Phosphorothioate backbone modifications of nucleotide-based drugs are potent platelet activators

Targeting Suppressive Oligonucleotide to Lymph Nodes Inhibits Toll-like Receptor-9-Mediated Activation of Adaptive Immunity

PURPOSE

This paper aims to investigate the immunoinhibitory properties of a lymph nodes-targeting suppressive oligonucleotide (ODN) for the potential treatment of autoimmune diseases or chronic inflammation.

METHODS

Synthetic suppressive ODN engineered with an albumin-binding diacyl lipid at the 5'-terminal (lipo-ODN) was synthesized. In vitro and in vivo experiments were designed to compare the immune suppressive properties of lipo-ODN and unmodified ODN. Cellular uptake and distribution, inhibition of Toll-like receptor (TLR) activation, lymph nodes (LN) draining, and the suppression of antigen-specific immune responses in an ovalbumin protein model was investigated.

RESULTS

Compared to unmodified ODN, lipid functionalized suppressive ODN demonstrated enhanced cellular uptake and TLR-9 specific immune suppression in TLR reporter cells. Additionally, injection of a low dose of lipid-modified suppressive ODN, but not the unconjugated ODN, accumulated in the draining LNs and exhibited potent inhibition of antigen-specific CD8⁺ T cell and B cell responses in vivo.

CONCLUSIONS

Targeting suppressive ODN to antigen presenting cells (APCs) in the local LNs is an effective approach to amplify the immune modulation mediated by ODN containing repetitive TTAGGG motif. This approach might be broadly applicable to target molecular adjuvants to the key immune cells in the LNs draining from disease site, providing a simple strategy to improve the efficacy of many molecular immune modulators.

Translational Implications of Platelets as Vascular First Responders

Platelets play a vital role in normal hemostasis to stem blood loss at sites of vascular injury by tethering and adhering to sites of injury, recruiting other platelets and blood cells to the developing clot, releasing vasoactive small molecules and proteins, and assembling and activating plasma coagulation proteins in a tightly regulated temporal and spatial manner. In synchrony with specific end products of coagulation, primarily cross-linked fibrin, a stable thrombus quickly forms. Far beyond physiological hemostasis and pathological thrombosis, emerging evidence supports platelets playing a pivotal role in vascular homeostasis, inflammation, cellular repair, regeneration, and wide range of autocrine and paracrine functions. In essence, platelets play both structural and functional roles as reporters, messengers, and active transporters surveying the vasculature for cues of environmental or developmental stimuli and participating as first responders.1 In this review, we will provide a contemporary perspective of platelet physiology, including fundamental, translational, and clinical constructs that apply directly to human health and disease.

Mechanobiology in vascular remodeling

Vascular remodeling is a common pathological process in cardiovascular diseases and includes changes in cell proliferation, apoptosis and differentiation as well as vascular homeostasis. Mechanical stresses, such as shear stress and cyclic stretch, play an important role in vascular remodeling. Vascular cells can sense the mechanical factors through cell membrane proteins, cytoskeletons and nuclear envelope proteins to initiate mechanotransduction, which involves intercellular signaling, gene expression, and protein expression to result in functional regulations. Non-coding RNAs, including microRNAs and long non-coding RNAs, are involved in the regulation of vascular remodeling processes. Mechanotransduction triggers a cascade reaction process through a complicated signaling network in cells. High-throughput technologies in combination with functional studies targeting some key hubs and bridging nodes of the network can enable the prioritization of potential targets for subsequent investigations of clinical translation. Vascular mechanobiology, as a new frontier field of biomechanics, searches for principles of stress-growth in vasculature to elucidate how mechanical factors induce biological effects that lead to vascular remodeling, with the goal of understanding the mechanical basis of the pathological mechanism of cardiovascular diseases at the cellular and molecular levels. Vascular mechanobiology will play a unique role in solving the key scientific problems of human physiology and disease, as well as generating important theoretical and clinical results.

