Effects And Mechanisms Of Cold-induced Rat White/brown Adipose Tissue Changes On Plasticity And Metabolism By SiO₂ Nanoparticles

Background: Concern has been growing about the potential risk of haze to human health because of the increasingly serious problem of air pollution. Haze is a combination of air particles and fog, the air particles problem has attracted much more attention. The health effects of particulate matter consist of increasing incidence of cardiovascular system and respiratory system disease, and aggravating the state of disease, and shortening the life expectancy. Studies have reported that inhaled ultrafine particles are more easily through the lung-blood barrier, deposition in the various tissues by the circulation of blood, and increasing health risks. Ultrafine particles can be called nanoparticles, which has a large proportion in particulate matter of the air. Because of nanomaterials are extensively used in industry and daily life, people are increasingly exposed to the nanoparticles. Because of low air pressure and slowly air flow, bring about the urban haze problems are more serious in winter, as the result more nanoparticles floating in the air, and inhaled with cold air. Although deepening studies on the health effects of nanoparticles, the research about the effects of nanoparticles on adipose tissues have not been reported. Adipose is divided into brown and white adipose tissue, brown adipose tissue is the exclusive non-shivering thermogenesis organ, plays an important role in energy metabolism, lipid deposit is the mainly function of white adipose tissue, adipose tissue is the major organs that producing heat and maintaining body temperature in winter. Adipose tissue dysfunction is closely related to obesity and other metabolic diseases. In this study, nano-SiO₂ particles as ultrafine particles representatives, investigate effects and mechanisms of cold-induced rat white/brown adipose tissue changes on plasticity and metabolism by SiO₂ nanoparticles, in order to provide a theoretical basis to reveal the potential hazard to human health of the winter haze, and the possible mechanism for the development of obesity and other metabolic diseases.Objective: The aim of this paper was to: 1. Study the effects of nano-SiO₂ on cold-induced the WAT browning and the secretion and metabolic function, and preliminary investigate the effect on the development of obesity and other metabolic diseases. 2. study the nano-SiO₂ and cold to assess the inflammation and oxidative stress in adipose tissues, explore the main effect factors on the process.2. Study the Effects of nano-SiO₂ combine with cold exposure on inflammatory response of adipose tissue, preliminary investigate the relationship of inflammation and white and brown adipose on plasticity.Methods:We used a series of experimental protocols to study the effect of nano-SiO₂ and cold in vivo and in vitro. 1. In animal study, male Sprague-Dawley rats were randomly assigned to nano-SiO₂ and/or cold exposure by four groups（control, nano-SiO₂, cold, nano-SiO₂ and cold, n=7 per group）. The rats in nano-SiO₂ and combined group were exposed to nano-SiO₂ by intratracheal instillation, while control and cold exposure group instilled solvent. The rats in cold and combined group were exposed to 4oC 4h/day four weeks. Histopathological techniques analysis, such as hematoxylin and eosin（H.E.） staining, observed the lung, epididymal white and interscapular brown adipose tissue of rats by optical microscopy. And observed the adipocytes ultrastructure by transmission electron microscopy（TEM）. We extracted the total RNA of WAT and BAT then reversed transcription to c DNA, defined the related genes expression by quantitative real-time PCR. Detected the level of pro-inflammatory cytokines in serum by enzyme linked immunosorbent assay（ELISA）.2. For in vitro study, cultured epididymal white adipocytes, then identified the cell by Oil Red O staining. MTT experiment was to assay the effects of different concentrations of nano-SiO₂ exposure and（or） low temperature treatment of 31°C on white adipocytes activity, so as to determine the concentration of subsequent experiments. The white adipocytes were seeded into two six-well plates and divided into 4 groups: control group, nano-SiO₂ exposure group, low temperature group, combined group. When cultured the white adipocytes in logarithmic phase, the nanoSiO₂ exposure group was 100ug/ml of nano-SiO₂ exposure, low temperature group was treated by 31°C, combined group was both of treated for 48 hours, the control group replaced with new culture medium and continue normal training. Defined the change of pro-inflammatory cytokines（interleukin 1β, 6, 8 and tumor necrosis factor α） expressions, white