Copper induced immunotoxicity promote differential apoptotic pathways in spleen and thymus

Inorganic copper, such as that in drinking water and copper supplements, largely bypasses the liver and enters the free copper pool of the blood directly and that promote immunosuppression. Nevertheless, the signaling pathways underlying copper-induced immune cell death remains largely unclear. According to our previous in vivo report, to evaluate the further details of the apoptotic mechanism, we have investigated how copper regulates apoptotic pathways in spleen and thymus. We have analyzed different protein expression by western blotting and immunohistochemistry and mRNA expression by RT-PCR and gel electrophoresis. We also have measured mitochondrial trans-membrane potential, ROS and CD4+ and CD8+ population by flow cytometry. Sub lethal doses of copper in spleen and thymus of in vivo Swiss albino mice promote different apoptotic pathways. In case of spleen, ROS generation and mitochondrial trans-membrane potential changes promotes intrinsic pathway of apoptosis that was p53 independent, ultimately leads to decrease in CD4+ T cell population and increase in CD8+ T cell population. However in case of thymus, ROS generation and mitochondrial trans-membrane potential changes lead to death receptor that regulate extrinsic and intrinsic pathways of apoptosis and the apoptotic mechanism which was p53 dependent. Due to copper treatment, thymic CD4+ T cell population decreased and CD8+ T cell population was increased or proliferated. Apart from the role of inflammation, our findings also have identified the role of other partially responsible apoptotic molecules like p27, p73, p62, poly (ADP-ribose) polymerase (PARP) that differentially changed due to copper treatment in spleen and thymus of Swiss albino mice. Present study firstly demonstrates how apoptotic pathways differentially regulate copper induced immunosuppression.

Highlights► Copper-induced ROS generation and mitochondrial trans-membrane potential changes result in different consequences in spleen and thymus. ► Inflammation appeared in both the spleen and thymus after to copper treatment. ► Apoptosis in the spleen appears to follow a p53-independent pathway. ► Apoptosis in the thymus appears to follow a p53-dependent intrinsic and extrinsic pathway. ► In both the spleen and thymus, the CD4+ T cell population decreased and CD8+ T cell population increased after copper treatment.