Faculty Bibliography

The pharmacological effects of type 2 diabetes (T2DM) medications on lipoprotein metabolism are difficult to assess in preclinical models because those created failure to replicate the human condition in which insulin deficiency is superimposed on obesity-related insulin resistance. To create a better model, we fed mice with high fat (HF) diet and treated the animals with low dose streptozotocin (STZ) to mimic T2DM. We used this model to evaluate the effects of canagliflozin (CANA), a drug that reduces plasma glucose by inhibiting the sodium-glucose transporter 2 (SGLT2), which mediates ~90% of renal glucose reabsorption] on lipid and lipoprotein metabolism. After 6 weeks of CANA (30 mg/kg/day) treatment, the increase in total plasma cholesterol in HF-STZ diabetic mice was reversed, but plasma triglycerides were not affected. Lipoprotein fractionation and cholesterol distribution analysis showed that CANA kept HDL-Cholesterol, LDL-Cholesterol, and IDL-Cholesterol levels steady while these lipoprotein species were increased in placebo- and insulin-treated control groups. CANA treatment of HF-STZ mice reduced post-heparin plasma lipoprotein lipase (LPL) activity at 2 (-40%) and 5 (-30%) weeks compared to placebo. Tissue-specific LPL activity following CANA treatment showed similar reduction. In summary, CANA prevented the total cholesterol increase in HF-STZ mice without effects on plasma lipids or lipoproteins, but did decrease LPL, implying a potential role of LPL-dependent lipoprotein metabolism in CANA action. These effects did not recapitulate the effect of SGLT2 inhibitors on lipids and lipoproteins in human, suggesting that a better murine T2DM model (such as the ApoB100 humanized CETP-overexpressing mouse) is needed next.

Lipid accumulation is a pathological feature of every type of kidney injury. Despite this striking histological feature, physiological accumulation of lipids in the kidney is poorly understood. We studied whether the accumulation of lipids in the fasted kidney are derived from lipoproteins or non-esterified fatty acids (NEFAs). With overnight fasting, kidneys accumulated triglyceride but had reduced levels of ceramide and glycosphingolipid species. Fasting led to a nearly 5-fold increase in kidney uptake of plasma [14C]oleic acid. Increasing circulating NEFAs using a beta adrenergic receptor agonist caused a 15-fold greater accumulation of lipid in the kidney, while mice with reduced NEFAs due to adipose tissue deficiency of adipose triglyceride lipase had reduced triglycerides. Cd36 mRNA increased 2-fold, and Angptl4, an LpL inhibitor, increased 10-fold. Fasting-induced kidney lipid accumulation was not affected by inhibition of LpL with poloxamer 407 or by use of mice with induced genetic LpL deletion. Despite the increase in CD36 expression with fasting, genetic loss of CD36 did not alter fatty acid uptake or triglyceride accumulation. Our data demonstrate that fasting-induced triglyceride accumulation in the kidney correlates with the plasma concentrations of NEFAs, but is not due to uptake of lipoprotein lipids and does not involve the fatty acid transporter CD36.

BACKGROUND & AIMS: CD36 has immuno-metabolic actions and is abundant in the small intestine on epithelial, endothelial and immune cells. We examined the role of CD36 in gut homeostasis using mice null for CD36 (CD36KO) and with CD36 deletion specific to enterocytes (Ent-CD36KO) or endothelial cells (EC-CD36KO). METHODS: Intestinal morphology was evaluated using immunohistochemistry and electron microscopy (EM). Intestinal inflammation was determined from neutrophil infiltration and expression of cytokines, toll-like receptors and COX-2. Barrier integrity was assessed from circulating lipopolysaccharide (LPS) and dextran administered intragastrically. Epithelial permeability to luminal dextran was visualized using two photon microscopy. RESULTS: The small intestines of CD36KO mice fed a chow diet showed several abnormalities including extracellular matrix (ECM) accumulation with increased expression of ECM proteins, evidence of neutrophil infiltration, inflammation and compromised barrier function. EM showed shortened desmosomes with decreased desmocollin 2 expression. Systemically, leukocytosis and neutrophilia were present together with 80% reduction of anti-inflammatory Ly6Clow monocytes. Bone marrow transplants supported the primary contribution of non-hematopoietic cells to the inflammatory phenotype. Specific deletion of endothelial but not of enterocyte CD36 reproduced many of the gut phenotypes of germline CD36KO mice including fibronectin deposition, increased interleukin 6, neutrophil infiltration, desmosome shortening and impaired epithelial barrier function. CONCLUSIONS: CD36 loss results in chronic neutrophil infiltration of the gut, impairs barrier integrity and systemically causes subclinical inflammation. Endothelial cell CD36 deletion reproduces the major intestinal phenotypes. The findings suggest an important role of the endothelium in etiology of gut inflammation and loss of epithelial barrier integrity.

