Inadequate mito-biogenesis in primary dermal fibroblasts from old humans is associated with impairment of PGC1A-independent stimulation.. Homo sapiens

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, which may be a cause or consequence of ageing. We report on a systematic study of human dermal fibroblasts retrieved from female donors aged 20-67years and analysed ex vivo at low population doubling precluding replicative senescence. According to gene set enrichment analysis of genome wide array data, the most prominent age-associated change of the transcriptome was decreased expression of mitochondrial genes. Consistent with that, mitochondrial content and cell proliferation declined with donor age. This was associated with upregulation of AMP-dependent protein kinase (AMPK), increased mRNA levels of PPARγ-coactivator 1α (PGC1A) and decreased levels of NAD(+)-dependent deacetylase sirtuin 1. In the old cells the PGC1A-mediated mito-biogenetic response to direct AMPK-stimulation by AICAR was undiminished, while the PGC1A-independent mito-biogenetic response to starvation was attenuated and accompanied by increased ROS-production. In summary, these observations suggest an age-associated decline in PGC1A-independent mito-biogenesis, which is insufficiently compensated by upregulation of the AMPK/PGC1A-axis leading under baseline conditions to decreased mitochondrial content and reductive overload of residual respiratory capacity. Overall design: 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.