An Allosteric Binding Site on Sortilin Regulates the Trafficking of VLDL, PCSK9, and LDLR in Hepatocytes.

ApoB lipoproteins (apo B-Lp) are produced in hepatocytes, and their secretion requires the cargo receptor sortilin. We examined the secretion of apo B-Lp-containing very low-density lipoprotein (VLDL), an LDL progenitor. Sortilin also regulates the trafficking of the subtilase PCSK9, which when secreted binds the LDL receptor (LDLR), resulting in its endocytosis and destruction at the lysosome. We show that the site 2 binding compound (cpd984) has multiple effects in hepatocytes, including (1) enhanced Apo-Lp secretion, (2) increased cellular PCSK9 retention, and (3) augmented levels of LDLR at the plasma membrane. We postulate that cpd984 enhances apo B-Lp secretion in part through binding the lipid phosphatidylinositol 3,4,5-trisphosphate (PIP3), which is present at higher levels on circulating VLDL form fed rats relative to after fasting. We attribute the enhanced VLDL secretion to its increased binding affinity for sortilin site 1 induced by cpd984 binding site 2. This hinders PCSK9 binding and secretion, which would subsequently prevent its binding to LDLR leading to its degradation. This suggests that site 2 is an allosteric regulator of site 1 binding. This effect is not limited to VLDL, as cpd984 augments binding of the neuropeptide neurotensin (NT) to sortilin site 1. Molecular dynamics simulations demonstrate that the C-terminus of NT (Ct-NT) stably binds site 1 through an electrostatic interaction. This was bolstered by the ability of Ct-NT to disrupt lower-affinity interactions between sortilin and the site 1 ligand PIP3. Together, these data show that binding cargo at sortilin site 1 is allosterically regulated through site 2 binding, with important ramifications for cellular lipid homeostasis involving proteins such as PCSK9 and LDLR.

Low Serum Paraoxonase-1 Activity Associates with Incident Cardiovascular Disease Risk in Subjects with Concurrently High Levels of High-Density Lipoprotein Cholesterol and C-Reactive Protein.

Paroxonase-1 (PON1) is a key enzyme that inhibits low-density lipoprotein oxidation and consequently atherogenesis. Here, we assessed whether low serum PON1 activity associates with incident cardiovascular disease (CVD) in subjects with high levels of high-density cholesterol (HDL-C) and C-reactive protein (CRP), a marker of low-grade systemic inflammation. Cox proportional-hazards modeling of incident CVD risk (11 years mean follow-up) adjusted for relevant clinical and biomarker covariates was performed on a population-based study (N = 7766) stratified into three groups: low CRP-(LR; event rate 4.9%); low HDL-C/high CRP-(HR1; event rate 14.4%); and high HDL-C/high CRP-(HR2; event rate 7.6%). Modeling results for PON1 activity in HR2 were significant and robust (hazard ratio/SD unit-0.68, 95% CI 0.55-0.83, p = 0.0003), but not so for LR and HR1. Analyses in HR2 of the interaction of PON1 with HDL-C, apoA-I, apoA-II, and apoE levels were significant only for PON1 with apoE (hazard ratio-1.77, 95% CI 1.29-2.41, p = 0.0003). Subsequent subgroup analysis revealed inverse risk dependence for apoE at low PON1 levels. In conclusion, in a population-based study of subjects with concurrently high HDL-C and CRP levels, low serum PON1 activity associates with incident CVD risk with risk accentuated at low apoE levels.

Compositional Features of HDL Particles Interact with Albuminuria to Modulate Cardiovascular Disease Risk.

Lipoproteins containing apolipoprotein B modify associations of elevated urinary albumin excretion (UAE) with cardiovascular disease (CVD). Additionally, it is known that elevated UAE alters high-density lipoprotein functionality. Accordingly, we examined whether HDL features might also modify UAE-associated CVD. Multivariable Cox proportional-hazards modeling was performed on participants of the PREVEND (Prevention of Renal and Vascular Endstage Disease) study at the baseline screening with standard lipid/lipoprotein analyses and, three-to-four years later (second screen), with nuclear magnetic resonance lipoprotein analyses focusing on HDL parameters including HDL particle (HDL-P) and apolipoprotein A-I concentrations. These were used with UAE and derived measures of HDL apoA-I content (apoA-I/HDL-C and apoA-I/HDL-P) in risk models adjusted for gender, age, apoB, diabetes, past CVD history, CRP and GFR. Interaction analysis was also performed. Baseline screening revealed significant associations inverse for HDL-C and apoA-I and direct for apoA-I/HDL-C. The second screening demonstrated associations inverse for HDL-P, large HDL-P, medium HDL-P, HDL size, and apoA-I/HDL-P. Significant interactions with UAE included apoA-I/HDL-C at the baseline screening, and apoA-I/HDL-P and medium HDL-P but not apoA-I/HDL-C at the second screening. We conclude that features of HDL particles including apoA-I/HDL-P, indicative of HDL apoA-I content, and medium HDL-P modify associations of elevated UAE with CVD risk.

