NF-κB is a key regulator of innate and adaptive immunity and is implicated in the pathogenesis of AKI. The cell type-specific functions of NF-κB in the kidney are unknown; however, the pathway serves distinct functions in immune and tissue parenchymal cells. We analyzed tubular epithelial-specific NF-κB signaling in a mouse model of ischemia-reperfusion injury (IRI)-induced AKI. NF-κB reporter activity and nuclear localization of phosphorylated NF-κB subunit p65 analyses in mice revealed that IRI induced widespread NF-κB activation in renal tubular epithelia and in interstitial cells that peaked 2-3 days after injury. To genetically antagonize tubular epithelial NF-κB activity, we generated mice expressing the human NF-κB super-repressor IκBαΔN in renal proximal, distal, and collecting duct epithelial cells. Compared with control mice, these mice exhibited improved renal function, reduced tubular apoptosis, and attenuated neutrophil and macrophage infiltration after IRI-induced AKI. Furthermore, tubular NF-κB-dependent gene expression profiles revealed temporally distinct functional gene clusters for apoptosis, chemotaxis, and morphogenesis. Primary proximal tubular cells isolated from IκBαΔN-expressing mice and exposed to hypoxia-mimetic agent cobalt chloride exhibited less apoptosis and expressed lower levels of chemokines than cells from control mice did. Our results indicate that postischemic NF-κB activation in renal tubular epithelia aggravates tubular injury and exacerbates a maladaptive inflammatory response.

TAMP ECL2 and claudins' ECL1 share functionally and structurally similar features involved in homo-/heterophilic tightening of cell-cell contacts. Tricellulin is a specific redox sensor and sealing element at 3-cell contacts and may compensate as a redox mediator for occludin loss at 2-cell contacts in vivo and in vitro. Molecular interaction mechanisms were proposed that contribute to tricellulin's function. In conclusion, tricellulin is a junctional redox regulator for ischemia-related alterations.

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Transient receptor potential vanilloid 4 (TRPV4) cation channels are functional in all renal vascular segments and mediate endothelium-dependent vasorelaxation. Moreover, they are expressed in distinct parts of the tubular system and activated by cell swelling. Ischaemia/reperfusion injury (IRI) is characterized by tubular injury and endothelial dysfunction. Therefore, we hypothesised a putative organ protective role of TRPV4 in acute renal IRI. IRI was induced in TRPV4 deficient (Trpv4 KO) and wild–type (WT) control mice by clipping the left renal pedicle after right–sided nephrectomy. Serum creatinine level was higher in Trpv4 KO mice 6 and 24 hours after ischaemia compared to WT mice. Detailed histological analysis revealed that IRI caused aggravated renal tubular damage in Trpv4 KO mice, especially in the renal cortex. Immunohistological and functional assessment confirmed TRPV4 expression in proximal tubular cells. Furthermore, the tubular damage could be attributed to enhanced necrosis rather than apoptosis. Surprisingly, the percentage of infiltrating granulocytes and macrophages were comparable in IRI–damaged kidneys of Trpv4 KO and WT mice. The present results suggest a renoprotective role of TRPV4 during acute renal IRI. Further studies using cell–specific TRPV4 deficient mice are needed to clarify cellular mechanisms of TRPV4 in IRI.

The pathways of NOTCH and PI3K/AKT are dysregulated in about 60% and 48% of T-cell acute lymphoblastic leukemia (T-ALL) patients, respectively. In this context, they interact and cooperate in controlling tumor cell biology. Here, we propose a novel mechanism by which the PI3K/AKT pathway regulates NOTCH1 in T-ALL, starting from the evidence that the inhibition of PI3K/AKT signaling induced by treatment with LY294002 or transient transfection with a dominant negative AKT mutant downregulates NOTCH1 protein levels and activity, without affecting NOTCH1 transcription. We showed that the withdrawal of PI3K/AKT signaling was associated to NOTCH1 phosphorylation in tyrosine residues and monoubiquitination of NOTCH1 detected by Ubiquitin capture assay. Co-immunoprecipitation assay and colocalization analysis further showed that the E3 ubiquitin ligase c-Cbl interacts and monoubiquitinates NOTCH1, activating its lysosomal degradation. These results suggest that the degradation of NOTCH1 could represent a mechanism of control by which NOTCH1 receptors are actively removed from the cell surface. This mechanism is finely regulated by the PI3K/AKT pathway in physiological conditions. In pathological conditions characterized by PI3K/AKT hyperactivation, such as T-ALL, the excessive AKT signaling could lead to NOTCH1 signaling dysregulation. Therefore, a therapeutic strategy directed to PI3K/AKT in T-ALL could contemporaneously inhibit the dysregulated NOTCH1 signaling. © 2015 Wiley Periodicals, Inc.

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The polyamines putrescine, spermidine and spermine are organic polycations that regulate many cell functions including proliferation and differentiation. It is known that certain genes of the polyamine system are dysregulated after kidney ischemia reperfusion injury. Here we examined the hypothesis that different forms of acute and chronic kidney injury lead to similar changes in the expression patterns of the polyamine system. In different models of acute and chronic kidney injury expression of genes involved in polyamine homeostasis were analyzed by RT‐qPCR and RNAScope. In these models, expression of catabolic enzymes (Aoc1 and Sat1) was upregulated, and the anabolic enzymes (Odc1, Sms) were downregulated. The putrescine‐degrading enzyme AOC1 exhibits the most striking changes. Interestingly, it can act together with ODC1 as gatekeepers of the polyamine system. The detected increase of Aoc1 takes place in the injured but regenerating proximal tubules. As a screening for stimuli of increased Aoc1 expression, we used mouse embryonic kidney explants. Here we observed changes of Aoc1expression under hypoxia and hyperosmotic conditions. These changes were further examined in mouse models of hypoxia. However, in vivo, hypoxia did not lead to changes of Aoc1 expression. Hyperosmolarity was confirmed as a stimulus by using the kidney cell lines M15 and 209/MDCT as well as cultured primary proximal tubules. Using reporter gene and RNA‐stability assays, we could show that the increase in Aoc1 expression is based on mRNA‐stabilization and transcriptional activation of one certain isoform. The activated isoform contains an additional set of 22 amino acids N‐terminally that lead to an altered subcellular localization. In conclusion, different models of kidney injury exhibit a similar pattern of dysregulation of the polyamine system with the most striking change being the upregulation of Aoc1 in proximal tubules. Using hyperosmolarity as a stimulus, we provide first insights into the regulation of Aoc1 under harmful conditions.