Endoglin is required in Pax3-derived cells for embryonic blood vessel formation

Mutations in endoglin, a TGFβ/BMP coreceptor, are causal for hereditary hemorrhagic telangiectasia (HHT). Endoglin-null (Eng-/-) mouse embryos die at embryonic day (E)10.5-11.5 due to defects in angiogenesis. In part, this is due to an absence of vascular smooth muscle cell differentiation and vessel investment. Prior studies from our lab and others have shown the importance of endoglin expression in embryonic development in both endothelial cells and neural crest stem cells. These studies support the hypothesis that endoglin may play cell-autonomous roles in endothelial and vascular smooth muscle cell precursors. However, the requirement for endoglin in vascular cell precursors remains poorly defined. Our objective was to specifically delete endoglin in neural crest- and somite-derived Pax3-positive vascular precursors to understand the impact on somite progenitor cell contribution to embryonic vascular development. Pax3Cre mice were crossed with Eng+/- mice to obtain compound mutant Pax3(Cre/+);Eng+/- mice. These mice were then crossed with homozygous endoglin LoxP-mutated (Eng(LoxP/LoxP)) mice to conditionally delete the endoglin gene in specific lineages that contribute to endothelial and smooth muscle constituents of developing embryonic vessels. Pax3(Cre/+);Eng(LoxP/)(-) mice showed a variety of vascular defects at E10.5, and none of these mice survived past E12.5. Embryos analyzed at E10.5 showed malformations suggestive of misdirection of the intersomitic vessels. The dorsal aorta showed significant dilation with associated vascular smooth muscle cells exhibiting disorganization and enhanced expression of smooth muscle differentiation proteins, including smooth muscle actin. These results demonstrate a requirement for endoglin in descendants of Pax3-expressing vascular cell precursors, and thus provides new insight into the cellular basis underlying adult vascular diseases such as HHT.

Osteopontin regulates renal apoptosis and interstitial fibrosis in neonatal chronic unilateral ureteral obstruction

Congenital obstructive nephropathy is a major cause of renal insufficiency in children. Osteopontin (OPN) is a phosphoprotein produced by the kidney that mediates cell adhesion and migration. We investigated the role of OPN in the renal response to unilateral ureteral obstruction (UUO) in neonatal mice. OPN null mutant (-/-) and wild-type (+/+) mice were subjected to sham operation or UUO within the first 2 days of life. At 7 and 21 days of age, fibroblasts (fibroblast-specific protein (FSP)-1), myofibroblasts (alpha-smooth muscle actin (SMA)), and macrophages (F4/80) were identified by immunohistochemical staining. Apoptotic cells were detected by terminal deoxy transferase uridine triphosphate nick end-labeling technique and interstitial collagen by Masson trichrome or picrosirius red stain. Compared to sham-operated or contralateral kidneys, obstructed kidneys showed increases in all parameters by 7 days, with further increases by 21 days. After 21 days UUO, there was an increase in tubular and interstitial apoptosis in OPN -/- mice as compared to +/+ animals (P<0.05). However, FSP-1- and alpha-SMA-positive cells and collagen in the obstructed kidney were decreased in OPN -/- compared to +/+ mice (P<0.05), whereas the interstitial macrophage population did not differ between groups. We conclude that OPN plays a significant role in the recruitment and activation of interstitial fibroblasts to myofibroblasts in the progression of interstitial fibrosis in the developing hydronephrotic kidney. However, OPN also suppresses apoptosis. Future approaches to limit the progression of obstructive nephropathy in the developing kidney will require targeting of specific renal compartments.

Abnormal pulmonary granuloma formation in osteopontin-deficient mice

Osteopontin is a novel cytokine that is expressed in pulmonary granulomatous disease such as sarcoidosis and tuberculosis. It can regulate macrophage and T cell migration, activation, and cytokine expression, yet its role in granuloma formation and evolution is unknown. We induced hypersensitivity pulmonary granulomas by embolizing Schistosoma mansoni eggs to the lungs of osteopontin-deficient (null mutant) mice and osteopontin-sufficient (wild-type control) mice. Granulomas from osteopontin-null animals were smaller at early time points and contained remarkably few macrophages and macrophage-derived epithelioid cells and giant cells. T cell accumulation was unaffected by osteopontin deficiency. These results demonstrate that osteopontin regulates macrophage accumulation during pulmonary granuloma formation, and may explain the impaired ability of osteopontin-deficient hosts to control mycobacterial disease.

Osteopontin is involved in the initiation of cutaneous contact hypersensitivity by inducing Langerhans and dendritic cell migration to lymph nodes

Osteopontin (OPN) is a chemotactic protein that attracts immune cells, to inflammatory sites. The sensitization phase of allergic cutaneous contact hypersensitivity (CHS) requires the migration of Langerhans cells/dendritic cells (LCs/DCs) from skin to draining lymph nodes. Characterizing OPN function for LC/DC migration we found upregulated OPN expression in hapten sensitized skin and draining lymph nodes. OPN induces chemotactic LC/DC migration, initiates their emigration from the epidermis, and attracts LCs/DCs to draining lymph nodes by interacting with CD44 and alphav integrin. Furthermore, OPN-deficient mice have a significantly reduced CHS response that correlates with an impaired ability of OPN-deficient mice to attract LCs/DCs to draining lymph nodes. In conclusion, OPN is an important factor in the initiation of CHS by guiding LCs/DCs from skin into lymphatic organs.

