βB2-Crystallin Promotes Axonal Regeneration in the Injured Optic Nerve in Adult Rats

The purpose of the study was to further scrutinize the potential of beta B2-crystallin in supporting regeneration of injured retinal ganglion cell axons both in vitro and in vivo. Retinal explants obtained from animals after treatment either with lens injury (LI) alone or with combined LI 5 days or 3 days before or simultaneously with an optic nerve crush (ONC) were cultured for 96 h under regenerative conditions, and the regenerating axons were quantified and compared with untreated controls. These measurements were then repeated with LI replaced by intravitreal injections of y-crystallin and p-crystallin at 5 days before ONC. Finally, 332-crystallin-overexpressing transfected neural progenitor cells (beta B2-crystallin-NPCs) in the eye were studied after crushing the optic nerve in vivo. Regeneration was monitored with the aid of immunoblotting of the retina and optic nerve both distal and proximal to the lesion site, and this was compared with controls that received injections of phosphate buffer only. LI performed 5 days or 3 days before ONC significantly promoted axonal outgrowth in vitro (p<0.001), while LI performed alone before explantation did not. Intravitreal injections of beta-crystallin and gamma-crystallin mimicked the effects of LI and significantly increased axonal regeneration in culture at the same time intervals (p<0.001). Western blot analysis revealed that crystallins were present in the proximal optic nerve stump at the lesion site in ONC, but were neither expressed in the undamaged distal optic nerve nor in uninjured tissue. beta B2-crystallin-NPCs supported the regeneration of cut optic nerve axons within the distal optic nerve stump in vivo. The reported data suggest that beta B2-crystallin-producing "cell factories" could be used to provide novel therapeutic drugs for central nervous system injuries.