AUTHOR=Gehrke Ella J. , Thompson Jacob , Kalmanek Emily , Stanley Sarah T. , Laird Joseph , Bhattarai Sajag , Lobeck Brianna , Mayer Sara , Mahoney Angela , Hassan Salma , Hsu Ying , Drack Arlene 

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

JOURNAL=Frontiers in Medicine

VOLUME=11

YEAR=2024

URL=https://www.frontiersin.org/journals/medicine/articles/10.3389/fmed.2024.1302119

DOI=10.3389/fmed.2024.1302119

ISSN=2296-858X

ABSTRACT=<sec id="sec1"><title>Introduction</title><p>X-linked retinoschisis (XLRS) is a vitreoretinal dystrophy caused by <italic>RS1</italic> 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 <italic>Rs1</italic> knockout (<italic>Rs1</italic>-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.</p></sec><sec id="sec2"><title>Methods</title><p><italic>Rs1</italic>-KO mice were subretinally injected with an AAV2/4 vector (<italic>n</italic> = 10) containing the <italic>RS1</italic> gene driven by an Ef1α promoter, a hypertonic buffer (<italic>n</italic> = 15) (180 mM NaCl 0.001% F68/PBS (pH 7.4)), or isotonic buffer (<italic>n</italic> = 7) (155.2 mM NaCl 0.001% F68/PBS, pH 7.0). A sham puncture group was also included (<italic>n</italic> = 6). Endpoints included electroretinogram (ERG), optical coherence tomography (OCT), a visually guided swim assay (VGSA), and immunohistochemistry.</p></sec><sec id="sec3"><title>Results</title><p>Unexpectedly, hypertonic buffer-injected eyes had reduced cyst severity at 1-month post-injection (MPI) (<italic>p</italic> &lt; 0.0001), higher amplitudes in cone-dominant ERGs persisting to 5 MPI (5 Hz flicker; <italic>p</italic> &lt; 0.0001; 3.0 flash; <italic>p</italic> = 0.0033) and a trend for improved navigational vision in the light compared to untreated <italic>Rs1</italic>-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) (<italic>n</italic> = 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 <italic>Rs1</italic>-KO eyes at 5–6 MPI (<italic>p</italic> = 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.</p></sec><sec id="sec4"><title>Discussion/conclusion</title><p>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.</p></sec>