Publications by authors named "Kari Alitalo"

359 Publications

VEGF-C/VEGFR-3 signaling in macrophages ameliorates acute lung injury.

Eur Respir J 2021 Aug 26. Epub 2021 Aug 26.

Department of Pulmonary Medicine, Allergy and Immunological Diseases, Iwate Medical University School of Medicine, Morioka, Japan.

Rationale: Successful recovery from acute lung injury requires inhibition of neutrophil influx and clearance of apoptotic neutrophils. However, the mechanisms underlying recovery remain unclear.

Objectives: We investigated the ameliorative effects of vascular endothelial growth factor receptor-3 (VEGFR-3)/VEGF-C signaling in macrophages in lipopolysaccharide-induced lung injury.

Methods: Lipopolysaccharides were intranasally injected into wild-type and transgenic mice. Gain- and loss- of VEGF-C/VEGFR-3 signaling function experiments employed adenovirus-mediated intranasal delivery of VEGF-C (Ad-VEGF-C vector) and soluble VEGFR-3, or, anti-VEGFR-3 blocking antibodies and mice with a deletion of VEGFR-3 in myeloid cells.

Measurements And Main Results: The early phase of lung injury was significantly alleviated by the overexpression of VEGF-C with increased levels of bronchoalveolar lavage fluid (BALF) interleukin (IL)-10, but worsened in the later phase by VEGFR-3 inhibition upon administration of Ad-sVEGFR-3 vector. Injection of anti-VEGFR-3 antibodies to the mice in the resolution phase inhibited recovery from lung injury. The VEGFR-3 deleted mice had a shorter survival time than littermates and more severe lung injury in the resolution phase. Alveolar macrophages in the resolution phase digested most of extrinsic apoptotic neutrophils, and VEGF-C/VEGFR-3 signaling increased efferocytosis upregulation of integrin alpha v in the macrophages. We also found that incubation with BALF from acute respiratory distress syndrome (ARDS) patients, but not from controls, decreases VEGFR-3 expression and the efficiency of IL-10 expression and efferocytosis in human monocyte-derived macrophages.

Conclusions: VEGFR-3/VEGF-C signaling in macrophages ameliorates experimental lung injury. This mechanism may provide an explanation also for ARDS resolution.
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http://dx.doi.org/10.1183/13993003.00880-2021DOI Listing
August 2021

3-hydroxy-L-kynurenamine is an immunomodulatory biogenic amine.

Nat Commun 2021 07 21;12(1):4447. Epub 2021 Jul 21.

Department of Pharmaceutical Sciences, University of Perugia, Perugia, Italy.

Tryptophan catabolism is a major metabolic pathway utilized by several professional and non-professional antigen presenting cells to maintain immunological tolerance. Here we report that 3-hydroxy-L-kynurenamine (3-HKA) is a biogenic amine produced via an alternative pathway of tryptophan metabolism. In vitro, 3-HKA has an anti-inflammatory profile by inhibiting the IFN-γ mediated STAT1/NF-κΒ pathway in both mouse and human dendritic cells (DCs) with a consequent decrease in the release of pro-inflammatory chemokines and cytokines, most notably TNF, IL-6, and IL12p70. 3-HKA has protective effects in an experimental mouse model of psoriasis by decreasing skin thickness, erythema, scaling and fissuring, reducing TNF, IL-1β, IFN-γ, and IL-17 production, and inhibiting generation of effector CD8 T cells. Similarly, in a mouse model of nephrotoxic nephritis, besides reducing inflammatory cytokines, 3-HKA improves proteinuria and serum urea nitrogen, overall ameliorating immune-mediated glomerulonephritis and renal dysfunction. Overall, we propose that this biogenic amine is a crucial component of tryptophan-mediated immune tolerance.
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http://dx.doi.org/10.1038/s41467-021-24785-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8295276PMC
July 2021

Lymphatic Malformations: Genetics, Mechanisms and Therapeutic Strategies.

Circ Res 2021 Jun 24;129(1):136-154. Epub 2021 Jun 24.

Wihuri Research Institute and Translational Cancer Medicine Program, Biomedicum, University of Helsinki, Finland (K.A.).

Lymphatic vessels maintain tissue fluid homeostasis by returning to blood circulation interstitial fluid that has extravasated from the blood capillaries. They provide a trafficking route for cells of the immune system, thus critically contributing to immune surveillance. Developmental or functional defects in the lymphatic vessels, their obstruction or damage, lead to accumulation of fluid in tissues, resulting in lymphedema. Here we discuss developmental lymphatic anomalies called lymphatic malformations and complex lymphatic anomalies that manifest as localized or multifocal lesions of the lymphatic vasculature, respectively. They are rare diseases that are caused mostly by somatic mutations and can present with variable symptoms based upon the size and location of the lesions composed of fluid-filled cisterns or channels. Substantial progress has been made recently in understanding the molecular basis of their pathogenesis through the identification of their genetic causes, combined with the elucidation of the underlying mechanisms in animal disease models and patient-derived lymphatic endothelial cells. Most of the solitary somatic mutations that cause lymphatic malformations and complex lymphatic anomalies occur in genes that encode components of oncogenic growth factor signal transduction pathways. This has led to successful repurposing of some targeted cancer therapeutics to the treatment of lymphatic malformations and complex lymphatic anomalies. Apart from the mutations that act as lymphatic endothelial cell-autonomous drivers of these anomalies, current evidence points to superimposed paracrine mechanisms that critically contribute to disease pathogenesis and thus provide additional targets for therapeutic intervention. Here, we review these advances and discuss new treatment strategies that are based on the recently identified molecular pathways.
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http://dx.doi.org/10.1161/CIRCRESAHA.121.318142DOI Listing
June 2021

NOTUM from Apc-mutant cells biases clonal competition to initiate cancer.

Nature 2021 06 2;594(7863):430-435. Epub 2021 Jun 2.

Division of Structural Biology, Wellcome Centre for Human Genetics, University of Oxford, Oxford, UK.

The tumour suppressor APC is the most commonly mutated gene in colorectal cancer. Loss of Apc in intestinal stem cells drives the formation of adenomas in mice via increased WNT signalling, but reduced secretion of WNT ligands increases the ability of Apc-mutant intestinal stem cells to colonize a crypt (known as fixation). Here we investigated how Apc-mutant cells gain a clonal advantage over wild-type counterparts to achieve fixation. We found that Apc-mutant cells are enriched for transcripts that encode several secreted WNT antagonists, with Notum being the most highly expressed. Conditioned medium from Apc-mutant cells suppressed the growth of wild-type organoids in a NOTUM-dependent manner. Furthermore, NOTUM-secreting Apc-mutant clones actively inhibited the proliferation of surrounding wild-type crypt cells and drove their differentiation, thereby outcompeting crypt cells from the niche. Genetic or pharmacological inhibition of NOTUM abrogated the ability of Apc-mutant cells to expand and form intestinal adenomas. We identify NOTUM as a key mediator during the early stages of mutation fixation that can be targeted to restore wild-type cell competitiveness and provide preventative strategies for people at a high risk of developing colorectal cancer.
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http://dx.doi.org/10.1038/s41586-021-03525-zDOI Listing
June 2021

Lysophosphatidylcholine in phospholipase A-modified LDL triggers secretion of angiopoietin 2.

