Development of spontaneous neuropathy in NF-κBp50-deficient mice by calcineurin-signal involving impaired NF-κB activation

Purpose: The transcriptional regulator, nuclear factor-kappa B (NF-κB)/Rel family are involved in neuronal cell death and survival. Previously, we reported that NF-κBp50-deficient (p50-deficient) mice exhibit many features resembling human normal tension glaucoma (NTG). The developmental mechanism of human NTG is not clearly understood, and a radical curative treatment has yet to be established. Our aim is to elucidate the signal cascade which mediates the spontaneous optic neuropathy in p50-deficient mice as a model of NTG.

Methods: To demonstrate the expression and activation of pro-apoptotic factors, which mediate the death of retinal ganglion cells (RGCs) in p50-deficient mice, western blot (WB) and luciferase reporter assays with retinas from p50-deficient and wild type mice, and cultured RGC-5 cells were performed. Furthermore, we tested the neuroprotective effects of chemical reagents (memantine, lomerizine, and tacrolimus) against N-methyl-D-aspartate (NMDA)-susceptible RGC damage according to in vitro experiments with RGC-5 cells. To elucidate the NF-κB-mediated death signaling, the effects of chemical reagents on spontaneous optic neuropathy were examined by histopathological studies.

Results: WB experiments and luciferase reporter assays showed that NF-κB-inducible BCL2-associated X protein (Bax) and a pro-apoptotic factor, activated Caspase 3 were expressed in the retina of p50-deficient mice as well as NMDA-treated RGC-5 cells. Further, the constitutively active cleaved forms of Calcineurin (CaN), which have been reported to lead to Apoptosis, were detected in the retina of p50-deficient mice as well as NMDA-treated RGC-5 cells. Pre-treatment with tacrolimus markedly protected RGC-5 cells from NMDA-induced neurotoxicity, and then both spontaneous RGC death and degenerative changes to the optic nerve in p50-deficient mice were significantly reduced by the chronic administration of tacrolimus. The experiments with cultured RGC-5 cells supported the results of histological examinations with p50-deficient mice, suggesting that CaN activation leads to NF-κB-induced Bax activation and Caspase 3 activation, and mediates spontaneous optic neuropathy in p50-deficient mice.

Conclusions: Research findings show that the chronic administration of tacrolimus significantly reduces spontaneous optic neuropathy in p50-deficient mice. We demonstrated a potential CaN signal cascade, which spontaneously induces age-dependent RGC death and degenerative optic nerve changes in p50-deficient mice.