When a single gene in a cell is turned on or off, its resulting presence or absence can affect the function and survival of the cell. Researchers from UCSF have successfully cataloged this effect in the human neuron by separately toggling each of the 20,000 genes in the human genome. In doing so, they have created a technique that can be employed for many different cell types, as well as a database where other researchers using the new technique can contribute similar knowledge.
To survey individual genes and learn more about their functions, researchers employed CRISPR activation/interference, or CRISPR a/I, which allows them to temporarily turn a single gene off or on and see how that change affects the expression of other genes. Among the most interesting of their findings was that switching off the gene for a protein called prosaposin, which normally assists with the cell's recycling of waste products, greatly increased the levels of oxidative stress. The study found that suppression of the gene led to buildup of a substance called age pigment, which has been seen in aging cells whose lysosomes no longer degrade material as efficiently. Additionally, the age pigment trapped iron, generating reactive oxygen molecules that triggered ferroptosis, an iron-dependent process that leads to cell death. The study was published in Nature Neuroscience.
"By simply inactivating a single gene, in only days we could generate a hallmark of aging that would normally take decades to develop in the human body,” said Martin Kampmann, associated professor of neuroscience at UCSF.
The team's next step is to perform similar screens on neurons made from stem cells derived from patients with mutations known to contribute to neurodegeneration, as well as look at other cells, such as astrocytes and microglia, that play roles in brain disease.
Photo: Super-resolution microscopy of a neuron shows the accumulation of lipids within lysosomes that occurs when the gene for prosaposin is suppressed. Credit: UCSF