An osmolarity dependent mechanism partially ameliorates retinal cysts and rescues cone function in a mouse model of X-linked retinoschisis.

INTRODUCTION

X-linked retinoschisis (XLRS) is a vitreoretinal dystrophy caused by gene mutations which disrupt retinoschisin-1 (RS1) function. Vital for retinal architecture, the absence of functional RS1 leads to the development of intraretinal cysts. Intravitreal injection of a gene therapy for treating XLRS caused ocular inflammation in high dose groups in a phase I/II clinical trial. This study investigates a low dose subretinal gene therapy in knockout (-KO) mice compared to injection of buffer alone. Observation of an unexpected therapeutic effect following the subretinal injection of the hypertonic buffer led to novel findings in XLRS.

METHODS

-KO mice were subretinally injected with an AAV2/4 vector ( = 10) containing the gene driven by an Ef1α promoter, a hypertonic buffer ( = 15) (180 mM NaCl 0.001% F68/PBS (pH 7.4)), or isotonic buffer ( = 7) (155.2 mM NaCl 0.001% F68/PBS, pH 7.0). A sham puncture group was also included ( = 6). Endpoints included electroretinogram (ERG), optical coherence tomography (OCT), a visually guided swim assay (VGSA), and immunohistochemistry.

RESULTS

Unexpectedly, hypertonic buffer-injected eyes had reduced cyst severity at 1-month post-injection (MPI) ( < 0.0001), higher amplitudes in cone-dominant ERGs persisting to 5 MPI (5 Hz flicker;  < 0.0001; 3.0 flash;  = 0.0033) and a trend for improved navigational vision in the light compared to untreated -KO eyes. To investigate the role of tonicity on this effect, an isotonic buffer-injected cohort was created (155.2 mM NaCl 0.001% F68/PBS, pH 7.0) ( = 7). Surprisingly, hypertonic buffer-injected eyes exhibited a greater reduction in cyst severity and demonstrated improved cone-dominant ERG metrics over isotonic buffer-injected and sham puncture eyes. An immunohistochemistry assay demonstrated greater cone density in hypertonic buffer-injected eyes than untreated -KO eyes at 5-6 MPI ( = 0.0198), suggesting a possible cone preservation mechanism. Moreover, our findings reveal a negative correlation between the peak severity of cysts and long-term ERG amplitudes in cone-dominant pathways, implying that effectively managing cysts could yield enduring benefits for cone function.

DISCUSSION/CONCLUSION: This study presents evidence that cyst resolution can be triggered through an osmolarity-dependent pathway, and early cyst resolution has long-term effects on cone signaling and survival, offering potential insights for the development of novel treatments for XLRS patients.