SIDT1-dependent absorption in the stomach mediates host uptake of dietary and orally administered microRNAs
Authors: Lei Dong
Xi Chen
Dangsheng Li
Chunni Zhang
Ke Zen
Yuyan Liu
Yanbo Wang
Minghui Liu
Jin Wang
Fan Zhang
Cheng Wang
Zhen Zhou
Chen Wang
Huimin Wu
Hanqin Li
Liangsheng Lu
Jie Xu
Qipeng Zhang
Chunyan Liu
Qun Chen
Chen-Yu Zhang
Fangyu Wang
Journal: Cell Research (2020)
Discipline: MOLECULAR BIOLOGY & GENETICS
Keywords: Dietary microRNAs; absorption mechanism; SIDT1; gastric pit cells; stomach
Affiliations: Nanjing Drum Tower Hospital Center of Molecular Diagnostic and Therapy, State Key Laboratory of Pharmaceutical Biotechnology, Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, NJU Advanced Institute of Life Sciences (NAILS), NJU Institute of AI Biomedicine and Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, 210023, China., Department of Gastroenterology and Hepatology, Jinling Hospital, Medical School of Nanjing University, Nanjing, Jiangsu, 210002, China., Department of Clinical Laboratory, Jinling Hospital, School of Medicine, Nanjing University, Nanjing, Jiangsu, 210002, China., Shanghai Institute of Biochemistry and Cell Biology, Center for Excellence in Molecular Cell Science, Chinese Academy of Sciences, Shanghai, 200031, China., Department of Gastroenterology and Hepatology, Jinling Hospital, Medical School of Nanjing University, Nanjing, Jiangsu, 210002, China. ., Nanjing Drum Tower Hospital Center of Molecular Diagnostic and Therapy, State Key Laboratory of Pharmaceutical Biotechnology, Jiangsu Engineering Research Center for MicroRNA Biology and Biotechnology, NJU Advanced Institute of Life Sciences (NAILS), NJU Institute of AI Biomedicine and Biotechnology, School of Life Sciences, Nanjing University, Nanjing, Jiangsu, 210023, China. .

Abstract:  Dietary microRNAs have been shown to be absorbed by mammals and regulate host gene expression, but the absorption mechanism remains unknown. Here, we show that SIDT1 expressed on gastric pit cells in the stomach is required for the absorption of dietary microRNAs. SIDT1-deficient mice show reduced basal levels and impaired dynamic absorption of dietary microRNAs. Notably, we identified the stomach as the primary site for dietary microRNA absorption, which is dramatically attenuated in the stomachs of SIDT1-deficient mice. Mechanistic analyses revealed that the uptake of exogenous microRNAs by gastric pit cells is SIDT1 and low-pH dependent. Furthermore, oral administration of plant-derived miR2911 retards liver fibrosis, and this protective effect was abolished in SIDT1-deficient mice. Our findings reveal a major mechanism underlying the absorption of dietary microRNAs, uncover an unexpected role of the stomach and shed light on developing small RNA therapeutics by oral delivery. 

Retracted: No

PubPeer comments:
 This is to express my curiosity and concern. Although one of the co-authors, Dangsheng Li, is working in the Shanghai Institute of Biochemistry and Cell Biology, he is not doing research in the Center for Excellence in Molecular Cell Science. Indeed, he is the deputy editor-in-chief of Cell Research, the journal publishing this study. , 
 1. Insufficient detail is provided for replication of the RNA sequencing study. There is no information on the quantity of liver used for RNA extraction, the time of collection, or the diet or recency of dietary intake. 20 micrograms of small RNA per animal are said to have been treated and then combined into one pool per 3-animal group. However, the amount of remaining RNA used to generate libraries is not given. 2. Despite the putative elimination of non-plant sequences prior to sequencing, and a very generous allowance of two mapping mismatches and two  shifts per sequence, only a small number of plant sequences could be mapped. Specifically, less than one-tenth of one-percent of the small RNA sequences. If one does not allow mismatches, this means that except for MIR166, none of the identified sequences is at a level exceeding 10 mapped reads per million total reads. Since there is also no way to assess variability (n=1 for each mouse strain), it is difficult to claim that such results can be distinguished from background. The only putative plant miRNA that seems to be an exception, MIR166, represents the majority of plant miRNA reads for both the WT and KO strains. The total number of reads in the KO strain is about one-third of the WT. Curiously, this is approximately the proportion of remaining endogenous RNAs after the treatment. For example, murine miR-21-5p is present in the KO mouse at about 40% of the level in the WT, and at overall amounts similar to the putative MIR166. 3. Seven years ago, a publication reported a blinded study conducted to replicate earlier results about LDLRAP1 and miR168a from the authors of this paper. The blinded study did not find any uptake of miR168a, and the effect of the raw rice diet on circulating cholesterol was found to be a starvation response to the nutritionally insufficient diet of rice that was eliminated in a control group that received both raw rice and a small amount of chow. It is concerning that the authors would not acknowledge and engage with these methods and findings, especially in study design. 4.  Exosomes were not separated or characterized according to field standards . The kit used to obtain putative exosomes is not specific for exosomes (endosome-origin extracellular vesicles) or for extracellular vesicles in general. It is a polymer precipitation method that brings down all particles in suspension. Thus, there is no basis for the claims about exosomes in this publication. ,