Co-treatments of vitamin D and mesenchymal stem cells effectively alleviate the diabetic kidney disease through attenuating the SIRT1-mediated pathways

Diabetic kidney disease (DKD) is still as a common chronic micro-vascular complication of type 1 diabetic (T1DM). Although many studies had verified the therapeutic potential of mesenchymal stem cells (MSCs) on the clinical treatment of the related complications associated with T1DM, especially the DKD, by preserving the balances of immune micro-environment and so on. However, the immunomodulatory capabilities of MSCs are still controversial on the the efficacy of DKD treatment primarily due to the variations on the immune micro-environment, which could be modulated by a variety of elements, such as the vitamin D (VD). Otherwise, its underlying molecular mechanisms have not yet been elucidated. Herein, the purpose of our study was to explore the synergistic effects of co-treatments with VD and MSCs in vivo and in vitro on the progression of DKD by attenuating the SIRT1-mediated pathways. Four-week-old male mice were fed with different VD diets for four weeks and established the T1DM models by administering the STZ (40 mg/kg) via intraperitoneal injection, which were then treated with BMSCs (bone MSCs) injection through the tail vein. After the euthanasia, the renal functions, pathological productors and VD metabolites were evaluated by the related biochemical indicators, flow cytometry analysis, staining techniques and immunofluorescence in the serum and/or renal tissues. Meanwhile, the mechanisms of SIRT1-mediated pathways underlying the amelioration of co-treatment with VD and MSCs on the renal injuries were examined by qRT-PCR, Western blotting and immunohistochemistry assays, which were then verified by the MPC5 cells in vitro with SIRT1-specific knockdown and over-expression under the treatment of high glucose (HG). Totally, co-treatments of VD and MSCs could more effectively ameliorate the disorders of glucose metabolism and renal injuries (KIM1, Podocin, ZEB1 and/or ZEB2) by boosting the concentrations of VD metabolites both in the STZ-induced T1DM mice models and MPC5 cells with HG treatment in vitro (P < 0.05). Moreover, the mechanism results indicated that co-treatments of VD and MSCs could improve the DKD such as the renal inflammation and fibrosis by attenuating the SIRT1 to inhibit the activation of TGFβ1/Smad pathways both in vivo and in vitro (P < 0.05). Furthermore, over-expression of SIRT1 could partly abolish the inflammation and fibrosis in vitro by attenuating the SIRT1-mediated TGFβ1/Smad3 pathways, which might be aggravated under the down-regulated expressions of SIRT1 in vitro (P < 0.05). Our findings had detailed the mechanisms underlying the amelioration of VD and MSCs related SIRT1-mediated pathways agonist on the DKD-like pathology both in vivo and in vitro, which could highlight the important potential of SIRT1 as a promising therapeutic target for the progression of DKD.