Chronic kidney disease (CKD) is a major cause of morbidity and mortality, affecting more than 10% of the world’s population. CKD is associated with excessive renal fibrosis, which leads to declining kidney function and eventual kidney failure. In CKD, glomerular mesangial cells (MC), resident fibroblasts and tubular epithelial cells undergo phenotypic activation and transition in response to profibrotic and proinflammatory cytokines such as transforming growth factor β1 (TGFβ1). These activated renal cells excessively produce extracellular matrix (ECM) proteins that replace functional renal tissue and lead to renal fibrosis. Caveolae are small omega-shaped invaginations of the plasma membrane that mediate signaling transduction events. Formation of caveolae require the protein caveolin-1 (cav-1). We have previously shown that the ability of MC to produce matrix proteins is dependent on cav-1 expression. Unfortunately, clinically targeting cav-1 within the kidneys, specifically within MC, is technically challenging and as of yet unfeasible. Thus, to better understand how cav-1 deletion is protective, we carried out a microarray screen comparing cav-1 wild-type (WT) and knockout (KO) MC. Here, we discovered significant up-regulation of a TGFβ superfamily inhibitory protein, follistatin (FST). FST specifically targets and neutralizes activin A (ActA) but not TGFβ1. TGFβ1 and ActA both belong to the TGFβ superfamily of cytokines and growth factors. While TGFβ1 itself is a known key mediator of renal fibrosis, therapies aimed at directly inhibiting TGFβ1 in kidney diseases have not been successful due to opposing profibrotic and anti-inflammatory effects. ActA has been shown to act as a strong profibrotic and proinflammatory agent in various organs, including the lungs and liver. We along with others have observed elevated levels of ActA within the kidneys and serum of mice and humans with CKD. Functionally, ActA has been shown to contribute to ECM production in the kidneys. Hence, we hypothesized that ActA inhibition through FST could prove beneficial in CKD. In this thesis, our first study elucidated a novel molecular pathway by which cav-1 regulates expression of the FST in MC. Our results indicate that FST is negatively regulated by cav-1 through a PI3K/PKC zeta/Sp1 transcriptional pathway. Our second study expands on these findings and tests whether exogenous FST administration protects against the progression of CKD in a surgical mouse model of CKD. Here, we discovered that FST acts as a reactive oxygen species (ROS) scavenger and that exogenous administration of FST protects against the development of CKD through the inhibition of renal fibrosis and oxidative stress. Lastly, our third study determined whether microRNAs (miRNAs) are implicated in post-transcriptionally regulating FST through cav-1 and whether these FST-targeting miRNAs can be utilized therapeutically to protect against the development and progression of CKD. Here, we determined that a FST-targeting miRNA, microRNA299a-5p, is significantly downregulated in cav-1 deficient MC, upregulated in vivo in a mouse model of CKD and that its inhibition, in vitro and in vivo protects against the accumulation of ECM proteins and renal fibrosis. These studies collectively suggest that FST is an effective therapeutic option for the management of CKD. / Thesis / Doctor of Philosophy (PhD) / Chronic kidney disease results from excessive fibrosis (scarring) within the kidneys. The goal of this thesis is to understand the molecular mechanisms involving the regulation of an antifibrotic protein, follistatin, in glomerular mesangial cells and to identify its therapeutic potential in chronic kidney disease. This thesis has identified that follistatin, an endogenous inhibitor of the profibrotic cytokine activin A, is regulated transcriptionally by Sp1 and post-transcriptionally by microRNA299a-5p. Furthermore, this thesis has demonstrated that exogenous recombinant follistatin administration protects against the progression of chronic kidney disease and that microRNA299a-5p targeting may be an alternative approach to block renal fibrosis. These studies collectively show that follistatin is an effective treatment for the management of chronic kidney disease.
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/24942 |
| Date | January 2019 |
| Creators | Mehta, Neel |
| Contributors | Krepinsky, Joan, Medical Sciences |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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