Impaired photoreceptor functions in the NgBR^R290H/R290H mouse

Abstract

Purpose : Nogo-B receptor (NgBR) is an essential component of the dolichol chain-elongation machinery. The R290H mutation of NgBR (NgBR-R290H) in human leads to generalized hypotonia, congenital scoliosis, central visual and hearing impairment, and early death. Liquid chromatography-mass spectrometry (LC-MS) analysis showed that dolichol profiles are shortened in individuals homozygous or heterozygous for NgBR-R290H. The present work investigates the functions of photoreceptors in the NgBR^R290H/R290H mouse.

Methods : Genetically modified mice with NgBR^R290H genotype were created by the knock-in (KI) technology. NgBR^R290H/R290H mice are viable but die in 8-9 weeks. Scotopic full-field ERGs were recorded from an 8 week old NgBR^R290H/R290H mouse and compared to an age-matched wild-type (wt) animal. Eyes were collected from the mouse after ERG recording, embedded in an Epon/Araldite mixture, and sectioned at 1 µm thickness to display the entire retina along the vertical meridian, and examined by light microscopy (LM). Lipids were extracted from plasma and liver samples using a modified Bligh-Dyer method, and dolichol analysis was performed by LC-MS.

Results : The NgBR^R290H/R290H genotype was confirmed by PCR. In the mutant mouse, the dolichol length distribution was one isoprene unit shorter thus dolichol 17 (D17) became the dominant species instead of dolichol 18 in wt animals. ERG recording showed that the a-wave was significantly reduced and the b-wave was flat in the mutant mouse. Surprisingly, the retinal structure remained to be normal in the NgBR^R290H/R290H mouse under LM. Rod photoreceptors had normal outer and inner segments, and the outer nuclear layers (ONL) is of normal thickness.

Conclusions : NgBR-R290H mutation in mice leads to shortened dolichol length distribution and functional impairment of photoreceptors with significant reduced ERG a- and b-wave. But the retinal structure is rather normal. It is remarkable that these results, including dolichol profiling and ERG abnormalities are very similar to those found in from mice homozygous to the DHDDS-K42E mutation. Our results from the NgBR^R290H/R290H mouse, along with similar findings from the DHDDS^{K42E/ K42E} mice, strongly suggest that dolichols play significant roles in the functions of photoreceptors, including phototransduction and neurotransmission.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.