The Function of Vascular Endothelial Growth Factor-B in the Heart

Despite intensive efforts, vascular growth factors have not yet provided significant help in the treatment of cardiovascular disease. This is likely to change as we gain a better understanding of the underlying biology of these growth factors as well as of their regulation and functions. Members of the vascular endothelial growth factor (VEGF) family are major regulators of blood and lymphatic vessel development and growth. VEGF is essential for vasculogenesis and angiogenesis, whereas VEGF-C is required for lymphatic development. The functions of VEGF-B, one of the younger members of the VEGF family, have however remained largely enigmatic. This study was undertaken in order to elucidate the role of VEGF-B in the regulation of myocardial and vascular function in the heart, a site of high endogenous expression, as well as its therapeutic potential. For this end, VEGF-B was first overexpressed in the mouse heart, before proceeding to a larger transgenic rat model better suited for studies of cardiovascular physiology. VEGF-B overexpression did not cause overt angiogenesis but led to an increase in the size of capillaries in the heart. Surprisingly, VEGF-B also increased the size of cardiomyocytes, resulting in myocardial hypertrophy. The transgenic animals had significantly lower blood pressure and heart rate than their wild type littermates, and the isolated transgenic mouse hearts seemed to perform better following short-term ischemia-reperfusion. Strikingly, in addition to myocardial growth, in rats VEGF-B induced impressive growth of the epicardial coronary arteries and their myocardial branches, which was associated with protection from myocardial infarction in vivo. However, in skeletal muscle and in the skin, VEGF-B did not significantly induce blood vessel growth, indicating that the heart is a site for specific effects of VEGF-B. These findings indicate that VEGF-B can act as a growth factor for cardiac vessels, which could have significant potential for therapeutic applications in cardiac insufficiency and/or ischemia. Importantly, compared with VEGF and placenta growth factor (PlGF), VEGF-B induced very little vascular permeability or inflammation. In contrast to a prevailing theory, VEGF-B did not increase fatty acid uptake in the heart in our models. Instead, VEGF-B seems to play a role in fine-tuning cardiac metabolism to meet energy demands during for example cell growth. Overall, VEGF-B has potential as a therapeutic growth factor in the ischemic heart, as it induces coordinated effects on cardiac blood vessels and cardiomyocytes, ultimately protecting the heart from ischemia.Sepelvaltimotauti on tällä hetkellä yleisin kuolinsyy maailmanlaajuisesti. Perinteiset hoidot eivät riitä kaikille sepelvaltimotautipotilaille, ja uusia hoitomuotoja tarvitaan. Yrityksistä huolimatta on ollut vaikea löytää sopivia kasvutekijöitä, joilla saisimme merkittävää hyötyä sydän- ja verisuonisairauksien hoidossa. Tämä todennäköisesti tulee muuttumaan, kun saamme uutta tietoa verisuonikasvutekijöiden biologiasta ja toiminnoista. Verisuonikasvutekijä VEGF-B kuuluu VEGF (vascular endothelial growth factor) kasvutekijäperheeseen, jonka jäsenet ovat elintärkeitä säätelijöitä veri- ja/tai imusuonten kehityksessä ja uudismuodostuksessa. VEGF-B löydettiin ensimmäistä kertaa hiiren ja ihmisen soluista yli viisitoista vuotta sitten, mutta sen toiminnallista merkitystä elimistössä tunnetaan yhä huonosti. Tämän tutkimuksen tavoite oli selvittää VEGF-B:n rooli sydänlihaksessa ja sydämen verisuonissa. Ensimmäisessä osatyössä osoitimme, että VEGF-B:n ylituotanto muuntogeenisessä hiirimallissa johti sydänlihassolujen kasvuun, eli hypertrofiaan, sekä sydämen hiussuonten suurenemiseen. Mielenkiintoista oli, että hiirillä oli merkitsevästi alhaisempi verenpaine ja sydämen syke. Lisäksi sydämet säilyttivät hyvän systolisen ja diastolisen toiminnan sydämen hypertrofiasta huolimatta. Toisessa osatyössä havaitsimme, että hypertrofian lisäksi VEGF-B:n ylituotanto muuntogeenisessä rottamallissa johti sydämen sepelvaltimopuuston kasvuun. VEGF-B ei lisännyt verisuonten läpäisevyyttä tai tulehdusta sydänlihaksessa kuten monet muut verisuonikasvutekijät. Tämä on tärkeä ominaisuus kasvutekijän turvallisuutta ajatellen. Pyrimme kolmannessa osatyössä selvittämään, voisiko VEGF-B:stä olla hyötyä kokeellisessa sydäninfarktimallissa, ja tuloksemme osoittivat, että VEGF-B:n ylituotanto suojaa hapenpuutteen aiheuttamilta vaurioilta rottamallissamme. Tällä tuloksella voi olla merkitystä tulevien hoitomuotojen kehittämisessä, sillä VEGF-B:llä näyttäisi olevan suotuisia vaikutuksia sekä sydämen verisuoniin että sydänlihassoluihin

