Optic atrophy gene 1 (OPA1) is a nuclear gene encoding a mitochondrial protein. Mutation of OPA1 is the most common cause for autosomal dominant optic atrophy (DOA). This condition primarily affects eyes, and is characterized by gradual vision loss, color vision defects, and temporal optic pallor. Previous studies have shown that OPA1 is ubiquitously expressed and serves as a gatekeeper for cytochrome-c release, and is important in mitochondrial fusion and ATP production. To understand the molecular mechanism by which OPA1 mutations cause optic atrophy and to facilitate the development of an effective therapeutic agent for optic atrophies, recently we have generated an Opa1 knockout model in Drosophila. By analyzing phenotypes in the developing and adult Drosophila eyes, we found that the heterozygous mutation of dOpa1, ortholog of human OPA1, caused by a P-element insertion results in no discernable eye phenotype under a microscope, but is instead associated with a shortened lifespan, whereas the homozygous mutation results in embryonic lethality. Taking advantage of the powerful Drosophila genetic techniques, we created eye-specific somatic mutants. The somatic homozygous mutation of dOpa1 in the eyes caused rough (mispatterning) and glossy (decreased lens deposition) eye phenotypes in adult flies, and was reversible by precise excision of the inserted P-element. Moreover, we also show that Superoxide dismutase 1 (SOD1), Vitamin E, and genetically overexpressed human SOD1 (hSOD1) is able to reverse the glossy eye phenotype of dOPA1 mutant large clones, further suggesting that ROS play an important role in cone and pigment cell death. Our preliminary results also show that some OPA1 mutations cause loss of vision, hearing, and other organ abnormalities. The hearing loss is associated with asynchronous cochlear conduction and cochlear implants provide remarkable results to restore hearing. Our central hypothesis is that mutations in OPA1 cause effects in multiple organs. In this study, we will perform mutation analysis on OPA1 with a readily available large patient population and recruit additional patients with optic atrophy if necessary. For patients with known OPA1 mutations, we will perform clinical evaluations to expand the clinical phenotypes, including hearing test, cochlear potential analysis and motor sensory abnormalities (Aim 1).
In Aim 2, we will further characterize phenotypes and identify the molecular mechanism by which dOpa1 mutations cause rough eyes. We will analyze the mutants for apoptosis in eye phenotypes and test the effectiveness of caspase inhibitor in reversing rough eye phenotypes.
In Aim 3, we will test the molecular mechanisms by which mutation of OPA1 affects the lifespan. Our preliminary results showed that mutation of dOpa1 causes increased production of ROS and poor tolerance to stress. We will examine superoxide dismutase (SOD) activity and mitochondrial respiration rate in our dOpa1 flies. Finally, we will test if antioxidants can rescue the shortened lifespan phenotype. We anticipate that this study will provide novel insights into the pathogenesis of optic atrophy and assist in the development of novel therapies to prevent vision loss. The clinical relevance of the proposed research is strengthened by studying an animal model and human subjects in parallel. Many degenerative retinal diseases share similar clinical features and therefore, the data from this study may be extended to those diseases.

Public Health Relevance

Optic atrophy gene 1 (OPA1) programs proteins found in mitochondria, the power plant of cells in our body. For example we have found that mutations of OPA1 cause optic atrophy as well as hearing loss. We were also surprised to find that Opa1 mutation affects the life span in fly. In this study, we will clinically evaluate patients with known mutation of OPA1 to further expand our understanding of the effects of this gene on other organs. We will closely discern how optic atrophy is caused in fly model. In addition, we can also use this model to screen drug for treatments of optic atrophy. By understanding how Opa1 affect the life span, we may develop a drug to prolong the life span. This study will allow us to understand how mutations of OPA1 cause optic atrophy and explore its novel function in lifespan and provide us a potential opportunity to develop treatments for the disease.

National Institute of Health (NIH)
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Neural Oxidative Metabolism and Death Study Section (NOMD)
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Chin, Hemin R
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University of California Irvine
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