VEGF-A splicing: the key to anti-angiogenic therapeutics?

Differential Expression of Vascular Endothelial Growth Factor-A165 Isoforms Between Intracranial Atherosclerosis and Moyamoya Disease

BACKGROUND

Vascular endothelial growth factor-A₁₆₅ (VEGF-A₁₆₅) has been identified as a combination of 2 alternative splice variants: proangiogenic VEGF-A₁₆₅a and antiangiogenic VEGF-A₁₆₅b. Intracranial atherosclerotic disease (ICAD) and moyamoya disease (MMD) are 2 main types of intracranial arterial steno-occlusive disorders with distinct capacities for collateral formation. Recent studies indicate that VEGF-A₁₆₅ regulates collateral growth in ischemia. Therefore, we investigated if there is a distinctive composition of VEGF-A₁₆₅ isoforms in ICAD and MMD.

METHODS

Sixty-six ICAD patients, 6 MMD patients, and 5 controls were enrolled in this prospective study. ICAD and MMD patients received intensive medical management upon enrollment. Surgery was offered to 9 ICAD patients who had recurrent ischemic events, 6 MMD patients, and 5 surgical controls without ICAD. VEGF-A₁₆₅a and VEGF-A₁₆₅b plasma levels were measured at baseline, within 1 week after patients having surgery, and at 1, 3, and 6 months after treatment.

RESULTS

A significantly higher baseline VEGF-A₁₆₅a/b ratio was observed in MMD compared to ICAD (P = .016). The VEGF-A₁₆₅a/b ratio increased significantly and rapidly after surgical treatment in ICAD (P = .026) more so than in MMD and surgical controls. In patients with ICAD receiving intensive medical management, there was also an elevation of the VEGF-A₁₆₅a/b ratio, but at a slower rate, reaching the peak at 3 months after initiation of treatment (baseline versus 3 months VEGF-A₁₆₅a/b ratio, P = .028).

CONCLUSIONS

Our study shows an increased VEGF-A₁₆₅a/b ratio in MMD compared to ICAD, and suggests that both intensive medical management and surgical revascularization elevate the VEGF-A₁₆₅a/b ratio in ICAD patients.

Targeting VEGF pathway to normalize the vasculature: an emerging insight in cancer therapy

Vascular normalization is a new concept of targeting angiogenesis to restore vessel structure and function and to increase blood perfusion and delivery of drugs. It has been confirmed that vascular normalization can decrease relapse and benefit other cancer therapy, including chemotherapy, radiotherapy, and immune cell therapy. The key point of this therapy is to inhibit pro-angiogenic factors and make it be balanced with anti-angiogenic factors, resulting in a mature and normal vessel characteristic. Vascular endothelial growth factor (VEGF) is a key player in the process of tumor angiogenesis, and inhibiting VEGF is a primary approach to tumor vessel normalization. Herein, we review newly uncovered mechanisms governing angiogenesis and vascular normalization of cancer and place emphasis on targeting VEGF pathway to normalize the vasculature. Also, important methods to depress VEGF pathway and make tumor vascular are discussed.

RBPs Play Important Roles in Vascular Endothelial Dysfunction Under Diabetic Conditions

Diabetes is one of the major health care problems worldwide leading to huge suffering and burden to patients and society. Diabetes is also considered as a cardiovascular disorder because of the correlation between diabetes and an increased incidence of cardiovascular disease. Vascular endothelial cell dysfunction is a major mediator of diabetic vascular complications. It has been established that diabetes contributes to significant alteration of the gene expression profile of vascular endothelial cells. Post-transcriptional regulation by RNA binding proteins (RBPs) plays an important role in the alteration of gene expression profile under diabetic conditions. The review focuses on the roles and mechanisms of critical RBPs toward diabetic vascular endothelial dysfunction. Deeper understanding of the post- transcriptional regulation by RBPs could lead to new therapeutic strategies against diabetic manifestation in the future.

The Cancer Spliceome: Reprograming of Alternative Splicing in Cancer

Alternative splicing allows for the expression of multiple RNA and protein isoforms from one gene, making it a major contributor to transcriptome and proteome diversification in eukaryotes. Advances in next generation sequencing technologies and genome-wide analyses have recently underscored the fact that the vast majority of multi-exon genes under normal physiology engage in alternative splicing in tissue-specific and developmental-specific manner. On the other hand, cancer cells exhibit remarkable transcriptome alterations partly by adopting cancer-specific splicing isoforms. These isoforms and their encoded proteins are not insignificant byproducts of the abnormal physiology of cancer cells, but either drivers of cancer progression or small but significant contributors to specific cancer hallmarks. Thus, it is paramount that the pathways that regulate alternative splicing in cancer, including the splicing factors that bind to pre-mRNAs and modulate spliceosome recruitment. In this review, we present a few distinct cases of alternative splicing in cancer, with an emphasis on their regulation as well as their contribution to cancer cell phenotype. Several categories of splicing aberrations are highlighted, including alterations in cancer-related genes that directly affect their pre-mRNA splicing, mutations in genes encoding splicing factors or core spliceosomal subunits, and the seemingly mutation-free disruptions in the balance of the expression of RNA-binding proteins, including components of both the major (U2-dependent) and minor (U12-dependent) spliceosomes. Given that the latter two classes cause global alterations in splicing that affect a wide range of genes, it remains a challenge to identify the ones that contribute to cancer progression. These challenges necessitate a systematic approach to decipher these aberrations and their impact on cancer. Ultimately, a sufficient understanding of splicing deregulation in cancer is predicted to pave the way for novel and innovative RNA-based therapies.

Real-Time Ligand Binding of Fluorescent VEGF-A Isoforms that Discriminate between VEGFR2 and NRP1 in Living Cells

Fluorescent VEGF-A isoforms have been evaluated for their ability to discriminate between VEGFR2 and NRP1 in real-time ligand binding studies in live cells using BRET. To enable this, we synthesized single-site (N-terminal cysteine) labeled versions of VEGF₁₆₅a, VEGF₁₆₅b, and VEGF₁₂₁a. These were used in combination with N-terminal NanoLuc-tagged VEGFR2 or NRP1 to evaluate the selectivity of VEGF isoforms for these two membrane proteins. All fluorescent VEGF-A isoforms displayed high affinity for VEGFR2. Only VEGF₁₆₅a-TMR bound to NanoLuc-NRP1 with a similar high affinity (4.4 nM). Competition NRP1 binding experiments yielded a rank order of potency of VEGF₁₆₅a > VEGF₁₈₉a > VEGF₁₄₅a. VEGF₁₆₅b, VEGF-Ax, VEGF₁₂₁a, and VEGF₁₁₁a were unable to bind to NRP1. There were marked differences in the kinetic binding profiles of VEGF₁₆₅a-TMR for NRP1 and VEGFR2. These data emphasize the importance of the kinetic aspects of ligand binding to VEGFR2 and its co-receptors in the dynamics of VEGF signaling.

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VEGF₁₆₅a, VEGF₁₂₁a, and VEGF₁₆₅b were single-site labeled with tetramethylrhodamine

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NanoBRET quantified that VEGF-A isoforms have similar binding properties at VEGFR2

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NRP1 expressed in live cells does not bind VEGF₁₆₅b, VEGF₁₂₁a, VEGF-Ax, or VEGF₁₁₁a

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VEGFR2 and NRP1 have markedly distinct kinetic profiles binding VEGF₁₆₅a-TMR

Sensory neuronal sensitisation occurs through HMGB-1-RAGE and TRPV1 in high-glucose conditions

Many potential causes for painful diabetic neuropathy have been proposed including actions of cytokines and growth factors. High mobility group protein B1 (HMGB1) is a RAGE (also known as AGER) agonist whose levels are increased in diabetes and that contributes to pain by modulating peripheral inflammatory responses. HMGB1 enhances nociceptive behaviour in naïve animals through an unknown mechanism. We tested the hypothesis that HMGB1 causes pain through direct neuronal activation of RAGE and alteration of nociceptive neuronal responsiveness. HMGB1 and RAGE expression were increased in skin and primary sensory (dorsal root ganglion, DRG) neurons of diabetic rats at times when pain behaviour was enhanced. Agonist-evoked TRPV1-mediated Ca2+ responses increased in cultured DRG neurons from diabetic rats and in neurons from naïve rats exposed to high glucose concentrations. HMGB1-mediated increases in TRPV1-evoked Ca2+ responses in DRG neurons were RAGE- and PKC-dependent, and this was blocked by co-administration of the growth factor splice variant VEGF-A165b. Pain behaviour and the DRG RAGE expression increases were blocked by VEGF-A165b treatment of diabetic rats in vivo Hence, we conclude that HMGB1-RAGE activation sensitises DRG neurons in vitro, and that VEGF-A165b blocks HMGB-1-RAGE DRG activation, which may contribute to its analgesic properties in vivo.

