Emerging roles of PLCγ1 in endothelial biology

Identification and regulation of EMT cells in vivo by laser stimulation

Cells undergoing epithelial-to-mesenchymal transition (EMT) exhibit significant plasticity, making them more tumorigenic, invasive, and stem-like. PLCG2 has been identified as being linked to EMT. Specifically, the PLCG2-high subpopulation of tumor cells shows strong correlations with metastasis. However, it remains unclear whether PLCG2 serves as a direct driver of EMT. In this study, we employ an in vivo photostimulation method using tightly focused femtosecond-laser scanning to activate intracellular Ca2+ signaling and induce PLCG2 upregulation. By constructing a subcutaneous tumor model with prostate cancer PC3 cells and single-cell RNA sequencing, we identify distinct cell populations, including cancer stem cells, epithelial tumor cells, proliferating cells, and EMT cells. Upon photostimulation, EMT cells are notably expanded among the primary tumor cells, while epithelial tumor cells decrease in number. During the tumor progression, treatment with a specific PLCG2 inhibitor effectively suppresses the growth of the primary tumor but has no significant impact on metastatic cells. These findings offer valuable insights into the role of PLCG2 in regulating EMT and tumor development.

Phosphoinositide-specific phospholipase C enzymes: Recent advances in a long journey

A journey that started with the discovery of phospholipase C catalysed inositol-lipid hydrolysis as a receptor-controlled signalling event, culminated in defining molecular properties and roles of phosphoinositide-specific phospholipase C (PLC) families. Currently, there are six classical (13 isoforms) and one atypical (3 isoforms) family, expressed in a wide range of mammalian cells where they perform key functions in intracellular signal transduction. We here highlight recent advances in the PLC field, mostly resulting from studies of the PLCγ family members, PLCγ1 and PLCγ2. These new discoveries include elucidation of their structural and functional properties as well as their roles in physiology and disease development. We also illustrate the involvement of classical PLC families in control of cellular processes mediated not only by the PtdIns(4,5)P2-derived second messengers, resulting from the PLC hydrolysis, but also by second messenger-independent consequences of PtdIns(4,5)P2 hydrolysis. Presented examples are focused on regulation of ion channels by PtdIns(4,5)P2.

Genomic landscape and preclinical models of angiosarcoma

Angiosarcoma is a cancer that develops in blood or lymphatic vessels that presents a significant clinical challenge due to its rarity and aggressive features. Clinical outcomes have not improved in decades, highlighting a need for innovative therapeutic strategies to treat the disease. Genetically, angiosarcomas exhibit high heterogeneity and complexity with many recurrent mutations. However, recent studies have identified some common features within anatomic and molecular subgroups. To identify potential therapeutic vulnerabilities, it is essential to understand and integrate the mutational landscape of angiosarcoma with the models that exist to study the disease. In this review, we will summarize the insights gained from reported genomic alterations in molecular and anatomic subtypes of angiosarcoma, discuss several potential actionable targets, and highlight the preclinical disease models available in the field.

Impaired degradation of PLCG1 by chaperone-mediated autophagy promotes cellular senescence and intervertebral disc degeneration

