Structure and mechanics of smooth muscle thin filaments
• Lab News
|Vascular smooth muscle cells must be able to bear and transmit forces while also sense and respond to both internally and externally applied forces. Failure to either properly sense or respond to external stresses is known to lead to several pathological cardiovascular conditions, including hypertension and smooth muscle hypertrophy. Here our overall goal is to understand the nature and regulation of cytoskeletal dynamics in vascular smooth muscle cells.Actin and its associated actin-binding proteins (ABPs) are key mechanical components of the cytoskeleton and are able to dynamically modulate cell mechanics through remodeling. In collaboration with Dr. Wang, we are studying the effects of ABPs on actin structure and dynamics using a custom-built total internal reflectance fluorescence (TIR) microscope and confocal microscopy (Collins et al., 2011; Jensen et al., 2012).We also determine the impact of vascular smooth muscle cytoskeletal actin-binding proteins (ABPs) on thin filament structure and mechanics. We focus on characterizing actin and cell mechanics and dynamics on scales ranging from the single filament to the entire cytoskeleton. To achieve this goal we collaborate with Dr. Lehman to carry out high-resolution electron microscopy, anchor helical reconstruction and single particle analysis of reconstituted thin filaments to define the molecular interactions of ABPs on actin. Corresponding strategies in our lab use laser-trapping and single molecule fluorescence methods to determine the effects of force on ABP-binding to F-actin and the effect of ABPs on the mechanical performance of thin filaments. Collaborative studies with the Dr. Weitz at Harvard University on crosslinked actin networks using bulk rheology are being used to characterize the effects of ABPs in a system that more closely mimics a cytoskeletal actin network.
We are now extending this work to intact cells. In collaboration with the Morgan lab we use custom-built magnetic tweezers to measure the mechanics and dynamic responses of the cytoskeleton to externally applied forces (Saphirstein et al., 2013). We are also using optical tweezers designed and constructed in the lab to manipulate injected beads in the cell interior to quantify the local mechanical environment in terms of the storage and loss moduli. Recent collaborative work with the Weitz lab on A7 cells provides critical information for how the cell, despite being a largely elastic material, can allow passive transport of objects much larger than the network mesh size (Guo et al., 2013).
Jensen M.H., Morris E.J., Gallant C. M., Morgan K.G., Weitz D.A., Moore J.R. (2013) Mechanism of calponin stabilization of crosslinked actin networks Biophysical Journal. Accepted.
Saphirstein R. J., Gao Y.Z., Jensen M.H., Gallant C.M., Vetterkind S., Moore J.R., Morgan K.G.(2013) The focal adhesion: a regulated component of aortic stiffness. PLoS One. 23;8(4):e62461. doi: 10.1371/journal.pone.0062461. PMCID: PMC3633884.
Guo M., Ehrlicher A.J., Mahammad S., Fabich H., Jensen M.H., Moore J.R., Fredberg J.J., GoldmanR.D., Weitz D.A. (2013) The role of vimentin intermediate filaments in cortical and cytoplasmic mechanics. Biophys J. 2013 105(7):1562-8. PMCID: PMC3791300.
Jensen M.H., Morris E.J., Huang R., Rebowski G., Dominguez R., Weitz D.A., Moore J.R., Wang C-L. (2012) The conformational state of actin filaments regulates branching by actin-related protein 2/3 (Arp2/3) complex. J Biol Chem. 287(37):31447-53 PMCID: PMC3438974
Moore, J. R., Leinwand, L., Warshaw, D. W. (2012) Understanding Cardiomyopathy PhenotypesBased on the Functional Impact of Mutations in the Myosin Motor. Circulation Res. 20;111:375-85.
Jensen M.H., Watt J., Hodgkinson J., Gallant C., Appel S., El-Mezgueldi M., Angelini T., Morgan K.G., Lehman W., and Moore J.R. (2012) Effects of basic calponin on the flexural mechanics and stability of F-actin Cytoskeleton 69(1):49-58. PMCID: PMC3355516.
Collins A., Huang R., Jensen M. H., Moore J.R., Lehman W., Wang Chih-Lueh Albert (2011) Structural studies on maturing actin filaments. BioArchitechture. 1:127-33. PMCID: PMC3173961
Greenberg, M., Wang, C-L., Lehman, W., Moore, J., (2008) Modulation of actin mechanics by caldesmon and tropomyosin. Cell Motility and Cytoskeleton. Feb;65(2):156-64 PMCID: PMC2975105