The role of cellular senescence in bone regeneration
Final Report Abstract
Our investigation into skeletal aging and age-related impairment of regeneration first focused on cellular senescence, a state, in which the cells completely stop dividing and change their behavior. We established a transposon-based system for inducing non-damage-induced cellular senescence in primary cells by mild overexpression of the cell growth inhibitors p16 and p21. In MSC the necessary experimental procedures led to unintended replicationinduced senescence and could therefore not be used. We therefore switched to fibroblasts and in cooperation with TP3 generated unique insights into the effects of different forms of senescence on extracellular matrix production, integrity, and matrix tensioning by these cells. We think that our results refine our view on cellular senescence in showing that a partial senescence without cellular damage might support wound healing. Furthermore, we contributed to a study that identified cellular “switches” that permit differentiation of MSC into chondrocytes. These findings might be used for regeneration-promoting interventions but require further investigations. We also studied the skeletal consequences of p16 and p21 deficiency. Impairing the senescence process in mice by deleting the Cdkn2a gene or removing Cdkn2a-expressing cells had no impact on fracture healing – at least in young adult animals. Mice deficient for p16 and p21 showed a mildly reduced trabecular bone density, which is in stark contrast to the increased growth of p16-deficient calvarial osteoblasts and suggests additional mechanisms controlling cell growth in vivo. We also searched for novel genetic factors influencing aging in humans. Analyzing several individuals with cataracts, absence of fat tissue, short stature and painful joint swellings we detected an identical change in the gene BUD13. Interestingly, fibroblasts from these individuals showed senescence and crumpled nuclei, which correlated with the severity of the disorder. BUD13 is the first gene involved in the splicing process that is associated with a premature aging syndrome. Cells with impaired BUD13 also had abnormal protein degradation in lysosomes. In two other families with aged-appearing children we detected novel genetic changes in the gene ATP6V1A. In addition to impaired protein degradation we also found evidence for abnormalities in the structure and function of the Golgi apparatus, a central organelle for the sorting, packaging, and modification of proteins and membranes within the cell. Although the initial work plan did not give the expected results we were able to generate relevant novel insights into the aging process and regeneration of connective tissues. Follow-up projects are planned to deepen our understanding and to use these insights for improving skeletal homeostasis and regeneration in aged individuals.
Publications
-
Expanding the clinical and molecular spectrum of ATP6V1A related metabolic cutis laxa. Journal of Inherited Metabolic Disease, 44(4), 972-986.
Vogt, Guido; El Choubassi, Naji; Herczegfalvi, Ágnes; Kölbel, Heike; Lekaj, Anja; Schara, Ulrike; Holtgrewe, Manuel; Krause, Sabine; Horvath, Rita; Schuelke, Markus; Hübner, Christoph; Mundlos, Stefan; Roos, Andreas; Lochmüller, Hanns; Karcagi, Veronika; Kornak, Uwe & Fischer‐Zirnsak, Björn
-
Alternative splicing of BUD13 determines the severity of a developmental disorder with lipodystrophy and progeroid features. Genetics in Medicine, 24(9), 1927-1940.
Kornak, Uwe; Saha, Namrata; Keren, Boris; Neumann, Alexander; Taylor Tavares, Ana Lisa; Piard, Juliette; Kopp, Johannes; Rodrigues Alves, João Guilherme; Rodríguez de los Santos, Miguel; El Choubassi, Naji; Ehmke, Nadja; Jäger, Marten; Spielmann, Malte; Pantel, Jean Tori; Lejeune, Elodie; Fauler, Beatrix; Mielke, Thorsten; Hecht, Jochen; Meierhofer, David; ... & Fischer-Zirnsak, Björn
-
The enhancer landscape predetermines the skeletal regeneration capacity of stromal cells. Science Translational Medicine, 15(688).
Hochmann, Sarah; Ou, Kristy; Poupardin, Rodolphe; Mittermeir, Michaela; Textor, Martin; Ali, Salaheddine; Wolf, Martin; Ellinghaus, Agnes; Jacobi, Dorit; Elmiger, Juri A. J.; Donsante, Samantha; Riminucci, Mara; Schäfer, Richard; Kornak, Uwe; Klein, Oliver; Schallmoser, Katharina; Schmidt-Bleek, Katharina; Duda, Georg N.; Polansky, Julia K.; ... & Strunk, Dirk
