Janet R. Sparrow

Binding of Anionic Phospholipids to Retinal Pigment Epithelium May Be Mediated by the Scavenger Receptor CD36

The specific recognition of negatively charged phospholipids in cell membranes has been suggested to play an important role in a variety of physiological and pathophysiological processes. Recent work (Rigotti, A., Acton, S. L., and Krieger, M. (1995) J. Biol. Chem. 270, 16221-16224) has described specific and tight binding of anionic phospholipids, such as phosphatidylserine (PS) and phosphatidylinositol (PI), to the class B scavenger receptors, CD36 and SR-B1. We have previously reported that CD36 is present on retinal pigment epithelium (RPE) and plays a role in the phagocytosis of photoreceptor outer segments (ROS), a function critical to the normal visual process (Ryeom, S. W., Sparrow, J. R., and Silverstein, R. L. (1996) J. Cell Sci. 109, 387-395). We now report that phospholipid liposomes PS and PI, but not phosphatidylethanolamine, bind specifically to RPE. Cross-competition experiments suggest that PS and PI recognize the same receptor on RPE, while immunoinhibition studies indicate that the receptor is CD36. RPE cells isolated from a mutant rat strain, the RPE of which does not express CD36 (Sparrow, J. R., Ryeom, S. W., Abumrad, N., Ibrahimi, A., and Silverstein, R. L. (1996) Exp. Eye Res., in press), did not bind PS or PI, further confirming the role of CD36. We also showed that purified ROS blocked binding and uptake of anionic phospholipid liposomes by RPE and that PS and PI liposomes blocked ROS uptake by RPE, suggesting that PS and PI on the ROS membrane may be the ligands on ROS recognized by CD36. This is the first demonstration that CD36-phospholipid interactions may play a role in normal physiology.

Sciatic nerve regeneration in ganglioside-treated rats

Abstract Local application of 0.25 mg ganglioside to the site of a crush in the rat sciatic nerve resulted in a 19 to 33% increase in the number of regenerating axons at 7 days after the lesion, although the maximum axonal outgrowth distance was not affected. Intraperitoneal injection of ganglioside (50 mg/kg) also had no effect on axonal outgrowth distance.

Immunohistochemical analysis of the neurotrophins BDNF and NT-3 and their receptors trk B, trk C, and p75 in the developing chick retina

The neurotrophins are trophic and mitogenic factors critical for the development of specific classes of neurons in the central and peripheral nervous systems. In the retina, BDNF and NT-3 have been shown to promote the survival of differentiated ganglion cells (Rodriguez-Tebar et al., 1989; De La Rosa et al., 1994). NT-3 has also been demonstrated to support the survival of amacrine cells and facilitates the differentiation of retinal neurons in culture (De La Rosa et al., 1994). Here, we examine immunohistochemically the expression of BDNF and NT-3 proteins, their cognate receptors, trk B and trk C, respectively, and the p75 neurotrophin receptor in the developing chick retina. At E8, the earliest stage of retinal development examined, all of these proteins exhibit diffuse expression throughout the width of the retina, with the strongest reactivity in the innermost layers. A gradual restriction in expression to ganglion cells and amacrine cells, the staining of which is most prominent at E15, is followed by a downregulation of expression with the strongest immunoreactivity persisting in the ganglion cell layer. Overlapping patterns of expression throughout embryonic development indicate a colocalization of the neurotrophins and their receptors, although NT-3 and p75 alone are present in the inner plexiform layer and only p75 is observed in the outer plexiform layer. Although some of the immunoreactivity for BDNF, NT-3, and their receptors in retina may reflect trophic mechanisms operating in association with the optic tectum and isthmo-optic nucleus, the colocalization of ligands and receptors in retina strengthens the assertion that these neurotrophins function locally during development.

Control of nitric oxide production by endogenous TGF-beta1 and systemic nitric oxide in retinal pigment epithelial cells and peritoneal macrophages.