Diabetes-induced microvascular complications at the level of the spinal cord: a contributing factor in diabetic neuropathic pain

KEY POINTS

Diabetes is thought to induce neuropathic pain through activation of dorsal horn sensory neurons in the spinal cord. Here we explore the impact of hyperglycaemia on the blood supply supporting the spinal cord and chronic pain development. In streptozotocin-induced diabetic rats, neuropathic pain is accompanied by a decline in microvascular integrity in the dorsal horn. Hyperglycaemia-induced degeneration of the endothelium in the dorsal horn was associated with a loss in vascular endothelial growth factor (VEGF)-A₁₆₅ b expression. VEGF-A₁₆₅ b treatment prevented diabetic neuropathic pain and degeneration of the endothelium in the spinal cord. Using an endothelial-specific VEGFR2 knockout transgenic mouse model, the loss of endothelial VEGFR2 signalling led to a decline in vascular integrity in the dorsal horn and the development of hyperalgesia in VEGFR2 knockout mice. This highlights that vascular degeneration in the spinal cord could be a previously unidentified factor in the development of diabetic neuropathic pain.

ABSTRACT

Abnormalities of neurovascular interactions within the CNS of diabetic patients is associated with the onset of many neurological disease states. However, to date, the link between the neurovascular network within the spinal cord and regulation of nociception has not been investigated despite neuropathic pain being common in diabetes. We hypothesised that hyperglycaemia-induced endothelial degeneration in the spinal cord, due to suppression of vascular endothelial growth factor (VEGF)-A/VEGFR2 signalling, induces diabetic neuropathic pain. Nociceptive pain behaviour was investigated in a chemically induced model of type 1 diabetes (streptozotocin induced, insulin supplemented; either vehicle or VEGF-A₁₆₅ b treated) and an inducible endothelial knockdown of VEGFR2 (tamoxifen induced). Diabetic animals developed mechanical allodynia and heat hyperalgesia. This was associated with a reduction in the number of blood vessels and reduction in Evans blue extravasation in the lumbar spinal cord of diabetic animals versus age-matched controls. Endothelial markers occludin, CD31 and VE-cadherin were downregulated in the spinal cord of the diabetic group versus controls, and there was a concurrent reduction of VEGF-A₁₆₅ b expression. In diabetic animals, VEGF-A₁₆₅ b treatment (biweekly i.p., 20 ng g^-1 ) restored normal Evans blue extravasation and prevented vascular degeneration, diabetes-induced central neuron activation and neuropathic pain. Inducible knockdown of VEGFR2 (tamoxifen treated Tie2CreER^T2 -vegfr2^flfl mice) led to a reduction in blood vessel network volume in the lumbar spinal cord and development of heat hyperalgesia. These findings indicate that hyperglycaemia leads to a reduction in the VEGF-A/VEGFR2 signalling cascade, resulting in endothelial dysfunction in the spinal cord, which could be an undiscovered contributing factor to diabetic neuropathic pain.

Alternative-splicing defects in cancer: Splicing regulators and their downstream targets, guiding the way to novel cancer therapeutics

Defects in alternative splicing are frequently found in human tumors and result either from mutations in splicing-regulatory elements of specific cancer genes or from changes in the regulatory splicing machinery. RNA splicing regulators have emerged as a new class of oncoproteins and tumor suppressors, and contribute to disease progression by modulating RNA isoforms involved in the hallmark cancer pathways. Thus, dysregulation of alternative RNA splicing is fundamental to cancer and provides a potentially rich source of novel therapeutic targets. Here, we review the alterations in splicing regulatory factors detected in human tumors, as well as the resulting alternatively spliced isoforms that impact cancer hallmarks, and discuss how they contribute to disease pathogenesis. RNA splicing is a highly regulated process and, as such, the regulators are themselves tightly regulated. Differential transcriptional and posttranscriptional regulation of splicing factors modulates their levels and activities in tumor cells. Furthermore, the composition of the tumor microenvironment can also influence which isoforms are expressed in a given cell type and impact drug responses. Finally, we summarize current efforts in targeting alternative splicing, including global splicing inhibition using small molecules blocking the spliceosome or splicing-factor-modifying enzymes, as well as splice-switching RNA-based therapeutics to modulate cancer-specific splicing isoforms. This article is categorized under: RNA in Disease and Development > RNA in Disease RNA Processing > Splicing Regulation/Alternative Splicing.

Management of VEGF-Targeted Therapy-Induced Hypertension

PURPOSE OF REVIEW

From a physiological point of view, VEGFs (vascular endothelial growth factors) and their receptors (VEGFR) play a critical role in vascular development angiogenesis, endothelial function, and vascular tone. On the pathological side, VEGF-VEGFR signaling may induce dysregulated angiogenesis, which contributes to the growth and to the spread of tumors, being essential for neoplastic proliferation and invasion.

RECENT FINDINGS

Pharmacological inhibition of VEGF-VEGFR is now a cornerstone in the treatment of many malignancies; however, treatment with VEGF inhibitors is commonly associated with an increase in blood pressure values. This side effect is strictly connected with the mechanism of action of these medications and might represent an index of therapy efficacy. The optimal management of this form of hypertension is, at present, not clear. Calcium channel blockers and renin-angiotensin system inhibitors probably represent the most appropriate classes of hypertensive dugs for the treatment of this condition; however, no conclusive data are presently available.

Vascular endothelial growth factors C and D may promote angiogenesis in the primate ovulatory follicle

Angiogenesis in the ovary occurs rapidly as the ovarian follicle transforms into a mature corpus luteum. Granulosa cells produce vascular endothelial growth factor A (VEGFA) in response to the ovulatory gonadotropin surge. VEGFA is established as a key mediator of angiogenesis in the primate ovulatory follicle. To determine if additional VEGF family members may be involved in angiogenesis within the ovulatory follicle, cynomolgus monkeys (Macaca fascicularis) received gonadotropins to stimulate multiple follicular development, and human chorionic gonadotropin (hCG) substituted for the luteinizing hormone surge to initiate ovulatory events. Granulosa cells of monkey ovulatory follicles contained mRNA and protein for VEGFC and VEGFD before and after hCG administration. VEGFC and VEGFD were detected in monkey follicular fluid and granulosa cell-conditioned culture media, suggesting that granulosa cells of ovulatory follicles secrete both VEGFC and VEGFD. To determine if these VEGF family members can stimulate angiogenic events, monkey ovarian microvascular endothelial cells (mOMECs) were obtained from monkey ovulatory follicles and treated in vitro with VEGFC and VEGFD. Angiogenic events are mediated via three VEGF receptors; mOMECs express all three VEGF receptors in vivo and in vitro. Exposure of mOMECs to VEGFC increased phosphorylation of AKT, while VEGFD treatment increased phosphorylation of both AKT and CREB. VEGFC and VEGFD increased mOMEC migration and the formation of endothelial cell sprouts in vitro. However, only VEGFD increased mOMEC proliferation. These findings suggest that VEGFC and VEGFD may work in conjunction with VEGFA to stimulate early events in angiogenesis of the primate ovulatory follicle.

Physiological Role of Vascular Endothelial Growth Factors as Homeostatic Regulators

The vascular endothelial growth factor (VEGF) family of proteins are key regulators of physiological systems. Originally linked with endothelial function, they have since become understood to be principal regulators of multiple tissues, both through their actions on vascular cells, but also through direct actions on other tissue types, including epithelial cells, neurons, and the immune system. The complexity of the five members of the gene family in terms of their different splice isoforms, differential translation, and specific localizations have enabled tissues to use these potent signaling molecules to control how they function to maintain their environment. This homeostatic function of VEGFs has been less intensely studied than their involvement in disease processes, development, and reproduction, but they still play a substantial and significant role in healthy control of blood volume and pressure, interstitial volume and drainage, renal and lung function, immunity, and signal processing in the peripheral and central nervous system. The widespread expression of VEGFs in healthy adult tissues, and the disturbances seen when VEGF signaling is inhibited support this view of the proteins as endogenous regulators of normal physiological function. This review summarizes the evidence and recent breakthroughs in understanding of the physiology that is regulated by VEGF, with emphasis on the role they play in maintaining homeostasis. © 2017 American Physiological Society. Compr Physiol 8:955-979, 2018.

Shift in VEGFA isoform balance towards more angiogenic variants is associated with tumor stage and differentiation of human hepatocellular carcinoma

BACKGROUND

Hepatocellular carcinoma (HCC) is the most common and aggressive type of malignant liver tumor. HCC progression depends significantly on its vascularization and formation of new blood vessels. Vascular endothelial growth factor A (VEGFA) is a crucial regulator of tumor vascularization and components of VEGF-induced cell signaling pathways are important targets of therapeutical drugs that demonstrated the highest efficiency in case of advanced HCC (sorafenib and regorafenib). VEGFA is expressed as a set of isoforms with different functional properties, thus VEGFA isoform expression pattern may affect tumor sensitivity to anti-angiogenic drugs. However, information about VEGFA isoforms expression in HCC is still incomplete and contradictory. The present study aims to quantitatively investigate VEGFA isoform expression aberrations in HCC tissue.

