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1.  Modeling the Neurovascular Niche: Unbiased Transcriptome Analysis of the Murine Subventricular Zone in Response to Hypoxic Insult 
PLoS ONE  2013;8(10):e76265.
Premature infants often experience chronic hypoxia, resulting in cognitive & motor neurodevelopmental handicaps. These sometimes devastating handicaps are thought to be caused by compromised neural precursor cell (NPC) repair/recovery resulting in variable central nervous system (CNS) repair/recovery. We have identified differential responses of two mouse strains (C57BL/6 & CD1) to chronic hypoxia that span the range of responsiveness noted in the premature human population. We previously correlated several CNS tissue and cellular behaviors with the different behavioral parameters manifested by these two strains. In this report, we use unbiased array technology to interrogate the transcriptome of the subventricular zone (SVZ) in these strains. Our results illustrate differences in mRNA expression in the SVZ of both C57BL/6 and CD1 mice following hypoxia as well as differences between C57BL/6 and CD1 SVZ under both normoxic and hypoxic conditions. Differences in expression were found in gene sets associated with Sox10-mediated neural functions that explain, in part, the differential cognitive and motor responsiveness to hypoxic insult. This may shed additional light on our understanding of the variable responses noted in the human premature infant population and facilitate early intervention approaches. Further interrogation of the differentially expressed gene sets will provide a more complete understanding of the differential responses to, and recovery from, hypoxic insult allowing for more informed modeling of the ranges of disease severity observed in the very premature human population.
doi:10.1371/journal.pone.0076265
PMCID: PMC3795763  PMID: 24146847
2.  Brain regional angiogenic potential at the neurovascular unit during normal aging 
Neurobiology of Aging  2011;33(5):1004.e1-1004.e16.
Given strong regional specialization of the brain, cerebral angiogenesis may be regionally modified during normal aging. To test this hypothesis, expression of a broad cadre of angiogenesis-associated genes was assayed at the neurovascular unit (NVU) in discrete brain regions of young vs. aged mice by laser capture microdissection coupled to quantitative real-time PCR. Complementary quantitative capillary density/branching studies were performed as well. Effects of physical exercise were also assayed to determine if age-related trends could be reversed. Additionally, gene response to hypoxia was probed to highlight age-associated weaknesses in adapting to this angiogenic stress. Aging impacted resting expression of angiogenesis-associated genes at the NVU in a region-dependent manner. Physical exercise reversed some of these age-associated gene trends, as well as positively influenced cerebral capillary density/branching in a region-dependent way. Lastly, hypoxia revealed a weaker angiogenic response in aged brain. These results suggest heterogeneous changes in angiogenic capacity of the brain during normal aging, and imply a therapeutic benefit of physical exercise that acts at the level of the NVU.
doi:10.1016/j.neurobiolaging.2011.09.022
PMCID: PMC3266473  PMID: 22019053
brain microvasculature; cerebral angiogenesis; normal aging; laser capture microdissection; neurovascular unit
3.  Short Term Interactions with Long Term Consequences: Modulation of Chimeric Vessels by Neural Progenitors 
PLoS ONE  2012;7(12):e53208.
Vessels are a critical and necessary component of most tissues, and there has been substantial research investigating vessel formation and stabilization. Several groups have investigated coculturing endothelial cells with a second cell type to promote formation and stabilization of vessels. Some have noted that long-term vessels derived from implanted cocultures are often chimeric consisting of both host and donor cells. The questions arise as to whether the coculture cell might impact the chimeric nature of the microvessels and can modulate the density of donor cells over time. If long-term engineered microvessels are primarily of host origin, any impairment of the host's angiogenic ability has significant implications for the long-term success of the implant. If one can modulate the host versus donor response, one may be able to overcome a host's angiogenic impairment. Furthermore, if one can modulate the donor contribution, one may be able to engineer microvascular networks to deliver molecules a patient lacks systemically for long times. To investigate the impact of the cocultured cell on the host versus donor contributions of endothelial cells in engineered microvascular networks, we varied the ratio of the neural progenitors to endothelial cells in subcutaneously implanted poly(ethylene glycol)/poly-L-lysine hydrogels. We found that the coculture of neural progenitors with endothelial cells led to the formation of chimeric host-donor vessels, and the ratio of neural progenitors has a significant impact on the long term residence of donor endothelial cells in engineered microvascular networks in vivo even though the neural progenitors are only present transiently in the system. We attribute this to the short term paracrine signaling between the two cell types. This suggests that one can modulate the host versus donor contributions using short-term paracrine signaling which has broad implications for the application of engineered microvascular networks and cellular therapy more broadly.
doi:10.1371/journal.pone.0053208
PMCID: PMC3531360  PMID: 23300890
4.  Characterization of the Natural History of Extracellular Matrix Production in Tissue-Engineered Vascular Grafts during Neovessel Formation 
Cells, Tissues, Organs  2011;195(1-2):60-72.
