GD3 synthase deletion alters retinal structure and impairs visual function in mice

Gangliosides are glycosphingolipids abundantly expressed in the vertebrate nervous system, and are classified into a‐, b‐, or c‐series according to the number of sialic acid residues. The enzyme GD3 synthase converts GM3 (an a‐series ganglioside) into GD3, a b‐series ganglioside highly expressed in the developing and adult retina. The present study evaluated the visual system of GD3 synthase knockout mice (GD3s–/–), morphologically and functionally. The absence of b‐ series gangliosides in the retinas of knockout animals was confirmed by mass spectrometry imaging, which also indicated an accumulation of a‐series gangliosides, such as GM3. Retinal ganglion cell (RGC) density was significantly reduced in GD3s–/– mice, with a similar reduction in the number of axons in the optic nerve. Knockout animals also showed a 15% reduction in the number of photoreceptor nuclei, but no difference in the bipolar cells. The area occupied by GFAP‐positive glial cells was smaller in GD3s–/– retinas, but the number of microglial cells/macrophages did not change. In addition to the morphological alterations, a 30% reduction in light responsiveness was detected through quantification of pS6‐expressing RGC, an indicator of neural activity. Furthermore, electroretinography (ERG) indicated a significant reduction in RGC and photoreceptor electrical activity in GD3s–/– mice, as indicated by scotopic ERG and pattern ERG (PERG) amplitudes. Finally, evaluation of the optomotor response demonstrated that GD3s–/– mice have reduced visual acuity and contrast sensitivity. These results suggest that b‐series gangliosides play a critical role in regulating the structure and function of the mouse visual system. Gangliosides are lipid molecules important in the developing and adult nervous system. GD3 synthase enzyme is necessary to synthesize several gangliosides, denominated b‐ and c‐series. Here, we evaluated the impact of GD3 synthase deletion on the structure and function of the visual system in adult mice. GD3 knockout mice had reductions in two retinal populations, retinal ganglion cells and photoreceptors, and also showed functional visual deficits. These results suggest that b‐series gangliosides play a critical role in mouse visual system, and GD3 knockout mice are a model to investigate ganglioside functions in the nervous system during development and adulthood.