Insulin resistance involvement in prevalence of familial dysbetalipoproteinemia in ε2ε2 subjects by Bayesian network modeling.

OBJECTIVE: Familial dysbetalipoproteinemia (FD) or Type III hyperlipoproteinemia is closely associated with the ε2ε2 genotype of the common APOE polymorphism although not all ε2 homozygotes develop FD indicating that additional factors play a role including insulin resistance (IR). The current study was undertaken to explore relationships and influences among factors, especially IR, that might elucidate FD progression pathways. METHODS: Bayesian network (BN) modeling, a probabilistic graphical exploratory data analysis tool that portrays relationships and influences among variables as simple diagrams, was applied to 52 e2e2 subjects. An algorithm based on apolipoprotein and lipid values identified 24 subjects having FD. BN modeling parameters included plasma apoE, HDL cholesterol (HDL-C), apolipoprotein A-I (apoA-I), apolipoprotein A-II (apoA-II), apoA-I/HDL-C ratio, apoA-II/HDL-C ratio, insulin, and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR). RESULTS: Modeling resulted in twenty network graphs. Each graph revealed apoE and the apoA-II/HDL-C ratio as sole determinants of FD prevalence. BN results did not demonstrate a direct role for insulin and HOMA-IR. However, multiple graphs in the set did reveal indirect influence of IR on FD prevalence as conveyed through the apoA-II/HDL-C ratio; while all remaining graphs in the set demonstrated the apoA-II/HDL-C ratio as directly influencing insulin levels and HOMA-IR. For apoE, the other determinant of FD prevalence, results revealed no relationship with IR parameters. CONCLUSIONS: In so far as insulin levels and HOMA-IR are associated with IR in e2e2 subjects, IR may act indirectly in FD progression via the apoA-II/HDL-C ratio; and/or the apoA-II/HDL-C ratio acts directly to promote IR.

Roles of high apolipoprotein E blood levels and HDL in development of familial dysbetalipoproteinemia in ε2ε2 subjects.

OBJECTIVE: Familial dysbetalipoproteinemia (FD) or Type III hyperlipoproteinemia is a mixed hyperlipidemia closely associated with the ε2ε2 genotype of the common APOE polymorphism although not all homozygotes progress to FD. Unlike the polymorphism, few studies explore effects of apolipoprotein E (apoE) blood levels on FD development. Likewise, despite the known apoE2 lipoprotein binding preference for high-density lipoprotein (HDL); little work exists exploring HDL in FD. Accordingly, this study was undertaken to investigate potential roles in FD development for apoE and HDL. Additionally, insulin and Homeostatic Model Assessment of Insulin Resistance (HOMA-IR) were investigated in view of reports linking insulin resistance to FD. METHODS: APOE genotyping and levels of apoE, apolipoprotein A-I (apoA-I), apolipoprotein A-II (apoA-II), insulin, HOMA-IR, lipids, and NMR lipoprotein analysis were determined in a cohort of healthy individuals (N=7169). A lipid-based algorithm identified FD in 24 of 52 e2e2 subjects. Logistic regression modeling assessed associations of FD development with measured variables. RESULTS: Univariate models revealed associations with FD significant and positive for apoE, apoA-II/apoA-I, apoA-I/HDL-C, apoA-II/HDL-C, and HOMA-IR. For HDL-C, association was significant but inverse. Results of multivariable models containing apoE with single parameters added revealed statistical significance only for the apoA-II/HDL-C ratio (OR 10.52, 95%CI 1.17-94.79, p=0.036) concurrent with significance for apoE (OR 2.21, 95%CI 1.06-4.65, p=0.035). Interaction was not demonstrated (p=0.36). NMR results revealed for FD versus nonFD subjects generally higher levels of VLDL and small HDL and for IDL few differences. CONCLUSION: High apoE and high apoA-II/HDL-C independently associate with FD development in ε2ε2 individuals.

Inflammatory markers modify the risk of recurrent coronary events associated with apolipoprotein A-I in postinfarction patients.

