Chronic dysregulation of metabolism is the hallmark of type 2 diabetes. Hyperinsulinemia and insulin resistance are often observed in conjunction with additional risk factors, including obesity, atherogenic dyslipidemia, hyperglycemia, hypertension, and a pro-thrombotic and pro-inflammatory state, which together, characterize the """"""""metabolic syndrome"""""""". Our research group has focused on NF-?B activation in type 2 diabetes, and we and others have identified 3 mechanisms leading to activation of NF-?B. First, we have reported increased expression of numerous NF-?B-regulated pro-inflammatory cytokines, chemokines, and growth factors in the renal cortex of db/db mice, indicating a dysregulated and prolonged activation of the NF-?B canonical pathway. Second, we have reported that diabetes alters NF-?B noncanonical pathway proteins in renal cortex, and we have localized these proteins to renal proximal tubular epithelial cells (pTEC). Third, we have identified another alternative pathway of NF-?B activation that involves phosphorylation of RelA serine536. Based on our animal studies, we postulate that diabetes activates both canonical and noncanonical NF-?B pathways, leading to renal inflammation. Since NF-?B activation is rapidly arrested, an important, unanswered question is why this does not occur in diabetic tissues, where canonical pathway activation of the innate immune response persists chronically. We hypothesize that diabetes-induced activation of NF-?B noncanonical pathways plays a causal role in prolonging the innate immune response activated by the canonical pathway, contributing significantly to the progression of complications. In order to test this hypothesis, we will use a human pTEC tissue culture system to probe molecular mechanisms involved in canonical vs. noncanonical NF- ?B pathway activation in response to stimuli that mimic the in vivo diabetic milieu.
In Aim 1, we will identify the time-dependent activation profile of the two NF-?B pathways in human pTEC exposed to elevated glucose, advanced glycated endproducts (AGE), and angiotensin-II (Ang-II) using NF-?B pathway-specific reporter-gene assays.
In Aim 2, we will explore the role of NIK in NF-?B noncanonical pathway activation induced by glucose, AGE and Ang-II by employing NIK-specific siRNA and by overexpressing NIK-wild type or kinase-dead, dominant-negative NIK mutants.
Aim 3 will characterize the activation kinetics and nuclear processing of RelB in human renal pTEC, and Aim 4 will determine the significance of RelA phosphorylation on serine536 as another alternative noncanonical NF-kB pathway signaling mechanism in pTEC. The results obtained from the proposed aims will provide invaluable insights into molecular mechanisms by which diabetes induces and maintains chronic inflammation in the kidney.
Our research group has focused on the role of inflammation and NF-?B activation in the pathogenesis of diabetic nephropathy in type 2 diabetes. Using human proximal tubular epithelial cells in tissue culture, together with in vivo manipulation of NF-?B proteins, we are exploring an important, unanswered question - why is NF-?B canonical pathway activation not rapidly arrested in diabetic tissues, where NF-?B activation of the innate immune response persists chronically. Results of this research have the potential to identify novel therapeutic targets to treat diabetic nephropathy.
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