Jeffery W. Walker, Ph.D. Professor Department of Physiology jwalker@physiology.wisc.edu

Cell Signaling in the Cardiovascular System

The long term objective of the research program is to identify cellular and molecular mechanisms that regulate heart muscle contraction. Force producing cells in the heart (myocytes) respond to a variety of extracellular stimuli including hormones, neurotransmitters, growth factors and mechanical stress. Receptors for many of these stimuli are coupled to the phosphoinositide/ diacylglycerol/protein kinase C signaling system, and our challenge is to elucidate the molecular details of how this pathway functions to regulate contractility, cardioprotection, gene expression, and growth. Signaling mechanisms involving protein kinase C are also likely to have important implications in the etiology and treatment of cardiac hypertrophy, heart failure and other disease conditions (e.g. diabetes) where cardiac function is impaired.

Several complementary approaches are being used to study protein kinase C mediated regulation of contractility in the mammalian heart. Mechanical, electrophysiological, and confocal fluorescence measurements on isolated cardiac myocytes are performed to evaluate the involvement of protein kinase C in pathways activated by surface receptors for alpha-adrenergics, endothelin-1A and adenosine, or by intracellular messengers such as inositol phosphates, calcium, diacylglycerols, and arachidonic acid. A leading hypothesis generated by our work is that the epsilon and delta isoforms of protein kinase C carryout distinct by complimentary functions. Protein kinase C-epsilon anchors at key sites on the sarcomere and enhances myocyte function by phosphorylating specific calcium channels and contractile proteins. Protein kinase C-delta translocates to the nucleus where it regulates gene expression. These hypothese are tested by biophysical, imaging and molecular approaches with an emphasis on identifying and manipulating organelle-specific anchoring proteins, and creating mutations in critical phosphorylations sites in cultured myocytes and in mouse hearts.

The laboratory is also actively involved in the development of caged compounds and fluorescent probes so that signaling mechanisms can be dissected with high temporal and spatial resolution using modern light microscopy. A variety of bioactive probes are currently under development including membrane permeases capable of carrying charged reagents across biological membranes, peptide inhibitors of protein kinase C translocation, toxins directed against calcium channels and other intracellular targets, and lipids and lipid-peptide conjugates directed at specific isoforms of protein kinases and phosphatases.

• Stelzer JE, Patel JR, Walker JW, and Moss RL. (2007). Differential roles of cardiac myosin-binding protein C and cardiac troponin I in the myofibrillar force responses to protein kinase A phosphorylation. Circ Res. 101:503-511. PMID 17641226
  
  
• Kang M, Chung KY, and Walker JW. (2007). G-protein coupled receptor signaling in myocardium: not for the faint of heart. Physiology (Bethesda). 22:174-184. PMID 17557938
  
  
• Chung KY and Walker JW. (2007). Interaction and inhibitory cross-talk between endothelin and ErbB receptors in the adult heart. Mol Pharmacol. 71:1494-1502. PMID 17332141
  

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