Citations

We report a technique to simultaneously measure fractional synthesis rates (FSR) of several muscle proteins that facilitate further understanding of translational regulation, a key step involved in gene expression in a tissue. Skeletal muscle samples were collected from five rats following bolus injection of [ring 13 C 6 ] phenylalanine. Muscle proteins were fractionated by differential centrifugation followed by separation of individual proteins by high resolution two‐dimensional gel electrophoresis. We identified 60 mitochondrial and 30 non‐mitochondrial proteins by liquid chromatography tandem mass spectrometry. Isotope enrichment of these 90 proteins was measured by gas chromatography tandem mass spectrometry, and FSR was calculated using the muscle tissue fluid isotopic enrichment as the precursor. Approximately 25 fold differences in the FSR of muscle proteins were observed, (e.g. FSR of structural protein such as myosin heavy chain‐1 = 0.19 %/h ± 0.03 and tropomysin‐4 = 0.16 ± 03 and that of mitochondrial proteins such as cytochrome c oxidase Va = 0.64 ± 0.07 and dihydrolipoamide dehydrogenase = 4.3 %/h ± 0.53). The current approach, based on in‐vivo metabolic labeling, to simultaneously measure FSR of multiple muscle proteins offers tremendous opportunity to study the regulation of skeletal muscle mitochondrial and non‐mitochondrial protein synthesis in various physiologic and pathologic states. Funding: NIH RO1 DK41973

Objective In contrast to intentionally restricting energy intake, restricting the eating window may be an option for treating obesity. By comparing time‐restricted eating (TRE) with an unrestricted (non‐TRE) control, it was hypothesized that TRE facilitates weight loss, alters body composition, and improves metabolic measures. Methods Participants (17 women and 3 men; mean [SD]: 45.5 [12.1] years; BMI 34.1 [7.5] kg/m 2 ) with a prolonged eating window (15.4 [0.9] hours) were randomized to TRE ( n = 11: 8‐hour window, unrestricted eating within window) versus non‐TRE ( n = 9: unrestricted eating) for 12 weeks. Weight, body composition (dual x‐ray absorptiometry), lipids, blood pressure, 2‐hour oral glucose tolerance, 2‐week continuous glucose monitoring, and 2‐week physical activity (actigraphy assessed) were measured during the pre‐ and end‐intervention periods. Results The TRE group significantly reduced the eating window (end‐intervention window: 9.9 [2.0] hours) compared with the non‐TRE group (end‐intervention window: 15.1 [1.1] hours) ( P < 0.01). Compared with non‐TRE, TRE decreased the number of eating occasions, weight, lean mass, and visceral fat (all P ≤ 0.05). Compared with preintervention measures, the TRE group reduced the number of eating occasions (−21.9% [30.1%]) and reduced weight (−3.7% [1.8%]), fat mass (−4% [2.9%]), lean mass (−3.0% [2.7%]), and visceral fat (−11.1% [13.4%]) (all P ≤ 0.05). Physical activity and metabolic measures remained unchanged. Conclusions In the setting of a randomized trial, TRE presents a simplified view of food intake that reduces weight.

