Human resident gut microbe Bacteroides thetaiotaomicron regulates colonic neuronal innervation and neurogenic function

BACKGROUND AND AIMS: As the importance of gut-brain interactions increases, understanding how specific gut microbes interact with the enteric nervous system (ENS), which is the first point of neuronal exposure becomes critical. Our aim was to understand how the dominant human gut bacterium Bacteroides thetaiotaomicron (Bt) regulates anatomical and functional characteristics of the ENS. METHODS: Neuronal cell populations, as well as enteroendocrine cells, were assessed in proximal colonic sections using fluorescent immunohistochemistry in specific pathogen-free (SPF), germ-free (GF) and Bt conventionalized-germ-free mice (Bt-CONV). RNA expression of tight junction proteins and toll-like receptors (TLR) were measured using qPCR. Colonic motility was analyzed using in vitro colonic manometry. RESULTS: Decreased neuronal and vagal afferent innervation observed in GF mice was normalized by Bt-CONV with increased neuronal staining in mucosa and myenteric plexus. Bt-CONV also restored expression of nitric oxide synthase expressing inhibitory neurons and of choline acetyltransferase and substance P expressing excitatory motor neurons comparable to those of SPF mice. Neurite outgrowth and glial cells were upregulated by Bt-CONV. RNA expression of tight junction protein claudin 3 was downregulated while TLR2 was upregulated by Bt-CONV. The enteroendocrine cell subtypes L-cells and enterochromaffin cells were reduced in GF mice, with Bt-CONV restoring L-cell numbers. Motility as measured by colonic migrating motor complexes (CMMCs) increased in GF and Bt-CONV. CONCLUSION: Bt, common gut bacteria, is critical in regulating enteric neuronal and enteroendocrine cell populations, and neurogenic colonic activity. This highlights the potential use of this resident gut bacteria for maintaining healthy gut function

Ex vivo study of human visceral nociceptors.

OBJECTIVE: The development of effective visceral analgesics free of deleterious gut-specific side effects is a priority. We aimed to develop a reproducible methodology to study visceral nociception in human tissue that could aid future target identification and drug evaluation. DESIGN: Electrophysiological (single unit) responses of visceral afferents to mechanical (von Frey hair (VFH) and stretch) and chemical (bradykinin and ATP) stimuli were examined. Thus, serosal afferents (putative nociceptors) were used to investigate the effect of tegaserod, and transient receptor potential channel, vanilloid 4 (TRPV4) modulation on mechanical responses. RESULTS: Two distinct afferent fibre populations, serosal (n=23) and muscular (n=21), were distinguished based on their differences in sensitivity to VFH probing and tissue stretch. Serosal units displayed sensitivity to key algesic mediators, bradykinin (6/14 units tested) and ATP (4/10), consistent with a role as polymodal nociceptors, while muscular afferents are largely insensitive to bradykinin (0/11) and ATP (1/10). Serosal nociceptor mechanosensitivity was attenuated by tegaserod (-20.8±6.9%, n=6, p<0.05), a treatment for IBS, or application of HC067047 (-34.9±10.0%, n=7, p<0.05), a TRPV4 antagonist, highlighting the utility of the preparation to examine the mechanistic action of existing drugs or novel analgesics. Repeated application of bradykinin or ATP produced consistent afferent responses following desensitisation to the first application, demonstrating their utility as test stimuli to evaluate analgesic activity. CONCLUSIONS: Functionally distinct subpopulations of human visceral afferents can be demonstrated and could provide a platform technology to further study nociception in human tissue

Mechanisms of activation of mouse and human enteroendocrine cells by nutrients

AstraZeneca, Wellcome Trust, Bowel and Cancer Research, Barts and the London Charity

Functional Roles of Peroxisome Proliferator-Activated Receptor β/δ in a Model of Relapsing-Remitting Experimental Autoimmune Encephalomyelitis