Kruppel-like factors (KLF) have important roles in metabolism. We previously found that KLF5 is a positive transcriptional regulator of peroxisome proliferator-activated receptor alpha (Ppara), a central regulator of cardiac fatty acid oxidation (FAO). Mice with cardiomyocyte-specific Klf5 ablation (alphaMHCKlf5 ) had reduced cardiac Ppara expression and FAO. At age 6-12 months these mice develop distinct cardiac dysfunction. The role of PPARalpha activation in I/R injury is unclear as both beneficial and detrimental effects have been reported. We aimed to study if Ppara expression changes during I/R are driven by KLF5 and explore its protective or detrimental role. Wild type mice were subjected to in vivo I/R or sham surgery. I/R resulted in an initial increase in Ppara, and its target gene pyruvate dehydrogenase kinase 4 (Pdk4) mRNA after 2h reperfusion, followed by decreased expression after 24h reperfusion. The Ppara expression is associated with parallel changes in cardiac Klf5 mRNA expression. Concurrent, there was a decrease of cardiac FAO-related genes carnitine palmitoyl-transferase 1beta (Cpt1b), very long chain acyl-CoA dehydrogenase (Vlcad), and acyl-CoA oxidase (Aox) in mice with I/R. To define the cell type causing the temporal changes in Klf5 and Ppara after I/R we isolated primary cardiomyocytes and fibroblasts. Our data suggest a similar effect in primary isolated cardiomyocytes only. Klf5 mRNA expression is increased after 2 hour hypoxia and normalized after 4 hour re-oxygenation in cardiomyocytes, whereas there are no changes after hypoxia/normoxia in fibroblasts. To assess the importance of cardiomyocyte KLF5 in I/R we used alphaMHC-Klf5 mice. Interestingly, despite reduced FAO, 7 month old alphaMHC-Klf5 mice subjected to I/R had a marked increase in mortality; 4 of 7 alphaMHCKlf5 mice died within the first 24h of reperfusion while no mortality was observed in age-matched wild type mice that underwent I/R. In conclusion, I/R is associated with an increase in Klf5 and Ppara in the first hours of reperfusion followed by a decrease in Klf5 and Ppara, likely accounted for by cardiomyocytes. Increased mortality for alphaMHC-Klf5 mice with I/R injury suggests that the initial increase may be an adaptive response that is critical for survival

3,5,3'-triiodo-L-thyronine (T3) and 3,5-diiodo-L-thyronine (T2), when administered to a model of familial hypercholesterolemia, i.e., low density lipoprotein receptor (LDLr)-knockout (Ldlr-/-) mice fed with a Western type diet (WTD), dramatically reduce circulating total and very low-density lipoprotein/LDL cholesterol with decreased liver apolipoprotein B (ApoB) production. The aim of the study was to highlight putative molecular mechanisms to manage cholesterol levels in the absence of LDLr. A comprehensive comparative profiling of changes in expression of soluble proteins in livers from Ldlr-/- mice treated with either T3 or T2 was performed. From a total proteome of 450 liver proteins, 25 identified proteins were affected by both T2 and T3, 18 only by T3 and 9 only by T2. Using in silico analyses, an overlap was observed with 11/14 pathways common to both iodothyronines, with T2 and T3 preferentially altering sub-networks centered around hepatocyte nuclear factor 4 alpha (HNF4alpha) and peroxisome proliferator-activated receptor alpha (PPARalpha), respectively. Both T2 and T3 administration significantly reduced nuclear HNF4alpha protein content, while T2, but not T3, decreased the expression levels of the HNFalpha transcriptional coactivator PGC-1alpha. Lower PPARalpha levels were found only following T3 treatment while both T3 and T2 lowered liver X receptor alpha (LXRalpha) nuclear content. Overall, this study, although it was not meant to investigate the use of T2 and T3 as a therapeutic agent, provides novel insights into the regulation of hepatic metabolic pathways involved in T3- and T2-driven cholesterol reduction in Ldlr-/- mice.

Hypertriglyceridemia is an independent risk factor for cardiovascular disease, and plasma triglycerides (TGs) correlate strongly with plasma apolipoprotein C-III (ApoC-III) levels. Antisense oligonucleotides (ASOs) for ApoC-III reduce plasma TGs in primates and mice, but the underlying mechanism of action remains controversial. We determined that a murine-specific ApoC-III-targeting ASO reduces fasting TG levels through a mechanism that is dependent on low-density lipoprotein receptors (LDLRs) and LDLR-related protein 1 (LRP1). ApoC-III ASO treatment lowered plasma TGs in mice lacking lipoprotein lipase (LPL), hepatic heparan sulfate proteoglycan (HSPG) receptors, LDLR, or LRP1 and in animals with combined deletion of the genes encoding HSPG receptors and LDLRs or LRP1. However, the ApoC-III ASO did not lower TG levels in mice lacking both LDLR and LRP1. LDLR and LRP1 were also required for ApoC-III ASO-induced reduction of plasma TGs in mice fed a high-fat diet, in postprandial clearance studies, and when ApoC-III-rich or ApoC-III-depleted lipoproteins were injected into mice. ASO reduction of ApoC-III had no effect on VLDL secretion, heparin-induced TG reduction, or uptake of lipids into heart and skeletal muscle. Our data indicate that ApoC-III inhibits turnover of TG-rich lipoproteins primarily through a hepatic clearance mechanism mediated by the LDLR/LRP1 axis.