METHODS

A total of 50 pairs of HCC and non-tumor tissue samples were used to evaluate the VEGFA isoform spectrum using RT-PCR and quantitatively estimate changes in isoform expression using RT-qPCR. Correlations between these changes and tumor clinicopathological characteristics were analyzed.

RESULTS

We identified VEGFA-189, VEGFA-165, and VEGFA-121 as predominant isoforms in liver tissue. Anti-angiogenic VEGFA-xxxb variants constituted no more than 5% of all mature VEGFA transcripts detected and their expression was not changed significantly in HCC tissue. We demonstrated for the first time that the least active variant VEGFA-189 is frequently repressed in HCC (p < 0.001), while no uniform changes were detected for potent angiogenesis stimulators VEGFA-165 and VEGFA-121. Isoform balance in HCC shifts from VEGFA-189 towards VEGFA-165 or VEGFA-121 in the majority of cases (p < 0.001). Changes in fractions, but not expression levels, of VEGFA-189 (decrease) and VEGFA-121 (increase) correlated with advanced Tumor-Node-Metastasis (TNM) and Barcelona Clinic Liver Cancer (BCLC) tumor stages (p < 0.05), VEGFA-189 fraction reduction was also associated with poor tumor differentiation (p < 0.05).

DISCUSSION

A distinct shift in VEGFA isoform balance towards more pro-angiogenic variants occurs in HCC tissue and may modulate overall impact of VEGFA signaling. We suppose that the ratio between VEGFA isoforms is an important parameter governing HCC angiogenesis that may affect HCC progression and be used for optimizing the strategy of HCC therapy by predicting the response to anti-angiogenic drugs.

VEGF Upregulation in Viral Infections and Its Possible Therapeutic Implications

Several viruses are recognized as the direct or indirect causative agents of human tumors and other severe human diseases. Vascular endothelial growth factor (VEGF) is identified as a principal proangiogenic factor that enhances the production of new blood vessels from existing vascular network. Therefore, oncogenic viruses such as Kaposi’s sarcoma herpesvirus (KSHV) and Epstein-Barr virus (EBV) and non-oncogenic viruses such as herpes simplex virus (HSV-1) and dengue virus, which lack their own angiogenic factors, rely on the recruitment of cellular genes for angiogenesis in tumor progression or disease pathogenesis. This review summarizes how human viruses exploit the cellular signaling machinery to upregulate the expression of VEGF and benefit from its physiological functions for their own pathogenesis. Understanding the interplay between viruses and VEGF upregulation will pave the way to design targeted and effective therapeutic approaches for viral oncogenesis and severe diseases.

Along the Central Dogma-Controlling Gene Expression with Small Molecules

The central dogma of molecular biology, that DNA is transcribed into RNA and RNA translated into protein, was coined in the early days of modern biology. Back in the 1950s and 1960s, bacterial genetics first opened the way toward understanding life as the genetically encoded interaction of macromolecules. As molecular biology progressed and our knowledge of gene control deepened, it became increasingly clear that expression relied on many more levels of regulation. In the process of dissecting mechanisms of gene expression, specific small-molecule inhibitors played an important role and became valuable tools of investigation. Small molecules offer significant advantages over genetic tools, as they allow inhibiting a process at any desired time point, whereas mutating or altering the gene of an important regulator would likely result in a dead organism. With the advent of modern sequencing technology, it has become possible to monitor global cellular effects of small-molecule treatment and thereby overcome the limitations of classical biochemistry, which usually looks at a biological system in isolation. This review focuses on several molecules, especially natural products, that have played an important role in dissecting gene expression and have opened up new fields of investigation as well as clinical venues for disease treatment.

New peptide MY1340 revert the inhibition effect of VEGF on dendritic cells differentiation and maturation via blocking VEGF-NRP-1 axis and inhibit tumor growth in vivo

The development and clinical application of immunostimulatory therapy provides us a new and exciting strategy in cancer treatment of which the agents act on crucial receptors. Given the fact that Neuropilin-1(NRP-1) is essential for vascular endothelial growth factor (VEGF) to inhibit LPS-dependent maturation of dendritic cells (DCs), it may present a potentially meaningful target in cancer immunotherapy. To explore this hypothesis, we synthesized a novel polypeptide called MY1340 consist of 32 amino acids with the aim of targeting VEGF-NRP-1 axis. Pull-down assay coupled with liquid chromatography-tandem mass spectrometry analysis (LC-MS/MS) was firstly conducted to identify NRP-1 as a potential MY1340 interacting protein, and the interaction between them was further confirmed by western blot. The competitive enzyme-linked immunosorbent assay (ELISA) results revealed that MY1340 was able to inhibit the binding between NRP-1 and VEGF with IC₅₀ 7.42 ng/ml, better than that of Tuftsin, although a natural ligand reportedly specific for the NRP-1 receptor. The presence of VEGF significantly reduced the expression of human leukocyte antigen-DR (HLA-DR), CD86 and CD11C on DCs, and this effect was reverted by MY1340-augment p65 NF-κB and ERK1/2 phosphorylation. We also present evidence that MY1340 is remarkably efficacious in the treatment of mice bearing subcutaneous liver cancer and induced DC maturation in the tumor environment in vivo. Taken together, these results indicate that MY1340 may represent a potential efficient immune therapeutic compound within disease that are rich in VEGF.

VEGF (Vascular Endothelial Growth Factor) and Fibrotic Lung Disease

Interstitial lung disease (ILD) encompasses a group of heterogeneous diseases characterised by varying degrees of aberrant inflammation and fibrosis of the lung parenchyma. This may occur in isolation, such as in idiopathic pulmonary fibrosis (IPF) or as part of a wider disease process affecting multiple organs, such as in systemic sclerosis. Anti-Vascular Endothelial Growth Factor (anti-VEGF) therapy is one component of an existing broad-spectrum therapeutic option in IPF (nintedanib) and may become part of the emerging therapeutic strategy for other ILDs in the future. This article describes our current understanding of VEGF biology in normal lung homeostasis and how changes in its bioavailability may contribute the pathogenesis of ILD. The complexity of VEGF biology is particularly highlighted with an emphasis on the potential non-vascular, non-angiogenic roles for VEGF in the lung, in both health and disease.

SRPKIN-1: A Covalent SRPK1/2 Inhibitor that Potently Converts VEGF from Pro-angiogenic to Anti-angiogenic Isoform

The SRPK family of kinases regulates pre-mRNA splicing by phosphorylating serine/arginine (SR)-rich splicing factors, signals splicing control in response to extracellular stimuli, and contributes to tumorigenesis, suggesting that these splicing kinases are potential therapeutic targets. Here, we report the development of the first irreversible SRPK inhibitor, SRPKIN-1, which is also the first kinase inhibitor that forms a covalent bond with a tyrosine phenol group in the ATP-binding pocket. Kinome-wide profiling demonstrates its selectivity for SRPK1/2, and SRPKIN-1 attenuates SR protein phosphorylation at submicromolar concentrations. Vascular endothelial growth factor (VEGF) is a known target for SRPK-regulated splicing and, relative to the first-generation SRPK inhibitor SRPIN340 or small interfering RNA-mediated SRPK knockdown, SRPKIN-1 is more potent in converting the pro-angiogenic VEGF-A165a to the anti-angiogenic VEGF-A165b isoform and in blocking laser-induced neovascularization in a murine retinal model. These findings encourage further development of SRPK inhibitors for treatment of age-related macular degeneration.

Electrophoretic cytopathology resolves ERBB2 forms with single-cell resolution

In addition to canonical oncoproteins, truncated isoforms and proteolysis products are implicated in both drug resistance and disease progression. In HER2-positive breast tumors, expression of truncated HER2 isoforms resulting from alternative translation and/or carboxy-terminal fragments (CTFs) resulting from proteolysis (collectively, t-erbB2) have been associated with shortened progression-free survival of patients. Thus, to advance clinical pathology and inform treatment decisions, we developed a high-selectivity cytopathology assay capable of distinguishing t-erbB2 from full-length HER2 expression without the need for isoform-specific antibodies. Our microfluidic, single-cell western blot, employs electrophoretic separations to resolve full-length HER2 from the smaller t-erbB2 in each ~28 pL single-cell lysate. Subsequently, a pan-HER2 antibody detects all resolved HER2 protein forms via immunoprobing. In analysis of eight breast tumor biopsies, we identified two tumors comprised of 15% and 40% t-erbB2-expressing cells. By single-cell western blotting of the t-erbB2-expressing cells, we observed statistically different ratios of t-erbB2 proteins to full-length HER2 expression. Further, target multiplexing and clustering analyses scrutinized signaling, including ribosomal S6, within the t-erbB2-expressing cell subpopulation. Taken together, cytometric assays that report both protein isoform profiles and signaling state offer cancer classification taxonomies with unique relevance to precisely describing drug resistance mechanisms in which oncoprotein isoforms/fragments are implicated.

