Targeting oncogenic pathways holds promise for brain tumor treatment, but inhibition of Sonic Hedgehog (SHH) signaling has failed in SHH-driven medulloblastoma. Cellular diversity within tumors and ...reduced lineage commitment can undermine targeted therapy by increasing the probability of treatment-resistant populations. Using single-cell RNA-seq and lineage tracing, we analyzed cellular diversity in medulloblastomas in transgenic, medulloblastoma-prone mice, and responses to the SHH-pathway inhibitor vismodegib. In untreated tumors, we find expected stromal cells and tumor-derived cells showing either a spectrum of neural progenitor-differentiation states or glial and stem cell markers. Vismodegib reduces the proliferative population and increases differentiation. However, specific cell types in vismodegib-treated tumors remain proliferative, showing either persistent SHH-pathway activation or stem cell characteristics. Our data show that even in tumors with a single pathway-activating mutation, diverse mechanisms drive tumor growth. This diversity confers early resistance to targeted inhibitor therapy, demonstrating the need to target multiple pathways simultaneously.
The bowel exhibits reflexes in the absence of CNS input. To do so, epithelial sensory transducers, such as enterochromaffin (EC) cells, activate the mucosal processes of intrinsic (IPANs) and ...extrinsic primary afferent (sensory) neurons. EC cells secrete serotonin (5-HT) in response to mucosal stimuli. Submucosal IPANs, which secrete acetylcholine and calcitonin gene-related peptide, initiate peristaltic and secretory reflexes and are activated via “5-HT1P” receptors. Release of neurotransmitters is enhanced by 5-HT4 receptors, which are presynaptic and strengthen neurotransmission in prokinetic pathways. 5-HT3 receptors mediate signaling to the CNS and thus ameliorate cancer chemotherapy-associated nausea and the visceral hypersensitivity of diarrhea-predominant irritable bowel syndrome (IBS-D); however, because 5-HT3 receptors also mediate fast ENS neurotransmission and activate myenteric IPANs, they may be constipating. 5-HT4 agonists are prokinetic and relieve discomfort and constipation in IBS-C and chronic constipation. 5-HT4 agonists do not initiate peristaltic and secretory reflexes but strengthen pathways that are naturally activated. Serotonergic signaling in the mucosa and the ENS is terminated by a transmembrane 5-HT transporter, SERT. Mucosal SERT and tryptophan hydroxylase-1 expression are decreased in experimental inflammation, IBS-C, IBS-D, and ulcerative colitis. Potentiation of 5-HT due to the SERT decrease could account for the discomfort and diarrhea of IBS-D, while receptor desensitization may cause constipation. Similar symptoms are seen in transgenic mice that lack SERT. The loss of mucosal SERT may thus contribute to IBS pathogenesis.
Background & Aims:
Serotonin (5-HT) is a critical signaling molecule in the gut. 5-HT released from enterochromaffin cells initiates peristaltic, secretory, vasodilatory, vagal, and nociceptive ...reflexes. Despite being pathophysiologically divergent, ulcerative colitis (UC) and irritable bowel syndrome (IBS) are both associated with clinical symptoms that include alterations in the normal patterns of motility, secretion, and sensation. Our aim was to test whether enteric 5-HT signaling is defective in these disorders.
Methods:
Rectal biopsy specimens were obtained from healthy controls and patients with UC, IBS with diarrhea (IBS-D), and IBS with constipation (IBS-C). Key elements of 5-HT signaling, including measures of 5-HT content, release, and reuptake, were analyzed with these samples.
Results:
Mucosal 5-HT, tryptophan hydroxylase 1 messenger RNA, serotonin transporter messenger RNA, and serotonin transporter immunoreactivity were all significantly reduced in UC, IBS-C, and IBS-D. The enterochromaffin cell population was decreased in severe UC samples but was unchanged in IBS-C and IBS-D. When 5-HT release was investigated under basal and mechanical stimulation conditions, no changes were detected in any of the groups relative to controls.
Conclusions:
These data show that UC and IBS are associated with similar molecular changes in serotonergic signaling mechanisms. While UC and IBS have distinct pathophysiologic properties, these data suggest that shared defects in 5-HT signaling may underlie the altered motility, secretion, and sensation. These findings represent the first demonstration of significant molecular alterations specific to the gut in patients with IBS and support the assertion that disordered gastrointestinal function in IBS involves changes intrinsic to the bowel.
Cerebral dopamine neurotrophic factor (CDNF) is neuroprotective for nigrostriatal dopamine neurons and restores dopaminergic function in animal models of Parkinson's disease (PD). To understand the ...role of CDNF in mammals, we generated CDNF knockout mice (Cdnf−/−), which are viable, fertile, and have a normal life-span. Surprisingly, an age-dependent loss of enteric neurons occurs selectively in the submucosal but not in the myenteric plexus. This neuronal loss is a consequence not of increased apoptosis but of neurodegeneration and autophagy. Quantitatively, the neurodegeneration and autophagy found in the submucosal plexus in duodenum, ileum and colon of the Cdnf−/− mouse are much greater than in those of Cdnf+/+ mice. The selective vulnerability of submucosal neurons to the absence of CDNF is reminiscent of the tendency of pathological abnormalities to occur in the submucosal plexus in biopsies of patients with PD. In contrast, the number of substantia nigra dopamine neurons and dopamine and its metabolite concentrations in the striatum are unaltered in Cdnf−/− mice; however, there is an age-dependent deficit in the function of the dopamine system in Cdnf−/− male mice analyzed. This is observed as D-amphetamine-induced hyperactivity, aberrant dopamine transporter function, and as increased D-amphetamine-induced dopamine release demonstrating that dopaminergic axon terminal function in the striatum of the Cdnf−/− mouse brain is altered. The deficiencies of Cdnf−/− mice, therefore, are reminiscent of those seen in early stages of Parkinson's disease.
