scholarly journals Characterization of a Novel Splicing Variant in Acylglycerol Kinase (AGK) Associated with Fatal Sengers Syndrome

2021 ◽  
Vol 22 (24) ◽  
pp. 13484
Author(s):  
Sofia Barbosa-Gouveia ◽  
Maria E. Vázquez-Mosquera ◽  
Emiliano Gonzalez-Vioque ◽  
Álvaro Hermida-Ameijeiras ◽  
Laura L. Valverde ◽  
...  

Mitochondrial functional integrity depends on protein and lipid homeostasis in the mitochondrial membranes and disturbances in their accumulation can cause disease. AGK, a mitochondrial acylglycerol kinase, is not only involved in lipid signaling but is also a component of the TIM22 complex in the inner mitochondrial membrane, which mediates the import of a subset of membrane proteins. AGK mutations can alter both phospholipid metabolism and mitochondrial protein biogenesis, contributing to the pathogenesis of Sengers syndrome. We describe the case of an infant carrying a novel homozygous AGK variant, c.518+1G>A, who was born with congenital cataracts, pielic ectasia, critical congenital dilated myocardiopathy, and hyperlactacidemia and died 20 h after birth. Using the patient’s DNA, we performed targeted sequencing of 314 nuclear genes encoding respiratory chain complex subunits and proteins implicated in mitochondrial oxidative phosphorylation (OXPHOS). A decrease of 96-bp in the length of the AGK cDNA sequence was detected. Decreases in the oxygen consumption rate (OCR) and the OCR:ECAR (extracellular acidification rate) ratio in the patient’s fibroblasts indicated reduced electron flow through the respiratory chain, and spectrophotometry revealed decreased activity of OXPHOS complexes I and V. We demonstrate a clear defect in mitochondrial function in the patient’s fibroblasts and describe the possible molecular mechanism underlying the pathogenicity of this novel AGK variant. Experimental validation using in vitro analysis allowed an accurate characterization of the disease-causing variant.

2004 ◽  
Vol 380 (1) ◽  
pp. 231-242 ◽  
Author(s):  
Lidia de BARI ◽  
Anna ATLANTE ◽  
Daniela VALENTI ◽  
Salvatore PASSARELLA

In the light of the occurrence of l-lactate dehydrogenase inside the mitochondrial matrix, we looked at whether isolated rat liver mitochondria can take up and metabolize l-lactate, and provide oxaloacetate outside mitochondria, thus contributing to a partial reconstruction of gluconeogenesis in vitro. We found that: (1) l-lactate (10 mM), added to mitochondria in the presence of a cocktail of glycolysis/gluconeogenesis enzymes and cofactors, can lead to synthesis of glyceraldehyde-3-phosphate at a rate of about 7 nmol/min per mg mitochondrial protein. (2) Three novel translocators exist to mediate l-lactate traffic across the inner mitochondrial membrane. An l-lactate/H+ symporter was identified by measuring fluorimetrically the rate of endogenous pyridine nucleotide reduction. Consistently, l-lactate oxidation was found to occur with P/O ratio=3 (where P/O ratio is the ratio of mol of ATP synthesized to mol of oxygen atoms reduced to water during oxidative phosphorylation) and with generation of membrane potential. Proton uptake, which occurred as a result of addition of l-lactate to RLM together with electron flow inhibitors, and mitochondrial swelling in ammonium l-lactate solutions were also monitored. l-Lactate/oxaloacetate and l-lactate/pyruvate anti-porters were identified by monitoring photometrically the appearance of l-lactate counter-anions outside mitochondria. These l-lactate translocators, which are distinct from the monocarboxylate carrier, were found to differ from each other in Vmax values and in inhibition and pH profiles, and proved to regulate mitochondrial l-lactate metabolism in vitro. The role of lactate/mitochondria interactions in gluconeogenesis is discussed.


