Deletion of the phosphoinositide 3-kinase p110gamma gene attenuates murine atherosclerosis

PI3K signaling promotes formation of lipid-laden foamy macrophages at the spinal cord injury site

After spinal cord injury (SCI), infiltrating macrophages undergo excessive phagocytosis of myelin and cellular debris, forming lipid-laden foamy macrophages. To understand their role in the cellular pathology of SCI, investigation of the foamy macrophage phenotype in vitro revealed a pro-inflammatory profile, increased reactive oxygen species (ROS) production, and mitochondrial dysfunction. Bioinformatic analysis identified PI3K as a regulator of inflammation in foamy macrophages, and inhibition of this pathway decreased their lipid content, inflammatory cytokines, and ROS production. Macrophage-specific inhibition of PI3K using liposomes significantly decreased foamy macrophages at the injury site after a mid-thoracic contusive SCI in mice. RNA sequencing and in vitro analysis of foamy macrophages revealed increased autophagy and decreased phagocytosis after PI3K inhibition as potential mechanisms for reduced lipid accumulation. Together, our data suggest that the formation of pro-inflammatory foamy macrophages after SCI is due to the activation of PI3K signaling, which increases phagocytosis and decreases autophagy.

Network Pharmacology and Molecular Docking Analysis of Active Compounds in Tualang Honey against Atherosclerosis

Atherosclerosis, a pathological condition marked by the accumulation of lipids and fibrous substances in the arterial walls, is a leading cause of heart failure and death. The present study aimed to utilize network pharmacology to assess the potential pharmacological effects of bioactive compounds in Tualang honey on atherosclerosis. This is significant as previous studies have indicated the cardioprotective effects of Tualang honey, yet a comprehensive evaluation using network pharmacology has yet to be conducted. The bioactive compounds in Tualang honey were screened and the potential gene targets for these compounds were predicted through Swiss Target Prediction and SuperPred databases. Atherosclerosis genes were retrieved from the OMIM, DisGeNet, and GeneCards databases. The interaction between these compounds and atherosclerosis genes was established through protein-protein interaction, gene ontology, and KEGG pathway analysis. The results of these analyses were then further confirmed through molecular docking studies using the AutoDock Tools software. The results revealed that 6 out of 103 compounds in Tualang honey met the screening criteria, with a total of 336 potential gene targets, 238 of which were shared with atherosclerosis. Further analysis showed that these active compounds had a good affinity with key targets and were associated with biological processes related to protein phosphorylation and inflammation as well as pathways related to lipid and atherosclerosis and other signaling pathways. In conclusion, the study provides insight into the potential pharmacological effects of Tualang honey bioactive compounds on atherosclerosis, supporting its use as a promising treatment for the disease.

Molecular Docking and Simulation Studies of Flavanone and its Derived Compounds on PI3K-AKT Pathway Targeting against Cancer

BACKGROUND

Flavanone compounds and their related derivatives are reported in controlling cell cycle, angiogenesis, and metastasis. Phosphoinositide 3-kinases is a major drug target.

METHODS

Crystalize structure of Phosphoinositide 3-kinases-Akt complex obtained from Protein Data Bank (PDBID: 3CQW) was selected as receptor protein and the binding site has been identified with PDBSum Database. Flavanone and its derivatives were retrieved using freely available existing drug databases like Drug Bank, Zinc, and PubChem. New derivatives were modified by altering the flavanone at Beta ring position. This modification would help in maintaining stable structural conformation and retaining better anticancer activity. Retrieved Flavanone derivatives from the drug database were docked against 3CQW Protein with the advanced docking tool FlexX. MD simulations of the best molecule were performed with the Desmond package by calculating nonbonding interactions such as electrostatic interaction and hydrogen bond stable and favorable conformations were calculated.

RESULTS

These interaction studies would help identify new potential drug candidates with the help of computer-aided drug designing techniques.

CONCLUSION

Natural chemicals have received a lot of attention because of their vast range of applications in human health and disease prevention without creating any negative side effects. Molecular docking is an essential approach for drug development since it allows for effective screening of potential therapeutics in a short time. We hypothesized in this paper that natural flavanone and its derivatives may be effective as Akt-1 inhibitors.

The role of PI3Kγ in the immune system: new insights and translational implications

Over the past two decades, new insights have positioned phosphoinositide 3-kinase-γ (PI3Kγ) as a context-dependent modulator of immunity and inflammation. Recent advances in protein structure determination and drug development have allowed for generation of highly specific PI3Kγ inhibitors, with the first now in clinical trials for several oncology indications. Recently, a monogenic immune disorder caused by PI3Kγ deficiency was discovered in humans and modelled in mice. Human inactivated PI3Kγ syndrome confirms the immunomodulatory roles of PI3Kγ and strengthens newly defined roles of this molecule in modulating inflammatory cytokine release in macrophages. Here, we review the functions of PI3Kγ in the immune system and discuss how our understanding of its potential as a therapeutic target has evolved.

Sesquiterpene Lactones as Promising Candidates for Cancer Therapy: Focus on Pancreatic Cancer

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive disease which confers to patients a poor prognosis at short term. PDAC is the fourth leading cause of death among cancers in the Western world. The rate of new cases of pancreatic cancer (incidence) is 10 per 100,000 but present a 5-year survival of less than 10%, highlighting the poor prognosis of this pathology. Furthermore, 90% of advanced PDAC tumor present KRAS mutations impacting in several oncogenic signaling pathways, many of them associated with cell proliferation and tumor progression. Different combinations of chemotherapeutic agents have been tested over the years without an improvement of significance in its treatment. PDAC remains as one the more challenging biomedical topics thus far. The lack of a proper early diagnosis, the notable mortality statistics and the poor outcome with the available therapies urge the entire scientific community to find novel approaches against PDAC with real improvements in patients' survival and life quality. Natural compounds have played an important role in the process of discovery and development of new drugs. Among them, terpenoids, such as sesquiterpene lactones, stand out due to their biological activities and pharmacological potential as antitumor agents. In this review, we will describe the sesquiterpene lactones with in vitro and in vivo activity against pancreatic tumor cells. We will also discuss the mechanism of action of the compounds as well as the signaling pathways associated with their activity.

Interleukin-36γ aggravates macrophage foam cell formation and atherosclerosis progression in ApoE knockout mice

Atherosclerosis-related cardiovascular diseases are the leading cause of mortality worldwide. Macrophage-derived foam cell formation is a critical early event in atherogenesis. However, the molecular pathways involved in this disease have not been fully elucidated. Interleukin (IL)-36 plays a crucial role in inflammation, and this study was conducted to investigate the possible role of IL-36γ in the pathogenesis and regulation of atherosclerosis. In this study, we show that IL-36γ regulates inflammatory responses and lipoprotein metabolic processes in macrophages and exerts its atherosclerosis-promoting effects by increasing macrophage foam cell formation and uptake of oxidized low-density lipoproteins. Mechanistically, IL-36γ specifically upregulates expression of the scavenger receptor CD36 through the phosphoinositide 3-kinase pathway in macrophages. These results contribute to our understanding of IL-36γ as a novel regulator of foam cell formation and atherogenesis progression.

How can we turn the PI3K/AKT/mTOR pathway down? Insights into inhibition and treatment of cancer

Introduction: The phosphatidylinositol 3-kinase/protein kinase-B/mammalian target of rapamycin (PI3K/AKT/mTOR) pathway is a fundamental regulator of cell proliferation and survival. Dysregulation in this pathway leads to the development of cancer. Accumulating evidence indicates that dysregulation in this pathway is involved in cancer initiation, progression, and recurrence. However, the pathway consists of various signal transducing factors related with cellular events, such as transformation, tumorigenesis, cancer progression, and drug resistance. Therefore, it is very important to determine the targets in this pathway for cancer therapy. Although many drugs inhibiting this signaling pathway are in clinical trials or have been approved for treating solid tumors and hematologic malignancies, further understanding of the signaling mechanism is required to achieve better therapeutic efficacy.Areas covered: In this review, we have describe the PI3K/AKT/mTOR pathway in detail, along with its critical role in cancer stem cells, for identifying potential therapeutic targets. We also summarize the recent developments in different types of signaling inhibitors.Expert opinion: Downregulation of the PI3K/AKT/mTOR pathway is very important for treating all types of cancers. Thus, further studies are required to establish novel prognostic factors to support the current progress in cancer treatment with emphasis on this pathway.

