Fibrosis and Immune Cell Infiltration Are Separate Events Regulated by Cell-Specific Receptor Notch3 Expression
Sabine Brandt, Tobias M. Ballhause, Anja Bernhardt, Annika Becker, Delia Lidia Șalaru, Hien Minh Le-Deffge, Alexander Fehr, Yan Fu, Lars Philipsen, Sonja Djudjaj, Andreas J. Müller, Rafael Kramann, Mahmoud M. Ibrahim, Robert Geffers, Chris Siebel, Berend Isermann, Florian H. Heidel, Jonathan A. Lindquist, Peter R. Mertens
Abstract
Significance Statement In patients with CKD, receptor Notch3 is strongly upregulated. Conversely, in experimental kidney disease models, Notch3 deficiency protects from organ damage. To determine whether Notch3 on immune cells or tissue-resident cells participates in the inflammatory response, animals with bone marrow chimerism were generated. These animal strains do not exhibit phenotypic differences in the absence of disease. However, after unilateral ureteral obstruction, distinct alterations in the immune response and organ fibrosis become apparent. Notch3 receptors expressed by immune cells are of relevance for transmigration into tissue; the receptors expressed by resident kidney cells orchestrate organ fibrosis. These events seem to be separable and distinct. Background Kidney injuries that result in chronic inflammation initiate crosstalk between stressed resident cells and infiltrating immune cells. In animal models, whole-body receptor Notch3 deficiency protects from leukocyte infiltration and organ fibrosis. However, the relative contribution of Notch3 expression in tissue versus infiltrating immune cells is unknown. Methods Chimeric mice deficient for Notch3 in hematopoietic cells and/or resident tissue cells were generated, and kidney fibrosis and inflammation after unilateral ureteral obstruction (UUO) were analyzed. Adoptive transfer of labeled bone marrow–derived cells validated the results in a murine Leishmania ear infection model. In vitro adhesion assays, integrin activation, and extracellular matrix production were analyzed. Results Fibrosis follows UUO, but inflammatory cell infiltration mostly depends upon Notch3 expression in hematopoietic cells, which coincides with an enhanced proinflammatory milieu ( e.g ., CCL2 and CCL5 upregulation). Notch3 expression on CD45 + leukocytes plays a prominent role in efficient cell transmigration. Functionally, leukocyte adhesion and integrin activation are abrogated in the absence of receptor Notch3. Chimeric animal models also reveal that tubulointerstitial fibrosis develops, even in the absence of prominent leukocyte infiltrates after ureteral obstruction. Deleting Notch3 receptors on resident cells blunts kidney fibrosis, ablates NF- κ B signaling, and lessens matrix deposition. Conclusions Cell-specific receptor Notch3 signaling independently orchestrates leukocyte infiltration and organ fibrosis. Interference with Notch3 signaling may present a novel therapeutic approach in inflammatory as well as fibrotic diseases.