Defects in chaperone-mediated autophagy (CMA) are associated with cellular senescence, but the mechanism remains poorly understood. Here, we found that CMA inhibition induced cellular senescence in a calcium-dependent manner and identified its role in TNF-induced senescence of nucleus pulposus cells (NPC) and intervertebral disc degeneration. Based on structural and functional proteomic screens, PLCG1 (phospholipase C gamma 1) was predicted as a potential substrate for CMA deficiency to affect calcium homeostasis. We further confirmed that PLCG1 was a key mediator of CMA in the regulation of intracellular calcium flux. Aberrant accumulation of PLCG1 caused by CMA blockage resulted in calcium overload, thereby inducing NPC senescence. Immunoassays on human specimens showed that reduced LAMP2A, the rate-limiting protein of CMA, or increased PLCG1 was associated with disc senescence, and the TNF-induced disc degeneration in rats was inhibited by overexpression of Lamp2a or knockdown of Plcg1. Because CMA dysregulation, calcium overload, and cellular senescence are common features of disc degeneration and other age-related degenerative diseases, the discovery of actionable molecular targets that can link these perturbations may have therapeutic value.Abbreviation: ATRA: all-trans-retinoic acid; BrdU: bromodeoxyuridine; CDKN1A/p21: cyclin dependent kinase inhibitor 1A; CDKN2A/p16-INK4A: cyclin dependent kinase inhibitor 2A; CMA: chaperone-mediated autophagy; DHI: disc height index; ER: endoplasmic reticulum; IP: immunoprecipitation; IP3: inositol 1,4,5-trisphosphate; ITPR/IP3R: inositol 1,4,5-trisphosphate receptor; IVD: intervertebral disc; IVDD: intervertebral disc degeneration; KD: knockdown; KO: knockout; Leu: leupeptin; MRI: magnetic resonance imaging; MS: mass spectrometry; N/L: NH4Cl and leupeptin; NP: nucleus pulposus; NPC: nucleus pulposus cells; PI: protease inhibitors; PLC: phospholipase C; PLCG1: phospholipase C gamma 1; ROS: reactive oxygen species; RT-qPCR: real-time quantitative reverse transcription PCR; SA-GLB1/β-gal: senescence-associated galactosidase beta 1; SASP: senescence-associated secretory phenotype; STV: starvation; TMT: tandem mass tag; TNF: tumor necrosis factor; TP53: tumor protein p53; UPS: ubiquitin-proteasome system.

Synthesis of a 13C/2H Labeled Building Block to Probe the Phosphotyrosine Interactome Using Biomolecular NMR Spectroscopy

Phosphotyrosine (pTyr) recognition coordinates the assembly of protein complexes, thus controlling key events of cell cycle, cell development and programmed cell death. Although many aspects of membrane receptor function and intracellular signal transduction have been deciphered in the last decades, the details of how phosphorylation alters protein-protein interaction and creates regulating switches of protein activity and localization often remains unclear. We developed a synthetic route to a protected phophotyrosine building block with isolated 13C-1H spins in the aromatic ring. The compound can be used for solid phase peptide synthesis (SPPS) and readily applied to study affinity, dynamics and interactions on an atomic level using NMR spectroscopy. As a first example, we prepared an isotopologue of a pTyr containing 12mer peptide (pY1021) as part of the platelet-derived growth factor to analyze the binding to the phospholipase C-γ (PLCγ-1) SH2 domain.

Hyperactive PLCG1 drives non-canonical signaling to promote cell survival

One of the long-standing questions in cell signaling field to identify and characterize key signaling nodes out of a complex network. Phospholipase Cγ1 (PLCG1) was identified as the most frequently mutated gene in adult T-cell leukemia/lymphoma, suggesting a critical function of PLCG1 in driving T cell activation. However, it remains unclear how these mutations regulate T cell physiology and pathology. Here we investigated three common leukemia/lymphoma associated mutations (R48W, S345F, and D1165H). We discovered that these mutations induced hyperactive T cell signaling and caused pro-survival phenotypes. PLCG1 mutants enhanced LAT condensation, calcium influx, and ERK activation. They promoted T cell proliferation, induced cell aggregation, and rendered resistance to vorinostat, an FDA-approved drug for cutaneous T-cell lymphoma. The resistance to vorinostat depended on ERK signaling and can be reversed with an ERK inhibitor. Mechanistically, alpha smooth muscle actin, which was specifically induced by PLCG1 mutants, directly bound PLCG1 to promote its activation. Together, these results demonstrated that hyperactive PLCG1 promoted T cell survival and drug resistance through inducing non-canonical signaling.

Coagulation factor XI regulates endothelial cell permeability and barrier function in vitro and in vivo

