Neuronal cell death and regeneration in diseases associated with advanced glycation end-products accumulation.

Abstract

Recent studies have shown that the glycation-associated damage is not limited to patients with diabetes. Because of their association with oxidative stress, advanced glycation end-products (AGEs) have also been implicated in many neurodegenerative diseases, such as Huntington disease, amyotrophic lateral sclerosis, and Alzheimer disease (Yan et al., 1996; Ma and Nicholson, 2004). As in other age-dependent neurodegenerative diseases of the brain, oxidative stress-associated age-dependent pathogenic processes are not unexpected in glaucoma because this disease is also more common in the elderly (Tezel et al. 2007). Growing evidence indicates that neuronal abnormalities including neuronal cell death are associated with the pathogenesis of early diabetic retinopathy. Our previous studies of human retinas indicate that mitochondrial- and caspase-dependent cell death pathways are associated with retinal neuronal cell degeneration in patients with diabetes (Oshitari et al., 2008). Brain-derived neurotrophic factor, neurotrophin-4 (NT-4), vascular endothelial growth factor (VEGF)120, VEGF164, taurine-conjugated ursodeoxycholic acid and citicoline had been studied and showed a survival effect on damaged retinal neurons induced by diabetic stress (Oshitari et al. 2003, 2010). It was also found that NT-4 had the best neuroprotective and regenerative effect under high glucose conditions (Oshitari et al, 2010). Earlier study indicated that the maximum rescue ratio of caspase-1, -3, -8, and -9 inhibitors in cultured retinas was 60% in damaged retinal ganglion cells (RGCs) (Oshitari and Adachi-Usami, 2003). Thus, at least 40% of neuronal cell death in damaged RGCs in cultured retinas should be related to caspase-independent cell death mechanisms. However, no reports have focused on caspase-independent cell death pathways under diabetic stress including AGEs exposure. Apoptosis-inducing factor (AIF) was the first mitochondrial protein shown to mediate cell death independent of caspase (Susin et al., 1996, 1999). It was initially characterized as a mitochondrial protein confined in the intermembrane space of healthy cells. In healthy cells, AIF is a mitochondrial flavin adenine dinucleotide (FAD)-dependent oxidoreductase that plays roles in redox control and oxidative phosphorylation (Modjtahedi et al., 2006).