Functionalizing cell-based therapy for age-related macular degeneration

Characterization of the effects of retinal pigment epithelium-conditioned media on porcine and aged human retina

BACKGROUND

Retinal pigment epithelium (RPE) cells produce neurotrophic factors that rescue photoreceptors from degeneration. Previously, we showed that conditioned medium (CM) from fetal vs adult RPE cells resulted in significantly better porcine retinal preservation, and possessed significantly higher levels of hepatocyte growth factor (HGF) and pigment epithelium-derived factor (PEDF). This study aimed to further describe the effects of human fetal RPE-CM on porcine and aged human retina, and to characterize its effects biochemically.

METHODS

RPE-CM was harvested from passage-2 fetal RPE, 7 days after passage, 24-hours after exposure to basal medium. After culture in RPE-CM, porcine retinal morphology was assessed with confocal microscopy. The effects of RPE-CM on porcine and aged human retina survival were assessed by cytotoxicity and apoptosis biochemical assays. To characterize RPE-CM biochemically, effects of heating, digesting with proteinase-K, dilution, concentration, and fractionation were tested. Recombinant proteins and neutralizing antibodies were used to identify proteins that might contribute to the salutary effects of RPE-CM on porcine retina.

RESULTS

Culturing porcine retina in RPE-CM significantly preserved outer nuclear layer width and the number of nuclei in cross-section, and significantly decreased photoreceptor axon retraction. RPE-CM decreased porcine retinal death by 17-34 % (p<0.05) compared to basal medium. Human retina from age-related macular degeneration (AMD) and non-AMD donors responded similarly after culture in RPE-CM. Heating, proteinase-K digestion, and dilution significantly diminished RPE-CM-mediated preservation of porcine retina, whereas concentrating RPE-CM significantly enhanced its preservation of porcine retina. Molecular cut filtration identified retina-preserving activity in the 3-100 kDa filtrate. PEDF or HGF at 90 % receptor occupancy significantly improved retinal preservation over 48 h of culture compared to basal medium. Neutralizing PEDF in RPE-CM decreased its ability to reduce retinal apoptosis by 23-27 % (p<0.05).

CONCLUSION

RPE-CM reduced biochemically and histologically measured degeneration in porcine retinae. This effect was concentration-dependent, and can be attributed to a protein component(s) in a 3-100 kDa molecular cut fraction. Human retina (including non-AMD and AMD Caucasian and non-AMD African-American) responds to culture in RPE-CM similarly to porcine retina. Receptor occupancy calculations and retinal viability data indicate that PEDF may be one of the components that contribute to retina preservation by RPE-CM.

Anti-sphingosine-1-phosphate monoclonal antibodies inhibit angiogenesis and sub-retinal fibrosis in a murine model of laser-induced choroidal neovascularization

The efficacy of novel monoclonal antibodies that neutralize the pro-angiogenic mediator, sphingosine-1-phosphate (S1P), were tested using in vitro and in vivo angiogenesis models, including choroidal neovascularization (CNV) induced by laser disruption of Bruch's membrane. S1P receptor levels in human brain choroid plexus endothelial cells (CPEC), human lung microvascular endothelial cells, human retinal vascular endothelial cells, and circulating endothelial progenitor cells were examined by semi-quantitative PCR. The ability of murine or humanized anti-S1P monoclonal antibodies (mAbs) to inhibit S1P-mediated microvessel tube formation by CPEC on Matrigel was evaluated and capillary density in subcutaneous growth factor-loaded Matrigel plugs was determined following anti-S1P treatment. S1P promoted in vitro capillary tube formation in CPEC consistent with the presence of cognate S1P(1-5) receptor expression by these cells and the S1P antibody induced a dose-dependent reduction in microvessel tube formation. In a murine model of laser-induced rupture of Bruch's membrane, S1P was detected in posterior cups of mice receiving laser injury, but not in uninjured controls. Intravitreous injection of anti-S1P mAbs dramatically inhibited CNV formation and sub-retinal collagen deposition in all treatment groups (p<0.05 compared to controls), thereby identifying S1P as a previously unrecognized mediator of angiogenesis and subretinal fibrosis in this model. These findings suggest that neutralizing S1P with anti-S1P mAbs may be a novel method of treating patients with exudative age-related macular degeneration by reducing angiogenesis and sub-retinal fibrosis, which are responsible for visual acuity loss in this disease.