A Molecular Profile of Focal Segmental Glomerulosclerosis from Formalin-Fixed, Paraffin-Embedded Tissue

Abstract

Focal segmental glomerulosclerosis (FSGS) is a common form of idiopathic nephrotic syndrome defined by the characteristic lesions of focal glomerular sclerosis and foot process effacement; however, its etiology and pathogenesis are unknown. We used mRNA isolated from laser-captured glomeruli from archived formalin-fixed, paraffin-embedded renal biopsies, until recently considered an unsuitable source of mRNA for microarray analysis, to investigate the glomerular gene expression profiles of patients with primary classic FSGS, collapsing FSGS (COLL), minimal change disease (MCD), and normal controls (Normal). Amplified mRNA was hybridized to an Affymetrix Human X3P array. Unsupervised (unbiased) hierarchical clustering revealed two distinct clusters delineating FSGS and COLL from Normal and MCD. Class comparison analysis of FSGS + COLL combined versus Normal + MCD revealed 316 significantly differentially regulated genes (134 up-regulated, 182 down-regulated). Among the differentially regulated genes were those known to be part of the slit diaphragm junctional complex and those previously described in the dysregulated podocyte phenotype. Analysis based on Gene Ontology categories revealed overrepresented biological processes of development, differentiation and morphogenesis, cell motility and migration, cytoskeleton organization, and signal transduction. Transcription factors associated with developmental processes were heavily overrepresented, indicating the importance of reactivation of developmental programs in the pathogenesis of FSGS. Our findings reveal novel insights into the molecular pathogenesis of glomerular injury and structural degeneration in FSGS.

Detection of Activated Parietal Epithelial Cells on the Glomerular Tuft Distinguishes Early Focal Segmental Glomerulosclerosis from Minimal Change Disease

“…This is a striking finding because, in the latter study, lasermicrocaptured glomerular tufts were analyzed, and the number of PECs should be limited. This finding by Hodgin et al 30 can be explained by migration of PECs onto the glomerular tuft and suggested that ectopic presence of PECs on the glomerular tuft can be used as a diagnostic marker for FSGS. ajp.amjpathol.org -The American Journal of Pathology…”

“…In that study, the researchers performed molecular profiling on laser-captured glomerular tufts from patients with FSGS and collapsing glomerulopathy and compared the profiles to those of patients with MCD. 30 Interestingly, approximately 46% (11 of 24) of the genes listed to be the highest up-regulated genes in the FSGS þ collapsing glomerulopathy group are normally expressed by PECs. This is a striking finding because, in the latter study, lasermicrocaptured glomerular tufts were analyzed, and the number of PECs should be limited.…”

CC Chemokine Ligand 18 in ANCA-Associated Crescentic GN

“…RNA of a very high quality was obtained (Supplemental Figure 1A). 21,22 RNA of sufficient quality for amplification and hybridization was obtained from 30 patients with ANCA-associated crescentic GN and 12 controls (preimplantation kidney biopsies of living or deceased kidney donors). The patient characteristics and clinical data of the group of patients from whom RNA was isolated were not significantly different from those from the remaining patients included in the study (Supplemental Table 1).…”

Glomerular parietal epithelial cells in kidney physiology, pathology, and repair

“…As more PECs invade the glomerular tuft, extracellular matrix proteins continually and progressively accumulate beyond this original site, ultimately leading to an advanced sclerotic lesion of FSGS. More recently, transcriptomic studies add further evidence for a role of PECs in matrix accumulation, wherein an abundance of genes considered 'PEC-specific' were detected in areas of sclerosis in human glomeruli [40]. Thus, one current view underlying the mechanism of segmental scarring in FSGS is that the extracellular matrix accumulation likely arises from two sources: injured podocytes and activated PECs.…”