Mitochondrial Dysfunction and Loss of Glutamate Uptake in Primary Astrocytes Exposed to Titanium Dioxide Nanoparticles

The proper function of astrocytes is critical for brain health as they are the most abundant cells in the brain which monitor ion homeostasis, recycle neurotransmitters and respond to tissue damage therefore disruption in astrocyte function can result in overall detrimental effects and has been linked with neurodegenerative diseases. Titanium Dioxide (TiO2) nanoparticles are currently the second most produced engineered nanomaterial in the world with vast usage in consumer products leading to recurrent human exposure. Animal studies indicate significant nanoparticle accumulation in the brain while cellular toxicity studies demonstrate negative effects on neuronal cell viability and function. However, the toxicological effects of nanoparticles on astrocytes have not been extensively investigated. Therefore, we determined the toxic effect of three different TiO2 nanoparticles (rutile, anatase and commercially available P25 TiO2 nanoparticles) on primary rat cortical astrocytes by evaluating events related to astrocytes functions and mitochondrial dysregulation: (1) glutamate uptake and glutamate transporter gene expression; (2) redox signaling mechanisms by measuring ROS production; and (3) the expression patterns of dynamin-related proteins (DRPs) and mitofusins 1 and 2, whose expression is central to mitochondrial dynamics. Anatase, Rutile and P25 were found to have LC50 values of 88.22±10.56ppm, 136.0±31.73ppm and 62.37±9.06ppm respectively indicating nanoparticle specific toxicity. All three TiO2 nanoparticles induced a significant loss in glutamate uptake and down-regulation of glutamate transporter expression, which is indicative of loss in vital astrocytes function. TiO2 nanoparticles also induced an increase in reactive oxygen species generation, decrease mitochondrial membrane potential and decrease mitochondrial dehydrogenase activity, suggesting mitochondria damage. TiO2 nanoparticle exposure altered expression patterns of DRPs at low concentrations (25ppm, 50ppm) and apoptotic fission at high concentrations (100ppm). Collectively, our data provide compelling evidence that TiO2 nanoparticles exposure has potential implications in astrocytes-mediated neurological dysfunction. Adviser: Srivatsan Kidamb