Metallothionein expression and localization in rat bone tissue after cadmium injection

We investigated the induction of metallothionein (MT) by cadmium (Cd) in the bone tissue of rats. To clarify the cell response to Cd in bone, the isoform-specific expression of MT mRNAs (MT-I and MT-II) was examined by reverse transcriptase-polymerase chain reaction (RT-PCR). Both MT-I and MT-II mRNA levels were increased within 3 h by Cd administration. MT (MT-I/MT-II) localization after single Cd injection were also confirmed by immunohistochemical studies. Notably, MT-positive cells were time-dependently increased, and the positive cells were mainly localized in osteocytes. The cell-specific induction of MT may be associated with Cd accumulation and Cd-induced bone injury in vivo. Furthermore, we also found that MT was consecutively expressed in some osteoclasts of control rats. This finding suggested a new role of osteoclasts in bone metabolism.