Activation of Wnt/β-catenin signaling in Muller glia protects photoreceptors in a mouse model of inherited retinal degeneration

The canonical Wnt/β-catenin ("Wnt") pathway is an essential signaling cascade in the embryonic central nervous system (CNS) that regulates neuronal differentiation and survival. Loss of Wnt signaling in developing and adult tissue has been implicated in numerous CNS diseases, but the precise role of Wnt in regulating neuronal survival, and how its absence could lead to disease, is not understood. In this study, we investigated the effect of Wnt activation on neuronal survival in the adult retina, and identified cellular and molecular mediators. Pan-retinal Wnt signaling activation using Wnt3a induced functional and morphological rescue of photoreceptor neurons in the rd10 mouse model of retinal degeneration. Furthermore, Wnt activation using constitutively active β-catenin specifically targeted to Muller glia increased photoreceptor survival and reduced markers of glial and neuronal remodeling. Wnt-induced photoreceptor protection was associated with elevated levels of the prosurvival protein Stat3, and was reduced by shRNA-mediated knock-down of Stat3, indicating cross-talk between survival pathways. Therefore, these data increase our understanding of the role of Wnt signaling in the retina, and identify radial Muller glia as important cellular mediators of Wnt activity.

Optic neuropathy associated with the use of over-the-counter sexual enhancement supplements

This case report details an association of the use of over-the-counter sexual enhancement supplements with atypical optic neuropathy. A 42-year-old man presented with right-sided headache and vision loss of the right eye, which deteriorated to a single quadrant of hand motion over 11 days. Serial orbital magnetic resonance imaging scans demonstrated progressive orbital optic nerve enhancement extending into the optic canal despite high-dose steroid treatment. The patient eventually admitted to using several over-the-counter sexual enhancement supplements prior to the onset of symptoms and throughout the course of his steroid treatment, which he subsequently discontinued. His vision improved to 20/200 with an expanded visual field. Anterior ischemic optic neuropathy has been reported in association with phosphodiesterase (PDE)-5 inhibitor use, but visual loss in association with unregulated sexual enhancement supplements has not been studied. While one case cannot establish association, our case is suggestive of potential dangers of over-the-counter sexual enhancement supplements, which may contain PDE-5 inhibitors, “male hormones,” and “substances that enhance blood production.” The case also underscores the importance of obtaining a careful history of supplements in patients with optic neuropathies.