Hepatocyte growth factor/scatter factor in the eye

Hepatocyte growth factor activates endothelial nitric oxide synthase by Ca(2+)- and phosphoinositide 3-kinase/Akt-dependent phosphorylation in aortic endothelial cells

Hepatocyte growth factor (HGF) causes endothelium-dependent vasodilation, but its relation to endothelial nitric oxide synthase (eNOS) activity remains to be elucidated. Treatment of bovine aortic endothelial cells with HGF increased eNOS activity within minutes, accompanied by an increase of activity-related site-specific phosphorylation of eNOS. The phosphorylation was completely abolished by pretreatment of the cells with a phosphoinositide 3-kinase (PI3K) inhibitor (wortmannin) and by transfection of dominant-negative Akt, and the enzyme activity was inhibited by wortmannin. In addition, eNOS activity and phosphorylation were abolished by pretreatment of the cells with an intracellular Ca(2+)-chelator, bis-(o-aminophenoxy)ethane-N,N,N',N'-tetra-acetic acid tetrakis(acetoxymethyl ester) (BAPTA/AM), with a suppression of Akt phosphorylation. These results suggest that HGF stimulates eNOS activity by a PI3K/Akt-dependent phosphorylation in a Ca(2+)-sensitive manner in vascular endothelial cells.

Targeting of mitogen-activated protein kinases and phosphatidylinositol 3 kinase inhibits hepatocyte growth factor/scatter factor-induced angiogenesis

BACKGROUND

Hepatocyte growth factor/scatter factor (HGF/SF) can sufficiently and independently induce pathophysiological angiogenesis. However, the treatment strategies have mostly been unsuccessful. The present study is the first to evaluate the possible targeting of downstream signals for the inhibition of HGF/SF-induced angiogenesis.

METHODS AND RESULTS

In a multichannel scratch assay with human endothelial cells (ECs), HGF/SF induced a strong and prolonged activation of MAPK and cell proliferation that was inhibited by PD98059 and LY294002/wortmannin, selective inhibitors of MAPK and PI3K signaling modules, respectively. Western blotting demonstrated a temporal relation between the activation of the two pathways. Chemical inhibition of the PI3K and MAPK signals inhibited HGF/SF-induced chemoinvasion of ECs in vitro and blocked the HGF/SF-induced neovascularization into a polymer scaffold in vivo, as quantified by vessel counts and the clearance of radioactive 133Xe.

CONCLUSIONS

These data indicate that MEK and PI3K inhibitors represent a promising approach to the clinical management of pathological conditions characterized by overt HGF/SF-induced angiogenesis.

Hepatocyte growth factor/scatter factor can induce angiogenesis independently of vascular endothelial growth factor

OBJECTIVE

Hepatocyte growth factor/scatter factor (HGF/SF) promotes vascular endothelial growth factor (VEGF) expression and induces angiogenesis in multiple pathological conditions. The present study was designed to delineate the HGF/SF and VEGF signaling cascades during angiogenesis by using PTK787, a selective VEGF receptor antagonist.

METHODS AND RESULTS

PTK787 produced a concentration-dependent (10(-8) to 10(-6) mol/L) inhibition of VEGF-induced angiogenesis, without altering the basal or HGF/SF-induced response in vitro. In contrast, the nonspecific kinase inhibitor genistein blocked the HGF/SF-induced effect. Both VEGF and HGF/SF induced a rapid phosphorylation of extracellular receptor kinases-1 and -2 (ERKs) and Akt. PTK787 inhibited the VEGF-induced activation of Akt and ERKs, without affecting the HGF/SF-induced phosphorylation. Treatment with VEGF and HGF/SF increased total neovascularization in a murine scaffold granuloma model, but no additive or synergistic interactions were observed. PTK787 (50 mg/kg) blocked the VEGF-induced response without altering the basal or HGF/SF-induced neovascularization.

CONCLUSIONS

We demonstrate that HGF/SF can induce angiogenesis independently of VEGF, possibly through the direct activation of the Akt and ERKs. These results demonstrate the necessity of a multitargeted approach for the rational design of newer therapies to inhibit pathophysiological angiogenesis.

Pathobiology of epiretinal and subretinal membranes: possible roles for the matricellular proteins thrombospondin 1 and osteonectin (SPARC)

Epiretinal and subretinal membranes are fibrocellular proliferations which form on the surfaces of the neuroretina as a sequel to a variety of ocular diseases. When these proliferations complicate rhegmatogenous retinal detachment (a condition known as proliferative vitreoretinopathy or PVR), the membranes often contain numerous retinal pigment epithelial (RPE) cells and a variety of extracellular proteins. The extracellular proteins include adhesive proteins like collagen, laminin and fibronectin. In addition, several matricellular proteins with potential counter-adhesive functions are present in the membranes. Two such matricellular proteins, thrombospondin 1 and osteonectin (or SPARC: Secreted Protein Acidic and Rich in Cysteine), tend to be co-distributed with the RPE cells in PVR membranes. By virtue of their counter-adhesive properties, thrombospondin 1 and SPARC may reduce RPE cell-matrix adhesion and so permit key RPE cellular activities (for example, migration or shape change) in periretinal membrane development. Furthermore, within a 'cocktail' containing other proteins such as the metalloproteinases and growth factors like the scatter factor/hepatocyte growth factor family, matricellular proteins may play a role in the RPE cell dissociation from Bruch's membrane, which characterises early PVR.

