Insights into Glomerular Cell Biology in Health and Disease

The integrity of the kidney glomerular filtration barrier relies on the health of its components, which include podocytes forming the final layer of the filtration barrier, and endothelial cells lining the glomerular capillaries. Both cell types are important for kidney development and normal kidney homeostasis, and their injury is implicated in a range of kidney diseases, notably diabetic kidney disease, the most common cause of kidney failure. Here, I used podocytes to explore novel autophagic regulation and paracrine communication mechanisms. By examining the phenotypic effects of JAK2 absence in podocytes, I identified a role for JAK2 in regulating podocyte autophagy completion, specifically through regulating the expression of a master regulator of lysosomal gene expression known as transcription factor TFEB. Since JAK2 has garnered attention as a promising therapeutic target for the treatment of diabetic kidney disease, I explored the effects of systemic JAK2 inhibition, and JAK2 deletion from podocytes in experimental models of diabetes. Pharmacological inhibition of JAK2 prevented progression of albuminuria and reduced urine excretion of the chemokine CCL2. Likewise, podocyte-specific JAK2 knockout resulted in a marked reduction in urine excretion of CCL2, which was also enriched in culture media conditioned by podocytes exposed to high glucose. Podocyte secreted CCL2 signaling via its receptor CCR2 induced glomerular endothelial activation, characterized by VCAM-1 upregulation, through a pathway regulated by p38 MAPK, MSK1/2, and phosphorylation of histone protein H3 on serine residue 10 (phospho-histone H3Ser10). Moreover, increased phospho-histone H3Ser10 levels were observed in the kidneys of diabetic endothelial nitric oxide synthase knockout mice and in the glomeruli of humans with diabetic kidney disease. Collectively, these findings: i) identified the homeostatic actions of JAK2 in podocyte autophagy, also raising the possibility that therapeutically modulating TFEB activity may improve podocyte health in glomerular disease; ii) highlight the anti-inflammatory effects of JAK2 inhibition and podocyte-specific JAK2 deletion in diabetes; and iii) demonstrate the influence that histone protein phosphorylation may have on gene activation in diabetic kidney disease.Ph.D