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

We investigated whether 1,25-dihydroxy-vitamin D (1,25(OH)D) 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)D. 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)D inhibited the proliferation of mesangial cells induced by hyperglycemia. 1,25(OH)D 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)D treatment. The phosphorylation of mammalian target of rapamycin was reduced by 1,25(OH)D treatment. Vitamin D receptor gene silencing blocked all of the above results. The current study demonstrates that 1,25(OH)D 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)D occurs partly through the DDIT4/TSC2/mTOR pathway.