Hendrikus L Granzier

Hendrikus L Granzier

Professor, BIO5 Institute
Professor, Biomedical Engineering
Professor, Cellular and Molecular Medicine
Professor, Genetics - GIDP
Professor, Molecular and Cellular Biology
Professor, Physiological Sciences - GIDP
Professor, Physiology
Primary Department
Department Affiliations
Contact
(520) 626-3641

Work Summary

Work Summary

Our research is focused on elucidating the structure and function of titin and nebulin, two large filamentous proteins found in muscle. We use a range of model systems with a major focus on KO and TG mouse models. The techniques that we use range from single molecule mechanics, (immuno) electron microscopy, exon microarray analysis, in vitro motility assays, low angle X-ray diffraction, cell physiology (including calcium imaging), muscle mechanics, and isolated heart physiology.

Research Interest

Research Interest

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.

Publications

Granzier, H., Ottenheijm, C. A., Fong, C., Vangheluwe, P., Wuytack, F., Babu, G. J., Periasamy, M., Witt, C. C., Labeit, S., & Granzier, H. L. (2008). Sarcoplasmic reticulum calcium uptake and speed of relaxation are depressed in nebulin-free skeletal muscle. FASEB journal : official publication of the Federation of American Societies for Experimental Biology, 22(8).

Previous work suggested that altered Ca(2+) homeostasis might contribute to dysfunction of nebulin-free muscle, as gene expression analysis revealed that the sarco(endo)plasmic reticulum Ca(2+)-ATPase (SERCA)-inhibitor sarcolipin (SLN) is up-regulated >70-fold in nebulin knockout mice, and here we tested this proposal. We investigated SLN protein expression in nebulin-free and wild-type skeletal muscle, as well as expression of other Ca(2+)-handling proteins. Ca(2+) uptake capacity was determined in isolated sarcoplasmic reticulum vesicles and in intact myofibers by measuring Ca(2+) transients. Muscle contractile performance was determined in skinned muscle activated with exogenous Ca(2+), as well as in electrically stimulated intact muscle. We found profound up-regulation of SLN protein in nebulin-free skeletal muscle, whereas expression of other Ca(2+)-handling proteins was not (calsequestrin and phospholamban) or was minimally (SERCA) affected. Speed of Ca(2+) uptake was >3-fold decreased in sarcoplasmic reticulum vesicles isolated from nebulin-free muscle as well as in nebulin-free intact myofibers. Ca(2+)-activated stress in skinned muscle and stress produced by intact nebulin-free muscle were reduced to a similar extent compared with wild type. Half-relaxation time was significantly longer in nebulin-free compared with wild-type muscle. Thus, the present study demonstrates for the first time that nebulin might also be involved in physiological Ca(2+) handling of the SR-myofibrillar system.

Leite, F. S., Minozzo, F. C., Kalganov, A., Cornachione, A. S., Cheng, Y., Leu, N. A., Han, X., Saripalli, C., Yates, J. R., Granzier, H., Kashina, A. S., & Rassier, D. E. (2016). Reduced passive force in skeletal muscles lacking protein arginylation. American journal of physiology. Cell physiology, 310(2), C127-35.

Arginylation is a posttranslational modification that plays a global role in mammals. Mice lacking the enzyme arginyltransferase in skeletal muscles exhibit reduced contractile forces that have been linked to a reduction in myosin cross-bridge formation. The role of arginylation in passive skeletal myofibril forces has never been investigated. In this study, we used single sarcomere and myofibril measurements and observed that lack of arginylation leads to a pronounced reduction in passive forces in skeletal muscles. Mass spectrometry indicated that skeletal muscle titin, the protein primarily linked to passive force generation, is arginylated on five sites located within the A band, an important area for protein-protein interactions. We propose a mechanism for passive force regulation by arginylation through modulation of protein-protein binding between the titin molecule and the thick filament. Key points are as follows: 1) active and passive forces were decreased in myofibrils and single sarcomeres isolated from muscles lacking arginyl-tRNA-protein transferase (ATE1). 2) Mass spectrometry revealed five sites for arginylation within titin molecules. All sites are located within the A-band portion of titin, an important region for protein-protein interactions. 3) Our data suggest that arginylation of titin is required for proper passive force development in skeletal muscles.

Li, F., Buck, D., De Winter, J., Kolb, J., Meng, H., Birch, C., Slater, R., Escobar, Y. N., Smith, J. E., Yang, L., Konhilas, J., Lawlor, M. W., Ottenheijm, C., & Granzier, H. L. (2015). Nebulin deficiency in adult muscle causes sarcomere defects and muscle-type-dependent changes in trophicity: novel insights in nemaline myopathy. Human molecular genetics, 24(18), 5219-33.

Nebulin is a giant filamentous protein that is coextensive with the actin filaments of the skeletal muscle sarcomere. Nebulin mutations are the main cause of nemaline myopathy (NEM), with typical adult patients having low expression of nebulin, yet the roles of nebulin in adult muscle remain poorly understood. To establish nebulin's functional roles in adult muscle, we studied a novel conditional nebulin KO (Neb cKO) mouse model in which nebulin deletion was driven by the muscle creatine kinase (MCK) promotor. Neb cKO mice are born with high nebulin levels in their skeletal muscles, but within weeks after birth nebulin expression rapidly falls to barely detectable levels Surprisingly, a large fraction of the mice survive to adulthood with low nebulin levels (

Slater, R. E., Strom, J. G., & Granzier, H. (2017). Effect of exercise on passive myocardial stiffness in mice with diastolic dysfunction. Journal of molecular and cellular cardiology, 108, 24-33.

Heart failure with preserved ejection fraction (HFpEF) is a complex syndrome, characterized by increased diastolic stiffness and a preserved ejection fraction, with no effective treatment options. Here we studied the therapeutic potential of exercise for improving diastolic function in a mouse model with HFpEF-like symptoms, the TtnΔIAjxn mouse model. TtnΔIAjxn mice have increased diastolic stiffness and reduced exercise tolerance, mimicking aspects of HFpEF observed in patients. We investigated the effect of free-wheel running exercise on diastolic function. Mechanical studies on cardiac muscle strips from the LV free wall revealed that both TtnΔIAjxn and wildtype (WT) exercised mice had a reduction in passive stiffness, relative to sedentary controls. In both genotypes, this reduction is due to an increase in the compliance of titin whereas ECM-based stiffness was unaffected. Phosphorylation of titin's PEVK and N2B spring elements were assayed with phospho-site specific antibodies. Exercised mice had decreased PEVK phosphorylation and increased N2B phosphorylation both of which are predicted to contribute to the increased compliance of titin. Since exercise lowers the heart rate we examined whether reduction in heart rate per se can improve passive stiffness by administering the heart-rate-lowering drug ivabradine. Ivabradine lowered heart rate in our study but it did not affect passive tension, in neither WT nor TtnΔIAjxn mice. We conclude that exercise is beneficial for decreasing passive stiffness and that it involves beneficial alterations in titin phosphorylation.

Granzier, H. L. (2015). Reply to Tskhovrebova et al.: Titin's IA junction does not control thick filament length. Proceedings of the National Academy of Sciences of the United States of America, 112(11), E1173.