RESUMEN
Mitochondria are bioenergetic, biosynthetic, and signaling organelles that are integral in stress sensing to allow for cellular adaptation to the environment. Therefore, it is not surprising that mitochondria are important mediators of tumorigenesis, as this process requires flexibility to adapt to cellular and environmental alterations in addition to cancer treatments. Multiple aspects of mitochondrial biology beyond bioenergetics support transformation, including mitochondrial biogenesis and turnover, fission and fusion dynamics, cell death susceptibility, oxidative stress regulation, metabolism, and signaling. Thus, understanding mechanisms of mitochondrial function during tumorigenesis will be critical for the next generation of cancer therapeutics.
Asunto(s)
Carcinogénesis , Mitocondrias/fisiología , Animales , HumanosRESUMEN
Mitochondrial sirtuins, SIRT3-5, are NAD+-dependent deacylases and ADP-ribosyltransferases that are critical for stress responses. However, a comprehensive understanding of sirtuin targets, regulation of sirtuin activity, and the relationships between sirtuins remains a key challenge in mitochondrial physiology. Here, we employ systematic interaction proteomics to elucidate the mitochondrial sirtuin protein interaction landscape. This work reveals sirtuin interactions with numerous functional modules within mitochondria, identifies candidate sirtuin substrates, and uncovers a fundamental role for sequestration of SIRT3 by ATP synthase in mitochondrial homeostasis. In healthy mitochondria, a pool of SIRT3 binds ATP synthase, but upon matrix pH reduction with concomitant loss of mitochondrial membrane potential, SIRT3 dissociates. This release correlates with rapid deacetylation of matrix proteins, and SIRT3 is required for recovery of membrane potential. In vitro reconstitution experiments, as well as analysis of CRISPR/Cas9-engineered cells, indicate that pH-dependent SIRT3 release requires H135 in the ATP5O subunit of ATP synthase. Our SIRT3-5 interaction network provides a framework for discovering novel biological functions regulated by mitochondrial sirtuins.
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Mitocondrias/metabolismo , Mapas de Interacción de Proteínas , Sirtuina 3/metabolismo , Acetilación , Adenosina Trifosfatasas/metabolismo , Animales , Proteínas Portadoras/metabolismo , Células HeLa , Humanos , Inmunoprecipitación , Proteínas de la Membrana/metabolismo , Ratones , Proteínas Mitocondriales/metabolismo , ATPasas de Translocación de Protón Mitocondriales , Sirtuinas/clasificación , Sirtuinas/metabolismoRESUMEN
Human cancers with activating RAS mutations are typically highly aggressive and treatment-refractory, yet RAS mutation itself is insufficient for tumorigenesis, due in part to profound metabolic stress induced by RAS activation. Here we show that loss of REDD1, a stress-induced metabolic regulator, is sufficient to reprogram lipid metabolism and drive progression of RAS mutant cancers. Redd1 deletion in genetically engineered mouse models (GEMMs) of KRAS-dependent pancreatic and lung adenocarcinomas converts preneoplastic lesions into invasive and metastatic carcinomas. Metabolic profiling reveals that REDD1-deficient/RAS mutant cells exhibit enhanced uptake of lysophospholipids and lipid storage, coupled to augmented fatty acid oxidation that sustains both ATP levels and ROS-detoxifying NADPH. Mechanistically, REDD1 loss triggers HIF-dependent activation of a lipid storage pathway involving PPARγ and the prometastatic factor CD36. Correspondingly, decreased REDD1 expression and a signature of REDD1 loss predict poor outcomes selectively in RAS mutant but not RAS wild-type human lung and pancreas carcinomas. Collectively, our findings reveal the REDD1-mediated stress response as a novel tumor suppressor whose loss defines a RAS mutant tumor subset characterized by reprogramming of lipid metabolism, invasive and metastatic progression, and poor prognosis. This work thus provides new mechanistic and clinically relevant insights into the phenotypic heterogeneity and metabolic rewiring that underlies these common cancers.
