RESUMO
Extracellular vesicles (EVs) are biomarkers and modifiers of human disease. EVs secreted by insulin-responsive tissues like skeletal muscle (SkM) and white adipose tissue (WAT) contribute to metabolic health and disease but the relative abundance of EVs from these tissues has not been directly examined. Human Protein Atlas data and directly measuring EV secretion in mouse SkM and WAT using an ex vivo tissue explant model confirmed that SkM tissue secretes more EVs than WAT. Differences in EV secretion between SkM and WAT were not due to SkM contraction but may be explained by differences in tissue metabolic capacity. We next examined how many EVs secreted from SkM tissue ex vivo and in vivo are myofiber-derived. To do this, a SkM myofiber-specific dual fluorescent reporter mouse was created. Spectral flow cytometry revealed that SkM myofibers are a major source of SkM tissue-derived EVs ex vivo and EV immunocapture indicates that â¼5% of circulating tetraspanin-positive EVs are derived from SkM myofibers in vivo. Our findings demonstrate that 1) SkM secretes more EVs than WAT, 2) many SkM tissue EVs are derived from SkM myofibers, and 3) SkM myofiber-derived EVs reach the circulation in vivo. These findings advance our understanding of EV secretion between metabolically active tissues and provide direct evidence that SkM myofibers secrete EVs that can reach the circulation in vivo.
Assuntos
Tecido Adiposo Branco/química , Tecido Adiposo Branco/metabolismo , Vesículas Extracelulares/química , Vesículas Extracelulares/metabolismo , Fibras Musculares Esqueléticas/química , Fibras Musculares Esqueléticas/metabolismo , Animais , Biomarcadores/sangue , Biomarcadores/metabolismo , Feminino , Masculino , Camundongos , Camundongos da Linhagem 129 , Camundongos Endogâmicos C57BL , Músculo Esquelético/química , Músculo Esquelético/metabolismo , Imagem Óptica/métodos , Estudos RetrospectivosRESUMO
Critical thinking and scientific communication are common learning objectives in physiology education. However, a lack of real-world application can limit the transfer of these skills to professional settings. For example, health and wellness professionals are often asked to give advice to clients and patients regarding the use of nutritional supplements, diets, and exercise programs. Giving sound advice on these questions requires the ability to find, interpret, and communicate the evidence to support or reject the use of a given intervention. "Evidence-based practice" (EBP) provides a philosophical framework for combining personal experience, client/patient values, and scientific evidence to give informed advice in a professional setting. Here, we describe the development and implementation of a semester-long EBP project in an introductory exercise physiology course. We discuss how specific components of the project are designed to enhance classroom equity, improve scientific communication, and integrate course content with the student's lived experience and personal interests.
Assuntos
Aprendizagem , Estudantes , Pessoal de Saúde , HumanosRESUMO
Oxidative phosphorylation (OXPHOS) efficiency, defined as the ATP-to-O ratio, is a critical feature of mitochondrial function that has been implicated in health, aging, and disease. To date, however, the methods to measure ATP/O have primarily relied on indirect approaches or entail parallel rather than simultaneous determination of ATP synthesis and O2 consumption rates. The purpose of this project was to develop and validate an approach to determine the ATP/O ratio in permeabilized fiber bundles (PmFBs) from simultaneous measures of ATP synthesis (JATP) and O2 consumption (JO2 ) rates in real time using a custom-designed apparatus. JO2 was measured via a polarigraphic oxygen sensor and JATP via fluorescence using an enzyme-linked assay system (hexokinase II, glucose-6-phosphate dehydrogenase) linked to NADPH production. Within the dynamic linear range of the assay system, ADP-stimulated increases in steady-state JATP mirrored increases in steady-state JO2 (r(2) = 0.91, P < 0.0001, n = 57 data points). ATP/O ratio was less than one under low rates of respiration (15 µM ADP) but increased to more than two at moderate (200 µM ADP) and maximal (2,000 µM ADP) rates of respiration with an interassay coefficient of variation of 24.03, 16.72, and 11.99%, respectively. Absolute and relative (to mechanistic) ATP/O ratios were lower in PmFBs (2.09 ± 0.251, 84%) compared with isolated mitochondria (2.44 ± 0.124, 98%). ATP/O ratios in PmFBs were not affected by the activity of adenylate kinase or creatine kinase. These findings validate an enzyme-linked respiratory clamp system for measuring OXPHOS efficiency in PmFBs and provide evidence that OXPHOS efficiency increases as energy demand increases.
