Cells sense and respond to the mechanical properties of the substrate they are grown on. Rigid plastic dishes and glass coverslips are simply not natural for cells. Using gels with tunable physical properties, we discovered that stem cells specify their lineage based in part on the stiffness of the substrate they are grown on. Nuclear mechanics adjusts to matrix stiffnes and enhances differentiation. Heart cells are also shown to beat best on substrates with muscle-like stiffness compared to the rigidity of scar tissue (as would be encountered following a heart attack).
Macrophages are professional phagocytes that play an important role in innate and acquired immunity because they can recognize foreign particles and dying (apoptotic) cells. Phagocytosis occurs through the extension of the plasma membrane around an extracellular particle and subsequent internalization. The activation of immune cells such as macrophages is regulated through a balance between activating and inhibiting signals. A protein called CD47 is expressed in all tissues and has been implicated as a marker of "self." We are currently studying the cell biology of this process with the ultimate goal of using nature's marker of self in biomedical applications.
Mass spectrometry (MS) based proteomics is a high throughput means to characterize and quantify abundant tissue/cell proteins and their modifications, and we have developed some novel methods and algorithms with MS. Cysteines that are buried in the core of a protein will not react as quickly with fluorescent tags as those on the surface and so looking at the fraction of cysteines that are labelled in different protein domains can beused to assess protein structure in intact cells as well as purified proteins. With MS we identify and quantify the differences, such as occurs when stem cells are grown on different matrices, or when disease-causing point mutations are expressed in cells, but MS is also used to elaborate the proteomes, phosphorylation, and much more. It complements and often surpasses Antibody methods such as immunoblotting.
Cys Shotgun Poster
Diblock copolymers consist of two connected chains, one hydrophobic and one hydrophilic. When they are put in water they self-assemble to form structures that sequester the hydrophobic block away from the water with the hydrophilic part exposed. The precise structures that form depend on several parameters such as chain length, charge, salt concentration and pH in the solvent, and temperature. We have investigated this rich phase behavior as well as the mechanical properties of these fascinating nano-assemblies. More recently we have discovered a charge induced phase separation in binary mixtures of diblock copolymers that leads to spotted vesicles and striped worms.
The structures formed by diblock copolymers in water are not only fascinating, they are also useful. They are promising candidates for drug delivery applications in which a drug is either encapsulated in a polymeric carrier or attached directly to one of the diblock molecules. We are taking advantage of the shape control in these systems to see whether rods behave differently from spheres in terms of their lifetime in circulation and biodistribution to ultimately exploit these properties for treating disease or aiding gene therapy.
Drug Delivery Poster
In addition to the affects of mechanics on cells, we are also interested in more fundamental studies to understand how proteins and protein assemblies give rise to their exceptional mechanical properties. This will ultimately enable the engineering of better biomimetic materials for cell culture, tissue engineering, and other applications. We use atomic force microscopy (AFM) to study the mechanics of single protein molecules and, using a new hybrid fluorescence/AFM, study the structure of protein assemblies and the interactions of cells with their substrates at the micro- to nanoscale.