Short Communication - Current Trends in Cardiology (2021) Volume 5, Issue 1

Optogenetic cardiac pacing and its applications

Airong Li^*, Rudolph E Tanzi^*

Department of Neurology, Genetics and Aging Research Unit, Massachusetts General Hospital and Harvard Medical School, Charlestown MA, United States

Corresponding Author:

Airong Li
Department of Neurology
Genetics and Aging Research Unit
Massachusetts General Hospital and Harvard Medical School
Charlestown MA, United States
E-mail: ali3@mgh.harvard.edu
Rudolph E. Tanzi
Department of Neurology
Genetics and Aging Research Unit
Massachusetts General Hospital and Harvard Medical School
Charlestown MA, United States
E-mail: rtanzi@mgh.harvard.edu

Accepted date: 04 January, 2021

Citation: Li A, Tanzi RE. Optogenetic cardiac pacing and its applications. Curr Trend Cardiol. 2021;5(1):1-4.

Abstract

Optogenetics combines the biological techniques of optics and genetics and uses light to control the activities of living tissues such as neurons and heart. Optogenetic actuators including channelrhodopsin (ChR), halorhodopsin (NpHR), and archaerhodopsin specifically provide for neuronal or cardiac controls. The clinical translation of cardiac optogenetics will include human and larger mammalian animal model applications and ultimately optogenetics may have the power to restore normal heart rhythm.

Keywords

Optogenetic cardiac pacing, Heart rhythm, Cardiac control.

Optogenetic Cardiac Pacing

Optogenetics uses light to control the activities of living tissues such as neurons and heart as a new biological technique that combines optics and genetics. Optical coherence tomography (OCT) can provide novel three-dimensional (3D) imaging [1-3] and when combined with OCT, optical coherence microscopy (OCM) provides high resolution imaging [4-10] that are 50 x-100 x greater than conventional ultrasound, MRI, or CT. OCT systems have already been successfully used in interventional cardiology [11], ophthalmology and optometry [12] and dermatology [13].

Optogenetic actuators including channelrhodopsin (ChR), halorhodopsin (NpHR), and archaerhodopsin can provide neuronal or cardiac control (bacterio-opsin) [14-15]. ChRs are sensory photoreceptors (rhodopsins) while NpHR is a chloride ion-specific light-gated ion and archaerhodopsin is the bacterio-opsin family of receptor proteins [16-22].

Optogenetics was named the Method of the Year 2010 and the "Breakthroughs of the Decade” by the research journals Nature Methods and Science, respectively (https://www.medinc.co.uk/ optogenetics-breakthrough-of-the-decade-by-dr-zulfiquar/). In 2015 the first Drosophila heart study using OCT was reported on the Discovery channel and in the Boston Globe (Light-powered hearts? https://www.bostonglobe.com/lifestyle/2015/10/25/lightpowered- hearts/ETWV7DZU6pwMNm1P59TLGL/story.html).

Drosophila Heart in Optogenetic Pacing

Marked morphological and functional changes in the Drosophila heart during development were observed in a longitudinal study. In the pupal stage the heartbeat is reduced dramatically and stops beating during pupae. A circadian clock gene dCry was shown to affect heart development and functioning [23].

An optogenetic pacing system has clearly showed mCherry fluorescence signal in the heart of a ChR₂-mCherry transgenic fly compared to a wild-type control fly [24]. Successful optogenetic pacing of ChR₂-expressing Drosophila at different developmental stages was shown [25].

Red light increases the excitability of the heart tissue and flies expressing ReaChR. Optogenetic fly models were able to be tachypaced under red light stimulation [26,27].

Cardiac Arrhythmia by Optogenetic Pacing

Optogenetics can treat cardiac arrhythmias [28]. Several experimental models showed photosensitive ion channels and pumps (opsins) by optogenetic pacing of cardiac preparations and the opsins can precisely stimulate or silence electrophysiological activity in cardiac cells [29]. Cardiomycytes that express ChR₂ can sensitively activate Ca²⁺ signaling properties [30] and transgenic mice expressing ChR₂ can control heart muscles in vivo. Stimulation of Gs-signaling by optogenetics showed a light sensitive Gs-protein coupled receptor in mice cardiac tissue [31]. Cardiac excitable media demonstrated in heart precisely to influence cardiac function and overall dynamics [32]. Near-infrared (NIR) light has the ability to penetrate tissue and therefore has the potential to manipulate cardiovascular diseases non-invasively [33]. Greater tissue depths are achieved with the red-shifted opsins than conventional bluesensitive channel-rhodopsins. Taken together these studies have increased our understanding of cardiac physiology.