Atherosclerosis 2021 06 2;327:87-99. Epub 2021 May 2.

Wihuri Research Institute, Biomedicum Helsinki, Haartmaninkatu 8, Helsinki, Finland. Electronic address:

Background And Aims: Secretory phospholipase A (PLA) hydrolyzes LDL phospholipids generating modified LDL particles (PLA-LDL) with increased atherogenic properties. Exocytosis of Weibel-Palade bodies (WPB) releases angiopoietin 2 (Ang2) and externalizes P-selectin, which both play important roles in vascular inflammation. Here, we investigated the effects of PLA-LDL on exocytosis of WPBs.

Methods: Human coronary artery endothelial cells (HCAECs) were stimulated with PLA- LDL, and its uptake and effect on Ang2 release, leukocyte adhesion, and intracellular calcium levels were measured. The effects of PLA-LDL on Ang2 release and WPB exocytosis were measured in and ex vivo in mice.

Results: Exposure of HCAECs to PLA-LDL triggered Ang2 secretion and promoted leukocyte-HCAEC interaction. Lysophosphatidylcholine was identified as a critical component of PLA-LDL regulating the WPB exocytosis, which was mediated by cell-surface proteoglycans, phospholipase C, intracellular calcium, and cytoskeletal remodeling. PLA-LDL also induced murine endothelial WPB exocytosis in blood vessels in and ex vivo, as evidenced by secretion of Ang2 in vivo, P-selectin translocation to plasma membrane in intact endothelial cells in thoracic artery and tracheal vessels, and reduced Ang2 staining in tracheal endothelial cells. Finally, in contrast to normal human coronary arteries, in which Ang2 was present only in the endothelial layer, at sites of advanced atherosclerotic lesions, Ang2 was detected also in the intima, media, and adventitia.

Conclusions: Our studies reveal PLA-LDL as a potent agonist of endothelial WPB exocytosis, resulting in increased secretion of Ang2 and translocation of P-selectin. The results provide mechanistic insight into PLA-LDL-dependent promotion of vascular inflammation and atherosclerosis.
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http://dx.doi.org/10.1016/j.atherosclerosis.2021.04.007DOI Listing
June 2021

VEGF-B Promotes Endocardium-Derived Coronary Vessel Development and Cardiac Regeneration.

Circulation 2021 Jan 18;143(1):65-77. Epub 2020 Nov 18.

Wihuri Research Institute and Translational Cancer Medicine Program, Faculty of Medicine (M.R., I.S., J.P., K.A.H., E.A., R.K., K.A.).

Background: Recent discoveries have indicated that, in the developing heart, sinus venosus and endocardium provide major sources of endothelium for coronary vessel growth that supports the expanding myocardium. Here we set out to study the origin of the coronary vessels that develop in response to vascular endothelial growth factor B (VEGF-B) in the heart and the effect of VEGF-B on recovery from myocardial infarction.

Methods: We used mice and rats expressing a VEGF-B transgene, VEGF-B-gene-deleted mice and rats, apelin-CreERT, and natriuretic peptide receptor 3-CreERT recombinase-mediated genetic cell lineage tracing and viral vector-mediated VEGF-B gene transfer in adult mice. Left anterior descending coronary vessel ligation was performed, and 5-ethynyl-2'-deoxyuridine-mediated proliferating cell cycle labeling; flow cytometry; histological, immunohistochemical, and biochemical methods; single-cell RNA sequencing and subsequent bioinformatic analysis; microcomputed tomography; and fluorescent- and tracer-mediated vascular perfusion imaging analyses were used to study the development and function of the VEGF-B-induced vessels in the heart.

Results: We show that cardiomyocyte overexpression of VEGF-B in mice and rats during development promotes the growth of novel vessels that originate directly from the cardiac ventricles and maintain connection with the coronary vessels in subendocardial myocardium. In adult mice, endothelial proliferation induced by VEGF-B gene transfer was located predominantly in the subendocardial coronary vessels. Furthermore, VEGF-B gene transduction before or concomitantly with ligation of the left anterior descending coronary artery promoted endocardium-derived vessel development into the myocardium and improved cardiac tissue remodeling and cardiac function.

Conclusions: The myocardial VEGF-B transgene promotes the formation of endocardium-derived coronary vessels during development, endothelial proliferation in subendocardial myocardium in adult mice, and structural and functional rescue of cardiac tissue after myocardial infarction. VEGF-B could provide a new therapeutic strategy for cardiac neovascularization after coronary occlusion to rescue the most vulnerable myocardial tissue.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.120.050635DOI Listing
January 2021

The GEF Trio controls endothelial cell size and arterial remodeling downstream of Vegf signaling in both zebrafish and cell models.

Nat Commun 2020 10 21;11(1):5319. Epub 2020 Oct 21.

Department of Cell and Developmental Biology, Institute of Zoology (ZOO), Karlsruhe Institute of Technology (KIT), Fritz Haber Weg 4, 76131, Karlsruhe, Germany.

Arterial networks enlarge in response to increase in tissue metabolism to facilitate flow and nutrient delivery. Typically, the transition of a growing artery with a small diameter into a large caliber artery with a sizeable diameter occurs upon the blood flow driven change in number and shape of endothelial cells lining the arterial lumen. Here, using zebrafish embryos and endothelial cell models, we describe an alternative, flow independent model, involving enlargement of arterial endothelial cells, which results in the formation of large diameter arteries. Endothelial enlargement requires the GEF1 domain of the guanine nucleotide exchange factor Trio and activation of Rho-GTPases Rac1 and RhoG in the cell periphery, inducing F-actin cytoskeleton remodeling, myosin based tension at junction regions and focal adhesions. Activation of Trio in developing arteries in vivo involves precise titration of the Vegf signaling strength in the arterial wall, which is controlled by the soluble Vegf receptor Flt1.
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http://dx.doi.org/10.1038/s41467-020-19008-0DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7578835PMC
October 2020

Expression of R-Spondin 1 in Apc Mice Suppresses Growth of Intestinal Adenomas by Altering Wnt and Transforming Growth Factor Beta Signaling.

Gastroenterology 2021 01 14;160(1):245-259. Epub 2020 Sep 14.

