Methyl Mercury Injury to CNS: Mitochondria at the Core of the Matter?

Methyl-mercury (MeHg) is one of the most hazardous environmental pollutants of great concern to public health and regulatory agencies because of its primary toxicity to the human central nervous system. The major source of MeHg exposure to the general population is through consumption of contaminated fish and other food products. MeHg, absorbed from the gastrointestinal tract, is easily transported across the blood-brain barrier (BBB). Cysteine-facilitated transport of MeHg into the brain has been demonstrated, and in particular a neutral amino acid transport system capable of mediating MeHg-cysteine uptake has been identified in astrocytes where MeHg accumulation induces cell swelling and inhibition of glutamate uptake. Elevation of glutamate levels in the extracellular space may, in turn, trigger or accelerate processes of excitotoxic neuro degeneration. The rising of extracellular glutamate levels is responsible for the sustained activation of glutamate receptors, hence enhancing Na+ influx and Ca2+ release from intracellular organelles that may trigger a biochemical cascade which promotes the reactive oxygen species (ROS) production. In this scenario, mitochondria may play a crucial role, as these organelles act as a buffer against cytosolic calcium and mediate ROS formation in cells. Herein, we summarize studies providing insights into the molecular and cellular mechanisms involved in MeHg-induced neuro degeneration with particular focus on the role of astrocytes and mitochondria. Indeed, mitochondria may be supposed to lie at the crossroads of a network of events (microtubule disorganization, Ca2+ dyshomeostasis, ROS generation) leading to neuro degeneration, although it is difficult to establish the upstream mechanisms and downstream effectors in this cascade of events.