Progressive kidney disease and ESRD are associated with high morbidity and mortality. Regardless of the cause of injury there is a stereotypical response leading to interstitial fibrosis. A key feature is the activation of extracellular matrix-producing myofibroblasts. Current therapies focus on nonspecific or supportive therapy. Understanding mechanisms of fibrosis will lead to new therapies. During the course of the current funding cycle we advanced our understanding of the role of sphingolipids in AKI. Sphingosine 1-phosphate (S1P), a pleiotrophic lysophospholipid that is involved in diverse functions such as cell growth and survival, lymphocyte trafficking, and vascular stability, has profound effects on the immune system and kidney injury. S1P is the product of sphingosine phosphorylation by two sphingosine kinase isoforms (SphK1 and SphK2) that have different subcellular localizations. Whereas SphK1 is cytoplasmic, SphK2 is localized in the nucleus, mitochondria and endoplasmic reticulum pointing to an intracellular/intranuclear signaling role of sphingosine 1-phosphate. We observed that Sphk2-/- mice had markedly attenuated renal fibrosis compared to Sphk1-/- or WT mice and marked tissue elevation of interferon gamma (IFN?). These findings led us to focus our renewal on the specific role of SphK2 and determine whether intranuclear SphK2 regulates tissue fibrosis. Our preliminary data provide a framework for the current proposal: 1) In 2 models of fibrosis (folic acid-induced nephropathy (FA-N) and disease progression after unilateral IRI) we found that mice deficient in SphK2 have markedly reduced fibrosis and high tissue expression of IFN?2) delayed administration of a novel inhibitor of SphK2 protects mice from fibrosis, 3) adoptive transfer of SphK2-deficient T cells, which produce high levels of IFN?, protects WT mice from fibrosis, 4) stimulation of fibroblasts cultured from Sphk2-/- are resistant to myofibroblast transformation and 5) combining microarray data and ChIP-seq of H3K27ac and high-throughput sequencing we have identified candidate genes with histone acetylations that may suppress fibrosis in kidneys of Sphk2-/- mice. We propose a series of in vitro and in vivo studies to better understand the role of SphK2 in kidney fibrosis. Our overall hypothesis is that: 1) the progression from AKI to fibrosis (or the process of repair and recovery after AKI) is regulated by SphK2 and 2) the absence or inhibition of SphK2 contributes to resistance to fibrosis.
Aim 1. To test the hypothesis that pharmacological inhibition of SphK2 or genetic deficiency of SphK2 attenuates or reverses kidney fibrosis.
Aim 2. To test the hypothesis that pharmacological inhibition of SphK2 blocks fibrosis or mice deficient of SphK2 are resistant to kidney fibrosis through regulation of local interstitial IFN?.
Aim 3. To test the hypothesis that SphK2 mediates epigenetic regulation of expression of key genes that can cause kidney fibrosis. These studies will help us understand how S1P regulates fibrosis/repair but they also have the potential to uncover genes important for various aspects of disease progression that may serve as targets for therapy.
Kidney disease is a major economic and public health burden in the United States and world wide with ever increasing rates of hospitalization and unacceptably high mortality in critically ill patients. Acute kidney injury may predispose patients to progression to chronic kidney disease (CKD) and end stage renal disease and ultimately shortened lifespan. The development of effective treatments for CKD, including fibrosis, is urgently needed and depends on a precise understanding of the molecular, cellular and immunological basis of fibrosis. The major goal of the current proposal is to further investigate the role of a class of enzymes, sphingosine kinases, which are important in sphingolipid metabolism, in mechanisms of kidney fibrosis and as target sites for treatment of fibrosis.
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