ABSTRACT

Loss of endothelial barrier function contributes to the pathophysiology of many inflammatory diseases. Coagulation factor XI (FXI) plays a regulatory role in inflammation. Although activation of FXI increases vascular permeability in vivo, the mechanism by which FXI or its activated form FXIa disrupts endothelial barrier function is unknown. We investigated the role of FXIa in human umbilical vein endothelial cell (HUVEC) or human aortic endothelial cell (HAEC) permeability. The expression patterns of vascular endothelial (VE)-cadherin and other proteins of interest were examined by western blot or immunofluorescence. Endothelial cell permeability was analyzed by Transwell assay. We demonstrate that FXIa increases endothelial cell permeability by inducing cleavage of the VE-cadherin extracellular domain, releasing a soluble fragment. The activation of a disintegrin and metalloproteinase 10 (ADAM10) mediates the FXIa-dependent cleavage of VE-cadherin, because adding an ADAM10 inhibitor prevented the cleavage of VE-cadherin induced by FXIa. The binding of FXIa with plasminogen activator inhibitor 1 and very low-density lipoprotein receptor on HUVEC or HAEC surfaces activates vascular endothelial growth receptor factor 2 (VEGFR2). The activation of VEGFR2 triggers the mitogen-activated protein kinase (MAPK) signaling pathway and promotes the expression of active ADAM10 on the cell surface. In a pilot experiment using an established baboon model of sepsis, the inhibition of FXI activation significantly decreased the levels of soluble VE-cadherin to preserve barrier function. This study reveals a novel pathway by which FXIa regulates vascular permeability. The effect of FXIa on barrier function may be another way by which FXIa contributes to the development of inflammatory diseases.

The impact of volatile anesthetics and propofol on phosphatidylinositol 4,5-bisphosphate signaling

Phosphatidylinositol 4,5-bisphosphate (PIP2), as well as other anionic phospholipids, play a pivotal role in various cellular processes, including ion channel regulation, receptor trafficking, and intracellular signaling pathways. The binding of volatile anesthetics and propofol to PIP2 leads to alterations in PIP2-mediated signaling causing modulation of ion channels such as ɣ-aminobutyric acid type A (GABAA) receptors, voltage-gated calcium channels, and potassium channels through various mechanisms. Additionally, the interaction between anionic phospholipids and G protein-coupled receptors plays a critical role in various anesthetic pathways, with these anesthetic-induced changes impacting PIP2 levels which cause cascading effects on receptor trafficking, including GABAA receptor internalization. This comprehensive review of various mechanisms of interaction provides insights into the intricate interplay between PIP2 signaling and anesthetic-induced changes, shedding light on the molecular mechanisms underlying anesthesia.

TM4SF1 is a molecular facilitator that distributes cargo proteins intracellularly in endothelial cells in support of blood vessel formation

Transmembrane-4 L-six family member-1 (TM4SF1) is an atypical tetraspanin that is highly and selectively expressed in proliferating endothelial cells and plays an essential role in blood vessel development. TM4SF1 forms clusters on the cell surface called TMED (TM4SF1-enriched microdomains) and recruits other proteins that internalize along with TM4SF1 via microtubules to intracellular locations including the nucleus. We report here that tumor growth and wound healing are inhibited in Tm4sf1-heterozygous mice. Investigating the mechanisms of TM4SF1 activity, we show that 12 out of 18 signaling molecules examined are recruited to TMED on the surface of cultured human umbilical vein endothelial cells (HUVEC) and internalize along with TMED; notable among them are PLCγ and HDAC6. When TM4SF1 is knocked down in HUVEC, microtubules are heavily acetylated despite normal levels of HDAC6 protein, and, despite normal levels of VEGFR2, are unable to proliferate. Together, our studies indicate that pathological angiogenesis is inhibited when levels of TM4SF1 are reduced as in Tm4sf1-heterozygous mice; a likely mechanism is that TM4SF1 regulates the intracellular distribution of signaling molecules necessary for endothelial cell proliferation and migration.

VEGF/VEGFR axis and its signaling in melanoma: Current knowledge toward therapeutic targeting agents and future perspectives

