Endothelium‐specific CYP2J2 overexpression attenuates age‐related insulin resistance

Ample evidences demonstrate that cytochrome P450 epoxygenase‐derived epoxyeicosatrienoic acids (EETs) exert diverse biological activities, which include potent vasodilatory, anti‐inflammatory, and cardiovascular protective effects. In this study, we investigated the effects of endothelium‐specific CYP2J2 overexpression on age‐related insulin resistance and metabolic dysfunction. Endothelium‐specific targeting of the human CYP epoxygenase, CYP2J2, transgenic mice (Tie2‐CYP2J2‐Tr mice) was utilized. The effects of endothelium‐specific CYP2J2 overexpression on aging‐associated obesity, inflammation, and peripheral insulin resistance were evaluated by assessing metabolic parameters in young (3 months old) and aged (16 months old) adult male Tie2‐CYP2J2‐Tr mice. Decreased insulin sensitivity and attenuated insulin signaling in aged skeletal muscle, adipose tissue, and liver were observed in aged adult male mice, and moreover, these effects were partly inhibited in 16‐month‐old CYP2J2‐Tr mice. In addition, CYP2J2 overexpression‐mediated insulin sensitization in aged mice was associated with the amelioration of inflammatory state. Notably, the aging‐associated increases in fat mass and adipocyte size were only observed in 16‐month‐old wild‐type mice, and CYP2J2 overexpression markedly prevented the increase in fat mass and adipocyte size in aged Tie2‐CYP2J2‐Tr mice, which was associated with increased energy expenditure and decreased lipogenic genes expression. Furthermore, these antiaging phenotypes of Tie2‐CYP2J2‐Tr mice were also associated with increased muscle blood flow, enhanced active‐phase locomotor activity, and improved mitochondrial dysfunction in skeletal muscle. Collectively, our findings indicated that endothelium‐specific CYP2J2 overexpression alleviated age‐related insulin resistance and metabolic dysfunction, which highlighted CYP epoxygenase‐EET system as a potential target for combating aging‐related metabolic disorders.     

The histone deacetylase inhibitor butyrate improves metabolism and reduces muscle atrophy during aging

Sarcopenia, the loss of skeletal muscle mass and function during aging, is a major contributor to disability and frailty in the elderly. Previous studies found a protective effect of reduced histone deacetylase activity in models of neurogenic muscle atrophy. Because loss of muscle mass during aging is associated with loss of motor neuron innervation, we investigated the potential for the histone deacetylase (HDAC) inhibitor butyrate to modulate age‐related muscle loss. Consistent with previous studies, we found significant loss of hindlimb muscle mass in 26‐month‐old C57Bl/6 female mice fed a control diet. Butyrate treatment starting at 16 months of age wholly or partially protected against muscle atrophy in hindlimb muscles. Butyrate increased muscle fiber cross‐sectional area and prevented intramuscular fat accumulation in the old mice. In addition to the protective effect on muscle mass, butyrate reduced fat mass and improved glucose metabolism in 26‐month‐old mice as determined by a glucose tolerance test. Furthermore, butyrate increased markers of mitochondrial biogenesis in skeletal muscle and whole‐body oxygen consumption without affecting activity. The increase in mass in butyrate‐treated mice was not due to reduced ubiquitin‐mediated proteasomal degradation. However, butyrate reduced markers of oxidative stress and apoptosis and altered antioxidant enzyme activity. Our data is the first to show a beneficial effect of butyrate on muscle mass during aging and suggests HDACs contribute to age‐related muscle atrophy and may be effective targets for intervention in sarcopenia and age‐related metabolic disease.     