Electronic device therapy (i.e., implantable pacemakers and cardioverter-defibrillators [ICDs]) largely provide the basis for current management of cardiac arrhythmias [34]. Arrhythmias such as atrial fibrillation (AF) can be treated by rapid antitachycardia pacing [35]. Mice cardiomyocytes showed electric shock functions in electrical defibrillation and elderly humans and Drosophila may similarly significantly reduce heart rate via electrical pacing [36- 39]. Rhythm disturbances were associated with an increase in age and light intensity was associated with NpHR stopping the heart rate in Drosophila [40,41].

Glutamatergic neurons provide extensive innervation to the adult heart in Drosophila metamorphosis. Pacemaker action potentials were demonstrated in muscles of the first abdominal cardiac chamber [42]. KCNQ₁ mutant Drosophila showed abnormal contractions and fibrillations and KCNQ₁ in humans is related to myocardial repolarization [43].

Drosophila genetic screens identify genes related to their functions. EGFR signaling regulates adult cardiac function while mutants in a fly orthologue of epidermal growth factor (EGF) rhomboid 3 have enlarged cardiac chambers and the Notch ortholog weary (wry) is associated with dilated cardiomyopathy [44,45]. Insulin-IGF receptor signaling showed regulation of age-dependent changes in cardiac function [46].

Chronic stability and excellent biocompatibility were achieved in small animals through multimodal and multisite pacing studies [47]. Direct viral delivery and functionality of opsins in cardiomyocytes has been demonstrated in vitro. A cell line can stably express the excitatory opsin, ChR₂ in vitro between the ChR₂-expressing donor cells and host cardiomyocytes [48]. Expression of the light activated ChR₂ can stimulate heart muscle in vitro and in mice demonstrated precise localized stimulation, constant prolonged depolarization of cardiomyocytes and cardiac tissue, Ca²⁺ homeostasis, electrical coupling and arrhythmogenic spontaneous extrabeats [49]. The delivery of ChR₂ transgene to several ventricular sites by diffuse illumination of hearts resulted in electrical synchronization and significant shortening of ventricular activation times [50]. Cardiac nonmyocytes in mouse hearts showed myocyte AP-like signals in cryoinjured scar border tissue indicating direct evidence of effects of heterocellular electrotonic coupling in the whole heart on cardiac electrical connectivity [51]. A high vulnerability to tachycardia of optically tachypaced human induced pluripotent stem-cardiomyocytes in 3D engineered heart tissue can be effectively terminated by ryanodine receptor stabilization, sodium or potassium channel inhibition [52]. Cultured mouse embryos showed optogenetic pacing with 4D (3D+time) OCT structural and Doppler imaging, which demonstrated that embryonic hearts can provide function efficiently and produce strong blood flows. Expressing the Channelrhodopsin-2 (ChR₂) transgene at one or more ventricular sites in rats allowed optogenetic pacing of the hearts at different beating frequencies with blue-light illumination.

OCT and its Clinical Applications in Heart

OCT requires optical stimulation to be delivered safely and with long-term efficiency. OCT can assess coronary vasculature in cardiovascular medicine and several clinical systems have become commercially available. Patients who have stable coronary artery disease can be assisted by OCT for a msore detailed lumen segmentation. On the other hand, in patients with acute coronary syndrome, OCT can offer 100% detection of intraluminal thrombus with in comparison to coronary angioscopy which detected plaques in 79% and stenosis in 24% of patients [53-57].

Optogenetics in the Future

The optogenetics field has made significant progress in heart research from its inception almost a decade ago. The clinical translation of cardiac optogenetics for human application is moving towards use as a tool in larger mammalian animal models [58]. Optogenetics may restore normal heart rhythm to increase the overall quality of life and action potential duration of ChR₂-or NpHR can be modulated in opsin-expressing rat cardiomyocytes [59-61]. Optogenetics may potentially have a therapeutic role in treating heart diseases.

