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Monitoring contractility in cardiac tissue with cellular resolution using biointegrated microlasers

Abstract

The contractility of cardiac cells is a key parameter that describes the biomechanical characteristics of the beating heart, but functional monitoring of three-dimensional cardiac tissue with single-cell resolution remains a major challenge. Here, we introduce microscopic whispering-gallery-mode lasers into cardiac cells to realize all-optical recording of transient cardiac contraction profiles with cellular resolution. The brilliant emission and high spectral sensitivity of microlasers to local changes in refractive index enable long-term tracking of individual cardiac cells, monitoring of drug administration, accurate measurements of organ-scale contractility in live zebrafish, and robust contractility sensing through hundreds of micrometres of rat heart tissue. Our study reveals changes in sarcomeric protein density as an underlying factor to cardiac contraction. More broadly, the use of novel micro- and nanoscopic lasers as non-invasive, biointegrated optical sensors brings new opportunities to monitor a wide range of physiological parameters with cellular resolution.

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Fig. 1: The principle of microlaser-based intracellular sensing in neonatal mouse cardiomyocytes.
Fig. 2: Transient redshifts of microlaser emission are caused by changes in the intracellular refractive index.
Fig. 3: Microlasers monitor cellular contractility.
Fig. 4: Single-cell tracking and contractility sensing under compromised conditions.
Fig. 5: Multimodal sensing and in vivo integration.
Fig. 6: Living myocardial slices and deep tissue contractility sensing.

Data availability

The research data underpinning this publication can be accessed at https://doi.org/10.17630/97927f1f-a111-46d0-8d41-038771733b73 (ref. 49).

Code availability

The custom-made computer code is available at https://doi.org/10.17630/97927f1f-a111-46d0-8d41-038771733b73 (ref. 49).

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Acknowledgements

We thank S. A. Sharples for assistance with the preparation of myocardial slices. This research was financially supported by the European Research Council under the European Union’s Horizon 2020 Framework Programme (FP/2014-2020)/ERC grant agreement no. 640012 (ABLASE), by EPSRC (grant no. EP/P030017/1) and by the RS Macdonald Charitable Trust. S.J.P. acknowledges funding by the Royal Society of Edinburgh (Biomedical Fellowship) and the British Heart Foundation (grant no. FS/17/9/32676). S.J.P. and G.B.R. acknowledge support from The Wellcome Trust Institutional Strategic Support Fund to the University of St Andrews (grant no. 204821/Z/16/A). M.S. acknowledges funding by the European Commission (Marie Skłodowska-Curie Individual Fellowship, 659213) and the Royal Society (Dorothy Hodgkin Fellowship, DH160102; grant no. RGF\R1\180070).

Author information

Authors and Affiliations

Authors

Contributions

M.S. designed, performed and analysed laser experiments and imaging. L.W. contributed to lasing experiments and B.C. contributed to sarcomere length measurements. I.R.M.B. and L.W. developed refractive index fitting and peak fitting software, respectively. A.M. and M.S. prepared neonatal cardiomyocyte cultures with support from G.B.M. G.B.R. prepared isolated cardiomyocytes and A.M.D. prepared cardiac slices under supervision of S.J.P. S.J.P. and M.S. designed physiological experiments in isolated cardiomyocytes and cardiac slices. C.S.T. supported the preparation of zebrafish. P.L.A. performed two-photon microscopy. M.S. and M.C.G. conceived the project and wrote the manuscript with contributions from all authors.

Corresponding authors

Correspondence to Marcel Schubert or Malte C. Gather.

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Supplementary information

Supplementary Information

Supplementary Discussion, Figs. 1–14, captions for Supplementary Videos 1–5.

Reporting Summary

Supplementary Video 1

Visualization of the data acquisition and analysis workflow. a, DIC microscopy time-lapse video of a spontaneously beating neonatal cardiomyocyte. The internalized microlaser is seen as circular object in the centre of the cell. Images were acquired with a ×60 oil immersion objective at a rate of 100 Hz. b, The WGM spectrum of the microlaser acquired simultaneously with DIC images. Dotted vertical lines mark the laser mode position at diastole. c, Centre position of the laser mode at around 519.75 nm obtained after peak fitting of the spectrum in a. d, External refractive index next calculated by the look-up table algorithm that, at each time point, compares the positions of the five laser modes shown in b to a database of simulated spectra. All panels are synchronized in time and played in real time.

Supplementary Video 2

Video-rate fluorescence microscopy of the three neonatal cardiomyocytes shown in Fig. 3d (main text). Cells were labelled with SiR-actin to visualize sarcomeric actin inside the myofibrils. The microlasers are seen as dark circular objects. Experiment performed in triplicate for a total of n = 12 cells.

Supplementary Video 3

Large field of view fluorescence video-rate microscopy of neonatal cardiomyocytes shown in Supplementary Fig. 7. Cells were labelled with SiR-actin to visualize sarcomeric actin.

Supplementary Video 4

Multimodal imaging of cellular calcium dynamics and contractility. a, Fluorescence microscopy time-lapse video of the adult cardiomyocyte shown in Fig. 5a (main text). The cell was labelled with the calcium-sensitive dye XRhod1 and images were recorded at a rate of 50 Hz. b, Smoothed external refractive index \(n_{{\mathrm{ext}}}^ \ast\) measured by a microlaser located on top of the cell. A longer time trace is shown in Supplementary Fig. 10. c, Fluorescence intensity profile normalized to the intensity at resting phase obtained from the video shown in a. All panels are synchronized in time.

Supplementary Video 5

In vivo contractility measurement by a microlaser attached to the atrium of a zebrafish embryo (3 dpf). The simultaneously acquired microlaser spectra and the calculated external refractive index are shown in Supplementary Fig. 11 and Fig. 5g (main text), respectively. A measurement performed at a more posterior position of the heart is shown in Supplementary Fig. 13.

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Schubert, M., Woolfson, L., Barnard, I.R.M. et al. Monitoring contractility in cardiac tissue with cellular resolution using biointegrated microlasers. Nat. Photonics 14, 452–458 (2020). https://doi.org/10.1038/s41566-020-0631-z

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