BACKGROUND: Laboratory findings have suggested that systemic and vascular inflammation can impair the antiatherogenic function of high-density lipoproteins (HDLs). However, evidence from population studies is sparse. OBJECTIVE: The objective of the study was to assess if blood inflammatory markers modify the risk of recurrent coronary events associated with apolipoprotein A-I (apoA-I) and HDL cholesterol (HDL-C) among postinfarction patients. METHODS: ApoA-I, HDL-C, and inflammatory markers (C-reactive protein [CRP], serum amyloid A (SAA), fibrinogen, von Willebrand factor [vWF], and D-dimer) were measured from blood samples of 1028 patients drawn 2 months after an index myocardial infarction (MI). Patients were followed up for the composite coronary endpoint (nonfatal MI, coronary death, or unstable angina) for an average of 26 months. Cox proportional hazard models were used to assess effect modifications for the association of apoA-I and HDL-C with coronary risk by each inflammatory marker. RESULTS: CRP significantly modified the risk of recurrent coronary events associated with apoA-I. Among the entire population, multivariable-adjusted hazard ratios associated with each standard deviation increase in apoA-I for those with low and high CRP levels were 0.89 and 1.35, respectively (P value for interaction = .008). vWF was a significant effect modifier of the apoA-I/coronary risk association only among diabetic patients (hazard ratios were 0.56 and 1.43, for diabetic patients with low and high vWF levels, respectively; P value for interaction = .002). No effect modification was observed for the HDL-C/coronary risk association. CONCLUSION: Among stable post-MI patients, CRP modified the risk of recurrent coronary events associated with apoA-I. VWF modified this association only among the diabetic subgroup.

Phosphatidylinositol (3,4,5)-trisphosphate binds to sortilin and competes with neurotensin: Implications for very low density lipoprotein binding.

Sortilin is a multi-ligand sorting receptor that interacts with B100-containing VLDL and LDL as well as other ligands including neurotensin (NT). The current study investigates the hypothesis that phosphatidylinositol (3,4,5)-trisphosphate (PIP3) generated downstream of insulin action can directly bind to sortilin. NT binds to sortilin at a well characterized site via its carboxy terminus (C-term). Using a crystal structure of human sortilin (hsortilin), PIP3 is predicted to bind at this C-term site. Binding of PIP3 to hsortilin is demonstrated using surface plasmon resonance (SPR) flowing PIP3 nanodiscs over immobilized hsortilin. Studies were performed using SPR where dibutanoyl PIP3 is shown to compete with NT for sortilin binding. Rat VLDL and LDL were evaluated for PIP3 content immunologically using monoclonal antibodies directed against PIP3. Rat plasma VLDL contained three times more immunoreactive PIP3 than LDL per µg of protein. Because VLDL contains additional ligands that bind sortilin, to distinguish specific PIP3 binding, we used PIP3 liposomes. Liposome floatation assays were used to demonstrate PIP3 liposome binding to sortilin. Using SPR and immobilized hsortilin, the C-term NT tetrapeptide (P-Y-I-L) is shown to bind to hsortilin. A compound (cpd984) was identified with strong theoretical binding to the site on sortilin involved in NT N-terminal binding. When cpd984 is co-incubated with the tetrapeptide, the affinity of binding to sortilin is increased. Similarly, the affinity of PIP3 liposome binding increased in the presence of cpd984. Overall, results demonstrate that sortilin is a PIP3 binding protein with binding likely to occur at the C-term NT binding site. The presence of multiple ligands on B100-containing lipoproteins, VLDL and LDL, raises the interesting possibility for increased interaction with sortilin based on the presence of PIP3.

Sortilin facilitates VLDL-B100 secretion by insulin sensitive McArdle RH7777 cells.

Studies examining the relationship between cellular sortilin and VLDL-B100 secretion demonstrate inconsistent results. Current studies explore the possibility that discrepancies may be related to insulin sensitivity. McArdle RH7777 cells (McA cells) cultured under serum enriched conditions lose sensitivity to insulin. Following incubation in serum-free DMEM containing 1% BSA, McA cells become insulin responsive and demonstrate reduced apo B secretion. Current studies indicate that insulin sensitive McA cells express lower cellular sortilin that corresponds with reduction in VLDL-B100 secretion without changes in mRNA of either sortilin or apo B. When sortilin expression is further reduced by siRNA knockdown (KD), there are additional decreases in VLDL-B100 secretion. A crystal structure of human sortilin (hsortilin) identifies two binding sites on the luminal domain for the N- and C-termini of neurotensin (NT). A small organic compound (cpd984) was identified that has strong theoretical binding to the N-terminal site. Both cpd984 and NT bind hsortilin by surface plasmon resonance. In incubations with insulin sensitive McA cells, cpd984 was shown to enhance VLDL-B100 secretion at each level of sortilin KD suggesting cpd984 acted through sortilin in mediating its effect. Current results support a role for sortilin to facilitate VLDL-B100 secretion which is limited to insulin sensitive McA cells. Inconsistent reports of the relationship between VLDL-B100 secretion and sortilin in previous studies may relate to differing functions of sortilin in VLDL-B100 secretion depending upon insulin sensitivity.

