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Background: Serotonin transporter (SLC6A4; SERT) plays a key role in regulating the availability of 5-HT (5-hydroxytryptamine, a neurotransmitter and hormone) in the brain and the gut mucosa. A decrease in intestinal SERT expression, associated with increased availability of 5-HT, is implicated in the pathogenesis of infectious and inflammatory disorders of the gut. Therefore, it is critical to understand the regulation of SERT, as a novel target for the treatment of gastrointestinal disorders. In this regard, long noncoding RNAs (LncRNAs, small transcripts >200 nucleotides) are known to modulate gene expression via chromatin remodeling, transcriptional and posttranscriptional mechanisms. Notably, elevated levels of LncRNA H19 are observed in IBD patients and mouse models of inflammation and are known to promote mucosal regeneration and wound healing and restore the intestinal homeostasis. Whether LncRNA H19 regulates SERT expression remains unknown and was the focus of the current study. Methods: Caco-2 cells were transiently transfected with either H19 mammalian expression vector or H19 siRNA using Lipofectamine 2000. Protein and mRNA expression was measured by immunoblotting and real-time PCR, respectively. Age-matched H19 lncRNA- deficient mice and wild-type (WT) littermates were used to determine the role of genetic deletion of H19 on SERT expression in ileum. Results: H19 overexpression in Caco-2 cells increased SERT mRNA levels (~13-fold; p<0.05) at 48h post-transfection compared to an empty vector. Consistent with the mRNA levels, H19 also increased SERT protein expression (~2-fold, p<0.05). Furthermore, siRNA-mediated knockdown of H19 in Caco-2 cells resulted in a significant decrease in SERT mRNA levels (~80%, p<0.05). Parallel to the in vitro results, H19 deficient mice also showed a significant decrease in SERT mRNA expression (~69 %, p<0.05) in the ileum compared to the WT mice. Interestingly, in comparison to WT, the expression of other key transporters involved in intestinal NaCl absorption (SLC9A3, SLC26A3, and SLC26A6) remained unaltered in H19 deficient mice. Conclusion: These data demonstrate a novel role of LncRNA H19 in regulating the expression of SERT in the intestine under physiological conditions. We speculate that H19 mediated increase in SERT expression may provide valuable insights into the mechanisms restoring decreased SERT expression in inflammatory or infectious diseases of the gut. (Supported by VA/NIH). VA and NIH This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.