Engineering a Kidney Organoid Model to Investigate Fibronectin-TGF-beta Signaling in Renal Fibrosis

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Chronic kidney disease (CKD) is estimated to affect approximately 11-13% of the global population. CKD is driven by scarring of kidney tissue, a process known as “renal fibrosis”. This process is dramatically affected by both the protein TGF-beta, which is secreted by inflammatory cells, and the protein fibronectin, which is a structural protein assembled into fibrils by cells to build new tissue. The process of fibrosis is confounded by two issues. First, TGF-beta induces cells to assemble fibronectin into fibrils, while fibronectin fibrils bind TGF-beta and induce cells to respond to it; this feedback makes it difficult to separate cause-and-effect in fibrosis. Second, multiple cell types in the kidney can secrete TGF-beta, secrete fibronectin, and assemble fibronectin into fibrils, making it difficult to distinguish the contributions of different cell types to the progression of fibrosis. This project will address this complexity by developing hollow spheres of kidney cells that mimic kidney tissue. Removal/ inhibition of specific cell types and/or elements of TGF-beta and fibronectin signaling will allow for a deeper understanding of how these proteins contribute to renal fibrosis. The impact of this work will be expanded by developing a four-session symposium targeted to high school students and community college students from under-represented communities that focuses on the fundamentals of kidney function and cell biology.CKD is driven by renal fibrosis, which is a process of excess assembly of extracellular matrix. The interplay between the immune cytokine TGF-beta and the extracellular matrix protein fibronectin in renal fibrosis is incompletely understood. In response to inflammatory signals, the cytokine TGF-beta is released from immune cells. TGF-beta drives increased secretion of the extracellular matrix protein fibronectin and subsequent assembly of fibronectin into a scaffold of fibrils. Immune cell-derived TGF-beta also drives an increased secretion of endogenous TGF-beta, which subsequently binds to the scaffold of fibronectin fibrils. Collectively, these drive alterations in renal tubule morphology, renal tubule function, and extracellular matrix remodeling that occur during renal fibrosis. In this work, a reductionist approach will be used to identify the contribution of fibronectin fibril assembly, endogenous TGF-beta secretion, and TGF-beta/fibronectin tethering to renal fibrosis and kidney damage. To better understand their respective roles, renal tubule spheroids will be engineered that will serve as a platform for investigating TGF-beta/fibronectin interactions in renal fibrosis. This renal tissue mimetic will consist of renal epithelial cells, fibroblasts, and pericytes, as well as relevant tubulo-interstitial extracellular matrix components. The work will first determine if these renal mimetics recapitulate kidney tubule polarity and tubular function and will demonstrate that known inducers of renal fibrosis drive similar changes in the renal spheroids. The following system elements will then be perturbed: i) the assembly of fibronectin into extracellular matrix fibrils, ii) the expression and secretion of endogenous TGF-beta, and iii) the localization and tethering of TGF-beta to fibronectin fibrils to better understand the interactions between these key constituents.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.