Data in support of a central role of plasminogen activator inhibitor-2 polymorphism in recurrent cardiovascular disease risk in the setting of high HDL cholesterol and C-reactive protein using Bayesian network modeling.

Data is presented that was utilized as the basis for Bayesian network modeling of influence pathways focusing on the central role of a polymorphism of plasminogen activator inhibitor-2 (PAI-2) on recurrent cardiovascular disease risk in patients with high levels of HDL cholesterol and C-reactive protein (CRP) as a marker of inflammation, "Influences on Plasminogen Activator Inhibitor-2 Polymorphism-Associated Recurrent Cardiovascular Disease Risk in Patients with High HDL Cholesterol and Inflammation" (Corsetti et al., 2016; [1]). The data consist of occurrence of recurrent coronary events in 166 post myocardial infarction patients along with 1. clinical data on gender, race, age, and body mass index; 2. blood level data on 17 biomarkers; and 3. genotype data on 53 presumptive CVD-related single nucleotide polymorphisms. Additionally, a flow diagram of the Bayesian modeling procedure is presented along with Bayesian network subgraphs (root nodes to outcome events) utilized as the data from which PAI-2 associated influence pathways were derived (Corsetti et al., 2016; [1]).

Influences on plasminogen activator inhibitor-2 polymorphism-associated recurrent cardiovascular disease risk in patients with high HDL cholesterol and inflammation.

BACKGROUND AND AIMS: Evidence continues to accumulate that athero-protective effects of high-density lipoprotein (HDL) depend to some degree on effective HDL functionality and that such functionality can become degraded in the setting of chronic inflammation. To investigate this issue, we have studied a group of post-myocardial infarction patients with high levels of C-reactive protein as an indicator of chronic inflammation and with concurrently high levels of HDL cholesterol. For these patients we have demonstrated high-risk for recurrent cardiac events as well as a strong association of risk with a polymorphism of the gene (SERPINB2) for plasminogen activator inhibitor-2 (PAI-2) presumptively reflective of an important role for fibrinolysis in risk. However, additional processes might be involved. The current work sought to characterize processes underlying how PAI-2 might be involved in the generation of risk. METHODS: Multivariate population data were leveraged using Bayesian network modeling, a graphical probabilistic approach for knowledge discovery, to generate networks reflective of influences on PAI-2 polymorphism-associated risk. RESULTS: Modeling results revealed three individual networks centering on the PAI-2 polymorphism with specific features providing information relating to how the polymorphism might associate with risk. These included racial dependency, platelet clot initiation and propagation, oxidative stress, inflammation effects on HDL metabolism and coagulation, and induction and termination of fibrinolysis. CONCLUSIONS: Beyond direct association of a PAI-2 polymorphism with recurrent risk in post-myocardial infarction patients, results suggest that PAI-2 likely plays a key role leading to risk through multiple pathophysiologic processes. Such knowledge could potentially be valuable with individualization of patient care.

Insulin dependent apolipoprotein B degradation and phosphatidylinositide 3-kinase activation with microsomal translocation are restored in McArdle RH7777 cells following serum deprivation.

Previous studies in rat hepatocytes demonstrated that insulin-dependent apolipoprotein (apo) B degradation (IDAD) is lost when cells are maintained for 3 d under enriched culture conditions. Loss of IDAD correlates with increased expression of protein tyrosine phosphatase 1B (PTP1B) known to be associated with resistance to insulin signaling in the liver. McArdle RH7777 hepatoma (McA) cells cultured in serum containing medium are resistant to IDAD; demonstrate a 30% increase in apo B secretion, and express increased levels of PTP1B protein and mRNA. In addition, insulin-stimulated Class I phosphatidylinositide 3-kinase (PI3K) activity of anti-pY immunoprecipitates is severely blunted. IDAD resistance in McA cells correlates with diminished translocation of insulin-stimulated pY-IRS1 to intracellular membranes. Incubation of McA cells with RK682, a protein tyrosine phosphatase inhibitor, is sufficient to restore IDAD in resistant McA cells. Overall, results further support the importance of Class I PI3K activity in IDAD, and suggest that loss of this activity is sufficient to cause resistance. Although other factors are involved in downstream events including sortilin binding to apo B, autophagy, and lysosomal degradation, loss of signal generation and reduced localization of Class I PI3K to intracellular membranes plays a significant role in IDAD resistance.

