BCLXL gene therapy moderates neuropathology in the DBA/2J mouse model of inherited glaucoma

Abstract

Axonal degeneration of retinal ganglion cells (RGCs) causes blindness in glaucoma. Currently, there are no therapies that target axons to prevent them from degenerating. Activation of the BAX protein has been shown to be the determining step in the intrinsic apoptotic pathway that causes RGCs to die in glaucoma. A putative role for BAX in axonal degeneration is less well elucidated. BCLXL (BCL2L1) is the primary antagonist of BAX in RGCs. We developed a mCherry-BCLXL fusion protein, which prevented BAX recruitment and activation to the mitochondria in tissue culture cells exposed to staurosporine. This fusion protein was then packaged into adeno-associated virus serotype 2, which was used to transduce RGCs after intravitreal injection and force its overexpression. Transduced RGCs express mCherry-BCLXL throughout their somas and axons along the entire optic tract. In a model of acute optic nerve crush, the transgene prevented the recruitment of a GFP-BAX fusion protein to mitochondria and provided long-term somal protection up to 12 weeks post injury. To test the efficacy in glaucoma, DBA/2J mice were transduced at 5 months of age, just prior to the time they begin to exhibit ocular hypertension. Gene therapy with mCherry-BCLXL did not affect the longitudinal history of intraocular pressure elevation compared to naive mice but did robustly attenuate both RGC soma pathology and axonal degeneration in the optic nerve at both 10.5 and 12 months of age. BCLXL gene therapy is a promising candidate for glaucoma therapy.

BclXL (Bcl2l1) gene therapy lessens retinal ganglion cell soma loss but not axonal degeneration after acute axonal injury

“…1C ). Therefore, consistent with previous reports [ 6 , 10 ], BclX L overexpression improved RGC somal survival after axonal injury. These data suggest loss of BCLX L activity in the soma contributes to RGC somal degeneration in glaucoma and could also possibly contribute to degeneration of the axonal compartment.…”

“…Of note, as assessed by the percentage of mCherry+ RBPMS + cells, AAV2.2-Pgk-mCherry-BclX L transduced ~76% of RGCs (Fig. 1A ), consistent with previously published results [ 6 ]. Five days post-CONC, BclX L AAV retinas had significantly fewer dying (cCASP3+) RGCs (Fig.…”

“…Recently, it was shown that overexpression of BclX L protected the entire RGC in DBA/2J glaucoma [ 6 ]. BCLX L inhibits BAX induction and is the principal pro-survival family member of the Bcl2 gene family expressed in RGCs [ 7 ].…”

“…To study the compartment-specific effects of BclX L overexpression after CONC, BclX L was overexpressed ( BclX L AAV ) in the retinas of C57BL/6J mice (aged 3–7 months) by bilateral intravitreal delivery of AAV2.2-Pgk-mCherry-BclX L vector, performed as previously described [ 6 ]. Control animals (WT) were bilaterally intravitreally injected with volume-matched PBS.…”

“…Given that BclX L overexpression protected RGC axons and somas in a model of ocular hypertension [ 6 ], it remained important to distinguish whether somal BCLX L confers protection to the RGC axon, or if axonal BCLX L affords this protection. To investigate this, axonal degeneration of BclX L AAV and WT optic nerves was assessed after CONC.…”