Apoptosis is present in the primate macula at all ages

Abstract 

Background: It has become increasingly clear that apoptosis is a main event in photoreceptor cell death in a variety of retinal degenerations. We investigated the role of apoptosis in the physiologically aging primate macula.Methods: Twenty maculae of rhesus monkeys, aged 6–34 years, were investigated. Apoptosis was determined in formalin-fixed, paraffin-embedded eyes using the TUNEL (TdT-mediated dUTP-biotin nick end labeling) method and quantitatively analyzed. Morphology of TUNEL-positive cells was studied by confocal laser microscopy and transmission electron microscopy. The thickness of the outer nuclear layer (ONL) was determined by image analysis. Furthermore, expression of apoptosis-regulating proteins Bcl-x, Fas and Fas Ligand was studied by immunohistochemistry.  Results: TUNEL-positive nuclei showed apoptotic features on confocal laser microscopy. They were scattered and sparsely found in the macula, most frequently in the ONL. The thickness of the ONL decreased with increasing age. Apoptosis was found equally distributed at all ages, although in the two oldest maculae up to 13 times more apoptosis was found. Expression of Bcl-x, Fas and Fas Ligand was equal at all ages.Conclusion: Our findings indicate that apoptosis in the primate macula occurs at all ages at similar rates, possibly increasing in the oldest age group, and may account for the decreasing thickness of the primate macula with age.