Short-Term Irisin Treatment Enhanced Neurotrophin Expression Differently in the Hippocampus and the Prefrontal Cortex of Young Mice

As a result of physical exercise, muscle releases multiple exerkines, such as "irisin", which is thought to induce pro-cognitive and antidepressant effects. We recently demonstrated in young healthy mice the mitigation of depressive behaviors induced by consecutive 5 day irisin administration. To understand which molecular mechanisms might be involved in such effect, we here studied, in a group of mice previously submitted to a behavioral test of depression, the gene expression of neurotrophins and cytokines in the hippocampus and prefrontal cortex (PFC), two brain areas frequently investigated in the depression pathogenesis. We found significantly increased mRNA levels of nerve growth factor (NGF) and fibroblast growth factor 2 (FGF-2) in the hippocampus and brain-derived growth factor (BDNF) in the PFC. We did not detect a difference in the mRNA levels of interleukin 6 (IL-6) and IL-1β in both brain regions. Except for BDNF in the PFC, two-way ANOVA analysis did not reveal sex differences in the expression of the tested genes. Overall, our data evidenced a site-specific cerebral modulation of neurotrophins induced by irisin treatment in the hippocampus and the PFC, contributing to the search for new antidepressant treatments targeted at single depressive events with short-term protocols.

FNDC5 Causes Resistance to Sorafenib by Activating the PI3K/Akt/Nrf2 Pathway in Hepatocellular Carcinoma Cells

In this study, we aimed to reveal the resistance mechanism of hepatocellular carcinoma (HCC) cells to sorafenib by exploring the effect of FNDC5 on sorafenib-induced ferroptosis in HCC cells. We compared the expression level of FNDC5 between sorafenib-resistant and sorafenib-sensitive HCC cell lines and the level of ferroptosis between the groups after treatment with sorafenib. We knocked down FNDC5 in drug-resistant cell lines and overexpressed it in sorafenib-sensitive HCC cell lines to further demonstrate the role of FNDC5 in sorafenib-induced ferroptosis. Using PI3K inhibitors, we revealed the specific mechanism by which FNDC5 functions. In addition, we verified our findings obtained in in vitro experiments using a subcutaneous tumorigenic nude mouse model. The findings revealed that FNDC5 inhibits sorafenib-induced ferroptosis in HCC cells. In addition, FNDC5 activated the PI3K/Akt pathway, which in turn promoted the nuclear translocation of Nrf2 and increased the intracellular antioxidant response, thereby conferring resistance to ferroptosis. Our study provides novel insights for improving the efficacy of sorafenib.

Aerobic exercise training-induced irisin secretion is associated with the reduction of arterial stiffness via nitric oxide production in adults with obesity

This study aimed to clarify whether muscle-derived irisin secretion induced by aerobic exercise training is involved in reduction of arterial stiffness via arterial nitric oxide (NO) productivity in obesity. In animal study, 16 Otsuka Long-Evans Tokushima Fatty (OLETF) rats with obesity were randomly divided into 2 groups: sedentary control (OLETF-CON) and 8-week aerobic treadmill training (OLETF-EX) groups. In human study, 15 subjects with obesity completed 8-week aerobic exercise training for 45 min at 60%-70% peak oxygen uptake intensity for 3 days/week. As a result of animal study, carotid-femoral pulse wave velocity (cfPWV) was decreased, and arterial phosphorylation levels of AMP-activated protein kinase (AMPK), protein kinase B (Akt), and endothelial NO synthase (eNOS), circulating levels of nitrite/nitrate (NOx) and irisin, and muscle messenger RNA expression of fibronectin type III domain containing 5 (Fndc5) were increased in the OLETF-EX group compared with OLETF-CON group. In a human study, regular aerobic exercise reduced cfPWV and elevated circulating levels of NOx and irisin. Furthermore, change in circulating irisin levels by regular exercise was positively correlated with circulating NOx levels and was negatively correlated with cfPWV. Thus, aerobic exercise training-induced increase in irisin secretion may be related to reduction of arterial stiffness achieved by NO production via activated arterial AMPK-Akt-eNOS signaling pathway in obesity. Novelty Aerobic exercise training promoted irisin secretion with upregulation of muscle Fndc5 gene expression in rats with obesity. Irisin affected the activation of arterial AMPK-Akt-eNOS signaling by aerobic exercise training. Increased serum irisin level by aerobic exercise training was associated with reduction of arterial stiffness in obese adults.

