Environmental arsenic pollution induced liver oxidative stress injury by regulating miR-155 through inhibition of AUF1

Arsenic (As), a common environmental pollutant, has become a hot topic in recent years due to its potentially harmful effects. Liver damage being a central clinical feature of chronic arsenic poisoning. However, the underlying mechanisms remain unclear. We demonstrated that arsenic can lead to oxidative stress in the liver and result in structural and functional liver damage, significantly correlated with the expression of AUF1, Dicer1, and miR-155 in the liver. Interestingly, knockdown AUF1 promoted the up-regulatory effects of arsenic on Dicer1 and miR-155 and the inhibitory effects on SOD1, which exacerbated oxidative damage in rat liver. However, overexpression of AUF1 reversed the up-regulatory effects of arsenic on Dicer1 and miR-155, restored arsenic-induced SOD1 depletion, and attenuated liver oxidative stress injury. Further, we verified the mechanism and targets of miR-155 in regulating SOD1 by knockdown/overexpression of miR-155 and nonsense mutant SOD1 3'UTR experiments. In conclusion, these results powerfully demonstrate that arsenic inhibits AUF1 protein expression, which in turn reduces the inhibitory effect on Dicer1 expression, which promotes miR-155 to act on the SOD1 3'UTR region after high expression, thus inhibiting SOD1 protein expression and enzyme activity, and inducing liver injury. This finding provides a new perspective for the mechanism research and targeted prevention of arsenic poisoning, as well as scientific evidence for formulating strategies to prevent and control environmental arsenic pollution.

Updating mRNA variants of the human RSK4 gene and their expression in different stressed situations

We determined RNA spectrum of the human RSK4 (hRSK4) gene (also called RPS6KA6) and identified 29 novel mRNA variants derived from alternative splicing, which, plus the NCBI-documented ones and the five we reported previously, totaled 50 hRSK4 RNAs that, by our bioinformatics analyses, encode 35 hRSK4 protein isoforms of 35-762 amino acids. Many of the mRNAs are bicistronic or tricistronic for hRSK4. The NCBI-normalized NM_014496.5 and the protein it encodes are designated herein as the Wt-1 mRNA and protein, respectively, whereas the NM_001330512.1 and the long protein it encodes are designated as the Wt-2 mRNA and protein, respectively. Many of the mRNA variants responded differently to different situations of stress, including serum starvation, a febrile temperature, treatment with ethanol or ethanol-extracted clove buds (an herbal medicine), whereas the same stressed situation often caused quite different alterations among different mRNA variants in different cell lines. Mosifloxacin, an antibiotics and also a functional inhibitor of hRSK4, could inhibit the expression of certain hRSK4 mRNA variants. The hRSK4 gene likely uses alternative splicing as a handy tool to adapt to different stressed situations, and the mRNA and protein multiplicities may partly explain the incongruous literature on its expression and comports.

Hesperidin Protects Against High-Fat Diet-Induced Lipotoxicity in Rats by Inhibiting Pyroptosis

It is currently thought that excess fatty acid-induced lipotoxicity in hepatocytes is a critical initiator in the development of nonalcoholic fatty liver disease (NAFLD). Lipotoxicity can induce hepatocyte death; thus, reducing lipotoxicity is one of the most effective therapeutic methods to combat NAFLD. Abundant evidence has shown that hesperidin (HSP), a type of flavanone mainly found in citrus fruits, is able to ameliorate NAFLD, but the molecular mechanisms are unclear. We previously reported that pyroptosis contributed to NAFLD development and that inhibiting pyroptosis contributed to blunting the progression of NAFLD in rat models. Therefore, we questioned whether HSP could contribute to ameliorating NAFLD by modulating pyroptosis. In this study, a high-fat diet (HFD) induced dyslipidemia and hepatic lipotoxicity in rats, and HSP supplementation ameliorated dyslipidemia and insulin resistance. In addition, the HFD also caused pyroptosis in the liver and pancreas, while HSP supplementation ameliorated pyroptosis. In vitro, we found that HSP ameliorated palmitic acid-induced lipotoxicity and pyroptosis in HepG2 and INS-1E cells. In conclusion, we showed for the first time that HSP has a protective effect against liver and pancreas damage in terms of pyroptosis and provides a novel mechanism for the protective effects of HSP on NAFLD.

