Establishment of a functional ovine fetoplacental artery endothelial cell line with a prolonged life span

Differential expression of serum amyloid A1 and A3 in bovine epithelia

Serum amyloid A (SAA) is both an amyloidogenic protein of amyloid A amyloidosis and an acute phase protein in most animal species. Although SAA isoforms, such as SAA1, 2, 3, and 4, have been identified in cattle, their biological functions are not completely understood. Previous studies using mice indicated that SAA3 mRNA expression increased by stimulation with Escherichia coli and lipopolysaccharide (LPS) in colonic epithelial cells, and subsequently the SAA3 protein enhanced the expression of mucin2 (MUC2) mRNA, which is the major component of the colonic mucus layer. These results suggest that SAA3 plays a role in host innate immunity against bacterial infection in the intestine. In this study, a novel anti-bovine SAA3 monoclonal antibody was produced and SAA3 expression levels in bovine epithelia were examined in vitro and in vivo using real-time PCR and immunohistochemistry (IHC). SAA3 mRNA expression, but not that of SAA1, was enhanced by LPS stimulus in bovine small intestinal and mammary glandular epithelial cells in vitro. Moreover, in bovine epithelia (small intestine, mammary gland, lung, and uterus) obtained from four Holstein dairy cows from a slaughterhouse, SAA3 mRNA expression was higher than that of SAA1. Furthermore, using IHC, SAA3 protein expression was observed in bovine epithelia, whereas SAA1 protein was not. These results suggest that in cattle, SAA3 plays an immunological role against bacterial infection in epithelial tissues, including the small intestine, mammary gland, lung, and uterus.

Establishment and characterization of transformed goat primary cells by expression of simian virus 40 large T antigen for orf virus propagations

Due to the limited host range of orf virus (ORFV), primary cells derived from its natural hosts, such as goats and sheep, are recommended for isolation and propagation of wild type ORFV. This situation limits the option for the study of virus-host interaction during ORFV infection since primary cells only support a few numbers of passages. SV40 T antigen is a viral oncoprotein that can abrogate replicative senescence, leading to an extended life span of cells. In this study, the transformation of two goat primary cells, fibroblast (FB) and testis (GT) cells, were achieved by stably expressing SV40 T antigen using the lentiviral technique. The presence of the gene encoding SV40 T antigen was validated by polymerase chain reaction (PCR) and western blot analyses. As evidenced by immunofluorescent microscopy, the two types of cells expressing SV40 T antigen (namely, FBT and GTT) were purified to homogeneity. Moreover, faster growth kinetics and a lower serum dependency were noticed in FBT and GTT, as compared with their counterpart parental cells. FBT and GTT remain permissive and can form plaque of ORFV, despite with different profiles; generally speaking, with SV40 T expression, ORFV forms plaques with smaller size and distinct margin. Most importantly, the prolonged life span of goat FBT and GTT serves as an ideal cell culture resource for ORFV isolation from the field, studies of ORFV pathogenesis and efficient vaccine development.

Immortalization of swine umbilical vein endothelial cells (SUVECs) with the simian virus 40 large-T antigen

Implementation of the swine umbilical vein endothelial cells (SUVECs) model in vitro can be instrumental in determining the biology of endothelial cells. We have generated an immortalized endothelial cell line, G-1410, using Simian virus 40 T-antigen (SV40 T-ag) primarily to overcome the short life span before the onset of senescence and high variability among enzymatically isolated cells of primary cultures. Fast proliferating cells were selected from cultures and, after a fifth passage, examined for the presence of the SV40 T-ag by PCR and immunocytochemistry. Phase contrast and transmission electron microscopy revealed that G-1410 cells did not differ morphologically from SUVECs. The G-1410 cells exhibited positive staining for vascular endothelial (VE)-cadherin and von Willebrand factor (vWF), and formed capillary-like tube structures on Matrigel. Despite the strong oncogenic signal provided by SV40 T-ag, these transformed G-1410 cells have remained karyotypically normal and non-tumorigenic. G-1410 cells also responded to stimulation with VEGF, FGF-2, and newborn calf serum. Moreover, G-1410 cells showed elevated expression of VEGF120, VEGF164 (VEGF-A), and FGF-2 at both mRNA and protein levels. In conclusion, based on the cytological and functional evaluation of the newly obtained immortalized cell line, it can be concluded that G-1410 cells provide a useful tool for studying the effects of VEGF and FGF systems, and other signal transduction pathways related to angiogenesis.

