Current Projects
Pathobiology of Cardiac Dyssynchrony and Resynchronization This NIH-funded Program Project has undertaken the first detailed assessment of how the failing heart is impacted at the cellular and molecular level by dyssynchronous contraction and the subsequent restoration of synchrony from bi-ventricular pacing. Cardiac resynchronzation therapy (CRT) entered the treatment arsenal for heart failure patients in the early part of the 21st century, and is to date the only treatment yet developed that can acutely and chronically improve systolic function of the heart and yet also enhance long term survival. Our research uses a canine model of heart failure with dyssynchrony and then resynchronization, and studies how this influences cell signaling including cell survival and growth modulators, excitation contraction coupling, adrenergic cascades, energetics and mitochondrial function, and myofilament proteins and calcium sensitivity. Recent studies in circulation have revealed marked improvements in survival (1), beta-adrenergic responses (2), repolarizing and calcium currents (3), myocardial gene expression heterogeneity, and mitochondrial function and protein modification by CRT. New work is exploring how CRT impacts the myofilaments, and the mechanisms for adrenergic upregulation. Studies are conducted principally at the molecular, cellular, and muscle level.
Regulation of Cardiac Stress Response by PDE5a This NIH funded study is determining how the cGMP-selective phosphodiesterase PDE5a regulates cardiac myocyte adrenergic and hypertrophic responses. Our study from 2005 (4) first proposed that inhibitors of PDE5a such as sildenafil can suppress maladaptive cardiac hypertrophy and dysfunction from sustained pressure-overload. More recent studies have identified mechanisms for these effects involving a number of critical protein kinases, phosphatases, and regulators of G-couple signaling (5). Ongoing research involves development of novel mouse models with targeted modification of PDE5a expression in myoyctes, novel fluorescent probes to investigate cGMP regulation in the heart, cell-based studies to dissect signaling pathways and functional consequences of PDE5a/cGMP regulation.
Mechanisms underlying the role of sarcomere protein mutations in cardiac failure and hypertrophy This long-standing Program Project centered at the University of Vermont has focused on how site mutations in myosin and myosin binding protein C contribute to hypertrophic cardiomyopathy (HCM) and/or failure. The recent focus is on MyBP-C, the most commonly mutated protein in patients with HCM, and in particular how post-translational modifications and changes in its actin binding domain influence its regulation of cardiac contraction. Our recent work highlighted how these changes impact the kinetics of systole and diastolic, and how MyBP-C is central to sustaining normal systole and the control of chamber filling time by heart rate(6). Future studies will examine the role of selective phosphorylation modifications on rest and stress-stimulated muscle and chamber contractile and relaxation kinetics.
Redox-Nitrosative Stress and Cardiac Remodeling This newly funded study (Leducq Foundation, Kass USA Coordinator) aims to study how oxidant and nitrosative stress result in modifications of cardiac stress responses and to ultimately develop new approaches to ameliorate the pathology that these signaling cascades induce. While anti-oxidant therapy has been a target for some time, the results have been generally disappointing. Our hypothesis is that more targeted modification of the specific oxidant enzymes involved with ROS generation and/or the proteins that are specifically affected will yield a new ear of more successful therapeutic options. The Network involves leading laboratories in the United States and Europe, (the latter including France, Italy, Germany, and the United Kingdom), with fellows being able to integrate experience in multiple laboratories to engage in novel collaborative research. The Hopkins labs will focus on the oxidant and nitrosative modulation by cGMP-PDEs and PKG, as well as amelioration of NOS uncoupling (7).
Methodologies
One of the hallmarks of the laboratory is its integration of a variety of levels of investigation, from subcellular and molecular signaling all the way up to intact large mammalian models with chronic instrumentation and conscious studies. Trainees can gain experience in advanced molecular biology methods, and physiology at the cell and whole organ level. The lab is known for its expertise in pressure-volume relation analysis in the intact heart, first fully developed by Kass and colleagues in the early 1980's, and expanded to human and other mammalian models including mouse. Cells are studied in culture systems, using physiologic analysis of function and ion (e.g. calcium) regulation, and with force-length control for mechanical perturbations and myofilament analysis. Core facilities and close collaborators offer advanced microscopy methods, non-invasive imaging, and pathology. Our animal models include a canine model of failure (tachypacing), rat and mouse models of disease, including infarction and pressure-overload, neurohormonal infusion models, and many genetically engineered strains used to assess targeted signaling.
References 1. Chakir, K., Daya,S.K., Tunin, R.S., Helm, R.H., Byrne, M.J., Dimaano, V.L., Lardo, A.C., Abraham, T.P., Tomaselli, G.F., and Kass, D.A. 2008. Reversal of global apoptosis and regional stress kinase activation by cardiac resynchronization. Circulation 117:1369-1377.
2. Chakir, K., Daya,S.K., Aiba,T., Tunin,R.S., Dimaano,V.L., Abraham,T.P., Jaques,K., Lai,E.W., Pacak,K., Zhu,W.Z. et al 2009. Mechanisms of enhanced beta-adrenergic reserve from cardiac resynchronization therapy. Circulation 119:1231-1240.
3. Aiba, T., Hasketh, G.G., Barth, A.S., Liu, T., Daya, S.K., Chakir, K., Dimaano, V.L., Abraham,T.P., O'Rourke, B., Akar, F.G. et al 2009. Electrophysioloigcal consequences of dyssynchronous heart failure and its restoration by resynchronization therapy. Circulation 119:1220-1230.
4. Takimoto, E., Champion, H.C., Li, M., Belardi, D., Ren, S., Rodriguez, E.R., Bedja, D., Gabrielson, K.L., Wang, Y., and Kass, D.A. 2005. Chronic inhibition of cyclic GMP phosphodiesterase 5A prevents and reverses cardiac hypertrophy. Nat. Med. 11:214-222.
5. Takimoto, E., Koitabashi, N., Hsu, S., Ketner, E.A., Nagayama, T., Bedja D., Gabrielson K., Blanton, R., Siderovski, D.P., Mendelsohn, M.E. et al 2009. RGS2 mediates cardiac compensation to pressure-overload and anti-hypertrophic effects of PDE5 inhibition. J Clin Invest 119:408-420.
6. Nagayama, T., Takimoto, E., Sadayappan, S., Mudd, J.O., Seidman, J.G., Robbins, J., and Kass, D.A. 2007. Control of in vivo left ventricular contraction/relaxation kinetics by myosin binding protein C: protein kinase A phosphorylation dependent and independent regulation. Circulation 116:2399-2408.
7. Takimoto, E., Champion, H.C., Li, M., Ren, S., Rodriguez, E.R., Tavazzi, B., Lazzarino, G., Paolocci, N., Gabrielson, K.L., Wang, Y. et al 2005. Oxidant stress from nitric oxide synthase-3 uncoupling stimulates cardiac pathologic remodeling from chronic pressure load. J Clin. Invest 115:1221-1231.