Mitochondrial Utilization of Competing Fuels Is Altered in Insulin Resistant Skeletal Muscle of Non-obese Rats (Goto-Kakizaki)

The paradox of fatty-acid β-oxidation in muscle insulin resistance: Metabolic control and muscle heterogeneity

The skeletal muscle is a metabolically heterogeneous tissue that plays a key role in maintaining whole-body glucose homeostasis. It is well known that muscle insulin resistance (IR) precedes the development of type 2 diabetes. There is a consensus that the accumulation of specific lipid species in the tissue can drive IR. However, the role of the mitochondrial fatty-acid β-oxidation in IR and, consequently, in the control of glucose uptake remains paradoxical: interventions that either inhibit or activate fatty-acid β-oxidation have been shown to prevent IR. We here discuss the current theories and evidence for the interplay between β-oxidation and glucose uptake in IR. To address the underlying intricacies, we (1) dive into the control of glucose uptake fluxes into muscle tissues using the framework of Metabolic Control Analysis, and (2) disentangle concepts of flux and catalytic capacities taking into account skeletal muscle heterogeneity. Finally, we speculate about hitherto unexplored mechanisms that could bring contrasting evidence together. Elucidating how β-oxidation is connected to muscle IR and the underlying role of muscle heterogeneity enhances disease understanding and paves the way for new treatments for type 2 diabetes.

How soon do metabolic alterations and oxidative distress precede the reduction of muscle mass and strength in Wistar rats in aging process?

Here we investigate metabolic changes, the antioxidant system and the accumulation of oxidative damage in muscles with different fiber types during the aging process in Wistar rats and try to map how sooner the changes occur. To do so, 30 male Wistar rats were submitted to behavioral evaluation to determine voluntary strength in the 11, 15, and 19 month old rats, measuring the energy metabolism, antioxidant system, oxidative damage and structure in the soleus and extensor digitorum longus muscles. We detected structural and metabolic changes in both muscles, especially in the EDL of 15 month old rats and in the soleus of 19 month old rats. In the 15 month old rats, there was a reduction in the cross-sectional area of the fibers, and a reduction in the proportion of type I fibers, accompanied by an increase in fiber density and the amount of type IIA fibers. This change in the fiber profile was followed by an increase in the activity of anaerobic metabolism enzymes, suggesting a reduction in the oxidative capacity of the muscle. In addition, there was an increase in the rate of lipid peroxidation, accompanied by a reduced antioxidant capacity. In the 19 month old rats, these disturbances got stronger. In summary, the present study demonstrated that before functional disturbances, there was an accumulation of oxidative damage and structural changes in the skeletal muscle beginning at 15 months old in the EDL and the soleus only in the biochemical parameters. Therefore, the metabolic alterations occurred at 15 months old and not before.

Mitochondria and Oxidative Stress as a Link between Alzheimer's Disease and Diabetes Mellitus

This review is devoted to the problems of the common features linking metabolic disorders and type 2 diabetes with the development of Alzheimer's disease. The pathogenesis of Alzheimer's disease closely intersects with the mechanisms of type 2 diabetes development, and an important risk factor for both pathologies is aging. Common pathological mechanisms include both factors in the development of oxidative stress, neuroinflammation, insulin resistance, and amyloidosis, as well as impaired mitochondrial dysfunctions and increasing cell death. The currently available drugs for the treatment of type 2 diabetes and Alzheimer's disease have limited therapeutic efficacy. It is important to note that drugs used to treat Alzheimer's disease, in particular acetylcholinesterase inhibitors, show a positive therapeutic potential in the treatment of type 2 diabetes, while drugs used in the treatment of type 2 diabetes can also prevent a number of pathologies characteristic for Alzheimer's disease. A promising direction in the search for a strategy for the treatment of type 2 diabetes and Alzheimer's disease may be the creation of complex multi-target drugs that have neuroprotective potential and affect specific common targets for type 2 diabetes and Alzheimer's disease.

Two weeks of high-intensity interval training increases skeletal muscle mitochondrial respiration via complex-specific remodeling in sedentary humans