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Metabolismo de los Lípidos/genética , Factores de Transcripción/genética , Factores de Transcripción/metabolismo , Proteínas ras/genética , Animales , Línea Celular Tumoral , Progresión de la Enfermedad , Ácidos Grasos/metabolismo , Células HEK293 , Humanos , Ratones , Ratones SCID , Mutación , Oxidación-ReducciónRESUMEN
Non-genetic mechanisms have recently emerged as important drivers of cancer therapy failure1, where some cancer cells can enter a reversible drug-tolerant persister state in response to treatment2. Although most cancer persisters remain arrested in the presence of the drug, a rare subset can re-enter the cell cycle under constitutive drug treatment. Little is known about the non-genetic mechanisms that enable cancer persisters to maintain proliferative capacity in the presence of drugs. To study this rare, transiently resistant, proliferative persister population, we developed Watermelon, a high-complexity expressed barcode lentiviral library for simultaneous tracing of each cell's clonal origin and proliferative and transcriptional states. Here we show that cycling and non-cycling persisters arise from different cell lineages with distinct transcriptional and metabolic programs. Upregulation of antioxidant gene programs and a metabolic shift to fatty acid oxidation are associated with persister proliferative capacity across multiple cancer types. Impeding oxidative stress or metabolic reprogramming alters the fraction of cycling persisters. In human tumours, programs associated with cycling persisters are induced in minimal residual disease in response to multiple targeted therapies. The Watermelon system enabled the identification of rare persister lineages that are preferentially poised to proliferate under drug pressure, thus exposing new vulnerabilities that can be targeted to delay or even prevent disease recurrence.
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Ciclo Celular , Linaje de la Célula , Recurrencia Local de Neoplasia/tratamiento farmacológico , Recurrencia Local de Neoplasia/patología , Neoplasias/tratamiento farmacológico , Neoplasias/patología , Antioxidantes/metabolismo , Ciclo Celular/efectos de los fármacos , Línea Celular Tumoral , Linaje de la Célula/efectos de los fármacos , Proliferación Celular/efectos de los fármacos , Supervivencia Celular/efectos de los fármacos , Células Clonales/efectos de los fármacos , Células Clonales/metabolismo , Células Clonales/patología , Código de Barras del ADN Taxonómico , Ácidos Grasos/metabolismo , Regulación Neoplásica de la Expresión Génica , Humanos , Lentivirus/genética , Recurrencia Local de Neoplasia/genética , Neoplasias/genética , Neoplasias/metabolismo , Proteínas Oncogénicas/antagonistas & inhibidores , Oxidación-Reducción , Estrés Oxidativo , Especies Reactivas de Oxígeno/metabolismo , Transcripción Genética/efectos de los fármacosRESUMEN
MCL-1 is a BCL-2 family protein implicated in the development and chemoresistance of human cancer. Unlike its anti-apoptotic homologs, Mcl-1 deletion has profound physiologic consequences, indicative of a broader role in homeostasis. We report that the BCL-2 homology 3 (BH3) α helix of MCL-1 can directly engage very long-chain acyl-CoA dehydrogenase (VLCAD), a key enzyme of the mitochondrial fatty acid ß-oxidation (FAO) pathway. Proteomic analysis confirmed that the mitochondrial matrix isoform of MCL-1 (MCL-1Matrix) interacts with VLCAD. Mcl-1 deletion, or eliminating MCL-1Matrix alone, selectively deregulated long-chain FAO, causing increased flux through the pathway in response to nutrient deprivation. Transient elevation in MCL-1 upon serum withdrawal, a striking increase in MCL-1 BH3/VLCAD interaction upon palmitic acid titration, and direct modulation of enzymatic activity by the MCL-1 BH3 α helix are consistent with dynamic regulation. Thus, the MCL-1 BH3 interaction with VLCAD revealed a separable, gain-of-function role for MCL-1 in the regulation of lipid metabolism.
