In vitro and in vivo inhibition of mTOR by 1,25-dihydroxyvitamin D3 to improve early diabetic nephropathy via the DDIT4/TSC2/mTOR pathway

Abstract

We investigated whether 1,25-dihydroxy-vitamin D₃ (1,25(OH)₂D₃) could improve early diabetic nephropathy through the DNA-damage-inducible transcript 4/tuberous sclerosis 2/mammalian target of rapamycin pathway. Rat mesangial cells were cultured in media containing normal glucose or high glucose and were treated with or without 1,25(OH)₂D₃. Mesangial cells proliferation was measured. Streptozotocin-induced diabetic rats were injected intravenously with a recombinant lentivirus against the rat vitamin D receptor gene. Urinary and serum albumin, fasting plasma glucose, serum triglyceride, total cholesterol, calcium, parathyroid hormone and serum 25-dihydroxy-vitamin D (25(OH)D) levels, mean glomerular volume, glomerular basement membrane thickness and total kidney volume were determined. The expressions of vitamin D receptor, DNA-damage-inducible transcript 4, and mammalian target of rapamycin were measured. 1,25(OH)₂D₃ inhibited the proliferation of mesangial cells induced by hyperglycemia. 1,25(OH)₂D₃ also significantly reduced albumin excretion, mean glomerular volume, glomerular basement membrane, and total kidney volume in rats with diabetic nephropathy. The expression of DNA-damage-inducible transcript 4 was elevated by 1,25(OH)₂D₃ treatment. The phosphorylation of mammalian target of rapamycin was reduced by 1,25(OH)₂D₃ treatment. Vitamin D receptor gene silencing blocked all of the above results. The current study demonstrates that 1,25(OH)₂D₃ can effectively inhibit mesangial cells proliferation induced by hyperglycemia, thus suppressing the development of diabetic nephropathy. This study also shows that the nephron-protective effect of 1,25(OH)₂D₃ occurs partly through the DDIT4/TSC2/mTOR pathway.

Keywords: DDIT4; Diabetic nephropathy; Proliferation; Vitamin D; mTOR.