A possible role for hypoxia-induced apelin expression in enteric cell proliferation

Intestinal inflammation and hypoxia are closely related stressors that affect the gastrointestinal tract. It is known that hypoxia-inducible factors (HIFs) regulate gene expression in low-oxygen environments. Apelin, a peptide that binds to the APJ receptor, is present in the GI tract. However, the role of apelin in hypoxia-induced changes remains unclear. This gap motivated researchers to explore how hypoxia influences apelin and APJ expression. Prior research has shown that apelin levels increase during inflammation. No prior work had resolved whether apelin contributes to epithelial cell proliferation under hypoxic conditions. This uncertainty drove the current investigation into apelin's potential role in cellular responses to hypoxia. Understanding this mechanism could provide insight into GI tract adaptation to stress.

The aim of this study was to determine how hypoxia affects apelin and APJ expression in the gastrointestinal tract. Researchers wanted to assess whether apelin influences epithelial cell proliferation under hypoxic conditions. They focused on rat pups to model acute hypoxia and its effects. The study also sought to identify if HIF regulates apelin transcription. By examining mRNA levels in different GI regions, they aimed to clarify apelin's role in cellular responses. They tested apelin treatment during hypoxia to see if it alters proliferation rates. The researchers also evaluated whether apelin's effects depend on the presence of hypoxia. Their goal was to provide evidence for apelin's involvement in epithelial cell adaptation to hypoxia.

The researchers exposed rat pups to acute hypoxia and measured apelin and APJ mRNA levels in the liver, stomach-duodenum, and colon. They also tested apelin treatment during hypoxia to observe its effects on APJ expression. In vitro experiments were conducted to confirm the hypoxia-induced changes in apelin and APJ. They used promoter analysis to determine if HIF regulates apelin transcription. Epithelial cell proliferation was assessed in hypoxic and normoxic conditions. Apelin treatment was applied during hypoxia to evaluate its impact on cell growth. The study compared proliferation rates between hypoxia-only and hypoxia-plus-apelin groups. They also evaluated whether apelin alone, without hypoxia, affects cell proliferation.

Exposure to acute hypoxia increased apelin mRNA levels in the liver, stomach-duodenum, and colon by 10-, 2-, and 2-fold, respectively. Hypoxia also elevated APJ mRNA levels in the colon. Apelin treatment during hypoxia further increased APJ mRNA expression. In vitro hypoxia similarly raised apelin and APJ mRNA levels. The hypoxia-induced apelin expression was linked to HIF activity. HIF binding to the apelin promoter was necessary for this effect. Acute hypoxia reduced gastric and colonic epithelial cell proliferation. However, apelin treatment during hypoxia increased proliferation by 50%.

The study suggests that hypoxia increases apelin and APJ expression in the gastrointestinal tract. This increase appears to be mediated by HIF binding to the apelin promoter. Apelin treatment during hypoxia enhances APJ expression further. The researchers propose that apelin may help counteract the negative effects of hypoxia on epithelial cell proliferation. Apelin treatment alone, without hypoxia, did not affect proliferation. These findings imply that apelin functions in part to stimulate cell growth under hypoxic conditions. The authors suggest that apelin's role in the GI tract may be to support tissue adaptation during stress. This study provides evidence for apelin's involvement in epithelial cell responses to hypoxia.