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Acil-CoA Deshidrogenasa de Cadena Larga/metabolismo , Metabolismo de los Lípidos/fisiología , Proteína 1 de la Secuencia de Leucemia de Células Mieloides/metabolismo , Ácido Palmítico/metabolismo , Acil-CoA Deshidrogenasa de Cadena Larga/genética , Animales , Línea Celular , Ratones , Ratones Noqueados , Proteína 1 de la Secuencia de Leucemia de Células Mieloides/genética , Oxidación-Reducción , Estructura Secundaria de ProteínaRESUMEN
Energy balance and nutrient availability are key determinants of cellular decisions to remain quiescent, proliferate, or differentiate into a mature cell. After assessing its environmental state, the cell must rewire its metabolism to support distinct cellular outcomes. Mechanistically, how metabolites regulate cell fate decisions is poorly understood. We used adipogenesis as our model system to ascertain the role of metabolism in differentiation. We isolated adipose tissue stromal vascular fraction cells and profiled metabolites before and after adipogenic differentiation to identify metabolic signatures associated with these distinct cellular states. We found that differentiation alters nucleotide accumulation. Furthermore, inhibition of nucleotide biosynthesis prevented lipid storage within adipocytes and downregulated the expression of lipogenic factors. In contrast to proliferating cells, in which mechanistic target of rapamycin complex 1 is activated by purine accumulation, mechanistic target of rapamycin complex 1 signaling was unaffected by purine levels in differentiating adipocytes. Rather, our data indicated that purines regulate transcriptional activators of adipogenesis, peroxisome proliferator-activated receptor γ and CCAAT/enhancer-binding protein α, to promote differentiation. Although de novo nucleotide biosynthesis has mainly been studied in proliferation, our study points to its requirement in adipocyte differentiation.
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Adipogénesis , Metabolismo de los Lípidos , Nucleótidos , Animales , Ratones , Células 3T3-L1 , Adipocitos/citología , Adipocitos/metabolismo , Diferenciación Celular , Diana Mecanicista del Complejo 1 de la Rapamicina/genética , Diana Mecanicista del Complejo 1 de la Rapamicina/metabolismo , PPAR gamma/genética , PPAR gamma/metabolismo , Nucleótidos/biosíntesis , Purinas/metabolismo , Proteína alfa Potenciadora de Unión a CCAAT/genética , Proteína alfa Potenciadora de Unión a CCAAT/metabolismo , Transducción de SeñalRESUMEN
The physical characteristics of brown adipose tissue (BAT) are defined by the presence of multilocular lipid droplets (LDs) within the brown adipocytes and a high abundance of iron-containing mitochondria, which give it its characteristic color. Normal mitochondrial function is, in part, regulated by organelle-to-organelle contacts. For example, the contact sites that mediate mitochondria-LD interactions are thought to have various physiological roles, such as the synthesis and metabolism of lipids. Aging is associated with mitochondrial dysfunction, and previous studies show that there are changes in mitochondrial structure and the proteins that modulate organelle contact sites. However, how mitochondria-LD interactions change with aging has yet to be fully clarified. Therefore, we sought to define age-related changes in LD morphology and mitochondria-lipid interactions in BAT. We examined the three-dimensional morphology of mitochondria and LDs in young (3-month) and aged (2-year) murine BAT using serial block face-scanning electron microscopy and the Amira program for segmentation, analysis, and quantification. Our analyses showed reductions in LD volume, area, and perimeter in aged samples in comparison to young samples. Additionally, we observed changes in LD appearance and type in aged samples compared to young samples. Notably, we found differences in mitochondrial interactions with LDs, which could implicate that these contacts may be important for energetics in aging. Upon further investigation, we also found changes in mitochondrial and cristae structure for the mitochondria interacting with LDs. Overall, these data define the nature of LD morphology and organelle-organelle contacts during aging and provide insight into LD contact site changes that interconnect biogerontology with mitochondrial function, metabolism, and bioactivity in aged BAT.
