The nervous system plays an important role in the regulation of epithelial homeostasis and has also been postulated to play a role in tumorigenesis. We provide evidence that proper innervation is critical at all stages of gastric tumorigenesis. In three separate mouse models of gastric cancer, surgical or pharmacological denervation of the stomach (bilateral or unilateral truncal vagotomy, or local injection of botulinum toxin type A) markedly reduced tumor incidence and progression, but only in the denervated portion of the stomach. Vagotomy or botulinum toxin type A treatment also enhanced the therapeutic effects of systemic chemotherapy and prolonged survival. Denervation-induced suppression of tumorigenesis was associated with inhibition of Wnt signaling and suppression of stem cell expansion. In gastric organoid cultures, neurons stimulated growth in a Wnt-mediated fashion through cholinergic signaling. Furthermore, pharmacological inhibition or genetic knockout of the muscarinic acetylcholine M3 receptor suppressed gastric tumorigenesis. In gastric cancer patients, tumor stage correlated with neural density and activated Wnt signaling, whereas vagotomy reduced the risk of gastric cancer. Together, our findings suggest that vagal innervation contributes to gastric tumorigenesis via M3 receptor–mediated Wnt signaling in the stem cells, and that denervation might represent a feasible strategy for the control of gastric cancer.

The gut contains a large 5-HT pool in enterochromaffin (EC) cells and a smaller 5-HT pool in the enteric nervous system (ENS). During development, enteric neurons are generated asynchronously. We tested hypotheses that serotonergic neurons, which arise early, affect development/survival of later-born dopaminergic, GABAergic, nitrergic, and calcitonin gene-related peptide-expressing neurons and are essential for gastrointestinal motility. 5-HT biosynthesis depends on tryptophan hydroxylase 1 (TPH1) in EC cells and on TPH2 in neurons; therefore, mice lacking TPH1 and/or TPH2 distinguish EC-derived from neuronal 5-HT. Deletion of TPH2, but not TPH1, decreased myenteric neuronal density and proportions of dopaminergic and GABAergic neurons but did not affect the extrinsic sympathetic innervation of the gut; intestinal transit slowed in mice lacking TPH2 mice, but gastric emptying accelerated. Isolated enteric crest-derived cells (ENCDCs) expressed the serotonin reuptake transporter (SERT) and 15 subtypes of 5-HT receptor. Addition of 5-HT to cultures of isolated ENCDCs promoted total and dopaminergic neuronal development. Rings of SERT-immunoreactive terminal axons surrounded myenteric dopaminergic neurons and SERT knock-out increased intestinal levels of dopamine metabolites, implying that enteric dopaminergic neurons receive a serotonergic innervation. Observations suggest that constitutive gastrointestinal motility depends more on neuronal than EC cell serotonin; moreover, serotonergic neurons promote development/survival of some classes of late-born enteric neurons, including dopaminergic neurons, which appear to innervate and activate in the adult ENS.

The enteric serotonin reuptake transporter (SERT) has been proposed to play a critical role in serotonergic neurotransmission and in the initiation of peristaltic and secretory reflexes. We analyzed potential compensatory mechanisms and enteric function in the bowels of mice with a targeted deletion of SERT. The guts of these animals were found to lack mRNA encoding SERT; moreover, high-affinity uptake of 5-HT into epithelial cells, mast cells, and enteric neurons was present in the SERT ϩ/ϩ bowel but absent in the SERT Ϫ/Ϫ bowel. However, both the SERT ϩ/ϩ gut and the Ϫ/Ϫ gut expressed molecules capable of transporting 5-HT, but with affinities and selectivity much lower than those of SERT. These included the dopamine transporter (DAT) and polyspecific organic cation transporters OCT-1 and OCT-3. DAT and OCT immunoreactivities were present in both the submucosal and myenteric plexuses, and the OCTs were also located in the mucosal epithelium. 5-HT was found in all of its normal sites in the SERT Ϫ/Ϫ bowel, which contained mRNA encoding tryptophan hydroxylase, but no 5-HT was present in the blood of SERT Ϫ/Ϫ animals. Stool water and colon motility were increased in most SERT Ϫ/Ϫ animals; however, the increase in motility (diarrhea) occasionally alternated irregularly with decreased motility (constipation). The watery diarrhea is probably attributable to the potentiation of serotonergic signaling in SERT Ϫ/Ϫ mice, whereas the transient constipation may be caused by episodes of enhanced 5-HT release leading to 5-HT receptor desensitization.

