Effect of low expression of PTHrp receptor on proliferation of tibial growth plate chondrocytes in chronic renal insufficiency young rats

Abstract

Objective: To observe the effect of parathyroid hormone-related protein (PTHrp) receptor on the proliferation of tibial growth plate chondrocytes in chronic renal insufficiency (CRI) young rats. Methods: Two-week-old male SD rats were randomly divided into two groups: (1) Sham group (n=6), only left ureter was exposed; (2) CRI group(n=6), left ureter was ligated to induce chronic renal insufficiency. Rats were sacrificed 2 weeks after operation and the blood concentration of PTHrp was detected by intracardiac blood sampling. Chondrocytes isolated from growth plate in two groups were cultured in vitro to P3 generation. The level of PTHrp receptor in chondrocytes was observed by immunohistochemistry and quantitative analysis was completed by Western blot. The proliferation rate of chondrocytes from two groups at 24 h was detected by using 5-ethynyl-2'-deoxyuridine (EDU) technique. Three types of PTHrp receptor mRNA plasmids (overexpressed, empty vector and knockdown) were used to treat the chondrocytes from CRI group. The mRNA and protein levels of PTHrp receptor were detected after 24 h and 48 h intervention, respectively. The chondrocyte proliferation rate at 24 h was detected by EDU. Results: Blood concentration of PTHrp in CRI group was higher than that in Sham group [(1.36±0.42) ng/L vs (0.77±0.21) ng/L, t=3.913, P=0.001]. The results of Western blot showed that the level of PTHrp receptor in growth plate chondrocytes from CRI group decreased (0.15±0.07 vs 0.41±0.13, t=5.569, P<0.001). Chondrocyte proliferation rate of CRI group was lower than that in Sham group at 24 h [(11.3±3.1)% vs (24.6±5.7)%, t=6.482, P<0.001]. The mRNA and protein levels of PTHrp receptor increased in chondrocytes of CRI group after intervention with overexpressed plasmid. The chondrocyte proliferation rate increased at 24 h. On the contrary, the mRNA and protein levels of PTHrp receptor decreased afer intervention with knockdown plasmid, and the chondrocyte proliferation rate also decreased [overexpression: (22.8±6.5)%, empty carrier: (10.2±4.3)%, knockdown: (5.6±2.1)%, F=29.840, P<0.001]. Conclusion: Increased PTHrp concentration in the blood of CRI young rats leads to decreased PTHrp receptors in growth plate chondrocytes, which results in decreasing PTHrp activity and proliferation rate of chondrocyte.