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While much research has examined the use of glucose and glutamine by tumor cells, many cancers instead prefer to metabolize fats. Despite the pervasiveness of this phenotype, knowledge of pathways that drive fatty acid oxidation (FAO) in cancer is limited. Prolyl hydroxylase domain proteins hydroxylate substrate proline residues and have been linked to fuel switching. Here, we reveal that PHD3 rapidly triggers repression of FAO in response to nutrient abundance via hydroxylation of acetyl-coA carboxylase 2 (ACC2). We find that PHD3 expression is strongly decreased in subsets of cancer including acute myeloid leukemia (AML) and is linked to a reliance on fat catabolism regardless of external nutrient cues. Overexpressing PHD3 limits FAO via regulation of ACC2 and consequently impedes leukemia cell proliferation. Thus, loss of PHD3 enables greater utilization of fatty acids but may also serve as a metabolic and therapeutic liability by indicating cancer cell susceptibility to FAO inhibition.
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Acetil-CoA Carboxilasa/metabolismo , Ácidos Grasos/metabolismo , Regulación Neoplásica de la Expresión Génica , Prolina Dioxigenasas del Factor Inducible por Hipoxia/metabolismo , Leucemia Mieloide Aguda/metabolismo , Prolina/metabolismo , Acetil-CoA Carboxilasa/antagonistas & inhibidores , Acetil-CoA Carboxilasa/química , Acetil-CoA Carboxilasa/genética , Secuencia de Aminoácidos , Animales , Línea Celular Tumoral , Células HEK293 , Humanos , Hidroxilación , Prolina Dioxigenasas del Factor Inducible por Hipoxia/química , Prolina Dioxigenasas del Factor Inducible por Hipoxia/genética , Células K562 , Leucemia Mieloide Aguda/genética , Leucemia Mieloide Aguda/mortalidad , Leucemia Mieloide Aguda/patología , Masculino , Redes y Vías Metabólicas/genética , Ratones , Ratones Endogámicos NOD , Modelos Moleculares , Trasplante de Neoplasias , Oxidación-Reducción , Prolina/química , ARN Interferente Pequeño/genética , ARN Interferente Pequeño/metabolismo , Transducción de Señal , Homología Estructural de Proteína , Análisis de SupervivenciaRESUMEN
With sparse treatment options, cardiac disease remains a significant cause of death among humans. As a person ages, mitochondria breakdown and the heart becomes less efficient. Heart failure is linked to many mitochondria-associated processes, including endoplasmic reticulum stress, mitochondrial bioenergetics, insulin signaling, autophagy, and oxidative stress. The roles of key mitochondrial complexes that dictate the ultrastructure, such as the mitochondrial contact site and cristae organizing system (MICOS), in aging cardiac muscle are poorly understood. To better understand the cause of age-related alteration in mitochondrial structure in cardiac muscle, we used transmission electron microscopy (TEM) and serial block facing-scanning electron microscopy (SBF-SEM) to quantitatively analyze the three-dimensional (3-D) networks in cardiac muscle samples of male mice at aging intervals of 3 mo, 1 yr, and 2 yr. Here, we present the loss of cristae morphology, the inner folds of the mitochondria, across age. In conjunction with this, the three-dimensional (3-D) volume of mitochondria decreased. These findings mimicked observed phenotypes in murine cardiac fibroblasts with CRISPR/Cas9 knockout of Mitofilin, Chchd3, Chchd6 (some members of the MICOS complex), and Opa1, which showed poorer oxidative consumption rate and mitochondria with decreased mitochondrial length and volume. In combination, these data show the need to explore if loss of the MICOS complex in the heart may be involved in age-associated mitochondrial and cristae structural changes.NEW & NOTEWORTHY This article shows how mitochondria in murine cardiac changes, importantly elucidating age-related changes. It also is the first to show that the MICOS complex may play a role in outer membrane mitochondrial structure.
