New work by Bouck and colleagues now gives evidence that a natural protein, pigment epithelium-derived factor (PEDF), is a potent inhibitor of abnormal blood vessel growth in a murine model of ocular ...neovascularization. This provides compelling evidence that PEDF may be pivotal in controlling both normal and abnormal blood vessel growth.
Cultured pigment epithelial cells of the fetal human retina secrete a protein, pigment epithelium-derived factor (PEDF), that induces a neuronal phenotype in cultured human retinoblastoma cells. ...Morphological changes include the induction of an extensive neurite meshwork and the establishment of corona-like cellular aggregates surrounding a central lumen. The differentiated cells also show increases in the expression of neuron-specific enolase and the 200-kDa neurofilament subunit. Amino acid and DNA sequence data demonstrate that PEDF belongs to the serine protease inhibitor (serpin) family. The PEDF gene contains a typical signalpeptide sequence, initiator methionine codon, and polyadenylylation signal and matches the size of other members of the serpin superfamily (e.g., α1-antitrypsin). It lacks homology, however, at the putative serpin reactive center. Thus, PEDF could exert a paracrine effect in the embryonic retina, influencing neuronal differentiation by a mechanism that does not involve classic inhibition of serine protease activity.
The retinal degenerations (RDs) are a family of inherited retinal degenerative diseases (dystrophies) that lead to vision loss. Although phenotypically very different, the RDs have several ...characteristics in common. They all are caused by gene mutations or at least have a genetic component in the etiology. They all lead to photoreceptor dysfunction, many leading to the death of both rod and cone photoreceptors. The mechanism of cell death in most of the RDs seems to be through the process of apoptosis. It is estimated that more than fifteen million people around the world have vision loss due to an inherited RD. Many of these are patients with the dry form of age-related macular degeneration (AMD) who retain partial functional vision. However, some have other degenerative conditions such as retinitis pigmentosa, Leber congenital amaurosis or wet AMD and can suffer from severe vision loss or total blindness.
Heme oxygenase-1 is an important enzyme that degrades heme, a pro-oxidant, leading to the formation of antioxidant molecules. In this study we demonstrate by immunocytochemistry close association of ...heme oxygenase-1 with Alzheimer neurofibrillary pathology and with the neurofibrillary tangles found in progressive supranuclear palsy and subacute sclerosing panencephalitis. In Alzheimer's disease, using two different rabbit antisera against heme oxygenase-1 protein, we localized, using immunocytochemical methods, heme oxygenase-1 to neurofibrillary tangles, senile plaque neurites, granulovacuolar degeneration, and neuropil threads. Only light background staining was seen in young controls and sporadic lesion-related immunoreactivity in age-matched controls. The increase in heme oxygenase-1 protein in association with the neurofibrillary pathology of Alzheimer's disease and other diseases characterized by neurofibrillary tangles supports the notion that the generation of free radicals and oxidative stress plays a role in the pathogenesis of neurofibrillary pathology.
To investigate the role of abnormal lipid metabolism in Bietti crystalline dystrophy.
Cultured human lymphocytes and fibroblasts from patients with Bietti crystalline dystrophy (BCD) were incubated ...in the presence of (14)C18:3n-3 or (14)C18:2n-6. Incorporation into the cellular lipid pools and further metabolism by desaturation or elongation were monitored by thin-layer chromatography and HPLC. Results were compared with those in normal control subjects and patients with Wolman disease (WD).
