Signaling of Prostaglandin E Receptors, EP3 and EP4 Facilitates Wound Healing and Lymphangiogenesis with Enhanced Recruitment of M2 Macrophages in Mice

Prostanoids Regulate Angiogenesis and Lymphangiogenesis in Pathological Conditions

Angiogenesis, the formation of new blood vessels from the preexistent microvasculature, is an essential component of wound repair and tumor growth. Nonsteroidal anti-inflammatory drugs that suppress prostanoid biosynthesis are known to suppress the incidence and progression of malignancies including colorectal cancers, and also to delay the wound healing. However, the precise mechanisms are not fully elucidated. Accumulated results obtained from prostanoid receptor knockout mice indicate that a prostaglandin E-type receptor signaling EP3 in the host microenvironment is critical in tumor angiogenesis inducing vascular endothelial growth factor A (VEGF-A). Further, lymphangiogenesis was also enhanced by EP signaling via VEGF-C/D inductions in pathological settings. These indicate the importance of EP receptor to facilitate angiogenesis and lymphangiogenesis in vivo. Prostanoids act beyond their commonly understood activities in smooth muscle contraction and vasoactivity, both of which are quick responses elicited within several seconds on stimulations. Prostanoid receptor signaling will be a potential therapeutic target for disease conditions related to angiogenesis and lymphangiogenesis.

The cell membrane as biofunctional material for accelerated bone repair

The cell (plasma) membrane is enriched with numerous receptors, ligands, enzymes, and phospholipids that play important roles in cell-cell and cell-extracellular matrix interactions governing, for instance, tissue development and repair. We previously showed that plasma membrane nanofragments (PMNFs) act as nucleation sites for bone formation in vivo, and induce in vitro mineralization within 1 day. In this study, we optimized the methods for generating, isolating, and applying PMNFs as a cell-free therapeutic to expedite bone defect repair. The PMNFs were isolated from different mouse cell lines (chondrocytes, osteoblasts, and fibroblasts), pre-conditioned, lyophilized, and subsequently transplanted into 2 mm critical-sized calvarial defects in mice (n = 75). The PMNFs from chondrocytes, following a 3-day pre-incubation, significantly accelerated bone repair within 2 weeks, through a coordinated attraction of macrophages, endothelial cells, and osteoblasts to the healing site. In vitro experiments confirmed that PMNFs enhanced cell adhesion. Comparison of the PMNF efficacy with phosphatidylserine, amorphous calcium phosphate (ACP), and living cells confirmed the unique ability of PMNFs to promote accelerated bone repair. Importantly, PMNFs promoted nearly complete integration of the regenerated bone with native tissue after 6 weeks (% non-integrated bone area = 15.02), contrasting with the partial integration (% non-integrated bone area = 56.10; p < 0.01, Student's test) with transplantation of ACP. Vickers microhardness tests demonstrated that the regenerated bone after 6 weeks (30.10 ± 1.75) exhibited hardness similar to native bone (31.07 ± 2.46). In conclusion, this is the first study to demonstrate that cell membrane can be a promising cell-free material with multifaceted biofunctional properties that promote accelerated bone repair. STATEMENT OF SIGNIFICANCE.

Cellular and molecular mechanisms of skin wound healing

Wound healing is a complex process that involves the coordinated actions of many different tissues and cell lineages. It requires tight orchestration of cell migration, proliferation, matrix deposition and remodelling, alongside inflammation and angiogenesis. Whereas small skin wounds heal in days, larger injuries resulting from trauma, acute illness or major surgery can take several weeks to heal, generally leaving behind a fibrotic scar that can impact tissue function. Development of therapeutics to prevent scarring and successfully repair chronic wounds requires a fuller knowledge of the cellular and molecular mechanisms driving wound healing. In this Review, we discuss the current understanding of the different phases of wound healing, from clot formation through re-epithelialization, angiogenesis and subsequent scar deposition. We highlight the contribution of different cell types to skin repair, with emphasis on how both innate and adaptive immune cells in the wound inflammatory response influence classically studied wound cell lineages, including keratinocytes, fibroblasts and endothelial cells, but also some of the less-studied cell lineages such as adipocytes, melanocytes and cutaneous nerves. Finally, we discuss newer approaches and research directions that have the potential to further our understanding of the mechanisms underpinning tissue repair.

Two transcriptionally and functionally distinct waves of neutrophils during mouse acute liver injury

BACKGROUND

Neutrophils are key mediators of inflammation during acute liver injury (ALI). Emerging evidence suggests that they also contribute to injury resolution and tissue repair. However, the different neutrophil subsets involved in these processes and their kinetics are undefined. Herein, we characterized neutrophil kinetics and heterogeneity during ALI.

METHODS

We used the carbon tetrachloride model of ALI and employed flow cytometry, tissue imaging, and quantitative RT-PCR to characterize intrahepatic neutrophils during the necroinflammatory early and late repair phases of the wound healing response to ALI. We FACS sorted intrahepatic neutrophils at key time points and examined their transcriptional profiles using RNA-sequencing. Finally, we evaluated neutrophil protein translation, mitochondrial function and metabolism, reactive oxygen species content, and neutrophil extracellular traps generation.

RESULTS

We detected 2 temporarily distinct waves of neutrophils during (1) necroinflammation (at 24 hours after injury) and (2) late repair (at 72 hours). Early neutrophils were proinflammatory, characterized by: (1) upregulation of inflammatory cytokines, (2) activation of the noncanonical NF-κB pathway, (3) reduction of protein translation, (4) decreased oxidative phosphorylation, and (5) higher propensity to generate reactive oxygen species and neutrophil extracellular traps. In contrast, late neutrophils were prorepair and enriched in genes and pathways associated with tissue repair and angiogenesis. Finally, early proinflammatory neutrophils were characterized by the expression of a short isoform of C-X-C chemokine receptor 5, while the late prorepair neutrophils were characterized by the expression of C-X-C chemokine receptor 4.

