Bone Marrow-derived Inflammatory Cells Research Articles

WITHDRAWN: Engineered knockout of TRPA1 inhibits laser-induced choroidal neovascularization along with associated TGFb1 expression and neutrophil infiltration

We examined the effects of gene ablation and chemical inhibition of transient receptor potential ankyrin 1 (TRPA1) on the growth of experimental argon laser-induced choroidal neovascularization (CNV) in mice. CNV was induced in the eyes of 6 - 8-week-old mice by argon laser irradiation and observed expression. This reaction was compared between TRPA1-null (KO) mice and wild-type (WT) mice. Gene expression analysis was performed in laser-injured tissues on day 1 and 3. CNV growth was evaluated on day 14. Finally, reciprocal bone marrow transplantation was performed between each genotype of mice to identify the responsible components of either recipient tissue or bone marrow-derived inflammatory cells. Results showed that laser irradiation successfully induced CNV growth at the site of laser injury. The size of induced CNV was significantly smaller in KO mice as compared with WT mice at day 14, as examined by angiography with fluorescein isothiocyanate-dextran. Invasion of neutrophils, but not macrophages, was suppressed in association with suppression of expression of transforming growth factor β1 in laser-irradiated KO tissues. Bone marrow transplantation indicated that the genotype of the recipient mouse, but not of inflammatory cells, is attributable to the KO phenotype. Systemic administration of a TRPA1 antagonist also downsized the CNV in a WT mouse. In conclusion, TRPA1 signal in local tissue cells is involved in the growth of laser-induced CNV. The phenotype was not attributable to both vascular endothelial cells and inflammatory cells. Blocking TRPA1 signal could be a potential treatment strategy for CNV-related ocular diseases. (244 words).

Donor Mesenchymal Stem Cells Program Bone Marrow, Altering Macrophages, and Suppressing Endometriosis in Mice.

Endometriosis is a chronic inflammatory gynecological disorder regulated by estrogen and characterized by the growth of endometrial tissue outside the uterus. We have previously demonstrated that mesenchymal stem cells (MSCs) contribute directly to endometriosis. Here, we investigated an indirect effect; we hypothesized that MSCs may also impact the bone marrow (BM) by regulating bone marrow-derived inflammatory cells. Endometriosis was induced in mice by transplanting uterine tissue into recipient mice followed by BM transplant. Control or MSC conditioned BM was injected retro-orbitally. Direct administration of MSCs outside of the setting of BM conditioning did not alter endometriosis. Coculture of an undifferentiated macrophage cell line with MSCs in vitro led to a reduction of M1 and increased M2 macrophages as determined by fluorescence-activated cell sorting and western blot. Conditioning of BM with MSCs and transplantation into a mouse model inhibited endometriotic lesion development and reduced lesion volume by sevenfold compared to BM transplant without MSCs conditioning. Immunohistochemistry and immunofluorescence showed that MSC conditioned BM reduced the infiltration of macrophages and neutrophils into endometriotic lesions by twofold and decreased the proportion of M1 compared to M2 macrophages, reducing inflammation and likely promoting tissue repair. Expression of several inflammatory markers measured by quantitative real-time polymerase chain reaction, including tumor necrosis factor alpha and CXCR4, was decreased in the conditioned BM. Donor MSCs were not detected in recipient BM or endometriotic lesions, suggesting that MSCs actively program the transplanted BM. Taken together, these data show that individual characteristics of BM have an unexpected role in the development of endometriosis. BM remodeling and alterations in the inflammatory response are also potential treatments for endometriosis. Identification of the molecular basis for BM programing by MSCs will lead to a better understanding of the immune system contribution to this disease and may lead to new therapeutic targets for endometriosis.

Progress in research on tumor microenvironment-based spatial omics technologies.