Assessing single-stranded oligonucleotide drug-induced effects in vitro reveals key risk factors for thrombocytopenia

Single-stranded oligonucleotides (ON) comprise a promising therapeutic platform that enables selective modulation of currently undruggable targets. The development of novel ON drug candidates has demonstrated excellent efficacy, but in certain cases also some safety liabilities were reported. Among them are events of thrombocytopenia, which have recently been evident in late stage trials with ON drugs. The underlying mechanisms are poorly understood and the risk for ON candidates causing such events cannot be sufficiently assessed pre-clinically. We investigated potential thrombocytopenia risk factors of ONs and implemented a set of in vitro assays to assess these risks. Our findings support previous observations that phosphorothioate (PS)-ONs can bind to platelet proteins such as platelet collagen receptor glycoprotein VI (GPVI) and activate human platelets in vitro to various extents. We also show that these PS-ONs can bind to platelet factor 4 (PF4). Binding to platelet proteins and subsequent activation correlates with ON length and connected to this, the number of PS in the backbone of the molecule. Moreover, we demonstrate that locked nucleic acid (LNA) ribosyl modifications in the wings of the PS-ONs strongly suppress binding to GPVI and PF4, paralleled by markedly reduced platelet activation. In addition, we provide evidence that PS-ONs do not directly affect hematopoietic cell differentiation in culture but at higher concentrations show a pro-inflammatory potential, which might contribute to platelet activation. Overall, our data confirm that certain molecular attributes of ONs are associated with a higher risk for thrombocytopenia. We propose that applying the in vitro assays discussed here during the lead optimization phase may aid in deprioritizing ONs with a potential to induce thrombocytopenia.

Phosphodiester backbone of the CpG motif within immunostimulatory oligodeoxynucleotides augments activation of Toll-like receptor 9

Toll-like receptor 9 (TLR9) stimulatory CpG-containing oligodeoxynucleotides (ODNs) with phosphorothioate backbones have successfully replaced the naturally occurring agonists of TLR9 in drug development due to their increased stability. Replacing the nonbridging oxygen with a sulfur atom in the phosphate linkage of ODNs has been accepted as having a minor impact on the chemical and physical properties of the agonists. Here, we report that the TLR9 binding site exhibits a strong bias in favor of a phosphodiester backbone over the phosphorothioate backbone of the CpG motif. Furthermore, we show that while single point mutations of W47, W96 and K690 within the TLR9 binding site retains full TLR9 activation by phosphodiester-based ODNs, activation by phosphorothioate-based ODNs is strongly impaired. The substitution of a phosphorothioate linkage for a phosphodiester linkage of just the CpG motif considerably improves the activation potency of a phosphorothioate-based oligonucleotide for human B-cells and plasmacytoid dendritic cells, as well as for mouse bone marrow-derived dendritic cells and macrophages. Our results highlight the functional significance of the phosphodiester linkage of a CpG dinucleotide for binding, which is important in designing improved immunostimulatory TLR9 agonists.

MicroRNAs in dysfunctional adipose tissue: cardiovascular implications

In this review, we focus on the emerging role of microRNAs, non-coding RNAs that regulate gene expression and signaling pathways, in dysfunctional adipose tissue. We highlight current paradigms of microRNAs involved in adipose differentiation and function in depots such as white, brown, and beige adipose tissues and potential implications of microRNA dysregulation in human disease such as obesity, inflammation, microvasculature dysfunction, and related cardiovascular diseases. We highlight accumulating studies indicating that adipocyte-derived microRNAs may not only serve as biomarkers of cardiometabolic disease, but also may directly regulate gene expression of other tissues. Finally, we discuss the future prospects, challenges, and emerging strategies for microRNA delivery and targeting for therapeutic applications in cardiovascular disease states associated with adipocyte dysfunction.

MicroRNAs in Cardiovascular Disease

Micro-ribonucleic acids (miRNAs) are in the spotlight as post-transcriptional regulators of gene expression. More than 1,000 miRNAs are encoded in the human genome. In this review, we provide an introduction to miRNA biology and research methodology, and highlight advances in cardiovascular research to date. This includes the potential of miRNAs as therapeutic targets in cardiac and vascular disease, and their use as novel biomarkers. Although some miRNA therapies are already undergoing clinical evaluation, we stress the importance of integrating current knowledge of miRNA biology into a systemic context. Discovery studies focus on miRNA effects within one specific organ, whereas the expression of most miRNAs is not restricted to a single tissue. Because most miRNA-based therapies act systemically, this may preclude widespread clinical use. The development of more targeted interventions will bolster well-informed clinical applications, increasing the chances of success and minimizing the risk of setbacks for miRNA-based therapeutics.

