Vascular adaptation to a dysfunctional endothelium as a consequence of Shb deficiency

Perspectives on Vascular Regulation of Mechanisms Controlling Selective Immune Cell Function in the Tumor Immune Response

The vasculature plays a major role in regulating the tumor immune cell response although the underlying mechanisms explaining such effects remain poorly understood. This review discusses current knowledge on known vascular functions with a viewpoint on how they may yield distinct immune responses. The vasculature might directly influence selective immune cell infiltration into tumors by its cell surface expression of cell adhesion molecules, expression of cytokines, cell junction properties, focal adhesions, cytoskeleton and functional capacity. This will alter the tumor microenvironment and unleash a plethora of responses that will influence the tumor’s immune status. Despite our current knowledge of numerous mechanisms operating, the field is underexplored in that few functions providing a high degree of specificity have yet been provided in relation to the enormous divergence of responses apparent in human cancers. Further exploration of this field is much warranted.

Mouse Breast Carcinoma Monocytic/Macrophagic Myeloid-Derived Suppressor Cell Infiltration as a Consequence of Endothelial Dysfunction in Shb-Deficient Endothelial Cells Increases Tumor Lung Metastasis

Metastasis reflects both the inherent properties of tumor cells and the response of the stroma to the presence of the tumor. Vascular barrier properties, either due to endothelial cell (EC) or pericyte function, play an important role in metastasis in addition to the contribution of the immune system. The Shb gene encodes the Src homology-2 domain protein B that operates downstream of tyrosine kinases in both vascular and immune cells. We have investigated E0771.lmb breast carcinoma metastasis in mice with conditional deletion of the Shb gene using the Cdh5-Cre^ERt2 transgene, resulting in inactivation of the Shb-gene in EC and some hematopoietic cell populations. Lung metastasis from orthotopic tumors, tumor vascular and immune cell characteristics, and immune cell gene expression profiles were determined. We found no increase in vascular leakage that could explain the observed increase in metastasis upon the loss of Shb expression. Instead, Shb deficiency in EC promoted the recruitment of monocytic/macrophagic myeloid-derived suppressor cells (mMDSC), an immune cell type that confers a suppressive immune response, thus enhancing lung metastasis. An MDSC-promoting cytokine/chemokine profile was simultaneously observed in tumors grown in mice with EC-specific Shb deficiency, providing an explanation for the expanded mMDSC population. The results demonstrate an intricate interplay between tumor EC and immune cells that pivots between pro-tumoral and anti-tumoral properties, depending on relevant genetic and/or environmental factors operating in the microenvironment.

Transcriptome analysis of human Leydig cell tumours reveals potential mechanisms underlying its development

Leydig cell tumours are the most common sex cord-stromal tumours. In the last years, apparent increased incidence is noted while aetiology of the tumour is still unknown. Therefore, here, we focused on the genetics of Leydig cell tumours using the next-generation sequencing. Leydig cell micronodules were revealed in patients with azoospermia who were qualified for testicular biopsy. Complete gene set of Leydig cell tumours was compared with transcriptome of healthy Leydig cells obtained from donors. Bioinformatic analysis of the obtained sequencing data revealed alterations in expression of 219 transcripts. We showed, for the first time, that a significant proportion of differentially expressed genes is directly involved in regulation of apoptotic process, which downregulation might be important to Leydig cell tumour development. Additionally, we found a significant upregulation of heat shock protein genes that might be a unique feature of Leydig cell tumours when compared to other tumour types. Our study offers fundamental transcriptomic data for future studies on human Leydig cell tumour that are crucial to determine its causes. Moreover, presented here the in-depth analysis and discussion of alterations observed in tumour transcriptome may be important for the diagnosis and therapy of this pathology.

