NLRP3 inflammasome knockout mice are protected against ischemic but not cisplatin-induced acute kidney injury.

We have demonstrated that caspase-1 is a mediator of both cisplatin-induced acute kidney injury (AKI) and ischemic AKI. As caspase-1 is activated in the inflammasome, we investigated the inflammasome in cisplatin-induced and ischemic AKI. Mice were injected with cisplatin or subjected to bilateral renal pedicle clamping. Immunoblot analysis of whole kidney after cisplatin-induced AKI revealed: 1) an increase in apoptosis-associated Speck-like protein containing a caspase recruitment domain (ASC), the major protein that complexes with nucleotide-binding oligomerization domain, leucine-rich repeat and pyrin domain containing proteins (NLRP) 1 or 3 to form the inflammasome; 2) an increase in caspase-1 activity, caspase-5, and NLRP1, components of the NLRP1 inflammasome; and 3) a trend toward increased NLRP3. To determine whether the NLRP3 inflammasome plays an injurious role in cisplatin-induced AKI, we studied NLRP knockout (NLRP3(-/-)) mice. In cisplatin-induced AKI, the blood urea nitrogen, serum creatinine, acute tubular necrosis score, and tubular apoptosis score were not significantly decreased in NALP3(-/-) mice compared with wild-type mice. We have previously demonstrated the injurious role of caspase-1 in ischemic AKI. NLRP3, but not ASC or NLRP1, is increased in ischemic AKI. NLRP3(-/-) mice with ischemic AKI had significantly lower blood urea nitrogen, serum creatinine, and acute tubular necrosis and apoptosis scores than the wild-type controls. The difference in protection against cisplatin-induced AKI compared with ischemic AKI in NLRP3(-/-) mice was not explained by the differences in proinflammatory cytokines interleukin (IL)-1ß, IL-6, chemokine (C-X-C motif) ligand 1, or tumor necrosis factor α. NLRP3 inflammasome is a mediator of ischemic AKI but not cisplatin-induced AKI, and further investigation of the NLRP1 inflammasome in cisplatin-induced AKI should prove interesting.

IL-33 exacerbates acute kidney injury.

Inflammation contributes to the pathogenesis of acute kidney injury (AKI). IL-33 is a proinflammatory cytokine, but its role in AKI is unknown. Here we observed increased protein expression of full-length IL-33 in the kidney following induction of AKI with cisplatin. To determine whether IL-33 promotes injury, we administered soluble ST2 (sST2), a fusion protein that neutralizes IL-33 activity by acting as a decoy receptor. Compared with cisplatin-induced AKI in untreated mice, mice treated with sST2 had fewer CD4 T cells infiltrate the kidney, lower serum creatinine, and reduced acute tubular necrosis (ATN) and apoptosis. In contrast, administration of recombinant IL-33 (rIL-33) exacerbated cisplatin-induced AKI, measured by an increase in CD4 T cell infiltration, serum creatinine, ATN, and apoptosis; this did not occur in CD4-deficient mice, suggesting that CD4 T cells mediate the injurious effect of IL-33. Wildtype mice that received cisplatin and rIL-33 also had higher levels of the proinflammatory chemokine CXCL1, which CD T cells produce, in the kidney compared with CD4-deficient mice. Mice deficient in the CXCL1 receptor also had lower serum creatinine, ATN, and apoptosis than wildtype mice following cisplatin-induced AKI. Taken together, IL-33 promotes AKI through CD4 T cell-mediated production of CXCL1. These data suggest that inhibiting IL-33 or CXCL1 may have therapeutic potential in AKI.

Mediators of inflammation in acute kidney injury.

Acute kidney injury (AKI) remains to be an independent risk factor for mortality and morbidity. Inflammation is now believed to play a major role in the pathophysiology of AKI. It is hypothesized that in ischemia, sepsis and nephrotoxic models that the initial insult results in morphological and/or functional changes in vascular endothelial cells and/or in tubular epithelium. Then, leukocytes including neutrophils, macrophages, natural killer cells, and lymphocytes infiltrate into the injured kidneys. The injury induces the generation of inflammatory mediators like cytokines and chemokines by tubular and endothelial cells which contribute to the recruiting of leukocytes into the kidneys. Thus, inflammation has an important role in the initiation and extension phases of AKI. This review will focus on the mediators of inflammation contributing to the pathogenesis of AKI.

Apoptosis and autophagy in cold preservation ischemia.

BACKGROUND: Prolonged cold ischemia (CI) is a risk factor for the development of delayed graft function that predicts reduced 5-year kidney transplant survival. CI results in caspase-3 activation, tubular injury, and apoptosis. Autophagy, a highly conserved pathway that permits recycling of nutrients within the cell during stress, is linked to apoptosis. We hypothesized that CI during kidney preservation would induce autophagy. We sought to determine apoptosis and autophagic flux in CI. METHODS: Autophagic flux and apoptosis were examined in kidneys of wild-type and green fluorescent protein (GFP)-microtubule-associated protein1 light chain 3 (LC3) transgenic mice that were subjected to 48 hr of CI. Autophagic flux was determined by performing experiments with and without bafilomycin A1. RESULTS: CI alone significantly increased the number of apoptotic cells/hpf, caspase-3/7 activity, and protein expression of autophagy markers LC3 II and autophagy-related protein 5. To determine the effect of inhibiting autophagic flux on apoptosis, kidneys of wild-type and GFP-LC3 transgenic mice were subjected to 48 hr of CI in the presence of lysosomal inhibitor bafilomycin A1. The combination of CI and bafilomycin A1 suppressed autophagic flux and significantly reduced the number of apoptotic cells/hpf, caspase-3/7 activity, LC3 II (both by immunoblot and in GFP-LC3 transgenic mice), and autophagy-related protein 5 protein expression. CONCLUSION: In summary, we have shown that autophagy and autophagic flux are reduced in cold ischemic kidneys treated with bafilomycin A1. Reduced autophagy and autophagic flux were associated with a significant reduction in apoptotic cell death, which may provide a therapeutic rationale for including bafilomycin A1 in University of Wisconsin solution during organ preservation.