Biophotonic Analysis of Embryonic Cardiodynamics
Andrew L. Lopez, III - Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA
Shang Wang - Department of Biomedical Engineering, Stevens Institute of Technology, 1 Castle Point Terrace, Hoboken, NJ 07030, USA
Irina Larina - Department of Molecular Physiology and Biophysics, Baylor College of Medicine, One Baylor Plaza, Houston, TX, 77030, USA
Abstract
Congenital heart defects (CHD) are common and occur in nearly 1% of all live births. Moreover, cardiovascular (CV) failures are the leading cause of birth defect-related deaths in infants. It is established that biomechanical stimuli are critical regulators of CV development. Thus, defining how mechanical factors are integrated with genetic pathways to coordinate mammalian heart tube development and function will factor into strategies for new therapeutic interventions to treat/prevent CHD in humans. To address this critical need, we have established optical approaches for live, high-resolution imaging and manipulation of mouse embryo cardiodynamics. Our approach combines live mouse embryo culture with structural and functional OCT imaging, second harmonic generation (SHG) microscopy and optogenetics. We have developed methods for acquisition, synchronization, of the developing beating heart with spatial resolution of about 4μm, and 4D angiography approach to visualize dynamics of blood flows without staining within beating embryonic hearts. Toward understanding of the pumping mechanism, one of intriguing findings revealed that the heart wall at neighboring sites accelerates in coordination to generate very high retrograde flows, which was only found at the site of valve development, suggesting that it might be critical in this process. The extracellular matrix (ECM), and particularly fibrillar collagen, are central to heart biomechanics, regulating tissue strength, elasticity and contractility. Our studies using SHG microscopy revealed cardiac fibers, such as collagen, coinciding with areas of higher mechanical load through the earliest stages of heart development, and suggested regulatory role of heart contraction in establishment of mechanical homeostasis. To control cardiac contraction, we have established optogenetic cardiac pacing in embryos that express the light-activated, transmembrane channel—Channelrhodopsin2—only in the heart. We have integrated a pulsed 473nm laser with our lab-built optical coherence tomography system to control embryonic heart beat frequency, and generate 4D (3D+time) images of the heart to extract structural and functional information such as heart wall and blood flow velocity to validate and measure changes in heart biomechanics. Paced hearts will be imaged with SHG and image processed to determine changes in collagen content and organization due to altered contraction. This work will be the first-time use of a non-contact approach to test the consequences of altered mechanics in early heart development.
Speaker
Andrew L. Lopez, III
Baylor College of Medicine
United States of America
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