Chronic Inhaled Benzene Exposure Exacerbates Atherosclerosis in LDL Receptor-Knockout Mice

Background. Benzene is a ubiquitous environmental pollutant generated by a variety of natural and anthropological sources. It is a known carcinogen and hematopoietic toxin; however, little is known about benzene's potential atherogenicity. Hypothesis. Inhaled benzene induces atherogenesis by increasing vascular inflammation in LDL receptor Knockout (LDLR-KO) mice. Methods. Male LDLR-KO mice were exposed to HEPA-filtered air or benzene (1 ppm, 6h/day, 5days/week) for 24 weeks. For the last 12 weeks of exposure, the mice were maintained on a western diet. The single nuclei RNA sequencing (snRNAseq) of aortae was performed at Novogene. For in vitro experiments, splenic naive T cells were exposed to 1 μM of hydroquinone (HQ) for 24 hours, and intracellular ROR-gamma levels were measured by flow cytometry. Results. Benzene inhalation increased the aortic valve lesion area by more than 25% (P<0.05) in LDLR-KO mice. Using snRNAseq, eleven major cell types were detected, including T cells and vascular smooth muscle cells (VSMC). Benzene increased the number of T cells by 2.5-fold, proliferating T-cells by 5.8-fold, and VSMC by 1.6-fold, suggesting increased cellularity and reduced plaque stability. In addition, benzene upregulated Th17 polarization marker Rorc and negative regulators of apoptosis Rag1 and Bcl11b while significantly attenuating the expression of proliferation inhibitor Ms4a4b in T cells. In VSMC, benzene downregulated extracellular matrix organization genes and upregulated platelet degranulation pathways. Polarization of T cells into Th17 was confirmed by HQ-dependent upregulation of ROR-gamma in vitro. Conclusion. Our data suggest that inhaled benzene exposure compromises plaque cellularity and stability by facilitating T-cell proliferation and polarization, which coincides with the degradation of smooth muscle extracellular matrix and platelet activation.