Stabilization of mitochondria-associated endoplasmic reticulum membranes regulates Aβ generation in a three-dimensional neural model of Alzheimer's disease.

Introduction: We previously demonstrated that regulating mitochondria-associated endoplasmic reticulum (ER) membranes (MAMs) affects axonal Aβ generation in a well-characterized three-dimensional (3D) neural Alzheimer's disease (AD) model. MAMs vary in thickness and length, impacting their functions. Here, we examined the effect of MAM thickness on Aβ in our 3D neural model of AD.

Transcriptional regulation in the absence of inositol trisphosphate receptor calcium signaling.

The activation of IP receptor (IPR) Ca channels generates agonist-mediated Ca signals that are critical for the regulation of a wide range of biological processes. It is therefore surprising that CRISPR induced loss of all three IPR isoforms (TKO) in HEK293 and HeLa cell lines yields cells that can survive, grow and divide, albeit more slowly than wild-type cells. In an effort to understand the adaptive mechanisms involved, we have examined the activity of key Ca dependent transcription factors (NFAT, CREB and AP-1) and signaling pathways using luciferase-reporter assays, phosphoprotein immunoblots and whole genome transcriptomic studies.

Systematic mapping of mitochondrial calcium uniporter channel (MCUC)-mediated calcium signaling networks.

The mitochondrial calcium uniporter channel (MCUC) mediates mitochondrial calcium entry, regulating energy metabolism and cell death. Although several MCUC components have been identified, the molecular basis of mitochondrial calcium signaling networks and their remodeling upon changes in uniporter activity have not been assessed. Here, we map the MCUC interactome under resting conditions and upon chronic loss or gain of mitochondrial calcium uptake.

MICU1 and MICU2 control mitochondrial calcium signaling in the mammalian heart.

Activating Ca-sensitive enzymes of oxidative metabolism while preventing calcium overload that leads to mitochondrial and cellular injury requires dynamic control of mitochondrial Ca uptake. This is ensured by the mitochondrial calcium uptake (MICU)1/2 proteins that gate the pore of the mitochondrial calcium uniporter (mtCU). MICU1 is relatively sparse in the heart, and recent studies claimed the mammalian heart lacks MICU1 gating of mtCU.

Supralinear Dependence of the IP Receptor-to-Mitochondria Local Ca Transfer on the Endoplasmic Reticulum Ca Loading.

Calcium signal propagation from endoplasmic reticulum (ER) to mitochondria regulates a multitude of mitochondrial and cell functions, including oxidative ATP production and cell fate decisions. Ca transfer is optimal at the ER-mitochondrial contacts, where inositol 1,4,5-trisphosphate (IP) receptors (IP3R) can locally expose the mitochondrial Ca uniporter (mtCU) to high [Ca] nanodomains. The Ca loading state of the ER (Ca) can vary broadly in physiological and pathological scenarios, however, the correlation between Ca and the local Ca transfer is unclear.

Answer to Gerber et al. "Autosomal recessive pathogenic MSTO1 variants in hereditary optic atrophy".

Gal et al address the issues raised by Gerber et al and reiterate that patients in their study showed decreased Misato homolog 1 (MSTO1) mRNA and protein levels, but also confirm finding of Gerber et al that the mutation is in MSTO2p pseudogene. Whether MSTO2p variant contributes to the observed decrease in MSTO1 levels in patients remains unclear.

MICU1 controls the sensitivity of the mitochondrial Ca uniporter to activators and inhibitors.

Mitochondrial Ca homeostasis loses its control in many diseases and might provide therapeutic targets. Mitochondrial Ca uptake is mediated by the uniporter channel (mtCU), formed by MCU and is regulated by the Ca-sensing gatekeeper, MICU1, which shows tissue-specific stoichiometry. An important gap in knowledge is the molecular mechanism of the mtCU activators and inhibitors.

Fuel oxidation under the control of mitochondrial shape and dynamics.

How mitochondrial shape and substrate-specific metabolism are related has been a difficult question to address. Here, new work by Ngo et al (2023) reports that mitochondrial shape-long versus fragmented-determines the activity of β-oxidation of long-chain fatty acids, supporting a novel role for mitochondrial fission products as β-oxidation hubs.

MICU1 occludes the mitochondrial calcium uniporter in divalent-free conditions.

Mitochondrial Ca uptake is mediated by the mitochondrial uniporter complex (mtCU) that includes a tetramer of the pore-forming subunit, MCU, a scaffold protein, EMRE, and the EF-hand regulatory subunit, MICU1 either homodimerized or heterodimerized with MICU2/3. MICU1 has been proposed to regulate Ca uptake via the mtCU by physically occluding the pore and preventing Ca flux at resting cytoplasmic [Ca] (free calcium concentration) and to increase Ca flux at high [Ca] due to cooperative activation of MICUs EF-hands. However, mtCU and MICU1 functioning when its EF-hands are unoccupied by Ca is poorly studied due to technical limitations.

Apoptotic cell death in disease-Current understanding of the NCCD 2023.

Apoptosis is a form of regulated cell death (RCD) that involves proteases of the caspase family. Pharmacological and genetic strategies that experimentally inhibit or delay apoptosis in mammalian systems have elucidated the key contribution of this process not only to (post-)embryonic development and adult tissue homeostasis, but also to the etiology of multiple human disorders. Consistent with this notion, while defects in the molecular machinery for apoptotic cell death impair organismal development and promote oncogenesis, the unwarranted activation of apoptosis promotes cell loss and tissue damage in the context of various neurological, cardiovascular, renal, hepatic, infectious, neoplastic and inflammatory conditions.

