The skin as a mirror of the aging process in the human organism--state of the art and results of the aging research in the German National Genome Research Network 2 (NGFN-2)

Abstract

As our society is growing older, the consequences of aging have begun to gain particular attention. Improvement of quality of life at old age and prevention of age-associated diseases have become the main focus of the aging research. The process of aging in humans is complex and underlies multiple influences, with the probable involvement of heritable and various environmental factors. In particular, hormones are decisively involved in the generation of aging. Over time, important circulating hormones decline due to a reduced secretion of the pituitary, the adrenal glands and the gonads or due to an intercurrent disease. Among them, serum levels of growth factors and sexual steroids show significant aging-associated changes. Within the scope of the Explorative Project 'Genetic aetiology of human longevity' supported by the German National Genome Research Network 2 (NGFN-2) an in vitro model of human hormonal aging has been developed. Human SZ95 sebocytes were maintained under a hormone-substituted environment consisting of growth factors and sexual steroids in concentrations corresponding to those circulating in 20- and in 60-year-old women. Eight hundred and ninety-nine genes showed a differential expression in SZ95 sebocytes maintained under the 20- and 60-year-old hormone mixture, respectively. Among them genes were regulated which are involved in biological processes which are all hallmarks of aging. The most significantly altered signaling pathway identified was that of the transforming growth factor-beta (TGF-beta). A disturbed function of this cascade has been associated with tumorigenesis, i.e. in pancreatic, prostate, intestine, breast, and uterine cancer. Interestingly, genes expressed in signaling pathways operative in age-associated diseases such as Huntington's disease (HD), dentatorubral-pallidoluysian atrophy (DRPLA), and amyotrophic lateral sclerosis (ALS) were also identified. These data demonstrate that skin and its appendages may represent an adequate model for aging research. Hormones interact in a complex fashion, and aging may be partly attributed to the changes in their circulating blood levels. Furthermore, a disturbed hormone status may partially act towards the manifestation of neurodegenerative diseases. Thus, these results could be a basis for an integrated and interdisciplinary approach to the analysis of the aging process.