The gut contains the bulk of the body's serotonin (5-hydroxytryptamine, 5-HT); nevertheless, the physiological role that enteric 5-HT plays has not been determined. 5-HT is linked to gastrointestinal ...(GI) motility; increased intraluminal pressure causes enterochromaffin (EC) cells to secrete 5-HT, which stimulates intrinsic primary afferent neurons that initiate peristaltic reflexes. 5-HT is also an enteric neurotransmitter. Surprisingly, deletion of tryptophan hydroxylase-1 (TPH1), upon which 5-HT biosynthesis in EC cells depends, does not alter constitutive GI motility, whereas deletion of TPH2, upon which biosynthesis of neuronal 5-HT depends, slows intestinal transit and accelerates gastric emptying. TPH1 deletion, however, protects mice from experimental inflammation; 5-HT potentiation and TPH2 deletion each make inflammation more severe. Neuronal 5-HT is neuroprotective and recruits stem cells to give rise to new enteric neurons in adult mice. Mucosal 5-HT, therefore, may mobilize inflammatory effectors, which protect the gut from invasion, whereas neuronal 5-HT shields enteric neurons from inflammatory damage.
Doublecortin-like kinase 1 protein (DCLK1) is a gastrointestinal tuft cell marker that has been proposed to identify quiescent and tumor growth-sustaining stem cells. DCLK1⁺ tuft cells are increased ...in inflammation-induced carcinogenesis; however, the role of these cells within the gastrointestinal epithelium and their potential as cancer-initiating cells are poorly understood. Here, using a BAC-CreERT-dependent genetic lineage-tracing strategy, we determined that a subpopulation of DCLK1⁺ cells is extremely long lived and possesses rare stem cell abilities. Moreover, genetic ablation of Dclk1 revealed that DCLK1⁺ tuft cells contribute to recovery following intestinal and colonic injury. Surprisingly, conditional knockdown of the Wnt regulator APC in DCLK1⁺ cells was not sufficient to drive colonic carcinogenesis under normal conditions; however, dextran sodium sulfate-induced (DSS-induced) colitis promoted the development of poorly differentiated colonic adenocarcinoma in mice lacking APC in DCLK1⁺ cells. Importantly, colonic tumor formation occurred even when colitis onset was delayed for up to 3 months after induced APC loss in DCLK1⁺ cells. Thus, our data define an intestinal DCLK1⁺ tuft cell population that is long lived, quiescent, and important for intestinal homeostasis and regeneration. Long-lived DCLK1⁺ cells maintain quiescence even following oncogenic mutation, but are activated by tissue injury and can serve to initiate colon cancer.
Autism spectrum disorder (ASD) is an increasingly common behavioral condition that frequently presents with gastrointestinal (GI) disturbances. It is not clear, however, how gut dysfunction relates ...to core ASD features. Multiple, rare hyperfunctional coding variants of the serotonin (5-HT) transporter (SERT, encoded by SLC6A4) have been identified in ASD. Expression of the most common SERT variant (Ala56) in mice increases 5-HT clearance and causes ASD-like behaviors. Here, we demonstrated that Ala56-expressing mice display GI defects that resemble those seen in mice lacking neuronal 5-HT. These defects included enteric nervous system hypoplasia, slow GI transit, diminished peristaltic reflex activity, and proliferation of crypt epithelial cells. An opposite phenotype was seen in SERT-deficient mice and in progeny of WT dams given the SERT antagonist fluoxetine. The reciprocal phenotypes that resulted from increased or decreased SERT activity support the idea that 5-HT signaling regulates enteric neuronal development and can, when disturbed, cause long-lasting abnormalities of GI function. Administration of a 5-HT4 agonist to Ala56 mice during development prevented Ala56-associated GI perturbations, suggesting that excessive SERT activity leads to inadequate 5-HT4-mediated neurogenesis. We propose that deficient 5-HT signaling during development may contribute to GI and behavioral features of ASD. The consequences of therapies targeting SERT during pregnancy warrant further evaluation.
