ChREBP is activated by reductive stress and mediates GCKR-associated metabolic traits.

Common genetic variants in glucokinase regulator (GCKR), which encodes GKRP, a regulator of hepatic glucokinase (GCK), influence multiple metabolic traits in genome-wide association studies (GWASs), making GCKR one of the most pleiotropic GWAS loci in the genome. It is unclear why. Prior work has demonstrated that GCKR influences the hepatic cytosolic NADH/NAD+ ratio, also referred to as reductive stress. Here, we demonstrate that reductive stress is sufficient to activate the transcription factor ChREBP and necessary for its activation by the GKRP-GCK interaction, glucose, and ethanol. We show that hepatic reductive stress induces GCKR GWAS traits such as increased hepatic fat, circulating FGF21, and circulating acylglycerol species, which are also influenced by ChREBP. We define the transcriptional signature of hepatic reductive stress and show its upregulation in fatty liver disease and downregulation after bariatric surgery in humans. These findings highlight how a GCKR-reductive stress-ChREBP axis influences multiple human metabolic traits.

miR-10b-5p rescues leaky gut linked with gastrointestinal dysmotility and diabetes.

BACKGROUND/AIM: Diabetes has substantive co-occurrence with disorders of gut-brain interactions (DGBIs). The pathophysiological and molecular mechanisms linking diabetes and DGBIs are unclear. MicroRNAs (miRNAs) are key regulators of diabetes and gut dysmotility. We investigated whether impaired gut barrier function is regulated by a key miRNA, miR-10b-5p, linking diabetes and gut dysmotility. METHODS: We created a new mouse line using the Mb3Cas12a/Mb3Cpf1 endonuclease to delete mir-10b globally. Loss of function studies in the mir-10b knockout (KO) mice were conducted to characterize diabetes, gut dysmotility, and gut barrier dysfunction phenotypes in these mice. Gain of function studies were conducted by injecting these mir-10b KO mice with a miR-10b-5p mimic. Further, we performed miRNA-sequencing analysis from colonic mucosa from mir-10b KO, wild type, and miR-10b-5p mimic injected mice to confirm (1) deficiency of miR-10b-5p in KO mice, and (2) restoration of miR-10b-5p after the mimic injection. RESULTS: Congenital loss of mir-10b in mice led to the development of hyperglycemia, gut dysmotility, and gut barrier dysfunction. Gut permeability was increased, but expression of the tight junction protein Zonula occludens-1 was reduced in the colon of mir-10b KO mice. Patients with diabetes or constipation- predominant irritable bowel syndrome, a known DGBI that is linked to leaky gut, had significantly reduced miR-10b-5p expression. Injection of a miR-10b-5p mimic in mir-10b KO mice rescued these molecular alterations and phenotypes. CONCLUSIONS: Our study uncovered a potential pathophysiologic mechanism of gut barrier dysfunction that links both the diabetes and gut dysmotility phenotypes in mice lacking miR-10b-5p. Treatment with a miR-10b-5p mimic reversed the leaky gut, diabetic, and gut dysmotility phenotypes, highlighting the translational potential of the miR-10b-5p mimic.

Transcriptome profiling of subepithelial PDGFRα cells in colonic mucosa reveals several cell-selective markers.

Subepithelial platelet-derived growth factor receptor alpha (PDGFRα)+ cells found in the colonic mucosal tissue come in close contact with epithelial cells, immune cells, neurons, capillaries, and lymphatic networks. Mucosal subepithelial PDGFRα+ cells (MuPαC) are important regulators in various intestinal diseases including fibrosis and inflammation. However, the transcriptome of MuPαC has not yet been elucidated. Using Pdgfra-eGFP mice and flow cytometry, we isolated colonic MuPαC and obtained their transcriptome data. In analyzing the transcriptome, we identified three novel, and selectively expressed, markers (Adamdec1, Fin1, and Col6a4) found in MuPαC. In addition, we identified a unique set of MuPαC-enriched genetic signatures including groups of growth factors, transcription factors, gap junction proteins, extracellular proteins, receptors, cytokines, protein kinases, phosphatases, and peptidases. These selective groups of genetic signatures are linked to the unique cellular identity and function of MuPαC. Furthermore, we have added this MuPαC transcriptome data to our Smooth Muscle Genome Browser that contains the transcriptome data of jejunal and colonic smooth muscle cells (SMC), interstitial cells of Cajal (ICC), and smooth muscle resident PDGFRα+ cells: (https://med.unr.edu/physio/transcriptome). This online resource provides a comprehensive reference of all currently known genetic transcripts expressed in primary MuPαC in the colon along with smooth muscle resident PDGFRα cells, SMC, and ICC in the murine colon and jejunum.

Metalloendopeptidase ADAM-like Decysin 1 (ADAMDEC1) in Colonic Subepithelial PDGFRα+ Cells Is a New Marker for Inflammatory Bowel Disease.

