[Biology of aging]

The biology of aging, a modest branch of medical sciences at the beginning of this century experienced a considerable development as a result of the importance and urgency of problems it has to solve. In this short review only a schematic presentation of this science can be tempted. Clinical epidemiological studies revealed the differential decline of quantifiable physiological functions with quite different kinetics. The fastest decline was noticed for the elastic tissues such as the lung and the blood vessels, both rich in extracellular matrix (ECM), that is connective tissues. Such tissues contain cells able to proliferate (mitotic cells) and extracellular matrix. Aging studies of such tissues should thus comprise the analysis of cellular aging and the aging of the ECM as well as the age-dependent modifications of cell-matrix interactions. The "Hayflick limit" is the limited number of population doubling for such cells in culture is obeyed by the cells of these tissues. It appears however that this limit is not reached during the actual life time of our species. The mechanisms underlying this limit at the level of the genome are now actively studied and start to be understood. The age-dependent modifications of the relative rates of biosynthesis of ECM-macromolecules appears to be regulated independently of cell proliferation. Post-synthetic matrix undergoes also age-dependent modifications such as crosslinking attributed to the Maillard reaction, proteolytic degradation and free radical damage. The result is a progressively modified ECM in its structure and function.(ABSTRACT TRUNCATED AT 250 WORDS)