Slc26a3 (DRA) in the Gut: Expression, Function, Regulation, Role in Infectious Diarrhea and Inflammatory Bowel Disease

p-hydroxy benzaldehyde attenuates intestinal epithelial barrier dysfunction caused by colitis via activating the HNF-1β/SLC26A3 pathway

Background

Intestinal epithelial barrier dysfunction is intricately linked to the pathogenesis of ulcerative colitis (UC). Dietary interventions that bolster intestinal epithelial barrier function can effectively thwart UC onset. Our prior research revealed that p-Hydroxy benzaldehyde (HD), a phenolic compound from Nostoc commune (an edible cyanobacterium), markedly upregulated the expression of E-cadherin, a pivotal protein in intestinal mucosa, thereby mitigating mucosal damage in mice afflicted with dextran sulfate sodium (DSS)-induced colitis. Nevertheless, the precise molecular mechanisms underpinning HD's ameliorative effects on intestinal epithelial barrier dysfunction remain elusive.

Methods

Dextran sodium sulfate (DSS)-induced colitis mouse model was established, and the successful establishment of the model was determined by evaluating the changes in body weight, disease activity index (DAI), colonic histopathology, and white blood cell count. Transmission electron microscopy (TEM) observed the ultrastructural changes of intestinal villi. The levels of inflammatory factors ( IFN-γ IL-13 ) and intestinal permeability indicators (FITC-Dextran, DAO, ET, and D-LA ) were detected by Enzyme-linked immunosorbent assay (ELISA). Western blotting (WB) and immunohistochemistry (IHC) were used to detect the expression of intestinal barrier integrity-related factors such as tight junction protein TJs (ZO-1, occludin) and adhesion junction protein AJs (E-cadherin). Furthermore, WB, Pull-down assay, drug affinity reaction target stability (DARTS) assay, molecular docking and molecular dynamics (MD) simulation were used to determine the potential target and molecular mechanism of HD.

Results

HD intervention significantly alleviated the symptoms of colitis mice, inhibited the weight loss and colon shortening, reduced DAI score and colon pathological score, maintained the ultrastructure of intestinal villi in colon tissue, and significantly reduced the inflammatory factors IFN-γ, IL-13 and the number of white blood cells in colon tissue of colitis mice. HD could also reduce the levels of FITC-Dextran, DAO, ET, and D-LA and increase the expression of ZO-1, occludin, and E-cadherin in the colonic tissues of colitis mice, thereby maintaining the impaired intestinal barrier function caused by colitis. Mechanically, HD augmented the expression of hepatocyte nuclear factor 1β (HNF-1β) and DRA. Adeno-associated virus (AAV)-HNF-1β shRNA or Lentivirus-mediated HNF-1β knockdown effectively abolished HD-induced intestinal barrier protection, as well as the promotion of solute carrier family 26 member 3 (SLC26A3) expression levels. SLC26A3 siRNA effectively reversed the inhibition of intestinal permeability by HD. Pull-down assay, DARTS analysis, molecular docking, and MD results showed high binding strength, interaction efficiency and remarkable stability between HNF-1β and HD.

Conclusion

This study elucidates HD's role in forestalling intestinal epithelial barrier disruption under colitis conditions. Mechanistic investigations revealed that HD fortifies TJs and AJs expression via the HNF-1β/SLC26A3 pathway, thus preserving the lower intestinal epithelial barrier's integrity in UC.

Butyrate Inhibits the HDAC8/NF-κB Pathway to Enhance Slc26a3 Expression and Improve the Intestinal Epithelial Barrier to Relieve Colitis

Dietary fiber is known to promote the production of short-chain fatty acids (SCFAs) by gut bacteria, which can enhance intestinal epithelial barrier function and ameliorate intestinal inflammation in patients with inflammatory bowel disease (IBD). Interestingly, some IBD patients show reduced expression of solute carrier family member 3 (Slc26a3) in intestinal epithelial cells. The objective of this research was to investigate the interaction between SCFAs and Slc26a3 during colitis and assess how this interaction affects intestinal epithelial barrier function. We showed that butyrate alleviated colonic inflammation in a dose-dependent manner in a dextran sulfate sodium salt (DSS)-induced colitis model. Consistent with this, butyrate increased Slc26a3 and tight junction protein levels. In addition, butyrate inhibited histone deacetylase (HDAC) levels and significantly increased the expression of Slc26a3 by the acetylation of histones in Caco-2BBe cells. The utilization of a pan-HDAC inhibitor or inhibitors specific to certain classes of HDACs revealed that butyrate primarily suppressed HDAC8 to blunt the NF-κB pathways and enhance the expression of Slc26a3. Notably, we demonstrated that HDAC8 activation counteracted the beneficial effect of butyrate in DSS-induced colitis. Therefore, we concluded that butyrate improves the expression of Slc26a3 via inhibition of the HDAC8/NF-κB pathway, leading to increased intestinal epithelial barrier function.

