To investigate the effects of active vitamin D₃ on the expression of vitamin D receptor(VDR)and angiotensin Ⅱ in the human proximal tubular epithelial cells HK-2 induced by high glucose.

Cultured HK-2 cells were divided into the following five groups: (1)control group (5.5 mmol/L glucose), (2)mannitol group (5.5 mmol/L glucose + 19.5 mmol/L mannitol), (3)high glucose group (25.0 mmol/L glucose), (4)high glucose + 1, 25-(OH)₂D₃ group (25.0 mmol/L glucose + 1, 25-(OH)₂D_3, for 1.0×10^-6, 1.0×10^-7, 1.0×10^-8 mol/L respectively), (5)high glucose + 1, 25-(OH)₂D₃+ siRNA VDR group(25.0 mmol/L glucose + 1, 25-(OH)₂D_3, 10^-6 mol/ L + siRNA VDR) . The expression of VDR mRNA and protein were detected by real-time quantitative PCR and western blot, respectively. Dual luciferase reporter gene assay was used to detect VDR gene transcription activity. Radioimmunoassay was used to examine the expression of angiotensin Ⅱ. Significance between different groups was compared by one-way analysis of variance. The q-test was used to evaluate the differences in means between groups. P<0.05 were considered to be statistically significant.

Compared with the control group, the mRNA, protein expression and gene transcription activity of VDR in the high glucose group were lower(1.34±0.22 vs 2.47±0.31, 0.51±0.06 vs 1.14±0.13, 0.51±0.21 vs 1.42±0.28, all P<0.05). The mRNA expression, protein expression and gene transcription activity of VDR were up-regulated by 1, 25-(OH)₂D₃ in a dose dependent manner in HK-2 cells induced by high glucose(1.96±0.31 vs 1.34±0.22, 0.93±0.08 vs 0.51±0.06, 1.12±0.23 vs 0.51±0.21, all P<0.05). Compared with the control group, high glucose significantly induced the expression of angiotensin Ⅱ in HK-2 cells((88±10) vs (17±2) ng/L, P<0.05). The expression of angiotensin Ⅱ was significantly down-regulated by 1, 25-(OH)₂D₃ in a dose dependent manner in HK-2 cells induced by high glucose((44±5) vs (88±10) ng/L, P<0.05), while the effect was abolished after silencing VDR by siRNA((87±12) vs (88±10) ng/L, P>0.05).

Angiotensin Ⅱ could be reversely regulated by 1, 25-(OH)₂D₃ in the human proximal tubular epithelial cells induced by high glucose via a VDR-mediated mechanism. The finding could be of particular value in the prevention of diabetic nephropathy.

Active vitamin D₃; High glucose; Tubular epithelial cells; Receptor; Angiotensin Ⅱ