Publications by authors named "Timothy S McMillen"

19 Publications

  • Page 1 of 1

Increasing fatty acid oxidation elicits a sex-dependent response in failing mouse hearts.

J Mol Cell Cardiol 2021 May 12;158:1-10. Epub 2021 May 12.

Mitochondria and Metabolism Center, Department of Anesthesiology and Pain Medicine, University of Washington, Republican Street 850, 98109 Seattle, WA, USA. Electronic address:

Background: Reduced fatty acid oxidation (FAO) is a hallmark of metabolic remodeling in heart failure. Enhancing mitochondrial long-chain fatty acid uptake by Acetyl-CoA carboxylase 2 (ACC2) deletion increases FAO and prevents cardiac dysfunction during chronic stresses, but therapeutic efficacy of this approach has not been determined.

Methods: Male and female ACC2 f/f-MCM (ACC2KO) and their respective littermate controls were subjected to chronic pressure overload by TAC surgery. Tamoxifen injection 3 weeks after TAC induced ACC2 deletion and increased FAO in ACC2KO mice with pathological hypertrophy.

Results: ACC2 deletion in mice with pre-existing cardiac pathology promoted FAO in female and male hearts, but improved cardiac function only in female mice. In males, pressure overload caused a downregulation in the mitochondrial oxidative function. Stimulating FAO by ACC2 deletion caused unproductive acyl-carnitine accumulation, which failed to improve cardiac energetics. In contrast, mitochondrial oxidative capacity was sustained in female pressure overloaded hearts and ACC2 deletion improved myocardial energetics. Mechanistically, we revealed a sex-dependent regulation of PPARα signaling pathway in heart failure, which accounted for the differential response to ACC2 deletion.

Conclusion: Metabolic remodeling in the failing heart is sex-dependent which could determine the response to metabolic intervention. The findings suggest that both mitochondrial oxidative capacity and substrate preference should be considered for metabolic therapy of heart failure.
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http://dx.doi.org/10.1016/j.yjmcc.2021.05.004DOI Listing
May 2021

Heterogeneous expression of CFTR in insulin-secreting β-cells of the normal human islet.

PLoS One 2020 2;15(12):e0242749. Epub 2020 Dec 2.

Pacific Northwest Research Institute, Seattle, WA, United States of America.

Cystic fibrosis (CF) is due to mutations in the CF-transmembrane conductance regulator (CFTR) and CF-related diabetes (CFRD) is its most common co-morbidity, affecting ~50% of all CF patients, significantly influencing pulmonary function and longevity. Yet, the complex pathogenesis of CFRD remains unclear. Two non-mutually exclusive underlying mechanisms have been proposed in CFRD: i) damage of the endocrine cells secondary to the severe exocrine pancreatic pathology and ii) intrinsic β-cell impairment of the secretory response in combination with other factors. The later has proven difficult to determine due to low expression of CFTR in β-cells, which results in the general perception that this Cl-channel does not participate in the modulation of insulin secretion or the development of CFRD. The objective of the present work is to demonstrate CFTR expression at the molecular and functional levels in insulin-secreting β-cells in normal human islets, where it seems to play a role. Towards this end, we have used immunofluorescence confocal and immunofluorescence microscopy, immunohistochemistry, RT-qPCR, Western blotting, pharmacology, electrophysiology and insulin secretory studies in normal human, rat and mouse islets. Our results demonstrate heterogeneous CFTR expression in human, mouse and rat β-cells and provide evidence that pharmacological inhibition of CFTR influences basal and stimulated insulin secretion in normal mouse islets but not in islets lacking this channel, despite being detected by electrophysiological means in ~30% of β-cells. Therefore, our results demonstrate a potential role for CFTR in the pancreatic β-cell secretory response suggesting that intrinsic β-cell dysfunction may also participate in the pathogenesis of CFRD.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0242749PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7710116PMC
January 2021

Enhancing fatty acid oxidation negatively regulates PPARs signaling in the heart.

J Mol Cell Cardiol 2020 09 24;146:1-11. Epub 2020 Jun 24.

