Human Molecular Genetics Advance Access published online on July 2, 2007
Human Molecular Genetics, doi:10.1093/hmg/ddm166
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Intrinsic mitochondrial dysfunction in ATM-deficient lymphoblastoid cells
1 Department of Pathology and Laboratory Medicine, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095-1732, USA 2 Department of Human Genetics, David Geffen School of Medicine at UCLA, Los Angeles, CA 90095, USA
* To whom correspondence should be addressed at: Department of Pathology and Laboratory Medicine, The David Geffen School of Medicine, University of California, 675 Charles E. Young Drive South, MRL 4-173, Los Angeles, CA 90095-1732 USA. Tel: +1 310 8257618; Email: rgatti{at}mednet.ucla.edu
Received April 10, 2007; Revised May 31, 2007; Accepted June 25, 2007
One of the characteristic features of cells from patients with ataxia telangiectasia (A-T) is that they are in a state of continuous oxidative stress and exhibit constitutive activation of pathways that normally respond to oxidative damage. In this report, we investigated whether the oxidative stress phenotype of A-T cells might be a reflection of an intrinsic mitochondrial dysfunction. Mitotracker Red staining showed that the structural organization of mitochondria in A-T cells was abnormal compared to wild-type. Moreover, A-T cells harbored a much larger population of mitochondria with decreased membrane potential ( 
) than control cells. In addition, the basal expression levels of several nuclear DNA-encoded oxidative damage responsive genes whose proteins are targeted to the mitochondria - polymerase gamma, mitochondrial topoisomerase I, peroxiredoxin 3, and manganese superoxide dismutase - are elevated in A-T cells. Consistent with these results, we found that overall mitochondrial respiratory activity was diminished in A-T compared to wild-type cells. Treating A-T cells with the antioxidant, alpha lipoic acid (ALA), restored mitochondrial respiration rates to levels approaching those of wild-type. When wild-type cells were transfected with ATM-targeted siRNA we observed a small but significant reduction in the respiration rates of mitochondria. Moreover, mitochondria in A-T cells induced to stably express full-length ATM, exhibited respiration rates approaching those of wild-type cells. Taken together, our results provide evidence for an intrinsic mitochondrial dysfunction in A-T cells, and implicate a requirement for ATM in the regulation of mitochondrial function.
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