IP3 receptor isoforms differently regulate ER-mitochondrial contacts and local calcium transfer

Contact sites of endoplasmic reticulum (ER) and mitochondria locally convey calcium signals between the IP3 receptors (IP3R) and the mitochondrial calcium uniporter, and are central to cell survival. It remains unclear whether IP3Rs also have a structural role in contact formation and whether the different IP3R isoforms have redundant functions. Using an IP3R-deficient cell model rescued with each of the three IP3R isoforms and an array of super-resolution and ultrastructural approaches we demonstrate that IP3Rs are required for maintaining ER-mitochondrial contacts. This role is independent of calcium fluxes. We also show that, while each isoform can support contacts, type 2 IP3R is the most effective in delivering calcium to the mitochondria. Thus, these studies reveal a non-canonical, structural role for the IP3Rs and direct attention towards the type 2 IP3R that was previously neglected in the context of ER-mitochondrial calcium signaling

Murine MPDZ-linked hydrocephalus is caused by hyperpermeability of the choroid plexus.

Though congenital hydrocephalus is heritable, it has been linked only to eight genes, one of which is MPDZ Humans and mice that carry a truncated version of MPDZ incur severe hydrocephalus resulting in acute morbidity and lethality. We show by magnetic resonance imaging that contrast medium penetrates into the brain ventricles of mice carrying a Mpdz loss-of-function mutation, whereas none is detected in the ventricles of normal mice, implying that the permeability of the choroid plexus epithelial cell monolayer is abnormally high. Comparative proteomic analysis of the cerebrospinal fluid of normal and hydrocephalic mice revealed up to a 53-fold increase in protein concentration, suggesting that transcytosis through the choroid plexus epithelial cells of Mpdz KO mice is substantially higher than in normal mice. These conclusions are supported by ultrastructural evidence, and by immunohistochemistry and cytology data. Our results provide a straightforward and concise explanation for the pathophysiology of Mpdz-linked hydrocephalus

Perturbed mitochondria-ER contacts in live neurons that model the amyloid pathology of Alzheimer\u27s disease.

The use of fixed fibroblasts from familial and sporadic Alzheimer\u27s disease patients has previously indicated an upregulation of mitochondria-ER contacts (MERCs) as a hallmark of Alzheimer\u27s disease. Despite its potential significance, the relevance of these results is limited because they were not extended to live neurons. Here we performed a dynamic in vivo analysis of MERCs in hippocampal neurons from McGill-R-Thy1-APP transgenic rats, a model of Alzheimer\u27s disease-like amyloid pathology. Live FRET imaging of neurons from transgenic rats revealed perturbed \u27lipid-MERCs\u27 (gap width \u3c10 nm), while \u27Ca2+-MERCs\u27 (10-20 nm gap width) were unchanged. In situ TEM showed no significant differences in the lipid-MERCs:total MERCs or lipid-MERCs:mitochondria ratios; however, the average length of lipid-MERCs was significantly decreased in neurons from transgenic rats as compared to controls. In accordance with FRET results, untargeted lipidomics showed significant decreases in levels of 12 lipids and bioenergetic analysis revealed respiratory dysfunction of mitochondria from transgenic rats. Thus, our results reveal changes in MERC structures coupled with impaired mitochondrial functions in Alzheimer\u27s disease-related neurons.This article has an associated First Person interview with the first author of the paper

Capture at the ER-Mitochondrial Contacts Licenses IP

Endoplasmic reticulum-mitochondria contacts (ERMCs) are restructured in response to changes in cell state. While this restructuring has been implicated as a cause or consequence of pathology in numerous systems, the underlying molecular dynamics are poorly understood. Here, we show means to visualize the capture of motile IP3 receptors (IP3Rs) at ERMCs and document the immediate consequences for calcium signaling and metabolism. IP3Rs are of particular interest because their presence provides a scaffold for ERMCs that mediate local calcium signaling, and their function outside of ERMCs depends on their motility. Unexpectedly, in a cell model with little ERMC Ca2+ coupling, IP3Rs captured at mitochondria promptly mediate Ca2+ transfer, stimulating mitochondrial oxidative metabolism. The Ca2+ transfer does not require linkage with a pore-forming protein in the outer mitochondrial membrane. Thus, motile IP3Rs can traffic in and out of ERMCs, and, when ‘parked’, mediate calcium signal propagation to the mitochondria, creating a dynamic arrangement that supports local communication

Defective dimerization of FoF1-ATP synthase secondary to glycation favors mitochondrial energy deficiency in cardiomyocytes during aging