Department of Anesthesiology and Pain Medicine, Mitochondria and Metabolism Center, University of Washington, Seattle, WA 98109, USA. Electronic address:

High fatty acid oxidation (FAO) is associated with lipotoxicity, but whether it causes lipotoxic cardiomyopathy remains controversial. Molecular mechanisms that may be responsible for FAO-induced lipotoxic cardiomyopathy are also elusive. In this study, increasing FAO by genetic deletion of acetyl-CoA carboxylase 2 (ACC2) did not induce cardiac dysfunction after 16 weeks of high fat diet (HFD) feeding. This suggests that increasing FAO, per se, does not cause metabolic cardiomyopathy in obese mice. We compared transcriptomes of control and ACC2 deficient mouse hearts under chow- or HFD-fed conditions. ACC2 deletion had a significant impact on the global transcriptome including downregulation of the peroxisome proliferator-activated receptors (PPARs) signaling and fatty acid degradation pathways. Increasing fatty acids by HFD feeding normalized expression of fatty acid degradation genes in ACC2 deficient mouse hearts to the same level as the control mice. In contrast, cardiac transcriptome analysis of the lipotoxic mouse model (db/db) showed an upregulation of PPARs signaling and fatty acid degradation pathways. Our results suggest that enhancing FAO by genetic deletion of ACC2 negatively regulates PPARs signaling through depleting endogenous PPAR ligands, which can serve as a negative feedback mechanism to prevent excess activation of PPAR signaling under non-obese condition. In obesity, excessive lipid availability negates the feedback mechanism resulting in over activation of PPAR cascade, thus contributes to the development of cardiac lipotoxicity.
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http://dx.doi.org/10.1016/j.yjmcc.2020.06.008DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7494556PMC
September 2020

ATP binding without hydrolysis switches sulfonylurea receptor 1 (SUR1) to outward-facing conformations that activate K channels.

J Biol Chem 2019 03 26;294(10):3707-3719. Epub 2018 Dec 26.

Pacific Northwest Diabetes Research Institute, Seattle, Washington 98122, and

Neuroendocrine-type ATP-sensitive K (K) channels are metabolite sensors coupling membrane potential with metabolism, thereby linking insulin secretion to plasma glucose levels. They are octameric complexes, (SUR1/Kir6.2), comprising sulfonylurea receptor 1 (SUR1 or ABCC8) and a K-selective inward rectifier (Kir6.2 or KCNJ11). Interactions between nucleotide-, agonist-, and antagonist-binding sites affect channel activity allosterically. Although it is hypothesized that opening these channels requires SUR1-mediated MgATP hydrolysis, we show here that ATP binding to SUR1, without hydrolysis, opens channels when nucleotide antagonism on Kir6.2 is minimized and SUR1 mutants with increased ATP affinities are used. We found that ATP binding is sufficient to switch SUR1 alone between inward- or outward-facing conformations with low or high dissociation constant, , values for the conformation-sensitive channel antagonist [H]glibenclamide ([H]GBM), indicating that ATP can act as a pure agonist. Assembly with Kir6.2 reduced SUR1's for [H]GBM. This reduction required the Kir N terminus (KNtp), consistent with KNtp occupying a "transport cavity," thus positioning it to link ATP-induced SUR1 conformational changes to channel gating. Moreover, ATP/GBM site coupling was constrained in WT SUR1/WT Kir6.2 channels; ATP-bound channels had a lower for [H]GBM than ATP-bound SUR1. This constraint was largely eliminated by the Q1179R neonatal diabetes-associated mutation in helix 15, suggesting that a "swapped" helix pair, 15 and 16, is part of a structural pathway connecting the ATP/GBM sites. Our results suggest that ATP binding to SUR1 biases K channels toward open states, consistent with SUR1 variants with lower values causing neonatal diabetes, whereas increased values cause congenital hyperinsulinism.
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http://dx.doi.org/10.1074/jbc.RA118.005236DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6416425PMC
March 2019

The neuronal KCl co-transporter 2 (Slc12a5) modulates insulin secretion.

Sci Rep 2017 05 11;7(1):1732. Epub 2017 May 11.

Department of Pharmacology and Toxicology, Wright State University, School of Medicine, Dayton, OH, 45435, USA.

Intracellular chloride concentration ([Cl]) in pancreatic β-cells is kept above electrochemical equilibrium due to the predominant functional presence of Cl loaders such as the NaK2Cl co-transporter 1 (Slc12a2) over Clextruders of unidentified nature. Using molecular cloning, RT-PCR, Western blotting, immunolocalization and in vitro functional assays, we establish that the "neuron-specific" KCl co-transporter 2 (KCC2, Slc12a5) is expressed in several endocrine cells of the pancreatic islet, including glucagon secreting α-cells, but particularly in insulin-secreting β-cells, where we provide evidence for its role in the insulin secretory response. Three KCC2 splice variants were identified: the formerly described KCC2a and KCC2b along with a novel one lacking exon 25 (KCC2a-S25). This new variant is undetectable in brain or spinal cord, the only and most abundant known sources of KCC2. Inhibition of KCC2 activity in clonal MIN6 β-cells increases basal and glucose-stimulated insulin secretion and Ca uptake in the presence of glibenclamide, an inhibitor of the ATP-dependent potassium (K)-channels, thus suggesting a possible mechanism underlying KCC2-dependent insulin release. We propose that the long-time considered "neuron-specific" KCC2 co-transporter is expressed in pancreatic islet β-cells where it modulates Ca-dependent insulin secretion.
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http://dx.doi.org/10.1038/s41598-017-01814-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5431760PMC
May 2017

