Human iPSC disease modelling reveals functional and structural defects in retinal pigment epithelial cells harbouring the m.3243A > G mitochondrial DNA mutation

Valeria Chichagova, Dean Hallam, Joseph Collin, Adriana Buskin, Gabriele Saretzki, Lyle Armstrong, Patrick Yu Wai Man, Majlinda Lako, David H Steel, Apollo-University Of Cambridge Repository, Apollo-University Of Cambridge Repository
The m.3243A > G mitochondrial DNA mutation was originally described in patients with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes. The phenotypic spectrum of the m.3243A > G mutation has since expanded to include a spectrum of neuromuscular and ocular manifestations, including reduced vision with retinal degeneration, the underlying mechanism of which remains unclear. We used dermal fibroblasts, from patients with retinal pathology secondary to the m.3243A > G
more » ... he m.3243A > G mutation to generate heteroplasmic induced pluripotent stem cell (hiPSC) clones. RPE cells differentiated from these hiPSCs contained morphologically abnormal mitochondria and melanosomes, and exhibited marked functional defects in phagocytosis of photoreceptor outer segments. These findings have striking similarities to the pathological abnormalities reported in RPE cells studied from post-mortem tissues of affected m.3243A > G mutation carriers. Overall, our results indicate that RPE cells carrying the m.3243A > G mutation have a reduced ability to perform the critical physiological function of phagocytosis. Aberrant melanosomal morphology may potentially have consequences on the ability of the cells to perform another important protective function, namely absorption of stray light. Our in vitro cell model could prove a powerful tool to further dissect the complex pathophysiological mechanisms that underlie the tissue specificity of the m.3243A > G mutation, and importantly, allow the future testing of novel therapeutic agents. The minimum prevalence of the m.3243A > G mutation in the mitochondrial gene MT-TL1 encoding tRNA Leucine (UUR) has been estimated at 3.5 per 100,000 in the UK population 1 . It can result in a broad phenotypic spectrum ranging from the classical syndrome of mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) to varying combinations of neurological and ophthalmological manifestations 2,3 . The molecular mechanisms underlying the pathogenesis of the m.3243A > G mutation are complex and not fully understood, although a primary defect in mitochondrial translation is a possible explanation 4 . Typically, high energy demand organs are affected resulting in a multisystem presentation 5 , with 58% of patients having four or more clinical symptoms compared with 12% of patients who are monosymptomatic 6 . Ocular abnormalities are a common finding in patients with the m.3243A > G mutation with over half of all patients developing at least one ophthalmological manifestation, in particular progressive external ophthalmoplegia and ptosis, but also visual Published: xx xx xxxx OPEN 2 Scientific RepoRts | 7: 12320 |
doi:10.17863/cam.43014 fatcat:wemvxgqtkjax7bec2ifyyzvxoi