Epidermal growth factor receptor signalling mediates growth hormone-induced growth of chondrocytes from sex hormone-inhibited adolescent rats

Summary 1. Growth hormone (GH) has been demonstrated to overcome the inappropriate deceleration of growth rate in children with central precocious puberty treated with gonadotropin‐releasing hormone analogue (GnRHa). However, the underlying mechanisms remain largely unclear. In the present study, we investigated the potential involvement of the epidermal growth factor receptor (EGFR) pathway in the growth promotion by GH using in vitro cultured growth plate chondrocytes isolated from adolescent rats treated with GnRHa. 2. Chondrocytes were stimulated with GH in the presence or absence of the Janus tyrosine kinase (JAK) 2 inhibitor AG490 (1, 10 and 100 nmol/L), the EGFR kinase inhibitor AG1478 (0.1, 1 and 10 nmol/L), U0126 (an inhibitor of extracellular signal‐regulated kinase (Erk) activation; 10 μmol/L) or a neutralizing antibody against epidermal growth factor (EGF Ab; 0.1, 1 and 10 μg/mL). The proliferation of chondrocytes was assessed by the 3‐(4,5‐dimethyl‐2 thiazoyl)‐2,5‐diphenyl‐2H‐tetrazolium bromide assay and immunostaining for proliferating cell nuclear antigen (PCNA). Phosphorylation of Erk1/2 and EGFR was detected by western‐blotting. Intracellular mRNA and extracellular protein levels of EGF were detected using reverse transcription–polymerase chain reaction and ELISA, respectively. 3. Growth hormone promoted the proliferation of chondrocytes, which was correlated with increased phosphorylation of Erk1/2 and EGFR and enhanced expression of EGF. Pretreatment with AG490, AG1478, U0126 or EGF Ab completely or partially inhibited the proliferation of chondrocytes and activation of Erk1/2 and EGFR. Pretreatment with AG490, AG1478, or U0126 partially inhibited the expression of EGF. 4. The findings indicate that GH promotes chondrocyte proliferation by activating EGFR signalling.