Effect of mitochondrial quantity and quality controls in white adipose tissue on healthy lifespan: Essential roles of GH/IGF-1-independent pathways in caloric restriction-mediated metabolic remodeling

Long-term caloric restriction is a conventional and reproducible dietary intervention to improve whole body metabolism, suppress age-related pathophysiology, and extend lifespan. The beneficial actions of caloric restriction are widely accepted to be regulated in both growth hormone/insulin-like growth factor 1-dependent and -independent manners. Although growth hormone/insulin-like growth factor 1-dependent regulatory mechanisms are well described, those occurring independent of growth hormone/insulin-like growth factor 1 are poorly understood. In this review, we focus on molecular mechanisms of caloric restriction regulated in a growth hormone/insulin-like growth factor 1-independent manner. Caloric restriction increases mitochondrial quantity and improves mitochondrial quality by activating an axis involving sterol regulatory element binding protein-c/peroxisome proliferator-activated receptor γ coactivator-1α/mitochondrial intermediate peptidase in a growth hormone/insulin-like growth factor 1-independent manner, particularly in white adipose tissue. Fibroblast growth factor 21 is also involved in this axis. Moreover, the axis may be regulated by lower leptin signaling. Thus, caloric restriction appears to induce beneficial actions partially by regulating mitochondrial quantity and quality in white adipose tissue in a growth hormone/insulin-like growth factor 1-independent manner.