Vitamin D ameliorates the inflammation, oxidative stress and mitophagy to enhance the protective effects of MSCs on the pancreatic injury

Abstract

Recently, mesenchymal stem cells (MSCs) therapy has emerged as a revolutionary breakthrough in the treatment of T1DM. Nevertheless, its therapeutic efficacy is controversial due to the influence of diverse micro-environment including vitamin D (VD) deficiency. Moreover, it still remains unclear whether VD intervention could enhance the protective effects of MSCs via related pathways. Herein, the purpose of our study was to evaluate the roles of VD in augmenting the protective effects of MSCs on the pancreatic injury by affecting the inflammation, oxidative stress and mitophagy through both in vivo and in vitro experiments. Three-week-old male C57BL/6J mice were respectively fed with different VD diets for 3 weeks. Subsequently, a T1DM mouse model was established through intraperitoneal injection of streptozotocin (STZ) and then treated with MSCs via the tail vein. Then, their metabolic parameters, pancreatic histology, and indicators of oxidative stress and inflammation, as well as mRNA and protein expressions of related genes were analyzed in the serum, pancreatic and/or spleen tissues. Moreover, the roles of VD on the inflammation, oxidative stress, apoptosis, cellular and mitochondrial reactive oxygen species (ROS), and mitophagy were explored using the mouse islet β-cells (MIN-6) in vitro, which was then accurately verified by inhibiting the mitophagy as the Chloroquine (CQ). Herein, among the STZ-induced T1DM mice, VD interventions could effectively enhance the protective effects of MSCs on the insulin secretion and glucose metabolism in the VD+MSCs+T1DM group, as was evidenced by a significantly improved pancreatic β-cell structure, lower concentrations of serum glucose and higher glucose reserve capacity ( P < 0.05). Simultaneously, it could alleviate the pancreatic injury, as manifested by higher expressions of Bcl-2/Bax and lower levels of Caspase 3 than those in the T1DM, VD+T1DM and/or MSCs+T1DM groups ( P < 0.05). Moreover, comparing with the aforementioned three groups, VD+MSCs+T1DM group exhibited lower expressions of TNF-α , Foxp3 , IL17A , cd68 , Mcp1 and higher levels of Beclin-1 , Pink1 , Parkin in the pancreatic tissues, as well as higher contents of serum GSH, CAT, SOD and lower MDA ( P < 0.05). Furthermore, comparing with the HG, VD + HG and/or MSCs + HG groups in vitro, VD + HG+MSCs interventions could ameliorate the percents of HG-induced cellular apoptosis, with lower expressions of Bax , Caspase 3 and TOMM20, and higher levels of genes related to VD metabolism such as CYP27A1 , CYP24A1 and VDR ( P < 0.05). Meanwhile, it could also reduce the contents of cellular and mitochondrial ROS with higher contents of SOD, CAT, GSH, GSH/GSSG and lower levels of MDA ( P < 0.05). It was accompanied by the enhanced mitophagy, as indicated by higher expressions of Pink1 and Parkin , which could be partly diminished by inhibiting the mitophagy with CQ ( P < 0.05). In sum, appropriate VD intervention both in vivo and vitro could ameliorate the inflammation, oxidative stress and mitophagy to enhance the protective effects of MSCs, suggesting that the clinicians ought to meticulously monitor the VD concentrations among the T1DM patients prior to contemplating the utilization of MSCs as a potential therapeutic approach in the future.