RESUMO
STIM1 is an endoplasmic reticulum (ER) protein that modulates the activity of a number of Ca2+ transport systems. By direct physical interaction with ORAI1, a plasma membrane Ca2+ channel, STIM1 activates the ICRAC current, whereas the binding with the voltage-operated Ca2+ channel CaV1.2 inhibits the current through this latter channel. In this way, STIM1 is a key regulator of Ca2+ signaling in excitable and non-excitable cells, and altered STIM1 levels have been reported to underlie several pathologies, including immunodeficiency, neurodegenerative diseases, and cancer. In both sporadic and familial Alzheimer's disease, a decrease of STIM1 protein levels accounts for the alteration of Ca2+ handling that compromises neuronal cell viability. Using SH-SY5Y cells edited by CRISPR/Cas9 to knockout STIM1 gene expression, this work evaluated the molecular mechanisms underlying the cell death triggered by the deficiency of STIM1, demonstrating that STIM1 is a positive regulator of ITPR3 gene expression. ITPR3 (or IP3R3) is a Ca2+ channel enriched at ER-mitochondria contact sites where it provides Ca2+ for transport into the mitochondria. Thus, STIM1 deficiency leads to a strong reduction of ITPR3 transcript and ITPR3 protein levels, a consequent decrease of the mitochondria free Ca2+ concentration ([Ca2+]mit), reduction of mitochondrial oxygen consumption rate, and decrease in ATP synthesis rate. All these values were normalized by ectopic expression of ITPR3 in STIM1-KO cells, providing strong evidence for a new mode of regulation of [Ca2+]mit mediated by the STIM1-ITPR3 axis.
Assuntos
Sinalização do Cálcio , Receptores de Inositol 1,4,5-Trifosfato/metabolismo , Mitocôndrias/metabolismo , Proteínas de Neoplasias/metabolismo , Molécula 1 de Interação Estromal/metabolismo , Linhagem Celular Tumoral , Regulação para Baixo , Técnicas de Inativação de Genes , Humanos , Proteínas de Neoplasias/genética , Molécula 1 de Interação Estromal/genéticaRESUMO
Mitochondrial division requires division of both the inner and outer mitochondrial membranes (IMM and OMM, respectively). Interaction with endoplasmic reticulum (ER) promotes OMM division by recruitment of the dynamin Drp1, but effects on IMM division are not well characterized. We previously showed that actin polymerization through ER-bound inverted formin 2 (INF2) stimulates Drp1 recruitment in mammalian cells. Here, we show that INF2-mediated actin polymerization stimulates a second mitochondrial response independent of Drp1: a rise in mitochondrial matrix calcium through the mitochondrial calcium uniporter. ER stores supply the increased mitochondrial calcium, and the role of actin is to increase ER-mitochondria contact. Myosin IIA is also required for this mitochondrial calcium increase. Elevated mitochondrial calcium in turn activates IMM constriction in a Drp1-independent manner. IMM constriction requires electron transport chain activity. IMM division precedes OMM division. These results demonstrate that actin polymerization independently stimulates the dynamics of both membranes during mitochondrial division: IMM through increased matrix calcium, and OMM through Drp1 recruitment.
Assuntos
Actinas/metabolismo , Divisão Celular/fisiologia , Retículo Endoplasmático/metabolismo , Proteínas dos Microfilamentos/metabolismo , Mitocôndrias/metabolismo , Membranas Mitocondriais/metabolismo , Cálcio/metabolismo , Linhagem Celular Tumoral , Dinaminas , Forminas , GTP Fosfo-Hidrolases/genética , GTP Fosfo-Hidrolases/metabolismo , Humanos , Transporte de Íons/fisiologia , Proteínas Associadas aos Microtúbulos/genética , Proteínas Associadas aos Microtúbulos/metabolismo , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismoRESUMO
Clearance of apoptotic cells (ACs) by phagocytes (efferocytosis) prevents post-apoptotic necrosis and dampens inflammation. Defective efferocytosis drives important diseases, including atherosclerosis. For efficient efferocytosis, phagocytes must be able to internalize multiple ACs. We show here that uptake of multiple ACs by macrophages requires dynamin-related protein 1 (Drp1)-mediated mitochondrial fission, which is triggered by AC uptake. When mitochondrial fission is disabled, AC-induced increase in cytosolic calcium is blunted owing to mitochondrial calcium sequestration, and calcium-dependent phagosome formation around secondarily encountered ACs is impaired. These defects can be corrected by silencing the mitochondrial calcium uniporter (MCU). Mice lacking myeloid Drp1 showed defective efferocytosis and its pathologic consequences in the thymus after dexamethasone treatment and in advanced atherosclerotic lesions in fat-fed Ldlr-/- mice. Thus, mitochondrial fission in response to AC uptake is a critical process that enables macrophages to clear multiple ACs and to avoid the pathologic consequences of defective efferocytosis in vivo.