Spatial omics technology integrates the concept of space into omics research and retains the spatial information of tissues or organs while obtaining molecular information. It is characterized by the ability to visualize changes in molecular information and yields intuitive and vivid visual results. Spatial omics technologies include spatial transcriptomics, spatial proteomics, spatial metabolomics, and other technologies, the most widely used of which are spatial transcriptomics and spatial proteomics. The tumor microenvironment refers to the surrounding microenvironment in which tumor cells exist, including the surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, various signaling molecules, and extracellular matrix. A key issue in modern tumor biology is the application of spatial omics to the study of the tumor microenvironment, which can reveal problems that conventional research techniques cannot, potentially leading to the development of novel therapeutic agents for cancer. This paper summarizes the progress of research on spatial transcriptomics and spatial proteomics technologies for characterizing the tumor immune microenvironment.

The Role of Myeloid-Derived Suppressor Cells in the Treatment of Pancreatic Cancer.

Pancreatic cancer has the highest mortality rate of all major cancers, with a 5-year survival rate of about 10%. Early warning signs and symptoms of pancreatic cancer are vague or nonexistent, and most patients are diagnosed in Stage IV, when surgery is not an option for about 80%-85% of patients. For patients with inoperable pancreatic cancer, current conventional treatment modalities such as chemotherapy and radiotherapy (RT) have suboptimal efficacy. Tumor progression is closely associated with the tumor microenvironment, which includes peripheral blood vessels, bone marrow-derived inflammatory cells, fibroblasts, immune cells, signaling molecules, and extracellular matrix. Tumor cells affect the microenvironment by releasing extracellular signaling molecules, inducing peripheral immune tolerance, and promoting tumor angiogenesis. In turn, the immune cells of the tumor affect the survival and proliferation of cancer cells. Myeloid-derived suppressor cells are key cellular components in the tumor microenvironment and exert immunosuppressive functions by producing cytokines, recognizing other immune cells, and promoting tumor growth and metastasis. Myeloid-derived suppressor cells are the main regulator of the tumor immune response and a key target for tumor treatments. Since the combination of RT and immunotherapy is the main strategy for the treatment of pancreatic cancer, it is very important to understand the immune mechanisms which lead to MDSCs generation and the failure of current therapies in order to develop new target-based therapies. This review summarizes the research advances on the role of Myeloid-derived suppressor cells in the progression of pancreatic cancer and its treatment application in recent years.

MESENCHYMAL STEM CELLS INDUCE BONE MARROW MEMORY TO REDUCE INFLAMMATION AND ENDOMETRIOSIS

Endometriosis is a chronic inflammatory gynecological disorder regulated by estrogen and characterized by the growth of endometrial tissue outside the uterus. Inflammation contributes to the pelvic pain, infertility and systemic effects of the disease. Mesenchymal stem cells contribute directly to endometriosis however they may also impact the bone marrow, regulating bone marrow-derived inflammatory cells. Here, we investigate the effect of mesenchymal stem cells on BM derived inflammatory cells using a murine model of endometriosis.

Pyruvate dehydrogenase kinase/lactate axis: a therapeutic target for neovascular age-related macular degeneration identified by metabolomics.

Neovascular age-related macular degeneration (nAMD) is the leading cause of blindness in aging populations. Here, we applied metabolomics to human sera of patients with nAMD during an active (exudative) phase of the pathology and found higher lactate levels and a shift in the lipoprotein profile (increased VLDL-LDL/HDL ratio). Similar metabolomics changes were detected in the sera of mice subjected to laser-induced choroidal neovascularization (CNV). In this experimental model, we provide evidence for two sites of lactate production: first, a local one in the injured eye, and second a systemic site associated with the recruitment of bone marrow-derived inflammatory cells. Mechanistically, lactate promotes the angiogenic response and M2-like macrophage accumulation in the eyes. The therapeutic potential of our findings is demonstrated by the pharmacological control of lactate levels through pyruvate dehydrogenase kinase (PDK) inhibition by dichloroacetic acid (DCA). Mice treated with DCA exhibited normalized lactate levels and lipoprotein profiles, and inhibited CNV formation. Collectively, our findings implicate the key role of the PDK/lactate axis in AMD pathogenesis and reveal that the regulation of PDK activity has potential therapeutic value in this ocular disease. The results indicate that the lipoprotein profile is a traceable pattern that is worth considering for patient follow-up. KEY MESSAGES: Lactate and lipoprotein profile are associated with the active phase of AMD and CNV development. Lactate is a relevant and functional metabolite correlated with AMD progression. Modulating lactate through pyruvate dehydrogenase kinase led to a decrease of CNV progression. Pyruvate dehydrogenase kinase is a new therapeutic target for neovascular AMD.

