miR-23a-3p causes cellular senescence by targeting hyaluronan synthase2: Possible implication for skin aging.

Even though aging and cellular senescence appear to be linked the biological mechanisms interconnecting these two processes remain to be unravelled. Therefore, miRNA profiles were analyzed ex vivo by gene array in fibroblasts isolated from young and old human donors. Expression of several miRNAs was positively correlated with donor age. Among those miR-23a-3p was shown to target hyaluronan-synthase 2. Hyaluronan (HA) is a polysaccharide of the extracellular matrix that critically regulates the phenotype of fibroblasts. Indeed, both aged and senescent fibroblasts showed increased miR-23a-3p expression and secreted significantly lower amounts of HA compared to young and non senescent fibroblasts. Ectopic overexpression of miR-23a-3p in non senescent fibroblasts led to decreased HAS2 mediated HA-synthesis, upregulation of senescence associated markers and decreased proliferation. In addition, siRNA mediated downregulation of HAS2 and pharmacologic inhibition of HA-synthesis by 4-methylumbelliferone mimicked the effects of miR-23a-3p. In vivo, miR-23a-3p was upregulated and HAS2 was downregulated in the skin of old mice versus young mice. Inhibition of HA-synthesis by 4-methylumbelliferone in mice reduced dermal hydration and viscoelasticity thereby mimicking an aged skin phenotype. Taken together, these findings appear to link miR-23a-3p and the HA-microenvironment as effector mechanisms in both dermal aging and senescence

Proteome-wide analysis reveals an age-associated cellular phenotype of <em>in situ</em> aged human fibroblasts.

We analyzed anex vivo model of in situ aged human dermal fibroblasts, obtained from 15 adult healthy donors from three different age groups using an unbiased quantitative proteome-wide approach applying label-free mass spectrometry. Thereby, we identified 2409 proteins, including 43 proteins with an age-associated abundance change. Most of the differentially abundant proteins have not been described in the context of fibroblasts&#39; aging before, but the deduced biological processes confirmed known hallmarks of aging and led to a consistent picture of eight biological categories involved in fibroblast aging, namely proteostasis, cell cycle and proliferation, development and differentiation, cell death, cell organization and cytoskeleton, response to stress, cell communication and signal transduction, as well as RNA metabolism and translation. The exhaustive analysis of protein and mRNA data revealed that 77 % of the age-associated proteins were not linked to expression changes of the corresponding transcripts. This is in line with an associated miRNA study and led us to the conclusion that most of the age-associated alterations detected at the proteome level are likely caused post-transcriptionally rather than by differential gene expression. In summary, our findings led to the characterization of novel proteins potentially associated with fibroblast aging and revealed that primary cultures of in situ aged fibroblasts are characterized by moderate age-related proteomic changes comprising the multifactorial process of aging