Aging; Dicarbonyl stress; MitochondriaEnvelliment; Estrès dicarbonílic; MitocondrisEnvejecimiento; Estrés dicarbonílico; MitocondriasAged cardiomyocytes develop a mismatch between energy demand and supply, the severity of which determines the onset of heart failure, and become prone to undergo cell death. The FoF1-ATP synthase is the molecular machine that provides >90% of the ATP consumed by healthy cardiomyocytes and is proposed to form the mitochondrial permeability transition pore (mPTP), an energy-dissipating channel involved in cell death. We investigated whether aging alters FoF1-ATP synthase self-assembly, a fundamental biological process involved in mitochondrial cristae morphology and energy efficiency, and the functional consequences this may have. Purified heart mitochondria and cardiomyocytes from aging mice displayed an impaired dimerization of FoF1-ATP synthase (blue native and proximity ligation assay), associated with abnormal mitochondrial cristae tip curvature (TEM). Defective dimerization did not modify the in vitro hydrolase activity of FoF1-ATP synthase but reduced the efficiency of oxidative phosphorylation in intact mitochondria (in which membrane architecture plays a fundamental role) and increased cardiomyocytes’ susceptibility to undergo energy collapse by mPTP. High throughput proteomics and fluorescence immunolabeling identified glycation of 5 subunits of FoF1-ATP synthase as the causative mechanism of the altered dimerization. In vitro induction of FoF1-ATP synthase glycation in H9c2 myoblasts recapitulated the age-related defective FoF1-ATP synthase assembly, reduced the relative contribution of oxidative phosphorylation to cell energy metabolism, and increased mPTP susceptibility. These results identify altered dimerization of FoF1-ATP synthase secondary to enzyme glycation as a novel pathophysiological mechanism involved in mitochondrial cristae remodeling, energy deficiency, and increased vulnerability of cardiomyocytes to undergo mitochondrial failure during aging.This work was supported by the Instituto de Salud Carlos III of the Spanish Ministry of Health (FIS-PI19-01196) and a grant from the Sociedad Española de Cardiología (SEC/FEC-INV-BAS 217003

Sexual Dimorphism in Bidirectional Sr-Mitochondria Crosstalk in Ventricular Cardiomyocytes

Calcium transfer into the mitochondrial matrix during sarcoplasmic reticulum (SR) Ca2+ release is essential to boost energy production in ventricular cardiomyocytes (VCMs) and match increased metabolic demand. Mitochondria from female hearts exhibit lower mito-[Ca2+] and produce less reactive oxygen species (ROS) compared to males, without change in respiration capacity. We hypothesized that in female VCMs, more efficient electron transport chain (ETC) organization into supercomplexes offsets the deficit in mito-Ca2+ accumulation, thereby reducing ROS production and stress-induced intracellular Ca2+ mishandling. Experiments using mitochondria-targeted biosensors confirmed lower mito-ROS and mito-[Ca2+] in female rat VCMs challenged with β-adrenergic agonist isoproterenol compared to males. Biochemical studies revealed decreased mitochondria Ca2+ uniporter expression and increased supercomplex assembly in rat and human female ventricular tissues vs male. Importantly, western blot analysis showed higher expression levels of COX7RP, an estrogen-dependent supercomplex assembly factor in female heart tissues vs males. Furthermore, COX7RP was decreased in hearts from aged and ovariectomized female rats. COX7RP overexpression in male VCMs increased mitochondrial supercomplexes, reduced mito-ROS and spontaneous SR Ca2+ release in response to ISO. Conversely, shRNA-mediated knockdown of COX7RP in female VCMs reduced supercomplexes and increased mito-ROS, promoting intracellular Ca2+ mishandling. Compared to males, mitochondria in female VCMs exhibit higher ETC subunit incorporation into supercomplexes, supporting more efficient electron transport. Such organization coupled to lower levels of mito-[Ca2+] limits mito-ROS under stress conditions and lowers propensity to pro-arrhythmic spontaneous SR Ca2+ release. We conclude that sexual dimorphism in mito-Ca2+ handling and ETC organization may contribute to cardioprotection in healthy premenopausal females

Endosomes: Guardians Against [Ru(Phen)3]2+ Photo-action In Endothelial Cells During In Vivo pO2 Detection?

