Beta-cell ABCA1 influences insulin secretion, glucose homeostasis and response to thiazolidinedione treatment

MicroRNA Sequences Modulated by Beta Cell Lipid Metabolism: Implications for Type 2 Diabetes Mellitus

Alterations in lipid metabolism within beta cells and islets contributes to dysfunction and apoptosis of beta cells, leading to loss of insulin secretion and the onset of type 2 diabetes. Over the last decade, there has been an explosion of interest in understanding the landscape of gene expression which influences beta cell function, including the importance of small non-coding microRNA sequences in this context. This review sought to identify the microRNA sequences regulated by metabolic challenges in beta cells and islets, their targets, highlight their function and assess their possible relevance as biomarkers of disease progression in diabetic individuals. Predictive analysis was used to explore networks of genes targeted by these microRNA sequences, which may offer new therapeutic strategies to protect beta cell function and delay the onset of type 2 diabetes.

Association between preoperative lipid profiles and new-onset diabetes after transplantation in Chinese kidney transplant recipients: A retrospective cohort study

Background

This study investigated the association between the preoperative lipid profiles and new‐onset diabetes after transplantation (NODAT) in Chinese kidney transplant recipients (KTRs).

Methods

In this study, of 1140 KTRs registered between January 1993 and March 2018 in Zhongshan Hospital, Fudan University, 449 were enrolled. Clinical data, obtained through a chart review of the patient records in the medical record system, were evaluated, and NODAT was diagnosed based on the American Diabetes Association guidelines. Multivariate Cox regression analysis was conducted to determine whether the preoperative lipid profiles in KTRs were independently associated with NODAT incidence. The preoperative lipid profiles were analyzed as continuous variables and grouped into tertiles. Smooth curve fitting was used to confirm the linear associations.

Results

During a median follow‐up of 28.03 (interquartile range 12.00–84.23) months, 104 of the 449 (23.16%) participants developed NODAT. The multivariate model analysis, adjusted for all potential covariates, showed that increased values of the following parameters were associated with NODAT (hazard ratio, 95% confidence interval): preoperative total cholesterol (TC; 1.25, 1.09–1.58, p = 0.0495), low‐density lipoprotein cholesterol (LDL‐C; 1.33, 1.02–1.75, p = 0.0352), non‐high‐density lipoprotein cholesterol (non‐HDL‐C; 1.41, 1.09–1.82, p = 0.0084), TC/HDL‐C (1.28, 1.06–1.54, p = 0.0109), and non‐HDL‐C/HDL‐C (1.26, 1.05–1.52, p = 0.0138). However, the association between the preoperative triglyceride, HDL‐C, or TG/HDL‐C and NODAT was not significant.

Conclusions

Preoperative TC, LDL‐C, non‐HDL‐C, TC/HDL‐C, and non‐HDL‐C/HDL‐C were independent risk factors for NODAT.

Current Diagnosis and Management of Tangier Disease

Tangier disease is a genetic disorder characterized by an absence or extremely low level of high-density lipoprotein (HDL)-cholesterol (HDL-C). It is caused by a dysfunctional mutation of the ATP-binding cassette transporter A1 (ABCA1) gene, the mandatory gene for generation of HDL particles from cellular cholesterol and phospholipids, and it appears in an autosomal recessive hereditary profile. To date, 35 cases have been reported in Japan and 109 cases outside Japan. With dysfunctional mutations in both alleles (homozygotes or compound heterozygotes), the HDL-C level is mostly less than 5 mg/dL and there is 10 mg/dL or less of apolipoprotein A-I (apoA-I), the major protein component of HDL. In patients with Tangier disease, major physical findings are orange-colored pharyngeal tonsils, hepatosplenomegaly, corneal opacity, lymphadenopathy, and peripheral neuropathy. Although patients tend to have decreased low-density lipoprotein (LDL)-cholesterol (LDL-C) levels, premature coronary artery disease is frequently observed. No specific curative treatment is currently available, so early identification of patients and preventing atherosclerosis development are crucial. Management of risk factors other than low HDL-C is also important, such as LDL-C levels, hypertension and smoking. Additionally, treatment for glucose intolerance might be required because impaired insulin secretion from pancreatic beta cells has occasionally been reported.

HDL Cholesterol and Non-Cardiovascular Disease: A Narrative Review

High density lipoprotein (HDL) cholesterol has traditionally been considered the “good cholesterol”, and most of the research regarding HDL cholesterol has for decades revolved around the possible role of HDL in atherosclerosis and its therapeutic potential within atherosclerotic cardiovascular disease. Randomized trials aiming at increasing HDL cholesterol have, however, failed and left questions to what role HDL cholesterol plays in human health and disease. Recent observational studies involving non-cardiovascular diseases have shown that high levels of HDL cholesterol are not necessarily associated with beneficial outcomes as observed for age-related macular degeneration, type II diabetes, dementia, infection, and mortality. In this narrative review, we discuss these interesting associations between HDL cholesterol and non-cardiovascular diseases, covering observational studies, human genetics, and plausible mechanisms.

Apolipoprotein Mimetic Peptides: An Emerging Therapy against Diabetic Inflammation and Dyslipidemia

Obesity has achieved epidemic status in the United States, resulting in an increase in type 2 diabetes mellitus, dyslipidemia, and cardiovascular disease. Numerous studies have shown that inflammation plays a key role in the development of insulin resistance and diabetic complications. HDL cholesterol levels are inversely associated with coronary heart disease in humans. The beneficial effect of HDL is due, in part, to apolipoproteins A-I and E, which possess anti-inflammatory properties. The functional quality of HDL, however, may be reduced in the context of diabetes. Thus, raising levels of functional HDL is an important target for reducing inflammation and diabetic complications. Apo A-I possesses eight alpha-helical sequences, most of which form class A amphipathic helical structures. Peptides belonging to this class inhibit atherogenesis in several mouse models. Additional peptides based on structural components of apoE have been shown to mediate a rapid clearance of atherogenic lipoproteins in dyslipidemic mice. In this review, we discuss the efficacy of apolipoprotein mimetic peptides in improving lipoprotein function, reducing inflammation, and reversing insulin resistance and cardiometabolic disease processes in diabetic animals.

ABCA1 69C>T Polymorphism and the Risk of Type 2 Diabetes Mellitus: A Systematic Review and Updated Meta-Analysis

Background

The ATP-binding cassette transporter A1 (ABCA1) is likely associated with the risk of type 2 diabetes mellitus (T2DM) via β cell function modification, but the evidence on the association remains unclear. This study aimed to investigate the relationship between the ABCA1 69C>T polymorphism and the risk of T2DM through a systematic review and meta-analysis.

Materials and Methods

The PubMed, Web of Science, and Embase databases were searched for qualified studies published until August 2020. Studies that included the association between the ABCA1 69C>T polymorphism and the risk of T2DM were reviewed. The odds ratios (ORs) and 95% confidence intervals (CIs) were evaluated.

Results

We analyzed data from a total of 10 studies involving 17,742 patients. We found that the CC or CT genotype was associated with increased risk of T2DM than the TT genotype (OR, 1.41; 95% CI, 1.02-1.93). In the Asian population, the C allele carriers had a higher risk of T2DM than those with the TT genotype; the ORs of the CC and CT genotypes were 1.80 (95% CI, 1.21-2.68) and 1.61 (95% CI, and 1.29-2.01), respectively.

Conclusions

This meta-analysis confirmed that the ABCA1 69C>T genotype showed a decrease risk of T2DM compared to the CC or CT genotypes.