Decreased expression of DRA (SLC26A3) by a p38-driven IL-1α response contributes to diarrheal disease following in vivo challenge with Brachyspira spp

In this study, we uncovered the novel mechanism of IL-1α-mediated downregulated in adenoma (DRA) (SLC26A3) downregulation in the context of Brachyspira spp.-induced malabsorptive diarrhea. Experimentally infected pigs with Brachyspira spp. had significantly reduced DRA expression in the colon accompanied by IL-1α upregulation. This response was recapitulated in vitro by exposing Caco-2 cells to either Brachyspira lysate or IL-1α. Both p38 and MAPK-activated protein kinase 2 (MAPKAPK-2 also referred as MK-2) showed an increased phosphorylation after exposure to either. SB203580 application, a p38 inhibitor blocked the MK-2 phosphorylation and attenuated the DRA and IL-1α response to both lysate and IL-1α. Exposure to IL-1 receptor antagonist (IL-1RA) produced a similar response. In addition, exposure of cells to either of these blockers without IL-1α or lysate results in increased DRA and decreased IL-1α expression, revealing that DRA needs IL-1α signaling for basal physiological expression. Dual inhibition with both blockers completely inhibited the effect from IL-1α while significantly attenuating the response from Brachyspira lysate, suggesting a minor contribution from another pathway. Together this demonstrates that Brachyspira activates p38 MAPK signaling driving IL-1α expression, which activates IL-1R1 causing DRA downregulation while also driving upregulation of IL-1α through p38 in a positive feedback mechanism. In conclusion, we elucidated a major pathway involved in DRA downregulation and its role in Brachyspira-induced diarrhea. In addition, these observations will aid in our understanding of other inflammatory and infectious diarrhea conditions.NEW & NOTEWORTHY The diarrheal disease caused by the two infectious spirochete spp. B. hyodysenteriae and B. hampsonii reduced the expression of DRA (SLC26A3), a major Cl-/HCO-3 exchanger involved in Cl- absorption. This is attributed to the upregulation of IL-1α driven by p38 MAPK. This work also describes a potential new mechanism in inflammatory diseases while showing the importance of IL-1α in maintaining DRA levels.

Deficiency of SLC26A3 promotes jejunal barrier damage in metabolic disease-susceptible transgenic pigs

Intestinal disorders are common in metabolic syndrome. However, their pathogenesis is still not fully understood. Pig and human intestines are highly similar in terms of associated metabolic processes. Here, we successfully constructed a metabolic disease-susceptible transgenic (TG) Bama pig model by knocking in three humanized disease risk genes with the CRISPR/Cas9 technique to assess its potential as a model for human intestinal diseases and explore the possible pathological mechanisms involved. We found that jejunal barrier integrity was disrupted and that the infiltration of inflammatory cells increased in TG pigs after high-fat and high-sucrose diet (HFHSD) treatment. We revealed significant differences in the transcriptome, associated microbiome profiles and microbial metabolite short-chain fatty acid (SCFA) content of the jejunum of TG pigs. Notably, we found that SLC26A3 was significantly downregulated in TG pigs. Knockdown or overexpression of the SLC26A3 gene in IPEC-J2 cells significantly affected the expression of MUC2, MUC13 and occludin. Furthermore, in vitro experiments further verified that CDX2 directly regulated the expression of SLC26A3. Mechanistically, CDX2 mediated intestinal barrier function by enhancing the expression of SLC26A3 by binding to its promoter region between -1120 and - 1070 bp. TG pigs represent a promising model that provides new insights into preclinical research on human intestinal metabolic diseases associated with metabolic disorders and revealed that SLC26A3 may be a potential therapeutic target for intestinal metabolic diseases.

Akkermansia muciniphila Protects Against Antibiotic-Associated Diarrhea in Mice

Probiotics are used to prevent antibiotic-associated diarrhea (AAD) via the restoration of the gut microbiota. However, the precise effects of Akkermansia muciniphila (Akk), which is a promising probiotics, on AAD are unknown. Here, AAD models were established via the administration of lincomycin and ampicillin with or without pasteurized Akk or Amuc_1100 treatment. A diffusion test revealed that Akk was susceptible to the majority of the antibiotics, such as ampicillin. These effects were confirmed by the reduced Akk abundance in AAD model mice. Pasteurized Akk or Amuc_1100 significantly decreased the diarrhea status score and colon injury of AAD model mice. Additionally, these treatments significantly decreased the relative abundance of Citrobacter at genus level and reshaped the metabolic function of gut microbiota. Notably, pasteurized Akk or Amuc_1100 significantly changed the serum metabolome of AAD model mice. In addition, pasteurized Akk or Amuc_1100 suppressed intestinal inflammation by upregulating the expression of GPR109A and SLC5A8 and downregulating the expression of TNFα, IFNγ, IL1β, and IL6. Furthermore, they enhanced water and electrolyte absorption by upregulating AQP4, SLC26A3, and NHE3. Pasteurized Akk or Amuc_1100 also restored intestinal barrier function by ameliorating the downregulation of ZO-1, OCLN, CLDN4, and Muc2 in AAD model mice. In summary, optimizing intestinal health with pasteurized Akk or Amuc_1100 may serve as an approach for preventing AAD.

Effects of the Interaction between Rumen Microbiota Density-VFAs-Hepatic Gluconeogenesis on the Adaptability of Tibetan Sheep to Plateau

During the adaptive evolution of animals, the host and its gut microbiota co-adapt to different elevations. Currently, there are few reports on the rumen microbiota-hepato-intestinal axis of Tibetan sheep at different altitudes. Therefore, the purpose of this study was to explore the regulatory effect of rumen microorganism-volatile fatty acids (VFAs)-VFAs transporter gene interactions on the key enzymes and genes related to gluconeogenesis in Tibetan sheep. The rumen fermentation parameters, rumen microbial densities, liver gluconeogenesis activity and related genes were determined and analyzed using gas chromatography, RT-qPCR and other research methods. Correlation analysis revealed a reciprocal relationship among rumen microflora-VFAs-hepatic gluconeogenesis in Tibetan sheep at different altitudes. Among the microbiota, Ruminococcus flavefaciens (R. flavefaciens), Ruminococcus albus (R. albus), Fibrobactersuccinogenes and Ruminobacter amylophilus (R. amylophilus) were significantly correlated with propionic acid (p < 0.05), while propionic acid was significantly correlated with the transport genes monocarboxylate transporter 4 (MCT4) and anion exchanger 2 (AE2) (p < 0.05). Propionic acid was significantly correlated with key enzymes such as pyruvate carboxylase, phosphoenolpyruvic acid carboxylase and glucose (Glu) in the gluconeogenesis pathway (p < 0.05). Additionally, the expressions of these genes were significantly correlated with those of the related genes, namely, forkhead box protein O1 (FOXO1) and mitochondrial phosphoenolpyruvate carboxykinase 2 (PCK2) (p < 0.05). The results showed that rumen microbiota densities differed at different altitudes, and the metabolically produced VFA contents differed, which led to adaptive changes in the key enzyme activities of gluconeogenesis and the expressions of related genes.