Aerobic training remodels the quantity and quality (function per unit) of skeletal muscle mitochondria to promote substrate oxidation, however, there remain key gaps in understanding the underlying mechanisms during initial training adaptations. We used short-term high-intensity interval training (HIIT) to determine changes to mitochondrial respiration and regulatory pathways that occur early in remodeling. Fifteen normal-weight sedentary adults started seven sessions of HIIT over 14 days and 14 participants completed the intervention. We collected vastus lateralis biopsies before and 48 h after HIIT to determine mitochondrial respiration, RNA sequencing, and Western blotting for proteins of mitochondrial respiration and degradation via autophagy. HIIT increased respiration per mitochondrial protein for lipid (+23% P = 0.020), complex I (+18%, P = 0.0015), complex I + II (+14%, P < 0.0001), and complex II (+24% P < 0.0001). Transcripts that increased with HIIT identified several gene sets of mitochondrial respiration, particularly for complex I, whereas transcripts that decreased identified pathways of DNA and chromatin remodeling. HIIT lowered protein abundance of autophagy markers for p62 (-19%, P = 0.012) and LC3 II/I (-20%, P = 0.004) in whole tissue lysates but not isolated mitochondria. Meal tolerance testing revealed HIIT increased the change in whole body respiratory exchange ratio and lowered cumulative plasma insulin concentrations. Gene transcripts and respiratory function indicate remodeling of mitochondria within 2 wk of HIIT. Overall changes are consistent with increased protein quality driving rapid improvements in substrate oxidation.NEW & NOTEWORTHY Aerobic training stimulates mitochondrial metabolism in skeletal muscle that is linked to improvements to whole body fuel metabolism. The mechanisms driving changes to the quantity and quality (function per unit) of mitochondria are less known. We used seven sessions of high-intensity interval training (HIIT) to determine functional changes and mechanisms of mitochondrial remodeling in skeletal muscle. HIIT increased mitochondrial respiration per mass for fatty acids, complex I, and complex II substrates. HIIT-induced remodeling pathways including gene transcripts for mitochondrial respiration (via RNA sequencing of muscle tissue) and proteins related to complex I respiration. We conclude that an early feature of aerobic training is increased mitochondrial protein quality via improved respiration and induction of mitochondrial transcriptional patterns.

Blood Neuroexosomal Mitochondrial Proteins Predict Alzheimer Disease in Diabetes

There is accumulating evidence that mitochondrial dysfunction is associated with the contribution of diabetes to Alzheimer disease (AD) progression. Neuronal mitochondrial proteins are found in plasma neuronal-derived exosomes (NDEs) at levels that reflect those in brain neurons. Here, we tested the performance of mitochondrial proteins in plasma NDEs to predict cognitive decline and brain injury in participants with diabetes. The study participants with type 2 diabetes mellitus (T2DM) included 41 cognitively normal control subjects, 97 individuals with mild cognitive impairment (MCI) (68 individuals with stable MCI; 29 individuals with progressive MCI), and 36 patients with AD dementia. Plasma neuroexosomal proteins were measured by ELISA kits. Spearman correlation was used to test associations between plasma neuroexosomal mitochondrial proteins and other core biomarkers of AD. Diagnostic accuracy for progressive MCI and AD was obtained for mitochondrial proteins using receiver operating characteristic curve analyses. The associations of mitochondrial proteins with the conversion from MCI to AD were assessed by Cox proportional hazard regression analysis. Plasma levels of neuroexosomal NADH ubiquinone oxidoreductase core subunit S3 (NDUFS3) and succinate dehydrogenase complex subunit B (SDHB) were significantly lower in patients with T2DM with AD dementia and progressive MCI than in cognitively normal subjects (P < 0.001 for both groups). We also found that plasma neuroexosomal NDUFS3 and SDHB levels were lower in progressive MCI subjects than in stable MCI subjects. Both plasma neuroexosomal NDUFS3 and SDHB offer diagnostic utility for AD. Low plasma neuroexosomal SDHB levels significantly predicted conversion from MCI to AD. In addition, low mitochondrial protein levels were associated with the rate of hippocampal and gray matter atrophy and reduced AD signature cortical thickness in progressive MCI over the follow-up period. These data suggest that both plasma neuroexosomal NDUFS3 and SDHB are already increased at the early clinical stage of AD, and indicate the promise of plasma neuroexosomal mitochondrial proteins as diagnostic and prognostic biomarkers for the earliest symptomatic stage of AD in participants with diabetes.

Whole-Body Vibration Promotes Skeletal Muscle Restructuring and Reduced Obesogenic Effect of MSG in Wistar Rats

The negative changes of obesity to the locomotor system are a major concern in the current scenario, where obesity and metabolic syndrome are recurrent in Western societies. A physical exercise is an important tool as a way to rehabilitate obesity, highlighting whole-body vibration, as it is an easy-access modality with few restrictions. In this sense, we sought to evaluate the effect of whole-body vibration on the extensor digitorum longus muscle on a monosodium glutamate-induced obesity model. The main findings of the present study are related to the ability of the treatment with vibration to reduce the obesogenic characteristics and slow down the dyslipidemic condition of the animals. Likewise, the vibration promoted by the vibrating platform was essential in the recovery of the muscle structure, as well as the recovery of the muscle's oxidative capacity, initially compromised by obesity.

