Activated mTORC1 promotes long-term cone survival in retinitis pigmentosa mice
Aditya Venkatesh, … , Markus A. Rüegg, Claudio Punzo
Aditya Venkatesh, … , Markus A. Rüegg, Claudio Punzo
Published March 23, 2015
Citation Information: J Clin Invest. 2015;125(4):1446-1458. https://doi.org/10.1172/JCI79766.
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Research Article Genetics Neuroscience Ophthalmology

Activated mTORC1 promotes long-term cone survival in retinitis pigmentosa mice

Abstract

Retinitis pigmentosa (RP) is an inherited photoreceptor degenerative disorder that results in blindness. The disease is often caused by mutations in genes that are specific to rod photoreceptors; however, blindness results from the secondary loss of cones by a still unknown mechanism. Here, we demonstrated that the mammalian target of rapamycin complex 1 (mTORC1) is required to slow the progression of cone death during disease and that constitutive activation of mTORC1 in cones is sufficient to maintain cone function and promote long-term cone survival. Activation of mTORC1 in cones enhanced glucose uptake, retention, and utilization, leading to increased levels of the key metabolite NADPH. Moreover, cone death was delayed in the absence of the NADPH-sensitive cell death protease caspase 2, supporting the contribution of reduced NADPH in promoting cone death. Constitutive activation of mTORC1 preserved cones in 2 mouse models of RP, suggesting that the secondary loss of cones is caused mainly by metabolic deficits and is independent of a specific rod-associated mutation. Together, the results of this study address a longstanding question in the field and suggest that activating mTORC1 in cones has therapeutic potential to prolong vision in RP.

Authors

Aditya Venkatesh, Shan Ma, Yun Z. Le, Michael N. Hall, Markus A. Rüegg, Claudio Punzo

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Figure 7

Loss of Casp2 slows cone death.

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Loss of Casp2 slows cone death. (A) Western blot analyses of full-length...
(A) Western blot analyses of full-length and cleaved CASP2 in retinal extracts from the indicated genotypes (left blot) and in cell culture extracts (right blot) from HEK293 cells, HEK293 cells transfected with full-length Casp2, and in extracts from the photoreceptor-enriched retinoblastoma cell line Y79. (B) Immunofluorescence to detect active CASP2 (green signal indicates FITC-labeled CASP2 activity peptide) and red-green opsin (red signal) in retinae of 2-month-old animals. Top row, left to right: Retinal flat mount showing the CASP2-active zone (between the dotted lines) of cell death progressing toward the periphery. Middle panel: No CASP2 activity was detected in the absence of Casp2. Right panel: Higher magnification of central-to-peripheral death wave is demarked by the dotted line. To the left of the line, little CASP2 activity was seen, and many cells still expressed red-green opsin (red signal), while to the right of the line, there were few red-green opsin–positive cells and many cells positive for activated CASP2. Bottom panels: higher magnification showing that cells with more CASP2 activity (arrowheads) had pyknotic nuclei and less red-green opsin immunoreactivity as opposed to cells with more red-green opsin immunoreactivity (arrows; blue signal indicates nuclear DAPI). (C) Representative retinal flat mounts from mice of the indicated genotypes at 10 and 20 weeks of age. (D) Quantification of cone survival in rd1 and Casp2–/– rd1 mice at the indicated time points. Numbers in the bars represent the number of retinae analyzed. *P < 0.05 by Student’s t test. (E) Immunofluorescence analyses to detect cone arrestin (red signal) and PNA (green signal; blue signal indicates nuclear DAPI) in retinal cryosections from 20-week-old WT and Casp2–/– mice.