Hypoxia Could Induce Endoplasmic-Reticulum Stress by Regulating the Expression of β-Catenin Via Low-Density Lipoprotein Receptor-Related Protein 6 Pathway

Abstract

Background: Wnt/β-catenin was reported as an important pathway regulated by hypoxia, however, the exact mechnism has not been elucidated. Methods: Fecal 16S RNA sequencing and microarray were performed to selected the potential biomarks of LPR6 during the regulation of hypoxia on Wnt/β-catenin. Phosphorylated elF2α was detected for endoplasmic-reticulum stress. The ubiquitylation of β-catenin was determined by Immunoprecipitation. LRP6 was added to investigate the biological role on β-catenin. LRP6 intestinal knockout mice and LRP6 overexpression mice was established to verify the effects of LPR6 on tight junction proteins, endoplasmic-reticulum stress, and β-catenin expression. Two drugs curcumin and auranofin were used to explore the effects of LRP6 on the intestinal tight junction proteins. Findings: Inhibition of β-catenin and activation of ER stress induced by hypoxia. ER stress could decrease the expression of β-catenin through ubiquitylation via LRP6. Increased expression level of β-catenin, DKK1, and tight junction proteins, and decreased phosphorylated elF2α were found in LRP6 transgenic mice, while opposite results was found in the group of LRP6 intestinal knockout mice. Administration of curcumin and auranofin further verify the effects of LRP6 on the intestinal tight junction proteins. Interpretation: Hypoxia could induce endoplasmic-reticulum stress by regulating the expression of β-catenin via LRP6 pathway, leading to the intestinal barrier dysfunction. Funding Statement: This work was financially supported by National Natural Science Foundation of China (No. 81670480, 81570189), Training Program of the Major Research Plan of the Natural Science Foundation of Guangdong Province (2014A030308004), and High level talents in Guangdong Province special support plan - Youth Science and technology innovation talents (2015TQ01R334), Major Scientific Research Projects at Provincial Level in Guangdong General University (2017KZDXM068). Declaration of Interests: The authors have declared that no conflict of interest exists. Ethics Approval Statement: The study protocol and experiments were conducted according to the guidelines of the Institutional Animal Care and Use Committee of Guangzhou Medical University and were approved by the Institutional Ethics Committee of Guangzhou Medical University.