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Background: Receptor-interacting protein kinase 3 (RIPK3), a component of necroptosis pathways, may have an independent role in inflammation. It has been unclear which RIPK3-expressing cells are responsible for the anti-inflammatory effect of overall Ripk3 deficiency and whether Ripk3 deficiency protects against kidney inflammation occurring in the absence of tubular cell death., Methods: We used chimeric mice with bone marrow from wild-type and Ripk3 -knockout mice to explore RIPK3's contribution to kidney inflammation in the presence of folic acid-induced acute kidney injury AKI (FA-AKI) or absence of AKI and kidney cell death (as seen in systemic administration of the cytokine TNF-like weak inducer of apoptosis [TWEAK])., Results: Tubular and interstitial cell RIPK3 expressions were increased in murine AKI. Ripk3 deficiency decreased NF- κ B activation and kidney inflammation in FA-AKI but did not prevent kidney failure. In the chimeric mice, RIPK3-expressing bone marrow-derived cells were required for early inflammation in FA-AKI. The NLRP3 inflammasome was not involved in RIPK3's proinflammatory effect. Systemic TWEAK administration induced kidney inflammation in wild-type but not Ripk3 -deficient mice. In cell cultures, TWEAK increased RIPK3 expression in bone marrow-derived macrophages and tubular cells. RIPK3 mediated TWEAK-induced NF- κ B activation and inflammatory responses in bone marrow-derived macrophages and dendritic cells and in Jurkat T cells; however, in tubular cells, RIPK3 mediated only TWEAK-induced Il-6 expression. Furthermore, conditioned media from TWEAK-exposed wild-type macrophages, but not from Ripk3 -deficient macrophages, promoted proinflammatory responses in cultured tubular cells., Conclusions: RIPK3 mediates kidney inflammation independently from tubular cell death. Specific targeting of bone marrow-derived RIPK3 may limit kidney inflammation without the potential adverse effects of systemic RIPK3 targeting., (Copyright © 2022 by the American Society of Nephrology.)

Renal inflammation has a key role in the onset and progression of immune- and nonimmune-mediated renal diseases. Therefore, the search for novel anti-inflammatory pharmacologic targets is of great interest in renal pathology. JQ1, a small molecule inhibitor of bromodomain and extraterminal (BET) proteins, was previously found to preserve renal function in experimental polycystic kidney disease. We report here that JQ1-induced BET inhibition modulated the in vitro expression of genes involved in several biologic processes, including inflammation and immune responses. Gene silencing of BRD4, an important BET protein, and chromatin immunoprecipitation assays showed that JQ1 alters the direct association of BRD4 with acetylated histone-packaged promoters and reduces the transcription of proinflammatory genes (IL-6, CCL-2, and CCL-5). In vivo, JQ1 abrogated experimental renal inflammation in murine models of unilateral ureteral obstruction, antimembrane basal GN, and infusion of Angiotensin II. Notably, JQ1 downregulated the expression of several genes controlled by the NF-κB pathway, a key inflammatory signaling pathway. The RelA NF-κB subunit is activated by acetylation of lysine 310. In damaged kidneys and cytokine-stimulated renal cells, JQ1 reduced the nuclear levels of RelA NF-κB. Additionally, JQ1 dampened the activation of the Th17 immune response in experimental renal damage. Our results show that inhibition of BET proteins reduces renal inflammation by several mechanisms: chromatin remodeling in promoter regions of specific genes, blockade of NF-κB pathway activation, and modulation of the Th17 immune response. These results suggest that inhibitors of BET proteins could have important therapeutic applications in inflammatory renal diseases., (Copyright © 2017 by the American Society of Nephrology.)

AKI is histologically characterized by necrotic cell death and inflammation. Diverse pathways of regulated necrosis have been reported to contribute to AKI, but the molecular regulators involved remain unclear. We explored the relative contributions of ferroptosis and necroptosis to folic acid (FA)-induced AKI in mice. FA-AKI in mice associates with lipid peroxidation and downregulation of glutathione metabolism proteins, features that are typical of ferroptotic cell death. We show that ferrostatin-1 (Fer-1), an inhibitor of ferroptosis, preserved renal function and decreased histologic injury, oxidative stress, and tubular cell death in this model. With respect to the immunogenicity of ferroptosis, Fer-1 prevented the upregulation of IL-33, an alarmin linked to necroptosis, and other chemokines and cytokines and prevented macrophage infiltration and Klotho downregulation. In contrast, the pancaspase inhibitor zVAD-fmk did not protect against FA-AKI. Additionally, although FA-AKI resulted in increased protein expression of the necroptosis mediators receptor-interacting protein kinase 3 (RIPK3) and mixed lineage domain-like protein (MLKL), targeting necroptosis with the RIPK1 inhibitor necrostatin-1 or genetic deficiency of RIPK3 or MLKL did not preserve renal function. Indeed, compared with wild-type mice, MLKL knockout mice displayed more severe AKI. However, RIPK3 knockout mice with AKI had less inflammation than their wild-type counterparts, and this effect associated with higher IL-10 concentration and regulatory T cell-to-leukocyte ratio in RIPK3 knockout mice. These data suggest that ferroptosis is the primary cause of FA-AKI and that immunogenicity secondary to ferroptosis may further worsen the damage, although necroptosis-related proteins may have additional roles in AKI., (Copyright © 2016 by the American Society of Nephrology.)