Chai, Xinyi

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.

Using 32 immune cell surface markers, we identified 23 monocyte clusters in murine blood. Diabetic gastroparesis was associated with a significant decrease in two circulating classical monocyte-like clusters and an upregulation of the Ccr2-Ccl2 axis in the gastric muscularis propria, suggesting increased tissue monocyte migration. This study offers new targets by pointing to a possible role for two classical monocyte subsets connected to the Ccr2- Ccl2 axis.