Role of intracellular complement activation in kidney fibrosis

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PROJECT SUMMARY / ABSTRACT The prevalence of Chronic Kidney Disease (CKD) in the US is high and continues to rise in our aging population. Independent of the cause of CKD, tubulointerstitial fibrosis and glomerulosclerosis represent major pathways of progression of kidney disease, however, there are no approved drugs to treat kidney fibrosis that could ameliorate progression of CKD. In recent studies we demonstrated that locally synthesized and activated kidney complement components drive the pathogenesis of kidney fibrosis. The complement system is of major importance in innate and adaptive immunity, but dysregulated complement has been shown to play a major role in kidney injury. Our pilot data, leveraging single nuclear RNA sequencing (snRNAseq), indicate cell-specific compartmentation of complement components, particularly of C3 and C5 in RTE cells. Our data also indicate that these components ligand their cognate receptors, C3aR and C5aR1, on kidney macrophages in murine models of kidney fibrosis. In preliminary datasets, genetic deletion of these factors in a cell-specific manner imparted significant protection against renal scarring. Thus, the central hypothesis to be tested in this application is that intrinsic expression of complement components from kidney cells, their processing to active fragments and activation of their cognate receptors are key to the progressive loss of kidney function and scaring. This hypothesis will be investigated via the following independent, but complementary, specific aims: Aim 1: Delineate the intracellular expression of complement components by kidney cells. We will use snRNAseq in murine kidney fibrosis to delineate cell type-specific expression of complement components and their receptors. We will confirm data by proteomic approaches and identify the processing machinery generating active secretory fragments from complement components. Aim 2. Determine the importance of RTE-derived C3 for renal physiology and fibrosis. We will use mice engineered to lack C3 specifically in RTE cells to determine the relevance of intracellular complement for renal physiology and injury-induced fibrosis. We will study mice lacking the C3ar1 receptor on either kidney or myeloid cells to establish whether there is an obligate requirement for autocrine or paracrine C3 signaling. Aim 3. Determine the impact of C5a/C5aR1 axis activation on macrophages for the induction of kidney fibrosis or repair. We will validate our preliminary observations that macrophage-specific deletion of C5ar1 reduces fibrosis. We will determine whether C5ar1 directly affects macrophage phenotype and function, or whether C5ar1 macrophages promote scarring by recruiting and activating inflammatory T cells. Collectively, this proposal will establish a comprehensive atlas of complement component expression in kidney cells in healthy and injured kidneys, establish key mechanisms of these pathways in kidney scarring and enable clinical targeting of these pathways with therapeutically relevant strategies.