Assuntos
Mitocôndrias/metabolismo , Mitocôndrias/fisiologia , Fibras Musculares Esqueléticas/metabolismo , Fibras Musculares Esqueléticas/fisiologia , Difosfato de Adenosina/metabolismo , Trifosfato de Adenosina/metabolismo , Adenilato Quinase/metabolismo , Animais , Glucosefosfato Desidrogenase/metabolismo , Hexoquinase/metabolismo , Masculino , Camundongos , Camundongos Endogâmicos C57BL , NADP/metabolismo , Fosforilação Oxidativa , Consumo de Oxigênio/fisiologiaRESUMO
The loss of strength in combination with constant fatigue is a burden on cancer patients undergoing chemotherapy. Doxorubicin, a standard chemotherapy drug used in the clinic, causes skeletal muscle dysfunction and increases mitochondrial H2O2 We hypothesized that the combined effect of cancer and chemotherapy in an immunocompetent breast cancer mouse model (E0771) would compromise skeletal muscle mitochondrial respiratory function, leading to an increase in H2O2-emitting potential and impaired muscle function. Here, we demonstrate that cancer chemotherapy decreases mitochondrial respiratory capacity supported with complex I (pyruvate/glutamate/malate) and complex II (succinate) substrates. Mitochondrial H2O2-emitting potential was altered in skeletal muscle, and global protein oxidation was elevated with cancer chemotherapy. Muscle contractile function was impaired following exposure to cancer chemotherapy. Genetically engineering the overexpression of catalase in mitochondria of muscle attenuated mitochondrial H2O2 emission and protein oxidation, preserving mitochondrial and whole muscle function despite cancer chemotherapy. These findings suggest mitochondrial oxidants as a mediator of cancer chemotherapy-induced skeletal muscle dysfunction.
Assuntos
Antineoplásicos/farmacologia , Catalase/efeitos dos fármacos , Doxorrubicina/farmacologia , Mitocôndrias Musculares/efeitos dos fármacos , Músculo Esquelético/efeitos dos fármacos , Animais , Neoplasias da Mama/tratamento farmacológico , Catalase/genética , Catalase/metabolismo , Modelos Animais de Doenças , Complexo I de Transporte de Elétrons/efeitos dos fármacos , Complexo I de Transporte de Elétrons/metabolismo , Complexo II de Transporte de Elétrons/efeitos dos fármacos , Complexo II de Transporte de Elétrons/metabolismo , Feminino , Peróxido de Hidrogênio/metabolismo , Camundongos , Camundongos Transgênicos , Mitocôndrias Musculares/enzimologia , Mitocôndrias Musculares/metabolismo , Contração Muscular/efeitos dos fármacos , Músculo Esquelético/fisiopatologia , Oxirredução/efeitos dos fármacos , Proteínas/efeitos dos fármacos , Proteínas/metabolismoRESUMO
Cellular proteins rely on reversible redox reactions to establish and maintain biological structure and function. How redox catabolic (NAD+/NADH) and anabolic (NADP+/NADPH) processes integrate during metabolism to maintain cellular redox homoeostasis, however, is unknown. The present work identifies a continuously cycling mitochondrial membrane potential (ΔΨm)-dependent redox circuit between the pyruvate dehydrogenase complex (PDHC) and nicotinamide nucleotide transhydrogenase (NNT). PDHC is shown to produce H2O2 in relation to reducing pressure within the complex. The H2O2 produced, however, is effectively masked by a continuously cycling redox circuit that links, via glutathione/thioredoxin, to NNT, which catalyses the regeneration of NADPH from NADH at the expense of ΔΨm. The net effect is an automatic fine-tuning of NNT-mediated energy expenditure to metabolic balance at the level of PDHC. In mitochondria, genetic or pharmacological disruptions in the PDHC-NNT redox circuit negate counterbalance changes in energy expenditure. At the whole animal level, mice lacking functional NNT (C57BL/6J) are characterized by lower energy-expenditure rates, consistent with their well-known susceptibility to diet-induced obesity. These findings suggest the integration of redox sensing of metabolic balance with compensatory changes in energy expenditure provides a potential mechanism by which cellular redox homoeostasis is maintained and body weight is defended during periods of positive and negative energy balance.