Comprehensive analysis of differential long non-coding RNA and messenger RNA expression in cholelithiasis using high-throughput sequencing and bioinformatics

Background

The etiology of gallstone disease (GSD) has not been fully elucidated. Consequently, the primary objective of this study was to scrutinize and provisionally authenticate the distinctive expression profiles of long non-coding RNAs (lncRNAs) and messenger RNAs (mRNAs) in GSD.

Methods

RiboNucleic Acid (RNA) sequencing was used on four paired human gallbladder samples for the purpose of this study. Differentially expressed lncRNAs (DElncRNAs) and mRNAs (DEmRNAs) were identified and subjected to analysis of their biological functions. The Pearson's correlation coefficients between DElncRNAs and DEmRNAs were computed to construct a co-expression network delineating their associations. Furthermore, both cis- and trans-regulatory networks of selected lncRNAs were established and visualized. Additionally, a competing endogenous RNA (ceRNA) regulatory network was constructed. To validate the RNA-sequencing data, we performed a Quantitative Real-time Polymerase Chain Reaction (RT-qPCR) on 10 paired human gallbladder samples, assessing the expressions of the top 4 DEmRNAs and DElncRNAs in gallstone and control samples.

Results

A total of 934 DEmRNAs and 304DElncRNAs were successfully identified. Functional enrichment analysis indicated a predominant involvement in metabolic-related biological functions. Correlation analysis revealed a strong association between the expressions of 597 DEmRNAs and 194 DElncRNAs. Subsequently, both a cis-lncRNA-mRNA and a trans-lncRNA-Transcription Factor (TF)-mRNA regulatory network were meticulously constructed. Additionally, a ceRNA network, comprising of 24 DElncRNAs, 201 DEmRNAs, and 120 predicted miRNAs, was established. Furthermore, using RT-qPCR, we observed significant upregulation of AC004692.4, HECW1-IT1, SFRP4, and COMP, while LINC01564, SLC26A3, RP1-27K12.2, and GSTA2 exhibited marked downregulation in gallstone samples. Importantly, these findings were consistent with the sequencing.

Conclusion

We conducted a screening process to identify DElncRNAs and DEmRNAs in GSD. This approach contributes to a deeper understanding of the genetic factors involved in the etiology of gallstones.

Bicarbonate secretion and acid/base sensing by the intestine

The transport of bicarbonate across the enterocyte cell membrane regulates the intracellular as well as the luminal pH and is an essential part of directional fluid movement in the gut. Since the first description of "active" transport of HCO3- ions against a concentration gradient in the 1970s, the fundamental role of HCO3- transport for multiple intestinal functions has been recognized. The ion transport proteins have been identified and molecularly characterized, and knockout mouse models have given insight into their individual role in a variety of functions. This review describes the progress made in the last decade regarding novel techniques and new findings in the molecular regulation of intestinal HCO3- transport in the different segments of the gut. We discuss human diseases with defects in intestinal HCO3- secretion and potential treatment strategies to increase luminal alkalinity. In the last part of the review, the cellular and organismal mechanisms for acid/base sensing in the intestinal tract are highlighted.

Traditional herbal pair Portulacae Herba and Granati Pericarpium alleviates DSS-induced colitis in mice through IL-6/STAT3/SOCS3 pathway

BACKGROUND

Portulacae Herba and Granati Pericarpium pair (PGP) is a traditional Chinese herbal medicine treatment for colitis, clinically demonstrating a relatively favorable effect on relieving diarrhea and abnormal stools. However, the underlying mechanism remain uncertain.

PURPOSE

The present study intends to evaluate the efficacy of PGP in treating colitis in mice and investigate its underlying mechanism.

METHODS

The protective effect of PGP against colitis was determined by monitoring body weight, colon length, colon weight, and survival rate in mice. Colonic inflammation was assessed by serum cytokine levels, colonic H&E staining, and local neutrophil infiltration. The reversal of intestinal epithelial barrier damage by PGP was subsequently analyzed with Western blot and histological staining. Furthermore, RNA-seq analysis and molecular docking were performed to identify potential pathways recruited by PGP. Following the hints of the transcriptomic results, the role of PGP through the IL-6/STAT3/SOCS3 pathway in DSS-induced colitis mice was verified by Western blot.

RESULTS

DSS-induced colitis in mice was significantly curbed by PGP treatment. PGP treatment significantly mitigated DSS-induced colitis in mice, as evidenced by improvements in body weight, DAI severity, survival rate, and inflammatory cytokines levels in serum and colon. Moreover, PGP treatment up-regulated the level of Slc26a3, thereby increasing the expressions of the tight junction/adherens junction proteins ZO-1, occludin and E-cadherin in the colon. RNA-seq analysis revealed that PGP inhibits the IL-6/STAT3/SOCS3 pathway at the transcriptional level. Molecular docking indicated that the major components of PGP could bind tightly to the proteins of IL-6 and SOCS3. Meanwhile, the result of Western blot revealed that the IL-6/STAT3/SOCS3 pathway was inhibited at the protein level after PGP administration.

