Wan, Junxiang

Suppression of insulin-like growth factor-1 (IGF-1) signaling extends mammalian life span and protects against a range of age-related diseases. Unexpectedly, we found that reduced IGF-1 signaling fails to extend the life span of mitochondrial mutator mice. Most of the longevity pathways that are normally initiated by IGF-1 suppression were either blocked or blunted in the mutator mice. These observations suggest that the prolongevity effects of IGF-1 suppression critically depend on the integrity of the mitochondrial genome, revealing an unexpected hierarchy in the pathways that control mammalian aging. Together, these findings deepen our understanding of the interactions between the hallmarks of aging and underscore the need for interventions that preserve the integrity of the mitochondrial genome.

ABSTRACT Suppression of insulin-like growth factor-1 (IGF-1) signaling extends mammalian lifespan and protects against a range of age-related diseases. Surprisingly though, we found that reduced IGF-1 signaling fails to extend the lifespan of mitochondrial mutator mice. Accordingly, most of the longevity pathways that are normally initiated by IGF-1 suppression were either blocked or blunted in the mutator mice. These observations suggest that the pro-longevity effects of IGF-1 suppression critically depend on the integrity of the mitochondrial genome and that mitochondrial mutations may impose a hard limit on mammalian lifespan. Together, these findings deepen our understanding of the interactions between the hallmarks of aging and underscore the need for interventions that preserve the integrity of the mitochondrial genome.

Cardiac fibrosis is a biological process that increases with age and contributes to myocardial dysfunction. Humanin (HN) is an endogenous mitochondria-derived peptide that has cytoprotective effects and reduces oxidative stress. The present study aimed to test the hypothesis that chronic supplementation of exogenous HN in middle-aged mice could prevent and reverse cardiac fibrosis and apoptosis in the aging heart. Female C57BL/6N mice at 18 mo of age received 14-mo intraperitoneal injections of vehicle (old group; n = 6) or HN analog (HNG; 4 mg/kg 2 times/wk, old + HNG group, n = 8) and were euthanized at 32 mo of age. C57BL/6N female mice (young group, n = 5) at 5 mo of age were used as young controls. HNG treatment significantly increased the ratio of cardiomyocytes to fibroblasts in aging hearts, as shown by the percentage of each cell type in randomly chosen fields after immunofluorescence staining. Furthermore, the increased collagen deposition in aged hearts was significantly reduced after HNG treatment, as indicated by picrosirius red staining. HNG treatment also reduced in aging mice cardiac fibroblast proliferation (5′-bromo-2-deoxyuridine staining) and attenuated transforming growth factor-β1, fibroblast growth factor-2, and matrix metalloproteinase-2 expression (immunohistochemistry or real-time PCR). Myocardial apoptosis was inhibited in HNG-treated aged mice (TUNEL staining). To decipher the pathway involved in the attenuation of the myocardial fibrosis by HNG, Western blot analysis was done and showed that HNG upregulated the Akt/glycogen synthase kinase -3β pathway in aged mice. Exogenous HNG treatment attenuated myocardial fibrosis and apoptosis in aged mice. The results of the present study suggest a role for the mitochondria-derived peptide HN in the cardioprotection associated with aging. NEW & NOTEWORTHY Cardiac fibrosis is a biological process that increases with age and contributes to myocardial dysfunction. Humanin is an endogenous mitochondria-derived peptide that has cytoprotective effects and reduces oxidative stress. Here, we demonstrate, for the first time, that exogenous humanin treatment attenuated myocardial fibrosis and apoptosis in aging mice. We also detected upregulated Akt/glycogen synthase kinase-3β pathway in humanin analog-treated mice, which might be the mechanism involved in the cardioprotective effect of humanin analog in aging mice.

Humanin is a small endogenous antiapoptotic peptide, originally identified as protective against Alzheimer's disease, but subsequently also found on human endothelium as well as carotid artery plaques. Endothelial dysfunction is a precursor to the development of atherosclerotic plaques, which are characterized by a highly proinflammatory, reactive oxygen species, and apoptotic milieu. Previous animal studies demonstrated that humanin administration may improve endothelial function. Thus the aim of this study was to test the hypothesis that patients with coronary endothelial dysfunction have reduced systemic levels of humanin. Forty patients undergoing coronary angiography and endothelial function testing were included and subsequently divided into two groups based on coronary blood flow (CBF) response to intracoronary acetylcholine (normal ≥ 50% increase from baseline, n = 20 each). Aortic plasma samples were obtained at the time of catheterization for the analysis of humanin levels and traditional biomarkers of atherosclerosis including C-reactive protein, Lp-Pla2, and homocysteine. Baseline characteristics were similar in both groups. Patients with coronary endothelial dysfunction (change in CBF = −33 ± 25%) had significantly lower humanin levels (1.3 ± 1.1 vs. 2.2 ± 1.5 ng/ml, P = 0.03) compared with those with normal coronary endothelial function (change in CBF = 194 ± 157%). There was a significant and positive correlation between improved CBF and humanin levels ( P = 0.0091) not seen with changes in coronary flow reserve ( P = 0.76). C-reactive protein, Lp-Pla2, and homocysteine were not associated with humanin levels. Thus we observed that preserved human coronary endothelial function is uniquely associated with higher systemic humanin levels, introducing a potential diagnostic and/or therapeutic target for patients with coronary endothelial function.