Assuntos
Peróxido de Hidrogênio/metabolismo , Potencial da Membrana Mitocondrial/fisiologia , Mitocôndrias Musculares/enzimologia , NADP Trans-Hidrogenase Específica para A ou B/metabolismo , NADP/metabolismo , Complexo Piruvato Desidrogenase/metabolismo , Animais , Inibidores Enzimáticos/farmacologia , Potencial da Membrana Mitocondrial/efeitos dos fármacos , Camundongos , Mitocôndrias Musculares/genética , Proteínas Mitocondriais/antagonistas & inibidores , Proteínas Mitocondriais/genética , Proteínas Mitocondriais/metabolismo , NADP/genética , NADP Trans-Hidrogenase Específica para A ou B/antagonistas & inibidores , NADP Trans-Hidrogenase Específica para A ou B/genética , Oxirredução/efeitos dos fármacos , Complexo Piruvato Desidrogenase/antagonistas & inibidores , Complexo Piruvato Desidrogenase/genéticaRESUMO
Thioredoxin-interacting protein (TXNIP) is an α-arrestin family member involved in redox sensing and metabolic control. Growing evidence links TXNIP to mitochondrial function, but the molecular nature of this relationship has remained poorly defined. Herein, we employed targeted metabolomics and comprehensive bioenergetic analyses to evaluate oxidative metabolism and respiratory kinetics in mouse models of total body (TKO) and skeletal muscle-specific (TXNIP(SKM-/-)) Txnip deficiency. Compared with littermate controls, both TKO and TXNIP(SKM-/-) mice had reduced exercise tolerance in association with muscle-specific impairments in substrate oxidation. Oxidative insufficiencies in TXNIP null muscles were not due to perturbations in mitochondrial mass, the electron transport chain, or emission of reactive oxygen species. Instead, metabolic profiling analyses led to the discovery that TXNIP deficiency causes marked deficits in enzymes required for catabolism of branched chain amino acids, ketones, and lactate, along with more modest reductions in enzymes of ß-oxidation and the tricarboxylic acid cycle. The decrements in enzyme activity were accompanied by comparable deficits in protein abundance without changes in mRNA expression, implying dysregulation of protein synthesis or stability. Considering that TXNIP expression increases in response to starvation, diabetes, and exercise, these findings point to a novel role for TXNIP in coordinating mitochondrial fuel switching in response to nutrient availability.
Assuntos
Proteínas de Transporte/metabolismo , Metabolismo Energético , Mitocôndrias/metabolismo , Músculo Esquelético/metabolismo , Oxirredutases/metabolismo , Tiorredoxinas/metabolismo , Animais , Proteínas de Transporte/genética , Metabolômica , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Mitocôndrias/genética , Músculo Esquelético/enzimologia , Oxirredução , Tiorredoxinas/genéticaRESUMO
Aging is the primary risk factor for most neurodegenerative diseases, including Alzheimer's disease. Major hallmarks of brain aging include neuroinflammation/immune activation and reduced neuronal health/function. These processes contribute to cognitive dysfunction (a key risk factor for Alzheimer's disease), but their upstream causes are incompletely understood. Age-related increases in transposable element (TE) transcripts might contribute to reduced cognitive function with brain aging, as the reverse transcriptase inhibitor 3TC reduces inflammation in peripheral tissues and TE transcripts have been linked with tau pathology in Alzheimer's disease. However, the effects of 3TC on cognitive function with aging have not been investigated. Here, in support of a role for TE transcripts in brain aging/cognitive decline, we show that 3TC: (a) improves cognitive function and reduces neuroinflammation in old wild-type mice; (b) preserves neuronal health with aging in mice and Caenorhabditis elegans; and (c) enhances cognitive function in a mouse model of tauopathy. We also provide insight on potential underlying mechanisms, as well as evidence of translational relevance for these observations by showing that TE transcripts accumulate with brain aging in humans, and that these age-related increases intersect with those observed in Alzheimer's disease. Collectively, our results suggest that TE transcript accumulation during aging may contribute to cognitive decline and neurodegeneration, and that targeting these events with reverse transcriptase inhibitors like 3TC could be a viable therapeutic strategy.
