Understanding the role of SOX9 in kidney fibrosis

Abstract

Chronic kidney disease (CKD) is a significant public health issue with its prevalence set to rise worldwide. Despite this, treatment options to slow or reverse the progression of CKD remain very limited. Moderate to severe CKD is associated with numerous health problems including increased mortality. If the underlying cause of CKD leads to kidney failure, the only options are dialysis or transplantation associated with significant complications. A common histological finding in CKD, regardless of the cause, is activation of the myofibroblast resulting in dysregulated extracellular matrix (ECM) deposition or fibrosis. This leads to a disruption of the normal kidney architecture and loss of nephron function. Unfortunately, despite its urgent need, there is currently no approved anti-fibrotic therapy for kidney fibrosis. Many developmental pathways have been noted to re- activate in injury and promote myofibroblast activation. Understanding the mechanisms behind this could be a route to developing new therapies in CKD. This thesis identifies three regulators of myofibroblast activity in kidney fibrosis; sex-determining region Y-box 9 (SOX9), Neuron navigator 3 (NAV3) and Integrin alpha 11 (ITGA11). SOX9, a transcription factor, is a master regulator of ECM production both in development and fibrosis. Data from this thesis shows that SOX9 is persistently expressed in mesenchymal cells at several stages of kidney development. Although expression is limited in normal adult kidney, SOX9 is re- activated in pro-fibrotic myofibroblasts in disease, resulting in worsening kidney fibrosis. Loss of Sox9 in unilateral ureteric obstruction (UUO)-induced fibrosis resulted in an improvement in scarring and fibrotic markers. Although these data suggest SOX9 inactivation may be a route to anti-fibrotic drugs, targeting a transcription factor is more difficult therapeutically. To address this, transcriptomics was carried out on WT and SOX9-null kidneys following UUO to discover downstream regulators as potential anti-fibrotic targets. Through this analysis, NAV3 was identified as a SOX9 regulated protein and verified in vivo and in vitro. NAV3 is involved in actin polymerisation and cell migration in development. Although not previously studied in fibrosis, this thesis observed that Nav3 loss resulted in reduced pericyte migration and fewer alpha smooth muscle actin (α−SMA) stress fibers. These data indicate a novel mechanism through which SOX9 regulates myofibroblast migration via NAV3. ITGA11, a novel collagen binding integrin, is known to regulate SOX9 via mechano-sensitive Yes-associated protein 1 (YAP1). This integrin was interrogated in kidney fibrosis by creation of an Itga11-venus reporter mouse. This and in situ hybridisation localised its up-regulation in myofibroblasts in kidney fibrosis. Taken together, this thesis indicates NAV3 and ITGA11 as promising targets for the development of anti-fibrotic therapies in treating kidney fibrosis.

Date of Award	31 Dec 2019
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Philip Kalra (Supervisor), Darren Green (Supervisor) & Karen Piper Hanley (Supervisor)