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

Mitochondrial deficits are associated with heart failure, aging and neurode generative diseases. Mitochondrial participation in cellular signaling lead ing to gene expression was examined in vascular smooth muscle-derived cells with varying degrees of mitochondrial damage. Cells were created by long-t erm treatment with low doses of ethidium bromide to selectively damage mito chondrial 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. H t30, Ht10 and Ht5 cells also showed reduced complex I function and oxygen u tilization. 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 signali ng neurotrophic protein mediating neuronal survival. Basal NGF secretion ra tes and NGF mRNA levels were decreased along with the reduction in mitochon drial enzyme function (Ht100 > Ht30 less than or equal to Ht10 greater than or equal to Ht5). Cells with reduced mitochondrial activity also showed ab normal responses to the stimulation of NGF output. Thrombin and phorbol est er elevated NGF production from Ht100, Ht30 and Ht10 cells, but not from Ht 5 cells. Ht30 cells, despite secreting less NGF basally than Ht100 cells, r eached a similar or greater NGF output upon stimulation. Mitogens increased NGF output and NGF mRNA levels with the largest effect on NGF protein in H t30 cells. Free radical production and the ability of cells to respond to N GF-inducing agents were related. These data suggest that chronic impairment of mitochondrial function associates with disturbances in cellular product ion of a signaling protein. (C) 1999 Elsevier Science B.V. All rights reser ved.