Dexamethasone treatment and ICAM-1 deficiency impair VEGF-induced angiogenesis in adult brain

Identification of New Markers of Angiogenic Sprouting Using Transcriptomics: New Role for RND3

BACKGROUND

New blood vessel formation requires endothelial cells to transition from a quiescent to an invasive phenotype. Transcriptional changes are vital for this switch, but a comprehensive genome-wide approach focused exclusively on endothelial cell sprout initiation has not been reported.

METHODS

Using a model of human endothelial cell sprout initiation, we developed a protocol to physically separate cells that initiate the process of new blood vessel formation (invading cells) from noninvading cells. We used this model to perform multiple transcriptomics analyses from independent donors to monitor endothelial gene expression changes.

RESULTS

Single-cell population analyses, single-cell cluster analyses, and bulk RNA sequencing revealed common transcriptomic changes associated with invading cells. We also found that collagenase digestion used to isolate single cells upregulated the Fos proto-oncogene transcription factor. Exclusion of Fos proto-oncogene expressing cells revealed a gene signature consistent with activation of signal transduction, morphogenesis, and immune responses. Many of the genes were previously shown to regulate angiogenesis and included multiple tip cell markers. Upregulation of SNAI1 (snail family transcriptional repressor 1), PTGS2 (prostaglandin synthase 2), and JUNB (JunB proto-oncogene) protein expression was confirmed in invading cells, and silencing JunB and SNAI1 significantly reduced invasion responses. Separate studies investigated rounding 3, also known as RhoE, which has not yet been implicated in angiogenesis. Silencing rounding 3 reduced endothelial invasion distance as well as filopodia length, fitting with a pathfinding role for rounding 3 via regulation of filopodial extensions. Analysis of in vivo retinal angiogenesis in Rnd3 heterozygous mice confirmed a decrease in filopodial length compared with wild-type littermates.

CONCLUSIONS

Validation of multiple genes, including rounding 3, revealed a functional role for this gene signature early in the angiogenic process. This study expands the list of genes associated with the acquisition of a tip cell phenotype during endothelial cell sprout initiation.

Endothelial cell activation by interleukin-1 and extracellular matrix laminin-10 occurs via the YAP signalling pathway

Laminin-10 (LM-10) is a key regulator of blood-brain barrier (BBB) repair after hypoxia and inflammation. Here we investigated the signalling mechanisms regulated by LM-10 in human brain endothelial cell line hCMEC/D3 in response to interleukin(IL)-1beta(β) in vitro. LM-10 promoted endothelial proliferation and repair of an endothelial monolayer after scratch injury, and upregulated IL-1β-induced ICAM-1 and VCAM-1 expression. IL-1β and LM-10 regulated YAP signalling pathway in endothelial cells leading to differential expression of YAP target genes, ctgf and serpine-1, providing evidence that the YAP signalling pathway could be a new therapeutic target for the treatment of BBB dysfunction in CNS diseases.

Investigating the effects of dexamethasone on blood-brain barrier permeability and inflammatory response following focused ultrasound and microbubble exposure