CONCLUSIONS

This study underscores the phenotypic and functional heterogeneity of neutrophils and their dual role in inflammation and tissue repair during ALI.

Lymphatic vessel: origin, heterogeneity, biological functions, and therapeutic targets

Lymphatic vessels, comprising the secondary circulatory system in human body, play a multifaceted role in maintaining homeostasis among various tissues and organs. They are tasked with a serious of responsibilities, including the regulation of lymph absorption and transport, the orchestration of immune surveillance and responses. Lymphatic vessel development undergoes a series of sophisticated regulatory signaling pathways governing heterogeneous-origin cell populations stepwise to assemble into the highly specialized lymphatic vessel networks. Lymphangiogenesis, as defined by new lymphatic vessels sprouting from preexisting lymphatic vessels/embryonic veins, is the main developmental mechanism underlying the formation and expansion of lymphatic vessel networks in an embryo. However, abnormal lymphangiogenesis could be observed in many pathological conditions and has a close relationship with the development and progression of various diseases. Mechanistic studies have revealed a set of lymphangiogenic factors and cascades that may serve as the potential targets for regulating abnormal lymphangiogenesis, to further modulate the progression of diseases. Actually, an increasing number of clinical trials have demonstrated the promising interventions and showed the feasibility of currently available treatments for future clinical translation. Targeting lymphangiogenic promoters or inhibitors not only directly regulates abnormal lymphangiogenesis, but improves the efficacy of diverse treatments. In conclusion, we present a comprehensive overview of lymphatic vessel development and physiological functions, and describe the critical involvement of abnormal lymphangiogenesis in multiple diseases. Moreover, we summarize the targeting therapeutic values of abnormal lymphangiogenesis, providing novel perspectives for treatment strategy of multiple human diseases.

Ontogenesis of the Mouse Ocular Surface Lymphatic Vascular Network

Purpose

Ocular lymphatic vessels play major physiological role in eye homeostasis and their dysfunction can contribute to the progression of several eye diseases. In this study, we characterized their spatiotemporal development and the cellular mechanisms occurring during their ontogenesis in the mouse eye.

Methods

Whole mount immunofluorescent staining and imaging by standard or lightsheet fluorescence microscopy were performed on late embryonic and early postnatal eye mouse samples.

Results

We observed that the ocular surface lymphatic vascular network develops at the early postnatal stages (between P0 and P5) from two nascent trunks arising at the nasal side on both sides of the nictitating membrane. These nascent vessels further branch and encircle the whole eye surface by sprouting lymphangiogenesis. In addition, we got evidence for the existence of a transient lymphvasculogenesis process generating lymphatic vessel fragments that will mostly formed the corneolimbal lymphatic vasculature which further connect to the conjunctival lymphatic network. Our results also support that CD206-positive macrophages can transdifferentiate and then integrate into the lymphatic neovessels.

Conclusions

Several complementary cellular processes participate in the development of the lymphatic ocular surface vasculature. This knowledge paves the way for the design of new therapeutic strategies to interfere with ocular lymphatic vessel formation when needed.

Thromboxane prostanoid signaling in macrophages attenuates lymphedema and facilitates lymphangiogenesis in mice : TP signaling and lymphangiogenesis

BACKGROUND

Accumulating evidence suggests that prostaglandin E2, an arachidonic acid (AA) metabolite, enhances lymphangiogenesis in response to inflammation. However, thromboxane A2 (TXA2), another AA metabolite, is not well known. Thus, this study aimed to determine the role of thromboxane prostanoid (TP) signaling in lymphangiogenesis in secondary lymphedema.

METHODS AND RESULTS

Lymphedema was induced by the ablation of lymphatic vessels in mouse tails. Compared with wild-type mice, tail lymphedema in Tp-deficient mice was enhanced, which was associated with suppressed lymphangiogenesis as indicated by decreased lymphatic vessel area and pro-lymphangiogenesis-stimulating factors. Numerous macrophages were found in the tail tissues of Tp-deficient mice. Furthermore, the deletion of TP in macrophages increased tail edema and decreased lymphangiogenesis and pro-lymphangiogenic cytokines, which was accompanied by increased numbers of macrophages and gene expression related to a pro-inflammatory macrophage phenotype in tail tissues. In vivo microscopic studies revealed fluorescent dye leakage in the lymphatic vessels in the wounded tissues.

CONCLUSIONS

The results suggest that TP signaling in macrophages promotes lymphangiogenesis and prevents tail lymphedema. TP signaling may be a therapeutic target for improving lymphedema-related symptoms by enhancing lymphangiogenesis.

