Lack of Raptor in the neural retina causes abnormalities in retinal vascular development, disorganization of retinal lamination and loss of visual acuity

Abstract

Purpose : The mechanistic target of rapamycin (mTOR) kinase exists in two distinct complexes, mTORC1 and mTORC2, with only mTORC1 containing the regulatory-associated protein of mTOR (Raptor). mTORC1 is a key regulatory control point of metabolism and protein synthesis. Little is known about the role of mTORC1 in retinal physiology. To determine if mTORC1 is necessary for retinal development the effect of negating mTORC1 function in the embryonic neural retina on visual acuity and retinal anatomy was examined.

Methods : Six3cre mice were bred with Rptor^f/f mice to cause conditional knockout (cKO) of Raptor expression in the neural retina beginning at approximately embryonic day 9. Six3cre-Rptor^f/f mice were compared to Six3cre and to Rptor^f/f controls. PCR confirmed Rptor gene editing and qRT-PCR confirmed a decrease of Raptor mRNA expression in whole retinas. Optokinetic response monitoring was used to examine visual acuity at 8 weeks of age. Optical coherence tomography (OCT) was used to examine retinal morphology and the presence of hyaloid vessels at 3 and 8 weeks of age. H&E staining of paraffin embedded retinal sections was used to examine retinal thickness and layer organization at 8 weeks of age. Calretinin immunofluorescence (IF) was used to examine lamination of the inner plexiform layer (IPL). Isolectin B4 (IB4) staining of flat-mounted retinas and hyaloid vasculaturefrom mice at postnatal day 12 (P12) was used to examine hyaloid vessel regression and retinal vessel development.

Results : Lack of mTORC1 resulted in a 90% deficit in mean visual acuity at 8 weeks of age compared to controls. OCT and H&E staining showed asymmetric thinness of the temporal retina and disorganization of retinal layers in 94% of Rptor cKO eyes. Calretinin IF demonstrated disorganization of amacrine cell processes strata in the inner plexiform layer (IPL). OCT also revealed the presence of persistent hyaloid vessels with associated retinal traction in Rptor cKO eyes at both 3 (100%) and 8 weeks (78%) of age. IB4 staining of P12 retinas revealed varying degrees (20-100%) of avascular area in Rptor cKO retinas, which was associated with degree of hyaloid vessel persistence.

Conclusions : Neural mTORC1 function is necessary for normal retinal development, hyaloid vessel regression, retinal vessel formation and visual acuity.

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