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Jonathan Lin, Andrea Santeford, Teresa Chen, Mitsukuni Yoshida, Shin-ichiro Imai, Rajendra S Apte; Pathologic poly(ADP-ribose) polymerase (PARP) activation contributes to retinal degeneration in mice with retinal NAD+ deficiency. Invest. Ophthalmol. Vis. Sci. 2017;58(8):4533.
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© ARVO (1962-2015); The Authors (2016-present)
We previously demonstrated that the dominant mammalian NAD+ biosynthetic pathway mediated by nicotinamide phosphoribosyltransferase (NAMPT) is essential for photoreceptor survival and vision in mice. However, why photoreceptors are exquisitely sensitive to perturbations in the NAMPT-mediated pathway remains unclear. This study tests the hypothesis that NAD+ utilization due to pathologic poly(ADP-ribose) polymerase (PARP) activation contributes to retinal degeneration in mice with retinal NAD+ deficiency.
We generated mice with Nampt deleted specifically from rod photoreceptors (Nampt-rod/-rod) using the Cre-lox system and quantified retinal PARP activation by Western blotting. Next, we measured the reductive capacity and cell survival of 661W photoreceptor cells treated with various combinations of the NAMPT inhibitor FK866 (20 μM) and the PARP inhibitors ABT-888 (2 nM) and BYK204165 (400 nM) with the WST-1 and calcein AM assays, respectively. Finally, we gave Nampt-rod/-rod mice daily intraperitoneal injections of ABT-888 (20 mg/kg body weight) beginning at postnatal day 5 (P5) and tested retinal function at P28-P30 with electroretinography (ERG). For all analysis, we considered p < .05 to be statistically significant.
We found that retinas from 3-week-old Nampt-rod/-rod mice contained more PARylated proteins at 3 weeks compared to NamptF/F littermates, indicating substantial PARP activation. In addition, treatment with either PARP inhibitor ABT-888 or BYK204165 significantly reduced the toxic effect of FK866-mediated NAMPT inhibition on the reductive capacity (p < .01) and cell survival (p < .05) of photoreceptor cells. Finally, Nampt-rod/-rod mice treated daily with the PARP inhibitor ABT-888 beginning at P5 had improved scotopic (p < .05) and photopic (p < .01) ERG responses compared to vehicle-treated Nampt-rod/-rod mice at P28-P30.
Our results show that pathologic PARP activation contributes to retinal degeneration in mice with retinal NAD+ deficiency. Our findings suggest that PARP inhibition may have therapeutic efficacy against diverse blinding diseases. Future studies will test whether PARP activation is pathologic in other mouse models of retinal degeneration and explore the therapeutic efficacy of using PARP inhibitors in conjunction with NAD+ intermediates.
This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.
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