Inhibition of TP signaling promotes endometriosis growth and neovascularization

Endometriosis is highly dependent on angiogenesis and lymphangiogenesis. Prostaglandin E2, an arachidonic acid metabolite, has been shown to promote the formation of new blood and lymphatic vessels. However, the role of another arachidonic acid metabolite, thromboxane A2 (TXA2) in angiogenesis and lymphangiogenesis during endometriosis remains largely unexplored. Using a murine model of ectopic endometrial transplantation, fragments from the endometrium of WT donor mice were transplanted into the peritoneal walls of recipient WT mice (WT→WT), resulting in an increase in both the area and density of blood and lymphatic vessels. Upon transplantation of endometrial tissue from thromboxane prostanoid (TP) receptor (TXA2 receptor)‑deficient (TP‑/‑) mice into TP‑/‑ mice (TP‑/‑→TP‑/‑), an increase in implant growth, angiogenesis, and lymphangiogenesis were observed along with upregulation of pro‑angiogenic and lymphangiogenic factors, including vascular endothelial growth factors (VEGFs). Similar results were obtained using a thromboxane synthase (TXS) inhibitor in WT→WT mice. Furthermore, TP‑/‑→TP‑/‑ mice had a higher number of F4/80+ cells than that of WT→WT mice, with increased expression of genes related to the anti‑inflammatory macrophage phenotype in endometrial lesions. In cultured bone marrow (BM)‑derived macrophages, the levels of VEGF‑A, VEGF‑C, and VEGF‑D decreased in a TP‑dependent manner. Furthermore, TP signaling affected the polarization of cultured BM‑derived macrophages to the anti‑inflammatory phenotype. These findings imply that inhibition of TP signaling promotes endometrial implant growth and neovascularization.

A biologically active lipid, thromboxane, as a regulator of angiogenesis and lymphangiogenesis

Thromboxane (TX) and prostaglandins are metabolites of arachidonic acid, a twenty-carbon unsaturated fatty acid, and have a variety of actions that are exerted via specific receptors. Angiogenesis is defined as the formation of new blood vessels from pre-existing vascular beds and is a critical component of pathological conditions, including inflammation and cancer. Lymphatic vessels play crucial roles in the regulation of interstitial fluid, immune surveillance, and the absorption of dietary fat from the intestine; and they are also involved in the pathogenesis of various diseases. Similar to angiogenesis, lymphangiogenesis, the formation of new lymphatic vessels, is a critical component of pathological conditions. The TP-dependent accumulation of platelets in microvessels has been reported to enhance angiogenesis under pathological conditions. Although the roles of some growth factors and cytokines in angiogenesis and lymphangiogenesis have been well characterized, accumulating evidence suggests that TX induces the production of proangiogenic and prolymphangiogenic factors through the activation of adenylate cyclase, and upregulates angiogenesis and lymphangiogenesis under disease conditions. In this review, we discuss the role of TX as a regulator of angiogenesis and lymphangiogenesis, and its emerging importance as a therapeutic target.

Intestinal Lymphatic Dysfunction in Kidney Disease

Kidney disease is associated with adverse consequences in many organs beyond the kidney, including the heart, lungs, brain, and intestines. The kidney-intestinal cross talk involves intestinal epithelial damage, dysbiosis, and generation of uremic toxins. Recent studies reveal that kidney injury expands the intestinal lymphatics, increases lymphatic flow, and alters the composition of mesenteric lymph. The intestinal lymphatics, like blood vessels, are a route for transporting potentially harmful substances generated by the intestines. The lymphatic architecture and actions are uniquely suited to take up and transport large macromolecules, functions that differentiate them from blood vessels, allowing them to play a distinct role in a variety of physiological and pathological processes. Here, we focus on the mechanisms by which kidney diseases result in deleterious changes in intestinal lymphatics and consider a novel paradigm of a vicious cycle of detrimental organ cross talk. This concept involves kidney injury-induced modulation of intestinal lymphatics that promotes production and distribution of harmful factors, which in turn contributes to disease progression in distant organ systems.

Immune-interacting lymphatic endothelial subtype at capillary terminals drives lymphatic malformation

Oncogenic mutations in PIK3CA, encoding p110α-PI3K, are a common cause of venous and lymphatic malformations. Vessel type-specific disease pathogenesis is poorly understood, hampering development of efficient therapies. Here, we reveal a new immune-interacting subtype of Ptx3-positive dermal lymphatic capillary endothelial cells (iLECs) that recruit pro-lymphangiogenic macrophages to promote progressive lymphatic overgrowth. Mouse model of Pik3caH1047R-driven vascular malformations showed that proliferation was induced in both venous and lymphatic ECs but sustained selectively in LECs of advanced lesions. Single-cell transcriptomics identified the iLEC population, residing at lymphatic capillary terminals of normal vasculature, that was expanded in Pik3caH1047R mice. Expression of pro-inflammatory genes, including monocyte/macrophage chemokine Ccl2, in Pik3caH1047R-iLECs was associated with recruitment of VEGF-C-producing macrophages. Macrophage depletion, CCL2 blockade, or anti-inflammatory COX-2 inhibition limited Pik3caH1047R-driven lymphangiogenesis. Thus, targeting the paracrine crosstalk involving iLECs and macrophages provides a new therapeutic opportunity for lymphatic malformations. Identification of iLECs further indicates that peripheral lymphatic vessels not only respond to but also actively orchestrate inflammatory processes.

Aiphanol, a multi-targeting stilbenolignan, potently suppresses mouse lymphangiogenesis and lymphatic metastasis

