Comprehensive assessment of physiological responses in women during the ESA dry immersion VIVALDI microgravity simulation.

Astronauts in microgravity experience multi-system deconditioning, impacting their inflight efficiency and inducing dysfunctions upon return to Earth gravity. To fill the sex gap of knowledge in the health impact of spaceflights, we simulate microgravity with a 5-day dry immersion in 18 healthy women (ClinicalTrials.gov Identifier: NCT05043974). Here we show that dry immersion rapidly induces a sedentarily-like metabolism shift mimicking the beginning of a metabolic syndrome with a drop in glucose tolerance, an increase in the atherogenic index of plasma, and an impaired lipid profile. Bone remodeling markers suggest a decreased bone formation coupled with an increased bone resorption. Fluid shifts and muscular unloading participate to a marked cardiovascular and sensorimotor deconditioning with decreased orthostatic tolerance, aerobic capacity, and postural balance. Collected datasets provide a comprehensive multi-systemic assessment of dry immersion effects in women and pave the way for future sex-based evaluations of countermeasures.

Metabolic and cardiovascular adaptations to an 8-wk lifestyle weight loss intervention in younger and older obese men.

The number of older obese adults is increasing worldwide. Whether obese adults show similar health benefits in response to lifestyle interventions at different ages is unknown. The study enrolled 25 obese men (body mass index: 31-39 kg/m2) in two arms according to age (30-40 and 60-70 yr old). Participants underwent an 8-wk intervention with moderate calorie restriction (∼20% below individual energy requirements) and supervised endurance training resulting in ∼5% weight loss. Body composition was measured using dual energy X-ray absorptiometry. Insulin sensitivity was assessed during a hypersinsulinemic-euglycemic clamp. Cardiometabolic profile was derived from blood parameters. Subcutaneous fat and vastus lateralis muscle biopsies were used for ex vivo analyses. Two-way repeated-measure ANOVA and linear mixed models were used to evaluate the response to lifestyle intervention and comparison between the two groups. Fat mass was decreased and bone mass was preserved in the two groups after intervention. Muscle mass decreased significantly in older obese men. Cardiovascular risk (Framingham risk score, plasma triglyceride, and cholesterol) and insulin sensitivity were greatly improved to a similar extent in the two age groups after intervention. Changes in adipose tissue and skeletal muscle transcriptomes were marginal. Analysis of the differential response to the lifestyle intervention showed tenuous differences between age groups. These data suggest that lifestyle intervention combining calorie restriction and exercise shows similar beneficial effects on cardiometabolic risk and insulin sensitivity in younger and older obese men. However, attention must be paid to potential loss of muscle mass in response to weight loss in older obese men.NEW & NOTEWORTHY Rise in obesity and aging worldwide are major trends of critical importance in public health. This study addresses a current challenge in obesity management. Do older obese adults respond differently to a lifestyle intervention composed of moderate calorie restriction and supervised physical activity than younger ones? The main conclusion of the study is that older and younger obese men similarly benefit from the intervention in terms of cardiometabolic risk.

Influence of Acute and Chronic Exercise on Abdominal Fat Lipolysis: An Update.

Exercise is a powerful and effective preventive measure against chronic diseases by increasing energy expenditure and substrate mobilization. Long-duration acute exercise favors lipid mobilization from adipose tissue, i.e., lipolysis, as well as lipid oxidation by skeletal muscles, while chronic endurance exercise improves body composition, facilitates diet-induced weight loss and long-term weight maintenance. Several hormones and factors have been shown to stimulate lipolysis in vitro in isolated adipocytes. Our current knowledge supports the view that catecholamines, atrial natriuretic peptide and insulin are the main physiological stimuli of exercise-induced lipolysis in humans. Emerging evidences indicate that contracting skeletal muscle can release substances capable of remote signaling to organs during exercise. This fascinating crosstalk between skeletal muscle and adipose tissue during exercise is currently challenging our classical view of the physiological control of lipolysis, and provides a conceptual framework to better understand the pleotropic benefits of exercise at the whole-body level.

Growth and differentiation factor 15 is secreted by skeletal muscle during exercise and promotes lipolysis in humans.