DNA Backbone Sulfur-Modification Expands Microbial Growth Range under Multiple Stresses by its anti-oxidation function

DNA phosphorothioate (PT) modification is a sulfur modification on the backbone of DNA introduced by the proteins DndA-E. It has been detected within many bacteria isolates and metagenomic datasets, including human pathogens, and is considered to be widely distributed in nature. However, little is known about the physiological function of this modification, and thus its evolutionary significance and application potential remains largely a mystery. In this study, we focused on the advantages of DNA PT modification to bacterial cells coping with environmental stresses. We show that the mesophile Escherichia coli and the extremophile Shewanella piezotolerans both expanded their growth ranges following exposure to extreme temperature, salinity, pH, pressure, UV, X-ray and heavy metals as a result of DNA phophorothioation. The phophorothioated DNA reacted to both H₂O₂ and hydroxyl radicals in vivo, and protected genomic DNA as well as sensitive enzymes from intracellular oxidative damage. We further demonstrate that this process has evolved separate from its associated role in DNA restriction and modification. These findings provide a physiological role for a covalent modification widespread in nature and suggest possible applications in biotechnology and biomedicine.

microRNA inhibitors: Natural and artificial sequestration of microRNA

MicroRNA (miRNAs) is post-transcriptional regulator of mRNA. However, the prevalence and activity of miRNA are regulated by other regulators. miRNA inhibitors are natural or artificial RNA transcripts that sequestrate miRNAs and decrease or even eliminate miRNA activity. Competing endogenous RNAs (ceRNAs) are natural and intracellular miRNA inhibitors that compete to bind to shared miRNA recognition elements (MREs) to decrease microRNA availability and relieve the repression of target RNAs. In recent years, studies have revealed that ceRNA crosstalk is involved in many pathophysiological processes and adds a new dimension to miRNA regulation. Artificial miRNA inhibitors are RNA transcripts that are synthesized via chemical and genetic methods. Artificial miRNA inhibitors can be used in miRNA loss-of-function research and gene therapies for certain diseases. In this review, we summarize the recent advances in the two different types of miRNA inhibitors.

Assessment of the Effects of 2'-Methoxyethyl Antisense Oligonucleotides on Platelet Count in Cynomolgus Nonhuman Primates

Decreases in platelet (PLT) counts observed in nonhuman primates (NHPs) given 2'-O-methoxyethyl modified antisense inhibitors (2'-MOE ASOs) have been reported, but the incidence and severity of the change vary considerably between sequences, studies, and animals. This article will broadly illustrate the spectrum of effects on PLT count in NHPs. From queries of an NHP safety database representing over 102 independent 2'-MOE ASOs, from 61 studies and >2200 NHPs, two patterns of PLT changes emerged. The first is a consistent and reproducible decrease in group mean values, observed with about 30% of the compounds, in which PLT count typically remains ≥150K cells/μL. The second is a sporadic decrease in PLTs to <50K cells/μL (2%-4% incidence at doses >5 mg/kg) that is often not reproducible. In both cases, the reduction in PLT count is dose dependent and reversible. The human relevance of PLT change observed in NHPs was investigated using ISIS 404173. In a chronic NHP study (20 mg/kg/wk for 26 weeks), a gradual decrease in group mean PLT count was observed at ≥10 mg/kg/wk, which plateaued by 13 weeks generally within the normal range and was maintained through 26 weeks of treatment. However, PLT counts <50K cells/μL occurred in 1 of 16 NHP at 10 mg/kg/wk and 3 of 16 NHP at 20 mg/kg/wk. In a 26-week double-blind, placebo-controlled Phase 2 trial, 62 patients were treated with 200 mg/wk ISIS 404173 (∼3.3 mg/kg/wk) there was an increased incidence of PLT count >30% decreased compared to baseline but no incidence of PLT <75K cells/μL. Based on these data, the consistent, self-limiting PLT reduction seen in NHP may translate to humans, but these changes appear to be of limited clinical significance. However, NHPs appear to overpredict the incidence of sporadic PLT <50K cells/μL compared to humans.

