Hirschsprung disease arises when enteric neural crest cells fail to migrate and differentiate properly during development, leaving the distal intestine devoid of the myenteric and submucosal nerve plexuses that normally coordinate peristalsis. The result is abdominal distension and refractory constipation, typically treated by surgically removing the aganglionic segment and reconstructing the bowel. Yet a substantial proportion of patients continues to suffer long-term complications, including enterocolitis, anastomotic strictures, fecal soiling, persistent constipation, and the need for reoperation. These persistent problems have intensified the search for the molecular mechanisms underlying the disease, and the new work points squarely at the glial microenvironment.

Enteric glial cells are the most abundant non-neuronal component of the enteric nervous system, and they are far more than passive scaffolding. They maintain epithelial integrity, coordinate neuro-immune signaling, and support neuronal survival. Recent single-cell RNA sequencing studies have revealed that glia exist in multiple transcriptionally distinct states, some of which resemble reactive microglia in the brain. In tumor-associated macrophages, researchers have described a CXCL9-to-SPP1 polarization axis that separates anti-inflammatory from pro-disease functional states. Whether enteric glia undergo a comparable polarization program in Hirschsprung disease had never been established, and that question became the starting point for the investigation.

The team began with an integrated single-cell transcriptomic analysis of colonic tissue from a mouse model of Hirschsprung disease based on loss of the endothelin receptor B gene, Ednrb, alongside wild-type controls. Among the five transcriptionally distinct glial subclusters they identified, one stood out: a subcluster enriched for both TXNRD1 and SPP1 that expanded markedly in disease samples, while a subcluster marked by Apoe shrank. Enrichment analyses of this expanded population highlighted extracellular matrix organization, cell adhesion, focal adhesion, and PI3K-Akt and MAPK signaling programs. Computational modeling of ligand-receptor interactions further showed that this subcluster engaged in the strongest predicted communication with enteric neurons of any glial population, including a predicted VCAM1-NCAM1 signaling axis.

To probe the regulatory logic behind this glial remodeling, the researchers turned to network-based virtual perturbation using the scTenifoldNet framework, which simulates gene knockout or overexpression within an inferred gene regulatory network. Both virtual knockout and virtual overexpression of TXNRD1 converged on regulatory programs involving redox control, ERK/MAPK-associated immediate-early response genes, and stress-associated glial features. Virtual overexpression produced a more focused pathological shift, with SPP1 emerging as the most prominently perturbed gene. These in silico results positioned TXNRD1, a central regulator of intracellular redox homeostasis, as a plausible upstream driver of the disease-associated glial state.

Human tissue evidence followed. Proteomic profiling of paired proximal dilated and stenotic colonic segments from children undergoing pull-through surgery revealed marked TXNRD1 upregulation in the stenotic, aganglionic tissue, together with significant enrichment of the MAPK signaling pathway. Validation in eight paired patient samples using quantitative PCR, western blotting, and immunofluorescence confirmed elevated TXNRD1 alongside increased phosphorylation of Raf, MEK, and ERK, while the stress kinases p38 and JNK showed no significant changes, indicating selective activation of the ERK branch of the MAPK cascade. Immunofluorescence staining also showed that SPP1 was increased and CXCL9 reduced within S100β-positive enteric glia in the stenotic segments, mirroring the single-cell findings in human tissue.

The mechanistic experiments in cultured rat enteric glial cells tied these observations together. When the researchers overexpressed TXNRD1, the cells selectively increased ERK phosphorylation, elevated their production of SPP1, suppressed CXCL9, accumulated reactive oxygen species, migrated less effectively, and secreted less glial cell line-derived neurotrophic factor, or GDNF. Treatment with the ERK inhibitor SCH772984 partially restored CXCL9 expression and blunted SPP1 upregulation, while the antioxidant N-acetyl-L-cysteine reduced ROS accumulation, dampened ERK activation, and reversed the SPP1-high/CXCL9-low polarization. Notably, ERK inhibition did not normalize ROS levels, suggesting that redox dysregulation acts upstream of ERK/MAPK signaling rather than as a downstream consequence.