CONCLUSION

PGP could alleviate colonic inflammation and reverse damage to the intestinal epithelial barrier in DSS-induced colitis mice. The underlying mechanism involves the inhibition of the IL-6/STAT3/SOCS3 pathway.

Cronkhite‒Canada syndrome as inflammatory hamartomatous polyposis: new evidence from whole transcriptome sequencing of colonic polyps

BACKGROUND

Cronkhite-Canada syndrome (CCS) is a rare, nonhereditary disease characterized by diffuse gastrointestinal polyposis and ectodermal abnormalities. Although it has been proposed to be a chronic inflammatory condition, direct evidence of its pathogenesis is lacking. This study aims to investigate the pathophysiology of CCS by analyzing transcriptomic changes in the colonic microenvironment.

METHODS

Next-generation sequencing-based genome-wide transcriptional profiling was performed on colonic hamartomatous polyps from four CCS patients and normal colonic mucosa from four healthy volunteers. Analyses of differential expression and multiple enrichment analyses were conducted from the molecular level to the cellular level. Quantitative real-time PCR (qRT-PCR) was carried out to validate the sequencing accuracy in samples from six CCS patients and six healthy volunteers.

RESULTS

A total of 543 differentially expressed genes were identified, including an abundance of CC- and CXC-chemokines. Innate immune response-related pathways and processes, such as leukocyte chemotaxis, cytokine production, IL-17, TNF, IL-1 and NF-kB signaling pathways, were prominently enhanced in CCS colonic polyps. Upregulation of wound healing, epithelial-mesenchymal transition, Wnt, and PI3K-Akt signaling pathways were also observed. Enrichment analyses at different levels identified extracellular structure disorganization, dysfunction of the gut mucosal barrier, and increased angiogenesis. Validation by qRT-PCR confirmed increased expression of the LCN2, IL1B, CXCL1, and CXCL3 genes in CCS colonic polyps.

CONCLUSIONS

This case-control whole transcriptome analysis of active CCS colonic hamartomatous polyps revealed intricate molecular pathways, emphasizing the role of the innate immune response, extracellular matrix disorganization, inflammatory cell infiltration, increased angiogenesis, and potential epithelial to mesenchymal transition. These findings supports CCS as a chronic inflammatory condition and sheds light on potential therapeutic targets, paving the way for more effective and personalized management of CCS in the future.

SLC26 Anion Transporters

Solute carrier family 26 (SLC26) is a family of functionally diverse anion transporters found in all kingdoms of life. Anions transported by SLC26 proteins include chloride, bicarbonate, and sulfate, but also small organic dicarboxylates such as fumarate and oxalate. The human genome encodes ten functional homologs, several of which are causally associated with severe human diseases, highlighting their physiological importance. Here, we review novel insights into the structure and function of SLC26 proteins and summarize the physiological relevance of human members.

Identification of GUCA2A and COL3A1 as prognostic biomarkers in colorectal cancer by integrating analysis of RNA-Seq data and qRT-PCR validation

By 2030, it is anticipated that there will be 2.2 million new instances of colorectal cancer worldwide, along with 1.1 million yearly deaths. Therefore, it is critical to develop novel biomarkers that could help in CRC early detection. We performed an integrated analysis of four RNA-Seq data sets and TCGA datasets in this study to find novel biomarkers for diagnostic, prediction, and as potential therapeutic for this malignancy, as well as to determine the molecular mechanisms of CRC carcinogenesis. Four RNA-Seq datasets of colorectal cancer were downloaded from the Sequence Read Archive (SRA) database. The metaSeq package was used to integrate differentially expressed genes (DEGs). The protein-protein interaction (PPI) network of the DEGs was constructed using the string platform, and hub genes were identified using the cytoscape software. The gene ontology and KEGG pathway enrichment analysis were performed using enrichR package. Gene diagnostic sensitivity and its association to clinicopathological characteristics were demonstrated by statistical approaches. By using qRT-PCR, GUCA2A and COL3A1 were examined in colon cancer and rectal cancer. We identified 5037 differentially expressed genes, including (4752 upregulated, 285 downregulated) across the studies between CRC and normal tissues. Gene ontology and KEGG pathway analyses showed that the highest proportion of up-regulated DEGs was involved in RNA binding and RNA transport. Integral component of plasma membrane and mineral absorption pathways were identified as containing down-regulated DEGs. Similar expression patterns for GUCA2A and COL3A1 were seen in qRT-PCR and integrated RNA-Seq analysis. Additionally, this study demonstrated that GUCA2A and COL3A1 may play a significant role in the development of CRC.

