The etiology of Condylar hyperplasia (CH) of human temporomandibular joint (TMJ) remains largely unknown. Our previous study has demonstrated that enriched insulin-like growth factor-1(IGF-1) was expressed in the proliferation and hypertrophic layers of CH cartilage. Accordingly, this study was aimed to investigate whether IGF-1 regulates CH chondrocytes proliferation in condylar cartilage overgrowth and explore the molecular mechanism of IGF-1 involved in.
Chondrocytes were isolated from 6 CH and 3 normal cartilage (NC) specimens and cultured in alginate beads or monolayer, treated with IGF-1 or specific inhibitors such as 7-[trans-3-[(azetidin-1-yl)methyl]cyclobutyl]-5-(3-benzyloxyphenyl)-7H-pyrrolo[2,3-d]pyrimidin-4-amine (NVP-AEW541), U0126, and LY294002. Thereafter, cellular proliferation capacity was evaluated by Cell Viability Analyzer (alginate beads culture) or 3-(4,5-dimethylthiazo(-2-yl)-2,5-diphenyltetrazolium bromide (MTT) (monolayer culture). Gene expression levels of IGF-1, IGF-1 receptor (IGF-1R), collagen type II, type X and those genes associated with proliferation were evaluated by realtime PCR. Protein levels of IGF-1 and IGF-1R synthesized by CH chondrocytes were accessed by enzyme-linked immunosorbent assay (ELISA) and western blotting.
CH chondrocytes enhanced cellular proliferation capacity and expressed significantly higher levels of messenger RNA (mRNA) and protein expressions of IGF-1 and IGF-1R, as compared with NC chondrocytes. Furthermore, enriched IGF-1 enhanced CH chondrocytes proliferation, up-regulated the expressions of specific genes associated with cellular proliferation and elevated the gene expression of collagen type II A1 (COL2A1). Besides, IGF-1-mediated CH chondrocytes proliferation mainly depended on the mitogen-activated protein kinase (MAPK)-ERK pathway.
IGF-1 promotes human TMJ cartilage overgrowth in the developing process of CH by enhancing chondrocytes proliferation via MAPK-ERK pathway.