VEGF-C and angiopoietins in lymphangiogenesis

Angiogenesis and lymphangiogenesis occur during development as the result of tightly coordinated signalling programs to generate two hierarchically organised vascular systems. All tissues and organs are dependent on a functional blood vasculature for oxygen and nutrients, whereas the lymphatic vasculature functions to collect excess tissue fluid, passing it through lymph nodes for immune surveillance, and returning it to the blood circulation. Effectors that control developmental angiogenesis and lymphangiogenesis are also involved in pathological settings, and therefore potential targets for therapy. Vascular endothelial growth factor (VEGF) and angiopoietin (Ang) growth factors, signalling through endothelial VEGFR and Tie receptors, have been established as key regulators of angiogenic and lymphangiogenic processes in development and disease. In this study, we aimed to obtain a clearer understanding of the vascular effects of stimulation by VEGF-C, Ang1 and Ang2, all known to be involved in lymphangiogenesis. In cell culture models, we found that both intrinsic and microenvironmental regulatory mechanisms are involved in the regulation of endothelial cell phenotypes, and distinct responses to VEGF signalling are induced by specific receptor pathways in different endothelial cell types. Surprisingly, we also found that Ang1 induces sprouting lymphangiogenesis in vivo by a VEGFR-3 dependent mechanism, establishing Ang1 as a novel lymphangiogenic factor. Using inducible transgenic mouse models, we found that VEGF-C-induced lymphatic hyperplasia persisted independently of the growth factor, indicating that short pro-lymphangiogenic therapy could lead to lasting improvements in tissue oedema. While VEGF-C had blood vessel effects in embryos, no angiogenic side effects were observed in adult tissues. Furthermore, inducible transgenic expression of Ang2 during embryonic development confirmed Ang2 as an important regulator of lymphatic remodelling and mural cell contacts. The unexpected similarity of the lymphatic maturation defects caused by excess Ang2 to those observed in Ang2 deficient mice demonstrated that correct doses of Ang2 are crucial for the control of lymphatic development. Unlike Ang1, Ang2 did not induce lymphatic sprouting. Although Ang1 has been shown to be able to substitute for Ang2 during developmental lymphangiogenesis, their lymphatic effects are not identical. These findings further our understanding of the basic mechanisms of angiogenesis and lymphangiogenesis, important for the future development of targeted therapies for vascular diseases such as cancer, inflammation, lymphoedema and ischemia. VEGF-C and Ang1 especially emerged as promising candidates for pro-lymphangiogenic therapy.

