Mitochondria crowd your cells, roving descendants of ancient bacteria that were long ago co-opted to serve as power plants, turning food into adenosine triphosphate (ATP), the energy store chemical used to power cellular machinery. As a legacy of their bacterial origins, mitochondria carry their own DNA, separate from that in the cell nucleus. Making ATP is a messy business, creating all sorts of reactive molecules as byproducts, and that mitochondrial DNA is more vulnerable than the safely enclosed nuclear DNA. The balance of evidence strongly implicates mitochondrial DNA damage as one of the contributing causes of aging. A damaged gene can no longer be used as a blueprint for the process of gene expression that produces the protein machinery that is vital to the operation of a mitochondrion, and from there matters only go downhill - it's a long road that ends up at atherosclerosis, neurodegeneration, and many other forms of advanced age-related degeneration.
Thus finding ways to repair mitochondrial DNA (mtDNA) is of great importance - but this is still a minority field of science in comparison to stem cell medicine or cancer research. Nonetheless, mitochondrial repair has been attracting some attention in the past week, as an important new line of research made it to the press release and publicity stage. The technique demonstrated is not really repair, per se, more a method of working around damage to mitochondrial genes - but it looks to be a great improvement over existing methodologies in terms of cost, time, and difficulty. This may enable broader and faster progress towards therapies that can remove the harm caused by damaged mitochondria. You might peruse these recent posts for more details on the work:
- A General Method for Correcting Mitochondrial Mutations
- SENS Foundation on Recent Mitochondrial Research
The new method is a way to deliver more or less arbitrary RNA to mitochondria, which should allow for continued function even after mutational damage to important genes. Production of RNA is a first step in the convoluted process of gene expression - by which genes are used as a blueprint for proteins - so it's quite possible to skip the gene and start with the RNA. This shortcut is the basis for a range of modern life science research, and one obvious use is to correct for a missing or damaged gene: find a way to provide the patient with an ongoing supply of suitably crafted RNA molecules targeted to the right places in his or her cells and it won't matter that the gene is broken.
I should note that there are only thirteen genes in the mitochondria that are important for the purposes of this discussion, but the process of producing repairs or workarounds for each one has been hard, very different for each of them, slow, and difficult up until this point. A method that works in a very similar way for all of them is a big deal.
The researchers presented on their work in RNA last year at SENS5, and I see that the SENS Foundation volunteers moved up the presentation video in the queue for processing and posted it to YouTube today:
A decline in the function of mitochondria may contribute to the aging process and age-related disorders. A functional decline could arise from accumulated mtDNA mutations over time, leading to reduced oxidative phosphorylation and other untoward effects on mitochondrial activities. Strategies that restore mitochondrial function could potentially offset key aspects of aging decline. RNA import into mammalian mitochondria is considered essential for replication, transcription, and translation of the mitochondrial genome but the pathway(s) and factors that control this import are poorly understood.
In recent studies we have shown a role for polynucleotide phosphorylase (PNPASE) in regulating the import of nuclear-encoded RNAs into the mitochondrial matrix. ... A mitochondrial RNA targeting signal was identified that enables the import of heterologous RNAs in a PNPASE-dependent manner. Combined, our studies show an unanticipated role for PNPASE in mediating the translocation of RNAs into mitochondria and provide a potential therapeutic route for halting or reversing the decline in mitochondrial function with aging.
In short, the researchers have found a mechanism that can be hijacked in order to import RNA into the mitochondria as desired.