Novel growth factors involved in the pathogenesis of proliferative vitreoretinopathy

AIMS

To determine whether hepatocyte growth factor (HGF) and connective tissue growth factor (CTGF) are expressed in human specimens of proliferative vitreoretinopathy (PVR) and to propose a model of PVR pathogenesis based upon the known activities of these growth factors. Methods Immunohistochemical methods (ABC Elite) were used to demonstrate the presence of HGF and CTGF in cryostat sections of five human PVR membranes.

RESULTS

In each of the five PVR membranes, stromal cells were immunohistochemically positive for both HGF and CTGF. Based upon this information and the known actions of these growth factors, a model of PVR pathogenesis was developed. In this model, injury of the retina induces an inflammatory response that upregulates HGF expression inducing the formation of multilayered groups of migratory retinal pigment epithelial cells (RPE). These RPE, present in a provisional extracellular matrix, come in contact with vitreous containing TGF-beta. The TGF-beta is activated, upregulating expression of CTGF. Under the influence of TGF-beta and CTGF, RPE become myofibroblastic and fibrosis ensues. Retinal traction induces further detachment continuing the cycle of retinal injury.

CONCLUSIONS

HGF and CTGF are expressed in PVR membranes and may play important roles in the pathogenesis of PVR. The expression and function of these growth factors should be critically examined in human PVR specimens, in in vitro cultures of RPE, and in animal models of PVR.

Hepatocyte growth factor is associated with poor prognosis of malignant gliomas and is a predictor for recurrence of meningioma

BACKGROUND

Hepatocyte growth factor (HGF) is a cytokine that participates in multiple cell functions; it promotes proliferation, motility, and morphogenesis of epithelial cells. Some malignant tumors, such as breast carcinoma, bronchogenic carcinoma, and multiple myeloma, overexpress it and its receptor. Hepatocyte growth factor is also present in normal astrocytes; therefore, it is important to investigate whether HGF participates in the pathophysiology of malignant gliomas and other brain tumors. Intratumoral concentration of HGF in human intracranial neoplasms was measured and correlated with prognosis, tumor recurrence, vasogenic edema, cell proliferation index, and vascular density.

METHODS

Hepatocyte growth factor concentration was measured in 62 intracranial tumors, including 16 anaplasic astrocytomas (AA), 16 glioblastoma multiformes (GM), 11 meningiomas, 9 hypophyseal adenomas, 7 oligodendrogliomas, and 3 cordomas, and in 4 samples of nonneoplastic brain tissue. The following parameters were correlated with HGF values: survival and tumor recurrence, cell proliferation index and vascular density as determined by immunohistopathologic analysis, and peritumoral edema as seen by magnetic resonance imaging.

RESULTS

Hepatocyte growth factor concentration (pg/mL) was significantly higher in malignant gliomas (AA and GM) than in adenomas, oligodendrogliomas, and nonneoplastic brain tissue, but it was similar to that of meningiomas. Mean survival of patients with AA was 16.5 +/- 3.6 months and for patients with GM 12.3 +/- 1.3 months. Hepatocyte growth factor concentration was higher in GM than in AA (15,844 +/- 2504 vs. 7499 +/- 1703, P = 0.0375) and was correlated with the cell proliferation index and with poor prognosis. Likewise, mean tumoral concentration of HGF was higher in meningiomas that relapsed than in those without recurrence (22,887 +/- 6489 vs. 2090 +/- 497, P = 0.008).

CONCLUSIONS

Intratumoral concentration of HGF in gliomas is associated with malignancy and poor prognosis. High HGF is also found in meningiomas and is related with long term recurrence. The current findings suggest that the routine measurement of HGF may be used as a predictive factor for planning therapeutic strategies in both malignant gliomas and meningiomas. The potential use of HGF inhibitors or antagonists for therapy of these tumors should be explored.