ABCG1 regulates mouse adipose tissue macrophage cholesterol levels and ratio of M1 to M2 cells in obesity and caloric restriction.

J Lipid Res 2015 Dec 21;56(12):2337-47. Epub 2015 Oct 21.

Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington, Seattle, WA 98109-8050 Diabetes and Obesity Center of Excellence, University of Washington, Seattle, WA 98109-8050

In addition to triacylglycerols, adipocytes contain a large reserve of unesterified cholesterol. During adipocyte lipolysis and cell death seen during severe obesity and weight loss, free fatty acids and cholesterol become available for uptake and processing by adipose tissue macrophages (ATMs). We hypothesize that ATMs become cholesterol enriched and participate in cholesterol clearance from adipose tissue. We previously showed that ABCG1 is robustly upregulated in ATMs taken from obese mice and further enhanced by caloric restriction. Here, we found that ATMs taken from obese and calorie-restricted mice derived from transplantation of WT or Abcg1-deficient bone marrow are cholesterol enriched. ABCG1 levels regulate the ratio of classically activated (M1) to alternatively activated (M2) ATMs and their cellular cholesterol content. Using WT and Abcg1(-/-) cultured macrophages, we found that Abcg1 is most highly expressed by M2 macrophages and that ABCG1 deficiency is sufficient to retard macrophage chemotaxis. However, changes in myeloid expression of Abcg1 did not protect mice from obesity or impaired glucose homeostasis. Overall, ABCG1 modulates ATM cholesterol content in obesity and weight loss regimes leading to an alteration in M1 to M2 ratio that we suggest is due to the extent of macrophage egress from adipose tissue.
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http://dx.doi.org/10.1194/jlr.M063354DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4655989PMC
December 2015

Genetic modulation of diabetic nephropathy among mouse strains with Ins2 Akita mutation.

Physiol Rep 2014 Nov 26;2(11). Epub 2014 Nov 26.

Division of Metabolism, Endocrinology and Nutrition, Department of Medicine, University of Washington, Seattle, Washington, USA.

Diabetic nephropathy (DN) is a major complication of diabetes and the leading cause of end-stage renal disease. DN is characterized by changes in kidney structure and function but the underlying genetic and molecular factors are poorly understood. We used a mouse diversity panel to explore the genetic basis of DN traits in mice carrying the Ins2 Akita mutation. Twenty-eight Akita strains were generated by breeding this panel to DBA/2.Akita mice. Male F1 diabetic and nondiabetic littermates were evaluated for DN-related traits. Urine albumin-to-creatinine ratios (ACRs), volume and cystatin C as well as blood urea nitrogen and lipoprotein levels varied significantly among the diabetic strains. For most Akita strains, ACR values increased 2- to 6-fold over euglycemic control values. However, six strains exhibited changes in ACR exceeding 10-fold with two strains (NOD/ShiLt and CBA) showing 50- to 83- fold increases. These increases are larger than previously reported among available DN mouse models establishing these strains as useful for additional studies of renal function. ACRs correlated with cystatin C (P = 0.0286), a measure of hyperfiltration and an interstitial tubular marker associated with DN onset in humans suggesting that tubule damage as well as podocyte-stress contributed to reduced kidney function assessed by ACR. Although large changes were seen for ACRs, severe nephropathology was absent. However, glomerular hypertrophy and collagen IV content were found to vary significantly among strains suggesting a genetic basis for early onset features of DN. Our results define the range of DN phenotypes that occur among common inbred strains of mice.
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http://dx.doi.org/10.14814/phy2.12208DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4255814PMC
November 2014

Genetic determinants of atherosclerosis, obesity, and energy balance in consomic mice.

Mamm Genome 2014 Dec 8;25(11-12):549-63. Epub 2014 Jul 8.

Institute for Systems Biology, 401 North Terry Ave, Seattle, WA, 98109, USA.

