Issue published June 1, 2000

E ndothelial precursor cells (EPCs) have been identified in adult peripheral blood. We examined whether EPCs could be isolated from umbilical cord blood, a rich source for hematopoietic progenitors, and whether in vivo transplantation of EPCs could modulate postnatal neovascularization. Numerous cell clusters, spindle-shaped and attaching (AT) cells, and cord-like structures developed from culture of cord blood mononuclear cells (MNCs). Fluorescence-trace experiments revealed that cell clusters, AT cells, and cord-like structures predominantly were derived from CD34-positive MNCs (MNC^CD34+). AT cells and cell clusters could be generated more efficiently from cord blood MNCs than from adult peripheral blood MNCs. AT cells incorporated acetylated-LDL, released nitric oxide, and expressed KDR, VE-cadherin, CD31, and von Willebrand factor but not CD45. Locally transplanted AT cells survived and participated in capillary networks in the ischemic tissues of immunodeficient nude rats in vivo. AT cells thus had multiple endothelial phenotypes and were defined as a major population of EPCs. Furthermore, laser Doppler and immunohistochemical analyses revealed that EPC transplantation quantitatively augmented neovascularization and blood flow in the ischemic hindlimb. In conclusion, umbilical cord blood is a valuable source of EPCs, and transplantation of cord blood–derived EPCs represents a promising strategy for modulating postnatal neovascularization.

T he PHSRN sequence of the plasma fibronectin (pFn) cell-binding domain induces human keratinocytes and fibroblasts to invade the naturally serum-free extracellular matricies of sea urchin embryos. The potency of acetylated, amidated PHSRN (Ac-PHSRN-NH₂) is significantly increased, making it more active on a molar basis than the 120-kDa cell-binding domain of pFn. Arginine is important to this activity because PHSAN and PHSEN are inactive, as is a randomized sequence peptide, Ac-HSPNR-NH₂. One treatment with Ac-PHSRN-NH₂ stimulates reepithelialization and contraction of dermal wounds in healing-impaired, obese diabetic C57BL6/KsJ db/db mice. Wound closure is equally rapid in treated db/db and db/+ mice and may be more rapid than in untreated nondiabetic db/+ littermates. In contrast, treatment with either Ac-HSPNR-NH₂ or normal saline (NS) has no effect. Analysis of sectioned db/db wounds shows that, in contrast to treatment with Ac-HSPNR-NH₂ or NS, a single Ac-PHSRN-NH₂ treatment stimulates keratinocyte and fibroblast migration into wounds, enhances fibroplasia and vascularization in the provisional matrix, and stimulates the formation of prominent fibers that may be associated with wound contraction.

R ecent studies indicate that tissue factor (TF) acts in embryogenesis, metastasis, and angiogenesis. Three independent groups showed that targeted disruption of the murine TF (mTF) gene results in 90% lethality of mTF null embryos at embryonic days 9.5–10.5. We have demonstrated that expression of wild-type human TF (hTF) from a minigene rescues the embryonic lethality of mTF null embryos. To investigate the role of TF in embryogenesis, we made mutant hTF minigenes whose products either bound FVII/VIIa at a reduced level or lacked the cytoplasmic domain. Two independent transgenic lines expressing the hTF extracellular domain mutant failed to rescue the embryonic lethality of mTF null embryos, suggesting that FVII/VIIa binding by TF, proteolytic activity by the TF/FVIIa complex, or both were required for embryogenesis. In contrast, two transgenic lines expressing the hTF cytoplasmic domain mutant rescued the embryonic lethality of mTF null embryos, indicating that the cytoplasmic domain of TF was not required for embryogenesis. We propose that TF/FVIIa-dependent extracellular protease activity is required for embryogenesis.

H ypoxia is a well-recognized stimulus for pulmonary blood vessel remodeling and pulmonary hypertension development. One mechanism that may account for these effects is the direct action of hypoxia on the expression of specific genes involved in vascular smooth muscle cell (SMC) proliferation. Previous studies demonstrated that the serotonin (5-hydroxytryptamine; 5-HT) transporter (5-HTT) mediates the mitogenic activity of 5-HT in pulmonary vascular SMCs and is overexpressed during hypoxia. Thus, 5-HT-related mitogenic activity is increased during hypoxia. Here, we report that mice deficient for 5-HTT (5-HTT^–/–) developed less hypoxic pulmonary hypertension and vascular remodeling than paired 5-HTT^+/+ controls. When maintained under normoxia, 5-HTT^–/–-mutant mice had normal hemodynamic parameters, low blood 5-HT levels, deficient platelet 5-HT uptake, and unchanged blood levels of 5-hydroxyindoleacetic acid, a metabolite of 5-HT. After exposure to 10% O₂ for 2 or 5 weeks, the number and medial wall thickness of muscular pulmonary vessels were reduced in hypoxic 5-HTT^–/– mice as compared with wild-type paired controls. Concomitantly, right ventricular systolic pressure was lower and right ventricle hypertrophy less marked in the mutant mice. This occurred despite potentiation of acute hypoxic pulmonary vasoconstriction in the 5-HTT^–/– mice. These data further support a key role of 5-HTT in hypoxia-induced pulmonary vascular SMC proliferation and pulmonary hypertension.