Translational Cancer Medicine Program, Research Programs Unit, Faculty of Medicine, University of Helsinki, Helsinki, Finland; iCAN Digital Precision Cancer Medicine Flagship, University of Helsinki and Helsinki University Hospital, Helsinki, Finland; Wihuri Research Institute, Biomedicum Helsinki, Helsinki, Finland. Electronic address:

Background & Aims: Mutations in the APC gene and other genes in the Wnt signaling pathway contribute to development of colorectal carcinomas. R-spondins (RSPOs) are secreted proteins that amplify Wnt signaling in intestinal stem cells. Alterations in RSPO genes have been identified in human colorectal tumors. We studied the effects of RSPO1 overexpression in Apc mutant mice.

Methods: An adeno associated viral vector encoding RSPO1-Fc fusion protein, or control vector, was injected into Apcmice. Their intestinal crypts were isolated and cultured as organoids. which were incubated with or without RSPO1-Fc and an inhibitor of transforming growth factor beta receptor (TGFBR). Livers were collected from mice and analyzed by immunohistochemistry. Organoids and adenomas were analyzed by quantitative reverse-transcription PCR, single cell RNA sequencing, and immunohistochemistry.

Results: Intestines from Apc mice injected with the vector encoding RSPO1-Fc had significantly deeper crypts, longer villi, with increased EdU labeling, indicating increased proliferation of epithelial cells, in comparison to mice given control vector. AAV-RSPO1-Fc-transduced Apc mice also developed fewer and smaller intestinal tumors and had significantly longer survival times. Adenomas of Apc mice injected with the RSPO1-Fc vector showed a rapid increase in apoptosis and in the expression of Wnt target genes, followed by reduced expression of messenger RNAs and proteins regulated by the Wnt pathway, reduced cell proliferation, and less crypt branching than adenomas of mice given the control vector. Addition of RSPO1 reduced the number of adenoma organoids derived from Apc mice and suppressed expression of Wnt target genes but increased phosphorylation of SMAD2 and transcription of genes regulated by SMAD. Inhibition of TGFBR signaling in organoids stimulated with RSPO1-Fc restored organoid formation and expression of genes regulated by Wnt. The TGFBR inhibitor restored apoptosis in adenomas from Apc mice expressing RSPO1-Fc back to the same level as in the adenomas from mice given the control vector.

Conclusions: Expression of RSPO1 in Apc mice increases apoptosis and reduces proliferation and Wnt signaling in adenoma cells, resulting in development of fewer and smaller intestinal tumors and longer mouse survival. Addition of RSPO1 to organoids derived from adenomas inhibits their growth and promotes proliferation of intestinal stem cells that retain the APC protein; these effects are reversed by TGFB inhibitor. Strategies to increase the expression of RSPO1 might be developed for the treatment of intestinal adenomas.
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http://dx.doi.org/10.1053/j.gastro.2020.09.011DOI Listing
January 2021

Characterization of mutations associated with primary lymphedema.

Sci Transl Med 2020 09;12(560)

Wihuri Research Institute, Biomedicum Helsinki, Haartmaninkatu 8, 00290 Helsinki, Finland.

Primary lymphedema is caused by developmental and functional defects of the lymphatic vascular system that result in accumulation of protein-rich fluid in tissues, resulting in edema. The 28 currently known genes causing primary lymphedema can explain <30% of cases. Angiopoietin 1 (ANGPT1) and ANGPT2 function via the TIE1-TIE2 (tyrosine kinase with immunoglobulin-like and epidermal growth factor-like domains 1 and 2) receptor complex and α5β1 integrin to form an endothelial cell signaling pathway that is critical for blood and lymphatic vessel formation and remodeling during embryonic development, as well as for homeostasis of the mature vasculature. By screening a cohort of 543 individuals affected by primary lymphedema, we identified one heterozygous de novo whole-gene deletion and four heterozygous missense mutations. Functional analyses revealed three missense mutations that resulted in decreased ANGPT2 secretion and inhibited the secretion of wild-type (WT)-ANGPT2, suggesting that they have a dominant-negative effect on ANGPT2 signaling. WT-ANGPT2 and soluble mutants T299M and N304K activated TIE1 and TIE2 in an autocrine assay in human lymphatic endothelial cells. Molecular modeling and biophysical studies showed that amino-terminally truncated ANGPT subunits formed asymmetrical homodimers that bound TIE2 in a 2:1 ratio. The T299M mutant, located in the dimerization interphase, showed reduced integrin α5 binding, and its expression in mouse skin promoted hyperplasia and dilation of cutaneous lymphatic vessels. These results demonstrate that primary lymphedema can be associated with mutations and provide insights into TIE1 and TIE2 activation mechanisms.
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http://dx.doi.org/10.1126/scitranslmed.aax8013DOI Listing
September 2020

VEGF-C protects the integrity of the bone marrow perivascular niche in mice.

Blood 2020 10;136(16):1871-1883

Wihuri Research Institute, Helsinki, Finland.

Hematopoietic stem cells (HSCs) reside in the bone marrow (BM) stem cell niche, which provides a vital source of HSC regulatory signals. Radiation and chemotherapy disrupt the HSC niche, including its sinusoidal vessels and perivascular cells, contributing to delayed hematopoietic recovery. Thus, identification of factors that can protect the HSC niche during an injury could offer a significant therapeutic opportunity to improve hematopoietic regeneration. In this study, we identified a critical function for vascular endothelial growth factor-C (VEGF-C), that of maintaining the integrity of the BM perivascular niche and improving BM niche recovery after irradiation-induced injury. Both global and conditional deletion of Vegfc in endothelial or leptin receptor-positive (LepR+) cells led to a disruption of the BM perivascular niche. Furthermore, deletion of Vegfc from the microenvironment delayed hematopoietic recovery after transplantation by decreasing endothelial proliferation and LepR+ cell regeneration. Exogenous administration of VEGF-C via an adenoassociated viral vector improved hematopoietic recovery after irradiation by accelerating endothelial and LepR+ cell regeneration and by increasing the expression of hematopoietic regenerative factors. Our results suggest that preservation of the integrity of the perivascular niche via VEGF-C signaling could be exploited therapeutically to enhance hematopoietic regeneration.
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http://dx.doi.org/10.1182/blood.2020005699DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7568034PMC
October 2020

Distinct fibroblast subsets regulate lacteal integrity through YAP/TAZ-induced VEGF-C in intestinal villi.

Nat Commun 2020 08 14;11(1):4102. Epub 2020 Aug 14.

Center for Vascular Research, Institute for Basic Science (IBS), Daejeon, 34141, Republic of Korea.

