PARTIAL CHARACTERIZATION OF A PUTATIVE NEW GROWTH-FACTOR PRESENT IN PATHOLOGICAL HUMAN VITREOUS

Background: Several growth factors have been implicated in the develop ment of proliferative eye diseases, and some of those are present in h uman vitreous (HV). The effects of HV on cellular responses which modu late proliferative cell processes were studied. This study describes t he partial characterization of a vitreous factor activity which does n ot correspond to any of the previously reported growth factors in path ological HV. Methods: Vitreous humour was obtained from medical vitrec tomies, from patients with PDR and PVR. The biological activity of the vitreous factor was determined by its ability to increase cytosolic c alcium concentration ([Ca2+](i)) increase production of inositol phosp hates, and induce cell proliferation in the cell line EGFR T17. In som e experiments other cell lines, such as NIH 3T3, 3T3-L1, FRTL5, A431, PC12, Y79, and GH(3), were also employed. Measurement of [Ca2+](i) in cell suspensions was performed using the fluorescent Ca2+ indicator fu ra-2. The activity of the factor present in HV was compared with other growth factors by means of: (a) [Ca2+](i) mobilization pattern, (b) s equential homologous and heterologous desensitization of receptors, (c ) effects of phorbol esters on their action, and (d) inactivation afte r treatment with different proteolytic enzymes. Results: The HV-induce d cell proliferation and increases in [Ca-2i](i) concentration were ch aracterized by a peculiar time pattern. The different approaches used ruled out its identity with PDGF, bFGF, EGF, TGF-beta, IGFs, TNF-alpha , NGF, and other compounds such as ATP, angiotensin I, and bradykinin. Vitreous factor actions are mediated by specific receptors apparently regulated by PKC. This factor is able to induce [Ca2+](i) mobilizatio n in most of the cell lines studied, indicating that its effects are n ot tissue specific. Conclusions: These results suggest the presence of a growth factor activity in pathological HV which may be due to the p resence of an undescribed growth factor in the eye.