Pulse-chase experiments with labeled fatty acids in all groups showed that, after 1 hour, radioactivity was largely confined to the triacylglyceride (TG) and choline phosphoglyceride (CPG) pools. However, after several hours, radioactivity was transferred from the TG and CPG pools, some going to the serine and ethanolamine phosphoglyceride (SPG and EPG) pools. Fibroblasts from all groups showed direct transfer of fatty acids (FAs) into CPG and EPG. Incorporation of labeled FAs into the EPG pool paralleled extensive desaturation and elongation of 18:2n-6 to 22:5n-6 and 18:3n-3 to 22:6n-3. Fibroblasts from patients with WD (a lysosomal acid lipase deficiency characterized by excessive lipid accumulation), showed higher incorporation of 18:2n-6 into TGs than did normal or BCD fibroblasts. Conversely, fibroblasts from patients with BCD showed lower conversion of 18:3n-3, but not of 18:2n-6, into polyunsaturated FAs (PUFAs) than those of normal subjects or patients with WD. This was true for total FAs, CPGs, and EPGs. Similar results were found in both fibroblasts and lymphocytes; however, unlike fibroblasts, lymphocytes from normal subjects showed similar levels of incorporation of FAs into EPGs and CPGs. In contrast, incorporation of 18:3n-3 into EPGs was decreased in lymphocytes from patients with BCD.
BCD is characterized by a lower than normal conversion of FA precursors into n-3 PUFA, whereas there is a higher than normal level of n-6 and n-3 FAs incorporation into TGs in cells from patients with WD. These findings raise the possibility that abnormal lipid metabolism associated with BCD is the result of deficient lipid binding, elongation, or desaturation in contrast to the lysosomal acid lipase deficiency found in Wolman disease.
: Pigment epithelium‐derived factor (PEDF) is a survival factor for cerebellar granule cells in culture. In the present study, we have investigated the ability of a recombinant form of PEDF (rPEDF) ...to protect against glutamate neurotoxicity. When rPEDF was added to cerebellar granule cell cultures 30 min before addition of 100 µM glutamate, glutamate‐induced neuronal death was significantly reduced. The protective effect of rPEDF was dose‐dependent in the range from 0.023 to 7.0 nM (1–500 ng/ml), with a half‐maximal dose of 0.47 nM. An antibody to rPEDF blocked this protective effect. Measurement of intraneuronal free calcium levels demonstrated that rPEDF raised the basal calcium content. However, after the elevation of intracellular calcium in response to administration of glutamate, rPEDF reduced the plateau level seen in the presence of glutamate. These data show that PEDF can protect neurons against glutamate‐induced neurotoxicity, possibly via a calcium‐related pathway. The finding that only 30 min of preincubation is required for the neuroprotective effect, significantly faster than other known neurotrophic factors, suggests that PEDF may be useful clinically as a neuroprotective agent in the CNS.
The effect of intense visible light (light damage) on the expression of heme oxygenase 1 (HO-1), a protein induced by oxidative stress, was investigated in the rat retina. A sensitive reverse ...transcription-PCR assay demonstrated the expression of mRNA for HO-1 as well as HO-2, the noninducible HO form, in the normal retina. As analyzed by Northern blotting, however, HO-1 mRNA was barely detectable under normal circumstances. After exposure to intense visible light, retinas had markedly higher HO-1 mRNA levels than unexposed controls, with increases up to 52- and 98-fold at 12 and 24 hr of exposure, respectively. Intense light exposure also resulted in an increase in HO-1 protein. In contrast, no appreciable change in HO-2 mRNA or protein was observed. The increase in HO-1 message was more pronounced in rats previously reared in the dark than in those reared in a weak cyclic-light environment. A marked decrease from the high level of HO-1 mRNA induced by light insult was observed when the animals were allowed to recover in the dark for 24 hr after light exposure. Most important, treatment of animals with 1,3-dimethylthiourea, a synthetic antioxidant, prior to light exposure effectively blocked the increase in HO-1 mRNA. Thus, HO-1 is a sensitive marker for assessing light-induced insult in the retina. Since increased expression of HO-1 is thought to be a cellular defense against oxidative damage, its expression may play an important role in protecting the retina against light damage.
