GH signaling in human adipose and muscle tissue during 'feast and famine': amplification of exercise stimulation following fasting compared to glucose administration

Gut microbiota and transcriptome dynamics in every-other-day fasting are associated with neuroprotection in rats with spinal cord injury

Introduction

Every-other-day fasting (EODF) is a classical intermittent fasting (IF) mode with neuroprotective effects that promotes motor function recovery after spinal cord injury (SCI) in rats. However, its dynamic effects on the gut microbiota and spinal cord transcriptome remain unknown.

Methods

In this study, 16S rRNA sequencing and RNA-seq analysis were used to investigate the effects of ad libitum (AL) and EODF dietary modes on the structural characteristics of rat gut microbiota in rats and the spinal cord transcriptome at various time points after SCI induction.

Results

Our results showed that both dietary modes affected the bacterial community composition in SCI rats, with EODF treatment inducing and suppressing dynamic changes in the abundances of potentially anti-inflammatory and pro-inflammatory bacteria. Furthermore, the differentially expressed genes (DEGs) enriched after EODF intervention in SCI rats were associated with various biological events, including immune inflammatory response, cell differentiation, protein modification, neural growth, and apoptosis. In particular, significant spatiotemporal differences were apparent in the DEGs associated with neuroprotection between the EODF and AL interventions. These DGEs were mainly focused on days 1, 3, and 7 after SCI. The relative abundance of certain genera was significantly correlated with DEGs associated with neuroprotective effects in the EODF-SCI group.

Discussion

Our results showed that EODF treatment may exert neuroprotective effects by modulating the transcriptome expression profile following SCI in rats. Furthermore, gut microbiota may be partially involved in mediating these effects.

Reassessing the evidence: prandial state dictates glycaemic responses to exercise in individuals with type 1 diabetes to a greater extent than intensity

Recent guidelines suggest that adding anaerobic (high intensity or resistance) activity to an exercise session can prevent blood glucose declines that occur during aerobic exercise in individuals with type 1 diabetes. This theory evolved from earlier study data showing that sustained, anaerobic activity (high intensity cycling) increases blood glucose levels in these participants. However, studies involving protocols where anaerobic (high intensity interval) and aerobic exercise are combined have extremely variable glycaemic outcomes, as do resistance exercise studies. Scrutinising earlier studies will reveal that, in addition to high intensity activity (intervals or weight lifting), these protocols had another common feature: participants were performing exercise after an overnight fast. Based on these findings, and data from recent exercise studies, it can be argued that participant prandial state may be a more dominant factor than exercise intensity where glycaemic changes in individuals with type 1 diabetes are concerned. As such, a reassessment of study outcomes and an update to exercise recommendations for those with type 1 diabetes may be warranted.

The acromegaly lipodystrophy

Growth hormone (GH) and insulin-like growth factor 1 (IGF-1) are essential to normal growth, metabolism, and body composition, but in acromegaly, excesses of these hormones strikingly alter them. In recent years, the use of modern methodologies to assess body composition in patients with acromegaly has revealed novel aspects of the acromegaly phenotype. In particular, acromegaly presents a unique pattern of body composition changes in the setting of insulin resistance that we propose herein to be considered an acromegaly-specific lipodystrophy. The lipodystrophy, initiated by a distinctive GH-driven adipose tissue dysregulation, features insulin resistance in the setting of reduced visceral adipose tissue (VAT) mass and intra-hepatic lipid (IHL) but with lipid redistribution, resulting in ectopic lipid deposition in muscle. With recovery of the lipodystrophy, adipose tissue mass, especially that of VAT and IHL, rises, but insulin resistance is lessened. Abnormalities of adipose tissue adipokines may play a role in the disordered adipose tissue metabolism and insulin resistance of the lipodystrophy. The orexigenic hormone ghrelin and peptide Agouti-related peptide may also be affected by active acromegaly as well as variably by acromegaly therapies, which may contribute to the lipodystrophy. Understanding the pathophysiology of the lipodystrophy and how acromegaly therapies differentially reverse its features may be important to optimizing the long-term outcome for patients with this disease. This perspective describes evidence in support of this acromegaly lipodystrophy model and its relevance to acromegaly pathophysiology and the treatment of patients with acromegaly.

Skeletal Muscle Transcriptomic Comparison Between Men and Women in Response to Acute Sprint Exercise

Background: Acute sprint exercise is a time-efficient physical activity that improves cardiorespiratory fitness in younger and middle-aged adults. Growing evidence has demonstrated that acute sprint exercise provides equal to or superior health benefits compared with moderate-intensity continuous training, which will dramatically increase aerobic capacity, insulin sensitivity, and muscle capillarization. Although the beneficial effects of acute sprint exercise are well documented, the mechanisms behind how acute sprint exercise prevents disease and benefits health are less understood.