Background
The extracellular matrix (ECM) is a critical determinant of neovessel integrity. Materials and Methods: Thirty-six (polyglycolic acid + polycaprolactone and poly lactic acid) tissue-engineered vascular grafts seeded with syngeneic bone marrow mononuclear cells were implanted as inferior vena cava interposition grafts in C57BL/6 mice. Specimens were characterized using immunohistochemical staining and qPCR for representative ECM components in addition to matrix metalloproteinases (MMPs). Total collagen, elastin, and glycosaminoglycan (GAG) contents were determined. MMP activity was measured using zymography.
Results
Collagen production on histology demonstrated an initial increase in type III at 1 week followed by type I production at 2 weeks and type IV at 4 weeks. Gene expression of both type I and type III peaked at 2 weeks, whereas type IV continued to increase over the 4-week period. Histology demonstrated fibrillin-1 deposition at 1 week followed by elastin production at 4 weeks. Elastin gene expression significantly increased at 4 weeks, whereas fibrillin-1 decreased at 4 weeks. GAG demonstrated abundant production at each time point on histology. Gene expression of decorin significantly increased at 4 weeks, whereas versican decreased over time. Biochemical analysis showed that total collagen production was greatest at 2 weeks, and there was a significant increase in elastin and GAG production at 4 weeks. Histological characterization of MMPs showed abundant production of MMP-2 at each time point, while MMP-9 decreased over the 4-week period. Gene expression of MMP-2 significantly increased at 4 weeks, whereas MMP-9 significantly decreased at 4 weeks.
Conclusions
ECM production during neovessel formation is characterized by early ECM deposition followed by extensive remodeling.
doi:10.1159/000331405
PMCID: PMC3257815  PMID: 21996715
Tissue engineering; Extracellular matrix; Vascular remodeling; Collagen; Elastin
5.  Cyclic Strain Delays the Expression of Tissue Factor Induced by Thrombin in Human Umbilical Vein Endothelial Cells 
Most studies of tissue factor (TF) expression in endothelial cells (EC) are performed under stationary culture conditions. The purpose of this study was to determine the influence of mechanical stimuli such as cyclic strain (CS) on the expression of TF in EC exposed to thrombin (Thr). Human umbilical vein endothelial cells (HUVEC) were exposed to 4 U·mL−1 Thr in the presence or absence of 10% average CS at 60 cycles·min−1 and then TF expression was measured. TF messenger RNA (mRNA) expression peaked at 2 hours in HUVEC exposed to Thr, but at 4 hours in HUVEC exposed to both Thr + CS. TF expression was inhibited by p38 and extracellular signal-regulated protein kinase (ERK) inhibitors. For both Thr or Thr + CS stimuli, p38 and ERK activity peaked at 5 minutes (p < 0.05). Nuclear factor-kappa B levels remained high in the Thr group but not in the Thr + CS group, while Egr-1 levels were elevated in the Thr + CS group. We demonstrated CS-delayed, Thr-induced TF mRNA expression in HUVEC, which may be modulated by p38 and ERK inhibitors.
doi:10.1055/s-0031-1284475
PMCID: PMC3331651  PMID: 22942631
Hemodynamic forces; thrombin; endothelium; tissue factor; atherosclerosis
6.  USING PROTEOMICS IN PERINATAL AND NEONATAL SEPSIS. HOPES AND CHALLENGES FOR THE FUTURE 
PURPOSE OF THE REVIEW:
Particularities of the fetal immune response to infection cause a heightened inflammatory state that acts synergistically with microbial insult to induce damage. Proteomics offers the opportunity for detecting fetuses at risk of sepsis and neurological injury.