Effects of IGF‐1 isoforms on muscle growth and sarcopenia

The decline in skeletal muscle mass and strength occurring in aging, referred as sarcopenia, is the result of many factors including an imbalance between protein synthesis and degradation, changes in metabolic/hormonal status, and in circulating levels of inflammatory mediators. Thus, factors that increase muscle mass and promote anabolic pathways might be of therapeutic benefit to counteract sarcopenia. Among these, the insulin‐like growth factor‐1 (IGF‐1) has been implicated in many anabolic pathways in skeletal muscle. IGF‐1 exists in different isoforms that might exert different role in skeletal muscle. Here we study the effects of two full propeptides IGF‐1Ea and IGF‐1Eb in skeletal muscle, with the aim to define whether and through which mechanisms their overexpression impacts muscle aging. We report that only IGF‐1Ea expression promotes a pronounced hypertrophic phenotype in young mice, which is maintained in aged mice. Nevertheless, examination of aged transgenic mice revealed that the local expression of either IGF‐1Ea or IGF‐1Eb transgenes was protective against age‐related loss of muscle mass and force. At molecular level, both isoforms activate the autophagy/lysosome system, normally altered during aging, and increase PGC1‐α expression, modulating mitochondrial function, ROS detoxification, and the basal inflammatory state occurring at old age. Moreover, morphological integrity of neuromuscular junctions was maintained and preserved in both MLC/IGF‐1Ea and MLC/IGF‐1Eb mice during aging. These data suggest that IGF‐1 is a promising therapeutic agent in staving off advancing muscle weakness.     

Methionine restriction restores a younger metabolic phenotype in adult mice with alterations in fibroblast growth factor 21

Methionine restriction (MR) decreases body weight and adiposity and improves glucose homeostasis in rodents. Similar to caloric restriction, MR extends lifespan, but is accompanied by increased food intake and energy expenditure. Most studies have examined MR in young animals; therefore, the aim of this study was to investigate the ability of MR to reverse age‐induced obesity and insulin resistance in adult animals. Male C57BL/6J mice aged 2 and 12 months old were fed MR (0.172% methionine) or control diet (0.86% methionine) for 8 weeks or 48 h. Food intake and whole‐body physiology were assessed and serum/tissues analyzed biochemically. Methionine restriction in 12‐month‐old mice completely reversed age‐induced alterations in body weight, adiposity, physical activity, and glucose tolerance to the levels measured in healthy 2‐month‐old control‐fed mice. This was despite a significant increase in food intake in 12‐month‐old MR‐fed mice. Methionine restriction decreased hepatic lipogenic gene expression and caused a remodeling of lipid metabolism in white adipose tissue, alongside increased insulin‐induced phosphorylation of the insulin receptor (IR) and Akt in peripheral tissues. Mice restricted of methionine exhibited increased circulating and hepatic gene expression levels of FGF21, phosphorylation of eIF2a, and expression of ATF4, with a concomitant decrease in IRE1α phosphorylation. Short‐term 48‐h MR treatment increased hepatic FGF21 expression/secretion and insulin signaling and improved whole‐body glucose homeostasis without affecting body weight. Our findings suggest that MR feeding can reverse the negative effects of aging on body mass, adiposity, and insulin resistance through an FGF21 mechanism. These findings implicate MR dietary intervention as a viable therapy for age‐induced metabolic syndrome in adult humans.     

Aging leads to a programmed loss of brown adipocytes in murine subcutaneous white adipose tissue

Insulin sensitivity deteriorates with age, but mechanisms remain unclear. Age‐related changes in the function of subcutaneous white adipose tissue (sWAT) are less characterized than those in visceral WAT. We hypothesized that metabolic alterations in sWAT, which in contrast to epididymal WAT, harbors a subpopulation of energy‐dissipating UCP1+ brown adipocytes, promote age‐dependent progression toward insulin resistance. Indeed, we show that a predominant consequence of aging in murine sWAT is loss of ‘browning’. sWAT from young mice is histologically similar to brown adipose tissue (multilocular, UCP1+), but becomes morphologically white by 12 months of age. Correspondingly, sWAT expression of ucp1 precipitously declines (~300‐fold) between 3 and 12 months. Loss continues into old age (24 months) and is inversely correlated with the development of insulin resistance. Additional age‐dependent changes in sWAT include lower expression of adbr3 and higher expression of maoa, suggesting reduced local adrenergic tone as a potential mechanism. Indeed, treatment with a β3‐adrenergic agonist to compensate for reduced tone rescues the aged sWAT phenotype. Age‐related changes in sWAT are not explained by the differences in body weight; mice subjected to 40% caloric restriction for 12 months are of body weight similar to 3‐month‐old ad lib fed mice, but display sWAT resembling that of age‐matched ad lib fed mice (devoid of brown adipose‐like morphology). Overall, findings identify the loss of ‘browning’ in sWAT as a new aging phenomenon and provide insight into the pathogenesis of age‐associated metabolic disease by revealing novel molecular changes tied to systemic metabolic dysfunction.     