Metabolic diseases such as obesity and atherosclerosis result from complex interactions between environmental factors and genetic variants. A panel of chromosome substitution strains (CSSs) was developed to characterize genetic and dietary factors contributing to metabolic diseases and other biological traits and biomedical conditions. Our goal here was to identify quantitative trait loci (QTLs) contributing to obesity, energy expenditure, and atherosclerosis. Parental strains C57BL/6 and A/J together with a panel of 21 CSSs derived from these progenitors were subjected to chronic feeding of rodent chow and atherosclerotic (females) or diabetogenic (males) test diets, and evaluated for a variety of metabolic phenotypes including several traits unique to this report, namely fat pad weights, energy balance, and atherosclerosis. A total of 297 QTLs across 35 traits were discovered, two of which provided significant protection from atherosclerosis, and several dozen QTLs modulated body weight, body composition, and circulating lipid levels in females and males. While several QTLs confirmed previous reports, most QTLs were novel. Finally, we applied the CSS quantitative genetic approach to energy balance, and identified three novel QTLs controlling energy expenditure and one QTL modulating food intake. Overall, we identified many new QTLs and phenotyped several novel traits in this mouse model of diet-induced metabolic diseases.
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http://dx.doi.org/10.1007/s00335-014-9530-2DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4241139PMC
December 2014

Copper chelation by tetrathiomolybdate inhibits vascular inflammation and atherosclerotic lesion development in apolipoprotein E-deficient mice.

Atherosclerosis 2012 Aug 16;223(2):306-13. Epub 2012 Jun 16.

Linus Pauling Institute and Department of Biochemistry & Biophysics, Oregon State University, Corvallis, OR 97331, USA.

Endothelial activation, which is characterized by upregulation of cellular adhesion molecules and pro-inflammatory chemokines and cytokines, and consequent monocyte recruitment to the arterial intima are etiologic factors in atherosclerosis. Redox-active transition metal ions, such as copper and iron, may play an important role in endothelial activation by stimulating redox-sensitive cell signaling pathways. We have shown previously that copper chelation by tetrathiomolybdate (TTM) inhibits LPS-induced acute inflammatory responses in vivo. Here, we investigated whether TTM can inhibit atherosclerotic lesion development in apolipoprotein E-deficient (apoE-/-) mice. We found that 10-week treatment of apoE-/- mice with TTM (33-66 ppm in the diet) reduced serum levels of the copper-containing protein, ceruloplasmin, by 47%, and serum iron by 26%. Tissue levels of "bioavailable" copper, assessed by the copper-to-molybdenum ratio, decreased by 80% in aorta and heart, whereas iron levels of these tissues were not affected by TTM treatment. Furthermore, TTM significantly attenuated atherosclerotic lesion development in whole aorta by 25% and descending aorta by 45% compared to non-TTM treated apoE-/- mice. This anti-atherogenic effect of TTM was accompanied by several anti-inflammatory effects, i.e., significantly decreased serum levels of soluble vascular cell and intercellular adhesion molecules (VCAM-1 and ICAM-1); reduced aortic gene expression of VCAM-1, ICAM-1, monocyte chemotactic protein-1, and pro-inflammatory cytokines; and significantly less aortic accumulation of M1 type macrophages. In contrast, serum levels of oxidized LDL were not reduced by TTM. These data indicate that TTM inhibits atherosclerosis in apoE-/- mice by reducing bioavailable copper and vascular inflammation, not by altering iron homeostasis or reducing oxidative stress.
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http://dx.doi.org/10.1016/j.atherosclerosis.2012.06.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3417757PMC
August 2012

Deficiency of lymphotoxin-α does not exacerbate high-fat diet-induced obesity but does enhance inflammation in mice.

Am J Physiol Endocrinol Metab 2012 Apr 7;302(8):E961-71. Epub 2012 Feb 7.

Department of Medicine, Div. of Metabolism, Endocrinology, and Nutrition, Univ. of Washington, Seattle, WA 98109-8050, USA.

