Synergistic effect of Bcl-2 and BAG-1 on the prevention of photoreceptor cell death

PURPOSE: Ectopic expression of Bcl-2 in photoreceptors of mice with retinal degenerative disease slows progression of the disease. BAG-1 has previously been shown to augment the inhibitory effect of Bcl-2 on programmed cell death in cultured cell systems. This study was designed to determine whether the coexpression of BAG-1 and Bcl-2 in the photoreceptors of mice with an autosomal dominant form of retinitis pigmentosa (RP) would enhance the protective effect provided by Bcl-2 alone. METHODS: An expression vector using the 5' regulatory region of the murine opsin gene was used to target the expression of BAG-1 specifically to photoreceptor cells of mice. The BAG-1 transgenic mice were crossed to Bcl-2 transgenics to obtain animals that coexpress the two transgenes in photoreceptor cells. BAG-1/Bcl-2 animals were then crossed to an RP mouse model (a transgenic line overexpressing the S334ter rhodopsin mutant) to assess the effect of coexpression of BAG-1 and Bcl-2 on retinal degeneration. Morphologic analysis was performed on retinas isolated at various times after birth to monitor disease progression. RESULTS: High levels of BAG-1 expression resulted in retinal degeneration that was not prevented by Bcl-2 expression. However, coexpression of appropriate levels of BAG-1 and Bcl-2 was found to have a profound inhibitory effect on retinal degeneration caused by overexpression of a mutant rhodopsin transgene. Whereas expression of Bcl-2 alone was previously found to delay degeneration of the retina from 2 weeks to approximately 4 weeks of age, coexpression of BAG-1 and Bcl-2 inhibited photoreceptor cell death for as long as 7 to 9 weeks. CONCLUSIONS: The synergistic effect against photoreceptor cell death produced by the coexpression of Bcl-2 and BAG-1 indicates that these proteins can function in concert to prevent cell death. At the correct dosage, coexpression of Bcl-2 and BAG-1 may serve as a potential means to treat retinal degenerative diseases.