Osteoporosis is a low bone mass disease most often caused by an increase in bone resorption not compensated by a similar hike in bone formation1. Since gut–derived serotonin (GDS) inhibits bone formation2, we asked whether hampering its biosynthesis could treat osteoporosis through an anabolic mechanism. To that end we synthesized and used LP533401, a small molecule inhibitor of Tph1, the initial enzyme in GDS biosynthesis. Oral administration once daily for up to 6 weeks of this small molecule prevents the development of and fully rescues, in a dose–dependent manner, osteoporosis in ovariectomized rodents because of an isolated increase in bone formation. These results provide a proof of principle that inhibiting GDS biosynthesis could become a novel anabolic treatment for osteoporosis.

Parkinson disease (PD) is a neurodegenerative disease with motor as well as non-motor signs in the gastrointestinal tract that include dysphagia, gastroparesis, prolonged gastrointestinal transit time, constipation and difficulty with defecation. The gastrointestinal dysfunction commonly precedes the motor symptoms by decades. Most PD is sporadic and of unknown etiology, but a fraction is familial. Among familial forms of PD, a small fraction is caused by missense (A53T, A30P and E46K) and copy number mutations in SNCA which encodes alpha-synuclein, a primary protein constituent of Lewy bodies, the pathognomonic protein aggregates found in neurons in PD. We set out to develop transgenic mice expressing mutant alpha-synuclein (either A53T or A30P) from insertions of an entire human SNCA gene as models for the familial disease. Both the A53T and A30P lines show robust abnormalities in enteric nervous system (ENS) function and synuclein-immunoreactive aggregates in ENS ganglia by 3 months of age. The A53T line also has abnormal motor behavior but neither demonstrates cardiac autonomic abnormalities, olfactory dysfunction, dopaminergic neurotransmitter deficits, Lewy body inclusions or neurodegeneration. These animals recapitulate the early gastrointestinal abnormalities seen in human PD. The animals also serve as an in vivo system in which to investigate therapies for reversing the neurological dysfunction that target alpha-synuclein toxicity at its earliest stages.

Single-atom catalysts (SACs) have emerged as one of the most promising alternatives to noble metal-based catalysts for highly efficient oxygen reduction reaction (ORR). While SACs can offer notable benefits in terms of lowering overall catalyst cost, there is still room for improvement regarding catalyst activity. To this end, we designed and successfully fabricated an ORR electrocatalyst in which atomic clusters are embedded in an atomically dispersed Fe–N–C matrix (FeAC@FeSA–N–C), as shown by comprehensive measurements using aberration-corrected scanning transmission electron microscopy (AC-STEM) and X-ray absorption spectroscopy (XAS). The half-wave potential of FeAC@FeSA–N–C is 0.912 V (versus reversible hydrogen electrode (RHE)), exceeding that of commercial Pt/C (0.897 V), FeSA–N–C (0.844 V), as well as the half-wave potentials of most reported non-platinum-group metal catalysts. The ORR activity of the designed catalyst stems from single-atom active centers but is markedly enhanced by the presence of Fe nanoclusters, as confirmed by both experimental measurements and theoretical calculations.

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Serotonin (5-HT) regulates peristaltic and secretory reflexes in the gut. The serotonin reuptake transporter (SERT; SLC6A4), which inactivates 5-HT, is expressed in the intestinal mucosa and the enteric nervous system. Stool water content is increased and colonic motility is irregular in mice with a targeted deletion of SERT. We tested the hypotheses that 5-HT plays a role in regulating intestinal inflammation and that the potentiation of serotonergic signaling that results from SERT deletion is proinflammatory. Rectal installation of 2,4,6-trinitrobenzene sulfonic acid (TNBS) was used to induce an immune-mediated colitis, which was compared in SERT knockout mice and littermate controls. Intestinal myeloperoxidase and histamine levels were significantly increased, whereas the survival rate and state of health were significantly decreased in TNBS-treated mice that lacked SERT. Deletion of SERT thus increases the severity of TNBS colitis. These data suggest that 5-HT and its SERT-mediated termination play roles in intestinal immune/inflammatory responses in mice.