Restoration of Optic Nerve Function Driven by In Vivo Multimodal Electrical Stimulation

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Project Summary To date, no therapy exists to restore vision to the over 64 million people worldwide who are legally blind from diseases that damage the optic nerve. Although current approaches for regenerating the optic nerve have successfully directed long distance axon regeneration, these strategies are still limited by the fact that 1) efficacy has generally been demonstrated when therapies were initiated before axon injury, which has limited clinical application; 2) they may carry a risk of neoplastic conversion and thus may not be readily deployed prophylactically; and 3) incidences of off target axon regeneration have been reported, indicating a need not just for signals that promote but also ones that direct axon growth to intended targets. Our multi-disciplinary collaboration between electrical engineers, neuroscientists, electrophysiologists, and neurosurgeons has enabled the collection of compelling preliminary data demonstrating that exogenously applied electric fields (EFs) control the direction of retinal ganglion cell (RGC) axon growth, in-vitro. In vivo, stimulation with asymmetric waveforms was found to be effective at directing full-length optic nerve regeneration, without evidence of aberrant targeting, and restoring partial visual function (local field potential recordings in the superior colliculus and pattern electroretinogram) after crush injury. Interestingly, stimulation with symmetric waveforms was more effective at promoting RGC survival than asymmetric waveforms. The discovery that different waveforms (asymmetric versus symmetric) may activate distinct signaling pathways that control different cellular behaviors provides a unique opportunity to assess for synergistic effects from combined stimulation. Here, we propose to compare the efficacy of combined symmetric and asymmetric EF stimulation on restoring visual function over either treatment alone. Additionally, although EF stimulation with asymmetric waveforms was successful at restoring partial visual function, local field potential amplitudes within the superior colliculus were lower and latencies longer than in normal controls. Whether this dysfunction stems from ineffective RGC synaptic transmission (spatial summation) or absence of myelin (temporal summation) or both is unknown. Here, we propose to employ immunohistochemical, transsynaptic viral labeling techniques, and electrophysiology experiments to interrogate the source of this signaling deficiency. If successful, experiments proposed here have the potential to advance EF application into a strategy that, when applied synergistically with other approaches for RGC axon regeneration, can help regenerate the optic nerve and restore visual function of patients blinded by optic neuropathies.