Paediatrics (RCH) - Research Publications
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ItemCharacterization of the retinal pigment epithelium in Friedreich ataxia.(Elsevier BV, 2015-12)We assessed structural elements of the retina in individuals with Friedreich ataxia (FRDA) and in mouse models of FRDA, as well as functions of the retinal pigment epithelium (RPE) in FRDA using induced pluripotent stem cells (iPSCs). We analyzed the retina of the FRDA mouse models YG22R and YG8R containing a human FRATAXIN (FXN) transgene by histology. We complemented this work with post-mortem evaluation of eyes from FRDA patients. Finally, we derived RPE cells from patient FRDA-iPSCs to assess oxidative phosphorylation (OXPHOS) and phagocytosis. We showed that whilst the YG22R and YG8R mouse models display elements of retinal degeneration, they do not recapitulate the loss of retinal ganglion cells (RGCs) found in the human disease. Further, RPE cells differentiated from human FRDA-iPSCs showed normal OXPHOS and we did not observe functional impairment of the RPE in Humans.
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ItemMitochondrial DNA Variation and Disease Susceptibility in Primary Open-Angle Glaucoma(ASSOC RESEARCH VISION OPHTHALMOLOGY INC, 2018-09)PURPOSE: To determine whether mitochondrial DNA haplogroups or rare variants associate with primary open-angle glaucoma in subjects of European descent. METHODS: A case-control comparison of age- and sex-matched cohorts of 90 primary open-angle glaucoma patients and 95 population controls. Full mitochondrial DNA sequences from peripheral blood were generated by next-generation sequencing and compared to the revised Cambridge Reference Sequence to define mitochondrial haplogroups and variants. RESULTS: Most subjects were of the major European haplogroups H, J, K, U, and T. Logistic regression analysis showed haplogroup U to be significantly underrepresented in male primary open-angle glaucoma subjects (odds ratio 0.25; 95% confidence interval [CI] 0.09-0.67; P = 0.007; Bonferroni multiple testing P = 0.022). Variants in the mitochondrial DNA gene MT-ND2 were overrepresented in the control group (P = 0.005; Bonferroni multiple testing correction P = 0.015). CONCLUSIONS: Mitochondrial DNA ancestral lineages modulate the risk for primary open-angle glaucoma in populations of European descent. Haplogroup U and rare variants in the mitochondrial DNA-encoded MT-ND2 gene may be protective against primary open-angle glaucoma. Larger studies are warranted to explore haplogroup associations with disease risk in different ethnic groups and define biomarkers of primary open-angle glaucoma endophenotypes to target therapeutic strategies.
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ItemMitochondrial replacement in an iPSC model of Leber's hereditary optic neuropathy(IMPACT JOURNALS LLC, 2017-04)Cybrid technology was used to replace Leber hereditary optic neuropathy (LHON) causing mitochondrial DNA (mtDNA) mutations from patient-specific fibroblasts with wildtype mtDNA, and mutation-free induced pluripotent stem cells (iPSCs) were generated subsequently. Retinal ganglion cell (RGC) differentiation demonstrates increased cell death in LHON-RGCs and can be rescued in cybrid corrected RGCs.
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ItemFriedreich's ataxia induced pluripotent stem cell-derived cardiomyocytes display electrophysiological abnormalities and calcium handling deficiency(IMPACT JOURNALS LLC, 2017-05)We sought to identify the impacts of Friedreich's ataxia (FRDA) on cardiomyocytes. FRDA is an autosomal recessive degenerative condition with neuronal and non-neuronal manifestations, the latter including progressive cardiomyopathy of the left ventricle, the leading cause of death in FRDA. Little is known about the cellular pathogenesis of FRDA in cardiomyocytes. Induced pluripotent stem cells (iPSCs) were derived from three FRDA individuals with characterized GAA repeats. The cells were differentiated into cardiomyocytes to assess phenotypes. FRDA iPSC- cardiomyocytes retained low levels of FRATAXIN (FXN) mRNA and protein. Electrophysiology revealed an increased variation of FRDA- cardiomyocyte beating rates which was prevented by addition of nifedipine, suggestive of a calcium handling deficiency. Finally, calcium imaging was performed and we identified small amplitude, diastolic and systolic calcium transients confirming a deficiency in calcium handling. We defined a robust FRDA cardiac-specific electrophysiological profile in patient-derived iPSCs which could be used for high throughput compound screening. This cell-specific signature will contribute to the identification and screening of novel treatments for this life-threatening disease.
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ItemIncrease in mitochondrial DNA mutations impairs retinal function and renders the retina vulnerable to injury(WILEY, 2011-08)Mouse models that accumulate high levels of mitochondrial DNA (mtDNA) mutations owing to impairments in mitochondrial polymerase γ (PolG) proofreading function have been shown to develop phenotypes consistent with accelerated aging. As increase in mtDNA mutations and aging are risk factors for neurodegenerative diseases, we sought to determine whether increase in mtDNA mutations renders neurons more vulnerable to injury. We therefore examined the in vivo functional activity of retinal neurons and their ability to cope with stress in transgenic mice harboring a neural-targeted mutant PolG gene with an impaired proofreading capability (Kasahara, et al. (2006) Mol Psychiatry11(6):577-93, 523). We confirmed that the retina of these transgenic mice have increased mtDNA deletions and point mutations and decreased expression of mitochondrial oxidative phosphorylation enzymes. Associated with these changes, the PolG transgenic mice demonstrated accelerated age-related loss in retinal function as measured by dark-adapted electroretinogram, particularly in the inner and middle retina. Furthermore, the retinal ganglion cell-dominant inner retinal function in PolG transgenic mice showed greater vulnerability to injury induced by raised intraocular pressure, an insult known to produce mechanical, metabolic, and oxidative stress in the retina. These findings indicate that an accumulation of mtDNA mutations is associated with impairment in neural function and reduced capacity of neurons to resist external stress in vivo, suggesting a potential mechanism whereby aging central nervous system can become more vulnerable to neurodegeneration.