Transcriptomics and metabolomics study in mouse kidney of the molecular mechanism underlying energy metabolism response to hypoxic stress in highland areas
Exposure to hypoxia disrupts energy metabolism and induces inflammation. However, the pathways and mechanisms underlying energy metabolism disorders caused by hypoxic conditions remain unclear. In this study, we constructed a hypoxic animal model and applied transcriptomic and non-targeted metabolomics techniques to further investigate the pathways and mechanisms of hypoxia exposure that disrupt energy metabolism. Transcriptome results showed that 3007 genes were significantly differentially expressed under hypoxic exposure, and Gene Ontology (GO) annotation analysis and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analysis showed that the differentially expressed genes (DEGs) were mainly involved in energy metabolism and were significantly enriched in the tricarboxylic acid (TCA) cycle and oxidative phosphorylation (OXPHOS) pathway. Differential genes in the TCA cycle (IDH3A, SUCLA2, and MDH2) and OXPHOS pathway (NDUFA3, NDUFS7, UQCRC1, CYC1, and UQCRFS1) were validated using mRNA and protein expression, and the results showed downregulation. The results of non-targeted metabolomics showed that 365 significant differential metabolites were identified under plateau hypoxia stress. KEGG enrichment analysis showed that the differential metabolites were mainly enriched in metabolic processes, such as energy metabolism, nucleotide metabolism, and amino acid metabolism. Hypoxia exposure disrupted the TCA cycle and reduced the synthesis of amino acids and nucleotides by decreasing the concentrations of cis-aconitate, a-ketoglutarate, NADH, NADPH, most amino acids, purines, and pyrimidines. Bioinformatics analysis was used to identify inflammatory genes related to hypoxia exposure, and some inflammatory genes were selected for verification. We found that the mRNA and protein expression levels of IL1B, IL12B, S100A8, and S100A9 in kidney tissues were upregulated under hypoxic exposure. Our results suggest that hypoxia exposure inhibits the TCA cycle and OXPHOS signalling pathway by inhibiting IDH3A, SUCLA2, MDH2, NDUFFA3, NDUFS7, UQCRC1, CYC1, and UQCRFS1, thereby suppressing energy metabolism, inducing amino acid and nucleotide deficiency, and promoting inflammation, ultimately leading to kidney damage. Overall design: In this study, C57BL/6 mice were raised at an altitude of 4200 meters (altitude hypoxia group, HKT) and 400 meters (altitude normoxic group, PKC), respectively. After 30 days, the kidney tissue of the mice was aseptically taken out. By measuring the blood gas analysis index and the mRNA and protein expression level of HIF-1a, it is proved that the establishment of hypoxic animal mouse model is successful. By comparing the renal index and HE staining results of two groups of mice, it was found that hypoxia induced renal tissue damage in mice. Furthermore, the two groups of kidney tissues were transcriptomically sequenced, and the reliability of sequencing results was verified by detecting differentially expressed genes (DEGs) by RT-QPCR technology. Through the enrichment analysis of DEGs, it was found that hypoxia induced changes in energy metabolism of mouse kidney tissues.