Biology subjects

Sarker, R.

Publications and source records attributed to Sarker, R..

8 recordsLinked to original sources

bioRxiv2025

Differential Regulation of NHE3 Expression in Type 1 and Type 2 Diabetic Intestine: Impaired Endosomal Regulation of NHE3 Expression in Type 1 Diabetes

Chronic diarrhea is a frequent gastrointestinal complication in both type 1 (T1D) and type 2 diabetes (T2D), though the underlying mechanisms differ: T1D is linked to autonomic neuropathy and disrupted transporter regulation, while T2D is often linked to medications and intestinal inflammation. Using streptozotocin-induced mouse models of T1D and T2D, we observed increased luminal fluid in the small intestine of both. Given the role of Na+/H+ exchanger 3 (NHE3) in fluid absorption and its loss in most diarrheal diseases, we examined NHE3 expression across intestinal segments. In T1D, NHE3 protein was significantly reduced in the duodenum and jejunum without changes in mRNA, suggesting post-transcriptional regulation. In contrast, T2D mice exhibited reduced NHE3 protein and mRNA, restricted to the proximal colon. To investigate mechanisms underlying NHE3 loss in T1D, we evaluated endosomal scaffolding proteins involved in NHE3 trafficking. While our previous work showed that the Sorting Nexin-27 (SNX27)-retromer complex does not regulate NHE3 protein stability, we found that SNX17 was significantly decreased in the small intestine of T1D mice but unchanged in T2D. SNX17 knockdown in SK-CO15 cells reduced NHE3 activity and stability. A GST pull-down assay showed that SNX17 interacts with the C-terminus of NHE3. Mutation of the NHE3 distal NPxY motif disrupted this interaction, leading to reduced NHE3 expression and increased degradation. These findings reveal segment-specific and mechanistically distinct causes of diabetic diarrhea in T1D versus T2D, and identify SNX17 loss as a contributor to reduced NHE3 stability and activity in T1D, likely promoting diabetic diarrhea. New and NoteworthyThis study identifies distinct mechanisms of impaired sodium absorption contributing to diabetic diarrhea in type-1 and type-2 diabetes. We identify SNX17 as a novel regulator of NHE3 in the small intestine, showing that SNX17 loss in T1D contributes to post-translational NHE3 destabilization. In contrast, T2D-associated NHE3 downregulation is transcriptional and confined to the colon. These findings reveal disease- and region-specific regulatory pathways that drive impaired fluid absorption in diabetes, with direct implications for the development of targeted therapies. Graphical abstract Schematic overview of differential NHE3 regulation in diabetic diarrhea.In Type 1 Diabetes (T1D), reduced SNX17 expression in the small intestine causes increased degradation of NHE3 and impaired sodium absorption. In Type 2 Diabetes (T2D), SNX17 levels remain unchanged in the small intestine, but NHE3 expression is transcriptionally downregulated in the proximal colon. These distinct mechanisms contribute to segment-specific differential regulation of NHE3 in T1 and T2D diabetes. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=101 SRC="FIGDIR/small/675364v1_ufig1.gif" ALT="Figure 1"> View larger version (37K): org.highwire.dtl.DTLVardef@eabf0aorg.highwire.dtl.DTLVardef@1a46891org.highwire.dtl.DTLVardef@cd2d5corg.highwire.dtl.DTLVardef@5d185b_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2025

Partially differentiated enterocytes in ileal and distal-colonic human F508del-CF-enteroids 1 secrete fluid in response to forskolin and linaclotide.

Constipation causes significant morbidity in Cystic Fibrosis (CF) patients. Using CF patient (F508del) derived ex vivo ileal and distal colonic/rectal enteroids as a model and the Forskolin Induced Swelling Assay (FIS), we compared CFTR mediated fluid secretion in human enterocytes across the crypt-villus axis. CFTR expression and FIS decreased as enterocytes differentiated from crypt to become partially differentiated and then mature villus cells. While there was no FIS response in undifferentiated (crypt enterocytes) F508del-CF enteroids, partially differentiated F508del-CF enteroids had a swelling response to forskolin (cAMP) and linaclotide (cGMP) which was [~]48%, and [~]67% of the response in healthy enteroids, respectively and was prevented by a CFTR inhibitor. Also, linaclotide and a general PDE inhibitor independently enhanced combined CFTR-modulator-induced FIS response from partially differentiated F508del-CF enteroids. These findings demonstrate that partially differentiated ileal and distal colonic F508del-CFTR enteroids can be stimulated to secrete fluid by cAMP and cGMP.

physiology↗

bioRxiv2024

Is the nematode Strongyloides stercoralis a zoonosis from dogs? - a population genetics approach.