The high incidence of lymphatic metastasis is closely related to poor prognosis and mortality in cancers. Potent inhibitors to prevent pathological lymphangiogenesis and lymphatic spread are urgently needed. The VEGF-C-VEGFR3 pathway plays a vital role in driving lymphangiogenesis and lymph node metastasis. In addition, COX2 in tumor cells and tumor-associated macrophages (TAMs) facilitates lymphangiogenesis. We recently reported that aiphanol, a natural stilbenolignan, attenuates tumor angiogenesis by repressing VEGFR2 and COX2. In this study, we evaluated the antilymphangiogenic and antimetastatic potency of aiphanol using in vitro, ex vivo and in vivo systems. We first demonstrated that aiphanol directly bound to VEGFR3 and blocked its kinase activity with an half-maximal inhibitory concentration (IC50) value of 0.29 μM in an in vitro ADP-GloTM kinase assay. Furthermore, we showed that aiphanol (7.5-30 μM) dose-dependently counteracted VEGF-C-induced proliferation, migration and tubular formation of lymphatic endothelial cells (LECs), which was further verified in vivo. VEGFR3 knockdown markedly mitigated the inhibitory potency of aiphanol on lymphangiogenesis. In 4T1-luc breast tumor-bearing mice, oral administration of aiphanol (5 and 30 mg· kg-1 ·d-1) dose-dependently decreased lymphatic metastasis and prolonged survival time, which was associated with impaired lymphangiogenesis, angiogenesis and, interestingly, macrophage infiltration. In addition, we found that aiphanol decreased the COX2-dependent secretion of PGE2 and VEGF-C from tumor cells and macrophages. These results demonstrate that aiphanol is an appealing agent for preventing lymphangiogenesis and lymphatic dissemination by synergistically targeting VEGFR3 and inhibiting the COX2-PGE2-VEGF-C signaling axis.

Alloantigen-activated (AAA) CD4+ T cells reinvigorate host endogenous T cell immunity to eliminate pre-established tumors in mice

BACKGROUND

Cancer vaccines that induce endogenous antitumor immunity represent an ideal strategy to overcome intractable cancers. However, doing this against a pre-established cancer using autologous immune cells has proven to be challenging. "Allogeneic effects" refers to the induction of an endogenous immune response upon adoptive transfer of allogeneic lymphocytes without utilizing hematopoietic stem cell transplantation. While allogeneic lymphocytes have a potent ability to activate host immunity as a cell adjuvant, novel strategies that can activate endogenous antitumor activity in cancer patients remain an unmet need. In this study, we established a new method to destroy pre-developed tumors and confer potent antitumor immunity in mice using alloantigen-activated CD4⁺ (named AAA-CD4⁺) T cells.

METHODS

AAA-CD4⁺ T cells were generated from CD4⁺ T cells isolated from BALB/c mice in cultures with dendritic cells (DCs) induced from C57BL/6 (B6) mice. In this culture, allogeneic CD4⁺ T cells that recognize and react to B6 mouse-derived alloantigens are preferentially activated. These AAA-CD4⁺ T cells were directly injected into the pre-established melanoma in B6 mice to assess their ability to elicit antitumor immunity in vivo.

RESULTS

Upon intratumoral injection, these AAA-CD4⁺ T cells underwent a dramatic expansion in the tumor and secreted high levels of IFN-γ and IL-2. This was accompanied by markedly increased infiltration of host-derived CD8⁺ T cells, CD4⁺ T cells, natural killer (NK) cells, DCs, and type-1 like macrophages. Selective depletion of host CD8⁺ T cells, rather than NK cells, abrogated this therapeutic effect. Thus, intratumoral administration of AAA-CD4⁺ T cells results in a robust endogenous CD8⁺ T cell response that destroys pre-established melanoma. This locally induced antitumor immunity elicited systemic protection to eliminate tumors at distal sites, persisted over 6 months in vivo, and protected the animals from tumor re-challenge. Notably, the injected AAA-CD4⁺ T cells disappeared within 7 days and caused no adverse reactions.

CONCLUSIONS

Our findings indicate that AAA-CD4⁺ T cells reinvigorate endogenous cytotoxic T cells to eradicate pre-established melanoma and induce long-term protective antitumor immunity. This approach can be immediately applied to patients with advanced melanoma and may have broad implications in the treatment of other types of solid tumors.

Biologically active lipids in the regulation of lymphangiogenesis in disease states

Lymphatic vessels have crucial roles in the regulation of interstitial fluids, immune surveillance, and the absorption of dietary fat in the intestine. Lymphatic function is also closely related to the pathogenesis of various disease states such as inflammation, lymphedema, endometriosis, liver dysfunction, and tumor metastasis. Lymphangiogenesis, the formation of new lymphatic vessels from pre-existing lymphatic vessels, is a critical determinant in the above conditions. Although the effect of growth factors on lymphangiogenesis is well-characterized, and biologically active lipids are known to affect smooth muscle contractility and vasoaction, there is accumulating evidence that biologically active lipids are also important inducers of growth factors and cytokines that regulate lymphangiogenesis. This review discusses recent advances in our understanding of biologically active lipids, including arachidonic acid metabolites, sphingosine 1-phosphate, and lysophosphatidic acid, as regulators of lymphangiogenesis, and the emerging importance of the lymphangiogenesis as a therapeutic target.

The Macrophage Response Is Driven by Mesenchymal Stem Cell-Mediated Metabolic Reprogramming

Mesenchymal stem cells (MSCs) are multipotent adult stromal cells widely studied for their regenerative and immunomodulatory properties. They are capable of modulating macrophage plasticity depending on various microenvironmental signals. Current studies have shown that metabolic changes can also affect macrophage fate and function. Indeed, changes in the environment prompt phenotype change. Therefore, in this review, we will discuss how MSCs orchestrate macrophage’s metabolic plasticity and the impact on their function. An improved understanding of the crosstalk between macrophages and MSCs will improve our knowledge of MSC’s therapeutic potential in the context of inflammatory diseases, cancer, and tissue repair processes in which macrophages are pivotal.