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Mitocondrias , Miocardio , Humanos , Masculino , Ratones , Animales , Mitocondrias/metabolismo , Miocardio/metabolismo , Corazón , Envejecimiento , Transducción de Señal , Proteínas Mitocondriales/metabolismoRESUMEN
Metastasis remains the leading cause of cancer mortality, and reactive oxygen species (ROS) signaling promotes the metastatic cascade. However, the molecular pathways that control ROS signaling relevant to metastasis are little studied. Here, we identify SIRT3, a mitochondrial deacetylase, as a regulator of cell migration via its control of ROS signaling. We find that, although mitochondria are present at the leading edge of migrating cells, SIRT3 expression is down-regulated during migration, resulting in elevated ROS levels. This SIRT3-mediated control of ROS represses Src oxidation and attenuates focal adhesion kinase (FAK) activation. SIRT3 overexpression inhibits migration and metastasis in breast cancer cells. Finally, in human breast cancers, SIRT3 expression is inversely correlated with metastatic outcome and Src/FAK signaling. Our results reveal a role for SIRT3 in cell migration, with important implications for breast cancer progression.
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Neoplasias de la Mama/metabolismo , Movimiento Celular , Células Epiteliales/metabolismo , Quinasa 1 de Adhesión Focal/metabolismo , Proteínas de Neoplasias/metabolismo , Sirtuina 3/biosíntesis , Familia-src Quinasas/metabolismo , Neoplasias de la Mama/patología , Línea Celular Tumoral , Activación Enzimática , Células Epiteliales/patología , Femenino , Humanos , Metástasis de la Neoplasia , Especies Reactivas de Oxígeno , Sirtuina 3/metabolismoRESUMEN
Cells continually assess their energy and nutrient state to maintain growth and survival and engage necessary homeostatic mechanisms. Cell-autonomous responses to the fed state require the surveillance of the availability of amino acids and other nutrients. The mammalian target of rapamycin complex 1 (mTORC1) integrates information on nutrient and amino acid availability to support protein synthesis and cell growth. We identify the G protein-coupled receptor (GPCR) T1R1/T1R3 as a direct sensor of the fed state and amino acid availability. Knocking down this receptor, which is found in most tissues, reduces the ability of amino acids to signal to mTORC1. Interfering with this receptor alters localization of mTORC1, downregulates expression of pathway inhibitors, upregulates key amino acid transporters, blocks translation initiation, and induces autophagy. These findings reveal a mechanism for communicating amino acid availability through a GPCR to mTORC1 in mammals.
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Autofagia , Células Secretoras de Insulina/metabolismo , Proteínas/metabolismo , Receptores Acoplados a Proteínas G/genética , Receptores Acoplados a Proteínas G/metabolismo , Aminoácidos/metabolismo , Animales , Regulación hacia Abajo , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Insulina/metabolismo , Diana Mecanicista del Complejo 1 de la Rapamicina , Ratones , Ratones Noqueados , Complejos Multiproteicos , Biosíntesis de Proteínas , Interferencia de ARN , ARN Interferente Pequeño , Transducción de Señal , Serina-Treonina Quinasas TORRESUMEN
The kinesin family members (KIFs) KIF2A and KIF2C depolymerize microtubules, unlike the majority of other kinesins, which transport cargo along microtubules. KIF2A regulates the localization of lysosomes in the cytoplasm, which assists in activation of the mechanistic target of rapamycin complex 1 (mTORC1) on the lysosomal surface. We find that the closely related kinesin KIF2C also influences lysosomal organization in immortalized human bronchial epithelial cells (HBECs). Expression of KIF2C and, to a lesser extent, KIF2A in untransformed and mutant K-Ras-transformed cells is regulated by ERK1/2. Prolonged inhibition of ERK1/2 activation with PD0325901 mimics nutrient deprivation by disrupting lysosome organization and decreasing mTORC1 activity in HBEC, suggesting a long-term mechanism for optimization of mTORC1 activity by ERK1/2. We tested the hypothesis that up-regulation of KIF2C and KIF2A by ERK1/2 caused aberrant lysosomal positioning and mTORC1 activity in a mutant K-Ras-dependent cancer and cancer model. In Ras-transformed cells, however, mTORC1 activity and lysosome organization appear independent of ERK1/2 and these kinesins although ERK1/2 activity and the kinesins are required for Ras-dependent proliferation and migration. We conclude that mutant K-Ras repurposes these signaling and regulatory proteins to support the transformed phenotype.
