fatty liver disease (NAFLD) and impaired glycaemic control are closely linked, however, the pathophysiological mechanisms underpinning this bidirectional relationship remain unresolved. The high secretory capacity of the liver and impairments in protein secretion in NAFLD suggest that endocrine changes in the liver are likely to contribute to glycaemic defects. We identify hexosaminidase A (HEXA) as a NAFLD-induced hepatokine in both mice and humans. HEXA regulates sphingolipid metabolism, converting GM2 to GM3 gangliosides; sphingolipids that are primarily localized to cell surface lipid rafts. Using recombinant murine HEXA protein, an enzymatically inactive HEXA(R178H) mutant, or adeno-associated viral vectors to induce hepatocyte-specific overexpression of HEXA, we show that HEXA improves blood glucose control by increasing skeletal muscle glucose uptake in mouse models of insulin resistance and type 2 diabetes, with these effects being dependent on HEXA's enzymatic action. Mechanistically, HEXA remodels muscle lipid raft ganglioside composition, thereby increasing insulin-like growth factor 1 signalling and glucose transporter 4 localization to the cell surface. Disrupting lipid rafts reverses these HEXA-mediated effects. Together, this study identifies a novel pathway for inter-tissue communication between liver and skeletal muscle in the regulation of systemic glycaemic control.

Multi-substrate metabolic tracing reveals marked heterogeneity and dependency on fatty acid metabolism in human prostate cancer

Cancer cells undergo metabolic reprogramming to meet increased bioenergetic demands. Studies in cells and mice have highlighted the importance of oxidative metabolism and lipogenesis in prostate cancer, however, the metabolic landscape of human prostate cancer remains unclear. To address this knowledge gap, we performed radiometric (14C) and stable (13C) isotope tracing assays in precision-cut slices of patient-derived xenografts (PDXs). Glucose, glutamine, and fatty acid oxidation was variably upregulated in malignant PDXs compared to benign PDXs. De novo lipogenesis (DNL) and storage of free fatty acids into phospholipids and triacylglycerols were increased in malignant PDXs. There was no difference in substrate utilization between localized and metastatic PDXs and hierarchical clustering revealed marked metabolic heterogeneity across all PDXs. Mechanistically, glucose utilization was mediated by acetyl-CoA production rather than carboxylation of pyruvate, while glutamine entered the TCA cycle through transaminase reactions before being utilized via oxidative or reductive pathways. Blocking fatty acid uptake or fatty acid oxidation with pharmacological inhibitors was sufficient to reduce cell viability in PDX-derived organoids (PDXOs), whereas blockade of DNL, or glucose or glutamine oxidation induced variable and limited therapeutic efficacy. These findings demonstrate that human prostate cancer, irrespective of disease stage, can effectively utilize all metabolic substrates, albeit with marked heterogeneity across tumors. We also confirm that fatty acid uptake and oxidation are targetable metabolic dependencies in human prostate cancer. Implications: Prostate cancer utilizes multiple substrates to fuel energy requirements, yet pharmacological targeting of fatty acid uptake and oxidation reveals metabolic dependencies in localised and metastatic tumors.

Lipid droplets and ferroptosis as new players in brain cancer glioblastoma progression and therapeutic resistance

A primary brain tumor glioblastoma is the most lethal of all cancers and remains an extremely challenging disease. Apparent oncogenic signaling in glioblastoma is genetically complex and raised at any stage of the disease's progression. Many clinical trials have shown that anticancer drugs for any specific oncogene aberrantly expressed in glioblastoma show very limited activity. Recent discoveries have highlighted that alterations in tumor metabolism also contribute to disease progression and resistance to current therapeutics for glioblastoma, implicating an alternative avenue to improve outcomes in glioblastoma patients. The roles of glucose, glutamine and tryptophan metabolism in glioblastoma pathogenesis have previously been described. This article provides an overview of the metabolic network and regulatory changes associated with lipid droplets that suppress ferroptosis. Ferroptosis is a newly discovered type of nonapoptotic programmed cell death induced by excessive lipid peroxidation. Although few studies have focused on potential correlations between tumor progression and lipid droplet abundance, there has recently been increasing interest in identifying key players in lipid droplet biology that suppress ferroptosis and whether these dependencies can be effectively exploited in cancer treatment. This article discusses how lipid droplet metabolism, including lipid synthesis, storage, and use modulates ferroptosis sensitivity or tolerance in different cancer models, focusing on glioblastoma.