It has been shown ingestion of whey protein (WP) results in rapid systemic appearance rates of amino acids (AA) but in higher amino acid (AA) oxidation and whole body protein synthesis than in with casein (cas) ingestion which inhibits protein breakdown. To determine whether combined ingestion of both cas and WP in a meal containing carbohydrate has any disparate effects on protein economy in splanchnic and muscle beds we studied 12 healthy volunteers who ingested intrinsically labeled WP and Cas protein fractions. Following ingestion of 0.625 g·kg FFM −1 each of [ 15 N]WP and [ 13 C]Cas and 0.9 g·kg FFM −1 of lactose; or 0.625 g·kg FFM −1 each of [ 13 C]WP and [ 15 N]CAS and 0.9 g·kg FFM −1 of lactose blood samples were collected from femoral artery and vein and hepatic vein at frequent intervals. At 80–120 min, the rate of appearance (PheRa) of Phe at hepatic vein from WP and Cas were similar (5.5 (0.9) vs 5.2 (0.7) μmol, min −1 , but at 220–260 min, PheRa from WP was slower than PheRa from Cas (2.4 (0.5) vs 5.3 (1.2) μmol, min −1 , P<0.05). Retention rates of Phe in muscle (PheRd) absorbed from WP and Cas were similar at 80–120 min (0.8 (0.1) vs 0.9 (0.2) μmol, min −1 , ns) but was significantly lower for WP than Cas at 220–260 min (0.5 (0.1) vs 1.1 (0.3) μmol, min −1 , P<0.05). In conclusion Cas has more sustained systemic effects and muscle protein accretion than WP. The different metabolic effects of co‐ingested protein fractions have potential implications in designing appropriate nutritional support.

Insulin resistance associates with increased risk for cognitive decline and dementia; however, the underpinning mechanisms for this increased risk remain to be fully defined. As insulin resistance impairs mitochondrial oxidative metabolism and increases ROS in skeletal muscle, we considered whether similar events occur in the brain, which — like muscle — is rich in insulin receptors and mitochondria. We show that high-fat diet–induced (HFD-induced) brain insulin resistance in mice decreased mitochondrial ATP production rate and oxidative enzyme activities in brain regions rich in insulin receptors. HFD increased ROS emission and reduced antioxidant enzyme activities, with the concurrent accumulation of oxidatively damaged mitochondrial proteins and increased mitochondrial fission. Improvement of insulin sensitivity by both aerobic exercise and metformin ameliorated HFD-induced abnormalities. Moreover, insulin-induced enhancement of ATP production in primary cortical neurons and astrocytes was counteracted by the insulin receptor antagonist S961, demonstrating a direct effect of insulin resistance on brain mitochondria. Further, intranasal S961 administration prevented exercise-induced improvements in ATP production and ROS emission during HFD, supporting that exercise enhances brain mitochondrial function by improving insulin action. These results support that insulin sensitizing by exercise and metformin restores brain mitochondrial function in insulin-resistant states.

Diet-induced insulin resistance (IR) adversely affects human health and life span. We show that muscle-specific overexpression of human mitochondrial transcription factor A (TFAM) attenuates high-fat diet (HFD)–induced fat gain and IR in mice in conjunction with increased energy expenditure and reduced oxidative stress. These TFAM effects on muscle are shown to be exerted by molecular changes that are beyond its direct effect on mitochondrial DNA replication and transcription. TFAM augmented the muscle tricarboxylic acid cycle and citrate synthase facilitating energy expenditure. TFAM enhanced muscle glucose uptake despite increased fatty acid (FA) oxidation in concert with higher β-oxidation capacity to reduce the accumulation of IR-related carnitines and ceramides. TFAM also increased pAMPK expression, explaining enhanced PGC1α and PPARβ, and reversing HFD-induced GLUT4 and pAKT reductions. TFAM-induced mild uncoupling is shown to protect mitochondrial membrane potential against FA-induced uncontrolled depolarization. These coordinated changes conferred protection to TFAM mice against HFD-induced obesity and IR while reducing oxidative stress with potential translational opportunities.

The objective of this study is to determine whether AMP-activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma coactivator 1-α (PGC-1α), or peroxisome proliferator-activated receptor β (PPARβ) can independently mediate the increase of glucose transporter type 4 (GLUT4) expression that occurs in response to exercise training. We found that PPARβ can regulate GLUT4 expression without PGC-1α. We also found AMPK and PPARβ are important for maintaining normal physiological levels of GLUT4 protein in the sedentary condition as well following exercise training. However, AMPK and PPARβ are not essential for the increase in GLUT4 protein expression that occurs in response to exercise training. We discovered that AMPK activation increases PPARβ via myocyte enhancer factor 2A (MEF2A), which acted as a transcription factor for PPARβ. Furthermore, exercise training increases the cooperation of AMPK and PPARβ to regulate glucose uptake. In conclusion, cooperation between AMPK and PPARβ via NRF-1/MEF2A pathway enhances the exercise training mediated adaptive increase in GLUT4 expression and subsequent glucose uptake in skeletal muscle.