RECENT FINDINGS:
Molecular tools (16S-rRNA) demonstrate the diversity of microbial agents of intra-amniotic infection exceeds what is suspected clinically or is documented by cultures. The resulting inflammatory process has the potential to damage the fetus in utero. Stepwise algorithms [mass restricted (MR) score] have been developed to extract proteomic profiles characteristic of amniotic fluid (AF) inflammation. The MR score includes 4 proteomic biomarkers: defensin-2, defensin-1, S100A12 and S100A8 proteins. Other AF biomarkers relevant for preterm birth are S100A9 and insulin-like-growth-factor-binding protein 1 (IGFBP-1). S100A12, ligand for the receptor of advanced glycation end-products (RAGE), has the strongest association with histological chorioamnionitis and funisitis. Presence of S100A12 and S100A8 in AF is predictive of early-onset neonatal sepsis and poor neuro-developmental outcome.
SUMMARY:
Presence of AF proteomic biomarkers of inflammation is associated with increased inflammatory status of the fetus at birth. Future challenges are finding biomarkers that provide insight into molecular mechanisms of chronic fetal and neonatal cellular damage and identify candidates for early neuro-protection strategies.
doi:10.1097/QCO.0b013e32832a5963
PMCID: PMC2763282  PMID: 19395960
amniotic fluid; biomarkers; inflammation; defensin; calgranulin; S100 proteins
7.  VEGF-A and Semaphorin3A: Modulators of vascular sympathetic innervation 
Developmental biology  2009;334(1):119-132.
Sympathetic nerve activity regulates blood pressure by altering peripheral vascular resistance. Variations in vascular sympathetic innervation suggest that vascular-derived cues promote selective innervation of particular vessels during development. As axons extend towards peripheral targets, they migrate along arterial networks following gradients of guidance cues. Collective ratios of these gradients may determine whether axons grow towards and innervate vessels or continue past non-innervated vessels towards peripheral targets. Utilizing directed neurite outgrowth in a three-dimensional (3D) co-culture, we observed increased axon growth from superior cervical ganglion explants (SCG) towards innervated compared to non-innervated vessels, mediated in part by vascular endothelial growth factor (VEGF-A) and Semaphorin3A (Sema3A) which both signal via neuropilin-1 (Nrp1). Exogenous VEGF-A, delivered by high-expressing VEGF-A–LacZ vessels or by rhVEGF-A/alginate spheres, increased sympathetic neurite outgrowth while exogenous rhSema3A/Fc decreased neurite outgrowth. VEGF-A expression is similar between the innervated and non-innervated vessels examined. Sema3A expression is higher in non-innervated vessels. Spatial gradients of Sema3A and VEGF-A may promote differential Nrp1 binding. Vessels expressing high levels of Sema3A favor Nrp1-PlexinA1 signaling, producing chemorepulsive cues limiting sympathetic neurite outgrowth and vascular innervation; while low Sema3A expressing vessels favor Nrp1-VEGFR2 signaling providing chemoattractive cues for sympathetic neurite outgrowth and vascular innervation.
doi:10.1016/j.ydbio.2009.07.023
PMCID: PMC2871302  PMID: 19631637
Sympathetic innervation; Vascular endothelial growth factor-A; Semaphorin3A; Neuropilin-1; Superior cervical ganglion; Femoral artery; Carotid artery
8.  An Implantable Vascularized Protein Gel Construct That Supports Human Fetal Hepatoblast Survival and Infection by Hepatitis C Virus in Mice 
PLoS ONE  2010;5(4):e9987.
Background
Widely accessible small animal models suitable for the study of hepatitis C virus (HCV) in vivo are lacking, primarily because rodent hepatocytes cannot be productively infected and because human hepatocytes are not easily engrafted in immunodeficient mice.
Methodology/Principal Findings
We report here on a novel approach for human hepatocyte engraftment that involves subcutaneous implantation of primary human fetal hepatoblasts (HFH) within a vascularized rat collagen type I/human fibronectin (rCI/hFN) gel containing Bcl-2-transduced human umbilical vein endothelial cells (Bcl-2-HUVEC) in severe combined immunodeficient X beige (SCID/bg) mice. Maturing hepatic epithelial cells in HFH/Bcl-2-HUVEC co-implants displayed endocytotic activity at the basolateral surface, canalicular microvilli and apical tight junctions between adjacent cells assessed by transmission electron microscopy. Some primary HFH, but not Huh-7.5 hepatoma cells, appeared to differentiate towards a cholangiocyte lineage within the gels, based on histological appearance and cytokeratin 7 (CK7) mRNA and protein expression. Levels of human albumin and hepatic nuclear factor 4α (HNF4α) mRNA expression in gel implants and plasma human albumin levels in mice engrafted with HFH and Bcl-2-HUVEC were somewhat enhanced by including murine liver-like basement membrane (mLBM) components and/or hepatocyte growth factor (HGF)-HUVEC within the gel matrix. Following ex vivo viral adsorption, both HFH/Bcl-2-HUVEC and Huh-7.5/Bcl-2-HUVEC co-implants sustained HCV Jc1 infection for at least 2 weeks in vivo, based on qRT-PCR and immunoelectron microscopic (IEM) analyses of gel tissue.