Members of the Jagged/Notch gene families are expressed in injured arteries and regulate cell phenotype via alterations in cell matrix and cell-cell interaction

The Jagged/Notch signaling pathways control cell fate determination and differentiation, and their dysfunction is associated with human pathologies involving cardiovascular abnormalities. To determine the presence of these genes during vascular response to injury, we analyzed expression of Jagged1, Jagged2, and Notch1 through 4 after balloon catheter denudation of the rat carotid artery. Although low levels of Jagged1, Jagged2, and constitutive expression of Notch1 were seen in uninjured endothelium, expression of all was significantly increased in injured vascular cells. High Jagged1 expression was restricted to the regenerating endothelial wound edge, whereas Notch transcripts were abundant in endothelial and smooth muscle cells. To understand the basis for Jagged/Notch control of cellular phenotype, we studied an in vitro model of NIH3T3 cells transfected with a secreted form of the extracellular domain of Jagged1. We report that the soluble Jagged1 protein caused decreased cell-matrix adhesion and cell migration defects. Cadherin-mediated intercellular junctions as well as focal adhesions were modified in soluble Jagged1 transfectants, demonstrating that cell-cell contacts and adhesion plaques may be targets of Jagged/Notch activity. We suggest that Jagged regulation of cell-cell and cell-matrix interactions may contribute to the control of cell migration in situations of tissue remodeling in vivo.

Soluble Jagged 1 represses the function of its transmembrane form to induce the formation of the Src-dependent chord-like phenotype

We have previously demonstrated that the expression of the soluble extracellular domain of the transmembrane ligand for Notch receptors, Jagged 1 (sJ1), in NIH 3T3 cells results in the formation of a matrix-dependent chord-like phenotype, the loss of contact inhibition of growth, and an inhibition of pro-alpha 1(I) collagen expression. In an effort to define the mechanism by which sJ1 induces this phenotype, we report that sJ1 transfectants display biochemical and cytoskeletal alterations consistent with the activation of Src. Indeed, cotransfection of sJ1 transfectants with a dominant-negative mutant of Src resulted in the loss of matrix-dependent chord formation and correlated with the restoration of type I collagen expression and contact inhibition of growth. We also report that the sJ1-mediated induction of Src activity and related phenotypes, including chord formation, may result from the inhibition of endogenous Jagged 1-mediated Notch signaling since it was not possible to detect an sJ1-dependent induction of CSL-dependent transcription in these cells. Interestingly, NIH 3T3 cells transfected with dominant-negative (but not constitutively active) mutants of either Notch 1 or Notch 2 displayed a similar Src-related phenotype as the sJ1 transfectants. These data suggest that the ability of sJ1 to mediate chord formation is Src-dependent and requires the repression of endogenous Jagged 1-mediated Notch signaling, which is tolerant to the destabilization of the actin cytoskeleton, a mediator of cell migration.

Exaggerated left ventricular dilation and reduced collagen deposition after myocardial infarction in mice lacking osteopontin

Osteopontin (OPN), an extracellular matrix protein, is expressed in the myocardium with hypertrophy and failure. We tested the hypothesis that OPN plays a role in left ventricular (LV) remodeling after myocardial infarction (MI). Accordingly, OPN expression and LV structural and functional remodeling were determined in wild-type (WT) and OPN knockout (KO) mice 4 weeks after MI. Northern analysis showed increased OPN expression in the infarcted region, peaking 3 days after MI and gradually decreasing over the next 28 days. In the remote LV, OPN expression was biphasic, with peaks at 3 and 28 days. In situ hybridization and immunohistochemical analyses showed increased OPN mRNA and protein primarily in the interstitium. Infarct size, heart weight, and survival were similar in KO and WT mice after MI (P=NS), whereas the lung wet weight/dry weight ratio was increased in the KO mice (P<0.005 versus sham-operated mice). Peak LV developed pressure was reduced to a similar degree after MI in the KO and WT mice. The number of terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling (TUNEL)-positive myocytes was similar in KO and WT mice after MI. In contrast, post-MI LV chamber dilation was approximately twice as great in KO versus WT mice (P<0.001). Myocyte length increased after MI in WT mice (P<0.001) but not in KO mice. Electron microscopy showed increased collagen content in WT mice after MI but not in KO mice after MI. Type I collagen content was increased approximately 3-fold and approximately 7-fold in remote and infarcted regions, respectively, of WT hearts after MI but not in KO hearts (P<0.01 versus WT hearts). Likewise, Northern analyses showed increased collagen I(alpha(1)) mRNA after MI in remote regions of WT hearts but not in KO hearts. Thus, increased OPN expression plays an important role in regulating post-MI LV remodeling, at least in part, by promoting collagen synthesis and accumulation.