Cholesterol reduction has markedly reduced major cardiovascular disease (CVD) events and shown regression of atherosclerosis in some studies. However, CVD has for decades also been associated with increased levels of circulating triglyceride (TG)-rich lipoproteins. Whether this is due to a direct toxic effect of these lipoproteins on arteries or whether this is merely an association is unresolved. More recent genetic analyses have linked genes that modulate TG metabolism with CVD. Moreover, analyses of subgroups of hypertriglyceridemic (HTG) subjects in clinical trials using fibric acid drugs have been interpreted as evidence that TG reduction reduces CVD events. This review will focus on how HTG might cause CVD, whether TG reduction makes a difference, what pathophysiological defects cause HTG, and what options are available for treatment.

The global obesity epidemic and its impact on cardiovascular outcomes is a topic of ongoing debate and investigation in the cardiology community. It is well known that obesity is associated with multiple cardiovascular risk factors. Although life-style changes are the first line of therapy, they are often insufficient in achieving weight loss goals. Liraglutide, naltrexone/bupropion, and phentermine/topiramate are new agents that have been recently approved to treat obesity, but their effects on cardiovascular risk factors and outcomes are not well described. This review summarizes data currently available for these novel agents regarding drug safety, effects on major cardiovascular risk factors, impact on cardiovascular outcomes, outcomes research that is currently in progress, and areas of uncertainty. Given the impact of obesity on cardiovascular health, there is a pressing clinical need to understand the effects of these agents beyond weight loss alone.

Pulmonary surfactant is synthesized by type II pneumocytes and is mainly composed of phospholipids and minor amounts of cholesterol and specific proteins. Surfactant allows the lungs to inflate by decreasing alveolar surface tension and the work needed for inspiration in each breathing cycle. A delicate balance between synthesis, secretion, recycling and degradation of the lipids is required to maintain surfactant function and lung performance. Single nucleotide polymorphisms in the LDL receptor associated protein 1 (LRP-1) are associated with decreased lung function in patients with chronic obstructive pulmonary disease (COPD). But the function of LRP1 in the lung is not known. Amongst other roles, LRP-1 participates in liver lipoprotein metabolism, in adipocyte cell differentiation and in macrophage inflammatory cascades. We deleted LRP-1 in type II pneumocyte-derived A549 cells using stable transfection. LRP1 shRNA-treated cells and scrambled shRNA-treated cells were cultured in collagen coated transwell inserts at the air-liquid interphase, exposing the cellular basal side to the culture media and the apical side to the air. LRP-1 shRNA decreased surfactant phospholipid, cholesterol and cholesteryl esters on the apical surface of the cells. LRP-1 shRNA cells showed reduced gene expression of the rate limiting enzymes for fatty acid synthesis FAS, ACAT1 and SCD1, and of phosphatidylcholine synthesis enzymes choline transferase and choline kinase. Surprisingly, triglycerides and cholesteryl esters accumulated in intracellular lipid droplets in LRP-1 shRNA cells, while phospholipids and unesterified cholesterol were not changed when compared to scrambled shRNA cells. LRP-1 shRNA cells showed >3 fold overexpression of the fatty acid transporter CD36 and reduced gene expression of acyl-CoA oxidase. After an overnight incubation with fresh media in the basal side, LRP-1 shRNA cells showed higher media depletion of phospholipid, cholesterol esters and unesterifed cholesterol. Uptake of LDL-derived phosphatidylcholine was not altered by LRP-1 deletion, but the gene expression of phospholipid and cholesterol exporters ABCA1 and ABCG1 was reduced. Insulin signaling was affected by LRP-1 deletion. LRP-1 shRNA cells showed decreased protein expression of insulin receptor substrates 1 and 2 (IRS-1 and IRS-2) and increased phospho-serine IRS-1/total IRS-1 ratio. After IGF-1 treatment, LRP-1 shRNA cells failed to Tyr-phosphorylate the IGF-1 receptor b, and phosphorylation of the downstream target Akt was lower than in scrambled shRNA cells These data suggest that LRP-1 in type II pneumocytes is involved in lipid export, intracellular surfactant lipid metabolism and insulin signaling

The heart utilizes large amounts of fatty acids as energy providing substrates. The physiological balance of lipid uptake and oxidation prevents accumulation of excess lipids. Several processes that affect cardiac function, including ischemia, obesity, diabetes mellitus, sepsis, and most forms of heart failure lead to altered fatty acid oxidation and often also to the accumulation of lipids. There is now mounting evidence associating certain species of these lipids with cardiac lipotoxicity and subsequent myocardial dysfunction. Experimental and clinical data are discussed and paths to reduction of toxic lipids as a means to improve cardiac function are suggested.