We argue that the field of extracellular vesicle (EV) biology needs more transparent reporting to facilitate interpretation and replication of experiments. To achieve this, we describe EV-TRACK, a crowdsourcing knowledgebase (http://evtrack.org) that centralizes EV biology and methodology with the goal of stimulating authors, reviewers, editors and funders to put experimental guidelines into practice.

In all eukaryotic cells, the endoplasmic reticulum (ER) and the mitochondria establish a tight interplay, which is structurally and functionally modulated through a proteinaceous tether formed at specific subdomains of the ER membrane, designated mitochondria-associated membranes or MAMs. The tethering function of the MAMs allows the regulation of lipid synthesis and rapid transmission of calcium (Ca(2+)) signals between the ER and mitochondria, which is crucial to shape intracellular Ca(2+) signaling and regulate mitochondrial bioenergetics. Research on the molecular characterization and function of MAMs has boomed in the last few years and the list of signaling and structural proteins dynamically associated with the ER-mitochondria contact sites in physiological and pathological conditions, is rapidly increasing along with the realization of an unprecedented complexity underlying the functional role of MAMs. Besides their established role as a signaling hub for Ca(2+) and lipid transfer between ER and mitochondria, MAMs have been recently shown to regulate mitochondrial shape and motility, energy metabolism and redox status and to be central to the modulation of various key processes like ER stress, autophagy and inflammasome signaling. In this review we will discuss some emerging cell-autonomous and cell non-autonomous roles of the MAMs in mammalian cells and their relevance for important human diseases. This article is part of a Special Issue entitled: Calcium signaling in health and disease. Guest Editors: Geert Bultynck, Jacques Haiech, Claus W. Heizmann, Joachim Krebs, and Marc Moreau.

The oxysterol-binding protein (OSBP)-related proteins ORP5 and ORP8 have been shown recently to transport phosphatidylserine (PS) from the endoplasmic reticulum (ER) to the plasma membrane (PM) at ER-PM contact sites. PS is also transferred from the ER to mitochondria where it acts as precursor for mitochondrial PE synthesis. Here, we show that, in addition to ER-PM contact sites, ORP5 and ORP8 are also localized to ER-mitochondria contacts and interact with the outer mitochondrial membrane protein PTPIP51. A functional lipid transfer (ORD) domain was required for this localization. Interestingly, ORP5 and ORP8 depletion leads to defects in mitochondria morphology and respiratory function.

Loss of ER Ca homeostasis triggers endoplasmic reticulum (ER) stress and drives ER-PM contact sites formation in order to refill ER-luminal Ca. Recent studies suggest that the ER stress sensor and mediator of the unfolded protein response (UPR) PERK regulates intracellular Ca fluxes, but the mechanisms remain elusive. Here, using proximity-dependent biotin identification (BioID), we identified the actin-binding protein Filamin A (FLNA) as a key PERK interactor. Cells lacking PERK accumulate F-actin at the cell edges and display reduced ER-PM contacts. Following ER-Ca store depletion, the PERK-FLNA interaction drives the expansion of ER-PM juxtapositions by regulating F-actin-assisted relocation of the ER-associated tethering proteins Stromal Interaction Molecule 1 (STIM1) and Extended Synaptotagmin-1 (E-Syt1) to the PM. Cytosolic Ca elevation elicits rapid and UPR-independent PERK dimerization, which enforces PERK-FLNA-mediated ER-PM juxtapositions. Collectively, our data unravel an unprecedented role of PERK in the regulation of ER-PM appositions through the modulation of the actin cytoskeleton.

Mitochondria-associated membranes (MAMs) are central microdomains that fine-tune bioenergetics by the local transfer of calcium from the endoplasmic reticulum to the mitochondrial matrix. Here, we report an unexpected function of the endoplasmic reticulum stress transducer IRE1α as a structural determinant of MAMs that controls mitochondrial calcium uptake. IRE1α deficiency resulted in marked alterations in mitochondrial physiology and energy metabolism under resting conditions. IRE1α determined the distribution of inositol-1,4,5-trisphosphate receptors at MAMs by operating as a scaffold. Using mutagenesis analysis, we separated the housekeeping activity of IRE1α at MAMs from its canonical role in the unfolded protein response. These observations were validated in vivo in the liver of IRE1α conditional knockout mice, revealing broad implications for cellular metabolism. Our results support an alternative function of IRE1α in orchestrating the communication between the endoplasmic reticulum and mitochondria to sustain bioenergetics. Cellular organelles are no longer conceived as unconnected structures with isolated functions, but as dynamic and integrated compartments. The best-characterized membrane contact sites bridge the endoplasmic reticulum (ER) and mitochondria 1. The ER-the largest organelle in eukaryotic cells-controls protein folding, lipid synthesis and calcium storage. The folding capacity of the ER is constantly challenged by physiological demands and disease states. To sustain proteostasis, cells engage the unfolded protein response (UPR) 2 , a Carreras-Sureda et al.

