Inhibiting HSP90 attenuates nucleus pulposus fibrosis and pathological angiogenesis induced by macrophages via downregulating CEMIP.

Intervertebral disc (IVD) degeneration (IVDD) is usually accompanied by nucleus pulposus (NP) fibrosis and pathological angiogenesis, which are possibly associated with macrophage infiltration. Our previous researches revealed the destructive role of macrophages and the protective effects of inhibiting heat shock protein 90 (HSP90) in IVDD. Here, the effects of inhibiting HSP90 on NP fibrosis and pathological angiogenesis induced by macrophages are further investigated. Single-cell RNA sequencing analysis reveals the classification of fibrotic NP cell (NPC) clusters and healthy NPC clusters in human NP tissues, and fibrotic NPC clusters are possibly associated with angiogenesis-related biological processes. Immunostaining shows the spatial association between blood vessel ingrowth and macrophage infiltration, as well as elevated levels of cell migration inducing protein (CEMIP) and vascular endothelial growth factor A (VEGFA) in severely degenerated human IVD tissues. Particularly, HSP90 inhibitor 17-AAG ameliorates macrophage-induced fibrotic phenotype of NPCs via inhibiting CEMIP. M2 but not M1 macrophages promote the angiogenesis ability of endothelial cells (ECs), which is attenuated by 17-AAG or HSP90 siRNA. Reversing the fibrotic phenotype of NPCs by Cemip siRNA also mitigates the pro-angiogenesis effects of M2-CM-treated NPCs. Moreover, the murine IVDD model supports that 17-AAG ameliorates NP fibrosis and EC invasion in IVD tissues. In conclusion, inhibiting HSP90 attenuates two interrelated pathological processes, NP fibrosis and pathological angiogenesis induced by macrophages via downregulating CEMIP.