MORE THAN “JUST” A POWERHOUSE
When we hear the word mitochondria, most of us remember it described in high school biology class as the “powerhouse” of a cell. It is an apt moniker, and not just because mitochondria are the subcellular compartments that convert glucose from our diet into chemical energy that our cells can use to do work. These powerful compartments also play a role in such diverse cellular processes as cellular differentiation, cell death, and cell signaling.
It is not surprising that defects in mitochondrial function are associated with a whole range of diseases, including musculoskeletal diseases, metabolic diseases, and neurodegenerative diseases.
NEW DRUG TARGETS?
Mitochondrial biology is interesting to drug researchers because they contain their own DNA, distinct from the DNA found in the nucleus of human cells. Until recently, scientists assumed mitochondrial DNA mostly codes for enzymes involved in carrying out the chemical reactions needed to provide cellular energy. It turns out that mitochondrial DNA may also hold the recipe for proteins involved in various diseases.
For example, we now know certain versions of mitochondrial genes are associated with an increased or decreased risk of stroke. Preliminary studies also suggest a possible link between certain mitochondrial genes and other complex diseases such as Parkinson’s, Alzheimer’s, and diabetes, opening up exciting new possibilities for understanding human disease. It is also an untapped target for drug discovery.
COMPANIES TO WATCH
Mitochondrial medicine is still largely at the basic research stage, as investigators strive to better understand what role these tiny powerhouses play in a range of diseases. However, a few companies—both start-ups and established players alike—are beginning to take note of the field’s potential for new drug discovery.
Last fall, Mitokyne (Cambridge, MA) announced a new partnership with Astellas Pharma (Tokyo, Japan) to discover and develop drugs targeting mitochondrial function. Likewise, Edison Pharmaceuticals (Mountain View, CA) entered an alliance with Dainippon Sumitomo Pharma, also known as DSP (Osaka, Japan) to develop drugs for inherited mitochondrial diseases. Could these companies push mitochondrial medicine into the mainstream?
ALZHEIMER’S & MITOCHONDRIAL FUNCTION: CAUSE OR EFFECT?
Alzheimer’s disease (AD) is linked to mitochondrial dysfunction; however, scientists have been unsure as to whether or not this was a cause or a symptom of the disease.
Recent studies suggest that mitochondrial dysfunction may precede Alzheimer’s rather than the other way around. Swedish and German researchers report increased aging (including neuronal degeneration) in mice engineered to have increased levels of mitochondrial DNA mutations. A group of Spanish researchers reported finding decreased levels of mitochondrial DNA in the cerebrospinal fluid of people developing AD. This is a good predictor of the disease onset, suggesting causative role for mitochondrial irregularities.
These findings suggest a potential new way of thinking about Alzheimer’s treatment. Current studies mostly focus on reducing the primary physiologic hallmark of the disease – amyloid-beta (Aẞ) protein plaque formation in the brain. However, clinical trials of monoclonal antibodies targeting the amyloid-beta (Aẞ) protein plaques and of inhibitors of the enzyme beta-secretase (whose activity is required for the formation of Aẞ plaque) have been disappointing. The ability to detect and treat abnormalities in mitochondrial function before the onset of symptoms may prove to be a game-changer for this challenging disease.
MITOCHONDRIAL DNA REPLACEMENT: IVF IMPLICATIONS
Mitochondrial DNA is inherited maternally and this has a range of implications for IVF.
Why isn’t mitochondrial DNA also inherited paternally? Only the ova or egg (not the sperm) contain a supply of mitochondria.
Why does only the egg contain mitochondria? If the egg is fertilized by the sperm, the mitochondria grow and replicate along with the resulting zygote (fertilized egg), thus the mitochondria are passed on in subsequent rounds of cell division.
What implications does this have for the infertility industry? It is estimated that over five million babies have been born since the very first in vitro fertilization (IVF) procedure which occurred 36 years ago. IVF is a general term which spans many different procedures including a donor egg procedure. A donor egg is the process of third party reproduction in which a healthy egg produced by one woman is implanted into another woman who is unable to produce healthy eggs and therefore cannot get pregnant.
Donor egg is a proven technology—the first successful birth via donor egg occurred in 1983, making it nearly as old as the biotechnology industry itself. With a better understanding of genetics, patients are demanding refinements to this popular procedure. One includes transferring the healthy nuclear DNA from the egg of a patient with defective mitochondrial DNA into the enucleated egg of a donor, and then implanting that “hybrid” donor egg back into the patient. Currently, the FDA is considering what guidelines might be appropriate for this new technique.