Showing papers by "Kari Alitalo published in 2020"
TL;DR: In a mouse model of glioblastoma, treatment with VEGF-C increases lymphatic drainage in the central nervous system and improves the immune response, suggesting that modulating meningeal lymphatics could enhance checkpoint inhibitor therapy.
Abstract: 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 brain1-3. 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.
274 citations
TL;DR: It is shown that endothelial cells do not express angiotensin-converting enzyme-2 (ACE2), the SARS-CoV-2 receptor, and pericytes and microvascular smooth muscle cells express ACE2 in an organotypic manner, suggesting thatpericytes limit endothelial pro-thrombotic responses.
Abstract: Accumulating clinical observations suggest pathogenesis beyond viral pneumonia and its secondary consequences in COVID-19 patients. In particular, many patients develop profound hyperinflammation and hypercoagulopathy with disseminated thrombogenesis and thromboembolism, which we observe also in a Swedish COVID-19 intensive care patient cohort. To understand these vascular manifestations, it is important to establish the potential vascular entry point(s) of the SARS-CoV-2 virus, i.e. which vascular cell types express the SARS-CoV-2 receptor ACE2. We present data that ACE2 is specifically and highly expressed in microvascular pericytes, but absent from endothelial cells, perivascular macrophages and fibroblasts. Mice with pericyte ablation show increased expression and release of Von Willebrand Factor from microvascular endothelial cells, suggesting that pericytes orchestrate thrombogenic responses in neighboring endothelial cells. Identifying pericytes rather than endothelial cells as the ACE2-expressing cells in the vasculature may explain why hypertension, diabetes and obesity are risk factors for severe COVID-19 patients, as these conditions are characterized by an impaired endothelial barrier function, allowing SARS-CoV-2 to reach and infect the pericytes that are normally shielded from the blood behind an intact endothelial barrier. This novel COVID-19-pericyte hypothesis is testable, offers explanations for some of the most enigmatic and lethal aspects of COVID-19 and calls for further investigations into the possible benefits of preventive anticoagulant therapy.
109 citations
TL;DR: The results give new insight into the interconnection between immune cells and lymphatics in orchestration of cardiac repair after injury and show that resolution of cardiac inflammation after MI may be accelerated by therapeutic lymphangiogenesis based on adeno-associated viral gene delivery of VEGF-CC156S.
Abstract: Objective: Lymphatics play an essential pathophysiological role in promoting fluid and immune cell tissue clearance. Conversely, immune cells may influence lymphatic function and remodeling. Recent...
55 citations
TL;DR: It is shown that vascular growth is dependent on the upstream lymphangiogenic VEGF-C signalling, permitting effective therapeutic intervention for LM, and co-inhibition of the upstream VEGf-C/VEGFR3 and the downstream PI3K/mTOR pathways is achieved.
Abstract: 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 PIK3CAH1047R mutation, resulting in constitutive activation of the p110α PI3K, underlies both macrocystic and microcystic LMs in human. Using a mouse model of PIK3CAH1047R-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, PIK3CAH1047R 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.
49 citations
TL;DR: Results indicate that LymfactinⓇ is well tolerated, and the oncological safety aspects of Lymfacts will require a longer follow-up period.
Abstract: Summary 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 × 1010) and 12 a higher dose (1 × 1011) 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.
36 citations
TL;DR: The recently emerged controversial role of the lymphatic vessels in tumor dissemination and cancer immunotherapy is discussed.
Abstract: 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.
35 citations
TL;DR: 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.
Abstract: 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
33 citations
TL;DR: It is shown that VEGF-C expression in specialized IntSCs is regulated by YAP/TAZ, and VEGf-C is responsible for maintaining lacteal integrity, thus influencing dietary fat drainage into lacteals.
Abstract: 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. Intestinal stromal cells (IntSCs) play essential roles in maintaining intestinal homeostasis. Here the authors show that VEGF-C expression in specialized IntSCs is regulated by YAP/TAZ, and VEGF-C is responsible for maintaining lacteal integrity, thus influencing dietary fat drainage into lacteals.
29 citations
TL;DR: This work describes an alternative, flow independent model, involving enlargement of arterial endothelial cells, which results in the formation of large diameter arteries, using zebrafish embryos and endothelial cell models.
Abstract: 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.
26 citations
TL;DR: It is demonstrated that primary lymphedema can be associated with ANGPT2 mutations and provide insights into TIE1 and TIE2 activation mechanisms.
Abstract: 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 ANGPT2 whole-gene deletion and four heterozygous ANGPT2 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 ANGPT2 mutations and provide insights into TIE1 and TIE2 activation mechanisms.
26 citations
TL;DR: The 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, and may serve as a therapeutic option for the treatment of CNS autoimmune disease.
Abstract: 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.
TL;DR: 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.
TL;DR: It is shown that DG neurogenesis acts to replace lost neurons and restore lost functions even following massive (>50%) neuronal loss, and suggests hippocampal NSCs as a critical reservoir enabling recovery from catastrophic DG damage.
Abstract: 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.SIGNIFICANCE STATEMENT 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.
TL;DR: Combination treatment with anti-Ang2 and radiation improved tumor growth inhibition and extended the survival of mice with melanoma or colorectal tumors and Ang2 blocking rescued radiation-induced decreases in T cells and cells of the monocyte/macrophage lineage.
Abstract: 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. In vivo, 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.
TL;DR: It is demonstrated that PROX1 is needed for R MS cell stemness and growth in vitro, and for RMS tumor formation in mouse xenograft models, and that inhibiting this interaction could be a promising therapeutic approach.
Abstract: Rhabdomyosarcoma (RMS) is an aggressive pediatric soft tissue cancer in need for novel therapies. Here we show that the PROX1 transcription factor, which is essential for normal myoblast differentiation, is highly expressed in RMS tumors. We demonstrate that PROX1 is needed for RMS cell stemness and growth in vitro, and for RMS tumor formation in mouse xenograft models. In addition, we unveil that PROX1 is an essential for myogenic properties in RMS. PROX1 depletion reprogrammed the RMS transcriptome to resemble benign mesenchymal stem cells and repressed many of the previously identified RMS effector transcripts and myogenic genes. By using proximity labeling and mass spectrometry, we found that PROX1 interacts with the NuRD and CoREST complexes containing class I HDACs. Our studies reveal a major role of PROX1-HDAC interaction in RMS and give insights that inhibiting this interaction could be a promising therapeutic approach.