The rate limiting step of phagocytosis is the binding of collagen to specific receptors, which include β1 integrins and the discoidin domain receptor 1 (DDR1). While these two receptors may interact, the functional nature of these interactions is not defined. We examined the effects of DDR1 over-expression on β1 integrin function and determined that DDR1 over-expression enhanced cell attachment through β1 integrins. These data are consistent with data showing that DDR1 over-expression enhanced cell-surface, but not total, β1 integrin expression and activation. As shown by experiments with endoglycosidase H, DDR1 over-expression increased glycosylation of the β1 integrin subunit. Collectively these data indicate that DDR1 enhances β1 integrin interactions with fibrillar collagen, possibly by affecting the processing and trafficking of β1 integrins to the cell surface. Our data provide insight into the mechanisms by which fibrotic conditions such as cyclosporine A-induced gingival overgrowth are regulated.

The rate limiting step of phagocytosis is the binding of collagen to specific receptors, which include β1 integrins and the discoidin domain receptor 1 (DDR1). While these two receptors may interact, the functional nature of these interactions is not defined. We examined the effects of DDR1 over-expression on β1 integrin function and determined that DDR1 over-expression enhanced cell attachment through β1 integrins. These data are consistent with data showing that DDR1 over-expression enhanced cell-surface, but not total, β1 integrin expression and activation. As shown by experiments with endoglycosidase H, DDR1 over-expression increased glycosylation of the β1 integrin subunit. Collectively these data indicate that DDR1 enhances β1 integrin interactions with fibrillar collagen, possibly by affecting the processing and trafficking of β1 integrins to the cell surface. Our data provide insight into the mechanisms by which fibrotic conditions such as cyclosporine A-induced gingival overgrowth are regulated.

Les maladies rénales ont un impact socio-économique majeur sur la santé publique nécessitant le développement de nouvelles stratégies thérapeutiques. Le Récepteur à Domaine Discoïdine de type 1 (DDR1) est un récepteur non-intégrine des collagènes, à activité tyrosine-kinase. Son expression anormale est un facteur clé de la pathologie rénale qui promeut le développement de l’inflammation et de la fibrose.Ces travaux de thèse nous ont permis de démontrer que l'inhibition de DDR1 freinait la progression des maladies rénales dans trois modèles, dont l'un d'évolution aiguë, l'ischémie-reperfusion (I/R). Après I/R, les cellules épithéliales tubulaires proximales (CETP) exprimaient anormalement DDR1 et l'inhibition de ce récepteur empêchait l'acquisition d'un phénotype pro-inflammatoire par ce type cellulaire. Nous avons démontré in vitro que le stress du réticulum endoplasmique (RE), secondaire à l'hypoxie, était responsable de l'induction de DDR1, via l'activation du facteur de transcription CHOP. De plus, le profil d'expression de DDR1 dans des biopsies de patients transplantés était similaire à celui obtenu dans l'I/R expérimentale.Enfin, les résultats préliminaires obtenus dans un nouveau modèle de souris triples transgéniques ont montré l'installation d'une inflammation et d'une fibrose rénales secondaires à la surexpression génétiquement définie de DDR1 durant 4 semaines dans les cellules épithéliales tubulaires.En conclusion, nos résultats suggèrent que la surexpression de DDR1 joue un rôle délétère dans les néphropathies chroniques et aiguës, ce qui renforce l’intérêt du développement d’inhibiteurs spécifiques de DDR1 capables de bloquer la fonction de ce récepteur. / Renal diseases lead to severe long-term complications of kidney function and only few preventive and therapeutic options exist. Discoidin Domain Receptor 1 (DDR1) is a non-integrin collagen receptor expressed in several cell types within the kidney. Its abnormal expression has a deleterious role in experimental chronic kidney diseases (CKD) by promoting renal inflammation and fibrosis.The inhibition of DDR1 stopped the progression of renal disease in two models of experimental CKD and protected renal function and structure in a model of acute kidney disease, ischemia-reperfusion (I/R). DDR1 expression was strongly induced in proximal epithelial tubular cells (PETCs) after I/R. Moreover, isolated PETCs from DDR1 heterozygous mice after I/R did not acquire the pro-inflammatory phenotype displayed by PETCs from WT mice. Endoplasmic reticulum (ER) stress was responsible for DDR1 pathological expression in hypoxic PETCs after I/R through the activation of CHOP transcription factor. Interestingly, biopsies of transplant patients with prolonged ischemia during transplantation had a very similar expression profile of DDR1 in proximal tubules as in experimental I/R.Finally, DDR1 overexpression in epithelial tubular cells for four weeks, in a new conditional transgenic mouse model, led to the development of renal inflammation and fibrosis.To conclude, our results suggest that the genetically-induced or the pathological overexpression of DDR1 promotes renal inflammation and fibrosis. Thus, targeting DDR1 can be a promising strategy in the treatment of renal diseases.

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