MiR-330-5p inhibits intervertebral disk degeneration via targeting CILP

Mechanism of microRNA-124-3p targeting calpain-1 to affect the function of intervertebral disc nucleus pulposus cells

Intervertebral disc degeneration (IVDD) represents a major cause of lower back pain, whose prevalence rises with age. This study probed into the mechanism of microRNA (miR)-124-3p regulating function of nucleus pulposus cells (NPCs) by targeting calpain-1 (CAPN1). Rat IVD NPCs were cultured in vitro and transfected with miR-124-3p mimics, miR-124-3p inhibitor, oe-CAPN1 and their negative controls. The mRNA levels of miR-124-3p and CAPN1 were assessed by RT-qPCR. Cell proliferation, apoptosis and migration were evaluated by CCK-8, flow cytometry and Transwell assays. Levels of CAPN1 protein, apoptosis-related proteins (BAX, Cleaved-Caspase3, BCL-2) and extracellular matrix (ECM) proteins (Collagen II, Aggrecan, Fibronectin, Collagen I, matrix metalloproteinase [MMP]-13) were determined by Western blot. The target binding relationship between miR-124-3p and CAPN1 was verified by dual-luciferase assay. miR-124-3p overexpression facilitated NPC function and the maintenance of ECM homeostasis, as evidenced by increased NPC proliferation and migration, decreased apoptosis, elevated apoptosis-related protein BCL-2 level, diminished BAX and Cleaved-Caspase3 levels, reduced levels of ECM homeostasis-associated factors Collagen I and MMP-13 proteins, as well as raised levels of Collagen II, Aggrecan and Fibronectin proteins. Conversely, miR-124-3p knockdown brought about the opposite results. miR-124-3p targeted CAPN1. Furthermore, overexpression of CAPN1 partially reversed the regulatory effects of miR-124-3p on the ECM homeostasis, proliferation and migration in NPCs, and promoted apoptosis. miR-124-3p contributed to proliferation and migration of IVD NPCs, and reduced their apoptosis by inhibiting CAPN1 expression, thereby modulating ECM homeostasis and maintaining the function of IVD NPCs.

Current Perspectives on Nucleus Pulposus Fibrosis in Disc Degeneration and Repair

A growing body of evidence in humans and animal models indicates an association between intervertebral disc degeneration (IDD) and increased fibrotic elements in the nucleus pulposus (NP). These include enhanced matrix turnover along with the abnormal deposition of collagens and other fibrous matrices, the emergence of fibrosis effector cells, such as macrophages and active fibroblasts, and the upregulation of the fibroinflammatory factors TGF-β1 and IL-1/-13. Studies have suggested a role for NP cells in fibroblastic differentiation through the TGF-βR1-Smad2/3 pathway, inflammatory activation and mechanosensing machineries. Moreover, NP fibrosis is linked to abnormal MMP activity, consistent with the role of matrix proteases in regulating tissue fibrosis. MMP-2 and MMP-12 are the two main profibrogenic markers of myofibroblastic NP cells. This review revisits studies in the literature relevant to NP fibrosis in an attempt to stratify its biochemical features and the molecular identity of fibroblastic cells in the context of IDD. Given the role of fibrosis in tissue healing and diseases, the perspective may provide new insights into the pathomechanism of IDD and its management.