Rac1-dependent intracellular superoxide formation mediates vascular endothelial growth factor-induced placental angiogenesis in vitro

Vascular endothelial growth factor (VEGF) is one of the best characterized angiogenic factors controlling placental angiogenesis; however, how VEGF regulates placental angiogenesis has not yet completely understood. In this study, we found that all the components of assembling a functional NADPH oxidase (NOX2, p22(phox), p47(phox), p67(phox), and Rac1) are expressed in ovine fetoplacental artery endothelial cells (oFPAECs) in vitro and ex vivo. Treatment with VEGF (10 ng/ml) rapidly and transiently activated Rac1 in oFPAECs in vitro and increased Rac1 association with p67(phox) in 5 min. Intracellular superoxide formation began to significantly increase after 25-30 min of VEGF stimulation, which was mediated by both VEGFR1 and VEGFR2. VEGF also stimulated oFPAE cell proliferation and migration and enhanced the formation of tube-like structures on Matrigel matrix. In oFAPEC transfected with specific Rac1 small interfering RNA (siRNA, 40 nm), VEGF-induced intracellular superoxide formation was completely abrogated in association with a 78% reduction of endogenous Rac1. In oFPAE cells transfected with the specific Rac1 siRNA, but not with transfection reagent alone or scrambled control siRNA, VEGF-induced cell proliferation, migration, and tube-like structure formation were dramatically inhibited. Pretreatment of an NADPH oxidase inhibitor apocynin also abrogates the VEGF-stimulated intracellular superoxide production and DNA synthesis in oFPAECs. Taken together, our results demonstrated that a Rac1/Nox2-based NADPH oxidase system is present in placental endothelial cells. This NADPH oxidase system appears to generate the second messenger superoxide that plays a critical role in the signaling control of the VEGF-induced placental angiogenesis.

Suppression of protein phosphatase 2 differentially modulates VEGF- and FGF2-induced signaling in ovine fetoplacental artery endothelial cells

Vascular endothelial growth factor (VEGF) and fibroblast growth factor 2 (FGF2) elicit cellular responses via activation of protein kinases and phosphatases. We have reported that the MEK1/2/ERK1/2 and PI3K/AKT1 pathways are critical for VEGF- and FGF2-stimulated ovine fetoplacental artery endothelial (OFPAE) cell proliferation. We have also shown that protein phosphatase 3 (PPP3) differentially modulates VEGF- and FGF2-stimulated cell proliferation and activation of ERK1/2 and AKT1 in OFPAE cells. Herein, we investigated if protein phosphatase 2 (PPP2) modulated VEGF- and FGF2-induced ERK1/2, AKT1, and p38 MAPK activation and VEGF- and FGF2-stimulated cell proliferation in OFPAE cells. Small interfering RNA (siRNA) specifically targeting human PPP2CA catalytic subunit alpha (PPP2CA) was used to suppress PPP2CA expression in OFPAE cells. When compared with scrambled siRNA, PPP2CA siRNA decreased (p<0.05) PPP2CA protein levels (approximately 70%) and activity (approximately 50%) without altering protein levels of PPP3 catalytic subunit alpha (PPP3CA), nitric oxide synthase 3 (NOS3), ERK1/2, AKT1, and p38 MAPK. FGF2, but not VEGF rapidly (< or =5 min) induced p38 MAPK phosphorylation. Suppression of PPP2CA enhanced (p<0.05) VEGF-induced AKT1, but not ERK1/2 phosphorylation, whereas inhibited (p<0.05) FGF2-induced ERK1/2 and p38 MAPK and slightly attenuated FGF2-induced AKT1 phosphorylation. Suppression of PPP2CA did not significantly affect VEGF- and FGF2-stimulated OFPAE cell proliferation. Thus, suppression of PPP2CA alone differentially modulated VEGF- and FGF2-induced ERK1/2, AKT1, and p38 MAPK activation, without altering VEGF- and FGF2-stimulated cell proliferation in OFPAE cells. These data also suggest that signaling molecules other than ERK1/2, AKT1, and p38 MAPK are important mediators for VEGF- and FGF2-stimulated OFPAE cell proliferation after PPP2CA suppression.