Assuntos
Doença de Alzheimer , Disfunção Cognitiva , Humanos , Camundongos , Animais , Doença de Alzheimer/patologia , Inibidores da Transcriptase Reversa , Doenças Neuroinflamatórias , Disfunção Cognitiva/tratamento farmacológico , Disfunção Cognitiva/genética , Encéfalo/patologia , EnvelhecimentoRESUMO
Energy transfer between mitochondrial and cytosolic compartments is predominantly achieved by creatine-dependent phosphate shuttling (PCr/Cr) involving mitochondrial creatine kinase (miCK). However, ADP/ATP diffusion through adenine nucleotide translocase (ANT) and voltage-dependent anion carriers (VDACs) is also involved in this process. To determine if exercise alters the regulation of this system, ADP-stimulated mitochondrial respiratory kinetics were assessed in permeabilized muscle fibre bundles (PmFBs) taken from biopsies before and after 2 h of cycling exercise (60% ) in nine lean males. Concentrations of creatine (Cr) and phosphocreatine (PCr) as well as the contractile state of PmFBs were manipulated in situ. In the absence of contractile signals (relaxed PmFBs) and miCK activity (no Cr), post-exercise respiratory sensitivity to ADP was reduced in situ (up to 126% higher apparent K(m) to ADP) suggesting inhibition of ADP/ATP diffusion between matrix and cytosolic compartments (possibly ANT and VDACs). However this effect was masked in the presence of saturating Cr (no effect of exercise on ADP sensitivity). Given that the role of ANT is thought to be independent of Cr, these findings suggest ADP/ATP, but not PCr/Cr, cycling through the outer mitochondrial membrane (VDACs) may be attenuated in resting muscle after exercise. In contrast, in contracted PmFBs, post-exercise respiratory sensitivity to ADP increased with miCK activation (saturating Cr; 33% lower apparent K(m) to ADP), suggesting prior exercise increases miCK sensitivity in situ. These observations demonstrate that exercise increases miCK-dependent respiratory sensitivity to ADP, promoting mitochondrial-cytosolic energy exchange via PCr/Cr cycling, possibly through VDACs. This effect may mask an underlying inhibition of Cr-independent ADP/ATP diffusion. This enhanced regulation of miCK-dependent phosphate shuttling may improve energy homeostasis through more efficient coupling of oxidative phosphorylation to perturbations in cellular energy charge during subsequent bouts of contraction.
Assuntos
Difosfato de Adenosina/fisiologia , Creatina Quinase Mitocondrial/fisiologia , Exercício Físico/fisiologia , Músculo Esquelético/fisiologia , Animais , Humanos , Masculino , Contração Muscular , Ratos , Ratos Sprague-DawleyRESUMO
Assessment of mitochondrial ADP-stimulated respiratory kinetics in PmFBs (permeabilized fibre bundles) is increasingly used in clinical diagnostic and basic research settings. However, estimates of the Km for ADP vary considerably (~20-300 µM) and tend to overestimate respiration at rest. Noting that PmFBs spontaneously contract during respiration experiments, we systematically determined the impact of contraction, temperature and oxygenation on ADP-stimulated respiratory kinetics. BLEB (blebbistatin), a myosin II ATPase inhibitor, blocked contraction under all conditions and yielded high Km values for ADP of >~250 and ~80 µM in red and white rat PmFBs respectively. In the absence of BLEB, PmFBs contracted and the Km for ADP decreased ~2-10-fold in a temperature-dependent manner. PmFBs were sensitive to hyperoxia (increased Km) in the absence of BLEB (contracted) at 30 °C but not 37 °C. In PmFBs from humans, contraction elicited high sensitivity to ADP (Km<100 µM), whereas blocking contraction (+BLEB) and including a phosphocreatine/creatine ratio of 2:1 to mimic the resting energetic state yielded a Km for ADP of ~1560 µM, consistent with estimates of in vivo resting respiratory rates of <1% maximum. These results demonstrate that the sensitivity of muscle to ADP varies over a wide range in relation to contractile state and cellular energy charge, providing evidence that enzymatic coupling of energy transfer within skeletal muscle becomes more efficient in the working state.
