September 2016
Volume 57, Issue 12
Open Access
ARVO Annual Meeting Abstract  |   September 2016
AMP-activated protein kinase, a conserved energy biosensor, signals early neuronal pathogenesis in glaucoma through inhibition of the mammalian target of rapamycin
Author Affiliations & Notes
  • Nicolas A Belforte
    Neuroscience, University of Montreal Hospital Research Center, Montreal, Quebec, Canada
  • Jorge L Cueva Vargas
    Neuroscience, University of Montreal Hospital Research Center, Montreal, Quebec, Canada
  • Adriana Di Polo
    Neuroscience, University of Montreal Hospital Research Center, Montreal, Quebec, Canada
  • Footnotes
    Commercial Relationships   Nicolas Belforte, None; Jorge Cueva Vargas, None; Adriana Di Polo, None
  • Footnotes
    Support  Canadian Institutes of Health Research (CIHR), Fonds de recherche du Québec – Santé (FRQS).
Investigative Ophthalmology & Visual Science September 2016, Vol.57, No Pagination Specified. doi:
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      Nicolas A Belforte, Jorge L Cueva Vargas, Adriana Di Polo; AMP-activated protein kinase, a conserved energy biosensor, signals early neuronal pathogenesis in glaucoma through inhibition of the mammalian target of rapamycin. Invest. Ophthalmol. Vis. Sci. 201657(12):.

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      © ARVO (1962-2015); The Authors (2016-present)

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Abstract

Purpose : The adenosine monophosphate-activated protein kinase (AMPK) is an evolutionarily conserved serine/threonine kinase that plays a crucial role in maintaining energy homeostasis. AMPK is a biosensor that can detect minute fluctuations in AMP/ATP ratios, and becomes activated when endogenous AMP is high and ATP is low within the cell. Active AMPK can then inhibit the downstream mammalian target of rapamycin (mTOR), a key regulator of cell growth and protein synthesis. Here, we asked whether there is metabolic stress in experimental glaucoma and, if so, does it result in AMPK activation, loss of mTOR function and neurodegeneration?

Methods : Unilateral elevation of intraocular pressure was induced in C57BL/6 mice by injection of magnetic microbeads into the anterior chamber. AMPK or mTOR activity was assessed by immunohistochemistry with antibodies against phospho-AMPK or phospho-S6 respectively, in combination with RGC-specific markers. In vivo inhibition of AMPK was achieved by administration of compound C or by intravitreal injection of siRNA to selectively knockdown AMPK expression. mTORC1 function was inhibited with rapamycin. RGC soma or axons were quantified on Brn3a-labeled retinas or toluidine blue-stained optic nerve sections, respectively. RGC dendrites were analyzed in Thy1-YFP mice subjected to ocular hypertension followed by 3D reconstruction of dendritic arbors.

Results : Our data shows that ocular hypertension triggers rapid upregulation of AMPK activity in RGCs that results in marked loss of mTOR function in these neurons. AMPK inhibition with compound C or siRNA effectively restored mTOR activity and promoted robust RGC soma and axon survival. For example, 95% of RGCs (2983 ± 258 RGCs/mm2, mean ± S.E.M.) survived with compound C compared to 77% in vehicle-treated eyes (2430 ± 233 RGCs/ mm2, ANOVA, p<0.001) at 3 weeks after glaucoma induction. Moreover, recovery of mTOR function resulted in RGCs with longer dendrites and more complex arbors than control retinas. Administration of rapamycin obliterated RGC neuroprotection demonstrating that the response to AMPK modulation was mTORC1-dependent.

Conclusions : This study reveals that ocular hypertension leads to early metabolic stress in glaucoma which contributes to RGC damage through activation of the energy biosensor AMPK and loss of mTOR signaling in vulnerable neurons

This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.

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