Transforming growth factor beta mediates apoptosis in the ganglion cell layer during all programmed cell death periods of the developing murine retina

Transforming growth factor beta (TGF-β) is an extracellular signaling molecule known to mediate programmed cell death (PCD) in the developing retina. In the present study, we investigated the expression profiles and activity levels of TGF-β ligand and TGF-β receptors (TβR) during the successive physiological PCD periods of the developing postnatal mouse retina. The peak of TβR expression levels - revealed by Western Blots and MLEC assays - coincided with the main periods of postnatal (P) retinal murine PCD at P2, P9, and P15. Immunocytochemical studies showed that the localization of the TβRs is restricted to the ganglion cell layer. Application of a neutralizing anti-TGF-β antibody to E15 and P9 retinal cultures resulted in a significant decrease in the number of TUNEL-positive neurons specifically in the ganglion cell or prospective ganglion cell layer. Treatment of P2 and P15 organotypic murine retinal wholemount cultures with exogenous recombinant TGF-β significantly increased cell death levels. In the P15 retina, where PCD affects ganglion cells and photoreceptors, TGF-β induced cell death of large retinal ganglion cells, whereas small ganglion cells and photoreceptor neurons remained unaffected. Our data indicate that TGF-β mediated apoptosis during all postnatal retinal PCD phases specifically affects the fate of retinal ganglion cells.