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| 2. |
- Blackwood, Sarah J, et al.
(författare)
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Insulin resistance after a 3-day fast is associated with an increased capacity of skeletal muscle to oxidize lipids.
- 2023
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 324:5, s. E390-E401
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Tidskriftsartikel (refereegranskat)abstract
- There is a debate on whether lipid-mediated insulin resistance derives from an increased or decreased capacity of muscle to oxidize fats. Here we examine the involvement of muscle fiber composition in the metabolic responses to a 3-day fast (starvation, which results in increases in plasma lipids and insulin resistance) in two groups of healthy young subjects: 1, area occupied by type I fibers = 61.0 ± 11.8%; 2, type I area = 36.0 ± 4.9% (P<0.001). Muscle biopsies and intravenous glucose tolerance tests were performed after an overnight fast and after starvation. Biopsies were analyzed for muscle fiber composition and mitochondrial respiration. Indices of glucose tolerance and insulin sensitivity were determined. Glucose tolerance was similar in both groups after an overnight fast and deteriorated to a similar degree in both groups after starvation. In contrast, whole-body insulin sensitivity decreased markedly after starvation in group 1 (P<0.01), whereas the decrease in group 2 was substantially smaller (P=0.06). Non-esterified fatty acids and β-hydroxybutyrate levels in plasma after an overnight fast were similar between groups and increased markedly and comparably in both groups after starvation, demonstrating similar degrees of lipid load. The capacity of permeabilized muscle fibers to oxidize lipids was significantly higher in group 1 vs. 2, whereas there was no significant difference in pyruvate oxidation between groups. The data demonstrate that loss of whole-body insulin sensitivity after short-term starvation is a function of muscle fiber composition and is associated with an elevated rather than a diminished capacity of muscle to oxidize lipids.
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| 3. |
- Blackwood, Sarah J, et al.
(författare)
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Role of nitration in control of phosphorylase and glycogenolysis in mouse skeletal muscle.
- 2021
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 320:4, s. E691-E701
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Tidskriftsartikel (refereegranskat)abstract
- Phosphorylase is one of the most carefully studied proteins in history, but knowledge of its regulation during intense muscle contraction is incomplete. Tyrosine nitration of purified preparations of skeletal muscle phosphorylase results in inactivation of the enzyme and this is prevented by antioxidants. Whether an altered redox state affects phosphorylase activity and glycogenolysis in contracting muscle is not known. Here, we investigate the role of redox state in control of phosphorylase and glycogenolysis in isolated mouse fast-twitch (extensor digitorum longus, EDL) and slow-twitch (soleus) muscle preparations during repeated contractions. Exposure of crude muscle extracts to H2O2 had little effect on phosphorylase activity. However, exposure of extracts to peroxynitrite (ONOO-), a nitrating/oxidizing agent, resulted in complete inactivation of phosphorylase (half maximal inhibition at ~200 µM ONOO-), which was fully reversed by the presence of an ONOO-scavanger, dithiothreitol (DTT). Incubation of isolated muscles with ONOO- resulted in nitration of phosphorylase and marked inhibition of glycogenolysis during repeated contractions. ONOO- also resulted in large decreases in high-energy phosphates (ATP and phosphocreatine) in the rested state and following repeated contractions. These metabolic changes were associated with decreased force production during repeated contractions (to ~60% of control). In contrast, repeated contractions did not result in nitration of phosphorylase, nor did DTT or the general antioxidant N-acetylcysteine alter glycogenolysis during repeated contractions. These findings demonstrate that ONOO- inhibits phosphorylase and glycogenolysis in living muscle under extreme conditions. However, nitration does not play a significant role in control of phosphorylase and glycogenolysis during repeated contractions.
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| 4. |
- Boulet, Nathalie, et al.