VEGF-C/VEGFR-3 and PDGF-B/PDGFR-b pathways in embryonic lymphangiogenesis

The circulatory system comprises the blood vascular system and the lymphatic vascular system. These two systems function in parallel. Blood vessels form a closed system that delivers oxygen and nutrients to the tissues and removes waste products from the tissues, while lymphatic vessels are blind-ended tubes that collect extravasated fluid and cells from the tissues and return them back to blood circulation. Development of blood and lymphatic vascular systems occurs in series. Blood vessels are formed via vasculogenesis and angiogenesis whereas lymphatic vessels develop via lymphangiogenesis, after the blood vascular system is already functional. Members of the vascular endothelial growth factor (VEGF) family are regulators of both angiogenesis and lymphangiogenesis, while members of the platelet-derived growth factor (PDGF) family are major mitogens for pericytes and smooth muscle cells and regulate formation of blood vessels. Vascular endothelial growth factor C (VEGF-C) is the major lymphatic growth factor and signaling through its receptor vascular endothelial growth factor receptor 3 (VEGFR-3) is sufficient for lymphangiogenesis in adults. We studied the role of VEGF-C in embryonic lymphangiogenesis and showed that VEGF-C is absolutely required for the formation of lymph sacs from embryonic veins. VEGFR-3 is also required for normal development of the blood vascular system during embryogenesis, as Vegfr3 knockout mice die at mid-gestation due to failure in remodeling of the blood vessels. We showed that sufficient VEGFR-3 signaling in the embryo proper is required for embryonic angiogenesis and in a dosage-sensitive manner for embryonic lymphangiogenesis. Importantly, mice deficient in both VEGFR-3 ligands, Vegfc and Vegfd, developed a normal blood vasculature, suggesting VEGF-C- and VEGF-D- independent functions for VEGFR-3 in the early embryo. Platelet-derived growth factor B (PDGF-B) signals via PDGFR-b and regulates formation of blood vessels by recruiting pericytes and smooth muscle cells around nascent endothelial tubes. We showed that PDGF-B fails to induce lymphangiogenesis when overexpressed in adult mouse skin using adenoviral vectors. However, mouse embryos lacking Pdgfb showed abnormal lymphatic vessels, suggesting that PDGF-B plays a role in lymphatic vessel maturation and separation from blood vessels during embryogenesis. Lymphatic vessels play a key role in immune surveillance, fat absorption and maintenance of fluid homeostasis in the body. However, lymphatic vessels are also involved in various diseases, such as lymphedema and tumor metastasis. These studies elucidate the basic mechanisms of embryonic lymphangiogenesis and add to the knowledge of lymphedema and tumor metastasis treatments by giving novel insights into how lymphatic vessel growth could be induced (in lymphedema) or inhibited (in tumor metastasis).

First measurement of the ratio of branching fractions B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-)

This article presents the first measurement of the ratio of branching fractions B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-). Measurements in two control samples using the same technique B(B̅ 0→D+μ-ν̅ μ)/B(B̅ 0→D+π-) and B(B̅ 0→D*(2010)+μ-ν̅ μ)/B(B̅ 0→D*(2010)+π-) are also reported. The analysis uses data from an integrated luminosity of approximately 172  pb-1 of pp̅ collisions at √s=1.96  TeV, collected with the CDF II detector at the Fermilab Tevatron. The relative branching fractions are measured to be B(Λb0→Λc+μ-ν̅ μ)/B(Λb0→Λc+π-)=16.6±3.0(stat)±1.0(syst)+2.6/-3.4(PDG)±0.3(EBR), B(B̅ 0→D+μ-ν̅ μ)/B(B̅ 0→D+π-)= 9.9±1.0(stat)±0.6(syst)±0.4(PDG)±0.5(EBR), and B(B̅ 0→D*(2010)+μ-ν̅ μ)/B(B̅ 0→D*(2010)+π-)=16.5±2.3(stat)± 0.6(syst)±0.5(PDG)±0.8(EBR). The uncertainties are from statistics (stat), internal systematics (syst), world averages of measurements published by the Particle Data Group or subsidiary measurements in this analysis (PDG), and unmeasured branching fractions estimated from theory (EBR), respectively. This article also presents measurements of the branching fractions of four new Λb0 semileptonic decays: Λb0→Λc(2595)+μ-ν̅ μ, Λb0→Λc(2625)+μ-ν̅ μ, Λb0→Σc(2455)0π+μ-ν̅ μ, and Λb0→Σc(2455)++π-μ-ν̅ μ, relative to the branching fraction of the Λb0→Λc+μ-ν̅ μ decay. Finally, the transverse-momentum distribution of Λb0 baryons produced in pp̅ collisions is measured and found to be significantly different from that of B̅ 0 mesons, which results in a modification in the production cross-section ratio σΛb0/σB̅ 0 with respect to the CDF I measurement.