Mitochondrial‐targeted peptide rapidly improves mitochondrial energetics and skeletal muscle performance in aged mice

Mitochondrial dysfunction plays a key pathogenic role in aging skeletal muscle resulting in significant healthcare costs in the developed world. However, there is no pharmacologic treatment to rapidly reverse mitochondrial deficits in the elderly. Here, we demonstrate that a single treatment with the mitochondrial‐targeted peptide SS‐31 restores in vivo mitochondrial energetics to young levels in aged mice after only one hour. Young (5 month old) and old (27 month old) mice were injected intraperitoneally with either saline or 3 mg kg^?1 of SS‐31. Skeletal muscle mitochondrial energetics were measured in vivo one hour after injection using a unique combination of optical and ³¹P magnetic resonance spectroscopy. Age‐related declines in resting and maximal mitochondrial ATP production, coupling of oxidative phosphorylation (P/O), and cell energy state (PCr/ATP) were rapidly reversed after SS‐31 treatment, while SS‐31 had no observable effect on young muscle. These effects of SS‐31 on mitochondrial energetics in aged muscle were also associated with a more reduced glutathione redox status and lower mitochondrial H₂O₂ emission. Skeletal muscle of aged mice was more fatigue resistant in situ one hour after SS‐31 treatment, and eight days of SS‐31 treatment led to increased whole‐animal endurance capacity. These data demonstrate that SS‐31 represents a new strategy for reversing age‐related deficits in skeletal muscle with potential for translation into human use.     

Glycolytic fast‐twitch muscle fiber restoration counters adverse age‐related changes in body composition and metabolism

Aging is associated with the development of insulin resistance, increased adiposity, and accumulation of ectopic lipid deposits in tissues and organs. Starting in mid‐life there is a progressive decline in lean muscle mass associated with the preferential loss of glycolytic, fast‐twitch myofibers. However, it is not known to what extent muscle loss and metabolic dysfunction are causally related or whether they are independent epiphenomena of the aging process. Here, we utilized a skeletal‐muscle‐specific, conditional transgenic mouse expressing a constitutively active form of Akt1 to examine the consequences of glycolytic, fast‐twitch muscle growth in young vs. middle‐aged animals fed standard low‐fat chow diets. Activation of the Akt1 transgene led to selective skeletal muscle hypertrophy, reversing the loss of lean muscle mass observed upon aging. The Akt1‐mediated increase in muscle mass led to reductions in fat mass and hepatic steatosis in older animals, and corrected age‐associated impairments in glucose metabolism. These results indicate that the loss of lean muscle mass is a significant contributor to the development of age‐related metabolic dysfunction and that interventions that preserve or restore fast/glycolytic muscle may delay the onset of metabolic disease.     

Long‐term caloric restriction ameliorates deleterious effects of aging on white and brown adipose tissue plasticity

Age‐related increased adiposity is an important contributory factor in the development of insulin resistance (IR) and is associated with metabolic defects. Caloric restriction (CR) is known to induce weight loss and to decrease adiposity while preventing metabolic risk factors. Here, we show that moderate 20% CR delays early deleterious effects of aging on white and brown adipose tissue (WAT and BAT, respectively) function and improves peripheral IR. To elucidate the role of CR in delaying early signs of aging, young (3 months), middle‐aged (12 months), and old (20 months) mice fed al libitum and middle‐aged and old mice subjected to early‐onset CR were used. We show that impaired plasticity of subcutaneous WAT (scWAT) contributes to IR, which is already evident in middle‐aged mice. Moreover, alteration of thyroid axis status with age is an important factor contributing to BAT dysfunction in middle‐aged animals. Both defects in WAT and BAT/beige cells are ameliorated by CR. Accordingly, CR attenuated the age‐related decline in scWAT function and decreased the extent of fibro‐inflammation. Furthermore, CR promoted scWAT browning. In brief, our study identifies the contribution of scWAT impairment to age‐associated metabolic dysfunction and identifies browning in response to food restriction, as a potential therapeutic strategy to prevent the adverse metabolic effects in middle‐aged animals.     