The consequences for neurons were striking. In co-culture experiments with primary dorsal root ganglion neurons, TXNRD1-overexpressing glia increased neuronal apoptosis, impaired neuronal migration, reduced phosphorylation of the RET receptor and expression of its co-receptor GFRα1, downregulated the synaptic proteins PSD-95 and synaptophysin, and disrupted intracellular calcium homeostasis. Levels of the neurotrophic factors NGF and BDNF also fell in the co-culture system. Crucially, both ERK inhibition and supplementation with exogenous GDNF partially rescued these defects, implicating suppression of the GDNF/GFRα1/RET signaling axis as a key route by which the remodeled glia damage neuronal development and function.

The in vivo experiments provided the most compelling translational signal. The team generated Ednrb conditional knockout mice, which develop Hirschsprung-like phenotypes, and delivered an adeno-associated virus carrying TXNRD1-targeting shRNA by intraperitoneal injection at postnatal day 5. Knockdown of TXNRD1 markedly ameliorated the disease features, reducing abdominal distension, proximal colonic dilatation, distal stenosis, and fecal retention. Treated mice survived significantly longer, with four animals reaching the study endpoint, and fecal water content rose toward control levels, indicating improved intestinal function. At the molecular level, TXNRD1 suppression decreased SPP1, restored CXCL9, increased the neuronal marker TUJ1 and the neural crest marker p75, and upregulated the communication mediators NCAM1 and VCAM1 in the bowel.

The authors are careful to acknowledge the limitations of their work. The proteomic screen relied on only two paired patient samples, the validation cohorts were small, and the intraperitoneal viral delivery was not restricted to enteric glia, complicating cell-type-specific interpretation. Primary dorsal root ganglion neurons served as a surrogate for enteric neurons, and the temporal origins of the SPP1-high glial state remain unresolved, with lineage tracing and spatial transcriptomics needed to clarify its development. Even so, the study establishes a coherent mechanistic framework linking redox dysregulation, ERK/MAPK activation, pathological glial polarization, and neuronal dysfunction in Hirschsprung disease. By showing that enteric glia are active participants in the disease rather than passive bystanders, and that silencing TXNRD1 alleviates HSCR-like phenotypes in mice, the work nominates TXNRD1 and the glial polarization program it controls as promising targets for future therapies aimed at improving outcomes for children with this challenging disorder.

Subject of Research: The role of TXNRD1-driven enteric glial remodeling in neuronal dysfunction in Hirschsprung disease

Article Title: TXNRD1-driven enteric glial remodeling promotes neuronal dysfunction in Hirschsprung disease

Article References: Li, Y., Wang, Y., Jin, Z., Tang, C., Xia, X., Gong, Y., Du, Q., Huang, L., Li, Z., Liao, Y., He, S., Wang, B., Liu, Y., & Zheng, Z. (2026). TXNRD1-driven enteric glial remodeling promotes neuronal dysfunction in Hirschsprung disease. iScience, 29(10), Article 117636. https://doi.org/10.1016/j.isci.2026.117636

Image Credits: AI Generated

DOI: 10.1016/j.isci.2026.117636

Keywords: Hirschsprung disease, enteric glial cells, TXNRD1, SPP1, CXCL9, ERK/MAPK signaling, redox dysregulation, GDNF, single-cell RNA sequencing, enteric nervous system, Ednrb knockout mice, neurotrophic signaling

ETBF is a subtype of Bacteroides fragilis that carries the gene for Bacteroides fragilis toxin, known as BFT. The bacterium has been linked to diarrheal disease, inflammatory bowel disease and colorectal cancer, and colonization is known to be associated with long-term disturbances of intestinal motility. What remained unclear was precisely how a toxin famous for cleaving epithelial junctions could leave the gut’s movement machinery permanently impaired. The Shanghai team approached the question using mouse colonization models in which animals were inoculated with ETBF and followed over weeks, allowing the researchers to track both the microbial load and the structural integrity of the colonic myenteric plexus, the network of neurons embedded in the gut wall that orchestrates peristalsis.