VEGF-B-induced vascular growth leads to metabolic reprogramming and ischemia resistance in the heart

Peer reviewe

Transgenic Overexpression of Interleukin-1β Induces Persistent Lymphangiogenesis But Not Angiogenesis in Mouse Airways

These studies used bi-transgenic Clara cell secretory protein (CCSP)/IL-1β mice that conditionally overexpress IL-1β in Clara cells to determine whether IL-1β can promote angiogenesis and lymphangiogenesis in airways. Doxycycline treatment induced rapid, abundant, and reversible IL-1β production, influx of neutrophils and macrophages, and conspicuous and persistent lymphangiogenesis, but surprisingly no angiogenesis. Gene profiling showed many up-regulated genes, including chemokines (Cxcl1, Ccl7), cytokines (tumor necrosis factor α, IL-1β, and lymphotoxin-β), and leukocyte genes (S100A9, Aif1/Iba1). Newly formed lymphatics persisted after IL-1β overexpression was stopped. Further studies examined how IL1R1 receptor activation by IL-1β induced lymphangiogenesis. Inactivation of vascular endothelial growth factor (VEGF)-C and VEGF-D by adeno-associated viral vector-mediated soluble VEGFR-3 (VEGF-C/D Trap) completely blocked lymphangiogenesis, showing its dependence on VEGFR-3 ligands. Consistent with this mechanism, VEGF-C immunoreactivity was present in some Aif1/Iba1-immunoreactive macrophages. Because neutrophils contribute to IL-1β-induced lung remodeling in newborn mice, we examined their potential role in lymphangiogenesis. Triple-transgenic CCSP/IL-1β/CXCR2(-/-) mice had the usual IL-1β-mediated lymphangiogenesis but no neutrophil recruitment, suggesting that neutrophils are not essential. IL1R1 immunoreactivity was found on some epithelial basal cells and neuroendocrine cells, suggesting that these cells are targets of IL-1β, but was not detected on lymphatics, blood vessels, or leukocytes. We conclude that lymphangiogenesis triggered by IL-1β overexpression in mouse airways is driven by VEGF-C/D from macrophages, but not neutrophils, recruited by chemokines from epithelial cells that express IL1R1

VEGF-C and VEGF-D blockade inhibits inflammatory skin carcinogenesis.

VEGF-C and VEGF-D were identified as lymphangiogenic growth factors and later shown to promote tumor metastasis, but their effects on carcinogenesis are poorly understood. Here, we have studied the effects of VEGF-C and VEGF-D on tumor development in the murine multistep chemical carcinogenesis model of squamous cell carcinoma by using a soluble VEGF-C/VEGF-D inhibitor. After topical treatment with a tumor initiator and repeated tumor promoter applications, transgenic mice expressing a soluble VEGF-C/VEGF-D receptor (sVEGFR-3) in the skin developed significantly fewer squamous cell tumors with a delayed onset when compared with wild-type mice or mice expressing sVEGFR-3 lacking the ligand-binding site. Epidermal proliferation was reduced in the carcinogen-treated transgenic skin, whereas epidermal keratinocyte proliferation in vitro was not affected by VEGF-C or VEGF-D, indicating indirect effects of sVEGFR-3 expression. Importantly, transgenic mouse skin was less sensitive to tumor promoter-induced inflammation, with reduced angiogenesis and blood vessel leakage. Cutaneous leukocytes, especially macrophages, were reduced in transgenic skin without major changes in macrophage polarization or blood monocyte numbers. Several macrophage-associated cytokines were also reduced in transgenic papillomas, although the dermal macrophages themselves did not express VEGFR-3. These findings indicate that VEGF-C/VEGF-D are involved in shaping the inflammatory tumor microenvironment that regulates early tumor progression. Our results support the use of VEGF-C/VEGF-D-blocking agents not only to inhibit metastatic progression, but also during the early stages of tumor growth