Role of PI3K in the Progression and Regression of Atherosclerosis

Phosphatidylinositol 3 kinase (PI3K) is a key molecule in the initiation of signal transduction pathways after the binding of extracellular signals to cell surface receptors. An intracellular kinase, PI3K activates multiple intracellular signaling pathways that affect cell growth, proliferation, migration, secretion, differentiation, transcription and translation. Dysregulation of PI3K activity, and as aberrant PI3K signaling, lead to a broad range of human diseases, such as cancer, immune disorders, diabetes, and cardiovascular diseases. A growing number of studies have shown that PI3K and its signaling pathways play key roles in the pathophysiological process of atherosclerosis. Furthermore, drugs targeting PI3K and its related signaling pathways are promising treatments for atherosclerosis. Therefore, we have reviewed how PI3K, an important regulatory factor, mediates the development of atherosclerosis and how targeting PI3K can be used to prevent and treat atherosclerosis.

PI3Kγ Regulatory Protein p84 Determines Mast Cell Sensitivity to Ras Inhibition-Moving Towards Cell Specific PI3K Targeting?

Mast cells are the major effector cells in immunoglobulin E (IgE)-mediated allergy. The high affinity IgE receptor FcεRI, as well as G protein-coupled receptors (GPCRs) on the mast cell surface signals to phosphoinositide 3-kinase γ (PI3Kγ) to initiate degranulation, cytokine release, and chemotaxis. PI3Kγ is therefore considered as a target for treatment of allergic disorders. However, leukocyte PI3Kγ is key to many functions in innate and adaptive immunity, and attenuation of host defense mechanisms is an expected adverse effect that complicates treatment of chronic illnesses. PI3Kγ operates as a p110γ/p84 or p110γ/p101 complex, where p110γ/p84 requires Ras activation. Here we investigated if modulation of Ras-isoprenylation could target PI3Kγ activity to attenuate PI3Kγ-dependent mast cell responses without impairment of macrophage functions. In murine bone marrow-derived mast cells, GPCR stimulation triggers activation of N-Ras and H-Ras isoforms, which is followed by the phosphorylation of protein kinase B (PKB/Akt) relayed through PI3Kγ. Although K-Ras is normally not activated in Ras wild-type cells, it is able to compensate for genetically deleted N- and H-Ras isoforms. Inhibition of Ras isoprenylation with farnesyltransferase inhibitor FTI-277 leads to a significant reduction of mast cell degranulation, cytokine production, and migration. Complementation experiments expressing PI3Kγ adaptor proteins p84 or p101 demonstrated a differential sensitivity towards Ras-inhibition depending on PI3Kγ complex composition. Mast cell responses are exclusively p84-dependent and were effectively controlled by FTI-277. Similar results were obtained when GTP-Ras was inactivated by overexpression of the GAP-domain of Neurofibromin-1 (NF-1). Unlike mast cells, macrophages express p84 and p101 but are p101-dominated and thus remain functional under treatment with FTI-277. Our work demonstrates that p101 and p84 have distinct physiological roles, and that Ras dependence of PI3Kγ signaling differs between cell types. FTI-277 reduces GPCR-activated PI3Kγ  responses in p84-expressing but not p101-containing bone marrow derived cells. However, prenylation inhibitors have pleiotropic effects beyond Ras and non-tolerable side-effects that disfavor further clinical validation. Statins are, however, clinically well-established drugs that have previously been proposed to block mast cell degranulation by interference with protein prenylation. We show here that Simvastatin inhibits mast cell degranulation, but that this does not occur via Ras-PI3Kγ pathway alterations.

Smooth muscle cells-derived CXCL10 prevents endothelial healing through PI3Kγ-dependent T cells response

AIMS

Defects in efficient endothelial healing have been associated with complication of atherosclerosis such as post-angioplasty neoatherosclerosis and plaque erosion leading to thrombus formation. However, current preventive strategies do not consider re-endothelialization in their design. Here, we investigate mechanisms linking immune processes and defect in re-endothelialization. We especially evaluate if targeting phosphoinositide 3-kinase γ immune processes could restore endothelial healing and identify immune mediators responsible for these defects.

METHODS AND RESULTS

Using in vivo model of endovascular injury, we showed that both ubiquitous genetic inactivation of PI3Kγ and hematopoietic cell-specific PI3Kγ deletion improved re-endothelialization and that CD4+ T-cell population drives this effect. Accordingly, absence of PI3Kγ activity correlates with a decrease in local IFNγ secretion and its downstream interferon-inducible chemokine CXCL10. CXCL10 neutralization promoted re-endothelialization in vivo as the same level than those observed in absence of PI3Kγ suggesting a role of CXCL10 in re-endothelialization defect. Using a new established ex vivo model of carotid re-endothelialization, we showed that blocking CXCL10 restore the IFNγ-induced inhibition of endothelial healing and identify smooth muscle cells as the source of CXCL10 secretion in response to Th1 cytokine.

CONCLUSION

Altogether, these findings expose an unforeseen cellular cross-talk within the arterial wall whereby a PI3Kγ-dependent T-cell response leads to CXCL10 production by smooth muscle cells which in turn inhibits endothelial healing. Therefore, both PI3Kγ and the IFNγ/CXCL10 axis provide novel strategies to promote endothelial healing.

Role of the lncRNA-mRNA network in atherosclerosis using ox-low-density lipoprotein-induced macrophage-derived foam cells

Atherosclerosis (AS) is the leading cause of coronary heart disease, cerebral infarction, peripheral vascular disease, and other cardiovascular diseases, making it a major risk factor for high morbidity and mortality. Although long non-coding RNAs (lncRNAs) have been reported to play a role in AS, the specific effects of lncRNAs on AS remain largely unknown. Thus the purpose of this study was to explore the roles of mRNAs and lncRNAs in atherosclerosis via an ox-low-density lipoprotein induced macrophage-derived foam cell model. Microarray analysis identified a total of 50 688 mRNAs and 1514 lncRNAs, including 51 lncRNAs and 1730 mRNAs that were significantly dysregulated in the model group (p-adjust < 0.05 and |log 2FC| > 2). The results of gene ontology enrichment and Kyoto Encyclopedia of Genes and Genomes pathway analyses demonstrated that the dysregulated genes were associated with cell proliferation, cell apoptosis, and inflammatory responses. An lncRNA-mRNA co-expression network was created to further analyze the key regulatory genes. The lncRNAs Brip1os, Gm16586, AU020206, 9430034N14Rik, 2510016D11Rik, LNC_000709, Gm15472, Gm20703, and Dubr were identified as potential biomarkers in macrophage-derived foam cells. Based on 9 lncRNAs and 13 mRNAs, key genes influencing the degree of cell proliferation and cell apoptosis and the subsequent development of AS were identified. Q-PCR verified the key dysregulated genes. Thus, our results suggest potential therapeutic targets for AS and provide avenues for further research on AS pathogenesis.

THP-1 macrophage cholesterol efflux is impaired by palmitoleate through Akt activation

Lipoprotein lipase (LPL) is upregulated in atherosclerotic lesions and it may promote the progression of atherosclerosis, but the mechanisms behind this process are not completely understood. We previously showed that the phosphorylation of Akt within THP-1 macrophages is increased in response to the lipid hydrolysis products generated by LPL from total lipoproteins. Notably, the free fatty acid (FFA) component was responsible for this effect. In the present study, we aimed to reveal more detail as to how the FFA component may affect Akt signalling. We show that the phosphorylation of Akt within THP-1 macrophages increases with total FFA concentration and that phosphorylation is elevated up to 18 hours. We further show that specifically the palmitoleate component of the total FFA affects Akt phosphorylation. This is tied with changes to the levels of select molecular species of phosphoinositides. We further show that the total FFA component, and specifically palmitoleate, reduces apolipoprotein A-I-mediated cholesterol efflux, and that the reduction can be reversed in the presence of the Akt inhibitor MK-2206. Overall, our data support a negative role for the FFA component of lipoprotein hydrolysis products generated by LPL, by impairing macrophage cholesterol efflux via Akt activation.

