Science Concentrates SYNTHETIC BIOLOGY
Engineered cells control blood sugar Cells programmed to sense glucose and release insulin prevent hyperglycemia in diabetic mice A team of bioengineers has developed a possible alternative to daily insulin injections for people with type 1 diabetes. The researchers engineered human kidney cells to act like pancreatic β cells, namely to sense blood glucose levels and produce insulin accordingly (Science 2016, DOI: 10.1126/ science.aaf4006). When implanted in mice with type 1 diabetes, the cells prevent high blood glucose levels, also known as hyperglycemia. Scientists have been working on ways to restore β cells destroyed by the immune system in patients with type 1 diabetes. For example, doctors have tested therapies in which they transplant islet cells, which contain β cells, into patients. But these potential therapies suffer from the same problem, says Martin Fussenegger of the Swiss Federal Institute of Technology, Zurich: They involve cells the immune system will eventually destroy. “β cells are not very robust cells; that’s why we have diabetes,” he says. For that reason, Fussenegger and his colleagues decided to work with a heartier cell type, the human embryonic kidney (HEK) cell, and replicate the cellular circuitry that allows β cells to respond to blood glucose levels. β cells regulate glucose levels with the help of three types of proteins (shown): glucose transporters, potassium channels, and voltage-gated calcium channels. Glucose
cell mimics could reverse fatal insulin deficiency. The engineered cells also restored normal glucose levels faster than implanted human islet cells. John Pickup, a professor of diabetes and metabolism at King’s College London, says the new strategy is exciting, especially given its possible advantages over islet-cell-
enters β cells through the glucose transporters and is metabolized, producing adenosine triphosphate (ATP). As ATP levels increase, potassium channels shut down, stopping the outward flow of potassium ions Membrane Potassium potential from the cell. This changes the channel changes voltage across the cell membrane, which in turn Ca2+ Ca2+ K+ activates voltage-gat2+ K+ Ca ed calcium ion K+ channels. CalVoltage-gated ATP Glucose calcium channel cium ions then Metabolism Ca2+ flow into the cell and turn on Activate insulin gene expression Glucose gene transporter pathways that Insulin trigger insulin Insulin production production. Nucleus HEK cells already have a glucose transporter and Insulin a potassium channel, so Fussenegger and his colleagues just had to engineer the cells to express the calcium channel and a calcium-dependent gene circuit for insulin production. based therapies. Still, the kinetics of the To test the resulting cells, the team eninsulin release from the engineered cells capsulated them in alginate beads and imneeds further tuning to better mimic that of planted them in mice that had their β cells β cells. The implanted cells, he says, don’t destroyed chemically. The animals survived release the hormone fast enough to keep for the entire three-week experiment, while up with the typical blood glucose fluctuamice receiving nonengineered cells died tions a person experiences throughout the after a few days, demonstrating that the β day.—MICHAEL TORRICE
INFECTIOUS DISEASE
When HIV infects a person, the virus integrates its DNA into the genomes of the person’s immune system cells. Daily doses of antiretroviral drugs suppress replication of that viral DNA, but it’s not a cure. “An ideal situation would be a single treatment, rather than lifelong therapy,” says Atze T. Das of the University of Amsterdam. In a new study, Das and colleagues report progress on a possible one-time therapy. They permanently inactivated HIV in cultured human T cells using the CRISPR/Cas9 gene-editing system to dam-
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C&EN | CEN.ACS.ORG | DECEMBER 12/19, 2016
age its DNA (Cell Rep. 2016, DOI: 10.1016/j. celrep.2016.11.057). The technique works by designing a CRISPR component called a guide RNA to direct the Cas9 enzyme to a specific spot in an HIV gene. At that site, Cas9 cuts the DNA, and a mutation is introduced when the cell repairs the break. Earlier this year, the Amsterdam group and researchers from Chen Liang’s lab at McGill University separately showed that cutting HIV at just one site inhibits the virus initially, but eventually HIV finds a way
to continue replicating. In the new study, Das and colleagues show that using a pair of two different guide RNAs instead of one completely inhibits the virus and prevents it from escaping the cells. “We could cure the cell of HIV,” Das says. Liang says the results are an important confirmation that attacking HIV with CRISPR is a strategy worth pursuing. “I think we can improve it if we use three or four guide RNAs,” Liang says, suggesting that could make viral escape even more unlikely.—RYAN CROSS
CREDIT: ADPATED FROM SCIENCE
CRISPR knocks out HIV in cells
