Dr. Kiran Bhadriraju

Understanding how mechanical forces regulate biochemical events within living cells as they adhere to the extracellular matrix (ECM) is the focus of my work. The ECM is the meshwork of protein and carbohydrate surrounding cells, and in this adherent state, cell are constantly exposed to forces that mold their function. The protein myosin is the motor that is responsible for generating large forces within cells, such as during muscle contraction. During my doctoral research with Dr. Linda Hansen at the University of Minnesota, I developed an ATPase assay to measure myosin activity in living cells, and discovered that myosin activity is critical for hepatocyte (key liver cell type) spreading, cell stiffness maintenance, and proliferation. Importantly, we found that a protein called cyclin D1, which is often found altered in tumors, could overcome this role for myosin (Bhadriraju and Hansen, 2004). During my postdoctoral work with Dr. Christopher Chen at Johns Hopkins University and the University of Pennsylvania, I developed an in vitro kinase assay for a myosin-activating enzyme called Rho-associated kinase (ROCK). We discovered that in endothelial cells (the cells lining all blood vessels), ROCK is itself regulated by myosin-generated forces (Bhadriraju et al, Chen-2007). The application of microfabrication technologies to both micropattern cell adhesion in confined spaces, as well as measuring forces generated at the level of single cells (Tan et al, 2003), was an important component of this work. 

In my current research, I am collaborating with other researchers in the group on two specific areas of focus: 

1. Developing quantitative, validated, microscopy-based assays for protein activity. 
2. Relating specific characteristics of the extracellular matrix (ECM) to responses they evoke in cells. 

The first addresses the need for validated, quantitative microscopy based assays for intracellular protein activity within cells using antibody-based approaches. For the latter, I am using a model ECM composed of thin films of collagen fibrils developed at NIST (see Dr. John Elliott's bio-page for additional details), to examine how cells exert forces on and remodel the type I collagen ECM, and activate a different signaling pathways in response to distinct characteristics of the ECM. Specific details of the above areas of focus can be found on the project/programs page.

Vascular smooth muscle cells stained for: diphosphorylated myosin - green, filamentous actin - red, and nuclear DNA - blue

Publications:

Bhadriraju K. and Hansen L.K., 2002, Extracellular matrix- and cytoskeleton-dependent changes in cell shape and stiffness, Experimental Cell Research, 278(1), 92-100

Tan, J.L., Tien, J., Pirone, D.M., Gray, D.S., Bhadriraju, K. and Chen, C.S., 2002, Cells lying on a bed of microneedles: geometry and mechanics, Proceedings of the National Academy of Sciences U. S. A., 100(4), 1484 –1489

McBeath, R., Pirone, D.M., Nelson, C.M., Bhadriraju, K. and Chen, C.S., 2004, Cell shape, cytoskeletal tension, and RhoA regulate stem cell lineage commitment, Developmental Cell, 6(4), 483-495

Bhadriraju, K. and Hansen, L.K., 2004, Extracellular matrix-dependent myosin dynamics during G1-S phase cell cycle progression in hepatocytes, Experimental Cell Research, 300(2), 259-71

McDaniel, D., Shaw, G., Elliott, J.T., Bhadriraju, K., Meuse, C., Chung, K.H., Plant, A.L, 2007, The stiffness of collagen fibrils influences vascular smooth muscle cell phenotype, Biophysical Journal, 92(5), 1759-69.

Bhadriraju, K., Yang, M., Ruiz, S.A., Pirone, D.M., Tan, J.L. and Chen, C.S., 2007, Rho-ROCK signaling is regulated by cytoskeletal tension, Experimental Cell Research, 313(16), 3616-23.

Halter, M., Tona, A., Bhadriraju, K., Elliott, J.T. and Plant, A.L., 2007, Automated live cell imaging of GFP degradation in individual fibroblasts, Cytometry Part A, 71(10), 827-834.

Bhadriraju, K., Elliott, J.T., Nguyen, M., Plant, A.L., 2007, Quantifying myosin light chain phosphorylation in single adherent cells with automated fluorescence microscopy, BMC Cell Biology, 8:43.

Gray, D.S., Liu, W.F., Shen, C.J., Bhadriraju, K., Nelson, C.M., Chen, C.S., 2008, Engineering amount of cell-cell contact demonstrates biphasic proliferative regulation through RhoA and the actin cytoskeleton, Experimental Cell Research, 314(15), 2846-54.

Plant A.L., Bhadriraju, K., Spurlin, T.S. and Elliott, J.T., 2008, epub. Nov 5., Cell response to matrix mechanics: focus on collagen, BBA - Molecular Cell Research

Peterson, A., Halter, M.H., Tona, A., Bhadriraju, K., Plant A.L., 2009, Surface plasmon resonance imaging of cells and surface-associated fibronectin, BMC Cell Biology, 10:16.