Melanoma is responsible for most skin cancer-associated deaths globally. The progression of melanoma is influenced by a number of pathogenic processes. Understanding the VEGF/VEGFR axis, which includes VEGF-A, PlGF, VEGF-B, VEGF-C, and VEGF-D and their receptors, VEGFR-1, VEGFR-2, and VEGFR-3, is of great importance in melanoma due to its crucial role in angiogenesis. This axis generates multifactorial and complex cellular signaling, engaging the MAPK/ERK, PI3K/AKT, PKC, PLC-γ, and FAK signaling pathways. Melanoma cell growth and proliferation, migration and metastasis, survival, and acquired resistance to therapy are influenced by this axis. The VEGF/VEGFR axis was extensively examined for their potential as diagnostic/prognostic biomarkers in melanoma patients and results showed that VEGF overexpression can be associated with unfavorable prognosis, higher level of tumor invasion and poor response to therapy. MicroRNAs linking to the VEGF/VEGFR axis were identified and, in this review, divided into two categories according to their functions, some of them promote melanoma angiogenesis (promotive group) and some restrict melanoma angiogenesis (protective group). In addition, the approach of treating melanoma by targeting the VEGF/VEGFR axis has garnered significant interest among researchers. These agents can be divided into two main groups: anti-VEGF and VEGFR inhibitors. These therapeutic options may be a prominent step along with the modern targeting and immune therapies for better coverage of pathological processes leading to melanoma progression and therapy resistance.

VEGF counteracts shear stress-determined arterial fate specification during capillary remodeling

A key feature of arteriogenesis is capillary-to-arterial endothelial cell fate transition. Although a number of studies in the past two decades suggested this process is driven by VEGF activation of Notch signaling, how arteriogenesis is regulated remains poorly understood. Here we report that arterial specification is mediated by fluid shear stress (FSS) independent of VEGFR2 signaling and that a decline in VEGFR2 signaling is required for arteriogenesis to fully take place. VEGF does not induce arterial fate in capillary ECs and, instead, counteracts FSS-driven capillary-to-arterial cell fate transition. Mechanistically, FSS-driven arterial program involves both Notch-dependent and Notch-independent events. Sox17 is the key mediator of the FSS-induced arterial specification and a target of VEGF-FSS competition. These findings suggest a new paradigm of VEGF-FSS crosstalk coordinating angiogenesis, arteriogenesis and capillary maintenance.

Endothelial VEGFR2-PLCγ signaling regulates vascular permeability and antitumor immunity through eNOS/Src

Endothelial phospholipase Cγ (PLCγ) is essential for vascular development; however, its role in healthy, mature, or pathological vessels is unexplored. Here, we show that PLCγ was prominently expressed in vessels of several human cancer forms, notably in renal cell carcinoma (RCC). High PLCγ expression in clear cell RCC correlated with angiogenic activity and poor prognosis, while low expression correlated with immune cell activation. PLCγ was induced downstream of vascular endothelial growth factor receptor 2 (VEGFR2) phosphosite Y1173 (pY1173). Heterozygous Vegfr2Y1173F/+ mice or mice lacking endothelial PLCγ (Plcg1iECKO) exhibited a stabilized endothelial barrier and diminished vascular leakage. Barrier stabilization was accompanied by decreased expression of immunosuppressive cytokines, reduced infiltration of B cells, helper T cells and regulatory T cells, and improved response to chemo- and immunotherapy. Mechanistically, pY1173/PLCγ signaling induced Ca2+/protein kinase C-dependent activation of endothelial nitric oxide synthase (eNOS), required for tyrosine nitration and activation of Src. Src-induced phosphorylation of VE-cadherin at Y685 was accompanied by disintegration of endothelial junctions. This pY1173/PLCγ/eNOS/Src pathway was detected in both healthy and tumor vessels in Vegfr2Y1173F/+ mice, which displayed decreased activation of PLCγ and eNOS and suppressed vascular leakage. Thus, we believe that we have identified a clinically relevant endothelial PLCγ pathway downstream of VEGFR2 pY1173, which destabilizes the endothelial barrier and results in loss of antitumor immunity.

Mechanotransduction via endothelial adhesion molecule CD31 initiates transmigration and reveals a role for VEGFR2 in diapedesis

Engagement of platelet endothelial cell adhesion molecule 1 (PECAM, PECAM-1, CD31) on the leukocyte pseudopod with PECAM at the endothelial cell border initiates transendothelial migration (TEM, diapedesis). We show, using fluorescence lifetime imaging microscopy (FLIM), that physical traction on endothelial PECAM during TEM initiated the endothelial signaling pathway. In this role, endothelial PECAM acted as part of a mechanotransduction complex with VE-cadherin and vascular endothelial growth factor receptor 2 (VEGFR2), and this predicted that VEGFR2 was required for efficient TEM. We show that TEM required both VEGFR2 and the ability of its Y1175 to be phosphorylated, but not VEGF or VEGFR2 endogenous kinase activity. Using inducible endothelial-specific VEGFR2-deficient mice, we show in three mouse models of inflammation that the absence of endothelial VEGFR2 significantly (by ≥75%) reduced neutrophil extravasation by selectively blocking diapedesis. These findings provide a more complete understanding of the process of transmigration and identify several potential anti-inflammatory targets.

