Effects Of Bone Marrow-derived Mesenchymal Stem Cells On Islet Graft β Cell Early Apoptosis And Its Mechanism

Aims:The success of syngeneic islet transplantation to treat diabetes has been hindered by massive β cell early apoptosis. This study aimed to observe the effects of bone marrow-derived mesenchymal stem cells (BMSCs) on islets graft β cell early apoptosis and to investigate the possible underlying mechanism.Methods:BMSCs were obtained by whole bone marrow adherent cultivation method from BALB/c neonatal mice. Islets were separated using collagenase digestion method from BALB/c mice. Diabetic models of BALB/c mice were established by streptozotocin intraperitoneal injection (140mg/Kg). Diabetic mice were randomly subdivided into four groups:(1) islets alone group:350islets were injected under the renal capsule (n=19);(2) BMSCs+islets co-transplantation groups:350islets and7x105BMSCs were injected under the renal capsule (n=19);(3) BMSCs transplantation group:7x105BMSCs were injected under the renal capsule (n=6);(4) control group:equal RMPI1640fluid were injected under the renal capsule (n=6). Random blood glucose concentrations were monitored every1to4days. Intraperitoneal glucose tolerance test (IPGTT) was performed at7,14,28days after transplantation to measure insulin concentration.βcell apoptosis was detected by TUNEL combined insulin fluorescent staining at1,3,7,28days after transplantation. Ultrastructures of βcell were observed by transmission electron microscope. The expressions of binding immunoglobulin heavy chain protein (BIP) and CCAAT/enhancer-binding protein homologous protein(CHOP), endoplasmic reticulum stress relevant indicators, were detected by immunofluorescence.Results:(1) Blood glucose levels in co-transplantation group were significantly lower than those in islet alone group, BMSCs transplantation group and control group.(p<0.01)(2) Area under curve of blood glucose during IPGTT in co-transplantation group was significantly lower than that in islet alone group, BMSCs transplantation group and control group at14,28day after transplantation (p<0.05). Insulin concentrations in co-transplantation group were significantly higher than those in islets alone group, BMSCs transplantation group and control group.(p<0.05)(3) Apoptosis rate of βcell of co-transplantation group was significantly lower than that in islet alone group at1,3,7days after transplantation (day1:7.06±3.10%vs.15.18±6.23%, p<0.05; day3:5.50±2.70%vs.12.40±4.24%, p<0.05; day7:4.11±1.96vs.8.63±1.88, p<0.05).There was no significant difference between two groups at the28th day after transplantation (2.38±0.47vs.2.39±1.63p>0.05)(4) There was swelling and deformation of endoplasmic reticulum in βcell of islets alone group. While in co-transplantation group, the severity of endoplasmic reticulum abnormalities was lessened.(5)BIP and CHOP fluorescence intensity of βcell in co-transplantation group was significantly lower than that in islets alone group at1,3,7days after transplantation (For BIP, day1:0.052±0.024vs.0.086±0.036,p<0.05; day3:0.039±0.011vs.0.094±0.026,p<0.05; day7:0.023±0.008vs.0.043±0.013, p<0.05. For CHOP, dayl:0.042±0.012vs.0.099±0.025P<0.05; day3:0.044±0.014v.s.0.110±0.020, P<0.05; day7:0.022±0.008vs.0.055±0.008, P<0.05)。There was no significant difference between two groups at28day after transplantation. (BIP:0.050±0.017vs.0.049±0.003, p>0.05; CHOP:0.021±0.006vs.0.031±0.013,p>0.05).Conclusions:BMSCs decrease early apoptosis of graft islet β cells by reducing its endoplasmic reticulum stress responses.