Role of MicroRNA-423-5p in posttranscriptional regulation of the intestinal riboflavin transporter-3

Riboflavin mediates m6A modification targeted by miR408, promoting early somatic embryogenesis in longan

Plant somatic embryogenesis (SE) is an in vitro biological process wherein bipolar structures are induced to form somatic cells and regenerate into whole plants. MicroRNA (miRNA) is an essential player in plant SE. However, the mechanism of microRNA408 (miR408) in SE remains elusive. Here, we used stable transgenic technology in longan (Dimocarpus longan) embryogenic calli to verify the mechanism by which miR408 promotes cell division and differentiation of longan early SE. dlo-miR408-3p regulated riboflavin biosynthesis by targeting nudix hydrolase 23 (DlNUDT23), a previously unidentified gene mediating N6-methyladenosine (m6A) modification and influencing RNA homeostasis and cell cycle gene expression during longan early SE. We showed that DlMIR408 overexpression (DlMIR408-OE) promoted 21-nt miRNA biosynthesis. In DlMIR408-OE cell lines, dlo-miR408-3p targeted and downregulated DlNUDT23, promoted riboflavin biosynthesis, decreased flavin mononucleotide (FMN) accumulation, promoted m6A level, and influenced miRNA homeostasis. DNA replication, glycosylphosphatidylinositol (GPI)-anchor biosynthesis, the pentose phosphate pathway, and taurine and hypotaurine metabolism were also closely associated with riboflavin metabolism. In a riboflavin feeding assay, dlo-miR408-3p and pre-miR408 were upregulated and DlNUDT23 was downregulated, increasing the m6A level and cell division and differentiation in longan globular embryos. When riboflavin biosynthesis was inhibited, dlo-miR408-3p was downregulated and DlNUDT23 was upregulated, which decreased m6A modification and inhibited cell division but did not inhibit cell differentiation. FMN artificial demethylated m6A modification affected the homeostasis of precursor miRNA and miRNA. Our results revealed a mechanism underlying dlo-miR408-3p-activated riboflavin biosynthesis in which DlNUDT23 is targeted, m6A modification is dynamically mediated, and cell division is affected, promoting early SE in plants.

MicroRNA sensing and regulating microbiota-host crosstalk via diet motivation

Accumulating evidence has demonstrated that diet-derived gut microbiota participates in the regulation of host metabolism and becomes the foundation for precision-based nutritional interventions and the biomarker for potential individual dietary recommendations. However, the specific mechanism of the gut microbiota-host crosstalk remains unclear. Recent studies have identified that noncoding RNAs, as important elements in the regulation of the initiation and termination of gene expression, mediate microbiota-host communication. Besides, the cross-kingdom regulation of non-host derived microRNAs also influence microbiota-host crosstalk via diet motivation. Hence, understanding the relationship between gut microbiota, miRNAs, and host metabolism is indispensable to revealing individual differences in dietary motivation and providing targeted recommendations and strategies. In this review, we first present an overview of the interaction between diet, host genetics, and gut microbiota and collected some latest research associated with microRNAs modulated gut microbiota and intestinal homeostasis. Then, specifically described the possible molecular mechanisms of microRNAs in sensing and regulating gut microbiota-host crosstalk. Lastly, summarized the prospect of microRNAs as biomarkers in disease diagnosis, and the disadvantages of microRNAs in regulating gut microbiota-host crosstalk. We speculated that microRNAs could become potential novel circulating biomarkers for personalized dietary strategies to achieve precise nutrition in future clinical research implications.

MicroRNAs in the Regulation of Solute Carrier Proteins Behind Xenobiotic and Nutrient Transport in Cells

Altered metabolism, such as aerobic glycolysis or the Warburg effect, has been recognized as characteristics of tumor cells for almost a century. Since then, there is accumulating evidence to demonstrate the metabolic reprogramming of tumor cells, addiction to excessive uptake and metabolism of key nutrients, to support rapid proliferation and invasion under tumor microenvironment. The solute carrier (SLC) superfamily transporters are responsible for influx or efflux of a wide variety of xenobiotic and metabolites that are needed for the cells to function, as well as some medications. To meet the increased demand for nutrients and energy, SLC transporters are frequently dysregulated in cancer cells. The SLCs responsible for the transport of key nutrients for cancer metabolism and energetics, such as glucose and amino acids, are of particular interest for their roles in tumor progression and metastasis. Meanwhile, rewired metabolism is accompanied by the dysregulation of microRNAs (miRNAs or miRs) that are small, noncoding RNAs governing posttranscriptional gene regulation. Studies have shown that many miRNAs directly regulate the expression of specific SLC transporters in normal or diseased cells. Changes of SLC transporter expression and function can subsequently alter the uptake of nutrients or therapeutics. Given the important role for miRNAs in regulating disease progression, there is growing interest in developing miRNA-based therapies, beyond serving as potential diagnostic or prognostic biomarkers. In this article, we discuss how miRNAs regulate the expression of SLC transporters and highlight potential influence on the supply of essential nutrients for cell metabolism and drug exposure toward desired efficacy.

