Honors & Awards

  • Postdoctoral Fellow, Training Grant (T32) for Research Training in Myocardial Biology, Stanford University (2013-present)
  • Best Presentation, Spring Retreat, UC Davis Molecular, Cellular and Integrative Physiology (2013)
  • Pre-doctoral fellow, American Heart Association (2012-2013)
  • Awarded fellow, Achievement Rewards for College Scientists (2012-2013)
  • Dean?s Mentorship Award, UC Davis College of Biological Sciences (2012)
  • Selected Attendee, NAIST International Student Workshop (2011)
  • Pre-doctoral fellow, National Defense Science and Engineering Fellowship, Department of Defense (2009-2012)
  • Poster Award, Spring Retreat, UC Davis Molecular, Cellular and Integrative Physiology (2009)
  • Cum Laude, University of Washington (2006)
  • Departmental honors, University of Washington Department of Bioengineering (2006)

Boards, Advisory Committees, Professional Organizations

  • Member, American Heart Association (2012 - Present)
  • Member, Biophysical Society (2005 - Present)

Professional Education

  • Doctor of Philosophy, University of California Davis (2013)
  • Bachelor of Science, University of Washington (2006)

Stanford Advisors


All Publications

  • Time-dependent evolution of functional vs. remodeling signaling in induced pluripotent stem cell-derived cardiomyocytes and induced maturation with biomechanical stimulation FASEB JOURNAL Jung, G., Fajardo, G., Ribeiro, A. J., Kooiker, K. B., Coronado, M., Zhao, M., Hu, D., Reddy, S., Kodo, K., Sriram, K., Insel, P. A., Wu, J. C., Pruitt, B. L., Bernstein, D. 2016; 30 (4): 1464-1479


    Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) are a powerful platform for uncovering disease mechanisms and assessing drugs for efficacy/toxicity. However, the accuracy with which hiPSC-CMs recapitulate the contractile and remodeling signaling of adult cardiomyocytes is not fully known. We used ?-adrenergic receptor (?-AR) signaling as a prototype to determine the evolution of signaling component expression and function during hiPSC-CM maturation. In "early" hiPSC-CMs (less than or equal to d 30), ?2-ARs are a primary source of cAMP/PKA signaling. With longer culture, ?1-AR signaling increases: from 0% of cAMP generation at d 30 to 56.8 6.6% by d 60. PKA signaling shows a similar increase: 15.7 5.2% (d 30), 49.8 0.5% (d 60), and 71.0 6.1% (d 90). cAMP generation increases 9-fold from d 30 to 60, with enhanced coupling to remodeling pathways (e.g., Akt and Ca(2+)/calmodulin-dependent protein kinase type II) and development of caveolin-mediated signaling compartmentalization. By contrast, cardiotoxicity induced by chronic ?-AR stimulation, a major component of heart failure, develops much later: 5% cell death at d 30 vs. 55% at d 90. Moreover, ?-AR maturation can be accelerated by biomechanical stimulation. The differential maturation of ?-AR functional vs. remodeling signaling in hiPSC-CMs has important implications for their use in disease modeling and drug testing. We propose that assessment of signaling be added to the indices of phenotypic maturation of hiPSC-CMs.-Jung, G., Fajardo, G., Ribeiro, A. J. S., Kooiker, K. B., Coronado, M., Zhao, M., Hu, D.-Q., Reddy, S., Kodo, K., Sriram, K., Insel, P. A., Wu, J. C., Pruitt, B. L., Bernstein, D. Time-dependent evolution of functional vs. remodeling signaling in induced pluripotent stem cell-derived cardiomyocytes and induced maturation with biomechanical stimulation.

    View details for DOI 10.1096/fj.15-280982

    View details for Web of Science ID 000372629100009

  • Earning stripes: myosin binding protein-C interactions with actin PFLUGERS ARCHIV-EUROPEAN JOURNAL OF PHYSIOLOGY van Dijk, S. J., Bezold, K. L., Harris, S. P. 2014; 466 (3): 445-450


    Myosin binding protein-C (MyBP-C) was first discovered as an impurity during the purification of myosin from skeletal muscle. However, soon after its discovery, MyBP-C was also shown to bind actin. While the unique functional implications for a protein that could cross-link thick and thin filaments together were immediately recognized, most early research nonetheless focused on interactions of MyBP-C with the thick filament. This was in part because interactions of MyBP-C with the thick filament could adequately explain most (but not all) effects of MyBP-C on actomyosin interactions and in part because the specificity of actin binding was uncertain. However, numerous recent studies have now established that MyBP-C can indeed bind to actin through multiple binding sites, some of which are highly specific. Many of these interactions involve critical regulatory domains of MyBP-C that are also reported to interact with myosin. Here we review current evidence supporting MyBP-C interactions with actin and discuss these findings in terms of their ability to account for the functional effects of MyBP-C. We conclude that the influence of MyBP-C on muscle contraction can be explained equally well by interactions with actin as by interactions with myosin. However, because data showing that MyBP-C binds to either myosin or actin has come almost exclusively from in vitro biochemical studies, the challenge for future studies is to define which binding partner(s) MyBP-C interacts with in vivo.