Conclusion/Significance
The system described here thus provides the basis for a simple and robust small animal model of HFH engraftment that is applicable to the study of HCV infections in vivo.
doi:10.1371/journal.pone.0009987
PMCID: PMC2848675  PMID: 20376322
9.  Engineering angiogenesis following spinal cord injury: A coculture of neural progenitor and endothelial cells in a degradable polymer implant leads to an increase in vessel density and formation of the blood-spinal cord barrier 
Angiogenesis precedes recovery following spinal cord injury (SCI), and its extent correlates with neural regeneration suggesting that angiogenesis may play a role in repair. An important precondition for studying the role of angiogenesis is the ability to induce it in a controlled manner. Previously, we showed that a coculture of endothelial cells (ECs) and neural progenitor cells (NPCs) promoted the formation of stable tubes in vitro and stable, functional vascular networks in vivo in a subcutaneous model. We sought to test whether a similar coculture would lead to formation of stable functional vessels in the spinal cord following injury. We created microvascular networks in a biodegradable two component implant system and tested the ability of the coculture or controls (lesion control, implant alone, implant plus ECs, or implant plus NPCs) to promote angiogenesis in a rat hemisection model of spinal cord injury. The coculture implant led to a four fold increase in functional vessels compared to the lesion control, implant alone, or implant plus NPCs groups and a 2 fold increase in functional vessels over the implant plus ECs group. Furthermore, half of the vessels in the coculture implant exhibited positive staining for the endothelial barrier antigen, a marker for formation of the blood spinal cord barrier (BSB). No other groups showed positive staining for the BSB in the injury epicenter. This work provides a novel method to induce angiogenesis following SCI and a foundation for studying its role in repair.
doi:10.1111/j.1460-9568.2008.06567.x
PMCID: PMC2764251  PMID: 19120441
rat; microvasculature; neural progenitor cells; endothelial cells; hydrogel; scaffold; PLGA; blood-spinal cord barrier
10.  Fibroblast-type reticular stromal cells regulate the lymph node vasculature 
The lymph node vasculature is essential to immune function, but mechanisms regulating lymph node vascular maintenance and growth are not well understood. Vascular endothelial growth factor (VEGF) is an important mediator of lymph node endothelial cell proliferation in stimulated lymph nodes. It is expressed basally in lymph nodes and upregulated upon lymph node stimulation, but the identity of VEGF-expressing cells in lymph nodes is not known. We show that, at homeostasis, fibroblast-type reticular stromal cells (FRC) in the T zone and medullary cords are the principal VEGF-expressing cells in lymph nodes and that VEGF plays a role in maintaining endothelial cell proliferation, although peripheral node addressin (PNAd) pos endothelial cells are less sensitive than PNAdneg endothelial cells to VEGF blockade. Lymphotoxin beta receptor (LTβR) blockade reduces homeostatic VEGF levels and endothelial cell proliferation and LTβR stimulation of murine fibroblast-type cells upregulates VEGF expression, suggesting that LTβR signals on FRC regulates lymph node VEGF levels and, thereby, lymph node endothelial cell proliferation. At the initiation of immune responses, FRC remain the principal VEGF mRNA-expressing cells in lymph nodes, suggesting that FRC may play an important role in regulating vascular growth in stimulated nodes. In stimulated nodes, VEGF regulates the proliferation and expansion of both PNAdpos and PNAdneg endothelial cells. Together, these data suggest a role for FRC as paracrine regulators of lymph node endothelial cells and suggest that modulation of FRC VEGF expression may be a means to regulate lymph node vascularity and, potentially, immune function.
PMCID: PMC2562332  PMID: 18768843
Spleen and lymph nodes; Endothelial cells; Stromal cells; Rodent
11.  Matrix Metalloproteinase 9 Facilitates West Nile Virus Entry into the Brain▿  
Journal of Virology  2008;82(18):8978-8985.