The Role of BNIP3 and Blocked Autophagy Flux in Arsenic-Induced Oxidative Stress-Induced Liver Injury in Rats

Arsenic is a widely distributed environmental toxic substance in nature. Chronic arsenic exposure can cause permanent damage to the liver, resulting in the death of poisoned patients. However, the mechanism of liver damage caused by arsenic poisoning is yet unclear. Here, four different concentrations of sodium arsenite (NaAsO2) (0 mg/L (control group), 25 mg/L, 50 mg/L, and 100 mg/L group)were established to induce liver injury in rats. Taking this into account, the relationship and potential mechanisms of oxidative stress, Bcl-2/adenovirus E1B-19-kDa-interacting protein 3 (BNIP3), and inhibition of autophagy flux in liver injury caused by arsenic poisoning were studied. The results indicated that long-term exposure to NaAsO2 could induce oxidative stress, leading to high expression of BNIP3, thereby impaired autophagy flux, and ultimately resulting in liver damage. This research provides an important basis for future research on liver damage caused by chronic arsenic exposure and prevention and treatment with BNIP3 as the target.

Role of SESTRIN2/AMPK/ULK1 pathway activation and lysosomes dysfunction in NaAsO2-induced liver injury under oxidative stress

Arsenic, a serious environmental poison to human health, is widely distributed in nature. As the main organ of arsenic metabolism, liver is easily damaged. In the present study, we found that arsenic exposure can cause liver injury in vivo and in vitro, to date the underlying mechanism of which is yet unclear. Autophagy is a process that depends on lysosomes to degrade damaged proteins and organelles. Here, we reported that oxidative stress can be induced and then activated the SESTRIN2/AMPK/ULK1 pathway, damaged lysosomes, and finally induced necrosis upon arsenic exposure in rats and primary hepatocytes, which was characterized by lipidation of LC3II, the accumulation of P62 and the activation of RIPK1 and RIPK3. Similarly, lysosomes function and autophagy can be damaged under arsenic exposure, which can be alleviated after NAC treatment and aggravated by Leupeptin treatment in primary hepatocytes. Moreover, we also found that the transcription and protein expressions of necrotic-related indicators RIPK1 and RIPK3 in primary hepatocytes were decreased after P62 siRNA. Taken together, the results revealed that arsenic can induce oxidative stress, activate SESTRIN2/AMPK/ULK1 pathway to damage lysosomes and autophagy, and eventually induce necrosis to damage liver.

LC/MS/MS-Based Liver Metabolomics to Identify Chronic Liver Injury Biomarkers Following Exposure to Arsenic in Rats

Arsenic is a widespread natural metalloid element. Long-term chronic exposure to arsenic can lead to different degrees of liver injury. Although the etiology of this disease is well known, to date, the underlying mechanism of arsenic-induced liver injury remains unclear, and no specific treatment exists because of the complexity of arsenic. In the present study, potential biomarkers and metabolic pathways in the livers of Wistar rats treated with arsenic for 24 weeks were investigated using an integrated metabolic approach with an LC-Orbitrap Q Exactive™ HF-X mass spectrometer. Markedly increased liver levels of arsenic, alanine aminotransferase (ALT), alkaline phosphatase (ALP), and total bile acid (TBA) were detected in the arsenic treatment groups (P < 0.05). Furthermore, histopathological examination of liver tissues showed obviously swollen, loose cytoplasm and increased necrosis in the arsenic treatment groups compared with those in the control group (P < 0.05). Metabonomics results showed that 109 metabolites (variable importance in the projection (VIP) > 1; fold change > 2 or < 0.5; P adjusted < 0.05) changed significantly after exposure to arsenic and included 71 upregulated metabolites and 38 downregulated metabolites. Additionally, Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that 6 metabolic pathways with statistical significance-phenylalanine metabolism, pyruvate metabolism, glycolysis/gluconeogenesis, citrate cycle (TCA cycle), thiamine metabolism, and vitamin B6 metabolism-were selected, and 13 differential metabolites were detected to be involved in regulating these metabolic pathways. The present study could help identify potential biomarkers and their functions, as well as metabolic pathways, likely providing evidence for the early diagnosis, prevention, and mechanistic study of arsenism.