Method: We obtained differentially expressed genes in muscle (vastus lateralis) from men and women before and after an acute sprint exercise. Then, we identified hub genes from the protein–protein interaction (PPI) network of differentially expressed genes (DEGs) and key transcription factors in men and women related to acute sprint exercise. Finally, Kyoto Encyclopedia of Genes and Genomes (KEGG) and Gene Ontology (GO) enrichment analyses are performed on DEGs and sex-biased genes, respectively.

Results: First, we identified 127 sexually dimorphic genes in men (90 upregulated and 37 downregulated) and 75 genes in women (90 upregulated and 37 downregulated) in response to acute sprint exercise. Second, CEBPB, SMAD3, and CDKN1A are identified as the top three hub genes related to men-biased genes. Accordingly, the top three hub genes related to women-biased genes are JUN, ACTB, and SMAD7. In addition, CLOCK, ZNF217, and KDM2B are the top three enriched transcriptional factors in men-biased genes, while XLR, SOX2, JUND, and KLF4 are transcription factors enriched most in women-biased genes. Furthermore, based on GO and KEGG enrichment analyses, we identified potential key pathways in regulating the exercise-related response in men and women, respectively.

Conclusion: In this study, we found the difference in gene expression and enrichment pathways in muscle in men and women in response to acute sprint exercise. These results will shed new light on the mechanism underlying sex-based differences in skeletal muscle remodeling and metabolism related to acute sprint exercise, which may illustrate the mechanisms behind how acute sprint exercise prevents disease and benefits health.

Fasted condition in multicomponent training does not affect health parameters in physically active post-menopausal women

Diet and exercise are the main modifiable factors for cardiovascular disease and may be particularly important in older adults. We investigated the effects of fasting during 12 weeks of multicomponent training in the context of the aging process in physically active post-menopausal women.

METHOD

25 women (60.6 ± 8.9 years) were randomized into two groups: fed (FED, n=12) or fasted (FASTED, n=13) and submitted to multicomponent training. The participants underwent anthropometric, body composition, blood pressure, biochemical blood and physical fitness assessments.

RESULTS

There was a reduction in both groups for waist circumference [FED: 100.4±6.8 and 99.1±7.1 cm before and after the intervention, respectively; F = 4.214, p = 0.048; FASTED: 93.1±10.2 and 92.2±8.4 cm before and after the intervention, respectively; p = 0.039]. No significant changes were observed for the other outcomes.

DISCUSSION

The current research results, the first in the context of aging, agree with previous studies that analyzed chronic effects of fasting, showing that fasted exercise training did not improve anthropometric measurements, body composition, or blood markers compared to the fed condition after long-term exercise training. Together, these findings suggest that fasting during multicomponent training does not affect health parameters in physically active post-menopausal women.

Fasting May Alter Blood Glucose Responses to High-Intensity Interval Exercise in Adults With Type 1 Diabetes: A Randomized, Acute Crossover Study

OBJECTIVES

In individuals with type 1 diabetes (T1D), changes in blood glucose (BG) during high-intensity interval exercise (HIIE) are smaller than those observed during aerobic exercise. Study outcomes, however, have been variable, with some demonstrating significant BG decreases and others showing BG increases. This study compared BG outcomes between fasting (AME) and postprandial (PME) HIIE in T1D to test the hypothesis that AME would produce a BG increase, yet PME would cause BG to decline.

METHODS

Twelve (6 men and 6 women) physically active individuals with T1D performed two 45-minute exercise sessions (AME at 7:00 AM, PME at 5:00 PM) in random order, separated by at least 48 hours. Sessions consisted of a 10-minute warmup (50%VO_2peak), followed by 10-second sprints every 2 minutes for 24 minutes, and then an 11-minute cooldown. Capillary glucose was measured pre- and postexercise, and then 60 minutes postexercise. Interstitial glucose was recorded for 24 hours postexercise using continuous glucose monitoring.

RESULTS

AME caused capillary glucose to increase (from 7.6±1.4 to 9.2±2.9 mmol/L during exercise, and 9.9±2.8 mmol/L in recovery), whereas PME produced a decline in capillary glucose (from 9.9±3.1 to 9.5±3.4 mmol/L during exercise and 8.9±2.7 mmol/L during recovery; time × treatment interaction, p=0.014). PME was associated with a higher frequency of hyperglycemic events in the 6 hours and overnight (midnight to 6:00 AM) after exercise.

