Effect of Arsenic on Intracellular Calcium & Redox Homeostasis

Abstract

A range of environmental agents causes tissue injury that has been attributed to reactive oxygen species (ROS). Altered ROS production is commonly originated from the mitochondria and is associated with dysregulation of calcium (Ca2+) homeostasis and mitochondrial apoptosis. However, the causative pathways remain largely unknown because the fundamental roles of mitochondria in cell survival, cell signaling and dynamics are commonly mediated through local communication between mitochondria and other organelles, which have been difficult to directly monitor. Our aim is to develop fluorescent protein-based tools allowing sensitive and specific measurements of ROS and [Ca2+] at the mitochondria-endoplasmic reticulum (ER) interface. Applying these novel tools, we have studied the effects of environmental stress caused by arsenicon local mitochondria-ER communication and its impact for cell signaling, and cell physiology in primary mouse hepatocytes. Either acute addition (30 µM) or prolonged, overnight exposure (3 µM) to sodium arsenite has induced an increase in ROS. Upon prolonged arsenic exposure, these alterations were accompanied by a significant decrease in the cytoplasmic calcium signal to an IP3-linked agonist: a decrease was observed in the fraction of responsive cells, in the amplitude of the response as well as in the sustained phase. Regarding the acute effect of arsenic, we observed a progressive increase of the basal cytoplasmic [Ca2+] with a decrease in the amplitude of the IP3-linked calcium signal. Neither acute nor prolonged arsenic exposure impaired mitochondrial calcium uptake. Nevertheless, we documented increased mitochondrial calcium content in the prolonged arsenic exposure group. In conclusion, the results suggest that an initial component of the arsenic-induced hepatocyte injury is increased ROS, which is associated with impaired local mitochondria-ER calcium communication.