Deficiency of Interleukin-36 Receptor Protected Cardiomyocytes from Ischemia-Reperfusion Injury in Cardiopulmonary Bypass.

BackgroundInterleukin-36 has been demonstrated to be involved in inflammatory responses. Inflammatory responses due to ischemia-reperfusion injury following cardiopulmonary bypass (CPB) can cause heart dysfunction or damage.Material/MethodsThe CPB models were constructed in IL-36R−/−, IL-36RN−/−, and wild-type SD rats. Ultrasonic cardiography and ELISA were used to evaluate the cardiac function and measuring myocardial biomarker levels in different groups. TUNEL assay was used to evaluate apoptosis. Western blot assays and RT-PCR were performed to measure the expression of chemokines and secondary inflammatory cytokines in the heart. Oxidative stress in tissue and cultured cells was assessed using a DCFH-DA fluorescence probe and quantification of superoxide dismutase activity.ResultsImproved systolic function and decreased serum levels of myocardial damage biomarkers were found in IL-36R−/− rats compared to WT rats, while worse cardiac function and cardiomyocyte IR injury were observed in IL-36RN−/− rats compared to WT rats. TUNEL staining and Western blot analyses found that cardiomyocyte apoptosis and inflammation were significantly lower in the hearts of IL-36R−/− rats compared with that of WT rats. Oxidative stress was significantly lower in IL-36R−/− rats compared to WT rats. iNOS expression was significantly reduced, while eNOS expression was increased in the hearts of IL-36R−/− rats. Silencing of IL-36R expression in vitro activated SIRT1/FOXO1/p53 signaling in cardiomyocytes.ConclusionsIL-36R deficiency in cardiomyocytes repressed infiltration of bone marrow-derived inflammatory cells and oxidative stress dependent on SIRT1-FOXO1 signaling, thus protecting cardiomyocytes and improving cardiac function in CPB model rats.

Myeloid-derived suppressor cells: Roles in the tumor microenvironment and tumor radiotherapy.

Cancer progression is closely related to the tumor microenvironment in which the tumor exists, including surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, signaling molecules and the extracellular matrix. Tumors can influence the microenvironment by releasing extracellular signals, promoting tumor angiogenesis and inducing peripheral immune tolerance, while the immune cells in the microenvironment can impact the growth and evolution of cancerous cells. One of major cell components in the tumor microenvironment is myeloid-derived suppressor cells (MDSCs), which promote tumor growth and metastasis directly or indirectly by recognizing other immune cells, producing cytokines and exerting their immunosuppression functions. MDSCs have emerged as major regulators of immune responses in cancer and key targets for treating cancer. There are many limitations and side-effect in approaches of conventional cancer therapy, including radiotherapy. It has grown up to be a burgeoning field that a combination of radiotherapy and immunotherapy applied to cancer therapy. Therefore, it is fundamental to explore the immune mechanism in the process of cancer treatment. Here, we reviewed the recent progress of MDSCs in roles of the tumor microenvironment and tumor radiotherapy.

Obesity and gastrointestinal cancer: the interrelationship of adipose and tumour microenvironments.

Increasing recognition of an association between obesity and many cancer types exists, but how the myriad of local and systemic effects of obesity affect key cellular and non-cellular processes within the tumour microenvironment (TME) relevant to carcinogenesis, tumour progression and response to therapies remains poorly understood. The TME is a complex cellular environment in which the tumour exists along with blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, signalling molecules and the extracellular matrix. Obesity, in particular visceral obesity, might fuel the dysregulation of key pathways relevant to both the adipose microenvironment and the TME, which interact to promote carcinogenesis in at-risk epithelium. The tumour-promoting effects of obesity can occur at the local level as well as systemically via circulating inflammatory, growth factor and metabolic mediators associated with adipose tissue inflammation, as well as paracrine and autocrine effects. This Review explores key pathways linking visceral obesity and gastrointestinal cancer, including inflammation, hypoxia, altered stromal and immune cell function, energy metabolism and angiogenesis.