Abstract
Introduction
Live attenuated zoster vaccine (Zostavax) was used to test the hypothesis that constitutive level of interleukin 10 (IL-10), which may be high in elderly subjects, impairs ...vaccine efficacy. If constitutive IL-10 impairs vaccine efficacy, the effectiveness of viral vaccines might be improved by transient inhibition of IL-10 before vaccination.
Methods
Zostavax was given to 26 patients (age, 60–80 years). IL-10 and immunity to varicella zoster virus (VZV) were measured at baseline and after vaccination. Fluorescent antibody to membrane antigen (FAMA) assays and glycoprotein enzyme-linked immunosorbent assays (gpELISAs) were used to assess humoral immunity; anti–varicella virus T-cell responses were studied in a subset of subjects. In a prospective animal model, T-cell responses to chimeric vaccines against lymphocytic choriomeningitis virus (LCMV) were assessed in mice that express or lack IL-10.
Results
FAMA assays revealed significant boosting (by 4-fold) of humoral immunity, which occurred only in subjects (10 of 26) with a low constitutive IL-10 level (ie, <20 pg/mL); moreover, the Zostavax-induced FAMA and gpELISA responses were inversely related to the constitutive IL-10 level. Significant VZV-specific T-cell responses followed vaccination only in subjects with a low constitutive IL-10 level. Vaccine-induced LCMV-specific T-cell responses in mice lacking IL-10 were greater than in wild-type animals.
Conclusions
A high constitutive IL-10 level adversely affects vaccine efficacy.
The humoral and cellular responses of 26 elderly subjects to Zostavax were inversely proportional to constitutive interleukin 10 (IL-10) levels. IL-10 also depressed murine responses to vaccination against lymphocytic choriomeningitis virus. These observations support the hypothesis that IL-10 interferes with viral vaccine efficacy.
Osteoporosis is a disease of low bone mass most often caused by an increase in bone resorption that is not sufficiently compensated for by a corresponding increase in bone formation. As gut-derived ...serotonin (GDS) inhibits bone formation, we asked whether hampering its biosynthesis could treat osteoporosis through an anabolic mechanism (that is, by increasing bone formation). We synthesized and used LP533401, a small molecule inhibitor of tryptophan hydroxylase-1 (Tph-1), the initial enzyme in GDS biosynthesis. Oral administration of this small molecule once daily for up to six weeks acts prophylactically or therapeutically, in a dose-dependent manner, to treat 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 new anabolic treatment for osteoporosis.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Although the mature enteric nervous system (ENS) has been shown to retain stem cells, enteric neurogenesis has not previously been demonstrated in adults. The relative number of enteric neurons in ...wild-type (WT) mice and those lacking 5-HT(4) receptors knock-out (KO) was found to be similar at birth; however, the abundance of ENS neurons increased during the first 4 months after birth in WT but not KO littermates. Enteric neurons subsequently decreased in both WT and KO but at 12 months were significantly more numerous in WT. We tested the hypothesis that stimulation of the 5-HT(4) receptor promotes enteric neuron survival and/or neurogenesis. In vitro, 5-HT(4) agonists increased enteric neuronal development/survival, decreased apoptosis, and activated CREB (cAMP response element-binding protein). In vivo, in WT but not KO mice, 5-HT(4) agonists induced bromodeoxyuridine incorporation into cells that expressed markers of neurons (HuC/D, doublecortin), neural precursors (Sox10, nestin, Phox2b), or stem cells (Musashi-1). This is the first demonstration of adult enteric neurogenesis; our results suggest that 5-HT(4) receptors are required postnatally for ENS growth and maintenance.
The enteric nervous system (ENS) controls the gastrointestinal system. Enteric glia have long been regarded as the essential "glue" of the ENS. Now, however, two independent reports in this issue of ...the JCI provide compelling evidence that mouse enteric glia can also be neuronal precursors. These reports show that enteric glia give rise to neurons in vitro and that neurogenesis can be experimentally induced to occur in vivo in the adult mouse ENS. Unfortunately, glia do not constitutively replace neurons, and neurogenesis is not easily provoked. Although these new observations make it clear that clinical trials using glia to replace enteric neurons are more than premature, they are enticing for future research.
