Mutant PRPF8 causes widespread splicing changes in spliceosome components in retinitis pigmentosa patient RPE cells

Retinitis pigmentosa is a rare, progressive disease which affects photoreceptors and retinal pigment epithelial (RPE) cells with blindness as a final outcome. Despite high medical and social impact, there is currently no therapeutic options to slow down the progression or cure the disease. The development of effective therapies was largely hindered by high genetic heterogeneity, inaccessible disease tissue and unfaithful model organisms. The fact that components of ubiquitously expressed splicing factors lead to the retina-specific disease is an additional intriguing question. Herein, we sought to correlate the retinal cell type-specific disease phenotype with the splicing profile shown by a patient with autosomal recessive RP, caused by a mutation in pre–mRNA splicing factor 8 (PRPF8). In order to get insight into the role of PRPF8 in homeostasis and disease, we capitalize on the ability to generate patient-specific RPE cells and reveal differentially expressed genes unique to RPE cells. We found that spliceosomal complex and ribosomal functions are crucial in determining cell type specificity through differential expression and alternative splicing (AS), and that PRPF8 mutation causes global changes in splice site selection and exon inclusion that particularly affect genes involved in these cellular functions. This finding corroborates the hypothesis that retinal tissue identity is conferred by specific splicing program, and identifies retinal AS events as a framework towards the design of novel therapeutic opportunities. Overall design: Comparison between a patient diagnosed with autosomal dominant retinitis pigmentosa (adRP) bearing a mutation in PRPF8 (NM_006445:c.6974-6994del, p.Val2325_Glu2331del), and a healthy individual used as control. For both individuals, retinal pigment epithelium (RPE) cells were generated from reprogrammed dermal skin fibroblasts. Two samples per individual (patient and control) were therefore analyzed, namely iPSC-RPE cells and fibroblasts. Three independent experimental replicates per sample were generated.