Cellular insights into glomerular disease

Abstract

Glomerular disease is one of the main underlying causes of chronic kidney disease (CKD). The global burden of CKD is high and the number of patients needing renal replacement therapy is steadily increasing. Still, the pathogenesis of glomerular diseases remains partly unclear and there is a lack of specific and curative treatments. A better understanding of the cellular mechanisms during glomerular disease onset and progression is therefore needed. This thesis focuses on the role of podocytes and mesangial cells in the onset and progression of diabetic kidney disease (DKD) and IgA nephropathy (IgAN), respectively. Firstly, we investigated the role of cytoskeleton-associated protein 4 (CKAP4) and found that knockdown of CKAP4 in podocytes in vitro caused dysregulation of the actin cytoskeleton, microtubules and a loss of integrins. CKAP4 knockdown in zebrafish in vivo, resulted in proteinuria and foot process effacement. These findings are similar to the dysregulation of cytoskeleton in DKD, and since CKAP4 is downregulated in DKD, this indicates a crucial role for CKAP4 in the maintaining of foot process dynamics in podocytes. To examine differences between primary human mesangial cells (HMCs) in culture, and how this could potentially affect experimental outcomes, commercially available HMCs from two sources were compared. Our findings showed differences in morphological characteristics, response to the growth factor PDGF-BB and in their inflammatory response, highlighting the importance of considering differences in cultured primary HMCs when planning experiments. The interaction between IgA1 and HMCs, and how this is involved in onset of IgAN, was investigated. Our hypothesis was that the continuous deposition of IgA1 and galactose deficient IgA1 (gd-IgA1) containing immune complexes in the glomerulus during IgAN would affect the uptake and clearance of IgA1 by HMCs leading to deposit build up. We found that HMCs are able to internalize IgA1 through actin-dependent endocytosis, and that the uptake itself resulted in activation of cells. The knockdown of potential IgA receptors did not stop uptake of IgA1, indicating that uptake could potentially be receptor independent. With repeated stimulation of IgA1 the HMCs clearance capacity was hindered, which could be cause of IgA deposit build up during IgAN. In conclusion, our findings provide new insights into the contribution of podocytes and mesangial cells to glomerular diseases.