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In Fig. 1e the rate of mitochondrial H2O2 emission was incorrectly shown as being per second rather than per minute.
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Lipocalin-2 (LCN2) is an adipokine previously described for its contribution to numerous processes, including innate immunity and energy metabolism. LCN2 has also been demonstrated to be an extracellular matrix (ECM) regulator through its association with the ECM protease matrix metalloproteinase-9 (MMP-9). With the global rise in obesity and the associated comorbidities related to increasing adiposity, it is imperative to gain an understanding of the cross talk between adipose tissue and other metabolic tissues, such as skeletal muscle. Given the function of LCN2 on the ECM in other tissues and the importance of matrix remodeling in skeletal muscle regeneration, we examined the localization and expression of LCN2 in uninjured and regenerating wild-type skeletal muscle and assessed the impact of LCN2 deletion (LCN2-/-) on skeletal muscle repair following cardiotoxin injury. Though LCN2 was minimally present in uninjured skeletal muscle, its expression was increased significantly at 1 and 2 days postinjury, with expression present in Pax7-positive satellite cells. Although satellite cell content was unchanged, the ability of quiescent satellite cells to become activated was significantly impaired in LCN2-/- skeletal muscles. Skeletal muscle regeneration was also significantly compromised as evidenced by decreased embryonic myosin heavy chain expression and smaller regenerating myofiber areas. Consistent with a role for LCN2 in MMP-9 regulation, regenerating muscle also displayed a significant increase in fibrosis and lower ( P = 0.07) MMP-9 activity in LCN2-/- mice at 2 days postinjury. These data highlight a novel role for LCN2 in muscle regeneration and suggest that changes in adipokine expression can significantly impact skeletal muscle repair.
Assuntos
Lipocalina-2/genética , Metaloproteinase 9 da Matriz/genética , Músculo Esquelético/crescimento & desenvolvimento , Adipocinas/genética , Adipocinas/metabolismo , Tecido Adiposo/metabolismo , Tecido Adiposo/patologia , Animais , Regulação da Expressão Gênica/genética , Humanos , Lipocalina-2/metabolismo , Metaloproteinase 9 da Matriz/metabolismo , Camundongos , Camundongos Knockout , Músculo Esquelético/metabolismo , Mioblastos/metabolismo , Mioblastos/patologia , Regeneração/genética , Regeneração/fisiologia , Células Satélites de Músculo Esquelético/metabolismo , Células Satélites de Músculo Esquelético/patologia , Cicatrização/genéticaRESUMO
AIMS/HYPOTHESIS: A comprehensive assessment of skeletal muscle ultrastructure and mitochondrial bioenergetics has not been undertaken in individuals with type 1 diabetes. This study aimed to systematically assess skeletal muscle mitochondrial phenotype in young adults with type 1 diabetes. METHODS: Physically active, young adults (men and women) with type 1 diabetes (HbA1c 63.0 ± 16.0 mmol/mol [7.9% ± 1.5%]) and without type 1 diabetes (control), matched for sex, age, BMI and level of physical activity, were recruited (n = 12/group) to undergo vastus lateralis muscle microbiopsies. Mitochondrial respiration (high-resolution respirometry), site-specific mitochondrial H2O2 emission and Ca2+ retention capacity (CRC) (spectrofluorometry) were assessed using permeabilised myofibre bundles. Electron microscopy and tomography were used to quantify mitochondrial content and investigate muscle ultrastructure. Skeletal muscle microvasculature was assessed by immunofluorescence. RESULTS: Mitochondrial oxidative capacity was significantly lower in participants with type 1 diabetes vs the control group, specifically at Complex II of the electron transport chain, without differences in mitochondrial content between groups. Muscles of those with type 1 diabetes also exhibited increased mitochondrial H2O2 emission at Complex III and decreased CRC relative to control individuals. Electron tomography revealed an increase in the size and number of autophagic remnants in the muscles of participants with type 1 diabetes. Despite this, levels of the autophagic regulatory protein, phosphorylated AMP-activated protein kinase (p-AMPKαThr172), and its downstream targets, phosphorylated Unc-51 like autophagy activating kinase 1 (p-ULK1Ser555) and p62, was similar between groups. In addition, no differences in muscle capillary density or platelet aggregation were observed between the groups. CONCLUSIONS/INTERPRETATION: Alterations in mitochondrial ultrastructure and bioenergetics are evident within the skeletal muscle of active young adults with type 1 diabetes. It is yet to be elucidated whether more rigorous exercise may help to prevent skeletal muscle metabolic deficiencies in both active and inactive individuals with type 1 diabetes.
