Cell senescence: role in aging and age-related diseases.

Cell senescence is one of the major paradigms of aging research. It started with the demonstration by L. Hayflick of the limited number of divisions by normal, nontransformed cells, not shown by transformed malignant cells, this processes being largely regulated by the telomere-telomerase system. A complete renewal of this discipline came from the demonstration that cells can enter senescence at any time by an anti-oncogene-triggered pathway, enabling them to escape malignancy. The senescent cell became a major actor of the aging process, among others, by the acquisition of the senescence-associated secretory phenotype. This chapter is devoted to the regulatory process involved in the acquisition of the senescent cell phenotype and its role in organismal aging.

Role of the Maillard reaction in aging and age-related diseases. Studies at the cellular-molecular level.

Increase in life expectancy concerns most populations but more importantly developed countries. This increase is accompanied by the shift of chronic diseases to the senior population, especially cardiovascular diseases and diabetes type II. Aging mechanisms, mostly post-genetic, comprise among others the Maillard reaction which strongly contributes by several harmful processes to the age-dependent decline of tissue structure and function. Several of these mechanisms were studied in our laboratory at the cellular-molecular level and will be described in this review with respect to their role in aging and age-related pathologies, especially cardiovascular diseases.

[Fiftieth anniversary of the French Society for Connective Tissue Research]. / Cinquantenaire de la Société Française des Tissus Conjonctifs--introduction.

The Society was founded in 1962, at an international meeting organized at the Biomedical Institute rue des Saints-Pères, in Paris in the Department of Biochemistry headed at that time by Pr. Max F. Jayle, and published in the "Exposés Annuels de Biochimie Médicale" in 1963. At its beginnings a "Club", with a limited number of participants, it expanded rapidly into a Society, renamed recently "French Society of the Biology of Extracellular Matrix", with approximately 200 members working on a variety of subjects. Only six of these teams could present an oral report at the meeting of the Biological Society on January 18, 2012, celebrating this anniversary at the Curie Institute. A few more could send written contributions for this special issue of "Biologie Aujourd'hui". In this short introduction we shall recall some important stages of the developing connective tissue science. Besides such classical subjects, as the macromolecular components of connective tissue matrix, this discipline incorporated progressively receptors, integrins and other molecules, that mediate cell-matrix interactions.

[Theodor Huzella and the initiation of research on the interactions between cells and the extracellular matrix]. / Theodor Huzella et l'origine de la recherche sur l'interaction entre cellules et matrice extracellulaire.

Interactions between cells and the surrounding "biomatrix", mediated by receptors as integrins or the elastin receptor is the most important topic in up to date research on connective tissues. Looking for the origin of this concept, one finds the pioneering work of Theodor Huzella, professor of histology-embryology at the Medical University of Budapest during pre-world war II decades. Using time-laps micro-cinematography in reflected light, he visualized the important role of connective tissue fibers, prepared in his laboratory, for the oriented migration of normal and malignant cells. His theoretical explanations, attributing an "active" role to the elasticity of the argyrophilic fibrous network in the coordination of cell societies, can now be reinterpreted in the light of recent work on the mechanotransduction of "messages" from the extracellular matrix to the cell inside. We propose a succinct review of Huzella's work and theories reinterpreted in the light of up-to-date knowledge on cell-matrix interactions.

[Eye connective tissues: cornea and vitreous body]. / Recherches sur les tissus conjonctifs oculaires. La cornée et le corps vitré

The authors, ophtalmologist (Y.P.) and basic scientists (J.L.-R and L.R.), collaborated on eye-research since 1962 on normal and pathological aspects of eye tissues, considered as specialized forms of connective tissues, and on specific aspects of the physiology and pathology of the eye. This date coincides with the foundation of the French Society of Connective Tissues, which celebrates the 50th anniversary of its creation. We shall present here some of our work on the ontogenetic and phylogenetic aspects of the cornea, on its structure, function and regulation in normal and pathological states, taken from a large number of publications of our laboratories. Our work on cornea started with the study of the morphogenesis of its lamellar structure, made of collagen fibers and proteoglycans. This led us to the isolation and characterization of structural (or matrix) glycoproteins, a new class of matrix components, present also in all other connective tissues, and to the study of their biosynthesis by keratocytes. Corneal wounds and regeneration were also studied, as well as some corneal pathologies such as keratoconus. The confrontation of quantitative morphological methods with biochemical procedures were to yield important results on the mechanisms of the maintenance of corneal structure and function. Another series of studies concerned the vitreous where we detected, besides previously characterized components, such as hyaluronan and collagens, fibronectin which plays an important role in the adhesion of hyaluronan to the collagen network. Its age-dependent modifications were also studied, with a special focus on the role of reactive oxygen species (ROS)-mediated degradation of hyaluronan, especially important for the aging of the vitreous.