CONCLUSIONS

Fasting HIIE results in a different BG trajectory than postprandial exercise in T1D, and may be beneficial for hypoglycemia avoidance during exercise.

Altered metabolic and hormonal responses to moderate exercise in overweight/obesity

BACKGROUND

An adequate metabolic and hormonal response to the switch from rest to exercise is critical for the health benefits of exercise interventions. Previous work suggests that this response is impaired with overweight/obesity but the specific differences between overweight/obese and lean individuals remain unclear.

METHODS

We compared glucose and non-esterified fatty acid (NEFA) regulation and the changes of key homeostatic hormones during 45 min of moderate exercise between 17 overweight/obese and 28 lean premenopausal women. For this comparison, we implemented an exercise protocol at 60% of individual peak oxygen uptake, with frequent blood sampling and under fasting conditions.

RESULTS

We found that at the same exercise intensity in the overweight/obese and the lean group of women, the metabolic and hormonal response differed. In contrast to the lean group, the overweight/obese group portrayed an activation in the stress axis (adrenocorticotropic hormone (ACTH)/cortisol) and a lower growth hormone (hGH) response and exercise-increase of plasma NEFA. Both groups, however, displayed increased insulin sensitivity during exercise that was accompanied by a normalization of the elevated fasting glucose in the overweight/obese group after 15-20 min.

CONCLUSION

We conclude that the response to exercise in overweight/obese subjects indeed differs from that in lean individuals. Additionally, we demonstrate that exercise can elicit beneficial (improved glucose regulation) and unwanted effects (stress axis activation) in overweight/obese subjects at the same time. This second finding suggests that exercise interventions for overweight/obese subjects need careful consideration of intensity and dose in order to achieve the intended results and avoid acute, undesired reactions.

Temporal patterns of lipolytic regulators in adipose tissue after acute growth hormone exposure in human subjects: A randomized controlled crossover trial

Objective

Growth hormone (GH) stimulates lipolysis, but the underlying mechanisms remain incompletely understood. We examined the effect of GH on the expression of lipolytic regulators in adipose tissue (AT).

Methods

In a randomized, placebo-controlled, cross-over study, nine men were examined after injection of 1) a GH bolus and 2) a GH-receptor antagonist (pegvisomant) followed by four AT biopsies. In a second study, eight men were examined in a 2 × 2 factorial design including GH infusion and 36-h fasting with AT biopsies obtained during a basal period and a hyperinsulinemic-euglycemic clamp. Expression of GH-signaling intermediates and lipolytic regulators were studied by PCR and western blotting. In addition, mechanistic experiments in mouse models and 3T3-L1 adipocytes were performed.

Results

The GH bolus increased circulating free fatty acids (p < 0.0001) together with phosphorylation of signal transducer and activator of transcription 5 (STAT5) (p < 0.0001) and mRNA expression of the STAT5-dependent genes cytokine-inducible SH2-containing protein (CISH) and IGF-1 in AT. This was accompanied by suppressed mRNA expression of G0/G1 switch gene 2 (G0S2) (p = 0.007) and fat specific protein 27 (FSP27) (p = 0.002) and upregulation of phosphatase and tensin homolog (PTEN) mRNA expression (p = 0.03). Suppression of G0S2 was also observed in humans after GH infusion and fasting, as well as in GH transgene mice, and in vitro studies suggested MEK-PPARγ signaling to be involved.

Conclusions

GH-induced lipolysis in human subjects in vivo is linked to downregulation of G0S2 and FSP27 and upregulation of PTEN in AT. Mechanistically, in vitro data suggest that GH acts via MEK to suppress PPARγ-dependent transcription of G0S2. ClinicalTrials.govNCT02782221 and NCT01209429.

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Acute GH exposure in human subjects in vivo stimulates lipolysis and release of FFA together with GH signaling in adipose tissue.

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GH-induced lipolysis is associated with suppression of G0S2 and FSP27 and upregulation of PTEN in human subjects in vivo.

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Inhibition of MEK and activation of PPARγ abrogate GH-induced suppression of G0S2 mRNA expression in vitro.

HORMONAL REGULATION OF CARBOHYDRATE AND FAT METABOLISM IN WOMEN WITH DIFFERENT OBESITY TYPES IN THE FOOD DEPRIVATION TEST

CONTEXT

The dominant type of adipose tissue accumulation in the body is associated with the peculiarities of using key substrates in energy metabolism and their hormonal regulation. Hormonal and metabolic parameters were investigated in women with android and gynoid obesity before and after the short-term food deprivation test.

