The Absorption Mechanism Of Exogenous MiRNA In Mammals' Gastrointestinal Tract

MicroRNA(miRNA)are a class of small non-coding,single-strande RNA molecules about 22 nucleotides,and regulate genes by fully or partially complementary binding to the 3' untranslated sequence of the target mRNA.MicroRNA regulate the target gene at the post-transcriptional level by degradation of the target mRNA or translational inhibition.A lot of studies on MicroRNA have demonstrated that MicroRNA are highly conserved in evolution.MicroRNA have formed a complex and huge regulatory network.They are involved in various physiological and pathological processes.The source of MicroRNA in organisms is not limited to the synthesis in vivo.Our previous research found that MicroRNA from food can be absorbed into the peripheral blood and tissues,and may play the corresponding biological function in organisms,to achieve the goal of biological transboundary regulation.However,the mechanism of exogenous MicroRNA being absorbed by the digestive tract and transported to various organs remains need to reveal.The main research content of this dissertation is that SITD1 protein which homologous to SID protein mediates the transport of exogenous MicroRNA into mammals.Another homologous protein SIDT2 was previously reported to be located on the lysosomal membrane and may be involved in intracellular metabolism of MicroRNA.We found that the expression of SIDT1 and SIDT2 are distributed in almost all tissues of mice.SIDT1 expressed the highest level in gastric tissues and especially in gastric epithelial cells.We found mice could absorb MicroRNA into the blood and other tissues by gavage experiments.SIDT1 knockout mice had significantly lower ability to absorb MicroRNA than wild type mice.Cellular experiments have shown that cells can spontaneously uptake exogenous double-stranded,single-stranded MicroRNA.After knocking down the SIDT1 gene,the ability of the cells to uptake MicroRNA was significantly decreased.After overexpressing SITD1 protein,the ability of the knockout gene cells to uptake MicroRNA was restored.We simulated acidic conditions in the stomach and treated cells with different acid condition,and found that the ability of cells to uptake exogenous MicroRNA was significantly enhanced,suggesting that exogenous MicroRNA are mainly absorbed in the stomach.However,knockout gene mice and knockout gene cells can also absorb exogenous MicroRNA.We excluded cell endocytosis participates this process.There should be other mechanisms for the absorption of exogenous MicroRNA into the body.Further research is needed.We also used SIDT1 and SIDT2 knockout mice to breed SIDT1 and SIDT2 double-knockout mice and found that mice have phenotypes of developmental delays,accelerated aging,and difficult for maternal reproduction,this pending further research.