Metalloendopeptidase ADAM-Like Decysin 1 (ADAMDEC1) is an anti-inflammatory peptidase that is almost exclusively expressed in the gastrointestinal (GI) tract. We have recently found abundant and selective expression of Adamdec1 in colonic mucosal PDGFRα+ cells. However, the cellular origin for this gene expression is controversial as it is also known to be expressed in intestinal macrophages. We found that Adamdec1 mRNAs were selectively expressed in colonic mucosal subepithelial PDGFRα+ cells. ADAMDEC1 protein was mainly released from PDGFRα+ cells and accumulated in the mucosal layer lamina propria space near the epithelial basement membrane. PDGFRα+ cells significantly overexpressed Adamdec1 mRNAs and protein in DSS-induced colitis mice. Adamdec1 was predominantly expressed in CD45- PDGFRα+ cells in DSS-induced colitis mice, with only minimal expression in CD45+ CD64+ macrophages. Additionally, overexpression of both ADAMDEC1 mRNA and protein was consistently observed in PDGFRα+ cells, but not in CD64+ macrophages found in human colonic mucosal tissue affected by Crohn's disease. In summary, PDGFRα+ cells selectively express ADAMDEC1, which is localized to the colon mucosa layer. ADAMDEC1 expression significantly increases in DSS-induced colitis affected mice and Crohn's disease affected human tissue, suggesting that this gene can serve as a diagnostic and/or therapeutic target for intestinal inflammation and Crohn's disease.

Pathophysiological mechanisms underlying gastrointestinal symptoms in patients with COVID-19.

Gastrointestinal (GI) symptoms, such as diarrhea, abdominal pain, vomiting, and anorexia, are frequently observed in patients with coronavirus disease 2019 (COVID-19). However, the pathophysiological mechanisms connecting these GI symptoms to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infections remain elusive. Previous studies indicate that the entry of SARS-CoV-2 into intestinal cells leads to downregulation of angiotensin converting enzyme 2 (ACE2) receptors resulting in impaired barrier function. While intestinal ACE2 functions as a chaperone for the amino acid transporter B0AT1, the B0AT1/ACE2 complex within the intestinal epithelium acts as a regulator of gut microbiota composition and function. Alternations to the B0AT1/ACE2 complex lead to microbial dysbiosis through increased local and systemic immune responses. Previous studies have also suggested that altered serotonin metabolism may be the underlying cause of GI disorders involving diarrhea. The findings of elevated plasma serotonin levels and high fecal calprotectin in COVID-19 patients with diarrhea indicate that the viral infection evokes a systemic inflammatory response that specifically involves the GI. Interestingly, the elevated proinflammatory cytokines correlate with elevated serotonin and fecal calprotectin levels further supporting the evidence of GI inflammation, a hallmark of functional GI disorders. Moreover, the finding that rectal swabs of COVID-19 patients remain positive for SARS-CoV-2 even after the nasopharynx clears the virus, suggests that viral replication and shedding from the GI tract may be more robust than that of the respiratory tract, further indicating fecal-oral transmission as another important route of viral spread. This review summarized the evidence for pathophysiological mechanisms (impaired barrier function, gut inflammation, altered serotonin metabolism and gut microbiota dysbiosis) underlying the GI symptoms in patients with COVID-19.

Colonic Motility Is Improved by the Activation of 5-HT2B Receptors on Interstitial Cells of Cajal in Diabetic Mice.

BACKGROUND & AIMS: Constipation is commonly associated with diabetes. Serotonin (5-HT), produced predominantly by enterochromaffin (EC) cells via tryptophan hydroxylase 1 (TPH1), is a key modulator of gastrointestinal (GI) motility. However, the role of serotonergic signaling in constipation associated with diabetes is unknown. METHODS: We generated EC cell reporter Tph1-tdTom, EC cell-depleted Tph1-DTA, combined Tph1-tdTom-DTA, and interstitial cell of Cajal (ICC)-specific Kit-GCaMP6 mice. Male mice and surgically ovariectomized female mice were fed a high-fat high-sucrose diet to induce diabetes. The effect of serotonergic signaling on GI motility was studied by examining 5-HT receptor expression in the colon and in vivo GI transit, colonic migrating motor complexes (CMMCs), and calcium imaging in mice treated with either a 5-HT2B receptor (HTR2B) antagonist or agonist. RESULTS: Colonic transit was delayed in males with diabetes, although colonic Tph1+ cell density and 5-HT levels were increased. Colonic transit was not further reduced in diabetic mice by EC cell depletion. The HTR2B protein, predominantly expressed by colonic ICCs, was markedly decreased in the colonic muscles of males and ovariectomized females with diabetes. Ca2+ activity in colonic ICCs was decreased in diabetic males. Treatment with an HTR2B antagonist impaired CMMCs and colonic motility in healthy males, whereas treatment with an HTR2B agonist improved CMMCs and colonic motility in males with diabetes. Colonic transit in ovariectomized females with diabetes was also improved significantly by the HTR2B agonist treatment. CONCLUSIONS: Impaired colonic motility in mice with diabetes was improved by enhancing HTR2B signaling. The HTR2B agonist may provide therapeutic benefits for constipation associated with diabetes.

