Thursday, May 2, 2024
5/2/2024
Alport syndrome (AS) is a disorder of the glomerular filtration barrier caused by mutations in type IV collagen resulting in an abnormal development of the glomerular basement membrane (GBM) that ultimately leads to progressive chronic kidney disease (CKD) and renal failure. Although the genetic causes of AS are well established the biological mechanisms and complex molecular signaling regulating disease progression remain elusive. Contrary to the podocentric view of AS progression, our analysis on GEC transcriptome and lipidomic studies combined with Fluorescence Lifetime Imaging Microscopy suggest pathologic changes in cellular metabolism of lipids in GEC early in disease in our model of AS, Col4a5-/- mice, before podocyte detachment. In particular, we found 2-fold increase in triglyceride levels in GEC, which were associated with modulation of genes involved in fatty acid metabolism, including fatty acid synthase (FASN), and PPARa. In addition, we have supporting evidence that links altered lipid metabolism in GEC to VEGF mediated remodeling of caveolae and downstream signaling via the PI3K/Akt/mTORC1 pathway. Therefore, understanding the molecular mechanisms leading to the development of lipid metabolic changes and therefore glomerular endothelial dysfunction in AS will provide important insight into the molecular mechanisms of Alport progression. We also have evidence that extracellular vesicles derived from amniotic fluid stem cells (EVs) provide therapeutic benefit in AS mice, ameliorate glomerular injury, improve renal physiology and prolong survival. Proteome studies revealed expression of various angiogenic and lipogenic cargo in human EVs, including FASN. A spatial transcriptomic analysis of AS glomeruli injected with a single dose of human EVs resulted in regulation of lipid metabolism pathways to normal. These findings were confirmed in vitro by applying human EV to FASN knock-out GEC. Therefore, based on our preliminary supporting data we hypothesize that lipid dysregulation in GEC contributes to AS progression and that EVs can re-establish lipid metabolic homeostasis in GEC and prevent disease progression. In this project, we will use a novel in vitro 3D glomerulus-on-a-chip system, designed to mimic the glomerular filtration barrier and GEC of human origin to investigate how lipid metabolic changes following VEGF mediated remodeling of caveolae leads to GEC dysfunction. Using gain and loss of function studies, we will establish the role of lipids in lipid metabolic homeostasis in GEC, and the link to GEC dysfunction in AS. Lastly, we will assess the potential of EVs to restore lipid homeostasis in GEC as a rescue mechanism using different in vitro systems, and in vivo approaches. Successful completion of this proposal will significantly improve our knowledge on the role of glomerular endothelium in AS glomerulopathy. Knowledge gained from these studies can be applied to other CKD etiologies.
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