Nonfunctional TGF-β/ALK1/ENG signaling pathway supports neutrophil proangiogenic activity in hereditary hemorrhagic telangiectasia

The transforming growth factor β (TGF-β)/ALK1/ENG signaling pathway maintains quiescent state of endothelial cells, but at the same time, it regulates neutrophil functions. Importantly, mutations of this pathway lead to a rare autosomal disorder called hereditary hemorrhagic telangiectasia (HHT), characterized with abnormal blood vessel formation (angiogenesis). As neutrophils are potent regulators of angiogenesis, we investigated how disturbed TGF-β/ALK1/ENG signaling influences angiogenic properties of these cells in HHT. We could show for the first time that not only endothelial cells, but also neutrophils isolated from such patients are ENG/ALK1 deficient. This deficiency obviously stimulates proangiogenic switch of such neutrophils. Elevated proangiogenic activity of HHT neutrophils is mediated by the increased spontaneous degranulation of gelatinase granules, resulting in high release of matrix-degrading matrix metalloproteinase 9 (MMP9). In agreement, therapeutic disturbance of this process using Src tyrosine kinase inhibitors impaired proangiogenic capacity of such neutrophils. Similarly, inhibition of MMP9 activity resulted in significant impairment of neutrophil-mediated angiogenesis. All in all, deficiency in TGF-β/ALK1/ENG signaling in HHT neutrophils results in their proangiogenic activation and disease progression. Therapeutic strategies targeting neutrophil degranulation and MMP9 release and activity may serve as a potential therapeutic option for HHT.

Three-dimensional analyses of vascular network morphology in a murine lymph node by X-ray phase-contrast tomography with a 2D Talbot array

With growing molecular evidence for correlations between spatial arrangement of blood vasculature and fundamental immunological functions, carried out in distinct compartments of the subdivided lymph node, there is an urgent need for three-dimensional models that can link these aspects. We reconstructed such models at a 1.84 µm resolution by the means of X-ray phase-contrast imaging with a 2D Talbot array in a short time without any staining. In addition reconstructions are verified in immunohistochemistry staining as well as in ultrastructural analyses. While conventional illustrations of mammalian lymph nodes depict the hilus as a definite point of blood and lymphatic vessel entry and exit, our method revealed that multiple branches enter and emerge from an area that extends up to one third of the organ's surface. This could be a prerequisite for the drastic and location-dependent remodeling of vascularization, which is necessary for lymph node expansion during inflammation. Contrary to corrosion cast studies we identified B-cell follicles exhibiting a two times denser capillary network than the deep cortical units of the T-cell zone. In addition to our observation of high endothelial venules spatially surrounding the follicles, this suggests a direct connection between morphology and B-cell homing. Our findings will deepen the understanding of functional lymph node composition and lymphocyte migration on a fundamental basis.

During early stages of cancer, neutrophils initiate anti-tumor immune responses in tumor-draining lymph nodes

Tumor-draining lymph nodes (LNs) play a crucial role during cancer spread and in initiation of anti-cancer adaptive immunity. Neutrophils form a substantial population of cells in LNs with poorly understood functions. Here, we demonstrate that, during head and neck cancer (HNC) progression, tumor-associated neutrophils transmigrate to LNs and shape anti-tumor responses in a stage-dependent manner. In metastasis-free stages (N0), neutrophils develop an antigen-presenting phenotype (HLA-DR⁺CD80⁺CD86⁺ICAM1⁺PD-L1^-) and stimulate T cells (CD27⁺Ki67^highPD-1^-). LN metastases release GM-CSF and via STAT3 trigger development of PD-L1⁺ immunosuppressive neutrophils, which repress T cell responses. The accumulation of neutrophils in T cell-rich zones of LNs in N0 constitutes a positive predictor for 5-year survival, while increased numbers of neutrophils in LNs of N1-3 stages predict poor prognosis in HNC. These results suggest a dual role of neutrophils as essential regulators of anti-cancer immunity in LNs and argue for approaches fostering immunostimulatory activity of these cells during cancer therapy.