Pericyte dysfunction due to Shb gene deficiency increases B16F10 melanoma lung metastasis

Intravasation, vascular dissemination and metastasis of malignant tumor cells require their passage through the vascular wall which is commonly composed of pericytes and endothelial cells. We currently decided to investigate the relative contribution of these cell types to B16F10 melanoma metastasis in mice using an experimental model of host Shb gene (Src homology 2 domain-containing protein B) inactivation. Conditional inactivation of Shb in endothelial cells using Cdh5-CreERt2 resulted in decreased tumor growth, reduced vascular leakage, increased hypoxia and no effect on pericyte coverage and lung metastasis. RNAseq of tumor endothelial cells from these mice revealed changes in cellular components such as adherens junctions and focal adhesions by gene ontology analysis that were in line with the observed effects on leakage and junction morphology. Conditional inactivation of Shb in pericytes using Pdgfrb-CreERt2 resulted in decreased pericyte coverage of small tumor vessels with lumen, increased leakage, aberrant platelet-derived growth factor receptor B (PDGFRB) signaling and a higher frequency of lung metastasis without concomitant effects on tumor growth or oxygenation. Flow cytometry failed to reveal immune cell alterations that could explain the metastatic phenotype in this genetic model of Shb deficiency. It is concluded that proper pericyte function plays a significant role in suppressing B16F10 lung metastasis.

Temporal Dynamics of VEGFA-Induced VEGFR2/FAK Co-Localization Depend on SHB

Focal adhesion kinase (FAK) is essential for vascular endothelial growth factor-A (VEGFA)/VEGF receptor-2 (VEGFR2)-stimulated angiogenesis and vascular permeability. We have previously noted that presence of the Src homology-2 domain adapter protein B (SHB) is of relevance for VEGFA-stimulated angiogenesis in a FAK-dependent manner. The current study was conducted in order address the temporal dynamics of co-localization between these components in HEK293 and primary lung endothelial cells (EC) by total internal reflection fluorescence microscopy (TIRF). An early (<2.5 min) VEGFA-induced increase in VEGFR2 co-localization with SHB was dependent on tyrosine 1175 in VEGFR2. VEGFA also enhanced SHB co-localization with FAK. FAK co-localization with VEGFR2 was dependent on SHB since it was significantly lower in SHB deficient EC after VEGFA addition. Absence of SHB also resulted in a gradual decline of VEGFR2 co-localization with FAK under basal (prior to VEGFA addition) conditions. A similar basal response was observed with expression of the Y1175F-VEGFR2 mutant in wild type EC. The distribution of focal adhesions in SHB-deficient EC was altered with a primarily perinuclear location. These live cell data implicate SHB as a key component regulating FAK activity in response to VEGFA/VEGFR2.

The Cdh5-CreERT2 transgene causes conditional Shb gene deletion in hematopoietic cells with consequences for immune cell responses to tumors

The tamoxifen-responsive conditional Cdh5-CreERT2 is commonly used for endothelial cell specific conditional deletion of loxP-flanked gene sequences. To address the role of endothelial cell Shb gene for B16F10 melanoma immune responses, tamoxifen-injected Cdh5-CreERT2/WT and Cdh5-CreERT2/Shb^flox/flox mice received subcutaneous tumor cell injections. We observed a decrease of tumor myeloid cell Shb mRNA in the tamoxifen treated Cdh5-CreERT2/Shb^flox/flox mice, which was not present when the mice had undergone a preceding bone marrow transplantation using wild type bone marrow. Differences in CD4+/FoxP3+ Tregs were similarly abolished by a preceding bone marrow transplantation. In ROSA26-mTmG mice, Cdh5-CreERT2 caused detectable floxing in certain bone marrow populations and in spleen cells. Floxing in bone marrow could be detected two months after tamoxifen treatment. In the spleen, however, floxing was undetectable two months after tamoxifen treatment, suggesting that Cdh5-CreERT2 is operating in a non-renewable population of hematopoietic cells in this organ. These data suggest that conditional gene deletion in hematopoietic cells is a potential confounder in experiments attempting to assess the role of endothelial specific effects. A cautious approach to achieve an endothelial-specific phenotype would be to adopt a strategy that includes a preceding bone marrow transplantation.

