In vitro study of the effects of lens extract on rat retinal neuron survival and neurite outgrowth

Background: Optic nerve regeneration has previously been achieved by injuring the lens, which results in the release of lentogenic factors. However, these lentogenic factors are still unknown. Objectives: To investigate what were the lentogenic factors by examining the effects of lens extract and macrophage-conditioned medium (MCM) on the survival and the neurite outgrowth of rat retinal neurons in vitro. Methods: Retinal neurons were cultured in 4 groups: (1) Dulbecco's modified Eagle's medium (DMEM), (2) DMEMcontaining lens extract, (3) DMEM containing macrophage-conditioned medium (MCM-D), (4) DMEM and medium from macrophages grown with lens extract (MCM-L). Neurite outgrowth and neuron survival time were observed. The density of retinal neurons with neurites and the longest neurites of the cells were measured on days 1, 3 and 5. Results: Retinal neurons survive for 12-14 days in DMEM containing lens extract. However, the cells only survive for 6 days in DMEM and only 7 days in DMEM containing MCM-L or MCM-D. The present results indicate that lens extract may directly promote survival of rat retinal neurons and neurite outgrowth in vitro. The MCM also promoted cell survival and neurite outgrowth but its effects were weaker than that of the lens extract. We postulate that lens extract exerts its effect by direct neurotrophic effects and/or indirectly by activating macrophagesin vitro.