Osteopontin, a novel substrate for matrix metalloproteinase-3 (stromelysin-1) and matrix metalloproteinase-7 (matrilysin)

Osteopontin (OPN) is a secreted phosphoprotein shown to function in wound healing, inflammation, and tumor progression. Expression of OPN is often co-localized with members of the matrix metalloproteinase (MMP) family. We report that OPN is a novel substrate for two MMPs, MMP-3 (stromelysin-1) and MMP-7 (matrilysin). Three cleavage sites were identified for MMP-3 in human OPN, and two of those sites were also cleaved by MMP-7. These include hydrolysis of the human Gly166-Leu167, Ala201-Tyr202 (MMP-3 only), and Asp210-Leu211 peptide bonds. Only the N-terminal Gly-Leu cleavage site is conserved in rat OPN (Gly151-Leu152). These sites are distinct from previously reported cleavage sites in OPN for the proteases thrombin or enterokinase. We found evidence for the predicted MMP cleavage fragments of OPN in vitro in tumor cell lines, and in vivo in remodeling tissues such as the postpartum uterus, where OPN and MMPs are co-expressed. Furthermore, cleavage of OPN by MMP-3 or MMP-7 potentiated the function of OPN as an adhesive and migratory stimulus in vitro through cell surface integrins. We predict that interaction of MMPs with OPN at tumor and wound healing sites in vivo may be a mechanism of regulation of OPN bioactivity.

IL-8 and MCP-1 secretion is enhanced by the peptide-nucleic acid immunomodulator, Product R, in U937 cells and primary human monocytes

Product R (Reticulose) is a peptide-nucleic acid immunomodulator recently shown to enhance the expression of mRNAs encoding pro-inflammatory cytokines. Interleukin 8 (IL-8) and macrophage chemoattractant protein-1 (MCP-1) are pro-inflammatory chemokines involved in immune cell mobilization and stimulation. To determine whether Product R acts by upregulating these chemokines, we assayed its effects on the expression of IL-8 and MCP-1 mRNAs and proteins by human monocytic U937 cells and by adherent peripheral blood mononuclear cells (PBMCs). U937 cells were cultured for 0-21 days in media containing 0-20% Product R or phosphate-buffered saline (PBS). Compared to control cultures, cells cultured in Product R expressed increased amounts of IL-8 and MCP-1 mRNAs, as measured by reverse transcriptase-polymerase chain reaction (RT-PCR). Product R also increased secretion of IL-8 and MCP-1, as measured by enzyme-linked immunosorbent assay (ELISA), and boosted secretion induced by bacterial lipopolysaccharide (LPS), in a time- and dose-dependent manner. In adherent PBMCs, Product R increased IL-8 and MCP-1 secretion, but reduced LPS-induced MCP-1 secretion. While mRNAs encoding the IL-8 receptor, CXCR2, and the MCP-1 receptor, CCR2, were increased in U937 cells cultured in 5-10% Product R, we observed no change in binding of receptor-specific antibodies. These findings suggest that Product R upregulates the expression of IL-8 and MCP-1, which may boost immune system activity in virally-infected patients.

Pathophysiology of and prophylaxis against late ahmed glaucoma valve occlusion

PURPOSE

To understand the pathophysiology of late Ahmed Glaucoma Valve failures and devise strategies to minimize this problem.

METHODS

One hundred sixty eyes that had undergone Ahmed Glaucoma Valve implants by one surgeon were retrospectively reviewed. Six eyes with late (greater than 3 months) Ahmed Glaucoma Valve occlusion requiring operative intervention were identified. Two of these eyes underwent initial successful transcameral drainage tube irrigation and four initially required Ahmed Glaucoma Valve exchange. Intraoperative images, postoperative histologic analysis, and Ahmed Glaucoma Valve handling experiments were performed.

RESULTS

Two eyes with late occlusion (33%; 1.25% of total implants) were initially successfully treated with irrigation alone. A gap between the valve cover and valve body junction allowed fibrovascular ingrowth and produced valve failure ultimately in five of six eyes (83%; 3.1% of total implants). This gap could be produced by grasping the device along the center line, indenting the valve cover, and damaging the plastic rivets attaching the valve cover to the valve body. Handling the Ahmed Glaucoma Valve outside this "no touch zone" eliminated this problem.

CONCLUSIONS

Leaflet adhesion has a low incidence and may be treated by transcameral drainage tube irrigation. Late onset distal occlusion is best treated by Ahmed Glaucoma Valve exchange with respect for the "no touch zone." Respecting the "no touch zone over the valve mechanism should avoid creation of gaps between the valve cover and valve body junction, which allow secondary fibrovascular ingrowth.

A non-transmembrane form of Jagged-1 regulates the formation of matrix-dependent chord-like structures

Jagged-Notch interactions regulate a transmembrane ligand-receptor signaling pathway involved in the regulation of cell fate determination as well as myoblast and endothelial cell differentiation. To further examine the role of the transmembrane ligand, Jagged-1, in the regulation of cell differentiation, we stably transfected NIH 3T3 cells with a truncated form of Jagged(J)-1, which results in the secretion of a soluble(s) form of the protein. Comparison of gene expression by serial analysis demonstrated that among the 227 transcripts differentially regulated in the sJ-1 transfectants, the expression of the pro-alpha-2(I) collagen transcript and pro-alpha-1(I) collagen translation product was predominantly repressed in sJ-1 transfectants. When plated on extracellular matrices, sJ-1 transfectants formed prominent chord-like structures on type I collagen but not on fibrin, fibronectin, or vitronectin. While the sJ-1 transfectants exhibited growth kinetics similar to control cells and were unable to grow in soft agar, the cells were less sensitive to contact inhibition of growth in vitro and sJ-1 allografts formed tissue masses in nude mice after a prolonged latency period and exhibited an abundance of host-derived microvascular endothelial cells. These data suggest that J-1 may be able to modulate, in a matrix-dependent manner, the organization of cell to cell interactions including its ability to promote the development of chord-like structures.

