January 23, 2013
Squeezing Through Cell Membranes
Lee Rannals for redOrbit.com — Your Universe Online
[ Watch the Video: Delivering Large Molecules to Cells In Membranes ]
The membrane around living cells helps to regulate what gets in and out of the cell. This barrier helps control the cell´s internal environment, but makes it difficult for scientists to deliver large molecules like nanoparticles for imaging, or proteins that can reprogram them.
MIT scientists have found an efficient way to get those large molecules through the cell membrane by creating temporary holes. Large molecules floating outside the cell, such as RNA, proteins or nanoparticles, can just slide through the membrane during the disruption made by the team.
They were able to deliver reprogramming proteins and generate induced pluripotent stem cells with a success rate 10 to 100 times better than any existing method. They also used the process to deliver nanoparticles, including carbon nanotubes and quantum dots.
“It´s very useful to be able to get large molecules into cells. We thought it might be interesting if you could have a relatively simple system that could deliver many different compounds,” Klavs Jensen, the Warren K. Lewis Professor of Chemical Engineering and senior author of a paper published in the Proceedings of the National Academy of Sciences, said in a statement.
Previously, biologists have developed several ways to get large molecules into cells, but all of them have drawbacks. DNA or RNA can be packaged into viruses, but this approach carries a risk that some of the viral DNA could get integrated into the host cell.
Another way the scientists considered was to sneak large molecules into cells by tagging them with a short protein that can penetrate the cell membrane and draw the larger cargo along with it. However, these systems need to be re-engineered depending on the type of cell and material being delivered. Also, some of the nanoparticles end up trapped in protective sacs called endosomes inside the cells.
Electroporation is a more general approach that involves giving cells a jolt of electricity that opens up the cell membrane, damaging both cells and the material being delivered.
The new system works for many cell types, and the researchers have successfully tested it with more than a dozen types, including both human and mouse cells. It also works in cells taken directly from human patients.
The team is now pushing stem cell manipulation, which holds promise for treating a variety of diseases. They have also shown they can transform human fibroblast cells into pluripotent stem cells.
Another application is delivering quantum dots, which holds promise for labeling individual proteins or other molecules inside cells. Scientists have had trouble getting them through the cell membrane without getting trapped in endosomes.
Researchers showed that they could get quantum dots inside human cells grown in the lab without the particles becoming confined in endosomes or clumping together.
The team is exploring the possibility of using the new system for vaccination. Scientists, in theory, could remove immune cells from a patient, run them through the microfluidic device, and expose them to a viral protein. Once the cells are inside, they provide an immune response that would confer immunity against the viral protein.