Targeting of C-type lectin-like receptor 2 or P2Y12 for the prevention of platelet activation by immunotherapeutic CpG oligodeoxynucleotides

Essentials CpG oligodeoxynucleotide (ODN) immuotherapeutics cause undesired platelet activating effects. It is crucial to understand the mechanisms of these effects to identify protective strategies. CpG ODN-induced platelet activation depends on C-type lectin-like receptor 2 (CLEC-2) and P2Y12. Targeting CLEC-2 or P2Y12 fully prevents CpG ODN-induced platelet activation and thrombosis.

SUMMARY

Background Synthetic phosphorothioate-modified CpG oligodeoxynucleotides (ODNs) show potent immunostimulatory properties that are widely exploited in clinical trials of anticancer treatment. Unexpectedly, a recent study indicated that CpG ODNs activate human platelets via the immunoreceptor tyrosine-based activation motif (ITAM)-coupled receptor glycoprotein VI. Objective To further analyze the mechanisms of CpG ODN-induced platelet activation and identify potential inhibitory strategies. Methods In vitro analyses were performed on human and mouse platelets, and on cell lines expressing platelet ITAM receptors. CpG ODN platelet-activating effects were evaluated in a mouse model of thrombosis. Results We demonstrated platelet uptake of CpG ODNs, resulting in platelet activation and aggregation. C-type lectin-like receptor 2 (CLEC-2) expressed in DT40 cells bound CpG ODNs. CpG ODN uptake did not occur in CLEC-2-deficient mouse platelets. Inhibition of human CLEC-2 with a blocking antibody inhibited CpG ODN-induced platelet aggregation. CpG ODNs caused CLEC-2 dimerization, and provoked its internalization. They induced dense granule release before the onset of aggregation. Accordingly, pretreating platelets with apyrase, or inhibiting P2Y12 with cangrelor or clopidogrel, prevented CpG ODN platelet-activating effect. In vivo, intravenously injected CpG ODN interacted with platelets adhered to mouse injured endothelium, and promoted thrombus growth, which was inhibited by CLEC-2 deficiency or by clopidogrel. Conclusions CLEC-2 and P2Y12 are required for CpG ODN-induced platelet activation and thrombosis, and might be targeted to prevent adverse events in patients at risk.

Emerging Roles for MicroRNAs in Diabetic Microvascular Disease: Novel Targets for Therapy

Chronic, low-grade systemic inflammation and impaired microvascular function are critical hallmarks in the development of insulin resistance. Accordingly, insulin resistance is a major risk factor for type 2 diabetes and cardiovascular disease. Accumulating studies demonstrate that restoration of impaired function of the diabetic macro- and microvasculature may ameliorate a range of cardiovascular disease states and diabetes-associated complications. In this review, we focus on the emerging role of microRNAs (miRNAs), noncoding RNAs that fine-tune target gene expression and signaling pathways, in insulin-responsive tissues and cell types important for maintaining optimal vascular homeostasis and preventing the sequelae of diabetes-induced end organ injury. We highlight current pathophysiological paradigms of miRNAs and their targets involved in regulating the diabetic microvasculature in a range of diabetes-associated complications such as retinopathy, nephropathy, wound healing, and myocardial injury. We provide an update of the potential use of circulating miRNAs diagnostically in type I or type II diabetes. Finally, we discuss emerging delivery platforms for manipulating miRNA expression or function as the next frontier in therapeutic intervention to improve diabetes-associated microvascular dysfunction and its attendant clinical consequences.

Generating Aptamers Interacting with Polymeric Surfaces for Biofunctionalization

Common strategies for biofunctionalization of surfaces comprise the immobilization of bioactive molecules used as cell-binding ligands for cell recruitment. Besides covalent binding, multivalent noncovalent physical forces between substrate and ligand are an alternative way to equip surfaces with biomacromolecules. In this study, polymer binding ligands are screened by means of a DNA-based in vitro selection process. As candidate biomaterials poly(ether imide) (PEI), polystyrene, and poly[ethylene-co-(vinyl acetate)] are selected, due to their different chemical structure, but similar macroscopic interface properties, allowing physical interaction with nucleotide bases by varying valences. Multivalent interacting aptamers are successfully enriched by SELEX method and an area-wide surface functionalization is achieved, which can be used for further binding of bioactive molecules. In vitro selection against the polymers result in thymine-dominated aptamer binding motifs. The preferential interaction with thymine is attributed to its chemical structure, connected with a decreased electrostatic repulsion of the π-system and the hydrophobic character maximizing entropy. The aptamer binding stability correlates with available valences for interaction, resulting in a more stable functionalization of PEI.

