S-palmitoylation regulates the function of the mitochondria-associated endoplasmic reticulum membrane to alleviate the senescence of nucleus pulposus cells

Abstract

Intervertebral disc degeneration (IVDD) is the primary cause of spinal degenerative diseases. Nucleus pulposus (NP) cell senescence is a significant pathological manifestation of IVDD. Here, we constructed a hypoxia-induced NP cell model to clarify the mechanisms by which S-palmitoylation is involved in NPC senescence. The IP3R S-palmitoylation of NP cells was significantly reduced under hypoxic conditions, contributing to abnormalities in mitochondria-associated membranes (MAMs). The study found that cellular expression of Bax, Bcl-2, Cleaved-Caspase8, Cleaved-Caspase3, MMP3, and MMP13 was promoted, while COL2 and AGG expression was inhibited. The up-regulated palmitoylation-modifying enzyme DHHC6 can promote IP3R S-palmitoylation modification and regulate GRP75, VDAC1, Drp1, and Mfn2 expression. It can inhibit apoptosis in NP cells, reduce intracellular calcium and ROS levels, elevate mitochondrial membrane potential, and reduce γ-H2AX expression levels. It also inhibited the protein expression levels of hypoxia-induced apoptosis molecules, matrix-degrading enzymes, and up-regulated extracellular matrix protein expression. These results suggested that hypoxia-induced IP3R depalmitoylation might play a role in structural and functional abnormalities in MAMs, which trigger senescence in NP cells.