Mechanism underlying the targeted regulation of the SOD1 3'UTR by the AUF1/Dicer1/miR-155/SOD1 pathway in sodium arsenite-induced liver injury

Arsenic (As) is a natural hepatotoxicity inducer that is ubiquitous in water, soil, coal, and food. Studies have found that arsenite exposure elicits increased mRNA transcription and decreased protein expression of SOD1 in vivo and in vitro; however, the specific mechanisms remain unclear. Here, we established a model of arsenic-induced chronic liver injury by providing rats with drinking water containing different concentrations of sodium arsenite (NaAsO₂) and found that NaAsO₂ exposure decreased the mRNA and protein levels of AUF1 and the protein level of SOD1 and elevated the mRNA and protein levels of Dicer1 and miR-155 and the mRNA level of SOD1. Overexpression of AUF1 under NaAsO₂ stress in vitro induced Dicer1 mRNA and protein expression and decreased miR-155 levels, which could be reversed by AUF1 siRNA. In addition, miR-155 overexpression downregulated SOD1 mRNA and protein levels, although this change was inhibited after transfection with an miR-155 inhibitor. Taken together, our findings showed that NaAsO₂ could upregulate Dicer1 mRNA and protein, thereby increasing miR-155 expression by downregulating AUF1 mRNA and protein expression. A dual-luciferase reporter assay indicated that miR-155 decreased the mRNA and protein levels of SOD1 by targeting the SOD1 3'UTR, resulting in liver injury. This study provides an important research basis for further understanding the factors underlying arsenic-induced liver injury to improve the prevention and control strategies for arsenism.

Establishment of New Genetic Markers and Methods for Sex Determination of Mouse and Human Cells using Polymerase Chain Reactions and Crude DNA Samples

Background: The currently available methods for sexing human or mouse cells have weaknesses. Therefore, it is necessary to establish new methods. Methods: We used bioinformatics approach to identify genes that have alleles on both the X and Y chromosomes of mouse and human genomes and have a region showing a significant difference between the X and Y alleles. We then used polymerase chain reactions (PCR) followed by visualization of the PCR amplicons in agarose gels to establish these genomic regions as genetic sex markers. Results: Our bioinformatics analyses identified eight mouse sex markers and 56 human sex markers that are new, i.e. are previously unreported. Six of the eight mouse markers and 14 of the 56 human markers were verified using PCR and ensuing visualization of the PCR amplicons in agarose gels. Most of the tested and untested sex markers possess significant differences in the molecular weight between the X- and Y-derived PCR amplicons and are thus much better than most, if not all, previously-reported genetic sex markers. We also established several simple and essentially cost-free methods for extraction of crude genomic DNA from cultured cells, blood samples, and tissues that could be used as template for PCR amplification. Conclusion: We have established new sex genetic markers and methods for extracting genomic DNA and for sexing human and mouse cells. Our work may also lend some methodological strategies to the identification of new genetic sex markers for other organismal species.

