To investigate the effect of human umbilical cord mesenchymal stem cells (hUC-MSC) on the apoptosis of retinal ganglion cells (RGCs) in diabetic retinopathy (DR) model rats and on the regulation of p38 mitogen-activated protein kinase (p38MAPK) pathway.

Forty-five SPF male 8-week old SD rats were selected.The DR rat model was established by intraperitoneal injection of streptozotocin (STZ) combined with a high-sugar and high-fat diet.The fasting blood glucose (FBG) and body weight of the rats were measured every week during the high-sugar and high-fat diet, and fundus angiography was used to observe the circulation and leakage of retinal blood vessels.Forty rats with successful modeling were randomly divided into model group and hUC-MSC injection group according to the random number table method, with 20 rats in each group.Another 20 normal rats fed routinely were served as control group, and intraperitoneally injected with the same amount of citric acid buffer.The hUC-MSC injection group was injected intravitreously with hUC-MSC, and the control group and model group were injected intravitreously with the same amount of phosphate buffer saline (PBS). Fluoro gold (FG) retrograde tracer labeling RGCs was used to observe the number of survived RGCs.Hematoxylin-eosin staining was used to observe the pathological changes of retina.TUNEL method was used to observe the apoptosis of RGCs.Western blot was used to detect B cell lymphoma /leukemia-2 (Bcl-2), Bcl-2 associated X protein (Bax), p38MAPK and phosphorylated (p-) p38MAPK protein expression in retinal tissues.The use and care of the rats complied with the ARVO statement.The study protocol was approved by an Animal Ethics Committee of Zhengzhou central Hospital Affiliated to Zhengzhou University (NO.2980316).

The FBG of control rats was maintained at a normal level, and the body weight gradually increased over time, and was gradually decreased as the course of disease prolonged.The retinal blood vessels ran normally without fluorescein leakage in the control group.In the modeling group, the FBG was maintained at a high level, and the body weight increased slowly and gradually decreased with the prolongation of the disease course since the second week after modeling.The distal retinal vessels were found twisted with large area of capillary fluorescein leakage in the modeling group.The density of RGCs in the control group, model group and hUC-MSC injection group were (2 136.10±215.17), (849.40±167.82), (1 549.20±183.26) cells/mm², with significant overall differences (F=115.218, P<0.01). The density of RGCs in the model group and the hUC-MSC injection group were significantly lower than that of the control group, and the density of RGCs in the hUC-MSC injection group was significantly higher than that of the model group, and the differences were statistically significant (all at P<0.05). The retina in the control group was with clear structure, distinct layers, and a large number of complete RGCs.The number of RGCs in the model group was significantly reduced with nuclear pyknosis, thinned and atrophied RGC layer.The retinal structure was relatively complete, and there were more RGCs in the hUC-MSC injection group than the model group.The apoptosis rates of RGCs in the control group, model group and hUC-MSC injection group were (2.16±1.11)%, (43.47±2.26)%, (20.75±2.18)%, with significant overall difference (F=445.159, P<0.01). The apoptosis rates of RGCs in the model group and hUC-MSC injection group were significantly higher than that of the control group, and the apoptosis rate of RGCs in the hUC-MSC injection group was lower than that of the model group, and the differences were statistically significant (all at P<0.05). There were statistically significant differences in the relative expression levels of Bax, Bcl-2 and p-p38MAPK proteins in the retina tissues among the three groups (F=30.982, 12.526, 73.158, all at P<0.01). The relative expression of Bax and p-p38MAPK protein were significantly higher, and the relative expression of Bcl-2 protein was significantly lower in the hUC-MSC injection group and the hUC-MSC injection group than those of the control group, and the differences were statistically significant (all at P<0.05). The relative expression of Bax and p-p38MAPK protein was significantly lower, and the relative expression of Bcl-2 protein was significantly higher in the hUC-MSC injection group than those in the model group, and the differences were statistically significant (all at P<0.05). There was no significant difference in the relative expression of p38MAPK protein among the three groups (F=1.182, P=0.322).

Intravitreal injection of hUC-MSC can inhibit the apoptosis of RGCs in DR model rats and protect the retinal structure of rats, which may play an anti-apoptotic effect by inhibiting the p38MAPK signaling pathway.

Diabetic retinopathy; Human umbilical cord derived mesenchymal stem cells; Retinal ganglion cells; Apoptosis