Rationale: Clinical trials are currently underway to test the safety and efficacy of delivering therapeutic agents across the blood-brain barrier (BBB) using focused ultrasound and microbubbles (FUS+MBs). While acoustic feedback control strategies have largely minimized the risk of overt tissue damage, transient induction of inflammatory processes have been observed following sonication in preclinical studies. The goal of this work was to explore the potential of post-sonication dexamethasone (DEX) administration as a means to mitigate treatment risk. Vascular permeability, inflammatory protein expression, blood vessel growth, and astrocyte activation were assessed. Methods: A single-element focused transducer (transmit frequency = 580 kHz) and Definity^TM microbubbles were used to increase BBB permeability unilaterally in the dorsal hippocampi of adult male rats. Sonicating pressure was calibrated based on ultraharmonic emissions. Dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) was used to quantitatively assess BBB permeability at 15 min (baseline) and 2 hrs following sonication. DEX was administered following baseline imaging and at 24 hrs post-FUS+MB exposure. Expression of key inflammatory proteins were assessed at 2 days, and astrocyte activation and blood vessel growth were assessed at 10 days post-FUS+MB exposure. Results: Compared to saline-treated control animals, DEX administration expedited the restoration of BBB integrity at 2 hrs, and significantly limited the production of key inflammation-related proteins at 2 days, following sonication. Indications of FUS+MB-induced astrocyte activation and vascular growth were diminished at 10 days in DEX-treated animals, compared to controls. Conclusions: These results suggest that DEX provides a means of modulating the duration of BBB permeability enhancement and may reduce the risk of inflammation-induced tissue damage, increasing the safety profile of this drug-delivery strategy. This effect may be especially relevant in scenarios for which the goal of treatment is to restore or preserve neural function and multiple sonications are required.

Death or resolution: the "natural history" of pulmonary hypertension in bronchopulmonary dysplasia

OBJECTIVES

The primary objective was to describe the early "natural history" of pulmonary hypertension (PH) in the premature population. The secondary objective was to describe factors associated with poor outcomes in the premature population with PH at 36 weeks post-menstrual age (PMA).

STUDY DESIGN

Retrospective chart review of patients followed at our institution from 2000 to 2017 with echocardiographic (ECHO) evidence of PH at 36 weeks PMA, and born ≤ 32 weeks estimated gestational age (GA). Cox regression was used for survival analysis.

RESULTS

Sixty-one patients with PH (26.5 ± 1.5 weeks at birth) were included. All PH patients had bronchopulmonary dysplasia (BPD), with 89% considered severe; 38% were small for gestational age. Necrotizing enterocolitis requiring surgery was common (25%). Use of post-natal steroids (HR 11.02, p = 0.01) and increased severity of PH (HR 1.05, p < 0.001) were associated with mortality. Pulmonary vein stenosis (PVS) was documented in 26% of the PH cohort, but not associated with increased mortality. ECHO estimation of pulmonary artery pressure (PAP) was available in 84%. PAP was higher in those who died (sPAP/sBP ratio 1.09 ± 27 vs 0.83 ± 20 %, p = 0.0002). At follow-up (mean 250 ± 186 weeks PMA), 72% of the PH cohort was alive. Most survivors (66%) had resolution of their PH on their most recent ECHO; 31% remained on PH therapy.

CONCLUSION

PH resolved in most survivors in this study population. Mortality in those with BPD-PH was associated with male sex, post-natal steroid use, and increased severity of PH, but not with PVS.

Antenatal Corticosteroids: Who Should We Be Treating?

Antenatal corticosteroids remain one of the crucial interventions in those at risk for imminent preterm birth. Therapeutic benefits include reducing major complications of prematurity such as respiratory distress syndrome, intraventricular hemorrhage, and necrotizing enterocolitis, as well as an overall decrease in neonatal deaths. Optimal reductions in neonatal morbidity and mortality require a thoughtful review of the timing of administration. In addition, a thorough understanding is required of which patients maximally benefit from this intervention in the management and counseling of those at risk for preterm birth.

Impact of Blood Vessel Quantity and Vascular Expression of CD133 and ICAM-1 on Survival of Glioblastoma Patients

