U373MG cells are able to take up
aminochrome that induces
glutathione transferase M2-2 (GSTM2) expression in a concentration-dependent manner where 100 µM
aminochrome increases GSTM2 expression by 2.1-fold (P < 0.001) at 3 h. The uptake of (3)H-aminochrome into U373MG cells was significantly reduced in the presence of 2 µM
nomifensine (P < 0.001) 100 µM
imipramine (P < 0.001) and 50 mM
dopamine (P < 0.001). Interestingly, U373MG cells excrete GSTM2 into the
conditioned medium and the excretion was significantly increased (2.7-fold; P < 0.001) when the cells were pretreated with 50 µM
aminochrome for 3 h. The U373MG-conditioned medium containing GSTM2 protects SH-SY5Y cells incubated with 10 µM
aminochrome. The significant protection provided by U373MG-conditioned medium in SH-SY5Y cells incubated with
aminochrome was dependent on GSTM2 internalization into SH-SY5Y cells as evidenced by (i) uptake of (14)C-GSTM2 released from U373MG cells into SH-SY5Y cells, a process inhibited by anti-GSTM2 antiserum; (ii) lack of protection of U373MG-conditioned medium in the presence of anti-GSTM2 antiserum on SH-SY5Y cells treated with
aminochrome; and (iii) lack of protection of
conditioned medium from U373MGsiGST6 that expresses an
siRNA directed against GSTM2 on SH-SY5Y cells treated with
aminochrome. In conclusion, our results demonstrated that U373MG cells protect SH-SY5Y cells against
aminochrome neurotoxicity by releasing GSTM2 into the
conditioned medium and subsequent internalization of GSTM2 into SH-SY5Y cells. These results suggest a new mechanism of protection of dopaminergic neurons mediated by astrocytes by releasing GSTM2 into the intersynaptic space and subsequent internalization into dopaminergic neuron in order to protect these cells against
aminochrome neurotoxicity.