DNA Group Personnel:

Dr Sergey Kovalenko (Group Leader)

Dr Monirul Islam (Research Officer)

Dr George Kopsidas (Research Officer)

Dr Chunfang Zhang (Research Officer)

Aphrodite Caragounis (Graduate Assistant)

Christine Gange (Graduate Assistant)

Damien Heffernan (Graduate Assistant)

Rachael Weston (Graduate Assistant)

DNA Group:

The DNA group is led by Sergey Kovalenko, a scientist with much experience in cell and molecular biology, who is the longest standing member of the Centre apart from Professor Linnane.  Before joining us he held the position of Assistant Professor at the Research Institute for Animal Genetics and Breeding, St Petersburg, Russia.   He was then appointed as Postdoctoral JSPS Fellow in the laboratory of our collaborator Professor Takayuki Ozawa, Nagoya University, Japan, thereafter Visiting Professor at the Faculty of Medicine, University of Nagoya.

The members of this group have succeeded in refining an important technique known as XL-PCR (Extra Length Polymerase Chain Reaction).  The procedure developed enables the complete mitochondrial genome from very small numbers of cells to be copied and amplified millions of times.  The particular value of this development is that the full length genome can, for the first time, be replicated.  As a result, we obtain sufficient quantities of the DNA to allow us to observe and study it and it becomes possible to distinguish between the normal fully functional mitochondrial DNA and the smaller mutated molecules.  In this way a profile of the mitochondrial DNA from a tissue can be obtained and the extent of the DNA mutation in that tissue determined.

Using this technique we have demonstrated that skeletal muscle samples show that as the age of the subject increases, an increasing level of mutation, and consequent loss of full-length mitochondrial DNA occurs.   Most interestingly, as might be a priori anticipated from the knowledge that individuals age differently, age matched individuals (animals, humans) show different mtDNA mutation patterns.

If the reduction in the functional mitochondrial DNA is to be considered as playing a real role in the ageing process, it is necessary to demonstrate that it is accompanied by a reduction in the bioenergetic capacity of the tissues.  This we have now done.  We have used a dye that reveals the activity of cytochrome oxidase (COX), a key component of the energy producing respiratory chain.  When the stained tissue is examined under the microscope the level of activity of this enzyme can be seen.  A reduction in COX activity (and hence bioenergetic capacity) is observed in tissues with reduced levels of the normal full-length mitochondrial DNA.

The most convincing demonstration of this link has come from technically demanding experiments in which individual muscle fibres are micro dissected from the tissue and analyzed using our XL-PCR technique.  This work demonstrates that, with age, fibres accumulate with depleted COX activity and little detectable functional mitochondrial DNA.

The DNA group has also been studying mitochondrial DNA mutation in cardiac tissue as part of the collaboration with the Baker Institute.  Once again, a correlation has been observed between reduction of full-length mitochondrial DNA and reduction in bioenergy, albeit that the changes observed are much less than those which occur in skeletal muscle.  Thus, mitochondrial activity decline with age appears to play a role in cardiac function.

The observations made by the DNA Group are critical to the understanding of the role of mitochondrial DNA in the decline of bioenergy with age.  The mtDNA studies are primary to the establishment of a firm base for the development of a diagnostic capable of determining the bioenergy status of individuals and a possible therapeutic intervention.