Interfering with baffled B cells at the lupus tollway: Promises, successes, and failed expectations

B cells play an important role in systemic lupus erythematosus by acting not only as precursors of autoantibody-producing cells but also as antigen-presenting, cytokine-secreting, and regulatory cells. Unopposed activation of B cells through their B-cell receptor for antigen, as seen in B cells lacking Lyn kinase, results in systemic autoimmunity. The B-cell activating factor of the TNF family (BAFF), nucleic acid-sensing Toll-like receptors (TLRs), and type I interferon can affect B-cell survival and decrease their threshold for activation. Herein we discuss both direct and indirect strategies aimed at targeting B cells in patients with lupus by blocking BAFF, type I interferon, or TLR7 to TLR9. Although BAFF-depleting therapy with belimumab achieved approval for lupus, other BAFF inhibitors were much less beneficial in clinical trials. Inhibitors of the B-cell receptor for antigen signaling and antibodies against type I interferon are in the pipeline. The TLR7 to TLR9 blocker hydroxychloroquine has been in use in patients with lupus for more than 50 years, but oligonucleotide-based inhibitors of TLR7 to TLR9, despite showing promise in animal models of lupus, have not reached the primary end point in a recent phase 1 trial. These data point toward possible redundancies in B-cell signaling/survival pathways, which must be better understood before future clinical trials are executed.

MicroRNA Regulation of Atherosclerosis

Atherosclerosis and its attendant clinical complications, such as myocardial infarction, stroke, and peripheral artery disease, are the leading cause of morbidity and mortality in Western societies. In response to biochemical and biomechanical stimuli, atherosclerotic lesion formation occurs from the participation of a range of cell types, inflammatory mediators, and shear stress. Over the past decade, microRNAs (miRNAs) have emerged as evolutionarily conserved, noncoding small RNAs that serve as important regulators and fine-tuners of a range of pathophysiological cellular effects and molecular signaling pathways involved in atherosclerosis. Accumulating studies reveal the importance of miRNAs in regulating key signaling and lipid homeostasis pathways that alter the balance of atherosclerotic plaque progression and regression. In this review, we highlight current paradigms of miRNA-mediated effects in atherosclerosis progression and regression. We provide an update on the potential use of miRNAs diagnostically for detecting increasing severity of coronary disease and clinical events. Finally, we provide a perspective on therapeutic opportunities and challenges for miRNA delivery in the field.

RNA and RNP as Building Blocks for Nanotechnology and Synthetic Biology

Recent technologies that aimed to elucidate cellular function have revealed essential roles for RNA molecules in living systems. Our knowledge concerning functional and structural information of naturally occurring RNA and RNA-protein (RNP) complexes is increasing rapidly. RNA and RNP interaction motifs are structural units that function as building blocks to constitute variety of complex structures. RNA-central synthetic biology and nanotechnology are constructive approaches that employ the accumulated information and build synthetic RNA (RNP)-based circuits and nanostructures. Here, we describe how to design and construct synthetic RNA (RNP)-based devices and structures at the nanometer-scale for biological and future therapeutic applications. RNA/RNP nanostructures can also be utilized as the molecular scaffold to control the localization or interactions of target molecule(s). Moreover, RNA motifs recognized by RNA-binding proteins can be applied to make protein-responsive translational "switches" that can turn gene expression "on" or "off" depending on the intracellular environment. This "synthetic RNA and RNP world" will expand tools for nanotechnology and synthetic biology. In addition, these reconstructive approaches would lead to a greater understanding of building principle in naturally occurring RNA/RNP molecules and systems.