Drosophila genetic screens using OCT can identify additional cardiovascular-related genes and assess pre-clinical drug development cardiotoxicity, which account for approximately 20% of withdrawal of drugs from development [62-63]. Cardiotoxicity measures by electrophysiology are often low throughput and efficient high throughput screening tools that significantly reduce cost are needed. Overall, optogenetics is high throughput and automated tool for use in evaluating cardiotoxicity.

Acknowledgment

This work was supported by the NIH (R01HL156265, R15EB019704, R03AR063271 to A.L., and R01AG014713 and R01MH060009 to R.E.T., the NSF1455613 to A.L.), the Cure Alzheimer’s Fund (to R.E.T.).

Competing Interests

None

References

1. Huang D, Swanson EA, Lin CP, et al. Optical Coherence Tomography. Science. 1991; 254(5035):1178-81.
2. Fujimoto JG, Pitris C, Boppart SA, et al. Optical coherence tomography: An emerging technology for biomedical imaging and optical biopsy. Neoplasia.2000; 2(1-2):9-25.
3. Fujimoto JG. Optical coherence tomography for ultrahigh resolution in vivo imaging. Nat Biotechnol. 2003; 21(11):1361-7.
4. Izatt JA, Hee MR, Owen GM, et al. Optical coherence microscopy in scattering media. Opt Lett. 1994; 19(8):590-2.
5. Kempe M, Thon A, Rudolph W, et al. Resolution Limits of Microscopy through Scattering Layers. Optics Communications. 1994; 110(5-6):492-6.
6. Izatt JA, Kulkarni MD, Wang HW, et al. Optical coherence tomography and microscopy in gastrointestinal tissues. IEEE Journal of Selected Topics in Quantum Electronics 1996; 2(4):1017-28.
7. Kempe M, Rudolph W. Analysis of heterodyne and confocal microscopy for illumination with broad-bandwidth light. Journal of Modern Optics. 1996; 43(10): 2189-04.
8. Kempe M, Rudolph W, Welsch E. Comparative study of confocal and heterodyne microscopy for imaging through scattering media. Journal of the Optical Society of America A. 1996; 13(1):46-52.
9. Clark AL, Gillenwater A, Alizadeh-Naderi, R, et al. Detection and diagnosis of oral neoplasia with an optical coherence microscope. J Biomed Opt. 2004; 9(6):1271-80.
10. Aguirre AD, Hsiung P, Ko TH, et al. High-resolution optical coherence microscopy for high-speed, in vivo cellular imaging. Optics Letters. 2003; 28(21): 2064-66.
11. Yonetsu T, Kakuta T, Lee T, et al. Assessment of acute injuries and chronic intimal thickening of the radial artery after transradial coronary intervention by optical coherence tomography. Eur Heart J. 2010; 31(13):1608-15.
12. Povazay B, Hermann B, Hofer B, et al. Wide-field optical coherence tomography of the choroid in vivo. Invest Ophthalmol Vis Sci. 2009; 50(4):1856-63.
13. Ulrich M, Themstrup L, de Carvalho N, et al. Dynamic optical coherence tomography in dermatology. Dermatology. 2016; 232(3):298-311.
14. Nagel G, Ollig D, Fuhrmann M, et al. Channelrhodopsin-1: A light-gated proton channel in green algae. Science. 2002; 296 (5577):2395-8.
15. Zhang F, Wang LP, Brauner M, et al. Multimodal fast optical interrogation of neural circuitry. Nature. 2007; 446 (7136):633-9
16. Han X, Boyden ES. Multiple-color optical activation, silencing, and desynchronization of neural activity, with single-spike temporal resolution. PLOS One. 2007; 2(3):e299.
17. Gradinaru V, Thompson KR, Deisseroth K, et al. eNpHR: A Natronomonas halorhodopsin enhanced for optogenetic applications. Brain Cell Biol. 2008; 36(1-4): 129-39.
18. Gradinaru V, Mogri M, Thompson KR, et al. Optical deconstruction of parkinsonian neural circuitry. Science. 2009; 324(5925):354-9.
19. Inoue K, Ito S, Kato Y, et al. A natural light-driven inward proton pump. Nature Communications. 2016; 7:13415.
