Abstract
Purpose :
The pathology in X-linked retinoschisis (XLRS) causes the formation of intra-retinal schisis cavities in the inner retina beginning by P12. Water homeostasis in this region is maintained by Mueller cells with aquaporin-4 (AQP4) and Kir4.1 channels. To evaluate a possible role of AQP4 and Kir4.1 channels in XLRS, we examined AQP4 and Kir4.1 protein expression during post-natal retinal development of the Rs1 exon-1 del rat.
Methods :
Protocols were overseen by the UCD IACUC. Long Evans Rs1 exon-1 del and WT rats were used. Rats were sacrificed, eyes collected, fixed by freeze substitution method, paraffin-embedded, and sectioned (5um thick). Samples were labeled by H&E and immunohistochemistry using primary antibodies for Kir4.1 (1:1000; Alomone Labs; APC-035), aquaporin-4 (1:500; Alomone labs; AQP-004), isolectin GS (1:500; Invitrogen; I32450), glutamine synthetase (1:500; Millipore Sigma; MA5-27750), and secondary fluorescent Ab. Images were scanned by confocal microscopy.
Results :
The Rs1 exon-1 del rat model of XLRS begins to develop visible intra-retinal schisis cavities in the INL by P12, and progress to severe structural disruption of the INL by P15; these cavities resolve by P30. We explored whether this is from aberrant water handling in the inner retina by expression changes of Kir4.1 and AQP4. The Kir4.1 expression level and distribution pattern are indistinguishable from WT at P12 and are strongest at the retina surface and the deep capillary plexus. By P30, the Kir4.1 distribution is altered from WT and is evident along the Mueller cell processes running through the inner retina. Retinal AQP4 expression in XLRS is comparable to WT at P7 - P15, but by P30, expression is considerably greater than WT across the inner retina and vessels of the deep vascular plexus.
Conclusions :
1) As schisis cavities are already evident by P12 in the XLRS retina, while AQP4 and Kir4.1 distributions are unchanged from WT at P12, they are not likely to contribute to schisis fluid accumulation in the proximal retina.
2) However, as AQP4 expression is substantially upregulated across the proximal retina by P30, and Kir4.1 is redistributed in the inner retina along vessels and Mueller cells, they may assist in fluid removal, cavity consolidation, and return of retinal lamination.
3) The link between Rs1 expression and schisis cavity pathology remains unclear.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.