Emerging evidence suggests that intestinal stromal cells (IntSCs) play essential roles in maintaining intestinal homeostasis. However, the extent of heterogeneity within the villi stromal compartment and how IntSCs regulate the structure and function of specialized intestinal lymphatic capillary called lacteal remain elusive. Here we show that selective hyperactivation or depletion of YAP/TAZ in PDGFRβ IntSCs leads to lacteal sprouting or regression with junctional disintegration and impaired dietary fat uptake. Indeed, mechanical or osmotic stress regulates IntSC secretion of VEGF-C mediated by YAP/TAZ. Single-cell RNA sequencing delineated novel subtypes of villi fibroblasts that upregulate Vegfc upon YAP/TAZ activation. These populations of fibroblasts were distributed in proximity to lacteal, suggesting that they constitute a peri-lacteal microenvironment. Our findings demonstrate the heterogeneity of IntSCs and reveal that distinct subsets of villi fibroblasts regulate lacteal integrity through YAP/TAZ-induced VEGF-C secretion, providing new insights into the dynamic regulatory mechanisms behind lymphangiogenesis and lymphatic remodeling.
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http://dx.doi.org/10.1038/s41467-020-17886-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7428020PMC
August 2020

Lymphatic Vessels in Tumor Dissemination versus Immunotherapy.

Cancer Res 2020 09 30;80(17):3463-3465. Epub 2020 Jun 30.

Wihuri Research Institute and Translational Cancer Medicine Research Program, University of Helsinki, Biomedicum Helsinki, Helsinki, Finland.

During the growth of various cancers, primary tumors can escape antitumor immune responses of their host and eventually disseminate into distant organs. Peritumoral lymphatic vessels connect the primary tumor to lymph nodes, facilitating tumor entry into lymph nodes, systemic circulation, and metastasis. Lymph node metastases that occur frequently provide sites of tumor cell spread, whereas tumor antigen transfer into and presentation in tumor-draining lymph nodes induce activation of tumor-specific T-lymphocyte responses that can result in cytolytic targeting of the tumor. Here, we discuss the recently emerged controversial role of the lymphatic vessels in tumor dissemination and cancer immunotherapy.
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http://dx.doi.org/10.1158/0008-5472.CAN-20-0156DOI Listing
September 2020

Platelet-Specific PDGFB Ablation Impairs Tumor Vessel Integrity and Promotes Metastasis.

Cancer Res 2020 08 25;80(16):3345-3358. Epub 2020 Jun 25.

Department of Medical Biochemistry and Microbiology, Science for Life Laboratory, Uppsala University, Biomedical Center, Uppsala, Sweden.

Platelet-derived growth factor B (PDGFB) plays a crucial role in recruitment of PDGF receptor β-positive pericytes to blood vessels. The endothelium is an essential source of PDGFB in this process. Platelets constitute a major reservoir of PDGFB and are continuously activated in the tumor microenvironment, exposing tumors to the plethora of growth factors contained in platelet granules. Here, we show that tumor vascular function, as well as pericyte coverage is significantly impaired in mice with conditional knockout of PDGFB in platelets. A lack of PDGFB in platelets led to enhanced hypoxia and epithelial-to-mesenchymal transition in the primary tumors, elevated levels of circulating tumor cells, and increased spontaneous metastasis to the liver or lungs in two mouse models. These findings establish a previously unknown role for platelet-derived PDGFB, whereby it promotes and maintains vascular integrity in the tumor microenvironment by contributing to the recruitment of pericytes. SIGNIFICANCE: Conditional knockout of PDGFB in platelets demonstrates its previously unknown role in the maintenance of tumor vascular integrity and host protection against metastasis.
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http://dx.doi.org/10.1158/0008-5472.CAN-19-3533DOI Listing
August 2020

Pro-lymphangiogenic VEGFR-3 signaling modulates memory T cell responses in allergic airway inflammation.

Mucosal Immunol 2021 01 9;14(1):144-151. Epub 2020 Jun 9.

Pritzker School of Molecular Engineering, University of Chicago, Chicago, IL, USA.

In allergic airway inflammation, VEGFR-3-mediated lymphangiogenesis occurs in humans and mouse models, yet its immunological roles, particularly in adaptive immunity, are poorly understood. Here, we explored how pro-lymphangiogenic signaling affects the allergic response to house dust mite (HDM). In the acute inflammatory phase, the lungs of mice treated with blocking antibodies against VEGFR-3 (mF4-31C1) displayed less inflammation overall, with dramatically reduced innate and T-cell numbers and reduced inflammatory chemokine levels. However, when inflammation was allowed to resolve and memory recall was induced 2 months later, mice treated with mF4-31C1 as well as VEGF-C/-D knockout models showed exacerbated type 2 memory response to HDM, with increased Th2 cells, eosinophils, type 2 chemokines, and pathological inflammation scores. This was associated with lower CCL21 and decreased T in the lymph nodes. Together, our data imply that VEGFR-3 activation in allergic airways helps to both initiate the acute inflammatory response and regulate the adaptive (memory) response, possibly in part by shifting the T/Th2 balance. This introduces new immunomodulatory roles for pro-lymphangiogenic VEGFR-3 signaling in allergic airway inflammation and suggests that airway lymphatics may be a novel target for treating allergic responses.
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http://dx.doi.org/10.1038/s41385-020-0308-4DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7725864PMC
January 2021

Blockade of VEGF-C signaling inhibits lymphatic malformations driven by oncogenic PIK3CA mutation.

Nat Commun 2020 06 8;11(1):2869. Epub 2020 Jun 8.

Uppsala University, Department of Immunology, Genetics and Pathology, Dag Hammarskjölds väg 20, 751 85, Uppsala, Sweden.

Lymphatic malformations (LMs) are debilitating vascular anomalies presenting with large cysts (macrocystic) or lesions that infiltrate tissues (microcystic). Cellular mechanisms underlying LM pathology are poorly understood. Here we show that the somatic PIK3CA mutation, resulting in constitutive activation of the p110α PI3K, underlies both macrocystic and microcystic LMs in human. Using a mouse model of PIK3CA-driven LM, we demonstrate that both types of malformations arise due to lymphatic endothelial cell (LEC)-autonomous defects, with the developmental timing of p110α activation determining the LM subtype. In the postnatal vasculature, PIK3CA promotes LEC migration and lymphatic hypersprouting, leading to microcystic LMs that grow progressively in a vascular endothelial growth factor C (VEGF-C)-dependent manner. Combined inhibition of VEGF-C and the PI3K downstream target mTOR using Rapamycin, but neither treatment alone, promotes regression of lesions. The best therapeutic outcome for LM is thus achieved by co-inhibition of the upstream VEGF-C/VEGFR3 and the downstream PI3K/mTOR pathways.
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http://dx.doi.org/10.1038/s41467-020-16496-yDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7280302PMC
June 2020

Phase 1 Lymfactin Study: Short-term Safety of Combined Adenoviral VEGF-C and Lymph Node Transfer Treatment for Upper Extremity Lymphedema.

J Plast Reconstr Aesthet Surg 2020 Sep 18;73(9):1612-1621. Epub 2020 May 18.

Department of Plastic Surgery, Helsinki University Central Hospital and University of Helsinki, Helsinki, Finland. Electronic address:

Objective: To study the safety and tolerability of Lymfactin treatment combined with microvascular lymph node transfer surgery in patients with upper limb lymphedema.

