Manganese (Mn) is an essential trace element for normal human development and vital enzymatic activities. Because of its reactivity, it is also widely used in industrial processes, such as welding. However, occupational exposure to high levels of Mn has been implicated in a Parkinsonian-like syndrome known as manganism, affecting the dopaminergic system. Since the initial discovery of Mn-induced pathogenesis, much effort has been put forth to study the etiology of manganism, yet the primary biochemical changes have to be elucidated. In the present study, we use C. elegans to understand mechanisms of Mn transport across biological membranes and its cytotoxic effects.. We first report on survival of wild-type C. elegans upon acute 30 min Mn treatment, which is characterized by an LD50~42 mM. As expected, lethality appeared to be due to major osmoregulation defects affecting most epidermal tissues including epidermis, intestine and the excretory cell. We cloned the three C. elegans divalent-metal transporters and found that
smf-1 and
smf-3 are involved in Mn toxicity.
smf-1(
eh5) and
smf-3(
ok1035) mutants are hyper-resistant to Mn exposure (LD50~83 mM and 122 mM, respectively, p<0.001)whereas
smf-2(
gk133) mutant is similar to control (LD50~41 mM). On the other hand, at sublethal doses of Mn (>0,5 mM), we found that C. elegans dopaminergic neurons are preferentially affected and in a dose-dependent manner. Furthermore, we demonstrate that
dat-1(
ok157) and
dop-1(
vs100);
dop-2(
vs105);
dop-3(
vs106) mutants which exhibit high dopamine levels are significantly more sensitive (LD50~9 mM and 27 mM, respectively, p<0.001), whereas the dopamine-depleted
cat-1(
e1111) and
cat-2(
e1112) mutants are more resistant to Mn toxicity (LD50~100 mM and 130 mM, respectively, p<0.001). Our results suggest that dopamine metabolism directly contributes to the toxicity mechanism, most likely by promoting reactive oxygen species production.. Taken together our data imply the existence of conserved mechanisms for Mn transport and toxicity from the nematode to humans, and show that C. elegans is a valuable model for dissecting out Mn toxicity mechanisms. This project is funded by R01 ES10563 to MA.