Mitochondrial Oxidative Phosphorylation Transcriptome Alterations in Human Amyotrophic Lateral Sclerosis Spinal Cord and Blood

Abstract

Origins of onset and progression of motor neurodegeneration in amyotrophic lateral sclerosis (ALS) are not clearly known, but may include impairment of mitochondrial bioenergetics. We used quantitative PCR approaches to analyze the mitochondrial oxidative phosphorylation (OXPHOS) transcriptomes of spinal cord tissue and peripheral blood mononuclear cells (PBMC) from persons with sporadic ALS compared with those without neurological disease. Expression measurements of 88 different nuclear (n) and mitochondrial (mt) DNA-encoded OXPHOS genes showed mtDNA-encoded respiratory gene expression was significantly decreased in ALS spinal cord by 78-84% (ANOVA p < 0.002). We observed the same phenomenon in freshly isolated PBMC from ALS patients (reduced 24-35%, ANOVA p < 0.001) and reproduced it in a human neural stem cell model treated with 2',3'-dideoxycytidine (ddC) (reduced 52-78%, ANOVA p < 0.001). nDNA-encoded OXPHOS genes showed heterogeneously and mostly decreased expression in ALS spinal cord tissue. In contrast, ALS PBMC and ddC-treated stem cells showed no significant change in expression of nDNA OXPHOS genes compared with controls. Genes related to mitochondrial biogenesis (PGC-1α, TFAM, ERRα, NRF1, NRF2 and POLG) were queried with inconclusive results. Here, we demonstrate there is a systemic decrease in mtDNA gene expression in ALS central and peripheral tissues that support pursuit of bioenergetic-enhancing therapies. We also identified a combined nDNA and mtDNA gene set (n = 26), downregulated in spinal cord tissue that may be useful as a biomarker in the development of cell-based ALS models.

Differentiation of Human Neural Stem Cells into Motor Neurons Stimulates Mitochondrial Biogenesis and Decreases Glycolytic Flux

“…Our studies of human cervical spinal cord and peripheral blood MNCs from sALS subjects found reduced mtDNA gene expression and impaired mitobiogenesis signaling [29]. We do not yet know the origin(s) of this deficit in mitobiogenesis in ALS, except that it does not appear to be derived primarily from the decreased mtDNA gene expression [30].…”

“…By studying cells from living patients with associated clinical data, we hope to learn more about sporadic disease. Toward this goal, a recent study from our laboratory showed decreased mitochondrial-encoded gene expression in peripheral blood mononuclear cells (MNCs) of ALS patients compared with control, suggesting a systemic bioenergetic impairment [29]. If motor neurons differentiated from ALS iPSCs display the same mitochondrial dysfunction seen in postmortem tissue, they may be used as a model of sALS.…”

Mitochondrial Disorders May Mimic Amyotrophic Lateral Sclerosis at Onset

“…Hirano et al reported a 65-year-old ALS patient whose muscle biopsy showed 10% ragged- and alterations of the mitochondrial genome and transcriptome. [8][9][10][11][12][13][14] There are also indications that mtDNA deletions are more common in individuals with sporadic ALS as compared to healthy controls. 15 Mitochondrial dysfunction in ALS is often regarded as secondary following the exposure of mtDNA to increased oxidative stress.…”

Laser-captured spinal cord motorneurons from ALS subjects show increased gene expression in vacuolar ATPase networks

“…Our methods for acquisition of cervical spinal cord, isolation by LCM of motor neurons from cervical spinal cord sections, RNA isolation and amplification, cDNA generation and qPCR of mitochondrial genes have been previously described [26,38]. Methods for generation and quantitation of multiplex RNA-seq libraries from these amplified RNA's have also been described [38].…”