Agonist-Induced Activation of Transient Receptor Potential Vanilloid 4 Promotes Autophagy and Extracellular Matrix Synthesis in the Rat Intervertebral Disc.

Transient receptor potential vanilloid 4 (TRPV4), a mechanosensitive ion channel, has been implicated in intervertebral disc homeostasis; however, its role in autophagy regulation remains unclear. This study aimed to investigate whether agonist-induced TRPV4 activation promotes autophagy and extracellular matrix (ECM) synthesis in rat intervertebral discs. In vitro, rat nucleus pulposus (NP) cells were treated with the TRPV4 agonist (GSK1016790) under normal, serum-deprived, or interleukin-1β-stimulated conditions. Cell viability, intracellular Ca2+ influx, adenosine monophosphate-activated protein kinase/mammalian target of rapamycin (mTOR) (AMPK/mTOR) pathway, autophagy, ECM metabolism, apoptosis, and senescence were evaluated. In vivo, TRPV4 agonist was injected into the caudal discs subjected to temporary static compression, and disc changes were assessed by radiography, histomorphology, and immunofluorescence. In vitro, agonist-induced TRPV4 activation rapidly increased intracellular Ca2+ influx and enhanced AMPK phosphorylation. A noncytotoxic concentration of the TRPV4 agonist (10 nM) was selected after dose-response testing. Under the inflammatory stress, TRPV4 agonist enhanced autophagy, promoted ECM synthesis, and suppressed apoptosis and senescence, leading to improved NP cell viability. In vivo, TRPV4 agonist treatment preserved radiographic disc height (p<0.01), reduced histomorphological degeneration (p<0.01), and increased expression of COL2A1, Brachyury, p-AMPK (phosphorylated AMPK), and autophagy markers (p<0.01) compared with controls. These findings demonstrated that TRPV4 activation promotes autophagy and ECM synthesis via the AMPK/mTOR pathway in rat discs and attenuates stress-induced degeneration, suggesting TRPV4 as a potential therapeutic target for disc degeneration.