Apolipoprotein B attenuates albuminuria-associated cardiovascular disease in prevention of renal and vascular endstage disease (PREVEND) participants.

Whether urinary albumin excretion relates to higher levels of atherogenic apolipoprotein B fractions in the nondiabetic population is uncertain. Such a relationship could explain, in part, the association of elevated urinary albumin excretion with cardiovascular disease risk. We assessed the relationship of urinary albumin excretion with apolipoprotein B fractions and determined whether the association of elevated urinary albumin excretion with incident cardiovascular events is modified by high apolipoprotein B fraction levels. We performed a prospective study on 8286 nondiabetic participants (580 participants with cardiovascular disease; 4.9 years median follow-up time) with fasting lipids, apolipoprotein B, and urinary albumin excretion determined at baseline. With adjustment for sex and age, micro- and macroalbuminuria were associated with increased apolipoprotein B fractions (non-HDL cholesterol, LDL cholesterol, triglycerides, and apolipoprotein B). All four apolipoprotein B fractions modified associations of urinary albumin excretion with incident cardiovascular disease (hazard ratios for interaction terms ranged from 0.89 to 0.94 with 95% confidence intervals ranging from 0.84 to 0.99 and P values ranging from 0.001 to 0.02 by Cox proportional hazards modeling). These interactions remained present after additional adjustment for conventional risk factors, eGFR, cardiovascular history, and lipid-lowering and antihypertensive drug treatments. Such modification was also observed when urinary albumin excretion was stratified into normo-, micro-, and macroalbuminuria. We conclude that there is an association between elevated urinary albumin excretion and apolipoprotein B fraction levels and a negative interaction between these variables in their associations with incident cardiovascular events. Elevated urinary albumin excretion may share common causal pathways with high apolipoprotein B fractions in the pathogenesis of cardiovascular disease.

Plasminogen activator inhibitor-2 polymorphism associates with recurrent coronary event risk in patients with high HDL and C-reactive protein levels.

The objective of this work was to investigate whether fibrinolysis plays a role in establishing recurrent coronary event risk in a previously identified group of postinfarction patients. This group of patients was defined as having concurrently high levels of high-density lipoprotein cholesterol (HDL-C) and C-reactive protein (CRP) and was previously demonstrated to be at high-risk for recurrent coronary events. Potential risk associations of a genetic polymorphism of plasminogen activator inhibitor-2 (PAI-2) were probed as well as potential modulatory effects on such risk of a polymorphism of low-density lipoprotein receptor related protein (LRP-1), a scavenger receptor known to be involved in fibrinolysis in the context of cellular internalization of plasminogen activator/plansminogen activator inhibitor complexes. To this end, Cox multivariable modeling was performed as a function of genetic polymorphisms of PAI-2 (SERPINB, rs6095) and LRP-1 (LRP1, rs1800156) as well as a set of clinical parameters, blood biomarkers, and genetic polymorphisms previously demonstrated to be significantly and independently associated with risk in the study population including cholesteryl ester transfer protein (CETP, rs708272), p22phox (CYBA, rs4673), and thrombospondin-4 (THBS4, rs1866389). Risk association was demonstrated for the reference allele of the PAI-2 polymorphism (hazard ratio 0.41 per allele, 95% CI 0.20-0.84, p=0.014) along with continued significant risk associations for the p22phox and thrombospondin-4 polymorphisms. Additionally, further analysis revealed interaction of the LRP-1 and PAI-2 polymorphisms in generating differential risk that was illustrated using Kaplan-Meier survival analysis. We conclude from the study that fibrinolysis likely plays a role in establishing recurrent coronary risk in postinfarction patients with concurrently high levels of HDL-C and CRP as manifested by differential effects on risk by polymorphisms of several genes linked to key actions involved in the fibrinolytic process.

Insulin-dependent apolipoprotein B degradation is mediated by autophagy and involves class I and class III phosphatidylinositide 3-kinases.

