Elsevier

Journal of Environmental Sciences

Volume 85, November 2019, Pages 138-146
Journal of Environmental Sciences

LncRNA PU.1 AS regulates arsenic-induced lipid metabolism through EZH2/Sirt6/SREBP-1c pathway

https://doi.org/10.1016/j.jes.2019.05.019Get rights and content

Abstract

Arsenic (As) is an omnipresent metalloid toxicant, which has elicited serious environmental pollution and health risky problems. Previous studies have uncovered that the As exposure could also cause markedly reduction of serum triglycerides in mice. However, the regulation mechanisms are still largely unknown. The present study is aimed to elucidate the molecular mechanisms of lncRNAs in As-induced lipid metabolic disequilibrium. We demonstrated that lncRNA PU.1 AS was significantly induced in the liver of As-feed mice companied with lower serum triglycerides contents; further in vitro experiment confirmed that PU.1 AS regulated liver cells lipid accumulation by nile red fluorescence staining. Intensive mechanistic investigations illustrated that PU.1 AS could interact with EZH2 protein to regulate its downstream target gene expression, and As-induced PU.1 AS attenuated EZH2-supppressed Sirt6 expression, thereafter leading to a decreased SREBP-1c protein expression, as well as the diminished synthesis of triglycerides in hepatocytes. In conclusion, this study provided a new lncRNA-related regulatory signaling pathway participating in As-induced abnormal lipid metabolism.

Introduction

Arsenic (As) is a metalloid element with various chemical forms, which is widely distributed in the environment and causing chronic or acute human health problems (Alamolhodaei et al., 2015, IARC Working Group on the Evaluation of Carcinogenic Risks to Humans, 2004, Rodriguezlado et al., 2013). Therefore, As was defined as one of human carcinogens by the International Cancer Research Center (ICRC). Over and above the carcinogenic effect, As exposure has been verified to induce multiple toxic effects and complications, including neurovirulence, dermal toxicity and nephrotoxicity (Abdul et al., 2015). Several researches have indicated that As exposure may influence lipid metabolism (Ameer et al., 2015, Paul et al., 2011). Such as the chronic exposure of low-dose As could alter lipogenic genes expression, and further disturb serum triglycerides (TG) levels (Adebayo et al., 2015). The lipid metabolism disorders caused by As exposure would contribute to the occurrence of cardiovascular diseases (Song et al., 2017). It is known that some renowned regulatory molecules play multiunit roles in the As-associated adverse biological effects, such as the sterol regulatory element binding proteins (SREBP) (Adebayo et al., 2015, Cheng et al., 2016). However, the underlying molecular mechanisms are not fully understood, whether there are other more molecules involved in the regulation still need intensive study.

Long non-coding RNAs (lncRNAs) are non-protein coding RNAs longer than 200 nucleotides (Dempsey and Cui, 2017). It is well documented that lncRNAs play multiform roles in the regulation of fundamental biological processes, such as the cell proliferation, cell differentiation, cell metabolism, carcinogenesis and so on (Batista and Chang, 2013, Schmitz et al., 2016). Recent years, more and more evidences have showed that lncRNAs are also widely involved in the regulation of lipid metabolism. For example, lncRNA HULC could increase cholesterol and TG levels through activating the master regulator of adipogenesis in hepatocellular carcinoma (Cui et al., 2015). The antisense lncRNA AdipoQ AS was identified to restrain adipogenesis by inhibiting the translation of adiponectin (Cai et al., 2018). In addition, lncRNAs are also participated in the environmental pollutions-induced toxicological responses and various human disorders (Geisler and Coller, 2013, Karlsson and Baccarelli, 2016). For instance, lncRNA LINC00341 played a key role in the PM2.5-induced G2/M phase cell cycle arrest (Xu et al., 2017). And lncRNA MALAT1 was authenticated to work in the As-induced liver carcinogenesis and malignant transformation through reciprocal regulation with HIF-2α (Luo et al., 2016). Our previous data uncovered that lncRNA UCA1 antagonized As-induced autophagy-dependent cell death (Gao et al., 2018). Nevertheless, whether lncRNAs also engage in As-induced lipid metabolism dysregulation are still unknown.