West Nile virus (WNV) is the most-common cause of mosquito-borne encephalitis in the United States. Invasion of the brain by WNV is influenced by viral and host factors, and the molecular mechanism underlying disruption of the blood-brain barrier is likely multifactorial. Here we show that matrix metalloproteinase 9 (MMP9) is involved in WNV entry into the brain by enhancing blood-brain barrier permeability. Murine MMP9 expression was induced in the circulation shortly after WNV infection, and the protein levels remained high even when viremia subsided. In the murine brain, MMP9 expression and its enzymatic activity were upregulated and MMP9 was shown to partly localize to the blood vessels. Interestingly, we also found that cerebrospinal fluid from patients suffering from WNV contained increased MMP9 levels. The peripheral viremia and expression of host cytokines were not altered in MMP9−/− mice; however, these animals were protected from lethal WNV challenge. The resistance of MMP9−/− mice to WNV infection correlated with an intact blood-brain barrier since immunoglobulin G, Evans blue leakage into brain, and type IV collagen degradation were markedly reduced in the MMP9−/− mice compared with their levels in controls. Consistent with this, the brain viral loads, selected inflammatory cytokines, and leukocyte infiltrates were significantly reduced in the MMP9−/− mice compared to their levels in wild-type mice. These data suggest that MMP9 plays a role in mediating WNV entry into the central nervous system and that strategies to interrupt this process may influence the course of West Nile encephalitis.
doi:10.1128/JVI.00314-08
PMCID: PMC2546894  PMID: 18632868
12.  Differential Effects of Shear Stress and Cyclic Strain on Sp1 Phosphorylation by Protein Kinase Cζ Modulates Membrane Type 1–Matrix Metalloproteinase in Endothelial Cells 
Membrane type 1–matrix metalloproteinase (MT1-MMP) plays a key role in extracellular matrix remodeling, endothelial cell (EC) migration, and angiogenesis. Whereas cyclic strain (CS) increases MT1-MMP expression, shear stress (SS) decreases MT1-MMP expression. The aim of this study was to determine if changes in levels of Sp1 phosphorylation induced by protein kinase Cζ (PKCζ) in ECs exposed to SS but not CS are important for MT1-MMP expression. The results showed that SS increased Sp1 phosphorylation, which could be inhibited by pretreatment with PKCζ inhibitors. In the presence of PKCζ inhibitors, the SS-mediated decrease in MT1-MMP protein expression was also abolished. These data demonstrate that increased affinity of Sp1 for MT1-MMP’s promoter site occurs as a consequence of PKCζ -induced phosphorylation of Sp1 in response to SS, increasing Sp1 binding affinity for the promoter site, preventing Egr-1 binding, and consequently decreasing MT1-MMP expression.
doi:10.1080/10623320802092260
PMCID: PMC2644408  PMID: 18568943
Hemodynamic Forces; MMP; PKC; sp1 phosphorylation
13.  Modeling the Neurovascular Niche: Murine Strain Differences Mimic the Range of Responses to Chronic Hypoxia in the Premature Newborn 
Journal of neuroscience research  2008;86(6):1227-1242.
Preterm birth results in significant cognitive and motor disabilities, but recent evidence suggests that there is variable recovery over time. One possibility that may explain this variable recovery entails variable neurogenic responses in the subventricular zone (SVZ) following the period of chronic hypoxia experienced by these neonates. In this report, we have characterized the responses to chronic hypoxia of two mouse strains that represent a wide range of susceptibility to chronic hypoxia. We determined that C57BL/6 pups and neural progenitor cells (NPCs) derived from them exhibit a blunted response to hypoxic insult compared with CD-1 pups and NPCs. Specifically, C57BL/6 pups and NPCs exhibited blunted in vivo and in vitro proliferative and increased apoptotic responses to hypoxic insult. Additionally, C57BL/6 NPCs exhibited lower baseline levels and hypoxia-induced levels of selected transcription factors, growth factors, and receptors (including HIF-1α, PHD2, BDNF, VEGF, SDF-1, TrkB, Nrp-1, CXCR4, and NO) that determine, in part, the responsiveness to chronic hypoxic insult compared with CD-1 pups and NPCs, providing insight into this important and timely problem in perinatology.
doi:10.1002/jnr.21597
PMCID: PMC2644407  PMID: 18092360
brain ischemia and reperfusion; brain-derived neurotrophic factor; cell death; embryonic stem cells; neuronal survival
14.  Proteomic-Based Detection of a Protein Cluster Dysregulated during Cardiovascular Development Identifies Biomarkers of Congenital Heart Defects 
PLoS ONE  2009;4(1):e4221.
