Grover, Madhusudan

Age-related gastrointestinal dysfunction is common, but the mechanisms of aging-associated smooth muscle failure remain unclear. We show that aging in mice slows whole gut and colonic transit, increases regional stiffness, and reduces smooth muscle contractility. Inducible smooth muscle cell (SMC)– specific deletion of Piezo1 preserved youthful transit and force generation, whereas Piezo1 activation in young mice phenocopied aging-associated transit delay. Single-cell transcriptomics, RNA velocity, stiffness-controlled cell and tissue cultures, and pharmacologic studies revealed that Piezo1 couples increased stiffness to Ca 2+ –calcineurin–NFAT signaling, loss of contractile gene programs, leading to age- related contractile loss and contractile-to-synthetic SMC remodeling and gut wall stiffening. Human intestinal SMCs supported conservation of this pathway, and PIEZO1 gain-of-function carriers showed a trend toward delayed colonic transit. Thus, maladaptive SMC Piezo1 mechanotransduction is a targetable mechanism of aging-associated gut dysmotility. Aging alters organ structure, yet how these changes drive functional decline remains poorly defined. We show that progressive stiffening of the gut with age activates the mechanosensitive ion channel Piezo1 in smooth muscle cells, initiating a maladaptive response that impairs contractility and slows intestinal transit. On the other hand, deletion of smooth muscle Piezo1 prevents age-related gut dysmotility. These findings reveal that age-related physical shifts actively drive functional decline through mechanotransduction pathways. By identifying Piezo1 as a critical link between tissue mechanics and organ aging, this work provides a framework for understanding how mechanical cues contribute to age-related dysfunction in the gut and possibly other smooth muscle organs.

Background Irritable bowel syndrome (IBS) is a complex disorder of gut-brain interaction, with heterogeneous symptoms, no available biomarkers and limited pathogenetic insight. Objective To identify genetic risk factors and actionable mechanisms for future clinical translation in IBS. Design We conducted a genome-wide association study (GWAS) meta-analysis of IBS in 2 775 539 individuals from 22 biobanks. IBS genetics was studied across multiple ancestries, different case definitions and symptom-related subtypes. Heritability and genetic correlations with other traits were estimated, and Mendelian randomisation was used to test causal relationships. GWAS data were functionally annotated and fine-mapped to prioritise tissues, cell types, pathways, candidate genes, specific mechanisms and druggable targets. Results Significant heritability was only detected in individuals of European ancestry, with near-identical genetic architecture across case definitions. Genetic correlations with GI, psychiatric and cardiometabolic traits were observed, including causal relationships with triglyceride (TG) levels. Functional annotation of IBS risk loci highlighted cell types and pathways relevant to brain, enteric neuro-glial and cardiometabolic domains, as well as actionable targets like GCKR, a regulator of TG metabolism. Druggability analyses converged on cardiometabolic mechanisms, including TG modulation. IBS polygenic risk scores were derived and showed a significant association with case status in an independent case-control dataset, supporting further evaluation in external population-based and clinically ascertained cohorts. Conclusions This study provides the most comprehensive assessment of IBS genetics to date, demonstrating reproducible polygenic inheritance. We link IBS risk to convergent neurogastrointestinal and novel cardiometabolic mechanisms, highlight specific biological pathways and actionable mechanisms and outline translational opportunities emerging from integrated computational analyses.

ABSTRACT The enteric nervous system (ENS) is a complex peripheral neural network that coordinates gastrointestinal motility through highly organized synaptic communication. Although tissue-resident muscularis macrophages (MMs) closely associate with enteric neurons, whether they regulate enteric synaptic organization remains unknown. In the central nervous system (CNS), microglia sculpt neural circuits through complement-dependent synaptic remodeling, raising the possibility that analogous neuroimmune mechanisms operate in the gut. Here, we identify a previously unrecognized role for C1qa□ MMs in regulating enteric synaptic homeostasis and gastrointestinal motility. Using macrophage-specific constitutive and inducible C1qa deletion models, single-cell RNA sequencing, enteric synaptosome proteomics, physiology, and advanced imaging, we demonstrate that loss of MMs-derived C1qa increases enteric synaptic density without altering neuronal numbers. C1qa deficiency induced broad transcriptional changes in enteric neurons and macrophages, including altered synapse-associated, lysosomal, and endocytic programs. Proteomic analysis revealed that enteric synapses share a conserved molecular architecture with brain synapses while exhibiting distinct gastrointestinal-specific complement-associated synaptic networks enriched for structural and receptor-localization pathways. Functionally, macrophage-specific C1qa deletion altered excitatory and inhibitory enteric neurotransmission, enhanced cholinergic signaling, reduced nitrergic responses, and accelerated gastrointestinal transit, while smooth muscle responsiveness remained preserved. C1qa□ MMs displayed transcriptional and functional features consistent with a phagocytic synapse-remodeling phenotype, including enrichment of complement, lysosomal, and engulfment pathways. Loss of C1qa impaired macrophage phagocytic activity both in vitro and in vivo and was associated with synapse accumulation and altered macrophage morphology. Importantly, inducible deletion of C1qa in adulthood recapitulated the synaptic and motility phenotypes, demonstrating that C1qa□ MMs continuously regulate enteric synaptic organization beyond development. Together, these findings identify a complement-dependent neuroimmune mechanism that regulates enteric circuit organization and gut motility, establishing MMs as active modulators of adult ENS synaptic homeostasis. Abstract Figure

