Expression of EPO and related factors in the liver and kidney of plain and Tibetan sheep.

Erythropoietin (EPO), hypoxia-inducible factor-1α (HIF-1α), hypoxia-inducible factor-2α (HIF-2α), and vascular endothelial growth factor (VEGF) are key factors in the regulation of hypoxia, and can transcriptionally activate multiple genes under hypoxic conditions, thereby initiating large hypoxic stress in the network. The liver and kidneys are important metabolic organs of the body. We assessed the expression of EPO, HIF-1α, HIF-2α, and VEGF in liver and kidney tissues of plain and Tibetan sheep using hematoxylin and eosin staining, immunohistochemistry, and RT-qPCR. The results showed that EPO, HIF-1α, HIF-2α, and VEGF were expressed in tubular epithelial cells, collecting duct epithelial cells, mural epithelial cells, and the glomerular cytoplasm of Tibetan sheep, and their expression was significantly higher in Tibetan sheep than in plain sheep (P<0.05). EPO, HIF-1α, HIF-2α, and VEGF are expressed in hepatocytes, interlobular venous endothelial cells, and interlobular bile duct epithelial cells. In plain sheep, positive signals for EPO, HIF-1α, HIF-2α, and VEGF were localized mainly in interlobular venous endothelial cells, whereas VEGF and HIF-2α were negatively expressed in interlobular bile duct epithelial cells and positively expressed in EPO and HIF-1α. The differences in EPO, HIF-1α, and HIF-2α in Tibetan sheep were significantly higher than those in plain sheep (P<0.001). In the liver and kidney tissues of Tibetan sheep, EPO was associated with HIF-1α, HIF-2α, and VEGF (P<0.05). RT-qPCR results showed that EPO was not expressed, and HIF-1α, HIF-2α, and VEGF were expressed (P<0.05). The results showed that the expression of EPO, HIF-1α, HIF-2α, and VEGF in the kidney and liver of Tibetan sheep was higher than that in of plain sheep. Therefore, EPO, HIF-1α, HIF-2α, and VEGF may be involved in the adaptive response of plateau animals, which provides theoretical clarity to further explore the adaptive mechanism of plateau hypoxia in Tibetan sheep.