To Combat Alzheimer’s, Scientists Genetically Reprogram Brain Cells
by Ferris Jabr for Scientific American:We all lose brain cells as we get older. In people with neurodegenerative diseases such as Alzheimer’s, Parkinson’s and Huntington’s, neurons shrivel and die at alarming rates—perhaps three to four times faster than usual in Alzheimer’s, for example. Currently, no known drugs reliably halt or reverse such staggering cell death in people, although some drugs are thought to protect neurons from degradation.An alternative to saving dying neurons—or perhaps a future supplemental therapy—is creating brand new neurons. One way to accomplish this is transforming non-neuronal brain cells into functional neurons. On a cellular level, the brain is as diverse as a rainforest populated by many different species of trees. The human barin contains approximately 170 billion cells, 86 billion of which are neurons and 84 billion of which are glial cells—non-firing cells that assist neurons in various ways. Star-shaped cells known as astrocytes are perhaps the best-studied of the many various glial cells and researchers have had soem success converting astroyctes into neurons. Many of these studies, however, have used cells from very young rodent brains.A study published this week suggests that it’s possible to turn at least one class of adult human brain cells known as pericytes into functional neurons. The fact that pericytes help defend and heal the brain—and may retain some of the plasticity of stem cells—makes them all the more appealing as candidate replacements for damaged and dying neurons.Benedikt Berninger of Ludwig-Maximilians University Munich and his colleagues began their research project with the intent to study astrocytes, just as they have done many times before. They acquired 30 samples of brain tissue from people who were undergoing surgery for disorders such as epilepsy. Sometimes, in order to remove or treat a damaged or malfunctioning brain region, neurosurgeons cannot avoid slicing through healthy brain tissue. Surgeons routinely provide sections of such healthy tissue to researchers studying the brain.In the lab, Berninger and his teammates grew cultures of brain cells from the tissue samples and searched for astrocytes nestled among the tiny neural gardens. As it turned out, the cultures Berninger and his colleagues grew were mostly devoid of astrocytes. Instead, their Petri dish gardens were rife with pericytes—non-neuronal brain cells that wrap themselves around the brain’s delicate blood vessels, regulate blood flow to neurons and help maintain the blood-brain barrier, which protects neurons from bacteria and other pathogens. Pericytes are also known as proliferate in response to injury.Researchers recently showed, for example, that pericytes are essential for the formation of scar tissue in an injured spinal cord. Some evidence even suggests that certain kinds of pericytes boast the same flexibility as mesenchymal stem cells—they can turn into bone cells, fat cells or cartilage cells. Perhaps, Berninger and his colleagues reasoned, the plasticity of pericytes—coupled with their role in healing—might make them especially useful in future treatments for neurodegenerative diseases. So they decided to try changing pericytes into neurons by reprogramming their genomes.