GSE118615
Next-Generation Sequencing of Human Mitochondrial DNA (mtDNA) from Postmortem Brain and Blood
Purpose: To develop a pipeline (Splice-Break) for high-resolution quantification of mtDNA deletions, provide a catalogue of human mtDNA deletion breakpoints, and evaluate mtDNA deletions in brains from subjects with psychiatric disorders. Methods: 93 samples from human postmortem brain and blood were obtained from the Southwest Brain Bank (SBB) and University of California, Irvine (UCI) Brain Bank. Total DNA was extracted from frozen homogenate tissue and mtDNA was amplified/enriched using a single long-range PCR. Mitochondrial amplicons were purified by bead purification to retain both wild-type and deleted molecules (i.e., no gel excision was performed). mtDNA-enriched PCR amplicons were prepared for sequencing using standard Illumina protocols for DNA. Samples were sequenced 150-mer paired-end reads, in multiplex (96x per lane), on an unpatterned flowcell (HiSeq 2500). Fastq files were processed using our Splice-Break pipeline for the detection and relative quantification of mtDNA deletions. Results: A catalogue of 4,489 putative mitochondrial DNA (mtDNA) deletions, including their frequency and relative read rate, was produced. Analyses of 93 samples from postmortem brain and blood found 1) the 4,977bp “common deletion” was neither the most frequent deletion nor the most abundant; 2) brain contained significantly more mtDNA deletions than blood; 3) many high frequency deletions were previously reported in MitoBreak, suggesting they are present at low levels in metabolically active tissues and are not exclusive to individuals with diagnosed mitochondrial pathologies; 4) many individual deletions (and cumulative deletion metrics) had significant and positive correlations with age; and 5) the highest deletion burdens were observed in a subset of subjects with major depressive disorder (MDD), and these subjects had mtDNA deletion levels at or above those detected in typical deletion pathologies (e.g., Kearns-Sayre syndrome (KSS) muscle). Conclusions: Collectively, these data suggest the Splice-Break pipeline can detect and quantify mtDNA deletions at a high level of resolution. Overall design: 93 samples from human postmortem brain and blood are from 41 subjects with and without psychiatric diagnoses. SBB samples include paired anterior cingulate cortex (ACC) and dorsolateral prefrontal cortex (DLPFC) from 32 subjects. UCI samples include paired DLPFC and BLOOD samples from 9 subjects, 3 of which also had additional brain regions of the ACC, caudate nucleus (CAUN), hippocampus (HIPP), and putamen (PUT) evaluated.