The answer was stark. ETBF colonization triggered the loss of colonic myenteric neurons, and the effect depended entirely on BFT: mice colonized with a genetically engineered ETBF strain lacking the bft gene were largely protected. The toxin did not merely stun the neurons; it drove them into apoptosis, a programmed cell death routine. Critically, the neuronal loss and the accompanying motility dysfunction persisted even after the bacteria themselves had been cleared from the gut, a finding that echoes the clinical phenomenon of post-infectious gut disorders, in which symptoms linger long after the offending pathogen has disappeared. The researchers measured this dysfunction using gastrointestinal transit time and ex vivo recordings of colonic strip contractions, both of which deteriorated in colonized animals.

Having established that BFT kills enteric neurons, the team dissected the molecular pathway inside the cells. The toxin’s lethal signal, they found, runs through NOD1, an intracellular pattern-recognition receptor, which recruits its adaptor protein RIPK2 and then activates a caspase cascade: caspase-9, the initiator of the intrinsic apoptotic pathway, followed by caspase-3, the executioner. When the researchers knocked out Nod1 in mice, the BFT-induced neuronal apoptosis and dysmotility were markedly attenuated, confirming that this receptor, better known for sensing bacterial peptidoglycan and driving inflammatory responses, also functions as a death switch in enteric neurons when provoked by BFT. The pathway is notable because NOD1 has previously been identified as a functional receptor for BFT in cancer contexts, suggesting the toxin may have co-opted a host surveillance system for destructive purposes across multiple cell types.

The second half of the study addresses a question that has intrigued microbiome researchers for years: why do ETBF and Fusobacterium nucleatum so often appear together in diseased guts? Analyses of patient cohorts with inflammatory bowel disease and colorectal cancer revealed a positive correlation between the abundance of the two organisms, hinting at a cooperative rather than coincidental relationship. To test this directly, the researchers co-colonized mice with both species. The result was dramatic: the presence of F. nucleatum significantly aggravated the ETBF-induced loss of myenteric neurons and worsened gut dysmotility, and the effect again required bft, indicating that the oral pathobiont was not adding its own toxin but rather turning up the volume on ETBF’s.

The mechanism behind this microbial collusion proved to be a small molecule. F. nucleatum produces 2-hydroxybutyric acid, or 2HB, a metabolite generated through lactate dehydrogenase activity. When ETBF is exposed to 2HB, the toxin gene bft is transcribed at far higher levels. The team showed that 2HB physically binds to RprY, a regulatory protein in ETBF that normally represses bft transcription. By occupying RprY, the metabolite lifts this repression, derepressing the toxin gene without altering other virulence genes controlled by the regulator. In other words, one bacterium’s metabolic waste product acts as a molecular key that unlocks another bacterium’s most dangerous weapon. Administering 2HB to mice colonized with ETBF alone reproduced the aggravating effect, while F. nucleatum strains engineered to overproduce the metabolite intensified neurotoxicity further, and the researchers confirmed that multiple F. nucleatum subspecies produce 2HB in culture.

The clinical implications extend beyond motility. The study found that the enteric neuron loss and dysmotility induced by ETBF increased susceptibility to dextran sulfate sodium-induced colitis in mice, linking the neural damage to a weakened mucosal defense. This connects with a growing body of evidence that the enteric nervous system is not merely a passive conduit for brain signals but an active participant in intestinal immunity and barrier maintenance. Previous work has shown that other pathogens, from Shigella to Clostridioides difficile, can target enteric neurons, and that neuronal loss in conditions such as Chagas disease and Hirschsprung disease produces profound motility defects. The new study adds a bacterial cooperation model to this landscape, in which the composition of the microbiome determines how much toxin a colonizing pathogen actually delivers.

Human relevance was reinforced by tissue analyses. In colonic specimens from ulcerative colitis patients, the researchers detected the bft gene in mucosal tissue and observed myenteric neurons positive for NOD1, RIPK2, cleaved caspase-9 and cleaved caspase-3, the same molecular signature seen in the mouse model, with the staining pattern more prominent in patients suffering from constipation. While such observational data cannot prove causation in humans, the concordance between the animal pathway and the human tissue findings strengthens the case that the mechanism operates in clinical disease.