Effects of angiogenic growth factor combinations on retinal endothelial cells

The aim of this paper was to determine if growth factors, known to be upregulated in proliferative diabetic retinopathy, exerted combined effects on retinal endothelial cells. The authors explored the individual and collective actions of insulin-like growth factor I (IGF-I), vascular endothelial growth factor (VEGF), platelet-derived growth factor-BB (PDGF-BB), fibroblast growth factor-2 (FGF-2) and placenta growth factor (PlGF) on several parameters that reflect the angiogenic potential of endothelial cells. The effect of growth factors on cell migration and survival/proliferation was examined using primary cultures of bovine retinal endothelial cells (BREC). The authors also determined the growth factor action on capillary-like tube formation on a reconstituted basement membrane matrix and on the newly described phenomenon of secondary sprouting, in which endothelial cell colonies spontaneously survive, proliferate, migrate and invade the matrix after the original capillary-like tubes have collapsed. Sprouting cells were positive for von Willebrand factor and could aggregate into larger tubes with lumens. Incubation with VEGF+IGF-I or PlGF+FGF-2 enhanced tube stability by 40-50%, more than each growth factor alone or other combinations (5-20%). The concurrent addition of four growth factors did not improve the response seen with growth factor pairs. Surprisingly, PDGF-BB induced tube collapse. IGF-I and FGF-2 mildly enhanced BREC proliferation/survival (5-15%). However, VEGF+IGF-I or PlGF+FGF-2 increased BREC proliferation/survival by 25% under low serum conditions, whereas combinations of all four growth factors exerted a clearly synergistic effect (250% increase). PDGF-BB or FGF-2 stimulated secondary sprouting and were the only factors capable of exerting this effect alone. Even though VEGF, IGF-I or PlGF were not effective, if administered in pairs, they demonstrated increased responses. PDGF-BB was also able to enhance the effect of FGF-2+IGF-I+VEGF on BREC secondary sprouting, but not of any of them individually. No other growth factor tested was able to significantly improve the action of combinations of three other growth factors. VEGF increased cell migration in a wounded monolayer assay two-fold and PDGF-BB, 2.5 times, but other individual growth factors were ineffective. PlGF+FGF-2 enhanced cell migration more than each factor alone. VEGF+IGF-I+PlGF+FGF-2, however, increased cell migration four-fold. In summary, this study indicates that growth factors, overexpressed in diabetic retinopathy eyes, enhance the angiogenic characteristics of cultured cells (tube formation, proliferation, secondary sprouting and migration). Their effects, however, can be greatly augmented by other growth factors that alone exert little or no action. Therefore, diabetic retinal neovascularization may result from the additive or synergistic action of several growth factors.

Proliferative vitreoretinopathy: risk factors and pathobiology

Proliferative vitreoretinopathy (PVR) is still a major cause of failure of retinal detachment surgery. Despite a dramatic increase in our pathobiologic knowledge of PVR during the last 10 years, little of this information has been used to modify the surgical management of the disease, and, thus, the anatomic and functional results are still unsatisfactory. Collaborative research involving clinicians and basic researchers must be encouraged. PVR must be considered a multifactorial disease caused by interaction of several cells and intra- and extraocular factors. Therefore, therapeutic options based on the inhibition of one factor or phenomenon may be regarded with scepticism. To prevent PVR, it is necessary to determine the factors involved in its development, and because of its relatively small prevalence, large, prospective, multicenter studies seem necessary. In addition, clinical research must not be underestimated. PVR affects both sides of the retina and the retina itself, a point to which little attention has been paid and that is critical for surgical results. Therefore, a new classification that provides information about clinical relevance, such as the evolutionary stages of the disease (biologic activity) and the degree of surgical difficulty (location of the fibrotic process), seems necessary.

Hepatocyte growth factor is increased in the aqueous humor of glaucomatous eyes

PURPOSE

To assess the concentrations of hepatocyte growth factor (HGF) in the aqueous humor of eyes with glaucoma compared with control eyes with cataract only.

METHODS

Concentrations of HGF were measured in aqueous humor aspirates taken during anterior segment surgery from 84 patients, of whom 72 had glaucoma (38 cases of primary open-angle glaucoma, 17 angle-closure glaucoma, and 17 exfoliative glaucoma) and 12 had cataract only, using a sandwich enzyme-linked immunosorbent assay kit.

RESULTS

Hepatocyte growth factor was detected in all samples. The concentration in eyes with cataract only was 563.3 +/- 178.8 pg/mL (mean +/- standard deviation), which was significantly lower than that in eyes with glaucoma (967.1 +/- 514.7 pg/mL, P < 0.01). Eyes with exfoliative glaucoma had significantly higher HGF concentrations (1,425.5 +/- 586.7 pg/mL) than did eyes with primary open-angle glaucoma (855.0 +/- 341.5 pg/mL) and angle-closure glaucoma (759.4 +/- 511.4 pg/mL) (P < 0.01). There was no effect of age, sex, or history of medical, laser, or surgical treatment on the aqueous humor HGF concentration (P > 0.05). Aqueous humor and plasma HGF concentrations were measured and compared in 28 patients. The aqueous humor HGF concentration (908 +/- 586.2 pg/mL) was significantly higher (P < 0.01) than the plasma concentration (521.3 +/- 183.1 pg/mL). No significant correlation could be found between aqueous humor and plasma HGF concentrations.

CONCLUSIONS

The relatively high concentration of HGF in human aqueous humor suggests that HGF may play an important role in ocular physiology and disease. The higher concentration in patients with glaucoma may indicate a response to injury.