Abstract Interstitial cells of Cajal (ICC) regulate gastrointestinal motility by generating electrical slow waves that orchestrate downstream calcium (Ca 2 + ) waves and coordinate smooth muscle contractions. A reduced ICC number has been reported in diabetic gastroparesis patients and in mouse models of delayed gastric emptying (DGE). However, functional changes in ICC propagating across the gastric regions in intact stomach are not well understood. The aim of this study was to develop an imaging approach to visualize ICC Ca 2+ waves in mouse stomach and determine spatiotemporal changes in mice with DGE. Tamoxifen‐treated B6.GCaMP5‐KitCreERT2 female mice were used as non‐diabetic controls (Non‐Db), while mice treated with streptozocin to induce diabetes were categorized as having normal (Db‐NGE) or delayed (Db‐DGE) gastric emptying based on emptying of solids. The ICC Ca 2+ network was imaged from excised intact mouse stomachs and subsequently opened along the lesser curvature and pinned flat. ICC Ca 2+ waves typically propagated along the greater curvature from the fundus–corpus line toward the antrum. The propagation length of ICC Ca 2+ activity was significantly decreased in Db‐DGE compared to Non‐Db and Db‐NGE and correlated to longer GE times. There was also a decrease in frequency, and the velocity was significantly faster in stomachs from Db‐DGE compared to Non‐Db and Db‐NGE. All experimental groups exhibited similar proportions of aberrant Ca 2+ propagation patterns (e.g., retrograde waves), but ectopic initiation only occurred in Db‐DGE stomachs. Thus, DGE is possibly driven by dysfunction in Ca 2+ activity in the ICC network that propagates rapidly over short distances, resulting in uncoordinated, non‐phasic muscle activity. image Key points Dysfunction of the interstitial cells of Cajal (ICC) has been implicated in diabetic gastroparesis but the changes in spatiotemporal properties of ICC network activity are not known. We developed an ex vivo Ca 2+ imaging approach to visualize ICC network activity across the entire stomach and determined changes in ICC Ca 2+ activity in a diabetic mouse model of delayed gastric emptying (GE). Decreased frequency and increased velocity of ICC Ca 2+ activity was observed in stomachs of diabetic mice with delayed GE. Ectopic initiation was a key feature associated with delayed GE. The propagation length of ICC Ca 2+ activity was inversely correlated to GE times and significantly reduced in stomach preparations from diabetic mice with delayed GE.