Human visceral and subcutaneous adipose stem and progenitor cells retain depot-specific adipogenic properties during obesity

Abdominal obesity associates with cardiometabolic disease and an accumulation of lipids in the visceral adipose depot, whereas lipid accumulation in the subcutaneous depot is more benign. We aimed to further investigate whether the adipogenic properties where cell-intrinsic, or dependent on a depot-specific or obesity-produced microenvironment. We obtained visceral and subcutaneous biopsies from non-obese women (n = 14) or women living with morbid obesity (n = 14) and isolated adipose stem and progenitor cells (ASPCs) from the stromal vascular fraction of non-obese (n = 13) and obese (n = 13). Following in vitro differentiation into mature adipocytes, we observed a contrasting pattern with a lower gene expression of adipogenic markers and a higher gene expression of immunogenic markers in the visceral compared to the subcutaneous adipocytes. We identified the immunogenic factor BST2 as a marker for visceral ASPCs. The effect of obesity and insulin resistance on adipogenic and immunogenic markers in the in vitro differentiated cells was minor. In contrast, differentiation with exogenous Tumor necrosis factor resulted in increased immunogenic signatures, including increased expression of BST2, and decreased adipogenic signatures in cells from both depots. Our data, from 26 women, underscore the intrinsic differences between human visceral and subcutaneous adipose stem and progenitor cells, suggest that dysregulation of adipocytes in obesity mainly occurs at a post-progenitor stage, and highlight an inflammatory microenvironment as a major constraint of human adipogenesis.

Phosphoproteomics of three exercise modalities identifies canonical signaling and C18ORF25 as an AMPK substrate regulating skeletal muscle function

Exercise induces signaling networks to improve muscle function and confer health benefits. To identify divergent and common signaling networks during and after different exercise modalities, we performed a phosphoproteomic analysis of human skeletal muscle from a cross-over intervention of endurance, sprint, and resistance exercise. This identified 5,486 phosphosites regulated during or after at least one type of exercise modality and only 420 core phosphosites common to all exercise. One of these core phosphosites was S67 on the uncharacterized protein C18ORF25, which we validated as an AMPK substrate. Mice lacking C18ORF25 have reduced skeletal muscle fiber size, exercise capacity, and muscle contractile function, and this was associated with reduced phosphorylation of contractile and Ca2+ handling proteins. Expression of C18ORF25 S66/67D phospho-mimetic reversed the decreased muscle force production. This work defines the divergent and canonical exercise phosphoproteome across different modalities and identifies C18ORF25 as a regulator of exercise signaling and muscle function.

Transcriptomic and proteomic retinal pigment epithelium signatures of age-related macular degeneration

There are currently no treatments for geographic atrophy, the advanced form of age-related macular degeneration. Hence, innovative studies are needed to model this condition and prevent or delay its progression. Induced pluripotent stem cells generated from patients with geographic atrophy and healthy individuals were differentiated to retinal pigment epithelium. Integrating transcriptional profiles of 127,659 retinal pigment epithelium cells generated from 43 individuals with geographic atrophy and 36 controls with genotype data, we identify 445 expression quantitative trait loci in cis that are asssociated with disease status and specific to retinal pigment epithelium subpopulations. Transcriptomics and proteomics approaches identify molecular pathways significantly upregulated in geographic atrophy, including in mitochondrial functions, metabolic pathways and extracellular cellular matrix reorganization. Five significant protein quantitative trait loci that regulate protein expression in the retinal pigment epithelium and in geographic atrophy are identified - two of which share variants with cis- expression quantitative trait loci, including proteins involved in mitochondrial biology and neurodegeneration. Investigation of mitochondrial metabolism confirms mitochondrial dysfunction as a core constitutive difference of the retinal pigment epithelium from patients with geographic atrophy. This study uncovers important differences in retinal pigment epithelium homeostasis associated with geographic atrophy.

