The mir-465 family is upregulated with age and attenuates growth hormone signaling in mouse liver.

We analyzed the small RNA transcriptome from 5-month-old, 24-month-old, and 36-month-old mouse liver and found 56 miRNAs that changed their expression profile with age. Among these is a cluster of 18 miRNAs that are upregulated between 50- and 1,000-fold at 24 and 36 months of age. This cluster is located in a 60-kb region of the X-chromosome that is devoid of other coding sequences and is part of a lamin-associated domain. Potential targets of the miRNAs in the cluster suggest they may regulate several pathways altered in aging, including the PI3K-Akt pathway. Total transcriptome analyses indicate that expression of several potential genes in the PI3K-Akt pathway that may be targeted by the mir-465 family (mmu-mir-465a, mmu-mir-465b, and mmu-mir-465c) is downregulated with age. Transfection of the liver cell line AML12 with mir-465 family members leads to a reduction of three of these potential targets at the mRNA level: a 40% reduction of the growth hormone receptor (GHR), and a 25% reduction in Kitl and PPP2R3C. Further investigation of the GHR 3'UTR revealed that the mir-465 family directly targets the GHR mRNA. Cells transfected with mir-465 showed a reduction of JAK2 and STAT5 phosphorylation upon growth hormone (GH) stimulation, resulting in a reduction in insulin-like growth factor 1 (IGF-1) and IGF-1-binding protein 3 expression. With age, GH signaling falls and there is a reduction in circulating IGF-1. Our data suggest that an increase in expression of the mir-465 family with age may contribute to the reduction in the GH signaling.

Developmental Regulation of Mitochondrial Apoptosis by c-Myc Governs Age- and Tissue-Specific Sensitivity to Cancer Therapeutics.

It is not understood why healthy tissues can exhibit varying levels of sensitivity to the same toxic stimuli. Using BH3 profiling, we find that mitochondria of many adult somatic tissues, including brain, heart, and kidneys, are profoundly refractory to pro-apoptotic signaling, leading to cellular resistance to cytotoxic chemotherapies and ionizing radiation. In contrast, mitochondria from these tissues in young mice and humans are primed for apoptosis, predisposing them to undergo cell death in response to genotoxic damage. While expression of the apoptotic protein machinery is nearly absent by adulthood, in young tissues its expression is driven by c-Myc, linking developmental growth to cell death. These differences may explain why pediatric cancer patients have a higher risk of developing treatment-associated toxicities.