07:31pm Sunday 24 September 2017

Improved mitochondrial DNA repair protects heart from oxidative stress

Besides producing energy, mitochondria and particularly their small circular genome (mtDNA) seem to have rather unexpected roles in protecting our cells against the deleterious effects of free radicals, as it seems that improving the repair of mtDNA is alone sufficient to prevent heart muscle cells from dying under intense free radical exposure. The recent study (1) on this protective role of mtDNA, published by researchers from the Max-Planck Institute of Heart and Lung Research, University of Miami and the University of Eastern Finland, will help us to understand the cellular changes resulting from heart disease or cardiac aging and develop strategies for their prevention.

To produce energy, mitochondria need molecular oxygen. As a side product of this cellular respiration, mitochondria also produce highly reactive oxygen radicals which damage and degrade many cellular components, including DNA. Cellular senescence, as well as other aging processes, has been thought to be linked with chronic, long-term exposure to free radicals.

Cells defend themselves from the free radicals in various ways, including antioxidant enzymes such as superoxide dismutases (SOD). For example, mice lacking the mitochondrial SOD2 enzyme die soon after birth. However, reduced SOD2 activity results in very specific type of heart disease, cardiomyopathy, which is caused by the loss of heart muscle cells and successive replacement with connective tissue. This replacement fibrosis is similar to the aging related cardiomyopathy in humans. Mice with reduced SOD2 also have high levels of mtDNA mutations and difficulties in its replication. When these problems were overcome by transgenic expression of mitochondrial Twinkle-helicase also the heart cells survived and the cardiomyopathy was prevented despite the ongoing free radical exposure.

Further investigation revealed that the improved mtDNA integrity resulted in specific type of cell signaling, which inhibited programmed cell death and directed the heart cells towards damage-tolerance mode.

Because free radicals are an important source of damage after a heart stroke as well as in normal heart aging processes, the published study will help to open new opportunities in therapy as well as promoting healthy aging.

For more information contact:
Dr. Jaakko Pohjoismäki, Department of Biology, University of Eastern Finland
e-mail: Jaakko.Pohjoismaki@uef.fi, tel. +358-50-5744745.

(1) Pohjoismäki JL, Williams SL, Boettger T, Goffart S, Kim J, Suomalainen A, Moraes CT, Braun T. (2013). Overexpression of Twinkle-helicase protects cardiomyocytes from genotoxic stress caused by reactive oxygen species. Proc Natl Acad Sci U S A. doi: 10.1073/pnas.1303046110 http://www.pnas.org/content/early/2013/11/06/1303046110.abstract

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