Obstructive uropathy in the mouse: role of osteopontin in interstitial fibrosis and apoptosis

BACKGROUND

Osteopontin is a macrophage adhesive protein that is expressed by renal tubules in tubulointerstitial disease.

METHODS

To investigate the function of OPN, we induced tubulointerstitial disease in OPN null mutant (OPN-/-) and wild-type (OPN+/+) mice by unilateral ureteral ligation. Tissue was analyzed for macrophages (ED-1), types I and IV collagen deposition, TGF-beta expression, and for tubular and interstitial cell apoptosis.

RESULTS

Obstructed kidneys from both OPN-/- and OPN+/+ mice developed hydronephrosis, tubular atrophy, interstitial inflammation and fibrosis. OPN was absent in OPN-/- kidneys but was increased in obstructed OPN+/+ kidneys. Macrophage influx, measured by computer-assisted quantitative immunostaining, was less in OPN-/- mice compared to OPN+/+ mice at day 4 (threefold, P < 0.02), day 7 (fivefold, P < 0.02), but not at day 14. Interstitial deposition of types I and IV collagen were also two- to fourfold less in obstructed OPN-/- kidneys (P < 0.02). There was also a reduction of TGF-beta mRNA expression in the interstitium at day 7 (by in situ hybridization) and a near significant 34% reduction in cortical TGF-beta activity (P = 0.06) compared to obstructed OPN+/+ kidneys at day 14. Obstructed kidneys from OPN-/- mice also had more interstitial and tubular apoptotic cells (TUNEL assay) compared to obstructed OPN+/+ mice at all time points. The ability of OPN to act as a cell survival factor was also documented by showing that the apoptosis of serum-starved NRK52E renal epithelial cells was markedly enhanced in the presence of neutralizing anti-OPN antibody.

CONCLUSION

OPN mediates early interstitial macrophage influx and interstitial fibrosis in unilateral ureteral obstruction. OPN may also function as a survival factor for renal tubulointerstitial cells.

Attenuated host resistance against Mycobacterium bovis BCG infection in mice lacking osteopontin

Expression of the cytokine osteopontin (OPN) is elevated in granulomas caused by Mycobacterium tuberculosis. We tested the hypothesis that OPN contributes to host protection in a mouse model of mycobacterial infection. When infected with Mycobacterium bovis BCG, mice lacking a functional OPN gene had more severe infections characterized by heavier bacterial loads and a delayed clearance of the bacteria. The OPN-null mice had greater granuloma burdens consistent with the elevated bacterial load. The ability of osteopontin to facilitate the clearance of mycobacteria was most pronounced early after infection and appeared to be independent of known mediators of resistance to infection by mycobacteria: antigen-specific T-cell immunity, gamma interferon production, and nitric oxide production. BCG grew more rapidly in macrophages derived from OPN-null mice than in those from wild-type mice, demonstrating that the null phenotype was due to an intrinsic macrophage defect. These results indicate that osteopontin augments the host response against a mycobacterial infection and that it acts independently from other antimycobacterial resistance mechanisms.

Functions of the extracellular matrix and matrix degrading proteases during tumor progression

Cell interactions with extracellular matrices are important to pathological changes that occur during cell transformation and tumorigenesis. Several extracellular matrix proteins including fibronectin, thrombospondin-1, laminin, SPARC, and osteopontin have been suggested to modulate tumor phenotype by affecting cell migration, survival, or angiogenesis. Likewise, proteases including the matrix metalloproteinases (MMPs) are understood to not only facilitate migration of cells by degradation of matrices, but also to affect tumor formation and growth. We have recently demonstrated an in vivo role for the RGD-containing protein, osteopontin, during tumor progression, and found evidence for distinct functions in the host versus the tumor cells. Because of the compartmentalization and temporal regulation of MMP expression, it is likely that MMPs may also function dually in host stroma and the tumor cell. In addition, an important function of proteases appears to be not only degradation, but also cleavage of matrix proteins to generate functionally distinct fragments based on receptor binding, biological activity, or regulation of growth factors.

Del1 induces integrin signaling and angiogenesis by ligation of alphaVbeta3

Del1 is a novel extracellular matrix protein encoding three Notch-like epidermal growth factor repeats, an RGD motif, and two discoidin domains. Del1 is expressed in an endothelial cell-restricted pattern during early development. In studies reported here, recombinant baculovirus Del1 protein was shown to promote alphavbeta3-dependent endothelial cell attachment and migration. Attachment of endothelial cells to Del1 was associated with clustering of alphavbeta3, the formation of focal complexes, and recruitment of talin and vinculin into these complexes. These events were shown to be associated with phosphorylation of proteins in the focal complexes, including the time-dependent phosphorylation of p125(FAK), MAPK, and Shc. When recombinant Del1 was evaluated in an in ovo chick chorioallantoic membrane assay, it was found to have potent angiogenic activity. This angiogenic activity was inhibited by a monoclonal antibody directed against alphavbeta3, and an RAD mutant Del1 protein was inactive. Thus Del1 provides a unique autocrine angiogenic pathway for the embryonic endothelium, and this function is mediated in part by productive ligation of integrin alphavbeta3.