Loss of sirtuin 1 and mitofusin 2 contributes to enhanced ischemia/reperfusion injury in aged livers

Ischemia/reperfusion (I/R) injury is a causative factor contributing to morbidity and mortality during liver resection and transplantation. Livers from elderly patients have a poorer recovery from these surgeries, indicating reduced reparative capacity with aging. Mechanisms underlying this age‐mediated hypersensitivity to I/R injury remain poorly understood. Here, we investigated how sirtuin 1 (SIRT1) and mitofusin 2 (MFN2) are affected by I/R in aged livers. Young (3 months) and old (23–26 months) male C57/BL6 mice were subjected to hepatic I/R in vivo. Primary hepatocytes isolated from each age group were also exposed to simulated in vitro I/R. Biochemical, genetic, and imaging analyses were performed to assess cell death, autophagy flux, mitophagy, and mitochondrial function. Compared to young mice, old livers showed accelerated liver injury following mild I/R. Reperfusion of old hepatocytes also showed necrosis, accompanied with defective autophagy, onset of the mitochondrial permeability transition, and mitochondrial dysfunction. Biochemical analysis indicated a near‐complete loss of both SIRT1 and MFN2 after I/R in old hepatocytes, which did not occur in young cells. Overexpression of either SIRT1 or MFN2 alone in old hepatocytes failed to mitigate I/R injury, while co‐overexpression of both proteins promoted autophagy and prevented mitochondrial dysfunction and cell death after reperfusion. Genetic approaches with deletion and point mutants revealed that SIRT1 deacetylated K655 and K662 residues in the C‐terminus of MFN2, leading to autophagy activation. The SIRT1‐MFN2 axis is pivotal during I/R recovery and may be a novel therapeutic target to reduce I/R injury in aged livers.     

Hypothalamic gene transfer of BDNF promotes healthy aging in mice

The aging process and age‐related diseases all involve perturbed energy adaption and impaired ability to cope with adversity. Brain‐derived neurotrophic factor (BDNF) in the hypothalamus plays important role in regulation of energy balance. Our previous studies show that recombinant adeno‐associated virus (AAV)‐mediated hypothalamic BDNF gene transfer alleviates obesity, diabetes, and metabolic syndromes in both diet‐induced and genetic models. Here we examined the efficacy and safety of a built‐in autoregulatory system to control transgene BDNF expression mimicking the body's natural feedback systems in middle‐aged mice. Twelve‐month‐old mice were treated with either autoregulatory BDNF vector or yellow fluorescence protein (YFP) control, maintained on normal diet, and monitored for 28 weeks. BDNF gene transfer prevented the development of aging‐associated metabolic declines characterized by: preventing aging‐associated weight gain, reducing adiposity, reversing the decline of brown fat activity, increasing adiponectin while reducing leptin and insulin in circulation, improving glucose tolerance, increasing energy expenditure, alleviating hepatic steatosis, and suppressing inflammatory genes in the hypothalamus and adipose tissues. Moreover, BDNF treatment reduced anxiety‐like and depression‐like behaviors. These safety and efficacy data provide evidence that hypothalamic BDNF is a target for promoting healthy aging.     

IL10 deficiency promotes alveolar enlargement and lymphoid dysmorphogenesis in the aged murine lung

The connection between aging‐related immune dysfunction and the lung manifestations of aging is poorly understood. A detailed characterization of the aging IL10‐deficient murine lung, a model of accelerated aging and frailty, reconciles features of both immunosenescence and lung aging in a coherent model. Airspace enlargement developed in the middle‐aged (12 months old) and aged (20–22 months old) IL10‐deficient lung punctuated by an expansion of macrophages and alveolar cell apoptosis. Compared to wild‐type (WT) controls, the IL10‐deficient lungs from young (4‐month‐old) mice showed increased oxidative stress which was enhanced in both genotypes by aging. Active caspase 3 staining was increased in the alveolar epithelial cells of aged WT and mutant lungs but was greater in the IL10‐deficient milieu. Lung macrophages were increased in the aged IL10‐deficient lungs with exuberant expression of MMP12. IL10 treatment of naïve and M2‐polarized bone marrow‐derived WT macrophages reduced MMP12 expression. Conditioned media studies demonstrated the secretome of aged mutant macrophages harbors reduced AECII prosurvival factors, specifically keratinocyte growth factor (KGF) and hepatocyte growth factor (HGF), promotes cell death, and reduces survival of primary alveolar epithelial cells. Compared to WT controls, aged IL10‐deficient mice have increased parenchymal lymphoid collections comprised of a reduced number of apoptotic cells and B cells. We establish that IL10 is a key modulator of airspace homeostasis and lymphoid morphogenesis in the aging lung enabling macrophage‐mediated alveolar epithelial cell survival and B‐cell survival within tertiary lymphoid structures.     

