Tenascin X (TNX) is a matricellular protein involved in regulating cellular functions by interacting with other extracellular matrix (ECM) proteins within the cell matrix and has anti-adhesive properties evidenced in tumours and wound healing. TNX is the only member of the tenascin family that is lost in Joint Hypermobility Syndrome (JHS) and exerts a crucial architectural function. Of importance, TNX deficient and JHS patients have gastrointestinal (GI) dysfunction. Despite this association no study has described the role of TNX in the GI tract. Thus, the aim of this thesis was to characterise the expression of TNX in the stomach and colon in mouse and human tissue. Second, we aimed to elucidate the functional role of TNX using TNX knockout (TNX KO) mice. Expression studies revealed TNX in vagal afferent endings in the mouse, and myenteric cell bodies in human stomach. In colon, TNX strongly associated with cholinergic submucous and myenteric neurons in both species, however, was not found in CGRP positive fibres. Cell bodies in nodose ganglia, dorsal root ganglia, ventral and dorsal horn were also TNX positive. Functional studies in stomach, using single fibre electrophysiology showed TNX KO mice had increased vagal afferent mechanoreceptor sensitivity. Octanoic acid breath test revealed rapid gastric emptying in TNX KO. Colonic manometry showed the amplitude and frequency of colonic contractions were reduced in TNX KO mice, particularly in the distal colon. Ussing chamber studies measuring changes in ion flux (indirect measure of secretion) showed no major difference between TNX KO and wild type (WT) mice. The specific localisation of TNX with neuronal structures in the gut is shown here for the first time suggesting that TNX is more than just an architectural protein. Indeed, its role in specific GI functions supports this observation and provides a mechanism for GI symptoms in JHS.

La Ténascine-X (TNX) est une glycoprotéine architecturale de la matrice extracellulaire. Outre ce rôle, la TNX est également considérée comme une protéine matricellulaire qui est capable de réguler le comportement de cellules normales et tumorales. Toutefois, aucun mécanisme moléculaire et cellulaire ne permettait d'expliquer les effets cellulaires de la TNX, avant notre étude. Au laboratoire, nous avons démontré que le domaine C-terminal de type fibrinogène (FBG) de la TNX était capable d'induire l'activation du Transforming Growth Factor (TGF) bêta latent. En effet, les trois isoformes du TGF bêta sont sécrétées sous la forme de complexes inactifs formés à partir de liaisons non covalentes entre le TGF bêta mature et son propeptide N-terminal LAP (Latency Associated Peptide). Nous avons montré que le domaine FBG de la TNX interagissait physiquement avec le TGF bêta latent, in vitro et in vivo, et induisait un changement de conformation du complexe latent, afin de permettre son activation en une molécule bioactive. De plus, nous avons identifié l'intégrine alpha11 bêta1 comme un récepteur membranaire pour la TNX et nous avons montré que cette intégrine était cruciale pour le processus d'activation du TGF bêta latent par le domaine FBG. Nous avons également démontré que les Méprines alpha et bêta deux protéases de la famille des astacines, pouvaient cliver la TNX, permettant ainsi de libérer des fragments contenant le domaine FBG, capables d'activer le TGF bêta latent. Enfin, nous avons entamé une étude de la pertinence biologique de l'activation du TGF bêta latent par la TNX in vivo en analysant la voie de signalisation du TGF bêta dans des souris déficientes ou non en TNX / Tenascin-X (TNX) is an architectural glycoprotein of the extracellular matrix. Beyond this role, TNX is also considered as a matricellular protein that is able to regulate the behavior of normal and tumor cells. However, no molecular and cellular mechanism has been described to explain TNX cellular effects before our study. In the laboratory, we showed that the C-terminal fibrinogen-like domain (FBG) of TNX was able to induce the latent transforming growth factor (TGF beta activation. Indeed, the three TGF beta isoforms are secreted as inactive complexes formed from non-covalent bonds between the mature TGF beta and its N-terminal propeptide, called LAP (Latency Associated Peptide). We showed that the FBG domain of TNX physically interacted with the latent TGF beta, in vitro and in vivo, and induced a conformational change of the latent complex to allow its activation into a bioactive molecule. Furthermore, we identified alpha1 beta1 integrin as a cell-surface receptor for TNX and showed that this integrin was crucial for the FBG-induced latent TGF beta activation. We also demonstrated that Meprins alpha and beta, two proteases belonging to the astacin family, could cleave the TNX, thereby releasing fragments containing the FBG domain capable of activating latent TGF beta. Finally, we have initiated a study regarding the biological relevance of latent TGF beta activation by TNX in vivo by analyzing the TGF beta signaling pathway in wild type or TNX-deficient mice