Neonatal C57BL/6J and parkin mice respond differently following developmental manganese exposure: Result of a high dose pilot study
NEUROTOXICOLOGY
Authors: Foster, Melanie L.; Bartnikas, Thomas B.; Maresca-Fichter, Hailey C.; Mercadante, Courtney; Dash, Miriam; Miller, Chelsea; Dorman, David C.
Abstract
It has been suggested that childhood exposure to neurotoxicants may increase the risk of Parkinson's disease (PD) or other neurodegenerative disease in adults. Some recessive forms of PD have been linked to loss-of-function mutations in the Park2 gene that encodes for parkin. The purpose of this pilot study was to evaluate whether responses to neonatal manganese (Mn) exposure differ in mice with a Park2 gene defect (parkin mice) when compared with a wildtype strain (C57BL/6J). Neonatal parkin and C57BL/6J littermates were randomly assigned to 0,11, or 25 mg Mn/kg-day dose groups with oral exposures occurring from postnatal day (PND) 1 through PND 28. Motor activity was measured on PND 19-22 and 29-32. Tissue Mn concentrations were measured in liver, femur, olfactory bulb, frontal cortex, and striatum on PND 29. Hepatic and frontal cortex gene expression of Slc11a2, Slc40a1, Slc30a10, Hamp (liver only), and Park2 were also measured on PND 29. Some strain differences were seen. As expected, decreased hepatic and frontal cortex Park2 expression was seen in the parkin mice when compared with C57BL/6J mice. Untreated parkin mice also had higher liver and femur Mn concentrations when compared with the C57BL/6J mice. Exposure to >= 11 mg Mn/kg-day was associated with increased brain Mn concentrations in all mice, no strain difference was observed. Manganese exposure in C57Bl6, but not parkin mice, was associated with a negative correlation between striatal Mn concentration and motor activity. Manganese exposure was not associated with changes in frontal cortex gene expression. Decreased hepatic Slc30a10, Slc40a1, and Hamp expression were seen in PND 29 C57BL/6J mice given 25 mg Mn/kg-day. In contrast, Mn exposure was only associated with decreased Hamp expression in the parkin mice. Our results suggest that the Parkin gene defect did not increase the susceptibility of neonatal mice to adverse health effects associated with high-dose Mn exposure. (C) 2017 Elsevier B.V. All rights reserved.
Suppression of SLC11A2 Expression Is Essential to Maintain Duodenal Integrity During Dietary Iron Overload
AMERICAN JOURNAL OF PATHOLOGY
Authors: Shirase, Tomoyuki; Mori, Kiyoshi; Okazaki, Yasumasa; Itoh, Ken; Yamamoto, Masayuki; Tabuchi, Mitsuaki; Kishi, Fumio; Jiang, Li; Akatsuka, Shinya; Nakao, Kazuwa; Toyokuni, Shinya
Abstract
Iron is essential for the survival of mammals, but iron overload causes fibrosis and carcinogenesis. Reduced iron absorption and regulated release into circulation in duodenal mucosa constitute two major mechanisms of protection against dietary iron overload; however, their relative contribution remains elusive. To study the significance of the former process, we generated SLC11A2 transgenic mice (TGs) under the control of the chicken beta-actin promoter. TGs were viable and fertile, and displayed no overt abnormalities up to 20 months. No significant difference in iron concentration was observed in major solid organs between TGs and their wild-type littermates, suggesting that increased number of iron transporters does not lead to increased iron absorption. To test the sensitivity to iron overload, TGs and wild-type mice were fed with an iron-rich diet containing 2% ferric citrate. Iron supplementation caused suppression of endogenous duodenal SLC11A2 expression, down-regulation of duodenal ferroportin, and overexpression of hepatic hepcidin, precluding excessive iron uptake both in the TGs and wild-type mice. However, iron-treated TGs revealed increased mortality, resulting from oxidative mucosal damage leading to hemorrhagic erosion throughout the whole intestinal area. These findings suggest that reduced iron release from duodenal cells into circulation plays a role in mitigating excessive iron uptake from the diet and that finely regulated duodenal absorption is essential to protect intestinal mucosa from iron-induced oxidative damage. (Am J Pathol 2010, 177:677-685; DOI: 10.2353/ajpath.2010.090823)