Homeostatic and injury‐induced microglia behavior in the aging brain

Microglia cells are essential for brain homeostasis and have essential roles in neurodegenerative diseases. Aging is the main risk factor for most neurodegenerative diseases, and age‐related changes in microglia may contribute to the susceptibility of the aging brain to dysfunction and neurodegeneration. We have analyzed morphology and dynamic behavior of neocortical microglia in their physiological environment in young adult (3‐month‐old), adult (11‐ to 12‐month‐old), and aged (26‐ to 27‐month‐old) C57BL/6J‐Iba1‐eGFP mice using in vivo 2‐photon microscopy. Results show that surveying microglial cells in the neocortex exhibit age‐related soma volume increase, shortening of processes, and loss of homogeneous tissue distribution. Furthermore, microglial process speed significantly decreased with age. While only a small population of microglia showed soma movement in adult mice, the microglia population with soma movement was increased in aged mice. However, in response to tissue injury, the dynamic microglial response was age‐dependently diminished. These results provide novel insights into microglial behavior and indicate that microglial dysfunction in the aging brain may contribute to age‐related cognitive decline and neurodegenerative diseases.     

Responsiveness of dentate neurons generated throughout adult life is associated with resilience to cognitive aging

During aging, some individuals are resilient to the decline of cognitive functions whereas others are vulnerable. These inter‐individual differences in memory abilities have been associated with differences in the rate of hippocampal neurogenesis measured in elderlies. Whether the maintenance of the functionality of neurons generated throughout adult life is linked to resilience to cognitive aging remains completely unexplored. Using the immediate early gene Zif268, we analyzed the activation of dentate granule neurons born in adult (3‐month‐old), middle‐aged (12‐month‐old), or senescent (18‐month‐old) rats (n = 96) in response to learning when animals reached 21 months of age. The activation of neurons born during the developmental period was also examined. We show that adult‐born neurons can survive up to 19 months and that neurons generated 4, 10, or 19 months before learning, but not developmentally born neurons, are activated in senescent rats with good learning abilities. In contrast, aged rats with bad learning abilities do not exhibit activity‐dependent regulation of newborn cells, whatever their birthdate. In conclusion, we propose that resilience to cognitive aging is associated with responsiveness of neurons born during adult life. These data add to our current knowledge by showing that the aging of memory abilities stems not only from the number but also from the responsiveness of adult‐born neurons.     

Maintenance of muscle mass and load‐induced growth in Muscle RING Finger 1 null mice with age

Age‐related loss of muscle mass occurs to varying degrees in all individuals and has a detrimental effect on morbidity and mortality. Muscle RING Finger 1 (MuRF1), a muscle‐specific E3 ubiquitin ligase, is believed to mediate muscle atrophy through the ubiquitin proteasome system (UPS). Deletion of MuRF1 (KO) in mice attenuates the loss of muscle mass following denervation, disuse, and glucocorticoid treatment; however, its role in age‐related muscle loss is unknown. In this study, skeletal muscle from male wild‐type (WT) and MuRF1 KO mice was studied up to the age of 24 months. Muscle mass and fiber cross‐sectional area decreased significantly with age in WT, but not in KO mice. In aged WT muscle, significant decreases in proteasome activities, especially 20S and 26S β5 (20–40% decrease), were measured and were associated with significant increases in the maladaptive endoplasmic reticulum (ER) stress marker, CHOP. Conversely, in aged MuRF1 KO mice, 20S or 26S β5 proteasome activity was maintained or decreased to a lesser extent than in WT mice, and no increase in CHOP expression was measured. Examination of the growth response of older (18 months) mice to functional overload revealed that old WT mice had significantly less growth relative to young mice (1.37‐ vs. 1.83‐fold), whereas old MuRF1 KO mice had a normal growth response (1.74‐ vs. 1.90‐fold). These data collectively suggest that with age, MuRF1 plays an important role in the control of skeletal muscle mass and growth capacity through the regulation of cellular stress.     

