Cadmium exposure suppresses insulin secretion through mtROS-mediated mitochondrial dysfunction and inflammatory response in pancreatic beta cells.

ABSTRACT

BACKGROUND: Cadmium (Cd) exposure is a worldwide environmental threat to the public health and participates in the pathogenesis of multiple diseases. Epidemiologic research have established a direct relation between Cd exposure and diabetes development in humans. Although pancreatic ß-cell dysfunction has been considered as the major culprit in the pathogenesis of diabetes, there is a paucity of studies to elucidate the molecular mechanism of Cd toxicity on ß-cells. METHODS: To unveil the toxic effect and its underlying mechanism of Cd exposure on ß-cells, we used an in vitro MIN6 cell model of environment-relevant Cd exposure to elucidate the crucial role of mtROS-mediated mitochondrial dysfunction and inflammatory response in suppression of pancreatic ß-cell insulin secretion. RESULTS: We uncovered that Cd treatment suppresses cell viability and induces insulin secretion dysfunction in a dose-dependent manner. Moreover, Cd exposure elicits the inflammatory response, as indicated by increased IL-1ß, IL-6 and TNF-α expressions. Significant elevations of intracellular ROS and mitochondrial ROS levels were detected as early as 3 h after Cd treatment. In mitochondrial function analysis, we demonstrated that Cd treatment induced mitochondrial dysfunction and disorder of mitochondrial fission indicated by the significant decline in ATP production, the marked depolarization of mitochondrial membrane potential, the decrease in mtDNA copy numbers, the suppressions of mitochondrial transcription factor A (Tfam) and mitochondrial fission-related gene Drp1 expressions. Pretreatment with TEMPO, a specific mitochondrial ROS (mtROS) scavenger, efficiently antagonizes Cd cytotoxicity, which is indicated by attenuating Cd-induced mitochondrial dysfunction, suppressing IL-1ß, IL-6 and TNF-α expressions, ameliorating insulin production dysfunction and preserving cell viability in MIN6 cells. CONCLUSION: Our study demonstrates that Cd exposure induces an inflammatory response through mtROS-mediated mitochondrial dysfunction. Antagonism of mtROS production might be an effective strategy to prevent pancreatic toxicity from environment-relevant Cd exposure.