Ckmt1 is Dispensable for Mitochondrial Bioenergetics Within White/Beige Adipose Tissue

Within brown adipose tissue (BAT), the brain isoform of creatine kinase (CKB) has been proposed to regulate the regeneration of ADP and phosphocreatine in a futile creatine cycle (FCC) that stimulates energy expenditure. However, the presence of FCC, and the specific creatine kinase isoforms regulating this theoretical model within white adipose tissue (WAT), remains to be fully elucidated. In the present study, creatine did not stimulate respiration in cultured adipocytes, isolated mitochondria or mouse permeabilized WAT. Additionally, while creatine kinase ubiquitous-type, mitochondrial (CKMT1) mRNA and protein were detected in human WAT, shRNA-mediated reductions in Ckmt1 did not decrease submaximal respiration in cultured adipocytes, and ablation of CKMT1 in mice did not alter energy expenditure, mitochondrial responses to pharmacological β3-adrenergic activation (CL 316, 243) or exacerbate the detrimental metabolic effects of consuming a high-fat diet. Taken together, these findings solidify CKMT1 as dispensable in the regulation of energy expenditure, and unlike in BAT, they do not support the presence of FCC within WAT.

Exerkines in health, resilience and disease

The health benefits of exercise are well-recognized and are observed across multiple organ systems. These beneficial effects enhance overall resilience, healthspan and longevity. The molecular mechanisms that underlie the beneficial effects of exercise, however, remain poorly understood. Since the discovery in 2000 that muscle contraction releases IL-6, the number of exercise-associated signalling molecules that have been identified has multiplied. Exerkines are defined as signalling moieties released in response to acute and/or chronic exercise, which exert their effects through endocrine, paracrine and/or autocrine pathways. A multitude of organs, cells and tissues release these factors, including skeletal muscle (myokines), the heart (cardiokines), liver (hepatokines), white adipose tissue (adipokines), brown adipose tissue (baptokines) and neurons (neurokines). Exerkines have potential roles in improving cardiovascular, metabolic, immune and neurological health. As such, exerkines have potential for the treatment of cardiovascular disease, type 2 diabetes mellitus and obesity, and possibly in the facilitation of healthy ageing. This Review summarizes the importance and current state of exerkine research, prevailing challenges and future directions.

Proteomic analysis reveals exercise training induced remodelling of hepatokine secretion and uncovers syndecan-4 as a regulator of hepatic lipid metabolism

Objective

Non-alcoholic fatty liver disease (NAFLD) is linked to impaired lipid metabolism and systemic insulin resistance, which is partly mediated by altered secretion of liver proteins known as hepatokines. Regular physical activity can resolve NAFLD and improve its metabolic comorbidities, however, the effects of exercise training on hepatokine secretion and the metabolic impact of exercise-regulated hepatokines in NAFLD remain unresolved. Herein, we examined the effect of endurance exercise training on hepatocyte secreted proteins with the aim of identifying proteins that regulate metabolism and reduce NAFLD severity.

Methods

C57BL/6 mice were fed a high-fat diet for six weeks to induce NAFLD. Mice were exercise trained for a further six weeks, while the control group remained sedentary. Hepatocytes were isolated two days after the last exercise bout, and intracellular and secreted proteins were detected using label-free mass spectrometry. Hepatocyte secreted factors were applied to skeletal muscle and liver ex vivo and insulin action and fatty acid metabolism were assessed. Syndecan-4 (SDC4), identified as an exercise-responsive hepatokine, was overexpressed in the livers of mice using adeno-associated virus. Whole-body energy homeostasis was assessed by indirect calorimetry and skeletal muscle and liver metabolism was assessed using radiometric techniques.

Results

Proteomics analysis detected 2657 intracellular and 1593 secreted proteins from mouse hepatocytes. Exercise training remodelled the hepatocyte proteome, with differences in 137 intracellular and 35 secreted proteins. Bioinformatic analysis of hepatocyte secreted proteins revealed enrichment of tumour suppressive proteins and proteins involved in lipid metabolism and mitochondrial function, and suppression of oncogenes and regulators of oxidative stress. Hepatocyte secreted factors from exercise trained mice improved insulin action in skeletal muscle and increased hepatic fatty acid oxidation. Hepatocyte-specific overexpression of SDC4 reduced hepatic steatosis, which was associated with reduced hepatic fatty acid uptake, and blunted pro-inflammatory and pro-fibrotic gene expression. Treating hepatocytes with recombinant ectodomain of SDC4 (secreted form) recapitulated these effects with reduced fatty acid uptake, lipid storage and lipid droplet accumulation.

