Muscular system

The research goal of my laboratory is to understand the molecular motions and interactions of proteins involved in regulating contractile function of healthy cardiac and skeletal muscle, to determine the culprits of contractile dysfunction and remodeling in muscle disorders and cardiovascular disease, and then apply these insights to design novel therapies. We use biophysical approaches, such as time-resolved spectroscopy with site-directed probes to assess protein structural dynamics and mechanical measurements of isolated muscle fibers to assess contractile force and kinetics, in order to establish structure-function relationships inherent to the molecular, biochemical, and physiological mechanisms.

The long-term goal of research in my lab is to understand the molecular mechanisms of muscle contraction. I am especially interested in how contractile proteins of muscle sarcomeres regulate the force and speed of contraction in the heart. The question is important from both basic science and clinical perspectives because mutations in sarcomere proteins of muscle are a leading cause of hypertrophic cardiomyopathy (HCM), the most common cause of sudden cardiac death in the young and a prevalent cause of heart failure in adults. Myosin binding protein-C (MyBP-C) is a muscle regulatory protein that speeds actomyosin cycling kinetics in response to adrenaline (b-adrenergic stimuli) and is one of the two most commonly affected proteins linked to HCM. Currently, the major research focus in my lab is understanding the mechanisms by which cMyBP-C regulates contractile speed and mechanisms by which mutations in cMyBP-C cause disease. In pursuing these interests I have established a variety of approaches to investigate muscle contraction at molecular, cellular, and whole animal levels. Methods include single molecule atomic force microscopy (AFM), mechanical force measurements in permeabilized muscle cells, in vitro motility assays, biochemical enzyme and binding assays, immunofluorescent imaging, knockout/transgenic animal models and the development of a natural large animal model of HCM.

Carol Gregorio, PhD, performs research in her lab that is focused on identifying the components and molecular mechanisms regulating actin architecture in cardiac and skeletal muscle during normal development and disease. Control of actin filament lengths and dynamics is important for cell motility and architecture and is regulated in part by capping proteins that block elongation and depolymerization at both the fast-growing (barbed) and slow-growing (pointed) ends of the filaments. Striated muscle is an ideal model system to test for the functional properties of various actin regulatory proteins due to the precise organization and polarity of cytoskeletal components within repeating sarcomeric units (for example, the ~1 mm long actin filaments are easily resolved by light microscopy). Using this system, she can combine advanced cell biological and biochemical approaches with direct tests of physiological function in live beating muscle cells.The research objectives of the laboratory can be broadly summarized as follows: 1) understanding the cellular mechanisms involved in the assembly, regulation and maintenance of contractile proteins in cardiac muscle in health and disease; 2) deciphering the mechanisms critical for precisely specifying and maintaining the lengths of actin filaments; 3) discovery of novel models of de novo cardiac muscle assembly, with special emphasis on differentiating murine embryonic stem (ES) cells to study all stages of heart muscle development. Actin is an indispensable structural element of cells and is the major component of heart muscle. Changes in actin, caused by genetic mutations, which have been identified in humans, are a frequent cause of several forms of cardiomyopathy. Her lab is determining how genetic defects in this protein affect muscle force generation and muscle contraction, leading to sudden cardiac death.

Hendrikus Granzier, PhD, studies the mechanisms whereby the giant filamentous protein titin (the largest protein known) influence muscle structure and function. His lab has shown that titin functions as a molecular spring that mediates acute responses to changing pathophysiological states of the heart. They also study the role of titin in cardiac disease, using mouse models with specific modifications in the titin gene, including deciphering the mechanisms that are responsible for gender differences in diastolic dysfunction. An additional focus of Dr. Granzier’s lab is on nebulin, a major muscle protein that causes a severe skeletal muscle disease in humans. Based on previous work, they hypothesize that nebulin is a determinant of calcium sensitivity of contractile force. To test this and other concepts, he uses a nebulin knockout approach in the mouse. Research is multi-faceted and uses cutting-edge techniques at levels ranging across the single molecule, single cell, muscle, and the intact heart. His research group is diverse and has brought together individuals from several continents with expertise ranging from physics and chemistry to cell biology and physiology.