Mitochondrial impact on nerve growth factor production in vascular smooth muscle-derived cells

Abstract

Mitochondrial deficits are associated with heart failure, aging and neurodegenerative diseases. Mitochondrial participation in cellular signaling leading to gene expression was examined in vascular smooth muscle-derived cells with varying degrees of mitochondrial damage. Cells were created by long-term treatment with low doses of ethidium bromide to selectively damage mitochondrial DNA. Adenine nucleotide levels did not differ among cells. Ht100 cells had normal mitochondrial complex IV activity while Ht30 cells had 30%, Ht10 cells had 10% and Ht5 cells had 5% of control complex IV activity. Ht30, Ht10 and Ht5 cells also showed reduced complex I function and oxygen utilization. These cells were used to study the impact of chronic reductions in mitochondrial activity on nuclear gene expression. Nerve growth factor (NGF), a nuclear-encoded protein, was examined due to its role as a signaling neurotrophic protein mediating neuronal survival. Basal NGF secretion rates and NGF mRNA levels were decreased along with the reduction in mitochondrial enzyme function (Ht100>Ht30≤Ht10≥Ht5). Cells with reduced mitochondrial activity also showed abnormal responses to the stimulation of NGF output. Thrombin and phorbol ester elevated NGF production from Ht100, Ht30 and Ht10 cells, but not from Ht5 cells. Ht30 cells, despite secreting less NGF basally than Ht100 cells, reached a similar or greater NGF output upon stimulation. Mitogens increased NGF output and NGF mRNA levels with the largest effect on NGF protein in Ht30 cells. Free radical production and the ability of cells to respond to NGF-inducing agents were related. These data suggest that chronic impairment of mitochondrial function associates with disturbances in cellular production of a signaling protein.