Thymoquinone attenuates IgE-mediated allergic response via pi3k-Akt-NFκB pathway and upregulation of the Nrf2-HO1 axis

IgE-dependent reactions mediate the majority of allergic diseases. This study explores the effects of thymoquinone (Tq) on IgE-mediated allergic response in activated mast cells, basophils, and neutrophils. Tq treatment resulted in a dose-dependent decrease in levels of TNF-α and IL-4 in activated RBL-2H3 cells. Tq inhibited the degranulation of these cells with an IC₅₀ value of 56.37 µM. Moreover, the compound suppressed basophil activation induced through FcεRI receptors with an IC₅₀ value of 45.76 µM in heparinized human whole blood. Likewise, neutrophil migration and elastase activity were dose-dependently reduced. While Tq decreased the phosphorylation of Akt and NFκB in activated RBL-2H3 cells, it increased nuclear Nrf2 and HO-1 antioxidant proteins. Our results indicate that Tq possesses demonstrable activity in cellular models of IgE-mediated allergic reactions. PRACTICAL APPLICATIONS: The current study sheds light on the mechanistic pathways of Tq on IgE-based response in activated mast cells, basophils, and neutrophils. The output of this preclinical in vitro study may be translated into better chemotherapeutic applications of Tq and its analogs in the treatment of allergic inflammation. However, a detailed investigation of in vivo models is recommended.

PI3K inhibitors in thrombosis and cardiovascular disease

Phosphoinositide 3-kinases (PI3Ks) are lipid kinases that regulate important intracellular signalling and vesicle trafficking events via the generation of 3-phosphoinositides. Comprising eight core isoforms across three classes, the PI3K family displays broad expression and function throughout mammalian tissues, and the (patho)physiological roles of these enzymes in the cardiovascular system present the PI3Ks as potential therapeutic targets in settings such as thrombosis, atherosclerosis and heart failure. This review will discuss the PI3K enzymes and their roles in cardiovascular physiology and disease, with a particular focus on platelet function and thrombosis. The current progress and future potential of targeting the PI3K enzymes for therapeutic benefit in cardiovascular disease will be considered, while the challenges of developing drugs against these master cellular regulators will be discussed.

PI3Kγ (Phosphoinositide 3-Kinase γ) Regulates Vascular Smooth Muscle Cell Phenotypic Modulation and Neointimal Formation Through CREB (Cyclic AMP-Response Element Binding Protein)/YAP (Yes-Associated Protein) Signaling

Objective- Vascular smooth muscle cells (VSMCs) phenotype modulation is critical for the resolution of vascular injury. Genetic and pharmacological inhibition of PI3Kγ (phosphoinositide 3-kinase γ) exerts anti-inflammatory and protective effects in multiple cardiovascular diseases. This study investigated the role of PI3Kγ and its downstream effector molecules in the regulation of VSMC phenotypic modulation and neointimal formation in response to vascular injury. Approach and Results- Increased expression of PI3Kγ was found in injured vessel wall as well in cultured, serum-activated wild-type VSMCs, accompanied by a reduction in the expression of calponin and SM22α, 2 differentiation markers of VSMCs. However, the injury-induced downregulation of calponin and SM22α was profoundly attenuated in PI3Kγ^-/- mice. Pharmacological inhibition and short hairpin RNA knockdown of PI3Kγ (PI3Kγ-KD) markedly attenuated YAP (Yes-associated protein) expression and CREB (cyclic AMP-response element binding protein) activation but improved the downregulation of differentiation genes in cultured VSMCs accompanied by reduced cell proliferation and migration. Mechanistically, activated CREB upregulated YAP transcriptional expression through binding to its promoter. Ectopic expression of YAP strikingly repressed the expression of differentiation genes even in PI3Kγ-KD VSMCs. Moreover, established carotid artery ligation and chimeric mice models demonstrate that deletion of PI3Kγ in naïve PI3Kγ^-/- mice as well as in chimeric mice lacking PI3Kγ either in bone marrow or vascular wall significantly reduced neointimal formation after injury. Conclusions- PI3Kγ controls phenotypic modulation of VSMCs by regulating transcription factor CREB activation and YAP expression. Modulating PI3Kγ signaling on local vascular wall may represent a new therapeutic approach to treat proliferative vascular disease.

TLR4 (Toll-Like Receptor 4)-Dependent Signaling Drives Extracellular Catabolism of LDL (Low-Density Lipoprotein) Aggregates

OBJECTIVE

Aggregation and modification of LDLs (low-density lipoproteins) promote their retention and accumulation in the arteries. This is a critical initiating factor during atherosclerosis. Macrophage catabolism of agLDL (aggregated LDL) occurs using a specialized extracellular, hydrolytic compartment, the lysosomal synapse. Compartment formation by local actin polymerization and delivery of lysosomal contents by exocytosis promotes acidification of the compartment and degradation of agLDL. Internalization of metabolites, such as cholesterol, promotes foam cell formation, a process that drives atherogenesis. Furthermore, there is accumulating evidence for the involvement of TLR4 (Toll-like receptor 4) and its adaptor protein MyD88 (myeloid differentiation primary response 88) in atherosclerosis. Here, we investigated the role of TLR4 in catabolism of agLDL using the lysosomal synapse and foam cell formation. Approach and Results: Using bone marrow-derived macrophages from knockout mice, we find that TLR4 and MyD88 regulate compartment formation, lysosome exocytosis, acidification of the compartment, and foam cell formation. Using siRNA (small interfering RNA), pharmacological inhibition and knockout bone marrow-derived macrophages, we implicate SYK (spleen tyrosine kinase), PI3K (phosphoinositide 3-kinase), and Akt in agLDL catabolism using the lysosomal synapse. Using bone marrow transplantation of LDL receptor knockout mice with TLR4 knockout bone marrow, we show that deficiency of TLR4 protects macrophages from lipid accumulation during atherosclerosis. Finally, we demonstrate that macrophages in vivo form an extracellular compartment and exocytose lysosome contents similar to that observed in vitro for degradation of agLDL.

CONCLUSIONS

We present a mechanism in which interaction of macrophages with agLDL initiates a TLR4 signaling pathway, resulting in formation of the lysosomal synapse, catabolism of agLDL, and lipid accumulation in vitro and in vivo.

For Better or Worse: The Potential for Dose Limiting the On-Target Toxicity of PI 3-Kinase Inhibitors

The hyper-activation of the phosphoinositide (PI) 3-kinase signaling pathway is a hallmark of many cancers and overgrowth syndromes, and as a result, there has been intense interest in the development of drugs that target the various isoforms of PI 3-kinase. Given the key role PI 3-kinases play in many normal cell functions, there is significant potential for the disruption of essential cellular functions by PI 3-kinase inhibitors in normal tissues; so-called on-target drug toxicity. It is, therefore, no surprise that progress within the clinical development of PI 3-kinase inhibitors as single-agent anti-cancer therapies has been slowed by the difficulty of identifying a therapeutic window. The aim of this review is to place the cellular, tissue and whole-body effects of PI 3-kinase inhibition in the context of understanding the potential for dose limiting on-target toxicities and to introduce possible strategies to overcome these.

