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Summary Mitochondria shape cytosolic calcium ([Ca 2+ ] c ) transients and utilize the mitochondrial Ca 2+ ([Ca 2+ ] m ) in exchange for bioenergetics output. Conversely, dysregulated [Ca 2+ ] c causes [Ca 2+ ] m overload and induces permeability transition pore and cell death. Ablation of MCU-mediated Ca 2+ uptake exhibited elevated [Ca 2+ ] c and failed to prevent stress-induced cell death. The mechanisms for these effects remain elusive. Here, we report that mitochondria undergo a cytosolic Ca 2+ -induced shape change that is distinct from mitochondrial fission and swelling. [Ca 2+ ] c elevation, but not MCU-mediated Ca 2+ uptake, appears to be essential for the process we term mitochondrial shape transition (MiST). MiST is mediated by the mitochondrial protein Miro1 through its EF-hand domain 1 in multiple cell types. Moreover, Ca 2+ -dependent disruption of Miro1/KIF5B/tubulin complex is determined by Miro1 EF1 domain. Functionally, Miro1-dependent MiST is essential for autophagy/mitophagy that is attenuated in Miro1 EF1 mutants. Thus, Miro1 is a cytosolic Ca 2+ sensor that decodes metazoan Ca 2+ signals as MiST. [ABSTRACT FROM AUTHOR]

Summary Mitochondrial Ca 2+ Uniporter (MCU)-dependent mitochondrial Ca 2+ uptake is the primary mechanism for increasing matrix Ca 2+ in most cell types. However, a limited understanding of the MCU complex assembly impedes the comprehension of the precise mechanisms underlying MCU activity. Here, we report that mouse cardiomyocytes and endothelial cells lacking MCU regulator 1 (MCUR1) have severely impaired [Ca 2+ ] m uptake and I MCU current. MCUR1 binds to MCU and EMRE and function as a scaffold factor. Our protein binding analyses identified the minimal, highly conserved regions of coiled-coil domain of both MCU and MCUR1 that are necessary for heterooligomeric complex formation. Loss of MCUR1 perturbed MCU heterooligomeric complex and functions as a scaffold factor for the assembly of MCU complex. Vascular endothelial deletion of MCU and MCUR1 impaired mitochondrial bioenergetics, cell proliferation, and migration but elicited autophagy. These studies establish the existence of a MCU complex that assembles at the mitochondrial integral membrane and regulates Ca 2+ -dependent mitochondrial metabolism. [ABSTRACT FROM AUTHOR]

Summary Mitochondrial Ca2+ uniporter (MCU)-mediated Ca2+ uptake promotes the buildup of reducing equivalents that fuel oxidative phosphorylation for cellular metabolism. Although MCU modulates mitochondrial bioenergetics, its function in energy homeostasis in vivo remains elusive. Here we demonstrate that deletion of the Mcu gene in mouse liver (MCUΔhep) and in Danio rerio by CRISPR/Cas9 inhibits mitochondrial Ca2+ (m Ca2+) uptake, delays cytosolic Ca2+ (c Ca2+) clearance, reduces oxidative phosphorylation, and leads to increased lipid accumulation. Elevated hepatic lipids in MCUΔhep were a direct result of extramitochondrial Ca2+-dependent protein phosphatase-4 (PP4) activity, which dephosphorylates AMPK. Loss of AMPK recapitulates hepatic lipid accumulation without changes in MCU-mediated Ca2+ uptake. Furthermore, reconstitution of active AMPK, or PP4 knockdown, enhances lipid clearance in MCUΔhep hepatocytes. Conversely, gain-of-function MCU promotes rapid m Ca2+ uptake, decreases PP4 levels, and reduces hepatic lipid accumulation. Thus, our work uncovers an MCU/PP4/AMPK molecular cascade that links Ca2+ dynamics to hepatic lipid metabolism. Graphical Abstract Highlights • Mitochondrial Ca2+ powers FAO-dependent hepatocyte mitochondrial respiration • Hepatic MCU deletion promotes lipid accumulation and lowers ketone bodies • Blockade of m Ca2+ buffering enhances AMPK dephosphorylation through PP4 • Restoration of AMPK activity in MCUΔhep model improves lipid clearance Hepatic mitochondrial Ca2+ shapes bioenergetics and lipid homeostasis. Tomar et al. demonstrate that MCU-mediated c Ca2+ buffering serves as a crucial step in controlling hepatic fuel metabolism through an MCU/PP4/AMPK molecular cascade. Identification of these molecular signaling events aids in understanding how perturbation of mitochondrial ion homeostasis may contribute to the etiology of metabolic disorders. [ABSTRACT FROM AUTHOR]

