Bcl-2 Overexpression Does Not EnhanceIn Vivo Axonal Regeneration of Retinal Ganglion Cells after Peripheral Nerve Transplantation in Adult Mice

Abstract

Optic nerve (ON) injury in adult mammals causes retinal ganglion cell (RGC) death and subsequent visual loss. Recovery of vision requires both rescuing axotomized RGCs and inducing their axonal regeneration. Axotomized RGCs are significantly rescued by overexpression of bcl-2, an anti-apoptotic gene. However, whether bcl-2 affects axonal regeneration is controversial. In neonatal bcl-2 transgenic mice (bcl-2 mice), optic tract regeneration after tectal lesion was promoted (Chen et al., 1997), whereas ON regeneration after ON crush was not (Lodovichi et al., 2001). These conflicting results may be attributable to different environments between tectum and ON. We tested here whether bcl-2 overexpression enhances in vivo RGC axonal regeneration in adult mice through a permissive environment in the peripheral nerve (PN) graft. Four weeks after PN transplantation to the proximal ON stump, we assessed the number of surviving and regenerating RGCs by retrograde labeling. Although the survival rate in bcl-2 mice was significantly enhanced compared with that in wild-type (wt) mice, the regeneration rate was not enhanced. In both bcl-2 and wt mice, RT97 immunostaining of the PN-grafted retinas revealed some RGC axons regrowing intraretinally but repulsed at the optic disk. To circumvent this repulsive barrier, we directly transplanted the PN graft to the partially injured retina and compared regeneration rates between these mice. Here again the regeneration rate in bcl-2 mice did not exceed that in wt mice. These findings indicate that bcl-2 overexpression enhances survival but not axonal regeneration of adult RGCs even within a permissive environment.

Immunocytochemical localization of NTPDases1 and 2 in the neural retina of mouse and zebrafish

“…In mouse retina, this antibody mainly labeled processes of horizontal cells and axons of ganglion cells (Dräger et al, 1984;Inoue et al, 2002). In zebrafish retina, strong labeling was observed in rod and cone photoreceptor outer segments (Adamus et al, 1988).…”

siRNA-Mediated Knockdown of the mTOR Inhibitor RTP801 Promotes Retinal Ganglion Cell Survival and Axon Elongation by Direct and Indirect Mechanisms

“…1 Although spontaneous visual improvement occurs in a minority of patients, permanent visual impairment is frequent and currently there are no clinically effective treatments. [2][3][4] The RGC death, which commences within 5 to 6 days after ON injury with more than 90% RGC loss by 14 days, 5 is preventable by either downregulation of proapoptotic caspases [6][7][8] or upregulation of antiapoptotic mediators, such as Bcl-2 9,10 and Bcl-XL. 11 However, axon regeneration is not an inevitable correlate of RGC survival, as independent factors mediate both events.…”

Complementary research models and methods to study axonal regeneration in the vertebrate retinofugal system

“…However, the numbers of regenerated fibers remain quite low and the vast majority of RGCs just dies after axotomy (Watanabe et al 1997). Of note, next to the retrobulbar transplantation described above, also intraretinal transplantation has been performed, in which the PNG was inserted into the retina via a scleral perforation, resulting in a more permissive environment for outgrowth since the axotomised RGCs can access the PNG directly (So and Aguayo 1985;Berry et al 1996Berry et al , 1999Inoue et al 2000Inoue et al , 2002.…”