Production of 8-nitro-cGMP in osteocytic cells and its upregulation by parathyroid hormone and prostaglandin E2
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Osteocytes regulate bone remodeling, especially in response to mechanical loading and unloading of bone, with nitric oxide reported to play an important role in that process. In the present study, we found that 8-nitroguanosine 3′,5′-cyclic monophosphate (8-nitro-cGMP), a second messenger of nitric oxide in various types of cells, was produced by osteocytes in bone tissue as well as cultured osteocytic Ocy454 cells. The amount of 8-nitro-cGMP in Ocy454 cells increased during incubation with parathyroid hormone or prostaglandin E2, both of which are known to upregulate receptor activator of nuclear factor-κB ligand (RANKL) mRNA expression in osteocytes. On the other hand, exogenous 8-nitro-cGMP did not have effects on either the presence or absence of these bioactive substances. Furthermore, neither an inhibitor of nitric oxide synthase nor 8-bromo-cGMP, a cell-permeable analog of cGMP, showed remarkable effects on mRNA expression of sclerostin or RANKL. These results indicate that neither nitric oxide nor its downstream compounds, including 8-nitro-cGMP, alone are sufficient for induction of functional changes in osteocytes.
KeywordsOsteocytes Nitric oxide 8-Nitro-cGMP Parathyroid hormone
Ocy454 cells were generously provided by Dr. Paola Divieti Pajevic, Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, MA, USA.
This study was supported by grants from JSPS KAKENHI (15H05016, 15K11053) and the MEXT-Supported Program for the Strategic Research Foundation at Private Universities (S1411009), as well as by the Private University Research Branding Project from MEXT of Japan.
Compliance with ethical standards
All animal experiments were performed according to a protocol approved by the ethical board for animal experiments of Showa University (approval number 17055), in accordance with Japanese Governmental Law (No. 10069) for the care and use of laboratory animals.
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