A high‐fat diet reverses metabolic disorders and premature aging by modulating insulin and IGF1 signaling in SIRT6 knockout mice

Mammalian sirtuin 6 (SIRT6) is involved in the regulation of many essential processes, especially metabolic homeostasis. SIRT6 knockout mice undergo premature aging and die at age ~4 weeks. Severe glycometabolic disorders have been found in SIRT6 knockout mice, and whether a dietary intervention can rescue SIRT6 knockout mice remains unknown. In our study, we found that at the same calorie intake, a high‐fat diet dramatically increased the lifespan of SIRT6 knockout mice to 26 weeks (males) and 37 weeks (females), reversed multi‐organ atrophy, and reduced body weight, hypoglycemia, and premature aging. Furthermore, the high‐fat diet partially but significantly normalized the global gene expression profile in SIRT6 knockout mice. Regarding the mechanism, excessive glucose uptake and glycolysis induced by the SIRT6 deficiency were attenuated in skeletal muscle through inhibition of insulin and IGF1 signaling by the high‐fat diet. Similarly, fatty acids but not ketone bodies inhibited glucose uptake, glycolysis, and senescence in SIRT6 knockout fibroblasts, whereas PI3K inhibition antagonized the effects of a high‐fatty‐acid medium in vitro. Overall, the high‐fat diet dramatically reverses numerous consequences of SIRT6 deficiency through modulation of insulin and IGF1 signaling, providing a new basis for elucidation of SIRT6 and fatty‐acid functions and supporting novel therapeutic approaches against metabolic disorders and aging‐related diseases.     

Mitochondrial‐targeted catalase is good for the old mouse proteome,but not for the young: ‘reverse’ antagonistic pleiotropy?

Reactive oxygen species (ROS) are highly reactive oxygen‐containing molecules associated with aging and a broad spectrum of pathologies. We have previously shown that transgenic expression of the antioxidant enzyme catalase targeted to the mitochondria (mCAT) in mice reduces ROS, attenuates age‐related disease, and increases lifespan. However, it has been increasingly recognized that ROS also has beneficial roles in signaling, hormesis, stress response, and immunity. We therefore hypothesized that mCAT might be beneficial only when ROS approaches pathological levels in older age and might not be advantageous at a younger age when basal ROS is low. We analyzed abundance and turnover of the global proteome in hearts and livers of young (4 month) and old (20 month) mCAT and wild‐type (WT) mice. In old hearts and livers of WT mice, protein half‐lives were reduced compared to young, while in mCAT mice the reverse was observed; the longest half‐lives were seen in old mCAT mice and the shortest in young mCAT. Protein abundance of old mCAT hearts recapitulated a more youthful proteomic expression profile (P‐value < 0.01). However, young mCAT mice partially phenocopied the older wild‐type proteome (P‐value < 0.01). Age strongly interacts with mCAT, consistent with antagonistic pleiotropy in the reverse of the typical direction. These findings underscore the contrasting roles of ROS in young vs. old mice and indicate the need for better understanding of the interaction between dose and age in assessing the efficacy of therapeutic interventions in aging, including mitochondrial antioxidants.     

Food Intake‐independent Effects of CB1 Antagonism on Glucose and Lipid Metabolism

Overactivity of the endocannabinoid system (ECS) has been linked to abdominal obesity and other risk factors for cardiovascular disease and type 2 diabetes. Conversely, administration of cannabinoid receptor type 1 (CB1) antagonists reduces adiposity in obese animals and humans. This effect is only in part secondary to the anorectic action of CB1 agonists. In order to assess the actions of CB1 antagonism on glucose homeostasis, diet‐induced obese (DIO) rats received the CB1 antagonist rimonabant (10 mg/kg, intraperitoneally (IP)) or its vehicle for 4 weeks, or were pair‐fed to the rimonabant‐treated group for the same length of time. Rimonabant treatment transiently reduced food intake, while inducing body weight loss throughout the study. Rats receiving rimonabant had significantly less body fat and circulating leptin compared to both vehicle and pair‐fed groups. Rimonabant, but not pair‐feeding, also significantly decreased circulating nonesterified fatty acid (NEFA) and triacylglycerol (TG) levels, and reduced TG content in oxidative skeletal muscle. Although no effects were observed during a glucose tolerance test (GTT), rimonabant restored insulin sensitivity to that of chow‐fed, lean controls during an insulin tolerance test (ITT). Conversely, a single dose of rimonabant to DIO rats had no acute effect on insulin sensitivity. These findings suggest that in diet‐induced obesity, chronic CB1 antagonism causes weight loss and improves insulin sensitivity by diverting lipids from storage toward utilization. These effects are independent of the anorectic action of the drug.     