Pigment epithelium-derived factor (PEDF), purified from human fetal retinal pigment epithelium cell culture medium, was shown to potentiate the differentiation of human Y-79 retinoblastoma cells. To ...investigate potential neurotrophic effects of PEDF on neurons other than those of retinal derivation, we used cultures of cerebellar granule cells. The number of cerebellar granule cells was significantly larger in the presence of PEDF, as demonstrated by an assay for viable cells that uses 3-(4,5-dimethylthiazol-2-yl)-5-(3- carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium, inner salt, conversion, by cell count, and by immunocytochemistry. The effect of PEDF showed a dose-response relationship, with a larger effect in chemically defined medium than in serum-containing medium ED50 = 30 ng/ml (0.70 nM) in chemically defined medium and 100 ng/ml (2.3 nM) in serum-containing medium. PEDF had no effect on incorporation of bromodeoxyuridine (cell proliferation) or on neurofilament content (neurite outgrowth) measured by an enzyme-linked immunoadsorbent assay. These results demonstrate that PEDF has a neurotrophic survival effect on cerebellar granule cells in culture and suggest the possibility that it may affect other CNS neurons as well.
Retinal pigment epithelial (RPE) cells form a functional complex with photoreceptor neurons of the retina, interacting through the interphotoreceptor matrix (IPM). We now provide evidence that the ...gene for pigment epithelium-derived factor (PEDF), a protein possessing neurotrophic and neuronal-survival activities, is highly expressed by both fetal and young adult RPE cells. PEDF mRNA is present in RPE cells of the human eye at 17 weeks of gestation, demonstrating its potential for action in vivo during early retinal development. The PEDF protein is secreted in vivo where it constitutes a part of the fetal and adult IPM surrounding photoreceptor outer segments. A polyclonal PEDF antibody recognizes at least four isoforms of secreted human and bovine PEDF by two dimensional gel analysis, and detects a similar 50 kDa protein in the IPM of several other vertebrate species. Within soluble extracts of RPE cells, however, where little, if any, of the 50 kDa species can be detected, an immunoreactive 36 kDa protein is observed by Western blot analysis. By immunofluorescence, PEDF is localized intracellularly in association with the nucleus, presumptive secretory granules, and cytoskeletal elements of cultured RPE cells with PEDF and actin antibodies colocalizing to the same cytoskeletal structures. During initial stages of attachment, PEDF and actin also concentrate at the tips of pseudopods extended by the cultured RPE cells. However, with successive passages, synthesis, and secretion of the PEDF protein as well as transcription of its mRNA decrease and are lost by about 10 passages. In parallel, cultured RPE cells lose their proliferative potential and change from an epithelial-like morphology in early passages to a more fibroblast-like appearance by about the 10th passage. PEDF is thus apparently present intracellularly and extracellularly in both fetal and early adult periods where it could be involved in cellular differentiation and survival and with its loss, in the onset of senescence.
Pigment epithelium-derived factor (PEDF) is a neurotrophic protein present in low amounts in conditioned medium of cultured
fetal human retinal pigment epithelial cells. Recently, the PEDF cDNA has ...been cloned from a fetal human cDNA library, and
its derived amino acid sequence identified it as a member of the serine protease inhibitor (serpin) supergene family (Steele,
F. R., Chader, G. J., Johnson, L. V., and Tombran-Tink, J. (1993) Proc. Natl. Acad. Sci. U. S. A. 90, 1526-1530). We have
prepared recombinant expression constructs from the fetal human PEDF cDNA and obtained milligram amounts of biologically active
PEDF from Escherichia coli. The full-length open reading frame (Met1-Pro418) and a truncated form (Asp44-Pro418) were used
in our constructs. Induction from a vector containing the truncated PEDF version, named pEV-BH, produced a protein (BH) of
expected size (M(r) 42,800) associated with inclusion bodies, which contained 25-40% of expressed protein. After solubilization,
BH was highly purified by gel filtration and cation exchange chromatography. The NH2-terminal sequence of the purified protein
matched that of the pEV-BH construct. We have conducted neurite outgrowth assays in a human retinoblastoma Y-79 cell culture
system. Recombinant PEDF (BH) demonstrated neurotrophic activity, as reported for the native PEDF. Thus, unfolded and refolded
in vitro BH retained a potent biological activity. In parallel experiments, protease inhibition assays were performed. Recombinant
PEDF did not have an effect on trypsin, chymotrypsin, elastase, cathepsin G, endoproteinase Lys-C, endoproteinase Glu-C, or
subtilisin activity, suggesting that inhibition of known serine proteases is not the biochemical pathway for the PEDF neutrophic
activity.
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