Intersecting Mechanisms of Hypoxia and Prostaglandin E2-Mediated Inflammation in the Comparative Biology of Oral Squamous Cell Carcinoma

The importance of inflammation in the pathogenesis of cancer was first proposed by Rudolph Virchow over 150 years ago, and our understanding of its significance has grown over decades of biomedical research. The arachidonic acid pathway of inflammation, including cyclooxygenase (COX) enzymes, PGE2 synthase enzymes, prostaglandin E2 (PGE2) and PGE2 receptors has been extensively studied and has been associated with different diseases and different types of cancers, including oral squamous cell carcinoma (OSCC). In addition to inflammation in the tumour microenvironment, low oxygen levels (hypoxia) within tumours have also been shown to contribute to tumour progression. Understandably, most of our OSCC knowledge comes from study of this aggressive cancer in human patients and in experimental rodent models. However, domestic animals develop OSCC spontaneously and this is an important, and difficult to treat, form of cancer in veterinary medicine. The primary goal of this review article is to explore the available evidence regarding interaction between hypoxia and the arachidonic acid pathway of inflammation during malignant behaviour of OSCC. Overlapping mechanisms in hypoxia and inflammation can contribute to tumour growth, angiogenesis, and, importantly, resistance to therapy. The benefits and controversies of anti-inflammatory and anti-angiogenic therapies for human and animal OSCC patients will be discussed, including conventional pharmaceutical agents as well as natural products.

Roles of Thromboxane Receptor Signaling in Enhancement of Lipopolysaccharide-Induced Lymphangiogenesis and Lymphatic Drainage Function in Diaphragm

[Figure: see text].

Prostaglandin E2 Receptor 4 (EP4) as a Therapeutic Target to Impede Breast Cancer-Associated Angiogenesis and Lymphangiogenesis

The formation of new blood (angiogenesis) and lymphatic (lymphangiogenesis) vessels are major events associated with most epithelial malignancies, including breast cancer. Angiogenesis is essential for cancer cell survival. Lymphangiogenesis is critical in maintaining tumoral interstitial fluid balance and importing tumor-facilitatory immune cells. Both vascular routes also serve as conduits for cancer metastasis. Intratumoral hypoxia promotes both events by stimulating multiple angiogenic/lymphangiogenic growth factors. Studies on tumor-associated lymphangiogenesis and its exploitation for therapy have received less attention from the research community than those on angiogenesis. Inflammation is a key mediator of both processes, hijacked by many cancers by the aberrant expression of the inflammation-associated enzyme cyclo-oxygenase (COX)-2. In this review, we focus on breast cancer and showed that COX-2 is a major promoter of both events, primarily resulting from the activation of prostaglandin (PG) E receptor EP4 on tumor cells, tumor-infiltrating immune cells, and endothelial cells; and the induction of oncogenic microRNAs. The COX-2/EP4 pathway also promotes additional events in breast cancer progression, such as cancer cell migration, invasion, and the stimulation of stem-like cells. Based on a combination of studies using multiple breast cancer models, we show that EP4 antagonists hold a major promise in breast cancer therapy in combination with other modalities including immune check-point inhibitors.

The complex role of prostaglandin E2-EP receptor signaling in wound healing

Prostaglandins are critical lipid mediators involved in the wound healing response, with prostaglandin E₂ (PGE₂) being the most complex and exhibiting the most diverse physiological outputs. PGE₂ signals via four G protein-coupled receptors, termed EP-receptors 1-4 that induce distinct signaling pathways upon activation and lead to an array of different outputs. Recent studies examining the role of PGE₂ and EP receptor signaling in wound healing following various forms of tissue damage are discussed in this review.

RAMP1 signaling in immune cells regulates inflammation-associated lymphangiogenesis

Calcitonin gene-related peptide (CGRP) regulates inflammation via signaling through receptor activity-modifying protein (RAMP) 1. Here, we investigated the role of RAMP1 signaling in growth of lymphatic vessels during inflammation. Lymphangiogenesis in the diaphragm of RAMP1-deficient (^-/-) mice or their wild-type (WT) counterparts was induced by repeated intraperitoneal injection of lipopolysaccharide (LPS). Compared with WT mice, LPS-induced lymphangiogenesis in RAMP1^-/- mice was suppressed. This was accompanied by the reduced expression of vascular endothelial growth factor (VEGF)-C and VEGF-D. The number of CD4⁺ cells in diaphragm tissue from WT mice was greater than RAMP1^-/- mice. Removing CD4⁺ cells attenuated lymphangiogenesis and expression of VEGF-C and VEGF-D. CD4⁺ cells isolated from RAMP1^-/- mice exhibited reduced expression of VEGF-C and VEGF-D. The number of CD11b⁺ cells from RAMP1^-/- mice was higher than WT mice and was associated with the upregulated expression of genes related to pro-inflammatory macrophage phenotype and downregulation of reparative macrophage phenotype-related expression. When fluorescein isothiocyanate (FITC)-dextran was injected into the peritoneal cavity, the amount of residual FITC-dextran in WT mice was lower than that in RAMP1^-/- mice. The present results suggest that RAMP1 signaling in immune cells plays a critical role in inflammation-related lymphangiogenesis; therefore, it represents a novel target for controlling lymphangiogenesis.