Perhaps the most immediately actionable finding concerns therapy. The researchers tested Bifico, a commercially available probiotic formulation containing Bifidobacterium species, in their mouse model. Treatment attenuated the neuronal toxicity, improved intestinal motility and reduced the severity of subsequent colitis. Bifidobacterium longum alone recapitulated much of the protective effect, and the probiotic did not simply eradicate ETBF; rather, it appeared to interfere with the processes that drive toxin production and neuronal death. Given that probiotics are inexpensive, widely available and generally safe, the finding suggests a plausible strategy for preventing the long-term neurological consequences of ETBF colonization, although the authors and independent observers caution that mouse models do not always translate to human therapy and that controlled clinical trials would be needed.

The study, published in Nature Microbiology with the DOI 10.1038/s41564-026-02497-y, is likely to resonate across several fields at once. For microbiome researchers, it provides a textbook example of metabolic cross-feeding with pathological consequences, in which a diffusible small molecule from one species reprograms virulence gene expression in another. For neurogastroenterologists, it identifies a specific toxin-receptor-caspase axis that destroys the neurons governing bowel movement, offering potential drug targets in NOD1, RIPK2 or the caspases themselves. And for clinicians treating patients with post-infectious bowel dysfunction, irritable bowel symptoms or inflammatory bowel disease, it raises the possibility that screening for ETBF and F. nucleatum co-colonization, and perhaps manipulating the microbiome to reduce 2HB production or boost protective Bifidobacterium, could one day prevent the slow, silent loss of the gut’s own nervous system. The data and bacterial strains underlying the work have been deposited in public repositories, including a Zenodo archive of the neuronal RNA-sequencing data, allowing other laboratories to build on the findings immediately.

Subject of Research: Bacterial cooperation between Fusobacterium nucleatum and enterotoxigenic Bacteroides fragilis in enteric neuron loss and intestinal dysmotility

Article Title: Fusobacterium nucleatum enhances enterotoxigenic Bacteroides fragilis-mediated neuron loss and intestinal motility dysfunction

Article References: Zhang, Y., Zhao, Y., Zhang, L., Xuan, B., Wang, Z., Yu, B., Li, W., Huang, X., Zhou, Y., Ning, L., Ding, J., Jiang, Y., Hu, M., Shao, Y., Li, L., Gao, X., Chen, S., Chen, H., Wang, F., … Hong, J. (2026). Fusobacterium nucleatum enhances enterotoxigenic Bacteroides fragilis-mediated neuron loss and intestinal motility dysfunction. Nature Microbiology. https://doi.org/10.1038/s41564-026-02497-y

Image Credits: AI Generated

DOI: 10.1038/s41564-026-02497-y

Keywords: Fusobacterium nucleatum, enterotoxigenic Bacteroides fragilis, Bacteroides fragilis toxin, enteric nervous system, gut dysmotility, 2-hydroxybutyric acid, NOD1, apoptosis, gut microbiota, inflammatory bowel disease, probiotics, Bifidobacterium

The study was carried out by Johannes van der Haas, Marine Mantel, Laurène Leclair-Visonneau, Pascal Derkinderen, and colleagues working at Nantes Université, the University Hospital of Nantes, and the University Hospital of Angers, within the Enteric Nervous System in Gut and Brain Disorders research group (Inserm U1235). The team set out to quantify LRRK2 expression in colon biopsies obtained from patients with Crohn’s disease, patients with established Parkinson’s disease, patients with idiopathic REM sleep behavior disorder (iRBD), and healthy controls. Idiopathic REM sleep behavior disorder, in which affected individuals physically act out their dreams because the normal muscle atonia of REM sleep is lost, is one of the strongest clinical predictors of future Parkinson’s disease or related Lewy body disorders, making it a valuable population in which to search for the earliest peripheral markers of the disease process.