Phosphoinositide 3-kinase/protein kinase B inhibition restores regulatory T cell's function in pulmonary sarcoidosis

Sarcoidosis is a systemic granulomatous disease associated with Th1/ regulatory T cells (Treg) paradigm. PI3K/Akt signaling, critical for maintaining Treg's homeostasis, is aberrantly activated in sarcoidosis patients. Here we tested the role of the PI3K inhibitors, LY294002 and BKM120, in immune modulation in experimental pulmonary sarcoidosis, concerning Th1/Th17/Treg immune profile detected by fluorescence-activated cell sorting analysis or quantitative polymerase chain reaction, as well as the effect on Treg's suppressive functions. Our investigation showed abnormal activation of PI3K/Akt signaling both in lung and Treg in pulmonary sarcoidosis, along with decreased frequency and damaged function of Treg. Blockage of PI3K suppressed this signaling in Treg, rebalanced Th1/Treg, inhibited the production of inflammatory cytokines, and enhanced Treg's function. These results demonstrate the key role of the PI3K/Akt signaling in regulating Th1/Th2 rebalances and indicates that PI3K/Akt signaling is critical for the optimal Treg responses in pulmonary sarcoidosis. Thus, PI3K inhibitors have potential for therapeutic translation, and can be candidate for add-on drugs to treat pulmonary sarcoidosis.

PI3Kγ promotes vascular smooth muscle cell phenotypic modulation and transplant arteriosclerosis via a SOX9-dependent mechanism

Background

Transplant arteriosclerosis (TA) remains the major cause of chronic graft failure in solid organ transplantation. The phenotypic modulation of vascular smooth muscle cells (VSMCs) is a key event for the initiation and progression of neointimal formation and TA. This study aims to explore the role and underlying mechanism of phosphoinositide 3-kinases γ (PI3Kγ) in VSMC phenotypic modulation and TA.

Methods

The rat model of aortic transplantation was established to detect PI3Kγ expression and its role in neointimal formation and vascular remodeling in vivo. PI3Kγ shRNA transfection was employed to knockdown PI3Kγ gene. Aortic VSMCs was cultured and treated with TNF-α to explore the role and molecular mechanism of PI3Kγ in VSMC phenotypic modulation.

Findings

Activated PI3Kγ/p-Akt signaling was observed in aortic allografts and in TNF-α-treated VSMCs. Lentivirus-mediated shRNA transfection effectively inhibited PI3Kγ expression in medial VSMCs while restoring the expression of VSMC contractile genes, associated with impaired neointimal formation in aortic allografts. In cultured VSMCs, PI3Kγ blockade with pharmacological inhibitor or genetic knockdown markedly abrogated TNF-α-induced downregulation of VSMC contractile genes and increase in cellular proliferation and migration. Moreover, SOX9 located in nucleus competitively inhibited the interaction of Myocardin and SRF, while PI3Kγ inhibition robustly reduced SOX9 expression and its nuclear translocation and repaired the Myocardin/SRF association.

Interpretation

These results suggest that PI3Kγ plays a critical role in VSMC phenotypic modulation via a SOX9-dependent mechanism. Therefore, PI3Kγ in VSMCs may represent a promising therapeutic target for the treatment of TA.

Fund

National Natural Science Foundation of China.

Targeting the B-cell receptor pathway: a review of current and future therapies for non-Hodgkin's lymphoma

INTRODUCTION

The B-cell receptor (BCR) pathway is a crucial aspect of mature lymphocytes and is maintained in B-cell neoplasms. Many small module inhibitors targeting kinases within the BCR pathway are approved, with others in development, offering alternative treatment options to standard chemoimmunotherapy. Areas covered: This review covers both approved inhibitors and investigational inhibitors of spleen tyrosine kinase (SYK), Bruton's tyrosine kinase (BTK), and phosphoinositide-3-kinase (PI3K) in the treatment of B-cell lymphomas. To collect relevant articles, a literature search was completed through the use of PubMed and abstracts from ASH and ASCO national meetings. Search terms including non-Hodgkin lymphoma, and BCR inhibitors, as well as the individual drug names, were utilized. The majority of included studies are dated from 2012 to March 2018. Expert opinion: BCR pathway inhibitors, such as ibrutinib and idelalisib, are novel treatments for non-Hodgkin lymphomas. While providing alternative treatment options to those with high-risk disease, poor functional status, and relapsed disease, outside of chronic lymphocytic leukemia (CLL), they have been limited to the relapsed/refractory setting. Their mechanisms of action, off/on-target effects, and resistance patterns create unique therapeutic dilemmas. It is our opinion that more specific inhibitors, as well as combination therapy, will define the future for BCR inhibitors.

PI3K and Calcium Signaling in Cardiovascular Disease

Receptor signaling relays on intracellular events amplified by secondary and tertiary messenger molecules. In cardiomyocytes and smooth muscle cells, cyclic AMP (cAMP) and subsequent calcium (Ca²⁺) fluxes are the best characterized receptor-regulated signaling events. However, most of receptors able to modify contractility and other intracellular responses signal through a variety of other messengers, and whether these signaling events are interconnected has long remained unclear. For example, the PI3K (phosphoinositide 3-kinase) pathway connected to the production of the lipid second messenger PIP3/PtdIns(3,4,5)P3 (phosphatidylinositol (3,4,5)-trisphosphate) is potentially involved in metabolic regulation, activation of hypertrophy, and survival pathways. Recent studies, highlighted in this review, started to interconnect PI3K pathway activation to Ca²⁺ signaling. This interdependency, by balancing contractility with metabolic control, is crucial for cells of the cardiovascular system and is emerging to play key roles in disease development. Better understanding of the interplay between Ca²⁺ and PI3K signaling is, thus, expected to provide new ground for therapeutic intervention. This review explores the emerging molecular mechanisms linking Ca²⁺ and PI3K signaling in health and disease.

CFTR protects against vascular inflammation and atherogenesis in apolipoprotein E-deficient mice

Atherosclerosis is a chronic inflammatory disease of the vascular wall. Dysfunction of cystic fibrosis transmembrane conductance regulator (CFTR) has been shown to result in inflammatory responses in cystic fibrosis (CF) patients. However, little is known about the role of CFTR in vascular inflammation and atherogenesis. Our results showed that CFTR was dominantly expressed in macrophages of atherosclerotic plaque and reduced in aorta and aortic sinus from atherosclerotic apolipoprotein E-deficient (apoE^−/−) mice. In vivo administration of adenovirus encoding CFTR (Ad-CFTR) with apoE^−/− mice fed on high-fat diet (HFD) improved plaque stability by decreasing lipid accumulation and necrotic area and increasing smooth muscle cell content and collagen. The Ad-CFTR-treated mice also displayed reduced proinflammatory cytokines levels in aorta and peritoneal macrophages, whereas the anti-inflammatory M2 macrophage markers were increased. Confocal microscopy revealed that the infiltration of T lymphocytes, neutrophils, and macrophages in aortic sinus was markedly attenuated in Ad-CFTR-treated apoE^−/− mice. Moreover, in vitro experiments showed that overexpression of CFTR inhibited ox-LDL-induced the migration of peritoneal macrophages. Finally, it was observed that CFTR up-regulation suppressed NFκB and MAPKs activity induced by ox-LDL. Inhibition of JNK or ERK abrogated CFTR down-regulation induced NFκB activation, whereas NFκB inhibitor had no effect on JNK or ERK activation. Taken together, these results demonstrate that CFTR prevents inflammation and atherogenesis via inhibition of NFκB and MAPKs activation. Our data suggest that CFTR may present a potential therapeutic target for the treatment of vascular inflammation and development of atherosclerotic disease.

SGK1: The Dark Side of PI3K Signaling

Activation of the PI3K pathway is central to a variety of physiological and pathological processes. In these contexts, AKT is classically considered the de facto mediator of PI3K-dependent signaling. However, in recent years, accumulating data point to the existence of additional effectors of PI3K activity, parallel to and independent of AKT, that play critical and unique roles in mediating different developmental, homeostatic, and pathological processes. In this review, I summarize and discuss our current understanding of the function of the serine/threonine kinase SGK1 as a downstream effector of PI3K, and try to separate targets and pathways validated as uniquely SGK1-dependent from those shared with AKT.

