Expression of the diabetes risk gene wolframin (WFS1) in the human retina

Abstract

Wolfram syndrome 1 (WFS1, OMIM 222300), a rare genetic disorder characterized by optic nerve atrophy, deafness, diabetes insipidus and diabetes mellitus, is caused by mutations of WFS1, encoding WFS1/wolframin. Non-syndromic WFS1 variants are associated with the risk of diabetes mellitus due to altered function of wolframin in pancreatic islet cells, expanding the importance of wolframin. This study extends a previous report for the monkey retina, using immunohistochemistry to localize wolframin on cryostat and paraffin sections of human retina. In addition, the human retinal pigment epithelial (RPE) cell line termed ARPE-19 and retinas from both pigmented and albino mice were studied to assess wolframin localization. In the human retina, wolframin was expressed in retinal ganglion cells, optic axons and the proximal optic nerve. Wolframin expression in the human retinal pigment epithelium (RPE) was confirmed with intense cytoplasmic labeling in ARPE-19 cells. Strong labeling of the RPE was also found in the albino mouse retina. Cryostat sections of the mouse retina showed a more extended pattern of wolframin labeling, including the inner nuclear layer (INL) and photoreceptor inner segments, confirming the recent report of Kawano et al. [Kawano, J., Tanizawa, Y., Shinoda, K., 2008. Wolfram syndrome 1 (Wfs1) gene expression in the normal mouse visual system. J. Comp. Neurol. 510, 1-23]. Absence of these cells in the human specimens despite the use of human-specific antibodies to wolframin may be related to delayed fixation. Loss of wolframin function in RGCs and the unmyelinated portion of retinal axons could explain optic nerve atrophy in Wolfram Syndrome 1.

Figure 1

Representative overview of human retina and optic nerve immunostained for wolframin. Boxes in the upper panel designate regions of magnified images. A) Retina with optic nerve layer showing intense expression of wolframin in the nerve fiber layer and retinal ganglion cells. B) Optic nerve head with positive retinal ganglion cell axons. C) Transition to optic nerve with reduction of labeling at the interface of myelination. Magnification bar in upper panel equivalent to 100 μm; and magnification bar in panel A) equivalent to 40 μm for A) to C). Section is counterstained with cresyl violet.

Figure 2

Representative high power image of human retina immunoreactive for wolframin. Retinal ganglion cells are intensely labeled for wolframin. Section is counterstained with cresyl violet. Magnification bar equivalent to 40 μm.

Figure 3

Immunofluorescence labeling of wolframin in the retina of the albino mouse. A) Overview of cross section of the retina with different layers as indicated. B) Intense expression of wolframin expression in RPE. INL, inner nuclear layer; IPL, inner plexiform layer; ONL, outer nuclear layer; IS, layer of inner segments; RGC, retinal ganglion cell layer; and RPE, retinal pigment epithelium. Magnification bar in A) equivalent to 50 μm; and in B) to 25 μm.

Figure 4

Double immunofluorescence labeling for wolframin (red) and nuclear counter stain with DAPI (blue) in ARPE-19 cells illustrating intense labeling of the RPE cytoplasm. A) Overview. B) Detailed view of double labeled cell. C) Omission control with nuclear staining by DAPI only. Magnification bar shown in A) equivalent to 40 μm; and bar in B) to 25 μm for B) and C).