2015 ◽  
Vol 24 (10) ◽  
pp. 2952-2965 ◽  
Author(s):  
Luke E. Formosa ◽  
Masakazu Mimaki ◽  
Ann E. Frazier ◽  
Matthew McKenzie ◽  
Tegan L. Stait ◽  
...  

Blood ◽  
1995 ◽  
Vol 86 (7) ◽  
pp. 2481-2487 ◽  
Author(s):  
A Macho ◽  
M Castedo ◽  
P Marchetti ◽  
JJ Aguilar ◽  
D Decaudin ◽  
...  

Abstract In several models of lymphocyte apoptosis, two alterations of mitochondrial function precede advanced DNA fragmentation: (1) a reduction of mitochondrial transmembrane potential (delta psi m) and (2) an increase in mitochondrial generation of superoxide anion. Here we show that two fluorochromes allow for the identification of analogous mitochondrial perturbations in circulating T lymphocytes from human immunodeficiency virus (HIV)-1+ donors. The first among these fluorochromes, the cationic lipophilic dye DiOC6(3), measures delta psi m; the second marker, hydroethidine (HE), is nonfluorescent, unless it is oxidized by superoxide anions to the product ethidium (Eth). CD4+ or CD8+ cells from clinically asymptomatic HIV-1 carriers contain a significantly elevated percentage of cells endowed with enhanced HE --> Eth conversion and/or reduced DiOC6(3) uptake as compared with normal controls. Phenotypic characterization of (HE --> Eth)high cells from HIV+ donors shows that these cells possess a low delta psi m, thus demonstrating a functional alteration of mitochondria. In addition, (HE --> Eth)high cells display a reduced incorporation of the cardiolipin-specific dye nonyl-acridine orange (NAO), showing a structural defect of the cardiolipin-containing inner mitochondrial membrane. Control experiments involving rotenone, an inhibitor of the respiratory chain complex I, indicate that the reactive oxygen species responsible for HE --> Eth conversion is generated during mitochondrial electron transport. In synthesis, it appears that mitochondrial alterations occur in a significant percentage of circulating T lymphocytes from HIV-1 carriers. The extent of delta psi m reduction, as determined ex vivo, correlates with the frequency of cells undergoing DNA fragmentation after overnight in vitro culture. These observations may be important for the understanding and for the direct ex vivo quantitation of HIV-triggered lymphocyte destruction.


2008 ◽  
Vol 28 (13) ◽  
pp. 4424-4433 ◽  
Author(s):  
Dirk Schiller ◽  
Yu Chin Cheng ◽  
Qinglian Liu ◽  
William Walter ◽  
Elizabeth A. Craig

ABSTRACT Translocation of proteins from the cytosol across the mitochondrial inner membrane is driven by the action of the import motor, which is associated with the translocon on the matrix side of the membrane. It is well established that an essential peripheral membrane protein, Tim44, tethers mitochondrial Hsp70 (mtHsp70), the core of the import motor, to the translocon. This Tim44-mtHsp70 interaction, which can be recapitulated in vitro, is destabilized by binding of mtHsp70 to a substrate polypeptide. Here we report that the N-terminal 167-amino-acid segment of mature Tim44 is sufficient for both interaction with mtHsp70 and destabilization of a Tim44-mtHsp70 complex caused by client protein binding. Amino acid alterations within a 30-amino-acid segment affected both the release of mtHsp70 upon peptide binding and the interaction of Tim44 with the translocon. Our results support the idea that Tim44 plays multiple roles in mitochondrial protein import by recruiting Ssc1 and its J protein cochaperone to the translocon and coordinating their interactions to promote efficient protein translocation in vivo.


2010 ◽  
Vol 1352 ◽  
pp. 231-238 ◽  
Author(s):  
Estela Natacha Brandt Busanello ◽  
Carolina Maso Viegas ◽  
Alana Pimentel Moura ◽  
Anelise Miotti Tonin ◽  
Mateus Grings ◽  
...  

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