Background: The FOXO3a (forkhead box O3a)-BNIP3 (B-cell lymphoma 2/adenovirus E1B 19kDa interacting protein 3) pathway modulates mitochondrial dynamics and function and contributes to myocardial remodeling in rodent models of heart failure. We sought to investigate the expression of this pathway along with the expression of mitochondrial biogenesis (PGC-1α [peroxisome proliferator-activated receptor-γ coactivator-1α]), dynamics (DRP-1 [dynamin-related protein 1], OPA-1 [optic atrophy 1], and MFN 2 [mitofusin 2]), and oxidative phosphorylation (citrate synthase and electron transport chain complexes) markers and COX IV (cytochrome C oxidase) activity in myocardium from patients with valvular or ischemic heart disease and heart failure with preserved ejection fraction (HFpEF) or heart failure with reduced ejection fraction (HFrEF). Methods and Results: Subepicardial left ventricular biopsies (10×1×1 mm 3 ) were obtained at aortic valve replacement (HFpEF AVR , n=5; and HFrEF AVR , n=4), coronary artery bypass grafting (HFpEF CABG , n=5; and HFrEF CABG , n=5), or left ventricular assist device implantation (HFrEF LVAD , n=4). Subepicardial biopsies from patients with normal left ventricular function (n=2) and from donor hearts (n=3) served as controls (normal). Relative to normal, mitochondrial fragmentation and cristae destruction were evident, and mitochondrial area was decreased in HFpEF; 1.00±0.09 versus 0.71±0.08; P =0.016. These mitochondrial morphological changes were more pronounced in HFrEF (0.54±0.06); P =0.002 HFpEF versus HFrEF. BNIP3 (monomer+dimer) expression was increased in HFpEF (3.99±2.44) and in HFrEF (5.19±1.70) relative to normal; P =0.004 and P <0.001, respectively. However, BNIP3 monomer was increased in HFrEF (4.32±1.43) compared with normal (0.99±0.06) and HFpEF (1.97±0.90); P =0.001 and 0.004, respectively. The HFrEF group uniquely showed increase in DRP-1 expression (1.94±0.38) and decreases in PGC-1α expression (0.61±0.07) and COX IV activity (0.70±0.10) relative to normal; P =0.013, P <0.001, and P <0.001, respectively, with no significant change in electron transport chain complexes expression. Conclusions: These findings in human myocardium confirm studies in rodents where contractile dysfunction is associated with activation of the FOXO3a-BNIP3 pathway and altered mitochondrial dynamics, biogenesis, and function.

ABSTRACT Despite the strong association between diabetes and dementia, it remains to be fully elucidated how insulin deficiency adversely affects brain functions. We show that insulin deficiency in streptozotocin‐induced diabetic mice decreased mitochondrial ATP production and/or citrate synthase and cytochrome oxidase activities in the cerebrum, hypothalamus, and hippocampus. Concomitant decrease in mitochondrial fusion proteins and increased fission proteins in these brain regions likely contributed to altered mitochondrial function. Although insulin deficiency did not cause any detectable increase in reactive oxygen species (ROS) emission, inhibition of monocarboxylate transporters increased ROS emission and further reduced ATP production, indicating the causative roles of elevated ketones and lactate in counteracting oxidative stress and as a fuel source for ATP production during insulin deficiency. Moreover, in healthy mice, intranasal insulin administration increased mitochondrial ATP production, demonstrating a direct regulatory role of insulin on brain mitochondrial function. Proteomics analysis of the cerebrum showed that although insulin deficiency led to oxidative post‐translational modification of several proteins that cause tau phosphorylation and neurofibrillary degeneration, insulin administration enhanced neuronal development and neurotransmission pathways. Together these results render support for the critical role of insulin to maintain brain mitochondrial homeostasis and provide mechanistic insight into the potential therapeutic benefits of intranasal insulin.—Ruegsegger, G. N., Manjunatha, S., Summer, P., Gopala, S., Zabeilski, P., Dasari, S., Vanderboom, P. M., Lanza, I. R., Klaus, K. A., Nair, K. S. Insulin deficiency and intranasal insulin alter brain mitochondrial function: a potential factor for dementia in diabetes. FASEB J. 33, 4458–4472 (2019). www.fasebj.org