MICU1 regulates mitochondrial cristae structure and function independently of the mitochondrial Ca uniporter channel.

MICU1 is a calcium (Ca)-binding protein that regulates the mitochondrial Ca uniporter channel complex (mtCU) and mitochondrial Ca uptake. knockout mice display disorganized mitochondrial architecture, a phenotype that is distinct from that of mice with deficiencies in other mtCU subunits and, thus, is likely not explained by changes in mitochondrial matrix Ca content. Using proteomic and cellular imaging techniques, we found that MICU1 localized to the mitochondrial contact site and cristae organizing system (MICOS) and directly interacted with the MICOS components MIC60 and CHCHD2 independently of the mtCU.

disease-causing mutants have domain-specific effects on mitochondrial ultrastructure and fusion.

Inner mitochondrial membrane fusion and cristae shape depend on optic atrophy protein 1, OPA1. Mutations in lead to autosomal dominant optic atrophy (ADOA), an important cause of inherited blindness. The Guanosin Triphosphatase (GTPase) and GTPase effector domains (GEDs) of OPA1 are essential for mitochondrial fusion; yet, their specific roles remain elusive.

Capture at the ER-mitochondrial contacts licenses IP receptors to stimulate local Ca transfer and oxidative metabolism.

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 IP receptors (IP3Rs) at ERMCs and document the immediate consequences for calcium signaling and metabolism.

Altered composition of the mitochondrial Cauniporter in the failing human heart.

Heart failure (HF) is a leading cause of hospitalization and mortality worldwide. Yet, there is still limited knowledge on the underlying molecular mechanisms, because human tissue for research is scarce, and data obtained in animal models is not directly applicable to humans. Thus, studies of human heart specimen are of particular relevance.

Uncontrolled mitochondrial calcium uptake underlies the pathogenesis of neurodegeneration in MICU1-deficient mice and patients.

Dysregulation of mitochondrial Ca homeostasis has been linked to neurodegenerative diseases. Mitochondrial Ca uptake is mediated via the calcium uniporter complex that is primarily regulated by MICU1, a Ca-sensing gatekeeper. Recently, human patients with MICU1 loss-of-function mutations were diagnosed with neuromuscular and cognitive impairments.

Reduced ER-mitochondria connectivity promotes neuroblastoma multidrug resistance.

Most cancer deaths result from progression of therapy resistant disease, yet our understanding of this phenotype is limited. Cancer therapies generate stress signals that act upon mitochondria to initiate apoptosis. Mitochondria isolated from neuroblastoma cells were exposed to tBid or Bim, death effectors activated by therapeutic stress.

Fluorescent protein transgenic mice for the study of Ca and redox signaling.

Many unanswered questions of physiology and medicine require in vivo studies of cellular processes in murine models. These processes commonly depend on intracellular Ca and redox alterations. Fluorescent dyes have succeeded in real-time intracellular monitoring of Ca, redox and the different Reactive Oxygen Species (ROS) in single cells, but have seldomly been applied in vivo.

Fluorescence imaging detection of nanodomain redox signaling events at organellar contacts.

This protocol describes how to visualize, detect, and analyze redox signals (oxidative bursts) at the ER-mitochondrial interface. It uses drug-inducible crosslinking to target the genetically encoded glutathione redox sensor Grx1roGFP2 to organellar contact sites to measure local redox changes associated with transient depolarizations of the mitochondrial membrane potential (flickers). The strategy allows imaging of the oxidized to reduced glutathione ratio (GSSG:GSH) in subcellular regions below the diffraction limit with good temporal resolution and minimum phototoxicity.

OPA1 Modulates Mitochondrial Ca Uptake Through ER-Mitochondria Coupling.

Autosomal Dominant Optic Atrophy (ADOA), a disease that causes blindness and other neurological disorders, is linked to mutations. OPA1, dependent on its GTPase and GED domains, governs inner mitochondrial membrane (IMM) fusion and cristae organization, which are central to oxidative metabolism. Mitochondrial dynamics and IMM organization have also been implicated in Ca homeostasis and signaling but the specific involvements of OPA1 in Ca dynamics remain to be established.

Metabolic adaptation to the chronic loss of Ca signaling induced by KO of IP receptors or the mitochondrial Ca uniporter.

Calcium signaling is essential for regulating many biological processes. Endoplasmic reticulum inositol trisphosphate receptors (IPRs) and the mitochondrial Ca uniporter (MCU) are key proteins that regulate intracellular Ca concentration. Mitochondrial Ca accumulation activates Ca-sensitive dehydrogenases of the tricarboxylic acid (TCA) cycle that maintain the biosynthetic and bioenergetic needs of both normal and cancer cells.

Oxidative bursts of single mitochondria mediate retrograde signaling toward the ER.

The emerging role of mitochondria as signaling organelles raises the question of whether individual mitochondria can initiate heterotypic communication with neighboring organelles. Using fluorescent probes targeted to the endoplasmic-reticulum-mitochondrial interface, we demonstrate that single mitochondria generate oxidative bursts, rapid redox oscillations, confined to the nanoscale environment of the interorganellar contact sites. Using probes fused to inositol 1,4,5-trisphosphate receptors (IPRs), we show that Ca channels directly sense oxidative bursts and respond with Ca transients adjacent to active mitochondria.

Molecular pathophysiology of human MICU1 deficiency.

Aims: MICU1 encodes the gatekeeper of the mitochondrial Ca uniporter, MICU1 and biallelic loss-of-function mutations cause a complex, neuromuscular disorder in children. Although the role of the protein is well understood, the precise molecular pathophysiology leading to this neuropaediatric phenotype has not been fully elucidated. Here we aimed to obtain novel insights into MICU1 pathophysiology.