Distinct roles of osteopontin in host defense activity and tumor survival during squamous cell carcinoma progression in vivo

Secreted phosphoprotein 1 (spp1), the gene encoding osteopontin (OPN), is expressed in many human carcinomas, although its in vivo functions remain unclear. To delineate the role of OPN during tumor progression, we have subjected OPN null mutant mice to repeated applications of a mutagen/carcinogen to induce cutaneous squamous cell carcinoma. OPN null animals exhibited accelerated tumor growth and progression and had a greater number of metastases per animal compared with wild-type animals. However, metastases in the OPN null animals were significantly smaller than in controls. When injected into nude mice, the growth of OPN null tumor lines and the same lines engineered to reexpress spp1 recapitulated the growth differences observed in the progression study. These differences in tumor growth inversely correlated with the degree of macrophage infiltration. Slower-growing, OPN-producing tumors contained significantly more macrophages, although a higher proportion were mannose receptor positive, a characteristic of differentiated resting macrophages. In vitro, OPN null cell lines displayed decreased survival at clonal density compared with OPN-producing lines, an observation consistent with the smaller metastases of the OPN null mice. Overall, we provide evidence for a model where host-derived OPN acts as a macrophage chemoattractant, whereas tumor-derived OPN is able to inhibit macrophage function and enhances the growth or survival of metastases.

Altered wound healing in mice lacking a functional osteopontin gene (spp1)

Osteopontin (OPN) is an arginine-glycine-aspartate (RGD)- containing glycoprotein encoded by the gene secreted phosphoprotein 1 (spp1). spp1 is expressed during embryogenesis, wound healing, and tumorigenesis; however, its in vivo functions are not well understood. Therefore, OPN null mutant mice were generated by targeted mutagenesis in embryonic stem cells. In OPN mutant mice, embryogenesis occurred normally, and mice were fertile. Since OPN shares receptors with vitronectin (VN), we tested for compensation by creating mice lacking both OPN and VN. The double mutants were also viable, suggesting that other RGD-containing ligands replace the embryonic loss of both proteins. We tested the healing of OPN mutants after skin incisions, where spp1 was upregulated as early as 6 h after wounding. Although the tensile properties of the wounds were unchanged, ultrastructural analysis showed a significantly decreased level of debridement, greater disorganization of matrix, and an alteration of collagen fibrillogenesis leading to small diameter collagen fibrils in the OPN mutant mice. These data indicate a role for OPN in tissue remodeling in vivo, and suggest physiological functions during matrix reorganization after injury.

Altered wound healing in mice lacking a functional osteopontin gene (spp1)

Osteopontin (OPN) is an arginine-glycine-aspartate (RGD)- containing glycoprotein encoded by the gene secreted phosphoprotein 1 (spp1). spp1 is expressed during embryogenesis, wound healing, and tumorigenesis; however, its in vivo functions are not well understood. Therefore, OPN null mutant mice were generated by targeted mutagenesis in embryonic stem cells. In OPN mutant mice, embryogenesis occurred normally, and mice were fertile. Since OPN shares receptors with vitronectin (VN), we tested for compensation by creating mice lacking both OPN and VN. The double mutants were also viable, suggesting that other RGD-containing ligands replace the embryonic loss of both proteins. We tested the healing of OPN mutants after skin incisions, where spp1 was upregulated as early as 6 h after wounding. Although the tensile properties of the wounds were unchanged, ultrastructural analysis showed a significantly decreased level of debridement, greater disorganization of matrix, and an alteration of collagen fibrillogenesis leading to small diameter collagen fibrils in the OPN mutant mice. These data indicate a role for OPN in tissue remodeling in vivo, and suggest physiological functions during matrix reorganization after injury.

Altered wound healing in mice lacking a functional osteopontin gene (spp1)

Osteopontin (OPN) is an arginine-glycine-aspartate (RGD)- containing glycoprotein encoded by the gene secreted phosphoprotein 1 (spp1). spp1 is expressed during embryogenesis, wound healing, and tumorigenesis; however, its in vivo functions are not well understood. Therefore, OPN null mutant mice were generated by targeted mutagenesis in embryonic stem cells. In OPN mutant mice, embryogenesis occurred normally, and mice were fertile. Since OPN shares receptors with vitronectin (VN), we tested for compensation by creating mice lacking both OPN and VN. The double mutants were also viable, suggesting that other RGD-containing ligands replace the embryonic loss of both proteins. We tested the healing of OPN mutants after skin incisions, where spp1 was upregulated as early as 6 h after wounding. Although the tensile properties of the wounds were unchanged, ultrastructural analysis showed a significantly decreased level of debridement, greater disorganization of matrix, and an alteration of collagen fibrillogenesis leading to small diameter collagen fibrils in the OPN mutant mice. These data indicate a role for OPN in tissue remodeling in vivo, and suggest physiological functions during matrix reorganization after injury.