Assuntos
Músculo Esquelético/fisiologia , Miosinas/antagonistas & inibidores , Difosfato de Adenosina/metabolismo , Adulto , Animais , Creatina/metabolismo , Compostos Heterocíclicos de 4 ou mais Anéis/farmacologia , Humanos , Masculino , Mitocôndrias Musculares/metabolismo , Contração Muscular/efeitos dos fármacos , Fibras Musculares Esqueléticas , Músculo Esquelético/metabolismo , Fosfocreatina/metabolismo , Ratos , Respiração , TemperaturaRESUMO
Extracellular vesicles like exosomes are secreted by numerous cell types in a variety of tissues. Exosomes have been implicated in both aging and age-related disorders like Alzheimer's disease (AD). However, how aging and AD affect exosome biogenesis within and across cell types is poorly understood. Moreover, cells acquire characteristics based on tissue niche, but the impact of tissue residence on cell type exosome biogenesis is unknown. We explored the Tabula Muris Senis, Mayo RNA-seq and Rush Religious Order Study/Memory and Aging Project data sets to characterize the cell and tissue-specific effects of aging and AD on genes involved in exosome biogenesis. Specifically, we examined the age-dependent expression (age coefficient) of genes involved in exosome biogenesis (22 genes), exosome cargo (3 genes), and senescence (5 genes). Of the 131 cell populations (cell type × tissue) studied, 95 had at least 1 exosome biogenesis gene affected by age. The most common gene/transcript increased by age was charged multivesicular body protein 2A (CHMP2A) (54 cell populations). The most common gene/transcript decreased by age was syndecan-binding protein (SDCBP) (58 cell populations). The senescence-associated genes cyclin-dependent kinase 1A (CDKN1A) and CDKN2A were not related to changes in CHMP2A and SDCBP and were altered by age in fewer cell populations. Finally, individuals with AD had decreased CHMP2A and increased SDCBP expression, opposite of what is observed during mouse aging in the absence of disease. These findings indicate that exosome biogenesis gene expression is modified by age in many cell populations mostly independent of senescence, and may be further altered in AD.
Assuntos
Doença de Alzheimer , Exossomos , Vesículas Extracelulares , Envelhecimento/genética , Envelhecimento/metabolismo , Doença de Alzheimer/genética , Doença de Alzheimer/metabolismo , Animais , Encéfalo/metabolismo , Exossomos/genética , Exossomos/metabolismo , Vesículas Extracelulares/metabolismo , Humanos , Camundongos , Sinteninas/metabolismoRESUMO
Cancer is one of the most common age-related diseases, and over one-third of cancer patients will receive chemotherapy. One frequently reported side effect of chemotherapeutic agents like doxorubicin (Doxo) is impaired cognitive function, commonly known as "chemotherapy-induced cognitive impairment (CICI)", which may mimic accelerated brain aging. The biological mechanisms underlying the adverse effects of Doxo on the brain are unclear but could involve mitochondrial dysfunction. Here, we characterized brain (hippocampal) transcriptome and cognitive/behavioral changes in young mice treated with Doxo +/- the mitochondrial therapeutic MitoQ. We found that Doxo altered transcriptome/biological processes related to synaptic transmission and neurotransmitter function, neuronal health and behavior, and that these gene expression changes were: 1) similar to key differences observed in transcriptome data on brain aging; and 2) associated with related, aging-like behavioral differences, such as decreased exploration time and impaired novel object recognition test (NOR, an index of learning/memory) performance. Interestingly, MitoQ partially prevented Doxo-induced transcriptome changes in the brain, but it had no effect on behavior or cognitive function. Collectively, our findings are consistent with the idea that chemotherapeutic agents could induce neuronal/gene expression and behavioral changes similar to those that occur during brain aging. In this context, mitochondrial therapeutics may have potential as treatments for CICI at the biological level, but their effects on behavior/cognitive function require further investigation.
