Abstract:
Studies conducted at the Anaconda Smelter Site (Montana) show varying tissue concentrations of As, Pb, Cd, Cu, and Zn in resident small mammals. This provides a unique opportunity to study the effects of heavy metal mixtures on gene expression in wild rodent populations. Glutamate-cysteine ligase (GCL, the initiating and rate-limiting enzyme in glutathione synthesis) and metallothionein (MT) are known to increase with heavy metal exposures in mammalian tissues. This increase in GCL expression after sub-chronic heavy metal exposures suggests that such exposures may be associated with oxidative stress. However, few field-based studies have been conducted to test this hypothesis. Here, GCL and MT expression levels in the livers of deer mice (Peromyscus maniculatus) collected from plots at the Anaconda Smelter Site were measured with real-time quantitative PCR (RQ-PCR) and Western blot analyses. It was found that the two subunits if GCL (GCLc and GCLm) appear to be co-regulated, with their mRNA expression levels being high correlated (p<0.05, R2=0.52). GCLc mRNA expression was also significantly (p<0.05) increased with increasing liver cadmium concentrations overall, in males only, and in adults only. Juveniles and adult females showed no association between target gene expression and liver heavy metal concentrations. Given these observations, GCLc appears to be a more sensitive gene expression biomarker of chronic low-dose cadmium exposure than MT-1, and mRNA expression levels appear to be a more sensitive endpoint than protein expression levels. Also, given differences observed in gene expression between males, females, adults, and juveniles, age and gender should be considered as potential confounding variables in future field gene expression biomarker studies. Sponsored by NIEHS grants P42ES04696 and P30ES007033.