W e used a potent inhibitor of glucosylceramide synthase to test whether substrate deprivation could lower globotriaosylceramide levels in α-galactosidase A (α-gal A) knockout mice, a model of Fabry disease. C57BL/6 mice treated twice daily for 3 days with D-threo-1-ethylendioxyphenyl-2-palmitoylamino-3-pyrrolidino-propanol (D-t-EtDO-P4) showed a concentration-dependent decrement in glucosylceramide levels in kidney, liver, and spleen. A single intraperitoneal injection of D-t-EtDO-P4 resulted in a 55% reduction in renal glucosylceramide, consistent with rapid renal glucosylceramide metabolism. A concentration-dependent decrement in renal and hepatic globotriaosylceramide levels was observed in α-Gal A^– males treated for 4 weeks with D-t-EtDO-P4. When 8-week-old α-Gal A^– males were treated for 8 weeks with 10 mg/kg twice daily, renal globotriaosylceramide fell to below starting levels, consistent with an α-galactosidase A–independent salvage pathway for globotriaosylceramide degradation. Complications observed with another glucosylceramide synthase inhibitor, N-butyldeoxynojirimycin, including weight loss and acellularity of lymphatic organs, were not observed with D-t-EtDO-P4. These data suggest that Fabry disease may be amenable to substrate deprivation therapy.

T he restriction of viral receptors and coreceptors to the basolateral surface of airway epithelial cells has been blamed for the inefficient transfer of viral vectors to the apical surface of this tissue. We now report, however, that differentiated human airway epithelia internalize rAAV type-2 virus efficiently from their apical surfaces, despite the absence of known adeno-associated virus–2 (AAV-2) receptors or coreceptors at these sites. The dramatically lower transduction efficiency of rAAV infection from the apical surface of airway cells appears to result instead from differences in endosomal processing and nuclear trafficking of apically or basolaterally internalized virions. AAV capsid proteins are ubiquitinated after endocytosis, and gene transfer can be significantly enhanced by proteasome or ubiquitin ligase inhibitors. Tripeptide proteasome inhibitors increased persistent rAAV gene delivery from the apical surface >200-fold, to a level nearly equivalent to that achieved with basolateral infection. In vivo application of proteasome inhibitor in mouse lung augmented rAAV gene transfer from undetectable levels to a mean of 10.4 ± 1.6% of the epithelial cells in large bronchioles. Proteasome inhibitors also increased rAAV-2–mediated gene transfer to the liver tenfold, but they did not affect transduction of skeletal or cardiac muscle. These findings suggest that tissue-specific ubiquitination of viral capsid proteins interferes with rAAV-2 transduction and provides new approaches to circumvent this barrier for gene therapy of diseases such as cystic fibrosis.

C yclooxygenase-2 (COX-2; Ptgs2) acts as a tumor promoter in rodent models for colorectal cancer, but its precise role in carcinogenesis remains unclear. We evaluated the contribution of host-derived COX-1 and COX-2 in tumor growth using both genetic and pharmacological approaches. Lewis lung carcinoma (LLC) cells grow rapidly as solid tumors when implanted in C57BL/6 mice. We found that tumor growth was markedly attenuated in COX-2^–/–, but not COX-1^–/– or wild-type mice. Treatment of wild-type C57BL/6 mice bearing LLC tumors with a selective COX-2 inhibitor also reduced tumor growth. A decrease in vascular density was observed in tumors grown in COX-2^–/– mice when compared with those in wild-type mice. Because COX-2 is expressed in stromal fibroblasts of human and rodent colorectal carcinomas, we evaluated COX-2^–/– mouse fibroblasts and found a 94% reduction in their ability to produce the proangiogenic factor, VEGF. Additionally, treatment of wild-type mouse fibroblasts with a selective COX-2 inhibitor reduced VEGF production by 92%.

