Fibroblast senescence

Abstract

The knowledge on molecular mechanisms of ageing of cells, tissues and organs, and the importance of the skin as a relevant model for organ and organismal ageing in general has increased tremendously. The symptoms and consequences of skin ageing are mainly, although not exclusively, because of changes within the dermis as the dermal connective tissue with the resident fibroblasts is distinctly responsible for the physicomechanical properties of the skin-like tensile strength, resilience and stability, and, importantly, for the coordinated function of the epidermis, melanocytes and skin appendages. To address mechanisms of human ageing, experiments based on genetic manipulation are not feasible and much of our knowledge on molecules and pathways involved in human ageing stems from cell culture-based model systems such as human diploid fibroblasts. Results from tissue and cell culture models helped to establish mechanisms resulting in cellular ageing and the candidacy of certain genes as mediators of the senescent phenotype, however, their role in human ageing of distinct organs in vivo is often elusive. Therefore, assessing the causal role of mechanisms identified in vitro under in vivo and in situ conditions of model organisms and tissues including human skin represent an ongoing major goal in ageing research. Schriner S E, Linford N J, Martin G M, Treuting P, Ogburn C E, Emond M, Coskun P E, Ladiges W, Wolf N, Van Remmen H, Wallace D C, Rabinovitch P S. Extension of murine life span by overexpression of catalase targeted to mitochondria. Science 2005: 308: 1909–1911. Important paper showing that localized overexpression of the hydrogen peroxide detoxifying enzyme catalase in the mitochondria – where hydrogen peroxide is mainly generated – resulted in an increase in lifespan of 20% and, concomitantly, in the reduction in age-related damage in transgenic mice in vivo. This observation adds to the increasing evidence that the oxidative stress theory of ageing postulated by Harman in the 60’s is relevant for organismal ageing processes. Herbig U, Ferreira M, Condel L, Carey D, Sedivy J M. Cellular senescence in aging primates. Science 2006: 311: 1257. Very important paper showing that cellular senescence is not an in vitro artefact. By using a panel of senescence biomarkers like gammaH2Ax, SA-betagal, and p16, the authors convincingly showed that senescent cells do exist in vivo and are increasing in numbers in ageing baboons up to 15% of all cells in very old animals. This paper adds evidence to the hypothesis that senescent cells contribute to organismal ageing. Bodnar A G, Ouellette M, Frolkis M, Holt S E, Chiu C P, Morin G B, Harley C B, Shay J W, Lichtsteiner S, Wright W E. Extension of life-span by introduction of telomerase into normal human cells. Science 1998: 279: 349–352. Groundbreaking paper revealing that the telomeres are the counting replicometer in fibroblasts cell culture in vitro by expressing the telomerase in non-telomerase active diploid fibroblasts. The expression of telomerase resulted in the immortalisation of the fibroblasts. Dimri G P, Lee X, Basile G, Acosta M, Scott G, Roskelley C, Medrano E E, Linskens M, Rubelj I, Pereira-Smith O, Peacocke M, Campisi J. A biomarker that identifies senescent human cells in culture and in aging skin in vivo. Proc Nat Acad Sci USA 1995: 92: 9363–9367. First description of senescence-associated beta-galactosidase as an ageing biomarker in vivo and in vitro. Although it is now clear that SA-beta-gal is not only regulated by ageing its description led to an intensive analysis of the senescence status in fibroblasts. Campisi J. Senescent cells, tumor suppression, and organismal aging: good citizens, bad neighbors. Cell 2005: 120: 513–522. In this review the concept of cellular senescence as a tumor-suppressor mechanism is discussed in the light of convincing data available today. Also the authors put forward further evidence for the evolutionary point of view that cellular senescence represents an antagonistically pleiotropic response with suppression of cancer development in early-life at the cost of reduced longevity which is because of the accumulation and negative effects of senescent cells in the body in late-life. d’Adda di Fagagna F, Reaper P M, Clay-Farrace L, Fiegler H, Carr P, Von Zglinicki T, Saretzki G, Carter N P, Jackson S P. A DNA damage checkpoint response in telomere-initiated senescence. Nature 2003: 426: 194–198. This paper relates the telomere attrition to the DNA-damage response thereby integrating the known involvement of the DNA-damage response