86: Digital spatial profiling of glomerular gene expression in pauci-immune glomerulonephritis

Background: Pauci-immune focal necrotizing glomerulonephritis (piFNGN) is a remitting and recurring disease characterized by asynchronous focal necrosis of glomerular tuft segments resulting in scarring and loss of renal function. The lesions evolve over time during active disease phases and appear as heterogeneous patterns of injury in renal biopsies. Characterization of the underlying molecular processes using expression profiling is difficult because most methods involving analysis of bulk tissue, or dissociated single cells, disregard the heterogeneity of discrete lesions. Here, we use digital spatial profiling (DSP) to characterize protein and transcript expression in individual, morphologically distinct glomeruli from patients with piFNGN. Methods: 18 biopsies showing piFNGN were used for DSP according to assay’s instructions. Circular tissue annotations containing glomeruli were manually placed for analysis with the Nanostring GeoMX protein (n=120), immuno-oncology RNA (n=72) and Cancer Transcriptome Atlas (n=48) panels. Glomerular histomorphology was evaluated in adjacent serial sections. Expression data was processed by log transformation, quantile normalization and batch effect correction. Results: DSP demonstrated the differences in the expression of proteins and RNA targets between injured and apparently normal glomeruli that were expected based on previous studies of renal biopsies from vasculitis patients and transplant donors. In addition, DSP identified heterogeneous RNA and protein expression among individual glomeruli from the same biopsy and among glomeruli with similar morphological patterns of injury. This enabled us to identify differential gene expression signatures that correlated with morphological patterns of injury, and indicated involvement of specific inflammatory pathways. Conclusions: Our findings demonstrate the utility of DSP for characterizing heterogeneity of focal glomerular injury and identifying pathways of renal pathobiology in morphologically distinct lesions. Disclosures: Non