The Multifaceted Roles of PI3Kγ in Hypertension, Vascular Biology, and Inflammation

PI3Kγ is a multifaceted protein, crucially involved in cardiovascular and immune systems. Several studies described the biological and physiological functions of this enzyme in the regulation of cardiovascular system, while others stressed its role in the modulation of immunity. Although PI3Kγ has been historically investigated for its role in leukocytes, the last decade of research also dedicated efforts to explore its functions in the cardiovascular system. In this review, we report an overview recapitulating how PI3Kγ signaling participates in the regulation of vascular functions involved in blood pressure regulation. Moreover, we also summarize the main functions of PI3Kγ in immune responses that could be potentially important in the interaction with the cardiovascular system. Considering that vascular and immune mechanisms are increasingly emerging as intertwining players in hypertension, PI3Kγ could be an intriguing pathway acting on both sides. The availability of specific inhibitors introduces a perspective of further translational research and clinical approaches that could be exploited in hypertension.

Heat-killed Staphylococcus aureus reduces atherosclerosis by inducing anti-inflammatory macrophages

BACKGROUND

Staphylococcus aureus cell wall components can induce IL-10 responses by immune cells, which may be atheroprotective. Therefore, in this study, we investigated whether heat-killed S. aureus (HK-SA) could inhibit the development of atherosclerosis.

METHODS

Atherosclerosis-susceptible LDL receptor-deficient mice were administered intraperitoneal HK-SA twice weekly and fed a Western-type diet for 6 weeks.

RESULTS

HK-SA administration resulted in a 1.6-fold increase in IL-10 production by peritoneal macrophages and splenocytes, and a 12-fold increase in serum IL-10 levels. Moreover, aortic plaque ICAM-1, VCAM-1 and CCL2 expression levels were significantly downregulated by on average 40%. HK-SA-treated mice had reduced numbers of inflammatory Ly-6C(hi) monocytes as well as Th1 and Th17 cells in the circulation and spleen, respectively. Attenuated leucocyte recruitment resulted in a significant inhibition of macrophage and T cell infiltration in atherosclerotic plaques, culminating in a significant 34% reduction in the development of atherosclerosis. To determine the effects of intraperitoneal HK-SA treatment, we stimulated macrophages with HK-SA in vitro. This resulted in a significant toll-like receptor 2 (TLR2)-dependent increase in IL-10, arginase-1, iNOS, TNF-α, PD-L1, CCL22 and indoleamine 2,3-dioxygenase expression. It was found that phosphoinositide 3-kinase crucially determined the balance of pro- and anti-inflammatory gene expression. The HK-SA-induced macrophage phenotype resembled M2b-like immunoregulatory macrophages.

CONCLUSIONS

We have shown that HK-SA treatment induces strong anti-inflammatory IL-10 responses by macrophages, which are largely dependent on TLR2 and PI3K, and protects against the development of atherosclerosis. Commensalism with S. aureus could thus reduce cardiovascular events.

Macrophage IKKα Deficiency Suppresses Akt Phosphorylation, Reduces Cell Survival, and Decreases Early Atherosclerosis

OBJECTIVE

The IκB kinase (IKK) is an enzyme complex that initiates the nuclear factor κB transcription factor cascade, which is important in regulating multiple cellular responses. IKKα is directly associated with 2 major prosurvival pathways, PI3K/Akt and nuclear factor κB, but its role in cell survival is not clear. Macrophages play critical roles in the pathogenesis of atherosclerosis, yet the impact of IKKα signaling on macrophage survival and atherogenesis remains unclear.

APPROACH AND RESULTS

Here, we demonstrate that genetic IKKα deficiency, as well as pharmacological inhibition of IKK, in mouse macrophages significantly reduces Akt S(473) phosphorylation, which is accompanied by suppression of mTOR complex 2 signaling. Moreover, IKKα null macrophages treated with lipotoxic palmitic acid exhibited early exhaustion of Akt signaling compared with wild-type cells. This was accompanied by a dramatic decrease in the resistance of IKKα(-/-) monocytes and macrophages to different proapoptotic stimuli compared with wild-type cells. In vivo, IKKα deficiency increased macrophage apoptosis in atherosclerotic lesions and decreased early atherosclerosis in both female and male low-density lipoprotein receptor (LDLR)(-/-) mice reconstituted with IKKα(-/-) hematopoietic cells and fed with the Western diet for 8 weeks compared with control LDLR(-/-) mice transplanted with wild-type cells.

CONCLUSIONS

Hematopoietic IKKα deficiency in mouse suppresses Akt signaling, compromising monocyte/macrophage survival and this decreases early atherosclerosis.

Macrophage IKKα Deficiency Suppresses Akt Phosphorylation, Reduces Cell Survival, and Decreases Early Atherosclerosis

OBJECTIVE

The IκB kinase (IKK) is an enzyme complex that initiates the nuclear factor κB transcription factor cascade, which is important in regulating multiple cellular responses. IKKα is directly associated with 2 major prosurvival pathways, PI3K/Akt and nuclear factor κB, but its role in cell survival is not clear. Macrophages play critical roles in the pathogenesis of atherosclerosis, yet the impact of IKKα signaling on macrophage survival and atherogenesis remains unclear.

APPROACH AND RESULTS

Here, we demonstrate that genetic IKKα deficiency, as well as pharmacological inhibition of IKK, in mouse macrophages significantly reduces Akt S(473) phosphorylation, which is accompanied by suppression of mTOR complex 2 signaling. Moreover, IKKα null macrophages treated with lipotoxic palmitic acid exhibited early exhaustion of Akt signaling compared with wild-type cells. This was accompanied by a dramatic decrease in the resistance of IKKα(-/-) monocytes and macrophages to different proapoptotic stimuli compared with wild-type cells. In vivo, IKKα deficiency increased macrophage apoptosis in atherosclerotic lesions and decreased early atherosclerosis in both female and male low-density lipoprotein receptor (LDLR)(-/-) mice reconstituted with IKKα(-/-) hematopoietic cells and fed with the Western diet for 8 weeks compared with control LDLR(-/-) mice transplanted with wild-type cells.

CONCLUSIONS

Hematopoietic IKKα deficiency in mouse suppresses Akt signaling, compromising monocyte/macrophage survival and this decreases early atherosclerosis.

Wen-Xin Decoction ameliorates vascular endothelium dysfunction via the PI3K/AKT/eNOS pathway in experimental atherosclerosis in rats

Background

Nitric oxide (NO) is the most powerful vasodilator that inhibits leukocyte adhesion, platelet aggregation, and vascular smooth muscle cell proliferation. However, excessive NO can cause lipid peroxidation and direct endothelial cell damage. Therefore, investigation of the role of NO in artherosclerosis development is important. Wen-Xin Decoction (WXD) has been shown to relieve myocardial ischemia reperfusion injury and prevent leukocyte adhesion and invasion; in addition, it can accelerate angiogenesis and prevent platelet activation and aggregation. In this study, we focused on the NO pathway to further clarify the protective effects of WXD on the vascular endothelium in rat models of artherosclerosis.

Methods

Wistar rats were randomly divided into a normal group (n = 10) and a model group (n = 75). Rat models of atherosclerosis were generated by intraperitoneal vitamin D3 (3 months) injections and administration of a high-fat diet (3 months with vitamin D3 and 2 months alone). The model rats were randomly divided into five groups (n = 15 each): model (saline), atorvastatin (4.8 mg/kg/d atorvastatin), high-dose WXD (9 g/kg/d), medium-dose WXD (4.5 g/kg/d), and low-dose WXD (2.25 g/kg/d) groups. Each group received continuous drug or saline administration (suspended liquid gavage) for 30 days, following which all animals were sacrificed. The ultrastructure and histopathological changes of vascular endothelial cells and the expression of PI3K/AKT/eNOS and iNOS in the thoracic aorta tissue were analyzed.