Transgenic Overexpression of Interleukin-1β Induces Persistent Lymphangiogenesis But Not Angiogenesis in Mouse Airways

These studies used bi-transgenic Clara cell secretory protein (CCSP)/IL-1β mice that conditionally overexpress IL-1β in Clara cells to determine whether IL-1β can promote angiogenesis and lymphangiogenesis in airways. Doxycycline treatment induced rapid, abundant, and reversible IL-1β production, influx of neutrophils and macrophages, and conspicuous and persistent lymphangiogenesis, but surprisingly no angiogenesis. Gene profiling showed many up-regulated genes, including chemokines (Cxcl1, Ccl7), cytokines (tumor necrosis factor α, IL-1β, and lymphotoxin-β), and leukocyte genes (S100A9, Aif1/Iba1). Newly formed lymphatics persisted after IL-1β overexpression was stopped. Further studies examined how IL1R1 receptor activation by IL-1β induced lymphangiogenesis. Inactivation of vascular endothelial growth factor (VEGF)-C and VEGF-D by adeno-associated viral vector-mediated soluble VEGFR-3 (VEGF-C/D Trap) completely blocked lymphangiogenesis, showing its dependence on VEGFR-3 ligands. Consistent with this mechanism, VEGF-C immunoreactivity was present in some Aif1/Iba1-immunoreactive macrophages. Because neutrophils contribute to IL-1β–induced lung remodeling in newborn mice, we examined their potential role in lymphangiogenesis. Triple-transgenic CCSP/IL-1β/CXCR2(−/−) mice had the usual IL-1β-mediated lymphangiogenesis but no neutrophil recruitment, suggesting that neutrophils are not essential. IL1R1 immunoreactivity was found on some epithelial basal cells and neuroendocrine cells, suggesting that these cells are targets of IL-1β, but was not detected on lymphatics, blood vessels, or leukocytes. We conclude that lymphangiogenesis triggered by IL-1β overexpression in mouse airways is driven by VEGF-C/D from macrophages, but not neutrophils, recruited by chemokines from epithelial cells that express IL1R1

Overexpression of Vascular Endothelial Growth Factor-B in Mouse Heart Alters Cardiac Lipid Metabolism and Induces Myocardial Hypertrophy

Vascular Endothelial Growth Factor-B (VEGF-B) is poorly angiogenic but prominently expressed in metabolically highly active tissues, including the heart. We produced mice expressing a cardiac-specific VEGF-B transgene via the alpha myosin heavy chain promoter. Surprisingly, the hearts of the VEGF-B transgenic mice showed concentric cardiac hypertrophy without significant changes in heart function. The cardiac hypertrophy was due to an increased size of the cardiomyocytes. Blood capillary size was increased, while the number of blood vessels per cell nucleus remained unchanged. Despite the cardiac hypertrophy, the transgenic mice had lower heart rate and blood pressure than their littermates, and they responded similarly to angiotensin II-induced hypertension, confirming that the hypertrophy does not compromise heart function. Interestingly, the isolated transgenic hearts had less cardiomyocyte damage after ischemia. Significantly increased ceramide and decreased triglyceride levels were found in the transgenic hearts. This was associated with structural changes and eventual lysis of mitochondria, resulting in accumulation of intracellular vacuoles in cardiomyocytes and increased death of the transgenic mice, apparently due to mitochondrial lipotoxicity in the heart. These results suggest that VEGF-B regulates lipid metabolism, an unexpected function for an angiogenic growth factor