Binding and activation of AhR lead to cardiovascular aging

Shiheng Gui

Ruifang Fan

This AOP aims to elucidate the key biological pathways through which polycyclic aromatic hydrocarbons (PAHs) activate the aryl hydrocarbon receptor (AhR) and promote cardiovascular aging. AhR is a ligand-dependent transcription factor that plays a central role in regulating the expression of xenobiotic metabolism and detoxification-related enzymes (such as the CYP family); simultaneously, AhR is expressed in various tissue types including vascular endothelium, and its activation is closely associated with endothelial dysfunction, inflammatory responses, and vascular remodeling processes. As exogenous pollutants, PAHs may cause multi-system damage after entering the organism. In this AOP, the binding and activation of PAHs to AhR is defined as the Molecular Initiating Event (MIE). Subsequently, AhR signaling can directly or indirectly inhibit the expression or activity of SIRT1/SIRT6, serving as Key Event 1 (KE1), and induce DNA damage responses, further leading to upregulation of p16 and p21, accompanied by aging-related changes including enhanced systemic inflammation and oxidative stress, telomere attrition, and mitochondrial dysfunction. The persistent cellular damage described above ultimately drives structural and functional remodeling of the myocardium and vasculature, manifested as increased vascular calcium deposition, elevated blood pressure, and consequently the formation of cardiovascular aging as the Adverse Outcome (AO). We have identified multiple key events in this pathway and delineated the logical relationships between key events; based on this, we have constructed this AOP to describe the molecular mechanisms by which AhR binding and activation lead to cardiovascular aging.

Polycyclic aromatic hydrocarbons (PAHs) refer to hydrocarbon compounds containing two or more benzene rings in their molecular structure, primarily originating from incomplete combustion of organic matter(Zhang, 2017) . PAHs are widely distributed in environmental water, air, soil, and food. Dietary intake, respiration, and dermal contact are the main routes of PAH exposure, characterized by persistence, passivity, and inevitability, increasing cancer risk and causing high incidence of cardiovascular diseases. Numerous population epidemiological studies have shown that PAHs exposure are closely associated with the development of cardiovascular diseases such as hypertension, atherosclerosis, and ischemic heart disease(Curfs et al., 2004; Xu et al., 2021) . Given their widespread environmental distribution and potential toxicity, the United States Environmental Protection Agency (EPA) has listed 16 of them as priority controlled toxic organic pollutants. Therefore, it is necessary to assess the health risks of PAHs based on the AOP (Adverse Outcome Pathway) framework.

As the DNA damage effects of PAHs are widely recognized, previous research has primarily focused on the carcinogenic, teratogenic, and mutagenic effects induced by PAH-mediated DNA damage. However, DNA damage is also an important driving factor in accelerating cellular senescence, and cellular senescence is an important pathway for suppressing cellular malignant transformation; therefore, this Adverse Outcome Pathway (AOP) focuses on the association between PAH exposure and cardiovascular aging. However, current in vivo and in vitro evidence investigating PAH exposure-induced cardiovascular toxic effects remains relatively limited. Moreover, existing in vivo or in vitro studies typically focus on single or a few PAHs, and the exposure doses set are high, making it difficult to reflect the adverse effects of mixed PAHs at environmental doses on the cardiovascular system in the general population. Therefore, low-dose mixed animal exposure, cell experiments, and computer simulation studies are needed to investigate the adverse effects of mixed exposure to 16 priority-controlled PAHs on the cardiovascular system from the perspective of aging.

This AOP takes AhR activation as the initiating event; PAHs can directly activate AhR(Das et al., 2016), then directly or indirectly inhibit the expression of SIRT1/SIRT6 in the cardiovascular system, and induce DNA damage responses, further leading to upregulation of p16 and p21, accompanied by aging-related changes including enhanced systemic inflammation and oxidative stress, telomere attrition, and mitochondrial dysfunction (Bin et al., 2010; Malik and Czajka, 2013) . Experimental results can be obtained from various models, including experimental animals, mice, and cell lines. Among these, in vivo animal experiments, in vitro experiments, and computer simulation evidence can confirm the associations between the Molecular Initiating Event (MIE) and Key Event Relationships (KERs).