20. Kralj JM, Douglass AD, Hochbaum DR, et al. Optical recording of action potentials in mammalian neurons using a microbial rhodopsin. Nat Methods. 2011; 9 (1): 90-5.
21. El-Gaby M, Zhang Y, Wolf K, et al. Archaerhodopsin selectively and reversibly silences synaptic transmission through altered pH. Cell Rep. 2016; 16 (8):2259-68.
22. Enami N, Yoshimura K, Murakami M, et al. Crystal structures of archaerhodopsin-1 and -2: Common structural motif in archaeal light-driven proton pumps. J Mol Biol. 2006; 358(3):675-85.
23. Alex A, Li A, Zeng X, et al. A Circadian Clock Gene, Cry, Affects heart morphogenesis and function in drosophila as revealed by optical coherence microscopy. PLOSOne. 2015; 10 (9):e0137236.
24. Alex A, Li A, Tanzi RE, et al. Optogenetic pacing in Drosophila melanogaster. Sci Adv. 2015; 1(9):e1500639.
25. Jing M, Li A, Jerwick J, et al. Non-invasive red-light optogenetic control of Drosophila cardiac function. Commun Biol. 2020; 3(1):336.
26. Zhao D, Jerwick J, Airong Li, et al. FlyNet 2.0: Drosophila heart 3D (2D + time) segmentation in optical coherence microscopy images using a convolutional long short-term memory neural network. Biomedical Opt Express. 2020; 11(3):1568–79.
27. Jiang C, Li HT, Zhou YM, et al. Cardiac optogenetics: a novel approach to cardiovascular disease therapy. Europace. 2018; 20 (11):1741-9.
28. O'Shea C, Holmes AP, Winter J, et al. Cardiac optogenetics and optical mapping-overcoming spectral congestion in all-optical cardiac electrophysiology. Front Physiol. 2019; 10:182
29. Ferenczi EA, Tan X, Huang CL, et al. Principles of optogenetic methods and their application to cardiac experimental systems. Front Physiol. 2019; 10:1096.
30. Makowka P, Bruegmann T, Dusend V, et al. Optogenetic stimulation of Gs-signaling in the heart with high spatio-temporal precision. Nat Commun. 2019; 10(1): 1281.
31. Steinbeck JA, Choi SJ, Mrejeru A, et al. Optogenetics enables functional analysis of human embryonic stem cell-derived grafts in a Parkinson's disease model. Nat Biotechnol. 2015; 33(2):204-9.
32. Rao P, Wang L, Cheng Y, et al. Near-infrared light driven tissue-penetrating cardiac optogenetics via upconversion nanoparticles in vivo. Biomed Opt Express. 202; 11 (3):1401-16
33. Ambrosi CM, Entcheva E. Optogenetics' promise: Pacing and cardioversion by light? Future Cardiol. 2014; 10(1):1-4.
34. Adgey AAJ, Spence MS, Walsh SJ, et al. Theory and practice of defibrillation: Defibrillation for ventricular fibrillation. Heart. 2005; 91(1):118-25.
35. Crocini C, Ferrantini C, Coppini R, et al. Optogenetics design of mechanistically-based stimulation patterns for cardiac defibrillation. Sci Rep. 2016; 6: 35628
36. Burton RAB, Klimas A, Ambrosi CM, et al. Optical control of excitation waves in cardiac tissue. Nat Photonics. 2015; 9(12):813-16.
37. Majumder R, Feola I, Teplenin AS, et al. Optogenetics enables real-time spatiotemporal control over spiral wave dynamics in an excitable cardiac system. Elife. 2018; 7:e41076
38. Bingen BO, Engels MC, Schalij MJ, et al. Light-induced termination of spiral wave arrhythmias by optogenetic engineering of atrial cardiomyocytes. Cardiovasc Res. 2014; 104(1):194-205.
39. Paternostro G, Vignola C, Bartsch DU, et al. Age-associated cardiac dysfunction in Drosophila melanogaster. Circ Res. 2001; 88(10):1053-8.
40. Stanley CE, Mauss AS, Borst A, et al. The Effects of Chloride Flux on Drosophila Heart Rate. Methods Protoc. 2019; 2(3):73.
41. Dulcis D, Levine RB. Glutamatergic innervation of the heart initiates retrograde contractions in adult Drosophila melanogaster. J Neurosci. 2005; 25(2): 271-80.
42. Ocorr K, Reeves NL, Wessells RJ, et al. KCNQ potassium channel mutations cause cardiac arrhythmias in Drosophila that mimic the effects of aging. Proc Natl Acad Sci U S A. 2007; 104 (10):3943-8.
