Assessing mitochondrial phenotypes in a cybrid model of dry age-related macular degeneration

Dry age-related macular degeneration (DAMD) is the leading cause of vision loss in developed countries, yet there are no FDA-approved treatments currently available. Mitochondria play a significant role in the pathology of DAMD; the retinal pigment epithelium cells of patients with DAMD exhibit mitochondrial dysfunction, elevated levels of mitochondrial DNA lesions, and increased mitochondrial reactive oxygen species. Investigations into the mitochondrial contributions to DAMD are complex as human tissue is challenging to acquire, and animal models do not fully recapitulate disease phenotypes. Cytoplasmic hybrid (cybrid) cells, formed by depleting the mitochondria of an immortalized cell line and fusing with patient platelets, are a possible model for mitochondrial studies on DAMD. This study evaluates if cybrid models of DAMD recapitulate the mitochondrial hallmarks of the disease, including mitochondrial dysfunction, decreased mitochondrial protein levels, lipid accumulation, and mitochondrial DNA lesions.

The mitochondrial functions of five healthy and five DAMD cybrid cell lines were compared based on mitochondrial oxygen consumption rates, membrane potential, and protein expression. Secondary factors of mitochondrial dysfunction, including lipid accumulation and mitochondrial DNA stress response, were also examined.

Compared to healthy control cybrid lines, we found no alterations in bioenergetics, protein levels, and lipid accumulation in DAMD cybrid lines. Mitochondrial DNA stress responses were aberrant in DAMD cybrids compared to healthy controls, suggesting some conserved mitochondrial dysfunction.

Taken together, this study suggests that these DAMD cybrids do not fully recapitulate DAMD mitochondrial pathology, though this is limited to the study population of males with the H mtDNA haplogroup. However, there may be a niche for cybrid cell lines in investigating mitochondrial DNA phenotypes in patients with DAMD. This is likely because DAMD is a multifactorial disease, dependent upon an individual's genetics and the retinal microenvironment.