Neuropatia enterica in un modello murino di infezione del sistema nervoso enterico con Herpes simplex virus di tipo 1
Herpes simplex virus type 1 infection of murine enteric nervous system leads to gut neuropathy. The functional gastrointestinal disorders (FGIDs) are a heterogeneous group of chronic conditions characterized by disabling symptoms and decreased patients' quality of life (Corazziari et al. 2004; Talley et al. 2008) Among these diseases, the Irritable Bowel Syndrome (IBS) is the most relevant for the severe prognosis and the high social and economic burden (Drossman, 2006; Fichna and Storr, 2012; Quigley et al. 2012) In clinical practice, IBS is characterized by visceral hypersensitivity and altered bowel function (Larauche et al. 2012) Since the etiology is still poorly understood and no curative treatments are available, nowadays therapy for IBS is palliative and supportive but is notoriously unsatisfactory (Halland and Talley, 2012) Although the underlying pathophysiology of FGIDs is still undefined, there are several evidences suggesting that functional or anatomical alterations of the enteric nervous system (ENS) disrupt gastrointestinal homeostasis determining FGIDs (De Giorgio and Camilleri, 2004; Furness, 2012) Infectious agents, such as neurotropic viruses, have been proposed to infect and disrupt ENS integrity either directly or indirectly eliciting harmful inflammatory responses by the innate and adaptive immune system (Chen et al. 2003; Facco et al. 2008; Selgrad et al. 2009) Among common pathogens the Herpes simplex virus type 1 (HSV 1) shows several interesting features as candidate pathogen involved in FGIDs, being highly prevalent in human populations (Knipe and Cliffe, 2008) and able to infect ENS neurons (Gesser and Koo, 1996; Brun et al. 2010) Our research group has recently established a novel animal model in rodents where a persistent HSV 1 infection in ENS leads to intestinal motor abnormalities with no macroscopic histological damage or clinical signs of disease (Brun et al. 2010) The aim of my Ph.D. research project was to study the mechanisms responsible of the altered intestinal function secondary to HSV 1 infection of mice ENS. At 1 10 weeks after viral administration the presence of HSV 1 infection in the ENS determined time dependent alterations of enteric neural network architecture, shown by an altered distribution and/or expression of specific neural proteins, such as HuC/D, peripherin e bIII tubulin, and glial proteins, such as S100b and glial fibrillary acidic protein (GFAP; Qesari et al. 2011) These structural modifications in myenteric plexus were linked to changes in the equilibrium between excitatory and inhibitory neurotransmission, revealed by an increased expression of both enzymes, nitric oxide synthase (nNOS) acetylcholinetransferase (ChAT) and by a modified distribution of the vasoactive intestinal polypeptide (VIP) substance P (SP) and acetylcholinesterase (AChE) The presence of an unbalanced inhibitory/excitatory activity was further confirmed by experiments on tissue cultures from longitudinal muscle with myenteric plexus (LMMP) and on gut contractility of ileum segments, mounted vertically in organ baths. Depolarization evoked release of [3H]acetylcholine was significantly reduced for most of viral infection time course and in the same time neurally mediated cholinergic responses to electric field stimulation were significantly reduced in the early and late phases of infection. All these data suggest that HSV 1 infection induces structural alterations and changes in neural excitatory activity and/or neurotransmitters release, all signs of an underlying enteric neuropathy (Qesari et al. 2011) To study the role of innate immunity and of viral replication in the onset of HSV 1 infection induced gut neurodysfunction, mice deficient for Toll like receptor 2 (TLR2 KO) and ICP27 null HSV 1 (ICP27 KO) a mutant virus unable to replicate (Uprichard and Knipe, 1996) have subsequently been used. ICP27 KO administration induced anomalies in the ENS only in the early phases of infection to indicate an involvement of viral replication in the onset of enteric neuropathy only in the latest times of infection (Qesari et al. 2012) Recent studies have shown that an interaction between TLR2 and HSV 1 can trigger excessive signaling TLR2 dependent, leading to an excessive inflammation and tissue damage (Soberman et al. 2012) HSV 1 infection in the ENS of TLR2 KO mice induced only a reduction in nNOS positive neurons with no effects on myenteric plexus anatomy and intestinal contractile function. In conclusion, this study demonstrated that HSV 1 infection of mice ENS triggers TLR2 mediated immune responses which are consequently responsible of myenteric plexus structural abnormaities and changes in ileal contractile function. My results also highlight TLR2 as an attractive therapeutic target for an effective modulation of pathogenic immune responses and possibly for the treatment of viral associated neuropathies.