New evidence of an alternative iron uptake pathway in

MARTINEZ VIVOT ROCÍO; USACH V; LAVALLE LUCIA; SETTON CLARA PATRICIA

Uspallata, Mendoza

Congreso; V Neurotoxicity Society Meeting; 2011

Neurotoxicity Society

Schwann cells (SCs) originate from the neural crest cell lineage and are responsible for the myelination of the peripheral nervous system. During SCs development, precursors migrate along with the growing axons and proliferate rapidly at postnatal 2-4 day in rats. Loss of axonal contact, such as occurs after nerve injury or in isolated SCs in vitro, leads to down regulation of myelin genes expression. We have previously described that cultured SCs become de-differentiated acquiring a phenotype similar to SCs precursors and non-myelin forming SCs. Holotransferrin (hTf) prevented this de-differentiation, while apotransferrin (aTf) was unable to avoid such effect. This prodifferentiating effect suggests that iron or hTf are involved in the axonal signal that occurs physiologically during the maturation of SCs and which enables their survival. Whereas Tf-mediated iron uptake is considered to be the main route in most cells, there is also evidence for Tf independent mechanisms. In the present work we measured 59Fe uptake by liquid scintillation counting in cultured SCs submitted to different treatments and evaluated cells’ intracellular iron content by atomic absorption. No 59Fe uptake was detected in cells incubated in the presence of serum or aTf. However, cells treated with iron or hTf showed an increase in the 59Fe uptake, in agreement with intracellular iron content results. We evaluated TfR and Tf intracellular levels by Western blot (WB) analysis and observed that the expression of TfR increased in serum deprived SCs, but decreased TfR levels in the aTf (66%) and hTf (30%) treatments. Finally we chose DMT1 among the iron transporters described and evaluated its presence by WB analysis; which was demonstrated in nerve homogenate, isolated adult-rat myelin and cultured SCs. These data allow us to strongly consider the existence of a Tf independent iron uptake mechanism in SCs.Loss of axonal contact, such as occurs after nerve injury or in isolated SCs in vitro, leads to down regulation of myelin genes expression. We have previously described that cultured SCs become de-differentiated acquiring a phenotype similar to SCs precursors and non-myelin forming SCs. Holotransferrin (hTf) prevented this de-differentiation, while apotransferrin (aTf) was unable to avoid such effect. This prodifferentiating effect suggests that iron or hTf are involved in the axonal signal that occurs physiologically during the maturation of SCs and which enables their survival. Whereas Tf-mediated iron uptake is considered to be the main route in most cells, there is also evidence for Tf independent mechanisms. In the present work we measured 59Fe uptake by liquid scintillation counting in cultured SCs submitted to different treatments and evaluated cells’ intracellular iron content by atomic absorption. No 59Fe uptake was detected in cells incubated in the presence of serum or aTf. However, cells treated with iron or hTf showed an increase in the 59Fe uptake, in agreement with intracellular iron content results. We evaluated TfR and Tf intracellular levels by Western blot (WB) analysis and observed that the expression of TfR increased in serum deprived SCs, but decreased TfR levels in the aTf (66%) and hTf (30%) treatments. Finally we chose DMT1 among the iron transporters described and evaluated its presence by WB analysis; which was demonstrated in nerve homogenate, isolated adult-rat myelin and cultured SCs. These data allow us to strongly consider the existence of a Tf independent iron uptake mechanism in SCs.