Vascular toxicities with VEGF inhibitor therapies-focus on hypertension and arterial thrombotic events

The vascular endothelial growth factor (VEGF) signaling pathway (VSP) fulfills a cardinal role in endothelial cells and its inhibition has profound cardiovascular impact. This is true not only for the normal vasculature but also for the tumor vasculature when VSP inhibitors are used as anti-angiogenic therapies. Generalized endothelial dysfunction predisposes to vasoconstriction, atherosclerosis, platelet activation, and thrombosis (arterial more than venous). All of these have been reported with VSP inhibitors and collectively give rise to vascular toxicities, the most concerning of which are arterial thromboembolic events (ATE). VSP inhibitors include antibodies, acting extracelluarly on VEGF, such as bevacizumab and tyrosine kinases inhibitors, acting intracellularly on the kinase domain of VEGF receptors, such as sunintib and sorafenib. The addition of bevacizumab and VSP tyrosine kinase inhibitor therapy to the cancer treatment regimen is associated with a 1.5-2.5-fold and 2.3-4.6-fold increase risk of ATEs, respectively. Risk factors for ATEs while on VSP inhibitor therapy include age older than 65 years, previous thromboembolic events, history of atherosclerotic disease, and duration of VSP inhibitor therapy. In clinical practice, hypertension remains the most commonly noted vascular manifestation of VSP inhibition. Optimal blood pressure goals and preferred therapeutic strategies toward reaching these goals are not defined at present. This review summarizes current data on this topic and proposes a more intensive management approach to patients undergoing VSP inhibitor therapy including Systolic Blood PRessure Intervention Trial (SPRINT) blood pressure goals, pleiotropic vasoprotective agents such as angiotensin converting enzyme inhibitors, amlodipine, and carvedilol, high-dose statin therapy, and aspirin.

Induction by innate defence regulator peptide 1018 of pro-angiogenic molecules and endothelial cell migration in a high glucose environment

Synthetic innate defence regulator (IDR) peptides such as IDR-1018 modulate immunity to promote key protective functions including chemotaxis, wound healing, and anti-infective activity, while suppressing pro-inflammatory responses to non-pathological levels. Here we demonstrated that IDR-1018 induced, by up to 75-fold, pro-angiogenic VEGF-165 in keratinocytes but suppressed this isoform in endothelial cells. It also induced early angiogenin and prolonged anti-inflammatory TGFβ expression on endothelial cells, while suppressing early pro-inflammatory IL-1β expression levels. IDR-1018 also down-regulated the hypoxia induced transcription factor HIF-1α in both keratinocytes and endothelial cells. Consistent with these data, in an in vitro wound healing scratch assay, IDR-1018 induced migration of endothelial cells under conditions of hypoxia while in epithelial cells migration increased only under conditions of normoxia.

Targeting the pro-angiogenic forms of VEGF or inhibiting their expression as anti-cancer strategies

Tumor growth relies on oxygen and blood supply depending on neo-vascularization. This process is mediated by the Vascular Endothelial Growth Factor (VEGF) in many tumors. This paradigm has led to the development of specific therapeutic approaches targeting VEGF or its receptors. Despite their promising effects, these strategies have not improved overall survival of patients suffering from different cancers compared to standard therapies. We hypothesized that the existence of anti-angiogenic forms of VEGF VEGFxxxb which are still present in many tumors limit the therapeutic effects of the anti-VEGF antibodies bevacizumab/Avastin (BVZ). To test this hypothesis, we generated renal cell carcinoma cells (RCC) expressing VEGF165b. The incidence of tumors xenografts generated in nude mice and their growth were inferior to those obtained with control cells. Whereas BVZ had no effect on control tumors, it slowed-down the growth of tumor generated with VEGF165b expressing cells. A prophylactic immunization against the domain discriminating VEGF from VEGFxxxb isoforms inhibited the growth of tumor generated with two different syngenic tumor cell lines (melanoma (B16 cells) and RCC (RENCA cells)). Purified immunoglobulins from immunized mice also slowed-down tumor growth of human RCC xenografts in nude mice, producing a potent effect compared to BVZ in this model. Furthermore, down-regulating the serine-arginine-rich splicing factor 1 (SRSF1) or masking SRSF1 binding sites by 2'O-Methyl RNA resulted in the increase of the VEGFxxxb/VEGF ratio. Therefore, a vaccine approach, specific antibodies against pro-angiogenic forms of VEGF, or increasing the VEGFxxxb/VEGF ratio may represent new prophylactic or pro-active anti-cancer strategies.

Modulation of VEGF-A Alternative Splicing as a Novel Treatment in Chronic Kidney Disease

Vascular endothelial growth factor A (VEGF-A) is a prominent pro-angiogenic and pro-permeability factor in the kidney. Alternative splicing of the terminal exon of VEGF-A through the use of an alternative 3' splice site gives rise to a functionally different family of isoforms, termed VEGF-A_xxxb, known to have anti-angiogenic and anti-permeability properties. Dysregulation of the VEGF-A_xxx/VEGF-A_xxxb isoform balance has recently been reported in several kidney pathologies, including diabetic nephropathy (DN) and Denys-Drash syndrome. Using mouse models of kidney disease where the VEGF-A isoform balance is disrupted, several reports have shown that VEGF-A₁₆₅b treatment/over-expression in the kidney is therapeutically beneficial. Furthermore, inhibition of certain splice factor kinases involved in the regulation of VEGF-A terminal exon splicing has provided some mechanistic insight into how VEGF-A splicing could be regulated in the kidney. This review highlights the importance of further investigation into the novel area of VEGF-A splicing in chronic kidney disease pathogenesis and how future studies may allow for the development of splicing-modifying therapeutic drugs.

Predictive markers of anti-VEGF and emerging role of angiogenesis inhibitors as immunotherapeutics

The critical role of angiogenesis in promoting tumor growth and metastasis has been well established scientifically, and consequently blocking this pathway as a therapeutic strategy has demonstrated great clinical success for the treatment of cancer. The holy grail however, has been the identification of patients who derive significant survival benefit from this class of agents. Here we attempt to delineate the diverse mechanisms related to anti-VEGF including its role as an anti-vascular, anti-angiogenic or an anti-permeability factor and review the most promising predictive biomarkers interrogated in large clinical trials, that identify patients who may derive significant survival advantage with VEGF inhibition. Lastly, we describe the function of VEGF as an immunomodulator and illustrate the evidence for anti-VEGF in reprogramming the tumor milieu from an immunosuppressive to an immune permissive microenvironment in human cancers, thus elucidating the role of anti-VEGF as an optimal combination partner for immune checkpoint inhibitors.

Systems Pharmacology of VEGF165b in Peripheral Artery Disease

We built a whole‐body computational model to study the role of the poorly understood vascular endothelial growth factor (VEGF)_165b splice isoform in peripheral artery disease (PAD). This model was built and validated using published and new experimental data from cells, mice, and humans, and explicitly accounts for known properties of VEGF_165b: lack of extracellular matrix (ECM)‐binding and weak phosphorylation of vascular endothelial growth factor receptor‐2 (VEGFR2) in vitro. The resulting model captures all known information about VEGF_165b distribution and signaling in human PAD, and provides novel, nonintuitive insight into VEGF_165b mechanism of action in vivo. Although VEGF_165a and VEGF_165b compete for VEGFR2 in vitro, simulations show that these isoforms do not compete for VEGFR2 at much lower physiological concentrations. Instead, reduced VEGF_165a may drive impaired VEGFR2 signaling. The model predicts that VEGF_165b does compete for binding to VEGFR1, supporting a VEGFR1‐mediated response to anti‐VEGF_165b. The model predicts a key role for VEGF_165b in PAD, but in a different way than previously hypothesized.

Eosinophils: The unsung heroes in cancer?

Prolonged low-grade inflammation or smoldering inflammation is a hallmark of a cancer. Eosinophils are components of the immune microenvironment that modulates tumor initiation and progression. Although canonically associated with a detrimental role in allergic disorders, these cells can induce a protective immune response against helminthes, viral and bacterial pathogens. Eosinophils are a source of anti-tumorigenic (e.g., TNF-α, granzyme, cationic proteins, and IL-18) and protumorigenic molecules (e.g., pro-angiogenic factors) depending on the milieu. In several neoplasias (e.g., melanoma, gastric, colorectal, oral and prostate cancer) eosinophils play an anti-tumorigenic role, in others (e.g., Hodgkin's lymphoma, cervical carcinoma) have been linked to poor prognosis, whereas in yet others they are apparently innocent bystanders. These seemingly conflicting results suggest that the role of eosinophils and their mediators could be cancer-dependent. The microlocalization (e.g., peritumoral vs intratumoral) of eosinophils could be another important aspect in the initiation/progression of solid and hematological tumors. Increasing evidence in experimental models indicates that activation/recruitment of eosinophils could represent a new therapeutic strategy for certain tumors (e.g., melanoma). Many unanswered questions should be addressed before we understand whether eosinophils are an ally, adversary or neutral bystanders in different types of human cancers.

