ABSTRACT: 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.
