Platelet factor and cerebral vascular endothelium: platelet-induced mitogenesis

Platelet-derived endothelial cell growth factor

Platelet-derived endothelial cell growth factor (PD-ECGF) is a 45 kDa single chain polypeptide, which stimulates the DNA synthesis and chemotaxis of endothelial cells in vitro and angiogenesis in vivo. Purification from human platelets and cDNA cloning from a human placental cDNA library, revealed that PD-ECGF is a novel type of peptide without sequence similarity to hitherto known proteins. PD-ECGF is present in human platelets and placenta, and is produced by certain normal and transformed cultured cells; it lacks a hydrophobic leader sequence and most of the protein remains inside the producer cells. Analysis of PD-ECGF produced by cultured cells, revealed that it contains nucleotide(s) covalently bound to serine residues. The in vivo function of PD-ECGF is not known; its target cell specificity and tissue distribution suggest roles in angiogenesis of the placenta and in the maintenance of the integrity of the endothelial cell layer of blood vessels. PD-ECGF may have a clinical utility in the stimulation of wound healing and re-endothelialization of vessels.

Cerebral endothelial regeneration following experimental brain injury. Variation in the regeneration process according to the severity of injury

It is still unknown when and in which area endothelial regeneration occurs after brain injury, and to what extent such changes depend on the severity of the injury. We have, therefore, studied bromodeoxyuridine (BrdU) uptake by regenerating endothelial cells in two different groups of rats given cold lesions using immunohistochemistry employing anti-BrdU monoclonal antibody, anti-factor VIII-related antigen antibody and anti-glial fibrillary acidic protein antibody. The earliest evidence for the presence of BrdU-positive endothelial cells (BrdU + end) was observed at 2 days after injury, the injured endothelial cells regenerating from the edge toward the center of the lesion in both groups. We considered that edema fluid could act as an important factor, since at 2 days post-injury BrdU + end were not in contact with macrophages and were always found in Evans blue-stained areas. Study of endothelial cell kinetics also confirmed that the repair of injured endothelial cells was intimately involved in the reconstruction of the blood-brain barrier, since the time of disappearance of BrdU + end coincided with the disappearance of Evans blue-stained areas. The difference in the process of endothelial regeneration was first apparent on the 3rd day, there being no difference at 2 days.

Effect of serum from patients with idiopathic thrombocytopenic purpura on cultured endothelial cell growth

This study examined the effects of platelet-derived serum factors from patients with idiopathic thrombocytopenic purpura (ITP) on human umbilical cord vascular endothelial cell growth and DNA synthesis. Vascular endothelial cell growth factors were identified in the platelet extracts, and platelet-derived vascular endothelial cell growth factors with molecular weights of less than 10,000 were also identified in the sera. These growth factors were stable even after 30 minutes of heat treatment at 56 degrees C and acid treatment. When ITP patient serum was added to vascular endothelial cells, their growth capacity and DNA synthesis capacity were lower than when serum from normal subjects or patients with ITP in remission was added. This indicated that in ITP, impairment of vascular integrity and abnormal repair of the vascular walls that accompany thrombocytopenia may be causes of the predisposition to hemorrhage. The decrease in ITP of platelet-derived vascular endothelial cell growth factors with molecular weights of less than 10,000 was hypothesized to be a contributory factor.

Growth control in cerebral microvessel-derived endothelial cells

Endothelial (En) cells derived from the cerebral microvasculature were examined for their growth control properties. These cells were shown to be growth responsive to fetal bovine serum and arrested growth if serum was removed. They lend themselves to studies in chemically defined media since they survive well in serum-free medium with little or no proliferation. These cerebral microvessel En cells also respond to epidermal growth factor (EGF) and platelet-derived growth factor (PDGF), unlike some other endothelial cells. Similar to other endothelial cells, the En cells responded to fibroblast growth factor (FGF). The response to EGF and PDGF occurred in serum-free media, but only if both agents were present. The cells further responded mitogenically to conditioned media obtained from transformed endothelial cells. The En cells were found to bind EGF and displayed two orders of affinity as determined by Scatchard analysis, depending upon whether the cells were in confluent or subconfluent conditions. The data indicate that some endothelial cells respond to EGF and PDGF and that one mechanism for growth control of endothelial cells may be an ability to regulate high-affinity growth factor receptors for epidermal growth factor.

Proliferative response of human endothelial cultures to various types and treatments of human sera, to culture treatments and to various oxygen concentrations

Endothelial cells from the human umbilical vein were exposed to different human sera, differently treated serum, to various oxygen concentrations, and various culture treatments. Endothelial proliferation was determined by measuring the uptake of [3H]-thymidine by means of autoradiography and presented as thymidine labeling index (TI) values. TI values differed according to different serum concentrations, serum types, serum preparations (WBS-PDS) and serum pretreatments. Low oxygen concentrations in the incubator atmosphere induced an early DNA synthesis response without an increase in cell number. The addition of the protease inhibitors aprotinin and soybean trypsin inhibitor to the culture medium resulted in a dose dependent TI decrease, whereas PMSF showed no influence.