title: Pathological cyclic strain-induced apoptosis in human periodontal ligament cells through the RhoGDIα/caspase-3/PARP pathway.
abstract: OBJECTIVE
  Human periodontal ligament (PDL) cells incur changes in morphology and express proteins in response to cyclic strain. However, it is not clear whether cyclic strain, especially excessive cyclic strain, induces PDL cell apoptosis and if so, what mechanism(s) are responsible. The aim of the present study was to elucidate the molecular mechanisms by which pathological levels of cyclic strain induce human PDL cell apoptosis.
  
  
  METHODS
  Human PDL cells were obtained from healthy premolar tissue. After three to five passages in culture, the cells were subjected to 20% cyclic strain at a frequency of 0.1 Hz for 6 or 24 h using an FX-5000T system. Morphological changes of the cells were assessed by inverted phase-contrast microscopy, and apoptosis was detected by fluorescein isothiocyanate (FITC)-conjugated annexin V and propidium iodide staining followed by flow cytometry. Protein expression was evaluated by Western blot analysis.
  
  
  RESULTS
  The number of apoptotic human PDL cells increased in a time-dependent manner in response to pathological cyclic strain. The stretched cells were oriented parallel to each another with their long axes perpendicular to the strain force vector. Cleaved caspase-3 and poly-ADP-ribose polymerase (PARP) protein levels increased in response to pathological cyclic strain over time, while Rho GDP dissociation inhibitor alpha (RhoGDIα) decreased. Furthermore, knock-down of RhoGDIα by targeted siRNA transfection increased stretch-induced apoptosis and upregulated cleaved caspase-3 and PARP protein levels. Inhibition of caspase-3 prevented stretch-induced apoptosis, but did not change RhoGDIα protein levels.
  
  
  CONCLUSIONS
  The overall results suggest that pathological-level cyclic strain not only influenced morphology but also induced apoptosis in human PDL cells through the RhoGDIα/caspase-3/PARP pathway. Our findings provide novel insight into the mechanism of apoptosis induced by pathological cyclic strain in human PDL cells.
authors.affiliation: Department of Stomatology, First People's Hospital, Shanghai Jiao Tong University School of Medicine, Shanghai, China.
authors.forename: Li
authors.initials: L
authors.lastname: Wang
authors.forename: Jinsong
authors.initials: J
authors.lastname: Pan
authors.forename: Tingle
authors.initials: T
authors.lastname: Wang
authors.forename: Meng
authors.initials: M
authors.lastname: Song
authors.forename: Wantao
authors.initials: W
authors.lastname: Chen
mesh_terms: D000293:Adolescent; D017209:Apoptosis / Q000187:drug effects; D015153:Blotting, Western; D053148:Caspase 3 / Q000378:metabolism*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005434:Flow Cytometry; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D010513:Periodontal Ligament / Q000166:cytology* / Q000378:metabolism*; D011065:Poly(ADP-ribose) Polymerases / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha / Q000378:metabolism*
chemical_list: D004791:Enzyme Inhibitors; D062948:rho Guanine Nucleotide Dissociation Inhibitor alpha; D011065:Poly(ADP-ribose) Polymerases; D053148:Caspase 3