IFNAR1 Deficiency Impairs Immunostimulatory Properties of Neutrophils in Tumor-Draining Lymph Nodes

Tumor-draining lymph nodes (TDLNs) are the first organs where the metastatic spread of different types of cancer, including head and neck cancer (HNC), occurs and have therefore high prognostic relevance. Moreover, first anti-cancer immune responses have been shown to be initiated in such LNs via tumor-educated myeloid cells. Among myeloid cells present in TDLNs, neutrophils represent a valuable population and considerably participate in the activation of effector lymphocytes there. Tumor-supportive or tumor-inhibiting activity of neutrophils strongly depends on the surrounding microenvironment. Thus, type I interferon (IFN) availability has been shown to prime anti-tumor activity of these cells. In accordance, mice deficient in type I IFNs show elevated tumor growth and metastatic spread, accompanied by the pro-tumoral neutrophil bias. To reveal the mechanism responsible for this phenomenon, we have studied here the influence of defective type I IFN signaling on the immunoregulatory activity of neutrophils in TDLNs. Live imaging of such LNs was performed using two-photon microscopy in a transplantable murine HNC model. Catchup^IVM-red and Ifnar1^-/- (type I IFN receptor- deficient) Catchup^IVM-red mice were used to visualize neutrophils and to assess their interaction with T-cells in vivo. We have evaluated spatiotemporal patterns of neutrophil/T-cell interactions in LNs in the context of type I interferon receptor (IFNAR1) availability in tumor-free and tumor-bearing animals. Moreover, phenotypic and functional analyses were performed to further characterize the mechanisms regulating neutrophil immunoregulatory capacity. We demonstrated that inactive IFNAR1 leads to elevated accumulation of neutrophils in TDLNs. However, these neutrophils show significantly impaired capacity to interact with and to stimulate T-cells. As a result, a significant reduction of contacts between neutrophils and T lymphocytes is observed, with further impairment of T-cell proliferation and activation. This possibly contributes to the enhanced tumor growth in Ifnar1^-/- mice. In agreement with this, IFNAR1-independent activation of downstream IFN signaling using IFN-λ improved the immunostimulatory capacity of neutrophils in TDLNs and contributed to the suppression of tumor growth. Our results suggest that functional type I IFN signaling is essential for neutrophil immunostimulatory capacity and that stimulation of this signaling may provide a therapeutic opportunity in head and neck cancer patients.

SIRT1-mediated deacetylation of FOXO3a transcription factor supports pro-angiogenic activity of interferon-deficient tumor-associated neutrophils

Angiogenesis plays an important role during tumor growth and metastasis. We could previously show that Type I interferon (IFN)-deficient tumor-associated neutrophils (TANs) show strong pro-angiogenic activity, and stimulate tumor angiogenesis and growth. However, the exact mechanism responsible for their pro-angiogenic shift is not clear. Here, we set out to delineate the molecular mechanism and factors regulating pro-angiogenic properties of neutrophils in the context of Type I IFN availability. We demonstrate that neutrophils from IFN-deficient (Ifnar1^-/- ) mice efficiently release pro-angiogenic factors, such as VEGF, MMP9 or BV8, and thus significantly support the vascular normalization of tumors by increasing the maturation of perivascular cells. Mechanistically, we could show here that the expression of pro-angiogenic factors in neutrophils is controlled by the transcription factor forkhead box protein O3a (FOXO3a), which activity depends on its post-translational modifications, such as deacetylation or phosphorylation. In TANs isolated from Ifnar1^-/- mice, we observe significantly elevated SIRT1, resulting in SIRT1-mediated deacetylation of FOXO3a, its nuclear retention and activation. Activated FOXO3a supports in turn the transcription of pro-angiogenic genes in TANs. In the absence of SIRT1, or after its inhibition in neutrophils, elevated kinase MEK/ERK and PI3K/AKT activity is observed, leading to FOXO3a phosphorylation, cytoplasmic transfer and inactivation. In summary, we have found that FOXO3a is a key transcription factor controlling the angiogenic switch of neutrophils. Post-translational FOXO3a modifications regulate its transcriptional activity and, as a result, the expression of pro-angiogenic factors supporting development of vascular network in growing tumors. Therefore, targeting FOXO3a activity could provide a novel strategy of antiangiogenic targeted therapy for cancer.