LncRNA PU.1 AS is the antisense of transcription factor PU.1, which is one member of the ETS (E-twenty six) family and plays a pivotal role in hematopoiesis via regulating numerous genes within the lymphocytes and myeloid progenitor populations (Carotta et al., 2010, Ebralidze et al., 2008). Recently, PU.1 AS was reported to facilitate adipogenesis through inhibiting the translation of PU.1 in preadipocytes (Pang et al., 2013, Wei et al., 2014). But in this article, our results showed that PU.1 AS levels were significantly increased in the liver of chronic As-feed mice which exhibiting decreased serum TG contents, further mechanism analyses revealed that PU.1 AS contributed to the lipid homeostasis through inhibiting the suppression role of its partner Enhancer of Zeste Homolog 2 (EZH2) in sirtuin 6 (Sirt6) mRNA and protein expression, which subsequently leading to the decreased expression of SREBP-1c and lipid accumulation. The present study would open a new insight to understand the regulation of lncRNAs in systemic lipid homeostasis when under As threaten.

Section snippets

Animal experiments

Six-week-old C57BL/6 male mice were obtained from Beijing Vital River Laboratory Animal Technology (Beijing, China). Mice were randomly grouped into the control group and As-treated group, and exposed to 0 or 50 mg/L sodium arsenite in drinking water for 5 weeks, a period in full compliance with chronic exposure. Water was freshly replenished every 3–4 days to minimize the oxidation of sodium arsenite. At the end of the exposure period, control and As-treated mice were sacrificed after

Chronic exposure to low-dose As reduces serum TG levels in mice

Detection of serum samples showed the TG concentrations were decreased significantly in As-treated mice compared with control group (p < 0.05) (Fig. 1a). As exposure had no significant effect on the levels of T-CHO, LDL-C and HDL-C (Fig. 1b, c, d). The weight measurements of body, liver and fat around epididymides did not show significant effects of As treatment (Fig. S1). As exposure did not cause significant liver toxicity, as no changes were observed in the CRP levels, AST levels and ALT

Discussion and conclusion

As is an omnipresent environmental toxicant and poses enormous threatens to human health (Jomova et al., 2011, Vahter, 2008). Till now, extensive studies have demonstrated that lipid metabolic disorders are the adverse biological effects in response to long-term As exposure (Afolabi et al., 2015, Kozulhorvath et al., 2012). Whereas, the potential molecular mechanisms of As-induced imbalance within lipid metabolism remain elusive. In the As exposure experiment, we observed that the serum TG

Acknowledgments

This work was supported by the Strategic Priority Research Program of the Chinese Academy of Sciences (No. XDB14000000), the National Natural Science Foundation of China (Nos. 21507154, 21425731, 21637004 and 81570542). We thank the laboratory members for reagents and assistance with experiments.

References (45)

  • P. Halley et al.

    Regulation of the Apolipoprotein gene cluster by a long noncoding RNA

    Cell Rep.

    (2014)
  • P. Li et al.

    A liver-enriched long non-coding RNA, lncLSTR, regulates systemic lipid metabolism in mice

    Cell Metab.

    (2015)
  • H. Shimano et al.

    Sterol regulatory element-binding protein-1 as a key transcription factor for nutritional induction of lipogenic enzyme genes

    J. Biol. Chem.

    (1999)
  • R. Tao et al.

    Hepatic SREBP-2 and cholesterol biosynthesis are regulated by FoxO3 and Sirt6

    J. Lipid Res.

    (2013)
  • N. Wei et al.

    Knockdown of PU.1 mRNA and AS lncRNA regulates expression of immune-related genes in zebrafish Danio rerio

    Dev. Comp. Immunol.

    (2014)
  • Y. Xu et al.

    LncRNA LINC00341 mediates PM2.5-induced cell cycle arrest in human bronchial epithelial cells

    Toxicol. Lett.

    (2017)
  • X.Y. Zhao et al.

    A long noncoding RNA transcriptional regulatory circuit drives thermogenic adipocyte differentiation

    Mol. Cell

    (2014)
  • K.S.M. Abdul et al.

    Arsenic and human health effects: a review

    Environ. Toxicol. Pharmacol.

    (2015)
  • L.N. Abhyankar et al.

    Arsenic exposure and hypertension: a systematic review

    Environ. Health Perspect.

    (2011)
  • A.O. Adebayo et al.

    Chronic exposure to low-dose arsenic modulates lipogenic gene expression in mice

    J. Biochem. Mol. Toxicol.

    (2015)
  • O.K. Afolabi et al.

    Arsenic-induced dyslipidemia in male albino rats: comparison between trivalent and pentavalent inorganic arsenic in drinking water

    BMC Clin. Pharmacol.

    (2015)
  • M.T.M. Auley et al.

    Lipid metabolism and hormonal interactions: impact on cardiovascular disease and healthy aging

    Expert Rev. Endocrinol. Metab.

    (2014)
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