Background: VDAC1 mediates the transfer of pro-apoptotic Ca 2ϩ signals into mitochondria. Results: The BH4 domain of Bcl-XL, but not that of Bcl-2, targets VDAC1 and suppresses its pro-apoptotic Ca 2ϩ -flux properties. N-terminal VDAC1 peptide alleviates this effect of BH4-Bcl-XL. Conclusion: Bcl-XL via its BH4 domain inhibits VDAC1 activity. Significance: Bcl-2 and Bcl-XL differ in their BH4 domain biology by regulating ER and mitochondrial Ca 2ϩ -transport systems, respectively.

Hematopoietic stem cells (HSCs) in the fetal liver (FL) unlike adult bone marrow (BM) proliferate extensively, posing different metabolic demands. However, metabolic pathways responsible for the production of energy and cellular building blocks in FL HSCs have not been described. Here, we report that FL HSCs use oxygen dependent energy generating pathways significantly more than their BM counterparts. RNA-Seq analysis of E14.5 FL versus BM derived HSCs identified increased expression levels of genes involved in oxidative phosphorylation (OxPhos) and the citric acid cycle (TCA). We demonstrated that FL HSCs contain more mitochondria than BM HSCs, which resulted in increased levels of oxygen consumption and reactive oxygen species (ROS) production. Higher levels of DNA repair and antioxidant pathway gene expression may prevent ROS-mediated (geno)toxicity in FL HSCs. Thus, we here for the first time highlight the underestimated importance of oxygen dependent pathways for generating energy and building blocks in FL HSCs.

The tight cross talk between two essential organelles of the cell, the endoplasmic reticulum (ER) and mitochondria, is spatially and functionally regulated by specific microdomains known as the mitochondria-associated membranes (MAMs). MAMs are hot spots of Ca 2+ transfer between the ER and mitochondria, and emerging data indicate their vital role in the regulation of fundamental physiological processes, chief among them mitochondria bioenergetics, proteostasis, cell death, and autophagy. Moreover, and perhaps not surprisingly, it has become clear that signaling events regulated at the ER-mitochondria intersection regulate key processes in oncogenesis and in the response of cancer cells to therapeutics. ER-mitochondria appositions have been shown to dynamically recruit oncogenes and tumor suppressors, modulating their activity and protein complex formation, adapt the bioenergetic demand of cancer cells and to regulate cell death pathways and redox signaling in cancer cells. In this review, we discuss some emerging players of the ER-mitochondria contact sites in mammalian cells, the key processes they regulate and recent evidence highlighting the role of MAMs in shaping cell-autonomous and non-autonomous signals that regulate cancer growth.Keywords: endoplasmic reticulum, mitochondria, mitochondria-associated membranes, Ca 2+ signaling, eR stress, autophagy, inflammasome, cancer cell Abbreviations: AA, arachidonoyl; ATF4, activating transcription factor 4; ATG, autophagy-related gene; Bcl-2, B-cell lymphoma 2; Bcl-XL, B-cell lymphoma-extra large; BECN1, Beclin-1; Ca 2 + , calcium; Cav-1, caveolin-1; CL, cardiolipin; CNX, calnexin; cyt c, cytochrome c; Drp1, dynamin-related protein 1; ER, endoplasmic reticulum; Grp78, glucose-regulated protein 78; HK2, hexokinase 2; IL-1β, interleukin 1β; IL-18, interleukin 18; IP3, inositol trisphosphate; IP3R, inositol 1, 4, 5-trisphosphate receptor; IP3R3, inositol 1, 4, 5-trisphosphate receptor 3; IRE1, inositol requiring enzyme 1; MAMs, mitochondria-associated membranes; MAVS, mitochondrial antiviral-signaling protein; MCU, mitochondrial calcium uniporter; MFN2, mitofusin 2; mTORC2, mammalian target of rapamycin 2; NLRP3, NOD-like receptor family 3; OMM, outer mitochondrial membrane; ORP5, oxysterol-binding protein (OSBP)-related protein (ORP) 5; ORP8, oxysterol-binding protein (OSBP)-related protein (ORP) 8; PA, phosphatidic acid; PACS-2, phosphofurin acidic cluster sorting protein 2; PC, phosphatidylcholine; PE, phosphatidylethanolamine; PERK, double stranded RNA-activated protein kinase (PKR)-like ER kinase; PI, phosphatidylinositol; PM, plasma membrane; PML, promyelocytic leukemia; PP2A, protein phosphatase 2A; PS, phosphatidylserine; PTEN, phosphatase and tensin homolog deleted on chromosome 10; PTPIP51, protein tyrosine phosphatase-interacting protein 51; ROS, reactive oxygen species; SERCA, sarco/endoplasmic reticulum Ca 2+ ATPase; SERCA2b, sarco/endoplasmic reticulum Ca 2 + ATPase isoform 2b; Sigma1 receptor, S1R; StAR, cholesterol transport steroidogenic acute regula...