Metabolic Symbiosis and Immunomodulation: How Tumor Cell-Derived Lactate May Disturb Innate and Adaptive Immune Responses.

The tumor microenvironment (TME) is composed by cellular and non-cellular components. Examples include the following: (i) bone marrow-derived inflammatory cells, (ii) fibroblasts, (iii) blood vessels, (iv) immune cells, and (v) extracellular matrix components. In most cases, this combination of components may result in an inhospitable environment, in which a significant retrenchment in nutrients and oxygen considerably disturbs cell metabolism. Cancer cells are characterized by an enhanced uptake and utilization of glucose, a phenomenon described by Otto Warburg over 90 years ago. One of the main products of this reprogrammed cell metabolism is lactate. “Lactagenic” or lactate-producing cancer cells are characterized by their immunomodulatory properties, since lactate, the end product of the aerobic glycolysis, besides acting as an inducer of cellular signaling phenomena to influence cellular fate, might also play a role as an immunosuppressive metabolite. Over the last 10 years, it has been well accepted that in the TME, the lactate secreted by transformed cells is able to compromise the function and/or assembly of an effective immune response against tumors. Herein, we will discuss recent advances regarding the deleterious effect of high concentrations of lactate on the tumor-infiltrating immune cells, which might characterize an innovative way of understanding the tumor-immune privilege.

Tumor immune microenvironment: sanctuary of tumor and target for immunotherapy

The tumor immune microenvironment (TIME) is the cellular environment in which tumors exist. This includes: surrounding blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, lymphocytes, signaling molecules, immune checkpoint proteins and the extracellular matrix (ECM). The TIME plays a critical role in cancer progression and regulation. Tumors can influence the microenvironment by releasing extracellular signals, promoting tumor angiogenesis and inducing peripheral immune tolerance, while the immune cells in the microenvironment can affect the growth and evolution of cancerous cells. The molecules and cells in the TIME influence disease outcome by altering the balance of suppressive versus cytotoxic responses in the vicinity of the tumor. Having a better understanding of the tumor immune microenvironment will pave the way for identifying new targets for immunotherapies that promote cancer elimination.

The Therapeutic Potential of Targeting Tumor Microenvironment in Breast Cancer: Rational Strategies and Recent Progress.

The tumor microenvironment (TME) is cellular environment in addition to harboring carcinoma cells, consists of different components (e.g., blood vessels, immune cells, fibroblasts, bone marrow-derived inflammatory cells, lymphocytes, signaling molecules, and the extracellular matrix) that have an essential role on drug activity and efficacy. There is growing body of evidence showing its involvement in the progression and metastasis of different cancers, including breast cancer (BC). These observations provide a proof of concept of targeting TME compartments as a novel potential therapeutic approach in treatment of this malignancy, which is the main interested for current review. J. Cell. Biochem. 119: 111-122, 2018. © 2017 Wiley Periodicals, Inc.

Adeno-Associated Virus Overexpression of Angiotensin-Converting Enzyme-2 Reverses Diabetic Retinopathy in Type 1 Diabetes in Mice

