A mutant receptor tyrosine phosphatase, CD148, causes defects in vascular development.
(57/2034)
Vascularization defects in genetic recombinant mice have defined critical roles for a number of specific receptor tyrosine kinases. Here we evaluated whether an endothelium-expressed receptor tyrosine phosphatase, CD148 (DEP-1/PTPeta), participates in developmental vascularization. A mutant allele, CD148(DeltaCyGFP), was constructed to eliminate CD148 phosphatase activity by in-frame replacement of cytoplasmic sequences with enhanced green fluorescent protein sequences. Homozygous mutant mice died at midgestation, before embryonic day 11.5 (E11.5), with vascularization failure marked by growth retardation and disorganized vascular structures. Structural abnormalities were observed as early as E8.25 in the yolk sac, prior to the appearance of intraembryonic defects. Homozygous mutant mice displayed enlarged vessels comprised of endothelial cells expressing markers of early differentiation, including VEGFR2 (Flk1), Tal1/SCL, CD31, ephrin-B2, and Tie2, with notable lack of endoglin expression. Increased endothelial cell numbers and mitotic activity indices were demonstrated. At E9.5, homozygous mutant embryos showed homogeneously enlarged primitive vessels defective in vascular remodeling and branching, with impaired pericyte investment adjacent to endothelial structures, in similarity to endoglin-deficient embryos. Developing cardiac tissues showed expanded endocardial projections accompanied by defective endocardial cushion formation. These findings implicate a member of the receptor tyrosine phosphatase family, CD148, in developmental vascular organization and provide evidence that it regulates endothelial proliferation and endothelium-pericyte interactions. (+info)
Responses to antiangiogenesis treatment of spontaneous autochthonous tumors and their isografts.
(58/2034)
Preclinical studies typically use human tumor xenografts or murine tumor isografts. Tumor growth may be accelerated by in vivo passage, thus making these tumors more sensitive to some therapies than the original tumors. In the present study, by comparing the effects of DC101, an antimurine vascular endothelial growth factor receptor 2 (VEGFR2) monoclonal antibody, on spontaneous autochthonous tumors and their early generation transplants, we show that this growth acceleration is diminished by DC101 treatment. Spontaneous autochthonous tumors in aged C3H mice consisted of s.c. sarcomas and adenocarcinomas, and their growth rate was accelerated by in vivo passages. Anti-VEGFR2 treatment decreased vessel density, increased apoptosis, and reduced tumor growth in large (500 mm(3)) spontaneous autochthonous tumors. Anti-VEGFR2 treatment significantly delayed tumor growth and extended animal survival. Tumor growth acceleration by in vivo passage was diminished by DC101 treatment. To our knowledge, this is the first evaluation of antiangiogenic therapy in a spontaneous autochthonous tumor model, which may more closely resemble human tumors. Additionally, this is the first study to compare treatment response between the parental tumor and its isografts. Although passaged tumors behave differently, it is encouraging that the tumor growth rates under DC101 treatment are comparable among different passage generations. (+info)
HIV-1 Tat-mediated apoptosis in human brain microvascular endothelial cells.
(59/2034)
The integrity of the blood-brain barrier (BBB) is critical for normal brain function. Neuropathological abnormalities in AIDS patients have been associated with perivascular HIV-infected macrophages, gliosis, and abnormalities in the permeability of the BBB. The processes by which HIV causes these pathological conditions are not well understood. To characterize the mechanism by which HIV-1 Tat protein modulates human brain microvascular endothelial cell (HBMEC) functions, we studied the effects of HIV-1 Tat in modulating HBMEC apoptosis and permeability. Treatment of HBMEC with HIV-1 Tat led to Flk-1/KDR and Flt-4 receptor activation and the release of NO. The protein levels of endothelial NO synthase (NOS) and inducible NOS were increased by HIV-1 Tat stimulation. Importantly, HIV-1 Tat caused apoptosis of HBMEC, as evidenced by changes in the cleavage of poly(A)DP-ribose polymerase, DNA laddering, and incorporation of fluorescein into the nicked chromosomal DNA (TUNEL assay). HIV-1 Tat-mediated apoptosis in HBMEC was significantly inhibited in the presence of N-nitro-L-arginine methyl ester (an inhibitor of NOS) and wortmannin (a phosphoinositol 3-kinase inhibitor). Furthermore, HIV-1 Tat treatment significantly increased HBMEC permeability, and pretreatment with both N-nitro-L-arginine methyl ester and wortmannin inhibited the Tat-induced permeability. Taken together, these results indicate that dysregulated production of NO by HIV-1 Tat plays a pivotal role in brain endothelial injury, resulting in the irreversible loss of BBB integrity, which may lead to enhanced infiltration of virus-carrying cells across the BBB. (+info)
Focal adhesion kinase is required for blood vessel morphogenesis.