Key points
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Previous studies have indicated that neither neuronal nor mucosal 5‐hydroxytryptamine (5‐HT) are important for colonic migrating motor complexes (CMMCs) or faecal pellet propulsion. ...Therefore, tryptophan hydroxylase 1 knockout (TPH1KO) mice were used to examine the role of mucosal 5‐HT in generating CMMCs and faecal pellet propulsion, as TPH1 is the regulatory enzyme necessary for the synthesis of 5‐HT in enterochromaffin cells in the mucosa.
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Control mice generated a robust CMMC when the mucosa was mechanically stimulated, which was blocked by ondansetron (5‐HT3 antagonist), and could propagate faecal pellets that did not significantly distend the bowel, suggesting that they were propelled by mucosal reflexes in the absence of stretch reflexes.
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TPH1KO mice exhibited no mucosal reflexes, reduced responses to intraluminal distension and propelled only larger faecal pellets, suggesting that they relied upon stretch reflexes alone.
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In control mice, CMMCs, which can propel a faecal pellet, propagated in an oral to anal direction, whereas, in TPH1KO mice, they rarely propagated.
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Both the propagation and amplitude of CMMCs were reduced by ondansetron in control mice, whereas this drug did not affect CMMCs in TPH1KO mice.
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This suggests that 5‐HT release from the mucosa and stretch reflexes are important for normal colonic propulsion.
Although there is general agreement that mucosal 5‐hydroxytryptamine (5‐HT) can initiate peristaltic reflexes in the colon, recent studies have differed as to whether or not the role of mucosal 5‐HT is critical. We therefore tested the hypothesis that the secretion of 5‐HT from mucosal enterochromaffin (EC) cells is essential for the manifestation of murine colonic peristaltic reflexes. To do so, we analysed the mechanisms underlying faecal pellet propulsion in isolated colons of mice lacking tryptophan hydroxylase 1 (Tph1−/− mice), which is the rate‐limiting enzyme in the biosynthesis of mucosal but not neuronal 5‐HT. We used video analysis of faecal pellet propulsion, tension transducers to record colonic migrating motor complexes (CMMCs) and intracellular microelectrodes to record circular muscle activity occurring spontaneously or following intraluminal distension. When compared with control (Tph1+/+) mice, Tph1−/− animals exhibited: (1) an elongated colon; (2) larger faecal pellets; (3) orthograde propulsion followed by retropulsion (not observed in Tph1+/+ colon); (4) slower in vitro propulsion of larger faecal pellets (28% of Tph1+/+); (5) CMMCs that infrequently propagated in an oral to anal direction because of impaired descending inhibition; (6) reduced CMMCs and inhibitory responses to intraluminal balloon distension; (7) an absence of reflex activity in response to mucosal stimulation. In addition, (8) thin pellets that propagated along the control colon failed to do so in Tph1−/− colon; and (9) the 5‐HT3 receptor antagonist ondansetron, which reduced CMMCs and blocked their propagation in Tph1+/+ mice, failed to alter CMMCs in Tph1−/− animals. Our observations suggest that mucosal 5‐HT is essential for reflexes driven by mucosal stimulation and is also important for normal propagation of CMMCs and propulsion of pellets in the isolated colon.
The early appearance of serotonin and its receptors during prenatal development, together with the many effects serotonin exerts during CNS morphogenesis, strongly suggest that serotonin influences ...the development and maturation of the mammalian brain before it becomes a neuromodulator/neurotransmitter. Sites of early serotonin biosynthesis, however, have not been detected in mouse embryos or extraembryonic structures, suggesting that the main source of serotonin could be of maternal origin. This hypothesis was tested by using knockout mice lacking the tph1 gene, which is responsible for the synthesis of peripheral serotonin. Genetic crosses were performed to compare the phenotype of pups born from homozygous and heterozygous mothers. Observations provide the first clear evidence that (i) maternal serotonin is involved in the control of morphogenesis during developmental stages that precede the appearance of serotonergic neurons and (ii) serotonin is critical for normal murine development. Most strikingly, the phenotype of tph1-/- embryos depends more on the maternal genotype than on that of the concepti. Consideration of the maternal genotype may thus help to clarify the influence of other genes in complex diseases, such as mental illness.
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