Angiotensin-converting enzyme (ACE)-2 is the primary enzyme of the vasoprotective axis of the renin angiotensin system that regulates the classic renin angiotensin system axis. We aimed to determine whether local retinal overexpression of adenoassociated virus (AAV)-ACE2 prevents or reverses diabetic retinopathy. Green fluorescent protein (GFP)-chimeric mice were generated to distinguish resident (retinal) from infiltrating bone marrow-derived inflammatory cells and were made diabetic using streptozotocin injections. Retinal digestion using trypsin was performed and acellular capillaries enumerated. Capillary occlusion by GFP(+) cells was used to measure leukostasis. Overexpression of ACE2 prevented (prevention cohort: untreated diabetic, 11.3±1.4; ACE2 diabetic, 6.4±0.9 per mm(2)) and partially reversed (reversal cohort: untreated diabetic, 15.7±1.9; ACE2 diabetic, 6.5±1.2 per mm(2)) the diabetes-associated increase of acellular capillaries and the increase of infiltrating inflammatory cells into the retina (F4/80(+)) (prevention cohort: untreated diabetic, 24.2±6.7; ACE2 diabetic, 2.5±1.6 per mm(2); reversal cohort: untreated diabetic, 56.8±5.2; ACE2 diabetic, 5.6±2.3 per mm(2)). In both study cohorts, intracapillary bone marrow-derived cells, indicative of leukostasis, were only observed in diabetic animals receiving control AAV injections. These results indicate that diabetic retinopathy, andpossibly other diabetic microvascular complications, can be prevented and reversed by locally restoring the balance between the classic and vasoprotective renin angiotensin system.

Studies on the Tumor Vasculature and Coagulant Microenvironment.

Angiogenesis represents one aspect in the complex process that leads to the generation of the vascular tumor stroma. The related functional constituents include responses of endothelial, mural, bone marrow-derived, and resident inflammatory cells as well as activation of coagulation and fibrinolytic systems in blood. Multiple molecular and cellular effectors participate in these events, often in a tumor-specific manner and with changes enforced through the microenvironment, genetic evolution, and responses to anticancer therapies. To capture various elements of these interactions several surrogate assays have been devised, which can be mechanistically useful and are amenable to quantification, but are individually insufficient to describe the underlying complexity and are best used in a targeted and combinatorial manner. Below, we present a survey of angiogenesis assays and experimental approaches to analyze vascular events in cancer. We also provided specific examples of validated protocols, which are less described, but enable the straightforward analysis of vascular structures and coagulant properties of cancer cells in vivo and in vitro.

Altered protein secretions during interactions between adipose tissue- or bone marrow-derived stromal cells and inflammatory cells.

IntroductionParacrine effects can be exploited in cell-based therapies that secrete factors, such as chemokines and cytokines, and can recruit inflammatory cells to transplants. In this study, mouse adipose tissue-derived stromal cells (ASCs) and bone marrow-derived stromal cells (ST2 cells) were used to examine changes in paracrine interactions with inflammation cells.MethodsGreen fluorescent protein positive (GFP+) bone marrow cells (BMCs) were injected into an irradiated mouse via the femoral vein, and ASCs and ST2 cells were transplanted intradermally. Subsequently, an in vivo imaging system was used to observe behaviors of GFP+ BMCs. To detect bone marrow-derived inflammatory cells which migrated to the ASC and ST2 cell transplantation area, the sections were immunostained using antibodies against Gr1, CD11c, and F4/80, and secretory proteins were detected in culture medium using enzyme-linked immunosorbent assay.ResultsMany bone marrow-derived inflammatory cells migrated to ASC and ST2 cell transplantation sites. Among these, neutrophils were detected during the early period and macrophages were predominantly detected at a later point in time. Many chemokines, cytokines, growth factors, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) were secreted in abundance from ASCs, and the secretion increased by co-culturing with inflammatory cells, except for secretions of insulin-like growth factor-1, MMP-9 and MMP-13. Although secretions from ST2 cells were less than those from ASCs, co-culture with inflammatory cells increased these secretions to levels similar to those of ASCs. However, unlike ASCs, the ST2 cells did not secrete angiostatin, MMP-2, or MMP-3. Finally, ASCs secreted not only proinflammatory cytokines, angiogenic factors and MMPs but also anti-inflammatory cytokines, anti-angiogenesis factors, and TIMPs.ConclusionsThe effects of cell-based therapies using ASCs and ST2 cells are depended on paracrine effects that are mediated by chemokines, cytokines, growth factors, MMPs, and TIMPs, which comprise responses to interactions between transplanted cells and inflammatory cells. Moreover, paracrine effects of transplanted cells are influenced by inflammatory cells, and are moderated by a balance of secreted inhibitors.Electronic supplementary materialThe online version of this article (doi:10.1186/s13287-015-0052-y) contains supplementary material, which is available to authorized users.