Background: Upper limb lymphedema is a common clinical challenge after breast cancer surgery and/or radiotherapy. Lymfactin is an adenovirus type 5-based gene therapy involving expression of human vascular endothelial growth factor C (VEGF-C) in the damaged tissue. It aims to correct deficient lymphatic flow by promoting the growth and repair of lymphatic vessels.

Methods: In Phase I, Lymfactin was combined with microvascular lymph node transfer surgery to study the safety and tolerability of Lymfactin and the biodistribution of the viral vector in patients with upper limb lymphedema.

Results: Fifteen patients with breast cancer-associated secondary lymphedema of the upper arm were recruited between December 2016 and February 2018. Three patients received a lower dose (1 × 10) and 12 a higher dose (1 × 10) of viral particles, respectively. No dose-limiting toxicities were observed, and the study was completed with the pre-determined maximum dose. Commonly reported adverse events during the 12-month follow-up were common cold, fever, gastroenteritis, pain in the operation area, headache, muscle ache and elevated liver enzymes. Serious adverse events consisted of two erysipelas infections in the lymphedema arm (requiring hospitalization) and one hematoma of the flap donor site.

Conclusions: After 12 months' follow-up, results indicate that Lymfactin is well tolerated. The study continues with a 36-months efficacy and 5 years safety follow-up of the patients. The oncological safety aspects of Lymfactin will require a longer follow-up period.
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http://dx.doi.org/10.1016/j.bjps.2020.05.009DOI Listing
September 2020

Lymphatic and Immune Cell Cross-Talk Regulates Cardiac Recovery After Experimental Myocardial Infarction.

Arterioscler Thromb Vasc Biol 2020 07 14;40(7):1722-1737. Epub 2020 May 14.

From the Normandy University, UniRouen, Inserm (Institut National de la Santé et de la Recherche Médicale) UMR1096 (EnVI Laboratory), FHU REMOD-VHF, Rouen, France (H.M., A.D., V.T., I.B., J.P.H., S.R., J.R., S.F., V.R., P.M.).

Objective: Lymphatics play an essential pathophysiological role in promoting fluid and immune cell tissue clearance. Conversely, immune cells may influence lymphatic function and remodeling. Recently, cardiac lymphangiogenesis has been proposed as a therapeutic target to prevent heart failure after myocardial infarction (MI). We investigated the effects of gene therapy to modulate cardiac lymphangiogenesis post-MI in rodents. Second, we determined the impact of cardiac-infiltrating T cells on lymphatic remodeling in the heart. Approach and Results: Comparing adenoviral versus adeno-associated viral gene delivery in mice, we found that only sustained VEGF (vascular endothelial growth factor)-C therapy, achieved by adeno-associated viral vectors, increased cardiac lymphangiogenesis, and led to reduced cardiac inflammation and dysfunction by 3 weeks post-MI. Conversely, inhibition of VEGF-C/-D signaling, through adeno-associated viral delivery of soluble VEGFR3 (vascular endothelial growth factor receptor 3), limited infarct lymphangiogenesis. Unexpectedly, this treatment improved cardiac function post-MI in both mice and rats, linked to reduced infarct thinning due to acute suppression of T-cell infiltration. Finally, using pharmacological, genetic, and antibody-mediated prevention of cardiac T-cell recruitment in mice, we discovered that both CD4 and CD8 T cells potently suppress, in part through interferon-γ, cardiac lymphangiogenesis post-MI.

Conclusions: We show that resolution of cardiac inflammation after MI may be accelerated by therapeutic lymphangiogenesis based on adeno-associated viral gene delivery of VEGF-C. Conversely, our work uncovers a major negative role of cardiac-recruited T cells on lymphatic remodeling. Our results give new insight into the interconnection between immune cells and lymphatics in orchestration of cardiac repair after injury.
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http://dx.doi.org/10.1161/ATVBAHA.120.314370DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7310303PMC
July 2020

Blocking Angiopoietin-2 Promotes Vascular Damage and Growth Inhibition in Mouse Tumors Treated with Small Doses of Radiation.

Cancer Res 2020 06 20;80(12):2639-2650. Epub 2020 Apr 20.

Translational Cancer Medicine Program, University of Helsinki, Helsinki, Finland.

Abnormal vasculature in tumors leads to poor tissue perfusion and cytostatic drug delivery. Although drugs inducing vascular normalization, for example, angiopoietin-2 (Ang2)-blocking antibodies, have shown promising results in preclinical tumor models, clinical studies have so far shown only little efficacy. Because Ang2 is known to play a protective role in stressed endothelial cells, we tested here whether Ang2 blocking could enhance radiation-induced tumor vascular damage. Tumor-bearing mice were treated with anti-Ang2 antibodies every 3 or 4 days starting 3 days before 3 × 2 Gy or 4 × 0.5 Gy whole-body or tumor-focused radiation. Combination treatment with anti-Ang2 and radiation improved tumor growth inhibition and extended the survival of mice with melanoma or colorectal tumors. Single-cell RNA-sequencing revealed that Ang2 blocking rescued radiation-induced decreases in T cells and cells of the monocyte/macrophage lineage. In addition, anti-Ang2 enhanced radiation-induced apoptosis in cultured endothelial cells. , combination treatment decreased tumor vasculature and increased tumor necrosis in comparison with tumors treated with monotherapies. These results suggest that a combination of Ang2-blocking antibodies with radiation increases tumor growth inhibition and extends the survival of tumor-bearing mice. SIGNIFICANCE: These findings offer a preclinical rationale for further testing of the use of radiation in combination with Ang2-blocking antibodies to improve the overall outcome of cancer treatment.
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http://dx.doi.org/10.1158/0008-5472.CAN-20-0497DOI Listing
June 2020

Susceptibility to Cardiac Arrhythmias and Sympathetic Nerve Growth in VEGF-B Overexpressing Myocardium.

Mol Ther 2020 07 19;28(7):1731-1740. Epub 2020 Mar 19.

