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Peroxisomes contribute to intracellular calcium dynamics in cardiomyocytes and non-excitable cells.

ABSTRACT: Peroxisomes communicate with other cellular compartments by transfer of various metabolites. However, whether peroxisomes are sites for calcium handling and exchange has remained contentious. Here we generated sensors for assessment of peroxisomal calcium and applied them for single cell-based calcium imaging in HeLa cells and cardiomyocytes. We found that peroxisomes in HeLa cells take up calcium upon depletion of intracellular calcium stores and upon calcium influx across the plasma membrane. Furthermore, we show that peroxisomes of neonatal rat cardiomyocytes and human induced pluripotent stem cell-derived cardiomyocytes can take up calcium. Our results indicate that peroxisomal and cytosolic calcium signals are tightly interconnected both in HeLa cells and in cardiomyocytes. Cardiac peroxisomes take up calcium on beat-to-beat basis. Hence, peroxisomes may play an important role in shaping cellular calcium dynamics of cardiomyocytes.

SUBMITTER: Sargsyan Y

PROVIDER: S-EPMC8326789 | biostudies-literature | 2021 Sep

REPOSITORIES: biostudies-literature

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Peroxisomes contribute to intracellular calcium dynamics in cardiomyocytes and non-excitable cells.

Sargsyan Yelena Y Bickmeyer Uta U Gibhardt Christine S CS Streckfuss-Bömeke Katrin K Bogeski Ivan I Thoms Sven S

Life science alliance 20210730 9

Peroxisomes communicate with other cellular compartments by transfer of various metabolites. However, whether peroxisomes are sites for calcium handling and exchange has remained contentious. Here we generated sensors for assessment of peroxisomal calcium and applied them for single cell-based calcium imaging in HeLa cells and cardiomyocytes. We found that peroxisomes in HeLa cells take up calcium upon depletion of intracellular calcium stores and upon calcium influx across the plasma membrane. ...[more]

PMID: 34330788

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Project description:Non-excitable cells (NECs) such as cardiac myofibroblasts that are electrotonically coupled to cardiomyocytes affect conduction velocity (?) by representing a capacitive load (CL: increased membrane to be charged) and a resistive load (RL: partial depolarization of coupled cardiomyocytes). In this study, we untangled the relative contributions of both loading modalities to NEC-dependent arrhythmogenic conduction slowing. Discrimination between CL and RL was achieved by reversibly removing the RL component by light activation of the halorhodopsin-based hyperpolarizing membrane voltage actuator eNpHR3.0-eYFP (enhanced yellow fluorescent protein) expressed in communication-competent fibroblast-like NIH3T3 cells (3T3 HR cells) that served as a model of coupled NECs. Experiments were conducted with strands of neonatal rat ventricular cardiomyocytes coated at increasing densities with 3T3 HR cells. Impulse conduction along preparations stimulated at 2.5 Hz was assessed with multielectrode arrays. The relative density of 3T3 HR cells was determined by dividing the area showing eYFP fluorescence by the area covered with cardiomyocytes [coverage factor (CF)]. Compared to cardiomyocytes, 3T3 HR cells exhibited a depolarized membrane potential (-34 mV) that was shifted to -104 mV during activation of halorhodopsin. Without illumination, 3T3 HR cells slowed ? along the preparations from ?330 mm/s (control cardiomyocyte strands) to ?100 mm/s (CF = ?0.6). Illumination of the preparation increased the electrogram amplitudes and induced partial recovery of ? at CF > 0.3. Computer simulations demonstrated that the ? deficit observed during illumination was attributable in full to the CL represented by coupled 3T3 HR cells with ? showing a power-law relationship to capacitance with an exponent of -0.78 (simulations) and -0.99 (experiments). The relative contribution of CL and RL to conduction slowing changed as a function of CF with CL dominating at CF ? ?0.3, both mechanisms being equally important at CF = ?0.5, and RL dominating over CL at CF > 0.5. The finding that RL did not affect ? at CFs ? 0.3 is explained by the circumstance that, at the respective moderate levels of cardiomyocyte depolarization, supernormal conduction stabilized propagation. The findings provide experimental estimates for the dependence of ? on membrane capacitance in general and suggest that the myocardium can absorb moderate numbers of electrotonically coupled NECs without showing substantial alterations of ?.

Project description:Deterministic models of biochemical processes at the subcellular level might become inadequate when a cascade of chemical reactions is induced by a few molecules. Inherent randomness of such phenomena calls for the use of stochastic simulations. However, being computationally intensive, such simulations become infeasible for large and complex reaction networks. To improve their computational efficiency in handling these networks, we present a hybrid approach, in which slow reactions and fluxes are handled through exact stochastic simulation and their fast counterparts are treated partially deterministically through chemical Langevin equation. The classification of reactions as fast or slow is accompanied by the assumption that in the time-scale of fast reactions, slow reactions do not occur and hence do not affect the probability of the state. Our new approach also handles reactions with complex rate expressions such as Michaelis-Menten kinetics. Fluxes which cannot be modeled explicitly through reactions, such as flux of Ca(2+) from endoplasmic reticulum to the cytosol through inositol 1,4,5-trisphosphate receptor channels, are handled deterministically. The proposed hybrid algorithm is used to model the regulation of the dynamics of cytosolic calcium ions in mouse macrophage RAW 264.7 cells. At relatively large number of molecules, the response characteristics obtained with the stochastic and deterministic simulations coincide, which validates our approach in the limit of large numbers. At low doses, the response characteristics of some key chemical species, such as levels of cytosolic calcium, predicted with stochastic simulations, differ quantitatively from their deterministic counterparts. These observations are ubiquitous throughout dose response, sensitivity, and gene-knockdown response analyses. While the relative differences between the peak-heights of the cytosolic [Ca(2+)] time-courses obtained from stochastic (mean of 16 realizations) and deterministic simulations are merely 1%-4% for most perturbations, it is specially sensitive to levels of G(βγ) (relative difference as large as 90% at very low G(βγ)).

Dataset Information

Peroxisomes contribute to intracellular calcium dynamics in cardiomyocytes and non-excitable cells.

Publications

Peroxisomes contribute to intracellular calcium dynamics in cardiomyocytes and non-excitable cells.

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