Novel mutations in Malonyl-CoA-Acyl Carrier Protein Transacylase gene provoke autosomal recessive optic neuropathy

Abstract

Purpose : Inherited optic neuropathy is a heterogeneous group of disorders, in which degeneration of optic nerve causes bilateral vison loss from childhood or adolescence, in some cases with additional neurological abnormalities. Inherited optic neuropathy shows inheritance of dominant, mitochondrial and recessive patterns with designated diagnosis of dominant optic atrophy, Leber hereditary optic neuropathy or autosomal recessive optic neuropathy respectively. Here, we report the association of novel mutation in chromosomal gene Malonyl CoA-acyl carrier protein transacylase (MCAT) responsible for autosomal recessive mitochondrial optic neuropathy in a Chinese family.

Methods : Whole exome analysis was performed to identify mutations in consanguineous family. C-terminal FLAG-tagged MCAT WT, L81R, R212W and double L81R/R212W mutations in p3XFLAG-CMV vector was transfected in HEK293T cells respectively to observe protein expression by western. Immunoelectron microscopy for ultrastructure of mitochondria and intra-mitochondrial localization of MCAT variants were performed in transfected HEK293T cells. Endogenous Mcat knockdown by siRNA in 661W cells was monitored to investigate the impact on mitochondria physiology. The localization of gene expression was determined by in situ hybridization using mouse retina from P21 ICR mice. Specific Mcat knockout in mouse retinal ganglion cells (RGC) using Mcat floxed mouse was performed by intravitreal injection of AAV2-Cre.

Results : Novel double homozygous mutation p.L81R and pR212W in MCAT, a mitochondrial protein involved in fatty acid biosynthesis was identified as responsible for an autosomal recessive optic neuropathy. MCAT is expressed in RGC that are rich in mitochondria. The disease variants lead to structurally unstable MCAT protein with significantly reduced intracellular expression. RGC-specific knockdown of Mcat in mice, lead to an attenuated retinal neurofiber layer, that resembles the phenotype of optic neuropathy. MCAT encodes an enzyme that functions at the second step of mitochondrial fatty acid synthesis, which are essential for mitochondrial enzyme activities.

Conclusions : Novel double homozygous mutation in chromosomal gene MCAT was identified as responsible for autosomal recessive mitochondrial optic neuropathy in a Chinese consanguineous family.

This is a 2020 ARVO Annual Meeting abstract.

 

Overall structure of human MCAT and effect of the two mutations.