Inter-photoreceptor transfer of phototransduction and disc rim proteins correlates with improvement in retinal function

Abstract

Purpose : Retinal degeneration diseases can cause severe vision loss and even blindness. Unfortunately, the heterogeneity of pathogenic genetic variants has hindered the development of effective treatment. Recent evidence on the cytoplasmic transfer of physiological proteins between photoreceptor cells provides an avenue for new therapies. However, whether the transferred proteins contribute to homeostatic functions in acceptor photoreceptors remains unclear. Thus, we aim to study the functional effects of inter-photoreceptor protein transfer in retinal dysfunction mice.

Methods : Donor photoreceptor precursors from NRL-GFP mice (post-natal day 3-6) were transplanted into PRPH2-KO mice (Jackson Laboratories), and GNAT1-GNAT2 double knock-out mice (kind gift from Dr. Marie Burns and Dr. King-Wai Yau) with a nuclear tdTomato reporter (GNAT-DKO/NT). After 2-3 weeks, we assessed the optokinetic responses (OKR) of recipient mice. Control groups included: 1. mice grafted with dysfunctional photoreceptors; 2. phosphate-buffered saline sham injection; 3. non-injection controls. Immunohistochemistry analysis quantified protein transfer efficiency (intensity and area). Correlation analysis examined relationships between protein transfer efficiency, target protein abundance in donor, and OKR performance.

Results : Donor-derived physiological proteins were detected in recipient photoreceptors. In PRPH2-KO mice, transferred PRPH2 accounted for 43% and 73.4% of donor intensity and area, respectively. Transfer efficiency of PRPH2 positively correlated with both donor PRPH2 intensity and area. In GNAT-DKO/NT mice, transferred GNAT1 represented 71.5% and 11.8% of donor GNAT1 intensity and area, respectively. Transferred GNAT1 intensity positively correlated with donor intensity, while area showed no correlation. Notably, the OKR responses significantly improved in transplanted mice compared to controls. There was a positive correlation between the transfer efficiency of target proteins (PRPH2, GNAT1) and OKR responses in recipients.

Conclusions : Our study validates the ability of donor photoreceptors to transfer physiologic proteins to acceptor photoreceptors and provides novel evidence of their functional roles. Protein abundance in donor cells may influence their transfer to acceptor cells. Our findings provide rationale to develop therapeutic cytoplasmic transfer for retinal degenerative diseases.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.