Support of retinal ganglion cell survival and axon regeneration by lithium through a Bcl-2-dependent mechanism

PURPOSE. To explore whether lithium, a long-standing mood-stabilizing drug, can be used to induce expression of Bcl-2 and support the survival and regeneration of axons of retinal ganglion cells (RGCs). METHODS. Levels of expression of Bcl-2 in the retina were assessed with quantitative reverse transcription-polymerase chain reaction. To determine whether lithium directly supports the survival of and axon-regenerative functions of RGCs, various amounts of lithium were added to cultures of isolated RGCs. Anti-Thy1.2 antibodies-conjugated to magnetic beads were used to isolate the RGCs. In addition, retina-brain slice cocultures were prepared from tissues of Bcl-2-deficient or Bcl-2-transgenic mice and treated with various amounts of lithium. The effects of the expression of Bcl-2 on lithium-mediated functions were then analyzed. RESULTS. Normal mouse retina expressed very low levels of Bcl-2 after birth. Addition of lithium in the culture increased mRNA levels of Bcl-2 in retinas of postnatal mice in a dose-dependent manner. Moreover, lithium promoted not only the survival of RGCs but also the regeneration of their axons. Depleting or forcing the expression of Bcl-2 in RGCs eliminated the effects of lithium. CONCLUSIONS. Lithium supports both the survival and regeneration of RGC axons through a Bcl-2-dependent mechanism. This suggests that lithium may be used to treat glaucoma, optic nerve neuritis, the degeneration of RGCs and their nerve fibers, and other brain and spinal cord disorders involving nerve damage and neuronal cell loss. To achieve full regeneration of the severed optic nerve, it may be essential to combine lithium therapy with other drugs that mediate induction of a permissive environment in the mature central nervous system.