(60/2034)
The nonreceptor tyrosine kinase focal adhesion kinase (FAK) is a point of convergence for signals from extracellular matrix, soluble factors, and mechanical stimuli. Targeted disruption of the fak gene in mice leads to death at embryonic day 8.5 (E8.5). FAK-/- embryos have severely impaired blood vessel development. Gene expression and in vitro differentiation studies revealed that endothelial cell differentiation was comparable in FAK-/- and wild-type E8.5 embryos. We examined the role of FAK in blood vessel morphogenesis using an in vitro tubulogenesis assay and three different culture systems: FAK+/+ and FAK-/- embryoid bodies, FAK+/+ and FAK-/- endothelial cells, and human umbilical vein endothelial cells expressing antisense FAK, a dominant-negative fragment of FAK, or wild-type FAK. In all of these systems, endothelial cells deficient in FAK expression or function displayed a severely reduced ability to form tubules in Matrigel. These studies demonstrate clearly that the vascular defects in FAK-/- mice result from the inability of FAK-deficient endothelial cells to organize themselves into vascular networks, rather than from defects in tissue-specific differentiation. (+info)
Nitric oxide enhances angiogenesis via the synthesis of vascular endothelial growth factor and cGMP after stroke in the rat.
(61/2034)
We investigated the effects of NO on angiogenesis and the synthesis of vascular endothelial growth factor (VEGF) in a model of focal embolic cerebral ischemia in the rat. Compared with control rats, systemic administration of an NO donor, DETANONOate, to rats 24 hours after stroke significantly enlarged vascular perimeters and increased the number of proliferated cerebral endothelial cells and the numbers of newly generated vessels in the ischemic boundary regions, as evaluated by 3-dimensional laser scanning confocal microscopy. Treatment with DETANONOate significantly increased VEGF levels in the ischemic boundary regions as measured by ELISA. A capillary-like tube formation assay was used to investigate whether DETANONOate increases angiogenesis in ischemic brain via activation of soluble guanylate cyclase. DETANONOate-induced capillary-like tube formation was completely inhibited by a soluble guanylate cyclase inhibitor, 1H-[1,2,4]oxadiazolo[4,3-a]quinoxaline-1-one (ODQ). Blocking VEGF activity by a neutralized antibody against VEGF receptor 2 significantly attenuated DETANONOate-induced capillary-like tube formation. Moreover, systemic administration of a phosphodiesterase type 5 inhibitor (Sildenafil) to rats 24 hours after stroke significantly increased angiogenesis in the ischemic boundary regions. Sildenafil and an analog of cyclic guanosine monophosphate (cGMP) also induced capillary-like tube formation. These findings suggest that exogenous NO enhances angiogenesis in ischemic brain, which is mediated by the NO/cGMP pathway. Furthermore, our data suggest that NO, in part via VEGF, may enhance angiogenesis in ischemic brain. (+info)
Recruitment and activation of phospholipase Cgamma1 by vascular endothelial growth factor receptor-2 are required for tubulogenesis and differentiation of endothelial cells.