Kyynpurema koiralla, kirjallisuuskatsaus ja Yliopistollisen Eläinsairaalan potilasaineistoa vuosilta 2007 - 2008

Kyykäärme (Vipera berus) on Suomen ainoa myrkkykäärme, ja sitä esiintyy lähes koko maassa Pohjois-Lappia lukuun ottamatta. Kyy on yleensä helposti tunnistettavissa selän tummasta sahalaitakuviosta. Käärme ei ole perusluonteeltaan hyökkäävä, vaan pyrkii ensisijaisesti pakenemaan. Koira kuitenkin pääsee monesti yllättämään kyyn ennen kuin käärme ehtii paeta, jolloin se puolustautuessaan saattaa purra rajusti. Kaikki puremat eivät sisällä myrkkyä, vaan noin kolmasosa puremista on ns. kuivapuremia. Kyynpuremia raportoidaan eniten maalis- ja lokakuun välisenä aikana. Kyynpuremasta aiheutuvat oireet ovat koiralla vaihtelevia, ja eläimen voinnin kehittymisen ennustaminen ensioireiden perusteella on vaikeaa. Oireet vaihtelevat paikallisesta turvotuksesta henkeä uhkaavaan monielinvaurioon. Koiralla kuolleisuuden on raportoitu olevan 3,5 – 4 %. Kyynmyrkyn koostumusta ei vielä tarkalleen tunneta, mutta sen pääkomponentin muodostavat suurimolekyyliset proteiinit ja polypeptidit, joista osalla on entsymaattista aktiivisuutta. Lisäksi osalla myrkyn komponenteista vaikuttaisi olevan suoraa toksista vaikutusta kohdekudokseen, esimerkiksi munuaisiin. Keskeisintä kyynpureman patofysiologiassa on myrkyn sytotoksisen komponentin ja proteolyyttisten entsyymien aiheuttama verisuonten endoteelivaurio, jonka seurauksena suonet alkavat vuotaa. Kehittyvä voimakas kudosturvotus on kyynpureman tyypillisin oire, ja se ilmaantuu aina kahden tunnin sisällä puremasta, mikäli purema on sisältänyt myrkkyä. Nesteiden siirtyminen verisuoniston ulkopuolelle johtaa nopeasti hypovolemiaan ja shokkiin. Tärkeiden sisäelinten verenkierto heikkenee, jolloin solut kärsivät hapen ja ravinteiden puutteesta. Myrkky stimuloi myös sytokiinien tuotantoa ja vapautumista elimistöstä. Näiden farmakologisesti aktiivisten aineiden vapautuminen pahentaa systeemioireita, aiheuttaa lihasspasmeja ja on pääasiallisesti kyynpuremasta aiheutuvan voimakkaan kivun taustalla. Kyynmyrkyn sisältämät vieraat proteiinit voivat aiheuttaa myös anafylaktisen reaktion. Tutkimusosan aineisto koostuu 12 koirasta, joita hoidettiin kyynpureman takia Yliopistollisen Eläinsairaalan teho-osastolla vuosina 2007 – 2008. Koirista 10 toipui kotiutuskuntoon ja kaksi jouduttiin lopettamaan komplikaatioiden takia. Tutkimuksessa tarkasteltiin potilaiden virtsa- ja seeruminäytteistä määritettyjä munuaisten toimintaa kuvaavia laboratorioarvoja ja verrattiin lopetettujen koirien arvoja selvinneiden koirien vastaaviin. Tarkoituksena oli selvittää, onko selvinneiden ja lopetettujen välillä havaittavissa eroja, ja että onko tiettyjen laboratoriomääritysten perusteella mahdollista sanoa jotakin potilaan selviytymisennusteesta. Tuloksissa todettiin eroja selvinneiden ja lopetettujen koirien välillä. Virtsasta mitatut munuaisten solutuhoa kuvaavat entsyymiaktiivisuudet (AFOS/C ja GGT/C) sekä virtsan proteiinit kreatiniiniin suhteutettuna olivat lopetetulla selvästi korkeammat kuin selvinneillä koirilla. Myös seeruminäytteissä todettiin eroja. Tulosten perusteella vaikuttaakin siltä, että lopetetuilla koirilla vauriot munuaisissa olivat pahemmat kuin selvinneillä koirilla. Tutkimuksen aineisto oli kuitenkin niin pieni, että tuloksia voidaan pitää ainoastaan suuntaa antavina.