Pro-tumoral immune cell alterations in wild type and Shb-deficient mice in response to 4T1 breast carcinomas

To assess mechanisms responsible for breast carcinoma metastasis, 4T1 breast carcinomas were grown orthotopically in wild type or Shb knockout mice. Tumor growth, metastasis, vascular characteristics and immune cell properties were analyzed. Absence of Shb did not affect tumor growth although it increased lung metastasis. Shb knockout mouse tumors showed decreased redness and less developed vascular plexa located at the periphery of the tumors. No difference in overall tumor vascular density, leakage or pericyte coverage was noted between the genotypes although the average vessel size was smaller in the knockout. Tumors induced an increase of CD11b⁺ cells in spleen, lymph node, thymus, bone marrow and blood. Numbers of Shb knockout CD11b/CD8⁺ cells were decreased in lymph nodes and bone marrow of tumor bearing mice. Mice with tumors had reduced numbers of CD4⁺ lymphocytes in blood/lymphoid organs, whereas in most of these locations the proportion of CD4⁺ cells co-expressing FoxP3 was increased, suggesting a relative increase in Treg cells. This finding was reinforced by increased blood interleukin-35 (IL-35) in wild type tumor bearing mice. Shb knockout blood showed in addition an increased proportion of IL-35 expressing Treg cells, supporting the notion that absence of Shb further promotes tumor evasion from immune cell recognition. This could explain the increased number of lung metastases observed under these conditions. In conclusion, 4T1 tumors alter immune cell responses that promote tumor expansion, metastasis and escape from T cell recognition in an Shb dependent manner.

Hydrogen sulfide metabolism regulates endothelial solute barrier function

Hydrogen sulfide (H₂S) is an important gaseous signaling molecule in the cardiovascular system. In addition to free H₂S, H₂S can be oxidized to polysulfide which can be biologically active. Since the impact of H₂S on endothelial solute barrier function is not known, we sought to determine whether H₂S and its various metabolites affect endothelial permeability. In vitro permeability was evaluated using albumin flux and transendothelial electrical resistance. Different H₂S donors were used to examine the effects of exogenous H₂S. To evaluate the role of endogenous H₂S, mouse aortic endothelial cells (MAECs) were isolated from wild type mice and mice lacking cystathionine γ-lyase (CSE), a predominant source of H₂S in endothelial cells. In vivo permeability was evaluated using the Miles assay. We observed that polysulfide donors induced rapid albumin flux across endothelium. Comparatively, free sulfide donors increased permeability only with higher concentrations and at later time points. Increased solute permeability was associated with disruption of endothelial junction proteins claudin 5 and VE-cadherin, along with enhanced actin stress fiber formation. Importantly, sulfide donors that increase permeability elicited a preferential increase in polysulfide levels within endothelium. Similarly, CSE deficient MAECs showed enhanced solute barrier function along with reduced endogenous bound sulfane sulfur. CSE siRNA knockdown also enhanced endothelial junction structures with increased claudin 5 protein expression. In vivo, CSE genetic deficiency significantly blunted VEGF induced hyperpermeability revealing an important role of the enzyme for barrier function. In summary, endothelial solute permeability is critically regulated via exogenous and endogenous sulfide bioavailability with a prominent role of polysulfides.

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Polysulfide from cystathionine γ-lyase (CSE) and exogenous polysulfide donors increases endothelial permeability.

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The ability of polysulfide to increase permeability is associated with junction disruption and stress fiber formation.

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CSE expression in vivo regulates VEGF induced hyper-permeability.