Results

WXD increased NO levels, modulated the NO/ET-1 ratio, and promoted repair of the injured vascular endothelium in a dose-dependent manner. At a high dose, WXD regulated the NO/ET-1 ratio as effectively as atorvastatin; furthermore, it increased NO levels within the physiological range to prevent endothelial damage caused by excessive NO expression. Real-time polymerase chain reaction and Western blot analysis showed that WXD significantly upregulated the mRNA and protein expressions of PI3K, AKT, and eNOS mRNA and significantly increased AKT and eNOS phosphorylation.

Conclusions

Our results suggest that WXD protects and maintains the integrity of the vascular endothelium by activating the PI3K/AKT/eNOS pathway, decreasing iNOS expression, and promoting the release of physiological NO levels.

Variation in the Phosphoinositide 3-Kinase Gamma Gene Affects Plasma HDL-Cholesterol without Modification of Metabolic or Inflammatory Markers

Objective

Phosphoinositide 3-kinase γ (PI3Kγ) is a G-protein-coupled receptor-activated lipid kinase mainly expressed in leukocytes and cells of the cardiovascular system. PI3Kγ plays an important signaling role in inflammatory processes. Since subclinical inflammation is a hallmark of atherosclerosis, obesity-related insulin resistance, and pancreatic β-cell failure, we asked whether common genetic variation in the PI3Kγ gene (PIK3CG) contributes to body fat content/distribution, serum adipokine/cytokine concentrations, alterations in plasma lipid profiles, insulin sensitivity, insulin release, and glucose homeostasis.

Study Design

Using a tagging single nucleotide polymorphism (SNP) approach, we analyzed genotype-phenotype associations in 2,068 German subjects genotyped for 10 PIK3CG SNPs and characterized by oral glucose tolerance tests. In subgroups, data from hyperinsulinaemic-euglycaemic clamps, magnetic resonance spectroscopy of the liver, whole-body magnetic resonance imaging, and intravenous glucose tolerance tests were available, and peripheral blood mononuclear cells (PBMCs) were used for gene expression analysis.

Results

After appropriate adjustment, none of the PIK3CG tagging SNPs was significantly associated with body fat content/distribution, adipokine/cytokine concentrations, insulin sensitivity, insulin secretion, or blood glucose concentrations (p>0.0127, all; Bonferroni-corrected α-level: 0.0051). However, six non-linked SNPs displayed at least nominal associations with plasma HDL-cholesterol concentrations, two of them (rs4288294 and rs116697954) reaching the level of study-wide significance (p = 0.0003 and p = 0.0004, respectively). More precisely, rs4288294 and rs116697954 influenced HDL2-, but not HDL3-, cholesterol. With respect to the SNPs’ in vivo functionality, rs4288294 was significantly associated with PIK3CG mRNA expression in PBMCs.

Conclusions

We could demonstrate that common genetic variation in the PIK3CG locus, possibly via altered PIK3CG gene expression, determines plasma HDL-cholesterol concentrations. Since HDL2-, but not HDL3-, cholesterol is influenced by PIK3CG variants, PI3Kγ may play a role in HDL clearance rather than in HDL biogenesis. Even though the molecular pathways connecting PI3Kγ and HDL metabolism remain to be further elucidated, this finding could add a novel aspect to the pathophysiological role of PI3Kγ in atherogenesis.

PI3K signaling in arterial diseases: Non redundant functions of the PI3K isoforms

Cardiovascular diseases are the most common cause of death around the world. This includes atherosclerosis and the adverse effects of its treatment, such as restenosis and thrombotic complications. The development of these arterial pathologies requires a series of highly-intertwined interactions between immune and arterial cells, leading to specific inflammatory and fibroproliferative cellular responses. In the last few years, the study of phosphoinositide 3-kinase (PI3K) functions has become an attractive area of investigation in the field of arterial diseases, especially since inhibitors of specific PI3K isoforms have been developed. The PI3K family includes 8 members divided into classes I, II or III depending on their substrate specificity. Although some of the different isoforms are responsible for the production of the same 3-phosphoinositides, they each have specific, non-redundant functions as a result of differences in expression levels in different cell types, activation mechanisms and specific subcellular locations. This review will focus on the functions of the different PI3K isoforms that are suspected as having protective or deleterious effects in both the various immune cells and types of cell found in the arterial wall. It will also discuss our current understanding in the context of which PI3K isoform(s) should be targeted for future therapeutic interventions to prevent or treat arterial diseases.

Phosphoinositide 3-kinase: friend and foe in cardiovascular disease

Class I phosphoinositide 3-kinases (PI3Ks) are a family of lipid kinases activated by cell membrane receptors, either receptor tyrosine kinases (RTKs) or G protein–coupled receptors (GPCRs), to catalyze the production of the lipid second messenger phosphatidylinositol (3,4,5)-trisphosphate (PIP3). These enzymes engage multiple downstream intracellular signaling pathways controlling cell proliferation, survival and migration. In the cardiovascular system, the four class I PI3K isoforms, PI3Kα, PI3Kβ, PI3Kδ, and PI3Kγ are differentially expressed in distinct cell subsets which include cardiomyocytes, fibroblasts, endothelial, and vascular smooth muscle cells as well as leukocytes, suggesting specific functions for distinct PI3K isoenzymes. During the last decades, genetic disruption studies targeting different PI3K genes have elucidated the contribution of specific isoenzymes to cardiac and vascular function regulation, highlighting both beneficial and maladaptive roles. New layers of complexity in the function of PI3Ks have recently emerged, indicating that distinct PI3K isoforms are interconnected by various crosstalk events and can function not only as kinases, but also as scaffold proteins coordinating key signalosomes in cardiovascular health and disease. In this review, we will summarize major breakthroughs in the comprehension of detrimental and beneficial actions of PI3K signaling in cardiovascular homeostasis, and we will discuss recently unraveled cross-talk and scaffold mechanisms as well as the role of the less characterized class II and III PI3K isoforms.

The influence of dysfunctional signaling and lipid homeostasis in mediating the inflammatory responses during atherosclerosis

Atherosclerosis, the underlying cause of myocardial infarction and thrombotic cerebrovascular events, is responsible for the majority of deaths in westernized societies. Mortality from this disease is also increasing at a marked rate in developing countries due to the acquisition of a westernized lifestyle accompanied with elevated rates of obesity and diabetes. Atherosclerosis is recognized as a chronic inflammatory disorder associated with lipid accumulation and the development of fibrotic plaques within the walls of medium and large arteries. A range of immune cells, such as macrophages and T-lymphocytes, through the action of various cytokines, such as interleukins-1 and -33, transforming growth factor-β and interferon-γ, orchestrates the inflammatory response in this disease. The disease is also characterized by marked dysfunction in lipid homeostasis and signaling pathways that control the inflammatory response. This review will discuss the molecular basis of atherosclerosis with particular emphasis on the roles of the immune cells and cytokines along with the dysfunctional lipid homeostasis and cell signaling associated with this disease.

Pivotal Role of Serum- and Glucocorticoid-Inducible Kinase 1 in Vascular Inflammation and Atherogenesis

Objective—

Atherosclerosis, an inflammatory disease of arterial vessel walls, requires migration and matrix metalloproteinase (MMP)-9–dependent invasion of monocytes/macrophages into the vascular wall. MMP-9 expression is stimulated by transcription factor nuclear factor-κB, which is regulated by inhibitor κB (IκB) and thus IκB kinase. Regulators of nuclear factor-κB include serum- and glucocorticoid-inducible kinase 1 (SGK1). The present study explored involvement of SGK1 in vascular inflammation and atherogenesis.

