M2 macrophage-conditioned medium inhibits intervertebral disc degeneration in a tumor necrosis factor-α-rich environment

Inflammation is the primary pathological phenomenon associated with disc degeneration; the inflammatory cytokine tumor necrosis factor (TNF-alpha) plays a crucial role in this pathology. The anti-inflammatory and regenerative effects of M2 macrophages on nucleus pulposus cells (NPCs) in intervertebral disc degeneration (IDD) progression remain unknown. Here, M2 conditioned medium (M2CM) was harvested and purified from human acute monocytic leukaemia cell line (THP-1) cells and mouse peritoneal macrophages, respectively; it was used for culturing human NPCs and a mouse intervertebral disc (IVD) organ culture model. NPCs and IVD organ models were divided into three groups: group 1 treated with 10% fetal bovine serum (control); group 2 treated with 10 ng/ml TNF-alpha; and group 3 treated with 10 ng/ml TNF-alpha and M2CM (coculture group). After 2-14 days, cell proliferation, extracellular matrix synthesis, apoptosis, and NPC senescence were assessed. Cell proliferation was reduced in TNF-alpha-treated NPCs and inhibited in the M2CM co-culture treatment. Moreover, TNF-alpha treatment enhanced apoptosis, senescence, and expression of inflammatory factor-related genes, including interleukin-6, MMP-13, ADAMTS-4, and ADAMTS-5, whereas M2CM coculture significantly reversed these effects. In addition, co-culture with M2CM promoted aggrecan and collagen II synthesis, but reduced collagen I alpha 1 levels in TNF-alpha treatment groups. Using our established three-dimensional murine IVD organ culture model, we show that M2CM suppressed the inhibitory effect of TNF-alpha-rich environment. Therefore, co-culture with M2CM promotes cell proliferation and extracellular matrix synthesis and inhibits inflammation, apoptosis, and NPC senescence. This study highlights the therapeutic potential of M2CM for IDD.

Automated summary

This study reveals the therapeutic potential of M2 conditioned medium (M2CM) for intervertebral disc degeneration (IDD). M2CM from macrophages has anti-inflammatory and regenerative effects on nucleus pulposus cells (NPCs), promoting cell proliferation and extracellular matrix synthesis while inhibiting inflammation and apoptosis. These findings highlight the importance of M2CM in IDD treatment.