October 29, 2021 | LIFE | By Gabriella Casagrande | Illustration by Kira Schulist
It is estimated that every 40 seconds, someone in the U.S. has a stroke. Up to 66% of stroke patients will develop some visual loss. New research shows that there may be a promising way to restore vision through gene therapy. This research is still being animal-tested and developed, but it is more effective and safer than previous methods.
Blood is provided to our brains from our hearts through the internal carotid arteries and the vertebral arteries on both sides of the brain. When blood flow to the brain stops, a stroke occurs. The blood flow can be stopped due to a blockage in an artery (by clot or plaque), or by a burst blood vessel. Blockages account for approximately 87% of strokes.
Plaque is made when fat, cholesterol, cellular waste, calcium, and more residue build-up, resulting in the thickening of arteries (Atherosclerosis). Having to push past the plaque can cause blood to build up in areas of arteries and result in higher blood pressure. As blood builds up, clots form that can break off from the artery walls and move on to block smaller blood vessels.
Blood from our hearts brings nutrients and oxygen to our brains, which are necessary for the generation of energy from glucose (inadequate energy to power brain cells from lack of oxygen results in brain death). Since the brain cannot store oxygen for itself, neural tissue starts to die when blood flow stops.
Within a few minutes of being cut off from these supplies, the tissue has died; the resulting nerve damage blocks cellular communication, impairing functions such as memory, speech, movement, and vision. Generally, only the area immediately around the blockage or burst is affected.
Neural tissue cannot regenerate, meaning stroke damage is sometimes permanent. Neural pathways have the potential to remap themselves, however, this process is painful, slow, and doesn’t occur in all stroke patients.
A new study by Yu Tang and colleagues out of Purdue University shows us that gene therapy may be used to reverse visual damage caused by strokes, and that the new method could potentially be applied to motor damage as well. Previous research has identified that the protein NeuroD1 can activate specific genes (units of heredity made up of DNA) that can convert astrocytes into neurons. Neurons receive input from the world around us and relay the electrical signals necessary for us to respond.
Astrocytes are cells in the brain and spinal cord that do not carry electrical impulses but instead protect neurons. Gene therapy is the process of injecting (through IV or in a laboratory) a healthy gene into a cell; the genetic material is then taken up by other individual cells. With gene therapy, the researchers were able to use NeuroD1 to reprogram astrocyte cells into neurons, the cells that carry electrical information!
This research has only been tested on mice thus far.
Stroke was first induced in mice such that it affected visual centers of the brain. The extent of the vision loss was measured (through response to light), then gene therapy was administered to the affected areas. With time, the newly transformed neural cells were integrated into neural pathways, and the mice’s vision loss was restored (their response to light was again at normal levels).
Previous research on this topic led to the use of stem-cell therapy to restore vision. Although this can help, it has the potential to backfire as implanting new cells can cause an immune reaction, resulting in a patient’s rejection of the treatment.
In addition, this new research causes less damage to the brain tissue and is less difficult to implement than stem cell therapy. Other methods include attempting to strengthen existing neural tissue, a strenuous and not fully effective solution. Finally, more studies on this technique could lead to something similar being used to recover or improve motor function in stroke patients.