Approach and Results—

Gene-targeted apolipoprotein E (ApoE)–deficient mice without ( apoe −/− sgk1 +/+ ) or with ( apoe −/− sgk1 −/− ) additional SGK1 knockout received 16-week cholesterol-rich diet. According to immunohistochemistry atherosclerotic lesions in aorta and carotid artery, vascular CD45 + leukocyte infiltration, Mac-3 + macrophage infiltration, vascular smooth muscle cell content, MMP-2, and MMP-9 positive areas in atherosclerotic tissue were significantly less in apoe −/− sgk1 −/− mice than in apoe −/− sgk1 +/+ mice. As determined by Boyden chamber, thioglycollate-induced peritonitis and air pouch model, migration of SGK1-deficient CD11b + F4/80 + macrophages was significantly diminished in vitro and in vivo. Zymographic MMP-2 and MMP-9 production, MMP-9 activity and invasion through matrigel in vitro were significantly less in sgk1 −/− than in sgk1 +/+ macrophages and in control plasmid–transfected or inactive K127N SGK1-transfected than in constitutively active S422D SGK1-transfected THP-1 cells. Confocal microscopy revealed reduced macrophage number and macrophage MMP-9 content in plaques of apoe −/− sgk1 −/− mice. In THP-1 cells, MMP-inhibitor GM6001 (25 μmol/L) abrogated S422D SGK1-induced MMP-9 production and invasion. According to reverse transcription polymerase chain reaction, MMP-9 transcript levels were significantly reduced in sgk1 −/− macrophages and strongly upregulated in S422D SGK1-transfected THP-1 cells compared with control plasmid–transfected or K127N SGK1-transfected THP-1 cells. According to immunoblotting and confocal microscopy, phosphorylation of IκB kinase and inhibitor κB and nuclear translocation of p50 were significantly lower in sgk1 −/− macrophages than in sgk1 +/+ macrophages and significantly higher in S422D SGK1-transfected THP-1 cells than in control plasmid–transfected or K127N SGK1-transfected THP-1 cells. Treatment of S422D SGK1-transfected THP-1 cells with IκB kinase-inhibitor BMS-345541 (10 μmol/L) abolished S422D SGK1-induced increase of MMP-9 transcription and gelatinase activity.

Conclusions—

SGK1 plays a pivotal role in vascular inflammation during atherogenesis. SGK1 participates in the regulation of monocyte/macrophage migration and MMP-9 transcription via regulation of nuclear factor-κB.

The phosphoinositide 3-kinase signaling pathway is involved in the control of modified low-density lipoprotein uptake by human macrophages

The transformation of macrophages into lipid-loaded foam cells is a critical early event in the pathogenesis of atherosclerosis. Both receptor-mediated uptake of modified LDL, mediated primarily by scavenger receptors-A (SR-A) and CD36 along with other proteins such as lipoprotein lipase (LPL), and macropinocytosis contribute to macrophage foam cell formation. The signaling pathways that are involved in the control of foam cell formation are not fully understood. In this study, we have investigated the role of phosphoinositide 3-kinase (PI3K) in relation to foam cell formation in human macrophages. The pan PI3K inhibitor LY294002 attenuated the uptake of modified LDL and macropinocytosis, as measured by Lucifer Yellow uptake, by human macrophages. In addition, the expression of SR-A, CD36 and LPL was attenuated by LY294002. The use of isoform-selective PI3K inhibitors showed that PI3K-β, -γ and -δ were all required for the expression of SR-A and CD36 whereas only PI3K-γ was necessary in the case of LPL. These studies reveal a pivotal role of PI3K in the control of macrophage foam cell formation and provide further evidence for their potential as therapeutic target against atherosclerosis.

PI3K signalling in inflammation

PI3Ks regulate several key events in the inflammatory response to damage and infection. There are four Class I PI3K isoforms (PI3Kα,β,γ,δ), three Class II PI3K isoforms (PI3KC2α, C2β, C2γ) and a single Class III PI3K. The four Class I isoforms synthesise the phospholipid 'PIP3'. PIP3 is a 'second messenger' used by many different cell surface receptors to control cell movement, growth, survival and differentiation. These four isoforms have overlapping functions but each is adapted to receive efficient stimulation by particular receptor sub-types. PI3Kγ is highly expressed in leukocytes and plays a particularly important role in chemokine-mediated recruitment and activation of innate immune cells at sites of inflammation. PI3Kδ is also highly expressed in leukocytes and plays a key role in antigen receptor and cytokine-mediated B and T cell development, differentiation and function. Class III PI3K synthesises the phospholipid PI3P, which regulates endosome-lysosome trafficking and the induction of autophagy, pathways involved in pathogen killing, antigen processing and immune cell survival. Much less is known about the function of Class II PI3Ks, but emerging evidence indicates they can synthesise PI3P and PI34P2 and are involved in the regulation of endocytosis. The creation of genetically-modified mice with altered PI3K signalling, together with the development of isoform-selective, small-molecule PI3K inhibitors, has allowed the evaluation of the individual roles of Class I PI3K isoforms in several mouse models of chronic inflammation. Selective inhibition of PI3Kδ, γ or β has each been shown to reduce the severity of inflammation in one or more models of autoimmune disease, respiratory disease or allergic inflammation, with dual γ/δ or β/δ inhibition generally proving more effective. The inhibition of Class I PI3Ks may therefore offer a therapeutic opportunity to treat non-resolving inflammatory pathologies in humans. This article is part of a Special Issue entitled Phosphoinositides.

Role of phosphoinositide 3-kinase in the pathogenesis of acute pancreatitis

A large body of experimental and clinical data supports the notion that inflammation in acute pancreatitis has a crucial role in the pathogenesis of local and systemic damage and is a major determinant of clinical severity. Thus, research has recently focused on molecules that can regulate the inflammatory processes, such as phosphoinositide 3-kinases (PI3Ks), a family of lipid and protein kinases involved in intracellular signal transduction. Studies using genetic ablation or pharmacologic inhibitors of different PI3K isoforms, in particular the class I PI3Kδ and PI3Kγ, have contributed to a greater understanding of the roles of these kinases in the modulation of inflammatory and immune responses. Recent data suggest that PI3Ks are also involved in the pathogenesis of acute pancreatitis. Activation of the PI3K signaling pathway, and in particular of the class IB PI3Kγ isoform, has a significant role in those events which are necessary for the initiation of acute pancreatic injury, namely calcium signaling alteration, trypsinogen activation, and nuclear factor-κB transcription. Moreover, PI3Kγ is instrumental in modulating acinar cell apoptosis, and regulating local neutrophil infiltration and systemic inflammatory responses during the course of experimental acute pancreatitis. The availability of PI3K inhibitors selective for specific isoforms may provide new valuable therapeutic strategies to improve the clinical course of this disease. This article presents a brief summary of PI3K structure and function, and highlights recent advances that implicate PI3Ks in the pathogenesis of acute pancreatitis.

INTRACELLULAR SIGNALING BY BILE ACIDS

Bile acids, synthesized from cholesterol, are known to produce beneficial as well as toxic effects in the liver. The beneficial effects include choleresis, immunomodulation, cell survival, while the toxic effects include cholestasis, apoptosis and cellular toxicity. It is believed that bile acids produce many of these effects by activating intracellular signaling pathways. However, it has been a challenge to relate intracellular signaling to specific and at times opposing effects of bile acids. It is becoming evident that bile acids produce different effects by activating different isoforms of phosphoinositide 3-kinase (PI3K), Protein kinase Cs (PKCs), and mitogen activated protein kinases (MAPK). Thus, the apoptotic effect of bile acids may be mediated via PI3K-110γ, while cytoprotection induce by cAMP-GEF pathway involves activation of PI3K-p110α/β isoforms. Atypical PKCζ may mediate beneficial effects and nPKCε may mediate toxic effects, while cPKCα and nPKCδ may be involved in both beneficial and toxic effects of bile acids. The opposing effects of nPKCδ activation may depend on nPKCδ phosphorylation site(s). Activation of ERK1/2 and JNK1/2 pathway appears to mediate beneficial and toxic effects, respectively, of bile acids. Activation of p38α MAPK and p38β MAPK may mediate choleretic and cholestatic effects, respectively, of bile acids. Future studies clarifying the isoform specific effects on bile formation should allow us to define potential therapeutic targets in the treatment of cholestatic disorders.

Elastin-derived peptides potentiate atherosclerosis through the immune Neu1-PI3Kγ pathway

AIMS

Elastin is degraded during vascular ageing and its products, elastin-derived peptides (EP), are present in the human blood circulation. EP binds to the elastin receptor complex (ERC) at the cell surface, composed of elastin-binding protein (EBP), a cathepsin A and a neuraminidase 1. Some in vitro functions have clearly been attributed to this binding, but the in vivo implications for arterial diseases have never been clearly investigated.

