Biomedical subjects

Omar Benzakour

Publications and source records attributed to Omar Benzakour.

3 recordsLinked to original sources

PubMed2006

Endogenous factors derived from embryonic cortex regulate proliferation and neuronal differentiation of postnatal subventricular zone cell cultures.

In rodents, the subventricular zone (SVZ) harbours neural stem cells that proliferate and produce neurons throughout life. Previous studies showed that factors released by the developing cortex promote neurogenesis in the embryonic ventricular zone. In the present report, we studied in the rat the possible involvement of endogenous factors derived from the embryonic cortex in the regulation of the development of postnatal SVZ cells. To this end, SVZ neurospheres were maintained with explants or conditioned media (CM) prepared from embryonic day (E) 13, E16 or early postnatal cortex. We demonstrate that early postnatal cortex-derived factors have no significant effect on SVZ cell proliferation or differentiation. In contrast, E13 and E16 cortex release diffusible, heat-labile factors that promote SVZ cell expansion through increased proliferation and reduced cell death. In addition, E16 cortex-derived factors stimulate neuronal differentiation in both early postnatal and adult SVZ cultures. Fibroblast growth factor (FGF)-2- but not epidermal growth factor (EGF)-immunodepletion drastically reduces the mitogenic effect of E16 cortex CM, hence suggesting a major role of endogenous FGF-2 released by E16 cortex in the stimulation of SVZ cell proliferation. The evidence we provide here for the regulation of SVZ cell proliferation and neuronal differentiation by endogenous factors released from embryonic cortex may be of major importance for brain repair research.

Age Factors↗

PubMed2004

The tubulin-binding agent combretastatin A-4-phosphate arrests endothelial cells in mitosis and induces mitotic cell death.

The tubulin-binding agent combretastatin A-4-phosphate (CA-4-P), rapidly disrupts the vascular network of tumors leading to secondary tumor cell death. In vitro, CA-4-P destabilizes microtubules and causes endothelial cell death. In this study we analyze the mechanisms by which CA-4-P induces the death of proliferating endothelial cells. We demonstrate that at >/=7.5 nmol/L, CA-4-P damages mitotic spindles, arrests cells at metaphase, and leads to the death of mitotic cells with characteristic G(2)/M DNA content. Mitotic arrest was associated with elevated levels of cyclin B1 protein and p34(cdc2) activity. Inhibition of p34(cdc2) activity by purvalanol A caused mitotic-arrested cells to rapidly exit mitosis, suggesting that sustained p34(cdc2) activity was responsible for metaphase arrest. Pharmacological prevention of entry into mitosis protected cells from undergoing cell death, further establishing the link between mitosis and cell death induction by CA-4-P. CA-4-P-mediated cell death shared characteristics of apoptosis but was independent of caspase activation suggesting the involvement of a non-caspase pathway(s). These data suggest that induction of apoptosis in endothelial cells by CA-4-P is associated with prolonged mitotic arrest. Therefore, by activating cell death pathways, CA-4-P, in addition to being an effective anti-vascular agent, may also interfere with regrowth of blood vessels in the tumor.

Antineoplastic Agents, Phytogenic↗

PubMed2003

Activated protein C alters cytosolic calcium flux in human brain endothelium via binding to endothelial protein C receptor and activation of protease activated receptor-1.

Activated protein C (APC) exerts endothelial protein C receptor (EPCR)-dependent neuroprotective effects in a brain focal ischemia model and direct cellular effects on human umbilical vein endothelial cells (HUVECs) via protease-activated receptor-1 (PAR-1). Because PAR receptors are expressed in brain endothelium and mediate intracellular calcium concentration ([Ca2+]i) signaling, we hypothesized that APC may regulate intracellular [Ca2+] flux in human brain endothelial cells (BECs) via EPCR and PAR-1. Primary cortical BECs derived from human autopsies (early passage) and HUVECs were used for [Ca2+]i imaging fluorometry. Cells were exposed for 1 minute to APC, protein C zymogen, or mutant Ser360Ala-APC, and [Ca2+]i was monitored in the presence or absence of antibodies against PAR-1, PAR-2, PAR-3, or EPCR. APC, but not protein C zymogen or the active site mutant Ser360Ala-APC, induced dose-dependent [Ca2+]i release in human BECs (Delta[Ca2+]i max = 278.3 +/- 19.5 nM; EC50 for APC = 0.23 +/- 0.02 nM, n = 70 measurements). APC-induced [Ca2+]i signaling was abolished by a cleavage site blocking anti-PAR-1 antibody, whereas anti-PAR-2 and -PAR-3 antibodies were without effect. Antibody RCR252 that ablates APC binding to EPCR blocked APC-mediated [Ca2+]i signaling, whereas anti-EPCR antibody RCR92 that does not block APC binding did not abolish the APC-induced [Ca2+]i response. Experiments using HUVECs confirmed the findings for BECs. Thapsigargin inhibited the APC-induced [Ca2+]i signal, implicating the endoplasmic reticulum as a major source for the APC-induced [Ca2+]i release. These data suggest that APC regulates [Ca2+]i in human brain endothelium and in HUVECs by binding to EPCR and signaling via PAR-1.

Antibodies↗