Summary Ca 2+ dynamics and oxidative signaling are fundamental mechanisms for mitochondrial bioenergetics and cell function. The MCU complex is the major pathway by which these signals are integrated in mitochondria. Whether and how these coactive elements interact with MCU have not been established. As an approach toward understanding the regulation of MCU channel by oxidative milieu, we adapted inflammatory and hypoxia models. We identified the conserved cysteine 97 (Cys-97) to be the only reactive thiol in human MCU that undergoes S-glutathionylation. Furthermore, biochemical, structural, and superresolution imaging analysis revealed that MCU oxidation promotes MCU higher order oligomer formation. Both oxidation and mutation of MCU Cys-97 exhibited persistent MCU channel activity with higher [Ca 2+ ] m uptake rate, elevated mROS, and enhanced [Ca 2+ ] m overload-induced cell death. In contrast, these effects were largely independent of MCU interaction with its regulators. These findings reveal a distinct functional role for Cys-97 in ROS sensing and regulation of MCU activity. [ABSTRACT FROM AUTHOR]

Mitochondrial Ca 2+ uniporter (MCU)-mediated Ca 2+ uptake promotes the buildup of reducing equivalents that fuel oxidative phosphorylation for cellular metabolism. Although MCU modulates mitochondrial bioenergetics, its function in energy homeostasis in vivo remains elusive. Here we demonstrate that deletion of the Mcu gene in mouse liver (MCU Δhep ) and in Danio rerio by CRISPR/Cas9 inhibits mitochondrial Ca 2+ ( m Ca 2+ ) uptake, delays cytosolic Ca 2+ ( c Ca 2+ ) clearance, reduces oxidative phosphorylation, and leads to increased lipid accumulation. Elevated hepatic lipids in MCU Δhep were a direct result of extramitochondrial Ca 2+ -dependent protein phosphatase-4 (PP4) activity, which dephosphorylates AMPK. Loss of AMPK recapitulates hepatic lipid accumulation without changes in MCU-mediated Ca 2+ uptake. Furthermore, reconstitution of active AMPK, or PP4 knockdown, enhances lipid clearance in MCU Δhep hepatocytes. Conversely, gain-of-function MCU promotes rapid m Ca 2+ uptake, decreases PP4 levels, and reduces hepatic lipid accumulation. Thus, our work uncovers an MCU/PP4/AMPK molecular cascade that links Ca 2+ dynamics to hepatic lipid metabolism., (Copyright © 2019 The Authors. Published by Elsevier Inc. All rights reserved.)

Mitochondria shape cytosolic calcium ([Ca 2+ ] c ) transients and utilize the mitochondrial Ca 2+ ([Ca 2+ ] m ) in exchange for bioenergetics output. Conversely, dysregulated [Ca 2+ ] c causes [Ca 2+ ] m overload and induces permeability transition pore and cell death. Ablation of MCU-mediated Ca 2+ uptake exhibited elevated [Ca 2+ ] c and failed to prevent stress-induced cell death. The mechanisms for these effects remain elusive. Here, we report that mitochondria undergo a cytosolic Ca 2+ -induced shape change that is distinct from mitochondrial fission and swelling. [Ca 2+ ] c elevation, but not MCU-mediated Ca 2+ uptake, appears to be essential for the process we term mitochondrial shape transition (MiST). MiST is mediated by the mitochondrial protein Miro1 through its EF-hand domain 1 in multiple cell types. Moreover, Ca 2+ -dependent disruption of Miro1/KIF5B/tubulin complex is determined by Miro1 EF1 domain. Functionally, Miro1-dependent MiST is essential for autophagy/mitophagy that is attenuated in Miro1 EF1 mutants. Thus, Miro1 is a cytosolic Ca 2+ sensor that decodes metazoan Ca 2+ signals as MiST., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Objective: Aortic occlusion with an endoballoon is a well-established technique to facilitate robotic and minimally invasive mitral valve surgery. Use of the endoballoon has several relative contraindications including ascending aortic dilatation greater than 38 mm in size. We sought to review our experience using the endoballoon in cases of totally endoscopic mitral valve surgery with aortic diameters greater than 38 mm., Methods: A retrospective review of our single-site database was conducted to identify patients undergoing totally endoscopic mitral valve surgery by a single surgeon using an endoballoon and who had ascending aortic dilation. We defined aortic dilation as greater than 38 mm. Computed tomography was done preoperatively on all patients to evaluate the aortic anatomy as well as iliofemoral access vessels. Femoral artery cannulation was done in a standardized fashion to advance and position the endoballoon, to occlude the ascending aorta, and to deliver cardioplegia., Results: From October 2011 through June 2015, 196 patients underwent totally endoscopic mitral valve surgery using an endoballoon at our institution. Twenty-two patients (11.2%) had ascending aortic diameters greater than 38 mm (range, 38.1-46.6 mm; mean, 40.5 ± 2.5 mm). In these cases, there were no instances of aortic dissection or other injury due to balloon rupture, balloon migration, device movement leading to loss of occlusion, or inability to complete planned surgery due to occlusion failure., Conclusions: Our experience suggests that it is possible to successfully use endoaortic balloon occlusion in patients with ascending aortic dilation with proper preoperative imaging and planning.