Effects of repeated weight cycling on non-alcoholic steatohepatitis in diet-induced obese mice.

Lifestyle interventions remain the treatment of choice for patients with obesity and metabolic complications, yet are difficult to maintain and often lead to cycles of weight loss and regain (weight cycling). Literature on weight cycling remains controversial and we therefore investigated the association between weight cycling and metabolic complications using preexistent obese mice. Ldlr-/-.Leiden mice received a high-fat diet (HFD) for 20 weeks to induce obesity. Subsequently, weight-cycled mice were switched between the healthy chow diet and HFD for four 2-week periods and compared to mice that received HFD for the total study period. Repeated weight cycling tended to decrease body weight and significantly reduced fat mass, whereas adipose tissue inflammation was similar relative to HFD controls. Weight cycling did not significantly affect blood glucose or plasma insulin levels yet significantly reduced plasma free fatty acid and alanine transaminase/aspartate transaminase levels. Hepatic macrovesicular steatosis was similar and microvesicular steatosis tended to be increased upon weight cycling. Weight cycling resulted in a robust decrease in hepatic inflammation compared to HFD controls while hepatic fibrosis and atherosclerosis development were not affected. These results argue against the postulate that repeated weight cycling leads to unfavorable metabolic effects, when compared to a continuous unhealthy lifestyle, and in fact revealed beneficial effects on hepatic inflammation, an important hallmark of non-alcoholic steatohepatitis.

Translatability of mouse muscle-aging for humans: the role of sex.

Muscle-aging drives sarcopenia and is a major public health issue. Mice are frequently used as a model for human muscle-aging, however, research investigating their translational value is limited. In addition, mechanisms underlying muscle-aging may have sex-specific features in humans, but it is not yet assessed whether these are recapitulated in mice. Here, we studied the effects of aging on a functional, histological and transcriptional level at multiple timepoints in male and female mice (4, 17, 21 and 25 months), with particular emphasis on sex-differences. The effects of natural aging on the transcriptome of quadriceps muscle were compared to humans on pathway level. Significant loss of muscle mass occurred late, at 25 months, in both male (-17%, quadriceps) and female mice (-10%, quadriceps) compared to young control mice. Concomitantly, we found in female, but not male mice, a slower movement speed in the aged groups compared to the young mice (P < 0.001). Consistently, weighted gene co-expression network analysis revealed a stronger association between the aging-related reduction of movement and aging-related changes in muscle transcriptome of female compared to male mice (P < 0.001). In male, but not female mice, major distinctive aging-related changes occurred in the last age group (25 months), which highlights the necessity for careful selection of age using mice as a muscle-aging model. Furthermore, contrasting to humans, more aging-related changes were found in the muscle transcriptome of male mice compared to female mice (4090 vs. 2285 differentially expressed genes at 25 months, respectively). Subsequently, male mice recapitulated more muscle-aging related pathways characteristic for both male and female humans. In conclusion, our data show that sex has a critical effect on the mouse muscle-aging trajectory, although these do not necessarily reflect sex differences observed in the human muscle-aging trajectory.

Evidence for sex-specific intramuscular changes associated to physical weakness in adults older than 75 years.

BACKGROUND: Physical weakness is a key component of frailty, and is highly prevalent in older adults. While females have a higher prevalence and earlier onset, sex differences in the development of frailty-related physical weakness are hardly studied. Therefore, we investigated the intramuscular changes that differentiate between fit and weak older adults for each sex separately. METHODS: Male (n = 28) and female (n = 26) older adults (75 + years) were grouped on the basis of their ranks according to three frailty-related physical performance criteria. Muscle biopsies taken from vastus lateralis muscle were used for transcriptome and histological examination. Pairwise comparisons were made between the fittest and weakest groups for each sex separately, and potential sex-specific effects were assessed. RESULTS: Weak females were characterized by a higher expression of inflammatory pathways and infiltration of NOX2-expressing immune cells, concomitant with a higher VCAM1 expression. Weak males were characterized by a smaller diameter of type 2 (fast) myofibers and lower expression of PRKN. In addition, weakness-associated transcriptome changes in the muscle were distinct from aging, suggesting that the pathophysiology of frailty-associated physical weakness does not necessarily depend on aging. CONCLUSIONS: We conclude that physical weakness-associated changes in muscle are sex-specific and recommend that sex differences are taken into account in research on frailty, as these differences may have a large impact on the development of (pharmaceutical) interventions against frailty. TRIAL REGISTRATION NUMBER: The FITAAL study was registered in the Dutch Trial Register, with registration code NTR6124 on 14-11-2016 ( https://trialsearch.who.int/Trial2.aspx?TrialID=NTR6124 ). HIGHLIGHTS: • In female, but not male older adults, physical weakness was associated with a higher expression of intramuscular markers for inflammation. • In male, but not female older adults, physical weakness was associated with a smaller diameter of type 2 (fast) myofibers and lower PRKN expression. • Fit older adults (of both sexes) maintained expression levels comparable to young participants of weakness related genes, differing from frail participants.

Caloric Restriction Combined with Immobilization as Translational Model for Sarcopenia Expressing Key-Pathways of Human Pathology.