P arathyroid hormone (PTH) is an effective bone anabolic agent, but it must be administered parenterally. An orally active anabolic agent would provide a valuable alternative for treating osteoporosis. NPS 2143 is a novel, selective antagonist (a “calcilytic”) of the parathyroid cell Ca²⁺ receptor. Daily oral administration of NPS 2143 to osteopenic ovariectomized (OVX) rats caused a sustained increase in plasma PTH levels, provoking a dramatic increase in bone turnover but no net change in bone mineral density. Concurrent oral administration of NPS 2143 and subcutaneous infusion of 17β-estradiol also resulted in increased bone turnover. However, the antiresorptive action of estrogen decreased the extent of bone resorption stimulated by the elevated PTH levels, leading to an increase in bone mass compared with OVX controls or to either treatment alone. Despite the sustained stimulation to the parathyroid gland, parathyroid cells did not undergo hyperplasia. These data demonstrate that an increase in endogenous PTH secretion, induced by antagonism of the parathyroid cell Ca²⁺ receptor with a small molecule, leads to a dramatic increase in bone turnover, and they suggest a novel approach to the treatment of osteoporosis.

I ncreased plasma concentrations of angiotension II (Ang II) have been implicated in atherogenesis. To examine this relationship directly, we infused Ang II or vehicle for 1 month via osmotic minipumps into mature apoE^–/– mice. These doses of Ang II did not alter arterial blood pressure, body weight, serum cholesterol concentrations, or distribution of lipoprotein cholesterol. However, Ang II infusions promoted an increased severity of aortic atherosclerotic lesions. These Ang II–induced lesions were predominantly lipid-laden macrophages and lymphocytes; moreover, Ang II promoted a marked increase in the number of macrophages present in the adventitial tissue underlying lesions. Unexpectedly, pronounced abdominal aortic aneurysms were present in apoE^–/– mice infused with Ang II. Sequential sectioning of aneurysmal abdominal aorta revealed two major characteristics: an intact artery that is surrounded by a large remodeled adventitia, and a medial break with pronounced dilation and more modestly remodeled adventitial tissue. Although no atherosclerotic lesions were visible at the medial break point, the presence of hyperlipidemia was required because infusions of Ang II into apoE^+/+ mice failed to generate aneurysms. These results demonstrate that increased plasma concentrations of Ang II have profound and rapid effects on vascular pathology when combined with hyperlipidemia, in the absence of hemodynamic influences.

C hemokines and IFN-γ function as central regulators of inflammatory responses to vascular injury. Both classes of cytokines are upregulated during restenosis, a response to vascular injury that leads to recurrent atherosclerotic plaque growth, but the relative impact of each class of cytokines remains undetermined. M-T7 is a secreted myxoma viral immunomodulatory glycoprotein that functions both as a species-specific inhibitor of rabbit IFN-γ and as a chemokine-binding protein, interacting with a wide range of C, C-C, and C-X-C chemokines in a species-nonspecific fashion. We wished to (a) assess the efficacy of purified M-T7 protein in inhibiting intimal hyperplasia after angioplasty injury and (b) exploit unique species-specific functions of M-T7 in order to judge the relative importance of each cytokine class on plaque growth. Anesthetized New Zealand white rabbits and Sprague-Dawley rats received either M-T7 or control at the time of arterial angioplasty injury. Histological analysis at 28 days demonstrated significant reductions in intimal hyperplasia with M-T7 treatment in both models, with an associated early inhibition of inflammatory cell invasion. Purified M-T7 protein inhibits intimal hyperplasia after angioplasty injury in a species-nonspecific fashion, thus implicating the chemokine-binding activity as more critical for prevention of plaque growth after vascular injury.

T he induction of tumor-protective immunity against malignancies remains a major challenge in cancer immunotherapy. A novel, humanized anti-ganglioside-GD₂–IL-2 immunocytokine (hu14.18–IL-2) induced CD8⁺ T cells to eradicate established pulmonary metastases of B78-D14 murine melanoma, in a process that required help by CD4⁺ T cells and was mediated by the CD40/CD40 ligand (CD40L) interaction. The anti-tumor effect was diminished in mice deficient in CD4⁺ T-cells. Three lines of evidence show that CD4⁺ T-cell help was mediated by CD40/CD40L interaction but not by endogenous IL-2 production. First, the hu14.18–IL-2–induced anti-tumor response is partially abrogated in C57BL/6J CD40L knockout (KO) mice in contrast to C57BL/6J IL-2 KO animals, in which the immunocytokine was completely effective. Second, partial abrogation of the anti-tumor effect is induced with anti-CD40L antibodies to the same extent as with CD4⁺ T-cell depletion. Third, a complete anti-tumor response induced by hu14.18–IL-2 can be reconstituted in C57BL/6J CD40L KO mice by simultaneous stimulation with an anti-CD40 mAb. These results suggest that help provided by CD4⁺ T cells via CD40/CD40L interactions in our tumor model is crucial for effective immunotherapy with an IL-2 immunocytokine.