Insulin deficiency and uncontrolled diabetes lead to a catabolic state with decreased muscle strength, contributing to disease-related morbidity. FoxO transcription factors are suppressed by insulin and thus are key mediators of insulin action. To study their role in diabetic muscle wasting, we created mice with muscle-specific triple knockout of FoxO1/3/4 and induced diabetes in these M-FoxO-TKO mice with streptozotocin (STZ). Muscle mass and myofiber area were decreased 20–30% in STZ-Diabetes mice due to increased ubiquitin-proteasome degradation and autophagy alterations, characterized by increased LC3-containing vesicles, and elevated levels of phosphorylated ULK1 and LC3-II. Both the muscle loss and markers of increased degradation/autophagy were completely prevented in STZ FoxO-TKO mice. Transcriptomic analyses revealed FoxO-dependent increases in ubiquitin-mediated proteolysis pathways in STZ-Diabetes, including regulation of Fbxo32 (Atrogin1), Trim63 (MuRF1), Bnip3L, and Gabarapl. These same genes were increased 1.4- to 3.3-fold in muscle from humans with type 1 diabetes after short-term insulin deprivation. Thus, FoxO-regulated genes play a rate-limiting role in increased protein degradation and muscle atrophy in insulin-deficient diabetes.

SummaryObjectiveStudies of dehydroepiandrosterone (DHEA) therapy in older adults suggest sex‐specific effects on bone mineral density (BMD) and body composition, but the ability of a single study to reach this conclusion was limited. We evaluated the effects of DHEA on sex hormones, BMD, fat mass and fat‐free mass in older women and men enrolled in four similar clinical trials.DesignPooled analyses of data from four double‐blinded, randomized controlled trials.ParticipantsWomen (n = 295) and men (n = 290) aged 55 years or older who took DHEA or placebo tablet daily for 12 months.MeasurementsTwelve‐month changes in BMD, fat mass, fat‐free mass and serum DHEA sulphate (DHEAS), (17)estradiol, testosterone and insulin‐like growth factor‐1 (IGF‐1).ResultsWomen on DHEA had increases (mean ± SD; all P < 0.001 vs placebo) in DHEAS (231 ± 164 µg/dL), testosterone (18.6 ± 20.9 µg/dL), (17)estradiol (8.7 ± 11.0 pg/mL) and IGF‐1 (25.1 ± 52.3 ng/mL), and men had increases in DHEAS (269.0 ± 177 µg/dL; P < 0.01), (17)estradiol (4.8 ± 12.2 pg/m; P < 0.01) and IGF‐1 (6.3 ± 41.4 ng/mL; P < 0.05). Women on DHEA had increases in lumbar spine (1.0% ± 3.4%) and trochanter (0.5% ± 3.8%) BMD and maintained total hip BMD (0.0% ± 2.8%); men had no BMD benefit and a decrease in fat mass (−0.4 ± 2.6 kg; all P < 0.01 vs placebo).ConclusionsDehydroepiandrosterone therapy may be an effective approach for preserving bone and muscle mass in women. Key questions are (a) the extent to which longer duration DHEA can attenuate the loss of bone and muscle in women, and (b) whether DHEA has a more favourable benefit‐to‐risk profile for women than oestrogen therapy.