UCP3 in muscle wasting, a role in modulating lipotoxicity?

AbstractUCP3 has been postulated to function in the defense against lipid-induced oxidative muscle damage (lipotoxicity). We explored this hypothesis during cachexia in rats (zymosan-induced sepsis), a condition characterized by increased oxidative stress and supply of fatty acids to the muscle. Muscle UCP3 protein content was increased 2, 6 and 11 days after zymosan injection. Plasma FFA levels were increased at day 2, but dropped below control levels on days 6 and 11. Muscular levels of the lipid peroxidation byproduct 4-hydroxy-2-nonenal (4-HNE) were increased at days 6 and 11 in zymosan-treated rats, supporting a role for UCP3 in modulating lipotoxicity during cachexia

Adaptations in mitochondrial function parallel, but fail to rescue, the transition to severe hyperglycemia and hyperinsulinemia: a study in Zucker diabetic fatty rats.

Cross-sectional human studies have associated mitochondrial dysfunction to type 2 diabetes. We chose Zucker diabetic fatty (ZDF) rats as a model of progressive insulin resistance to examine whether intrinsic mitochondrial defects are required for development of type 2 diabetes. Muscle mitochondrial function was examined in 6-, 12-, and 19-week-old ZDF (fa/fa) and fa/+ control rats (n = 8-10 per group) using respirometry with pyruvate, glutamate, and palmitoyl-CoA as substrates. Six-week-old normoglycemic-hyperinsulinemic fa/fa rats had reduced mitochondrial fat oxidative capacity. Adenosine diphosphate (ADP)-driven state 3 and carbonyl cyanide p-trifluoromethoxyphenylhydrazone (FCCP)-stimulated state uncoupled (state u) respiration on palmitoyl-CoA were lower compared to controls (62.3 ± 9.5 vs. 119.1 ± 13.8 and 87.8 ± 13.3 vs. 141.9 ± 14.3 nmol O2/mg/min.). Pyruvate oxidation in 6-week-old fa/fa rats was similar to controls. Remarkably, reduced fat oxidative capacity in 6-week-old fa/fa rats was compensated for by an adaptive increase in intrinsic mitochondrial function at week 12, which could not be maintained toward week 19 (140.9 ± 11.2 and 57.7 ± 9.8 nmol O2/mg/min, weeks 12 and 19, respectively), whereas hyperglycemia had developed (13.5 ± 0.6 and 16.1 ± 0.3 mmol/l, weeks 12 and 19, respectively). This mitochondrial adaptation failed to rescue the progressive development of insulin resistance in fa/fa rats. The transition of prediabetes state toward advanced hyperglycemia and hyperinsulinemia was accompanied by a blunted increase in uncoupling protein-3 (UCP3). Thus, in ZDF rats insulin resistance develops progressively in the absence of mitochondrial dysfunction. In fact, improved mitochondrial capacity in hyperinsulinemic hyperglycemic rats does not rescue the progression toward advanced stages of insulin resistance

DGAT1 overexpression in muscle by in vivo DNA electroporation increases intramyocellular lipid content.

In adipose tissue, the microsomal enzyme 1,2-acyl CoA:diacylglyceroltransferase-1 (DGAT1) plays an important role in triglyceride storage. Because DGAT1 is expressed in skeletal muscle as well, we aimed to directly test the effect of DGAT1 on muscular triglyceride storage by overexpressing DGAT1 using in vivo DNA electroporation. A pcDNA3.1-DGAT1 construct in saline was injected in the left tibialis anterior muscle of rats, followed by the application of eight transcutaneous pulses, using the contralateral leg as sham-electroporated control. Electroporation of the DGAT1 construct led to significant overexpression of the DGAT1 protein. The functionality of DGAT1 overexpression is underscored by the pronounced diet-responsive increase in intramyocellular lipid (IMCL) storage. In chow-fed rats, DGAT1-positive myocytes showed significantly higher IMCL content compared with the control leg, which was almost devoid of IMCL (1.99 +/- 1.13% vs. 0.017 +/- 0.014% of total area fraction; P <0.05). High-fat feeding increased IMCL levels in both DGAT1-positive and control myocytes, resulting in very high IMCL levels in DGAT1-overexpressing myocytes (4.96 +/- 1.47% vs. 0.80 +/- 0.14%; P <0.05). Our findings indicate that DGAT1 contributes to the storage of IMCL and that in vivo DNA electroporation is a promising tool to examine the functional consequences of altered gene expression in mature skeletal muscle

Reduced incorporation of Fatty acids into triacylglycerol in myotubes from obese individuals with type 2 diabetes.