Gut nematode worms are important parasites of people and other animals. The parasitic nematode Strongyloides stercoralis infects an estimated 600 million people worldwide, and is one of the soil-transmitted helminthiases, a WHO-defined neglected tropical disease. It has long been suggested that human S. stercoralis infection may be a zoonosis from dogs. We investigated this by whole genome sequence analysis of S. stercoralis from sympatric human and dog populations in Asia. We find that human- and dog-derived S. stercoralis have genetically distinct nuclear genomes, but we also find evidence of rare cross infection. Analysis of the S. stercoralis mitochondrial genome reveals evidence of historical introgression between human- and dog-derived parasites. Based on these data we suggest that S. stercoralis was originally a parasite of canids, that began to infect humans when people domesticated dogs, since when human- and dog-derived parasites have differentiated, but have not become separate species. Significance StatementNematode worms infect approximately a quarter of the worlds human population; Strongyloides stercoralis infects some 600 million people. It has been suggested that S. stercoralis in people and dogs is the same parasite, such that some human infection is acquired zoonotically from dogs. It is important to understand the source of human Strongyloides infection to be able to control it and the harm that it causes. Our population genomic analyses of human- and dog-derived S. stercoralis in Asia show that these parasites are distinct, but also reveal rare cross infection events. Our results are consistent with S. stercoralis ancestrally being a parasite of dogs that began infecting people when dogs became domesticated.

genetics↗

bioRxiv2023

False positive glycopeptide identification via in-FAIMS fragmentation

High-field asymmetric waveform ion mobility spectrometry (FAIMS) separates glycopeptides in the gas phase prior to mass spectrometry (MS) analysis, thus offering the potential to analyze glycopeptides without prior enrichment. Several studies have demonstrated the ability of FAIMS to enhance glycopeptide detection but have primarily focused on N-glycosylation. Here, we evaluated FAIMS for O-glycoprotein and mucin-domain glycoprotein analysis using samples of varying complexity. We demonstrated that FAIMS was useful in increasingly complex samples, as it allowed for the identification of more glycosylated species. However, during our analyses, we observed a phenomenon called "in FAIMS fragmentation" (IFF) akin to in source fragmentation but occurring during FAIMS separation. FAIMS experiments showed a 2-5-fold increase in spectral matches from IFF compared to control experiments. These results were also replicated in previously published data, indicating that this is likely a systemic occurrence when using FAIMS. Our study highlights that although there are potential benefits to using FAIMS separation, caution must be exercised in data analysis because of prevalent IFF, which may limit its applicability in the broader field of O-glycoproteomics. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/542648v1_ufig1.gif" ALT="Figure 1"> View larger version (51K): org.highwire.dtl.DTLVardef@d94300org.highwire.dtl.DTLVardef@1bdc6dforg.highwire.dtl.DTLVardef@4b8ea8org.highwire.dtl.DTLVardef@82beed_HPS_FORMAT_FIGEXP M_FIG C_FIG

biochemistry↗

bioRxiv2022

Air-Liquid-Interface Reorganizes Membrane Lipid and Enhance Recruitment of Slc26a3 to Lipid-Rich Domains in Human Colon

Background and AimsCholesterol-rich membrane domains, also called lipid rafts (LR), are specialized membrane domains that provide a platform for intracellular signal transduction. Membrane proteins often cluster in LR that further aggregate into larger platform-like structures that are enriched in ceramide 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 which is enriched in LR. However, little is known regarding the mechanisms involved in the regulation of DRA activity. MethodsAir 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 confluent colonoid monolayer grown as submerged cultures. Confocal imaging was used to examine the dimensions of membrane microdomains that contain DRA. ResultsDRA expression and activity were enhanced by culturing 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 m 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 differentiation of colonoids along with enhancing basal and forskolin-stimulated DRA activity. ConclusionsALI increases DRA activity and expression by increasing ASMase activity and platform formation in Caco-2/BBe cells and by enhancing the differentiation of normal human colonoids. SynopsisAir-liquid interface (ALI) enhances total and brush border DRA expression and activity in Caco-2/BBe cells and human colonoids by causing differentiation of enterocytes and acid sphingomyelinase-dependent enhanced retention of DRA in ceramide-rich platform-like structures at the plasma membrane.

