Communication at the first visual synapse is mediated by L-type voltage-gated Cav1.4 Ca2+ channels. These channels are concentrated in the synaptic terminal beneath the ribbon, an organelle characteristic of synapses employing tonic neurotransmitter release. Mutation of Cav1.4 inhibits neurotransmission but can also prevent synaptic development. Loss of Cav1.4 can present as a variety of visual diseases, including congenital stationary night blindness or cone-rod dystrophy. We have validated that restoration of Cav1.4 in Cav1.4 knockout mice prior to synaptogenesis prevents these defects. But treatments for photoreceptor synaptic diseases are needed for mature individuals.
In Aim 1, we will test the efficiency of synaptic rescue when Cav1.4 expression is induced in these mice after synaptogenesis is normally complete. This will be accomplished by using a strategy of tamoxifen-inducible gene expression from plasmids electroporated into mouse photoreceptors, followed by morphological and functional characterization of the synapses that form in adulthood. Regardless of when Cav1.4 expression is desired for basic or pre-clinical studies, the limited efficiency of electroporation inhibits advances in this field. Viral mediated gene expression is very effective and safe in the retina with AAV being the preferred vector. However, AAV does not have the capacity to express large genes like Cav1.4.
In Aim 2, we will develop multiple AAV vectors expressing fragments of Cav1.4 engineered for post-translational recombination by trans-intein splicing and test the effectiveness of this strategy for achieving expression of Cav1.4 in adult mouse photoreceptors. Success in this area will not only accelerate research on Cav1.4 but could be adapted to other large genes that are prime candidates for retinal gene therapy but currently cannot be accommodated in AAV. Together, this work exploring the regenerative capacity of photoreceptor synapses and expansion of the utility of AAV for retinal gene therapy, will greatly advance efforts to save and restore vision.

Public Health Relevance

In this proposal, we will test the regenerative capacity of photoreceptor synapses and develop a method for making retinal gene therapy vectors for very large genes. Results of this work will advance efforts to create new treatments for blindness.

Agency
National Institute of Health (NIH)
Institute
National Eye Institute (NEI)
Type
Exploratory/Developmental Grants (R21)
Project #
5R21EY027054-02
Application #
9319321
Study Section
Neurotransporters, Receptors, and Calcium Signaling Study Section (NTRC)
Program Officer
Greenwell, Thomas
Project Start
2016-08-01
Project End
2018-07-31
Budget Start
2017-08-01
Budget End
2018-07-31
Support Year
2
Fiscal Year
2017
Total Cost
Indirect Cost
Name
University of Iowa
Department
Biochemistry
Type
Schools of Medicine
DUNS #
062761671
City
Iowa City
State
IA
Country
United States
Zip Code
52246