Evaluation of the effects of chemically different linkers on hepatic accumulations, cell tropism and gene silencing ability of cholesterol-conjugated antisense oligonucleotides

Cholesterol conjugation of oligonucleotides is an attractive way to deliver the oligonucleotides specifically to the liver. However cholesterol-conjugated antisense oligonucleotides (ASOs) mainly accumulate in non-parenchymal cells (NPCs) such as Kupffer cells. In this study, to increase the hepatic accumulation of cholesterol-conjugated ASOs, we prepared a variety of linkers for cholesterol conjugation to anti-Pcsk9 ASOs and examined their effects on pharmacological parameters. Hepatic accumulation of ASO was dramatically increased with cholesterol conjugation. The increase in hepatic accumulation depended largely on the linker chemistry of each cholesterol-conjugated ASO. In addition to hepatic accumulation, the cell tropism of each cholesterol-conjugated ASO tended to depend on their linker. Although a linker bearing a disulfide bond accumulated mainly in NPCs, hexamethylene succinimide linker accumulated mainly in hepatocytes. To estimate the benefits of releasing ASO from the conjugated cholesterol in hepatocyte, we designed another linker based on hexamethylene succinimide, which has a phosphodiester bond between the linker and the ASO. The cholesterol-conjugated ASO bearing such a phosphodiester bond showed a significantly improved Pcsk9 mRNA inhibitory effect compared to its counterpart, cholesterol-conjugated ASO with a phosphorothioate bond, while the hepatic accumulation of both cholesterol-conjugated ASOs was comparable, indicating the effectiveness of removing the conjugated cholesterol for ASO activity. In toxicity analysis, some of the linkers induced lethal toxicities when they were injected at high concentrations (>600μM). These toxicities were attributed to decreased platelet levels in the blood, suggesting an interaction between cholesterol-conjugated ASO and platelets. Our findings may provide a guideline for the design of molecule-conjugated ASOs.

Chemical modifications in the seed region of miRNAs 221/222 increase the silencing performances in gastrointestinal stromal tumor cells

Most GastroIntestinal Stromal Tumors (GISTs) are characterized by KIT gene overexpression, which in turn is regulated by levels of microRNA 221 and microRNA 222. GISTs can also be distinguished by their miRNAs expression profile in which miRNAs 221/222 result reduced in comparison with GI normal tissues. In this paper, to restore normal miRNAs levels and to improve the silencing performances of miRNAs 221/222, new miRNA mimics in which guide strands are modified by Phosphorothioate (PS) and/or 2'-O-methyl RNA (2'-OMe) inside and outside the seed region, were synthesized and tested in GIST48 cells. We evaluated the positional effect of the chemical modifications on the miRNAs silencing activity, compared to natural and several commercial miRNA mimics. Our results show that chemically modified miRNAs 221/222 with alternating 2'-OMe-PS and natural nucleotides in the seed region are effective inhibitors of KIT gene expression and exhibit increased stability in rat plasma. Besides, their transfection in GIST 48 cells showed significant effects on different cellular processes in which KIT plays a functional role for tumor development (such as migration, cell proliferation, and apoptosis). Therefore, modified miRNAs 221/222 may provide an alternative therapeutic option for GIST treatment also aimed to overcome drug resistance concerns.

Association of MicroRNAs and YRNAs With Platelet Function

RATIONALE

Platelets shed microRNAs (miRNAs). Plasma miRNAs change on platelet inhibition. It is unclear whether plasma miRNA levels correlate with platelet function.

OBJECTIVE

To link small RNAs to platelet reactivity.

METHODS AND RESULTS

Next-generation sequencing of small RNAs in plasma revealed 2 peaks at 22 to 23 and 32 to 33 nucleotides corresponding to miRNAs and YRNAs, respectively. Among YRNAs, predominantly, fragments of RNY4 and RNY5 were detected. Plasma miRNAs and YRNAs were measured in 125 patients with a history of acute coronary syndrome who had undergone detailed assessment of platelet function 30 days after the acute event. Using quantitative real-time polymerase chain reactions, 92 miRNAs were assessed in patients with acute coronary syndrome on different antiplatelet therapies. Key platelet-related miRNAs and YRNAs were correlated with platelet function tests. MiR-223 (rp=0.28; n=121; P=0.002), miR-126 (rp=0.22; n=121; P=0.016), and other abundant platelet miRNAs and YRNAs showed significant positive correlations with the vasodilator-stimulated phosphoprotein phosphorylation assay. YRNAs, miR-126, and miR-223 were also among the small RNAs showing the greatest dependency on platelets and strongly correlated with plasma levels of P-selectin, platelet factor 4, and platelet basic protein in the population-based Bruneck study (n=669). A single-nucleotide polymorphism that facilitates processing of pri-miR-126 to mature miR-126 accounted for a rise in circulating platelet activation markers. Inhibition of miR-126 in mice reduced platelet aggregation. MiR-126 directly and indirectly affects ADAM9 and P2Y12 receptor expression.