We hypothesized that skeletal muscle contraction produces a cellular stress signal, triggering adipose tissue lipolysis to sustain fuel availability during exercise. The present study aimed at identifying exercise-regulated myokines, also known as exerkines, able to promote lipolysis. Human primary myotubes from lean healthy volunteers were submitted to electrical pulse stimulation (EPS) to mimic either acute intense or chronic moderate exercise. Conditioned media (CM) experiments with human adipocytes were performed. CM and human plasma samples were analyzed using unbiased proteomic screening and/or ELISA. Real-time qPCR was performed in cultured myotubes and muscle biopsy samples. CM from both acute intense and chronic moderate exercise increased basal lipolysis in human adipocytes. Growth and differentiation factor 15 (GDF15) gene expression and secretion increased rapidly upon skeletal muscle contraction. GDF15 protein was upregulated in CM from both acute and chronic exercise-stimulated myotubes. We further showed that physiological concentrations of recombinant GDF15 protein increased lipolysis in human adipose tissue, while blocking GDF15 with a neutralizing antibody abrogated EPS CM-mediated lipolysis. We herein provide the first evidence to our knowledge that GDF15 is a potentially novel exerkine produced by skeletal muscle contraction and able to target human adipose tissue to promote lipolysis.

Natriuretic peptides enhance the oxidative capacity of human skeletal muscle.

Cardiac natriuretic peptides (NP) are major activators of human fat cell lipolysis and have recently been shown to control brown fat thermogenesis. Here, we investigated the physiological role of NP on the oxidative metabolism of human skeletal muscle. NP receptor type A (NPRA) gene expression was positively correlated to mRNA levels of PPARγ coactivator-1α (PGC1A) and several oxidative phosphorylation (OXPHOS) genes in human skeletal muscle. Further, the expression of NPRA, PGC1A, and OXPHOS genes was coordinately upregulated in response to aerobic exercise training in human skeletal muscle. In human myotubes, NP induced PGC-1α and mitochondrial OXPHOS gene expression in a cyclic GMP-dependent manner. NP treatment increased OXPHOS protein expression, fat oxidation, and maximal respiration independent of substantial changes in mitochondrial proliferation and mass. Treatment of myotubes with NP recapitulated the effect of exercise training on muscle fat oxidative capacity in vivo. Collectively, these data show that activation of NP signaling in human skeletal muscle enhances mitochondrial oxidative metabolism and fat oxidation. We propose that NP could contribute to exercise training-induced improvement in skeletal muscle fat oxidative capacity in humans.

Lipid mobilization in subcutaneous adipose tissue during exercise in lean and obese humans. Roles of insulin and natriuretic peptides.

The aim of this study was to evaluate the relative contributions of various hormones involved in the regulation of lipid mobilization in subcutaneous adipose tissue (SCAT) during exercise and to assess the impact of obesity on this regulation. Eight lean and eight obese men performed a 60-min cycle exercise bout at 50% of their peak oxygen uptake on two occasions: during intravenous infusion of octreotide (a somatostatin analog) or physiological saline (control condition). Lipolysis in SCAT was evaluated using in situ microdialysis. One microdialysis probe was perfused with the adrenergic blockers phentolamine and propranolol while another probe was perfused with the phosphodiesterase and adenosine receptor inhibitor aminophylline. Compared with the control condition, infusion of octreotide reduced plasma insulin levels in lean (from approximately 3.5 to 0.5 microU/ml) and in obese (from approximately 9 to 2 microU/ml), blunted the exercise-induced rise in plasma GH and epinephrine levels in both groups, and enhanced the exercise-induced natriuretic peptide (NP) levels in lean but not in obese subjects. In both groups, octreotide infusion resulted in higher exercise-induced increases in dialysate glycerol concentrations in the phentolamine-containing probe while no difference in lipolytic response was found in the aminophylline-containing probe. The results suggest that insulin antilipolytic action plays a role in the regulation of lipolysis during exercise in lean as well as in obese subjects. The octreotide-induced enhancement of exercise lipolysis in lean subjects was associated with an increased exercise-induced plasma NP response. Adenosine may contribute to the inhibition of basal lipolysis in both subject groups.

Gene expression profiling of human skeletal muscle in response to stabilized weight loss.