Altered skeletal muscle lipid metabolism is a hallmark feature of type 2 (T2D). Here we investigated muscle lipid turnover in T2D versus BMI- controls and examined if putative in vivo differences would be preserved myotubes.Male obese T2D individuals (T2D) (n=6) and their BMI-matched (C) (n=6) underwent a hyperinsulinemic-euglycemic clamp, VO2max test, underwater weighing and muscle biopsy of v. lateralis. 14C-palmitate and 14C-oleate oxidation rates and incorporation into lipids were measured tissue, as well as in primary myotubes.Palmitate oxidation (C: 0.99 +/- T2D: 0.53 +/- 0.07nmol/mg protein; P=0.03) and incorporation of fatty into triacylglycerol (TAG) (C: 0.45 +/- 0.13, T2D: 0.11 +/- 0.02nmol/mg P=0.047) were significantly reduced in muscle homogenates of T2D. These reductions were not retained for palmitate oxidation in primary myotubes (P=0.38); however, incorporation of FAs into TAG was lower in T2D oleate and P=0.11 for palmitate), with a strong correlation of TAG between muscle tissue and primary myotubes (r=0.848, P=0.008).Our data that the ability to incorporate FAs into TAG is an intrinsic feature of muscle cells that is reduced in individuals with T2D

Time resolution of the plastic scintillator strips with matrix photomultiplier readout for J-PET tomograph

Recent tests of a single module of the Jagiellonian Positron Emission Tomography system (J-PET) consisting of 30 cm long plastic scintillator strips have proven its applicability for the detection of annihilation quanta (0.511 MeV) with a coincidence resolving time (CRT) of 0.266 ns. The achieved resolution is almost by a factor of two better with respect to the current TOF-PET detectors and it can still be improved since, as it is shown in this article, the intrinsic limit of time resolution for the determination of time of the interaction of 0.511 MeV gamma quanta in plastic scintillators is much lower. As the major point of the article, a method allowing to record timestamps of several photons, at two ends of the scintillator strip, by means of matrix of silicon photomultipliers (SiPM) is introduced. As a result of simulations, conducted with the number of SiPM varying from 4 to 42, it is shown that the improvement of timing resolution saturates with the growing number of photomultipliers, and that the 2 x 5 configuration at two ends allowing to read twenty timestamps, constitutes an optimal solution. The conducted simulations accounted for the emission time distribution, photon transport and absorption inside the scintillator, as well as quantum efficiency and transit time spread of photosensors, and were checked based on the experimental results. Application of the 2 x 5 matrix of SiPM allows for achieving the coincidence resolving time in positron emission tomography of $\approx$ 0.170 ns for 15 cm axial field-of-view (AFOV) and $\approx$ 0.365 ns for 100 cm AFOV. The results open perspectives for construction of a cost-effective TOF-PET scanner with significantly better TOF resolution and larger AFOV with respect to the current TOF-PET modalities.Comment: To be published in Phys. Med. Biol. (26 pages, 17 figures

Decreased fatty acid beta-oxidation in riboflavin-responsive, multiple acylcoenzyme A dehydrogenase-deficient patients is associated with an increase in uncoupling protein-3

Decreased fatty acid beta-oxidation in riboflavin-responsive, multiple acylcoenzyme A dehydrogenase-deficient patients is associated with an increase in uncoupling protein-3.Russell AP, Schrauwen P, Somm E, Gastaldi G, Hesselink MK, Schaart G, Kornips E, Lo SK, Bufano D, Giacobino JP, Muzzin P, Ceccon M, Angelini C, Vergani L.Department of Medical Biochemistry, University of Geneva Medical Center, 1206 Geneva, Switzerland. [email protected], multiple acylcoenzyme A dehydrogenase deficiency (RR-MAD), a lipid storage myopathy, is characterized by, among others, a decrease in fatty acid (FA) beta-oxidation capacity. Muscle uncoupling protein 3 (UCP3) is up-regulated under conditions that either increase the levels of circulating free FA and/or decrease FA beta-oxidation. Using a relatively large cohort of seven RR-MAD patients, we aimed to better characterize the metabolic disturbances of this disease and to explore the possibility that it might increase UCP3 expression. A battery of biochemical and molecular tests were performed, which demonstrated decreases in FA beta-oxidation and in the activities of respiratory chain complexes I and II. These metabolic alterations were associated with increases of 3.1- and 1.7-fold in UCP3 mRNA and protein expression, respectively. All parameters were restored to control values after riboflavin treatment. We postulate that the up-regulation of UCP3 in RR-MAD is due to the accumulation of muscle FA/acylCoA. RR-MAD is an optimal model to support the hypothesis that UCP3 is involved in the outward translocation of an excess of FA from the mitochondria and to show that, in humans, the effects of FA on UCP3 expression are direct and independent of fatty acid beta-oxidation.<br/