Assuntos
Disfunção Cognitiva , Transcriptoma , Envelhecimento/genética , Animais , Encéfalo , Disfunção Cognitiva/induzido quimicamente , Disfunção Cognitiva/genética , Doxorrubicina , Humanos , CamundongosRESUMO
Exercise alone is often ineffective for treating obesity despite the associated increase in metabolic requirements. Decreased nonexercise physical activity has been implicated in this resistance to weight loss, but the mechanisms responsible are unclear. We quantified the metabolic cost of nonexercise activity, or "off-wheel" activity (OWA), and voluntary wheel running (VWR) and examined whether changes in OWA during VWR altered energy balance in chow-fed C57BL/6J mice (n = 12). Energy expenditure (EE), energy intake, and behavior (VWR and OWA) were continuously monitored for 4 days with locked running wheels followed by 9 days with unlocked running wheels. Unlocking the running wheels increased EE as a function of VWR distance. The metabolic cost of exercise (kcal/m traveled) decreased with increasing VWR speed. Unlocking the wheel led to a negative energy balance but also decreased OWA, which was predicted to mitigate the expected change in energy balance by â¼45%. A novel behavioral circuit involved repeated bouts of VWR, and roaming was discovered and represented novel predictors of VWR behavior. The integrated analysis described here reveals that the weight loss effects of voluntary exercise can be countered by a reduction in nonexercise activity.
Assuntos
Ingestão de Energia/fisiologia , Metabolismo Energético/fisiologia , Atividade Motora/fisiologia , Condicionamento Físico Animal/fisiologia , Animais , Comportamento Animal , Calorimetria Indireta , Masculino , Camundongos , Camundongos Endogâmicos C57BL , Obesidade , Redução de PesoRESUMO
Bcl-2 family proteins reorganize mitochondrial membranes during apoptosis, to form pores and rearrange cristae. In vitro and in vivo analysis integrated with human genetics reveals a novel homeostatic mitochondrial function for Bcl-2 family protein Bid. Loss of full-length Bid results in apoptosis-independent, irregular cristae with decreased respiration. Bid-/- mice display stress-induced myocardial dysfunction and damage. A gene-based approach applied to a biobank, validated in two independent GWAS studies, reveals that decreased genetically determined BID expression associates with myocardial infarction (MI) susceptibility. Patients in the bottom 5% of the expression distribution exhibit >4 fold increased MI risk. Carrier status with nonsynonymous variation in Bid's membrane binding domain, BidM148T, associates with MI predisposition. Furthermore, Bid but not BidM148T associates with Mcl-1Matrix, previously implicated in cristae stability; decreased MCL-1 expression associates with MI. Our results identify a role for Bid in homeostatic mitochondrial cristae reorganization, that we link to human cardiac disease.
Assuntos
Proteína Agonista de Morte Celular de Domínio Interatuante com BH3/metabolismo , Genômica , Cardiopatias/genética , Cardiopatias/prevenção & controle , Mitocôndrias/metabolismo , Mitocôndrias/ultraestrutura , Animais , Apoptose , Proteína Agonista de Morte Celular de Domínio Interatuante com BH3/química , Proteína Beclina-1/metabolismo , Respiração Celular , Fibrose , Regulação da Expressão Gênica , Estudo de Associação Genômica Ampla , Cardiopatias/patologia , Ventrículos do Coração/patologia , Humanos , Camundongos Endogâmicos C57BL , ATPases Mitocondriais Próton-Translocadoras , Mutação/genética , Células Progenitoras Mieloides/metabolismo , Infarto do Miocárdio/genética , Infarto do Miocárdio/patologia , Miócitos Cardíacos/metabolismo , Miócitos Cardíacos/patologia , Miócitos Cardíacos/ultraestrutura , Polimorfismo de Nucleotídeo Único/genética , Multimerização Proteica , Estrutura Secundária de Proteína , Subunidades Proteicas/metabolismo , Espécies Reativas de Oxigênio/metabolismo , Reprodutibilidade dos Testes , Regulação para CimaRESUMO
Obesity and insulin resistance often emerge from positive energy balance and generally are linked to low-grade inflammation. This low-grade inflammation has been called "meta-inflammation" because it is a consequence of the metabolic dysregulation that can accompany overnutrition. One means by which meta-inflammation is linked to insulin resistance is extracellular matrix expansion secondary to meta-inflammation, which we define here as "meta-fibrosis". The significance of meta-fibrosis is that it reflects a situation in which the extracellular matrix functions as a multi-level integrator of local (for example, mitochondrial reactive oxygen species production) and systemic (for example, inflammation) inputs that couple to cellular processes creating insulin resistance. While adipose tissue extracellular matrix remodeling has received considerable attention, it is becoming increasingly apparent that liver and skeletal muscle extracellular matrix remodeling also contributes to insulin resistance. In this review, we address recent advances in our understanding of energy balance, mitochondrial energetics, meta-inflammation, and meta-fibrosis in the development of insulin resistance.