Fetal High-Density Lipoproteins: Current Knowledge on Particle Metabolism, Composition and Function in Health and Disease

Cholesterol and other lipids carried by lipoproteins play an indispensable role in fetal development. Recent evidence suggests that maternally derived high-density lipoprotein (HDL) differs from fetal HDL with respect to its proteome, size, and function. Compared to the HDL of adults, fetal HDL is the major carrier of cholesterol and has a unique composition that implies other physiological functions. Fetal HDL is enriched in apolipoprotein E, which binds with high affinity to the low-density lipoprotein receptor. Thus, it appears that a primary function of fetal HDL is the transport of cholesterol to tissues as is accomplished by low-density lipoproteins in adults. The fetal HDL-associated bioactive sphingolipid sphingosine-1-phosphate shows strong vasoprotective effects at the fetoplacental vasculature. Moreover, lipoprotein-associated phospholipase A2 carried by fetal-HDL exerts anti-oxidative and athero-protective functions on the fetoplacental endothelium. Notably, the mass and activity of HDL-associated paraoxonase 1 are about 5-fold lower in the fetus, accompanied by an attenuation of anti-oxidative activity of fetal HDL. Cholesteryl ester transfer protein activity is reduced in fetal circulation despite similar amounts of the enzyme in maternal and fetal serum. This review summarizes the current knowledge on fetal HDL as a potential vasoprotective lipoprotein during fetal development. We also provide an overview of whether and how the protective functionalities of HDL are impaired in pregnancy-related syndromes such as pre-eclampsia or gestational diabetes mellitus.

[Exenatide promotes cholesterol efflux in pancreatic tissue of obese diabetic rats]

OBJECTIVE

To study the effect of exenatide on the expression of ABCA1 and cholesterol metabolism in the pancreas of obese diabetic rats.

OBJECTIVE

Twenty-four normal male SD rats and 18 obese diabetic rats (induced by high-fat feeding and STZ injection) were both divided equally into 2 groups for injections of saline or exenatide. After treatment for a week, the expression of ABCA1, cholesterol metabolism, and islet function of the rats were examined using real-time PCR, Western blotting, oil red O staining, cholesterol content determination, and HE staining.

OBJECTIVE

The expressions of ABCA1 at both mRNA and protein levels in pancreatic tissue were significantly lower in obese diabetic rats than in normal SD rats. The obese diabetic rats showed obvious lipid deposition and increased cholesterol content in the pancreatic tissue with significantly reduced islet volume and structural changes (P < 0.05); exenatide treatment of the diabetic rats significantly up-regulated ABCA1 expression, reduced lipid deposition and cholesterol content in pancreatic tissue, and increased number and volume of the islets, which presented with more orderly alignment (P < 0.05).

OBJECTIVE

Obese diabetic rats have lowered ABCA1 expression, cholesterol efflux block, and cholesterol accumulation in the pancreatic tissue. Exenatide can up-regulate ABCA1 expression and promote cholesterol efflux to reduce cholesterol content in the pancreatic tissue and improve islet function in obese diabetic rats.

Protection against Glucolipotoxicity by High Density Lipoprotein in Human PANC-1 Hybrid 1.1B4 Pancreatic Beta Cells: The Role of microRNA

High-density lipoproteins provide protection against the damaging effects of glucolipotoxicity in beta cells, a factor which sustains insulin secretion and staves off onset of type 2 diabetes mellitus. This study examines epigenetic changes in small non-coding microRNA sequences induced by high density lipoproteins in a human hybrid beta cell model, and tests the impact of delivery of a single sequence in protecting against glucolipotoxicity. Human PANC-1.1B4 cells were used to establish Bmax and Kd for [³H]cholesterol efflux to high density lipoprotein, and minimum concentrations required to protect cell viability and reduce apoptosis to 30mM glucose and 0.25 mM palmitic acid. Microchip array identified the microRNA signature associated with high density lipoprotein treatment, and one sequence, hsa-miR-21-5p, modulated via delivery of a mimic and inhibitor. The results confirm that low concentrations of high-density lipoprotein can protect against glucolipotoxicity, and report the global microRNA profile associated with this lipoprotein; delivery of miR-21-5p mimic altered gene targets, similar to high density lipoprotein, but could not provide sufficient protection against glucolipotoxicity. We conclude that the complex profile of microRNA changes due to HDL treatment may be difficult to replicate using a single microRNA, findings which may inform current drug strategies focused on this approach.

Proteostasis of Islet Amyloid Polypeptide: A Molecular Perspective of Risk Factors and Protective Strategies for Type II Diabetes

The possible link between hIAPP accumulation and β-cell death in diabetic patients has inspired numerous studies focusing on amyloid structures and aggregation pathways of this hormone. Recent studies have reported on the importance of early oligomeric intermediates, the many roles of their interactions with lipid membrane, pH, insulin, and zinc on the mechanism of aggregation of hIAPP. The challenges posed by the transient nature of amyloid oligomers, their structural heterogeneity, and the complex nature of their interaction with lipid membranes have resulted in the development of a wide range of biophysical and chemical approaches to characterize the aggregation process. While the cellular processes and factors activating hIAPP-mediated cytotoxicity are still not clear, it has recently been suggested that its impaired turnover and cellular processing by proteasome and autophagy may contribute significantly toward toxic hIAPP accumulation and, eventually, β-cell death. Therefore, studies focusing on the restoration of hIAPP proteostasis may represent a promising arena for the design of effective therapies. In this review we discuss the current knowledge of the structures and pathology associated with hIAPP self-assembly and point out the opportunities for therapy that a detailed biochemical, biophysical, and cellular understanding of its aggregation may unveil.

The Role of the ATP-Binding Cassette A1 (ABCA1) in Human Disease

Cholesterol homeostasis is essential in normal physiology of all cells. One of several proteins involved in cholesterol homeostasis is the ATP-binding cassette transporter A1 (ABCA1), a transmembrane protein widely expressed in many tissues. One of its main functions is the efflux of intracellular free cholesterol and phospholipids across the plasma membrane to combine with apolipoproteins, mainly apolipoprotein A-I (Apo A-I), forming nascent high-density lipoprotein-cholesterol (HDL-C) particles, the first step of reverse cholesterol transport (RCT). In addition, ABCA1 regulates cholesterol and phospholipid content in the plasma membrane affecting lipid rafts, microparticle (MP) formation and cell signaling. Thus, it is not surprising that impaired ABCA1 function and altered cholesterol homeostasis may affect many different organs and is involved in the pathophysiology of a broad array of diseases. This review describes evidence obtained from animal models, human studies and genetic variation explaining how ABCA1 is involved in dyslipidemia, coronary heart disease (CHD), type 2 diabetes (T2D), thrombosis, neurological disorders, age-related macular degeneration (AMD), glaucoma, viral infections and in cancer progression.

E17241 as a Novel ABCA1 (ATP-Binding Cassette Transporter A1) Upregulator Ameliorates Atherosclerosis in Mice

[Figure: see text].

A Common R219K Variant of ATP-Binding Cassette Transporter A1 Gene Alters Atherometabolic Traits in Pregnant Women With Gestational Diabetes Mellitus

BACKGROUND

ATP-binding cassette transporter A1 (ABCA1) has important roles in high-density lipoprotein (HDL) metabolism and reverse cholesterol transport, and is implicated in lipid-related disorders. Genetic variants are involved in the pathogenesis of gestational diabetes mellitus (GDM). The objective of this study was to investigate the association of rs2230806 (R219K), a single nucleotide polymorphism (SNP) in the lipid-related gene, with the risk of GDM and related traits.

METHODS

The SNP, rs2230806, was genotyped, and clinical and metabolic parameters were determined in 660 GDM patients and 1,097 control subjects. Genetic associations with related traits were also analyzed.

RESULTS

The genotype distributions were similar in GDM patients and normal controls. However, significant differences in the variables examined in the study subjects were noted across the three genotypes. The genotype at the rs2230806 polymorphism was significantly associated with HDL-cholesterol (HDL-C) levels and atherogenic index (AI) values in GDM patients and total cholesterol (TC) and low-density lipoprotein-cholesterol (LDL-C) levels in control subjects. Subgroup analysis showed that the polymorphism was associated with diastolic blood pressure, in addition to HDL-C levels and AI, in overweight/obese GDM patients, while it was associated with TC levels, AI, pre-pregnancy body mass index (BMI), and BMI at delivery in non-obese GDM patients. In addition, this polymorphism was associated with TC, LDL-C, and apoB levels in overweight/obese control subjects.

CONCLUSIONS

The rs2230806 polymorphism in the ABCA1 gene was associated with variations in atherometabolic traits in GDM patients, with characteristics of BMI dependency, but not with GDM. Our findings highlight a link between related phenotypes in women with GDM and genetic factors.

Transcriptomic and Quantitative Proteomic Profiling Reveals Signaling Pathways Critical for Pancreatic Islet Maturation

Pancreatic β-cell dysfunction and reduced insulin secretion play a key role in the pathogenesis of diabetes. Fetal and neonatal islets are functionally immature and have blunted glucose responsiveness and decreased insulin secretion in response to stimuli and are far more proliferative. However, the mechanisms underlying functional immaturity are not well understood. Pancreatic islets are composed of a mixture of different cell types, and the microenvironment of islets and interactions between these cell types are critical for β-cell development and maturation. RNA sequencing and quantitative proteomic data from intact islets isolated from fetal (embryonic day 19) and 2-week-old Sprague-Dawley rats were integrated to compare their gene and protein expression profiles. Ingenuity Pathway Analysis (IPA) was also applied to elucidate pathways and upstream regulators modulating functional maturation of islets. By integrating transcriptome and proteomic data, 917 differentially expressed genes/proteins were identified with a false discovery rate of less than 0.05. A total of 411 and 506 of them were upregulated and downregulated in the 2-week-old islets, respectively. IPA revealed novel critical pathways associated with functional maturation of islets, such as AMPK (adenosine monophosphate-activated protein kinase) and aryl hydrocarbon receptor signaling, as well as the importance of lipid homeostasis/signaling and neuronal function. Furthermore, we also identified many proteins enriched either in fetal or 2-week-old islets related to extracellular matrix and cell communication, suggesting that these pathways play critical roles in islet maturation. Our present study identified novel pathways for mature islet function in addition to confirming previously reported mechanisms, and provided new mechanistic insights for future research on diabetes prevention and treatment.

Structure and Function of Hepatobiliary ATP Binding Cassette Transporters

The liver is beyond any doubt the most important metabolic organ of the human body. This function requires an intensive crosstalk within liver cellular structures, but also with other organs. Membrane transport proteins are therefore of upmost importance as they represent the sensors and mediators that shuttle signals from outside to the inside of liver cells and/or vice versa. In this review, we summarize the known literature of liver transport proteins with a clear emphasis on functional and structural information on ATP binding cassette (ABC) transporters, which are expressed in the human liver. These primary active membrane transporters form one of the largest families of membrane proteins. In the liver, they play an essential role in for example bile formation or xenobiotic export. Our review provides a state of the art and comprehensive summary of the current knowledge of hepatobiliary ABC transporters. Clearly, our knowledge has improved with a breath-taking speed over the last few years and will expand further. Thus, this review will provide the status quo and will lay the foundation for new and exciting avenues in liver membrane transporter research.

β-Cell-Specific Deletion of HMG-CoA (3-hydroxy-3-methylglutaryl-coenzyme A) Reductase Causes Overt Diabetes due to Reduction of β-Cell Mass and Impaired Insulin Secretion

Inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase (HMGCR), statins, which are used to prevent cardiovascular diseases, are associated with a modest increase in the risk of new-onset diabetes. To investigate the role of HMGCR in the development of β-cells and glucose homeostasis, we deleted Hmgcr in a β-cell-specific manner by using the Cre-loxP technique. Mice lacking Hmgcr in β-cells (β-KO) exhibited hypoinsulinemic hyperglycemia as early as postnatal day 9 (P9) due to decreases in both β-cell mass and insulin secretion. Ki67-positive cells were reduced in β-KO mice at P9; thus, β-cell mass reduction was caused by proliferation disorder immediately after birth. The mRNA expression of neurogenin3 (Ngn3), which is transiently expressed in endocrine progenitors of the embryonic pancreas, was maintained despite a striking reduction in the expression of β-cell-associated genes, such as insulin, pancreatic and duodenal homeobox 1 (Pdx1), and MAF BZIP transcription factor A (Mafa) in the islets from β-KO mice. Histological analyses revealed dysmorphic islets with markedly reduced numbers of β-cells, some of which were also positive for glucagon. In conclusion, HMGCR plays critical roles not only in insulin secretion but also in the development of β-cells in mice.

The Variant rs1784042 of the SIDT2 Gene is Associated with Metabolic Syndrome through Low HDL-c Levels in a Mexican Population

The Mexican population has one of the highest prevalences of metabolic syndrome (MetS) worldwide. The aim of this study was to investigate the association of single-nucleotide polymorphisms (SNPs) with MetS and its components. First, we performed a pilot Genome-wide association study (GWAS) scan on a sub-sample derived from the Health Workers Cohort Study (HWCS) (n = 411). Based on GWAS results, we selected the rs1784042 and rs17120425 SNPs in the SIDT1 transmembrane family member 2 (SIDT2) gene for replication in the entire cohort (n = 1963), using predesigned TaqMan assays. We observed a prevalence of MetS in the HWCS of 52.6%. The minor allele frequency for the variant rs17120425 was 10% and 29% for the rs1784042. The SNP rs1784042 showed an overall association with MetS (OR = 0.82, p = 0.01) and with low levels of high-density lipoprotein (HDL-c) (odds ratio (OR) = 0.77, p = 0.001). The SNP rs17120425 had a significant association with type 2 diabetes (T2D) risk in the overall population (OR = 1.39, p = 0.033). Our results suggest an association of the rs1784042 and rs17120425 variants with MetS, through different mechanisms in the Mexican population. Further studies in larger samples and other populations are required to validate these findings and the relevance of these SNPs in MetS.

Cholesterol homeostasis: Researching a dialogue between the brain and peripheral tissues

Cholesterol homeostasis is a highly regulated process in human body because of its several functions underlying the biology of cell membranes, the synthesis of all steroid hormones and bile acids and the need of trafficking lipids destined to cell metabolism. In particular, it has been recognized that peripheral and central nervous system cholesterol metabolism are separated by the blood brain barrier and are regulated independently; indeed, peripherally, it depends on the balance between dietary intake and hepatic synthesis on one hand and its degradation on the other, whereas in central nervous system it is synthetized de novo to ensure brain physiology. In view of this complex metabolism and its relevant functions in mammalian, impaired levels of cholesterol can induce severe cellular dysfunction leading to metabolic, cardiovascular and neurodegenerative diseases. The aim of this review is to clarify the role of cholesterol homeostasis in health and disease highlighting new intriguing aspects of the cross talk between its central and peripheral metabolism.

R230C but not - 565C/T variant of the ABCA1 gene is associated with type 2 diabetes in Mexicans through an effect on lowering HDL-cholesterol levels

PURPOSE

Type 2 diabetes (T2D) and low serum concentration of high-density lipoprotein cholesterol (HDL-c) are common coexisting metabolic disorders. ABCA1 variants have been shown to be associated to these conditions. We sought to test the combined effect of two ABCA1 gene common variants, rs2422493 (- 565C > T) and rs9282541 (R230C) on HDL-c levels and T2D risk.

METHODS

Path analysis was conducted in 3,303 Mexican-mestizos to assess the specific contributions of rs2422493 and rs9282541 ABCA1 variants, insulin resistance, waist-to-height ratio (WHtR), and age on HDL-c levels and T2D risk. Participants were classified into four groups according to their ABCA1 variants carrier status: (i) the reference group carried wild type alleles for both ABCA1 variants (-/-), (ii)  +/-  were carriers of rs2422493 but non-carriers of rs9282541, (iii) -/+ for carriers of rs9282541 but not carriers of rs2422493 and (iv) carriers of minor alleles for both SNPs (+/+). Principal components from two previous genome-wide association studies were used to control for ethnicity.

RESULTS

We identified significant indirect effects on T2D risk mediated by HDL-c in groups -/+ and +/+ (β = 0.04; p = 0.03 and β = 0.06; p < 0.01, respectively) in comparison to the -/- reference group. Low concentrations of HDL-c were directly and significantly associated with increased T2D risk (β = -0.70; p < 0.01). WHtR, male gender, age, and insulin resistance were also associated with T2D risk (p < 0.05). There was no significant direct effect for any of the ABCA1 groups on T2D risk: p = 0.99, p = 0.58, and p = 0.91 for groups +/-, -/+, and +/+ respectively.

CONCLUSIONS

The ABCA1 rs9282541 (R230C) allele is associated with T2D in Mexicans through its effect on lowering HDL-c levels. This is the first report demonstrating that HDL-c levels act as an intermediate factor between an ABCA1 variant and T2D.

The type 2 diabetes gene product STARD10 is a phosphoinositide-binding protein that controls insulin secretory granule biogenesis

OBJECTIVE

Risk alleles for type 2 diabetes at the STARD10 locus are associated with lowered STARD10 expression in the β-cell, impaired glucose-induced insulin secretion, and decreased circulating proinsulin:insulin ratios. Although likely to serve as a mediator of intracellular lipid transfer, the identity of the transported lipids and thus the pathways through which STARD10 regulates β-cell function are not understood. The aim of this study was to identify the lipids transported and affected by STARD10 in the β-cell and the role of the protein in controlling proinsulin processing and insulin granule biogenesis and maturation.

METHODS

We used isolated islets from mice deleted selectively in the β-cell for Stard10 (βStard10KO) and performed electron microscopy, pulse-chase, RNA sequencing, and lipidomic analyses. Proteomic analysis of STARD10 binding partners was executed in the INS1 (832/13) cell line. X-ray crystallography followed by molecular docking and lipid overlay assay was performed on purified STARD10 protein.

RESULTS

βStard10KO islets had a sharply altered dense core granule appearance, with a dramatic increase in the number of "rod-like" dense cores. Correspondingly, basal secretion of proinsulin was increased versus wild-type islets. The solution of the crystal structure of STARD10 to 2.3 Å resolution revealed a binding pocket capable of accommodating polyphosphoinositides, and STARD10 was shown to bind to inositides phosphorylated at the 3' position. Lipidomic analysis of βStard10KO islets demonstrated changes in phosphatidylinositol levels, and the inositol lipid kinase PIP4K2C was identified as a STARD10 binding partner. Also consistent with roles for STARD10 in phosphoinositide signalling, the phosphoinositide-binding proteins Pirt and Synaptotagmin 1 were amongst the differentially expressed genes in βStard10KO islets.

CONCLUSION

Our data indicate that STARD10 binds to, and may transport, phosphatidylinositides, influencing membrane lipid composition, insulin granule biosynthesis, and insulin processing.

Lipid efflux mechanisms, relation to disease and potential therapeutic aspects

Lipids are hydrophobic and amphiphilic molecules involved in diverse functions such as membrane structure, energy metabolism, immunity, and signaling. However, altered intra-cellular lipid levels or composition can lead to metabolic and inflammatory dysfunction, as well as lipotoxicity. Thus, intra-cellular lipid homeostasis is tightly regulated by multiple mechanisms. Since most peripheral cells do not catabolize cholesterol, efflux (extra-cellular transport) of cholesterol is vital for lipid homeostasis. Defective efflux contributes to atherosclerotic plaque development, impaired β-cell insulin secretion, and neuropathology. Of these, defective lipid efflux in macrophages in the arterial walls leading to foam cell and atherosclerotic plaque formation has been the most well studied, likely because a leading global cause of death is cardiovascular disease. Circulating high density lipoprotein particles play critical roles as acceptors of effluxed cellular lipids, suggesting their importance in disease etiology. We review here mechanisms and pathways that modulate lipid efflux, the role of lipid efflux in disease etiology, and therapeutic options aimed at modulating this critical process.

High-density lipoproteins during sepsis: from bench to bedside

High-density lipoproteins (HDLs) represent a family of particle characterized by the presence of apolipoprotein A-I (apoA-I) and by their ability to transport cholesterol from peripheral tissues back to the liver conferring them a cardioprotective function. HDLs also display pleiotropic properties including antioxidant, anti-apoptotic, anti-thrombotic, anti-inflammatory, or anti-infectious functions. Clinical data demonstrate that HDL cholesterol levels decrease rapidly during sepsis and that these low levels are correlated with morbi-mortality. Experimental studies emphasized notable structural and functional modifications of HDL particles in inflammatory states, including sepsis. Finally, HDL infusion in animal models of sepsis improved survival and provided a global endothelial protective effect. These clinical and experimental studies reinforce the potential of HDL therapy in human sepsis. In this review, we will detail the different effects of HDLs that may be relevant under inflammatory conditions and the lipoprotein changes during sepsis and we will discuss the potentiality of HDL therapy in sepsis.

ABCA12 regulates insulin secretion from β-cells

Dysregulation of lipid homeostasis is intimately associated with defects in insulin secretion, a key feature of type 2 diabetes. Here, we explore the role of the putative lipid transporter ABCA12 in regulating insulin secretion from β-cells. Mice with β-cell-specific deletion of Abca12 display impaired glucose-stimulated insulin secretion and eventual islet inflammation and β-cell death. ABCA12's action in the pancreas is independent of changes in the abundance of two other cholesterol transporters, ABCA1 and ABCG1, or of changes in cellular cholesterol or ceramide content. Instead, loss of ABCA12 results in defects in the genesis and fusion of insulin secretory granules and increases in the abundance of lipid rafts at the cell membrane. These changes are associated with dysregulation of the small GTPase CDC42 and with decreased actin polymerisation. Our findings establish a new, pleiotropic role for ABCA12 in regulating pancreatic lipid homeostasis and insulin secretion.

ABCA1 Variants rs1800977 (C69T) and rs9282541 (R230C) Are Associated with Susceptibility to Type 2 Diabetes

OBJECTIVE

Accumulated evidence suggests that ATP-binding cassette A1 transporter (ABCA1) contributes to secreting insulin in pancreatic β-cells and amyloid beta formation. This study aimed to investigate the association between three single nucleotide polymorphisms (SNPs) of ABCA1 and susceptibility to type 2 diabetes mellitus (T2DM) in a Han Chinese population.

METHODS

A total of 996 T2DM patients and 1,002 controls were included in the study. Three SNPs in the ABCA1 gene, i.e., rs2230806 (R219K), rs1800977 (C69T), and rs9282541 (R230C), were genotyped by SNaPshot. A genotype model, an allele model, a dominant model, and a recessive model were used to assess susceptibility to T2DM.

RESULTS

There were significant associations between rs1800977 and T2DM in different genetic models (TT vs. CC, OR = 0.591 [0.446-0.793], p < 0.001; T vs. C, OR = 0.835 [0.735-0.949], p = 0.006; recessive model, OR = 0.583 [0.449-0.756], p < 0.001). There were also significant associations between rs9282541 and T2DM in different genetic models (CT vs. CC, OR = 1.690 [0.807-1.005], p = 0.048; T vs. C, OR = 1.756 [0.694-1.060], p = 0.029; dominant model, OR = 1.735 [0.715-1.034], p = 0.037).

CONCLUSION

Our case-control study showed that the two SNPs rs1800977 and rs9282541 in the ABCA1 gene are significantly associated with susceptibility to T2DM in our Han Chinese population. Study of further mechanisms should be performed before application to clinical therapy.

Role of ATP-binding cassette transporter A1 in suppressing lipid accumulation by glucagon-like peptide-1 agonist in hepatocytes

Objective

Adenosine triphosphate (ATP)-binding cassette transporter A1 (ABCA1) influences hepatic cholesterol transportation. Accumulation of hepatic cholesterol leads to fatty liver disease, which is improved by glucagon-like peptide 1 (GLP-1) in diabetes. Therefore, we analyzed the molecular mechanism in the regulation of hepatic ABCA1 by GLP-1 analogue exendin-4.

Methods

Hepatic ABCA1 expression and transcription were checked by western blotting, real-time polymerase chain reaction (PCR), and luciferase assay in HepG2 cells. Chromatin immunoprecipitation (ChIP) and site-directed mutagenesis were employed to determine transcriptional regulation of the ABCA1 gene. Prolactin regulatory element-binding (PREB)-transgenic mice were generated to access the effect of exendin-4 on improving lipid accumulation caused by a high-fat diet (HFD).

Results

Exendin-4 stimulated hepatic ABCA1 expression and transcription via the Ca²⁺/calmodulin (CaM)-dependent protein kinase kinase/CaM-dependent protein kinase IV (CaMKK/CaMKIV) pathway, whereas GLP-1 receptor antagonist exendin9-39 cancelled this effect. Therefore, exendin-4 decreased hepatic lipid content. ChIP showed that PREB could directly bind to the ABCA1 promoter, which was enhanced by exendin-4. Moreover, PREB stimulated ABCA1 promoter activity, and mutation of PREB-binding site in ABCA1 promoter cancelled exendin-4-enhanced ABCA1 promoter activity. Silencing of PREB attenuated the effect of exendin-4 and induced hepatic cholesterol accumulation. Blockade of CaMKK by STO-609 or siRNA cancelled the upregulation of ABCA1 and PREB induced by exendin-4. In vivo, exendin-4 or overexpression of PREB increased hepatic ABCA1 expression and decreased hepatic lipid accumulation and high plasma cholesterol caused by a HFD.

Conclusions

Our data shows that exendin-4 stimulates hepatic ABCA1 expression and decreases lipid accumulation by the CaMKK/CaMKIV/PREB pathway, suggesting that ABCA1 and PREB might be the therapeutic targets in fatty liver disease.

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The GLP-1R agonist exendin-4 suppressed lipid accumulation by upregulating ABCA1 expression in hepatocytes.

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Exendin-4 regulated the expression and transcription of hepatic ABCA1 via the CaMKK/CaMKIV/PREB pathway.

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Overexpression of PREB or exendin-4 protected mouse liver from fatty liver by upregulation of ABCA1.

HDL inhibits endoplasmic reticulum stress-induced apoptosis of pancreatic β-cells in vitro by activation of Smoothened

Loss of pancreatic β-cell mass and function as a result of sustained ER stress is a core step in the pathogenesis of diabetes mellitus type 2. The complex control of β-cells and insulin production involves hedgehog (Hh) signaling pathways as well as cholesterol-mediated effects. In fact, data from studies in humans and animal models suggest that HDL protects against the development of diabetes through inhibition of ER stress and β-cell apoptosis. We investigated the mechanism by which HDL inhibits ER stress and apoptosis induced by thapsigargin, a sarco/ER Ca²⁺-ATPase inhibitor, in β-cells of a rat insulinoma cell line, INS1e. We further explored effects on the Hh signaling receptor Smoothened (SMO) with pharmacologic agonists and inhibitors. Interference with sterol synthesis or efflux enhanced β-cell apoptosis and abrogated the anti-apoptotic activity of HDL. During ER stress, HDL facilitated the efflux of specific oxysterols, including 24-hydroxycholesterol (OHC). Supplementation of reconstituted HDL with 24-OHC enhanced and, in cells lacking ABCG1 or the 24-OHC synthesizing enzyme CYP46A1, restored the protective activity of HDL. Inhibition of SMO countered the beneficial effects of HDL and also LDL, and SMO agonists decreased β-cell apoptosis in the absence of ABCG1 or CYP46A1. The translocation of the SMO-activated transcription factor glioma-associated oncogene GLI-1 was inhibited by ER stress but restored by both HDL and 24-OHC. In conclusion, the protective effect of HDL to counter ER stress and β-cell death involves the transport, generation, and mobilization of oxysterols for activation of the Hh signaling receptor SMO.

Comorbidities of HIV infection: role of Nef-induced impairment of cholesterol metabolism and lipid raft functionality

Combination antiretroviral therapy has dramatically changed the outcome of HIV infection, turning it from a death sentence to a manageable chronic disease. However, comorbidities accompanying HIV infection, such as metabolic and cardio-vascular diseases, as well as cognitive impairment, persist despite successful virus control by combination antiretroviral therapy and pose considerable challenges to clinical management of people living with HIV. These comorbidities involve a number of pathological processes affecting a variety of different tissues and cells, making it challenging to identify a common cause(s) that would link these different diseases to HIV infection. In this article, we will present evidence that impairment of cellular cholesterol metabolism may be a common factor driving pathogenesis of HIV-associated comorbidities. Potential implications for therapeutic approaches are discussed.

Effects of Sodium-Glucose Cotransporter 2 Inhibition on Glucose Metabolism, Liver Function, Ascites, and Hemodynamics in a Mouse Model of Nonalcoholic Steatohepatitis and Type 2 Diabetes

Many blood glucose-lowering drugs cannot be used once patients with type 2 diabetes (T2D) and nonalcoholic fatty liver disease develop nonalcoholic steatohepatitis (NASH). Therefore, such patients often require insulin treatment. We aimed to determine the effect of sodium-glucose cotransporter 2 inhibitor (SGLT2i) dapagliflozin monotherapy on glucose metabolism in a mouse model of NASH/T2D, with a focus on its diuretic effects. To imitate ascites and to determine its severity by imaging, meglumine sodium amidotrizoate (MSA) was infused into the abdominal cavities of mice. The reduction in ascites induced by dapagliflozin was compared with that induced by furosemide using microcomputed tomography. The effects of each drug on hemodynamics were also compared. A dapagliflozin-related improvement in glucose tolerance was achieved in mice fed a high-fat diet (HFD) or an HFD + methionine-and-choline-deficient diet (MCDD). In dapagliflozin-treated NASH mice, hypoglycemia was not identified during 24-hour casual blood glucose monitoring. In the dapagliflozin and furosemide-treated groups, the time taken for the resolution of artificial ascites was significantly shorter than in the untreated group, and there were no significant differences between these groups. Furosemide significantly reduced the blood pressure and significantly increased the heart rate of the mice. Dapagliflozin caused a mild decrease in systolic, but not diastolic blood pressure, and the heart rate and circulating catecholamine and renin-aldosterone concentrations were unaffected. Dapagliflozin treatment improved glycemic control in the NASH mice versus untreated mice. Thus, dapagliflozin had a prompt diuretic effect but did not adversely affect the hemodynamics of mice with NASH and T2D. Therefore, it may be useful for the treatment of patients with both T2D and liver cirrhosis.

Apolipoprotein A-I primes beta cells to increase glucose stimulated insulin secretion

The increase of plasma levels of high-density lipoproteins and Apolipoprotein A-I (ApoA-I), its main protein component, has been shown to have a positive action on glucose disposal in type 2 diabetic patients. The current study investigates the unexplored function of ApoA-I to prime beta cells for improved insulin secretion. INS-1E rat clonal beta cells as well as isolated murine islets were used to study the effect of ApoA-I on responsiveness of the beta cells to high glucose challenge. Confocal and transmission electron microscopy were used to dissect ApoA-I mechanisms of action. Chemical endocytosis blockers were used to understand the role of ApoA-I internalization in mediating its positive effect. Pre-incubation of beta cells and isolated murine islets with ApoA-I augmented glucose stimulated insulin secretion. This effect appeared to be due to an increased reservoir of insulin granules at the cell membrane, as confirmed by confocal and transmission electron microscopy. Moreover, ApoA-I induced pancreatic and duodenal homeobox 1 (PDX1) shuttling from the cytoplasm to the nucleus, with the subsequent increase in the proinsulin processing enzyme protein convertase 1 (PC1/3). Finally, the blockade of ApoA-I endocytosis in beta cells resulted in a loss of ApoA-I positive action on insulin secretion. The proposed mechanisms of the phenomenon here described include ApoA-I internalization into beta cells, PDX1 nuclear translocation, and increased levels of proinsulin processing enzymes. Altogether, these events lead to an increased number of insulin granules.

Fine-tuning of microRNAs in Type 2 Diabetes Mellitus

Type 2 diabetes mellitus is a metabolic disease widely spread across industrialized countries. Sedentary lifestyle and unhealthy alimentary habits lead to obesity, boosting both glucose and fatty acid in the bloodstream and eventually, insulin resistance, pancreas inflammation and faulty insulin production or secretion, all of them very well-defined hallmarks of type 2 diabetes mellitus. miRNAs are small sequences of non-coding RNA that may regulate several processes within the cells, fine-tuning protein expression, with an unexpected and subtle precision and in time-frames ranging from minutes to days. Since the discovery of miRNA and their possible implication in pathologies, several groups aimed to find a relationship between type 2 diabetes mellitus and miRNAs. Here we discuss the pattern of expression of different miRNAs in cultured cells, animal models and diabetic patients. We summarize the role of the most important miRNAs involved in pancreas growth and development, insulin secretion and liver, skeletal muscle or adipocyte insulin resistance in the context of type 2 diabetes mellitus.

HDL Cholesterol Efflux Predicts Incident New-Onset Diabetes After Transplantation (NODAT) in Renal Transplant Recipients Independent of HDL Cholesterol Levels

In renal transplant recipients (RTRs), new-onset diabetes after transplantation (NODAT) is a frequent and serious complication limiting survival of graft and patient. However, the underlying pathophysiology remains incompletely understood. In vitro and in preclinical models, HDL can preserve β-cell function, largely by mediating cholesterol efflux, but this concept has not been evaluated in humans. This study investigated whether baseline cholesterol efflux capacity (CEC) in RTRs is associated with incident NODAT during follow-up. This prospective longitudinal study included 405 diabetes-free RTRs with a functioning graft for >1 year. During a median (interquartile range) follow-up of 9.6 (6.6-10.2) years, 57 patients (14.1%) developed NODAT. HDL CEC was quantified using incubation of human macrophage foam cells with apolipoprotein B-depleted plasma. Baseline CEC was significantly lower in patients developing NODAT during follow-up (median 6.84% [interquartile range 5.84-7.50%]) compared with the NODAT-free group (7.44% [6.46-8.60%]; P = 0.001). Kaplan-Meier analysis showed a lower risk for incident NODAT with increasing sex-stratified tertiles of HDL efflux capacity (P = 0.004). Linear regression analysis indicated that CEC is independently associated with incident NODAT (P = 0.04). In Cox regression analyses, CEC was significantly associated with NODAT (hazard ratio 0.53 [95% CI 0.38-0.76]; P < 0.001), independent of HDL cholesterol levels (P = 0.015), adiposity (P = 0.018), immunosuppressive medication (P = 0.001), and kidney function (P = 0.01). Addition of CEC significantly improved the predictive power of the Framingham Diabetes Risk Score (P = 0.004). This study establishes HDL CEC as a strong predictor of NODAT in RTRs, independent of several other recognized risk factors.

Attenuation Effects of Bulk and Nanosized ZnO on Glucose, Lipid Level, and Inflammation Profile in Obese Mice

ZnO and ZnO nanoparticles (ZnO NPs) are widely used in food packaging, food preservation, cosmetic preparation, and animal feed. ZnO is alleged showing multiple bioactivities including antimicrobial and anti-inflammation. It is hypothesized in this study that bulk ZnO and ZnO NPs could attenuate symptoms associated with high-fat-diet-induced obesity. Bulk ZnO and ZnO NPs with diameters of 30 and 90 nm were administered to high-fat-diet (HFD)-induced obese mice. Body weight, liver and fat tissue indices of ZnO-treated mice were decreased compared with those of obese mice (MOD). Blood glucose levels in oral glucose tolerant test and insulin tolerant test of ZnO-treated mice were lower than those of MOD. Serum lipid profile of ZnO-treated mice was ameliorated with lower total cholesterol, total triglyceride, and low-density lipoprotein cholesterol levels compared with that of MOD. In addition, the levels of serum IL-1β and LPS-binding protein were also decreased by ZnO treatment. Both bulk and nanosized ZnO could attenuate HFD-induced phenotypes related with obesity, but ZnO NP is more efficient to lower the fat index and bulk ZnO is better to restore the disturbed serum lipid profile.

Reciprocal Multifaceted Interaction Between HDL (High-Density Lipoprotein) and Myocardial Infarction

Despite decades of therapeutic advances, myocardial infarction remains a leading cause of death worldwide. Recent studies have identified HDLs (high-density lipoproteins) as a potential candidate for mitigating coronary ischemia/reperfusion injury via a broad spectrum of signaling pathways. HDL ligands, such as S1P (sphingosine-1-phosphate), Apo (apolipoprotein) A-I, clusterin, and miRNA, may influence the opening of the mitochondrial channel, insulin sensitivity, and production of vascular autacoids, such as NO, prostacyclin, and endothelin-1. In parallel, antioxidant activity and sequestration of oxidized molecules provided by HDL can attenuate the oxidative stress that triggers ischemia/reperfusion. Nevertheless, during myocardial infarction, oxidation and the capture of oxidized and proinflammatory molecules generate large phenotypic and functional changes in HDL, potentially limiting its beneficial properties. In this review, new findings from cellular and animal models, as well as from clinical studies, will be discussed to describe the cardioprotective benefits of HDL on myocardial infarction. Furthermore, mechanisms by which HDL modulates cardiac function and potential strategies to mitigate postmyocardial infarction risk damage by HDL will be detailed throughout the review.

Exosomes containing HIV protein Nef reorganize lipid rafts potentiating inflammatory response in bystander cells

HIV infection has a profound effect on “bystander” cells causing metabolic co-morbidities. This may be mediated by exosomes secreted by HIV-infected cells and containing viral factors. Here we show that exosomes containing HIV-1 protein Nef (exNef) are rapidly taken up by macrophages releasing Nef into the cell interior. This caused down-regulation of ABCA1, reduction of cholesterol efflux and sharp elevation of the abundance of lipid rafts through reduced activation of small GTPase Cdc42 and decreased actin polymerization. Changes in rafts led to re-localization of TLR4 and TREM-1 to rafts, phosphorylation of ERK1/2, activation of NLRP3 inflammasome, and increased secretion of pro-inflammatory cytokines. The effects of exNef on lipid rafts and on inflammation were reversed by overexpression of a constitutively active mutant of Cdc42. Similar effects were observed in macrophages treated with exosomes produced by HIV-infected cells or isolated from plasma of HIV-infected subjects, but not with exosomes from cells and subjects infected with ΔNef-HIV or uninfected subjects. Mice injected with exNef exhibited monocytosis, reduced ABCA1 in macrophages, increased raft abundance in monocytes and augmented inflammation. Thus, Nef-containing exosomes potentiated pro-inflammatory response by inducing changes in cholesterol metabolism and reorganizing lipid rafts. These mechanisms may contribute to HIV-associated metabolic co-morbidities.

HIV infects only a limited repertoire of cells expressing HIV receptors. Nevertheless, co-morbidities of HIV infection, such as atherosclerosis, dementia, renal impairment, myocardial pathology, abnormal haematopoiesis and others, involve dysfunction of cells that can not be infected by HIV. These co-morbidities persist even after successful application of antiretroviral therapy, when no virus is found in the blood. Many co-morbidities of HIV have a common element in their pathogenesis, impairment of cholesterol metabolism. In this study we show that HIV protein Nef released from infected cells in extracellular vesicles is taken up by un-infected (‘bystander’) cells impairing cholesterol metabolism in these cells. This impairment causes formation of excessive lipid rafts, re-localization of the inflammatory receptors into rafts, and triggers inflammation. These mechanisms may contribute to HIV-associated metabolic co-morbidities. Our work demonstrates how a single viral factor released from infected cells into circulation may cause a pleiotropy of pathogenic responses.

Pregnancy dietary cholesterol intake, major dietary cholesterol sources, and the risk of gestational diabetes mellitus: A prospective cohort study

BACKGROUND & AIMS

The Scientific Report of 2015 Dietary Guidelines Advisory Committee recommended the elimination of dietary cholesterol limits. However, cholesterol intake increases during pregnancy and studies regarding the association between dietary cholesterol and gestational diabetes mellitus (GDM) are limited. We evaluate the association of total dietary cholesterol and different sources of cholesterol intake during pregnancy, with GDM risk and blood glucose levels in a Chinese prospective cohort study.

METHODS

A total of 2124 pregnant women from the Tongji Maternal and Child Health Cohort was included. A validated semi-quantitative food frequency questionnaire was used to assess dietary cholesterol intake prior to GDM diagnosis. GDM was diagnosed by the 75-g 2-h oral glucose tolerance test. Cubic-restricted spline function and logistic regression analyses were used to evaluate the association between dietary cholesterol intake during pregnancy and GDM. Generalized linear models were conducted to examine the associations of cholesterol intake with fasting blood glucose (FBG), 1-h post-load blood glucose (PBG) and 2-h PBG.

RESULTS

The average dietary cholesterol intake was 379.1 mg/d, and cholesterol from eggs explained 64.2% of the variability. Total dietary cholesterol intake and cholesterol from eggs rather than other foods, were linearly associated with GDM risk, with adjusted OR for GDM of 2.10 (95%CI: 1.24, 3.58) for total cholesterol intake and 1.83 (95%CI: 1.08, 3.07) for cholesterol from eggs comparing the highest versus lowest quintile. A 100-mg/d increase in total cholesterol and cholesterol from eggs intake were associated with an increased GDM risk by 18% and 16%, respectively. Moreover, higher maternal dietary total cholesterol could increase FBG and 1-h PBG, while cholesterol from eggs increased FBG only.

CONCLUSION

Higher dietary cholesterol from eggs intake during pregnancy was associated with greater risk of GDM.

[Antidiabetic role of high density lipoproteins]

Disturbance in lipid metabolism can be both a cause and a consequence of the development of diabetes mellitus (DM). One of the most informative indicator of lipid metabolism is the ratio of atherogenic and antiatherogenic fractions of lipoproteins and their protein components. The review summarizes literature data and own results indicating the important role of high-density lipoprotein (HDL) and their main protein component, apolipoprotein A-I (apoA-I), in the pathogenesis of type 2 DM. On the one hand, HDL are involved in the regulation of insulin secretion by b-cells and insulin-independent absorption of glucose. On the other hand, insulin resistance and hyperglycemia lead to a decrease in HDL levels and cause modification of their protein component. In addition, HDL, possessing anti-inflammatory and mitogenic properties, provide anti-diabetic protection through systemic mechanisms. Thus, maintaining a high concentration of HDL and apoA-I in blood plasma and preventing their modification are important issues in the context of prevention and treatment of diabetes.

The direct effect of lobeglitazone, a new thiazolidinedione, on pancreatic beta cells: A comparison with other thiazolidinediones

AIMS

The direct effects of thiazolidinediones (TZDs) on pancreatic beta cells have been controversial. The aim of this study was to find out whether a novel TZD, lobeglitazone, has beneficial effects on pancreatic beta cells and db/db mice compared to those of other TZDs.

METHODS

INS-1 cells were incubated at a high-glucose concentration with various concentrations of troglitazone, rosiglitazone, pioglitazone, and lobeglitazone. Apoptosis and proliferation of beta cells, markers for ER stress and glucose-stimulated insulin secretion (GSIS) were assessed. In addition, C57BL/6 db/db mice were treated with pioglitazone or lobeglitazone for 4 weeks, and metabolic parameters and the configuration of pancreatic islets were also examined.

RESULTS

Lobeglitazone and other TZDs decreased INS-1 cell apoptosis in high-glucose conditions. Lobeglitazone and other TZDs significantly decreased hyperglycemia-induced increases in ER stress markers and increased GSIS. Metabolic parameters showed greater improvement in db/db mice treated with pioglitazone and lobeglitazone than in control mice. Islet size, cell proliferation, and beta cell mass were increased, and collagen surrounding the islets was decreased in treated mice.

CONCLUSIONS

Lobeglitazone showed beneficial effects on beta cell survival and function against hyperglycemia. The prosurvival and profunction effects of lobeglitazone were comparable to those of other TZDs.

Association of hemoglobin A1C with circulating metabolites in Dutch with European, African Surinamese and Ghanaian background

BACKGROUND

The prevalence of type 2 diabetes mellitus (T2DM) varies significantly across ethnic groups. A better understanding of the mechanisms underlying the variation in different ethnic groups may help to elucidate the pathophysiology of T2DM. The present work aims to generate a hypothesis regarding "why do subjects with African background have excess burden of T2DM?".