Sodium fluoride causes oxidative damage to silkworm (Bombyx mori) testis by affecting the oxidative phosphorylation pathway

Bombyx mori was used to study the molecular mechanism of fluoride induced reproductive toxicity. In our previous study, we confirmed the physiological and biochemical effects of NaF on reproductive toxicity, and we found that the molecular mechanism of NaF induced reproductive damage may be associated with the oxidative phosphorylation pathway. To further study the function of NaF exposure on the oxidative phosphorylation pathway in the testis in Bombyx mori, and the relationship between oxidative phosphorylation and oxidative stress, we measured the changes in the main ROS (O2- and H2O2) in the testis, the activity of the main electron transport chain complex enzymes in the oxidative phosphorylation pathway and the transcription levels of the corresponding genes; we additionally performed pathological observations of the silkworm testis after exposure to 200 mg/L NaF solution for different times. The content of O2- and H2O in the silkworm gonads increased significantly at 24 h, 72 h and 120 h after NaF stress. The activity of mitochondrial complexes I, III, IV and V in the silkworm testis was significantly greater than that in the control group. RT-PCR analysis suggested that the mRNA transcription levels of NADH-CoQ1, Cyt c reductase, Cyt c oxidase and ATP synthase genes were up-regulated significantly. Histopathological investigation showed that the damage to the silkworm testis was more severe with increasing NaF exposure times. These results indicated that NaF stress affects the NADH respiratory chain of the mitochondrial electron transport chain and increases the activity of related enzyme complexes, thus destroying the balance of the electron transport chain. Subsequently, the content of ROS in cells significantly increases, thus resulting in oxidative stress reactions in cells. These results enable better understanding of the testis-damaging molecular toxicological mechanism of NaF.

Refinement Impairments of Verbal-Performance Intelligent Quotient in Children Exposed to Fluoride Produced by Coal Burning

To explore the relationship between total intelligence quotient (IQ), verbal intelligence quotient (VIQ), performance intelligence quotient (PIQ), and fluoride exposure in children aged 8-12 years in coal-burning fluorosis area of Dafang County, Guizhou Province, China. The Wechsler Intelligence Scale for Children Revised in China (WISC-CR) was used to test the total IQ, VIQ, and PIQ in 99 children aged 8-12 years (55 in dental fluorosis group and 44 in control group). The differences in the intellectual levels between the two groups were compared, and the correlation between the intellectual level of children exposed to fluoride and the exposure dose of fluoride was analyzed. The VIQ, PIQ, and total IQ in the dental fluorosis group were 85.64 ± 16.53, 94.87 ± 12.73, and 88.51 ± 12.77, respectively, and these were lower than those in the control group (94.34 ± 16.04, 99.23 ± 12.44, and 96.64 ± 11.70, respectively). Significant difference was observed in VIQ and total IQ between the two groups (P = 0.002, P = 0.01), but not in the PIQ (P > 0.05). Each item of VIQ impairment (common sense, similar, arithmetic, vocabulary, and understanding) was significantly lower than those without VIQ impairment in the dental fluorosis group (P < 0.05). There was a significant difference in two items of building blocks and decoding between PIQ impairment and normal group (P < 0.05). Children with fluorosis in coal-burning areas had impaired IQ and obviously had impaired VIQ. Thus, the language learning ability should be strengthened in children exposed to fluorosis.

[Influence of chronic fluorosis on the expression of mitochondrial fission protein dynamin-related 1 in the cortical neurons of rats]

OBJECTIVE

To explore the changes of protein expression of mitochondrial fission gene dynamin-related 1(Drp 1) in the cortical neurons of rats with chronic fluorosis.

METHODS

A total of 120 one-month-old SD rats (each weighing approximately 100-120 g at the beginning of the experiment) were randomly divided into three groups, and fed with the different doses of fluoride containing in drinking water (untreated control containing 0 mg/L fluoride, and low-fluoride & high-fluoride supplemented with 10 and 50 mg/L fluoride,respectively). After 3 or 6 months exposure, 20 rats from each group were killed. Then the protein expression of mitochondrial fission gene, Drp1, was detected by immunohistochemistry and western-blotting method.