    View details for DOI 10.1007/s00424-013-1432-8

    View details for Web of Science ID 000331719400008

    View details for PubMedID 24442149

  • A Gain-of-Function Mutation in the M-domain of Cardiac Myosin-binding Protein-C Increases Binding to Actin JOURNAL OF BIOLOGICAL CHEMISTRY Bezold, K. L., Shaffer, J. F., Khosa, J. K., Hoye, E. R., Harris, S. P. 2013; 288 (30): 21496-21505


    The M-domain is the major regulatory subunit of cardiac myosin-binding protein-C (cMyBP-C) that modulates actin and myosin interactions to influence muscle contraction. However, the precise mechanism(s) and the specific residues involved in mediating the functional effects of the M-domain are not fully understood. Positively charged residues adjacent to phosphorylation sites in the M-domain are thought to be critical for effects of cMyBP-C on cross-bridge interactions by mediating electrostatic binding with myosin S2 and/or actin. However, recent structural studies revealed that highly conserved sequences downstream of the phosphorylation sites form a compact tri-helix bundle. Here we used site-directed mutagenesis to probe the functional significance of charged residues adjacent to the phosphorylation sites and conserved residues within the tri-helix bundle. Results confirm that charged residues adjacent to phosphorylation sites and residues within the tri-helix bundle are important for mediating effects of the M-domain on contraction. In addition, four missense variants within the tri-helix bundle that are associated with human hypertrophic cardiomyopathy caused either loss-of-function or gain-of-function effects on force. Importantly, the effects of the gain-of-function variant, L348P, increased the affinity of the M-domain for actin. Together, results demonstrate that functional effects of the M-domain are not due solely to interactions with charged residues near phosphorylatable serines and provide the first demonstration that the tri-helix bundle contributes to the functional effects of the M-domain, most likely by binding to actin.

    View details for DOI 10.1074/jbc.M113.474346

    View details for Web of Science ID 000328841900003

    View details for PubMedID 23782699

  • In the Thick of It HCM-Causing Mutations in Myosin Binding Proteins of the Thick Filament CIRCULATION RESEARCH Harris, S. P., Lyons, R. G., Bezold, K. L. 2011; 108 (6): 751-764


    In the 20 years since the discovery of the first mutation linked to familial hypertrophic cardiomyopathy (HCM), an astonishing number of mutations affecting numerous sarcomeric proteins have been described. Among the most prevalent of these are mutations that affect thick filament binding proteins, including the myosin essential and regulatory light chains and cardiac myosin binding protein (cMyBP)-C. However, despite the frequency with which myosin binding proteins, especially cMyBP-C, have been linked to inherited cardiomyopathies, the functional consequences of mutations in these proteins and the mechanisms by which they cause disease are still only partly understood. The purpose of this review is to summarize the known disease-causing mutations that affect the major thick filament binding proteins and to relate these mutations to protein function. Conclusions emphasize the impact that discovery of HCM-causing mutations has had on fueling insights into the basic biology of thick filament proteins and reinforce the idea that myosin binding proteins are dynamic regulators of the activation state of the thick filament that contribute to the speed and force of myosin-driven muscle contraction. Additional work is still needed to determine the mechanisms by which individual mutations induce hypertrophic phenotypes.

    View details for DOI 10.1161/CIRCRESAHA.110.231670

    View details for Web of Science ID 000288503700013

    View details for PubMedID 21415409

  • Functional Differences between the N-Terminal Domains of Mouse and Human Myosin Binding Protein-C JOURNAL OF BIOMEDICINE AND BIOTECHNOLOGY Shaffer, J. F., Wong, P., Bezold, K. L., Harris, S. P. 2010


    The N-terminus of cMyBP-C can activate actomyosin interactions in the absence of Ca2+, but it is unclear which domains are necessary. Prior studies suggested that the Pro-Ala rich region of human cMyBP-C activated force in permeabilized human cardiomyocytes, whereas the C1 and M-domains of mouse cMyBP-C activated force in permeabilized rat cardiac trabeculae. Because the amino acid sequence of the P/A region differs between human and mouse cMyBP-C isoforms (46% identity), we investigated whether species-specific differences in the P/A region could account for differences in activating effects. Using chimeric fusion proteins containing combinations of human and mouse C0, Pro-Ala, and C1 domains, we demonstrate here that the human P/A and C1 domains activate actomyosin interactions, whereas the same regions of mouse cMyBP-C are less effective. These results suggest that species-specific differences between homologous cMyBP-C isoforms confer differential effects that could fine-tune cMyBP-C function in hearts of different species.

    View details for DOI 10.1155/2010/789798

    View details for Web of Science ID 000277838800001

    View details for PubMedID 20379391

  • Contribution of the Myosin Binding Protein C Motif to Functional Effects in Permeabilized Rat Trabeculae JOURNAL OF GENERAL PHYSIOLOGY Razumova, M. V., Bezold, K. L., Tu, A., Regnier, M., Harris, S. P. 2008; 132 (5): 575-585


    Myosin binding protein C (MyBP-C) is a thick-filament protein that limits cross-bridge cycling rates and reduces myocyte power output. To investigate mechanisms by which MyBP-C affects contraction, we assessed effects of recombinant N-terminal domains of cardiac MyBP-C (cMyBP-C) on contractile properties of permeabilized rat cardiac trabeculae. Here, we show that N-terminal fragments of cMyBP-C that contained the first three immunoglobulin domains of cMyBP-C (i.e., C0, C1, and C2) plus the unique linker sequence termed the MyBP-C "motif" or "m-domain" increased Ca(2+) sensitivity of tension and increased rates of tension redevelopment (i.e., k(tr)) at submaximal levels of Ca(2+). At concentrations > or =20 microM, recombinant proteins also activated force in the absence of Ca(2+) and inhibited maximum Ca(2+)-activated force. Recombinant proteins that lacked the combination of C1 and the motif did not affect contractile properties. These results suggest that the C1 domain plus the motif constitute a functional unit of MyBP-C that can activate the thin filament.

    View details for DOI 10.1085/jgp.200810013

    View details for Web of Science ID 000266672800009

    View details for PubMedID 18955596

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