Bone morphogenetic protein 8A plays a role in the maintenance of spermatogenesis and the integrity of the epididymis

The murine Bmp8a and Bmp8b genes are tightly linked on mouse chromosome 4 and have similar expression during reproduction. Previous studies have shown that targeted mutagenesis of Bmp8b causes male infertility due to germ cell degeneration. To investigate the function of Bmp8a, we have inactivated the gene by homologous recombination. Heterozygous and homozygous Bmp8a mutants reveal normal embryonic and postnatal development. Despite high levels of Bmp8a expression in the deciduum, homozygous mutant females have normal fertility, suggesting that the gene is not essential for female reproduction. Bmp8a and Bmp8b are expressed in similar patterns in male germ cells. Unlike homozygous Bmp8btm1 mutants, homozygous Bmp8atm1 males do not show obvious germ cell defects during the initiation of spermatogenesis. However, germ cell degeneration is observed in 47% of adult homozygous Bmp8atm1 males, establishing a role of Bmp8a in the maintenance of spermatogenesis. A small proportion of the mating homozygous Bmp8atm1 males also show degeneration of the epididymal epithelium, indicating a novel role for BMPs in the control of epididymal function.

cDNA cloning of three cecropin-like antimicrobial peptides (Styelins) from the tunicate, Styela clava

We cloned precursors of three new antimicrobial peptides, Styelins C, D and E, from a pharyngeal cDNA library of a tunicate, Styela clava. Preprostyelins resembled dipteran preprocecropins, while the mature domain of Styelin C resembled Cecropin P1, an antimicrobial peptide purified from the porcine intestine. Beginning with the last 6 residues of their signal sequences, Styelin C and Cecropin 1 from Drosophila virilis had 8/11 identical amino acids (72.7%). Moreover, 4 of the last 6 residues of their mature peptide domains were also identical. Styelins were shorter, by 8 residues, than dipteran cecropins and preprostyelins contained a conserved, polyanionic C-terminal extension that was absent in preprocecropins. Delineation of cecropin-like antimicrobial peptides in a protochordate supports the antiquity of this family as effectors of innate immunity in animals and it increases the likelihood that additional cecropin-like peptides will be found among other evolutionary descendants of protochordates--vertebrates.

cDNA cloning of Clavanins: antimicrobial peptides of tunicate hemocytes

Clavanins are a family of alpha-helical antimicrobial peptides found in hemocytes of the tunicate, Styela clava. We examined a cDNA library prepared from pharyngeal tissues of S. clava and sequenced 24 clones that encoded prepropeptides of Clavanins A, C, D or E. These sequences indicated that Clavanins are synthesized as 9.2 kDa prepropeptides which contain a 19-residue signal peptide, followed in turn by a highly polar 'pro' region (LEERKSEEEK) with five glutamic acid residues, the 23 residues of the mature Clavanin peptide, the glycine residue needed for its amidation and a 27-residue polar C-terminal extension that is removed in later processing. Although the signal sequence and anionic propiece of Clavanin precursors share features with corresponding regions in precursors of the certain frog peptides, including ranalexin, gaegurins, dermaseptins and deltorphins, their unique multipartite structure suggests that they are not actually homologues of these amphibian peptides.

Neutralizing antibodies directed against osteopontin inhibit rat carotid neointimal thickening after endothelial denudation

Osteopontin is an arginine-glycine-aspartate-containing acidic glycoprotein with adhesive and migratory activities in vitro. We previously showed that osteopontin was highly expressed in injured rat arteries as well as in human atherosclerotic plaques. In contrast, uninjured blood vessels make very little osteopontin. In this report, we have investigated the role of osteopontin in rat neointima formation using neutralizing antibodies. Rats were treated with either nonimmune or antiosteopontin antibody and subjected to endothelial denudation of the carotid artery by using a balloon catheter. Two weeks after injury, intimal areas and cell numbers were significantly decreased (33% and 31%, respectively) in the antiosteopontin group compared with the nonimmune IgG group. No differences in carotid medial areas or cell numbers were observed. Intimal and medial replication rates, as measured by continuous bromodeoxyuridine infusion during the final week of the experimental protocol, were not significantly different between the two groups. No gross histological changes were noted in the intimas formed in the presence of either neutralizing or nonimmune antibody. In addition, no difference in early carotid medial cell replication rate was observed when antibodies were infused for 4 days after angioplasty. These data demonstrate for the first time a functional role for osteopontin in the process of carotid neointimal thickening in vivo and suggest that osteopontin plays an active role in the remodeling processes important for human atherosclerotic and restenotic lesion development.

The gene encoding bone morphogenetic protein 8B is required for the initiation and maintenance of spermatogenesis in the mouse

Bone morphogenetic protein 8B (BMP8B) is a member of the TGFbeta superfamily of growth factors. In the mouse, Bmp8b is expressed in male germ cells of the testis and trophoblast cells of the placenta, suggesting that it has a role in spermatogenesis and reproduction. To investigate these possibilities, we have generated mice with a targeted mutation in Bmp8b. Here, we show that homozygous Bmp8b(tm1blh) mutant males exhibit variable degrees of germ-cell deficiency and infertility. Detailed analysis reveals two separable defects in the homozygous mutant testes. First, during early puberty (2 weeks old or younger) the germ cells of all homozygous mutants either fail to proliferate or show a marked reduction in proliferation and a delayed differentiation. Second, in adults, there is a significant increase in programmed cell death (apoptosis) of spermatocytes, leading to germ-cell depletion and sterility. Sertoli cells and Leydig cells appear relatively unaffected in mutants. This study therefore provides the first genetic evidence that a murine germ cell-produced factor, BMP8B, is required for the resumption of male germ-cell proliferation in early puberty, and for germ-cell survival and fertility in the adult.

