CCR2-dependent monocytes gut-homing contributes to enteric neuroplastic changes in a mouse model of diet-induced obesity.

backgroundEnteric inflammation and immune cell activation promote enteric neuroplastic changes and CCR2-dependent monocyte recruitment, contributing to obesity-associated colonic dysmotility and chronic inflammation. Here, we examined the role of C-C motif chemokine ligand (CCL2)/C-C chemokine receptor 2 (CCR2)-mediated blood monocytes gut-homing in colonic motor dysfunctions in mice with high fat diet (HFD)-induced obesity.

methodsWild-type C57BL/6J mice were fed HFD or standard diet (SD) for 8 weeks. Subgroups received the CCR2 antagonist RS504393 (2 mg/kg/day, oral) or vehicle throughout the HFD intake. Body weight and body mass index (BMI) were monitored starting from HFD intake. Colonic transit was assessed by fecal pellet output. In vitro colonic contractility was evaluated by assessing substance P (SP)-induced contractile responses, along with analysis of SP-positive neurons. Immunohistochemistry was used to quantify CCR2⁺ monocytes and CD64⁺/Iba-1⁺ macrophages within the myenteric plexus. Colonic expression of CCL2 in enteric neurons (HuC/D⁺) and glial cells (GFAP⁺) was assessed. Gut vascular barrier integrity was evaluated via PV-1 expression and plasma lipopolysaccharide-binding protein (LBP) levels. The effects of CCR2 blockade on motility, neuronal SP expression, chemokine expression, and monocyte recruitment were analyzed.

resultsHFD mice displayed an increase in body weight and BMI. An altered in vivo colonic transit along with an increased in vitro tachykininergic contractions and myenteric SP immunopositivity were detected in HFD mice. HFD mice exhibited marked infiltration of monocyte-derived macrophages (CD64⁺, Iba-1⁺) within the muscularis layer, in close spatial association with SP-positive nerve fibers and neuromuscular vasculature. Increased CCL2 expression was observed in both enteric neurons and glial cells, alongside evidence of compromised gut vascular barrier function. Pharmacological CCR2 inhibition attenuated weight gain and significantly improved colonic transit. Moreover, CCR2 blockade normalized tachykininergic hyperactivity, reduced SP expression, decreased colonic CCL2 levels, and limited monocyte/macrophage accumulation in the enteric neuromuscular compartment.

conclusionDuring obesity, the activation of the CCL2/CCR2 pathway promotes the recruitment of blood-derived monocytes to the gut, driving neuroimmune remodelling within the enteric nervous system. Blood monocyte-derived macrophages modulate tachykininergic pathways, contributing to colonic dysmotility. Targeting CCR2-dependent gut immune cell trafficking may represent a novel therapeutic strategy for obesity-associated GI dysfunction.