Granule cargo release from bone marrow-derived cells sustains cardiac hypertrophy.

Bone marrow-derived inflammatory cells, including platelets, may contribute to the progression of pressure overload-induced left ventricular hypertrophy (LVH). However, the underlying mechanisms for this are still unclear. One potential mechanism is through release of granule cargo. Unc13-d(Jinx) (Jinx) mice, which lack Munc13-4, a limiting factor in vesicular priming and fusion, have granule secretion defects in a variety of hematopoietic cells, including platelets. In the current study, we investigated the role of granule secretion in the development of LVH and cardiac remodeling using chimeric mice specifically lacking Munc13-4 in marrow-derived cells. Pressure overload was elicited by transverse aortic constriction (TAC). Chimeric mice were created by bone marrow transplantation. Echocardiography, histology staining, immunohistochemistry, real-time polymerase chain reaction, enzyme-linked immunosorbent assay, and mass spectrometry were used to study LVH progression and inflammatory responses. Wild-type (WT) mice that were transplanted with WT bone marrow (WT→WT) and WT mice that received Jinx bone marrow (Jinx→WT) developed LVH and a classic fetal reprogramming response early (7 days) after TAC. However, at late times (5 wk), mice lacking Munc13-4 in bone marrow-derived cells (Jinx→WT) failed to sustain the cardiac hypertrophy observed in WT chimeric mice. No difference in cardiac fibrosis was observed at early or late time points. Reinjection of WT platelets or platelet releasate partially restored cardiac hypertrophy in Jinx chimeric mice. These results suggest that sustained LVH in the setting of pressure overload depends on one or more factors secreted from bone marrow-derived cells, possibly from platelets. Inhibiting granule cargo release may represent a novel target for preventing sustained LVH.

LRIG1 inhibits STAT3-dependent inflammation to maintain corneal homeostasis

Corneal integrity and transparency are indispensable for good vision. Cornea homeostasis is entirely dependent upon corneal stem cells, which are required for complex wound-healing processes that restore corneal integrity following epithelial damage. Here, we found that leucine-rich repeats and immunoglobulin-like domains 1 (LRIG1) is highly expressed in the human holoclone-type corneal epithelial stem cell population and sporadically expressed in the basal cells of ocular-surface epithelium. In murine models, LRIG1 regulated corneal epithelial cell fate during wound repair. Deletion of Lrig1 resulted in impaired stem cell recruitment following injury and promoted a cell-fate switch from transparent epithelium to keratinized skin-like epidermis, which led to corneal blindness. In addition, we determined that LRIG1 is a negative regulator of the STAT3-dependent inflammatory pathway. Inhibition of STAT3 in corneas of Lrig1-/- mice rescued pathological phenotypes and prevented corneal opacity. Additionally, transgenic mice that expressed a constitutively active form of STAT3 in the corneal epithelium had abnormal features, including corneal plaques and neovascularization similar to that found in Lrig1-/- mice. Bone marrow chimera experiments indicated that LRIG1 also coordinates the function of bone marrow-derived inflammatory cells. Together, our data indicate that LRIG1 orchestrates corneal-tissue transparency and cell fate during repair, and identify LRIG1 as a key regulator of tissue homeostasis.

Inhibition of Toll-like receptor 2 reduces cardiac fibrosis by attenuating macrophage-mediated inflammation