Assuntos
Macrófagos/citologia , Dinâmica Mitocondrial , Animais , Apoptose , Humanos , Macrófagos/metabolismo , Camundongos , Proteínas Associadas aos Microtúbulos/metabolismo , Mitocôndrias/metabolismo , Células Mieloides/metabolismo , Fagócitos/metabolismo , Fagossomos/metabolismoRESUMO
Fast inhibitory glycinergic transmission occurs in spinal cord, brainstem, and retina to modulate the processing of motor and sensory information. After synaptic vesicle fusion, glycine is recovered back to the presynaptic terminal by the neuronal glycine transporter 2 (GlyT2) to maintain quantal glycine content in synaptic vesicles. The loss of presynaptic GlyT2 drastically impairs the refilling of glycinergic synaptic vesicles and severely disrupts neurotransmission. Indeed, mutations in the gene encoding GlyT2 are the main presynaptic cause of hyperekplexia in humans. Here, we show a novel endogenous regulatory mechanism that can modulate GlyT2 activity based on a compartmentalized interaction between GlyT2, neuronal plasma membrane Ca(2+)-ATPase (PMCA) isoforms 2 and 3, and Na(+)/Ca(2+)-exchanger 1 (NCX1). This GlyT2·PMCA2,3·NCX1 complex is found in lipid raft subdomains where GlyT2 has been previously found to be fully active. We show that endogenous PMCA and NCX activities are necessary for GlyT2 activity and that this modulation depends on lipid raft integrity. Besides, we propose a model in which GlyT2·PMCA2-3·NCX complex would help Na(+)/K(+)-ATPase in controlling local Na(+) increases derived from GlyT2 activity after neurotransmitter release.
Assuntos
Proteínas da Membrana Plasmática de Transporte de Glicina/metabolismo , ATPases Transportadoras de Cálcio da Membrana Plasmática/metabolismo , Células Receptoras Sensoriais/metabolismo , Trocador de Sódio e Cálcio/metabolismo , Animais , Tronco Encefálico/citologia , Tronco Encefálico/efeitos dos fármacos , Tronco Encefálico/metabolismo , Regulação da Expressão Gênica , Proteínas da Membrana Plasmática de Transporte de Glicina/genética , Peptídeos e Proteínas de Sinalização Intercelular , Masculino , Microdomínios da Membrana/química , Microdomínios da Membrana/efeitos dos fármacos , Microdomínios da Membrana/metabolismo , Peptídeos/farmacologia , ATPases Transportadoras de Cálcio da Membrana Plasmática/antagonistas & inibidores , ATPases Transportadoras de Cálcio da Membrana Plasmática/genética , Terminações Pré-Sinápticas/efeitos dos fármacos , Cultura Primária de Células , Ligação Proteica , Ratos , Ratos Wistar , Células Receptoras Sensoriais/citologia , Células Receptoras Sensoriais/efeitos dos fármacos , Trocador de Sódio e Cálcio/antagonistas & inibidores , Trocador de Sódio e Cálcio/genética , Medula Espinal/citologia , Medula Espinal/efeitos dos fármacos , Medula Espinal/metabolismo , Transmissão Sináptica , Tioureia/análogos & derivados , Tioureia/farmacologia , beta-Ciclodextrinas/farmacologiaRESUMO
The neuronal glycine transporter GlyT2 plays a fundamental role in the glycinergic neurotransmission by recycling the neurotransmitter to the presynaptic terminal. GlyT2 is the main supplier of glycine for vesicle refilling, a process that is absolutely necessary to preserve quantal glycine content in synaptic vesicles. Alterations in GlyT2 activity modify glycinergic neurotransmission and may underlie several neuromuscular disorders, such as hyperekplexia, myoclonus, dystonia, and epilepsy. Indeed, mutations in the gene encoding GlyT2 are the main presynaptic