Background: Diabetic gastroparesis (DG) is associated with a loss in anti-inflammatory muscularis macrophages (MMs), contributing to delayed gastric emptying (DGE). Lyve1 macrophages, known for their anti-inflammatory phenotype, are involved in lipid metabolism across organs. While diabetes is typically associated with increased lipid levels, the dependence of lipid handling on altered function of Lyve1+ MMs in the stomach remains unknown. Aim: To investigate lipid accumulation in MMs and test the effect of palmitate and CD36 on Lyve1+ macrophages. Methods: FACS sorted CD45+ cells were isolated from the gastric muscularis of non-diabetic mice and analyzed using 10X Genomics Cellranger and Seurat package. Gene Set Enrichment Analysis was performed to identify enriched pathways. Separately, the cells underwent flow cytometry to identify Lyve1+/- MMs then determining lipid accumulation by LipidTox intensity. RAW 264.7 macrophage cells were cultured with macrophage colony stimulating factor (M-CSF), IL-4, and dexamethasone for 7 days to induce Lyve1 expression. RNA was collected from cells treated with palmitate and a CD36 inhibitor, Sulfosuccinimidyl oleate (SSO), for RT-qPCR. Lyve1+ and Lyve1- macrophages treated with 300µM palmitate overnight were collected for lipidomic analysis. Untargeted lipidomic analysis was done with Thermo Orbitrap Exploris 120, and data were analyzed using principal component analysis for group clustering and unpaired t-tests for differential analysis. Results: Unbiased clustering analysis revealed 6 transcriptionally distinct gastric MM populations, one of which was notably enriched in Lyve1 expression. Pathway analysis identified that Lyve1 enriched cluster was associated with lysosomal pathways and receptors involved in lipid uptake, such as CD36, as well as anti-inflammatory markers such as HO1 and CD206. Flow cytometry quantification showed that Lyve1+ MMs had higher accumulation of lipids compared to Lyve1- MMs (10.1±0.7 vs 2.9±0.2 mean fluorescence intensity/cell count, p=0.0002). RT-qPCR validated that Lyve1+ RAW 264.7 macrophages exhibited significantly higher expression of Lyve1 (6.95 times fold change, p=0.023) and CD36 (3.27 times fold change, p=0.011) compared to Lyve1- macrophages. Post palmitate treatment, Lyve1+ macrophages had increased expression of the pro-apoptotic gene caspase-3 (12.15-times fold change, p=0.033), as well as the fatty acid oxidation marker ACADM (4.98 times fold change, p=0.045). Notably, these differences were not found in the presence of SSO. Lipidomic analysis identified 171 differentially expressed lipids, particularly increased levels of ceramides and diacylglycerols in Lyve1+ macrophages compared to Lyve1- macrophages when both are treated with palmitate. Conclusions: Lyve1+ macrophages preferentially uptake lipids compared to Lyve1- macrophages consistent with increased expression of CD36. Lipid treatment of Lyve1+ macrophages increases expression of apoptosis and oxidation markers in a CD36-dependent manner that may lead to cell loss. These mechanisms may contribute to Lyve1+ MMs loss in DG. Funding: DK127992; DK129297; DK115255; ANMS Young Investigator grant; AGA grant#36; P30DK084567; Robert and Arlene Kogod Center on Aging Fundamental Mechanisms of Aging Award. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: Exogenous and endogenous polyamines are critical for gastrointestinal (GI) barrier integrity, of which putrescine, spermidine and spermine are most well studied. Our recent work shows n-acetylputrescine, a putrescine derivative, correlates with increased intestinal permeability and loss of microbial diversity. Despite this, bacterial mechanisms of n-acetylputrescine production or direct effects on barrier integrity are unknown. Aim: Determine the role of microbiota in shaping n-acetylputrescine abundance and the effect on barrier integrity. Methods: N-acetylputrescine effects on barrier were assessed both in vitro using Caco-2 and ex vivo in Ussing using colonic strips from conventional mice. Germ-free (GF) mice were monocolonized with wild-type E. coli (SK929) or E.coli SK930 (2-weeks, n=4mice/group), strains given by Dr. Shin Kurihara. E. coli SK930 is deficient in SpeC, SpeF and SpeB, genes generating putrescine, required for n-acetylputrescine production. Untargeted metabolomics (Metabolon) was performed on fecal pellets. Targeted isotope tracing with [13C6, 15N4]-arginine delivered via enema was done to track bacterial production of n-acetylputrescine by Fusobacterium varium, a known producer, in vivo with isotopolog labeling measured by LC/HRMS. Results: In vitro n-acetylputrescine (100mM) addition to Caco-2 monolayers caused significant barrier disruption compared to controls (%Baseline TER, 13.7±6.7 vs 102.8±9.4, 3h postexposure, n=3 p=0.0002), not seen at lower (10mM) concentration. N-acetylputrescine caused increased flux of 300Da fluorescein (12.6±2.0 vs 6.0±0.2 mg/mL, n=3 p=0.004) and 4kDa FITC-Dextran flux on Ussing compared to untreated controls (999±94 vs 562±121 ng/hr/cm2, n=3 p= 0.01). Mutant E. coli SK930 monocolonized mice had similar fecal n-acetylputrescine to GF animals. In contrast, wild type E. coli SK929 monocolonization led to significantly greater n-acetylputrescine (5-fold, FDR< 0.001) compared to SK930, indicating a bulk of n-acetylputrescine production is driven by bacterial mechanisms. Pathway enrichment analysis predicted decreased spermidine and spermine biosynthesis in SK930 monocolonization, indicative of impaired polyamine metabolism, compared to SK929 (FDR< 0.01). Targeted metabolomics on fecal pellets showed a shift in the production of isotopolog [13C1, 15N0]-N-acetylputrescine to increased isotopolog [13C4, 15N2]-N-acetylputrescine concentration after monocolonization with F. varium compared to GF mice (5.9±5.0 vs. 2.1±3.6 pg/mg stool, n=3mice/group p=0.05) suggesting microbiota driven shifts in n-acetylputrescine metabolism. Conclusion: Luminal n-acetylputrescine production and profile is driven by bacteria in the GI tract. Concentration dependent effects of n-acetylputrescine suggest insufficient regulation by intestinal microbiota can lead to accumulation of n-acetylputrescine and the intestinal barrier disruption seen in human studies. Ongoing studies aim to identify bacterial taxa critical for n-acetylputrescine suppression, the mechanisms involved, and impact on GI health. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