miR-200a-3p improves neonatal necrotizing enterocolitis by regulating RIPK1

BACKGROUND

Necrotizing enterocolitis (NEC) is an acquired disease, which mainly occurs in premature infants or sick newborns. microRNA (miR), as a common non-coding RNA in recent years, is found in many diseases. In this research, miR usefulin NEC is analyzed by GEO.

METHOD

The differentially expressed miRs in NEC were screened by analyzing GSE68054, and miR-200a-3p in IEC-6 cells induced by lipopolysaccharide (LPS) and serum of NEC children were detected by qRT-PCR. The role of miR-200a-3p in LPS-induced IEC-6 cells was tested using CCK-8, PI dyeing, and inflammatory cytokine detection. The direct downstream molecules of miR-200a-3p were identified using TargetScanHuman and verified by luciferase reporter gene assay. The mechanism of action was explored using western blot.

RESULTS

miR-200a-3p in IEC-6 treated with NEC and LPS was significantly decreased. In vitro experiments revealed that miR-200a-3p mimetic could inhibit IL-6 and TNF-α in IEC-6 cells induced by LPS and reduce the positive rate of PI. In addition, it was determined that receptor-interacting protein kinase 1 (RIPK1) was a downstream molecule of miR-200a-3p, and overexpression of RIPK1 could aggravate LPS-induced IEC-6 injury, while miR-200a-3p mimics could alleviate the overexpression of RIPK1. miR-200a-3p mimics inhibited the elevation of necrosis-related molecules and the interaction between RIPK1 and RIPK3 in LPS-induced IEC-6 cells.

CONCLUSION

miR-200a-3p can protect intestinal epithelial cells from LPS injury by inhibiting inflammation and necrosis mediated by RIPK1, which provides a possible target for NEC.

Recent advances in riboflavin transporter RFVT and its genetic disease

Riboflavin (vitamin B2) is essential for cellular growth and function. It is enzymatically converted to flavin mononucleotide (FMN) and flavin adenine dinucleotide (FAD), which participate in the metabolic oxidation-reduction reactions of carbohydrates, amino acids, and lipids. Human riboflavin transporters RFVT1, RFVT2, and RFVT3 have been identified and characterized since 2008. They are highly specific transporters of riboflavin. RFVT3 has functional characteristics different from those of RFVT1 and RFVT2. RFVT3 contributes to absorption in the small intestine, reabsorption in the kidney, and transport to the fetus in the placenta, while RFVT2 mediates the tissue distribution of riboflavin from the blood. Several mutations in the SLC52A2 gene encoding RFVT2 and the SLC52A3 gene encoding RFVT3 were found in patients with a rare neurological disorder known as Brown-Vialetto-Van Laere syndrome. These patients commonly present with bulbar palsy, hearing loss, muscle weakness, and respiratory symptoms in infancy or later in childhood. A decrease in plasma riboflavin levels has been observed in several cases. Recent studies on knockout mice and patient-derived cells have advanced the understanding of these mechanisms. Here, we summarize novel findings on RFVT1-3 and their genetic diseases and discuss their potential as therapeutic drugs.

Posttranscriptional regulation of thiamin transporter-1 expression by microRNA-200a-3p in pancreatic acinar cells

