PGC-1α in exercise and fasting-induced regulation of hepatic UPR in mice.

The aim of the present study was to test the hypothesis that PGC-1α is involved in the regulation of hepatic UPR and autophagy in response to both exercise and fasting in mice. Liver-specific PGC-1α knockout (LKO) mice and their floxed littermates (lox/lox) were used in two experimental parts. Liver and plasma were obtained from (1) fed and 18 h fasted mice and (2) immediately after, 2, 6, and 10 h after 1-h treadmill running as well as from resting mice, where one resting group was euthanized at time points corresponding to 0 and 2 h and another corresponding to 6 and 10 h of recovery. Hepatic eIF2α phosphorylation and sXBP1 mRNA content increased immediately after exercise and IRE1α phosphorylation as well as cleaved ATF6 protein content was higher 2 h into recovery than at rest in both genotypes. Fasting reduced hepatic IRE1α phosphorylation and protein content as well as PERK protein and sXBP1 mRNA content similarly in lox/lox and LKO mice. In addition, the hepatic LC3II/LC3I protein ratio increased immediately after exercise and with fasting in both genotypes, while fasting decreased p62 protein content in lox/lox mice. Liver-specific PGC-1α knockout did not affect these responses, but the LC3II/LC3I protein ratio was higher in LKO than lox/lox mice in both rest groups. In conclusion, the present study provides evidence for pathway-specific exercise-induced activation and fasting-induced downregulation of the UPR as well as exercise and fasting-induced regulation of autophagy in mouse liver. In addition, overall PGC-1α does not seem to be required for the fasting and exercise-induced regulation of UPR and autophagy, but may be involved in regulating basal hepatic autophagy.

PGC-1α in hepatic UPR during high-fat high-fructose diet and exercise training in mice.

Diet-induced obesity is associated with hepatic steatosis, which has been linked with activation of the unfolded protein response (UPR). PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in muscle and liver. Therefore, the aim of this study was to test the hypothesis that PGC-1α is required for exercise training-mediated prevention of diet-induced steatosis and UPR activation in liver. Male liver-specific PGC-1α knockout (LKO) and littermate floxed (lox/lox) mice were divided into two groups receiving either control diet (CON) or high-fat high-fructose diet (HFF). After 9 weeks, half of the HFF mice were treadmill exercise trained for 4 weeks (HFF+ExT), while the rest were kept sedentary. HFF resulted in increased body and liver weight, adiposity, hepatic steatosis and whole body glucose intolerance as well as decreased hepatic IRE1α phosphorylation. Exercise training prevented the HFF-induced weight gain and partially prevented increased liver weight, adiposity and glucose intolerance, but with no effect on liver triglycerides. In addition, BiP protein and CHOP mRNA content increased with exercise training compared with CON and HFF, respectively. Lack of PGC-1α in the liver only resulted in minor changes in the PERK pathway. In conclusion, this study provides evidence for dissociation between diet-induced hepatic triglyceride accumulation and hepatic UPR activation. In addition, PGC-1α was not required for maintenance of basal UPR in the liver and due to only minor exercise training effects on UPR further studies are needed to conclude on the potential role of PGC-1α in exercise training-induced adaptations in hepatic UPR.

Impact of liver PGC-1α on exercise and exercise training-induced regulation of hepatic autophagy and mitophagy in mice on HFF.

Hepatic autophagy has been shown to be regulated by acute exercise and exercise training. Moreover, high-fat diet-induced steatosis has been reported to be associated with impaired hepatic autophagy. In addition, autophagy has been shown to be regulated by acute exercise and exercise training in a PGC-1α dependent manner in skeletal muscle. The aim of this study was to test the hypotheses that high-fat high-fructose (HFF) diet changes hepatic autophagy and mitophagy, that exercise training can restore this through a PGC-1α-mediated mechanism, and that acute exercise regulates autophagy and mitophagy in the liver. Liver samples were obtained from liver-specific PGC-1α KO mice and their littermate Lox/Lox mice fed a HFF diet or a control diet for 13 weeks. The HFF mice were either exercise trained (ExT) on a treadmill the final 5 weeks or remained sedentary (UT). In addition, half of each group performed at the end of the intervention an acute 1 h exercise bout. HFF resulted in increased hepatic BNIP3 dimer and Parkin protein, while exercise training increased BNIP3 total protein without affecting the elevated BNIP3 dimer protein. In addition, exercise training reversed a HFF-induced increase in hepatic LC3II/LC3I protein ratio, as well as a decreased PGC-1α mRNA level. Acute exercise increased hepatic PGC-1α mRNA in HFF UT mice only. In conclusion, this indicates that exercise training in part reverses a HFF-induced increase in hepatic autophagy and capacity for mitophagy in a PGC-1α-independent manner. Moreover, HFF may blunt acute exercise-induced regulation of hepatic autophagy.

The impact of exercise training and resveratrol supplementation on gut microbiota composition in high-fat diet fed mice.

The aim of this study was to examine the effect of exercise training and dietary supplementation of resveratrol on the composition of gut microbiota and to test the hypothesis that exercise training and resveratrol can prevent high-fat diet (HFD)-induced changes in the gut microbiota. Mice fed a HFD supplemented with resveratrol (4 g/kg food) were protected against diet-induced obesity, while exercise trained HFD-fed animals (running on average 50 km/week) were not. Dietary resveratrol supplementation induced changes predominantly in the low-abundant bacteria, while exercise training induced changes in the high-abundant bacteria in the gut as analyzed by ADONIS test with Weighted UniFrac distances. Interestingly, the two interventions affected the gut microbiome independently of the inflammatory state of the HFD-fed animals as assessed by the systemic serum amyloid A levels. These results suggest that both resveratrol supplementation and regular physical activity modulate the composition of murine microbiota independently of the systemic inflammatory state. Moreover, the effects of exercise training on the microbiota seem to occur without changes in adiposity, while resveratrol-mediated alterations may relate to adipose tissue mass.

PGC-1α in aging and lifelong exercise training-mediated regulation of UPR in mouse liver.

Aging is associated with changes in several metabolic pathways affecting liver function including the adaptive unfolded protein response (UPR). On the other hand, exercise training has been shown to exert beneficial effects on metabolism in the liver and exercise training has been reported to affect hepatic UPR. PGC-1α is a transcriptional coactivator involved in exercise training-induced adaptations in skeletal muscle and liver. Therefore, the aim of the present study was to examine the impact of PGC-1α in aging and lifelong exercise training-induced hepatic UPR in mice. Liver was obtained from young (3months old), aged (15months old) and lifelong exercise trained aged wild-type (WT) and whole-body PGC-1α knockout (KO) mice. Hepatic BiP, IRE1α and cleaved ATF6 protein content increased, whereas PERK protein content was reduced with aging indicating both increased and decreased capacity of specific UPR pathways and increased activity of the ATF6 pathway in the liver with aging. Lifelong exercise training prevented the age-associated change in BiP and IRE1α protein, but not cleaved ATF6 protein and resulted in further decreased PERK protein. Taken together, the present study provides evidence that the capacity and activity of the three UPR pathways are differentially regulated in the liver with aging and lifelong exercise training. In addition, PGC-1α does not seem to regulate the activity of hepatic UPR in response to exercise training, but to influence the capacity of the liver to induce UPR in a pathway specific manner.