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•CDNF deficient mice exhibit age-dependent hypoplasia of submucosal enteric neurons.•The affected enteric neurons undergo degeneration and autophagy, not apoptosis.•Midbrain dopamine neurons are unaffected but dopamine function in the striatum is.•Phenotypes of Cdnf−/− mice are reminiscent to symptoms in early stage Parkinsonism.
Enterochromaffin cell-derived serotonin (5-HT) promotes intestinal inflammation. We tested hypotheses that peripheral tryptophan hydroxylase (TPH) inhibitors, administered orally, block 5-HT ...biosynthesis and deplete 5-HT from enterochromaffin cells sufficiently to ameliorate intestinal inflammation; moreover, peripheral TPH inhibitors fail to enter the murine enteric nervous system (ENS) or central nervous systems and thus do not affect constitutive gastrointestinal motility.
Two peripheral TPH inhibitors, LP-920540 and telotristat etiprate (LX1032; LX1606) were given orally to mice. Effects were measured on 5-HT levels in the gut, blood and brain, 5-HT immunoreactivity in the ENS, gastrointestinal motility and severity of trinitrobenzene sulfonic acid (TNBS)-induced colitis. Quantitation of clinical scores, histological damage and intestinal expression of inflammation-associated cytokines and chemokines with focused microarrays and real-time reverse transcriptase PCR were employed to evaluate the severity of intestinal inflammation.
LP-920540 and LX1032 reduced 5-HT significantly in the gut and blood but not in the brain. Neither LP-920540 nor LX1032 decreased 5-HT immunoreactive neurons or fibres in the myenteric plexus and neither altered total gastrointestinal transit time, colonic motility or gastric emptying in mice. In contrast, oral LP-920540 and LX1032 reduced the severity of TNBS-induced colitis; the expression of 24% of 84 genes encoding inflammation-related cytokines and chemokines was lowered at least fourfold and the reduced expression of 17% was statistically significant.
Observations suggest that that peripheral TPH inhibitors uncouple the positive linkage of enterochromaffin cell-derived 5-HT to intestinal inflammation. Because peripheral TPH inhibitors evidently do not enter the murine ENS, they lack deleterious effects on constitutive intestinal motility in mice.
Enteric glia are neural crest derivatives. Kabouridis et al. (2015) now show in adult animals that new glia arise within the ganglia of enteric plexuses and then migrate centripetally to colonize the ...mucosa. Remarkably, enteric microbiota regulate this critical migration.
Varicella zoster virus (VZV) is a highly infectious human pathogen; nevertheless, infectious virions are not released in vitro where infection is cell associated. Four VZV envelope glycoproteins ...contain mannose 6-phosphate (Man 6-P), and Man 6-P blocks infection of cells by cell-free VZV. Expression of antisense cDNA or siRNA-like transcripts were used to generate five stable human cell lines deficient in cation-independent mannose 6-phosphate receptors (MPR
ci). All 5 MPR
ci-deficient lines resisted infection by cell-free, but not cell-associated, VZV, secreted lysosomal enzymes, and released infectious virions when infected by cell-associated VZV. Intracellular MPR
ci thus appear to divert newly enveloped VZV to late endosomes, and plasmalemmal MPR
ci are necessary for entry by cell-free VZV. Biopsies from VZV-infected human skin supported the idea that because MPR
ci expression is naturally lost in maturing superficial epidermal cells, these cells do not divert VZV to endosomes and constitutively secrete infectious VZV.
The enteric nervous system (ENS) is the largest component of the autonomic nervous system, with neuron numbers surpassing those present in the spinal cord. The ENS has been called the 'second brain' ...given its autonomy, remarkable neurotransmitter diversity and complex cytoarchitecture. Defects in ENS development are responsible for many human disorders including Hirschsprung disease (HSCR). HSCR is caused by the developmental failure of ENS progenitors to migrate into the gastrointestinal tract, particularly the distal colon. Human ENS development remains poorly understood owing to the lack of an easily accessible model system. Here we demonstrate the efficient derivation and isolation of ENS progenitors from human pluripotent stem (PS) cells, and their further differentiation into functional enteric neurons. ENS precursors derived in vitro are capable of targeted migration in the developing chick embryo and extensive colonization of the adult mouse colon. The in vivo engraftment and migration of human PS-cell-derived ENS precursors rescue disease-related mortality in HSCR mice (Ednrb(s-l/s-l)), although the mechanism of action remains unclear. Finally, EDNRB-null mutant ENS precursors enable modelling of HSCR-related migration defects, and the identification of pepstatin A as a candidate therapeutic target. Our study establishes the first, to our knowledge, human PS-cell-based platform for the study of human ENS development, and presents cell- and drug-based strategies for the treatment of HSCR.
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