LRRK2, which stands for leucine-rich repeat kinase 2, is a large, multifunctional protein with both kinase and GTPase domains. Mutations in its gene are among the most common known genetic causes of familial and sporadic Parkinson’s disease, and pharmacological inhibitors of LRRK2 kinase activity are currently being evaluated in clinical trials. At the same time, genome-wide association studies identified LRRK2 as a susceptibility gene for Crohn’s disease, and functional work has shown that the protein participates in the interferon-gamma response and in host defense against pathogens. Macrophages exposed to interferon-gamma upregulate LRRK2 through an ERK5-dependent signaling pathway, and the protein modulates cytokine production in human monocytes and macrophages. This immunological pedigree made the gut, with its dense population of immune cells and its intimate contact with the microbiota, a natural place to look for LRRK2 dysregulation in disease.

Earlier work from the same Nantes group had already produced an unexpected result along these lines. In a 2021 study published in Acta Neuropathologica, the researchers reported that LRRK2 was actually reduced, not increased, in the gut of patients with Parkinson’s disease. A follow-up study in 2023 mapped LRRK2 expression in normal and pathological human gut tissue and in rodent enteric neural cell lines, clarifying which cell types produce the protein under physiological conditions. The new correspondence extends this line of investigation in two important directions. First, it establishes a positive control: Crohn’s disease, an unambiguously inflammatory bowel condition, where the hypothesis predicts upregulation. Second, it examines idiopathic REM sleep behavior disorder, allowing the researchers to ask whether colonic LRRK2 changes emerge before the motor symptoms of Parkinson’s disease appear.

The answer to the first question was clear. In colon biopsies from patients with Crohn’s disease, LRRK2 expression was significantly increased compared with healthy controls. This result fits seamlessly with a substantial body of experimental literature. Studies in cell culture have demonstrated that the inflammatory cytokine interferon-gamma induces LRRK2 expression in macrophages, and that tumor necrosis factor-alpha and interferon-gamma cooperate to modulate cytokine signaling in human monocytic cells. Mouse experiments have reinforced the connection: animals lacking LRRK2 show attenuated colitis progression, with better resolution of inflammation and restored homeostasis of the gut microbiota, while mice carrying LRRK2 mutations develop parkinsonian features when challenged with mild chronic colitis through activation of the TNF-alpha pathway. The elevation of LRRK2 in inflamed Crohn’s tissue is exactly what one would expect if the protein is an inducible component of the mucosal immune response.

The answer to the second question was more provocative. Colonic LRRK2 expression was not increased in patients with Parkinson’s disease, and it was not increased in patients with idiopathic REM sleep behavior disorder either. In other words, even at the prodromal stage of the Lewy body disease spectrum, when alpha-synuclein pathology is thought to be spreading through the peripheral nervous system and gastrointestinal symptoms are already common, the colonic upregulation of LRRK2 that a shared gut-brain mechanism would predict is simply absent. The authors had previously shown that LRRK2 is reduced in the Parkinson’s disease gut; the new data confirm that this is not merely a medication effect or a late-stage artifact, because the same pattern of non-elevation holds in drug-naïve or early prodromal iRBD patients who have not yet developed Parkinsonism.

This dissociation carries real conceptual weight for the field. The idea that Parkinson’s disease begins in the gut was propelled by landmark neuropathological studies showing that phosphorylated alpha-synuclein, the hallmark protein aggregate of Lewy body disorders, is distributed across multiple organs, including the gastrointestinal tract, in affected individuals. The presence of enteric alpha-synuclein pathology early in the disease course, together with the well-documented burden of gastrointestinal dysfunction in Parkinson’s patients, some studies showing that objective colonic dysfunction is far more prevalent than subjective constipation, gave rise to the notion that environmental or immunological insults in the gut might trigger or accelerate the neurodegenerative process. If colonic inflammation were a common initiating factor, one might expect inflammatory response genes such as LRRK2 to be activated in the Parkinson’s colon. The new findings argue against that simple model: the colonic biology of Parkinson’s disease, at least as reflected in LRRK2 expression, is distinct from the colonic biology of overt inflammatory bowel disease.