and brown adipocytes specific genes expression, secreted and metabolic gene（leptin, adiponectin） expression.Result:1. Effects of nano-SiO₂ and cold on the changes of the whole and adipose tissue in rats: compared to the other groups, the weight gained of rats was significant decrease by cold exposure, but the other groups had no significant difference. The coefficient of interscapular BAT: control（0.115 ± 0.015）%, nano-SiO₂ group（0.091 ± 0.018）%, cold exposure group（0.164 ± 0.038）%, nano-SiO₂ and cold group（ 0.136 ± 0.017）%, and the cold exposure group was significantly higher than other groups. The pathological analysis of adipose tissue, cold exposure group adipocytes had more organelles and a more compact structure, and was different from other groups. We performed TEM in adipose tissue found that the mitochondrias of adipocytes were large and round, and the numbers were relatively more, the other groups without those change. In addition, there were a large number of particles in brown adipocytes of nano-SiO₂ group and combined group. The quantitative real-time PCR analysis, the expressions of brown adipose tissue specific genes（UCP1 and PGC-1α） were significantly increase, and low white adipose tissue specific genes m RNA levels（Dpt and Hoxc9） in cold exposure group, but was different from other groups. The secreted and metabolic gene（leptin, adiponectin, AMP-activated protein kinase） expressions were significantly up-regulated in the cold exposure group, while the expression of the combined group was not different from that in the control group.2. Effects of nano-SiO₂ and cold on inflammatory response in rats: the histopathological analysis of lungs, each group had inflammatory response, but the nano-SiO₂ group and combined group were obviously, the combined group even lung consolidation. The pro-inflammatory cytokines（IL-1β, IL-6, IL-8 and TNF-α） expressions of white and brown adipose tissues were significantly up-regulated in the combined group. The concentration of IL-8 in serum was significant higher in combined group（9.91 ± 1.06） ng/L than in other groups（6.98 ± 0.93,7.38 ± 1.04,6.97 ± 1.17） ng/L, the concentration of TNF-α was significant increase in combined group（80.50 ± 8.02） ng/L compare to control（73.92 ± 4.97） ng/L, and the IL-6 of combined group was trend to up-regulated.3. Toxic effects of nano-SiO₂ and low temperature on white adipocytes: after treated white pro-adipocytes with low temperature and nano-SiO₂ forty-eight hours,cold or nano-SiO₂ inhibit the cell activity, and the inhibition of combined group was more obvious, and as dosage level ascended, the inhibition was increased signifivantly. The pro-inflammatory cytokines expressions of white adiposcytes were significantly up-regulated in the nano-SiO₂ group, and had a tendency of increase in cold exposure group, but the combined group was significant higher than other groups.4. Effects of nano-SiO₂ and low temperature on the browning of white adipocytes: after treatment, white adipose tissue specific genes were down-regulated and the brown tissue specific genes were up-regulated in cold exposure group, the nano-SiO₂ was in contrast to cold, but those effects were significantly inhibited by combined cold and nano-SiO₂. The LEP expression of white pro-adipocyte in nano-SiO₂ group was no significant difference, and the LEP expression was significant up-regulated in cold group, the expression was down-regulated nano-SiO₂ in combined group. The ADPN expression of white pro-adipocyte was trend to down-regulated by nano-SiO₂, and the expression of cold group was significantly down-regulated, and the combined group was obvious down-regulated.Conclusions:After cold exposure induce the decrease of body weight gain in rats, stimulate the production of BAT and the phenomenon of WAT browning, but after inhaled SiO₂ nanoparticles, which obvious inhibit the cold-induced response of adipose tissue, and aggravate inflammatory response, significantly impact on cold-induced BAT and WAT specific gene expression, and the gene expression changes of secretion and metabolism. Nano-SiO₂ induce the toxicity effect in white adipocytes, while combine with low temperature significantly increase the toxic effect. Nano-SiO₂ significantly inhibit the function of low temperature stimulate the browning and secretion of white adipocytes. Nano-SiO₂ lead to the increase of pro-inflammatory cytokines expressions in white adipocytes, significantly inhibit the effects of low temperature induced the increase of the secretion and thermogenesis gene expressions. Further points, Nano-SiO₂ passivation the phenomenon of cold-induced brown/white adipose plasticity, potential effect on thermogenesis and secretion function of adipose tissue.