Lymphotoxin-α (LTα) is secreted by lymphocytes and acts through tumor necrosis factor-α receptors and the LTβ receptor. Our goals were to determine whether LT has a role in obesity and investigate whether LT contributes to the link between obesity and adipose tissue lymphocyte accumulation. LT deficient (LT(-/-)) and wild-type (WT) mice were fed standard pelleted rodent chow or a high-fat/high-sucrose diet (HFHS) for 13 wk. Body weight, body composition, and food intake were measured. Glucose tolerance was assessed. Systemic and adipose tissue inflammatory statuses were evaluated by quantifying plasma adipokine levels and tissue macrophage and T cell-specific gene expression in abdominal fat. LT(-/-) mice were smaller (20%) and leaner (25%) than WT controls after 13 wk of HFHS diet feeding. LT(-/-) mice showed improved glucose tolerance, suggesting that, in WT mice, LT may impair glucose metabolism. Surprisingly, adipose tissue from rodent chow- and HFHS-fed LT(-/-) mice exhibited increased T lymphocyte and macrophage infiltration compared with WT mice. Despite the fact that LT(-/-) mice exhibited an enhanced inflammatory status at the systemic and tissue level even when fed rodent chow, they were protected from enhanced diet-induced obesity and insulin resistance. Thus, LT contributes to body weight and adiposity and is required to modulate the accumulation of immune cells in adipose tissue.
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http://dx.doi.org/10.1152/ajpendo.00447.2011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3330720PMC
April 2012

Obesity and weight loss result in increased adipose tissue ABCG1 expression in db/db mice.

Biochim Biophys Acta 2012 Mar 10;1821(3):425-34. Epub 2011 Dec 10.

Department of Medicine, Division of Metabolism, Endocrinology and Nutrition, and the Diabetes and Obesity Center of Excellence, University of Washington, Seattle, WA 98109, USA.

The prevalence of obesity has reached epidemic proportions and is associated with several co-morbid conditions including diabetes, dyslipidemia, cancer, atherosclerosis and gallstones. Obesity is associated with low systemic inflammation and an accumulation of adipose tissue macrophages (ATMs) that are thought to modulate insulin resistance. ATMs may also modulate adipocyte metabolism and take up lipids released during adipocyte lipolysis and cell death. We suggest that high levels of free cholesterol residing in adipocytes are released during these processes and contribute to ATM activation and accumulation during obesity and caloric restriction. Db/db mice were studied for extent of adipose tissue inflammation under feeding conditions of ad libitum (AL) and caloric restriction (CR). The major finding was a marked elevation in epididymal adipose ABCG1 mRNA levels with obesity and CR (6-fold and 16-fold, respectively) over that seen for lean wild-type mice. ABCG1 protein was also elevated for CR as compared to AL adipose tissue. ABCG1 is likely produced by cholesterol loaded ATMs since this gene is not highly expressed in adipocytes and ABCG1 expression is sterol mediated. Our data supports the concept that metabolic changes in adipocytes due to demand lipolysis and cell death lead to cholesterol loading of ATMs. Based on finding cholesterol-loaded peritoneal leukocytes with elevated levels of ABCG1 in CR as compared to AL mice, we suggest that pathways for cholesterol trafficking out of adipose tissue involve ATM egress as well as ABCG1 mediated cholesterol efflux. This article is part of a Special Issue entitled Advances in High Density Lipoprotein Formation and Metabolism: A Tribute to John F. Oram (1945-2010).
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http://dx.doi.org/10.1016/j.bbalip.2011.11.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3293702PMC
March 2012

Serum amyloid A facilitates the binding of high-density lipoprotein from mice injected with lipopolysaccharide to vascular proteoglycans.

Arterioscler Thromb Vasc Biol 2011 Jun 7;31(6):1326-32. Epub 2011 Apr 7.

Department of Medicine, University of Washington, Seattle, WA 98109, USA.

Objective: Levels of serum amyloid A (SAA), an acute-phase protein carried on high-density lipoprotein (HDL), increase in inflammatory states and are associated with increased risk of cardiovascular disease. HDL colocalizes with vascular proteoglycans in atherosclerotic lesions. However, its major apolipoprotein, apolipoprotein A-I, has no proteoglycan-binding domains. Therefore, we investigated whether SAA, which has proteoglycan-binding domains, plays a role in HDL retention by proteoglycans.

Methods And Results: HDL from control mice and mice deficient in both SAA1.1 and SAA2.1 (SAA knockout mice) injected with bacterial lipopolysaccharide (LPS) was studied. SAA mRNA expression in the liver and plasma levels of SAA increased dramatically in C57BL/6 mice after LPS administration, although HDL cholesterol did not change. Fast protein liquid chromatography analysis showed most of the SAA to be in HDL. Mass spectrometric analysis indicated that HDL from LPS-injected control mice had high levels of SAA1.1/2.1 and reduced levels of apolipoprotein A-I. HDL from LPS-injected control mice demonstrated high-affinity binding to biglycan relative to normal mouse HDL. In contrast, HDL from LPS-injected SAA knockout mice showed very little binding to biglycan, consistent with SAA facilitating the binding of HDL to vascular proteoglycans.

