Correct development and maturation of the enteric nervous system (ENS) is critical for survival. Early in life, the ENS requires significant refinement in order to adapt to the evolving needs of the tissue, changing from milk to solid food at the time of weaning. Here, we demonstrate that resident macrophages of the muscularis externa, MMφ, refine the ENS early in life by pruning synapses and phagocytosing abundant enteric neurons. After weaning, MMφ continue to closely interact with the ENS, acquire a microglia-like phenotype and are crucial for the survival of enteric neurons. Of note, this microglia-like phenotype is instructed by TGFβ produced by the ENS, introducing a novel reciprocal cell-cell communication responsible for the maintenance of the neuron-associated MMф niche in the gut. These findings elucidate a novel role of intestinal macrophages in ENS refinement early in life, and open new opportunities to treat intestinal neurodegenerative disorders by manipulating the ENSmacrophage niche.

Tauopathies are neurodegenerative diseases that are characterized by accumulation of hyperphosphorylated tau protein, higher-order aggregates, and tau filaments. Protein phosphatase 2A (PP2A) is a major tau dephosphorylating phosphatase, and a decrease in its activity has been demonstrated in tauopathies, including Alzheimer’s disease. Prolyl oligopeptidase is a serine protease that is associated with neurodegeneration, and its inhibition normalizes PP2A activity without toxicity under pathological conditions. Here, we assessed whether prolyl oligopeptidase inhibition could protect against tau-mediated toxicity in cellular models in vitro and in the PS19 transgenic mouse model of tauopathy carrying the human tau-P301S mutation. We show that inhibition of prolyl oligopeptidase with the inhibitor KYP-2047 reduced tau aggregation in tau-transfected HEK-293 cells and N2A cells as well as in human iPSC–derived neurons carrying either the P301L or tau-A152T mutation. Treatment with KYP-2047 resulted in increased PP2A activity and activation of autophagic flux in HEK-293 cells and N2A cells and in patient-derived iNeurons, as indicated by changes in autophagosome and autophagy receptor markers; this contributed to clearance of insoluble tau. Furthermore, treatment of PS19 transgenic mice for 1 month with KYP-2047 reduced tau burden in the brain and cerebrospinal fluid and slowed cognitive decline according to several behavioral tests. In addition, a reduction in an oxidative stress marker was seen in mouse brains after KYP-2047 treatment. This study suggests that inhibition of prolyl oligopeptidase could help to ameliorate tau-dependent neurodegeneration.

Background: Methods to study gastric emptying in rodents are time consuming or terminal, preventing repetitive assessment in the same animal. Magnetic resonance imaging (MRI) is a non-invasive technique increasingly used to investigate gastrointestinal function devoid of these shortcomings. Here, we evaluated MRI to measure gastric emptying in control animals and in two different models of gastroparesis.Methods: Mice were scanned using a 9.4 Tesla MR scanner. Gastric volume was measured by delineating the stomach lumen area. Control mice were scanned every 30 min after ingestion of a 0.2 g meal and stomach volume was quantified. The ability of MRI to detect delayed gastric emptying was evaluated in models of morphine-induced gastroparesis and streptozotocin-induced diabetes.Key Results: Magnetic resonance imaging reproducibly detected increased gastric volume following ingestion of a standard meal and progressively decreased with a half emptying time of 59 ± 5 min. Morphine significantly increased gastric volume measured at t = 120 min (saline: 20 ± 2 vs morphine: 34 ± 5 mm 3 ; n = 8-10; p < 0.001) and increased half emptying time using the breath test (saline: 85 ± 22 vs morphine: 161 ± 46 min; n = 10; p < 0.001). In diabetic mice, gastric volume assessed by MRI at t = 60 min (control: 23 ± 2 mm 3 ; n = 14 vs diabetic: 26 ± 5 mm 3 ; n = 18; p = 0.014) but not at t = 120 min (control: 21 ± 3 mm 3 ; n = 13 vs diabetic: 18 ± 5 mm 3 ; n = 18; p = 0.115) was significantly increased compared to nondiabetic mice. Conclusions and Inferences:Our data indicate that MRI is a reliable and reproducible tool to assess gastric emptying in mice and represents a useful technique to study gastroparesis in disease models or for evaluation of pharmacological compounds.

SummaryCorrect development and maturation of the enteric nervous system (ENS) is critical for survival. Early in life, the ENS requires significant refinement in order to adapt to the evolving needs of the tissue, changing from milk to solid food at the time of weaning. Here, we demonstrate that resident macrophages of the muscularis externa, MMϕ, refine the ENS early in life by pruning synapses and phagocytosing abundant enteric neurons. After weaning, MMϕ continue to closely interact with the ENS, acquire a microglia-like phenotype and are crucial for the survival of enteric neurons. Of note, this microglia-like phenotype is instructed by TGFβ produced by the ENS, introducing a novel reciprocal cell-cell communication responsible for the maintenance of the neuron-associated MMФ niche in the gut. These findings elucidate a novel role of intestinal macrophages in ENS refinement early in life, and open new opportunities to treat intestinal neurodegenerative disorders by manipulating the ENS-macrophage niche.