Lymphangiogenesis and accumulation of reparative macrophages contribute to liver repair after hepatic ischemia-reperfusion injury

Hepatic tissue repair plays a critical role in determining the outcome of hepatic ischemia-reperfusion (I/R) injury. Hepatic lymphatics participate in the clearance of dead tissues and contribute to the reparative process after acute hepatic injury; however, it remains unknown whether lymphangiogenesis in response to hepatic inflammation is involved in liver repair. Herein, we determined if hepatic lymphangiogenesis improves liver repair after hepatic I/R injury. Using a mouse model of hepatic I/R injury, we investigated hepatic lymphatic structure, growth, and function in injured murine livers. Hepatic I/R injury enhanced lymphangiogenesis around the portal tract and this was associated with increased expression of pro-lymphangiogenic growth factors including vascular endothelial growth factor (VEGF)-C and VEGF-D. Recombinant VEGF-D treatment facilitated liver repair in association with the expansion of lymphatic vessels and increased expression of genes related to the reparative macrophage phenotype. Treatment with a VEGF receptor 3 (VEGFR3) inhibitor suppressed liver repair, lymphangiogenesis, drainage function, and accumulation of VEGFR3-expressing reparative macrophages. VEGF-C and VEGF-D upregulated expression of genes related to lymphangiogenic factors and the reparative macrophage phenotype in cultured macrophages. These results suggest that activation of VEGFR3 signaling increases lymphangiogenesis and the number of reparative macrophages, both of which play roles in liver repair. Expanded lymphatics and induction of reparative macrophage accumulation may be therapeutic targets to enhance liver repair after hepatic injury.

Role of the PGE2 receptor in ischemia-reperfusion injury of the rat retina

Purpose

To investigate the function and expression of the PGE2 receptors EP1-4 in rat retinal ischemia-reperfusion (I/R) injury and to determine the regulatory role of resveratrol (RES) in this process.

Methods

In vitro, we stimulated primary astrocytes extracted from the optic disc of rats with epidermal growth factor (EGF) and RES, and detected the location of EP1-4 expression with immunofluorescence. The expression of antiglial fibrillary acidic protein (GFAP), EGF receptor (EGFR), inducible NOS (iNOS), and EP1-4 in astrocytes was detected with western blotting. In vivo, we established an I/R injury model and RES treatment model with Sprague-Dawley rats. Changes in the thickness of the inner retina were observed with hematoxylin and eosin (H&E) staining. EP1-4 localization in the retina was observed with immunohistochemistry. The expression of COX-2, iNOS, and EP1-4 in the control and model groups was detected with western blotting.

Results

In this study, immunofluorescence and immunohistochemistry showed that EP1-4 are expressed in astrocytes and the rat retina. EGF stimulation increased the expression of EGFR, iNOS, EP1, EP2, and EP4 in astrocytes. The expression of EP1-4 was statistically significantly increased on the third day after model induction, and EP1-4 expression decreased to normal levels on day 7. EGF and RES mediated the decrease in the expression of EP2. RES treatment significantly reduced retinal damage and RGC loss, as demonstrated by the relatively intact tissue structure on day 7 observed with H&E staining. Moreover, inflammation was associated with this I/R injury model, as demonstrated by the early induction of proinflammatory mediators, and this inflammation was significantly attenuated after RES treatment.

Conclusions

These results indicate that the COX-2/PGE2/EPs pathway is involved in retinal damage and astrocyte inflammation. In addition, the results suggest that the neuroprotective effects of RES may be associated with decreased production of inflammatory mediators. These results suggest that the PGE2 receptor may be a key factor in the treatment of neurodegenerative diseases, and that RES may be used as a possible therapeutic strategy for glaucoma.

Essential role of prostaglandin E2 and the EP3 receptor in lymphatic vessel development during zebrafish embryogenesis

Lymphatic endothelial cells arise from the venous endothelial cells in embryonic lymphatic development. However, the molecular mechanisms remain to be elucidated. We here report that prostaglandin (PG) E₂ plays essential roles in the embryonic lymphatic development through the EP3 receptor, one of the PGE₂ receptors. Knockdown of the EP3 receptor or inhibition of cyclooxygenases (COX; rate-limiting enzymes for PG synthesis) impaired lymphatic development by perturbing lymphatic specification during zebrafish development. These impairments by COX inhibition were recovered by treatment with sulprostone (EP1/3 agonist). Knockdown of the EP3 receptor further demonstrated its requirement in the expression of sex determining region Y-box 18 (sox18) and nuclear receptor subfamily 2, group F, member 2 (nr2f2), essential factors of the lymphatic specification. The EP3 receptor was expressed in the posterior cardinal vein (region of embryonic lymphatic development) and the adjacent intermediate cell mass (ICM) during the lymphatic specification. COX1 was expressed in the region more upstream of the posterior cardinal vein relative to the EP3 receptor, and the COX1-selective inhibitor impaired the lymphatic specification. On the other hand, two COX2 subtypes did not show distinct sites of expression around the region of expression of the EP3 receptor. Finally, we generated EP3-deficient zebrafish, which also showed defect in lymphatic specification and development. Thus, we demonstrated that COX1-derived PGE₂-EP3 pathway is required for embryonic lymphatic development by upregulating the expression of key factors for the lymphatic specification.

Roles of prostaglandins in tumor-associated lymphangiogenesis with special reference to breast cancer

