Identification of mouse SLC39A8 as the transporter responsible for cadmium-induced toxicity in the testis

Abstract

Testicular necrosis is a sensitive endpoint for cadmium (Cd 2؉ , Cd) toxicity across all species tested. Resistance to Cd-induced testicular damage is a recessive trait assigned to the Cdm locus on mouse chromosome 3. We first narrowed the Cdm-gene-containing region to 880 kb. SNP analysis of this region from two sensitive and two resistant inbred strains demonstrated a 400-kb haplotype block consistent with the Cd-induced toxicity phenotype; in this region is the Slc39a8 gene encoding a member of the solute-carrier superfamily. Slc39a8 encodes SLC39A8 (ZIP8), whose homologs in plant and yeast are putative zinc transporters. We show here that ZRT-, IRT-like protein (ZIP)8 expression in cultured mouse fetal fibroblasts leads to a >10-fold increase in the rate of intracellular Cd influx and accumulation and 30-fold increase in sensitivity to Cd-induced cell death. The complete ZIP8 mRNA and intron-exon splice junctions have no nucleotide differences between two sensitive and two resistant strains of mice; by using situ hybridization, we found that ZIP8 mRNA is prominent in the vascular endothelial cells of the testis of the sensitive strains of mice but absent in these cells of resistant strains. Slc39a8 is therefore the Cdm gene, defining sensitivity to Cd toxicity specifically in vascular endothelial cells of the testis. metal influx ͉ vascular endothelial cells ͉ solute carrier gene superfamily ͉ in situ hybridization C d is a toxic and carcinogenic nonessential metal (1), which can enter the body through the intestine, skin, and lung and accumulates in the kidney (1-3). The level of Cd in the environment has risen with advances in industrialization, and the role of Cd in human disease is of increasing concern. The mechanisms of Cd toxicity are poorly understood, although it is known that Cd exerts its effects intracellularly, and there are polypeptides such as metallothionein (4) and reduced glutathione (5) that bind Cd and afford protection. The subcellular events by which Cd is taken up by cells or removed from cells remain obscure, although such knowledge could provide potential therapeutic targets for protection or intervention against Cd toxicity. Several proteins transport Cd into bacteria, yeast, plants, and mammalian cells in culture (6-11), but their specific roles in causing toxicity are unclear; these studies underscore the difficulties in extrapolating from observations in cell culture to the intact animal.Nature has provided a fascinating genetic system as a foothold into identifying a gene involved in Cd toxicity. It is known that Cd-induced testicular necrosis is common across all animal species having testes: rodents, opossum, armadillos, frogs, pigeons, roosters, and fish (12-17). Cellular events that precede Cd-induced testicular toxicity indicate that vascular endothelial cell injury is the earliest and, perhaps, the causative event (16,(18)(19)(20)(21)(22)(23)(24).Some inbred mouse strains are resistant to Cd-induced testicular toxicity (25). The resistance phenotype segregates largely as a...

Protective role of zinc against the toxicity induced by exposure to cadmium during gestation and lactation on testis development

“…The protective effect of Zn may be due to interaction with Cd in the testis itself, where uptake of the two metals across endothelial cells occurs to gain access to the parenchyma. Earlier studies utilizing genetic approaches have shed light on the role of Zn transporters, such as zinc-iron related transporter proteins (ZIP8), in the uptake of Cd to the testis [52]. Moreover, Liu et al [53] demonstrated that Zn was the best inhibitor of ZIP8-mediated Cd uptake into cells and reported that this influx increased under condition of hypozincemia.…”

Cadmium in tobacco smokers: a neglected link to lung disease?

“…Single-dose inhalation of cadmium chloride (0.1%) in rats results in an acute increase of the GSSG/GSH ratio in cell-free BAL fluid, thereby indicating enhanced oxidative stress. Repeated inhalation of cadmium chloride (1 h per day for 3-5 weeks) also results in a progressive increase of GSH in the cell-free BAL fluid [8,[45][46][47][48][49][50]. Notably, the enzymatic activity of major antioxidants, including superoxide dismutase, catalase, glutathione peroxidase and glutathione reductase, is altered in response to cadmium exposure [51][52][53].…”

Adverse Effects of Low Level Heavy Metal Exposure on Male Reproductive Function

“…They also suggest that at least in certain rodent strains, MT may not be the principle cadmium binding protein in the testes and may not play a major role protecting testicular cells from cadmiuminduced toxicity. Several other cadmium transporters present in the testes have recently been identified including ZIP8 and tesmin, which contains an MTlike motif [Dalton et al 2005;He et al 2009;Martin et al 2007;Sugihara et al 1999]. These transporters may play more prominent roles in testicular metal binding.…”