Phototoxicity is a side-effect of in vitro and in vivo oxygen partial pressure (pO(2)) detection by luminescence lifetime measurement methods. Dichlorotris(1,10-phenanthroline)-ruthenium(II) hydrate ([Ru(Phen)(3)](2+)) is a water soluble pO(2) probe associated with low phototoxicity, which we investigated in vivo in the chick's chorioallantoic membrane (CAM) after intravenous or topical administration and in vitro in normal human coronary artery endothelial cells (HCAEC). In vivo, the level of intravenously injected [Ru(Phen)(3)](2+) decreases within several minutes, whereas the maximum of its biodistribution is observed during the first 2 h after topical application. Both routes are followed by convergence to almost identical "intra/extra-vascular" levels of [Ru(Phen)(3)](2+). In vitro, we observed that [Ru(Phen)(3)](2+) enters cells via endocytosis and is then redistributed. None of the studied conditions induced modification of lysosomal or mitochondrial membranes without illumination. No nuclear accumulation was observed. Without illumination [Ru(Phen)(3)](2+) induces changes in endoplasmic reticulum (ER)-to-Golgi transport. The phototoxic effect of [Ru(Phen)(3)](2+) leads to more marked ultrastructural changes than administration of [Ru(Phen)(3)](2+) only (in the dark). These could lead to disruption of Ca2+ homeostasis accompanied by mitochondrial changes or to changes in secretory pathways. In conclusion, we have demonstrated that the intravenous injection of [Ru(Phen)(3)](2+) into the CAM model mostly leads to extracellular localization of [Ru(Phen)(3)](2+), while its topical application induces intracellular localization. We have shown in vivo that [Ru(Phen)(3)](2+) induces minimal photo-damage after illumination with light doses larger by two orders of magnitude than those used for pO(2) measurements. This low phototoxicity is due to the fact that [Ru(Phen)(3)](2+) enters endothelial cells via endocytosis and is then redistributed towards peroxisomes and other endosomal and secretory vesicles before it is eliminated via exocytosis. Cellular response to [Ru(Phen)(3)](2+), survival or death, depends on its intracellular concentration and oxidation-reduction properties

Endomembrane-Associated Pre-embedding Immunogold Labeling

Aim To optimize the pre-embedding IG in stable cell lines and primary adult cardiomyocytes to get the most effective visualization of endomembrane/associated proteins: endo/sarcoplasmic reticulum Ca2+ release channels IP3 receptors and ryanodine receptors (IP3R, and RyR2) and the mitochondrial fission protein Drp1.https://jdc.jefferson.edu/pacbposters/1014/thumbnail.jp

The flashlights on a distinct role of protein kinase C delta: Phosphorylation of regulatory and catalytic domain upon oxidative stress in glioma cells

Glioblastoma multiforme are considered to be aggressive high-grade tumors with poor prognosis for patient survival. Photodynamic therapy is one of the adjuvant therapies which has been used for glioblastoma multiforme during last decade. Hypericin, a photosensitizer, can be employed in this treatment. We have studied the effect of hypericin on PKCS phosphorylation in U87 MG cells before and after light application. Hypericin increased PKCS phosphorylation at tyrosine 155 in the regulatory domain and serine 645 in the catalytic domain. However, use of the light resulted in apoptosis, decreased phosphorylation of tyrosine 155 and enhanced serine 645. The PKCS localization and phosphorylation of regulatory and catalytic domains were shown to play a distinct role in the anti-apoptotic response of glioma cells. We hypothesized that PKCS phosphorylated at the regulatory domain is primarily present in the cytoplasm and in mitochondria before irradiation, and it may participate in Bcl-2 phosphorylation. After hypericin and light application, PKCS phosphorylated at a regulatory domain which is in the nucleus. In contrast, PKCS phosphorylated at the catalytic domain may be mostly active in the nucleus before irradiation, but active in the cytoplasm after the irradiation. In summary, light-induced oxidative stress significantly regulates PKCS pro-survival and pro-apoptotic activity in glioma cells by its phosphorylation at serine 645 and tyrosine 155. (C) 2017 Elsevier Inc. All rights reserved

Spatial Separation of Mitochondrial Calcium Uptake and Extrusion for Energy-Efficient Mitochondrial Calcium Signaling in the Heart

Summary: Mitochondrial Ca2+ elevations enhance ATP production, but uptake must be balanced by efflux to avoid overload. Uptake is mediated by the mitochondrial Ca2+ uniporter channel complex (MCUC), and extrusion is controlled largely by the Na+/Ca2+ exchanger (NCLX), both driven electrogenically by the inner membrane potential (ΔΨm). MCUC forms hotspots at the cardiac mitochondria-junctional SR (jSR) association to locally receive Ca2+ signals; however, the distribution of NCLX is unknown. Our fractionation-based assays reveal that extensively jSR-associated mitochondrial segments contain a minor portion of NCLX and lack Na+-dependent Ca2+ extrusion. This pattern is retained upon in vivo NCLX overexpression, suggesting extensive targeting to non-jSR-associated submitochondrial domains and functional relevance. In cells with non-polarized MCUC distribution, upon NCLX overexpression the same given increase in matrix Ca2+ expends more ΔΨm. Thus, cardiac mitochondrial Ca2+ uptake and extrusion are reciprocally polarized, likely to optimize the energy efficiency of local calcium signaling in the beating heart. : Calcium signals control mitochondrial fuel generation. De La Fuente et al. report that in heart mitochondria, calcium uptake and extrusion are spatially separated; the most calcium-exposed area is an uptake hotspot, but it lacks extrusion to optimize signaling efficiency and minimize the energy expense of controlling mitochondrial function by calcium. Keywords: calcium signaling, NCLX distribution, mitochondrial Ca2+ uniporter distribution, cardiac excitation-energetics coupling, mitochondria-sarcoplasmic reticulum contact sites, Ca2+ mitochondria, cardiac muscl