(116) Tissue-specific Effects of MARS2 Deficiency Uncovered by Deep Profiling of Cardiac Mitochondrial Function

Background: Primary mitochondrial diseases (PMDs), affecting 1 in 4,000 to 5,000 live births, are among the most common inherited metabolic disorders in children and frequently involve multiple organ systems. One such PMD is Combined Oxidative Phosphorylation Deficiency 25 (COXPD25) caused by MARS2, which encodes mitochondrial methionyl-tRNA synthetase. MARS2 enzyme catalyzes the attachment of methionine to mitochondrial tRNAMet, a process required not only for the initiation of mitochondrial translation but also for incorporating methionine residues throughout mitochondrially encoded respiratory chain (RC) proteins. COXPD25 is a rare autosomal recessive disorder presenting in infancy and early childhood with intellectual disability, growth failure, and sensorineural hearing loss. Previous studies in patient-derived fibroblasts showed reduced Complex I (CI) and Complex IV (CIV) activities. Immunoblotting confirmed decreased NDUFB8 and COXII protein levels, markers of CI and CIV, respectively. However, the degree to which MARS2 deficiency affects different tissues and the mechanisms driving this tissue specificity remain largely unknown.

Objectives: To investigate tissue-specific mitochondrial dysfunction in the heart using a newly developed knock-in mouse model of COXPD25.

Design/Methods: A knock-in mouse model of COXPD25 was generated using CRISPR/Cas9 genome editing to introduce the MARS2 missense mutation R135W, which is homologous to the human patient mutation R142W. Homozygous MARS2R135W/R135W mice and wild-type littermates were used for all downstream analyses. Heart tissue was collected to assess mitochondrial RC enzyme activities, quantify RC protein expression by immunoblotting, and profile transcriptomic changes via RNA sequencing.

Results:

Conclusions: