Caveolin gene transfer improves glucose metabolism in diabetic mice

Oligonucleotide therapies for nonalcoholic steatohepatitis

Nonalcoholic steatohepatitis (NASH) represents a severe disease subtype of nonalcoholic fatty liver disease (NAFLD) that is thought to be highly associated with systemic metabolic abnormalities. It is characterized by a series of substantial liver damage, including hepatocellular steatosis, inflammation, and fibrosis. The end stage of NASH, in some cases, may result in cirrhosis and hepatocellular carcinoma (HCC). Nowadays a large number of investigations are actively under way to test various therapeutic strategies, including emerging oligonucleotide drugs (e.g., antisense oligonucleotide, small interfering RNA, microRNA, mimic/inhibitor RNA, and small activating RNA) that have shown high potential in treating this fatal liver disease. This article systematically reviews the pathogenesis of NASH/NAFLD, the promising druggable targets proven by current studies in chemical compounds or biological drug development, and the feasibility and limitations of oligonucleotide-based therapeutic approaches under clinical or pre-clinical studies.

Caveolin-1 Is Essential for the Improvement of Insulin Sensitivity through AKT Activation during Glargine Treatment on Diabetic Mice

Insulin treatment was confirmed to reduce insulin resistance, but the underlying mechanism remains unknown. Caveolin-1 (Cav-1) is a functional protein of the membrane lipid rafts, known as caveolae, and is widely expressed in mammalian adipose tissue. There is increasing evidence that show the involvement of Cav-1 in the AKT activation, which is responsible for insulin sensitivity. Our aim was to investigate the effect of Cav-1 depletion on insulin sensitivity and AKT activation in glargine-treated type 2 diabetic mice. Mice were exposed to a high-fat diet and subject to intraperitoneal injection of streptozotocin to induce diabetes. Next, glargine was administered to treat T2DM mice for 3 weeks (insulin group). The expression of Cav-1 was then silenced by injecting lentiviral-vectored short hairpin RNA (shRNA) through the tail vein of glargine-treated T2DM mice (CAV1-shRNA group), while scramble virus injection was used as a negative control (Ctrl-shRNA group). The results showed that glargine was able to upregulate the expression of PI3K and activate serine phosphorylation of AKT through the upregulation of Cav-1 expression in paraepididymal adipose tissue of the insulin group. However, glargine treatment could not activate AKT pathway in Cav-1 silenced diabetic mice. These results suggest that Cav-1 is essential for the activation of AKT and improving insulin sensitivity in type 2 diabetic mice during glargine treatment.

SMPDL3b modulates insulin receptor signaling in diabetic kidney disease

Sphingomyelin phosphodiesterase acid-like 3b (SMPDL3b) is a lipid raft enzyme that regulates plasma membrane (PM) fluidity. Here we report that SMPDL3b excess, as observed in podocytes in diabetic kidney disease (DKD), impairs insulin receptor isoform B-dependent pro-survival insulin signaling by interfering with insulin receptor isoforms binding to caveolin-1 in the PM. SMPDL3b excess affects the production of active sphingolipids resulting in decreased ceramide-1-phosphate (C1P) content as observed in human podocytes in vitro and in kidney cortexes of diabetic db/db mice in vivo. Podocyte-specific Smpdl3b deficiency in db/db mice is sufficient to restore kidney cortex C1P content and to protect from DKD. Exogenous administration of C1P restores IR signaling in vitro and prevents established DKD progression in vivo. Taken together, we identify SMPDL3b as a modulator of insulin signaling and demonstrate that supplementation with exogenous C1P may represent a lipid therapeutic strategy to treat diabetic complications such as DKD.

Myocyte membrane and microdomain modifications in diabetes: determinants of ischemic tolerance and cardioprotection

Cardiovascular disease, predominantly ischemic heart disease (IHD), is the leading cause of death in diabetes mellitus (DM). In addition to eliciting cardiomyopathy, DM induces a ‘wicked triumvirate’: (i) increasing the risk and incidence of IHD and myocardial ischemia; (ii) decreasing myocardial tolerance to ischemia–reperfusion (I–R) injury; and (iii) inhibiting or eliminating responses to cardioprotective stimuli. Changes in ischemic tolerance and cardioprotective signaling may contribute to substantially higher mortality and morbidity following ischemic insult in DM patients. Among the diverse mechanisms implicated in diabetic impairment of ischemic tolerance and cardioprotection, changes in sarcolemmal makeup may play an overarching role and are considered in detail in the current review. Observations predominantly in animal models reveal DM-dependent changes in membrane lipid composition (cholesterol and triglyceride accumulation, fatty acid saturation vs. reduced desaturation, phospholipid remodeling) that contribute to modulation of caveolar domains, gap junctions and T-tubules. These modifications influence sarcolemmal biophysical properties, receptor and phospholipid signaling, ion channel and transporter functions, contributing to contractile and electrophysiological dysfunction, cardiomyopathy, ischemic intolerance and suppression of protective signaling. A better understanding of these sarcolemmal abnormalities in types I and II DM (T1DM, T2DM) can inform approaches to limiting cardiomyopathy, associated IHD and their consequences. Key knowledge gaps include details of sarcolemmal changes in models of T2DM, temporal patterns of lipid, microdomain and T-tubule changes during disease development, and the precise impacts of these diverse sarcolemmal modifications. Importantly, exercise, dietary, pharmacological and gene approaches have potential for improving sarcolemmal makeup, and thus myocyte function and stress-resistance in this ubiquitous metabolic disorder.

Caveolin-1 in the Pathogenesis of Diabetic Nephropathy: Potential Therapeutic Target?

PURPOSE OF REVIEW

Diabetic nephropathy, a major microvascular complication of diabetes and the most common cause of end-stage renal disease, is characterized by prominent accumulation of extracellular matrix. The membrane microdomains caveolae, and their integral protein caveolin-1, play critical roles in the regulation of signal transduction. In this review we discuss current knowledge of the contribution of caveolin-1/caveolae to profibrotic signaling and the pathogenesis of diabetic kidney disease, and assess its potential as a therapeutic target.

RECENT FINDINGS

Caveolin (cav)-1 is key to facilitating profibrotic signal transduction induced by several stimuli known to be pathogenic in diabetic nephropathy, including the most prominent factors hyperglycemia and angiotensin II. Phosphorylation of cav-1 on Y14 is an important regulator of these responses. In vivo studies support a pathogenic role for caveolae in the progression of diabetic nephropathy. Targeting caveolin-1/caveolae would enable inhibition of multiple profibrotic pathways, representing a novel and potentially potent therapeutic option for diabetic nephropathy.

Heterozygous caveolin-3 mice show increased susceptibility to palmitate-induced insulin resistance

Insulin resistance and diabetes are comorbidities of obesity and affect one in 10 adults in the United States. Despite the high prevalence, the mechanisms of cardiac insulin resistance in obesity are still unclear. We test the hypothesis that the insulin receptor localizes to caveolae and is regulated through binding to caveolin‐3 (CAV3). We further test whether haploinsufficiency for CAV3 increases the susceptibility to high‐fat‐induced insulin resistance. We used in vivo and in vitro studies to determine the effect of palmitate exposure on global insulin resistance, contractile performance of the heart in vivo, glucose uptake in the heart, and on cellular signaling downstream of the IR. We show that haploinsufficiency for CAV3 increases susceptibility to palmitate‐induced global insulin resistance and causes cardiomyopathy. On the basis of fluorescence energy transfer (FRET) experiments, we show that CAV3 and IR directly interact in cardiomyocytes. Palmitate impairs insulin signaling by a decrease in insulin‐stimulated phosphorylation of Akt that corresponds to an 87% decrease in insulin‐stimulated glucose uptake in HL‐1 cardiomyocytes. Despite loss of Akt phosphorylation and lower glucose uptake, palmitate increased insulin‐independent serine phosphorylation of IRS‐1 by 35%. In addition, we found lipid induced downregulation of CD36, the fatty acid transporter associated with caveolae. This may explain the problem the diabetic heart is facing with the simultaneous impairment of glucose uptake and lipid transport. Thus, these findings suggest that loss of CAV3 interferes with downstream insulin signaling and lipid uptake, implicating CAV3 as a regulator of the IR and regulator of lipid uptake in the heart.

Identifying gene-gene interactions that are highly associated with Body Mass Index using Quantitative Multifactor Dimensionality Reduction (QMDR)

Background

Despite heritability estimates of 40–70 % for obesity, less than 2 % of its variation is explained by Body Mass Index (BMI) associated loci that have been identified so far. Epistasis, or gene-gene interactions are a plausible source to explain portions of the missing heritability of BMI.

Methods

Using genotypic data from 18,686 individuals across five study cohorts – ARIC, CARDIA, FHS, CHS, MESA – we filtered SNPs (Single Nucleotide Polymorphisms) using two parallel approaches. SNPs were filtered either on the strength of their main effects of association with BMI, or on the number of knowledge sources supporting a specific SNP-SNP interaction in the context of BMI. Filtered SNPs were specifically analyzed for interactions that are highly associated with BMI using QMDR (Quantitative Multifactor Dimensionality Reduction). QMDR is a nonparametric, genetic model-free method that detects non-linear interactions associated with a quantitative trait.

Results

We identified seven novel, epistatic models with a Bonferroni corrected p-value of association < 0.1. Prior experimental evidence helps explain the plausible biological interactions highlighted within our results and their relationship with obesity. We identified interactions between genes involved in mitochondrial dysfunction (POLG2), cholesterol metabolism (SOAT2), lipid metabolism (CYP11B2), cell adhesion (EZR), cell proliferation (MAP2K5), and insulin resistance (IGF1R). Moreover, we found an 8.8 % increase in the variance in BMI explained by these seven SNP-SNP interactions, beyond what is explained by the main effects of an index FTO SNP and the SNPs within these interactions. We also replicated one of these interactions and 58 proxy SNP-SNP models representing it in an independent dataset from the eMERGE study.

Conclusion

This study highlights a novel approach for discovering gene-gene interactions by combining methods such as QMDR with traditional statistics.

Electronic supplementary material

The online version of this article (doi:10.1186/s13040-015-0074-0) contains supplementary material, which is available to authorized users.

Targeting fatty acid metabolism to improve glucose metabolism

Disturbances in fatty acid metabolism in adipose tissue, liver, skeletal muscle, gut and pancreas play an important role in the development of insulin resistance, impaired glucose metabolism and type 2 diabetes mellitus. Alterations in diet composition may contribute to prevent and/or reverse these disturbances through modulation of fatty acid metabolism. Besides an increased fat mass, adipose tissue dysfunction, characterized by an altered capacity to store lipids and an altered secretion of adipokines, may result in lipid overflow, systemic inflammation and excessive lipid accumulation in non-adipose tissues like liver, skeletal muscle and the pancreas. These impairments together promote the development of impaired glucose metabolism, insulin resistance and type 2 diabetes mellitus. Furthermore, intrinsic functional impairments in either of these organs may contribute to lipotoxicity and insulin resistance. The present review provides an overview of fatty acid metabolism-related pathways in adipose tissue, liver, skeletal muscle, pancreas and gut, which can be targeted by diet or food components, thereby improving glucose metabolism.

Caveolins in cardioprotection - translatability and mechanisms

Translation of preclinical treatments for ischaemia-reperfusion injury into clinical therapies has been limited by a number of factors. This review will focus on a single mode of cardiac protection related to a membrane scaffolding protein, caveolin, which regulates protective signalling as well as myocyte ultrastructure in the setting of ischaemic stress. Factors that have limited the clinical translation of protection will be considered specifically in terms of signalling and structural defects. The potential of caveolin to overcome barriers to protection with the ultimate hope of clinical translation will be discussed.

Caveolin-1 expression and cavin stability regulate caveolae dynamics in adipocyte lipid store fluctuation

Adipocytes specialized in the storage of energy as fat are among the most caveolae-enriched cell types. Loss of caveolae produces lipodystrophic diabetes in humans, which cannot be reversed by endothelial rescue of caveolin expression in mice, indicating major importance of adipocyte caveolae. However, how caveolae participate in fat cell functions is poorly understood. We investigated dynamic conditions of lipid store fluctuations and demonstrate reciprocal regulation of caveolae density and fat cell lipid droplet storage. We identified caveolin-1 expression as a crucial step in adipose cell lines and in mice to raise the density of caveolae, to increase adipocyte ability to accommodate larger lipid droplets, and to promote cell expansion by increased glucose utilization. In human subjects enrolled in a trial of 8 weeks of overfeeding to promote fattening, adipocyte expansion response correlated with initial caveolin-1 expression. Conversely, lipid mobilization in cultured adipocytes to induce lipid droplet shrinkage led to biphasic response of cavin-1 with ultimate loss of expression of cavin-1 and -3 and EHD2 by protein degradation, coincident with caveolae disassembly. We have identified the key steps in cavin/caveolin interplay regulating adipocyte caveolae dynamics. Our data establish that caveolae participate in a unique cell response connected to lipid store fluctuation, suggesting lipid-induced mechanotension in adipocytes.

Polysaccharide nano-vesicular multidrug carriers for synergistic killing of cancer cells

Multi-drug delivery based on polymer nano-scaffolds is an essential protocol to be developed for better administration of anticancer drugs to enhance their therapeutic efficacies against cancer cells. Here, we report dual delivery polysaccharide nano-vesicles that are capable of loading and delivering both water soluble and water insoluble drugs together in a single polymer scaffold. The selective rupture of the nano-vesicular assembly under intracellular enzyme conditions allowed the simultaneous delivery of a hydrophobic drug camptothecin (CPT) and hydrophilic drug doxorubicin (DOX) supporting their synergistic killing of breast and colon cancer cells. The polysaccharide nano-vesicles have allowed us to address a few important questions regarding the need for multiple drug administration in cancer cells including (a) the role of simultaneous drug release, (b) antagonistic versus synergistic effects of drug combinations and (c) how these are affected by the ratio of drugs. Further, evaluation of the role of caveolae in endocytosis of these polymer scaffolds was also made. The vesicular scaffolds were found to preserve and deliver DOX resulting in 50-60% better killing of cancer cells than the free drug. Additionally, dual loaded nano-vesicles when compared to drug cocktails with individual drugs in separate nano-vesicles (at comparable molar ratios) suggest the relative drug concentration following release and mode of delivery to be both important in cancer cell killing. Results from these experiments have revealed newly developed polysaccharide nano-vesicles loaded with DOX and CPT drugs as potential candidates for improved breast cancer cell killing. Thus, these custom-designed polysaccharide nano-vesicles provide a new perspective on multi-anticancer drug delivery systems and their efficacy.

Hypothalamic miR-103 protects from hyperphagic obesity in mice

The role of neuronal noncoding RNAs in energy control of the body is not fully understood. The arcuate nucleus (ARC) of the hypothalamus comprises neurons regulating food intake and body weight. Here we show that Dicer-dependent loss of microRNAs in these neurons of adult (DicerCKO) mice causes chronic overactivation of the signaling pathways involving phosphatidylinositol-3-kinase (PI3K), Akt, and mammalian target of rapamycin (mTOR) and an imbalance in the levels of neuropeptides, resulting in severe hyperphagic obesity. Similarly, the activation of PI3K-Akt-mTOR pathway due to Pten deletion in the adult forebrain leads to comparable weight increase. Conversely, the mTORC1 inhibitor rapamycin normalizes obesity in mice with an inactivated Dicer1 or Pten gene. Importantly, the continuous delivery of oligonucleotides mimicking microRNAs, which are predicted to target PI3K-Akt-mTOR pathway components, to the hypothalamus attenuates adiposity in DicerCKO mice. Furthermore, loss of miR-103 causes strong upregulation of the PI3K-Akt-mTOR pathway in vitro and its application into the ARC of the Dicer-deficient mice both reverses upregulation of Pik3cg, the mRNA encoding the catalytic subunit p110γ of the PI3K complex, and attenuates the hyperphagic obesity. Our data demonstrate in vivo the crucial role of neuronal microRNAs in the control of energy homeostasis.