43. Yu L, Lee T, Lin N, et al. Affecting Rhomboid-3 function causes a dilated heart in adult Drosophila. PLOSGenet. 2010; 6(5):e1000969.
44. Kim IM, Wolf MJ, Rockman HA, et al. Gene deletion screen for cardiomyopathy in adult Drosophila identifies a new notch ligand. Circ Res. 2010; 106 (7):1233-43.
45. Luong N, Davies CR, Wessells RJ, et al. Activated FOXO-mediated insulin resistance is blocked by reduction of TOR activity. Cell Metab. 2006; 4 (2):133-42.
46. Gutruf P, Yin RT, Lee KB, et al. Wireless, battery-free, fully implantable multimodal and multisite pacemakers for applications in small animal models. Nat Commun. 2019;10 (1):5742.
47. Lopez AL, Wang S, Larina IV, et al. Optogenetic cardiac pacing in cultured mouse embryos under imaging guidance. J Biophotonics. 2020; 13 (11):e202000223.
48. Bruegmann T, Malan D, Hesse M, et al. Optogenetic control of heart muscle in vitro and in vivo. Nat Methods. 2010; 7 (11):897-900.
49. Nussinovitch U, Gepstein L. Optogenetics for in vivo cardiac pacing and resynchronization therapies. Nat Biotechnol. 2015; 33 (7):750-4.
50. Quinn TA, Camelliti P, Rog-Zielinska EA, et al. Electrotonic coupling of excitable and nonexcitable cells in the heart revealed by optogenetics. Proc Natl Acad Sci USA. 2016; 113 (51):14852-7.
51. Lemme M, Braren I, Prondzynski M, et al. Chronic intermittent tachypacing by an optogenetic approach induces arrhythmia vulnerability in human engineered heart tissue. Cardiovasc Res. 2020; 116 (8):1487-99.
52. Chamie D, Bezerra HG, Attizzani GF, et al. Incidence, predictors, morphological characteristics, and clinical outcomes of stent edge dissections detected by optical coherence tomography. JACC Cardiovasc Interv. 2013; 6(8):800-13.
53. Bezerra HG, Attizzani GF, Sirbu V, et al. Optical coherence tomography versus intravascular ultrasound to evaluate coronary artery disease and percutaneous coronary intervention. JACC Cardiovasc Interv. 2013; 6(3):228-36.
54. Fujino Y, Bezerra HG, Attizzani GF, et al. Frequency-domain optical coherence tomography assessment of unprotected left main coronary artery disease-a comparison with intravascular ultrasound. Catheter Cardiovasc Interv. 2013; 82 (3): E173-83.
55. Terashima M, Kaneda H, Suzuki T, et al. The Role of Optical Coherence Tomography in Coronary Intervention. Korean J Intern Med. 2012; 27(1):1–12.
56. Saito Y, Kobayashi Y. Update on Antithrombotic Therapy after Percutaneous Coronary Intervention. Intern Med. 2020; 59(3):311-21.
57. Boyle PM, Karathanos TV, Trayanova NA. Cardiac Optogenetics: 2018. JACC Clin Electrophysiol. 2018; 4(2):155-67.
58. Van Weerd JH, Christoffels VM. The formation and function of the cardiac conduction system. Development. 2016; 143(2):197-210.
59. Joshi J, Rubart M, Zhu W, et al. Optogenetics: Background, Methodological Advances and Potential Applications for Cardiovascular Research and Medicine. Front Bioeng Biotechnol. 2019; 7:466.
60. Park SA, Lee SR, Tung L, et al. Optical mapping of optogenetically shaped cardiac action potentials. Sci Rep. 2014; 4:6125.
61. Piccini JP, Whellan DJ, Berridge BR, et al. Current challenges in the evaluation of cardiac safety during drug development: Translational medicine meets the Critical Path Initiative. Am Heart J. 2009; 158(3):317-26.
62. Klimas A, Ambrosi CM, Yu J, et al. OptoDyCE as an automated system for high-throughput all-optical dynamic cardiac electrophysiology. Nat Commun. 2016; 7:11542.
63. Entcheva E, Bub G. All-optical control of cardiac excitation: Combined high-resolution optogenetic actuation and optical mapping. J Physiol. 2016; 594 (9):2503-10.