1. Loss of autophagy protein ATG5 impairs cardiac capacity in mice and humans through diminishing mitochondrial abundance and disrupting Ca2+ cyclingSenka Ljubojevic-Holzer, Simon Kraler, Nataša Djalinac, Mahmoud Abdellatif, Julia Voglhuber, Julia Schipke, Marlene Schmidt, Katharina-Maria Kling, Greta Therese Franke, Viktoria Herbst, Simon Sedej, 2022, original scientific article Abstract: Aims: Autophagy protects against the development of cardiac hypertrophy and failure. While aberrant Ca2+ handling promotes myocardial remodelling and contributes to contractile dysfunction, the role of autophagy in maintaining Ca2+ homeostasis remains elusive. Here, we examined whether Atg5 deficiency-mediated autophagy promotes early changes in subcellular Ca2+ handling in ventricular cardiomyocytes, and whether those alterations associate with compromised cardiac reserve capacity, which commonly precedes the onset of heart failure.
Methods and results: RT-qPCR and immunoblotting demonstrated reduced Atg5 gene and protein expression and decreased abundancy of autophagy markers in hypertrophied and failing human hearts. The function of ATG5 was examined using cardiomyocyte-specific Atg5-knockout mice (Atg5-/-). Before manifesting cardiac dysfunction, Atg5-/- mice showed compromised cardiac reserve in response to β-adrenergic stimulation. Consequently, effort intolerance and maximal oxygen consumption were reduced during treadmill-based exercise tolerance testing. Mechanistically, cellular imaging revealed that Atg5 deprivation did not alter spatial and functional organization of intracellular Ca2+ stores or affect Ca2+ cycling in response to slow pacing or upon acute isoprenaline administration. However, high-frequency stimulation exposed stunted amplitude of Ca2+ transients, augmented nucleoplasmic Ca2+ load, and increased CaMKII activity, especially in the nuclear region of hypertrophied Atg5-/- cardiomyocytes. These changes in Ca2+ cycling were recapitulated in hypertrophied human cardiomyocytes. Finally, ultrastructural analysis revealed accumulation of mitochondria with reduced volume and size distribution, meanwhile functional measurements showed impaired redox balance in Atg5-/- cardiomyocytes, implying energetic unsustainability due to overcompensation of single mitochondria, particularly under increased workload.
Conclusion: Loss of cardiac Atg5-dependent autophagy reduces mitochondrial abundance and causes subtle alterations in subcellular Ca2+ cycling upon increased workload in mice. Autophagy-related impairment of Ca2+ handling is progressively worsened by β-adrenergic signalling in ventricular cardiomyocytes, thereby leading to energetic exhaustion and compromised cardiac reserve.
Keywords: autophagy, beta-adrenergic signalling, calcium, cardiomyocytes, mitochondria
Published in DKUM: 26.09.2024; Views: 0; Downloads: 2
 Full text (1,87 MB)
This document has many files! More... |
2. Progressive glucose stimulation of islet beta cells reveals a transition from segregated to integrated modular functional connectivity patternsRene Markovič, Andraž Stožer, Marko Gosak, Jurij Dolenšek, Marko Marhl, Marjan Rupnik, 2015, original scientific article Abstract: Collective beta cell activity in islets of Langerhans is critical for the supply of insulin within an organism. Even though individual beta cells are intrinsically heterogeneous, the presence of intercellular coupling mechanisms ensures coordinated activity and a well-regulated exocytosis of insulin. In order to get a detailed insight into the functional organization of the syncytium, we applied advanced analytical tools from the realm of complex network theory to uncover the functional connectivity pattern among cells composing the intact islet. The procedure is based on the determination of correlations between long temporal traces obtained from confocal functional multicellular calcium imaging of beta cells stimulated in a stepwise manner with a range of physiological glucose concentrations. Our results revealed that the extracted connectivity networks are sparse for low glucose concentrations, whereas for higher stimulatory levels they become more densely connected. Most importantly, for all ranges of glucose concentration beta cells within the islets form locally clustered functional sub-compartments, thereby indicating that their collective activity profiles exhibit a modular nature. Moreover, we show that the observed non-linear functional relationship between different network metrics and glucose concentration represents a well-balanced setup that parallels physiological insulin release.
Keywords: endocrinology, computational biophysics, calcium signalling, biological physics
Published in DKUM: 23.06.2017; Views: 1467; Downloads: 353
Full text (957,14 KB)
This document has many files! More... |
3. Selective regulation of protein activity by complex Ca[sup]2+ oscillations : a theoretical studyBeate Knoke, Marko Marhl, Stefan Schuster, 2007, independent scientific component part or a chapter in a monograph Abstract: Calcium oscillations play an important role in intracellular signal transduction. As a second messenger, ▫$Ca^{2+}$▫ represents a link between several input signals and several target processes in the cell. Whereas the frequency of simple ▫$Ca^{2+}$▫ oscillations enables a selective activation of a specific protein and herewith a particular process, the question arises of how at the same time two or more classes of proteins can be specifically regulated. The question is general and concerns the problem of how one second messenger can transmit more than one signal simultaneously (bow-tie structure of signalling). To investigate whether a complex ▫$Ca^{2+}$▫ signal like bursting, a succession of low-peak and high-peak oscillatory phases, could selectively activate different proteins, several bursting patterns with simplified square pulses were applied in a theoretical model. The results indicate that bursting ▫$Ca^{2+}$▫ oscillations allow a differential regulation of two different calcium-binding proteins, and hence, perform the desired function.
Keywords: biophysics, calcium oscillations, cellular dynamics, mathematical models, signalling, bow-tie structures, bursting, decoding
Published in DKUM: 07.06.2012; Views: 2022; Downloads: 39
 Link to full text |
4. Spatio-temporal modelling explains the effect of reduced plasma membrane Ca[sup]2+[/sup] efflux on intracellular Ca[sup]2+[/sup] oscillations in hepatocytesMarko Marhl, Marko Gosak, Matjaž Perc, C. Jane Dixon, Anne K. Green, 2008, original scientific article Abstract: In many non-excitable eukaryotic cells, including hepatocytes, ▫$Ca^{2+}$▫ oscillations play a key role in intra- and intercellular signalling, thus regulating many cellular processes from fertilisation to death. Therefore, understanding the mechanisms underlying these oscillations, and consequently understanding how they may be regulated, is of great interest. In this paper, we study the influence of reduced ▫$Ca^{2+}$▫ plasma membrane efflux on ▫$Ca^{2+}$▫ oscillations in hepatocytes. Our previous experiments with carboxyeosin show that a reduced plasma membrane ▫$Ca^{2+}$▫ efflux increases the frequency of ▫$Ca^{2+}$▫ oscillations, but does not affect the duration of individual transients. This phenomenon can be best explained by taking into account not only the temporal,but also the spatial dynamics underlying the generation of ▫$Ca^{2+}$▫ oscillations in the cell. Here we divide the cell into a grid of elements and treat the ▫$Ca^{2+}$▫ dynamics as a spatio-temporal phenomenon. By converting an existing temporal model into a spatio-temporal one, we obtain theoretical predictions that are in much better agreement with the experimental observations.
Keywords: cellular signalling, calcium oscillations, intracellular oscilations, spatio-temporal dynamics, hepatocytes, stochastic simulations
Published in DKUM: 07.06.2012; Views: 1651; Downloads: 55
Link to full text |
