Mitochondrial dysfunction and subsequent energy failure is a contributing factor to degeneration of the substantia nigra pars compacta associated with
Parkinson's disease (PD). In this study, we investigate molecular events triggered by cell exposure to the mitochondrial toxin
1-methyl-4-phenylpyridine (MPP+) using whole genome-expression microarray, Western Blot and metabolic studies. The data show that MPP+ (500 μM) obstructs mitochondrial respiration/oxidative phosphorylation (OXPHOS) in mouse
neuroblastoma Neuro-2a cells, juxtaposing accelerated
glucose consumption and production of
lactic acid. While additional
glucose concentrations restored viability in the presence of MPP+ (500 μM), the loss of OXPHOS was sustained, suggesting that compensatory anaerobic metabolic systems were fulfilling required energy needs. Under these conditions, MPP+ initiated significant changes to the transcription of 439 genes of which 287 DAVID IDs were identified and subsequent functional annotation clusters identified. Prominent changes were as follows; MPP+ initiated loss of
mRNA for mitochondrial encoded 3-hydroxybutyratedehydrogenase, type 2(Bdh2), tv1,
NADH dehydrogenase 4,5 genes,
cytochrome b and
NADH dehydrogenase (ubiquinone)
flavoprotein 3, concomitant to rise in a mitochondrial fission gene;
ganglioside-induced differentiation-associated-protein 1 (GDAP1). The negative changes to OXPHOS components were accompanied by protective forces within the mitochondria espousing elevated ratio of anti/pro-apoptotic processes. These included a loss of apoptotic Bcl-2/adenovirus E1B 19-kDa-interacting
protein (BNIP3) and family with sequence similarity 162, member A (FAM162a) and rise of
heat shock protein 1 and Lon
peptidase 1. There were no changes indicative of
free radical damage (e.g. SOD, GSH-Px), rather MPP+ initiated significant elevation in
G protein signaling components (which trigger catabolic processes) and anaerobic metabolic systems involving
carboxylic acid/transamination reactions (e.g.
glutamate oxaloacetate transaminase 1 (GOT1), glutamic
pyruvate-
alanine transaminase 2 (GPT2),
cystathionase and redox
proteins such as
cytochrome b5 reductase 1 and
ferredoxin reductase. Counter-intuitively, the data show reduction of
mRNA in glycolytic processes [DAVID enrichment score 9.96 p value 1.90E-19], some corroborated by Western Blot, bringing in to question the sources of
lactate observed in the presence of MPP+. Examining this aspect, the data show that diverse
carboxylic acids (
succinate,
oxaloacetate and a-ketoglutarate) are capable of contributing to the
lactate pool in addition to phosph(enolpyruvate) or
pyruvate in the absence of
glucose by this cell line. In conclusion, these findings show that MPP+ negatively affects the transcriptome involved with complex I, but initiated an elevation of
G protein signaling and anaerobic metabolic systems involved with
nitrogen/
carboxylic acid metabolism. Future research will be required to elucidate the survival pathways that drive anaerobic substrate level phosphorylation, and define functional ramification to the loss of mitochondrial FAM162a and BNIP3
proteins.