SLC26A3/NHERF2-IκB/NFκB/p65 feedback loop suppresses tumorigenesis and metastasis in colorectal cancer

Colorectal cancer (CRC) is a formidable disease due to the intricate mechanisms that drive its proliferation and metastasis. Despite significant progress in cancer research, the integration of these mechanisms that influence cancer cell behavior remains elusive. Therefore, it is imperative to comprehensively elucidate the underlying mechanisms driving CRC proliferation and metastasis. In this study, we reported a novel role of SLC26A3 in suppressing CRC progression. We found that SLC26A3 expression was downregulated in CRC, which was proportionally correlated with survival. Our in vivo and in vitro experiments demonstrated that up-regulation of SLC26A3 inhibited CRC proliferation and metastasis, while down-regulation of SLC26A3 promoted CRC progression by modulating the expression level of IκB. Furthermore, we identified NHERF2 as a novel interacting protein of SLC26A3 responsible for stabilizing the IκB protein and removing ubiquitination modification. Mechanistically, SLC26A3 augmented the interaction between NHERF2 and IκB, subsequently reducing its degradation. This process inhibited the dissociation of p65 from the IκB/p65/p50 complex and reduced the translocation of p65 from the cytoplasm to the nucleus. Moreover, our investigation revealed that NF-κB/p65 directly bound to the promoter of SLC26A3, leading to a decline in its mRNA expression. Thus, SLC26A3 impeded the nuclear translocation of NF-κB/p65, enhancing the transcription of SLC26A3 and establishing a positive regulatory feedback loop in CRC cells. Collectively, these results suggest that a SLC26A3/NHERF2-IκB/NF-κB/p65 signaling loop suppresses proliferation and metastasis in CRC cells. These findings propose a novel SLC26A3-driven signaling loop that regulates proliferation and metastasis in CRC, providing promising therapeutic interventions and prognostic targets for the management of CRC.

Oxalate Homeostasis in Non-Stone-Forming Chronic Kidney Disease: A Review of Key Findings and Perspectives

Chronic kidney disease (CKD) is a significant global public health concern associated with high morbidity and mortality rates. The maintenance of oxalate homeostasis plays a critical role in preserving kidney health, particularly in the context of CKD. Although the relationship between oxalate and kidney stone formation has been extensively investigated, our understanding of oxalate homeostasis in non-stone-forming CKD remains limited. This review aims to present an updated analysis of the existing literature, focusing on the intricate mechanisms involved in oxalate homeostasis in patients with CKD. Furthermore, it explores the key factors that influence oxalate accumulation and discusses the potential role of oxalate in CKD progression and prognosis. The review also emphasizes the significance of the gut-kidney axis in CKD oxalate homeostasis and provides an overview of current therapeutic strategies, as well as potential future approaches. By consolidating important findings and perspectives, this review offers a comprehensive understanding of the present knowledge in this field and identifies promising avenues for further research.

SLC26A3 (DRA) is stimulated in a synergistic, intracellular Ca2+-dependent manner by cAMP and ATP in intestinal epithelial cells

In polarized intestinal epithelial cells, downregulated in adenoma (DRA) is an apical Cl-/[Formula: see text] exchanger that is part of neutral NaCl absorption under baseline conditions, but in cyclic adenosine monophosphate (cAMP)-driven diarrheas, it is stimulated and contributes to increased anion secretion. To further understand the regulation of DRA in conditions mimicking some diarrheal diseases, Caco-2/BBE cells were exposed to forskolin (FSK) and adenosine 5'-triphosphate (ATP). FSK and ATP stimulated DRA in a concentration-dependent manner, with ATP acting via P2Y1 receptors. FSK at 1 µM and ATP at 0.25 µM had minimal to no effect on DRA given individually; however, together, they stimulated DRA to levels seen with maximum concentrations of FSK and ATP alone. In Caco-2/BBE cells expressing the Ca2+ indicator GCaMP6s, ATP increased intracellular Ca2+ (Ca2+i) in a concentration-dependent manner, whereas FSK (1 µM), which by itself did not significantly alter Ca2+i, followed by 0.25 µM ATP produced a large increase in Ca2+ that was approximately equal to the elevation caused by 1 µM ATP. 1,2-Bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis(acetoxymethyl ester) (BAPTA-AM) pretreatment prevented the ATP and FSK/ATP synergistically increased the DRA activity and the increase in Ca2+i caused by FSK/ATP. FSK/ATP synergistic stimulation of DRA was similarly observed in human colonoids. In Caco-2/BBE cells, subthreshold concentrations of FSK (cAMP) and ATP (Ca2+) synergistically increased Ca2+i and stimulated DRA activity with both being blocked by BAPTA-AM pretreatment. Diarrheal diseases, such as bile acid diarrhea, in which both cAMP and Ca2+ are elevated, are likely to be associated with stimulated DRA activity contributing to increased anion secretion, whereas separation of DRA from Na+/H+ exchanger isoform-3 (NHE3) contributes to reduced NaCl absorption.NEW & NOTEWORTHY The BB Cl-/[Formula: see text] exchanger DRA takes part in both neutral NaCl absorption and stimulated anion secretion. Using intestinal cell line, Caco-2/BBE high concentrations of cAMP and Ca2+ individually stimulated DRA activity, whereas low concentrations, which had no/minimal effect, synergistically stimulated DRA activity that required a synergistic increase in intracellular Ca2+. This study increases understanding of diarrheal diseases, such as bile salt diarrhea, in which both cAMP and elevated Ca2+ are involved.