An association of metabolic syndrome constellation with cellular membrane caveolae

Metabolic syndrome (MetS) is a cluster of metabolic abnormalities that can predispose an individual to a greater risk of developing type-2 diabetes and cardiovascular diseases. The cluster includes abdominal obesity, dyslipidemia, hypertension, and hyperglycemia - all of which are risk factors to public health. While searching for a link among the aforementioned malaises, clues have been focused on the cell membrane domain caveolae, wherein the MetS-associated active molecules are colocalized and interacted with to carry out designated biological activities. Caveola disarray could induce all of those individual metabolic abnormalities to be present in animal models and humans, providing a new target for therapeutic strategy in the management of MetS.

Caveolae as plasma membrane sensors, protectors and organizers

Caveolae are submicroscopic, plasma membrane pits that are abundant in many mammalian cell types. The past few years have seen a quantum leap in our understanding of the formation, dynamics and functions of these enigmatic structures. Caveolae have now emerged as vital plasma membrane sensors that can respond to plasma membrane stresses and remodel the extracellular environment. Caveolae at the plasma membrane can be removed by endocytosis to regulate their surface density or can be disassembled and their structural components degraded. Coat proteins, called cavins, work together with caveolins to regulate the formation of caveolae but also have the potential to dynamically transmit signals that originate in caveolae to various cellular destinations. The importance of caveolae as protective elements in the plasma membrane, and as membrane organizers and sensors, is highlighted by links between caveolae dysfunction and human diseases, including muscular dystrophies and cancer.

Essential role of caveolin-3 in adiponectin signalsome formation and adiponectin cardioprotection

OBJECTIVE

Adiponectin (APN) system malfunction is causatively related to increased cardiovascular morbidity/mortality in diabetic patients. The aim of the current study was to investigate molecular mechanisms responsible for APN transmembrane signaling and cardioprotection.

METHODS AND RESULTS

Compared with wild-type mice, caveolin-3 knockout (Cav-3KO) mice exhibited modestly increased myocardial ischemia/reperfusion injury (increased infarct size, apoptosis, and poorer cardiac function recovery; P<0.05). Although the expression level of key APN signaling molecules was normal in Cav-3KO, the cardioprotective effects of APN observed in wild-type were either markedly reduced or completely lost in Cav-3KO. Molecular and cellular experiments revealed that APN receptor 1 (AdipoR1) colocalized with Cav-3, forming AdipoR1/Cav-3 complex via specific Cav-3 scaffolding domain binding motifs. AdipoR1/Cav-3 interaction was required for APN-initiated AMP-activated protein kinase (AMPK)-dependent and AMPK-independent intracellular cardioprotective signalings. More importantly, APPL1 and adenylate cyclase, 2 immediately downstream molecules required for AMPK-dependent and AMPK-independent signaling, respectively, formed a protein complex with AdipoR1 in a Cav-3 dependent fashion. Finally, pharmacological activation of both AMPK plus protein kinase A significantly reduced myocardial infarct size and improved cardiac function in Cav-3KO animals.

CONCLUSIONS

Taken together, these results demonstrated for the first time that Cav-3 plays an essential role in APN transmembrane signaling and APN anti-ischemic/cardioprotective actions.

