Osthole alleviates neuropathic pain by suppressing astrocytes activation and associated inflammatory responses via the PKCδ/TRPV4 signaling pathway

Activation of transient receptor potential vanilloid 4 (TRPV4) in astrocytes is crucial in the occurrence of neuropathic pain (NP). Osthole, a natural herbal component with anti-inflammatory and analgesic effects, can reduce intracellular calcium levels; however, its underlying mechanism remains incompletely understood. Protein kinase C-delta (PKCδ), a serine/threonine protein kinase, regulates calcium levels within the blood-brain barrier (BBB) through its interaction with TRPV4. Astrocytes are integral components of the BBB and play an important role in neuroinflammatory responses. Here, we investigated whether PKCδ is involved in the pharmacological inhibition of NP by osthole. Chronic compression of the dorsal root ganglion (CCD) in rats was used to construct NP animal models. Astrocytes were stimulated using lipopolysaccharide (LPS) to induce NP in vitro. Following CCD surgery, we found that PKCδ protein and its phosphorylated form were upregulated and astrocytes were activated. LPS upregulated intracellular calcium concentration and activated astrocytes, while the PKCδ inhibitors, siRNA of PKCδ, or osthole blocked this effect. In addition, PKCδ-induced astrocyte activation appears to be mediated through its interaction with TRPV4. Overexpression of PKCδ in astrocytes leads to upregulation of TRPV4 expression, increased intracellular calcium levels, and enhanced inflammatory responses-effects that can be reversed by TRPV4 inhibition. There was a positive feedback activation mechanism between PKCδ and TRPV4 during the development of NP. Finally, CCD surgery-induced NP and the associated inflammatory response were significantly alleviated by PKCδ inhibitors, TRPV4 inhibitors, and osthole. Collectively, these findings suggest that astrocyte activation in NP involves the upregulation of pathophysiological processes along the PKCδ/TRPV4/calcium signaling axis. Osthole exerts its potent analgesic effect by effectively inhibiting this pathway.

Astrocyte; Inflammation; Neuropathic pain; Osthole; Protein kinase C-delta; Transient receptor potential vanilloid 4.