T he bioactivity of endothelium-derived nitric oxide (NO) reflects its rates of production and of inactivation by superoxide (O₂^•–), a reactive species dismutated by extracellular superoxide dismutase (ecSOD). We have now examined the complementary hypothesis, namely that NO modulates ecSOD expression. The NO donor DETA-NO increased ecSOD expression in a time- and dose-dependent manner in human aortic smooth muscle cells. This effect was prevented by the guanylate cyclase inhibitor ODQ and by the protein kinase G (PKG) inhibitor Rp-8-CPT-cGMP. Expression of ecSOD was also increased by 8-bromo-cGMP, but not by 8-bromo-cAMP. Interestingly, the effect of NO on ecSOD expression was prevented by inhibition of the MAP kinase p38 but not of the MAP kinase kinase p42/44, suggesting that NO modulates ecSOD expression via cGMP/PKG and p38MAP kinase–dependent pathways, but not through p42/44MAP kinase. In aortas from mice lacking the endothelial nitric oxide synthase (eNOS), ecSOD was reduced more than twofold compared to controls. Treadmill exercise training increased eNOS and ecSOD expression in wild-type mice but had no effect on ecSOD expression in mice lacking eNOS, suggesting that this effect of exercise is meditated by endothelium-derived NO. Upregulation of ecSOD expression by NO may represent an important feed-forward mechanism whereby endothelial NO stimulates ecSOD expression in adjacent smooth muscle cells, thus preventing O₂^•–-mediated degradation of NO as it traverses between the two cell types.

A bdominal aortic aneurysms represent a life-threatening condition characterized by chronic inflammation, destructive remodeling of the extracellular matrix, and increased local expression of matrix metalloproteinases (MMPs). Both 92-kD gelatinase (MMP-9) and macrophage elastase (MMP-12) have been implicated in this disease, but it is not known if either is necessary in aneurysmal degeneration. We show here that transient elastase perfusion of the mouse aorta results in delayed aneurysm development that is temporally associated with transmural mononuclear inflammation, increased local production of several elastolytic MMPs, and progressive destruction of the elastic lamellae. Elastase-induced aneurysmal degeneration was suppressed by treatment with a nonselective MMP inhibitor (doxycycline) and by targeted gene disruption of MMP-9, but not by isolated deficiency of MMP-12. Bone marrow transplantation from wild-type mice prevented the aneurysm-resistant phenotype in MMP-9–deficient animals, and wild-type mice acquired aneurysm resistance after transplantation from MMP-9–deficient donors. These results demonstrate that inflammatory cell expression of MMP-9 plays a critical role in an experimental model of aortic aneurysm disease, suggesting that therapeutic strategies targeting MMP-9 may limit the growth of small abdominal aortic aneurysms.

T o study the roles of Na⁺-dependent H⁺ transporters, we characterized H⁺ efflux mechanisms in the pancreatic duct in wild-type, NHE2^–/–, and NHE3^–/– mice. The pancreatic duct expresses NHE1 in the basolateral membrane, and NHE2 and NHE3 in the luminal membrane, but does not contain NHE4 or NHE5. Basolateral Na⁺-dependent H⁺ efflux in the microperfused duct was inhibited by 1.5 μM of the amiloride analogue HOE 694, consistent with expression of NHE1, whereas the luminal activity required 50 μM HOE 694 for effective inhibition, suggesting that the efflux might be mediated by NHE2. However, disruption of NHE2 had no effect on luminal transport, while disruption of the NHE3 gene reduced luminal Na⁺-dependent H⁺ efflux by ∼45%. Notably, the remaining luminal Na⁺-dependent H⁺ efflux in ducts from NHE3^–/– mice was inhibited by 50 μM HOE 694. Hence, ∼55% of luminal H⁺ efflux (or HCO₃^– influx) in the pancreatic duct is mediated by a novel, HOE 694–sensitive, Na⁺-dependent mechanism. H⁺ transport by NHE3 and the novel transporter is inhibited by cAMP, albeit to different extents. We propose that multiple Na⁺-dependent mechanisms in the luminal membrane of the pancreatic duct absorb Na⁺ and HCO₃^– to produce a pancreatic juice that is poor in HCO₃^– and rich in Cl^– during basal secretion. Inhibition of the transporters during stimulated secretion aids in producing the HCO₃^–-rich pancreatic juice.