A.I. Virtanen Institute for Molecular Sciences, University of Eastern Finland, Yliopistonranta 1E, 70211 Kuopio, Finland; Heart Center, Kuopio University Hospital, Puijonlaaksontie 2, 70210 Kuopio, Finland. Electronic address:

VEGF-B gene therapy is a promising proangiogenic treatment for ischemic heart disease, but, unexpectedly, we found that high doses of VEGF-B promote ventricular arrhythmias (VAs). VEGF-B knockout, alpha myosin heavy-chain promoter (αMHC)-VEGF-B transgenic mice, and pigs transduced intramyocardially with adenoviral (Ad)VEGF- B186 were studied. Immunostaining showed a 2-fold increase in the number of nerves per field (76 vs. 39 in controls, p < 0.001) and an abnormal nerve distribution in the hypertrophic hearts of 11- to 20-month-old αMHC-VEGF-B mice. AdVEGF-B186 gene transfer (GT) led to local sprouting of nerve endings in pig myocardium (141 vs. 78 nerves per field in controls, p < 0.05). During dobutamine stress, 60% of the αMHC-VEGF-B hypertrophic mice had arrhythmias as compared to 7% in controls, and 20% of the AdVEGF-B186-transduced pigs and 100% of the combination of AdVEGF-B186- and AdsVEGFR-1-transduced pigs displayed VAs and even ventricular fibrillation. AdVEGF-B186 GT significantly increased the risk of sudden cardiac death in pigs when compared to any other GT with different VEGFs (hazard ratio, 500.5; 95% confidence interval [CI] 46.4-5,396.7; p < 0.0001). In gene expression analysis, VEGF-B induced the upregulation of Nr4a2, ATF6, and MANF in cardiomyocytes, molecules previously linked to nerve growth and differentiation. Thus, high AdVEGF-B186 overexpression induced nerve growth in the adult heart via a VEGFR-1 signaling-independent mechanism, leading to an increased risk of VA and sudden cardiac death.
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http://dx.doi.org/10.1016/j.ymthe.2020.03.011DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7335717PMC
July 2020

Angiopoietin-2 blockade ameliorates autoimmune neuroinflammation by inhibiting leukocyte recruitment into the CNS.

J Clin Invest 2020 04;130(4):1977-1990

Wihuri Research Institute and Translational Cancer Medicine Program, Faculty of Medicine, University of Helsinki, Helsinki, Finland.

Angiopoietin-2 (Ang2), a ligand of the endothelial Tie2 tyrosine kinase, is involved in vascular inflammation and leakage in critically ill patients. However, the role of Ang2 in demyelinating central nervous system (CNS) autoimmune diseases is unknown. Here, we report that Ang2 is critically involved in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), a rodent model of multiple sclerosis. Ang2 expression was induced in CNS autoimmunity, and transgenic mice overexpressing Ang2 specifically in endothelial cells (ECs) developed a significantly more severe EAE. In contrast, treatment with Ang2-blocking Abs ameliorated neuroinflammation and decreased spinal cord demyelination and leukocyte infiltration into the CNS. Similarly, Ang2-binding and Tie2-activating Ab attenuated the development of CNS autoimmune disease. Ang2 blockade inhibited expression of EC adhesion molecules, improved blood-brain barrier integrity, and decreased expression of genes involved in antigen presentation and proinflammatory responses of microglia and macrophages, which was accompanied by inhibition of α5β1 integrin activation in microglia. Taken together, our data suggest that Ang2 provides a target for increasing Tie2 activation in ECs and inhibiting proinflammatory polarization of CNS myeloid cells via α5β1 integrin in neuroinflammation. Thus, Ang2 targeting may serve as a therapeutic option for the treatment of CNS autoimmune disease.
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http://dx.doi.org/10.1172/JCI130308DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7108925PMC
April 2020

Age-Dependent Remarkable Regenerative Potential of the Dentate Gyrus Provided by Intrinsic Stem Cells.

J Neurosci 2020 01 20;40(5):974-995. Epub 2020 Jan 20.

Department of Developmental Biology and Cancer Research, Faculty of Medicine, Hebrew University, Jerusalem 91120, Israel,

Multiple insults to the brain lead to neuronal cell death, thus raising the question to what extent can lost neurons be replenished by adult neurogenesis. Here we focused on the hippocampus and especially the dentate gyrus (DG), a vulnerable brain region and one of the two sites where adult neuronal stem cells (NSCs) reside. While adult hippocampal neurogenesis was extensively studied with regard to its contribution to cognitive enhancement, we focused on their underestimated capability to repair a massively injured, nonfunctional DG. To address this issue, we inflicted substantial DG-specific damage in mice of either sex either by diphtheria toxin-based ablation of >50% of mature DG granule cells (GCs) or by prolonged brain-specific VEGF overexpression culminating in extensive, highly selective loss of DG GCs (thereby also reinforcing the notion of selective DG vulnerability). The neurogenic system promoted effective regeneration by increasing NSCs proliferation/survival rates, restoring a nearly original DG mass, promoting proper rewiring of regenerated neurons to their afferent and efferent partners, and regaining of lost spatial memory. Notably, concomitantly with the natural age-related decline in the levels of neurogenesis, the regenerative capacity of the hippocampus also subsided with age. The study thus revealed an unappreciated regenerative potential of the young DG and suggests hippocampal NSCs as a critical reservoir enabling recovery from catastrophic DG damage. Adult hippocampal neurogenesis has been extensively studied in the context of its role in cognitive enhancement, but whether, and to what extent can dentate gyrus (DG)-resident neural stem cells drive regeneration of an injured DG has remained unclear. Here we show that DG neurogenesis acts to replace lost neurons and restore lost functions even following massive (>50%) neuronal loss. Age-related decline of neurogenesis is paralleled by a progressive decline of regenerative capacity. Considering also the exceptional vulnerability of the DG to insults, these findings provide a further rationale for maintaining DG neurogenesis in adult life.
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http://dx.doi.org/10.1523/JNEUROSCI.1010-19.2019DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6989002PMC
January 2020

VEGF-C-driven lymphatic drainage enables immunosurveillance of brain tumours.

Nature 2020 01 15;577(7792):689-694. Epub 2020 Jan 15.

Department of Immunobiology, Yale University School of Medicine, New Haven, CT, USA.

Immune surveillance against pathogens and tumours in the central nervous system is thought to be limited owing to the lack of lymphatic drainage. However, the characterization of the meningeal lymphatic network has shed light on previously unappreciated ways that an immune response can be elicited to antigens that are expressed in the brain. Despite progress in our understanding of the development and structure of the meningeal lymphatic system, the contribution of this network in evoking a protective antigen-specific immune response in the brain remains unclear. Here, using a mouse model of glioblastoma, we show that the meningeal lymphatic vasculature can be manipulated to mount better immune responses against brain tumours. The immunity that is mediated by CD8 T cells to the glioblastoma antigen is very limited when the tumour is confined to the central nervous system, resulting in uncontrolled tumour growth. However, ectopic expression of vascular endothelial growth factor C (VEGF-C) promotes enhanced priming of CD8 T cells in the draining deep cervical lymph nodes, migration of CD8 T cells into the tumour, rapid clearance of the glioblastoma and a long-lasting antitumour memory response. Furthermore, transfection of an mRNA construct that expresses VEGF-C works synergistically with checkpoint blockade therapy to eradicate existing glioblastoma. These results reveal the capacity of VEGF-C to promote immune surveillance of tumours, and suggest a new therapeutic approach to treat brain tumours.
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http://dx.doi.org/10.1038/s41586-019-1912-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7100608PMC
January 2020

Anatomy and function of the vertebral column lymphatic network in mice.

Nat Commun 2019 10 9;10(1):4594. Epub 2019 Oct 9.

Université Pierre et Marie Curie Paris 06 UMRS1127, Sorbonne Université, Institut du Cerveau et de la Moelle Epinière, Paris, France.

