Robertson, G. B. | bioRxiv Science

bioRxiv2024

Knock out of the intracellular calcium conducting ion channel Mitsugumin 23 (MG23) protects against pressure overload induced left ventricular hypertrophy and cardiac dysfunction.

BackgroundIn cardiac dysfunction, intracellular Ca2+-dynamics are disrupted leading to leakage of Ca2+ from the sarcoplasmic reticulum (SR). This results in diminished cardiac contractility and impaired cardiac function. In cardiac tissue, the underlying molecular mechanisms responsible for RyR2-independent Ca2+ leak are poorly understood. Mitsugumin 23 (MG23) is an intracellular Ca2+-conducting ion channel located on ER/SR and nuclear membranes. We propose that MG23 contributes to regulation of intracellular Ca2+-homeostasis, and that altered MG23 function may drive progression of cardiac dysfunction. The aim of this research was to investigate the role of MG23 in SR Ca2+ leak, and whether knock out of Mg23 protects the heart against pressure-overload induced left ventricular hypertrophy. MethodsCardiac pressure-overload was induced in wild type (WT) and Mg23-knock out (KO) mice through subcutaneous Angiotensin II (AngII, 1.1 mg/kg/day) infusion via osmotic pump. After 10-days infusion, in vivo pressure-volume dynamics were measured by insertion of a pressure-volume catheter into the left ventricle. MG23 protein expression was assessed through Western blot analysis. Ventricular fibrosis and cardiomyocyte size were measured using histological and immunofluorescence approaches. Cardiomyocytes were isolated from WT and Mg23-KO hearts and intracellular Ca2+ dynamics assessed through live cell imaging using the Ca2+ indicator Fluo-4. ResultsAngII-induced cardiac pressure-overload increased expression of MG23 in WT mouse hearts. Knock out of Mg23 protected hearts against AngII-induced cardiac hypertrophy. Compared to WT animals, AngII treated Mg23-KO mice displayed a significant reduction in left ventricular fibrosis and displayed normal cardiac functioning. In Mg23-KO hearts, no alteration in expression of key Ca2+ handling proteins was identified, but cardiomyocytes displayed altered Ca2+ spark profiles consistent with a role for MG23 in SR Ca2+ leak. ConclusionMG23 plays a key role in driving Ca2+ dysregulation observed in the early pathological stages of pressure-overload induced heart failure.

physiology↗

bioRxiv2019

Monitoring contractility in single cardiomyocytes and whole hearts with bio-integrated microlasers

Cardiac regeneration and stem cell therapies depend critically on the ability to locally resolve the contractile properties of heart tissue1,2. Current regeneration approaches explore the growth of cardiac tissue in vitro and the injection of stem cell-derived cardiomyocytes3-6 (CMs) but scientists struggle with low engraftment rates and marginal mechanical improvements, leaving the estimated 26 million patients suffering from heart failure worldwide without effective therapy7-9. One impediment to further progress is the limited ability to functionally monitor injected cells as currently available techniques and probes lack speed and sensitivity as well as single cell specificity. Here, we introduce microscopic whispering gallery mode (WGM) lasers into beating cardiomyocytes 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, and accurate measurements of organ scale contractility in live zebrafish. Our study reveals changes in sarcomeric protein density as underlying factor to cardiac contraction which is of fundamental importance for understanding the mechano-biology of cardiac muscle activation. The ability to non-invasively assess functional properties of transplanted cells and engineered cardiac tissue will stimulate the development of novel translational approaches and the in vivo monitoring of physiological parameters more broadly. Likewise, the use of implanted microlasers as cardiac sensors is poised to inspire the adaptation of the most advanced optical tools known to the microresonator community, like quantum-enhanced single-molecule biosensing or frequency comb spectroscopy10.

biophysics↗