To investigate the effects of insulin-like growth factor 1 receptor (IGF1R) on proliferation and extracellular matrix synthesis in rat chondrocytes under cyclic mechanical stress.

The rat chondrocytes were isolated and cultured in vitro. They were randomly divided into four groups: 0 h stress group, 0.5 h stress group, 1 h stress group, and 2 h stress group; each group were treated by cyclic mechanical stretch stress treated for 0 h, 0.5 h, 1 h and 2 h respectively. Western Blot analysis was performed for IGF1R and phospho-IGF1R levels and chose an array of non-pressure cells as control of each group. The Gel-Pro Analyzer software was used for semi-quantitative analysis of gray value to compare the differences of phospho-IGF1R/total IGF1R between non-pressure and pressure groups in each time periods. The blank group and cyclic mechanical stretch treated cells were separately divided into control group and IGF1R-suppressor group which treated with Linsitinib or IGF1R shRNA. The expression of extracellular regulated protein kinases (ERK)1/2 and phospho-ERK1/2 were determined by Western blot 1 h later. After 8 h, collagen Ⅱ and aggrecan levels were analyzed by qPCR. Three days later, cell counting or CCK-8 assays were performed to examine the cell proliferation of each group.SPSS 18.0 software was used for statistical analysis, and student’s t test was used to compare the differences between the two groups.

In 0 h stress groups, the phospho-IGF1R levels had no difference(t=0.255, P=0.811). The levels of phospho-IGF1R were significantly increased in the cyclic mechanical stretch treated groups(t=-5.881, -6.172 , -10.518, all P<0.05). The inhibitors of IGF1R obviously decreased the phospho-ERK1/2 expression(OSI-906 suppressor group t=3.074, IGF1R shRNA suppressor group t=3.990, all P<0.05). The mRNA levels of collagen Ⅱ(OSI-906 suppressor group t=3.243, IGF1R shRNA suppressor group t=3.621, both P <0.05) and aggrecan (OSI-906 suppressor group t=3.128, IGF1R shRNA suppressor group t=3.608, both P <0.05)significantly reduced thus extracellular matrix synthesis was blocked because of IGF1R suppressors.The IGF1R inhibitors significantly contributed to the attenuation of cyclic mechanical stretch treated cells proliferation(OSI-906 suppressor group t=2.835, IGF1R shRNA suppressor group: t=3.467, all P <0.05).

Cyclic mechanical stretch converts mechanical signals into biochemical signals through the pressure receptor IGF1R and activates the ERK1/2 signaling pathway to promote chondrocyte proliferation and extracellular matrix synthesis.