Modulation of Eph-receptor signaling: implications for neurodegenerative disease and neural regeneration

Abstract

Purpose : Eph/Ephrin signaling is critical for proper development of the central nervous system (CNS), and in particular, the coordination of retinotopic projections. However, forward signaling through Eph-receptors is known to be repulsive to outgrowing neurites, responsible for inducing axonal growth cone collapse, restricting of mid-line crossing of axons, and even destabilizing synaptic connections. Recently, involvement of Eph-receptor activation has been associated with the onset of several neurodegenerative diseases of the CNS, including various retinopathies. This study explored the effect of antagonizing Eph-receptor activation using novel molecules on axonal growth dynamics, de novo neurite extension, and axonal regeneration following optic nerve crush

Methods : To test the effect of Eph-receptor masking on retinal ganglion cell (RGC) neurite outgrowth, we used commercially available small molecule specific inhibitors (NVP-BHG712) and peptides (SNEW and KYL), as well as our own library of pan-antagonistic peptides (xEFN) to the Eph-receptor families. We used in-vitro screening of the compounds on isolated mouse RGC, as well as in affinity binding studies between inhibitors and Eph-receptors. We further explored the use of our lead candidates in an animal model of optic nerve crush (ONC) and evaluated regenerative potential of the modulation

Results : We found that concurrently antagonizing the activation of multiple Eph-receptors led to higher number of sprouting neurites per RGC, longer overall neurite extension length, and significantly reduced number of collapsed growth cones when compared to single specific receptor inhibition in-vitro. We further found that antagonizing Eph-receptor activation could desensitize outgrowing neurites to repulsive Ephrin-coated surfaces, and that this repulsion was mediated in RGCs by multiple receptors of the Eph family. In ONC experiments, administration of xEFN antagonizing peptides led to preservation of RGC somas in the retina and axonal regeneration past the injury site

Conclusions : Our findings suggest that modulation of the repulsive cues in the CNS, like Ep-receptor activation can aid in the attenuation of degenerative processes and stimulate some level of regeneration. This modulation can be synergistically combined with attractive/neuroprotective strategies to enhance therapeutic avenues for regeneration

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.