BACKGROUND: Diet-induced weight reduction promotes a decrease in resting energy expenditure that could partly explain the difficulty in maintaining reduced body mass. Whether this reduction remains after stabilized weight loss is still controversial, and the molecular mechanisms are unknown. OBJECTIVE: The objective was to investigate the effect of a stabilized 10% weight loss on body composition, metabolic profile, and skeletal muscle gene expression profiling. DESIGN: Obese women were assigned to a 4-wk very-low-calorie diet, a 3-6-wk low-calorie diet, and a 4-wk weight-maintenance program to achieve a 10% weight loss. Resting energy expenditure, body composition, plasma variables, and skeletal muscle transcriptome were compared before weight loss and during stabilized weight reduction. RESULTS: Energy restriction caused an 11% weight loss. Stabilization to the new weight was accompanied by an 11% decrease in the resting metabolic rate normalized to the body cellular mass. A large number of genes were regulated with a narrow range of regulation. The main regulated genes were slow/oxidative fiber markers, which were overexpressed, and the gene encoding the glucose metabolism inhibitor PDK4, which tended to be down-regulated. The knowledge-based approach gene set enrichment analysis showed that a set of genes related to long-term calorie restriction was up-regulated, whereas sets of genes related to insulin, interleukin 6, and ubiquitin-mediated proteolysis were down regulated. CONCLUSIONS: Weight loss-induced decreases in resting metabolic rate persist after weight stabilization. Changes in skeletal muscle gene expression indicate a shift toward oxidative metabolism.

In vivo epinephrine-mediated regulation of gene expression in human skeletal muscle.

The stress hormone epinephrine produces major physiological effects on skeletal muscle. Here we determined skeletal muscle mRNA expression profiles before and during a 6-h epinephrine infusion performed in nine young men. Stringent statistical analysis of data obtained using 43000 cDNA element microarrays showed that 1206 and 474 genes were up- and down-regulated, respectively. Microarray data were validated using reverse transcription quantitative PCR. Gene classification was performed through data mining of Gene Ontology annotations, cluster analysis of regulated genes among 14 human tissues, and correlation analysis of mRNA and clinical parameter variations. Evidence of an autoregulatory control was provided by the regulation of key genes of the cAMP-dependent transcription pathway. Genes with known functional cAMP response elements were regulated by the hormone. The impact on metabolism was illustrated by coordinated regulations of genes involved in carbohydrate and protein metabolisms. Epinephrine had a profound effect on genes involved in immunity and inflammatory response, a previously unappreciated aspect of catecholamine action. Information on 526 mRNAs corresponded to genes of unknown function. These data define the molecular signatures of epinephrine action in human skeletal muscle. They may contribute to the understanding of skeletal muscle alterations observed in pathological conditions characterized by sympathetic nervous system overdrive.

Effects of jump training on procollagen alpha(1)(i) mRNA expression and its relationship with muscle collagen concentration.

The aim of this study was to examine the effects of a prolonged high-intensity exercise, jumping, on procollagen alpha(1)(I) mRNA level and collagen concentration in different muscles of trained (T) and control (C) rabbits. Procollagen alpha(1)(I) mRNA expression was much higher (2.8 to 23.5 times) in semimembranosus proprius (SMP), a slow-twitch oxidative muscle, than in extensor digitorum longus (EDL), rectus femoris (RF), and psoas major (Psoas) muscles, both fast-twitch mixed and glycolytic, whatever group was considered (p < 0.001). Procollagen alpha(1)(I) mRNA level also decreased significantly between 50 and 140 days in all muscles (0.001< p < 0.01). However, mRNA levels were 16 to 97% greater at 140 days in all muscles of T animals compared to C ones (0.01< p <0.05). Collagen concentrations of EDL and RF muscles were also higher (14 to 19%) in T than in C rabbits at 90 and 140 days (0.001 < p < 0.05). In the whole sample, collagen concentration was negatively associated with the procollagen alpha(1)(I) mRNA level in EDL and RF muscles (- 0.49 < r < (- 0.44, p < 0.05), while being positively related to mRNA expression in SMP and Psoas muscles (0.65 < r < 0.85, p < 0.01). It is concluded that jump training clearly restricts the decrease of procollagen (I) mRNA level and probably affects collagen synthesis level. In trained rabbit muscles, the maintenance of a better synthesis level could partly explain the higher collagen concentrations found in EDL and RF at 140 days. Nevertheless, the collagen degradation process seems to play the main role in the increase of total collagen concentration with age in EDL and RF muscles.

Acquirement of brown fat cell features by human white adipocytes.

