Although neurologic sequelae of acute kidney injury (AKI) are well described, the pathogenesis of acute uremic encephalopathy is poorly understood. This study examined the short-term effect of ischemic AKI on inflammatory and functional changes of the brain in mice by inducing bilateral renal ischemia for 60 min and studying the brains 24 h later. Compared with sham mice, mice with AKI had increased neuronal pyknosis and microgliosis in the brain. AKI also led to increased levels of the proinflammatory chemokines keratinocyte-derived chemoattractant and G-CSF in the cerebral cortex and hippocampus and increased expression of glial fibrillary acidic protein in astrocytes in the cortex and corpus callosum. In addition, extravasation of Evans blue dye into the brain suggested that the blood-brain barrier was disrupted in mice with AKI. Because liver failure also leads to encephalopathy, ischemic liver injury was induced in mice with normal renal function; neuronal pyknosis and glial fibrillary acidic protein expression were not increased, suggesting differential effects on the brain depending on the organ injured. For evaluation of the effects of AKI on brain function, locomotor activity was studied using an open field test. Mice subjected to renal ischemia or bilateral nephrectomy had moderate to severe declines in locomotor activity compared with sham-operated mice. These data demonstrate that severe ischemic AKI induces inflammation and functional changes in the brain. Targeting these pathways could reduce morbidity and mortality in critically ill patients with severe AKI.

Studies in humans and animal models have demonstrated that acute kidney injury (AKI) has a significant effect on the function of extrarenal organs. The combination of AKI and lung dysfunction is associated with 80% mortality; the lung, because of its extensive capillary network, is a prime target for AKI-induced effects. The study presented here tested the hypothesis that AKI leads to a vigorous inflammatory response and produces distinct genomic signatures in the kidney and lung. In a murine model of ischemic AKI, prominent global transcriptomic changes and histologic injury in both kidney and lung tissues were identified. These changes were evident at both early (6 h) and late (36 h) timepoints after 60-min bilateral kidney ischemia and were more prominent than similar timepoints after sham surgery or 30 min of ischemia. The inflammatory transcriptome (109 genes) of both organs changed with marked similarity, including the innate immunity genes Cd14, Socs3, Saa3, Lcn2, and Il1r2. Functional genomic analysis of these genes suggested that IL-10 and IL-6 signaling was involved in the distant effects of local inflammation, and this was supported by increased serum levels of IL-10 and IL-6 after ischemia-reperfusion. In summary, this is the first comprehensive analysis of concomitant inflammation-associated transcriptional changes in the kidney and a remote organ during AKI. Functional genomic analysis identified potential mediators that connect local and systemic inflammation, suggesting that this type of analysis may be a useful discovery tool for novel biomarkers and therapeutic drug development. Clinical studies have revealed a strong association between AKI and dysfunction of extrarenal organs, and more recently animal research has shown a significant causal effect of AKI on distant organ dysfunction. [1][2][3][4][5][6][7] Since the availability of dialysis, AKIassociated distant organ dysfunction constitutes the major cause of death in these patients, with the mortality rate still in the 50% range. Despite this frustrating outcome, little is known about the potential pathophysiological interactions between the kidney and extrarenal organs in critically ill patients. Numerous recent studies have demonstrated that outcomes of AKI are heavily dependent upon the severity of comorbid conditions. 8 -10 Isolated AKI has a much better prognosis than AKI associated with multiple organ failure, 11,12 and the presence of renal insufficiency continues to be a sensitive marker for poor outcome in the hospitalized patient. 13 Thus, there is an urgent need to study the systemic effects of AKI, and modern discovery tools have the potential to unveil novel diagnostic and therapeutic targets.Inflammation is a major component of the initiation and exacerbation of kidney injury during AKI, 14,15 and local inflammation of kidney tissues could be a source of the development of inflamma-

Oxidative stress is involved in acute kidney injury due to ischemia-reperfusion and chemotherapy-induced nephrotoxicity. To investigate their basic mechanisms we studied the role of nuclear factor-erythroid 2-p45-related factor 2 (Nrf2), a redox-sensitive transcription factor that regulates expression of several antioxidant and cytoprotective genes. We compared the responses of Nrf2-knockout mice and their wild-type littermates in established mouse models of ischemia-reperfusion injury and cisplatin-induced nephrotoxicity. Several Nrf2-regulated genes encoding antioxidant enzymes/proteins were significantly upregulated in the kidneys of wild type but not Nrf2-knockout mice following renal ischemia. Renal function, histology, vascular permeability, and survival were each significantly worse in the Nrf2 knockout mice. Further, proinflammatory cytokine and chemokine expression tended to increase after ischemia in the knockout compared to the wild-type mice. Treatment of the knockout mice with the antioxidants N-acetyl-cysteine or glutathione improved renal function. The knockout mice were more susceptible to cisplatin-induced nephrotoxicity, and this was blunted by N-acetyl-cysteine pretreatment. Our study demonstrates that Nrf2-deficiency enhances susceptibility to both ischemic and nephrotoxic acute kidney injury, and identifies this transcription factor as a potential therapeutic target in these injuries.

T and B lymphocytes have been implicated in the pathogenesis of renal ischemia reperfusion injury (IRI). The trafficking of lymphocytes into kidneys during IRI has been postulated to underlie this effect, but has not been rigorously studied. We therefore characterized the lymphocyte populations infiltrating into mouse kidneys 3 and 24 h after renal IRI. Immunohistochemistry and flow cytometry staining of kidney lymphocytes showed increased trafficking of CD3+ T cells and CD19+ B cells in both sham-operated and IRI mice 3 h after renal IRI. In the IRI mice, increased infiltration of NK1.1+ and CD4+NK1.1+ cells compared with normal and sham-operated mice was observed 3 and 24 h after renal IRI, respectively. After 24 h of renal IRI, the decreased percentages of CD3+, CD19+, and NK1.1+ populations in the IRI mice compared with control groups were observed. Increased TNF-α and IFN-γ production of kidney infiltration CD3+ T cells in IRI mice but not sham-operated mice was found. Unexpectedly, isolation and transfer of kidney-infiltrating lymphocytes 24 h after renal IRI into T cell-deficient mice reduced their functional and histological injury after renal IRI, suggesting that kidney-infiltrating lymphocytes could have a protective function. These quantitative, qualitative, and functional changes in kidney lymphocytes provide mechanistic insight into how lymphocytes modulate IRI, as well as demonstrating that abdominal surgery alone leads to lymphocyte changes in kidney.