Friends Turned Foes: Angiogenic Growth Factors beyond Angiogenesis

Angiogenesis, the formation of new blood vessels from pre-existing ones is a biological process that ensures an adequate blood flow is maintained to provide the cells with a sufficient supply of nutrients and oxygen within the body. Numerous soluble growth factors and inhibitors, cytokines, proteases as well as extracellular matrix proteins and adhesion molecules stringently regulate the multi-factorial process of angiogenesis. The properties and interactions of key angiogenic molecules such as vascular endothelial growth factors (VEGFs), fibroblast growth factors (FGFs) and angiopoietins have been investigated in great detail with respect to their molecular impact on angiogenesis. Since the discovery of angiogenic growth factors, much research has been focused on their biological actions and their potential use as therapeutic targets for angiogenic or anti-angiogenic strategies in a context-dependent manner depending on the pathologies. It is generally accepted that these factors play an indispensable role in angiogenesis. However, it is becoming increasingly evident that this is not their only role and it is likely that the angiogenic factors have important functions in a wider range of biological and pathological processes. The additional roles played by these molecules in numerous pathologies and biological processes beyond angiogenesis are discussed in this review.

Gene editing of the extra domain A positive fibronectin in various tumors, amplified the effects of CRISPR/Cas system on the inhibition of tumor progression

Background

The low efficiency of clustered, regularly interspaced, palindromic repeats-associated Cas (CRISPR/Cas) system editing genes in vivo limits the application. A components of the extracellular matrix (ECM), the extra domain A positive fibronectin (EDA+FN), may be a target for CRISPR/Cas system for the pro-oncogenic effects. The exclusion of EDA exon would alter the microenvironment and inhibit tumor progression, even the frequency of gene editing is still limited.

Results

The pro-oncogenic effects were confirmed by the exclusion of EDA exon from the fibronectin gene, as illustrated by the down-regulated proliferation, migration and invasion of CNE-2Z or SW480 cells (P<0.05). Furthermore, although the efficacy of EDA exon knockout through CRISPR/Cas system was shown to be low in vivo, the EDA+FN protein levels decrease obviously, inhibiting the tumor growth rate significantly (P<0.05), which was accompanied by a decrease in Ki-67 expression and microvessel numbers, and increased E-cadherin or decreased Vimentin expression (P<0.05).

Methods and materials

Human nasopharyngeal carcinoma cell line CNE-2Z, and the colorectal carcinoma cell line SW480 were transfected with CRISPR/Cas9 plasmids targeting EDA exon. The effects of the exclusion of EDA on the cell proliferation, motility and epithelial-mesenchymal transition (EMT) were investigated, and the western blot and real-time PCR were performed to analyze the underlying mechanisms. Furthermore, CRISPR/Cas9 plasmids were injected into xenograft tumors to knockout EDA exon in vivo, and tumor growth, cell proliferation, EMT rate, or vascularization were investigated using western blot, PCR and immunohistochemistry.

Conclusion

CRISPR/Cas system targeting ECM components was shown to be an effective method for the inhibition of tumor progression, as these paracrine or autocrine molecules are necessary for various tumor cells. This may represent a novel strategy for overcoming the drug evasion or resistance, in addition, circumventing the low efficiency of CRISPR/Cas system in vivo.

Silencing of semaphorin 3C suppresses cell proliferation and migration in MCF-7 breast cancer cells

Previous studies have suggested that semaphorin 3C (SEMA3C) is involved in the tumorigenesis and metastasis of a number of types of cancer. The aim of the present study was to investigate the role of SEMA3C in the proliferation and migration of MCF-7 breast cancer cells. Small interfering (si)RNA sequences targeting SEMA3C were constructed and transfected into MCF-7 cells in order to silence the expression of SEMA3C. Cell proliferation and migration were measured using CCK-8 and Transwell assays, respectively. Transfection with SEMA3C siRNA significantly downregulated the expression of SEMA3C in MCF-7 cells, and significantly suppressed cell proliferation and migration. Therefore, SEMA3C-targeted siRNA may be of potential use for the early diagnosis and treatment of breast cancer.

Blood vessel formation and function in bone

In addition to their conventional role as a conduit system for gases, nutrients, waste products or cells, blood vessels in the skeletal system play active roles in controlling multiple aspects of bone formation and provide niches for hematopoietic stem cells that reside within the bone marrow. In addition, recent studies have highlighted roles for blood vessels during bone healing. Here, we provide an overview of the architecture of the bone vasculature and discuss how blood vessels form within bone, how their formation is modulated, and how they function during development and fracture repair.

Differential Expression of VEGF-Axxx Isoforms Is Critical for Development of Pulmonary Fibrosis

RATIONALE

Fibrosis after lung injury is related to poor outcome, and idiopathic pulmonary fibrosis (IPF) can be regarded as an exemplar. Vascular endothelial growth factor (VEGF)-A has been implicated in this context, but there are conflicting reports as to whether it is a contributory or protective factor. Differential splicing of the VEGF-A gene produces multiple functional isoforms including VEGF-A₁₆₅a and VEGF-A₁₆₅b, a member of the inhibitory family. To date there is no clear information on the role of VEGF-A in IPF.

OBJECTIVES

To establish VEGF-A isoform expression and functional effects in IPF.

METHODS

We used tissue sections, plasma, and lung fibroblasts from patients with IPF and control subjects. In a bleomycin-induced lung fibrosis model we used wild-type MMTV mice and a triple transgenic mouse SPC-rtTA^+/-TetoCre^+/-LoxP-VEGF-A^+/+ to conditionally induce VEGF-A isoform deletion specifically in the alveolar type II (ATII) cells of adult mice.

MEASUREMENTS AND MAIN RESULTS

IPF and normal lung fibroblasts differentially expressed and responded to VEGF-A₁₆₅a and VEGF-A₁₆₅b in terms of proliferation and matrix expression. Increased VEGF-A₁₆₅b was detected in plasma of progressing patients with IPF. In a mouse model of pulmonary fibrosis, ATII-specific deficiency of VEGF-A or constitutive overexpression of VEGF-A₁₆₅b inhibited the development of pulmonary fibrosis, as did treatment with intraperitoneal delivery of VEGF-A₁₆₅b to wild-type mice.

CONCLUSIONS

These results indicate that changes in the bioavailability of VEGF-A sourced from ATII cells, namely the ratio of VEGF-A_xxxa to VEGF-A_xxxb, are critical in development of pulmonary fibrosis and may be a paradigm for the regulation of tissue repair.

VEGF as a potential target in lung cancer

Introduction The vascular endothelial growth factor A (VEGF) is the main mediator of angiogenesis. In addition, VEGF contributes to cancer growth and metastasis directly targeting tumor cells. VEGF overexpression and/or high VEGF serum levels have been reported in lung cancer. Areas covered We searched Pubmed for relevant preclinical studies with the terms 'lung cancer' 'VEGF' and 'in vivo'. We also searched the Clinicaltrials.gov database, the FDA and the EMA websites for the most recent updates on clinical development of anti-VEGF agents. Expert opinion VEGF plays an important role in sustaining the development and progression of lung cancer and it might represent an attractive target for therapeutic strategies. Nevertheless, clinical trials failed to attend the promising expectations deriving from preclinical studies with anti-VEGF agents. To improve the efficacy of anti-VEGF therapies in lung cancer, potential strategies might be the employment of combinatory therapies with immune checkpoint inhibitors or agents that inhibit signaling pathways and proangiogenic factors activated in response to VEGF blockade, and the identification of novel targets in the VEGF cascade. Finally, the identification of predictive markers might help to select patients who are more likely to respond to anti-angiogenic drugs.

Overexpression of Antiangiogenic Vascular Endothelial Growth Factor Isoform and Splicing Regulatory Factors in Oral, Laryngeal and Pharyngeal Squamous Cell Carcinomas

Background:

Overexpression of proangiogenic vascular endothelial growth factor A family VEGFA_xxx is associated with tumor growth and metastasis. The role of the alternatively spliced antiangiogenic family VEGFA_xxxb is poorly investigated in head and neck squamous cell carcinomas (HNSCCs). The antiangiogenic isoform binds to bevacizumab and its expression level could influence the treatment response and progression-free survival. In this study, the relative expression of VEGFA_xxx and VEGFA₁₆₅b isoforms and splicing regulatory factors genes was investigated in a series of HNSCCs.

Methods:

VEGFA_xxx, VEGFA₁₆₅b, SRSF6, SRSF5, SRSF1 and SRPK1 gene expression was quantified by quantitative real time PCR in 53 tissue samples obtained by surgery from HNSCC patients. Protein expression was evaluated by immunohistochemistry.

