Independent of its PPARgamma activity, dPGJ(2) protected cells from oxidative stress by elevating GSH and enhancing MAPK activation. Thus, dPGJ(2) may delay the development of dry-type age-related macular degeneration.

Although both vascular endothelial growth factor (VEGF) and fibroblast growth factor (FGF) receptors have been shown to be important in the regulation of vascular endothelial cell growth, the roles of phospholipase C (PLC)gamma and Ca(2+) in their downstream signaling cascades are still not clear. We have examined the effects of VEGF and FGF on PLCgamma phosphorylation and on changes in intracellular Ca(2+) levels in primary endothelial cells. VEGF stimulation leads to PLCgamma activation and increases in intracellular Ca(2+), which are correlated with mitogen-activated protein (MAP) kinase (MAPK) activation and cell growth. Inhibition of Ca(2+) increases by the Ca(2+) chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA)-AM resulted in marked inhibition of MAPK activation, which was shown to be linked to regulation of cell growth in these cells. In contrast, FGF stimulation did not lead to PLCgamma activation or to changes in intracellular Ca(2+) levels, although MAPK phosphorylation and stimulation of cell proliferation were observed. Neither BAPTA-AM nor the PLC inhibitor U-73122 had an effect on these FGF-stimulated responses. These data demonstrate a direct role for PLCgamma and Ca(2+) in VEGF-regulated endothelial cell growth, whereas this signaling pathway is not linked to FGF-mediated effects in primary endothelial cells. Thus endothelial cell-specific factors regulate the ability of VEGF receptors and FGF receptors to couple to this signaling pathway.

Oxidative stress causes retinal pigment epithelium (RPE) cell dysfunction and is a major risk factor leading to the development of dry-type age-related macular degeneration. Taking pharmacological and genetic approaches, we address the mechanisms by which sublethal oxidative stress inhibits RPE cell phagocytosis. Sublethal oxidative stress dose-dependently inhibited RPE cell phagocytosis of photoreceptor outer segments (POS) and activated AMP-activated protein kinase (AMPK) as determined by increased Thr 172 and Ser 79 phosphorylation of AMPK␣ and its substrate acetyl-CoA carboxylase, respectively. Similar to oxidative stress, 5-aminoimidazole-4-carboxamide riboside (AICAR), a pharmacological activator of AMPK, inhibited RPE cell phagocytosis of POS in a dose-dependent manner. Inhibition of RPE cell phagocytosis by AICAR was fully reversed by blockade of AICAR translocation into cells by dipyridamole or inhibition of AICAR conversion to ZMP by adenosine kinase inhibitor 5-iodotubercidin. In agreement, AICAR-induced activation of AMPK was abolished by preincubation with dipyridamole or 5-iodotubercidin. Knock-out experiments further revealed that ␣2 but not ␣1 AMPK was involved in RPE cell phagocytosis and that activation of ␣2 AMPK contributed to the inhibition of RPE cell phagocytosis by oxidative stress. Inhibition of RPE cell phagocytosis by activation of ␣2 AMPK was associated with a dramatic increase in acetyl-CoA carboxylase phosphorylation. In comparison, AMPK had no role in oxidative stress-induced breakdown of RPE barrier function. Taken together, reduction in POS load under oxidative stress might direct RPE cells to a self-protected status. Thus, activating AMPK could have therapeutic potential in treating dry macular degeneration.The retinal pigment epithelium (RPE) 2 is a monolayer of pigmented cells forming a part of the blood-retina barrier (1). Basal membrane of the RPE is in contact with Bruch membrane, whereas the apical membrane faces the photoreceptor outer segments. The close structural interactions of RPE cells with the outer retina indicate that the major functions of the RPE layer are to maintain the survival and normal functioning of photoreceptors by controlling nutrients/waste products exchange (2), phagocytosing shed outer segments (3), shuttling retinoids to synthesize visual pigments (4), and producing trophic factors necessary for photoreceptor survival. Failure of any one of these functions can result in degeneration of the retina, loss of visual function, and blindness.Age-related macular degeneration (AMD) is an idiopathic retinal degenerative disease that predominates in the elderly in the Western world as a cause of irreversible, profound vision loss (5, 6). The pathogenic mechanisms whereby environmental factors contribute to the development of AMD remain elusive. However, growing evidence indicates that oxidative stress injury to the RPE plays an important role in the etiology of AMD. The RPE is at high risk for oxidative injury due to its location in a highly oxygenated envi...

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