RESUMO
Haploinsufficiency of the melanocortin-4 receptor, the most common monogenetic obesity syndrome in humans, is associated with a reduction in autonomic tone, bradycardia, and incidence of obesity-associated hypertension. Thus, it has been assumed that melanocortin obesity syndrome may be protective with respect to obesity-associated cardiovascular disease. We show here that absence of the melanocortin-4 receptor (MC4R) in mice causes dilated cardiomyopathy, characterized by reduced contractility and increased left ventricular diameter. This cardiomyopathy is independent of obesity as weight matched diet induced obese mice do not display systolic dysfunction. Mc4r cardiomyopathy is characterized by ultrastructural changes in mitochondrial morphology and cardiomyocyte disorganization. Remarkably, testing of myocardial tissue from Mc4r-/- mice exhibited increased ADP stimulated respiratory capacity. However, this increase in respiration correlates with increased reactive oxygen species production - a canonical mediator of tissue damage. Together this study identifies MC4R deletion as a novel and potentially clinically important cause of heart failure.
Assuntos
Cardiomiopatia Dilatada/genética , Cardiomiopatia Dilatada/patologia , Receptor Tipo 4 de Melanocortina/deficiência , Difosfato de Adenosina/metabolismo , Animais , Respiração Celular/efeitos dos fármacos , Camundongos Endogâmicos C57BL , Camundongos Knockout , Mitocôndrias/ultraestrutura , Miocárdio/patologia , Miócitos Cardíacos/patologia , Espécies Reativas de Oxigênio/metabolismo , Espécies Reativas de Oxigênio/toxicidadeRESUMO
Diet-induced muscle insulin resistance is associated with expansion of extracellular matrix (ECM) components, such as collagens, and the expression of collagen-binding integrin, α2ß1. Integrins transduce signals from ECM via their cytoplasmic domains, which bind to intracellular integrin-binding proteins. The integrin-linked kinase (ILK)-PINCH-parvin (IPP) complex interacts with the cytoplasmic domain of ß-integrin subunits and is critical for integrin signaling. In this study we defined the role of ILK, a key component of the IPP complex, in diet-induced muscle insulin resistance. Wild-type (ILK(lox/lox)) and muscle-specific ILK-deficient (ILK(lox/lox)HSAcre) mice were fed chow or a high-fat (HF) diet for 16 weeks. Body weight was not different between ILK(lox/lox) and ILK(lox/lox)HSAcre mice. However, HF-fed ILK(lox/lox)HSAcre mice had improved muscle insulin sensitivity relative to HF-fed ILK(lox/lox) mice, as shown by increased rates of glucose infusion, glucose disappearance, and muscle glucose uptake during a hyperinsulinemic-euglycemic clamp. Improved muscle insulin action in the HF-fed ILK(lox/lox)HSAcre mice was associated with increased insulin-stimulated phosphorylation of Akt and increased muscle capillarization. These results suggest that ILK expression in muscle is a critical component of diet-induced insulin resistance, which possibly acts by impairing insulin signaling and insulin perfusion through capillaries.