Cranial lymphatic vessels (LVs) are involved in the transport of fluids, macromolecules and central nervous system (CNS) immune responses. Little information about spinal LVs is available, because these delicate structures are embedded within vertebral tissues and difficult to visualize using traditional histology. Here we show an extended vertebral column LV network using three-dimensional imaging of decalcified iDISCO-clarified spine segments. Vertebral LVs connect to peripheral sensory and sympathetic ganglia and form metameric vertebral circuits connecting to lymph nodes and the thoracic duct. They drain the epidural space and the dura mater around the spinal cord and associate with leukocytes. Vertebral LVs remodel extensively after spinal cord injury and VEGF-C-induced vertebral lymphangiogenesis exacerbates the inflammatory responses, T cell infiltration and demyelination following focal spinal cord lesion. Therefore, vertebral LVs add to skull meningeal LVs as gatekeepers of CNS immunity and may be potential targets to improve the maintenance and repair of spinal tissues.
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http://dx.doi.org/10.1038/s41467-019-12568-wDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6785564PMC
October 2019

High baseline Tie1 level predicts poor survival in metastatic breast cancer.

BMC Cancer 2019 Jul 24;19(1):732. Epub 2019 Jul 24.

Department of Oncology, Faculty of Medicine and Health Technology, Tampere University and Tays Cancer Centre, P.O. Box 100, FI-33014, Tampere, Finland.

Background: Angiopoietin growth factors (Angs) regulate angiogenesis and lymphangiogenesis by binding to the endothelial Tie2 receptor. Ang2 expression is elevated in tissue hypoxia and inflammation, which also induce cleavage of the extracellular domain of the orphan Tie1 receptor. Here we have examined if the concentrations of Ang2 and the soluble extracellular domain of Tie1 in patient plasma are associated with the prognosis of patients with metastatic breast cancer.

Methods: Plasma Tie1 and Ang2 levels were measured in metastatic breast cancer patients treated in a phase II trial with a taxane-bevacizumab combination chemotherapy in the first-line treatment setting. They were analyzed before treatment, after 6 weeks and 6 months of treatment, and at the final study visit. Using the median concentrations as cutoffs, Tie1 and Ang2 data were dichotomized into low and high concentration groups. Additionally, we analyzed Tie1 concentrations in plasma from 10 healthy women participating in a breast cancer primary prevention study.

Results: Plasma samples were available from 58 (89%) of the 65 patients treated in the trial. The baseline Tie1 levels of the healthy controls were significantly lower than those of the metastatic patients (p < 0.001). The overall survival of the patients with a high baseline Tie1 level was significantly shorter (multivariate HR 3.07, 95% CI 1.39-6.79, p = 0.005). Additionally, the progression-free survival was shorter for patients with a high baseline Tie1 level (multivariate HR 3.78, 95% CI 1.57-9.09, p = 0.003). In contrast, the baseline Ang2 levels had no prognostic impact in a multivariate Cox proportional hazard regression analysis. The combined analysis of baseline Tie1 and Ang2 levels revealed that patients with both high Tie1 and high Ang2 baseline levels had a significantly shorter overall survival than the patients with low baseline levels of both markers (multivariate HR for overall survival 4.32, 95% CI 1.44-12.94, p = 0.009).

Conclusions: This is the first study to demonstrate the prognostic value of baseline Tie1 plasma concentration in patients with metastatic breast cancer. Combined with the results of the Ang2 analyses, the patients with both high Tie1 and Ang2 levels before treatment had the poorest survival.

Trial Registration: Clinicaltrials.gov: NCT00979641, registration date 19-DEC-2008. The regional Ethics Committee: R08142M, registration date 18-NOV-2008.
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http://dx.doi.org/10.1186/s12885-019-5959-8DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6657075PMC
July 2019

KLK3/PSA and cathepsin D activate VEGF-C and VEGF-D.

Elife 2019 05 17;8. Epub 2019 May 17.

Individualized Drug Therapy Research Program, University of Helsinki, Helsinki, Finland.

Vascular endothelial growth factor-C (VEGF-C) acts primarily on endothelial cells, but also on non-vascular targets, for example in the CNS and immune system. Here we describe a novel, unique VEGF-C form in the human reproductive system produced via cleavage by kallikrein-related peptidase 3 (KLK3), aka prostate-specific antigen (PSA). KLK3 activated VEGF-C specifically and efficiently through cleavage at a novel N-terminal site. We detected VEGF-C in seminal plasma, and sperm liquefaction occurred concurrently with VEGF-C activation, which was enhanced by collagen and calcium binding EGF domains 1 (CCBE1). After plasmin and ADAMTS3, KLK3 is the third protease shown to activate VEGF-C. Since differently activated VEGF-Cs are characterized by successively shorter N-terminal helices, we created an even shorter hypothetical form, which showed preferential binding to VEGFR-3. Using mass spectrometric analysis of the isolated VEGF-C-cleaving activity from human saliva, we identified cathepsin D as a protease that can activate VEGF-C as well as VEGF-D.
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http://dx.doi.org/10.7554/eLife.44478DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6588350PMC
May 2019

Endothelial Cells Regulate Physiological Cardiomyocyte Growth via VEGFR2-Mediated Paracrine Signaling.

Circulation 2019 05 29;139(22):2570-2584. Epub 2019 Mar 29.

Wihuri Research Institute, Helsinki, Finland and Translational Cancer Biology Program, Research Programs Unit, Faculty of Medicine, University of Helsinki, Finland (R.K., K.A.H., M.R., K.A.).

Background: Heart failure, which is a major global health problem, is often preceded by pathological cardiac hypertrophy. The expansion of the cardiac vasculature, to maintain adequate supply of oxygen and nutrients, is a key determinant of whether the heart grows in a physiological compensated manner or a pathological decompensated manner. Bidirectional endothelial cell (EC)-cardiomyocyte (CMC) cross talk via cardiokine and angiocrine signaling plays an essential role in the regulation of cardiac growth and homeostasis. Currently, the mechanisms involved in the EC-CMC interaction are not fully understood, and very little is known about the EC-derived signals involved. Understanding how an excess of angiogenesis induces cardiac hypertrophy and how ECs regulate CMC homeostasis could provide novel therapeutic targets for heart failure.

Methods: Genetic mouse models were used to delete vascular endothelial growth factor (VEGF) receptors, adeno-associated viral vectors to transduce the myocardium, and pharmacological inhibitors to block VEGF and ErbB signaling in vivo. Cell culture experiments were used for mechanistic studies, and quantitative polymerase chain reaction, microarrays, ELISA, and immunohistochemistry were used to analyze the cardiac phenotypes.

