Major life transitions are always difficult because change costs energy. Recent findings have demonstrated how mitochondrial oxidative phosphorylation (OxPhos) defects increase the energetic cost of living and that excessive integrated stress response (ISR) signaling may prevent cellular identity transitions during development. In this perspective, we discuss general bioenergetic principles of life transitions and the costly molecular processes involved in reprograming the cellular hardware/software as cells shift identity. The energetic cost of cellular differentiation has not been directly quantified, representing a gap in knowledge. We propose that the ISR is an energetic checkpoint evolved to (i) prevent OxPhosdeficient cells from engaging in excessively costly transitions and (ii) allow ISRpositive cells to recruit systemic energetic resources by signaling via GDF15 and the brain.
Skeletal muscle plays a vital role in the regulation of systemic metabolism, partly through its secretion of endocrine factors which are collectively known as myokines. Altered myokine levels are associated with metabolic diseases, such as type 2 diabetes (T2D). The significance of interorgan crosstalk, particularly through myokines, has emerged as a fundamental aspect of nutrient and energy homeostasis. However, a comprehensive understanding of myokine biology in the setting of obesity and T2D remains a major challenge. In this review, we discuss the regulation and biological functions of key myokines that have been extensively studied during the past two decades, namely interleukin 6 (IL-6), irisin, myostatin (MSTN), growth differentiation factor 11 (GDF11), fibroblast growth factor 21 (FGF21), apelin, brain-derived neurotrophic factor (BDNF), meteorin-like (Metrnl), secreted protein acidic and rich in cysteine (SPARC), β-aminoisobutyric acid (BAIBA), Musclin, and Dickkopf 3 (Dkk3). Related to these, we detail the role of exercise in myokine expression and secretion together with their contributions to metabolic physiology and disease. Despite significant advancements in myokine research, many myokines remain challenging to measure accurately and investigate thoroughly. Hence, new research techniques and detection methods should be developed and rigorously tested. Therefore, developing a comprehensive perspective on myokine biology is crucial, as this will likely offer new insights into the pathophysiological mechanisms underlying obesity and T2D and may reveal novel targets for therapeutic interventions.
Atherosclerosis is the major contributor to cardiovascular mortality worldwide. Alternate day fasting (ADF) has gained growing attention due to its metabolic benefits. However, the effects of ADF on atherosclerotic plaque formation remain inconsistent and controversial in atherosclerotic animal models. The present study was designed to investigate the effects of ADF on atherosclerosis in apolipoprotein E-deficient (Apoe−/−) mice. Eleven-week-old male Apoe−/− mice fed with Western diet (WD) were randomly grouped into ad libitum (AL) group and ADF group, and ADF aggravated both the early and advanced atherosclerotic lesion formation, which might be due to the disturbed cholesterol profiles caused by ADF intervention. ADF significantly altered cholesterol metabolism pathways and down-regulated integrated stress response (ISR) in the liver. The hepatic expression of activating transcription factor 3 (ATF3) was suppressed in mice treated with ADF and hepatocyte-specific overexpression of Aft3 attenuated the effects of ADF on atherosclerotic plaque formation in Apoe−/− mice. Moreover, the expression of ATF3 could be regulated by Krüppel-like factor 6 (KLF6) and both the expressions of ATF3 and KLF6 were regulated by hepatic cellular ISR pathway. In conclusion, ADF aggravates atherosclerosis progression in Apoe−/− mice fed on WD. ADF inhibits the hepatic ISR signaling pathway and decreases the expression of KLF6, subsequently inhibiting ATF3 expression. The suppressed ATF3 expression in the liver mediates the deteriorated effects of ADF on atherosclerosis in Apoe−/− mice. The findings suggest the potentially harmful effects when ADF intervention is applied to the population at high risk of atherosclerosis.