BackgroundNanometer silicon dioxide (nano-SiO2) has a wide variety of applications in material sciences, engineering and medicine; however, the potential cell biological and proteomic effects of nano-SiO2 exposure and the toxic mechanisms remain far from clear.ResultsHere, we evaluated the effects of amorphous nano-SiO2 (15-nm, 30-nm SiO2). on cellular viability, cell cycle, apoptosis and protein expression in HaCaT cells by using biochemical and morphological analysis, two-dimensional differential gel electrophoresis (2D-DIGE) as well as mass spectrometry (MS). We found that the cellular viability of HaCaT cells was significantly decreased in a dose-dependent manner after the treatment of nano-SiO2 and micro-sized SiO2 particles. The IC50 value (50% concentration of inhibition) was associated with the size of SiO2 particles. Exposure to nano-SiO2 and micro-sized SiO2 particles also induced apoptosis in HaCaT cells in a dose-dependent manner. Furthermore, the smaller SiO2 particle size was, the higher apoptotic rate the cells underwent. The proteomic analysis revealed that 16 differentially expressed proteins were induced by SiO2 exposure, and that the expression levels of the differentially expressed proteins were associated with the particle size. The 16 proteins were identified by MALDI-TOF-TOF-MS analysis and could be classified into 5 categories according to their functions. They include oxidative stress-associated proteins; cytoskeleton-associated proteins; molecular chaperones; energy metabolism-associated proteins; apoptosis and tumor-associated proteins.ConclusionsThese results showed that nano-SiO2 exposure exerted toxic effects and altered protein expression in HaCaT cells. The data indicated the alterations of the proteins, such as the proteins associated with oxidative stress and apoptosis, could be involved in the toxic mechanisms of nano-SiO2 exposure.

Relationships between biodiversity and multiple ecosystem functions (that is, ecosystem multifunctionality) are context-dependent. Both plant and soil microbial diversity have been reported to regulate ecosystem multifunctionality, but how their relative importance varies along environmental gradients remains poorly understood. Here, we relate plant and microbial diversity to soil multifunctionality across 130 dryland sites along a 4,000 km aridity gradient in northern China. Our results show a strong positive association between plant species richness and soil multifunctionality in less arid regions, whereas microbial diversity, in particular of fungi, is positively associated with multifunctionality in more arid regions. This shift in the relationships between plant or microbial diversity and soil multifunctionality occur at an aridity level of ∼0.8, the boundary between semiarid and arid climates, which is predicted to advance geographically ∼28% by the end of the current century. Our study highlights that biodiversity loss of plants and soil microorganisms may have especially strong consequences under low and high aridity conditions, respectively, which calls for climate-specific biodiversity conservation strategies to mitigate the effects of aridification.

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Nano silicon dioxide (nano-SiO2) is becoming more and more widely applied in the fields of industry. The potential toxic effects of nano-SiO2 and its hazard to human health are drawing more attention. The mRNA expression of poly(ADP-ribose) polymerases-1(PARP-1), a pivotal repair gene, has been decreased by nano-SiO2 exposure. However, the effect of epigenetic modification on nano-SiO2-induced low PARP-1 expression has not been reported. In this study, HaCaT cells with or without DNA methyltransferase 1(DNMT1) knock down were incubated with nano-SiO2 and then further treated with DNMT inhibitor, 5-aza-2-deoxycytidine (DAC), which is a kind of key epigenetic modification reagents. Real-time Q-PCR and western blotting were used to examine the mRNA and protein expression of PARP-1. For promoter methylation status of PARP-1, methylation-specific PCR (MSP) and Bisulfite sequencing assay were performed. Results showed a dramatic decrease of PARP-1 expression on mRNA and protein level and a simultaneously obvious increase in the level of PARP-1 methylation in nano-SiO2-treated cells compared to the control group. Further, the expression and promoter methylation of PARP-1 in HaCaT cells were restored following DNMT1 knock down, suggesting that the effects of PARP-1 promoter hypermethylation are mediated at least in part by DNMT1. Taken together, methylation of PARP-1 promoter might be involved in the regulation of nano-SiO2-induced decrease of PARP-1 expression.