Glioblastoma (GB) is the most angiogenic tumor. Nevertheless, antiangiogenic therapy has not shown significant clinical efficacy. The aim of this study was to assess blood vessel characteristics on survival of GB patients. Surgically excised GB tissues were histologically examined for overall proportion of glomeruloid microvascular proliferation (MP) and the total number of blood vessels. Also, immunohistochemical vascular staining intensities of CD133 and ICAM-1 were determined. Vessel parameters were correlated with patients' overall survival. The survival time depended on the number of blood vessels (p = 0.03) but not on the proportion of MP. Median survival times for patients with low (<median) and high (≥median) number of blood vessels were 9.0 months (95% CI: 7.5–10.5) and 12.0 months (95% CI: 9.3–14.7). Also, median survival times for patients with low (<median) and high (≥median) vascular expression level of CD133 were 9.0 months (95% CI: 8.0–10.1) and 12.0 months (95% CI: 10.3–13.7). In contrast, the staining intensity of vascular ICAM-1 did not affect survival. In multivariate analysis, the number of blood vessels emerged as an independent predictor for longer overall survival (HR: 2.4, 95% CI: 1.2–5.0, p = 0.02). For success in antiangiogenic therapy, better understanding about tumor vasculature biology is needed.

Role of stress, depression, and aging in cognitive decline and Alzheimer's disease

Late-onset Alzheimer's disease (AD) is a chronic neurodegenerative disorder and the most common cause of progressive cognitive dysfunction and dementia. Despite considerable progress in elucidating the molecular pathology of this disease, we are not yet close to unraveling its etiopathogenesis. A battery of neurotoxic modifiers may underpin neurocognitive pathology via deleterious heterogeneous pathologic impact in brain regions, including the hippocampus. Three important neurotoxic factors being addressed here include aging, stress, and depression. Unraveling "upstream pathologies" due to these disparate neurotoxic entities, vis-à-vis cognitive impairment involving hippocampal dysfunction, is of paramount importance. Persistent systemic inflammation triggers and sustains neuroinflammation. The latter targets several brain regions including the hippocampus causing upregulation of amyloid beta and neurofibrillary tangles, synaptic and neuronal degeneration, gray matter volume atrophy, and progressive cognitive decline. However, what is the fundamental source of this peripheral inflammation in aging, stress, and depression? This chapter highlights and delineates the inflammatory involvement-i.e., from its inception from gut to systemic inflammation to neuroinflammation. It highlights an upregulated cascade in which gut-microbiota-related dysbiosis generates lipopolysaccharides (LPS), which enhances inflammation and gut's leakiness, and through a Web of interactions, it induces stress and depression. This may increase neuronal dysfunction and apoptosis, promote learning and memory impairment, and enhance vulnerability to cognitive decline.

Dexamethasone induces caveolin-1 in vascular endothelial cells: implications for attenuated responses to VEGF

Steroids exert direct actions on cardiovascular cells, although underlying molecular mechanisms remain incompletely understood. We examined if steroids modulate abundance of caveolin-1, a regulatory protein of cell-surface receptor pathways that regulates the magnitudes of endothelial response to vascular endothelial growth factor (VEGF). Dexamethasone, a synthetic glucocorticoid, induces caveolin-1 at both levels of protein and mRNA in a time- and dose-dependent manner in pharmacologically relevant concentrations in cultured bovine aortic endothelial cells. Aldosterone, a mineralocorticoid, but not the sex steroids 17β-estradiol, testosterone, or progesterone, elicits similar caveolin-1 induction. Caveolin-1 induction by dexamethasone and that by aldosterone were abrogated by RU-486, an inhibitor of glucocorticoid receptor, and by spironolactone, a mineralocorticoid receptor inhibitor, respectively. Dexamethasone attenuates VEGF-induced responses at the levels of protein kinases Akt and ERK1/2, small-G protein Rac1, nitric oxide production, and migration. When induction of caveolin-1 by dexamethasone is attenuated either by genetically by transient transfection with small interfering RNA or pharmacologically by RU-486, kinase responses to VEGF are rescued. Dexamethasone also increases expression of caveolin-1 protein in cultured human umbilical vein endothelial cells, associated with attenuated tube formation responses of these cells when cocultured with normal fibroblasts. Immunohistochemical analyses revealed that intraperitoneal injection of dexamethasone induces endothelial caveolin-1 protein in thoracic aorta and in lung artery in healthy male rats. Thus steroids functionally attenuate endothelial responses to VEGF via caveolin-1 induction at the levels of signal transduction, migration, and tube formation, identifying a novel point of cross talk between nuclear and cell-surface receptor signaling pathways.