Serotonin Deficiency Is Associated With Delayed Gastric Emptying.

BACKGROUND & AIMS: Gastrointestinal (GI) motility is regulated by serotonin (5-hydroxytryptamine [5-HT]), which is primarily produced by enterochromaffin (EC) cells in the GI tract. However, the precise roles of EC cell-derived 5-HT in regulating gastric motility remain a major point of conjecture. Using a novel transgenic mouse line, we investigated the distribution of EC cells and the pathophysiologic roles of 5-HT deficiency in gastric motility in mice and humans. METHODS: We developed an inducible, EC cell-specific Tph1CreERT2/+ mouse, which was used to generate a reporter mouse line, Tph1-tdTom, and an EC cell-depleted line, Tph1-DTA. We examined EC cell distribution, morphology, and subpopulations in reporter mice. GI motility was measured in vivo and ex vivo in EC cell-depleted mice. Additionally, we evaluated 5-HT content in biopsy and plasma specimens from patients with idiopathic gastroparesis (IG). RESULTS: Tph1-tdTom mice showed EC cells that were heterogeneously distributed throughout the GI tract with the greatest abundance in the antrum and proximal colon. Two subpopulations of EC cells were identified in the gut: self-renewal cells located at the base of the crypt and mature cells observed in the villi. Tph1-DTA mice displayed delayed gastric emptying, total GI transit, and colonic transit. These gut motility alterations were reversed by exogenous provision of 5-HT. Patients with IG had a significant reduction of antral EC cell numbers and 5-HT content, which negatively correlated with gastric emptying rate. CONCLUSIONS: The Tph1CreERT2/+ mouse provides a powerful tool to study the functional roles of EC cells in the GI tract. Our findings suggest a new pathophysiologic mechanism of 5-HT deficiency in IG.

miR-10b-5p Rescues Diabetes and Gastrointestinal Dysmotility.

BACKGROUND & AIMS: Interstitial cells of Cajal (ICCs) and pancreatic ß cells require receptor tyrosine kinase (KIT) to develop and function properly. Degeneration of ICCs is linked to diabetic gastroparesis. The mechanisms linking diabetes and gastroparesis are unclear, but may involve microRNA (miRNA)-mediated post-transcriptional gene silencing in KIT+ cells. METHODS: We performed miRNA-sequencing analysis from isolated ICCs in diabetic mice and plasma from patients with idiopathic and diabetic gastroparesis. miR-10b-5p target genes were identified and validated in mouse and human cell lines. For loss-of-function studies, we used KIT+ cell-restricted mir-10b knockout mice and KIT+ cell depletion mice. For gain-of-function studies, a synthetic miR-10b-5p mimic was injected in multiple diabetic mouse models. We compared the efficacy of miR-10b-5p mimic treatment vs antidiabetic and prokinetic medicines. RESULTS: miR-10b-5p is highly expressed in ICCs from healthy mice, but drastically depleted in ICCs from diabetic mice. A conditional knockout of mir-10b in KIT+ cells or depletion of KIT+ cells in mice leads to degeneration of ß cells and ICCs, resulting in diabetes and gastroparesis. miR-10b-5p targets the transcription factor Krüppel-like factor 11 (KLF11), which negatively regulates KIT expression. The miR-10b-5p mimic or Klf11 small interfering RNAs injected into mir-10b knockout mice, diet-induced diabetic mice, and TALLYHO polygenic diabetic mice rescue the diabetes and gastroparesis phenotype for an extended period of time. Furthermore, the miR-10b-5p mimic is more effective in improving glucose homoeostasis and gastrointestinal motility compared with common antidiabetic and prokinetic medications. CONCLUSIONS: miR-10b-5p is a key regulator in diabetes and gastrointestinal dysmotility via the KLF11-KIT pathway. Restoration of miR-10b-5p may provide therapeutic benefits for these disorders.

Smooth Muscle Transcriptome Browser: offering genome-wide references and expression profiles of transcripts expressed in intestinal SMC, ICC, and PDGFRα+ cells.

Transcriptome data on the quantitative numbers of transcriptional variants expressed in primary cells offer essential clues into specific cellular functions and biological processes. We have previously collected transcriptomes from primary smooth muscle cells (SMC), interstitial cells of Cajal (ICC), and PDGFRα+ cells (fibroblast-like cells) isolated from murine jejunal and colonic smooth muscle and/or mucosal tissues as well as transcriptomes from the associated tissues (jejunal smooth muscle, colonic smooth muscle, and colonic mucosa). In this study, we have built the Smooth Muscle Transcriptome Browser (SMTB), https://med.unr.edu/physio/transcriptome , a web-based, graphical user interface that offers genetic references and expression profiles of all transcripts expressed at both the cellular (SMC, ICC, and PDGFRα+ cells) and tissue level (smooth muscle and mucosal tissue). This browser brings new insights into the cellular and biological functions of the cell types in gastrointestinal smooth muscle biology.