cell biology↗

bioRxiv2022

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

In polarized intestinal epithelial cells, DRA is a brush border (BB) Cl-/HCO3- exchanger that is part of neutral NaCl absorption under baseline conditions but in cAMP driven diarrheas it is stimulated and contributes to increased anion secretion. To further understand regulation of DRA in conditions mimicking some diarrheal diseases, differentiated Caco-2/BBE cells were exposed to forskolin and ATP. Forskolin and ATP both acutely stimulated DRA in a concentration dependent manner. Forskolin at 1{micro}M and ATP at 0.25 {micro}M had minimal to no effect on DRA activity given individually; however, together, they stimulated DRA activity to levels seen with maximum concentrations of forskolin and ATP alone. In Caco-2/BBE cells expressing the Ca2+ indicator GCaMP6s, ATP alone increased Ca2+ in a concentration dependent manner, while forskolin (1 {micro}M), that by itself did not significantly alter Ca2+, followed by 0.25 {micro}M ATP produced a large increase in Ca2+ that was [~]equal to the elevation caused by 1 {micro}M ATP. BAPTA-AM pretreatment prevented the ATP and forskolin/ATP synergistic increased DRA activity and the increase in intracellular Ca2+ caused by ATP/forskolin. Conclusion: In Caco-2/BBE cells subthreshold concentrations of forskolin (cAMP) and ATP (Ca2+) synergistically increased intracellular Ca2+ 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, while separation of DRA from NHE3 contributes to reduced NaCl absorption.

physiology↗

bioRxiv2020

Chronic exposure of ErbB TKIs inhibits DRA expression and activity through an ERK/Elk-1/CREB/AP-1 dependent pathway

Diarrhea is the major side effect of first- and second-generation ErbB tyrosine kinase inhibitors (TKI), the mechanism of which remains incompletely understood. The current studies were carried out over the time frame that ErbB TKIs usually initiate diarrhea. We report in Caco-2/bbe cells that exposure of ErbB TKIs, but not non-ErbB TKIs for six days at clinically-relevant concentrations significantly reduced the expression of DRA and inhibited apical Cl-/HCO3-exchange activity. The ErbB TKIs decreased DRA expression through an ERK/Elk-1/CREB/AP-1 dependent pathway. The blockade of ERK phosphorylation by ErbB TKIs decreased the phosphorylation of Elk-1 and the amount of total and p-CREB, and reduced the expression of C-Fos, which is part of the AP-1 complex that maintain DRA expression. Altogether, our studies demonstrate that ErbB TKIs decrease expression and activity of DRA, which occurs over the time frame that these drugs clinically cause diarrhea, and since DRA is part of the intestinal neutral NaCl absorptive process, the reduced absorption is likely to represent a major contributor to the ErbB TKI-associated diarrhea.

pharmacology and toxicology↗

bioRxiv2018

cAMP stimulates SLC26A3 activity in human colon by a CFTR-dependent mechanism that does not require CFTR activity

Background & AimsDRA (SLC26A3) is an electroneutral Cl-/HCO3- exchanger that is present in the apical domain of multiple intestinal segments. An area that has continued to be poorly understood is related to DRA regulation in acute cAMP-related diarrheas, in which DRA appears to be both inhibited as part of NaCl absorption and stimulated to contribute to increased HCO3- secretion. Different cell models expressing DRA have shown that cAMP inhibits, stimulates or does not affect its activity.\n\nMethodsThis study reevaluated cAMP regulation of DRA using new \"tools\" including a successful knockout cell model, a specific DRA inhibitor (DRAinh-A250), specific antibodies, and a transport assay that did not rely on non-specific inhibitors. The studies compared DRA regulation in colonoids made from normal human colon with regulation in the colon cancer cell line, Caco-2.\n\nResultsDRA is an apical protein in human proximal colon, differentiated colonoid monolayers and Caco-2 cells. It is glycosylated and appears as two bands. cAMp(forskolin) acutely stimulated DRA activity in human colonoids and Caco-2 cells. In these cells, DRA is the predominant apical Cl-/HCO3- exchanger and is inhibited by DRAinh-A250 with IC50 of 0.5 mol/L and 0.2 {micro}mol/L, respectively. However, there was no effect of cAMP in HEK293/DRA cells that lacked CFTR. When CFTR was expressed in HEK293/DRA cells, cAMP also stimulated DRA activity. In all cases, cAMP stimulation of DRA was not inhibited by CFTRinh-172.\n\nConclusionsDRA is acutely stimulated by cAMP by a process that is CFTR-dependent but appears to be one of multiple regulatory effects of CFTR that does not require CFTR activity.

physiology↗