Short-term step reduction reduces CS activity without altering skeletal muscle markers of oxidative metabolism or insulin-mediated signalling in young males

Mitochondria are critical to skeletal muscle contractile function and metabolic health. Short-term periods of step reduction (SR) are associated with alterations in muscle protein turnover and mass. However, the effects of SR on mitochondrial metabolism/muscle oxidative metabolism and insulin-mediated signaling are unclear. We tested the hypothesis that the total and/or phosphorylated protein content of key skeletal muscle markers of mitochondrial/oxidative metabolism, and insulin-mediated signaling would be altered over 7 days of SR in young healthy males. Eleven, healthy, recreationally active males (means ± SE, age: 22 ± 1 yr, BMI: 23.4 ± 0.7 kg·m²) underwent a 7-day period of SR. Immediately before and following SR, fasted-state muscle biopsy samples were acquired and analyzed for the assessment of total and phosphorylated protein content of key markers of mitochondrial/oxidative metabolism and insulin-mediated signaling. Daily step count was significantly reduced during the SR intervention (13,054 ± 833 to 1,192 ± 99 steps·day⁻¹, P < 0.001). Following SR, there was a significant decline in maximal citrate synthase activity (fold change: 0.94 ± 0.08, P < 0.05) and a significant increase in the protein content of p-glycogen synthase (P-GS^S641; fold change: 1.47 ± 0.14, P < 0.05). No significant differences were observed in the total or phosphorylated protein content of other key markers of insulin-mediated signaling, oxidative metabolism, mitochondrial function, or mitochondrial dynamics (all P > 0.05). These results suggest that short-term SR reduces the maximal activity of citrate synthase, a marker of mitochondrial content, without altering the total or phosphorylated protein content of key markers of skeletal muscle mitochondrial metabolism and insulin signaling in young healthy males.

NEW & NOTEWORTHY Short-term (7 day) step reduction reduces the activity of citrate synthase without altering the total or phosphorylated protein content of key markers of skeletal muscle mitochondrial metabolism and insulin signaling in young healthy males.

Whole-body vibration promotes lipid mobilization in hypothalamic obesity rat

OBJECTIVES

This study aimed to analyze the effect of whole-body vibration (WBV) on metabolic parameters using the monosodium l-glutamate (MSG) model of obesity.

METHOD

MSG-obese rats that were exposed to WBV on a vibrating platform with 60 Hz frequency, 2 mm amplitude, three times/week, 10 min/day, during eight weeks (from postnatal day (PN) 80 to PN136). Blood glucose, creatine kinases (CK and CK-MB) and lipid profile through plasma and liver levels of lipids and lipoproteins were evaluated. Morphology and oxidative stress of adipose and hepatic tissues were further evaluated.

RESULTS

When performing a WBV exercise, animals showed contrasting metabolic responses. Vibration Control group (CTL-WBV) presented a reduction in CK and liver triacylglycerol, an increase in glucose, lactate, total cholesterol, liver cholesterol, and LDL while MSG Vibration group (MSG-WBV) showed an increase in total triacylglycerol, VLDL, lactate, CK, liver cholesterol, additional liver lipid peroxidation and LDL, total cholesterol and CKMB reduction.

CONCLUSION

Even although the MSG is a model of impacting injury, the metabolic demand of WBV exercise was able to induce mobilization of substrates, highlighting the lipid mobilization in obese animals, it should be used as a metabolic rehabilitation tool in patients with metabolic diseases, such as obesity and diabetes.

Dysfunctional Mitochondrial Dynamic and Oxidative Phosphorylation Precedes Cardiac Dysfunction in R120G-αB-Crystallin-Induced Desmin-Related Cardiomyopathy

Background The mutated α-B-Crystallin (CryABR120G) mouse model of desmin-related myopathy (DRM) shows an age-dependent onset of pathologic cardiac remodeling and progression of heart failure. CryABR120G expression in cardiomyocytes affects the mitochondrial spatial organization within the myofibrils, but the molecular perturbation within the mitochondria in the relation of the overall course of the proteotoxic disease remains unclear. Methods and Results CryABR120G mice show an accumulation of electron-dense aggregates and myofibrillar degeneration associated with the development of cardiac dysfunction. Though extensive studies demonstrated that these altered ultrastructural changes cause cardiac contractility impairment, the molecular mechanism of cardiomyocyte death remains elusive. Here, we explore early pathological processes within the mitochondria contributing to the contractile dysfunction and determine the pathogenic basis for the heart failure observed in the CryABR120G mice. In the present study, we report that the CryABR120G mice transgenic hearts undergo altered mitochondrial dynamics associated with increased level of dynamin-related protein 1 and decreased level of optic atrophy type 1 as well as mitofusin 1 over the disease process. In association with these changes, an altered level of the components of mitochondrial oxidative phosphorylation and pyruvate dehydrogenase complex regulatory proteins occurs before the manifestation of pathologic adverse remodeling in the CryABR120G hearts. Mitochondria isolated from CryABR120G transgenic hearts without visible pathology show decreased electron transport chain complex activities and mitochondrial respiration. Taken together, we demonstrated the involvement of mitochondria in the pathologic remodeling and progression of DRM-associated cellular dysfunction. Conclusions Mitochondrial dysfunction in the form of altered mitochondrial dynamics, oxidative phosphorylation and pyruvate dehydrogenase complex proteins level, abnormal electron transport chain complex activities, and mitochondrial respiration are evident on the CryABR120G hearts before the onset of detectable pathologies and development of cardiac contractile dysfunction.