Explaining How Altered IGF-1 Signaling Extends Life
Signs of progress in understanding the mechanisms of induced longevity through altered insulin/IGF-1 signaling are shown in this paper. This is one of the most-studied class of longevity mutations in lower animals, despite there being some debate over whether it is relevant to mammal biochemistry. Here, the basic mechanism is explained as being hormetic, centering on the mitochondria: researchers "elucidate a conserved mechanism through which reduced insulin-IGF1 signaling activates an AMP-kinase-driven metabolic shift toward oxidative proline metabolism. This, in turn, produces an adaptive mitochondrial [reactive oxygen species (ROS)] signal that extends worm life span. These findings further bolster the concept of mitohormesis as a critical component of conserved aging and longevity pathways. ... Impaired insulin and IGF-1 signaling (iIIS) in C. elegans daf-2 mutants extends life span more than 2-fold. Constitutively, iIIS increases mitochondrial activity and reduces reactive oxygen species (ROS) levels. By contrast, acute impairment of daf-2 in adult C. elegans reduces glucose uptake and transiently increases ROS. Consistent with the concept of mitohormesis, this ROS signal causes an adaptive response by inducing ROS defense enzymes, culminating in ultimately reduced ROS levels despite increased mitochondrial activity. Inhibition of this ROS signal by antioxidants reduces iIIS-mediated longevity by up to 60%. ... IIIS upregulates mitochondrial L-proline catabolism, and impairment of the latter impairs the life span-extending capacity of iIIS while L-proline supplementation extends C. elegans life span. Taken together, iIIS promotes L-proline metabolism to generate a ROS signal for the adaptive induction of endogenous stress defense to extend life span."