RESULTS

Dental fluorosis and urinary fluorosis were obviously found in the rats exposed to fluoride. At the experiment period of 3 months, the numbers of positive cells of Drp1 detected by immunohistochemistry changed. Compared with the control group (36.3 ± 5.8), the changes in low-fluoride group (34.7 ± 4.1) showed no significant difference (t = 1.5, P > 0.05),but the increase in high-fluoride group (45.0 ± 4.7) had statistical significance (t = 8.8, P < 0.05). The western-blotting method had consistent results. Compared with the control group (0.59 ± 0.03), a significant increase of the average topical density in low- fluoride (0.62 ± 0.03) and high-fluoride (0.71 ± 0.02) groups were found (t = 0.02,0.11, P < 0.05). At the experiment period of 6 months, the numbers of positive cells of Drp1 detected by immunohistochemistry significantly changed. Compared with the control group (33.2 ± 4.4), the number in low- fluoride and high-fluoride groups were separately (36.6 ± 3.8) and (39.4 ± 4.2),both increased significantly (t = 3.5,6.3, P < 0.05). Same results could be found in western-blotting method,compared with the control group (0.65 ± 0.06), the average topical density in low- fluoride (0.80 ± 0.09) and high-fluoride (0.76 ± 0.08) groups both increased significantly (t = 0.1,0.1, P < 0.05).

CONCLUSIONS

Taking excessive amount of fluoride might result in the changes of expression of Drp1, and the neurons damage from the chronic fluorosis might be associated with the hyperfunction of mitochondrial fusion.

[Changed expression of mito-fusion 1 and mitochondrial fragmentation in the cortical neurons of rats with chronic fluorosis]

OBJECTIVE

To observe the mitochondrial fragmentation and the expression of mito-fusion 1 gene in the cortical neurons of rats with chronic fluorosis, and to reveal their roles in mitochondria damage to neurons due to chronic fluorosis.

METHODS

SD rats were divided randomly into three groups of 20 each (a half females and a half males housed individually in stainless-steel cages), and fed with the different doses of fluoride containing in drinking water (untreated control containing 0 mg/L fluoride, and low-fluoride and high supplemented with 10 and 50 mg/L fluoride, respectively). After 3 or 6 months exposure, the mitochondrial morphology of the neurons in rat brains were observed by transmission electron microscopy (TEM), then the expression of mitochondrial fusion gene, Mfn1, were detected by immunohistochemistry and western-blotting, respectively.

RESULTS

Dental fluorosis was obvious in the rats exposed to excessive fluoride in their drinking water, that is, (16 rats out of 20) numbers of I° detal fluorosis in the low-fluoride group, and (11 rats out of 20) numbers of I° and (9 rats out of 20) numbers of II° detal fluorosis in the high-fluoride group were observed after 3 months exposure. Moreover, (14 rats out of 20) numbers of I° and (6 rats out of 20) numbers of II° detal fluorosis in the low-fluoride group and (6 rats out of 20) numbers of Io, (13 rats out of 20) numbers of II°, and (1 rats out of 20) numbers of III° detal fluorosis in the high-fluoride group were observed after 6 months exposure. And both of untreated controls without detal fluorosis were also observed. The urinary level of fluoride in the low-fluoride group (3.30 ± 1.18) mg/L and in the high-fluoride group (5.10 ± 0.35) were observed after 3 months exposure (F = 3.18, P < 0.05). Moreover, the urinary level of fluoride in the low-fluoride group (4.16 ± 1.39) mg/L and in the high-fluoride group (5.70 ± 1.70) mg/L were also observed after 6 months exposure (F = 3.17, P < 0.05). The normal mitochondrial morphology of neurons in rats without fluorosis was observed after 3 and 6 months, while the abnormal mitochondrial morphology of neurons with fluorosis was shown, presenting mitochondrial fragmentation with swollen cristae and even the fragmented, shortened or stacked punctuate membranes (section observation of three bullous mitochondrial-mitochondrial fission process) by TEM. As compared with controls (53.0 ± 4.54 and 1.21 ± 0.18) at the experiment period of 3 months, Mif1 protein analysis with immunocytochemical (the numbers of positive cells: 51.09 ± 6.25) and western-blotting (1.22 ± 0.26) were no significant difference for low fluoride group (t = 1.7, 1.1, P > 0.05); Mif1 protein analysis with immunocytochemical (the numbers of positive cells: 59.71 ± 5.64) and western-blotting (1.66 ± 0.20) were significantly increasing for high fluoride group (t = 2.1, 2.1, P < 0.05). As compared with controls (36.43 ± 4.04 and 1.00 ± 0.13) at the experiment period of 6 months, Mif1 protein analysis with immunocytochemical (the numbers of positive cells 20.05 ± 4.55 and 17.10 ± 3.86) and western-blotting (0.64 ± 0.08 and 0.39 ± 0.06) were significantly decreasing for the two fluoride group (t = 2.1, 2.2; 2.2, 2.2 respectively, all P value were < 0.05).