The Saga of kappa-elastin or the promotion of elastin degradation products from "garbage" to receptor agonists and pharmacologically active principles.

In this review article, dedicated to Prof. Ines Mandl, for her 90st birthday, some of the essential steps of our research over the years on elastin are described. Insoluble fibrous elastin could be "solubilized" by 1M KOH in 80% aqueous ethanol at room temperature. The large peptides obtained were designated kappa-elastin after a suggestion by I. Mandl. These peptides were widely used for biological, biochemical and pharmacological studies and were also commercialized and applied in "anti-aging" preparations. Kappa-elastin was used to demonstrate the importance of hydrophobic interactions in the stalilization of elastin fibers. It was used also as an "agonist" for studies on the elastin receptor and its age-dependent modifications (uncoupling). Kappa-elastin became also an important ingredient for dermocosmetology. This review spans several decades from the discovery of the first elastase, by Banga and Balo, in the 1950-ies to the pharmacological studies of the elastin receptor in the recent years.

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.

An original approach to aging: an appreciation of Fritz Verzár's contribution in the light of the last 50 years of gerontological facts and thinking.

The motivation of this review is the 120th anniversary of the birth of Fritz Verzár, founder of experimental gerontology. His major contributions to aging research are shortly reviewed and re-evaluated in the light of modern gerontological research. Verzár undertook aging research after his retirement from the Chair of Physiology at the Medical Faculty of Basel. His first experiments on aging of the rat tail tendon revealed an important mechanism of aging: an exponential increase of cross-linking of collagen fibres. This observation, correctly interpreted by Verzár as a new age-dependent mechanism, was shown later to be attributed to the Maillard reaction, the non-enzymatic glycosylation of protein (and nucleotide bases) amino groups followed by evolution of the reaction to advanced glycation end products (AGEs) involved in a number of harmful reactions. Many of these reactions were shown to be mediated by receptors recognizing AGE products (RAGEs). This was the first example of a post-synthetic (post-translational) reaction involved in the aging of biological macromolecules, especially those of the extracellular matrix. Verzár extended the research activity of his team to several other aspects of aging research, such as loss of muscular strength, nutritional requirements at high altitude, cell loss with aging, and ultrastructural studies, and started also the first longitudinal clinical study of aging in a Basel population. Modern gerontological research confirmed and extended Verzár's observations. His work on collagen cross-linking by glycation became of paramount importance in recent times because of the rapid increase of diabetes type II, combined with the metabolic syndrome, one of the major pathologies of modern times.

Fritz Verzár was born 120 years ago: his contribution to experimental gerontology through the collagen research as assessed after half a century.

F. Verzár's experiments on the age-dependent increase of cross-linking of rat tail tendons in the 1950s represented the first demonstration of age-dependent modifications of extracellular matrix (ECM) macromolecules. This discovery preceded by several years the demonstration of cell-aging and showed that body constituents considered as metabolically "inert" do exhibit age-dependent modifications at the molecular level. Progressively the physiological mechanisms of collagen cross-linking were elucidated and it became clear that this mechanism does not explain the Verzár phenomenon. It was progressively elucidated that the Maillard reaction was involved in the age-dependent cross-linking of collagen. The role of advanced glycation end products (AGEs) in collagen cross-linking, as well as their reaction with other macromolecules was convincingly demonstrated as an important factor of age-dependent modifications of cells and tissues. The Verzár phenomenon completed by the detailed chemistry of the Maillard reaction became thus a dominant paradigm in tissue aging. Verzár's name and discovery should therefore remain associated with these important progresses in aging research. The purpose of this review is to recall some of the details of Verzár's work which paved the way to his discovery and extended well beyond collagen aging.

Introduction: matrix biology in the 21st century. From a static-rheological role to a dynamic-signaling function.

These introductory remarks contain a succinct reminder of the developmental history of matrix biology, from the descriptive biochemistry of connective tissues to the up to date cell biology of extracellular matrices. The rapid growth of this discipline makes it prohibitive to give a complete coverage of recent results on all aspects of matrix biology and pathology. The articles in this special issue concern several of the ECM-macromolecules and some of their functional characteristics. No space remained for reviews on matrix related pathologies. As a partial compensation some recent aspects of cell-cell and cell-matrix interactions in malignant growth are mentioned in this introduction.

Cell-elastin interaction and signaling.

