Single-Nucleus RNA-Sequencing Identifies a Differential Profibrotic Response in Parietal Epithelial Cells in Primary Versus Maladaptive Focal Segmental Glomerulosclerosis

Introduction

Focal segmental glomerulosclerosis (FSGS) lesions occur in a wide range of clinical conditions that are all characterized by critical podocyte injury. Differentiating primary from maladaptive forms of FSGS remains challenging because of the absence of reliable biomarkers, resulting from a lack of insight into their pathophysiological differences.

Methods

We used single-nucleus RNA-sequencing (snRNA-seq) to identify differentially expressed transcriptional signatures in kidney biopsies of well-phenotyped primary versus maladaptive FSGS. We included cryopreserved kidney biopsy cores from adult patients with newly diagnosed primary FSGS (n = 9, all nephrotic), maladaptive FSGS (n = 9, all nonnephrotic), proteinuric controls (antiphospholipase A2 receptor antibody–positive membranous nephropathy [PLA2R+ MN], n = 3), and healthy controls (n = 4).

Results

We identified 120,751 high-quality nuclei, including 2471 podocytes and 1574 parietal epithelial cells (PECs). In primary FSGS, podocytes showed a more pronounced but not specific injury pattern with upregulation of immune pathways, such as antigen presentation, and mammalian target of rapamycin (mTOR) complex 1 (mTORC1)-signaling. Glomerular cell-cell interaction analysis showed increased profibrotic TGF-β and PDGFR-β signaling in primary FSGS PECs, which also upregulated genes that compose the normal PEC-derived extracellular matrix (ECM) (LAMB1, COL4A1, COL4A5, COL4A6). In maladaptive FSGS, podocytes showed few differentially expressed genes (DEGs) and PEC-PEC interactions predominated. Here, a (myo-)fibroblast-like PEC subpopulation upregulated non–type IV fibril- and network-forming collagens (COL1A1, COL5A1, COL8A1), which may further contribute to the development of glomerulosclerosis.

Conclusion

This study presents a single-cell transcriptional landscape of well-phenotyped patients with FSGS and provides evidence for a differential profibrotic PEC response in primary versus maladaptive FSGS.