cause of hyperekplexia in humans and produce congenital muscular dystonia type 2 (CMD2) in Belgian Blue cattle. GlyT2 function is strictly coupled to the sodium electrochemical gradient actively generated by the Na+/K+-ATPase (NKA). GlyT2 cotransports 3Na+/Cl-/glycine generating large rises of Na+ inside the presynaptic terminal that must be efficiently reduced by the NKA to preserve Na+ homeostasis. In this work, we have used high-throughput mass spectrometry to identify proteins interacting with GlyT2 in the CNS. NKA was detected as a putative candidate and through reciprocal coimmunoprecipitations and immunocytochemistry analyses the association between GlyT2 and NKA was confirmed. NKA mainly interacts with the raft-associated active pool of GlyT2, and low and high levels of the specific NKA ligand ouabain modulate the endocytosis and total expression of GlyT2 in neurons. The ouabain-mediated downregulation of GlyT2 also occurs in vivo in two different systems: zebrafish embryos and adult rats, indicating that this NKA-mediated regulatory mechanism is evolutionarily conserved and may play a relevant role in the physiological control of inhibitory glycinergic neurotransmission.
Assuntos
Regulação para Baixo , Proteínas da Membrana Plasmática de Transporte de Glicina/metabolismo , Neurônios/metabolismo , ATPase Trocadora de Sódio-Potássio/metabolismo , Proteínas de Peixe-Zebra/metabolismo , Animais , Tronco Encefálico/citologia , Endocitose , Regulação da Expressão Gênica no Desenvolvimento , Proteínas da Membrana Plasmática de Transporte de Glicina/genética , Homeostase , Masculino , Microdomínios da Membrana/metabolismo , Ouabaína/farmacologia , Ratos , Ratos Wistar , Sódio/metabolismo , ATPase Trocadora de Sódio-Potássio/antagonistas & inibidores , Medula Espinal/citologia , Peixe-Zebra , Proteínas de Peixe-Zebra/genéticaRESUMO
Hyperekplexia or startle disease is characterized by an exaggerated startle response, evoked by tactile or auditory stimuli, producing hypertonia and apnea episodes. Although rare, this orphan disorder can have serious consequences, including sudden infant death. Dominant and recessive mutations in the human glycine receptor (GlyR) α1 gene (GLRA1) are the major cause of this disorder. However, recessive mutations in the presynaptic Na(+)/Cl(-)-dependent glycine transporter GlyT2 gene (SLC6A5) are rapidly emerging as a second major cause of startle disease. In this study, systematic DNA sequencing of SLC6A5 revealed a new dominant GlyT2 mutation: pY705C (c.2114AâG) in transmembrane domain 11, in eight individuals from Spain and the United Kingdom. Curiously, individuals harboring this mutation show significant variation in clinical presentation. In addition to classical hyperekplexia symptoms, some individuals had abnormal respiration, facial dysmorphism, delayed motor development, or intellectual disability. We functionally characterized this mutation using molecular modeling, electrophysiology, [(3)H]glycine transport, cell surface expression, and cysteine labeling assays. We found that the introduced cysteine interacts with the cysteine pair Cys-311-Cys-320 in the second external loop of GlyT2. This interaction impairs transporter maturation through the secretory pathway, reduces surface expression, and inhibits transport function. Additionally, Y705C presents altered H(+) and Zn(2+) dependence of glycine transport that may affect the function of glycinergic neurotransmission in vivo.