The water-soluble vitamin B1 (thiamin) plays essential roles in normal metabolism and function of all human/mammalian cells, including the pancreatic acinar cells (PACs). PACs obtain thiamin from their surrounding circulation via transport across the plasma membrane, a process that is mediated by thiamin transporter (THTR)-1 and THTR-2. We have previously characterized different aspects of thiamin uptake by mouse and human primary PACs, but little is known about posttranscriptional regulation of the uptake event. We addressed this by focusing on the predominant thiamin transporter THTR-1 (encoded by SLC19A2 gene) in PACs. Transfecting pmirGLO-SLC19A2 3'-untranslated region (UTR) into mouse-derived PAC 266-6 cells leads to a significant reduction in luciferase activity compared with cells transfected with empty vector. Subjecting the SLC19A2 3'-UTR to different in silico algorithms identified multiple putative microRNA binding sites in this region. Focusing on miR-200a-3p (since it is highly expressed in mouse and human pancreas), we found that transfecting PAC 266-6 and human primary PACs (hPACs) with mimic miR-200a-3p leads to a significant inhibition of THTR-1 expression (both protein and mRNA levels) and in thiamin uptake. In contrast, transfection by miR-200a-3p inhibitor leads to an increase in THTR-1 expression and thiamin uptake. Additionally, truncating the region carrying miR-200a-3p binding site in SLC19A2 3'-UTR and mutating the binding site lead to abrogation in the inhibitory effect of this microRNA on luciferase activity in PAC 266-6. These results demonstrate that expression of THTR-1 and thiamin uptake in PACs is subject to posttranscriptional regulation by microRNAs.NEW & NOTEWORTHY The findings of this study show, for the first time, that the membrane transporter of vitamin B1, i.e., thiamin transporter-1 (THTR-1), is subject to regulation by microRNAs (specifically miR-200a-3p) in mouse and human primary pancreatic acinar cells (PACs). The results also show that this posttranscriptional regulation has functional consequences on the ability of PACs to take in the essential micronutrient thiamin.

Development of Novel Experimental Models to Study Flavoproteome Alterations in Human Neuromuscular Diseases: The Effect of Rf Therapy

Inborn errors of Riboflavin (Rf) transport and metabolism have been recently related to severe human neuromuscular disorders, as resulting in profound alteration of human flavoproteome and, therefore, of cellular bioenergetics. This explains why the interest in studying the “flavin world”, a topic which has not been intensively investigated before, has increased much over the last few years. This also prompts basic questions concerning how Rf transporters and FAD (flavin adenine dinucleotide) -forming enzymes work in humans, and how they can create a coordinated network ensuring the maintenance of intracellular flavoproteome. The concept of a coordinated cellular “flavin network”, introduced long ago studying humans suffering for Multiple Acyl-CoA Dehydrogenase Deficiency (MADD), has been, later on, addressed in model organisms and more recently in cell models. In the frame of the underlying relevance of a correct supply of Rf in humans and of a better understanding of the molecular rationale of Rf therapy in patients, this review wants to deal with theories and existing experimental models in the aim to potentiate possible therapeutic interventions in Rf-related neuromuscular diseases.

Up-regulation of miR-145 may contribute to repeated implantation failure after IVF-embryo transfer by targeting PAI-1

RESEARCH QUESTION

Repeated implantation failure (RIF) is a major limiting factor in assisted reproductive technology. As miR-145 (also known as MIR145) is up-regulated in patients with RIF, this study asked, what is the molecular mechanism underlying the affect of miR-145 on embryo implantation in RIF?

DESIGN

Ishikawa cells were infected with lentivirus containing miR-145 and miR-145 NC. Massive transcriptome data analyses and bioinformatics analysis were used to search for a potential candidate target of miR-145. The expression of the potential candidate target was detected using quantitative reverse transcription PCR (qRT-PCR) and western blotting in the Ishikawa cells infected with lentivirus containing miR-145 or miR-145 NC. Subsequently, a dual luciferase reporter assay was performed to verify whether the potential candidate target was a novel direct target of miR-145. In addition, expression of PAI-1 (plasminogen activator inhibitor 1, also known as SERPINE1) in endometrial tissue from women with RIF and in control endometrial tissue was examined using qRT-PCR and immunohistochemistry.

RESULTS

Based on massive transcriptome data analyses and bioinformatics analysis, PAI-1 was regarded as a potential candidate target of miR-145. miR-145 overexpression was achieved in Ishikawa cells. PAI-1 was confirmed as a direct target of miR-145 by bioinformatic analysis, qRT-PCR, western blotting and dual luciferase reporter assay. Further, results from the clinical sample indicated that at both the mRNA and protein levels, PAI-1 expression was down-regulated in endometrial tissues from women with RIF compared with control group women, and this was negatively related to miR-145 expression.

CONCLUSIONS

The study results suggests that miR-145 may target and down-regulate PAI-1 expression and influence embryo implantation in women with RIF who are undergoing IVF.

