Exercise Training-Enhanced Lipolytic Potency to Catecholamine Depends on the Time of the Day

Timing of exercise differentially impacts adipose tissue gain in male adolescent rats

OBJECTIVE

Circadian rhythms of metabolic, hormonal, and behavioral fluctuations and their alterations can impact health. An important gap in knowledge in the field is whether the time of the day of exercise and the age of onset of exercise exert distinct effects at the level of whole-body adipose tissue and body composition. The goal of the present study was to determine how exercise at different times of the day during adolescence impacts the adipose tissue transcriptome and content in a rodent model.

METHODS

Rats were subjected to one of four conditions during their adolescence: early active phase control or exercise (EAC or EAE; ZT13), and late active phase control or exercise (LAC or LAE; ZT23). The effects of exercise timing were assessed at the level of subcutaneous and visceral adipose tissue transcriptome, body composition, hypothalamic expression of orexigenic and anorexigenic genes, blood serum markers and 24-hour core body temperature patterns.

RESULTS

We found that late active phase exercise (ZT23) greatly upregulated pathways of lipid synthesis, glycolysis and NADH shuttles in LAE rats, compared to LAC or EAE. Conversely, LAE rats showed notably lower content of adipose tissue. In addition, LAE rats showed signs of impaired FGF21-adiponectin axis compared to other groups.

CONCLUSIONS

Finally, LAE rats showed higher post-exercise core body temperature compared to other groups. Our results thus indicate that our exercise protocol induced an unusual effect characterized by enhanced lipid synthesis but reduced adipose tissue content in late active phase but not early active phase exercise during adolescence.

Exercise ameliorates lipid droplet metabolism disorder by the PLIN2-LIPA axis-mediated lipophagy in mouse model of non-alcoholic fatty liver disease

Excessive hepatic lipid droplets (LDs) accumulation-induced lipid metabolism disorder contributes to the development of non-alcoholic fatty liver disease (NAFLD). Exercise is a promising therapeutic strategy for NAFLD. However, the mechanism by which exercise ameliorates NAFLD through regulating the catabolism of hepatic LDs remains unclear. In the present study, we investigated the effect of perilipin2 (PLIN2)-lysosomal acid lipase (LIPA) axis mediating exercise-triggered lipophagy in a high-fat diet (HFD)-induced NAFLD mouse model. Our results showed that exercise could reduce HFD-induced hepatic LDs accumulation and change the expression of lipolysis-related enzymes. Moreover, exercise upregulated the expression of microtubule associated protein 1 light chain 3 (LC3) and autophagy-related proteins, and downregulated sequestosome 1 (P62) expression and promoted autophagosomes formation. Interestingly, exercise downregulated PLIN2 expression, upregulated LIPA expression, and increased the activity of hepatic LIPA and serum levels of LIPA in the NAFLD mouse model. Further mechanistic studies demonstrated that adenosine monophosphate-activated protein kinase (AMPK) activator-5-Aminoimidazole-4-carboxamide ribonucleoside (AICAr) treatment significantly increased mRNA levels and protein expression of LIPA and LC3II and decreased levels of PLIN2 and P62 in palmitic acid (PA)-treated HepG2 cells. PLIN2 silencing and LIPA overexpression notably increased the mRNA level and protein expression of LC3II and decreased the mRNA level and protein expression of p62, respectively. In summary, our findings reveal novel insights into the effect of exercise on improving lipid droplet metabolism disorder in NAFLD. Enhancing the PLIN2-LIPA axis-mediated lipophagy may be one of the key mechanisms involved in NAFLD alleviation by exercise.

Circadian Dysfunction in Adipose Tissue: Chronotherapy in Metabolic Diseases

Essential for survival and reproduction, the circadian timing system (CTS) regulates adaptation to cyclical changes such as the light/dark cycle, temperature change, and food availability. The regulation of energy homeostasis possesses rhythmic properties that correspond to constantly fluctuating needs for energy production and consumption. Adipose tissue is mainly responsible for energy storage and, thus, operates as one of the principal components of energy homeostasis regulation. In accordance with its roles in energy homeostasis, alterations in adipose tissue's physiological processes are associated with numerous pathologies, such as obesity and type 2 diabetes. These alterations also include changes in circadian rhythm. In the current review, we aim to summarize the current knowledge regarding the circadian rhythmicity of adipogenesis, lipolysis, adipokine secretion, browning, and non-shivering thermogenesis in adipose tissue and to evaluate possible links between those alterations and metabolic diseases. Based on this evaluation, potential therapeutic approaches, as well as clock genes as potential therapeutic targets, are also discussed in the context of chronotherapy.