Background
Cardiovascular development is vital for embryonic survival and growth. Early gestation embryo loss or malformation has been linked to yolk sac vasculopathy and congenital heart defects (CHDs). However, the molecular pathways that underlie these structural defects in humans remain largely unknown hindering the development of molecular-based diagnostic tools and novel therapies.
Methodology/Principal Findings
Murine embryos were exposed to high glucose, a condition known to induce cardiovascular defects in both animal models and humans. We further employed a mass spectrometry-based proteomics approach to identify proteins differentially expressed in embryos with defects from those with normal cardiovascular development. The proteins detected by mass spectrometry (WNT16, ST14, Pcsk1, Jumonji, Morca2a, TRPC5, and others) were validated by Western blotting and immunoflorescent staining of the yolk sac and heart. The proteins within the proteomic dataset clustered to adhesion/migration, differentiation, transport, and insulin signaling pathways. A functional role for several proteins (WNT16, ADAM15 and NOGO-A/B) was demonstrated in an ex vivo model of heart development. Additionally, a successful application of a cluster of protein biomarkers (WNT16, ST14 and Pcsk1) as a prenatal screen for CHDs was confirmed in a study of human amniotic fluid (AF) samples from women carrying normal fetuses and those with CHDs.
Conclusions/Significance
The novel finding that WNT16, ST14 and Pcsk1 protein levels increase in fetuses with CHDs suggests that these proteins may play a role in the etiology of human CHDs. The information gained through this bed-side to bench translational approach contributes to a more complete understanding of the protein pathways dysregulated during cardiovascular development and provides novel avenues for diagnostic and therapeutic interventions, beneficial to fetuses at risk for CHDs.
doi:10.1371/journal.pone.0004221
PMCID: PMC2626248  PMID: 19156209
15.  Loss of MMP-2 disrupts skeletal and craniofacial development, and results in decreased bone mineralization, joint erosion, and defects in osteoblast and osteoclast growth 
Human molecular genetics  2007;16(9):1113-1123.
The “vanishing bone” or inherited osteolysis/arthritis syndromes represent a heterogeneous group of skeletal disorders characterized by mineralization defects of affected bones and joints. Differing in anatomical distribution, severity, and associated syndromic features, gene identification in each “vanishing bone” disorder should provide unique insights into genetic/molecular pathways contributing to the overall control of skeletal growth and development. We previously described and then demonstrated that the novel autosomal recessive osteolysis/arthritis syndrome, Multicentric Osteolysis with Arthritis (MOA [MIM #605156]), was caused by inactivating mutations in the MMP2 gene (1). These in vivo results were counterintuitive and unexpected since previous in vitro studies suggested that MMP-2 overexpression and increased activity, not deficiency, would result in the bone and joint features of MOA. The apparent lack of a murine model (2) has hindered studies on disease pathogenesis and, more fundamentally, in addressing the paradox of how functional loss of a single proteolytic enzyme results in an apparent increase in bone loss. Here, we report that Mmp2-/- mice display attenuated features of human MOA including progressive loss of bone mineral density, articular cartilage destruction, and abnormal long bone and craniofacial development. Moreover, these changes are associated with markedly and developmentally-restricted decreases in osteoblast and osteoclast numbers in vivo. Mmp2-/- mice have ∼50% fewer osteoblasts and osteoclasts than control littermates at 4 days of life but these differences have nearly resolved by 4 weeks of age. In addition, despite normal cell numbers in vivo at 8 weeks of life, Mmp2-/- bone marrow cells are unable to effectively support osteoblast and osteoclast growth and differentiation in culture. Targeted inhibition of MMP-2 using siRNA in human SaOS2 and murine MC3T3 osteoblast cell lines resulted in decreased cell proliferation rates. Taken together, our findings suggest that MMP-2 plays a direct role in early skeletal development and bone cell growth and proliferation. Thus, Mmp2-/- mice provide a valuable biologic resource for studying the pathophysiologic mechanisms underlying the human disease and defining the in vivo physiologic role of MMP-2.
doi:10.1093/hmg/ddm060
PMCID: PMC2576517  PMID: 17400654
16.  Leptin affects endocardial cushion formation by modulating EMT and migration via Akt signaling cascades 
The Journal of Cell Biology  2008;181(2):367-380.