Obesity, i.e. an excess of white adipose tissue (WAT), predisposes to the development of type 2 diabetes and cardiovascular disease. Brown adipose tissue is present in rodents but not in adult humans. It expresses uncoupling protein 1 (UCP1) that allows dissipation of energy as heat. Peroxisome proliferator-activated receptor gamma (PPAR gamma) and PPAR gamma coactivator 1 alpha (PGC-1 alpha) activate mouse UCP1 gene transcription. We show here that human PGC-1 alpha induced the activation of the human UCP1 promoter by PPAR gamma. Adenovirus-mediated expression of human PGC-1 alpha increased the expression of UCP1, respiratory chain proteins, and fatty acid oxidation enzymes in human subcutaneous white adipocytes. Changes in the expression of other genes were also consistent with brown adipocyte mRNA expression profile. PGC-1 alpha increased the palmitate oxidation rate by fat cells. Human white adipocytes can therefore acquire typical features of brown fat cells. The PPAR gamma agonist rosiglitazone potentiated the effect of PGC-1 alpha on UCP1 expression and fatty acid oxidation. Hence, PGC-1 alpha is able to direct human WAT PPAR gamma toward a transcriptional program linked to energy dissipation. However, the response of typical white adipocyte targets to rosiglitazone treatment was not altered by PGC-1 alpha. UCP1 mRNA induction was shown in vivo by injection of the PGC-1 alpha adenovirus in mouse white fat. Alteration of energy balance through an increased utilization of fat in WAT may be a conceivable strategy for the treatment of obesity.

The presence of a catalytically inactive form of hormone-sensitive lipase is associated with decreased lipolysis in abdominal subcutaneous adipose tissue of obese subjects.

Hormone-sensitive lipase (HSL)-L is a key enzyme in the mobilization of fatty acids from triglyceride stores in adipocytes. A shorter variant of HSL (HSL-S) was detected in humans. This one is generated through in-frame skipping of exon 6 during the processing of HSL mRNA and results in a protein devoid of lipase activity. The role of HSL-S is unknown. The aims of this study were to identify both HSL variants in adipose tissue biopsies and to determine if the presence of HSL-S is correlated to the lipolytic capacity of adipocytes. The study was performed in human abdominal subcutaneous adipocytes from two groups of seven obese subjects. In the group of subjects with both HSL proteins (L+S) group, two immunoreactive bands (80 and 88 kDa) were detected, whereas only the 88-kDa protein was detected in the group with only the wild-type HSL-protein (L group). In the L+S group, the HSL activity was 20% lower (P < 0.05) and the (S/S(+)) HSL mRNA ratio was twofold higher than in the L group (P < 0.05). The maximally lipolytic capacities measured from isolated adipocytes incubated with norepinephrine or other lipolytic agents were 40% lower in the L+S group (P < 0.05). These results suggest that the presence of the truncated HSL protein is associated with an impaired adipocyte lipolysis.

Regulation of human adipocyte gene expression by thyroid hormone.

Thyroid hormones are key regulators of metabolism. In adipose tissue, changes in thyroid status result in alterations of lipolytic capacity. The effects of these hormones are mediated by thyroid hormone receptors that modulate gene transcription. Very few target genes have been identified in adipose tissue. To investigate the effect of T(3) on gene expression in human adipocytes, primary cultures of human sc adipose tissue explants were treated with T(3). (32)P-labeled cDNA probes prepared from isolated adipocyte total RNA were hybridized to cDNA arrays representing 1,176 genes. Among the statistically significant variations in mRNA levels with more than 1.3-fold difference, 13 and 6 genes were positively and negatively regulated, respectively (n = 3). The genes encoded proteins that were involved in signal transduction, lipid metabolism, apoptosis, and inflammatory response. Using RT-competitive PCR, we showed a down-regulation of phosphodiesterase 3B, alpha(2A)-adrenergic receptor, and G protein alpha(i2) subunit mRNAs, and an up-regulation of beta(2)-adrenergic receptor mRNA. These regulations may explain the T(3)-mediated increase in catecholamine-induced lipolysis. The down-regulation of sterol regulatory element binding protein-1c, a transcription factor controlling lipogenic gene expression, may constitute a link between thyrotoxicosis and insulin resistance. Thus, these data suggest that T(3) modulates expression of genes with a wide range of function in human adipose tissue.