Effect of fibroblast growth factor 2 on degenerative endplate chondrocyte: From anabolism to catabolism

Endplate degeneration is characterized by an unbalance between the anabolism and catabolism of endplate chondrocyte (CH). Fibroblast growth factor 2 (FGF2) has been shown to promote cartilage repair by increasing articular CH anabolic activity. We aimed to explore the effect of FGF2 on the metabolism of endplate CH to elucidate whether FGF2 could be used as a therapy to delay the endplate degeneration.

We collected the endplate tissue from the patients and tested the collagen II mRNA level as the anabolic marker and the MMP-13 and TIMP-4 expression as the catabolic markers. The FGF2, FGF receptor 1 (FGFR1), and FGFR3 mRNA expression of the endplate tissue were also analyzed. Besides, we treated the CHs with exogenic FGF2 protein, measured the markers mentioned above, the proliferation and the apoptosis of the CHs. To compare the effect of FGF2 on the CHs with or without degeneration, we also induced CHs degeneration by interleukin-1β (IL-1β) stimulation and used the FGF2 protein to treat the degenerative CHs.

Severely degenerative endplate had a lower collagen II and TIMP-4 mRNA level, but it expressed a more massive amount of MMP-13, FGF2, and FGFR1. FGF2 supplement upregulated the FGFR1/FGFR3, TIMP-4, collagen II expression, and promoted the CHs proliferation. In the first 24 h of IL-1β treatment, the FGF2 mRNA expression was suppressed, but it significantly increased 48 h later. Meanwhile, the FGFR1 was upregulated, and FGFR3 was inhibited by IL-1β treatment. Interestingly, the FGF2 protein supplement accelerated the degenerative CHs catabolism by decreasing collagen II and TIPM-4 expression but increasing MMP-13. However, the FGF2 could promote the anabolism process in case of the blocking of FGFR1. The FGF2 supplement could also promote the proliferation and inhibited the apoptosis of degenerative CHs, which could be magnified by FGFR1 blocking.

The results demonstrate that FGF2 is upregulated in the highly degenerative endplate. The supplement of FGF2 contributes to the anabolism in the early phase of endplate degeneration. In the later stage of endplate degeneration, FGF2 turns to accelerate the catabolism, which can be rejected by the reasonable use of FGFR1 inhibitors.