Osteopontin and beta 3 integrin are coordinately expressed in regenerating endothelium in vivo and stimulate Arg-Gly-Asp-dependent endothelial migration in vitro

Osteopontin is an Arg-Gly-Asp (RGD)-containing acidic glycoprotein postulated to mediate cellular adhesion and migration in a growing number of normal and pathological conditions through interaction with integrin molecules. In this report, we have investigated the potential contributions of osteopontin and one of its receptors, the alpha v beta 3 integrin, to endothelial regenerative processes by using both in vivo and in vitro models. In vivo, uninjured rat arterial endothelium had undetectable levels of osteopontin and beta 3-integrin mRNA by in situ hybridization. After balloon catheter denudation, osteopontin mRNA levels correlated temporally and spatially with active endothelial proliferation and migration, with the highest levels observed at the wound edge between 8 hours and 2 weeks after injury, declining to uninjured levels at 6 weeks, when regeneration was complete. Osteopontin protein levels, as determined by immunocytochemistry, paralleled the time course of mRNA expression. Likewise, beta 3-integrin mRNA and protein levels were substantially elevated in regenerating endothelial cells but were not detectable in uninjured or healed endothelium. In vitro, rat smooth muscle cell-derived and bacterial expressed mouse recombinant osteopontins both stimulated the adhesion and directed migration of bovine aortic endothelial cells through interactions with the alpha v beta 3 receptor. Structural mutants of osteopontin confirmed the importance of the RGD domain for both adhesion and migration of endothelial cells through alpha v beta 3. These data suggest important roles for osteopontin and beta 3 integrin in regenerating endothelium.

Osteopontin expression in cardiovascular diseases

Adhesive interactions are recognized requirements for cellular proliferation, migration and differentiation during normal morphogenesis as well as disease. By differential cloning, osteopontin was identified as an adhesive protein upregulated during vascular remodeling and neointima formation in both rat models and human vascular diseases including atherosclerosis and restenosis. In functional studies, purified osteopontin promoted adhesion, focal contact formation, and migration of vascular smooth muscle and endothelial cells. Utilizing neutralizing antibodies, three integrin-type receptors, alpha v beta 3, alpha v beta 1, and alpha v beta 5 were found to support cellular adhesion to osteopontin. In contrast, only cells containing the alpha v beta 3 integrin could migrate towards an osteopontin gradient, demonstrating for the first time that different functions of osteopontin are mediated via distinct receptors. These results suggest a model whereby osteopontin, via its integrin-type receptors, contributes to vascular remodeling during development and disease by facilitating smooth muscle migration and simultaneously promoting endothelial coverage of the affected area.

The adhesive and migratory effects of osteopontin are mediated via distinct cell surface integrins. Role of alpha v beta 3 in smooth muscle cell migration to osteopontin in vitro

Osteopontin is an arginine-glycine-aspartate containing acidic glycoprotein postulated to mediate adhesion, migration, and biomineralization in diverse tissues. The mechanisms explaining this multifunctionality are not well understood, although it is known that one osteopontin receptor is the alpha v beta 3 integrin. In this work, we studied human smooth muscle cells varying in alpha v beta 3 levels to identify additional osteopontin receptors. We report that, in addition to alpha v beta 3, both alpha v beta 5 and alpha v beta 1 are osteopontin receptors. Moreover, the presence or absence of alpha v beta 3 on the cell surface altered the adhesive and migratory responses of smooth muscle cells to osteopontin. Adhesion of alpha v beta 3-deficient cell populations to osteopontin was only half that of cells containing alpha v beta 3, and migration toward an osteopontin gradient in the Boyden chamber was dependent on cell surface alpha v beta 3. Although alpha v beta 3-deficient smooth muscle cells were unable to migrate to osteopontin, they did migrate significantly in response to vitronectin and fibronectin. These findings represent the first description of alpha v beta 5 and alpha v beta 1 as osteopontin receptors and suggest that, while adhesion to osteopontin is supported by integrins containing beta 1, beta 3, and beta 5, migration in response to osteopontin appears to depend on alpha v beta 3. Thus, interaction with distinct receptors is one mechanism by which osteopontin may initiate multiple functions.

Benzoporphyrin derivative: a potent photosensitizer for photodynamic destruction of rabbit endometrium

OBJECTIVES

To determine the optimal pharmacokinetic characteristics for photodynamic endometrial destruction using topically applied benzoporphyrin derivative and to evaluate long-term morphologic effects in a rabbit model.

METHODS

Benzoporphyrin derivative pharmacokinetics were measured by analyzing frozen tissue sections 1.5-12 hours following topical administration. Photodynamic therapy was induced intraluminally 1.5 hours after drug application, and tissue morphology was evaluated by light and scanning electron microscopy 1 and 4 weeks after treatment.

RESULTS

The highest glandular and stromal fluorescence was observed 1.5 hours after topical administration. Relative fluorescence of the endometrial glands significantly exceeded that of stroma and myometrium mainly at 1.5 and 3 hours (P < .0001). Histology revealed persistent epithelial destruction with minimal regeneration. Stroma resembled scar tissue in the majority of sections. The bordering myometrium was loosened and invaded by connective tissue.

CONCLUSION

Topically applied benzoporphyrin derivative can be used for highly effective, long-lasting photodynamic destruction of rabbit endometrium. However, optical dosimetry can vary, particularly in the rabbit model, and this appears to affect long-term reepithelialization.

