RNA Alternative Splicing and Polyadenylation and Regulation of the Glomerular Filtration Barrier.

KEY POINTS: Alternative mRNA processing adds an important layer of transcriptome complexity in podocyte and slit diaphragm components during glomerular injury. Trans-elements and cis-elements may offer potential mechanisms to regulate alternative splicing and polyadenylation during podocyte injury. Antisense oligonucleotides can regulate mRNA processing events, thus offering a potential RNA-based therapeutic strategy to treat glomerular disease.

BACKGROUND

Glomerular disease, characterized by podocyte injury and proteinuria, can lead to CKD and kidney failure. We hypothesized that the glomerular pathophysiology is associated with mRNA alternative splicing and polyadenylation of glomerular genes and of critical podocyte and slit diaphragm components that regulate the filtration barrier.

METHODS

Glomerular damage, accompanied by proteinuria, was induced by puromycin amino-nucleoside or adriamycin to mimic human minimal change disease or FSGS, respectively, and RNA-seq analyses was performed. Alternatively spliced and polyadenylated events through differential exon and poly(A) site usage were queried in JunctionSeq and APATrap pipelines. These events were further mapped on podocyte and glomerular landscape, analyzed, and modulated for slit diaphragm components, and cis-regulatory and trans-regulatory elements were identified.

RESULTS

Altered glomerular mRNA processing by alternative splicing/polyadenylation was identified in 136/71 and 1875/746 genes in minimal change disease and FSGS models, respectively. Transcript annotation and prioritization of significant alternative splicing and polyadenylation identified key events in several podocyte and slit diaphragm genes with novel and established roles. Alternative splicing of critical slit diaphragm components, the tight junction protein 1 (TJP1)/Zona Occludens-1 (ZO1), and microtubule associating protein integral membrane protein 2b (ITM2B) was further characterized. Alternative polyadenylation of core members of the slit diaphragm, NPHS1, NPHS2, and NEPH1, was analyzed with potential alteration of microRNA-binding sites between the proximal versus distal poly (A) site usage in their mRNAs. Concomitantly, dysregulation of trans-regulatory elements (polyadenylation and splicing factors) was discovered in these models of nephropathies. In addition, beneficial proteinuria-reducing treatments, pioglitazone and GQ-16, reversed many alternatively spliced and polyadenylated events. Moreover, Genome-Wide Association Studies (GWAS) single nucleotide polymorphisms as potential cis-regulatory elements were identified in several genes from the human nephrotic syndrome database. Finally, we demonstrated proof-of-concept principle of chemically modified splice-switching oligonucleotides in modulating tight junction protein 1 splicing in podocytes.

CONCLUSIONS

Findings from our studies identified that glomerular pathophysiology and disruption of the filtration barrier is associated with alternative splicing and polyadenylation of glomerular genes, many of which are crucial determinants of podocyte structure and function and the slit diaphragm complex.

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