Intrarenal crystals trigger inflammation and renal cell necroptosis, processes that involve TNF receptor (TNFR) signaling. Here, we tested the hypothesis that TNFRs also have a direct role in tubular crystal deposition and progression of hyperoxaluria-related CKD. Immunohistochemical analysis revealed upregulated tubular expression of TNFR1 and TNFR2 in human and murine kidneys with calcium oxalate (CaOx) nephrocalcinosis-related CKD compared with controls. Western blot and mRNA expression analyses in mice yielded consistent data. When fed an oxalate-rich diet, wild-type mice developed progressive CKD, whereas , anddeficient mice did not. Despite identical levels of hyperoxaluria, , and-deficient mice also lacked the intrarenal CaOx deposition and tubular damage observed in wild-type mice. Inhibition of TNFR signaling prevented the induced expression of the crystal adhesion molecules, CD44 and annexin II, in tubular epithelial cells and, and treatment with the small molecule TNFR inhibitor R-7050 partially protected hyperoxaluric mice from nephrocalcinosis and CKD. We conclude that TNFR signaling is essential for CaOx crystal adhesion to the luminal membrane of renal tubules as a fundamental initiating mechanism of oxalate nephropathy. Furthermore, therapeutic blockade of TNFR might delay progressive forms of nephrocalcinosis in oxalate nephropathy, such as primary hyperoxaluria.

The atypical chemokine receptor 2 (ACKR2), also named D6, regulates local levels of inflammatory chemokines by internalization and degradation. To explore potential anti-inflammatory functions of ACKR2 in glomerulonephritis, we induced autologous nephrotoxic nephritis in C57/BL6 wild-type and Ackr2-deficient mice. Renal ACKR2 expression increased and localized to interstitial lymphatic endothelium during nephritis. At two weeks Ackr2mice developed increased albuminuria and urea levels compared to wild-type mice. Histological analysis revealed increased structural damage in the glomerular and tubulointerstitial compartments within Ackr2 kidneys. This correlated with excessive renal leukocyte infiltration of CD4 T cells and mononuclear phagocytes with increased numbers in the tubulointerstitium but not glomeruli in knockout mice. Expression of inflammatory mediators and especially markers of fibrotic tissue remodeling were increased along with higher levels of ACKR2 inflammatory chemokine ligands like CCL2 in nephritic Ackr2 kidneys. In vitro, Ackr2 deficiency in TNF-stimulated tubulointerstitial tissue but not glomeruli increased chemokine levels. These results are in line with ACKR2 expression in interstitial lymphatic endothelial cells, which also assures efflux of activated leukocytes into regional lymph nodes. Consistently, nephritic Ackr2 mice showed reduced adaptive cellular immune responses indicated by decreased regional T-cell activation. However, this did not prevent aggravated injury in the kidneys of Ackr2 mice with nephrotoxic nephritis due to simultaneously increased tubulointerstitial chemokine levels, leukocyte infiltration and fibrosis. Thus, ACKR2 is important in limiting renal inflammation and fibrotic remodeling in progressive nephrotoxic nephritis. Hence, ACKR2 may be a potential target for therapeutic interventions in immune complex glomerulonephritis.

The Duffy antigen/receptor for chemokines (DARC) is a chemokine-binding protein that is expressed on erythrocytes and renal endothelial cells. DARC-mediated endothelial transcytosis of chemokines may facilitate the renal recruitment of macrophages and T cells, as has been suggested for neutrophils. We studied the role of Darc in two mouse models of prolonged renal inflammation, one that primarily involves the tubulointerstitium (unilateral ureteral obstruction), and one that requires an adaptive immune response that leads to glomerulonephritis (accelerated nephrotoxic nephritis). Renal expression of Darc and its ligands was increased in both models. Leukocytes effectively infiltrated obstructed kidneys in Darc-deficient mice with pronounced T-cell infiltration at early time points. Development of interstitial fibrosis was comparable in both genotypes. Nephrotoxic nephritis was inducible in Darc-deficient mice, with both an increased humoral immune response and functional impairment during the early phase of disease. Leukocytes efficiently infiltrated kidneys of Darc-deficient mice, with increased cell numbers at early but not late time points. Taken together, renal inflammation developed more rapidly in DARC-deficient mice, without affecting the extent of renal injury at later time points. Thus, genetic elimination of Darc in mice does not prevent the development of renal infiltrates and may even enhance such development during the early phases of interstitial and glomerular diseases in mouse models of prolonged renal inflammation.

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