ANT1 deficient mice: a potential model of chronic progressive external ophthalmoplegia (CPEO)

Abstract

Abstract: : Purpose: Patients with chronic progressive external ophthalmoplegia (CPEO) have been shown to have mutations within the adenine nucleotide translocator 1 (ANT1), an ATP transporter that resides on the inner membrane of the mitochondria. Transgenically modified mice deficient in ANT1 have been shown to have mitochondrial myopathy and cardiomyopathy¹. Here we examine the anatomical and OXPHOS histochemistry of extraocular muscles (EOMs) in ANT1 deficient mice. Methods: EOMs of mutant and age–matched wild–type (WT) controls were fixed and embedded in plastic resin to obtain thick (0.5 µm) and thin (90 nm) sections. Thin sections were stained with uranyl acetate and lead citrate and examined by transmission electron microscopy (TEM). EOMs were examined for the structure, size, and number of mitochondria. EOMs for histochemical analysis were flash frozen and cryo–sectioned at 7 µm. Cross–sectional frozen sections were reacted with succinate dehydrogenase (SDH) and cytochrome C oxidase (COX) to determine OXPHOS activity between mutants and WT controls. Results: While the size and structure of mitochondria between the ANT1 KO mice and WT controls showed no apparent differences, there were approximately twice the number of mitochondria in the ANT1 KO mice compared to the controls. Histochemical analysis also showed a pronounced increase in both COX and SDH activities in the EOMs of ANT1 deficient mice compared to WT. Conclusion: The EOMs of ANT1 deficient mice had the typical appearance of mitochondrial myopathy with proliferation of mitochondria and increased accumulation of SDH and COX. These results suggest dysfunction of the EOMs in the ANT1 mice that may results in a CPEO phenotype. Future experiments will examine eye movements in the ANT1 KO mice. ¹Graham et al., 1997; Nature Gen. 16: 226–234.

Keywords: mitochondria • extraocular muscles: structure • microscopy: electron microscopy