[1]   Bin, P., Leng, S., Cheng, J., Pan, Z.-f., Duan, H., Dai, Y., Li, H.-s., Niu, Y., Liu, Q.-j., Liu, Q.-j., Zheng, Y.-x., 2010. [Association between telomere length and occupational polycyclic aromatic hydrocarbons exposure]. Zhonghua yu fang yi xue za zhi [Chinese journal of preventive medicine] 44 6, 535-538

[2]   Curfs, D.M., Lutgens, E., Gijbels, M.J., Kockx, M.M., Daemen, M.J., van Schooten, F.J., 2004. Chronic exposure to the carcinogenic compound benzo[a]pyrene induces larger and phenotypically different atherosclerotic plaques in ApoE-knockout mice. Am J Pathol 164, 101-108.10.1016/s0002-9440(10)63101-x

[3]   Das, D., Panda, P., Naik, P.P., Mukhopadhyay, S., Sinha, N., Bhutia, S., 2016. Phytotherapeutic approach: a new hope for polycyclic aromatic hydrocarbons induced cellular disorders, autophagic and apoptotic cell death. Toxicology Mechanisms and Methods 27, 1-54.10.1080/15376516.2016.1268228

[4]   Deng, C., Pu, J., Deng, Y., Xie, L., Yu, L., Liu, L., Guo, X., Sandin, S., Liu, H., Dai, L., 2022. Association between maternal smoke exposure and congenital heart defects from a case-control study in China. Sci Rep 12, 14973.10.1038/s41598-022-18909-y

[5]   Gan, T.E., Xiao, S.P., Jiang, Y., Hu, H., Wu, Y.H., Duerksen-Hughes, P.J., Sheng, J.Z., Yang, J., 2012. Effects of Benzo(a)pyrene on the Contractile Function of the Thoracic Aorta of Sprague-dawley Rats. Biomedical and Environmental Sciences 25, 549-556.https://doi.org/10.3967/0895-3988.2012.05.008

[6]   He, J., Pang, Q., Huang, C., Xie, J., Hu, J., Wang, L., Wang, C., Meng, L., Fan, R., 2022. Environmental dose of 16 priority-controlled PAHs mixture induce damages of vascular endothelial cells involved in oxidative stress and inflammation. Toxicology in Vitro 79, 105296.https://doi.org/10.1016/j.tiv.2021.105296

[7]   He, X.N., Xin, J.Y., Zhan, J.L., Wu, F.K., Hou, J., Sun, Z., Wang, J., Zhang, X.L., Bai, Y.C., 2021. Polycyclic aromatic hydrocarbons induce endothelial injury through miR‐155 to promote atherosclerosis. Environmental and Molecular Mutagenesis 62, 409-421.10.1002/em.22454

[8]   Lee, T.W., Kim, D.H., Ryu, J.Y., 2020. Association between urinary polycyclic aromatic hydrocarbons and hypertension in the Korean population: data from the Second Korean National Environmental Health Survey (2012-2014). Sci Rep 10, 17142.10.1038/s41598-020-74353-w

[9]   Li, C.-H., Lee, C.-C., Juang, H.-A., Kang, J.-J., 2004. Activation and up-regulation of nitric oxide synthase in human umbilical vein endothelial cells by polycyclic aromatic hydrocarbons. Toxicology letters 151, 367-374.10.1016/j.toxlet.2004.03.003

[10] Li, X., Feng, Y., Deng, H., Zhang, W., Kuang, D., Deng, Q., Dai, X., Lin, D., Huang, S., Xin, L., He, Y., Huang, K., He, M., Guo, H., Zhang, X., Wu, T., 2012. The dose-response decrease in heart rate variability: any association with the metabolites of polycyclic aromatic hydrocarbons in coke oven workers? PLoS One 7, e44562.10.1371/journal.pone.0044562

[11] Malik, A.N., Czajka, A., 2013. Is mitochondrial DNA content a potential biomarker of mitochondrial dysfunction? Mitochondrion 13, 481-492

[12] Xu, C., Liu, Q., Liang, J., Weng, Z., Xu, J., Jiang, Z., Gu, A., 2021. Urinary biomarkers of polycyclic aromatic hydrocarbons and their associations with liver function in adolescents. Environmental Pollution 278, 116842.https://doi.org/10.1016/j.envpol.2021.116842

[13] Yin, W., Hou, J., Xu, T., Cheng, J., Li, P., Wang, L., Zhang, Y., Wang, X., Hu, C., Huang, C., Yu, Z., Yuan, J., 2017. Obesity mediated the association of exposure to polycyclic aromatic hydrocarbon with risk of cardiovascular events. The Science of the total environment 616-617.10.1016/j.scitotenv.2017.10.238

[14] Zhang, S., Ou, K., Huang, J., Fang, L., Wang, C., 2021. In utero exposure to mixed PAHs causes heart mass reduction in adult male mice. Ecotoxicology and environmental safety 225, 112804.10.1016/j.ecoenv.2021.112804

[15] Zhang, Z., 2017. A review of polycyclic aromatic hydrocarbons (PAHs) research progress in China based on CNKI database. AIP Conference Proceedings 1820.10.1063/1.4977385