Chylomicrons Regulate Lacteal Permeability and Intestinal Lipid Absorption

BACKGROUND

Lymphatic vessels are responsible for tissue drainage, and their malfunction is associated with chronic diseases. Lymph uptake occurs via specialized open cell-cell junctions between capillary lymphatic endothelial cells (LECs), whereas closed junctions in collecting LECs prevent lymph leakage. LEC junctions are known to dynamically remodel in development and disease, but how lymphatic permeability is regulated remains poorly understood.

METHODS

We used various genetically engineered mouse models in combination with cellular, biochemical, and molecular biology approaches to elucidate the signaling pathways regulating junction morphology and function in lymphatic capillaries.

RESULTS

By studying the permeability of intestinal lacteal capillaries to lipoprotein particles known as chylomicrons, we show that ROCK (Rho-associated kinase)-dependent cytoskeletal contractility is a fundamental mechanism of LEC permeability regulation. We show that chylomicron-derived lipids trigger neonatal lacteal junction opening via ROCK-dependent contraction of junction-anchored stress fibers. LEC-specific ROCK deletion abolished junction opening and plasma lipid uptake. Chylomicrons additionally inhibited VEGF (vascular endothelial growth factor)-A signaling. We show that VEGF-A antagonizes LEC junction opening via VEGFR (VEGF receptor) 2 and VEGFR3-dependent PI3K (phosphatidylinositol 3-kinase)/AKT (protein kinase B) activation of the small GTPase RAC1 (Rac family small GTPase 1), thereby restricting RhoA (Ras homolog family member A)/ROCK-mediated cytoskeleton contraction.

CONCLUSIONS

Our results reveal that antagonistic inputs into ROCK-dependent cytoskeleton contractions regulate the interconversion of lymphatic junctions in the intestine and in other tissues, providing a tunable mechanism to control the lymphatic barrier.

Jujuboside B suppresses angiogenesis and tumor growth via blocking VEGFR2 signaling pathway

Jujuboside B (JuB), one of the main active triterpenoid saponins from the traditional Chinese medicine Ziziphus jujuba, possesses a wide range of pharmacological activities. However, it is unknown whether JuB can inhibit tumor angiogenesis, a crucial step in solid tumor growth. In this study, we found that JuB significantly inhibited the proliferation, migration, and tube formation of human umbilical vein endothelial cells in a dose-dependent manner. JuB also suppressed angiogenesis in chick embryo chorioallantoic membranes and Matrigel plugs. Moreover, through angiogenesis inhibition, JuB delayed the growth of human HCT-15 colorectal cancer xenograft in mice. Western blot assay demonstrated that JuB inhibited the phosphorylation of VEGFR2 and its key downstream protein kinases, such as Akt, FAK, Src, and PLCγ1. In conclusion, the antiangiogenic potency and molecular mechanism of JuB are revealed for the first time, indicating that this triterpene saponin may be further explored as a potential drug candidate or lead compound for antiangiogenic cancer therapy.

221S-1a inhibits endothelial proliferation in pathological angiogenesis through ERK/c-Myc signaling