METHODS

In the current study, we performed metabolite profiling of plasma samples derived from 773 subjects of three ethnic groups (Dutch with European, Ghanaian and African Surinamese background). We performed Bayesian lognormal regression analyses to assess associations between HbA1c and circulating metabolites.

RESULTS

Here we show that subjects with African Surinamese and Ghanaian background had similar associations of HbA1c with circulating amino acids and triglyceride-rich lipoproteins as subjects with European background. In contrast, subjects with Ghanaian and African Surinamese background had different associations of HbA1c with acetoacetate, small LDL particle and small HDL particle concentrations, compared to the subjects with European background.

CONCLUSIONS

On the basis of the observations, we hypothesize that the excess burden of T2DM in subjects with African background may be due to impaired cholesterol efflux capacity or abnormal cholesterol uptake.

Apolipoprotein A-I improves pancreatic β-cell function independent of the ATP-binding cassette transporters ABCA1 and ABCG1

Apolipoprotein A-I (apoA-I), the main protein constituent of HDLs, increases insulin synthesis and insulin secretion in pancreatic β cells. ApoA-I also accepts cholesterol that effluxes from cells expressing ATP-binding cassette transporter A1 (ABCA1) and ATP-binding cassette transporter G₁ (ABCG1). Mice with conditional deletion of ABCA1 and ABCG1 in β cells [β-double knockout (DKO) mice] have increased islet cholesterol levels and reduced glucose-stimulated insulin secretion (GSIS). The project asks whether metabolic pathways are dysregulated in β-DKO mouse islets and whether this can be corrected, and GSIS improved, by treatment with apoA-I. β-DKO mice were treated with apoA-I or PBS, and islets were isolated for determination of GSIS. Total RNA was extracted from β-DKO and control mouse islets for microarray analysis. Metabolic pathways were interrogated by functional enrichment analysis. ApoA-I treatment improved GSIS in β-DKO but not control mouse islets. Plasma lipid and lipoprotein levels and islet cholesterol levels were also unaffected by treatment with apoA-I. Cholesterol metabolism, glucose metabolism, and inflammation pathways were dysregulated in β-DKO mouse islets. This was not corrected by treatment with apoA-I. In summary, apoA-I treatment improves GSIS by a cholesterol-independent mechanism, but it does not correct metabolic dysregulation in β-DKO mouse islets.-Hou, L., Tang, S., Wu, B. J., Ong, K.-L., Westerterp, M., Barter, P. J., Cochran, B. J., Tabet, F., Rye, K.-A. Apolipoprotein A-I improves pancreatic β-cell function independent of the ATP-binding cassette transporters ABCA1 and ABCG1.

ABCA1 and metabolic syndrome; a review of the ABCA1 role in HDL-VLDL production, insulin-glucose homeostasis, inflammation and obesity

ATP-binding cassette transporter A1 (ABCA1) is an integral cell-membrane protein that mediates the rate-limiting step of high density lipoprotein (HDL) biogenesis and suppression of inflammation by triggering a number of signaling pathways via interacting with an apolipoprotein acceptor. The hepatic ABCA1 is involved in regulation of very low density lipoprotein (VLDL) production by affecting the apolipoprotein B trafficking and lipidation of VLDL particles. This protein is involved in protecting the function of pancreatic β-cells and insulin secretion by cholesterol homeostasis. Adipose tissue lipolysis is associated with ABCA1 activity. This transporter is involved in controlling obesity and insulin sensitivity by regulating triglyceride (TG) lipolysis and influencing on adiponectin, visfatin, leptin, and GLUT4 genes expression. The ABCA1 of skeletal muscle cells play a role in increasing the glucose uptake by enhancing the Akt phosphorylation and transferring GLUT4 to the plasma membrane. Abnormal status of ABCA1-regulated phenotypes is observed in metabolic syndrome. This syndrome is associated with the occurrence of many diseases. This review is a summary of the role of ABCA1 in HDL and VLDL production, homeostasis of insulin and glucose, suppression of inflammation and obesity controlling to provide a better insight into the association of this protein with metabolic syndrome.

AAV8-mediated gene transfer of microRNA-132 improves beta cell function in mice fed a high-fat diet

MicroRNAs have emerged as essential regulators of beta cell function and beta cell proliferation. One of these microRNAs, miR-132, is highly induced in several obesity models and increased expression of miR-132 in vitro modulates glucose-stimulated insulin secretion. The aim of this study was to investigate the therapeutic benefits of miR-132 overexpression on beta cell function in vivo. To overexpress miR-132 specifically in beta cells, we employed adeno-associated virus (AAV8)-mediated gene transfer using the rat insulin promoter in a double-stranded, self-complementary AAV vector to overexpress miR-132. Treatment of mice with dsAAV8-RIP-mir132 increased miR-132 expression in beta cells without impacting expression of miR-212 or miR-375. Surprisingly, overexpression of miR-132 did not impact glucose homeostasis in chow-fed animals. Overexpression of miR-132 did improve insulin secretion and hence glucose homeostasis in high-fat diet-fed mice. Furthermore, miR-132 overexpression increased beta cell proliferation in mice fed a high-fat diet. In conclusion, our data show that AAV8-mediated gene transfer of miR-132 to beta cells improves beta cell function in mice in response to a high-fat diet. This suggests that increased miR-132 expression is beneficial for beta cell function during hyperglycemia and obesity.

ATP-binding cassette transporter A1 (ABCA1) expression in adipose tissue and its modulation with insulin resistance in obesity

PURPOSE

Adipose tissue dysfunction is at the center of metabolic dysfunctions associated with obesity. Through studies in isolated adipocytes and mouse models, ATP-binding cassette transporter A1 (ABCA1) expression in the adipose tissue has been shown to regulate high-density lipoprotein (HDL) cholesterol levels in the circulation and insulin sensitivity at both adipose tissue and whole-body levels. We aimed to explore the possible link between ABCA1 expression in the adipose tissue and metabolic derangements associated with obesity in humans.

PATIENTS AND METHODS

This exploratory study among individuals who were lean (body mass index [BMI]: 22.3±0.34 kg/m², n=28) and obese (BMI: 44.48±5.3 kg/m², n=34) compared the expression of ABCA1, adiponectin and GLUT4 (SLC2A4) in visceral and subcutaneous adipose tissue using quantitative real-time PCR and immunohistochemistry. Homeostatic model assessment for insulin resistance (HOMA-IR) and adipose tissue insulin resistance (adipo-IR) were used as insulin resistance markers.

RESULTS

Visceral adipose tissue from individuals who were obese had significantly lower ABCA1 (P=0.04 for mRNA and protein) and adiponectin (P=0.001 for mRNA) expression compared to that from lean individuals. Subcutaneous adipose tissue did not show any significant difference in the expression. When individuals were divided into insulin-sensitive (IS) and insulin-resistant (IR) groups based on HOMA-IR, IR individuals had lower ABCA1 (P=0.0001 for mRNA and P=0.009 for protein) expression compared to IS individuals in visceral adipose tissue, but not in subcutaneous adipose tissue. The difference was significant after adjusting for age, gender and BMI. ABCA1 mRNA expression in visceral adipose tissue correlated negatively with both HOMA-IR (r=-0.44, P=0.0003) and adipo-IR (r=-0.35, P=0.005) after adjusting for age, gender and BMI. ABCA1 expression in either visceral or subcutaneous adipose tissue did not have any significant correlation with HDL cholesterol levels or mean adipocyte area.

CONCLUSION

Obesity and insulin resistance are associated with lower expression of ABCA1 in visceral adipose tissue in humans.