Ups and downs of aging studies in vitro: the crooked path of science

Expression of senescence-associated beta-galactosidase (SA-beta-Gal) by human skin fibroblasts, effect of advanced glycation end-products and fucose or rhamnose-rich polysaccharides

Expression by cells of the SA-beta-Gal was shown to be a reliable indicator of the switch mechanism used by cells to enter the senescent phenotype. We used this method in order to explore the variation of SA-beta-Gal-positive cells with passage number and time spent in culture. Both parameters produced an increase of SA-beta-Gal-positive cells. The addition of a Maillard-product (advanced glycation end-product=AGE) to the fibroblast cultures also increased SA-beta-Gal expression. Fucose- and rhamnose-rich oligo- and polysaccharides (FROPs and RROPs, respectively) provided a significant protection against this AGE-induced increase of SA-beta-Gal-positive cells. It is speculated that these processes might well play an important role in skin aging.

The effect of cell-matrix interactions and aging on the malignant process

The malignant process, transformation of normal cells, proliferation, and metastasis formation, was considered as if originating from one single cell. Although the intrinsic mechanisms of transformation from the normal to the malignant state were both confirmed, an increasing body of evidence points to the surrounding matrix and cell-matrix interactions as major players in this process. Some of the most important arguments in favor of this contention are cited and commented in this chapter. Another important question concerns the relationship between the aging process and malignant transformation. A few decades ago, the frequency of clinically manifest tumors of several organs and tissues appeared to increase with age. As, however, average life expectancy increased rapidly over the last decades, clinical frequency of malignant tumors did not follow this tendency. It was argued that late in life the malignant process appears to decline. This justly inspired several teams to study the relationship between cellular senescence and malignant transformation. This is now an actively growing field which deserves special attention. Some of the pertinent experimental and theoretical arguments in favor of an antioncogene-mediated switch between these two processes are also reviewed with the caveat that this important and new subject of basic and clinical research on the malignant process is just at its beginning. It will certainly take an increasing importance during the coming years and decades with the hope to contribute to answer one of the most burning questions concerning the aging process: will life expectancy continue to increase linearly as predicted by some gerontologists, or will life expectancy level off or even decline as predicted by other epidemiologists. The relationship between cellular senescence and malignant transformation will play in this respect an important role.

Aging cell culture: methods and observations

Culturing and subcultivation of normal human diploid fibroblasts have advanced our understanding of the molecular events involved in aging. This progress is leading to the development of therapies that slow or ablate the adverse physiological and pathological changes associated with aging. It has been established that normal human diploid fibroblasts can proliferate in culture for only finite periods of time. Hayflick and Moorhead and others have described numerous types of cells, ranging from fetal to adult, that were incapable of indefinite proliferation. There are many ways to study aging in vitro, and this chapter summarizes some laboratory procedures.

Aging, from basic research to pathological applications

This introductory chapter tentatively draws a parallel between some of the highlights of basic aging research and their incidence for the understanding of age-associated pathologies. Some of the most important mechanisms described for cell- and tissue-aging, such as limited cell-proliferation, "parasitic" reactions, such as non-enzymatic glycation, ROS-production, uncontrolled proteolysis involving matricryptic sites, receptor loss and uncoupling appear to be the most promising links between those two approaches to fundamental and clinical gerontology. Some of the "parasitic", epigenetic, post-translational reactions lead to vicious circles which over the years might well produce cell- and tissue-damage as seen in most age-associated diseases. There is little doubt that the better understanding of these relationships will also prove helpful for pharmacological research as related to the age-associated pathologies.

[The Brugada syndrome]

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Differential response of mature TrkA/p75(NTR) expressing human and pig oligodendrocytes: aging, does it matter?

A differential morphological response of mature oligodendrocytes (OL) isolated from human and pig brains to the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) and to the nerve growth factor (NGF) was observed. In both cases, OL regenerate their processes; however, the rate and the extension of the process formation of human OL were behind that of pig OL. Presumably, the advanced age of the human tissue in these experiments might have contributed to this decrease in process formation, an effect that was already observed for rat OL [Yong et al. (1991) J Neurosci Res 29:87-99]. The less effectivity of NGF via TrkA, which was immunocytochemically shown in human OL, and of TPA via the protein kinase C (PKC) pathway, may have its common focus on the mitogen-activated protein kinase (MAPK) cascade. In this context, it was noted that only a few studies on aging of mature OL are available. It is conceivable that age-related changes in the properties of OL could be an important factor for their cellular responsiveness during longer lasting demyelinating diseases such as multiple sclerosis. Hence, this review would like to provide a basis for future investigations on the aging of mature OL. The data presently available suggest a preliminary classification of mature OL into three categories.