| BackgroundNickel （Ni） is widely used heavy metal in model industry. Industrial processing-relatedanthropogenic activities provide a considerable amount of Ni in the environment as a resultof mining, smelting, cement-production, combustion of fossil fuels, incineration of sewagesludge, electroplating. As a result, human exposure to Ni, both occupational and dietary, issuffered by its health hazard. Ni ingested by human distributes into multiple organs, andmanifests multiple toxicities, including neurotoxicity. However, the exact mechanism ofnickel’s neurotoxicity is not well understood. Mitochondrial dysfunction is the primarypathogenesis of various neurologic syndrome, and route by which the environment stimulusexert their neurotoxicity. In recently reports, the activation of regulation-axis which isconsisted by hypoxia-inducible factor-1alpha （HIF-1α）, miRNA210, and iron-sulfur clusterassemble scaffold （ISCU） participates in the mitochondrial function inhibition duringhypoxia condition. As well as, nickel induces the accumulation of HIF-1α in normoxia.Therefore, the purpose of this study is to investigate the role of mitochondrial dysfunctionin Ni-induced neurotoxicity, and to explore whether the activation of regulation-axisunderlies the Ni caused mitochondrial dysfunction.Methods①Kunming mice were orally administered nickel chloride （NiCl2）, andneurobehavioral performance was evaluated using the Morris water maze and open fieldtests at different time points. Ni amounts in neurologic tissues and mitochondrial functionalstates, including O2consumption, ATP concentrations, lactate concentrations, ratios ofNADH/NAD, oxidative stress and iron-sulfur cluster （FeS） containing metabolism enzymesin the cerebral cortex were analyzed at the same time points at which neurobehavioralchanges were evident.②The cell viability and LDH release were applied to evaluate the cytotoxicity ofNiCl2on primary cultured neurons and Neuro2a cell line. Parallel, the effects of Ni on cellular ROS levels, ATP concentrations, mitochondrial membrane potential and mtDNAcopy number and mtRNA transcript level were assayed for identification the Ni-inducedmitochondrial dysfunction. In addition, the pretreatments of mitochondrial protective agents,melatonin and L-carnitine, before Ni exposures were used to elucidate whether they couldprotest against the Ni-induced cytotoxicity through maintaining the mitochondria function.③The expression levels of HIF-1α, miRNA210, ISCU were measured after NiCl2exposure. Then, the microRNA slices which mimic or inhibit the expression of miRNA210were transfected into cells. The expression of ISCU, mitochondrial function and activity ofFeS enzymes were assayed in transfected cells. Finally, the expression of HIF-1α,miRNA210and ISCU were investigated in the cerebral cortex of Ni-treated mice.Results①50mg Ni/kg WT NiCl2administration caused deficits in both spatial memory andexploring activity in mice and that nickel was deposited in their cerebral cortex.Mitochondrial dysfunction manifested as decreased O2consumption and ATPconcentrations, lactate and NADH accumulation, and oxidative stress. Meanwhile, theactivity of prototypical iron-sulfur clusters （ISCs） containing enzymes that are known tocontrol aerobic metabolism, including complex I and aconitase, were inhibited followingnickel deposition.②NiCl2treatment significantly increased the cell viability loss and lactatedehydrogenase （LDH） release in primary cultured neurons and Neuro2a cells. In addition,nickel exposure significantly elevated reactive oxygen species （ROS） and malondialdehyde（MDA） levels disrupted the mitochondrial membrane potential, ATP concentrations anddecreased mtDNA copy numbers and mtRNA transcript levels in both kind of cells.However, all of the cytotoxicity and mitochondrial dysfunctions that were triggered bynickel were efficiently attenuated by pretreatment with melatonin and L-carnitine.③NiCl2exposure lead to significant HIF-1α, rather than HIF-1β, accumulation inNeuro2a cells. MiRNA210was overexpressed by nickel treatment following a dose andtime-dependent manner, which accompanied with ISCU down-regulation. The gain-andloss-of-function assays revealed that miRNA210controlled the ISCU suppression, energymetabolism alternation and ISCs contained metabolic enzymes inactivation under nickelexposure. Dual luciferase reporter assay revealed that ISCU was the direct target ofmiRNA210. In the cerebral cortex of Ni-treated mice, it was found that high levels of HIF-1α and miRNA210, low levels of ISCU.ConclusionOverall, our data suggest that Ni-induced mitochondrial dysfunction may result in theneurotoxicity of nickel which manifested as neurobehavioral changes in mice andcytotoxicity in nerve cells. In nickel exposure conditions, the activation ofHIF-1α-miRNA210-ISCU regulation-axis, which contributed to inhibition of FeS assembleand inactivation of FeS containing metabolism enzymes, may be the mechanism thatunderlies the Ni-induced mitochondrial dysfunction. A better understanding of how nickelimpacts mitochondrial function may provide insight into the prevention of nickelneurotoxicity. |
