The human-specific RPGR isoform RPGRs14/15 and the clinically approved Rho/ROCK inhibitor Ripasudil represent therapeutic options to address RPGR-associated defects.

Pathogenic variants in the RPGR gene are the primary cause of photoreceptor degeneration in X-linked retinitis pigmentosa (RP). Previous studies have linked RPGR dysfunction to defects in ciliary structure and actin turnover. RPGR encodes three major isoforms--RPGR1-19, RPGRORF15, and the human-specific RPGRs14/15--yet the function of RPGRs14/15 remains poorly understood. There is an urgent unmet need for effective treatments targeting RPGR-associated RP. We generated RPGR mutant hTERT-RPE1 cell lines and found that the loss of all RPGR isoforms resulted in pronounced ciliary defects, including aberrant cilia length and segmentation, along with disrupted actin turnover. Strikingly, cells expressing only the human-specific isoform RPGRs14/15closely resembled wild-type controls and were largely protected from these defects, underscoring a critical role for RPGRs14/15 in maintaining ciliary integrity and actin dynamics. Furthermore, we demonstrated that pharmacological disruption of actin polymerization with cytochalasin D (CytoD) in control cells mimicked the ciliary abnormalities seen in RPGR_KO cells. Conversely, treatment with Ripasudil--a clinically approved Rho/ROCK inhibitor--rescued both ciliary and actin-related defects in RPGR_KO lines without observable side effects. In summary, our findings highlight the therapeutic relevance of the human-specific isoform RPGRs14/15 and identify Ripasudil as a promising candidate for treating RPGR-associated retinal degeneration. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=127 SRC="FIGDIR/small/653106v1_ufig1.gif" ALT="Figure 1"> View larger version (31K): org.highwire.dtl.DTLVardef@1e1e6ccorg.highwire.dtl.DTLVardef@1f79a9eorg.highwire.dtl.DTLVardef@c8119forg.highwire.dtl.DTLVardef@fce447_HPS_FORMAT_FIGEXP M_FIG C_FIG