Increases of M2a macrophages and fibrosis in aging muscle are influenced by bone marrow aging and negatively regulated by muscle‐derived nitric oxide

Muscle aging is associated with changes in myeloid cell phenotype that may influence age‐related changes in muscle structure. We tested whether preventing age‐related reductions in muscle neuronal nitric oxide synthase (nNOS) would obviate age‐related changes in myeloid cells in muscle. Our findings show that muscle aging is associated with elevations of anti‐inflammatory M2a macrophages that can increase muscle fibrosis. Expression of a muscle‐specific nNOS transgene in mice prevented age‐related increases in M2a macrophages. Transgene expression also reduced expression of collagens and decreased muscle fibrosis. The nNOS transgene prevented age‐related increases in arginase‐1 but did not influence TGFβ expression, indicating that the transgene may prevent age‐related muscle fibrosis by inhibiting the arginase‐dependent profibrotic pathway. Although aged satellite cells or fibro‐adipogenic precursor (FAPs) cells also promote fibrosis, transgene expression had no effect on the expression of key signaling molecules that regulate fibrogenic activity of those cells. Finally, we tested whether increases in M2a macrophages and the associated increase in fibrosis were attributable to aging of myeloid lineage cells. Young bone marrow cells (BMCs) were transplanted into young or old mice, and muscles were collected 8 months later. Muscles of young mice receiving young BMCs showed no effect on M2a macrophage number or collagen accumulation compared to age‐matched, nontransplanted controls. However, muscles of old mice receiving young BMCs showed fewer M2a macrophages and less accumulation of collagen. Thus, the age‐related increase in M2a macrophages in aging muscle and the associated muscle fibrosis are determined in part by the age of bone marrow cells.     

Satellite cells isolated from aged or dystrophic muscle exhibit a reduced capacity to promote angiogenesis in vitro

Deficits in skeletal muscle function exist during aging and muscular dystrophy, and suboptimal function has been related to factors such as atrophy, excessive inflammation and fibrosis. Ineffective muscle regeneration underlies each condition and has been attributed to a deficit in myogenic potential of resident stem cells or satellite cells. In addition to reduced myogenic activity, satellite cells may also lose the ability to communicate with vascular cells for coordination of myogenesis and angiogenesis and restoration of proper muscle function. Objectives of the current study were to determine the angiogenic-promoting capacity of satellite cells from two states characterized by dysfunctional skeletal muscle repair, aging and Duchenne muscular dystrophy. An in vitro culture model composed of satellite cells or their conditioned media and rat adipose tissue microvascular fragments (MVF) was used to examine this relationship. Microvascular fragments cultured in the presence of rat satellite cells from adult muscle donors (9–12 month of age) exhibited greater indices of angiogenesis (endothelial cell sprouting, tubule formation and extensive branching) than MVF co-cultured with satellite cells from aged muscle donors (24 month of age). We sought to determine if the differential degree of angiogenesis we observed in the co-culture setting was due to soluble factors produced by each satellite cell age group. Similar to the co-culture experiment, conditioned media produced by adult satellite cells promoted greater angiogenesis than that of aged satellite cells. Next, we examined differences in angiogenesis-stimulating ability of satellite cells from 12 mo old MDX mice or age-matched wild-type mice. A reduction in angiogenesis activity of media conditioned by satellite cells from dystrophic muscle was observed as compared to healthy muscle. Finally, we found reduced gene expression of hypoxia-inducible factor 1α (HIF-1α) and vascular endothelial growth factor (VEGF) in both aged and dystrophic satellite cells compared to their adult and normal counterparts, respectively. These results indicate that functional deficits in satellite cell activities during aging and diseased muscle may extend to their ability to communicate with other cells in their environment, in this case cells involved in angiogenesis.