Micro shuttles and laser remote control: Jacobs University develops new research method on intracellular processes of living cells
The groups of Sebastian Springer and Matthias Winterhalter at Jacobs University, together with scientist from the Max Planck Institute of Colloids and Interfaces and collaborators from the United Kingdom have developed micrometer-sized capsules to introduce defined amounts of experimental substances into living cells, which can be opened remotely by laser pulse at a controlled point in time to release the material and follow the biological response by microscopy. To validate the method the scientists released fluorescently labelled peptides inside living cells, thereby successfully triggering and documenting a cellular process known as antigen presentation, which is part of the immune response against viruses. Their findings are reported in the current online issue of Small (DOI: 10.1002/smll.200900809).August 17, 2009
The capsules, which have a diameter of two micrometers (about the size of a bacterium), were built by wrapping strands of a polymeric, metabolism resistant material netlike around a mineral core, which is then dissolved in acid, leaving an empty shell. The empty porous capsules were soaked in a solution of the peptides used in the experiment and heated gently, which shrank the shells and trapped a defined amount of peptide solution inside. The loaded capsules were introduced into live cells by a technique known as electroporation, a kind of electroshock treatment, which makes the cell walls permeable for micrometer sized particles. The cells survived this treatment and kept the capsules inside.
Then, the capsules, the walls of which contain nano-sized gold particles, were exposed to an infra-red laser beam that does not harm the cells but heats up the gold particles through resonance oscillation, thus melting the capsule walls and releasing the peptides inside the cells. The researchers observed that the fluorescently labelled peptides spread out in the cells and were taken up by components of the immune system known as MHC proteins, which displayed them at the cell surface just as they do with peptides that the cell itself generates. This process of antigen presentation activates the killer T cells of the immune system.
"What is exciting about this achievement", says Prof. Sebastian Springer, "is that microcapsule release can be used for so many purposes in biology. We use it to study the transport of the MHC proteins of the immune system to the cell surface, which will help us understand how viruses are recognized by the immune system. But we could also shuttle nucleic acids into cells in order to reprogram them genetically, or proteins that alter a cell's behavior. All these we can release in individual cells and then observe the consequences under the microscope."
Prof. Matthias Winterhalter adds: "In the future, it will also be possible to extract materials from cells with this technique. We put magnetic nano particles into the shells of the capsules, and then we can retrieve them from the cells with a magnet and analyze their contents. This allows the study of the contents and properties of single cells - very important when you are working with patient samples, where not much material is available, or when you are an industry researcher who performs high-throughput screening. We are also working on a machine that does all these steps automatically, so it can be used by biologists anywhere in the world."
Is there a medical use for the microcapsules? Since their hard shells protect their contents, capsules could be injected into the bloodstream to bring drugs into tumors or into virus-infected cells. Prof. Springer: "This is especially important when you want to deliver drugs that are water-soluble: They cannot penetrate into cells on their own, but once inside our capsules, they get across the cell membrane. But before putting the capsules into patients, many questions have to be solved, some of which are: How can we direct the capsules to the right cells? How doe we get them inside by a natural uptake process? How do we release the drugs?”
It is some of these questions that the researchers are addressing in their current work.