The role of the Src Homology-2 domain containing protein B (SHB) in β cells

This review will describe the SH2-domain signaling protein Src Homology-2 domain containing protein B (SHB) and its role in various physiological processes relating in particular to glucose homeostasis and β cell function. SHB operates downstream of several tyrosine kinase receptors and assembles signaling complexes in response to receptor activation by interacting with other signaling proteins via its other domains (proline-rich, phosphotyrosine-binding and tyrosine-phosphorylation sites). The subsequent responses are context-dependent. Absence of Shb in mice has been found to exert effects on hematopoiesis, angiogenesis and glucose metabolism. Specifically, first-phase insulin secretion in response to glucose was impaired and this effect was related to altered characteristics of focal adhesion kinase activation modulating signaling through Akt, ERK, β catenin and cAMP. It is believed that SHB plays a role in integrating adaptive responses to various stimuli by simultaneously modulating cellular responses in different cell-types, thus playing a role in maintaining physiological homeostasis.

Shb deficiency in endothelium but not in leucocytes is responsible for impaired vascular performance during hindlimb ischaemia

AIM

Myeloid cells have been suggested to participate in angiogenesis and regulation of vascular function. Shb-deficient mice display both vascular and myeloid cell abnormalities with possible consequences for recovery after hindlimb ischaemia. This study was conducted in order to assess the contribution of Shb deficiency in myeloid cells to impaired vascular function in ischaemia.

METHODS

Wild type and Shb-deficient mice were subjected to peritoneal vascular endothelial growth factor A (VEGFA) followed by intraperitoneal lavage, after which blood and peritoneal cells were stained for myeloid markers. VEGFA-induced leucocyte recruitment to cremaster muscle was investigated using intravital microscopy of both mouse strains. Blood flow after femoral artery ligation was determined on chimeric mice after bone marrow transplantation.

RESULTS

No differences in neutrophil numbers or cell surface phenotypes were detected. Moreover, neutrophil extravasation in VEGFA-activated cremaster muscle was unaffected by Shb deficiency. However, blood and peritoneal CXCR4+ monocytes/macrophages were reduced in response to intraperitoneal VEGFA but not lipopolysaccharide (LPS) in the absence of Shb. Furthermore, the macrophage population in ischaemic muscle was unaffected by Shb deficiency after 2 days but reduced 7 days after injury. The bone marrow transplantation experiments revealed that mice with wild type vasculature showed better blood flow than those with Shb-deficient vasculature irrespective of leucocyte genotype.

CONCLUSION

The observed aberrations in myeloid cell properties in Shb-deficient mice are likely consequences of an abnormal vascular compartment and are not responsible for reduced muscle blood flow. Structural vascular abnormalities seem to be the primary cause of poor vascular performance under provoked vascular stress in this genetic model.

Vascular dysfunction and increased metastasis of B16F10 melanomas in Shb deficient mice as compared with their wild type counterparts

Background

Shb is a signaling protein downstream of vascular endothelial growth factor receptor-2 and Shb deficiency has been found to restrict tumor angiogenesis. The present study was performed in order to assess metastasis in Shb deficiency using B16F10 melanoma cells.

Methods

B16F10 melanoma cells were inoculated subcutaneously on wild type or Shb +/− mice. Primary tumors were resected and lung metastasis determined after tumor relapse. Lung metastasis was also assessed after bone marrow transplantation of wild type bone marrow to Shb +/− recipients and Shb +/− bone marrow to wild type recipients. Primary tumors were subject to immunofluorescence staining for CD31, VE-cadherin, desmin and CD8, RNA isolation and isolation of vascular fragments for further RNA isolation. RNA was used for real-time RT-PCR and microarray analysis.

Results

Numbers of lung metastases were increased in Shb +/− or −/− mice and this coincided with reduced pericyte coverage and increased vascular permeability. Gene expression profiling of vascular fragments isolated from primary tumors and total tumor RNA revealed decreased expression of different markers for cytotoxic T cells in tumors grown on Shb +/− mice, suggesting that vascular aberrations caused altered immune responses.

Conclusions

It is concluded that a unique combinatorial response of increased vascular permeability and reduced recruitment of cytotoxic CD8+ cells occurs as a consequence of Shb deficiency in B16F10 melanomas. These changes may promote tumor cell intravasation and metastasis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1269-y) contains supplementary material, which is available to authorized users.