(62/2034)
Vascular endothelial growth factor-mediated angiogenic signal transduction relay is achieved by coordinated induction of endothelial cell proliferation, migration, and differentiation. These complex cellular processes are most likely controlled by activation of both cooperative and antagonistic signals by vascular endothelial growth factor receptors (VEGFRs). Here, we investigated the contribution of tyrosine-phosphorylated residues of VEGFR-2/fetal liver kinase-1 to endothelial cell proliferation and differentiation and activation of signaling proteins. Mutation of tyrosine 1006 of VEGFR-2 to phenylalanine severely impaired the ability of this receptor to stimulate endothelial cell differentiation and tubulogenesis. Paradoxically, the mutant receptor stimulated endothelial cell proliferation far better than the wild-type receptor. Further analysis showed that tyrosine 1006 is responsible for phospholipase Cgamma1 (PLCgamma1) activation and intracellular calcium release in endothelial cells. Activation of PLCgamma1 was selectively mediated by tyrosine 1006. Mutation of tyrosines 799, 820, 949, 994, 1080, 1173, and 1221 had no measurable effect on the ability of VEGFR-2 to stimulate PLCgamma1 activation. Association of VEGFR-2 with PLCgamma1 was mainly established between tyrosine 1006 and the C-terminal SH2 domain of PLCgamma1 in vitro and in vivo. Taken together, the results indicate that phosphorylation of tyrosine 1006 is essential for VEGFR-2-mediated PLCgamma1 activation, calcium flux, and cell differentiation. More importantly, VEGFR-2-mediated endothelial cell proliferation is inversely correlated with the ability of VEGFR-2 to associate with and activate PLCgamma1. (+info)
Expression of vascular endothelial growth factor isoforms and receptors Flt-1 and KDR during the peri-implantation period in the mink, Mustela vison.
(63/2034)
Expression of vascular endothelial growth factor (VEGF) isoforms and its receptors, Flt-1 and KDR, was investigated during the period of peri-implantation in mink, a species that displays obligate embryonic diapause. Uterine samples were collected during diapause, embryo activation, and implantation from pseudopregnant and anestrous animals and analyzed by semiquantitative reverse transcription polymerase chain reaction and immunohistochemistry. The abundance of mRNA of VEGF isoforms 120, 164, and 188 was highest during late embryo activation and at implantation. VEGF protein was localized to the glandular epithelium at all stages of peri-implantation, whereas the luminal epithelium lacked VEGF reactivity during diapause. Endometrial stroma and luminal and glandular epithelia were positive for VEGF in implanted uteri. The invasive trophoblast cells of the implanting embryo were intensively stained. High levels of VEGF mRNA in pseudopregnant uteri indicates that VEGF upregulation leading to implantation is dependent upon maternal rather than embryonic factors. The abundance of the two receptors, KDR and Flt-1, increased in the uterus during implantation. Low levels of the receptors in pseudopregnant uteri compared with those containing activated or implanted embryos indicates that the embryo regulates receptor expression. These results demonstrate VEGF and VEGF receptor expression during early gestation in mink and suggest that maternal and embryonic input regulates different aspects of the angiogenic process. (+info)
Intravenous administration of human bone marrow stromal cells induces angiogenesis in the ischemic boundary zone after stroke in rats.
(64/2034)
We tested the hypothesis that intravenous infusion of human bone marrow stromal cells (hMSCs) promotes vascular endothelial growth factor (VEGF) secretion, VEGF receptor 2 (VEGFR2) expression and angiogenesis in the ischemic boundary zone (IBZ) after stroke. hMSCs (1x10(6)) were intravenously injected into rats 24 hours after middle cerebral artery occlusion (MCAo). Laser scanning confocal microscopy (LSCM), immunohistochemistry and ELISA were performed to assay angiogenesis and levels of human and rat VEGF in the host brain, respectively. In addition, capillary-like tube formation was measured using mouse brain-derived endothelial cells (MBDECs). Morphological and three dimensional image analyses revealed significant (P<0.05) increases in numbers of enlarged and thin walled blood vessels and numbers of newly formed capillaries at the boundary of the ischemic lesion in rats (n=12) treated with hMSCs compared with numbers in rats (n=12) treated with PBS. ELISA measurements showed that treatment with hMSCs significantly (P<0.05) raised endogenous rat VEGF levels in the IBZ from 10.5+/-1.7 ng/mL in the control group to 17.5+/-1.6 ng/mL in the hMSC-treated group. In addition, treatment with hMSCs increased endogenous VEGFR2 immunoreactivity. In vitro, when MBDECs were incubated with the supernatant obtained from cultured hMSCs, capillary-like tube formation was significantly (P<0.01) induced. However, hMSC-induced capillary-like tube formation was significantly (P<0.01) inhibited when the endothelial cells were incubated with the supernatant from hMSCs in the presence of a neutralizing anti-VEGFR2. These data suggest that treatment of stroke with hMSCs enhances angiogenesis in the host brain and hMSC-enhanced angiogenesis is mediated by increases in levels of endogenous rat VEGF and VEGFR2. (+info)