Proteome-wide analysis of in situ aged fibroblasts

Aging is a multifactorial process that is characterized by distinct molecular and biological changes [1]. However, deciphering the molecular and cellular mechanisms of aging in vivo is far from complete. It has been suggested that the aging process of the skin is mainly determined by alterations of its dermal stroma consisting predominantly of fibroblasts and the extracellular matrix [2, 3]. In this context the stromal-epithelial interactions by senescent fibroblasts is also discussed to contribute to age-related pathology, including cancer [3]. The homeostasis of the dermis is primarily based on cellular adaptation and damage clearance and thereby prone to age-related changes. As the major cell source in the dermis and a long-lived cell system, dermal fibroblasts are able to accumulate aging-associated alterations and adapt their cellular functions. A broadly applied fibroblast aging model is based on the limited replicative lifespan of these cells. Although senescence is one of the hallmarks of aging [1], it is unclear to which extent senescence induced in vitro is a representative model for cell and organ aging in vivo. Moreover, most studies analyzing aging of fibroblasts in vivo and in vitro focused on single genes or pathways, while comprehensive investigations of aging-associated alterations at the proteome-, transcriptome-and miRNAome-wide levels are sparse [4]. We analyzed an ex 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 [5]. We identified a total of 2409 proteins, including 43 proteins with a significant age-associated expression, whereof 20 and 23 proteins exhibit positive and negative correlation with age, respectively. Most of the differentially abundant proteins have not been described in the context of fibroblasts' aging before, but the deduced biological processes confirmed known hallmarks of aging [1]. Based on the integration of comprehensive data sets from expression studies at the protein [5], mRNA [6] and miRNA [7] levels, we presented a synoptic view of molecular changes associated with the aging of human dermal fibroblasts in the skin. We demonstrated that 47 % and 63 % of the proteins and transcripts, respectively identified in these cells exhibited a constant abundance across different donor age groups suggesting that in situ aged fibroblasts exhibit a moderate age-associated cellular phenotype [5]. A further observation supporting the moderate age-associated cellular phenotype was the low number of significantly changed mRNAs (137), proteins (43) and miRNAs (12). …