{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,4,29]],"date-time":"2026-04-29T20:15:23Z","timestamp":1777493723437,"version":"3.51.4"},"reference-count":39,"publisher":"Wiley","issue":"1","license":[{"start":{"date-parts":[[2020,5,30]],"date-time":"2020-05-30T00:00:00Z","timestamp":1590796800000},"content-version":"vor","delay-in-days":150,"URL":"http:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100004731","name":"Natural Science Foundation of Zhejiang Province","doi-asserted-by":"publisher","award":["LY19H060005"],"award-info":[{"award-number":["LY19H060005"]}],"id":[{"id":"10.13039\/501100004731","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100001809","name":"National Natural Science Foundation of China","doi-asserted-by":"publisher","award":["81501908"],"award-info":[{"award-number":["81501908"]}],"id":[{"id":"10.13039\/501100001809","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":["onlinelibrary.wiley.com"],"crossmark-restriction":true},"short-container-title":["BioMed Research International"],"published-print":{"date-parts":[[2020,1]]},"abstract":"<jats:p>Intervertebral disc (IVD) degeneration is associated with local inflammation and increased expression of neurotrophins. Acidic microenvironment is believed to cause the progression of IVD degeneration. However, there is a paucity of information regarding the relationship between acidic microenvironment and the inflammation and expression of neurotrophins in IVD. G\u2010protein\u2010coupled receptor 4 (GPR4) is a pH\u2010sensing receptor, which can activate the inflammation and increase the expression levels of nerve growth factor in acidic microenvironment. In this study, culture media with pH\u20097.2 (representing the normal IVD\u2010like acidic condition) and pH\u20096.5 (degenerated IVD\u2010like acidic condition) were prepared. The gene and protein expression levels of GPR4 in SD rat nucleus pulposus cells were determined under the acidic conditions. And cyclic AMP (cAMP), the second messenger of GPR4, was assayed. Furthermore, the expression levels of receptor activator of nuclear factor <jats:italic>\u03ba<\/jats:italic> B (RANK), RANKL ligand (RANKL), osteoprotegerin (OPG), nerve growth factor (NGF), brain\u2010derived neurotrophic factor (BDNF), and neurotrophin\u20103 (NT\u20103) were also determined. To clarify the involvement of GPR4 in the upregulation of the expression of RANK\/RANKL\/OPG system and neurotrophins, gene knockdown and forced expression of GPR4 and inhibiting its downstream cAMP accumulation and Ca<jats:sup>2+<\/jats:sup> mobilization were performed. The alternation of the expression levels of matrix metalloproteinase\u20103 (MMP\u20103), MMP\u201013, and aggrecanase\u20102 (ADAMTS\u20105) were evaluated by RT\u2010PCR and western blot. The results showed that GPR4 was expressed in rat nucleus pulposus cells, and the expression was upregulated under the degenerated IVD\u2010like acidic microenvironment. cAMP accumulation levels were increased under the degenerated IVD\u2010like acidic culture conditions. The expression levels of RANK, RANKL, OPG, NGF, and BNDF were significantly upregulated under the degenerated IVD\u2010like acidic microenvironment. GPR4 knockdown and reduction of cAMP by the inhibitor SQ22536 abolished the upregulation of the expression of RANK, RANKL, OPG, NGF, and BNDF under the degenerated IVD\u2010like acidic microenvironment. On the opposite, acidosis\u2010induced cAMP accumulation and upregulation of RANK, RANKL, OPG, NGF, and BNDF were further promoted by GPR4 overexpression. The expression levels of MMP\u20103, MMP\u201013, and ADAMTS\u20105 were upregulated under the degenerated IVD\u2010like acidic condition, which can be promoted or attenuated by GPR4 overexpression or knockdown, respectively. We concluded that GPR4\u2010mediated cAMP accumulation was involved in the increased expression of RANK\/RANKL\/OPG system and neurotrophins by nucleus pulposus cells under the degenerated IVD\u2010like acidic microenvironment.<\/jats:p>","DOI":"10.1155\/2020\/1328436","type":"journal-article","created":{"date-parts":[[2020,5,30]],"date-time":"2020-05-30T23:30:38Z","timestamp":1590881438000},"update-policy":"https:\/\/doi.org\/10.1002\/crossmark_policy","source":"Crossref","is-referenced-by-count":12,"title":["Involvement of the G\u2010Protein\u2010Coupled Receptor 4 in the Increased Expression of RANK\/RANKL\/OPG System and Neurotrophins by Nucleus Pulposus Cells under the Degenerated Intervertebral Disc\u2010Like Acidic 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