Compartmentalizing VEGF-induced ERK2/1 signaling in placental artery endothelial cell caveolae: a paradoxical role of caveolin-1 in placental angiogenesis in vitro

On vascular endothelial growth factor (VEGF) stimulation, both VEGF R1 and R2 receptors were phosphorylated in ovine fetoplacental artery endothelial (oFPAE) cells. Treatment with VEGF stimulated both time- and dose-dependent activation of ERK2/1 in oFPAE cells. VEGF-induced ERK2/1 activation was mediated by VEGFR2, but not VEGFR1, and was linked to intracellular calcium, protein kinase C, and Raf-1. VEGF stimulated oFPAE cell proliferation, migration, and tube formation in vitro. Blockade of ERK2/1 pathway attenuated VEGF-induced cell proliferation and tube formation but failed to inhibit migration in oFPAE cells. Disruption of caveolae by cholesterol depletion with methyl-beta-cyclodextrin or by down-regulation of its structural protein caveolin-1 blunted VEGF-induced ERK2/1 activation, proliferation, and tube formation in oFPAE cells, indicating an essential role of integral caveolae in these VEGF-induced responses. Adenoviral overexpression of caveolin-1 and addition of a caveolin scaffolding domain peptide also inhibited VEGF-stimulated ERK2/1 activation, cell proliferation, and tube formation in oFPAE cells. Furthermore, molecules comprising the ERK2/1 signaling module, including VEGFR2, protein kinase Calpha, Raf-1, MAPK kinase 1/2, and ERK2/1, resided with caveolin-1 in caveolae. VEGF transiently stimulated ERK2/1 activation in the caveolae similarly as in intact cells. Caveolae disruption greatly diminished ERK2/1 activation by VEGF in oFPAE cell caveolae. We conclude that caveolae function as a platform for compartmentalizing the VEGF-induced ERK2/1 signaling module. Caveolin-1 and caveolae play a paradoxical role in regulating VEGF-induced ERK2/1 activation and in vitro angiogenesis as evidenced by the similar inhibitory effects of down-regulation and overexpression of caveolin-1 and disruption of caveolae in oFPAE cells.

Protein phosphatase 3 differentially modulates vascular endothelial growth factor- and fibroblast growth factor 2-stimulated cell proliferation and signaling in ovine fetoplacental artery endothelial cells

A critical process for vascular endothelial growth factor (VEGF)- and fibroblast growth factor 2 (FGF2)-regulated cellular function is reversible protein phosphorylation, which is tightly controlled by a balance of protein kinases and phosphatases. We have reported that in ovine fetoplacental artery endothelial (OFPAE) cells, VEGF and FGF2 stimulate cell proliferation in part via activation of mitogen-activated protein kinase kinase 1/2 (MAP2K1/2)/mitogen-activated protein kinase 3/1 (MAPK3/1) and phosphoinositide 3-kinase (PI3K)/v-akt murine thymoma viral oncogene homolog 1 (AKT1) pathways. In the present study, we examined if protein phosphatase 3 (PPP3) mediated VEGF- and FGF2-stimulated OFPAE cell proliferation via modulating activation of MAPK3/1 and AKT1. Small interfering RNA (siRNA) targeting human PPP3 catalytic subunit alpha (PPP3CA) was used to suppress PPP3CA protein expression in OFPAE cells. Compared with the scrambled siRNA, PPP3CA siRNA decreased PPP3CA protein levels by approximately 97% without altering protein levels of protein phosphatase 2 catalytic subunit alpha, total MAPK3/1, total AKT1, or glyceraldehyde-3-phosphate dehydrogenase. Knockdown of PPP3CA protein expression enhanced VEGF-stimulated, but not FGF2-stimulated, cell proliferation. Knockdown of PPP3CA protein expression did not significantly affect VEGF-induced MAPK3/1 and AKT1 phosphorylation but attenuated FGF2-induced MAPK3/1 and AKT1 phosphorylation. Thus, to our knowledge, the present study is the first to demonstrate successful knockdown of PPP3CA protein expression in any cell model using a single pair of double-strained siRNA. Moreover, specific knockdown of PPP3CA protein expression enhances VEGF-stimulated, but not FGF2-stimulated, OFPAE cell proliferation and attenuates FGF2-induced, but not VEGF-induced, MAPK3/1 and AKT1 activation. Thus, PPP3CA differentially modulates the VEGF- and FGF2-stimulated cell proliferation and signaling cascades in OFPAE cells. These data also suggest that signaling molecules other than MAPK3/1 and AKT1 play an important role in VEGF- and FGF2-stimulated cell proliferation after knockdown of PPP3CA in OFPAE cells.