Regulation of cell proliferation and malignant potential by irisin in endometrial, colon, thyroid and esophageal cancer cell lines

OBJECTIVE

Irisin is a novel hormone that has been proposed to mediate the beneficial effects of exercise on metabolism, including body weight regulation and insulin resistance. No previous studies have evaluated whether irisin may regulate cell proliferation and malignant potential of obesity-related cancer cell lines.

MATERIALS/METHODS

Cell proliferation and malignant potential i.e. cell adhesion and colony formation were studied in vitro using human and mouse obesity-related cancer cell lines i.e. endometrial (KLE and RL95-2), colon (HT29 and MCA38), thyroid (SW579 and BHP7) and esophageal (OE13 and OE33).

RESULTS

We observed that, in contrast to metformin, cell proliferation is not regulated by irisin in a dose-dependent manner in human and mouse obesity-related cancer cell lines. Specifically, physiological (5 to 10 nmol/L) and high physiological/pharmacological (50 to 100 nmol/L) concentrations of irisin had no effect on cell proliferation when compared to control in human and mouse endometrial, colon, thyroid and esophageal cancer cell lines. Also, we observed that, in contrast to metformin, neither physiological nor high physiological/pharmacological concentrations of irisin regulate cell adhesion and/or colony formation in human and mouse endometrial, colon, thyroid and esophageal cancer cell lines.

CONCLUSIONS

Our data suggest that irisin, in physiological and high physiological/pharmacological concentrations, has no in vitro effect on cell proliferation and malignant potential of obesity-related cancer cell lines. Future work is needed to determine the regulation of irisin levels and any physiological effects it may have on obesity-related cancers in vivo in animals and humans.

Irisin levels correlate with energy expenditure in a subgroup of humans with energy expenditure greater than predicted by fat free mass

OBJECTIVE

Obesity is a result of chronic overconsumption of calories relative to the amount of energy expended. While fat free mass can account for ~80% of the variance in energy expenditure, there is still considerable variability in energy requirements between individuals that cannot be explained. We hypothesized that responsiveness to the recently discovered myokine, irisin, which has been touted to increase energy expenditure via activation of brown adipocytes in rodents and possibly humans, may explain some of the variability in energy expenditure.

MATERIALS/METHODS

Post-menopausal women (n=17) spent 24-h in a whole room indirect calorimeter. During the study day, subjects remained sedentary and consumed meals tailored to their energy requirements. Plasma irisin, leptin and adiponectin were measured in samples taken from each subject.

RESULTS

Our results suggest that in general, irisin levels do not correlate with 24-h energy expenditure, however, for a subpopulation irisin levels and energy expenditure are highly correlative.

CONCLUSION

Irisin may help explain some of the observed variability in individual energy requirements that cannot be accounted for by fat free mass. Therefore, interventions designed to increase irisin action may prove to be promising avenues for the treatment of obesity.

Elevated skeletal muscle irisin precursor FNDC5 mRNA in obese OLETF rats

OBJECTIVE

There is debate as to whether fibronectin type III domain containing 5 (FNDC5) and its protein product irisin are therapeutic targets for obesity-associated maladies. Thus, we sought to examine FNDC5 mRNA within skeletal muscle of obese/diabetic-prone Otsuka Long-Evans Tokushima Fatty (OLETF) rats versus lean/healthy Long Evans Tokushima Otsuka (LETO) rats. We hypothesized that FNDC5 expression would be greater in obese (OLETF) versus lean (LETO) animals.

MATERIALS/METHODS

Triceps muscle of 30-32week old OLETF and LETO rats were assayed for FNDC5 and PGC1α mRNA levels. Body composition and circulating biomarkers of the OLETF and LETO rats were also correlated with skeletal muscle FNDC5 mRNA expression patterns in order to examine potential relationships that may exist.

RESULTS

OLETF rats exhibited twice the amount of triceps FNDC5 mRNA compared to LETO rats (p<0.01). Significant positive correlations existed between triceps muscle FNDC5 mRNA expression patterns versus fat mass (r=0.70, p=0.008), as well as plasma leptin (r=0.82, p<0.001). PGC1α mRNA levels were also highly correlated with FNDC5 mRNA (r=0.85, p<0.001). In subsequent culture experiments, low and high physiological doses of leptin had no effect on PGC1α mRNA or FNDC5 mRNA levels in C2C12 myotubes. Paradoxically, circulating irisin concentrations tended to be higher in a second cohort of LETO versus OLETF rats (p=0.085).

CONCLUSION

These results reveal a positive association between total body adiposity and skeletal muscle FNDC5 gene expression. Of interest, circulating irisin levels tended to be lower in OLETF rats. Further research is needed to examine whether other adipose tissue-derived factors up-regulate FNDC5 transcription and/or inhibit irisin biosynthesis from FNDC5.