Clinical, histopathologic and molecular features of idiopathic and diabetic nodular mesangial sclerosis in humans

Abstract

Background: Idiopathic nodular mesangial sclerosis, also called idiopathic nodular glomerulosclerosis (ING), is a rare clinical entity with an unclear pathogenesis. The hallmark of this disease is the presence of nodular mesangial sclerosis on histology without clinical evidence of diabetes mellitus or other predisposing diagnoses. To achieve insights into its pathogenesis, we queried the clinical, histopathologic and transcriptomic features of ING and nodular diabetic nephropathy (DN).

Methods: All renal biopsy reports accessioned at Indiana University Health from 2001 to 2016 were reviewed to identify 48 ING cases. Clinical and histopathologic features were compared between individuals with ING and DN (n = 751). Glomeruli of ING (n = 5), DN (n = 18) and reference (REF) nephrectomy (n = 9) samples were isolated by laser microdissection and RNA was sequenced. Immunohistochemistry of proline-rich 36 (PRR36) protein was performed.

Results: ING subjects were frequently hypertensive (95.8%) with a smoking history (66.7%). ING subjects were older, had lower proteinuria and had less hyaline arteriolosclerosis than DN subjects. Butanoate metabolism was an enriched pathway in ING samples compared with either REF or DN samples. The top differentially expressed gene, PRR36, had increased expression in glomeruli 248-fold [false discovery rate (FDR) P = 5.93 × 10-6] compared with the REF and increased 109-fold (FDR P = 1.85 × 10-6) compared with DN samples. Immunohistochemistry revealed a reduced proportion of cells with perinuclear reaction in ING samples as compared to DN.

Conclusions: Despite similar clinical and histopathologic characteristics in ING and DN, the uncovered transcriptomic signature suggests that ING has distinct molecular features from nodular DN. Further study is warranted to understand these relationships.

Keywords: PRR36; diabetic nephropathy; laser microdissection; nodule; transcriptomics.

FIGURE 1

Selection process for determining members of the ING cohort. Using NLP of all biopsy reports, a total of 1062 unique individuals had a first native renal biopsy with a ‘nodule’, ‘nodularity’, ‘nodular mesangial sclerosis’ or other ‘nodular’ features. Electronic data capture identified 833 subjects as having DM. A manual chart review of the remaining 229 cases excluded individuals with evident DM on chart review, lack of sufficient data to exclude DM, inconsistent pathology, a paraprotein or insufficient immunofluorescence. Forty-eight cases were consistent with a diagnosis of ING.

FIGURE 2

An example of ING (A) and diabetic glomerulosclerosis (B) on periodic acid–Schiff staining of paraffin-embedded sections are given. Electron microscopy images are pictured for ING (C) and DN (D).

FIGURE 3

An example of neovascularization at the vascular pole of a glomerulus in a sample with nodular mesangial sclerosis. A subset of arterioles is labeled with arrows.

FIGURE 4

(A) Unsupervised heatmap including dendrogram illustrating the relative gene expression between ING, nodular DN and REF samples. (B) PCA plot showing gene expression clustering of the samples. The REF samples cluster more closely while the ING and nodular DN transcriptomic signatures are more broadly distributed.

FIGURE 5

Volcano plot illustrating differentially expressed transcripts between ING and REF samples (A) and ING versus nodular DN (nodular glomerulosclerosis) (B). PRR36 was differentially expressed in ING compared with both REF and diabetic nodular samples. Horizontal dotted lines represent FDR <0.05. Vertical dotted lines represent log₂ fold change (FC) >0.25. (C) Enriched pathways in the ING and REF analysis. (D) Enriched pathways in ING and diabetic analysis.

FIGURE 6

A transcriptogram network analysis was performed for two comparisons. (A) Idiopathic nodular samples (ING) and REF samples were compared revealing enrichment of the pathways listed (all P < 0.05 after multiple testing correction). (B) Idiopathic nodular samples and diabetic nodular glomerulosclerosis samples (diabetics) were compared revealing enrichment of the pathways listed (all P < 0.05 after multiple testing correction). In each transcriptogram, genes are ordered on the x-axis according to known protein–protein interactions. The top panel coveys the regional expression difference and direction of effect of ING (blue line) as compared with the normalized expression for the REF or diabetic expression (black line). In the second panel, regional corrected significance is provided. In the bottom panel, selected significant pathways are plotted with their degree of enrichment.

FIGURE 7

Immunohistochemistry of PRR36 in (A) idiopathic nodular samples (n = 5) and (B) nodular DN samples (n = 5). (C) The proportion of cells with perinuclear expression per glomerulus. In idiopathic nodular samples, 31.7% of cells had a perinuclear reaction compared with 63.1% of diabetic samples (P = 0.01). Each dot represents the proportion of cells with expression in a glomerulus. Between four and six nonobsolescent glomeruli were counted per section.