Conclusion: SAA enrichment of HDL under inflammatory conditions plays an important role in the binding of HDL to vascular proteoglycans.
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http://dx.doi.org/10.1161/ATVBAHA.111.226159DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3129975PMC
June 2011

Roles for cathepsins S, L, and B in insulitis and diabetes in the NOD mouse.

J Autoimmun 2010 Mar 6;34(2):96-104. Epub 2009 Aug 6.

Department of Immunology and Howard Hughes Medical Institute, University of Washington, Seattle, WA 98109-8050, USA.

We developed a panel of non-obese diabetic (NOD) mice deficient in major lysosomal cysteine proteases (cathepsins S, L and B) to identify protease enzymes essential for autoimmune diabetes. Null alleles for cathepsins (Cts) S, L or B were introgressed onto the NOD genetic background with 19 Idd markers at homozygosity. Diabetes onset was determined among females aged up to 6 months. We evaluated insulitis and sialadenitis in tissues using histology and computer assisted morphology. NOD mice deficient in Ctss or Ctsb were partially protected from diabetes with incidence at 33% and 28%, respectively, versus wild-type NOD (69%; p < 0.00001). NODs lacking cathepsin L (Ctsl-/-) are completely protected from IDDM, as originally shown by others. Ctsl, Ctss, or Ctsb heterozygous mice were able to develop IDDM, although incidence levels were significantly lower for Ctsb+/- (50%) and Ctsl+/- (55%) as compared to NODs (69%; p < 0.03). Ctsl-/- mice contain functional, diabetogenic T cells and an enriched Foxp3+ regulatory T cell population, and diabetes resistance was due to the presence of an expanded population of regulatory T cells. These data provide additional information about the potency of the diabetogenic T cell population in Ctsl-/- mice which were comparable in potency to wild-type NOD mice. These data illustrate the critical contribution of each of these proteases in determining IDDM in the NOD mouse and provide a useful set of models for further studies.
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http://dx.doi.org/10.1016/j.jaut.2009.07.003DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2822044PMC
March 2010

Receptors for tumor necrosis factor-alpha play a protective role against obesity and alter adipose tissue macrophage status.

Endocrinology 2009 Sep 28;150(9):4124-34. Epub 2009 May 28.

Department of Medicine, Division of Metabolism, Endocrinology, andNutrition and the Diabetes and Obesity Center of Excellence, School of Public Health and Community Medicine, University of Washington, Seattle,Washington 98109-8050, USA

TNF-alpha signals through two receptors, TNFR1 and TNFR2. Our goals were: 1) determine the role of TNFRs in obesity and metabolic disease and 2) investigate whether TNFRs contribute to the link between obesity and adipose tissue macrophage infiltration and polarization. R1(-/-)R2(-/-) (RKO) and wild-type (WT) mice were fed standard chow or a high-fat/high-sucrose diet (HFHS) over 14 wk. Body composition, food intake, and energy expenditure were measured. Oral glucose tolerance and insulin sensitivity tests assessed glucose homeostasis. Adipose tissue and systemic inflammatory status were evaluated by quantifying plasma adipokine levels and macrophage-specific gene expression in fat. RKO mice were heavier (10%) and fatter (18%) than WT controls at 4 wk of age and were 26% heavier and 50% fatter than WT after 14 wk of HFHS diet feeding. Age- and diet-adjusted 24-h oxygen consumption, activity, and respiratory exchange ratio were significantly reduced in RKO mice. Obese RKO mice were markedly insulin resistant, suggesting that intact TNFR signaling is not required for the effect of obesity to impair glucose metabolism. Adipose tissue from HFHS-fed RKO mice exhibited increased macrophage infiltration, but compared with WT mice, macrophage phenotypic markers featured a predominance of antiinflammatory M2 over proinflammatory M1 cells. TNFRs play a physiological role to limit body weight and adiposity by modestly increasing metabolic rate and fatty acid oxidation, and they are required for obesity-induced activation of adipose tissue macrophages. Despite these effects, TNFRs are not required for obesity-induced insulin resistance.
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http://dx.doi.org/10.1210/en.2009-0137DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2736076PMC
September 2009

Overexpression of apolipoprotein A5 in mice is not protective against body weight gain and aberrant glucose homeostasis.

Metabolism 2009 Apr;58(4):560-7

Department of Medicine, Division of Metabolism, Endocrinology and Nutrition, University of Washington, Seattle, WA, USA.

