AGEs/RAGE-Related Neurodegeneration: daf-16 as a Mediator, Insulin as an Ameliorant, and C. elegans as an Expedient Research Model

C. elegans-An Emerging Model to Study Metal-Induced RAGE-Related Pathologies

The receptor for advanced glycation end products (RAGE), a multi-ligand receptor, is mostly associated with promoting inflammation and oxidative stress. In addition to advanced glycation end products (AGEs), its ligands include High mobility group box 1 protein (HMGB-1), S-100 proteins and beta-sheet fibrils. The effects of several metals and metalloids on RAGE expression and activation have been recently studied: in vivo and in vitro exposure to methylmercury, selenium, zinc, manganese, and arsenic was associated with a variety of RAGE-related alterations and behavioral impairments, which are mostly dependent upon the administration procedure (local vs. systemic) and age during exposure. Recently, C. elegans has been proposed as a potential novel model for studying RAGE-related pathologies; preliminary data regarding such model and its potential contribution to the study of metal-induced RAGE-related pathologies are discussed.

A C. elegans Model for the Study of RAGE-Related Neurodegeneration

The receptor for advanced glycation products (RAGE) is a cell surface, multi-ligand receptor belonging to the immunoglobulin superfamily; this receptor is implicated in a variety of maladies, via inflammatory pathways and induction of oxidative stress. Currently, RAGE is being studied using a limited number of mammalian in vivo, and some complementary in vitro, models. Here, we present a Caenorhabditis elegans model for the study of RAGE-related pathology: a transgenic strain, expressing RAGE in all neurons, was generated and subsequently tested behaviorally, developmentally, and morphologically. In addition to RAGE expression being associated with a significantly shorter lifespan, the following behavioral observations were made when RAGE-expressing worms were compared to the wild type: RAGE-expressing worms showed an impaired dopaminergic system, evaluated by measuring the fluorescent signal of GFP tagging; these worms exhibited decreased locomotion-both general and following ethanol exposure-as measured by counting body bends in adult worms; RAGE expression was also associated with impaired recovery of quiescence and pharyngeal pumping secondary to heat shock, as a significantly smaller fraction of RAGE-expressing worms engaged in these behaviors in the 2 h immediately following the heat shock. Finally, significant developmental differences were also found between the two strains: RAGE expression leads to a significantly smaller fraction of hatched eggs 24 h after laying and also to a significantly slower developmental speed overall. As evidence for the role of RAGE in a variety of neuropathologies accumulates, the use of this novel and expedient model should facilitate the elucidation of relevant underlying mechanisms and also the development of efficient therapeutic strategies.