CONCLUSIONS

Levels of platelet-related plasma miRNAs and YRNAs correlate with platelet function tests in patients with acute coronary syndrome and platelet activation markers in the general population. Alterations in miR-126 affect platelet reactivity.

Fibrin activates GPVI in human and mouse platelets

The glycoprotein VI (GPVI)-Fc receptor γ (FcRγ) chain is the major platelet signaling receptor for collagen. Paradoxically, in a FeCl3 injury model, occlusion, but not initiation of thrombus formation, is delayed in GPVI-deficient and GPVI-depleted mice. In this study, we demonstrate that GPVI is a receptor for fibrin and speculate that this contributes to development of an occlusive thrombus. We observed a marked increase in tyrosine phosphorylation, including the FcRγ chain and Syk, in human and mouse platelets induced by thrombin in the presence of fibrinogen and the αIIbβ3 blocker eptifibatide. This was not seen in platelets stimulated by a protease activated receptor (PAR)-4 peptide, which is unable to generate fibrin from fibrinogen. The pattern of tyrosine phosphorylation was similar to that induced by activation of GPVI. Consistent with this, thrombin did not induce tyrosine phosphorylation of Syk and the FcRγ chain in GPVI-deficient mouse platelets. Mouse platelets underwent full spreading on fibrin but not fibrinogen, which was blocked in the presence of a Src kinase inhibitor or in the absence of GPVI. Spreading on fibrin was associated with phosphatidylserine exposure (procoagulant activity), and this too was blocked in GPVI-deficient platelets. The ectodomain of GPVI was shown to bind to immobilized monomeric and polymerized fibrin. A marked increase in embolization was seen following FeCl3 injury in GPVI-deficient mice, likely contributing to the delay in occlusion in this model. These results demonstrate that GPVI is a receptor for fibrin and provide evidence that this interaction contributes to thrombus growth and stability.

MicroRNAs in cardiovascular ageing

MicroRNAs (miRs) have emerged as potent regulators of pathways in physiological and disease contexts. This review focuses on the role of miRs in ageing of the cardiovascular system. Several miRs have been described to be regulated during ageing and some of these miRs are involved in the regulation of ageing-related processes. We discuss the roles of miR-34, miR-217 and miR-29, which are induced during ageing in the vasculature. The roles of miR-34, miR-29 (age-induced) and miR-18/19, which are decreased during ageing in the heart, are discussed as well. Furthermore, numerous miRs that play a role in diseases associated with ageing, like diabetes, atherosclerosis, hypertension, cardiac hypertrophy and atrial fibrillation, are also briefly discussed. miRs also serve as circulating biomarkers for cardiovascular ageing or ageing-associated diseases. Finally, pharmacological modulation of ageing-related miRs might become a promising strategy to combat cardiovascular ageing in a clinical setting.

Prospects for Therapeutic Targeting of MicroRNAs in Human Immunological Diseases

MicroRNAs (miRNAs) are endogenous oligoribonucleotides with exciting therapeutic potential. Early studies established a clear role for miRNAs in leukocyte biology. The first miRNA-based therapy, miravirsen, is now in phase 2 clinical trials, making the reality of these therapies undeniable. The capacity for miRNAs to fine-tune inflammatory signaling make them attractive treatment targets for immunological diseases. Nonetheless, the degree of redundancy among miRNAs, coupled with the promiscuity of miRNA binding sites in the transcriptome, require consideration when designing miRNA-directed interventions. Altered miRNA expression occurs across a range of inflammatory conditions, including inflammatory bowel disease, arthritis, and diabetes. However, very few studies successfully treated murine models of immunological diseases with miRNA-based approaches. While discussing recent studies targeting miRNAs to treat immunological conditions, we also reflect on the risks of miRNA targeting and showcase some newer delivery systems that may improve the pharmacological profile of this class of therapeutics.