Screening for mitochondrial tRNA variants in 200 patients with systemic lupus erythematosus.

Introduction: Systemic lupus erythematosus (SLE) is a common autoimmune disease with unknown etiology. Recently, a growing number of evidence suggested that mitochondrial dysfunctions played active roles in the pathogenesis of SLE, but its detailed mechanism remains largely undetermined. The aim of this study was to analysis the frequencies of mitochondrial tRNA (mt-tRNA) variants in Chinese individuals with SLE.

Methods: We carried out a mutational screening of mt-tRNA variants in a cohort of 200 patients with SLE and 200 control subjects by PCR-Sanger sequencing. The potential pathogenicity of mt-tRNA variants were evaluated by phylogenetic conservation and haplogroup analyses. In addition, trans-mitochondrial cybrid cell lines were established, mitochondrial functions including ATP, reactive oxygen species (ROS), mitochondrial DNA (mtDNA) copy number, mitochondrial membrane potential (MMP), superoxide dismutase (SOD) and mt-RNA transcription were analyzed in cybrids with and without these putative pathogenic mt-tRNA variants.

Results: We identified five possible pathogenic variants: tRNAVal G1606A, tRNALeu(UUR) A3243G, tRNAIle A4295G, tRNAGly T9997C, and tRNAThr A15924G that only found in SLE patients but were absent in controls. Interestingly, these variants were located at extremely conserved nucleotides of the corresponding tRNAs and may alter tRNAs' structure and function. Furthermore, cells carrying these tRNA variants had much lower levels of ATP, mtDNA copy number, MMP and SOD than controls, by contrast, the levels of ROS increased significantly (p<0.05 for all). Furthermore, a significantly reductions in mt-ND1, ND2, ND3, ND5 and A6 mRNA expression were observed in cells with these mt-tRNA variants, while compared with controls. Thus, failures in tRNAs metabolism caused by these variants would impair mitochondrial translation, and subsequently lead to mitochondrial dysfunction that was involved in the progression and pathogenesis of SLE.

Conclusions: Our study suggested that mt-tRNA variants were important causes for SLE, screening for mt-tRNA pathogenic variants was recommended for early detection and prevention for this disorder.