The Impact of Exercise on Immunity, Metabolism, and Atherosclerosis

Physical exercise represents an effective preventive and therapeutic strategy beneficially modifying the course of multiple diseases. The protective mechanisms of exercise are manifold; primarily, they are elicited by alterations in metabolic and inflammatory pathways. Exercise intensity and duration strongly influence the provoked response. This narrative review aims to provide comprehensive up-to-date insights into the beneficial effects of physical exercise by illustrating the impact of moderate and vigorous exercise on innate and adaptive immunity. Specifically, we describe qualitative and quantitative changes in different leukocyte subsets while distinguishing between acute and chronic exercise effects. Further, we elaborate on how exercise modifies the progression of atherosclerosis, the leading cause of death worldwide, representing a prime example of a disease triggered by metabolic and inflammatory pathways. Here, we describe how exercise counteracts causal contributors and thereby improves outcomes. In addition, we identify gaps that still need to be addressed in the future.

The different effects of intramuscularly-injected lactate on white and brown adipose tissue in vivo

BACKGROUND

Lactate is an important product of glycolysis metabolism during exercise and has long been recognized as an important metabolic signaling molecule involved in inhibiting lipolysis and promoting lipogenesis, which consequently leads to regulated adipose tissue metabolism. However, recent studies have shown that lactate promotes the browning of white adipose tissue (WAT), which induces heat production and energy expenditure and ultimately causes weight loss. These studies assessing the effects of lactate on lipid metabolism in adipose tissue have revealed conflicting data, making it an important area worthy of further research.

METHODS

In this study, using intramuscular injection of lactate to the gastrocnemius, we identified the role of lactate treatment on lipid metabolism and mitochondrial biogenesis of white adipose tissue and brown adipose tissue (BAT).

RESULTS

Our results showed that lactate treatment activated the cAMP/PKA signaling pathway and promoted the expression of lipolysis-related proteins (AMPK, HSL, ATGL) and mitochondrial biomarkers (PGC-1α, COXIV) of WAT, while BAT showed an opposite trend after lactate treatment. Further studies showed that lactate treatment significantly increased serum epinephrine and promoted β3-AR protein expression in WAT and significantly decreased in BAT.

CONCLUSION

Our study shows that lactate seems to regulate β3-adrenergic receptors differently in WAT and BAT, thereby eliciting disparate responses in adipose tissue.

Exercise improves lipid droplet metabolism disorder through activation of AMPK-mediated lipophagy in NAFLD

AIM

To emphasize the mechanism of the effect of exercise on lipid droplet (LD) metabolism disorder in nonalcoholic fatty liver disease (NAFLD).

MAIN METHODS

C57BL/6J mice were randomly divided into three groups: The first group was fed with a normal diet (CON), the second group was fed a high-fat diet (HF), and finally group with a high-fat diet intervention and swim training (HF-EX). The total intervention period was 16 weeks. RT-PCR and Western blot were performed to evaluate the effect of exercise on LDs metabolism and the AMPK pathway. Histopathological examinations and immunofluorescence were performed to evaluate the lipid deposition and lipophagy in the liver.

KEY FINDINGS

Exercise reduced liver steatosis and insulin resistance along with the stimulation of AMPK/SIRT1 signaling and downstream regulation of lipid metabolism. In addition, exercise increased the expression of autophagy marker and colocalization of LC3 and LAMP1 with LDs.

SIGNIFICANCE

Exercise stimulated AMPK/SIRT1 and activated lipophagy in NAFLD. Enhancing lipophagy may be one of the key mechanisms of regulation and resolution of NAFLD by exercise.

Metabolomic Profiles in Adipocytes Differentiated from Adipose-Derived Stem Cells Following Exercise Training or High-Fat Diet

Controlling the differentiation potential of adipose-derived stem cells (ADSCs) is attracting attention as a new strategy for the prevention and treatment of obesity. Here, we aimed to observe the effect of exercise training (TR) and high-fat diet (HFD) on the metabolic profiles of ADSCs-derived adipocytes. The rats were divided into four groups: normal diet (ND)-fed control (ND-SED), ND-fed TR (ND-TR), HFD-fed control (HFD-SED), and HFD-fed TR (HFD-TR). After 9 weeks of intervention, ADSCs of epididymal and inguinal adipose tissues were differentiated into adipocytes. In the metabolome analysis of adipocytes after isoproterenol stimulation, 116 metabolites were detected. The principal component analysis demonstrated that ADSCs-derived adipocytes segregated into four clusters in each fat pad. Amino acid accumulation was greater in epididymal ADSCs-derived adipocytes of ND-TR and HFD-TR, but lower in inguinal ADSCs-derived adipocytes of ND-TR, than in the respective controls. HFD accumulated several metabolites including amino acids in inguinal ADSCs-derived adipocytes and more other metabolites in epididymal ones. Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that TR mainly affected the pathways related to amino acid metabolism, except in inguinal ADSCs-derived adipocytes of HFD-TR rats. These findings provide a new way to understand the mechanisms underlying possible changes in the differentiation of ADSCs due to TR or HFD.