The study also speaks to an epidemiological puzzle. Meta-analyses encompassing more than 13.4 million individuals have reported that inflammatory bowel disease is associated with an increased risk of subsequently developing Parkinson’s disease, and experimental work suggests that mild chronic colitis can exacerbate intracerebral inflammation in mouse models of the disease through LRRK2-mediated regulation of NF-kappaB activation and inhibition of the antioxidant regulator Nrf2. How can inflammatory bowel disease raise Parkinson’s risk if the Parkinson’s colon does not show LRRK2 upregulation? One possibility is that the relevant inflammatory signal is transient or occurs in a specific window, or that only a subset of inflammatory bowel disease patients, perhaps those with particular genetic backgrounds or microbiome configurations, experience the gut-to-brain propagation that animal models simulate. Another possibility, highlighted by the Nantes group’s related work, is that subtler immune changes are present in the prodromal gut. Indeed, the same consortium recently reported elevated levels of the inflammatory cytokines interleukin-1beta and interleukin-8 in the colon of patients with isolated REM sleep behavior disorder, even in the absence of measurable changes in intestinal permeability. Cytokine elevation without LRRK2 induction suggests that prodromal Parkinson’s involves a distinctive, low-grade inflammatory signature rather than a full-throttle interferon-driven response of the kind seen in Crohn’s disease.

From a methodological standpoint, the study benefits from a carefully assembled clinical cohort. Sigmoid biopsies from the iRBD, Parkinson’s disease, and control groups were collected under a protocol approved by the local Committee for the Protection of Persons (Comité de Protection des Personnes Ouest VI) and registered on ClinicalTrials.gov under identifier NCT04652843. Colonic biopsies from Crohn’s disease patients were obtained through the biobank federation of the University Hospital of Nantes under approval number DC-2008-402. The work was supported by grants from Nantes University Hospital, France Parkinson, SFN/Novartis, and the Fondation de France, with PhD and fellowship support for several of the young investigators involved. The authors declare no competing interests, and the data supporting the findings are available from the corresponding author upon reasonable request.

For the broader research community, the message is one of disciplined specificity. LRRK2 appears to be a sensitive readout of mucosal inflammation, a marker that lights up robustly in Crohn’s disease where interferon-gamma and related cytokine cascades are active, but it is not a universal marker of the gut involvement that characterizes Parkinsonian disorders. Therapeutic strategies that target LRRK2 kinase activity, currently in development for Parkinson’s disease, will therefore need to reckon with the possibility that the protein’s expression and function in the Parkinson’s gut follow rules different from those governing it in inflammatory bowel disease. Conversely, for Crohn’s disease researchers, the confirmed upregulation of LRRK2 in inflamed colon tissue strengthens the case for exploring LRRK2-targeted anti-inflammatory approaches, an idea already supported by the mitigating effects of LRRK2 deficiency in experimental colitis. As the search for peripheral biomarkers of prodromal Parkinson’s disease intensifies, this study provides a sober and valuable data point: the inflammatory fingerprint of Crohn’s disease is real and measurable in the colon, but it does not stamp itself onto the prodromal Parkinsonian gut, at least not through LRRK2. Untangling what does change in that tissue, cytokine by cytokine and cell type by cell type, remains the next great challenge for the gut-brain axis in neurodegeneration.

Subject of Research: Colonic expression of the LRRK2 protein in Crohn's disease, Parkinson's disease and idiopathic REM sleep behavior disorder

Article Title: Colonic LRRK2 expression is increased in Crohn’s disease but not in Parkinson’s disease and idiopathic RBD

Article References: van der Haas, J., Mantel, M., Sellier-Montaigne, L., de Guilhem de Lataillade, A., Durand, T., Oullier, T., Le Berre, C., Letournel, F., Rolli-Derkinderen, M., Leclair-Visonneau, L., & Derkinderen, P. (2026). Colonic LRRK2 expression is increased in Crohn’s disease but not in Parkinson’s disease and idiopathic RBD. Acta Neuropathologica, 152(1), Article 38. https://doi.org/10.1007/s00401-026-03087-2

Image Credits: AI Generated

DOI: 10.1007/s00401-026-03087-2

Keywords: LRRK2, Crohn's disease, Parkinson's disease, REM sleep behavior disorder, colon, inflammation, alpha-synuclein, gut-brain axis, enteric nervous system, interferon-gamma, biomarkers, neurodegeneration