Specific electron transport chain abnormalities in amyotrophic lateral sclerosis

Abstract

In an amyotrophic lateral sclerosis (ALS) patient who also had an IgA gammopathy, autopsy studies identified the IgA in the surviving motor neurons. Further, the IgA bound the surface of isolated bovine motor neurons and inhibited neuronal proliferation in culture. To determine the pathologic basis of this IgA interaction with motor neurons, a neuroblastoma cDNA library was generated and screened with the IgA monoclonal antibody. Reactive clones were identified as flavin adenine dinucleotide (FAD) synthetase. To extend this finding to ALS in general, quantitative RT-PCRs were performed on blood samples from 26 ALS and 30 control blood samples to determine mRNA expression levels of FAD synthetase and other electron transport chain proteins, specifically riboflavin kinase (RFK), cytochrome C1 (CYC1), and succinate dehydrogenase complex subunit B (SDHB). All expression levels were measured against a control enzyme glyceraldehyde-3-phosphate dehydrogenase (GAPDH). Expression levels for a non-respiratory chain protein (beta-actin) were also measured. We found that FAD synthetase expression levels were decreased in ALS samples compared to expression levels in controls (P = 0.0151). Expression levels for RFK, CYC1, and SDHB were also significantly decreased in the ALS group (P = 0.0025, P = 0.0002, and P < 0.0001, respectively). As control, expression levels for beta-actin did not show a significant difference between ALS and control groups (P = 0.2118). Our data show that a reduction in electron transport proteins, namely FAD synthetase, RFK, CYC1, and SDHB, is seen in patients with ALS. It is possible that this may have an effect on oxygen-dependent metabolic pathways. Human motor neurons may be particularly susceptible to injury if there is sub-optimal oxidative metabolism.

ALS disrupts spinal motor neuron maturation and aging pathways within gene co-expression networks

“…Our analysis revealed that respiratory chain components decreased expression during spMN maturation, consistent with observations in ALS patient blood [44]. Additionally, DNA repair pathways decreased expression as spMNs mature, suggesting a reduced ability to mitigate oxidative DNA damage.…”

FAD Synthesis and Degradation in the Nucleus Create a Local Flavin Cofactor Pool

“…The corresponding products differ from each other at either the N-or C-terminal region, with the longest one being isoform 1, localized in mitochondria (8,23). A FADS migrating on SDS-PAGE with a molecular mass of 65 kDa was also identified in human neurons (26). Different from humans, only a single transcript corresponding to a predicted product of 490 amino acids (54.6 kDa) is at the moment reported for rats in Ensembl (accession number ENSRNOP00000028030) and NCBI Entrez gene (gene identifier 751787.)…”

“…Other post-translational modifications were not predicted (i.e., O-glycosylations) or predicted with a low probability (i.e., sumoylation, using both the SUMOplot TM analysis program and Sumosp 2.0 software (56)). Tissue distribution and subcellular localization of these isoforms are still uncharacterized (8,26) and represent one of the ongoing research efforts in our laboratory. Whatever the isoform details, to our knowledge this is the first evidence that FAD synthesis occurs in the nucleus, and we postulate that, as hypothesized by others (27), this event could be linked to the biogenesis and flavinylation of nuclear flavoproteome (Fig.…”

“…The possibility of other subcellular localizations, different from cytosol and mitochondria, has not been excluded by the available studies. In fact, in two recent papers, a plasma membrane localization in neuronal cells (26) and a nuclear localization, presumably associated to the nuclear flavoprotein lysine-specific demethylases in adipocytes (27), have been suggested for FADS.…”

Role of Mitochondrial Dysfunction in Motor Neuron Degeneration in ALS

“…Some cases of ALS have been described as a mitochondriopathy (Finsterer, 2002(Finsterer, , 2003 including a mitochondrial DNA www.intechopen.com mutation in the gene encoding subunit I of the mitochondrial respiratory chain complex IV (Comi et al, 1998). The electron transport chain proteins FAD synthetase, riboflavin kinase, cytochrome C1, and succinate dehydrogenase complex subunit B expression were significantly decreased in some ALS patients (Lin et al, 2009). In the mSOD1 mice or cell culture familial ALS model, complexes I, II and IV of the electron transport chain exhibit decreased enzyme activities, even at early stages of the disease Mattiazzi et al, 2002;Menzies et al, 2002a,b).…”