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Downregulation of miR-15b is associated with increased SIRT4 expression in premature senescence and photoaging of the skin

ABSTRACT: Sirtuins are deacetylases or ADP-ribosyltransferases which are implicated in multiple pathways involved in metabolism and life-span regulation. Here, we link the mitochondrial sirtuin SIRT4, which overexpression negatively impacts on mitochondrial oxidative capacity, with premature senescence and skin aging. Accordingly, SIRT4 mRNA levels were significantly increased in vitro in human dermal fibroblasts after repetitive UVB exposure or in senescence triggered by mitotic spindle stress or ionizing radiation. Similarly, analysis of SIRT4 expression in vivo in human skin revealed upregulation of SIRT4 mRNA levels in the dermal compartment of photaged skin as compared with the dermis of intrinsically aged skin. In all our in vitro models, upregulation of SIRT4 expression was associated with decreased levels of miR-15b. Also, in human skin, highest copy numbers of miR-15b mRNA were detected in the epidermis, and epidermal expression was significantly reduced in photoaged skin as compared with intrinsically aged skin. Reduced miR-15b expression is most likely causally linked to increased SIRT4 expression because we found that (i) miR-15b displays a conserved and direct binding site within the 3'-untranslated region of the SIRT4 gene as demonstrated by luciferase reporter assays and (ii) transfection of oligonucleotides mimicking miR-15b function was sufficient to prevent SIRT4 upregulation in senescent cells in vitro. Thus, we propose that miR-15b acts as a negative regulator of SIRT4 expression to antagonize mitochondrial dysfunction and hence cellular senescence as well as tissue aging, in particular photoaging of the skin.

ORGANISM(S): Homo sapiens

PROVIDER: GSE45729 | GEO | 2016/06/08

SECONDARY ACCESSION(S): PRJNA196140

REPOSITORIES: GEO

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Project description:Extrinsic skin ageing converges on the dermis, a post-mitotic tissue compartment consisting of extracellular matrix and long-lived fibroblasts prone to damage accumulation and maladaptation. Aged human fibroblasts exhibit mitochondrial and nuclear dysfunctions, but it is unclear whether these are cause or consequence of ageing. We report on a systematic study of human dermal fibroblasts retrieved from female donors aged 20-67 years and analyzed in primary culture at low population doubling precluding replicative senescence. Genome-wide array analysis failed to detect significant (>2-fold) age-related expression changes for individual genes, but gene set enrichment analysis revealed down regulation of many genes involved in mitochondrial metabolism and respiratory electron transport, extracellular matrix maintenance, cell cycle progression and protein translation. Consistent with these changes, mitochondrial content, respiratory function and cell proliferation declined with donor age. This was associated with inadequate nuclear mito-biogenesis, hypo- phosphorylation of AMP-dependent protein kinase alpha and upregulation of the alpha2-isoform, suggesting that inadequate mito-nuclear signalling could be the leading event entailing decreased expression of mitochondrial genes and compensatory down regulation of proliferation and protein synthesis. The comparatively few genes exhibiting age-associated up regulation were associate with cholesterol metabolism, immune reactions and mRNA processing, possibly also reflecting adaptation to inadequate mitochondrial function. Donors: 15 human female donors included in the study were aged 20, 21, 23, 26, 26, 40, 41, 42, 43, 49, 60, 62, 63, 64 and 67 years, thus covering the age spectrum 20 – 67 years and providing five biological replicates for each of the age groups “young” (20-30 years), “middle” (40-50 years) and “old” (60-70 years). Human dermal fibroblasts were isolated from skin specimen removed in the course of cosmetic surgery from the bottom side of female breast. Isolation and primary culture of the cells followed published procedures (Tigges and others 2013). Cells were not expanded beyond 12 population doublings, while replicative cell cycle arrest was determined to not occur before 40 population doublings.

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Downregulation of miR-15b is associated with increased SIRT4 expression in premature senescence and photoaging of the skin

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