Diurnal-and sex-related difference of metallothionein expression in mice

BACKGROUND Metallothionein (MT) is a small, cysteine-rich, metal-binding protein that plays an important role in protecting against toxicity of heavy metal and chemicals. This study was aimed to define diurnal and sex variation of MT in mice. METHODS Adult mice were maintained in light- and temperature-controlled facilities for 2 weeks with light on at 8:00 and light off at 20:00. The blood, liver, and kidneys were collected every 4 h during the 24 h period. Total RNA was isolated, purified, and subjected to real-time RT-PCR analysis and MT protein was determined by western blot and the Cd/hemoglobin assay. RESULTS The diurnal variations in mRNA levels of MT-1 and MT-2in liver were dramatic, up to a 40-foldpeak/trough ratio. MT mRNA levels in kidneys and blood also showed diurnal variation, up to 5-fold peak/trough ratio. The diurnal variation of MT mRNAs resembled the clock gene albumin site D-binding protein (Dbp), and was anti-phase to the clock gene Brain and Muscle ARNT-like Protein 1 (Bmal1) in liver and kidneys. The peaks of MT mRNA levels were higher in females than in males. Hepatic MT protein followed a similar pattern, with about a 3-fold difference. CONCLUSION MT mRNA levels and protein showed diurnal- and sex-variation in liver, kidney, and blood of mice, which could impact the body defense against toxic stimuli.