Early Solid Diet Supplementation Influences the Proteomics of Rumen Epithelium in Goat Kids

It is well known that solid diet supplementation in early life can significantly promote rumen development and metabolic function in young ruminants. However, the changes in the expressed proteome and related metabolism in rumen epithelium in response to a supplemented solid diet remain unclear. In this study, rumen epithelial tissue from goats in three diet regimes including milk replacer only (MRO), milk replacer supplemented concentrate (MRC), and milk replacer supplemented concentrate plus alfalfa pellets (MCA) were collected for measurement of the expression of epithelial proteins using proteomic technology (six per group). The results showed that solid diet significantly improved the growth performance of goats, enhanced the ability of rumen fermentation, and promoted the development of epithelial papilla (p < 0.05). Proteome analysis revealed the distinct difference in the expressed protein in the MRC and MCA group compared with the MRO group (42 upregulated proteins and 79 downregulated proteins in MRC; 38 upregulated proteins and 73 downregulated proteins in MCA). Functional analysis showed that solid diet supplementation activated a variety of molecular functions in the epithelium, including protein binding, ATP binding, structural constituent of muscle, etc., in the MRC and MCA groups. Meanwhile, the expression of proteins related to fatty acid metabolism, the PPAR signaling pathway, valine, leucine, and isoleucine degradation, and butanoate metabolism were upregulated, being stimulated by solid feed. In contrast, the proteins associated with carbohydrate digestion and absorption and glycosaminoglycan degradation were downregulated. In addition, the protein expression of enzymes involved in ketone body synthesis in the rumen was generally activated, which was caused by solid feed. In summary, solid feed promoted the development of rumen epithelium by changing the expression of proteins related to fatty acid metabolism, energy synthesis, and signal transduction. The ketone body synthesis pathway might be the most important activated pathway, and provides energy for rumen development.

The Air-Liquid Interface Reorganizes Membrane Lipids and Enhances the Recruitment of Slc26a3 to Lipid-Rich Domains in Human Colonoid Monolayers

Cholesterol-rich membrane domains, also called lipid rafts (LRs), are specialized membrane domains that provide a platform for intracellular signal transduction. Membrane proteins often cluster in LRs that further aggregate into larger platform-like structures that are enriched in ceramides and are called ceramide-rich platforms (CRPs). The role of CRPs in the regulation of intestinal epithelial functions remains unknown. Down-regulated in adenoma (DRA) is an intestinal Cl-/HCO3- antiporter that is enriched in LRs. However, little is known regarding the mechanisms involved in the regulation of DRA activity. The air-liquid interface (ALI) was created by removing apical media for a specified number of days; from 12-14 days post-confluency, Caco-2/BBe cells or a colonoid monolayer were grown as submerged cultures. Confocal imaging was used to examine the dimensions of membrane microdomains that contained DRA. DRA expression and activity were enhanced in Caco-2/BBe cells and human colonoids using an ALI culture method. ALI causes an increase in acid sphingomyelinase (ASMase) activity, an enzyme responsible for enhancing ceramide content in the plasma membrane. ALI cultures expressed a larger number of DRA-containing platforms with dimensions >2 µm compared to cells grown as submerged cultures. ASMase inhibitor, desipramine, disrupted CRPs and reduced the ALI-induced increase in DRA expression in the apical membrane. Exposing normal human colonoid monolayers to ALI increased the ASMase activity and enhanced the differentiation of colonoids along with basal and forskolin-stimulated DRA activities. ALI increases DRA activity and expression by increasing ASMase activity and platform formation in Caco-2/BBe cells and by enhancing the differentiation of colonoids.

Is intestinal transport dysfunctional in COVID-19-related diarrhea?

Diarrhea, often severe, is a recognized and frequently early symptom during acute COVID-19 infection and may persist or develop for the first time in patients with long-COVID, with socioeconomic consequences. Diarrheal mechanisms in these cases are poorly understood. There is evidence for disruption of intestinal epithelial barrier function and also for changes in the gut microbiome, which is critical for gut immunity and metabolism. Whether the SARS-CoV-2 virus has adverse effects on intestinal transport proteins is unclear. However, the ability of the virus to inhibit expression and activity of an aldosterone-regulated epithelial sodium (Na+) channel (ENaC) present in human distal colon, which is responsible for Na+ and water salvage, points to possible disruption of other intestinal transport proteins during COVID-19 infection. In this Perspective, we develop this idea by highlighting possible intestinal transport protein targets for the SARS-CoV-2 virus and discussing how their interactions might be explored in the laboratory.

The genetics of monogenic intestinal epithelial disorders

Monogenic intestinal epithelial disorders, also known as congenital diarrheas and enteropathies (CoDEs), are a group of rare diseases that result from mutations in genes that primarily affect intestinal epithelial cell function. Patients with CoDE disorders generally present with infantile-onset diarrhea and poor growth, and often require intensive fluid and nutritional management. CoDE disorders can be classified into several categories that relate to broad areas of epithelial function, structure, and development. The advent of accessible and low-cost genetic sequencing has accelerated discovery in the field with over 45 different genes now associated with CoDE disorders. Despite this increasing knowledge in the causal genetics of disease, the underlying cellular pathophysiology remains incompletely understood for many disorders. Consequently, clinical management options for CoDE disorders are currently limited and there is an urgent need for new and disorder-specific therapies. In this review, we provide a general overview of CoDE disorders, including a historical perspective of the field and relationship to other monogenic disorders of the intestine. We describe the genetics, clinical presentation, and known pathophysiology for specific disorders. Lastly, we describe the major challenges relating to CoDE disorders, briefly outline key areas that need further study, and provide a perspective on the future genetic and therapeutic landscape.

