title: The role of cellular senescence on the cyclic stretching-mediated activation of MAPK and ALP expression and activity in human periodontal ligament fibroblasts.
abstract: Mechanical loading is considered to be a major parameter of the periodontal ligament (PDL) remodeling and differentiation. However, the molecular mechanisms that translate these forces to cellular responses are not fully elucidated. Especially, although aging affects PDL homeostasis, the role of cellular senescence on the activation of signaling pathways in periodontal ligament fibroblasts (PDLF) in response to mechanical stimulation has not been studied yet. Here, we present evidence showing that cyclic mechanical stimulation activates ERK, JNK and p38 MAPK in young (early-passage) human PDLF, in a RhoK-dependent manner. This response was found to be independent of the substratum (i.e. fibronectin or collagen) on which these cells grow. Stretching up-regulates also c-fos, a classical cellular response to mechanical deformation. Inhibition of ERK and JNK reduces, while that of p38 enhances stress-mediated c-fos expression. In addition, cyclic stretching stimulates the expression and activity of alkaline phosphatase (ALP), an early marker of osteoblastic differentiation. We have recently shown that senescent human PDLF have a significantly decreased expression of ALP, linked to an inability towards osteoblastic differentiation. Here, we found that senescent PDLF are able to respond to cyclic mechanical stretching by activating ERK, JNK and p38 MAPK, with similar kinetics compared to young cells, and by up-regulating c-fos and ALP expression and activity. However, even after stimulation, ALP levels in senescent cells are still much lower compared to the basal levels of their young counterparts, suggesting that senescence impairs the differentiation of human PDLF when subjected to cyclic mechanical deformation.
authors.affiliation: Laboratory of Cell Proliferation & Ageing, Institute of Biosciences & Applications, National Centre for Scientific Research "Demokritos", P. Grigoriou Str, Ag. Paraskevi, 15310 Athens, Greece; Department of Orthodontics, School of Dentistry, University of Athens, 2 Thivon Str, Goudi, 11527 Athens, Greece. Electronic address: dikons@gmail.com.
authors.forename: Dimitrios
authors.initials: D
authors.lastname: Konstantonis
authors.affiliation: Laboratory of Cell Proliferation & Ageing, Institute of Biosciences & Applications, National Centre for Scientific Research "Demokritos", P. Grigoriou Str, Ag. Paraskevi, 15310 Athens, Greece. Electronic address: adamadiapap@yahoo.com.
authors.forename: Adamantia
authors.initials: A
authors.lastname: Papadopoulou
authors.affiliation: Department of Orthodontics, School of Dentistry, University of Athens, 2 Thivon Str, Goudi, 11527 Athens, Greece. Electronic address: mmakou@dent.uoa.gr.
authors.forename: Margarita
authors.initials: M
authors.lastname: Makou
authors.affiliation: Department of Orthodontics and Paediatric Dentistry, University of Zurich, 11 Plattenstrasse Str, 8032 Zurich, Switzerland. Electronic address: theodore.eliades@zzmk.uzh.ch.
authors.forename: Theodore
authors.initials: T
authors.lastname: Eliades
authors.affiliation: Cellular and Molecular Biomechanics Unit, Department of Biological Chemistry, Medical School, University of Athens, 75M. Asias Str, Goudi, 11527 Athens, Greece. Electronic address: tegk.84@gmail.com.
authors.forename: Efthimia
authors.initials: E
authors.lastname: Basdra
authors.affiliation: Laboratory of Cell Proliferation & Ageing, Institute of Biosciences & Applications, National Centre for Scientific Research "Demokritos", P. Grigoriou Str, Ag. Paraskevi, 15310 Athens, Greece. Electronic address: dkletsas@bio.demokritos.gr.
authors.forename: Dimitris
authors.initials: D
authors.lastname: Kletsas
mesh_terms: D000469:Alkaline Phosphatase / Q000378:metabolism; D002454:Cell Differentiation; D002478:Cells, Cultured; D016922:Cellular Senescence; D005347:Fibroblasts / Q000502:physiology*; D006801:Humans; D020935:MAP Kinase Signaling System; D040542:Mechanotransduction, Cellular; D010006:Osteoblasts / Q000166:cytology / Q000378:metabolism; D010513:Periodontal Ligament / Q000166:cytology*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D014157:Transcription Factors; D000469:Alkaline Phosphatase
keywords: ALP; Cyclic mechanical stimulation; MAPK; Periodontal ligament fibroblasts; Senescence; c-fos