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Aminoácidos/metabolismo , Transformación Celular Neoplásica/metabolismo , Transformación Celular Neoplásica/patología , Cinesinas/metabolismo , Proteínas Proto-Oncogénicas/metabolismo , Proteínas ras/metabolismo , Autofagia , Línea Celular Transformada , Línea Celular Tumoral , Células Epiteliales/enzimología , Células Epiteliales/patología , Quinasas MAP Reguladas por Señal Extracelular/antagonistas & inhibidores , Quinasas MAP Reguladas por Señal Extracelular/metabolismo , Humanos , Lisosomas/metabolismo , Sistema de Señalización de MAP Quinasas , Diana Mecanicista del Complejo 1 de la Rapamicina , Complejos Multiproteicos/metabolismo , Neoplasias/metabolismo , Neoplasias/patología , Fosforilación , Transporte de Proteínas , Proteínas Proto-Oncogénicas p21(ras) , ARN Interferente Pequeño/metabolismo , Proteínas Quinasas S6 Ribosómicas/metabolismo , Serina-Treonina Quinasas TOR/metabolismoRESUMEN
The mitogen-activated protein kinase ERK2 is able to elicit a wide range of context-specific responses to distinct stimuli, but the mechanisms underlying this versatility remain in question. Some cellular functions of ERK2 are mediated through regulation of gene expression. In addition to phosphorylating numerous transcriptional regulators, ERK2 is known to associate with chromatin and has been shown to bind oligonucleotides directly. ERK2 is activated by the upstream kinases MEK1/2, which phosphorylate both tyrosine 185 and threonine 183. ERK2 requires phosphorylation on both sites to be fully active. Some additional ERK2 phosphorylation sites have also been reported, including threonine 188. It has been suggested that this phospho form has distinct properties. We detected some ERK2 phosphorylated on T188 in bacterial preparations of ERK2 by mass spectrometry and further demonstrate that phosphomimetic substitution of this ERK2 residue impairs its kinase activity toward well-defined substrates and also affects its DNA binding. We used electrophoretic mobility shift assays with oligonucleotides derived from the insulin gene promoter and other regions to examine effects of phosphorylation and mutations on the binding of ERK2 to DNA. We show that ERK2 can bind oligonucleotides directly. Phosphorylation and mutations alter DNA binding and support the idea that signaling functions may be influenced through an alternate phosphorylation site.
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Proteína Quinasa 1 Activada por Mitógenos/genética , Proteína Quinasa 1 Activada por Mitógenos/metabolismo , Oligonucleótidos/genética , Oligonucleótidos/metabolismo , Animales , Proteína Quinasa 1 Activada por Mitógenos/química , Mutación/fisiología , Oligonucleótidos/química , Fosforilación/fisiología , Unión Proteica/fisiología , Estructura Secundaria de Proteína , RatasRESUMEN
Autistic adults (AA) have the highest unemployment rate relative to other groups, regardless of disability status. Systemic changes are needed to acquire and retain AA in science, technology, engineering, mathematics, and medicine (STEMM). Here, we discuss the unique challenges AA face in STEMM and possible solutions to overcome them.
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Sirtuins are NAD+-dependent protein lysine deacylases implicated in aging-related diseases. Mammalian Sirtuin 4 (Sirt4) is located in mitochondria and a potential therapeutic target for cancer and metabolic diseases, but no potent and selective Sirt4 inhibitors have been reported. Here, we describe the identification of potent Sirt4-specific small-molecule inhibitors. Testing hits from a target-based virtual screen revealed 12 active compounds. A focused screen based on two top compounds, followed by structure-assisted design of derivatives, yielded four first-in-class potent Sirt4 inhibitors. Kinetic analyses indicate compound competition with the acyl peptide substrate, consistent with the docking models and implicating Sirt4's unique acyl binding site. The compounds indeed show preference for Sirt4 over other isoforms, with one of them (69) being highly isoform selective, and they are active in cells. Our results provide first lead compounds and mechanistic insights for optimization toward Sirt4-specific inhibitors useful as experimental tools and potential therapeutics.