(författare)
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Thermogenic recruitment of brown and brite/beige adipose tissues is not obligatorily associated with macrophage accretion or attrition
- 2021
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 320:2, s. E359-E378
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Tidskriftsartikel (refereegranskat)abstract
- Cold- and diet-induced recruitment of brown adipose tissue (BAT) and the browning of white adipose tissue (WAT) are dynamic processes, and the recruited state attained is a state of dynamic equilibrium, demanding continuous stimulation to be maintained. An involvement of macrophages, classical proinflammatory (M1) or alternatively activated anti-inflammatory (M2), is presently discussed as being an integral part of these processes. If these macrophages play a mediatory role in the recruitment process, such an involvement would have to be maintained in the recruited state. We have, therefore, investigated whether the recruited state of these tissues is associated with macrophage accretion or attrition. We found no correlation (positive or negative) between total UCP1 mRNA levels (as a measure of recruitment) and proinflammatory macrophages in any adipose depot. We found that in young chow-fed mice, cold-induced recruitment correlated with accretion of anti-inflammatory macrophages; however, such a correlation was not seen when cold-induced recruitment was studied in diet-induced obese mice. Furthermore, the anti-inflammatory macrophage accretion was mediated via β1/β2-adrenergic receptors; yet, in their absence, and thus in the absence of macrophage accretion, recruitment proceeded normally. We thus conclude that the classical recruited state in BAT and inguinal (brite/beige) WAT is not paralleled by macrophage accretion or attrition. Our results make mediatory roles for macrophages in the recruitment process less likely.NEW & NOTEWORTHY A regulatory or mediatory role—positive or negative—for macrophages in the recruitment of brown adipose tissue is presently discussed. As the recruited state in the tissue is a dynamic process, maintenance of the recruited state would need persistent alterations in macrophage complement. Contrary to this expectation, we demonstrate here an absence of alterations in macrophage complement in thermogenically recruited brown—or brite/beige—adipose tissues. Macrophage regulation of thermogenic capacity is thus less likely.
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| 5. |
- Frøbert, Anne Mette, et al.
(författare)
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Circulating insulin-like growth factor (IGF) system adaptations in hibernating brown bears indicate increased tissue IGF availability
- 2022
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : HighWire Press. - 0193-1849 .- 1522-1555. ; 323:3, s. E307-E318
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Tidskriftsartikel (refereegranskat)abstract
- Brown bears conserve muscle and bone mass during six months of inactive hibernation. The molecular mechanisms underlying hibernation physiology may have translational relevance for human therapeutics. We hypothesize that protective mechanisms involve increased tissue availability of the insulin-like growth factors (IGFs). In subadult Scandinavian Brown Bears, we observed that mean plasma IGF-1 and IGF-2 during hibernation was reduced to 36±10% and 56±15%, respectively, compared to the active state (N=12). Western ligand blotting identified IGFBP-3 as the major IGF binding protein in the active state, while IGFBP-2 was co-dominant during hibernation. Acid labile subunit (ALS) levels in hibernation were 41±16% those of the active state (N=6). Analysis of available grizzly bear RNA sequencing data revealed unaltered liver mRNA IGF-1, IGFBP-2, and IGFBP-3 levels, whereas ALS was significantly reduced during hibernation (N=6). Reduced ALS synthesis and circulating levels during hibernation should prompt a shift from ternary IGF/IGFBP/ALS to smaller binary IGF/IGFBP complexes, thereby increasing IGF tissue availability. Indeed, Size Exclusion Chromatography of bear plasma, demonstrate a shift to lower molecular weight IGF-containing complexes in the hibernating versus the active state. Further, we note that the major IGF-2 mRNA isoform expressed in liver in both Scandinavian brown bears and grizzly bears was an alternative splice variant in which Ser29 was replaced with a tetrapeptide possessing a positively charged Arg residue. Homology modelling of the bear IGF-2/IGFBP-2 complex showed the tetrapeptide in proximity to the heparin binding domain involved in bone-specific targeting of this complex. In conclusion, this study provides data which suggest that increased IGF tissue availability combined with tissue-specific targeting contribute to tissue preservation in hibernating bears.
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| 6. |
- Galvão Valdivia, Luís Felipe, et al.