Tamoxifen-induced, intestinal-specific deletion of Slc5a6 in adult mice leads to spontaneous inflammation: involvement of NF-κB, NLRP3, and gut microbiota

The sodium-dependent multivitamin transporter (SMVT; SLC5A6) is involved in intestinal absorption of vitamin B7 (biotin). We have previously shown that mice with an embryonic intestinal-specific SMVT knockout (KO) develop biotin deficiency and severe spontaneous intestinal inflammation in addition to growth retardation, developmental delays, and death within the first 6-7 wk of life. The profound morbidity and mortality associated with the SMVT-KO has limited our ability to further characterize the intestinal inflammation and other sequelae of this deletion in adult mice with a mature gut microbiota. To overcome this limitation, we generated an intestine-specific, tamoxifen-inducible, conditional SMVT-KO (SMVT-icKO). Our results showed that adult SMVT-icKO mice have reduced body weight, biotin deficiency, shorter colonic length, and bloody diarrhea compared with age- and sex-matched control littermates. All SMVT-icKO mice also developed spontaneous intestinal inflammation associated with induction of calprotectin (S100a8/S100a9), proinflammatory cytokines (IL-1β, TNF-α, IFN-γ, and IL-6), and an increase in intestinal permeability. Additionally, the intestines of SMVT-icKO showed activation of the NF-κB pathway and the nucleotide-binding domain and leucine-rich repeat pyrin 3 domain (NLRP3) inflammasome. Notably, administration of broad-spectrum antibiotics reduced lethality and led to normalization of intestinal inflammation, proinflammatory cytokines, altered mucosal integrity, and reduced expression of the NLRP3 inflammasome. Overall, these findings support our conclusion that the biotin transport pathway plays an important role in the maintenance of intestinal homeostasis, and that NF-κB and the NLRP3 inflammasome, as well as gut microbiota, drive the development of intestinal inflammation when SMVT is absent.NEW & NOTEWORTHY This study demonstrates that deletion of the intestinal biotin uptake system in adult mice leads to the development of spontaneous gut inflammation and that luminal microbiota plays a role in its development.

Identification of transmembrane protein 237 as a novel interactor with the intestinal riboflavin transporter-3 (RFVT-3): role in functionality and cell biology

The apically localized riboflavin (RF) transporter-3 (RFVT-3) is involved in intestinal absorption of vitamin B2. Previous studies have characterized different physiological/biological aspects of the RFVT-3, but there is a lack of knowledge regarding possible existence of interacting partner(s) and consequence of interaction(s) on its function/cell biology. To address the latter, we performed yeast two-hybrid (Y2H) screening of a human colonic cDNA library and have identified transmembrane protein 237 (TMEM237) as a putative interactor with the human (h)RFVT-3; the interaction was further confirmed via "1-by-1" Y2H assay that involved appropriate positive and negative controls. TMEM237 was found to be highly expressed in human native intestine and in human intestinal epithelial cell lines; further, confocal images showed colocalization of the protein with hRFVT-3. The interaction between TMEM237 with hRFVT-3 in human intestinal epithelial HuTu-80 cells was established by coimmunoprecipitation. Expressing TMEM237 in HuTu-80 cells led to a significant induction in RF uptake, while its knockdown (with the use of gene-specific siRNA) led to a significant reduction in uptake. Transfecting TMEM237 into HuTu-80 cells also led to a marked enhancement in hRFVT-3 protein stability (reflected by an increase in the protein half-life). Interestingly, the level of expression of TMEM237 was found to be markedly reduced following treatment with TNF-α (a proinflammatory cytokine that inhibits intestinal RF uptake), while its expression was significantly upregulated following treatment with butyrate (an inducer of intestinal RF uptake). These findings identify TMEM237 as an interactor with the intestinal hRFVT-3 and show that the interaction has physiological/biological significance.

MicroRNA-103a regulates sodium-dependent vitamin C transporter-1 expression in intestinal epithelial cells

Intestinal absorption of ascorbic acid (AA) occurs via a Na+-dependent carrier-mediated process facilitated through the human sodium-dependent vitamin C transporters-1 &-2 (hSVCT1 and hSVCT2). Many studies have shown that hSVCT1 (product of the SLC23A1 gene) is expressed on the apical membrane of polarized enterocytes where it mediates AA absorption. hSVCT1 expression levels are therefore an important determinant of physiological vitamin C homeostasis. However, little is known about posttranscriptional mechanisms that regulate hSVCT1 expression in intestinal epithelia. In this study, we investigated regulation of hSVCT1 by microRNA (miRNA). A pmirGLO-SLC23A1-3'-UTR construct transfected into human intestinal cell lines (Caco-2 and NCM460 cells) showed markedly reduced luciferase activity. Bioinformatic analysis of the SLC23A1-3'-UTR predicted five miRNA binding sites (miR-103a, miR-107, miR-328, miR-384, and miR-499-5p) in the 3'-UTR. Expression of mature miR-103a was markedly higher compared to the other four putative miRNA regulators in both intestinal cell lines and mouse jejunal mucosa. Addition of a miR-103a mimic, but not a miR-103a mutant construct, markedly reduced the luminescence of the pmirGLO-SLC23A1-3'-UTR reporter. Reciprocally, addition of a miR-103a inhibitor significantly increased luciferase reporter activity. Addition of the miR-103a mimic led to a significant inhibition in AA uptake, associated with decreased hSVCT1 mRNA and protein expression in Caco-2 cells. In contrast, the miR-103a inhibitor increased AA uptake, associated with increased levels of hSVCT1 mRNA and protein. These findings provide the first evidence for posttranscriptional regulation of hSVCT1 by miRNA in intestinal epithelial cells.