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Mitocondrias , Sirtuinas , Animales , Mitocondrias/metabolismo , Isoformas de Proteínas/metabolismo , Sitios de Unión , Lisina/química , Proteínas Mitocondriales/metabolismo , Mamíferos/metabolismoRESUMEN
Mitochondria are required for energy production and even give brown adipose tissue (BAT) its characteristic color due to their high iron content and abundance. The physiological function and bioenergetic capacity of mitochondria are connected to the structure, folding, and organization of its inner-membrane cristae. During the aging process, mitochondrial dysfunction is observed, and the regulatory balance of mitochondrial dynamics is often disrupted, leading to increased mitochondrial fragmentation in aging cells. Therefore, it is hypothesized that significant morphological changes in BAT mitochondria and cristae will be present with aging. A quantitative 3D electron microscopy approach is developed to map cristae network organization in mouse BAT to test this hypothesis. Using this methodology, the 3D morphology of mitochondrial cristae is investigated in adult (3-month) and aged (2-year) murine BAT tissue via serial block face-scanning electron microscopy (SBF-SEM) and 3D reconstruction software for manual segmentation, analysis, and quantification. Upon investigation, an increase is found in mitochondrial volume, surface area, and complexity and decreased sphericity in aged BAT, alongside significant decreases in cristae volume, area, perimeter, and score. Overall, these data define the nature of the mitochondrial structure in murine BAT across aging.
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Tejido Adiposo Pardo , Membranas Mitocondriales , Animales , Ratones , Tejido Adiposo Pardo/metabolismo , Mitocondrias/metabolismo , Metabolismo Energético/fisiología , EnvejecimientoRESUMEN
The physical characteristics of brown adipose tissue (BAT) are defined by the presence of multilocular lipid droplets (LD) within the brown adipocytes and a high abundance of iron-containing mitochondria, which give it its characteristic color. Normal mitochondrial function is, in part, regulated by organelle-to-organelle contacts. Particularly, the contact sites that mediate mitochondria-LD interactions are thought to have various physiological roles, such as the synthesis and metabolism of lipids. Aging is associated with mitochondrial dysfunction, and previous studies show that there are changes in mitochondrial structure and proteins that modulate organelle contact sites. However, how mitochondria-LD interactions change with aging has yet to be fully clarified. Therefore, we sought to define age-related changes in LD morphology and mitochondria-lipid interactions in BAT. We examined the three-dimensional morphology of mitochondria and LDs in young (3-month) and aged (2-year) murine BAT using serial block face-scanning electron microscopy and the Amira program for segmentation, analysis, and quantification. Analysis showed reductions in LD volume, area, and perimeter in aged samples compared to young samples. Additionally, we observed changes in LD appearance and type in aged samples compared to young samples. Notably, we found differences in mitochondrial interactions with LDs, which could implicate that these contacts may be important for energetics in aging. Upon further investigation, we also found changes in mitochondrial and cristae structure for mitochondria interacting with LD lipids. Overall, these data define the nature of LD morphology and organelle-organelle contacts during aging and provide insight into LD contact site changes that interconnect biogerontology and mitochondrial functionality, metabolism, and bioactivity in aged BAT.
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The kidney filters nutrient waste and bodily fluids from the bloodstream, in addition to secondary functions of metabolism and hormone secretion, requiring an astonishing amount of energy to maintain its functions. In kidney cells, mitochondria produce adenosine triphosphate (ATP) and help maintain kidney function. Due to aging, the efficiency of kidney functions begins to decrease. Dysfunction in mitochondria and cristae, the inner folds of mitochondria, is a hallmark of aging. Therefore, age-related kidney function decline could be due to changes in mitochondrial ultrastructure, increased reactive oxygen species (ROS), and subsequent alterations in metabolism and lipid composition. We sought to understand if there is altered mitochondrial ultrastructure, as marked by 3D morphological changes, across time in tubular kidney cells. Serial block facing-scanning electron microscope (SBF-SEM) and manual segmentation using the Amira software were used to visualize murine kidney samples during the aging process at 3 months (young) and 2 years (old). We found that 2-year mitochondria are more fragmented, compared to the 3-month, with many uniquely shaped mitochondria observed across aging, concomitant with shifts in ROS, metabolomics, and lipid homeostasis. Furthermore, we show that the mitochondrial contact site and cristae organizing system (MICOS) complex is impaired in the kidney due to aging. Disruption of the MICOS complex shows altered mitochondrial calcium uptake and calcium retention capacity, as well as generation of oxidative stress. We found significant, detrimental structural changes to aged kidney tubule mitochondria suggesting a potential mechanism underlying why kidney diseases occur more readily with age. We hypothesize that disruption in the MICOS complex further exacerbates mitochondrial dysfunction, creating a vicious cycle of mitochondrial degradation and oxidative stress, thus impacting kidney health.