(författare)
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Cold acclimation and pioglitazone combined increase thermogenic capacity of brown and white adipose tissues but this does not translate into higher energy expenditure in mice
- 2023
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Ingår i: American Journal of Physiology. Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 324:4, s. E358-E373
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Tidskriftsartikel (refereegranskat)abstract
- Cold acclimation and pharmacological peroxisome proliferator-activated receptor γ (PPARγ) activation have each earlier been shown to recruit brown adipose tissue (BAT) and beige adipocytes thermogenic machinery, enhancing uncoupling protein 1 (UCP1)-mediated thermogenic capacity. We here investigated whether cold acclimation and PPARγ agonism combined have additive effects in inducing brown and beige adipocytes UCP1 content and whether this translates into a higher thermogenic capacity and energy expenditure. C57BL/6J mice treated or not with pioglitazone (30 mg/kg/day) were maintained at 21°C or exposed to cold (7°C) for 15 days and evaluated for thermogenic capacity, energy expenditure and interscapular BAT (iBAT) and inguinal white adipose tissue (iWAT) mass, morphology, UCP1 content and gene expression, glucose uptake and oxygen consumption. Cold acclimation and PPARγ agonism combined synergistically increased iBAT and iWAT total UCP1 content and mRNA levels of the thermogenesis-related proteins PGC1a, CIDEA, FABP4, GYK, PPARa, LPL, GLUTs (GLUT1 in iBAT and GLUT4 in iWAT), and ATG when compared to cold and pioglitazone individually. This translated into a stronger increase in body temperature in response to the β3-adrenergic agonist CL316,243 and iBAT and iWAT respiration induced by succinate and pyruvate in comparison to that seen in either cold-acclimated or pioglitazone-treated mice. However, basal energy expenditure, BAT glucose uptake and glucose tolerance were not increased above that seen in cold-acclimated untreated mice. In conclusion, cold acclimation and PPARγ agonism combined induced a robust increase in brown and beige adipocytes UCP1 content and thermogenic capacity, much higher than each treatment individually. However, our findings enforce the concept that increases in total UCP1 do not innately lead to higher energy expenditure.
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| 7. |
- Heikela, H., et al.
(författare)
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Hydroxysteroid (17 beta) dehydrogenase 12 is essential for metabolic homeostasis in adult mice
- 2020
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Ingår i: American Journal of Physiology-Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 319:3
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Tidskriftsartikel (refereegranskat)abstract
- Hydroxysteroid 17 beta dehydrogenase 12 (HSD17B12) is suggested to be involved in the elongation of very long chain fatty acids. Previously. we have shown a pivotal role for the enzyme during mouse development. In the present study we generated a conditional Hsd17b12 knockout (HSD17B12cKO) mouse model by breeding mice homozygous for a floxed Hsd17b12 allele with mice expressing the tamoxifen-inducible Cre recombinase at the ROSA26 locus. Gene inactivation was induced by administering tamoxifen to adult mice. The gene inactivation led to a 20% loss of body weight within 6 days, associated with drastic reduction in both white (83% males, 75% females) and brown (65% males. 60% females) fat, likely due to markedly reduced food and water intake. Furthermore, the knockout mice showed sickness behavior and signs of liver toxicity. specifically microvesicular hepatic steatosis and increased serum alanine aminotransferase (4.6-fold in males, 7.7-fold in females). The hepatic changes were more pronounced in females than males. Proinflammatory cytokines, such as interleukin-6 (IL-6), IL-17, and granulocyte colony-stimulating factor, were increased in the HSD17B12cKO mice indicating an inflammatory response. Serum lipidomics study showed an increase in the amount of dihydroceramides, despite the dramatic overall loss of lipids. In line with the proposed role for HSD17B12 in fatty acid elongation, we observed accumulation of ceramides, dihydroceramides, hexosylceramides, and lactosylceramides with shorter than 18-carbon fatty acid side chains in the serum. The results indicate that HSD17B12 is essential for proper lipid homeostasis and HSD17B12 deficiency rapidly results in fatal systemic inflammation and lipolysis in adult mice.
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| 8. |
- Khilji, M. S., et al.
(författare)
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The inducible β5i proteasome subunit contributes to proinsulin degradation in GRP94-deficient β-cells and is overexpressed in type 2 diabetes pancreatic islets
- 2020
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Ingår i: American Journal of Physiology - Endocrinology and Metabolism. - 0193-1849. ; 318:6
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Tidskriftsartikel (refereegranskat)abstract
- Proinsulin is a misfolding-prone protein, and its efficient breakdown is critical when β-cells are confronted with high-insulin biosynthetic demands, to prevent endoplasmic reticulum stress, a key trigger of secretory dysfunction and, if uncompensated, apoptosis. Proinsulin degradation is thought to be performed by the constitutively expressed standard proteasome, while the roles of other proteasomes are unknown. We recently demonstrated that deficiency of the proinsulin chaperone glucoseregulated protein 94 (GRP94) causes impaired proinsulin handling and defective insulin secretion associated with a compensated endoplasmic reticulum stress response. Taking advantage of this model of restricted folding capacity, we investigated the role of different proteasomes in proinsulin degradation, reasoning that insulin secretory dynamics require an inducible protein degradation system. We show that the expression of only one enzymatically active proteasome subunit, namely, the inducible β5i-subunit, was increased in GRP94 CRISPR/Cas9 knockout (KO) cells. Additionally, the level of β5i-containing intermediate proteasomes was significantly increased in these cells, as was β5i-related chymotrypsin-like activity. Moreover, proinsulin levels were restored in GRP94 KO upon β5i small interfering RNA-mediated knockdown. Finally, the fraction of β-cells expressing the β5i subunit is increased in human islets from type 2 diabetes patients. We conclude that β5i is an inducible proteasome subunit dedicated to the degradation of mishandled proinsulin. Copyright © 2020 the American Physiological Society.
