[Age-dependent changes in connective tissue]

Alterations of the various connective tissues with aging are investigated by combined morphological and biochemical methods. The aging of connective tissues depends on aging of informational- and structural-macromolecules. Aging-dependent alterations of proteoglycans/GAG and collagen can be caused by changes in genetic information or in the cellular information-coded synthesis, but also by changes in the controls of the various metabolic processes of connective tissue cells. The activities of enzymes involved in the anabolism and the catabolism of proteoglycans/GAG and collagen show reductions with aging, but do not show age-specific variations. The aging of connective tissues is rather a dynamic process (with measurable metabolic parameters of the various connective tissue cells and their products) than a passive or so-called degenerative connective tissue process. The bradytrophy concept of connective tissue cannot be accepted any longer, because connective tissue cells partly have metabolic rates at the same level as parenchymal cells. Furthermore, parenchymal cells can synthesize and degrade mesenchymal structural macromolecules. Connective tissue aging is demonstrated on 3 organ groups: 1. on typical mesenchymal organs: aorta, cartilage and skin, 2. on organs, which are mainly composed by connective tissue: heart and lung, 3. on connective tissues of parenchymal organs: liver and kidney. These various organs exhibit some common basic processes but also differences in connective tissue aging, which are due to the different composition of proteoglycans/GAG and collagen types, and on structure and function. The aging of connective tissues is of special importance for the aging of organs. Besides alterations of cells and GAG, the very important aging fibrosis in several mesenchymal and parenchymal organs is demonstrated and discussed. The connective tissue aging of organs is one of the reasons why the frequency of diseases increases with aging and diseases are grafted more strongly on aging cells, tissues, organs and organisms.