Lymphangiogenesis (formation of new lymphatic vessels), unlike angiogenesis, has been a lesser-focused field in cancer biology, because of earlier controversy regarding whether lymphatic metastasis occurs via pre-existing or newly formed lymphatics. Recent evidence reveals that peri-tumoral or intra-tumoral lymphangiogenesis is a precursor for lymphatic metastasis in most carcinomas and melanomas. Two major lymphangiogenic factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, are produced by cancer cells or immune cells such as macrophages in the tumor-stroma to promote sprouting of lymphatics from lymphatic endothelial cells (LEC) or LEC precursors (LECP) by binding to their primary (high affinity) receptor VEGF-R3 or secondary receptors VEGF-R2, neuropilin (NRP)2 and α9/β1 integrin. Many other growth factors/receptors such as VEGF-A/VEGF-R2, fibroblast growth factor (FGF)2/FGF-R, platelet-derived growth factor (PDGF)/PDGF-R, hepatocyte growth factor (HGF)/C-Met, angiopoietins (Ang)1, 2/Tie2, and chemokines/ chemokine receptors (CCL21/CCR7, CCL12/CCR4) can also stimulate LEC sprouting directly or indirectly. This review deals with the roles of prostaglandins (PG), in particular PGE2, in cancer-associated lymphangiogenesis, with special emphasis on breast cancer. We show that cyclooxygenase (COX)-2 expression by breast cancer cells or tumor stroma leading to high PGE2 levels in the tumor milieu promotes lymphangiogenesis and lymphatic metastases, resulting from binding of PGE2 to PGE receptors (EP, in particular EP4) on multiple cell types: tumor cells, tumor-infiltrating immune cells, and LEC. EP4 activation on cancer cells and macrophages upregulated VEGF-C/D production to stimulate LEC sprouting. Furthermore, ligation of EP4 with PGE2 on cancer or host cells can initiate a new cascade of molecular events leading to cross-talk between cancer cells and LEC, facilitating lymphangiogenesis and lympho-vascular transport of cancer cells. We make a case for EP4 as a potential therapeutic target for breast cancer.

Association of anti-inflammatory and antiangiogenic therapies negatively influences prostate cancer progression in TRAMP mice

BACKGROUND

Chronic inflammation has been implicated in cancer etiology and angiogenesis is stimulated in this disease. In prostate, the crosstalk between malignant epithelial cells and their microenvironment is an essential step of tumorigenesis during which glandular stroma undergo changes designated as reactive stroma. Thus, the aim herewith was to evaluate the effects of associating anti-inflammatory and antiangiogenic therapies on cancer progression, correlating them with steroid hormone receptor (AR and ERα), reactive stroma (vimentin, αSMA, and TGF-β), and cell proliferation (PCNA) markers expression in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) model.

METHODS

TRAMP mice (12-week old) were divided into the groups: Control (TRCON): received the vehicles used for drug dilution; Celecoxib (TRCEL): received oral doses of the anti-inflammatory drug celecoxib (15 mg/kg) twice daily; Nintedanib (TRNTB): received oral doses of the antiangiogenic drug nintedanib (10 mg/kg) daily; Nintedanib+Celecoxib (TRNTCEL): received the combination of drugs. After 6 weeks, mice were euthanized and ventral prostate samples were harvested for morphological, immunohistochemical, and Western blotting analyses.

RESULTS

While celecoxib led to fibromuscular hypertrophy attenuation, nintedanib significantly reduced the incidence of well-differentiated adenocarcinoma (WDAC) foci in relation to controls, both when administered per se or in association to celecoxib. Furthermore, drug combination was associated with unique effects, including lower incidence of HGPIN lesions; lower AR stromal distribution; changes in ERα localization from epithelial nuclei to stroma as well as significant decrease of TGF-β levels and associated angiogenesis. In parallel, all treatments applied resulted in reduced inflammatory marker and vimentin (VIM) expression.

CONCLUSIONS

Celecoxib plus nintedanib is an effective antitumor combination against prostate cancer progression in TRAMP mice, showing remarkable efficacy in relation to isolated therapies. Importantly, this efficacy might be due to drug association effect on driving AR and mainly ERα distribution in the prostatic tissue towards benign patterns. In addition, celecoxib and nintedanib impaired the development of a stromal reaction by reducing the recruitment of reactive stroma cells and maintaining a normal smooth muscle cell-rich prostate stroma in TRAMP mice. Collectively, these findings pointed to the beneficial effects of combining anti-inflammatory and antiangiogenic strategies to prevent or delay prostatic tumorigenesis.

PGE2 -induced migration of human brain endothelial cell is mediated though protein kinase A in cooperation of EP receptors

PGE₂ plays a critical role in angiogenesis, ischemic, and neuro-inflammatory disorders of the brain, which breakdown the blood-brain barrier (BBB). However, the effects of PGE₂ on human brain endothelial cell (HBECs) migration, a key process in the angiogenic response and BBB stability, are not well defined. In this study, we investigated the mechanism of PGE₂ in HBECs migration in vitro. Here we showed that PGE₂ stimulated migration of HBECs in a dose-time and matrix-dependent manner, evaluated by the Boyden chamber assay, but other prostanoids failed to do so. PGE₂ receptor (EP2; butaprost), EP3 (sulprostone), and EP4 (PGE₁ -OH) receptor agonists stimulated HBECs migration, but the silencing of EP significantly attenuated this effect. EP1 agonist (11-trinor PGE₁ ) had no effect on HBECs migration on silencing of the EP1 receptor. We further showed that PGE₂ stimulated cAMP production and activated protein kinase A (PKA), whereas pretreatment with the adenyl cyclase inhibitor (dideoxyadenosine; 1 μM) or PKA inhibitors, H89 (0.5 μM)/PKAI (1 μM), completely abrogated PGE₂ -induced migration. Furthermore, silencing of the EP2/EP4 receptors significantly inhibited PGE₂ -induced cAMP and PKA activation, whereas EP3 receptor silencing failed to do so. These results suggest that PGE₂ regulates HBEC migration via cooperation of EP2, EP3, and EP4 receptors. Coupling of PGE₂ to these receptors resulted in increased production of cAMP, which regulates HBEC migration via PKA pathway. The elucidation of molecular events involved is critical for the development of targeted strategies to treat cerebrovascular diseases associated with dysregulated angiogenesis.