Multiple sclerosis (MS) is a chronic neurodegenerative disease characterized by lesions that form within the central nervous system which induce symptoms such as muscle weakness and paralysis. Many aspects of MS, ranging from causation to immunopathology, are currently under investigation as little is known of the factors that contribute to and exacerbate this disease. Presently, evidence suggests MS to be an inflammatory disease mediated by an autoimmune response to an unknown antigen. Results from clinical studies as well as animal models such as experimental autoimmune encephalomyelitis (EAE) suggest MS is initiated and maintained by immune cells such as Th1 lymphocytes. As a result, therapeutics prescribed to MS patients’ focus on modulating the inflammatory response so as to minimize myelin loss and CNS damage. Peroxisome proliferator-activated receptors (PPARs) are a family of transcription factors that show promise as potential targets for MS therapeutics. The PPAR sub-types, PPARα and PPARγ, have been shown to inhibit the propagation of inflammatory pathways and decrease the activity of pro-inflammatory cells in a number of inflammation driven diseases including rheumatoid arthritis and atherosclerosis. The anti-inflammatory role of PPARβ/δ is less well known, although preliminary studies suggest activation of this receptor may potentiate the activity of other transcription factors involved in inhibiting inflammatory pathways. As the PPAR family of transcription factors exhibit similar functions, it is hypothesized that the PPARβ/δ sub-type may have immunomodulatory effects that are comparable and complimentary to PPARα and –γ. This thesis describes a novel model of relapsing-remitting EAE (RR-EAE) that presents a disease course where EAE relapses are followed by periods of recovery that are characterized by the absence of clinical symptoms. Furthermore, a therapeutic intervention study carried out using this model demonstrates that the PPARγ agonist pioglitazone can decrease the severity of a relapse episode when drug treatment begins prior to a predicted relapse event. The inhibition of immune cell infiltration into the CNS and decreased immune cell activity mediated by pioglitazone, suggests that this ligand modulates the immune response. These results indicate that pioglitazone may be an effective treatment for relapsing-remitting MS. To examine the role of PPARβ/δ in RR-EAE and explore its effect on the activity of inflammatory cells, PPARβ/δ knockout mice were used due to the current lack of specific antagonists for this receptor. PPARβ/δ wild-type mice developed RR-EAE when immunized using protocol intended to induce this disease course. PPARβ/δ knockout mice however, developed chronic EAE when immunized in the same manner. Consistent with sustained clinical symptoms, CNS immune cell infiltration and activity was maintained throughout the disease in PPARβ/δ knockout mice. In contrast, the presence of immune cells within the CNS and consequent activity fluctuated according to the relapse and recovery pattern of disease in PPARβ/δ wild-type mice. PPARβ/δ appears to modulate inflammation by potentiating the apoptosis of activated T cells. Therefore, PPARβ/δ agonists may be potential candidates for MS treatment

A model of experimental autoimmune encephalomyelitis (EAE) in C57BL/6 mice for the characterisation of intervention therapies

Multiple sclerosis (MS) and its different forms are Studied in the animal model experimental autoimmune encephalomyelitis (EAE). Relapsing-remitting MS. the most common form of the disease can be induced in mice where clinical symptoms fluctuate in severity over time. However. the animal model does not experience periods of recovery where clinical signs are absent, unlike the human disease. We have developed a novel model of relapsing-remitting EAE in C57BL/6 mice immunised with myelin oligodendrocyte glycoprotein (MOG) peptide and Quil A as adjuvant. These animals have relapses that are followed by periods of recovery, during which time the animals do not exhibit illness. Furthermore. administration of the PPAR gamma agonist pioglitazone prior to a predicted relapse prevents the expected development of symptoms in a dose-dependent fashion. Immune cell infiltration into white matter of the CNS and decreased production of inflammatory cytokine IFN-gamma in treated animals were also observed. Our model will be a valuable tool in assessing intervention therapies for RR-MS sufferers. (c) 2007 Elsevier B.V. All rights reserved