Matrix biology expanded its sphere of interest over the recent decades from its original rheological-morphological functions to incorporate control of cell phenotype during development and maturation. Aging and age-related pathologies are accompanied by matrix remodeling, loss of phenotypic traits as during atherogenesis or tumor growth. Most of these recently discovered functions are related to signaling by matrix components to cells through cell-membrane receptors. Some of the signaling molecules are produced by proteolytic degradation of macromolecules of the extracellular matrix. Such peptides (matrikins or matricryptins) exhibit biological functions absent in the native molecule from which these peptides were derived. Some of these novel activities are potentially harmful and appear to be involved in the age-dependent alterations of tissue structure and functions as well as in related pathologies.

Elastin peptides induced oxidation of LDL by phagocytic cells.

The degradation products of one of the major component of vascular wall, elastin, have several important biological activities. Elastin peptides (KE) are mostly generated during vascular aging and the atherosclerotic process. They induce free radical and proteases production from cells, which are the major components of the atherosclerotic process. In the present study, we investigated whether the interaction between elastin peptides and neutrophils as well as monocytes contributes to low density lipoproteins (LDL) oxidation, being one of the most important initiator of the chronic inflammatory process contributing to the development of atherosclerosis. Here, we present data on the link between the elastin degradation products and LDL oxidation by the chemotactically attracted neutrophils and monocytes. The KE as well as the active epitope, the hexapeptide VGVAPG is able, in a differential concentration and time dependence, to induce the oxidation of LDL. KE is able to induce via the production of free radicals by neutrophils the oxidation of LDL very rapidly and in higher concentration compared to monocytes. These effects of KE are occurring through the stimulation of the 67 kDa elastin-laminin receptor (ELR), as demonstrated by the uncoupling effect of lactose. In our present study, the HDL was able to decrease the LDL oxidation by KE. This is a new mechanism by which elastin peptides might participate in the initiation and progression of the atherosclerotic process.

Presence and active synthesis of the 67 kDa elastin-receptor in human circulating white blood cells.

Early after the identification of the elastin-receptor (El-R) on mesenchymal cells, it was demonstrated that phagocytic cells and lymphocytes could also respond to elastin peptides. Nevertheless, the level of El-R expression has never been demonstrated on immune cells and no data exist whether these cells actively synthesize this El-R. Thus, our aim in the present work was to study the expression and number of El-R on white blood cells (WBC) using a specific 67 kDa El-R antibody and to demonstrate the presence of mRNA corresponding to the gene coding for El-R. Our results show that messenger RNA corresponding to the presumptive gene coding for the 67 kDa El-R subunit could be detected in all three WBC-types investigated. On all of these WBC, the presence of El-R could be demonstrated, however their number and their function varied following the cell type. The presence of El-R is very important for the interaction of circulating cell with the matrix as these cells intervene during atherosclerosis and in host defence.

[Epigenetic post-transcriptional mechanisms for regulating physiological functions, and their decline during aging]. / Mécanismes épigénétiques post-transcriptionnels des regulations des fonctions physiologiques et de leur déclin au cours du vieillissement.

Sequencing of genomes did not reveal the "secret of life" and left biologists and philosophers unsatisfied. It became clear that post-genetic, epigenetic (taken in a wide sense, post-translational) events play an important role even during development and adult homeostasis. Such mechanisms become predominant during aging, and explain the differential decline of functions (aging in "spare-parts"). Some of these post-translational mechanisms, leading to auto-amplifying vicious circles, will be described.

The age-dependent vasodilatation and endothelial calcium influx induced by elastin peptides are modulated by extracellular glucose level.

Elastin peptides have been shown to produce many biological effects on various cell types, including an endothelium- and NO-dependent vasodilatation mediated by extracellular calcium influx and intracellular calcium elevation. Under normal concentration of extracellular glucose, the vasodilatory effect is observed in adult rats and is lost with age. Here, we have studied the consequences of extracellular glucose level changes on these effects triggered by elastin peptides (10(-4)-10(-3) mg ml(-1)), on 6- and 30-month-old rats, using the tension myography and the patch-clamp techniques. Our results show that low (0 mM) or high (33 mM) extracellular glucose concentrations abolish the extracellular calcium influx induced, under normal glucose level (11 mM), by the elastin peptides in cultured human endothelial cells. Also, low or high glucose abolish the vasodilatory action of elastin peptides observed on aorta rings from adult rats under normal glucose concentration. On the contrary, a dilation of aged rat aorta is observed in the presence of elastin peptides and high glucose, whereas such dilation is not observed when the elastin peptides are added in the presence of normal glucose concentration. In aging, a restoration by high glucose of the NO-dependent vasodilatation induced by elastin peptides could enhance the production of damaging peroxynitrite, potentially altering the structure and function of the blood vessels. These results could be of importance in the evaluation and treatment of aged patients with pathophysiological dysregulations of the circulating glucose level, such as in diabetes, age-related glucose intolerance, or low glucose levels caused by inappropriate glucose control treatments.