Endothelial precursor cells promote angiogenesis in hepatocellular carcinoma

AIM: To investigate the role of bone marrow-derived endothelial progenitor cells (EPCs) in the angiogenesis of hepatocellular carcinoma (HCC).

METHODS: The bone marrow of HCC mice was reconstructed by transplanting green fluorescent protein (GFP) + bone marrow cells. The concentration of circulating EPCs was determined by colony-forming assays and fluorescence-activated cell sorting. Serum and tissue levels of vascular endothelial growth factor (VEGF) and colony-stimulating factor (CSF) were quantified by enzyme-linked immunosorbent assay. The distribution of EPCs in tumor and tumor-free tissues was detected by immunohistochemistry and real-time polymerase chain reaction. The incorporation of EPCs into hepatic vessels was examined by immunofluorescence and immunohistochemistry. The proportion of EPCs in vessels was then calculated.

RESULTS: The HCC model was successful established. The flow cytometry analysis showed the mean percentage of CD133CD34 and CD133VEGFR2 double positive cells in HCC mice was 0.45% ± 0.16% and 0.20% ± 0.09% respectively. These values are much higher than in the sham-operation group (0.11% ± 0.13%, 0.05% ± 0.11%, n = 9) at 14 d after modeling. At 21 d, the mean percentage of circulating CD133CD34 and CD133VEGFR2 cells is 0.23% ± 0.19%, 0.25% ± 0.15% in HCC model vs 0.05% ± 0.04%, 0.12% ± 0.11% in control. Compared to the transient increase observed in controls, the higher level of circulating EPCs were induced by HCC. In addition, the level of serum VEGF and CSF increased gradually in HCC, reaching its peak 14 d after modeling, then slowly decreased. Consecutive sections stained for the CD133 and CD34 antigens showed that the CD133+ and CD34+ VEGFR2 cells were mostly recruited to HCC tissue and concentrated in tumor microvessels. Under fluorescence microscopy, the bone-marrow (BM)-derived cells labeled with GFP were concentrated in the same area. The relative levels of CD133 and CD34 gene expression were elevated in tumors, around 5.0 and 3.8 times that of the tumor free area. In frozen liver sections from HCC mice, cells co-expressing CD133 and VEGFR2 were identified by immunohistochemical staining using anti-CD133 and VEGFR2 antibodies. In tumor tissue, the double-positive cells were incorporated into vessel walls. In immunofluorescent staining. These CD31 and GFP double positive cells are direct evidence that tumor vascular endothelial cells (VECs) come partly from BM-derived EPCs. The proportion of GFP CD31 double positive VECs (out of all VECs) on day 21 was around 35.3% ± 21.2%. This is much higher than the value recorded on day 7 group (17.1% ± 8.9%). The expression of intercellular adhesion molecule 1, vascular adhesion molecule 1, and VEGF was higher in tumor areas than in tumor-free tissues.

CONCLUSION: Mobilized EPCs were found to participate in tumor vasculogenesis of HCC. Inhibiting EPC mobilization or recruitment to tumor tissue may be an efficient strategy for treating HCC.

Anti-proliferative effect of glucocorticoids on mesenchymal cells in juvenile angiofibromas

BACKGROUND

Glucocorticoids (GCs) not only regulate metabolic and inflammatory mechanisms, but also are known to suppress tumor growth. Despite previous detection of glucocorticoid receptors (GRs) in juvenile angiofibromas, their distribution and function have not further been studied.

METHODS

Juvenile angiofibroma tissue (n = 30), nasal mucosa specimens (n = 10), subepithelial stroma of nasal mucosa (n = 20), and primary fibroblasts from juvenile angiofibroma (n = 6) and nasal mucosa samples (n = 6) were analyzed by quantitative reverse transcriptase-polymerase chain reaction (RT-PCR) and immunofluorescence staining. The antiproliferative effect of GCs (dexamethasone, prednisolone, and hydrocortisone) in vitro was assessed using a bromdeoxyuridine (BrdU) assay.

