Study of Macular Tomography and its Correlation with Visual Function and Analysis of Human Rhodopsin Gene in Retinitis Pigmentosa
Date Issued
2012
Date
2012
Author(s)
Chen, Yuh-Fang
Abstract
Retinitis pigmentosa (RP) refers to a group of genetic disorders of the retina that primarily affect the rod photoreceptors, and the cone photoreceptors can also be affected as the disease progresses. It is important to predict and monitor the progression of this disease because a patient’s quality of life is closely related to visual function. Although the macula is usually less affected and well-preserved until late-stage RP, it determines a vast majority of visual functions; hence, evaluating its structure and function is important for determining the quality of life for RP patients. On the other hand, since RP is a genetic disorder, clarifying its genetics is important to gene therapy in the future. More than 100 mutations of rhodopsin have been identified to be associated with RP, and mostly autosomal dominant RP (ADRP). The majority of rhodopsin-associated ADRP is caused by protein misfolding and ER retention. However, several questions still remain unanswered. First of all, macular tomographic change with age and its correlation with visual function in RP are not comprehensive. Secondly, how different domains of rhodopsin work together to accomplish the assembly process and how mutations of rhodopsin interrupt with this process are still unclear. As a consequence, we divided the whole study into two parts: part I was a clinical study which focused on the macular tomography and its correlation with visual function in RP; part II was a laboratory study which focused on the analysis of human rhodopsin gene in RP.
Part I: the clinical tudy
Purpose: The present study was designed to analyze macular tomography in patients of different ages with RP and correlate their visual function with macular thickness, which was measured by optical coherence tomography (OCT).
Materials and methods: 75 RP patients and 75 controls were stratified into three age groups and the macular thickness was measured by OCT. The tomography was subdivided into three circular zones, four quadrants, and nine areas for analysis. Ophthalmic examinations, which involved ophthalmoscopic examinations, dark adaptation tests, visual acuities (VA), visual field (VF) examinations, electrooculography (EOG) and color-sense discrimination tests were performed.
Results: Macular thickness of the RP patients decreased in the middle age group (45-55-year-old), whereas the oldest group showed an increased thickness. The thickness of the outer inferior area remained virtually unchanged, whereas the thickness of the inner temporal area showed the most fluctuation with age. In terms of circular sections, the most dramatic changes in macular thickness were observed in the fovea, and the aging effect decreased outwards to the outer ring. Furthermore, the thickness of the fovea was more important than the thickness of the inner ring and the outer ring for EOG, VA and color sense discrimination in RP patients.
Conclusion: In middle age RP patients, the macular thickness decreased, whereas an increased thickness was observed in patients older than 55 years. In addition, the inner temporal area was the most fragile, and the outer inferior area was the least affected in patients with RP.
Part II: the laboratory study
Purpose: In this study, we aimed to evaluate rhodopsin folding, exiting the ER and intracellular localization through expression of the rhodopsin fragments in COS-1 cells as well as in the transgenic zebrafish.
Materials and methods: We cloned human rhodopsin cDNA, which was then divided into the N-terminal domain, the C-terminal domain, and the fragment between the N- and C-terminal domains, and examined their intracellular expression in vitro and in vivo. We introduced a point mutation, either F45L or G51V, into this fragment and observed the intracellular localization of these mutants in COS-1 cells and in the zebrafish.
Results: It revealed all of the truncated rhodopsin fragments except for the C-terminal domain and the full-length rhodopsin which had some plasma membrane localization, formed aggregates nearby or within the ER in COS-1 cells; however, the N-terminally truncated rhodopsin fragment, the C-terminal domain, and the full-length rhodopsin could traffic to the ROS in the zebrafish. Besides, the F45L mutation and the G51Vmutation in the rhodopsin fragment between the N- and C-terminal domains produced different effects on the aggresome formation and the intracellular distribution of the mutants both in vivo and in vitro.
Conclusion: This current study provided new information about the mutant rhodopsin as well as the treatment of the RP in humans in the future.
Since RP is one of the leading causes of blindness in the working age all over the world, we believe that this study will contribute to better understanding of links between RP, its visual function changes and the associated genes. And, this will further contribute to genetic counseling and gene therapy in the future.
Subjects
retinitis pigmentosa
optical coherence tomography
visual field
electrooculography
Farnsworth Munsell 100-Hue test
rhodopsin
zebrafish
SDGs
Type
thesis
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