Background: The molecular contributors of the mitochondrial Ca2+ uptake, which is essential for metabolism-secretion coupling in β-cells, are unknown.Results: Knockdown of MICU1 and MCU reduced agonist- and depolarization-induced mitochondrial Ca2+ sequestration, ATP production, and d-glucose-stimulated insulin secretion.Conclusion: MICU1 and MCU are integral to metabolism-secretion coupling in β-cells.Significance: The presented data identify MICU1 and MCU as important contributors to pancreatic β-cell function.

Background/Aims: Resveratrol and its derivate piceatannol are known to induce cancer cell-specific cell death. While multiple mechanisms of actions have been described including the inhibition of ATP synthase, changes in mitochondrial membrane potential and ROS levels, the exact mechanisms of cancer specificity of these polyphenols remain unclear. This paper is designed to reveal the molecular basis of the cancer-specific initiation of cell death by resveratrol and piceatannol. Methods: The two cancer cell lines EA.hy926 and HeLa, and somatic short-term cultured HUVEC were used. Cell viability and caspase 3/7 activity were tested. Mitochondrial, cytosolic and endoplasmic reticulum Ca²⁺ as well as cytosolic and mitochondrial ATP levels were measured using single cell fluorescence microscopy and respective genetically-encoded sensors. Mitochondria-ER junctions were analyzed applying super-resolution SIM and ImageJ-based image analysis. Results: Resveratrol and piceatannol selectively trigger death in cancer but not somatic cells. Hence, these polyphenols strongly enhanced mitochondrial Ca²⁺ uptake in cancer exclusively. Resveratrol and piceatannol predominantly affect mitochondrial but not cytosolic ATP content that yields in a reduced SERCA activity. Decreased SERCA activity and the strongly enriched tethering of the ER and mitochondria in cancer cells result in an enhanced MCU/Letm1-dependent mitochondrial Ca²⁺ uptake upon intracellular Ca²⁺ release exclusively in cancer cells. Accordingly, resveratrol/piceatannol-induced cancer cell death could be prevented by siRNA-mediated knock-down of MCU and Letm1. Conclusions: Because their greatly enriched ER-mitochondria tethering, cancer cells are highly susceptible for resveratrol/piceatannol-induced reduction of SERCA activity to yield mitochondrial Ca²⁺ overload and subsequent cancer cell death.

Recent studies revealed that mitochondrial Ca2+ channels, which control energy flow, cell signalling and death, are macromolecular complexes that basically consist of the pore-forming mitochondrial Ca2+ uniporter (MCU) protein, the essential MCU regulator (EMRE), and the mitochondrial Ca2+ uptake 1 (MICU1). MICU1 is a regulatory subunit that shields mitochondria from Ca2+ overload. Before the identification of these core elements, the novel uncoupling proteins 2 and 3 (UCP2/3) have been shown to be fundamental for mitochondrial Ca2+ uptake. Here we clarify the molecular mechanism that determines the UCP2/3 dependency of mitochondrial Ca2+ uptake. Our data demonstrate that mitochondrial Ca2+ uptake is controlled by protein arginine methyl transferase 1 (PRMT1) that asymmetrically methylates MICU1, resulting in decreased Ca2+ sensitivity. UCP2/3 normalize Ca2+ sensitivity of methylated MICU1 and, thus, re-establish mitochondrial Ca2+ uptake activity. These data provide novel insights in the complex regulation of the mitochondrial Ca2+ uniporter by PRMT1 and UCP2/3.

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Transforming growth factor-β (TGF-β) is a common mediator of cancer progression and fibrosis. Fibrosis can be a significant pathology in multiple organs, including the heart. In this review, we explain how inhibitors of TGF-β signaling can work as antifibrotic therapy. After cardiac injury, profibrotic mediators such as TGF-β, angiotensin II, and endothelin-1 simultaneously activate cardiac fibroblasts, resulting in fibroblast proliferation and migration, deposition of extracellular matrix proteins, and myofibroblast differentiation, which ultimately lead to the development of cardiac fibrosis. The consequences of fibrosis include a wide range of cardiac disorders, including contractile dysfunction, distortion of the cardiac structure, cardiac remodeling, and heart failure. Among various molecular contributors, TGF-β and its signaling pathways which play a major role in carcinogenesis are considered master fibrotic mediators. In fact, recently the inhibition of TGF-β signaling pathways using small molecule inhibitors, antibodies, and gene deletion has shown that the progression of several cancer types was suppressed. Therefore, inhibitors of TGF-β signaling are promising targets for the treatment of tissue fibrosis and cancers. In this review, we discuss the molecular mechanisms of TGF-β in the pathogenesis of cardiac fibrosis and cancer. We will review recent in vitro and in vivo evidence regarding antifibrotic and anticancer actions of TGF-β inhibitors. In addition, we also present available clinical data on therapy based on inhibiting TGF-β signaling for the treatment of cancers and cardiac fibrosis.