Pathological angiogenesis plays a major role in many disease processes, including cancer and diabetic retinopathy. Antiangiogenic therapy is a potential management for pathologic angiogenesis. The novel synthetic compound 221S-1a, derived from captopril, tanshinol and borneol, may have antiangiogenic properties. On the basis of MS, NMR and HPLC analysis, the structure of 221S-1a was identified. The cellular uptake and metabolism of this compound was also observed. Next, the antiangiogenic properties of 221S-1a were evaluated in tumor-xenograft and OIR models in vivo. The inhibitory properties of 221S-1a on endothelial cell proliferation, migration, tube formation and sprouting were detected in vitro. Furthermore, 221S-1a induced G1/S phase arrest was detected by PI staining flow cytometry analysis and Cyclin D, Cyclin E expression. 221S-1a inhibited ERK1/2 activation and nuclear translocation, in addition to downregulation of c-Myc, a transcription factor that regulates cell cycle progression. Molecular docking indicated the interaction of 221S-1a with the ATP-binding site of ERK2, leading to the inhibition of ERK2 phosphorylation and a concomitant inhibition of ERK1 phosphorylation. In conclusion, 221S-1a inhibited the G1/S phase transition by blocking the ERK1/2/c-Myc pathway to reduce tumor and OIR retinal angiogenesis. These novel findings suggest that 221S-1a is a potential pharmacologic candidate for treating pathological angiogenesis.

Yangjing capsule improves oligoasthenozoospermia by promoting nitric oxide production through PLCγ1/AKT/eNOS pathway

Background: Oligoasthenozoospermia is an important factor leading to male infertility. Yangjing capsule (YC), a traditional Chinese preparation, displays beneficial effects on male infertility. However, whether YC could improve oligoasthenozoospermia remains unclear. Methods: In this study, we aimed to explore the effect of YC in the treatment of oligoasthenozoospermia. Male Sprague-Dawley (SD) rats were treated with 800 mg/kg ornidazole once daily for 30 days to induce in vivo oligoasthenozoospermia; primary Sertoli cells were treated with 400 μg/mL ornidazole for 24 h to induce in vitro oligoasthenozoospermia. Results: We found that YC improved the testicle and epididymis weight, sperm concentration, sperm progressive motility, serum testosterone, fertility rate and testis morphology in ornidazole-exposed rats and enhanced cell survival in ornidazole-stimulated primary Sertoli cells. YC also inhibited the ornidazole-caused decrease in nitric oxide (NO) generation and the phosphorylation of phospholipase C γ1 (PLCγ1), AKT, and eNOS in vivo and in vitro in oligoasthenozoospermia. Furthermore, the knockdown of PLCγ1 blunted the beneficial effects of YC in vitro. Conclusion: Collectively, our data suggested that YC protected against oligoasthenozoospermia by promoting NO levels through the PLCγ1/AKT/eNOS pathway.

Critical role of mitogen-inducible gene 6 in restraining endothelial cell permeability to maintain vascular homeostasis

Although mitogen-inducible gene 6 (MIG6) is highly expressed in vascular endothelial cells, it remains unknown whether MIG6 affects vascular permeability. Here, we show for the first time a critical role of MIG6 in limiting vascular permeability. We unveil that genetic deletion of Mig6 in mice markedly increased VEGFA-induced vascular permeability, and MIG6 knockdown impaired endothelial barrier function. Mechanistically, we reveal that MIG6 inhibits VEGFR2 phosphorylation by binding to the VEGFR2 kinase domain 2, and MIG6 knockdown increases the downstream signaling of VEGFR2 by enhancing phosphorylation of PLCγ1 and eNOS. Moreover, MIG6 knockdown disrupted the balance between RAC1 and RHOA GTPase activation, leading to endothelial cell barrier breakdown and the elevation of vascular permeability. Our findings demonstrate an essential role of MIG6 in maintaining endothelial cell barrier integrity and point to potential therapeutic implications of MIG6 in the treatment of diseases involving vascular permeability. Xing et al. (2022) investigated the critical role of MIG6 in vascular permeability. MIG6 deficiency promotes VEGFA-induced vascular permeability via activation of PLCγ1-Ca²⁺-eNOS signaling and perturbation of the balance in RAC1/RHOA activation, resulting in endothelial barrier disruption.

Conformational alteration in glycan induces phospholipase Cβ1 activation and angiogenesis

BACKGROUND

In endothelial cells, phospholipase C (PLC) β1-activated Ca²⁺ is a crucial second messenger for the signaling pathways governing angiogenesis. PLCβ1 is inactivated by complexing with an intracellular protein called translin-associated factor X (TRAX). This study demonstrates specific interactions between Globo H ceramide (GHCer) and TRAX, which highlight a new angiogenic control through PLCβ1 activation.

