Purpose:
After optic nerve crush (ONC) injury, mature retinal ganglion cells (RGC) are unable to regenerate their severed axons and eventually die through apoptotic mechanisms. This study was conducted to determine whether intravitreal administration of siRNAs namely, PF-04523655 targeted against RTP801 (also known as REDD1, a negative regulator of the mTOR pathway) and/or QPI1007 targeted against Caspase-2 (a pro-apoptotic gene expressed in mature RGC after injury) could promote RGC survival and axon regeneration after an ONC injury.
Methods:
Wistar rats received a bilateral ONC that transected 100% RGC axons on day 0, this was immediately followed by an intravitreal injection of either PBS (vehicle), siEGFP (negative control), or the following combinatorial therapies: PF-04523655+QPI1007, PF-04523655+siEGFP or QPI1007+siEGFP. Animals received additional siRNA injections on days 8 and 16 and, on day 24, eyes and optic nerves were harvested and prepared for histological examination. Optic nerves were immunostained for growth associated protein-43 (GAP-43) to assess RGC axonal regeneration whilst retinal sections were stained for βIII-tubulin to evaluate RGC survival.
Results:
Treatment with QPI1007+siEGFP or PF-04523655+siEGFP significantly increased RGC survival compared to siEGFP and PBS treatments (Figure 1A). These neuroprotective effects were enhanced by the combinatorial administration of QPI1007 and PF-04523655. When given together, PF-04523655 and QPI1007 caused a significant increase in RGC survival (~95%) compared to QPI1007 and PF-04523655 mono-therapies (~79%). Furthermore, treatment with PF-04523655 promoted significant RGC axonal regeneration into the distal stump of the optic nerve (for distances of up to 1200µm), irrespective of whether it was administered alone or in combination with QPI1007 (Figure 1B).
Conclusions:
PF-04523655 and QPI1007 alone or in combination may be effective therapies for promoting RGC survival, whereas PF-04523655 may be also efficient in promoting axonogenesis after RGC injury.
Keywords: gene transfer/gene therapy • cell survival • apoptosis/cell death