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Dejuan Kong, Heather Hager, Sumathi Shanmugam, Lynda Elghazi, Patrice E Fort, Thomas W Gardner, Steven F. Abcouwer; Roles of Mechanistic Target of Rapamycin Complexes in Retinal Development and Visual Function. Invest. Ophthalmol. Vis. Sci. 2019;60(9):6032.
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© ARVO (1962-2015); The Authors (2016-present)
Mechanistic target of rapamycin (mTOR) is a serine-threonine kinase that is central to trophic factor responses and nutrient sensing pathways that regulate cell metabolism, growth, proliferation and survival. mTOR forms two major signaling complexes, mTORC1 and mTORC2, containing Raptor and Rictor proteins, respectively. We examined the roles of mTOR and its complexes in retinal development and physiology by conditional knockout (cKO) of mTOR, Rptor and Rctor genes in the embryonic retina.
mTORf/f, Rptorf/f and Rctorf/f mice were crossed with Six3cre mice to cause cKO of mTOR complexes in retinal precursor cells as well as in astrocyte precursor cells (APC) within the optic stalk. APC-targeted recombination was confirmed by breeding Six3cre mice with mT/mG Cre-reporter mice. Retinal APCs, astrocyte network and vasculature formation were evaluated by immunofluorescence (IF) of flat mounted neonatal retinas. Retinal structure was determined by optical coherence tomography (OCT) and histology. Retinal organization and neuron populations were evaluated by IF of retinal sections with antibodies to cell-specific marker proteins. Visual function was assessed by optokinetic reflex testing of visual acuity (VA) and electroretinography (ERG).
cKO of mTOR or Rptor caused nearly complete loss of VA. mTOR cKO retinas exhibited a nearly total lack of vascular development, with retarded APC migration and astrocyte network formation. The effects of Rptor cKO were similar but less absolute, with 20-100% of retinal area being avascular at postnatal day 14. Retinas of adult mTOR and Rptor cKO mice had abnormally thin layers and 30-50% reductions in ganglion, amacrine and horizontal cell numbers. In contrast, Rctor cKO mice exhibited seemingly normal retinal development and structure. However, Rctor cKO caused a significant 15% reduction of VA and a surprising 60-75% decrease in ERG response b-wave amplitudes, with no significant a-wave effects. Rctor cKO mice also exhibited a nearly complete loss of the mTORC2 substrate protein kinase C alpha (PKCα) from bipolar cells.
Lack of mTORC1 function caused a dramatic defect in retinal development. mTORC2 may be necessary for bipolar cell depolarization in response to phototransduction. These findings reveal a profound role of mTOR signaling in both retinal development and normal retinal physiology.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.
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