Apolipoprotein A5 (APOA5) is expressed primarily in the liver and modulates plasma triglyceride levels in mice and humans. Mice overexpressing APOA5 exhibit reduced plasma triglyceride levels. Because there is a tight association between plasma triglyceride concentration and traits of the metabolic syndrome, we used transgenic mice overexpressing human APOA5 to test the concept that these mice would be protected from diet-induced obesity and insulin resistance. Male and female transgenic and wild-type mice on the FVB/N genetic background were fed standard rodent chow or a diet rich in fat and sucrose for 18 weeks, during which time clinical phenotypes associated with obesity and glucose homeostasis were measured. We found that APOA5 transgenic (A5tg) mice were resistant to diet-induced changes in plasma triglyceride but not total cholesterol levels. Body weights were similar between the genotypes for females and males, although male A5tg mice showed a modest but significant increase in the relative size of inguinal fat pads. Although male A5tg mice showed a significantly increased ratio of plasma glucose to insulin, profiles of glucose clearance as evaluated after injections of glucose or insulin failed to reveal any differences between genotypes. Overall, our data showed that there was no advantage to responses to diet-induced obesity with chronic reduction of plasma triglyceride levels as mediated by overexpression of APOA5.
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http://dx.doi.org/10.1016/j.metabol.2008.11.018DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2689095PMC
April 2009

Dietary cholesterol worsens adipose tissue macrophage accumulation and atherosclerosis in obese LDL receptor-deficient mice.

Arterioscler Thromb Vasc Biol 2008 Apr 31;28(4):685-91. Epub 2008 Jan 31.

Department of Medicine, University of Washington, 1959 NE Pacific Street, Seattle, WA 98195-6426, USA.

Objective: Chronic systemic inflammation accompanies obesity and predicts development of cardiovascular disease. Dietary cholesterol has been shown to increase inflammation and atherosclerosis in LDL receptor-deficient (LDLR(-/-)) mice. This study was undertaken to determine whether dietary cholesterol and obesity have additive effects on inflammation and atherosclerosis.

Methods And Results: LDLR(-/-) mice were fed chow, high-fat, high-carbohydrate (diabetogenic) diets without (DD) or with added cholesterol (DDC) for 24 weeks. Effects on adipose tissue, inflammatory markers, and atherosclerosis were studied. Despite similar weight gain between DD and DDC groups, addition of dietary cholesterol increased insulin resistance relative to DD. Adipocyte hypertrophy, macrophage accumulation, and local inflammation were observed in intraabdominal adipose tissue in DD and DDC, but were significantly higher in the DDC group. Circulating levels of the inflammatory protein serum amyloid A (SAA) were 4.4-fold higher in DD animals and 15-fold higher in DDC animals than controls, suggesting chronic systemic inflammation. Hepatic SAA mRNA levels were similarly elevated. Atherosclerosis was increased in the DD-fed animals and further increased in the DDC group.

Conclusions: Obesity-induced macrophage accumulation in adipose tissue is exacerbated by dietary cholesterol. These local inflammatory changes in adipose tissue are associated with insulin resistance, systemic inflammation, and increased atherosclerosis in this mouse model.
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http://dx.doi.org/10.1161/ATVBAHA.107.157685DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2767166PMC
April 2008

Dietary alpha-lipoic acid supplementation inhibits atherosclerotic lesion development in apolipoprotein E-deficient and apolipoprotein E/low-density lipoprotein receptor-deficient mice.

Circulation 2008 Jan 24;117(3):421-8. Epub 2007 Dec 24.

Linus Pauling Institute, Oregon State University, 571 Weniger Hall, Corvallis, OR 97331, USA.

Background: Vascular inflammation and lipid deposition are prominent features of atherosclerotic lesion formation. We have shown previously that the dithiol compound alpha-lipoic acid (LA) exerts antiinflammatory effects by inhibiting tumor necrosis factor-alpha- and lipopolysaccharide-induced endothelial and monocyte activation in vitro and lipopolysaccharide-induced acute inflammatory responses in vivo. Here, we investigated whether LA inhibits atherosclerosis in apolipoprotein E-deficient (apoE-/-) and apoE/low-density lipoprotein receptor-deficient mice, 2 well-established animal models of human atherosclerosis.

