Wolfram Syndrome murine models: phenotyping and gene therapy

Abstract

Purpose : Wolfram Syndrome (WS) is an early onset genetic disease (1/160,000) featuring diabetes mellitus and progressive optic neuropathy, ensuing mutations in the WFS1 gene in humans. We aimed to model the visual aspects of WS and to rescue the phenotype with an intravitreal gene therapy (GT).

Methods : Visual acuity was measured via optokinetic reflex (OR) for 1, 3 and 6 months old Wfs1^+/+ and Wfs1^-/- mice with deleted exon 8 of Wfs1. At 6 months of age the mice were also tested for retinal ganglion cell (RGC) function (post-scotopic threshold response (PSTR), electroretinogram (ERG)) and eye physiology (eye fundus, optic coherence tomography (OCT)). RGC and axonal loss were quantified after hematoxylin and eosin coloration of retinal sections and electron microscopy of optic nerve sections, respectively.
The intravitreal bilateral AAV-2/2-CMV-WFS1-driven GT was administered to 1 month old Wfs1^+/+ and Wfs1^-/- mice, and followed by OR, PSTR, ERG, OCT, eye fundus observation with quantification of RGC and axonal loss.
The Wfs1^+/+ and Wfs1^E864K/E864K mice, were similarly phenotyped at 1 and 3 months of age.

Results : Wfs1^-/- mice showed progressive loss of visual acuity accompanied by optic disc pallor, thinning of the RGC and nerve fiber layer (NFL), with loss of axons in the optic nerve. The number of RGCs remained unaffected along with normal electrical responses in PSTR and ERG. GT improved the visual acuity of Wfs1^-/- mice and the optic disc pallor decreased, however OCT showed no improvement.
PSTR and ERG both revealed drastic loss of RGC function already for 1 month old Wfs1^E864K/E864K mice. At 3 months of age, the optic disc displayed irregular shape and signs of diabetic retinopathy were observed. However, neither the number of RGC nor the thickness of the RGC/NFL layer were diminished.

Conclusions : The functional and physiological changes in Wfs1^-/- mice show a WS phenotype related to axonal degeneration. Since the disease manifestation in Wfs1^E864K/E864K mice has an early onset and also expresses a strong ophthalmic phenotype, we propose to use it as another model of WS. The preliminary results of the gene therapy offer treatment possibilities for the WS patients and should be continued with both murine models.

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.