title: Role of the Parathyroid Hormone Type 1 Receptor (PTH1R) as a Mechanosensor in Osteocyte Survival.
abstract: Osteocytes have a major role in the control of bone remodeling. Mechanical stimulation decreases osteocyte apoptosis and promotes bone accrual, whereas skeletal unloading is deleterious in both respects. PTH1R ablation or overexpression in osteocytes in mice produces trabecular bone loss or increases bone mass, respectively. The latter effect was related to a decreased osteocyte apoptosis. Here, the putative role of PTH1R activation in osteocyte protection conferred by mechanical stimulation was assessed. Osteocytic MLO-Y4 cells were subjected to mechanical stimuli represented by hypotonic shock (216 mOsm/kg) or pulsatile fluid flow (8 Hz, 10 dynes/cm(2)) for a short pulse (10 min), with or without PTH1R antagonists or after transfection with specific PTHrP or PTH1R siRNA. These mechanical stimuli prevented cell death induced within 6 hours by etoposide (50 μM), related to PTHrP overexpression; and this effect was abolished by the calcium antagonist verapamil (1 μM), a phospholipase C (PLC) inhibitor (U73122; 10 μM), and a PKA activation inhibitor, Rp-cAMPS (25 μM), in these cells. Each mechanical stimulus also rapidly induced β-catenin stabilization and nuclear ERK translocation, which were inhibited by the PTH1R antagonist PTHrP(7-34) (1 μM), or PTH1R siRNA, and mimicked by PTHrP(1-36) (100 nM). Mechanical stretching by hypotonic shock did not affect cAMP production but rapidly (<1 min) stimulated Ca(i)(2+) transients in PTH1R-overexpressing HEK-293 cells and in MLO-Y4 cells, in which calcium signaling was unaffected by the presence of a PTHrP antiserum or PTHrP siRNA but inhibited by knocking down PTH1R. These novel findings indicate that PTH1R is an important component of mechanical signal transduction in osteocytic MLO-Y4 cells, and that PTH1R activation by PTHrP-independent and dependent mechanisms has a relevant role in the prosurvival action of mechanical stimulus in these cells.
authors.affiliation: Instituto de, Investigación Sanitaria (IIS)-, Fundación Jiménez Díaz, Universidad Autónoma de Madrid (UAM) and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad (RETICEF), Madrid, Spain.
authors.forename: Marta
authors.initials: M
authors.lastname: Maycas
authors.affiliation: Instituto de, Investigación Sanitaria (IIS)-, Fundación Jiménez Díaz, Universidad Autónoma de Madrid (UAM) and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad (RETICEF), Madrid, Spain.
authors.forename: Juan A
authors.initials: JA
authors.lastname: Ardura
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad San Pablo-CEU, Madrid, Spain.
authors.forename: Luis F
authors.initials: LF
authors.lastname: de Castro
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad San Pablo-CEU, Madrid, Spain.
authors.forename: Beatriz
authors.initials: B
authors.lastname: Bravo
authors.affiliation: Instituto de Medicina Molecular Aplicada (IMMA), Facultad de Medicina, Universidad San Pablo-CEU, Madrid, Spain.
authors.forename: Arancha R
authors.initials: AR
authors.lastname: Gortázar
authors.affiliation: Instituto de, Investigación Sanitaria (IIS)-, Fundación Jiménez Díaz, Universidad Autónoma de Madrid (UAM) and Red Temática de Investigación Cooperativa en Envejecimiento y Fragilidad (RETICEF), Madrid, Spain.
authors.forename: Pedro
authors.initials: P
authors.lastname: Esbrit
mesh_terms: D000818:Animals; D002118:Calcium / Q000378:metabolism; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D007038:Hypotonic Solutions / Q000494:pharmacology; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D051379:Mice; D008954:Models, Biological; D010011:Osteocytes / Q000166:cytology* / Q000187:drug effects / Q000378:metabolism*; D044162:Parathyroid Hormone-Related Protein / Q000494:pharmacology; D044168:Receptor, Parathyroid Hormone, Type 1 / Q000378:metabolism*; D051176:beta Catenin / Q000378:metabolism
chemical_list: D007038:Hypotonic Solutions; D044162:Parathyroid Hormone-Related Protein; D044168:Receptor, Parathyroid Hormone, Type 1; D051176:beta Catenin; D000242:Cyclic AMP; D048049:Extracellular Signal-Regulated MAP Kinases; D002118:Calcium
keywords: MECHANICAL STIMULUS; MLO-Y4 CELLS; OSTEOCYTE SURVIVAL; PTH TYPE 1 RECEPTOR; PTHRP