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The liver, the largest internal organ and a metabolic hub, undergoes significant declines due to aging, affecting mitochondrial function and increasing the risk of systemic liver diseases. How the mitochondrial three-dimensional (3D) structure changes in the liver across aging, and the biological mechanisms regulating such changes confers remain unclear. In this study, we employed Serial Block Face-Scanning Electron Microscopy (SBF-SEM) to achieve high-resolution 3D reconstructions of murine liver mitochondria to observe diverse phenotypes and structural alterations that occur with age, marked by a reduction in size and complexity. We also show concomitant metabolomic and lipidomic changes in aged samples. Aged human samples reflected altered disease risk. To find potential regulators of this change, we examined the Mitochondrial Contact Site and Cristae Organizing System (MICOS) complex, which plays a crucial role in maintaining mitochondrial architecture. We observe that the MICOS complex is lost during aging, but not Sam50. Sam50 is a component of the sorting and assembly machinery (SAM) complex that acts in tandem with the MICOS complex to modulate cristae morphology. In murine models subjected to a high-fat diet, there is a marked depletion of the mitochondrial protein SAM50. This reduction in Sam50 expression may heighten the susceptibility to liver disease, as our human biobank studies corroborate that Sam50 plays a genetically regulated role in the predisposition to multiple liver diseases. We further show that changes in mitochondrial calcium dysregulation and oxidative stress accompany the disruption of the MICOS complex. Together, we establish that a decrease in mitochondrial complexity and dysregulated metabolism occur with murine liver aging. While these changes are partially be regulated by age-related loss of the MICOS complex, the confluence of a murine high-fat diet can also cause loss of Sam50, which contributes to liver diseases. In summary, our study reveals potential regulators that affect age-related changes in mitochondrial structure and metabolism, which can be targeted in future therapeutic techniques.
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Therapeutics that discriminate between the genetic makeup of normal cells and tumour cells are valuable for treating and understanding cancer. Small molecules with oncogene-selective lethality may reveal novel functions of oncoproteins and enable the creation of more selective drugs. Here we describe the mechanism of action of the selective anti-tumour agent erastin, involving the RAS-RAF-MEK signalling pathway functioning in cell proliferation, differentiation and survival. Erastin exhibits greater lethality in human tumour cells harbouring mutations in the oncogenes HRAS, KRAS or BRAF. Using affinity purification and mass spectrometry, we discovered that erastin acts through mitochondrial voltage-dependent anion channels (VDACs)--a novel target for anti-cancer drugs. We show that erastin treatment of cells harbouring oncogenic RAS causes the appearance of oxidative species and subsequent death through an oxidative, non-apoptotic mechanism. RNA-interference-mediated knockdown of VDAC2 or VDAC3 caused resistance to erastin, implicating these two VDAC isoforms in the mechanism of action of erastin. Moreover, using purified mitochondria expressing a single VDAC isoform, we found that erastin alters the permeability of the outer mitochondrial membrane. Finally, using a radiolabelled analogue and a filter-binding assay, we show that erastin binds directly to VDAC2. These results demonstrate that ligands to VDAC proteins can induce non-apoptotic cell death selectively in some tumour cells harbouring activating mutations in the RAS-RAF-MEK pathway.