Neutrophil dynamics, plasticity and function in acute neurodegeneration following neonatal hypoxia-ischemia

Neonatal encephalopathy following hypoxia-ischemia (HI) is a major cause of long-term morbidity and mortality in children. Even though HI-induced neuroinflammation, involving infiltration of peripheral immune cells into the CNS has been associated with disease pathogenesis, the specific role of neutrophils is highly debated. Due to immaturity of the neonatal immune system, it has been assumed that neutrophils are less clinically relevant in neonatal HI-induced brain injury. In the present study, we demonstrate that neutrophils are rapidly activated in the neonatal brain after exposure to experimental HI, revealed by an enhanced proportion of CD86⁺ cells and an increased expression of CD11b compared to splenic and blood neutrophils. Furthermore, production of reactive oxygen species and the proportion of hyperactivated/aged (CXCR4⁺CD62L^-) cells was enhanced in brain compared to peripheral neutrophils. Delayed neutrophil depletion, initiated 12 h after HI resulted in reduced cellular neurodegeneration, associated with reduced micro- and astroglial activation. In the present study, we uncovered a new complex switch of the phenotype in brain neutrophils, which may offer new possibilities for the development of selective therapeutic approaches by modulation of neutrophils in the early post-hypoxic disease phase.

Impaired Release of Neutrophil Extracellular Traps and Anemia-Associated T Cell Deficiency in Hereditary Hemorrhagic Telangiectasia

Hereditary hemorrhagic telangiectasia (HHT) is characterized by mucocutaneous telangiectases and visceral vascular malformations. Individuals suffering from HHT have a significantly increased risk of bacterial infections, but the mechanisms involved in this are not clear. White blood cell subpopulations were estimated with flow cytometry in 79 patients with HHT and 45 healthy individuals, and association with clinicopathological status was assessed. A prominent decrease in absolute numbers of T cells in HHT was revealed (0.7 (0.5-1.1) vs. 1.3 (0.8-1.6), 10⁶/mL, p < 0.05), and in multivariate regression analysis, hemoglobin level was associated with lymphopenia (OR = 0.625, 95% CI: 0.417-0.937, p < 0.05). Although no changes in absolute numbers of neutrophils and monocytes were observed, we revealed a significant impairment of neutrophil antibacterial functions in HHT (n = 9), compared to healthy individuals (n = 7), in vitro. The release of neutrophil extracellular traps (NETs) against Pseudomonas aeruginosa MOI10 was significantly suppressed in HHT (mean area per cell, mm²: 76 (70-92) vs. 121 (97-128), p < 0.05), due to impaired filamentous actin organization (% of positive cells: 69 (59-77) vs. 92 (88-94), p < 0.05). To conclude, this study reveals the categories of patients with HHT that are prone to immunosuppression and require careful monitoring, and suggests a potential therapeutic strategy based on the functional activation of neutrophils.

Detrimental Effect of Type I IFNs During Acute Lung Infection With Pseudomonas aeruginosa Is Mediated Through the Stimulation of Neutrophil NETosis

Pseudomonas aeruginosa is an opportunistic multidrug-resistant pathogen, able to grow in biofilms. It causes life-threatening complications in diseases characterized by the up-regulation of type I interferon (IFN) signaling, such as cancer or viral infections. Since type I IFNs regulate multiple functions of neutrophils, which constitute the first line of anti-bacterial host defense, in this work we aimed to study how interferon-activated neutrophils influence the course of P. aeruginosa infection of the lung. In lungs of infected IFN-sufficient WT mice, significantly elevated bacteria load was observed, accompanied by the prominent lung tissue damage. At the same time IFN-deficient animals seem to be partly resistant to the infection. Lung neutrophils from such IFN-deficient animals release significantly lower amounts of neutrophil extracellular traps (NETs) and reactive oxygen species (ROS), as compared to WT neutrophils. Of note, such IFN-deficient neutrophils show significantly decreased capacity to stimulate biofilm formation by P. aeruginosa. Reduced biofilm production impairs in turn the survival of bacteria in a lung tissue. In line with that, treatment of neutrophils with recombinant IFN-β enhances their NETosis and stimulates biofilm formation by Pseudomonas after co-incubation with such neutrophils. Possibly, bacteria utilizes neutrophil-derived NETs as a scaffold for released biofilms. In agreement with this, in vivo treatment with ROS-scavengers, NETs disruption or usage of the bacterial strains unable to bind DNA, suppress neutrophil-mediated biofilm formation in the lungs. Together, our findings indicate that the excessive activation of neutrophils by type I IFNs leads to their boosted NETosis that in turn triggers biofilm formation by P. aeruginosa and supports its persistence in the infected lung. Targeting these mechanisms could offer a new therapeutic approach to prevent persistent bacterial infections in patients with diseases associated with the up-regulation of type I IFNs.