Toll-like receptor 2 (TLR2) is an important player in innate immunity, and recent studies have identified TLR2 as a critical mediator in cardiovascular diseases. Here, we investigated the involvement of TLR2 in angiotensin (Ang) II-induced cardiac fibrosis and the underlying mechanisms. TLR2 knockout (TLR2 KO) mice (B6.129-Tlr2(tm1Kir)/) or wild-type (WT) mice (C57BL/6) treated with neutralizing anti-TLR2 antibody (T2.5) were used. The expression of TLR2 mRNA and protein in the heart was significantly up-regulated on days 1, 3, and 7 after Ang II infusion (1500 ng/kg/min). Enhanced expression of TLR2 was mainly detected in macrophages and neutrophils that had infiltrated into the heart. Both knockout of TLR2 and inhibition of TLR2 by neutralizing antibody ameliorated cardiac fibrosis induced by Ang II. This improvement was associated with a reduction in the infiltration of inflammatory cells, especially macrophages, the production of inflammatory cytokines, chemokines, and the activation of nuclear factor-κB. Bone marrow transplantation experiments between WT and TLR2 KO mice revealed that Ang II-induced cardiac fibrosis is mainly mediated by bone marrow-derived inflammatory cells. Mechanically, the deficiency of TLR2 inhibits macrophage-dependent cardiac fibroblast activation through TGFβ/Smad2/3 pathway. Inhibition of TLR2 protects against Ang II-induced cardiac fibrosis by attenuating macrophage recruitment and the inflammatory response in the heart and may be a novel potential therapeutic target for hypertensive heart disease.

Mice with Mutations in Fas and Fas Ligand Demonstrate Increased Herpetic Stromal Keratitis following Corneal Infection with HSV-1

HSV-1 infection of the cornea leads to a potentially blinding immunoinflammatory lesion of the cornea, termed herpetic stromal keratitis. It has also been shown that one of the factors limiting inflammation of the cornea is the presence of Fas ligand (FasL) on corneal epithelium and endothelium. In this study, the role played by FasL expression in the cornea following acute infection with HSV-1 was determined. Both BALB/c and C57BL/6 (B6) mice with HSV-1 infection were compared with their lpr and gld counterparts. Results indicated that mice bearing mutations in the Fas Ag (lpr) displayed the most severe disease, whereas the FasL-defective gld mouse displayed an intermediate phenotype. It was further demonstrated that increased disease was due to lack of Fas expression on bone marrow-derived cells. Of interest, although virus persisted slightly longer in the corneas of mice bearing lpr and gld mutations, the persistence of infectious virus in the trigeminal ganglia was the same for all strains infected. Further, B6 mice bearing lpr and gld mutations were also more resistant to virus-induced mortality than were wild-type B6 mice. Thus, neither disease nor mortality correlated with viral replication in these mice. Collectively, the findings indicate that the presence of FasL on the cornea restricts the entry of Fas(+) bone marrow-derived inflammatory cells and thus reduces the severity of HSK.

Bone marrow-derived cells play a key role in tissue regeneration

Vascular endothelial growth factor (VEGF) regulates vasculogenesis and angiogenesis by signaling through two tyrosine kinase receptors, VEGF receptor-1(VEGFR1) and VEGFR2. Whereas VEGF/VEGFR2 signaling contributes to the regulation of endothelial cell lineage differentiation and proliferation, VEGF/VEGFR1 signaling in hematopoietic lineage cells can promote the mobilization of hematopoietic stem cells and induce bone marrow regeneration. These data suggest that there is a significant interaction between post-natal angiogenesis and hematopoiesis. We reported that the activation of VEGF/VEGFR and chemokine stromal cell-derived factor-1(CXCL12)/CXCR4 signal pathways induce the mobilization of bone marrow-derived hematopoietic lineage cells. It was shown that these pathways regulate bone marrow cell differentiation and proliferation by activating matrix metalloproteinases (MMP) causing MMP-mediated hematopoietic factor, Kit ligand processing. Moreover, we have also reported that CXCL12 and VEGF are released from bone marrow-derived inflammatory cells like neutrophils or platelets. It was demonstrated that CXCR4 positive and VEGFR1 positive lineage cells, also called hemangiocytes, can produce angiopoetin-2 which can recruit hematopoietic stem cells from the bone marrow and work as molecular HUB by augmenting revascularization in the “neo-vascular niche”. Recently, we showed that activation of the fibrinolytic system resulted in the constitutive activation of MMPs causing Kit ligand release, which promoted bone marrow regeneration after myelosuppression. These data imply that the fibrinolytic system might also play a role in regulating neoangiogenesis during tissue regeneration. Here, we will introduce recent studies from our group and several novel concepts in our current understanding of the regulation of angiogenesis.