Scientists have already come up with a technique to prevent parents from passing on mitochondrial diseases to their children, but it has been met with ethical concerns and has yet to gain widespread approval. For those already afflicted with such a disease, however, there are few options as no cures are currently in existence. But we could be edging closer to achieving this, as scientists have just developed a method that could potentially treat patients by replacing diseased tissue with healthy cells grown in the lab.
Using the same technique that allows the creation of the so-called “three-parent babies,” scientists were able to create a stem cell line derived from a diseased patient that contained healthy, mutation-free mitochondria. Since stem cells can be prompted to assume an identity of one's choice, the researchers believe they could offer a stepping stone towards personalized, regenerative medicine in patients afflicted with mitochondrial disease.
“Current care for mitochondrial diseases is limited to addressing patient symptoms, but falls short from providing a definitive cure,” study author Andre Terzic, Center for Regenerative Medicine at Mayo Clinic, said in a statement. “Resetting or replacing disease-corrupted mitochondria to produce healthy patient-derived stem cells paves the way towards targeting the root cause of the problem.”
Mitochondria are the tiny, sausage-shaped powerhouses of the cell. Only passed down the maternal line, these organelles have their own genome, called mitochondrial DNA. And just like the DNA residing within the nucleus, which governs our traits, mitochondrial genes can experience mutations that can cause disease. As the mitochondria generate energy, these diseases predominantly affect energy-hungry tissues like muscles, the heart and the brain.
In a bid to fix these unhealthy structures, scientists from the Salk Institute and Oregon Health and Science University first collected skin cells from patients with severe mitochondrial diseases and then reverted them back to a blank slate state, creating what are known as induced pluripotent stem cells. These have the ability to turn into virtually any cell in the body if the right cues are given. Since patients’ cells usually possess a mixture of both functional and defective mitochondria, the resulting pool of stem cells was a mixed bag of healthy and sick, so all the researchers had to do was pluck out the good ones.
Although this may work for some, often patients do not have sufficient, or any, healthy mitochondria, so the researchers also came up with another, very different technique to ultimately achieve the same goal. Mitochondria reside in the cytoplasm of the cell, the gel-like fluid that sits between the nucleus and the membrane, so researchers removed the nucleus of a healthy donor egg cell and swapped it with the nucleus obtained from patient skin cells. By stimulating its growth, the researchers were able to generate a supply of stem cells that were free of mutated mitochondria. These techniques have been published in Nature.
Since scientists know how to coax stem cells into becoming specialized cells, the researchers hope to ultimately use these techniques to create a healthy pool of patient-derived cells that could be transplanted into patients, replacing the diseased tissue. However, one expert pointed out to the BBC the difficulties of achieving this in organs within which cell turnover rates are low, such as the brain. In the meantime, the cells may offer scientists a window of opportunity to examine the effects of mitochondrial mutations on cell development.