Both in vivo and in vitro experiments demonstrate that transforming growth factor‐β1 (TGF‐β1) suppresses expression of the inducible form of nitric oxide synthase (iNOS). In this study, we examined the effects of exogenous and endogenous TGF‐β1 on retinal pigment epithelial (RPE) cells and resident peritoneal macrophages ex vivo using cells from TGF‐β1 null (TGF‐β1 ‐/‐) mice or age‐matched wild‐type (TGF‐β1 +/+) or heterozygous (TGF‐β1 +/‐) littermates. RPE cells from both TGF‐β1 ‐/‐ mice and TGF‐β1 +/+ littermates produced NO and were immunocytochemically positive for iNOS protein only following treatment with interferon‐γ (IFN‐γ) and bacterial lipopolysaccharide (LPS); however, RPE cells from TGF‐β1 ‐/‐ mice produced 40% more NO than cells from TGF‐β1 +/+ mice. In contrast, resident peritoneal macrophages from both TGF‐β1 +/+ and TGF‐β1 ‐/‐ mice expressed iNOS protein without stimulation and in the absence of detectable production of NO. The expression of iNOS was increased by treatment with IFN‐γ, resulting in detectable levels of NO. Macrophages from TGF‐β1 +/+ mice appeared to produce NO in a manner inversely proportional to the serum content of NO2 ‐ and NO3 ‐ of the mice from which the cells were obtained; no such correlation existed in TGF‐β1 +/‐ or TGF‐β1 ‐/‐ mice. Treatment of RPE cells or macrophages from both TGF‐β1 +/+ and TGF‐β1 ‐/‐ mice with exogenous TGF‐β1 decreased both iNOS protein and NO production. These findings demonstrate a novel role of endogenous TGF‐β1 in coupling systemic NO production to the production of NO by macrophages, and demonstrate that endogenous and exogenous TGF‐β1 can act differently to suppress NO production. J. Leukoc. Biol. 60: 261–270; 1996.

Role of fast axonal transport in regeneration of goldfish optic axons.

Publisher Summary This chapter provides evidence that the goldfish optic tectum contains factors that can influence axonal outgrowth and possibly other aspects of optic nerve regeneration. It investigates the possible role of the tectum by determining the effects of removing the lobe of the tectum to which the regenerating axons normally project. The increased supply of material that is generated by goldfish retinal ganglion cells during regeneration is essential for the maintenance of axonal outgrowth. Although the normal level of transport is apparently adequate for the initiation of outgrowth and the first few days of elongation, a critical point is reached in about 8 days when this supply is no longer sufficient. The cell body reaction in these neurons involves the increased production of axonally transported proteins, but not necessarily the production of new proteins. The presence of the optic tectum influences not only the production of axonally transported proteins, but also their disposition in new axon segments. This influence is not effective to a significant degree, until after the regenerating axons have reached the tectum.

Prior collateral sprouting enhances axonal regeneration

Abstract Regeneration is accelerated in axons which have undergone collateral sprouting prior to crushing.

Iris Neovascularizadon in Proliferative Vitreoretinopathy

Purpose: The purpose of this study is to report on the prevalence, incidence, and associated risk factors of iris neovascularization in nondiabetic patients undergoing vitrectomy for retinal detachment complicated by proliferative vitreoretinopathy (PVR). Methods: The authors conducted a retrospective review of 141 consecutive nondiabetic patients undergoing vitrectomy for recurrent retinal detachment resulting from PVR. Univariate and multivariate analyses were performed on all patients to determine which preoperative, intraoperative, and postoperative factors were associated with the development of postoperative iris neovascularization. Results: Twenty-seven of the 141 (19%) patients were noted with preoperative and/or postoperative iris neovascularization. Four of eight patients presenting with preoperative iris neovascularization had complete regression after successful reattachment of the retina. Results of analysis of the remaining 133 patients without iris neovascularization preoperatively showed residual retinal detachment as the most significant risk factor for postoperative iris neovascularization. In the absence of panretinal photocoagulation, none of the 27 patients developed neovascular glaucoma. Conclusions: The development of iris neovascularization preoperatively or postoperatively is not necessarily a predictor of a poor anatomic and/or visual result. Iris neovascularization in PVR rarely if ever progresses to neovascular glaucoma. Panretinal photocoagulation is not indicated in these patients. Retinal reattachment is the most important factor in the prevention and/or resolution of postoperative iris neovascularization. The development of iris neovascularization in PVR appears to be a multifactorial process requiring multiple variables acting in concert.