MicroRNAs 103 and 107 regulate insulin sensitivity. Nature. 2011;474:649-653. [PMID: 21654750 DOI: 10.1038/nature10112]

Defects in insulin signalling are among the most common and earliest defects that predispose an individual to the development of type 2 diabetes. MicroRNAs have been identified as a new class of regulatory molecules that influence many biological functions, including metabolism. However, the direct regulation of insulin sensitivity by microRNAs in vivo has not been demonstrated. Here we show that the expression of microRNAs 103 and 107 (miR-103/107) is upregulated in obese mice. Silencing of miR-103/107 leads to improved glucose homeostasis and insulin sensitivity. In contrast, gain of miR-103/107 function in either liver or fat is sufficient to induce impaired glucose homeostasis. We identify caveolin-1, a critical regulator of the insulin receptor, as a direct target gene of miR-103/107. We demonstrate that caveolin-1 is upregulated upon miR-103/107 inactivation in adipocytes and that this is concomitant with stabilization of the insulin receptor, enhanced insulin signalling, decreased adipocyte size and enhanced insulin-stimulated glucose uptake. These findings demonstrate the central importance of miR-103/107 to insulin sensitivity and identify a new target for the treatment of type 2 diabetes and obesity.

MicroRNAs 103 and 107 regulate insulin sensitivity

Defects in insulin signalling are among the most common and earliest defects that predispose an individual to the development of type 2 diabetes. MicroRNAs have been identified as a new class of regulatory molecules that influence many biological functions, including metabolism. However, the direct regulation of insulin sensitivity by microRNAs in vivo has not been demonstrated. Here we show that the expression of microRNAs 103 and 107 (miR-103/107) is upregulated in obese mice. Silencing of miR-103/107 leads to improved glucose homeostasis and insulin sensitivity. In contrast, gain of miR-103/107 function in either liver or fat is sufficient to induce impaired glucose homeostasis. We identify caveolin-1, a critical regulator of the insulin receptor, as a direct target gene of miR-103/107. We demonstrate that caveolin-1 is upregulated upon miR-103/107 inactivation in adipocytes and that this is concomitant with stabilization of the insulin receptor, enhanced insulin signalling, decreased adipocyte size and enhanced insulin-stimulated glucose uptake. These findings demonstrate the central importance of miR-103/107 to insulin sensitivity and identify a new target for the treatment of type 2 diabetes and obesity.

Cardiovascular comorbidities of type 2 diabetes mellitus: defining the potential of glucagonlike peptide-1-based therapies

The global epidemic of diabetes mellitus (~95% type 2 diabetes) has been fueled by a parallel increase in obesity and overweight. Together, these metabolic disease epidemics have contributed to the increasing incidence and prevalence of cardiovascular disease. The accumulation of metabolic and cardiovascular risk factors in patients with type 2 diabetes--risk factors that may exacerbate one another--complicates treatment. Inadequate treatment, treatment that fails to achieve goals, increases the risk for cardiovascular morbidity and mortality. From a clinical perspective, type 2 diabetes is a cardiovascular disease, an observation that is supported by a range of epidemiologic, postmortem, and cardiovascular imaging studies. Vascular wall dysfunction, and particularly endothelial dysfunction, has been posited as a "common soil" linking dysglycemic and cardiovascular diseases. Vascular wall dysfunction promoted by environmental triggers (e.g., sedentary lifestyle) and metabolic triggers (chronic hyperglycemia, obesity) has been associated with the upregulation of reactive oxygen species and chronic inflammatory and hypercoagulable states, and as such with the pathogenesis of type 2 diabetes, atherosclerosis, and cardiovascular disease. Glucagon-like peptide-1 (GLP)-1, an incretin hormone, and synthetic GLP-1 receptor agonists represent promising new areas of research and therapeutics in the struggle not only against type 2 diabetes but also against the cardiovascular morbidity and mortality associated with type 2 diabetes. In a number of small trials in humans, as well as in preclinical and in vitro studies, both native GLP-1 and GLP-1 receptor agonists have demonstrated positive effects on a range of cardiovascular disease pathologies and clinical targets, including such markers of vascular inflammation as high-sensitivity C-reactive protein, plasminogen activator inhibitor-1, and brain natriuretic peptide. Reductions in markers of dyslipidemia such as elevated levels of triglycerides and free fatty acids have also been observed, as have cardioprotective functions. Larger trials of longer duration will be required to confirm preliminary findings. In large human trials, GLP-1 receptor agonists have been associated with significant reductions in both blood pressure and weight.