关键词: 牦牛, 小肠, 低氧, 丙酮酸脱氢酶激酶1(PDK1), 缺氧诱导因子1α(HIF-1α), 血管内皮生长因子(VEGF)

Abstract:

【Objective】This study aimed to investigate the differential expression of hypoxia-related factors—Pyruvate dehydrogenase kinase 1 (PDK1), Hypoxia-inducible factor-1α (HIF-1α), Transforming growth factor-β (TGF-β), Vascular endothelial growth factor (VEGF), Mothers against decapentaplegic homolog 2 (Smad2), and Mothers against decapentaplegic homolog 3 (Smad3)—in the small intestinal tissues of yaks, to elucidate the intestinal adaptation mechanisms of yaks to hypoxic environments.【Method】Small intestinal tissues (duodenum, jejunum, and ileum) from plateau yaks and plain yellow cattle were selected as research subjects. Hematoxylin-eosin staining (H.E), periodic acid-Schiff staining (PAS), Masson’s trichrome staining, and immunohistochemical staining were performed. Tissue sections after staining were photographed under a light microscope. Image analysis software was used to measure villus height (V) and crypt depth (C) in H.E-stained sections, as well as the average optical density (AOD) of PAS, Masson, and immunohistochemical staining. The average optical density value was employed to represent positive expression results, thereby investigating the distribution characteristics and expression differences of hypoxia-related factors in different species and intestinal segments.【Result】H.E staining results indicated that the V/C ratio (villus height/crypt depth), an indicator of intestinal digestion, in both yaks and yellow cattle was significantly higher in the duodenum compared to the jejunum and ileum (P<0.05). Furthermore, the duodenal V/C ratio of yaks was significantly higher than that of yellow cattle (P<0.05). PAS staining showed that PAS-positive substances were expressed with significantly higher intensity in the duodenum than in the jejunum and ileum (P<0.05), with strong positive expression observed in the striated border, goblet cells, and Paneth cells. The expression in all intestinal segments of yaks was significantly higher than in yellow cattle (P<0.05). Masson's trichrome staining results revealed significant interspecies and segmental differences in collagen fiber content within the small intestinal tissues of both yaks and yellow cattle (P<0.05). Specifically, the proportion of collagen fibers in the duodenum and jejunum of yellow cattle was significantly higher than in the corresponding segments of yaks (P<0.05). Immunohistochemical analysis detected distinct positive brown-yellow expression of PDK1, HIF-1α, TGF-β, and VEGF in the small intestinal tissues, primarily localized to the striated border, Paneth cells, and goblet cells. Differences in intestinal gland expression were observed between species: weak positive expression was seen in the duodenal and jejunal glands of yellow cattle, while strong positive expression was observed in the corresponding locations in yaks. Tissue segment analysis showed that the expression levels of these factors were significantly higher in the duodenum than in the jejunum (P<0.05). Regarding species differences, the overall expression levels in yak small intestinal tissues were significantly higher than in yellow cattle (P<0.05). However, the expression patterns of Smad2 and Smad3 differed from those of the aforementioned factors. The expressions of Smad2 and Smad3 in the duodenum were significantly lower than those in the ileum and jejunum, respectively (P<0.05). Furthermore, the expression of Smad2/3 in the duodenum and ileum of yaks was significantly lower than in yellow cattle (P<0.05), while in the jejunum of yaks, it was significantly higher than in yellow cattle (P<0.05).【Conclusion】Results from H&E staining, special staining, and immunohistochemical staining revealed significant differences between yaks and yellow cattle in the morphological structure, carbohydrate distribution, and expression of hypoxia-related factors in the small intestine. These findings suggest that yak intestines possess unique structural and molecular adaptive features to hypoxia, and that factors such as PDK1, HIF-1α, and VEGF may play important roles in the intestinal hypoxic adaptation mechanisms of yaks. This study provides fundamental data for research on intestinal adaptation in high-altitude animals and offers a reference for exploring the mechanisms and prevention of hypoxia-related intestinal diseases.

Key words: yak, small intestine, hypoxia, pyruvate dehydrogenase kinase 1 (PDK1), hypoxia inducible factor 1α (HIF-1α), vascular endothelial growth factor (VEGF)