Studies of postpartum mammary gland involution reveal novel pro-metastatic mechanisms

Postpartum involution is the process by which the lactating mammary gland returns to the pre-pregnant state after weaning. Expression of tumor-promotional collagen, upregulation of matrix metalloproteinases, infiltration of M2 macrophages, and remodeling of blood and lymphatic vasculature are all characteristics shared by the involuting mammary gland and breast tumor microenvironment. The tumor promotional nature of the involuting mammary gland is perhaps best evidenced by cases of postpartum breast cancer (PPBC), or those cases diagnosed within 10 years of most recent childbirth. Women with PPBC experience more aggressive disease and higher risk of metastasis than nulliparous patients and those diagnosed outside the postpartum window. Semaphorin 7a (SEMA7A), cyclooxygenase-2 (COX-2), and collagen are all expressed in the involuting mammary gland and, together, predict for decreased metastasis free survival in breast cancer. Studies investigating the role of these proteins in involution have been important for understanding their contributions to PPBC. Postpartum involution thus represents a valuable model for the identification of novel molecular drivers of PPBC and classical cancer hallmarks. In this review, we will highlight the similarities between involution and cancer in the mammary gland, and further define the contribution of SEMA7A/COX-2/collagen interplay to postpartum involution and breast tumor progression and metastasis.

Macrophage Polarization in Leishmaniasis: Broadening Horizons

Leishmaniasis is a vector-borne neglected tropical disease that affects more than 700,000 people annually. Leishmania parasites cause the disease, and different species trigger a distinct immune response and clinical manifestations. Macrophages are the final host cells for the proliferation of Leishmania parasites, and these cells are the key to a controlled or exacerbated response that culminates in clinical manifestations. M1 and M2 are the two main macrophage phenotypes. M1 is a pro-inflammatory subtype with microbicidal properties, and M2, or alternatively activated, is an anti-inflammatory/regulatory subtype that is related to inflammation resolution and tissue repair. The present review elucidates the roles of M1 and M2 polarization in leishmaniasis and highlights the role of the salivary components of the vector and the action of the parasite in the macrophage plasticity.

RAMP1 signaling improves lymphedema and promotes lymphangiogenesis in mice

BACKGROUND

Secondary lymphedema commonly arises as a complication of cancer surgery and radiation treatment; however, the underlying mechanisms are poorly understood. Receptor activity-modifying protein 1 (RAMP1) forms a complex with calcitonin receptor-like receptor to generate the receptor for calcitonin gene-related peptide. The present study examined whether RAMP1 plays a role in increased lymphangiogenesis during secondary lymphedema.

METHODS

A model of lymphedema was generated by surgical removal of pre-existing lymphatic vessels from the subcutaneous tissue on the tails of RAMP1-deficient (RAMP1-/-) mice and their wild-type (WT) counterparts. The maximum diameter of the tail, lymphangiogenesis, and macrophage recruitment were then examined.

RESULTS

Compared with that in WT mice, lymphedema in the tails in RAMP1-/- mice was sustained, with suppressed lymphangiogenesis and reduced expression of vascular endothelial growth factor-C and vascular endothelial growth factor receptor 3 at the distal edge of the lesions. The newly formed lymphatic vessels in RAMP1-/- mice were dilated, with impaired lymphatic flow. RAMP1 was expressed by macrophages recruited into edematous tail tissues distal to the wound. The number of macrophages in RAMP1-/- mice was higher than that in WT mice. Expression of messenger RNA encoding M1 macrophage-related genes, including tumor necrosis factor-α and interleukin-1, was higher in RAMP1-/- mice than in WT mice, whereas expression of messenger RNA encoding M2 macrophage genes, including interleukin-10, was lower.

CONCLUSIONS

RAMP1 signaling improves lymphedema and accelerates lymphangiogenesis associated with reduced recruitment of pro-inflammatory macrophages.

Minimizing Skin Scarring through Biomaterial Design

Wound healing continues to be a major burden to patients, though research in the field has expanded significantly. Due to an aging population and increasing comorbid conditions, the cost of chronic wounds is expected to increase for patients and the U.S. healthcare system alike. With this knowledge, the number of engineered products to facilitate wound healing has also increased dramatically, with some already in clinical use. In this review, the major biomaterials used to facilitate skin wound healing will be examined, with particular attention allocated to the science behind their development. Experimental therapies will also be evaluated.

Human Mesenchymal stem cells program macrophage plasticity by altering their metabolic status via a PGE2-dependent mechanism

Mesenchymal stem cells (MSCs) are speculated to act at macrophage-injury interfaces to mediate efficient repair. To explore this facet in-depth this study evaluates the influence of MSCs on human macrophages existing in distinct functional states. MSCs promoted macrophage differentiation, enhanced respiratory burst and potentiated microbicidal responses in naïve macrophages (Mφ). Functional attenuation of inflammatory M1 macrophages was associated with a concomitant shift towards alternatively activated M2 state in MSC-M1 co-cultures. In contrast, alternate macrophage (M2) activation was enhanced in MSC-M2 co-cultures. Elucidation of key macrophage metabolic programs in Mo/MSC, M1/MSC and M2/MSC co-cultures indicated changes in Glucose transporter1 (GLUT1 expression/glucose uptake, IDO1 protein/activity, SIRTUIN1 and alterations in AMPK and mTOR activity, reflecting MSC-instructed metabolic shifts. Inability of Cox2 knockdown MSCs to attenuate M1 macrophages and their inefficiency in instructing metabolic shifts in polarized macrophages establishes a key role for MSC-secreted PGE2 in manipulating macrophage metabolic status and plasticity. Functional significance of MSC-mediated macrophage activation shifts was further validated on human endothelial cells prone to M1 mediated injury. In conclusion, we propose a novel role for MSC secreted factors induced at the MSC-macrophage interface in re-educating macrophages by manipulating metabolic programs in differentially polarized macrophages.