Results:

VEGFA_xxx and VEGFA₁₆₅b were overexpressed in HNSCCs. Elevated protein expression was also confirmed. However, VEGFA isoforms demonstrated differential expression according to anatomical sites. VEGFA_xxx was overexpressed in pharyngeal tumors while the VEGFA₁₆₅b isoform was up-regulated in oral tumors. The VEGFA₁₆₅b isoform was also positively correlated with expression of the splicing regulatory genes SRSF1, SRSF6 and SRSF5.

Conclusions:

We concluded that VEGFA_xxx and VEGFA₁₆₅b isoforms are overexpressed in HNSCCs and the splicing regulatory factors SRSF1, SRSF6, SRSF5 and SRPK1 may contribute to alternative splicing of the VEGFA gene. The findings for the differential expression of the antiangiogenic isoform in HNSCCs could facilitate effective therapeutic strategies for the management of these tumors.

Two-faced Fcab prevents polymerization with VEGF and reveals thermodynamics and the 2.15 Å crystal structure of the complex

Fcabs (Fc domain with antigen-binding sites) are promising novel therapeutics. By engineering of the C-terminal loops of the CH3 domains, 2 antigen binding sites can be inserted in close proximity. To elucidate the binding mode(s) between homodimeric Fcabs and small homodimeric antigens, the interaction between the Fcabs 448 and CT6 (having the AB, CD and EF loops and the C-termini engineered) with homodimeric VEGF was investigated. The crystal structures of these Fcabs, which form polymers with the antigen VEGF in solution, were determined. However, construction of heterodimeric Fcabs (JanusFcabs: one chain Fc-wt, one chain VEGF-binding) results in formation of distinct JanusFcab–VEGF complexes (2:1), which allowed elucidation of the crystal structure of the JanusCT6–VEGF complex at 2.15 Å resolution. VEGF binding to Janus448 and JanusCT6 is shown to be entropically unfavorable, but enthalpically favorable. Structure-function relationships are discussed with respect to Fcab design and engineering strategies.

The mutant p53-ID4 complex controls VEGFA isoforms by recruiting lncRNA MALAT1

The abundant, nuclear-retained, metastasis-associated lung adenocarcinoma transcript 1 (MALAT1) has been associated with a poorly differentiated and aggressive phenotype of mammary carcinomas. This long non-coding RNA (lncRNA) localizes to nuclear speckles, where it interacts with a subset of splicing factors and modulates their activity. In this study, we demonstrate that oncogenic splicing factor SRSF1 bridges MALAT1 to mutant p53 and ID4 proteins in breast cancer cells. Mutant p53 and ID4 delocalize MALAT1 from nuclear speckles and favor its association with chromatin. This enables aberrant recruitment of MALAT1 on VEGFA pre-mRNA and modulation of VEGFA isoforms expression. Interestingly, VEGFA-dependent expression signatures associate with ID4 expression specifically in basal-like breast cancers carrying TP53 mutations. Our results highlight a key role for MALAT1 in control of VEGFA isoforms expression in breast cancer cells expressing gain-of-function mutant p53 and ID4 proteins.

VEGF-A165 b protects against proteinuria in a mouse model with progressive depletion of all endogenous VEGF-A splice isoforms from the kidney

Key points

Progressive depletion of all vascular endothelial growth factor A (VEGF‐A) splice isoforms from the kidney results in proteinuria and increased glomerular water permeability, which are both rescued by over‐expression of VEGF‐A₁₆₅b only.

VEGF‐A₁₆₅b rescues the increase in glomerular basement membrane and podocyte slit width, as well as the decrease in sub‐podocyte space coverage, produced by VEGF‐A depletion.

VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule in glomerular endothelial cells and glomerular capillary circumference.

VEGF‐A₁₆₅b has opposite effects to VEGF‐A₁₆₅ on the expression of genes involved in endothelial cell migration and proliferation.

Abstract

Chronic kidney disease is strongly associated with a decrease in the expression of vascular endothelial growth factor A (VEGF‐A). However, little is known about the contribution of VEGF‐A splice isoforms to kidney physiology and pathology. Previous studies suggest that the splice isoform VEGF‐A₁₆₅b (resulting from alternative usage of a 3′ splice site in the terminal exon) is protective for kidney function. In the present study, we show, in a quad‐transgenic model, that over‐expression of VEGF‐A₁₆₅b alone is sufficient to rescue the increase in proteinuria, as well as glomerular water permeability, in the context of progressive depletion of all VEGF‐A isoforms from the podocytes. Ultrastructural studies show that the glomerular basement membrane is thickened, podocyte slit width is increased and sub‐podocyte space coverage is reduced when VEGF‐A is depleted, all of which are rescued in VEGF‐A₁₆₅b over‐expressors. VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule‐1 in glomerular endothelial cells and glomerular capillary circumference. Mechanistically, it increases VEGF receptor 2 expression both in vivo and in vitro and down‐regulates genes involved in migration and proliferation of endothelial cells, otherwise up‐regulated by the canonical isoform VEGF‐A₁₆₅. The results of the present study indicate that manipulation of VEGF‐A splice isoforms could be a novel therapeutic avenue in chronic glomerular disease.

Progressive depletion of all vascular endothelial growth factor A (VEGF‐A) splice isoforms from the kidney results in proteinuria and increased glomerular water permeability, which are both rescued by over‐expression of VEGF‐A₁₆₅b only.

VEGF‐A₁₆₅b rescues the increase in glomerular basement membrane and podocyte slit width, as well as the decrease in sub‐podocyte space coverage, produced by VEGF‐A depletion.

VEGF‐A₁₆₅b restores the expression of platelet endothelial cell adhesion molecule in glomerular endothelial cells and glomerular capillary circumference.

VEGF‐A₁₆₅b has opposite effects to VEGF‐A₁₆₅ on the expression of genes involved in endothelial cell migration and proliferation.

Pro- and antiangiogenic VEGF and its receptor status for the severity of diabetic retinopathy

PURPOSE

Alteration of pro- and antiangiogenic homeostasis of vascular endothelial growth factor (VEGF) isoforms in patients with hyperglycemia seems crucial but substantially unexplored at least quantitatively for diabetic retinopathy (DR). Therefore, in the present study we aimed to estimate the difference between the pro- (VEGF₁₆₅a) and antiangiogenic (VEGF₁₆₅b) VEGF isoforms and its soluble receptors for severity of DR.

METHODS

The study included 123 participants (diabetic retinopathy: 81, diabetic control: 20, non-diabetic control: 22) from the Regional Institute of Ophthalmology, Kolkata. The protein levels of VEGF₁₆₅a (proangiogenic), VEGF₁₆₅b (antiangiogenic), VEGF receptor 1 (VEGFR1), VEGFR2, and VEGFR3 in plasma were determined with enzyme-linked immunosorbent assay (ELISA).

RESULTS

An imbalance in VEGF homeostasis, a statistically significant concomitant increase (p<0.0001) in the level of VEGF₁₆₅a and a decrease in the level of VEGF₁₆₅b, was observed with the severity of the disease. Increased differences between VEGF₁₆₅a and VEGF₁₆₅b i.e. VEGF₁₆₅a-b concomitantly increased statistically significantly with the severity of the disease (p<0.0001), patients with diffuse diabetic macular edema (DME) with proliferative DR (PDR) had the highest imbalance. The plasma soluble form of VEGFR2 concentration consistently increased statistically significantly with the severity of the disease (p<0.0001).

CONCLUSIONS

The increased difference or imbalance between the pro- (VEGF₁₆₅a) and antiangiogenic (VEGF₁₆₅b) homeostasis of the VEGF isoforms, seems crucial for an adverse prognosis of DR and may be a better explanatory marker compared with either VEGF isoform.

TRPV4 Activation Contributes Functional Recovery from Ischemic Stroke via Angiogenesis and Neurogenesis

The endothelial transient receptor potential cation channel subfamily V member 4 (TRPV4) plays a crucial role in vascular remodeling; however, TRPV4-mediated angiogenesis after ischemic neuronal death as a neurorestorative strategy has not yet been thoroughly examined. In this study, we first tested whether TRPV4 activation can improve functional recovery in rats subjected to transient brain ischemia. The possible mechanisms for TRPV4 activation-promoted functional recovery were explored. A TRPV4 agonist, 4α-phorbol 12,13-didecanoate (4α-PDD), was intravenously injected via the tail vein at 6 h and 1, 2, 3, 4 days after ischemic stroke. The treatment reduced infarct volume by almost 50% (14.7 ± 3.7 vs. 29.2 ± 6.2%; p < 0.0001) and improved functional outcomes (p = 0.03) on day 5. To explore the therapeutic mechanism, we measured endothelial nitric oxide synthase (eNOS) expression and phosphorylation, vascular endothelial growth factor A (VEGFA) signaling, and neural stem/progenitor cells (NPCs). TRPV4 activation significantly increased eNOS expression and phosphorylation (serine 1177) by more than 2-fold in the ischemic region. The expressions of VEGFA and VEGF receptor-2 were significantly higher in the treated animals, especially an increase of the proangiogenic VEGFA_164a isoform while a decrease of the antiangiogenic VEGFA_165b isoform. We evaluated angiogenesis by detecting microvessel density in ischemic region. Using the immunohistochemistry staining, we found that 4α-PDD treatment caused a 3.4-fold increase of microvessel density (p < 0.0001). In addition, NPC proliferation and migration in the ischemic hemisphere were increased by 3-fold and 5-fold, respectively. In conclusion, our data suggest that TRPV4 activation by 4α-PDD may improve poststroke functional improvement through angiogenesis and neurogenesis.