via the tumor suppressor p53 with replicative senescence. Ressler S, Bartkova J, Niederegger H, Bartek J, Scharffetter-Kochanek K, Jansen-Dürr P, Wlaschek M. p16INK4a qualifies as a robust biomarker of cellular aging in human skin. Aging Cell 2006: 5: 379–390. This paper shows that the cyclin-dependent kinase inhibitor p16INK4a is a reliable cellular senescence biomarker for the detection of senescent cells in human skin in vivo. Chen Q, Ames B N. Senescence-like growth arrest induced by hydrogen peroxide in human diploid fibroblast F65 cells. Proc Natl acad Sci USA 1994: 91: 4130–4134. One of the first papers on stress-induced premature senescence showing that hydrogen peroxide is able to induce senescence in fibroblasts. This paper opened a new field of stress-induced premature senescence research with the characterization of many stimuli able to induce cellular senescence in culture like UVB, psoralen plus UVA, hyperoxia and others. Parrinello S, Samper E, Krtolica A, Goldstein J, Melov S, Campisi J. Oxygen sensitivity severely limits the replicative lifespan of murine fibroblasts. Nat Cell Biol 2003: 5: 741–747. In this paper, Judith Campisi and co-workers showed that the hyperoxic conditions used in cell culture at least in murine fibroblasts limit their lifespan. These data underline the point that increased oxidative stress occurs in cell culture because of the non-physiologic culture conditions further substantiating the role of oxidative stress in cellular ageing. Strassburger M, Bloch W, Sulyok S, Schueller J, Keist A F, Schmidt A, Wenk J, Peters T, Wlaschek M, Lenart J, Krieg T, Hafner M, Kümin A, Werner S, Müller W, Scharffetter-Kochanek K. Heterozygous deficiency of manganese superoxide dismutase results in severe lipid peroxidation and spontaneous apoptosis in murine myocard in vivo. Free Rad Biol Med 2005: 38: 1458–1470. The authors report that the heterozygous deficiency of the manganese superoxide dismutase representing the first antioxidant enzymatic defense in mitochondia, results in oxidative damage of the heart adding new evidence to the oxidative stress theory of ageing and the necessity of a balanced antioxidant defense. Ma W, Wlaschek M, Brenneisen P, Schneider L A, Hommel C, Hellweg C, Sauer H, Wartenberg M, Herrmann G, Meewes C, Boukamp P, Scharffetter-Kochanek K. Human dermal fibroblasts escape from the long-term phenocopy of senescence induced by psoralen photoactivation. Exp Cell Res 2002: 274: 299–309. In the psoralen plus UVA-irradiation induced premature senescence model of intrinsic fibroblast ageing, the authors show that after a long-term of growth cessation, the recurrence of the proliferative potential can be observed without immortalisation or transformation of the fibroblasts. This leads to the important question whether at least for stress-induced premature senescence a rejuvenation of the fibroblasts with hallmarks of intrinsic ageing to juvenile, mitotically active cells is possible and could be induced. Beauséjour C M, Krtolica A, Galimi F, Narita M, Lowe S W, Yaswen P, Campisi J. Reversal of human cellular senescence: roles of the p53 and p16 pathways. EMBO J 2003: 22: 4212–4222. Detailed and causal analysis of the role of p53 and p16 in cellular senescence revealing the molecular pathways of p53 and p16 as important barriers against unlimited growth. Hovest M G, Brüggenolte N, Hosseini K S, Krieg T, Herrmann G. Senescence of human fibroblasts after psoralen photoactivation is mediated by ATR kinase and persistent DNA damage foci at telomeres. Mol Biol Cell 2006: 17: 1758–1767. In the psoralen plus UVA-irradiation induced premature senescence model of intrinsic ageing, the authors substantiate the importance of the DNA-damage pathways in the induction of the premature senescence phenotype in fibroblasts. Briganti S, Wlaschek M, Hinrichs C, Bellei B, Flori E, Treiber N, Iben S, Picardo M, Scharffetter-Kochanek K. Small molecular antioxidants effectively protect from PUVA-induced oxidative stress responses underlying fibroblast senescence and photoaging. Free Radic Biol Med 2008: May 17 [Epub ahead of print]. Here the authors show that the plethora of oxidative stress responses in PUVA-treated premature senescent fibroblasts can be successfully addressed by different antioxidants. Notably, the rescue of senescence features by chemically distinct small molecule antioxidants clearly depends on the type of the oxidative damage and its location at distinct cellular compartments. Krtolica A, Parrinello S, Lockett S, Desprez P Y, Campisi J. Senescent fibroblasts promote epithelial cell growth and tumorigenesis: a