Low Ca diet leads to increased Ca retention by changing the gut flora and ileal pH value in laying hens

Osteoporosis is a common degenerative metabolic bone disease in caged laying hens. Intensive egg production mobilizing large amounts of Ca from bone for eggshell formation, consequently leading to Ca deficiency, has been recognized as a critical factor causing osteoporosis in commercial laying hens. The aim of this study was to examine the effect of Ca deficiency on the function of the gut microbiota-bone axis and related egg production traits and bone health in laying hens. Twenty-four 48-week-old laying hens were fed a control diet (Control, 3.72%) or a low Ca diet (LC, 2.04%) for 60 d (n = 12). Compared to the Control hens, the LC hens had higher levels of alkaline phosphatase and tartrate resistant acid phosphatase (P < 0.05) with lower bone strength, eggshell thickness, and eggshell strength (P < 0.05). In addition, the LC hens had higher plasma estradiol concentrations, while having lower concentrations of interleukin-1 (IL-1) and IL-6. The LC hens also had a lower pH value in the ileum with an increased Ca retention. The principal co-ordinates analysis showed significantly separate cecal microbiota populations between the Control and LC hens. The Prevotellaceae_UCG-001, Subdoligranulum, Peptococcus, and Eubacterium_hallii_group (P < 0.05) were higher, while the CHKC1001 and Sutterella (P < 0.05) were lower at the genus level in the LC hens. In addition, Prevotellaceae_UCG-001, Subdoligranulum and Eubacterium_hallii_group had a negative correlation, while Sutterella was positively correlated with ileal pH values. The transcriptome analysis revealed that the low Ca diet caused 20 and 31 genes to be significantly up- and down-regulated, respectively. The gene expressions of cystic fibrosis transmembrane conductance regulator, solute carrier family 26 member 3 of the anion exchangers, and mitogen-activated protein kinase 12 of pro-inflammatory factors were lower in the LC birds, which was correlated with the lower ileal pH values. These results suggest that the hens with low Ca diet-induced osteoporosis have an increased intestinal Ca retention with a decreased ileal pH value, correlated with the changes in Prevotellaceae_UCG-001, Subdoligranulum, and Eubacterium_hallii_group of beneficial genera. The results provide insights for further understanding and preventing osteoporosis in laying hens.

Loss of SLC26A3 Results in Colonic Mucosal Immune Dysregulation via Epithelial-Immune Cell Crosstalk

BACKGROUND & AIMS

Down-regulation of chloride transporter SLC26A3 or down-regulated in adenoma (DRA) in colonocytes has recently been linked to the pathogenesis of ulcerative colitis (UC). Because exaggerated immune responses are one of the hallmarks of UC, these current studies were undertaken to define the mechanisms by which loss of DRA relays signals to immune cells to increase susceptibility to inflammation.

METHODS

NanoString Immunology Panel, fluorescence assisted cell sorting, immunoblotting, immunofluorescence, and quantitative real-time polymerase chain reaction assays were used in wild-type and DRA knockout (KO) mice. Interleukin (IL)-33 blocking was used to determine specific changes in immune cells and co-housing/broad spectrum antibiotics administration, and ex vivo studies in colonoids were conducted to rule out the involvement of microbiota. Colonoid-derived monolayers from healthy and UC patient biopsies were analyzed for translatability.

RESULTS

There was a marked induction of Th2 (>2-fold), CD4⁺ Th2 cells (∼8-fold), RORγt⁺ Th17, and FOXP3⁺ regulatory T cells (Tregs). DRA KO colons also exhibited a robust induction of IL-33 (>8-fold). In vivo studies using blocking of IL-33 established that T2 immune dysregulation (alterations in ILC2, Th2, and GATA3⁺ iTregs) in response to loss of DRA was due to altered epithelial-immune cell crosstalk via IL-33.

CONCLUSIONS

Loss of DRA in colonocytes triggers the release of IL-33 to drive a type 2 immune response. These observations emphasize the critical importance of DRA in mucosal immune homeostasis and its implications in the pathogenesis of UC.

The rs12532734 Polymorphism Near the Solute Carrier 26A3 Gene Locus Is Associated With Gallstone Disease in Children

Gallstones are increasingly frequent in children. In this candidate gene study, we genotyped 5 gene variants ( ANO1 , SPTLC3 , TMEM147 , TNRC6B , rs12532734) from a recent gallstone genome-wide association study (GWAS) in a cohort of 214 children with gallstones and 172 gallstone-free adult controls. In total, 138 genotyped children presented with symptomatic gallstone disease, 47 underwent cholecystectomy, and 126 received ursodeoxycholic acid (UDCA) as therapy for stones. Among 5 tested variants, the rs12532734 polymorphism modulated the gallstone risk in the studied cohort. Its genotype distribution significantly ( P = 0.025) departed from the Hardy-Weinberg equilibrium among cases, and the common allele was associated with increased odds of developing gallstones at young age (OR = 1.69, P = 0.014). SLC26A3 is the nearest gene to rs12532734 and is involved in the transepithelial bicarbonate and chloride transport. The association of rs12532734 with pediatric gallstones is a novel finding warranting further investigations also with regard to biliary bicarbonate flux and bile composition.

Pediococcus acidilactici Promotes the Longevity of C. elegans by Regulating the Insulin/IGF-1 and JNK/MAPK Signaling, Fat Accumulation and Chloride Ion

Probiotics are known to contribute to the anti-oxidation, immunoregulation, and aging delay. Here, we investigated the extension of lifespan by fermented pickles-origin Pediococcus acidilactici (PA) in Caenorhabditis elegans (C. elegans), and found that PA promoted a significantly extended longevity of wild-type C. elegans. The further results revealed that PA regulated the longevity via promoting the insulin/IGF-1 signaling, JNK/MAPK signaling but not TOR signaling in C. elegans, and that PA reduced the reactive oxygen species (ROS) levels and modulated expression of genes involved in fatty acids uptake and lipolysis, thus reducing the fat accumulation in C. elegans. Moreover, this study identified the nrfl-1 as the key regulator of the PA-mediated longevity, and the nrfl-1/daf-18 signaling might be activated. Further, we highlighted the roles of one chloride ion exchanger gene sulp-6 in the survival of C. elegans and other two chloride ion channel genes clh-1 and clh-4 in the prolonged lifespan by PA-feeding through the modulating expression of genes involved in inflammation. Therefore, these findings reveal the detailed and novel molecular mechanisms on the longevity of C. elegans promoted by PA.