Sodium Butyrate Enhances Intestinal Riboflavin Uptake via Induction of Expression of Riboflavin Transporter-3 (RFVT3)

BACKGROUND

Uptake of riboflavin (RF) by intestinal epithelial cells occurs via a specific carrier-mediated process that involves the apically localized RF transporter-3 (RFVT3). Previous studies have shown that sodium butyrate (NaB) affects intestinal uptake of other substrates and expression of their membrane transporters, but its effect on intestinal uptake of RF and expression of RFVT3 has not been examined.

AIMS

To investigate the effect of NaB on intestinal RF uptake process and expression of the RFVT3.

METHODS

Two experimental models were used in this study: Human-derived intestinal epithelial Caco-2 cells and ex vivo mouse colonoids. ³H-RF uptake assay, Western blot, RT-qPCR, and chromatin immunoprecipitation assay were performed.

RESULTS

Treating Caco-2 cells with NaB led to a significant increase in carrier-mediated RF uptake. This increase was associated with a significant induction in the level of expression of the hRFVT3 protein, mRNA, and heterogenous nuclear RNA (hnRNA). Similarly, treating mouse colonoids with NaB led to a marked increase in the level of expression of the mRFVT3 protein, mRNA, and hnRNA. NaB did not affect hRFVT3 mRNA stability, rather it caused significant epigenetic changes (histone modifications) in the SLC52A3 gene where an increase in H3Ac and a reduction in H3K27me3 levels were observed in the NaB-treated Caco-2 cells compared to untreated controls.

CONCLUSION

These findings demonstrate that NaB up-regulates intestinal RF uptake and that the effect appears to be mediated, at least in part, at the level of transcription of the SLC52A3 gene and may involve epigenetic mechanism(s).

Gastrointestinal Handling of Water-Soluble Vitamins

Nine compounds are classified as water-soluble vitamins, eight B vitamins and one vitamin C. The vitamins are mandatory for the function of numerous enzymes and lack of one or more of the vitamins may lead to severe medical conditions. All the vitamins are supplied by food in microgram to milligram quantities and in addition some of the vitamins are synthesized by the intestinal microbiota. In the gastrointestinal tract, the vitamins are liberated from binding proteins and for some of the vitamins modified prior to absorption. Due to their solubility in water, they all require specific carriers to be absorbed. Our current knowledge concerning each of the vitamins differs in depth and focus and is influenced by the prevalence of conditions and diseases related to lack of the individual vitamin. Because of that we have chosen to cover slightly different aspects for the individual vitamins. For each of the vitamins, we summarize the physiological role, the steps involved in the absorption, and the factors influencing the absorption. In addition, for some of the vitamins, the molecular base for absorption is described in details, while for others new aspects of relevance for human deficiency are included. © 2018 American Physiological Society. Compr Physiol 8:1291-1311, 2018.

MicroRNA-485-5p reduces O-GlcNAcylation of Bmi-1 and inhibits colorectal cancer proliferation

Emerging evidences showed that miRNAs are involved in the oncogenesis of many cancers. Here, miRNA microarray analysis was performed to screen the significant miRNAs involved in the progression of colorectal cancer (CRC), miR-485-5p was chosen for further study. We found that the expression of miR-485-5p was significantly lower in CRC specimens and cell lines. In addition, low expression level of miR-485-5p is correlated with tumor progression and poor survival in CRC patients. Based on in vitro and in vivo assays, we found that miR-485-5p significantly inhibits CRC proliferation. Moreover, our results showed that miR-485-5p inhibits cell proliferation by reducing Bmi-1 protein expression, which has been reported to control the proliferation of many cancers. Mechanistically, OGT is a direct target of miR-485-5p, and miR-485-5p could inhibit the O-GlcNAcylation level of Bmi-1 by OGT. Overall, these results suggested that as a tumor suppressor, miR-485-5p may regulate CRC cells proliferation, which could regulate the O-GlcNAcylation and the stability of Bmi-1 through targeting OGT. This may give insight into a novel mechanism and therapy of CRC growth.