RESULTS

An upregulation of GR transcripts and protein was shown in juvenile angiofibroma tissue and primary mesenchymal cells compared to nasal mucosa. Application of GCs resulted in a significantly higher antiproliferative effect on juvenile angiofibroma versus nasal mucosa fibroblasts in vitro.

CONCLUSION

Expression of GRs and antiproliferative effects of GCs on juvenile angiofibroma fibroblasts offer novel options for the treatment of this unique fibrovascular tumor.

Dexamethasone inhibits ICAM-1 and MMP-9 expression and reduces brain edema in intracerebral hemorrhagic rats

BACKGROUND

The molecular mechanism of hemorrhagic stroke is unclear, and the identification of therapeutic agents for attenuating post-stroke brain damage remains an unresolved challenge. Dexamethasone (DEX) is used clinically to treat spinal cord injury and brain tumor patients by reducing edema formation, but has produced conflicting results in stroke management.

METHODS

In this study, intracerebral hemorrhage (ICH) was induced in rats by intracranial stereotactic injection of collagenase into the caudate nucleus. DEX was given immediately and 3 days after ICH. The expression of intercellular adhesion molecule-1 (ICAM-1), matrix metalloproteinase-9 (MMP-9), nuclear factor (NF)-κB, and IκB were analyzed by Western blotting, and perihematomal edema formation was evaluated by magnetic resonance imaging.

RESULTS

The results showed that ICH caused an increase of ICAM-1 and MMP-9 expression from 4 h to 7 days, which was inhibited following the administration of DEX. The perihematomal edema volume in ICH rats was high, with two peak periods at 12 h and 3 days, which was also reduced in DEX-treated groups. Furthermore, the administration of DEX not only maintained IκB in cytoplasm, but also decreased NF-κB elevation in the nucleus at 3 and 5 days in ICH rats.

CONCLUSIONS

In conclusion, these data show that DEX successfully reduced post-stroke brain edema by decreasing MMP-9 and ICAM-1 levels, partially through the IκB/NF-κB signaling pathway. The timing of DEX administration in relation to the onset of brain injury may be critical.

Effect of prenatal glucocorticoids on cerebral vasculature of the developing brain

BACKGROUND AND PURPOSE

Prenatal glucocorticoids prevent germinal matrix hemorrhage in premature infants. The underlying mechanism, however, is elusive. Germinal matrix is enriched with angiogenic vessels exhibiting paucity of pericytes and glial fibrillary acidic protein-positive astrocyte end feet. Therefore, we asked whether glucocorticoid treatment would suppress angiogenesis and enhance periendothelial coverage by pericytes and glial fibrillary acidic protein-positive end feet in the germinal matrix microvasculature.

METHODS

We treated pregnant rabbits with intramuscular betamethasone and delivered pups prematurely by cesarean section at E29 (term=32 days). Endothelial turnover, vascular density, pericyte coverage, glial fibrillary acidic protein-positive end feet, cell death, and growth factors orchestrating angiogenesis, including vascular endothelial growth factor, angiopoietins, transforming growth factor-beta, and platelet-derived growth factor-B, were compared between betamethasone-treated and untreated pups. Similar comparisons were done between autopsy materials from premature infants exposed and unexposed to prenatal glucocorticoids.

RESULTS

Antenatal glucocorticoid treatment reduced endothelial proliferation, vascular density, and vascular endothelial growth factor expression in the germinal matrix of both rabbits and humans. The pericyte coverage was greater in glucocorticoid-treated rabbit pups and human infants than in controls, but not the glial fibrillary acidic protein-positive end feet coverage. Transforming growth factor-beta, but not angiopoietins and platelet-derived growth factor-B, were elevated in glucocorticoid-treated rabbit pups compared with controls. Betamethasone treatment induced apoptosis, neuronal degeneration, and gliosis in rabbit pups. However, there was no evidence of increased cell death in glucocorticoid-exposed human infants.

