Decreased Parietal Epithelial Cell Density Is Linked to Podocyte Depletion and Predictors of Kidney Disease Progression

Background: Glomerulosclerosis is a common final pathway that leads to chronic kidney disease (CKD). Rodent models of glomerular disease suggest parietal epithelial cells (PECs) may participate in the pathogenesis of chronic glomerular disease. However, little is known about the function of PECs in humans. This project aimed to develop and deploy tools to measure the relationship between PEC and podocyte populations and clinical and histopathological metrics of kidney disease in humans. Methods: Kidney tissue samples were obtained from patients undergoing total nephrectomy enrolled in the PRECISE cohort at the University of Michigan. Tissue sections were stained with Periodic Acid Schiff (PAS) and for Wilms tumor 1 (WT1). Digitized images were used to train a U-Net-based deep learning pipeline that quantified PEC and podocyte densities in over 20,000 human glomeruli. Histopathologic analysis was compared with single-cell RNA sequencing (scRNA-seq) of kidneys from a subset of patients. Results: The study population included 85 patients with a median age of 61 years and an EGFR of 83.7 ml/min/1.73 m2. We found 98.2% of PECs were WT1+ across all samples, allowing use of WT1 to identify both PECs and podocytes in the same section, depending on their histologic location. The Dice similarity scores for identifying PECs and podocytes with our analysis pipeline were 0.69±0.17 and 0.72±0.11, respectively, indicating accuracy similar to trained human experts. There was a striking correlation between average per patient PEC and podocyte densities (R = 0.80, P = 8.1x10-26). PEC density declined with age (R = -0.43, P = 3.5x10-4) and in patients with diabetes (32% decrease, P = 1.5x10-3). PEC density was negatively correlated with the fraction of abnormal glomeruli (R = -0.28, P = 2.9x10-2). Within the subset of patients with scRNA-seq data (N = 26), PECs from patients from the lowest tertile of PEC density showed evidence of PEC stress, including upregulation of HSPA1B. Conclusion: PEC and podocyte densities are tightly correlated. PEC density also correlates with risks for CKD progression, including age and diabetes, and early histopathologic evidence of chronic glomerular disease. These observations support a link between PEC population and the progression of CKD. Funding: NIDDK Support, Private Foundation Support