Cadmium induced ROS alters M1 and M3 receptors, leading to SN56 cholinergic neuronal loss, through AChE variants disruption

Abstract

Cadmium, an environmental neurotoxic compound, produces cognitive disorders, although the mechanism remains unknown. Previously, we described that cadmium induces a more pronounced cell death on cholinergic neurons from basal forebrain (BF). This effect, partially mediated by M1 receptor blockade, triggering it through AChE splices variants alteration, may explain cadmium effects on learning and memory processes. Cadmium has been also reported to induce oxidative stress generation leading to M2 and M4 muscarinic receptors alteration, in hippocampus and frontal cortex, which are necessary to maintain cell viability and cognitive regulation, so their alteration in BF could also mediate this effect. Moreover, it has been reported that antioxidant treatment could reverse cognitive disorders, muscarinic receptor and AChE variants alterations induced by cadmium. Thus, we hypothesized that cadmium induced cell death of BF cholinergic neurons is mediated by oxidative stress generation and this mechanism could produce this effect, in part, through AChE variants altered by muscarinic receptors disruption. To prove this, we evaluated in BF SN56 cholinergic neurons, whether cadmium induces oxidative stress and alters muscarinic receptors, and their involvement in the induction of cell death through alteration of AChE variants. Our results show that cadmium induces oxidative stress, which mediates partially the alteration of AChE variants and M2 to M4 muscarinic receptors expression and blockage of M1 receptor. In addition, cadmium induced oxidative stress generation by M1 and M3 receptors alteration through AChE variants disruption, leading to cell death. These results provide new understanding of the mechanisms contributing to cadmium harmful effects on cholinergic neurons.