CONCLUSIONS

Prenatal glucocorticoid suppresses vascular endothelial growth factor and elevates transforming growth factor-beta levels, which results in angiogenic inhibition, trimming of neovasculature, and enhanced pericyte coverage. These changes contribute to stabilizing the germinal matrix vasculature, thereby reducing its propensity to hemorrhage. Prenatal glucocorticoid exposure does not induce neural cell death in humans, unlike rabbits.

Cross-talk between vascular endothelial growth factor and matrix metalloproteinases in the induction of neovascularization in vivo

Matrix metalloproteinases (MMPs), a specialized group of enzymes capable of proteolytically degrading extracellular matrix proteins, have been postulated to play an important role in angiogenesis. It has been suggested that MMPs can regulate neovascularization using mechanisms other than simple remodeling of the capillary basement membrane. To determine the interplay between vascular endothelial growth factor (VEGF) and MMPs, we investigated the induction of angiogenesis by recombinant active MMPs and VEGF in vivo. Using a rat corneal micropocket in vivo angiogenesis assay, we observed that the active form of MMP-9 could induce neovascularization in vivo when compared with the pro- form of the enzyme as a control. This angiogenic response could be inhibited by neutralizing VEGF antibody, which suggests that MMPs acts upstream of VEGF. Additional in vitro studies using extracellular matrix loaded with radiolabeled VEGF determined that active MMPs can enzymatically release sequestered VEGF. Interestingly, in vivo angiogenesis induced by VEGF could be inhibited by MMP inhibitors, indicating that MMPs also act downstream of VEGF. In addition, inflammation plays an important role in the induction of angiogenesis mediated by both VEGF and MMPs. Our results suggest that MMPs act both upstream and downstream of VEGF and imply that potential combination therapies of VEGF and MMP inhibitors may be a useful therapeutic approach in diseases of pathological neovascularization.

Protopanaxadiol and protopanaxatriol bind to glucocorticoid and oestrogen receptors in endothelial cells

BACKGROUND AND PURPOSE

Ginsenosides are used widely for medicinal purposes, but the mechanisms of their action are still unclear, although there is some evidence that these effects are mediated by nuclear receptors. Here we examined whether two metabolites of ginsenoside, protopanaxadiol (g-PPD) and protopanaxatriol (g-PPT), could modulate endothelial cell functions through the glucocorticoid receptor (GR) and oestrogen receptor (ER). EXPERIMENT APPROACHES: The effects of g-PPD and g-PPT on intracellular calcium ion concentration ([Ca(2+)](i)) and nitric oxide (NO) production in human umbilical vein endothelial cells (HUVECs) were measured using Fura-2-acetoxymethyl ester, 4-amino-5-methylamino-2',7'-difluorofluorescein and Griess reagent. Effects on expression of GR and ER isoforms in HUVECs were determined using reverse transcriptase-/real-time PCR and immunocytochemistry. Phosphorylation of endothelial NO synthase (eNOS) was assessed by Western blotting.

RESULTS

Ginsenoside protopanaxadiol and g-PPT increased [Ca(2+)](i), eNOS phosphorylation and NO production in HUVECs, which were inhibited by the GR antagonist, RU486, the ER antagonist, ICI 182,780 and siRNA targeting GR or ERbeta. The NO production was Ca(2+)-dependent and the [Ca(2+)](i) elevation in HUVECs resulted from both intracellular Ca(2+) release and extracellular Ca(2+) influx.

CONCLUSIONS AND IMPLICATIONS

Ginsenoside protopanaxadiol and g-PPT were functional ligands for both GR and ERbeta, through which these ginsenoside metabolites exerted rapid, non-genomic effects on endothelial cells.