Pharmacology of Modulators of Alternative Splicing

More than 95% of genes in the human genome are alternatively spliced to form multiple transcripts, often encoding proteins with differing or opposing function. The control of alternative splicing is now being elucidated, and with this comes the opportunity to develop modulators of alternative splicing that can control cellular function. A number of approaches have been taken to develop compounds that can experimentally, and sometimes clinically, affect splicing control, resulting in potential novel therapeutics. Here we develop the concepts that targeting alternative splicing can result in relatively specific pathway inhibitors/activators that result in dampening down of physiologic or pathologic processes, from changes in muscle physiology to altering angiogenesis or pain. The targets and pharmacology of some of the current inhibitors/activators of alternative splicing are demonstrated and future directions discussed.

VEGF isoforms have differential effects on permeability of human pulmonary microvascular endothelial cells

BACKGROUND

Alternative splicing of Vascular endothelial growth factor-A mRNA transcripts (commonly referred as VEGF) leads to the generation of functionally differing isoforms, the relative amounts of which have potentially significant physiological outcomes in conditions such as acute respiratory distress syndrome (ARDS). The effect of such isoforms on pulmonary vascular permeability is unknown. We hypothesised that VEGF₁₆₅a and VEGF₁₆₅b isoforms would have differing effects on pulmonary vascular permeability caused by differential activation of intercellular signal transduction pathways.

METHOD

To test this hypothesis we investigated the physiological effect of VEGF₁₆₅a and VEGF₁₆₅b on Human Pulmonary Microvascular Endothelial Cell (HPMEC) permeability using three different methods: trans-endothelial electrical resistance (TEER), Electric cell-substrate impedance sensing (ECIS) and FITC-BSA passage. In addition, potential downstream signalling pathways of the VEGF isoforms were investigated by Western blotting and the use of specific signalling inhibitors.

RESULTS

VEGF₁₆₅a increased HPMEC permeability using all three methods (paracellular and transcellular) and led to associated VE-cadherin and actin stress fibre changes. In contrast, VEGF₁₆₅b decreased paracellular permeability and did not induce changes in VE-cadherin cell distribution. Furthermore, VEGF₁₆₅a and VEGF₁₆₅b had differing effects on both the phosphorylation of VEGF receptors and downstream signalling proteins pMEK, p42/44MAPK, p38 MAPK, pAKT and peNOS. Interestingly specific inhibition of the pMEK, p38 MAPK, PI3 kinase and eNOS pathways blocked the effects of both VEGF₁₆₅a and VEGF₁₆₅b on paracellular permeability and the effect of VEGF₁₆₅a on proliferation/migration, suggesting that this difference in cellular response is mediated by an as yet unidentified signalling pathway(s).

CONCLUSION

This study demonstrates that the novel isoform VEGF₁₆₅a and VEGF₁₆₅b induce differing effects on permeability in pulmonary microvascular endothelial cells.

Central nervous system involvement in acute lymphoblastic leukemia is mediated by vascular endothelial growth factor

In acute lymphoblastic leukemia (ALL), central nervous system (CNS) involvement is a major clinical concern. Despite nondetectable CNS leukemia in many cases, prophylactic CNS-directed conventional intrathecal chemotherapy is required for relapse-free survival, indicating subclinical CNS manifestation in most patients. However, CNS-directed therapy is associated with long-term sequelae, including neurocognitive deficits and secondary neoplasms. Therefore, molecular mechanisms and pathways mediating leukemia-cell entry into the CNS need to be understood to identify targets for prophylactic and therapeutic interventions and develop alternative CNS-directed treatment strategies. In this study, we analyzed leukemia-cell entry into the CNS using a primograft ALL mouse model. We found that primary ALL cells transplanted onto nonobese diabetic/severe combined immunodeficiency mice faithfully recapitulated clinical and pathological features of meningeal infiltration seen in patients with ALL. ALL cells that had entered the CNS and were infiltrating the meninges were characterized by high expression of vascular endothelial growth factor A (VEGF). Although cellular viability, growth, proliferation, and survival of ALL cells were found to be independent of VEGF, transendothelial migration through CNS microvascular endothelial cells was regulated by VEGF. The importance of VEGF produced by ALL cells in mediating leukemia-cell entry into the CNS and leptomeningeal infiltration was further demonstrated by specific reduction of CNS leukemia on in vivo VEGF capture by the anti-VEGF antibody bevacizumab. Thus, we identified a mechanism of ALL-cell entry into the CNS, which by targeting VEGF signaling may serve as a novel strategy to control CNS leukemia in patients, replacing conventional CNS-toxic treatment.

Are Mast Cells MASTers in Cancer?

Prolonged low-grade inflammation or smoldering inflammation is a hallmark of cancer. Mast cells form a heterogeneous population of immune cells with differences in their ultra-structure, morphology, mediator content, and surface receptors. Mast cells are widely distributed throughout all tissues and are stromal components of the inflammatory microenvironment that modulates tumor initiation and development. Although canonically associated with allergic disorders, mast cells are a major source of pro-tumorigenic (e.g., angiogenic and lymphangiogenic factors) and antitumorigenic molecules (e.g., TNF-α and IL-9), depending on the milieu. In certain neoplasias (e.g., gastric, thyroid and Hodgkin's lymphoma) mast cells play a pro-tumorigenic role, in others (e.g., breast cancer) a protective role, whereas in yet others they are apparently innocent bystanders. These seemingly conflicting results suggest that the role of mast cells and their mediators could be cancer specific. The microlocalization (e.g., peritumoral vs intratumoral) of mast cells is another important aspect in the initiation/progression of solid and hematologic tumors. Increasing evidence in certain experimental models indicates that targeting mast cells and/or their mediators represent a potential therapeutic target in cancer. Thus, mast cells deserve focused consideration also as therapeutic targets in different types of tumors. There are many unanswered questions that should be addressed before we understand whether mast cells are an ally, adversary, or innocent bystanders in human cancers.

Vascular endothelial growth factor-A165b ameliorates outer-retinal barrier and vascular dysfunction in the diabetic retina

Diabetic retinopathy (DR) is one of the leading causes of blindness in the developed world. Characteristic features of DR are retinal neurodegeneration, pathological angiogenesis and breakdown of both the inner and outer retinal barriers of the retinal vasculature and retinal pigmented epithelial (RPE)–choroid respectively. Vascular endothelial growth factor (VEGF-A), a key regulator of angiogenesis and permeability, is the target of most pharmacological interventions of DR. VEGF-A can be alternatively spliced at exon 8 to form two families of isoforms, pro- and anti-angiogenic. VEGF-A₁₆₅a is the most abundant pro-angiogenic isoform, is pro-inflammatory and a potent inducer of permeability. VEGF-A₁₆₅b is anti-angiogenic, anti-inflammatory, cytoprotective and neuroprotective. In the diabetic eye, pro-angiogenic VEGF-A isoforms are up-regulated such that they overpower VEGF-A₁₆₅b. We hypothesized that this imbalance may contribute to increased breakdown of the retinal barriers and by redressing this imbalance, the pathological angiogenesis, fluid extravasation and retinal neurodegeneration could be ameliorated. VEGF-A₁₆₅b prevented VEGF-A₁₆₅a and hyperglycaemia-induced tight junction (TJ) breakdown and subsequent increase in solute flux in RPE cells. In streptozotocin (STZ)-induced diabetes, there was an increase in Evans Blue extravasation after both 1 and 8 weeks of diabetes, which was reduced upon intravitreal and systemic delivery of recombinant human (rh)VEGF-A₁₆₅b. Eight-week diabetic rats also showed an increase in retinal vessel density, which was prevented by VEGF-A₁₆₅b. These results show rhVEGF-A₁₆₅b reduces DR-associated blood–retina barrier (BRB) dysfunction, angiogenesis and neurodegeneration and may be a suitable therapeutic in treating DR.