Conclusions

Remodelling of hepatokine secretion is an adaptation to regular exercise training that induces changes in metabolism in the liver and skeletal muscle. SDC4 is a novel exercise-responsive hepatokine that decreases fatty acid uptake and reduces steatosis in the liver. By understanding the proteomic changes in hepatocytes with exercise, these findings have potential for the discovery of new therapeutic targets for NAFLD.

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Exercise training remodels hepatokine secretion.

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Exercise regulated secreted factors improve insulin action in skeletal muscle.

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Syndecan-4 (SDC4) is a novel exercise-induced hepatokine.

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SDC4 reduces hepatic fatty acid uptake and hepatic steatosis.

Personalized Medicine for Prostate Cancer: Is Targeting Metabolism a Reality?

Prostate cancer invokes major shifts in gene transcription and metabolic signaling to mediate alterations in nutrient acquisition and metabolic substrate selection when compared to normal tissues. Exploiting such metabolic reprogramming is proposed to enable the development of targeted therapies for prostate cancer, yet there are several challenges to overcome before this becomes a reality. Herein, we outline the role of several nutrients known to contribute to prostate tumorigenesis, including fatty acids, glucose, lactate and glutamine, and discuss the major factors contributing to variability in prostate cancer metabolism, including cellular heterogeneity, genetic drivers and mutations, as well as complexity in the tumor microenvironment. The review draws from original studies employing immortalized prostate cancer cells, as well as more complex experimental models, including animals and humans, that more accurately reflect the complexity of the in vivo tumor microenvironment. In synthesizing this information, we consider the feasibility and potential limitations of implementing metabolic therapies for prostate cancer management.

Skeletal muscle NOX4 is required for adaptive responses that prevent insulin resistance

Reactive oxygen species (ROS) generated during exercise are considered integral for the health-promoting effects of exercise. However, the precise mechanisms by which exercise and ROS promote metabolic health remain unclear. Here, we demonstrate that skeletal muscle NADPH oxidase 4 (NOX4), which is induced after exercise, facilitates ROS-mediated adaptive responses that promote muscle function, maintain redox balance, and prevent the development of insulin resistance. Conversely, reductions in skeletal muscle NOX4 in aging and obesity contribute to the development of insulin resistance. NOX4 deletion in skeletal muscle compromised exercise capacity and antioxidant defense and promoted oxidative stress and insulin resistance in aging and obesity. The abrogated adaptive mechanisms, oxidative stress, and insulin resistance could be corrected by deleting the H₂O₂-detoxifying enzyme GPX-1 or by treating mice with an agonist of NFE2L2, the master regulator of antioxidant defense. These findings causally link NOX4-derived ROS in skeletal muscle with adaptive responses that promote muscle function and insulin sensitivity.

Intergenerational effects of a paternal Western diet during adolescence on offspring gut microbiota, stress reactivity, and social behavior

The global consumption of highly processed, calorie-dense foods has contributed to an epidemic of overweight and obesity, along with negative consequences for metabolic dysfunction and disease susceptibility. As it becomes apparent that overweight and obesity have ripple effects through generations, understanding of the processes involved is required, in both maternal and paternal epigenetic inheritance. We focused on the patrilineal effects of a Western-style high-fat (21%) and high-sugar (34%) diet (WD) compared to control diet (CD) during adolescence and investigated F0 and F1 mice for physiological and behavioral changes. F0 males (fathers) showed increased body weight, impaired glycemic control, and decreased attractiveness to females. Paternal WD caused significant phenotypic changes in F1 offspring, including higher body weights of pups, increased Actinobacteria abundance in the gut microbiota (ascertained using 16S microbiome profiling), a food preference for WD pellets, increased male dominance and attractiveness to females, as well as decreased behavioral despair. These results collectively demonstrate the long-term intergenerational effects of a Western-style diet during paternal adolescence. The behavioral and physiological alterations in F1 offspring provide evidence of adaptive paternal programming via epigenetic inheritance. These findings have important implications for understanding paternally mediated intergenerational inheritance, and its relevance to offspring health and disease susceptibility.