Contribution of bone marrow-derived cells associated with brain angiogenesis is primarily through leukocytes and macrophages

OBJECTIVE

We investigated the role of bone marrow-derived cells (BMDCs) in an angiogenic focus, induced by VEGF stimulation.

METHODS AND RESULTS

BM from GFP donor mice was isolated and transplanted into lethally irradiated recipients. Four weeks after transplantation, groups of mice received adeno-associated viral vector (AAV)-VEGF or AAV-lacZ gene (control) injection and were euthanized at 1 to 24 weeks. BMDCs were characterized by double-labeled immunostaining. The function of BMDCs was further examined through matrix metalloproteinase (MMP)-2 and -9 activity. We found that capillary density increased after 2 weeks, peaked at 4 weeks (P<0.01), and sustained up to 24 weeks after gene transfer. GFP-positive BMDCs infiltration in the angiogenic focus began at 1 week, peaked at 2 weeks, and decreased thereafter. The GFP-positive BMDCs were colocalized with CD45 (94%), CD68 (71%), 5% Vimentin (5%), CD31/von Willebrand factor (vWF) (1%), and alpha-smooth muscle actin (alpha -SMA, 0.5%). Infiltrated BMDCs expressed MMP-9. MMP-9 KO mice confirmed the dependence of the angiogenic response on MMP-9 availability.

CONCLUSIONS

Nearly all BMDCs in the angiogenic focus showed expression for leukocytes/macrophages, indicating that BMDCs minimally incorporated into the neovasculature. Colocalization of MMPs with GFP suggests that BMDCs play a critical role in VEGF-induced angiogenic response through up-regulation of MMPs.

A review of the foreign-body response to subcutaneously-implanted devices: the role of macrophages and cytokines in biofouling and fibrosis

The biological response to implanted biomaterials in mammals is a complex series of events that involves many biochemical pathways. Shortly after implantation, fibrinogen and other proteins bind to the device surface, a process known as biofouling. Macrophages then bind to receptors on the proteins, join into multinucleated giant cells, and release transforming growth factor beta and other inflammatory cytokines. In response to these signals, quiescent fibroblasts are transformed into myofibroblasts, which synthesize procollagen via activation of Smad mediators. The procollagen becomes crosslinked after secretion into the extracellular space. Mature crosslinked collagen and other extracellular matrix proteins gradually contribute to formation of a hypocellular dense fibrous capsule that becomes impermeable or hypopermeable to many compounds. Porous substrates and angiogenic growth factors can stimulate formation of microvessels, which to some extent can maintain analyte delivery to implanted sensors. However, stimulation by vascular endothelial growth factor alone may lead to formation of leaky, thin-walled, immature vessels. Other growth factors are most probably needed to act upon these immature structures to create more robust vessels.During implantation of foreign bodies, the foreign-body response is difficult to overcome, and thousands of biomaterials have been tested. Biomimicry (i.e., creating membranes whose chemical structure mimics natural cellular compounds) may diminish the response, but as of this writing, it has not been possible to create a stealth material that circumvents the ability of the mammalian surveillance systems to distinguish foreign from self.

Stress, depression, and neuroplasticity: a convergence of mechanisms

Increasing evidence demonstrates that neuroplasticity, a fundamental mechanism of neuronal adaptation, is disrupted in mood disorders and in animal models of stress. Here we provide an overview of the evidence that chronic stress, which can precipitate or exacerbate depression, disrupts neuroplasticity, while antidepressant treatment produces opposing effects and can enhance neuroplasticity. We discuss neuroplasticity at different levels: structural plasticity (such as plastic changes in spine and dendrite morphology as well as adult neurogenesis), functional synaptic plasticity, and the molecular and cellular mechanisms accompanying such changes. Together, these studies elucidate mechanisms that may contribute to the pathophysiology of depression. Greater appreciation of the convergence of mechanisms between stress, depression, and neuroplasticity is likely to lead to the identification of novel targets for more efficacious treatments.