Sub-3mm spatial resolution from a large monolithic LaBr3 (Ce) scintillator

Abstract A Compton camera prototype for ion beam range monitoring via prompt (< 1 ns) gamma detection in hadron therapy is being developed and characterized at the Medical Physics Department of LMU Munich. The system consists of a large (50x50x30 mm3) monolithic LaBr3(Ce) scintillation crystal as absorber component to detect the multi-MeV Compton scattered photons, together with a stack of 6 double-sided silicon strip detectors (DSSSD) acting as scatterer component. Key ingredient of the γ-source reconstruction is the determination of the γ-ray interaction position in the scintillator, which is read out by a 256-fold segmented multi-anode photomultiplier tube (PMT). From simulations an angular resolution of about 1.5o for the photon source reconstruction can be expected for the energy range around 3 – 5 MeV, provided that a spatial resolution of 3 mm can be reached in the absorbing scintillator [1]. Therefore, particular effort was dedicated to characterize this latter property as a function of the γ-ray energy. Intense, tightly collimated 137Cs and 60Co photon sources were used for 2D irradiation scans (step size 0.5 mm) as prerequisite for studying the performance of the "k-Nearest-Neighbors" algorithm developed at TU Delft [2] (together with its variant "Categorical Average Pattern", CAP) and extending its applicability into the energy range beyond the original 511 keV. In this paper we present our most recent interaction position analysis in the absorbing scintillator, leading to a considerably improved value for the spatial resolution: systematic studies were performed as a function of the k-NN parameters and the PMT segmentation. A trend of improving spatial resolution with increasing photon energy was confirmed, resulting in the realization of the presently optimum spatial resolution of 2.9(1) mm @1.3 MeV, thus reaching the design specifications of the Compton camera absorber. The specification goal was reached also for a reduced PMT segmentation of 8x8 anode segments (each with 6x6 mm2 active area), thus allowing to reduce the complexity of the signal processing while preserving the performance

Partial hexokinase II knockout results in acute ischemia-reperfusion damage in skeletal muscle of male, but not female, mice

Cellular studies have demonstrated a protective role of mitochondrial hexokinase against oxidative insults. It is unknown whether HK protective effects translate to the in vivo condition. In the present study, we hypothesize that HK affects acute ischemia–reperfusion injury in skeletal muscle of the intact animal. Male and female heterozygote knockout HKII (HK(+/-)), heterozygote overexpressed HKII (HK(tg)), and their wild-type (WT) C57Bl/6 littermates mice were examined. In anesthetized animals, the left gastrocnemius medialis (GM) muscle was connected to a force transducer and continuously stimulated (1-Hz twitches) during 60 min ischemia and 90 min reperfusion. Cell survival (%LDH) was defined by the amount of cytosolic lactate dehydrogenase (LDH) activity still present in the reperfused GM relative to the contralateral (non-ischemic) GM. Mitochondrial HK activity was 72.6 ± 7.5, 15.7 ± 1.7, and 8.8 ± 0.9 mU/mg protein in male mice, and 72.7 ± 3.7, 11.2 ± 1.4, and 5.9 ± 1.1 mU/mg in female mice for HK(tg), WT, and HK(+/-), respectively. Tetanic force recovery amounted to 33 ± 7% for male and 17 ± 4% for female mice and was similar for HK(tg), WT, and HK(+/-). However, cell survival was decreased (p = 0.014) in male HK(+/-) (82 ± 4%LDH) as compared with WT (98 ± 5%LDH) and HK(tg) (97 ± 4%LDH). No effects of HKII on cell survival was observed in female mice (92 ± 2% LDH). In conclusion, in this mild model of acute in vivo ischemia–reperfusion injury, a partial knockout of HKII was associated with increased cell death in male mice. The data suggest for the first time that HKII mediates skeletal muscle ischemia–reperfusion injury in the intact male animal

Uncoupling protein 3 content is decreased in skeletal muscle of patients with type 2 diabetes.

Diabetes 2001 Dec;50(12):2870-3 Related Articles, Books, LinkOut Uncoupling protein 3 content is decreased in skeletal muscle of patients with type 2 diabetes. Schrauwen P, Hesselink MK, Blaak EE, Borghouts LB, Schaart G, Saris WH, Keizer HA. Department of Human Biology, Maastricht University, Maastricht, the Netherlands. [email protected] Recently, a role for uncoupling protein-3 (UCP3) in carbohydrate metabolism and in type 2 diabetes has been suggested. Mice overexpressing UCP3 in skeletal muscle showed reduced fasting plasma glucose levels, improved glucose tolerance after an oral glucose load, and reduced fasting plasma insulin levels. However, data regarding the expression of UCP3 in patients with type 2 diabetes is inconsistent, and so far, there have been no reports of UCP3 protein content. Here we compared, for the first time, the protein levels of UCP3 in vastus lateralis muscle in 14 male type 2 diabetic patients (age 49.8 +/- 2.1 years; BMI 27.2 +/- 1.2 kg/m(2); mean +/- SE) with 16 male control subjects (age 48.0 +/- 1.9 years; BMI 23.4 +/- 0.6 kg/m(2)). We found that UCP3 protein levels were twice as low in patients with type 2 diabetes compared with control subjects (117 +/- 16 vs. 58 +/- 12 AU; P = 0.007). There was no correlation between UCP3 content and BMI. In conclusion, UCP3 content is lower in type 2 diabetic patients compared with healthy control subjects. These results are consistent with a role for UCP3 in glucose homeostasis and suggest a role for UCP3 in type 2 diabetes