Development of Potent, Selective SRPK1 Inhibitors as Potential Topical Therapeutics for Neovascular Eye Disease

Serine/arginine-protein kinase 1 (SRPK1) regulates alternative splicing of VEGF-A to pro-angiogenic isoforms and SRPK1 inhibition can restore the balance of pro/antiangiogenic isoforms to normal physiological levels. The lack of potency and selectivity of available compounds has limited development of SRPK1 inhibitors, with the control of alternative splicing by splicing factor-specific kinases yet to be translated. We present here compounds that occupy a binding pocket created by the unique helical insert of SRPK1, and trigger a backbone flip in the hinge region, that results in potent (<10 nM) and selective inhibition of SRPK1 kinase activity. Treatment with these inhibitors inhibited SRPK1 activity and phosphorylation of serine/arginine splicing factor 1 (SRSF1), resulting in alternative splicing of VEGF-A from pro-angiogenic to antiangiogenic isoforms. This property resulted in potent inhibition of blood vessel growth in models of choroidal angiogenesis in vivo. This work identifies tool compounds for splice isoform selective targeting of pro-angiogenic VEGF, which may lead to new therapeutic strategies for a diversity of diseases where dysfunctional splicing drives disease development.

Mechanisms regulating angiogenesis underlie seasonal control of pituitary function

Seasonal changes in mammalian physiology, such as those affecting reproduction, hibernation, and metabolism, are controlled by pituitary hormones released in response to annual environmental changes. In temperate zones, the primary environmental cue driving seasonal reproductive cycles is the change in day length (i.e., photoperiod), encoded by the pattern of melatonin secretion from the pineal gland. However, although reproduction relies on hypothalamic gonadotrophin-releasing hormone output, and most cells producing reproductive hormones are in the pars distalis (PD) of the pituitary, melatonin receptors are localized in the pars tuberalis (PT), a physically and functionally separate part of the gland. How melatonin in the PT controls the PD is not understood. Here we show that melatonin time-dependently acts on its receptors in the PT to alter splicing of vascular endothelial growth factor (VEGF). Outside the breeding season (BS), angiogenic VEGF-A stimulates vessel growth in the infundibulum, aiding vascular communication among the PT, PD, and brain. This also acts on VEGF receptor 2 (VEGFR2) expressed in PD prolactin-producing cells known to impair gonadotrophin secretion. In contrast, in the BS, melatonin releases antiangiogenic VEGF-A_xxxb from the PT, inhibiting infundibular angiogenesis and diminishing lactotroph (LT) VEGFR2 expression, lifting reproductive axis repression in response to shorter day lengths. The time-dependent, melatonin-induced differential expression of VEGF-A isoforms culminates in alterations in gonadotroph function opposite to those of LTs, with up-regulation and down-regulation of gonadotrophin gene expression during the breeding and nonbreeding seasons, respectively. These results provide a mechanism by which melatonin can control pituitary function in a seasonal manner.

RNA-Sequencing data supports the existence of novel VEGFA splicing events but not of VEGFAxxxb isoforms

Vascular endothelial growth factor (VEGFA), a pivotal regulator of angiogenesis and valuable therapeutic target, is characterised by alternative splicing which generates three principal isoforms, VEGFA₁₂₁, VEGFA₁₆₅ and VEGFA₁₈₉. A second set of anti-angiogenic isoforms termed VEGFA_xxxb that utilise an alternative splice site in the final exon have been widely reported, with mRNA detection based principally upon RT-PCR assays. We sought confirmation of the existence of the VEGFA_xxxb isoforms within the abundant RNA sequencing data available publicly. Whilst sequences derived specifically from each of the canonical VEGFA isoforms were present in many tissues, there were no sequences derived from VEGFA_xxxb isoforms. Sequencing of approximately 50,000 RT-PCR products spanning the exon 7–8 junction in 10 tissues did not identify any VEGFA_xxxb transcripts. The absence or extremely low expression of these transcripts in vivo indicates that VEGFA_xxxb isoforms are unlikely to play a role in normal physiology. Our analyses also revealed multiple novel splicing events supported by more reads than previously reported for VEGFA₁₄₅ and VEGFA₁₄₈ isoforms, including three from novel first exons consistent with existing transcription start site data. These novel VEGFA isoforms may play significant roles in specific cell types.

Biology and therapeutic implications of VEGF-A splice isoforms and single-nucleotide polymorphisms in colorectal cancer

Tumor growth, dissemination and metastasis are dependent on angiogenesis. The predominant vascular endothelial growth factor (VEGF) isoform that plays a major role in angiogenesis is VEGF-A. Indeed, VEGF-A is implicated in promoting angiogenesis of numerous solid malignancies, including colorectal cancer (CRC). A large body of preclinical and clinical evidence indicates that the expression of specific VEGF-A isoforms represents a predominant pro-angiogenic factor, which is associated with formation of metastases and poor prognosis in CRC patients. Different isoforms of human VEGF-A have been identified, all of which arise from alternative splicing of the primary transcript of a single gene. Notably, it has been recently demonstrated that expression of type 3 isoform pattern is significantly correlated with venous involvement in CRC as well as in progression to metastatic colorectal cancer (mCRC), although it remains unclear what proportion of CRC tumors express these isoforms. This review highlights the importance of investigating the genetic and the epigenetic variations in VEGF-A pathways in CRC, the functions of different VEGF-A isoforms and their potential application as prognostic markers and/or therapeutic targets. Better understanding of the mechanisms controlling angiogenesis in liver metastases is necessary to address the limitations of current anti-angiogenic therapies.

Angiogenesis in the atherosclerotic plaque

Atherosclerosis is a multifocal alteration of the vascular wall of medium and large arteries characterized by a local accumulation of cholesterol and non-resolving inflammation. Atherothrombotic complications are the leading cause of disability and mortality in western countries. Neovascularization in atherosclerotic lesions plays a major role in plaque growth and instability. The angiogenic process is mediated by classical angiogenic factors and by additional factors specific to atherosclerotic angiogenesis. In addition to its role in plaque progression, neovascularization may take part in plaque destabilization and thromboembolic events. Anti-angiogenic agents are effective to reduce atherosclerosis progression in various animal models. However, clinical trials with anti-angiogenic drugs, mainly anti-VEGF/VEGFR, used in anti-cancer therapy show cardiovascular adverse effects, and require additional investigations.

Immunogenicity and efficacy of a rationally designed vaccine against vascular endothelial growth factor in mouse solid tumor models

Vascular endothelial growth factor (VEGF) plays an important role in the progression of various cancers. The VEGF-specific antibody bevacizumab combined with chemotherapy was shown to significantly improve progression-free survival in certain cancers. However, repeated administration is necessary for effective suppression of VEGF, thereby making the therapy expensive and cumbersome. Thus, it is urgent to develop alternative reagents such as VEGF vaccines. Here we report that DTT-VEGF, a VEGF-based antigen consisting of the receptor-binding domain of VEGF and diphtheria toxin T domain (DTT), not only stimulated neutralizing antibody response, but also induced type 1 immune response as well as anti-tumor cytotoxic T lymphocytes in mice when administered with aluminum hydroxide adjuvant. The antibodies triggered by DTT-VEGF immunization inhibited the binding of VEGF to VEGF receptor and downregulated the serum VEGF levels in tumor-bearing mice. VEGF-specific IgG2a and IgG2b antibodies as well as type 1 cytokines were stimulated by DTT-VEGF vaccination. The splenocytes from DTT-VEGF-immunized mice showed cytotoxic activity against B16-F10 cells expressing VEGF. Extensive necrosis with severe hemorrhage and enhanced CD8+ T cell infiltration were observed in tumors from DTT-VEGF-immunized mice. The percentages of CD31+ vascular areas in the tumor sections from DTT-VEGF-immunized mice were significantly lower than those of control mice. DTT-VEGF significantly inhibited tumor growth in preventive and therapeutic vaccination settings in mouse models. Our data suggest that DTT is an effective antigen carrier to break immune self-tolerance and our vaccine design has potential to be used for human cancer therapy.

qFlow Cytometry-Based Receptoromic Screening: A High-Throughput Quantification Approach Informing Biomarker Selection and Nanosensor Development

Nanosensor-based detection of biomarkers can improve medical diagnosis; however, a critical factor in nanosensor development is deciding which biomarker to target, as most diseases present several biomarkers. Biomarker-targeting decisions can be informed via an understanding of biomarker expression. Currently, immunohistochemistry (IHC) is the accepted standard for profiling biomarker expression. While IHC provides a relative mapping of biomarker expression, it does not provide cell-by-cell readouts of biomarker expression or absolute biomarker quantification. Flow cytometry overcomes both these IHC challenges by offering biomarker expression on a cell-by-cell basis, and when combined with calibration standards, providing quantitation of biomarker concentrations: this is known as qFlow cytometry. Here, we outline the key components for applying qFlow cytometry to detect biomarkers within the angiogenic vascular endothelial growth factor receptor family. The key aspects of the qFlow cytometry methodology include: antibody specificity testing, immunofluorescent cell labeling, saturation analysis, fluorescent microsphere calibration, and quantitative analysis of both ensemble and cell-by-cell data. Together, these methods enable high-throughput quantification of biomarker expression.