METHODS AND RESULTS

Here, we demonstrate that chronic doses of EP injected into mouse models of atherosclerosis increase atherosclerotic plaque size formation. Similar effects were observed following an injection of a VGVAPG peptide, suggesting that the ERC mediates these effects. The absence of phosphoinositide 3-kinase γ (PI3Kγ) in bone marrow-derived cells prevented EP-induced atherosclerosis development, demonstrating that PI3Kγ drive EP-induced arterial lesions. Accordingly, in vitro studies showed that PI3Kγ was required for EP-induced monocyte migration and ROS production and that this effect was dependent upon neuraminidase activity. Finally, we showed that degradation of elastic lamellae in LDLR(-/-) mice fed an atherogenic diet correlated with atherosclerotic plaque formation. At the same time, the absence of the cathepsin A-neuraminidase 1 complex in cells of the haematopoietic lineage abolished atheroma plaque size progression and decreased leucocytes infiltration, clearly demonstrating the role of this complex in atherogenesis and suggesting the involvement of endogenous EP.

CONCLUSION

Altogether, this work identifies EP as an enhancer of atherogenesis and defines the Neuraminidase 1/PI3Kγ signalling pathway as a key mediator of this function in vitro and in vivo.

Kinase AKT controls innate immune cell development and function

The critical roles of kinase AKT in tumour cell proliferation, apoptosis and protein synthesis have been widely recognized. But AKT also plays an important role in immune modulation. Recent studies have confirmed that kinase AKT can regulate the development and functions of innate immune cells (neutrophil, macrophage and dendritic cell). Studies have shown that different isoforms of kinase AKT have different effects in regulating immunity-related diseases, mainly through the mammalian target of rapamycin-dependent or -independent pathways. The purpose of this review is to illustrate the immune modulating effects of kinase AKT on innate immune cell development, survival and function.

Inhibition of phosphoinositide 3-kinase γ attenuates inflammation, obesity, and cardiovascular risk factors

Phosphoinositide 3-kinase γ (PI3Kγ) plays a central role in inflammation, allergy, cardiovascular, and metabolic disease. Obesity is accompanied by chronic, low-grade inflammation. As PI3Kγ plays a major role in leukocyte recruitment, targeting of PI3Kγ has been considered to be a strategy for attenuating progression of obesity to insulin resistance and type 2 diabetes. Indeed, PI3Kγ null mice are protected from high fat diet-induced obesity, metabolic inflammation, fatty liver, and insulin resistance. The lean phenotype of the PI3Kγ-null mice has been linked to increased thermogenesis and energy expenditure. Surprisingly, the increase in fat mass and metabolic aberrations were not linked to PI3Kγ activity in the hematopoietic compartment. Thermogenesis and oxygen consumption are modulated by PI3Kγ lipid kinase-dependent and -independent signaling mechanisms. PI3Kγ signaling controls metabolic and inflammatory stress, and may provide an entry point for therapeutic strategies in metabolic disease, inflammation, and cardiovascular disease.

Molecular biology of atherosclerosis

At least 468 individual genes have been manipulated by molecular methods to study their effects on the initiation, promotion, and progression of atherosclerosis. Most clinicians and many investigators, even in related disciplines, find many of these genes and the related pathways entirely foreign. Medical schools generally do not attempt to incorporate the relevant molecular biology into their curriculum. A number of key signaling pathways are highly relevant to atherogenesis and are presented to provide a context for the gene manipulations summarized herein. The pathways include the following: the insulin receptor (and other receptor tyrosine kinases); Ras and MAPK activation; TNF-α and related family members leading to activation of NF-κB; effects of reactive oxygen species (ROS) on signaling; endothelial adaptations to flow including G protein-coupled receptor (GPCR) and integrin-related signaling; activation of endothelial and other cells by modified lipoproteins; purinergic signaling; control of leukocyte adhesion to endothelium, migration, and further activation; foam cell formation; and macrophage and vascular smooth muscle cell signaling related to proliferation, efferocytosis, and apoptosis. This review is intended primarily as an introduction to these key signaling pathways. They have become the focus of modern atherosclerosis research and will undoubtedly provide a rich resource for future innovation toward intervention and prevention of the number one cause of death in the modern world.

PI3Kγ kinase activity is required for optimal T-cell activation and differentiation

Phosphatidylinositol-3-kinase gamma (PI3Kγ) is a leukocyte-specific lipid kinase with signaling function downstream of G protein-coupled receptors to regulate cell trafficking, but its role in T cells remains unclear. To investigate the requirement of PI3Kγ kinase activity in T-cell function, we studied T cells from PI3Kγ kinase-dead knock-in (PI3Kγ^KD/KD) mice expressing the kinase-inactive PI3Kγ protein. We show that CD4⁺ and CD8⁺ T cells from PI3Kγ^KD/KD mice exhibit impaired TCR/CD28-mediated activation that could not be rescued by exogenous IL-2. The defects in proliferation and cytokine production were also evident in naïve and memory T cells. Analysis of signaling events in activated PI3Kγ^KD/KD T cells revealed a reduction in phosphorylation of protein kinase B (AKT) and ERK1/2, a decrease in lipid raft formation, and a delay in cell cycle progression. Furthermore, PI3Kγ^KD/KD CD4⁺ T cells displayed compromised differentiation toward Th1, Th2, Th17, and induced Treg cells. PI3Kγ^KD/KD mice also exhibited an impaired response to immunization and a reduced delayed-type hypersensitivity to Ag challenge. These findings indicate that PI3Kγ kinase activity is required for optimal T-cell activation and differentiation, as well as for mounting an efficient T cell-mediated immune response. The results suggest that PI3Kγ kinase inhibitors could be beneficial in reducing the undesirable immune response in autoimmune diseases.

PI3K p110γ deletion attenuates murine atherosclerosis by reducing macrophage proliferation but not polarization or apoptosis in lesions

Atherosclerosis is an inflammatory disease regulated by infiltrating monocytes and T cells, among other cell types. Macrophage recruitment to atherosclerotic lesions is controlled by monocyte infiltration into plaques. Once in the lesion, macrophage proliferation in situ, apoptosis, and differentiation to an inflammatory (M1) or anti-inflammatory phenotype (M2) are involved in progression to advanced atherosclerotic lesions. We studied the role of phosphoinositol-3-kinase (PI3K) p110γ in the regulation of in situ apoptosis, macrophage proliferation and polarization towards M1 or M2 phenotypes in atherosclerotic lesions. We analyzed atherosclerosis development in LDLR^−/−p110γ^+/− and LDLR^−/−p110γ^−/− mice, and performed expression and functional assays in tissues and primary cells from these and from p110γ^+/− and p110γ^−/− mice. Lack of p110γ in LDLR^−/− mice reduces the atherosclerosis burden. Atherosclerotic lesions in fat-fed LDLR^−/−p110γ^−/− mice were smaller than in LDLR^−/−p110γ^+/− controls, which coincided with decreased macrophage proliferation in LDLR^−/−p110γ^−/− mouse lesions. This proliferation defect was also observed in p110γ^−/− bone marrow-derived macrophages (BMM) stimulated with macrophage colony-stimulating factor (M-CSF), and was associated with higher intracellular cyclic adenosine monophosphate (cAMP) levels. In contrast, T cell proliferation was unaffected in LDLR^−/−p110γ^−/− mice. Moreover, p110γ deficiency did not affect macrophage polarization towards the M1 or M2 phenotypes or apoptosis in atherosclerotic plaques, or polarization in cultured BMM. Our results suggest that higher cAMP levels and the ensuing inhibition of macrophage proliferation contribute to atheroprotection in LDLR^−/− mice lacking p110γ. Nonetheless, p110γ deletion does not appear to be involved in apoptosis, in macrophage polarization or in T cell proliferation.