METHODS

Globo-series glycosphingolipids (GSLs), including GHCer and stage-specific embryonic antigen-3 ceramide (SSEA3Cer), were analyzed using enzyme-linked immunosorbent assay (ELISA) and Biacore for their binding with TRAX. Angiogenic activities of GSLs in human umbilical vein endothelial cells (HUVECs) were evaluated. Molecular dynamics (MD) simulation was used to study conformations of GSLs and their molecular interactions with TRAX. Fluorescence resonance energy transfer (FRET) analysis of HUVECs by confocal microscopy was used to validate the release of PLCβ1 from TRAX. Furthermore, the in vivo angiogenic activity of extracellular vesicles (EVs) containing GHCer was confirmed using subcutaneous Matrigel plug assay in mice.

RESULTS

The results of ELISA and Biacore analysis showed a stable complex between recombinant TRAX and synthetic GHCer with KD of 40.9 nM. In contrast, SSEA3Cer lacking a fucose residue of GHCer at the terminal showed ~ 1000-fold decrease in the binding affinity. These results were consistent with their angiogenic activities in HUVECs. The MD simulation indicated that TRAX interacted with the glycan moiety of GHCer at amino acid Q223, Q219, L142, S141, and E216. At equilibrium the stable complex maintained 4.6 ± 1.3 H-bonds. TRAX containing double mutations with Q223A and Q219A lost its ability to interact with GHCer in both MD simulation and Biacore assays. Removal of the terminal fucose from GHCer to become SSEA3Cer resulted in decreased H-bonding to 1.2 ± 1.0 by the MD simulation. Such specific H-bonding was due to the conformational alteration in the whole glycan which was affected by the presence or absence of the fucose moiety. In addition, ELISA, Biacore, and in-cell FRET assays confirmed the competition between GHCer and PLCβ1 for binding to TRAX. Furthermore, the Matrigel plug assay showed robust vessel formation in the plug containing tumor-secreted EVs or synthetic GHCer, but not in the plug with SSEA3Cer. The FRET analysis also indicated the disruption of colocalization of TRAX and PLCβ1 in cells by GHCer derived from EVs.

CONCLUSIONS

Overall, the fucose residue in GHCer dictated the glycan conformation for its complexing with TRAX to release TRAX-sequestered PLCβ1, leading to Ca²⁺ mobilization in endothelial cells and enhancing angiogenesis in tumor microenvironments.

PLCβ2 Promotes VEGF-Induced Vascular Permeability

BACKGROUND

Regulation of vascular permeability is critical to maintaining tissue metabolic homeostasis. VEGF (vascular endothelial growth factor) is a key stimulus of vascular permeability in acute and chronic diseases including ischemia reperfusion injury, sepsis, and cancer. Identification of novel regulators of vascular permeability would allow for the development of effective targeted therapeutics for patients with unmet medical need.

METHODS

In vitro and in vivo models of VEGFA-induced vascular permeability, pathological permeability, quantitation of intracellular calcium release and cell entry, and phosphatidylinositol 4,5-bisphosphate levels were evaluated with and without modulation of PLC (phospholipase C) β2.

RESULTS

Global knock-out of PLCβ2 in mice resulted in blockade of VEGFA-induced vascular permeability in vivo and transendothelial permeability in primary lung endothelial cells. Further work in an immortalized human microvascular cell line modulated with stable knockdown of PLCβ2 recapitulated the observations in the mouse model and primary cell assays. Additionally, loss of PLCβ2 limited both intracellular release and extracellular entry of calcium following VEGF stimulation as well as reduced basal and VEGFA-stimulated levels of phosphatidylinositol 4,5-bisphosphate compared to control cells. Finally, loss of PLCβ2 in both a hyperoxia-induced lung permeability model and a cardiac ischemia:reperfusion model resulted in improved animal outcomes when compared with wild-type controls.

CONCLUSIONS

The results implicate PLCβ2 as a key positive regulator of VEGF-induced vascular permeability through regulation of both calcium flux and phosphatidylinositol 4,5-bisphosphate levels at the cellular level. Targeting of PLCβ2 in a therapeutic setting may provide a novel approach to regulating vascular permeability in patients.