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| 9. |
- Kopietz, Franziska, et al.
(författare)
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Inhibition of AMPK activity in response to insulin in adipocytes : involvement of AMPK pS485, PDEs, and cellular energy levels
- 2020
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Ingår i: American Journal of Physiology - Endocrinology and Metabolism. - : American Physiological Society. - 1522-1555 .- 0193-1849. ; 319:3, s. 459-471
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Tidskriftsartikel (refereegranskat)abstract
- Insulin resistance in obesity and type 2 diabetes has been shown to be associated with decreased de novo fatty acid (FA) synthesis in adipose tissue. It is known that insulin can acutely stimulate FA synthesis in adipocytes; however, the mechanisms underlying this effect are unclear. The rate-limiting step in FA synthesis is catalyzed by acetyl-CoA carboxylase (ACC), known to be regulated through inhibitory phosphorylation at S79 by the AMP-activated protein kinase (AMPK). Previous results from our laboratory showed an inhibition of AMPK activity by insulin, which was accompanied by PKB-dependent phosphorylation of AMPK at S485. However, whether the S485 phosphorylation is required for insulin-induced inhibition of AMPK or other mechanisms underlie the reduced kinase activity is not known. To investigate this, primary rat adipocytes were transduced with a recombinant adenovirus encoding AMPK-WT or a nonphosphorylatable AMPK S485A mutant. AMPK activity measurements by Western blot analysis and in vitro kinase assay revealed that WT and S485A AMPK were inhibited to a similar degree by insulin, indicating that AMPK S485 phosphorylation is not required for insulin-induced AMPK inhibition. Further analysis suggested an involvement of decreased AMP-to-ATP ratios in the insulin-induced inhibition of AMPK activity, whereas a possible contribution of phosphodiesterases was excluded. Furthermore, we show that insulin-induced AMPK S485 phosphorylation also occurs in human adipocytes, suggesting it to be of an importance yet to be revealed. Altogether, this study increases our understanding of how insulin regulates AMPK activity, and with that, FA synthesis, in adipose tissue.
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| 10. |
- Lawenius, Lina, et al.
(författare)
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Development of a synbiotic that protects against ovariectomy-induced trabecular bone loss
- 2022
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Ingår i: American Journal of Physiology-Endocrinology and Metabolism. - : American Physiological Society. - 0193-1849 .- 1522-1555. ; 322:4
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Tidskriftsartikel (refereegranskat)abstract
- The gut microbiome has the capacity to regulate bone mass. The aim of this study was to develop a nutritional synbiotic dietary assemblage at an optimal dose to maintain bone mass in ovariectomized (Ovx) mice. We performed genomic analyses and in vitro experiments in a large collection of bacterial and fungal strains (>4,000) derived from fresh fruit and vegetables to identify candidates with the synergistic capacity to produce bone-protective short-chain fatty acids (SCFA) and vitamin K2. The candidate SBD111-A, composed of Lactiplantibacillus plantarum, Levilactobacillus brevis, Leuconostoc mesenteroides, Pseudomonas fluorescens, and Pichia kudriavzevii together with prebiotic dietary fibers, produced high levels of SCFA in vitro and protected against Ovx-induced trabecular bone loss in a dose-dependent manner in mice. Metagenomic sequencing revealed that SBD111-A changed the taxonomic composition and enriched specific pathways for synthesis of bone-protective SCFA, vitamin K2, and branched-chain amino acids in the gut microbiome. NEW & NOTEWORTHY We performed genomic analyses and in vitro experiments in a collection of bacterial and fungal strains. We identified a combination (SBD111-A) that produced high levels of SCFA in vitro and protected against ovariectomy-induced bone loss in a dose-dependent manner in mice. Metagenomic sequencing revealed that SBD111-A changed the taxonomic composition and function of the gut microbiome and enriched pathways for synthesis of bone-protective SCFA, vitamin K2, and branched-chain amino acids.
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