Transfer of Manipulated Tumor-associated Neutrophils into Tumor-Bearing Mice to Study their Angiogenic Potential In Vivo

The contribution of neutrophils to the regulation of tumorigenesis is getting increased attention. These cells are heterogeneous, and depending on the tumor milieu can possess pro- or anti-tumor capacity. One of the important cytokines regulating neutrophil functions in a tumor context are type I interferons. In the presence of interferons, neutrophils gain anti-tumor properties, including cytotoxicity or stimulation of the immune system. Conversely, the absence of an interferon signaling results in prominent pro-tumor activity, characterized with strong stimulation of tumor angiogenesis. Recently, we could demonstrate that pro-angiogenic properties of neutrophils depend on the activation of nicotinamide phosphoribosyltransferase (NAMPT) signaling pathway in these cells. Inhibition of this pathway in tumor-associated neutrophils leads to their potent anti-angiogenic phenotype. Here, we demonstrate our newly established model allowing in vivo evaluation of tumorigenic potential of manipulated tumor-associated neutrophils (TANs). Shortly, pro-angiogenic tumor-associated neutrophils can be isolated from tumor-bearing interferon-deficient mice and repolarized into anti-angiogenic phenotype by blocking of NAMPT signaling. The angiogenic activity of these cells can be subsequently evaluated using an aortic ring assay. Anti-angiogenic TANs can be transferred into tumor-bearing wild type recipients and tumor growth should be monitored for 14 days. At day 14 mice are sacrificed, tumors removed and cut with their vascularization assessed. Overall, our protocol provides a novel tool to in vivo evaluate angiogenic capacity of primary cells, such as tumor-associated neutrophils, without a need to use artificial neutrophil cell line models. vc.

NAMPT signaling is critical for the proangiogenic activity of tumor-associated neutrophils

Tumor-associated neutrophils (TANs) regulate many processes associated with tumor progression, and depending on the microenvironment, they can exhibit pro- or antitumor functions. However, the molecular mechanisms regulating their tumorigenicity are not clear. Using transplantable tumor models, we showed here that nicotinamide phosphoribosyltransferase (NAMPT), a molecule involved in CSF3R downstream signaling, is essential for tumorigenic conversion of TANs and their pro-angiogenic switch. As a result tumor vascularization and growth are strongly supported by these cells. Inhibition of NAMPT in TANs leads to their antitumor conversion. Adoptive transfer of such TANs into B16F10-tumor bearing mice attenuates tumor angiogenesis and growth. Of note, we observe that the regulation of NAMPT signaling in TANs, and its effect on the neutrophil tumorigenicity, are analogous in mice and human. NAMPT is up-regulated in TANs from melanoma and head-and-neck tumor patients, and its expression positively correlates with tumor stage. Mechanistically, we found that targeting of NAMPT suppresses neutrophil tumorigenicity by inhibiting SIRT1 signaling, thereby blocking transcription of pro-angiogenic genes. Based on these results, we propose that NAMPT regulatory axis is important for neutrophils to activate angiogenic switch during early stages of tumorigenesis. Thus, identification of NAMPT as the critical molecule priming protumor functions of neutrophils provides not only mechanistic insight into the regulation of neutrophil tumorigenicity, but also identifies a potential pathway that may be targeted therapeutically in neutrophils. This, in turn, may be utilized as a novel mode of cancer immunotherapy.