Background: As part of the bidirectional gut-brain communication system that influences gastrointestinal function, vagal pathways coordinate with the activity of interstitial cells of Cajal (ICC) to regulate gastric motility. Impairments in ICC slow wave activity and altered vagal tone have been implicated in diabetic gastroparesis and obesity, but technical limitations have restricted our ability to measure integrated and bidirectional activity in vagal-ICC pathways. Furthermore, the influence of physiological and meal-induced stimuli like gastric distension on these pathways is not well understood. We aimed to develop a calcium imaging approach in ex vivo nodose ganglion-vagus nerve-stomach preparations to investigate vagal-ICC pathways and test the effects of gastric distension on vagal activation, ICC network activity, and their functional interactions. Methods: Calcium imaging was performed in ex vivo preparations, in which the stomach and vagus nerves (with or without the ganglion) remain intact. EIIa-GCaMP6 (n=3) and cKit-GCaMP6 (n=3) mice were used to image Ca 2 + signals from both vagal neurons and ICC or ICC alone, respectively. Two-minute recordings were captured in the following stomach conditions: (1) Undistended; (2) Undistended + vagal nerve stimulation (VNS, 20 Hz, 1 s); (3) Distended (0.25 ml volume distension); (4) Distended + VNS. Ca 2 + signals in ICC and neurons, along with tissue displacement, were analyzed using Image J. Data from both GCaMP models were pooled for ICC. Results: Acute gastric distension significantly activated vagal sensory neurons in nodose ganglion compared to baseline (p=0.0193), and VNS evoked Ca 2 + responses in ICC and neurons, confirming intact nerve pathways. Both VNS and gastric distension altered the direction of ICC propagation, significantly increasing retrograde waves (p=0.0025 and p=0.0032, respectively), and VNS had no effect on retrograde waves in distended stomachs. VNS and distension also reduced length of propagation of anterograde ICC waves (p=0.019 and p=0.0004, respectively), and again, VNS effects were not observed during distension. VNS increased the velocity of ICC wave propagation, but only in undistended stomach (p=0.0283). Finally, VNS increased ICC pacemaker frequency regardless of the distension state (p=0.0123). Conclusion: Both acute gastric distension and VNS altered ICC network activity, with similar effects on network parameters. However, most of the VNS effects on ICC were blocked during distension. VNS increased the frequency of ICC network waves in both undistended and distended stomachs, suggesting that VNS can influence ICC pacemakers regardless of distension state. These findings have important implications for designing therapeutic strategies for gastroparesis. This abstract was presented at the American Physiology Summit 2026 and is only available in HTML format. There is no downloadable file or PDF version. The Physiology editorial board was not involved in the peer review process.

ABSTRACT Background Patients with gastroparesis (Gp) can have a variety of symptoms. Apart from use of prokinetics, symptomatic therapies for the predominant symptom (PrS) are used. Aims (1) To classify Gp patients based on their PrS; (2) To determine differences in Gp symptoms, gastric emptying (GE), quality of life (QOL), treatments, and symptom improvement among Gp patients with different PrS. Methods Gp patients were enrolled in a multicenter registry and followed for 96‐weeks. Patients recorded their PrS and completed questionnaires assessing symptoms and QOL at enrollment and at follow up visits. Results Of 1013 Gp patients (361 diabetic, 607 idiopathic, 45 post‐fundoplication), the PrS were nausea (31%), vomiting (20%), abdominal pain (20%), bloating (9%), fullness (4%), GERD (4%), constipation (3%). Abdominal pain was more often a PrS in idiopathics, whereas vomiting was more often a PrS in diabetics. QOL scores were lower in the abdominal pain PrS group. PrS was associated with greater use of directed symptomatic treatment (antiemetic agents and gastric electrical stimulation for nausea and vomiting, prokinetic agents for vomiting and fullness, and constipation medications for constipation). Of 555 patients followed over 48 weeks, GCSI improved by ≥ 1 in 26% overall, more often in patients with initial PrS of nausea (32%) and bloating (35%) and less often for initial PrS of fullness (13%) or abdominal pain (15%). Conclusions In Gp patients, the most common PrS were nausea, vomiting, and abdominal pain. PrS is associated with QOL, treatments utilized, and patient outcomes. Thus, the PrS of a patient with Gp provides useful information about their present condition and future outcome.

