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Rac1 selective activation improves retina ganglion cell survival and regeneration
Erika Lorenzetto1, Michele Ettorre, Valeria Pontelli
1Department of Neurological, Neuropsychological, Morphological and Motor Sciences, Section of Physiology, University of Verona, Verona, Italy.
Abstract:
In adult mammals, after optic nerve injury, retinal ganglion cells (RGCs) do not regenerate their axons and most of them die by apoptosis within a few days. Recently, several strategies that activate neuronal intracellular pathways were proposed to prevent such degenerative processes. The rho-related small GTPase Rac1 is part of a complex, still not fully understood, intracellular signaling network, mediating in neurons many effects, including axon growth and cell survival. However, its role in neuronal survival and regeneration in vivo has not yet been properly investigated. To address this point we intravitreally injected selective cell-penetrating Rac1 mutants after optic nerve crush and studied the effect on RGC survival and axonal regeneration. We injected two well-characterized L61 constitutively active Tat-Rac1 fusion protein mutants, in which a second F37A or Y40C mutation confers selectivity in downstream signaling pathways. Results showed that, 15 days after crush, both mutants were able to improve survival and to prevent dendrite degeneration, while the one harboring the F37A mutation also improved axonal regeneration. The treatment with F37A mutant for one month did not improve the axonal elongation respect to 15 days. Furthermore, we found an increase of Pak1 T212 phosphorylation and ERK1/2 expression in RGCs after F37A treatment, whereas ERK1/2 was more activated in glial cells after Y40C administration. Our data suggest that the selective activation of distinct Rac1-dependent pathways could represent a therapeutic strategy to counteract neuronal degenerative processes in the retina.
Insights
Selective Rac1 mutants promote retinal ganglion cell survival and axonal regeneration after optic nerve injury. The F37A mutant enhanced both survival and regeneration, offering a potential therapeutic strategy for retinal degenerative diseases.
Area of Science:
- Neuroscience
- Ophthalmology
- Regenerative Medicine
Background:
- Adult mammalian retinal ganglion cells (RGCs) lack axonal regeneration capacity post-optic nerve injury, leading to cell death.
- Intracellular signaling pathways, including the rho-related small GTPase Rac1, are implicated in neuronal survival and axon growth but their in vivo role in RGCs is unclear.
Purpose of the Study:
- To investigate the in vivo role of Rac1 in RGC survival and axonal regeneration following optic nerve injury.
- To evaluate the therapeutic potential of selective Rac1 mutants in preventing RGC degeneration and promoting axon regrowth.
Main Methods:
- Intravitreal injection of selective, constitutively active Tat-Rac1 fusion protein mutants (F37A and Y40C) into adult mammals after optic nerve crush.
- Assessment of RGC survival, dendrite degeneration, and axonal regeneration at 15 days and 1 month post-injury.
- Analysis of downstream signaling pathway activation, including Pak1 and ERK1/2 phosphorylation/expression.
Main Results:
- Both F37A and Y40C Rac1 mutants significantly improved RGC survival and prevented dendrite degeneration 15 days post-crush.
- The F37A mutant demonstrated enhanced axonal regeneration compared to the Y40C mutant.
- Axonal elongation did not further improve with F37A treatment beyond 15 days.
- F37A treatment increased Pak1 and ERK1/2 activation in RGCs, while Y40C primarily activated ERK1/2 in glial cells.
Conclusions:
- Selective activation of distinct Rac1-dependent pathways can counteract RGC degenerative processes after optic nerve injury.
- The F37A Rac1 mutant shows promise as a therapeutic agent for promoting RGC survival and axonal regeneration.
- Targeting specific Rac1 signaling pathways may offer a novel strategy for treating retinal injuries and neurodegenerative conditions.