The prevalence of sarcopenia is increasing while it is often challenging, expensive and time-consuming to test the effectiveness of interventions against sarcopenia. Translational mouse models that adequately mimic underlying physiological pathways could accelerate research but are scarce. Here, we investigated the translational value of three potential mouse models for sarcopenia, namely partial immobilized (to mimic sedentary lifestyle), caloric restricted (CR; to mimic malnutrition) and a combination (immobilized & CR) model. C57BL/6J mice were calorically restricted (-40%) and/or one hindleg was immobilized for two weeks to induce loss of muscle mass and function. Muscle parameters were compared to those of young control (4 months) and old reference mice (21 months). Transcriptome analysis of quadriceps muscle was performed to identify underlying pathways and were compared with those being expressed in aged human vastus lateralis muscle-biopsies using a meta-analysis of five different human studies. Caloric restriction induced overall loss of lean body mass (-15%, p<0.001), whereas immobilization decreased muscle strength (-28%, p<0.001) and muscle mass of hindleg muscles specifically (on average -25%, p<0.001). The proportion of slow myofibers increased with aging in mice (+5%, p<0.05), and this was not recapitulated by the CR and/or immobilization models. The diameter of fast myofibers decreased with aging (-7%, p<0.05), and this was mimicked by all models. Transcriptome analysis revealed that the combination of CR and immobilization recapitulated more pathways characteristic for human muscle-aging (73%) than naturally aged (21 months old) mice (45%). In conclusion, the combination model exhibits loss of both muscle mass (due to CR) and function (due to immobilization) and has a remarkable similarity with pathways underlying human sarcopenia. These findings underline that external factors such as sedentary behavior and malnutrition are key elements of a translational mouse model and favor the combination model as a rapid model for testing the treatments against sarcopenia.

Sex differences in skeletal muscle-aging trajectory: same processes, but with a different ranking.

Sex differences in muscle aging are poorly understood, but could be crucial for the optimization of sarcopenia-related interventions. To gain insight into potential sex differences in muscle aging, we recruited young (23 ± 2 years, 13 males and 13 females) and old (80 ± 3.5 years, 28 males and 26 females) participants. Males and females in both groups were highly matched, and vastus lateralis muscle parameters of old versus young participants were compared for each sex separately, focusing on gene expression. The overall gene expression profiles separated the sexes, but similar gene expression patterns separated old from young participants in males and females. Genes were indeed regulated in the same direction in both sexes during aging; however, the magnitude of differential expression was sex specific. In males, oxidative phosphorylation was the top-ranked differentially expressed process, and in females, this was cell growth mediated by AKT signaling. Findings from RNA-seq data were studied in greater detail using alternative approaches. In addition, we confirmed our data using publicly available data from three independent human studies. In conclusion, top-ranked pathways differ between males and females, but were present and altered in the same direction in both sexes. We conclude that the same processes are associated with skeletal muscle aging in males and females, but the differential expression of those processes in old vs. young participants is sex specific.

Diet and exercise reduce pre-existing NASH and fibrosis and have additional beneficial effects on the vasculature, adipose tissue and skeletal muscle via organ-crosstalk.

BACKGROUND: Non-alcoholic steatohepatitis (NASH) has become one of the most common liver diseases and is still without approved pharmacotherapy. Lifestyle interventions using exercise and diet change remain the current treatment of choice and even a small weight loss (5-7%) can already have a beneficial effect on NASH. However, the underlying molecular mechanisms of exercise and diet interventions remain largely elusive, and it is unclear whether they exert their health effects via similar or different pathways. METHODS: Ldlr-/-.Leiden mice received a high fat diet (HFD) for 30 weeks to establish a severe state of NASH/fibrosis with simultaneous atherosclerosis development. Groups of mice were then either left untreated (control group) or were treated for 20 weeks with exercise (running wheel), diet change (switch to a low fat chow diet) or the combination thereof. The liver and distant organs including heart, white adipose tissue (WAT) and muscle were histologically examined. Comprehensive transcriptome analysis of liver, WAT and muscle revealed the organ-specific effects of exercise and diet and defined the underlying pathways. RESULTS: Exercise and dietary change significantly reduced body weight, fat mass, adipocyte size and improved myosteatosis and muscle function with additive effects of combination treatment. WAT inflammation was significantly improved by diet change, tended to be reduced with exercise, and combination therapy had no additive effect. Hepatic steatosis and inflammation were almost fully reversed by exercise and diet change, while hepatic fibrosis tended to be improved with exercise and was significantly improved with diet change. Additive effects for the combination therapy were shown for liver steatosis and associated liver lipids, and atherosclerosis, but not for hepatic inflammation and fibrosis. Pathway analysis revealed complementary effects on metabolic pathways and lipid handling processes, thereby substantiating the added value of combined lifestyle treatment. CONCLUSIONS: Exercise, diet change and the combination thereof can reverse established NASH/fibrosis in obese Ldlr-/-.Leiden mice. In addition, the lifestyle interventions had beneficial effects on atherosclerosis, WAT inflammation and muscle function. For steatosis and other parameters related to adiposity or lipid metabolism, exercise and dietary change affected more distinct pathways that acted complementary when the interventions were combined resulting in an additive effect for the combination therapy on important endpoints including NASH and atherosclerosis. For inflammation, exercise and diet change shared several underlying pathways resulting in a net similar effect when the interventions were combined.