Endothelial COX-2 induction by hypoxia liberates 6-keto-PGF1 alpha, a potent epithelial secretagogue

Fluid Flow Regulation of Revascularization and Cellular Organization in a Bioengineered Liver Platform

OBJECTIVE

Modeling of human liver development, especially cellular organization and the mechanisms underlying it, is fundamental for studying liver organogenesis and congenital diseases, yet there are no reliable models that mimic these processes ex vivo.

DESIGN

Using an organ engineering approach and relevant cell lines, we designed a perfusion system that delivers discrete mechanical forces inside an acellular liver extracellular matrix scaffold to study the effects of mechanical stimulation in hepatic tissue organization.

RESULTS

We observed a fluid flow rate-dependent response in cell distribution within the liver scaffold. Next, we determined the role of nitric oxide (NO) as a mediator of fluid flow effects on endothelial cells. We observed impairment of both neovascularization and liver tissue organization in the presence of selective inhibition of endothelial NO synthase. Similar results were observed in bioengineered livers grown under static conditions.

CONCLUSION

Overall, we were able to unveil the potential central role of discrete mechanical stimulation through the NO pathway in the revascularization and cellular organization of a bioengineered liver. Last, we propose that this organ bioengineering platform can contribute significantly to the identification of physiological mechanisms of liver organogenesis and regeneration and improve our ability to bioengineer livers for transplantation.

Evaluation of VEGF-mediated signaling in primary human cells reveals a paracrine action for VEGF in osteoblast-mediated crosstalk to endothelial cells

Communication between endothelial and bone cells is crucial for controlling vascular supply during bone growth, remodeling, and repair but the molecular mechanisms coordinating this intercellular crosstalk remain ill-defined. We have used primary human and rat long bone-derived osteoblast-like cells (HOB and LOB) and human umbilical vein endothelial cells (HUVEC) to interrogate the potential autocrine/paracrine role of vascular endothelial cell growth factor (VEGF) in osteoblast:endothelial cell (OB:EC) communication and examined whether prostaglandins (PG), known modulators of both OB and EC behavior, modify VEGF production. We found that the stable metabolite of PGI2, 6-keto-PGF(1alpha) and PGE2, induced a concentration-dependent increase in VEGF release by HOBs but not ECs. In ECs, VEGF promoted early ERK1/2 activation, late cyclooxygenase-2 (COX-2) protein induction, and release of 6-keto-PGF1alpha. In marked contrast, no significant modulation of these events was observed in HOBs exposed to VEGF, but LOBs clearly exhibited COX-dependent prostanoid release (10-fold less than EC) following VEGF treatment. A low level of osteoblast-like cell responsiveness to exogenous VEGF was supported by VEGFR2/Flk-1 immunolabelling and by blockade of VEGF-mediated prostanoid generation by a VEGFR tyrosine kinase inhibitor (TKI). HOB alkaline phosphatase (ALP) activity was increased following long-term non-contact co-culture with ECs and exposure of ECs to VEGF in this system further increased OB-like cell differentiation and markedly enhanced prostanoid release. Our studies confirm a paracrine EC-mediated effect of VEGF on OB-like cell behavior and are the first supporting a model in which prostanoids may facilitate this unidirectional VEGF-driven OB:EC communication. These findings may offer novel regimes for modulating pathological bone remodeling anomalies through the control of the closely coupled vascular supply.

Expression of cyclooxygenase-2 and epidermal growth factor receptor in primary and recurrent glioblastoma multiforme

PURPOSE

To investigate the pattern and level of cyclooxygenase-2 (COX-2) expression in a series of high grade primary and recurrent glioblastoma multiforme (GBM) and correlation with time to recurrence and patients' survival following therapy. The relationship between COX-2 and epidermal growth factor receptor (EGFR) immunoreactivities was evaluated.

MATERIALS AND METHODS

Specimens of 14 primary and 14 recurrent GBMs (eight pairs) following surgery and full course radiation therapy were processed for immunostaining on COX-2 and EGFR. Tumor cell positivity was semi-quantitatively scored. COX-2 scores of the primary tumor and recurrence were correlated with the time to radiological tumor progression and patients' survival.

RESULTS

COX-2 positive tumor cells were disseminated throughout the tumor parenchyma. The intensity and pattern of COX-2 expression were heterogeneous, with predominant expression in areas surrounding tumor necrosis. Scoring of COX-2 positivity revealed values between 1 and 80% of the cells. Primary GBMs with COX-2 expression levels between 25% and 70% of the tumor cells showed a shorter time to radiological recurrence than GBMs with <10% COX-2 positive tumor cells (respectively, 219 +/- 50 and 382 +/- 77 days). No correlation was found between the COX-2 expression in the primary tumor and patients' survival (r (s) = -0.073) following therapy. No correlation was found either between COX-2 and EGFR immunoreactivity.

CONCLUSIONS

Immunohistochemical expression of COX-2 in GBM showed large variation. Hence, determination of COX-2 expression in tumor specimen for each individual might be relevant for selection of those patients, who could benefit from adjuvant therapy with selective COX-2 inhibitors.

Lipid mediator networks and leukocyte transmigration

In intact tissues, vascular endothelial cells lie anatomically positioned as the central coordinator of inflammation. Endothelia communicate with underlying cells (e.g. smooth muscle, fibroblasts, epithelia) in ways that both coordinate leukocyte trafficking, and control the composition of the inflammatory microenvironment. Such coordination occurs through both direct communication (e.g. cell adhesion) as well as via soluble mediators liberated at sites of inflammation (e.g. chemokines, cytokines, lipids). Locally generated mediators bind to surface receptors, and mediate both physiologic and pathophysiologic functional responses. Important in this regard, both endothelial and subendothelial cell populations express enzymes capable of utilizing arachidonic acid substrates to generate bioactive lipid mediators (e.g. lipoxygenases, cyclooxygenases). Such lipid mediators can signal via autocrine or paracrine pathways and, depending on the tissue microenvironment, can convey a pro- or anti-inflammatory message. This review will highlight recent studies characterizing inflammatory responses to lipid mediators liberated at sites of inflammation, with a particular emphasis on neutrophil (polymorphonuclear leukocyte or PMN) trafficking.