Repair mechanism of radiation‐induced salivary gland injury by hypoxia‐pretreated human urine‐derived stem cell exosomes

Objective To explore the protective effect of human urine‐derived stem cell exosomes (hUSC‐Exos) on radiation‐induced salivary gland (SG) injuries in Sprague Dawley rats. Methods Fresh adult urine was collected, and primary hUSCs were isolated and identified. The hUSCs were hypoxia‐pretreated with 1% oxygen for 24 h and then transferred to a normoxic culture environment for 24 h. The hUSC‐Exos were collected and identified for exosomes. A radiation‐induced injury model was established in the rats, and exosomes were introduced by local injection in the SG and tail vein. The submandibular gland was excised for morphological observation 1 week later. Immunohistochemical detection of the glandular tissue was conducted by α‐smooth muscle actin (a‐SMA), stem cell growth factor receptor (c‐Kit) staining, and periodic acid–Schiff staining. Qualitative polymerase chain reaction and western blot analysis were adopted to detect the gene and protein expression of Wnt3a, GSK3β, and Axin. Results In both the normoxic and hypoxic hUSC‐Exo groups, microvesicular structures with bilayer membranes of approximately 80 nm in diameter were detected, and the expressions of CD9 and CD63 were detected by nanoflow cytometry. Compared with the control group, in the radiation‐induced injury model group, the expression of a‐SMA was significantly higher, the expression of c‐Kit was significantly lower, and the expressions of Wnt3a, GSK3β, and Axin were significantly upregulated; the differences were statistically significant (p