Mitochondrial Ca2+ uptake is a vital process that controls distinct cell and organelle functions. Mitochondrial calcium uptake 1 (MICU1) was identified as key regulator of the mitochondrial Ca2+ uniporter (MCU) that together with the essential MCU regulator (EMRE) forms the mitochondrial Ca2+ channel. However, mechanisms by which MICU1 controls MCU/EMRE activity to tune mitochondrial Ca2+ signals remain ambiguous. Here we established a live-cell FRET approach and demonstrate that elevations of cytosolic Ca2+ rearranges MICU1 multimers with an EC50 of 4.4 μM, resulting in activation of mitochondrial Ca2+ uptake. MICU1 rearrangement essentially requires the EF-hand motifs and strictly correlates with the shape of cytosolic Ca2+ rises. We further show that rearrangements of MICU1 multimers were independent of matrix Ca2+ concentration, mitochondrial membrane potential, and expression levels of MCU and EMRE. Our experiments provide novel details about how MCU/EMRE is regulated by MICU1 and an original approach to investigate MCU/EMRE activation in intact cells.

Although the cardioprotective effects of glucagon-like peptide-1 and its analogs have been reported, the exact mechanisms of the glucagon-like peptide-1 receptor (GLP-1R) signaling pathway in the heart are still unclear. Activation of the GLP-1R has been shown to increase cAMP levels, thus eliciting protein kinase A- and exchange protein activated by cAMP (Epac)-dependent signaling pathways in pancreatic β-cells. However, which pathway plays an important role in the antioxidant and antiapoptotic effects of GLP-1R activation in the heart is not known. In this study, we demonstrated that stimulation of GLP-1Rs with exendin-4 attenuated H2O2-induced reactive oxygen species production and increased the synthesis of antioxidant enzymes, catalase, glutathione peroxidase-1, and manganese superoxide dismutase that is dependent on Epac. Additionally, exendin-4 has an antiapoptotic effect by decreasing a number of apoptotic cells, inhibiting caspase-3 activity, and enhancing the expression of antiapoptotic protein B-cell lymphoma 2, which is mediated through both protein kinase A- and Epac-dependent pathways. These data indicate a critical role for Epac in GLP-1R-mediated cardioprotection.

Background and Purpose: Cardiac fibrosis is characterized by an increase in fibroblast proliferation, overproduction of extracellular matrix proteins, and the formation of myofibroblast that express α-smooth muscle actin (α-SMA). Endothelin-1 (ET-1) is involved in the pathogenesis of cardiac fibrosis. Overstimulation of endothelin receptors induced cell proliferation, collagen synthesis, and α-SMA expression in cardiac fibroblasts. Although adenosine was shown to have cardioprotective effects, the molecular mechanisms by which adenosine A2 receptor inhibit ET-1-induced fibroblast proliferation and α-SMA expression in cardiac fibroblasts are not clearly identified.Experimental Approach: This study aimed at evaluating the mechanisms of cardioprotective effects of adenosine receptor agonist in rat cardiac fibroblast by measurement of cell proliferation, and mRNA and protein levels of α-SMA.Key results: Stimulation of adenosine subtype 2B (A2B) receptor resulted in the inhibition of ET-1-induced fibroblast proliferation, and a reduction of ET-1-induced α-SMA expression that is dependent on cAMP/Epac/PI3K/Akt signaling pathways in cardiac fibroblasts. The data in this study confirm a critical role for Epac signaling on A2B receptor-mediated inhibition of ET-1-induced cardiac fibrosis via PI3K and Akt activation.Conclusion and Implications: This is the first work reporting a novel signaling pathway for the inhibition of ET-1-induced cardiac fibrosis mediated through the A2B receptor. Thus, A2B receptor agonists represent a promising perspective as therapeutic targets for the prevention of cardiac fibrosis.