Short-Chain Fatty Acids Reduced Renal Calcium Oxalate Stones by Regulating the Expression of Intestinal Oxalate Transporter SLC26A6

Renal calcium oxalate (CaOx) stone is a common urologic disease with a high prevalence and recurrence rate. However, short-chain fatty acids (SCFAs) are less often reported in the prevention of urolithiasis. This study aimed to explore the effect of SCFAs on the renal CaOx stone formation and the underlying mechanisms. Ethylene glycol was used to induce renal CaOx crystals in rats. SCFAs (acetate, propionate, or butyrate) were added as supplements to the drinking water with or without antibiotics. Because intestinal oxalate transporters SLC26A6 and SLC26A3 regulate the excretion and absorption of oxalate in the intestine, we injected adeno-associated virus 9 (AAV9)-SLC26A6-shRNA (short hairpin RNA) and AAV9-SLC26A3 into the tail vein of rats to suppress SLC26A6 and overexpress SLC26A3 expression in the intestine, respectively, to explore the role of SLC26A3 and SLC26A6 (SLC26A3/6) in the reduction of renal CaOx crystals induced by SCFAs. Results showed that SCFAs reduced renal CaOx crystals and urinary oxalate levels but, however, increased the abundance of SCFA-producing bacteria and cecum SCFA levels. SCFA supplements still reduced renal crystals and urinary oxalate after gut microbiota depletion. Propionate and butyrate downregulated intestinal oxalate transporter SLC26A3 expression, while acetate and propionate upregulated SLC26A6 expression, both in vivo and in vitro. AAV9-SLC26A3 exerted a protective effect against renal crystals, while AAV9-SLC26A6-shRNA contributed to the renal crystal formation even though the SCFAs were supplemented. In conclusion, SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones. IMPORTANCE Some studies found that the relative abundances of short-chain-fatty-acid (SCFA)-producing bacteria were lower in the gut microbiota of renal stone patients than healthy controls. Our previous study demonstrated that SCFAs could reduce the formation of renal calcium oxalate (CaOx) stones, but the mechanism is still unknown. In this study, we found that SCFAs (acetate, propionate, and butyrate) reduced the formation of renal calcium oxalate (CaOx) crystals and the level of urinary oxalate. Depleting gut microbiota increased the amount of renal crystals in model rats, and SCFA supplements reduced renal crystals and urinary oxalate after gut microbiota depletion. Intestinal oxalate transporter SLC26A6 was a direct target of SCFAs. Our findings suggested that SCFAs could reduce urinary oxalate and renal CaOx stones through the oxalate transporter SLC26A6 in the intestine. SCFAs may be new supplements for preventing the formation of renal CaOx stones.

Clostridioides difficile: innovations in target discovery and potential for therapeutic success

INTRODUCTION

Clostridioides difficile infection (CDI) remains a worldwide clinical problem. Increased incidence of primary infection, occurrence of hypertoxigenic ribotypes, and more frequent occurrence of drug resistant, recurrent, and non-hospital CDI, emphasizes the urgent unmet need of discovering new therapeutic targets.

AREAS COVERED

We searched PubMed and Web of Science databases for articles identifying novel therapeutic targets or treatments for C. difficile from 2001 to 2021. We present an updated review on current preclinical efforts on designing inhibitory compounds against these drug targets and indicate how these could become the focus of future therapeutic approaches. We also evaluate the increasing exploitability of gut microbial-derived metabolites and host-derived therapeutics targeting VEGF-A, immune targets and pathways, ion transporters, and microRNAs as anti-C. difficile therapeutics, which have yet to reach clinical trials. Our review also highlights the therapeutic potential of re-purposing currently available agents . We conclude by considering translational hurdles and possible strategies to mitigate these problems.

EXPERT OPINION

Considerable progress has been made in the development of new anti-CDI drug candidates. Nevertheless, a greater comprehension of CDI pathogenesis and host-microbe interactions is beginning to uncover potential novel therapeutic targets, which can be exploited to plug gaps in the CDI drug discovery pipeline.

Sauna dehydration as a new physiological challenge model for intestinal barrier function

The intestinal barrier plays a crucial role in maintaining gut health, and an increased permeability has been linked to several intestinal and extra-intestinal disorders. There is an increasing demand for interventions aimed at strengthening this barrier and for in vivo challenge models to assess their efficiency. This study investigated the effect of sauna-induced dehydration on intestinal barrier function (clinicaltrials.gov: NCT03620825). Twenty healthy subjects underwent three conditions in random order: (1) Sauna dehydration (loss of 3% body weight), (2) non-steroidal anti-inflammatory drug (NSAID) intake, (3) negative control. Intestinal permeability was assessed by a multi-sugar urinary recovery test, while intestinal damage, bacterial translocation and cytokines were assessed by plasma markers. The sauna dehydration protocol resulted in an increase in gastroduodenal and small intestinal permeability. Presumably, this increase occurred without substantial damage to the enterocytes as plasma intestinal fatty acid-binding protein (I-FABP) and liver fatty acid-binding protein (L-FABP) were not affected. In addition, we observed significant increases in levels of lipopolysaccharide-binding protein (LBP), IL-6 and IL-8, while sCD14, IL-10, IFN-ɣ and TNF-α were not affected. These results suggest that sauna dehydration increased intestinal permeability and could be applied as a new physiological in vivo challenge model for intestinal barrier function.