ABSTRACT Background Infection enteritis is associated with the development of irritable bowel syndrome (IBS) and functional dyspepsia. Aim This study aimed to examine the long‐term risk of IBS and functional dyspepsia, and associated health care utilisation following infection enteritis. Methods We conducted a retrospective cohort study using TriNetX U.S. Network. Adults with infection enteritis were identified and matched to controls, balancing demographics and comorbidities. Primary outcomes were the risk of incident IBS and functional dyspepsia diagnoses at 1, 5, and 10 years. Secondary outcomes were rates of IBS‐ and functional dyspepsia‐related medications, endoscopy, abdominal imaging, and hospitalizations. Pathogen‐specific and multivariate analyses were performed to assess variations in IBS risk. Results After matching, 202,244 patients were identified in each study cohort. At 1 year of follow‐up, the infection enteritis cohort had higher rates of IBS (RR = 2.35; 95% CI: 2.14–2.59), functional dyspepsia (RR = 2.02; 95% CI: 1.84–2.22), use of IBS‐related medications (RR = 1.29; 95% CI: 1.26–1.31), functional dyspepsia‐related medications (RR = 1.56; 95% CI: 1.55–1.59), abdominal imaging (RR = 2.42; 95% CI: 2.29–2.54), and Oesophagogastroduodenoscopy/colonoscopy (RR = 1.57; 95% CI: 1.50–1.65). These risks remained significantly higher in the IE cohort at 5 and 10 years. Salmonella/Shigella (RR = 6.48), and Giardia lamblia (RR = 5.05) had the highest risk of developing incident IBS. Conclusion Infection enteritis was associated with increased risk of IBS and functional dyspepsia, rates of related medication use, and greater healthcare utilisation.

ABSTRACT Background and Aims Alpha‐gal syndrome (AGS) is an IgE‐mediated hypersensitivity to galactose‐α‐1,3‐galactose, triggered by tick bites. It typically presents with delayed onset allergic or gastrointestinal symptoms after red meat consumption. This study aims to evaluate the prevalence of clinical symptoms and outcomes in AGS patients. Methods A systematic search of PubMed, Embase, and Cochrane Central was conducted to identify studies with at least five AGS patients that utilized alpha‐gal IgE for diagnosis and reported symptomatology. A random‐effects model calculated pooled prevalence and 95% confidence intervals (CIs) for clinical characteristics of AGS. Results Of the 739 studies screened, 15 met the inclusion criteria, comprising 1162 AGS patients (57% female). Urticaria was identified as the most prevalent symptom (63.8%, CI: 34.5–88.3, I 2 = 98.8%). At least one gastrointestinal symptom was reported in 69.2% of patients (CI: 49.3–85.9, I 2 = 97.5%), including abdominal pain (58.3%, CI: 36.0–78.9, I 2 = 96.0%), diarrhea (41.7%, CI: 22.3–62.5, I 2 = 93.4%), nausea (39.1%, CI: 29.2–49.6, I 2 = 79.1%), and vomiting (31.1%, CI: 21.9–41.2, I 2 = 70.4%). Tick bite history was recalled by 78.7% (CI: 46.4–98.1; I 2 = 99.1%), and 91.8% (CI: 84.6–96.8; I 2 = 70.3%) had symptom onset ≥ 1 h post red meat intake. Symptomatic improvement was observed in 86.5% (CI: 73.9–95.4, I 2 = 80.9%) of patients, with complete resolution in 42.7% (CI: 26.4–59.8, I 2 = 73.8%). Conclusion AGS typically presents with delayed onset allergic and GI symptoms after red meat intake, often with tick bite history. Majority of patients report symptomatic improvement on follow‐up.