Osteopontin promotes vascular cell adhesion and spreading and is chemotactic for smooth muscle cells in vitro

Osteopontin is an Arg-Gly-Asp-containing acidic phosphoprotein recently shown to be upregulated in vascular smooth muscle during rat arterial neointima formation and in human atherosclerotic plaques. Functional studies showed that osteopontin promoted adhesion of both cultured aortic endothelial cells and aortic smooth muscle cells. Adhesion of vascular cells to osteopontin was dose dependent and half maximal when solutions containing 7 and 30 nmol/L osteopontin were used to coat wells for endothelial and smooth muscle cells, respectively. Smooth muscle cells adherent to osteopontin were spread after 60 minutes, whereas endothelial cells remained round, although flattened, at this time point but were spread at 90 minutes. Cell spreading on osteopontin was accompanied by the formation of focal adhesion plaques. A newly developed anti-osteopontin antibody completely inhibited adhesion of both cell types to osteopontin but not to fibronectin or vitronectin. In addition, the peptide GRGDSP blocked adhesion to osteopontin, suggesting that integrins mediate Arg-Gly-Asp-dependent adhesion. Indeed, an antibody against the alpha v beta 3 integrin neutralized adhesion of both endothelium and smooth muscle cells to osteopontin by approximately 50%, demonstrating that alpha v beta 3 is one osteopontin receptor on vascular cells. Osteopontin also promoted the migration of smooth muscle cells in a Boyden-type chamber, with half-maximal effects observed at 77 nmol/L osteopontin. Checkerboard analysis demonstrated that this stimulus was chemotactic in nature. Our findings suggest that osteopontin may be functionally important as an adhesive and chemotactic molecule for vascular cells, particularly when levels of osteopontin are dramatically increased, as is the case after arterial angioplasty and in atherosclerotic plaques.

Microtubule disruption stimulates DNA synthesis in bovine endothelial cells and potentiates cellular response to basic fibroblast growth factor

Cultured endothelial cells characteristically form a monolayer and become quiescent at saturation density. This study shows that microtubule destabilization in confluent cultures of bovine aortic endothelial cells stimulates fibroblast growth factor 2 (FGF-2, bFGF)-dependent DNA synthesis. Twenty-four hours after addition of the microtubule-disrupting drug colchicine, tritiated thymidine incorporation increases up to fivefold when compared to control cultures. Significant stimulation is seen with doses from 0.05 to 1.0 microgram/ml. The effect of colchicine is quantitatively similar to stimulation of the same cultures with 5 ng/ml FGF-2. Furthermore, the stimulation of DNA synthesis by colchicine can be completely blocked by the addition of a neutralizing antibody to FGF-2. This suggests that colchicine may stimulate bovine aortic endothelial cells by modulating endogenous FGF-2/receptor interactions or that colchicine acts by a different mechanism that requires the growth factor for mitogenicity. The combined effects of colchicine and FGF-2 are more than additive, which supports the idea that microtubule disruption may facilitate cellular response to FGF-2. Cytochalasin B, preventing actin polymerization, inhibits the mitogenic response to FGF-2 but not the response to colchicine. These results are best interpreted as evidence that colchicine stimulates endothelial cell DNA synthesis by a pathway that requires endogenous FGF-2 and may be facilitating cellular responsiveness to the growth factor by disrupting the monolayer via the cytoskeleton.

Comparison of gene expression in bovine aortic endothelium in vivo versus in vitro. Differences in growth regulatory molecules

Many studies of the endothelium have assumed equivalence between cultured confluent cells and an endothelial lining in vivo. We compared gene expression of bovine aortic endothelial cells (BAECs) in culture versus freshly isolated cells from bovine aortas. Our technique of harvesting in vivo tissue yielded cells that were endothelial by the criteria of their containing von Willebrand factor (vWF) and lacking smooth muscle alpha-actin, by both immunocytochemistry and mRNA analyses. We found that several genes are overexpressed when BAECs are placed into culture, including basic fibroblast growth factor, platelet-derived growth factor B-chain, and thrombospondin. On the other hand, message for vWF is highly expressed in vivo and at lower levels in confluent cultures. The transcripts for transforming growth factor-beta, plakoglobin, and flg (fms-like gene, FGF receptor-1) are comparable in vitro and in vivo. These results demonstrate that significant changes in gene expression occur in the transition from in vivo conditions to tissue culture of endothelial cells. Studies of in vitro endothelium may poorly reflect a quiescent endothelial lining in vivo but may be more similar to cells responding to injury or angiogenic stimuli.

Growth control and morphogenesis in the development and pathology of arteries

We briefly review and compare the current knowledge of growth mechanisms for the mitogenic response of endothelial cells and smooth-muscle cells to injury. For the endothelium, this focuses on the evidence that growth control involves two components: an endogenous inhibition mechanism, which can be overcome either by fibroblast growth factor (FGF) or by other agents that disrupt cell-cell junctions, and a separate mechanism, which requires FGF to allow cells to respond to a mitogenic effect. The smooth-muscle cell story is more complex; however, there is evidence here as well of an endogenous inhibitory mechanism, which may be overcome by a wide variety of agents. Platelet-derived growth factor, long seen as a major mitogen, does not itself now appear to be a major mitogen in vivo. In contrast, FGF also seems to play a major role in initiating smooth-muscle replication. Other molecules, including angiotensin II, bradykinin, thrombin, and catecholamines, are beginning to appear to play major roles in control of smooth-muscle replication in vivo as well.