Environmental temperature impact on bone and cartilage growth

Environmental temperature can have a surprising impact on extremity growth in homeotherms, but the underlying mechanisms have remained elusive for over a century. Limbs of animals raised at warm ambient temperature are significantly and permanently longer than those of littermates housed at cooler temperature. These remarkably consistent lab results closely resemble the ecogeographical tenet described by Allen's "extremity size rule," that appendage length correlates with temperature and latitude. This phenotypic growth plasticity could have adaptive significance for thermal physiology. Shortened extremities help retain body heat in cold environments by decreasing surface area for potential heat loss. Homeotherms have evolved complex mechanisms to maintain tightly regulated internal temperatures in challenging environments, including "facultative extremity heterothermy" in which limb temperatures can parallel ambient. Environmental modulation of tissue temperature can have direct and immediate consequences on cell proliferation, metabolism, matrix production, and mineralization in cartilage. Temperature can also indirectly influence cartilage growth by modulating circulating levels and delivery routes of essential hormones and paracrine regulators. Using an integrated approach, this article synthesizes classic studies with new data that shed light on the basis and significance of this enigmatic growth phenomenon and its relevance for treating human bone elongation disorders. Discussion centers on the vasculature as a gateway to understanding the complex interconnection between direct (local) and indirect (systemic) mechanisms of temperature-enhanced bone lengthening. Recent advances in imaging modalities that enable the dynamic study of cartilage growth plates in vivo will be key to elucidating fundamental physiological mechanisms of long bone growth regulation.

Absence of the adaptor protein Shb potentiates the T helper type 2 response in a mouse model of atopic dermatitis

Aberrant regulation of T helper (Th) cell maturation is associated with a number of autoimmune conditions, including allergic disorders and rheumatoid arthritis. The Src homology domain protein B (Shb) adaptor protein was recently implicated as a regulator of Th cell differentiation. Shb is an integral component of the T-cell receptor (TCR) signalling complex and in the absence of Shb the TCR is less responsive to stimulation, resulting in the preferential development of Th2 responses under conditions of in vitro stimulation. In the present study, we extend those observations to an in vivo situation using a murine model of atopic dermatitis. Shb knockout mice develop more pronounced symptoms of atopic dermatitis with increased localized oedema, epidermal hyperplasia and IgE production. Dermal infiltration of mast cells, eosinophils, CD4(+) Th cells and F4/80(+) macrophages was also significantly increased in Shb-deficient mice. This correlated with elevated transcription of the hallmark Th2 cytokines interleukin-4 and interleukin-5. The loss of Shb therefore alters TCR signalling ability, thereby favouring the development of Th2-driven inflammation and exacerbating symptoms of allergy.

VEGFA and tumour angiogenesis

In this review we summarize the current understanding of signal transduction downstream of vascular endothelial growth factor A (VEGFA) and its receptor VEGFR2, and the relationship between these signal transduction pathways and the hallmark responses of VEGFA, angiogenesis and vascular permeability. These physiological responses involve a number of effectors, including extracellular signal-regulated kinases (ERKs), Src, phosphoinositide 3 kinase (PI3K)/Akt, focal adhesion kinase (FAK), Rho family GTPases, endothelial NO and p38 mitogen-activated protein kinase (MAPK). Several of these factors are involved in the regulation of both angiogenesis and vascular permeability. Tumour angiogenesis primarily relies on VEGFA-driven responses, which to a large extent result in a dysfunctional vasculature. The reason for this remains unclear, although it appears that certain aspects of the VEGFA-stimulated angiogenic milieu (high level of microvascular density and permeability) promote tumour expansion. The high degree of redundancy and complexity of VEGFA-driven tumour angiogenesis may explain why tumours commonly develop resistance to anti-angiogenic therapy targeting VEGFA signal transduction.