Methods And Results: Four-week-old female apoE-/- mice (n=20 per group) or apoE/low-density lipoprotein receptor-deficient mice (n=21 per group) were fed for 10 weeks a Western-type chow diet containing 15% fat and 0.125% cholesterol without or with 0.2% (wt/wt) R,S-LA or a normal chow diet containing 4% fat without or with 0.2% (wt/wt) R-LA, respectively. Supplementation with LA significantly reduced atherosclerotic lesion formation in the aortic sinus of both mouse models by approximately 20% and in the aortic arch and thoracic aorta of apoE-/- and apoE/low-density lipoprotein receptor-deficient mice by approximately 55% and 40%, respectively. This strong antiatherogenic effect of LA was associated with almost 40% less body weight gain and lower serum and very low-density lipoprotein levels of triglycerides but not cholesterol. In addition, LA supplementation reduced aortic expression of adhesion molecules and proinflammatory cytokines and aortic macrophage accumulation. These antiinflammatory effects of LA were more pronounced in the aortic arch and the thoracic aorta than in the aortic sinus, reflecting the corresponding reductions in atherosclerosis.

Conclusions: Our study shows that dietary LA supplementation inhibits atherosclerotic lesion formation in 2 mouse models of human atherosclerosis, an inhibition that appears to be due to the "antiobesity," antihypertriglyceridemic, and antiinflammatory effects of LA. LA may be a useful adjunct in the prevention and treatment of atherosclerotic vascular diseases.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.107.725275DOI Listing
January 2008

Tesaglitazar, a dual peroxisome proliferator-activated receptor alpha/gamma agonist, reduces atherosclerosis in female low density lipoprotein receptor deficient mice.

Atherosclerosis 2007 Nov 9;195(1):100-9. Epub 2007 Jan 9.

Department of Medicine, University of Washington, Seattle, WA, USA.

Objective: The transcription factors, peroxisome proliferator-activated receptors (PPAR) alpha (alpha) and gamma (gamma), which are involved in lipid and glucose homeostasis, also exert modulatory actions on vascular cells where they exhibit anti-inflammatory and anti-proliferative properties. Hence, PPAR agonists potentially can affect atherogenesis both via metabolic effects and direct effects on the vessel wall. We tested whether the dual PPAR-alpha/gamma agonist, tesaglitazar (TZ), would reduce atherosclerosis in a non-diabetic, atherosclerosis-prone mouse model, independent of effects on plasma lipids.

Methods And Results: Low-density lipoprotein receptor deficient (LDLr-/-) mice were fed a Western type diet consisting of 21% butterfat and 0.15% cholesterol, with or without TZ 0.5 micromol/kg of diet, for 12 weeks. TZ reduced atherosclerosis in the female, but not male, LDLr-/- mice without affecting cholesterol and triglyceride levels, HDL binding to biglycan, or the inflammatory markers serum amyloid A (SAA) and serum amyloid P (SAP). TZ also decreased adiposity in both genders.

Conclusions: TZ reduced atherosclerosis in the female LDLr-/- mice via lipid-independent mechanisms, probably at least in part by direct actions on the vessels. The body weight changes in these mice are different from the effects of dual PPAR agonists seen in humans.
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http://dx.doi.org/10.1016/j.atherosclerosis.2006.12.012DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2702263PMC
November 2007

Expression of human myeloperoxidase by macrophages promotes atherosclerosis in mice.

Circulation 2005 May 23;111(21):2798-804. Epub 2005 May 23.

Department of Medicine, University of Washington, Seattle, WA 98109-8050, USA.

Background: Myeloperoxidase (MPO) colocalizes with macrophages in the human artery wall, and its characteristic oxidation products have been detected in atherosclerotic lesions. Thus, oxidants produced by the enzyme might promote atherosclerosis. However, macrophages in mouse atherosclerotic tissue do not express MPO. Therefore, mice are an inappropriate model for testing the role of MPO in vascular disease. To overcome this problem, we generated and studied transgenic (Tg) mice that contained the human MPO gene.

Methods And Results: We produced human MPO-Tg mice with use of a Visna virus promoter. To confine MPO expression to macrophages, we lethally irradiated LDL receptor-deficient mice and repopulated their bone marrow with cells from wild-type mice or MPO-Tg mice. Despite having similarly high levels of cholesterol after maintenance on a high-fat, high-cholesterol diet, the MPO-Tg animals developed a 2-fold greater atherosclerotic area in the aorta than did mice transplanted with wild-type bone marrow (P=0.00003).

Conclusions: Our observations indicate that expression of human MPO in macrophages promotes atherosclerosis in hypercholesterolemic mice, raising the possibility that the enzyme might be a potential therapeutic target for preventing cardiovascular disease in humans.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.104.516278DOI Listing
May 2005