Blood circulation is dependent on heart valves to direct blood flow through the heart and great vessels. Valve development relies on epithelial to mesenchymal transition (EMT), a central feature of embryonic development and metastatic cancer. Abnormal EMT and remodeling contribute to the etiology of several congenital heart defects. Leptin and its receptor were detected in the mouse embryonic heart. Using an ex vivo model of cardiac EMT, the inhibition of leptin results in a signal transducer and activator of transcription 3 and Snail/vascular endothelial cadherin–independent decrease in EMT and migration. Our data suggest that an Akt signaling pathway underlies the observed phenotype. Furthermore, loss of leptin phenocopied the functional inhibition of αvβ3 integrin receptor and resulted in decreased αvβ3 integrin and matrix metalloprotease 2, suggesting that the leptin signaling pathway is involved in adhesion and migration processes. This study adds leptin to the repertoire of factors that mediate EMT and, for the first time, demonstrates a role for the interleukin 6 family in embryonic EMT.
doi:10.1083/jcb.200708197
PMCID: PMC2315681  PMID: 18411306
17.  Role of C5 in the development of airway inflammation, airway hyperresponsiveness, and ongoing airway response 
Journal of Clinical Investigation  2005;115(6):1590-1600.
The role of complement component C5 in asthma remains controversial. Here we examined the contribution of C5 at 3 critical checkpoints during the course of disease. Using an mAb specific for C5, we were able to evaluate the contribution of C5 during (a) the initiation of airway inflammation, (b) the maintenance of airway hyperresponsiveness (AHR), and (c) sustainment of an ongoing airway response to allergen provocation. Our results indicate that C5 is probably activated intrapulmonarily after infections or exposures to allergen and C5 inhibition has profound effects at all 3 critical checkpoints. In contrast to an earlier report, C5-deficient mice with established airway inflammation did not have elevated AHR to nonspecific stimuli. In the presence of airway inflammation, C5a serves as a direct link between the innate immune system and the development of AHR by engaging directly with its receptors expressed in airways. Through their powerful chemotactic and cell activation properties, both C5a and C5b-9 regulate the downstream inflammatory cascade, which results in a massive migration of inflammatory cells into the bronchial airway lumen and triggers the release of multiple harmful inflammatory mediators. This study suggests that targeting C5 is a potential clinical approach for treating patients with asthma.
doi:10.1172/JCI22906
PMCID: PMC1090470  PMID: 15902311
18.  Noninvasive imaging of myocardial angiogenesis following experimental myocardial infarction 
Journal of Clinical Investigation  2004;113(12):1684-1691.
Noninvasive imaging strategies will be critical for defining the temporal characteristics of angiogenesis and assessing efficacy of angiogenic therapies. The αvβ3 integrin is expressed in angiogenic vessels and represents a potential novel target for imaging myocardial angiogenesis. We demonstrated the localization of an indium-111–labeled (111In-labeled) αvβ3-targeted agent in the region of injury-induced angiogenesis in a chronic rat model of infarction. The specificity of the targeted αvβ3-imaging agent for angiogenesis was established using a nonspecific control agent. The potential of this radiolabeled αvβ3-targeted agent for in vivo imaging was then confirmed in a canine model of postinfarction angiogenesis. Serial in vivo dual-isotope single-photon emission–computed tomographic (SPECT) imaging with the 111In-labeled αvβ3-targeted agent demonstrated focal radiotracer uptake in hypoperfused regions where angiogenesis was stimulated. There was a fourfold increase in myocardial radiotracer uptake in the infarct region associated with histological evidence of angiogenesis and increased expression of the αvβ3 integrin. Thus, angiogenesis in the heart can be imaged noninvasively with an 111In-labeled αvβ3-targeted agent. The noninvasive evaluation of angiogenesis may have important implications for risk stratification of patients following myocardial infarction. This approach may also have significant clinical utility for noninvasively tracking therapeutic myocardial angiogenesis.
doi:10.1172/JCI200420352
PMCID: PMC420502  PMID: 15199403
19.  Elevated glucose inhibits VEGF-A–mediated endocardial cushion formation 
The Journal of Cell Biology  2003;160(4):605-615.