Assuntos
Diabetes Mellitus Tipo 1/metabolismo , Mitocôndrias/metabolismo , Músculo Esquelético/metabolismo , Músculo Esquelético/ultraestrutura , Adulto , Índice de Massa Corporal , Cálcio/química , Diabetes Mellitus Tipo 1/patologia , Metabolismo Energético , Exercício Físico/fisiologia , Feminino , Humanos , Peróxido de Hidrogênio/metabolismo , Insulina/metabolismo , Masculino , Microscopia Eletrônica de Transmissão , Microscopia de Fluorescência , Mitocôndrias/ultraestrutura , Músculo Esquelético/patologia , Consumo de Oxigênio , Adulto JovemRESUMO
Childhood obesity is a growing worldwide problem. In adults, lower cold-induced brown adipose tissue (BAT) activity is linked to obesity and metabolic dysfunction; this relationship remains uncertain in children. In this cross-sectional study, we compared cold-induced supraclavicular (SCV) BAT activity (percent change in proton density fat fraction [PDFF]) within the SCV region after 1 h of whole-body cold exposure (18°C), using MRI in 26 boys aged 8-10 years: 13 with normal BMI and 13 with overweight/obesity. Anthropometry, body composition, hepatic fat, visceral adipose tissue (VAT), and pre- and postcold PDFF of the subcutaneous adipose tissue (SAT) in the posterior neck region and the abdomen were measured. Boys with overweight/obesity had lower cold-induced percent decline in SCV PDFF compared with those with normal BMI (1.6 ± 0.8 vs. 4.7 ± 1.2%, P = 0.044). SCV PDFF declined significantly in boys with normal BMI (2.7 ± 0.7%, P = 0.003) but not in boys with overweight/obesity (1.1 ± 0.5%, P = 0.053). No cold-induced changes in the PDFF of either neck SAT (-0.89 ± 0.7%, P = 0.250, vs. 0.37 ± 0.3%, P = 0.230) or abdominal SAT (-0.39 ± 0.5%, P = 0.409, and 0.25 ± 0.2%, P = 0.139, for normal BMI and overweight/obesity groups, respectively) were seen. The cold-induced percent decline in SCV PDFF was inversely related to BMI (r = -0.39, P = 0.047), waist circumference (r = -0.48, P = 0.014), and VAT (r = -0.47, P = 0.014). Thus, in young boys, as in adults, BAT activity is lower in those with overweight/obesity, suggesting that restoring activity may be important for improving metabolic health.
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Tecido Adiposo Marrom , Obesidade Infantil , Tecido Adiposo , Tecido Adiposo Marrom/diagnóstico por imagem , Tecido Adiposo Marrom/metabolismo , Adulto , Antropometria , Criança , Estudos Transversais , Humanos , Imageamento por Ressonância Magnética , Masculino , Sobrepeso/metabolismo , Obesidade Infantil/metabolismo , PrótonsRESUMO
BACKGROUND: Muscle wasting and weakness in Duchenne muscular dystrophy (DMD) causes severe locomotor limitations and early death due in part to respiratory muscle failure. Given that current clinical practice focuses on treating secondary complications in this genetic disease, there is a clear need to identify additional contributions in the aetiology of this myopathy for knowledge-guided therapy development. Here, we address the unresolved question of whether the complex impairments observed in DMD are linked to elevated mitochondrial H2 O2 emission in conjunction with impaired oxidative phosphorylation. This study performed a systematic evaluation of the nature and degree of mitochondrial-derived H2 O2 emission and mitochondrial oxidative dysfunction in a mouse model of DMD by designing in vitro bioenergetic assessments that attempt to mimic in vivo conditions known to be critical for the regulation of mitochondrial bioenergetics. METHODS: Mitochondrial bioenergetics were compared with functional and histopathological indices of myopathy early in DMD (4 weeks) in D2.B10-DMDmdx /2J mice (D2.mdx)-a model that demonstrates severe muscle weakness. Adenosine diphosphate's (ADP's) central effect of attenuating H2 O2 emission while stimulating respiration was compared under two models of mitochondrial-cytoplasmic phosphate exchange (creatine independent and dependent) in muscles that stained positive for membrane damage (diaphragm, quadriceps, and white gastrocnemius). RESULTS: Pathway-specific analyses revealed that Complex I-supported maximal H2 O2 emission was elevated concurrent with a reduced ability of ADP to attenuate emission during respiration in all three muscles (mH2 O2 : +17 to +197% in D2.mdx vs. wild type). This was associated with an impaired ability of ADP to stimulate respiration at sub-maximal and maximal kinetics (-17 to -72% in D2.mdx vs. wild type), as well as a loss of creatine-dependent mitochondrial phosphate shuttling in diaphragm and quadriceps. These changes largely occurred independent of mitochondrial density or abundance of respiratory chain complexes, except for quadriceps. This muscle was also the only one exhibiting decreased calcium retention capacity, which indicates increased sensitivity to calcium-induced permeability transition pore opening. Increased H2 O2 emission was accompanied by a compensatory increase in total glutathione, while oxidative stress markers were unchanged. Mitochondrial bioenergetic dysfunctions were associated with induction of mitochondrial-linked caspase 9, necrosis, and markers of atrophy in some muscles as well as reduced hindlimb torque and reduced respiratory muscle function. CONCLUSIONS: These results provide evidence that Complex I dysfunction and loss of central respiratory control by ADP and creatine cause elevated oxidant generation during impaired oxidative phosphorylation. These dysfunctions may contribute to early stage disease pathophysiology and support the growing notion that mitochondria are a potential therapeutic target in this disease.