RESULTS

At baseline, at gynoid obesity as compared to android obesity, the women's blood contained lower glucose and insulin levels and higher FFA levels. The reaction to food deprivation manifested by a decrease in glucose level and an increase in FFA level in the blood is less pronounced in women with gynoid obesity than in those with android obesity. At the same time, a similar (though varying in expression) decrease in insulin level and elevated levels of glucagon, growth hormone and thyroxine were revealed in women's blood in both groups. Blood cortisol level increased in women with gynoid obesity and remained unchanged in those with android obesity.

CONCLUSIONS

More pronounced activation of hormonal mechanisms for maintaining blood glucose levels at gynoid obesity as compared to android one suggests that glucose is the preferable substrate for energy metabolism at gynoid obesity in women.

Targeted sequencing analysis of PPARG identifies a risk variant associated with obstructive sleep apnea in Chinese Han subjects

PURPOSE

Obstructive sleep apnea (OSA) is a common disorder characterized by recurrent episodes of partial or complete upper airway obstruction. OSA susceptibility is associated with multiple genetic, environmental, and developmental factors. The PPARG rs1801282 (G/C) polymorphism has been associated with OSA in obese Indian subjects, whereas no such association has been reported in Chinese Han subjects. Potential associations between other PPARG variants and OSA have not been investigated in Chinese Han populations. The aim of this study was to identify genetic variants of PPARG in unrelated Chinese Han patients with OSA and to investigate potential associations between these variants and OSA.

METHODS

We performed a cross-sectional study of 233 individuals with OSA and 93 control individuals. A portable diagnostic device was used to diagnose OSA. Targeted sequencing was conducted to identify PPARG variants. Associations between PPARG variants and OSA were analyzed using multivariate regression.

RESULTS

Three PPARG single-nucleotide polymorphisms were identified and the genotype frequencies of the rs1801282 polymorphism differed significantly. Subjects with the PPARG rs1801282 CG genotype had decreased risk of having OSA compared with subjects with the CC genotype after adjusting for confounding effects.

CONCLUSIONS

We identified a variant of PPARG associated with the occurrence of OSA in Chinese Han populations.

Insulin inhibits autophagy signaling independent of counter-regulatory hormone levels, but does not affect the effects of exercise

Acute exercise increases autophagic signaling through ULK1 in human skeletal muscle during both anabolic and catabolic conditions. The aim of the present study was to investigate if changes in ULK1 Ser⁵⁵⁵ phosphorylation during exercise are reflected by changes in phosphorylation of a newly identified ULK1 substrate (ATG14 Ser²⁹), and to elucidate the involvement of circulatory hormones in regulation of autophagy in human skeletal muscle. We show that one hour of cycling exercise increases ATG14 Ser29 phosphorylation during both hyperinsulinemic euglycemic and euinsulinemic euglycemic conditions. This could suggest that counter-regulatory hormones stimulate autophagy in skeletal muscle, as circulating concentrations of these hormones are highly elevated during exercise. Furthermore, ATG14 Ser²⁹ correlated positively with ULK1 phosphorylation, suggesting that ULK1 Ser⁵⁵⁵ (activating site) phosphorylation reflects ULK1 kinase activity. In a separate series of experiments, we show that insulin stimulates ULK1 phosphorylation at Ser⁷⁵⁷ (inhibitory site) in both hypoglycemic and euglycemic conditions, suggesting that counter-regulatory hormones (such as epinephrine, norepinephrine, growth hormone and glucagon) have limited effects on autophagy signaling in human skeletal muscle. In conclusion, one hour of cycling exercise increases phosphorylation of ATG14 at Ser²⁹ in a pattern that mirrors ULK1 phosphorylation at Ser⁵⁵⁵. Moreover, insulin effects on autophagy signaling in human skeletal muscle are independent of hypoglycemic and euglycemic conditions.

The Impact of Adipose Tissue on Insulin Resistance in Acromegaly

Adipose tissue (AT) is recognized as key contributor to the systemic insulin resistance and overt diabetes seen in metabolic syndrome. Acromegaly is a disease characterized by excessive secretion of growth hormone (GH) and insulin-like growth factor I (IGF-I). GH is known both for its action on AT and for its detrimental effect on glucose metabolism and insulin signaling. In active acromegaly, while body fat deports are diminished, insulin resistance is increased. Early studies have demonstrated defects in insulin action, both at the hepatic and extrahepatic (i.e., muscle and fat) levels, in active disease. This review discusses recent data suggesting that AT inflammation, altered AT distribution, and impaired adipogenesis are potential mechanisms contributing to systemic insulin resistance in acromegaly.