Inflammation and ischemia-induced lung angiogenesis

A role for inflammation in modulating the extent of angiogenesis has been shown for a number of organs. The present study was undertaken to evaluate the importance of leukocyte subpopulations for systemic angiogenesis of the lung after left pulmonary artery ligation (LPAL) in a mouse model of chronic pulmonary thromboembolism. Since we (24) previously showed that depletion of neutrophils did not alter the angiogenic outcome, we focused on the effects of dexamethasone pretreatment (general anti-inflammatory) and gadolinium chloride treatment (macrophage inactivator) and studied Rag-1(-/-) mice (T/B lymphocyte deficient). We measured inflammatory cells in bronchoalveolar lavage fluid and lung homogenate macrophage inflammatory protein-2 (MIP-2) and IL-6 protein levels within 24 h after LPAL and systemic blood flow to the lung 14 days after LPAL with labeled microspheres as a measure of angiogenesis. Blood flow to the left lung was significantly reduced after dexamethasone treatment compared with untreated control LPAL mice (66% decrease; P < 0.05) and significantly increased in T/B lymphocyte-deficient mice (88% increase; P < 0.05). Adoptive transfer of splenocytes (T/B lymphocytes) significantly reversed the degree of angiogenesis observed in the Rag-1(-/-) mice back to the level of control LPAL. Average number of lavaged macrophages for each group significantly correlated with average blood flow in the study groups (r(2) = 0.9181; P = 0.01 different from 0). Despite differences in angiogenesis, left lung homogenate MIP-2 and IL-6 did not differ among study groups. We conclude that inflammatory cells modulate the degree of angiogenesis in this lung model where lymphocytes appear to limit the degree of neovascularization, whereas monocytes/macrophages likely promote angiogenesis.

Chronic hydrocephalus-induced hypoxia: increased expression of VEGFR-2+ and blood vessel density in hippocampus

Chronic hydrocephalus (CH) is a neurological disease characterized by increased cerebrospinal fluid volume and pressure that is often associated with impaired cognitive function. By and large, CH is a complex and heterogeneous cerebrospinal fluid (CSF) disorder where the exact site of brain insult is uncertain. Several mechanisms including neural compression, fiber stretch, and local or global hypoxia have been implicated in the underlying pathophysiology of CH. Specifically, the hippocampus, which plays a significant role in memory processing and is in direct contact with expanding CSF ventricles, may be involved. Using our model of chronic hydrocephalus, we quantified the density of vascular endothelial growth factor receptor 2 (VEGFR-2(+)) neurons, glial, endothelial cells, and blood vessels in hippocampal regions CA1, CA2-3, dentate gyrus and hilus using immunohistochemical and stereological methods. Density and %VEGFR-2(+) cell populations were estimated for CH animals (2-3 weeks vs. 12-16 weeks) and surgical controls (SC). Overall, we found approximately six- to eightfold increase in the cellular density of VEGFR-2(+) and more than double blood vessel density (BVd) in the hippocampus of CH compared with SC. There were no significant regional differences in VEGFR-2(+) cellular and BVd expression in the CH group. VEGFR-2(+) and BVds were significantly related to changes in CSF volume (P<or=0.05), and not intracranial pressure (ICP). The %VEGFR-2(+) was significantly greater in CH than SC (P<or=0.05), and was significantly correlated with BVd (P<or=0.05). These results showed that CH elicited a profound increase in VEGFR-2(+) in hippocampus that corresponded to increased BVd. It was unclear whether increased VEGFR-2(+) and blood vessel expression was related to focal compression alone or in combination with global ischemia/hypoxia conditions as previously described. These findings suggest that VEGFR-2 may play an adaptive role in angiogenesis after CH-induced hypoxia. Modulation of vascular endothelial growth factor/VEGFR-2(+) may be important in developing treatments for hypoxic conditions including hydrocephalus and other forms of cerebral ischemia.