CONCLUSIONS

Taking excessive amount of fluoride might result in the mitochondrial fragmentation for the changed expression of Mfn1, and the neurons damage from the chronic fluorosis might be associated with the dysfunction of mitochondrial fusion.

[Alteration of mitochondrial distribution and gene expression of fission 1 protein in cortical neurons of rats with chronic fluorosis]

OBJECTIVE

To investigate the changes of mitochondrial distribution in axon/soma and the expression of mitochondrial fission 1 (Fis1) protein in the cortical neurons of rats with chronic fluorosis.

METHODS

Sixty SD rats were divided into 3 groups (20 each) according to weight hierarchy and fed with different concentrations of fluoride in drinking water (0, 10 and 50 mg/L, respectively) for 6 months. Images of mitochondria and tubulin labeled by immunofluorescence COXIV and tubulin-α were captured with fluorescence microscope. Fis1 protein expression in cortical neurons was analyzed with immunohistochemistry and Western blot. The expression of Fis1 mRNA was detected with real-time PCR.

RESULTS

Varying degrees of dental fluorosis and increased fluoride contents in urine were observed in the rats receiving additional fluoride in drinking water. In the cortical neurons of rats fed with 10 mg/L and 50 mg/L fluoride, the numbers of neuronal soma stained with COXIV(34.8 ± 4.7 and 39.3 ± 3.0, respectively), and the expression of Fis1 protein (immunohistochemistry: 54.0 ± 3.6 and 51.3 ± 4.1, respectively; Western blot: 2.9 ± 0.4 and 2.6 ± 0.6, respectively) and mRNA (3773 ± 1292 and 1274 ± 162, respectively) was markedly increased as compared with controls (4.4 ± 2.3, 25.2 ± 2.5, 1.8 ± 0.2 and 277 ± 73) over the experimental period of 6 months.

CONCLUSIONS

Excessive intake of fluoride results in an altered mitochondrial distribution in axon and soma in cortical neurons (i.e., the increase in soma and the decrease in axon), increased expression of Fis1 gene and enhanced mitochondrial fission. The altered mitochondrial distribution may be related to the high expression level of Fis1 and a functional disorder of mitochondria.

[Polymorphism of DXYS267 locus and application of its Y-specific single nucleotide substitutions]

OBJECTIVE

To investigate the polymorphism of DXYS267 locus in China Han population and find the application and characters of its Y-specific single nucleotide substitutions.

METHODS

The locus was analyzed by PCR and PAGE in silver-staining. The Y-specific STR was amplified with newly designed primers according to the Y-specific single nucleotide substitutions.

RESULTS

Six alleles were detected in Han population in Wuhan. Exact tests demonstrated that genotype frequencies did not deviate from Hardy-Weinberg equilibrium. Heterozygosity of DXYS267 was 0.6706, discrimination power (DP) was 0.8433, and the probability of paternity exclusion (PE) was 0.5957. The Y-specific STR of DXYS267 was successfully amplified with the new primer. The 4 alleles for Y-STR were detected with haplotype diversity (HD) 0.6372.

CONCLUSION

The DXYS267 locus is appropriate for individual identification and paternity testing. The new primer is useful for individual and paternity testing involving brothers and mixed stains.

[Application of the age-associated injure in mitochondrial DNA]

Nowadays, the injury in human mitochondrial DNA (mtDNA) is well known to accumulate in various tissues with age. It's significant to further investigate and then apply it to estimation of the age at parenchymas.