June 2017
Volume 58, Issue 8
Open Access
ARVO Annual Meeting Abstract  |   June 2017
Regeneration of retinal ganglion cell dendrites and synapses after axonal injury: the role of insulin on regrowth and reconnection
Author Affiliations & Notes
  • Jessica Agostinone
    Neurosciences, University of Montreal, CRCHUM, Montreal, Quebec, Canada
  • Wan-Qing Yu
    Biological structure, University of Washington, Seattle, Washington, United States
  • Rachel O Wong
    Biological structure, University of Washington, Seattle, Washington, United States
  • Adriana Di Polo
    Neurosciences, University of Montreal, CRCHUM, Montreal, Quebec, Canada
  • Footnotes
    Commercial Relationships   Jessica Agostinone, None; Wan-Qing Yu, None; Rachel Wong, None; Adriana Di Polo, None
  • Footnotes
    Support  CIHR
Investigative Ophthalmology & Visual Science June 2017, Vol.58, 2955. doi:
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      Jessica Agostinone, Wan-Qing Yu, Rachel O Wong, Adriana Di Polo; Regeneration of retinal ganglion cell dendrites and synapses after axonal injury: the role of insulin on regrowth and reconnection. Invest. Ophthalmol. Vis. Sci. 2017;58(8):2955.

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

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Abstract

Purpose : Evidence indicates that axonal injury triggers early alterations in retinal ganglion cell (RGC) dendrites leading to substantial deficits. In this study, we asked whether dendrites can be stimulated to regenerate and reconnect with pre-synaptic targets once they have retracted. Specifically, we investigated the role of insulin, a potent activator of the mammalian target of rapamycin (mTOR), on dendritic and synaptic regeneration.

Methods : Optic nerve axotomy was performed in mice expressing yellow fluorescent protein in RGCs. Insulin was administered daily starting at three days after injury, when dendrites have substantially retracted. To investigate the mechanisms of insulin action, the following compounds were used: i) rapamycin, an inhibitor of mTOR complex 1 (TORC1), ii) siRNA against rictor, an essential component of mTOR complex 2 (TORC2). Gold particles coated with CMV:tdTomato and CMV:PSD95-YFP, which has been previously used as a synaptic marker, were biolistically delivered to visualize RGC glutamatergic postsynaptic sites. Seven days post-lesion, RGC dendritic trees and synapses were 3D-reconstructed using Imaris (Bitplane) and analyzed. RGC survival was assessed by quantification of RBPMS-labeled cells.

Results : Our data show that insulin promotes remarkable dendrite regeneration, restoring dendritic length, field area, and complexity to values found in naïve retinas (N=5/group, 40-50 RGCs/group). Importantly, insulin induced robust regeneration of excitatory synapses in OFF-transient, OFF- and aON-sustained RGCs. Inhibition of only TORC1 resulted in loss of dendritic tree complexity, while length and field area were preserved. In contrast, blockade of TORC2 resulted in reduced dendritic length and field area but did not alter complexity. Insulin also stimulated RGC survival which was dependent on both TORC1 and TORC2 activity.

Conclusions : Our data support several important conclusions: 1) insulin promotes substantial RGC dendrites and likely synapse regeneration after axonal injury, 2) both mTOR complexes are required for successful dendritic regeneration, with TORC1 controlling tree complexity and TORC2 governing dendrite length and arbor area, 3) insulin stimulates robust RGC survival through TORC1 and TORC2 activation. Strategies to regenerate dendrites and synaptic connections in injured RGCs may have implications to restore vision in glaucoma

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

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