link between cancer and aging. Proc Natl Acad Sci USA 2001: 98: 12072–12077. The authors describe a molecular mechanism by which ageing in case of senescent fibroblasts promotes the neoplastic transformation of preneoplastic epithelial cells and direct the focus on the important role of the microenvironment in ageing and carcinogenesis. Berneburg M, Grether-Beck S, Kürten V, Ruzicka T, Briviba K, Sies H, Krutmann J. Singlet oxygen mediates the UVA-induced generation of the photoaging associated mitochondrial common deletion. J Biol Chem 1999: 274: 15345–15349. These studies provide evidence for the involvement of reactive oxygen species in the generation of ageing-associated mitochondrial DNA lesions in human cells and indicate a previously unrecognized role of singlet oxygen in photoageing of human skin. In a later paper these authors provide evidence that these mitochondrial mutations represent long-term in vivo biomarkers for actinic damage in the human skin. Fisher G J, Varani J, Vorhees J J. Looking older: fibroblast collapse and therapeutic implications. Arch Dermatol 2008: 144: 666–672. This is a state of the art review on mechanisms underlying fibroblast ageing and what can be performed in terms of prevention and therapy. Wang Z, Boudjelal M, Kang S, Vorhees J J, Fisher G J. Ultraviolet irradiation of human skin causes functional vitamin A-deficiency, preventable by all-trans retinoic acid and pre-treatment. Nat Med 1999: 5: 418–422. The authors report that ultraviolet irradiation substantially reduced the mRNA and protein of the two major nuclear retinoid receptors in human skin in vivo. The resulting functional vitamin A-deficiency contributes to skin ageing and the unprotected upregulation of matrix-degrading metalloproteinases. Kligman L H. The hairless mouse model for photoaging. Clin Dermatol 1996: 14: 185–195. Lorraine Kligman has much contributed to develop a relevant hairless murine model to study both intrinsic as well as photoageing/extrinsic ageing. As in humans, with chronic ultraviolet irradiation these mice develop elastic fibre hyperplasia, followed by elastosis and ultrastructural degradation. Also the collagen metabolism is altered following chronic UVA- or UVB exposure. This model is suitable to study the protective effects of sunscreens, and the potential protective properties of pharma- and phytochemicals. Passos J F, Saretzki G, Ahmed S, Nelson G, Richter T, Peters H, Wappler I, Birket M J, Harold G, Schaeuble K, Birch-Mahin M A, Kirkwood T B, von Zglinicki T. Mitochondrial dysfunction accounts for the stochastic heterogeneity in telomere-dependent senescence. PLoS Biol 2007: 5: e110. The authors provide evidence for an intimate connection in the normal replicative senesence of human dermal fibroblasts between oxidative stress and telomere-dependent effects on cell proliferation. They suggest that mitochondrial dysfunction largely determines the age-related development of the extensive cell-to-cell variation in cell division potential. Li G Z, Eller M S, Firoozabadi R, Gilchrest B A. Evidence that exposure of the telomere 3′-overhang sequence induces senescence. Proc Natl Acad Sci USA 2003: 100: 527–531. The authors convincingly report that a 1-week exposure to oligonucleotide homologs to the 3′-overhang sequence TTAGGG (T-oligo) specifically induced a senescent phenotype in cultured human fibroblasts, mimicking serial passage. They propose that the treatment with T-oligos homologs to the 3′-overhang because of the telomere disruption occurring with critical telomere shortening triggers DNA-damage responses and a state reflecting or mimicking fibroblast senescence. Bernerd F, Asselineau D, Vioux C, Chevallier-Lagente O, Bouadjar B, Sarasin A, Magnaldo T. Clues to epidermal cancer proneness revealed by reconstruction of DNA in repair-deficient xeroderma pigmentosum skin in vitro. Proc Natl Acad Sci USA 2001: 98: 78117–78122. Xeroderma pigmentosum (XP) is a hereditary disease with severe deficiency in nucleotide excision repair. Individuals suffering from XP are prone to premature fibroblast ageing and skin cancer. The authors of this paper use a 3-dimensional skin equivalent. They convincingly demonstrate that XP fibroblasts, in contrast to fibroblasts of healthy volunteers, drive the invasiveness and proliferation of XP keratinocytes. The paper presents seminal work in the direction that fibroblasts senescence may drive epithelial transformation. Thanks to the help of Abbott, Chanel, Galderma International, Laboratoires Bailleul, Laboratoires Pierre Fabre, La Roche Posay Laboratoire Pharmaceutique, Leo Pharma, and L.V.M.H.