Results: Both EC deletion of VEGF receptor (VEGFR)-1 and adeno-associated viral vector-mediated delivery of the VEGFR1-specific ligands VEGF-B or placental growth factor into the myocardium increased the coronary vasculature and induced CMC hypertrophy in adult mice. The resulting cardiac hypertrophy was physiological, as indicated by preserved cardiac function and exercise capacity and lack of pathological gene activation. These changes were mediated by increased VEGF signaling via endothelial VEGFR2, because the effects of VEGF-B and placental growth factor on both angiogenesis and CMC growth were fully inhibited by treatment with antibodies blocking VEGFR2 or by endothelial deletion of VEGFR2. To identify activated pathways downstream of VEGFR2, whole-genome transcriptomics and secretome analyses were performed, and the Notch and ErbB pathways were shown to be involved in transducing signals for EC-CMC cross talk in response to angiogenesis. Pharmacological or genetic blocking of ErbB signaling also inhibited part of the VEGF-B-induced effects in the heart.

Conclusions: This study reveals that cross talk between the EC VEGFR2 and CMC ErbB signaling pathways coordinates CMC hypertrophy with angiogenesis, contributing to physiological cardiac growth.
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http://dx.doi.org/10.1161/CIRCULATIONAHA.118.036099DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6553980PMC
May 2019

Dural lymphatics regulate clearance of extracellular tau from the CNS.

Mol Neurodegener 2019 02 27;14(1):11. Epub 2019 Feb 27.

Department of Neurology, Hope Center for Neurological Disorders, Knight Alzheimer's Disease Research Center, Washington University in St. Louis, St. Louis, MO, 63110, USA.

Background: Alzheimer's disease is characterized by two main neuropathological hallmarks: extracellular plaques of amyloid-β (Aβ) protein and intracellular aggregates of tau protein. Although tau is normally a soluble monomer that bind microtubules, in disease it forms insoluble, hyperphosphorylated aggregates in the cell body. Aside from its role in AD, tau is also involved in several other neurodegenerative disorders collectively called tauopathies, such as progressive supranuclear palsy (PSP), corticobasal degeneration (CBD), some forms of frontotemporal dementia, and argyrophilic grain disease (AGD). The prion hypothesis suggests that after an initial trigger event, misfolded forms of tau are released into the extracellular space, where they spread through different brain regions, enter cells, and seeding previously normal forms. Thus understanding mechanisms regulating the clearance of extracellular tau from the CNS is important. The discovery of a true lymphatic system in the dura and its potential role in mediating Aβ pathology prompted us to investigate its role in regulating extracellular tau clearance.

Methods: To study clearance of extracellular tau from the brain, we conjugated monomeric human tau with a near-infrared dye cypate, and injected this labeled tau in the parenchyma of both wild-type and K14-VEGFR3-Ig transgenic mice, which lack a functional CNS lymphatic system. Following injection we performed longitudinal imaging using fluorescence molecular tomography (FMT) and quantified fluorescence to calculate clearance of tau from the brain. To complement this, we also measured tau clearance to the periphery by measuring plasma tau in both groups of mice.

Results: Our results show that a significantly higher amount of tau is retained in the brains of K14-VEGFR3-Ig vs. wild type mice at 48 and 72 h post-injection and its subsequent clearance to the periphery is delayed. We found that clearance of reference tracer human serum albumin (HSA) was also significantly delayed in the K14-VEGFR3-Ig mice.

Conclusions: The dural lymphatic system appears to play an important role in clearance of extracellular tau, since tau clearance is impaired in the absence of functional lymphatics. Based on our baseline characterization of extracellular tau clearance, future studies are warranted to look at the interaction between tau pathology and efficiency of lymphatic function.
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http://dx.doi.org/10.1186/s13024-019-0312-xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6391770PMC
February 2019

Gut microbiota regulates lacteal integrity by inducing VEGF-C in intestinal villus macrophages.

EMBO Rep 2019 04 19;20(4). Epub 2019 Feb 19.

Center for Vascular Research, Institute for Basic Science, Daejeon, Korea

A lacteal is a blunt-ended, long, tube-like lymphatic vessel located in the center of each intestinal villus that provides a unique route for drainage of absorbed lipids from the small intestine. However, key regulators for maintaining lacteal integrity are poorly understood. Here, we explore whether and how the gut microbiota regulates lacteal integrity. Germ depletion by antibiotic treatment triggers lacteal regression during adulthood and delays lacteal maturation during the postnatal period. In accordance with compromised lipid absorption, the button-like junction between lymphatic endothelial cells, which is ultrastructurally open to permit free entry of dietary lipids into lacteals, is significantly reduced in lacteals of germ-depleted mice. Lacteal defects are also found in germ-free mice, but conventionalization of germ-free mice leads to normalization of lacteals. Mechanistically, VEGF-C secreted from villus macrophages upon MyD88-dependent recognition of microbes and their products is a main factor in lacteal integrity. Collectively, we conclude that the gut microbiota is a crucial regulator for lacteal integrity by endowing its unique microenvironment and regulating villus macrophages in small intestine.
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http://dx.doi.org/10.15252/embr.201846927DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6446200PMC
April 2019

Systemic Blockade of ACVR2B Ligands Protects Myocardium from Acute Ischemia-Reperfusion Injury.

Mol Ther 2019 03 24;27(3):600-610. Epub 2019 Jan 24.

Research Unit of Biomedicine, Department of Pharmacology and Toxicology, University of Oulu, 90220 Oulu, Finland; Medical Research Center Oulu, Oulu University Hospital and University of Oulu, 90220 Oulu, Finland.

Activin A and myostatin, members of the transforming growth factor (TGF)-β superfamily of secreted factors, are potent negative regulators of muscle growth, but their contribution to myocardial ischemia-reperfusion (IR) injury is not known. The aim of this study was to investigate if activin 2B (ACVR2B) receptor ligands contribute to myocardial IR injury. Mice were treated with soluble ACVR2B decoy receptor (ACVR2B-Fc) and subjected to myocardial ischemia followed by reperfusion for 6 or 24 h. Systemic blockade of ACVR2B ligands by ACVR2B-Fc was protective against cardiac IR injury, as evidenced by reduced infarcted area, apoptosis, and autophagy and better preserved LV systolic function following IR. ACVR2B-Fc modified cardiac metabolism, LV mitochondrial respiration, as well as cardiac phenotype toward physiological hypertrophy. Similar to its protective role in IR injury in vivo, ACVR2B-Fc antagonized SMAD2 signaling and cell death in cardiomyocytes that were subjected to hypoxic stress. ACVR2B ligand myostatin was found to exacerbate hypoxic stress. In addition to acute cardioprotection in ischemia, ACVR2B-Fc provided beneficial effects on cardiac function in prolonged cardiac stress in cardiotoxicity model. By blocking myostatin, ACVR2B-Fc potentially reduces cardiomyocyte death and modifies cardiomyocyte metabolism for hypoxic conditions to protect the heart from IR injury.
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http://dx.doi.org/10.1016/j.ymthe.2019.01.013DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6404100PMC
March 2019
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