RIPK1-targeted therapy alleviates intervertebral disc degeneration via inhibiting nucleus pulposus PANoptosis

Abstract

Intervertebral disc degeneration (IVDD) is a major contributor to lumbar diseases, including low back pain, herniation, and stenosis. Despite significant efforts, there have been limited improvements in treatments to alleviate IVDD. The nucleus pulposus (NP) is a crucial component of the intervertebral disc (IVD), responsible for secreting aggrecan, collagen II, and other extracellular matrix components. Programmed cell death (PCD) of NP cells is believed to play a central role in IVDD. RIPK1 is a key mediator of PCD and recently reported PANoptosis, playing essential role in kidney injury, arteriosclerosis, and acute or chronic inflammation-related diseases. We collected varied degenerated human IVD specimens to examine the expression of RIPK1 and downstream cell death-related markers, including GSDMD, Caspase3, and MLKL, which are indicative of pyroptosis, apoptosis, necroptosis, or the recently denominated PANoptosis. In vitro, we performed RIPK1 knockdown and overexpression to study their effects on IVDD. in vivo, we constructed RIPK1 conditional knockout (CKO) mice to confirm the role of RIPK1 in IVDD. We also utilized a small molecule targeted inhibitor to explore its effects on IVDD in vitro and in vivo. Phosphorylated RIPK1 (p-RIPK1) was significantly increased during IVDD in both human and mouse models. Knockout of RIPK1 effectively alleviated IVDD, as evidenced by the RIPK1 cko mice. Further pathological staining and western blot analysis revealed the overexpression of GSDMD, Caspase3, and MLKL, indicating that RIPK1-mediated PANoptosis plays a crucial role in IVDD. in vitro, overexpression of RIPK1 in NP cells exacerbated PANoptosis and degeneration, while RIPK1 knockdown inhibited these processes. We developed a RIPK1-targeted small molecular inhibitor, compound 3-47, which demonstrated superior efficacy in inhibiting p-RIPK1. Both in vitro and in vivo, 3-47 showed remarkable effects in alleviating IVDD by inhibiting RIPK1-mediated PANoptosis. RIPK1-mediated PANoptosis of NP cells plays a critical role in IVDD. The molecular inhibitor 3-47 could effectively delay IVDD progression in mice, highlighting its therapeutic potential.

Keywords: Intervertebral disc degeneration; Nucleus pulposus; PANoptosis; RIPK1; Small molecule inhibitor.