Insulin acutely stimulates the degradation of apolipoprotein B (apo B) which decreases very low density lipoprotein (VLDL) secretion by liver. Insulin-dependent apo B degradation (IDAD) occurs following phosphatidylinositide 3-kinase (PI3K) activation and involves lysosomal degradation. Insulin suppression of apo B secretion is blocked by over-expression of phosphatase and tensin homologue (PTEN) in McArdle RH7777 (McA) cells suggesting the importance of Class I PI3K generated PI (3,4,5) triphosphate (PIP3) in IDAD. Classical autophagy inhibitors including 3-methyladenine, L-asparagine and bafilomycin A1 also blocked the ability of insulin to suppress apo B secretion by rat hepatocytes (RH) suggesting that IDAD occurs through an autophagy-related mechanism. IDAD is also blocked following over-expression in McA cells of a dominant negative kinase-defective Vps34, a class III PI3K that generates PI 3-monophosphate required for autophagy. Vps34 inhibition of IDAD occurs without altering insulin-dependent S473 phosphorylation of Akt indicating PI3K/PIP3/Akt signaling is intact. Cellular p62/SQSTM1, an inverse indicator of autophagy, is increased with insulin treatment consistent with the known ability of insulin to inhibit autophagy, and therefore the role of insulin in utilizing components of autophagy for apo B degradation is unexpected. Thapsigargan, an inducer of endoplasmic reticulum (ER) stress, and a recently demonstrated autophagy inhibitor, blocked apo B secretion which contrasted with other autophagy inhibitors and mutant Vps34 results which were permissive with respect to apo B secretion. Pulse chase studies indicated that intact B100 and B48 proteins were retained in cells treated with thapsigargan consistent with their accumulation in autophagosomal vacuoles. Differences between IDAD and ER stress-coupled autophagy mediated by thapsgargin suggest that IDAD involves an unique form of autophagy. Insulin action resulting in hepatic apo B degradation is novel and important in understanding regulation of hepatic VLDL metabolism.

Insulin suppression of apolipoprotein B in McArdle RH7777 cells involves increased sortilin 1 interaction and lysosomal targeting.

Insulin suppresses secretion of very low density lipoprotein (VLDL) apolipoprotein (apo) B in primary rodent hepatocytes (RH) by favoring the degradation of B100, the larger form of apo B, through post-endoplasmic reticulum proteolysis. Sortilin 1 (sort1), a multi-ligand sorting receptor, has been proposed as a mediator of lysosomal B100 degradation by directing B100 in pre-VLDL to lysosomes rather than allowing maturation to VLDL and secretion. The purpose of our studies was to investigate the role of sort1 in insulin-dependent degradation of apo B. Using liver derived McArdle RH7777 (McA) cells, we demonstrate that insulin suppresses VLDL B100 secretion via a phosphatidylinositide 3-kinase (PI3K) dependent process that is inhibitable by wortmannin in a fashion similar to RH. Using McA cells and in situ cross-linking, we demonstrate that insulin acutely (30min) stimulates the interaction of B100 with sort1. The insulin-induced interaction of sort1-B100 is markedly enhanced when lysosomal degradation is inhibited by Bafilomycin A1 (BafA1), an inhibitor of lysosomal acidification. As BafA1 also prevents insulin suppressive effects on apo B secretion, our results suggest that sort1-B100 interaction stimulated by insulin transiently accumulates with BafA1 and favors B100 secretion by default.

Reactive Oxygen Species, SUMOylation, and Endothelial Inflammation.

Although the exact mechanism through which NADPH oxidases (Nox's) generate reactive oxygen species (ROS) is still not completely understood, it is widely considered that ROS accumulation is the cause of oxidative stress in endothelial cells. Increasing pieces of evidence strongly indicate the role for ROS in endothelial inflammation and dysfunction and subsequent development of atherosclerotic plaques, which are causes of various pathological cardiac events. An overview for a causative relationship between ROS and endothelial inflammation will be provided in this review. Particularly, a crucial role for specific protein SUMOylation in endothelial inflammation will be presented. Given that SUMOylation of specific proteins leads to increased endothelial inflammation, targeting specific SUMOylated proteins may be an elegant, effective strategy to control inflammation. In addition, the involvement of ROS production in increasing the risk of recurrent coronary events in a sub-group of non-diabetic, post-infarction patients with elevated levels of HDL-cholesterol will be presented with the emphasis that elevated HDL-cholesterol under certain inflammatory conditions can lead to increased incidence of cardiovascular events.