Atrioventricular (AV) septal defects resulting from aberrant endocardial cushion (EC) formation are observed at increased rates in infants of diabetic mothers. EC formation occurs via an epithelial-mesenchymal transformation (EMT), involving transformation of endocardial cells into mesenchymal cells, migration, and invasion into extracellular matrix. Here, we report that elevated glucose inhibits EMT by reducing myocardial vascular endothelial growth factor A (VEGF-A). This effect is reversed with exogenous recombinant mouse VEGF-A165, whereas addition of soluble VEGF receptor-1 blocks EMT. We show that disruption of EMT is associated with persistence of platelet endothelial cell adhesion molecule-1 (PECAM-1) and decreased matrix metalloproteinase-2 (MMP-2) expression. These findings correlate with retention of a nontransformed endocardial sheet and lack of invasion. The MMP inhibitor GM6001 blocks invasion, whereas explants from PECAM-1 deficient mice exhibit MMP-2 induction and normal EMT in high glucose. PECAM-1–negative endothelial cells are highly motile and express more MMP-2 than do PECAM-1–positive endothelial cells. During EMT, loss of PECAM-1 similarly promotes single cell motility and MMP-2 expression. Our findings suggest that high glucose-induced inhibition of AV cushion morphogenesis results from decreased myocardial VEGF-A expression and is, in part, mediated by persistent endocardial cell PECAM-1 expression and failure to up-regulate MMP-2 expression.
doi:10.1083/jcb.200209014
PMCID: PMC2173755  PMID: 12591918
VEGF-A165; PECAM-1; MMP-2; endocardial cushion; epithelial-mesenchymal transformation; glucose/diabetic embryopathy
20.  Altered vascular permeability and early onset of experimental autoimmune encephalomyelitis in PECAM-1–deficient mice 
Platelet/endothelial cell adhesion molecule-1 (PECAM-1, CD31), a 130-kDa glycoprotein member of the Ig superfamily of transmembrane proteins, is expressed on endothelial cells, platelets, and subsets of leukocytes. It functions as a cell adhesion molecule as well as a scaffolding molecule capable of modulating cellular signaling pathways. In this study, using PECAM-1–deficient (KO) mice, as well as cells derived from these mice, we demonstrate that the absence of PECAM-1 expression is associated with an early onset of clinical symptoms during experimental autoimmune encephalomyelitis (EAE), a mouse model for the human autoimmune disease multiple sclerosis. During EAE, mononuclear cell extravasation and infiltration of the CNS occur at earlier time points in PECAM-KO mice than in wild-type mice. In vitro, T lymphocyte transendothelial migration across PECAM-KO endothelial cells is enhanced, regardless of expression of PECAM-1 on transmigrating T cells. Additionally, cultured PECAM-KO endothelial cells exhibit prolonged permeability changes in response to histamine treatment compared with PECAM-1–reconstituted endothelial cells. Lastly, we demonstrate an exaggerated and prolonged CNS vascular permeability during the development of EAE and a delay in restoration of dermal vascular integrity following histamine challenge in PECAM-KO mice.
doi:10.1172/JCI13595
PMCID: PMC150854  PMID: 11827998
21.  Cell Migration in the Immune System: the Evolving Inter-Related Roles of Adhesion Molecules and Proteinases 
Developmental Immunology  2000;7(2-4):103-116.
Leukocyte extravasation into perivascular tissue during inflammation and lymphocyte homing to lymphoid organs involve transient adhesion to the vessel endothelium, followed by transmigration through the endothelial cell (EC) layer and establishment of residency at the tissue site for a period of time. In these processes, leukocytes undergo multiple attachments to, and detachments from, the vessel-lining endothelial cells, prior to transendothelial cell migration. Transmigrating leukocytes must traverse a subendothelial basement membrane en route to perivascular tissues and utilize enzymes known as matrix metalloproteinases to make selective clips in the extracellular matrix components of the basement membrane. This review will focus on the evidence for a link between adhesion of leukocytes to endothelial cells, the induction of matrix metalloproteinases mediated by engagement of adhesion receptors on leukocytes, and the ability to utilize these matrix metalloproteinases to facilitate leukocyte invasion of tissues. Leukocytes with invasive phenotypes express high levels of MMPs, and expression of MMPs enhances the migratory and invasive properties of these cells. Furthermore, MMPs may be used by lymphocytes to proteolytically cleave molecules such as adhesion receptors and membrane bound cytokines, increasing their efficiency in the immune response. Engagement of leukocyte adhesion receptors may modulate adhesive (modulation of integrin affinities and expression), synthetic (proteinase induction and activation), and surface organization (clustering of proteolyric complexes) behaviors of invasive leukocytes. Elucidation of these pathways will lead to better understanding of controlling mechanisms in order to develop rational therapeutic approaches in the areas of inflammation and autoimmunity.
doi:10.1155/2000/79045
PMCID: PMC2276058  PMID: 11097205
T lymphocyte; endothelial cell; matrix metalloproteinase; inflammation; transendothelial migration; integrins; cell adhesion molecules

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