Functional properties of hyalocytes under PDGF-rich conditions.
OBJECTIVE
To investigate the functional properties and intracellular signaling of hyalocytes under platelet-derived growth factor (PDGF)-rich conditions.


METHODS
The hyalocytes were isolated from bovine eyes and identified by immunocytochemistry and electron microscope. The expression of PDGF receptor alpha/beta and its phosphorylation in response to PDGF-BB was analyzed by Western blot analysis. PDGF-BB-induced proliferation and migration were evaluated by thymidine uptake and Boyden's chemotaxis assay. The expression of the urokinase-type plasminogen activator (uPA) gene and the fibrinolytic activity were assessed by Northern blotting and fibrin zymography. An in vitro type I collagen gel contraction assay was performed to determine the effect of PDGF-BB on cellular contraction.


RESULTS
The hyalocytes were immunocytochemically positive for S-100 and negative for glial fibrillary acidic protein (GFAP) and cytokeratin, as previously described. The electron microscope demonstrated that hyalocytes possess lysosome-like granules, mitochondria, and micropinocytotic vesicles in their cytoplasm. The hyalocytes expressed PDGF receptor alpha and beta, both of which were immediately phosphorylated in response to PDGF-BB. PDGF-BB also activated p85 PI3-kinase, p44/p42 mitogen-activated protein (MAP) kinase and p38 MAP kinase. PDGF-BB induced thymidine uptake and migration in a concentration-dependent (0-10 ng/mL) manner. Inhibitors of the respective kinases prohibited PDGF-BB-dependent thymidine uptake and migration with the exception of the p44/p42 MAP kinase inhibitor, which displayed no inhibitory effects on migration. PDGF-BB increased uPA gene expression and fibrinolytic activity. Collagen gel contraction observed under PDGF-BB-rich conditions was not prohibited by the respective inhibitors investigated.


CONCLUSIONS
The hyalocytes demonstrated macrophage-like characteristics and may have both physiologic and pathologic roles, such as the maintenance of vitreous transparency through fibrinolytic activity and the pathogenesis of proliferative-vitreoretinal diseases through cellular proliferation and vitreous hyper-contraction.
Noda
Yoshihiro
Y
Department of Ophthalmology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan.
Hata
Yasuaki
Y
Hisatomi
Toshio
T
Nakamura
Yuka
Y
Hirayama
Kumiko
K
Miura
Muneki
M
Nakao
Shintaro
S
Fujisawa
Kimihiko
K
Sakamoto
Taiji
T
Ishibashi
Tatsuro
T
D000818:Animals; D000077214:Becaplermin; D015153:Blotting, Western; D002417:Cattle; D018929:Cell Culture Techniques; D002455:Cell Division; D002465:Cell Movement; D002633:Chemotaxis; D005904:Glial Fibrillary Acidic Protein / Q000378:metabolism; D007150:Immunohistochemistry; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology*; D020574:Proto-Oncogene Proteins c-sis; D020796:Receptor, Platelet-Derived Growth Factor alpha / Q000378:metabolism; D020797:Receptor, Platelet-Derived Growth Factor beta / Q000378:metabolism; D009418:S100 Proteins / Q000378:metabolism; D013936:Thymidine / Q000378:metabolism; D014822:Vitreous Body / Q000166:cytology* / Q000187:drug effects / Q000502:physiology*
D005904:Glial Fibrillary Acidic Protein; D010982:Platelet-Derived Growth Factor; D020574:Proto-Oncogene Proteins c-sis; D009418:S100 Proteins; D000077214:Becaplermin; D019869:Phosphatidylinositol 3-Kinases; D020796:Receptor, Platelet-Derived Growth Factor alpha; D020797:Receptor, Platelet-Derived Growth Factor beta; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D013936:Thymidine