Induction Of Inflammatory Responses In Human Bronchial Epithelial Cells By Pb²⁺-Containing Model PM_2.5 Particles Via Downregulation Of A Long Nod-Coding RNA Lnc-PCK1-2:1

Fine particulate matter with aerodynamic diameters less than 2.5 ?m(PM2.5)are extremely hazardous to human health,especially ultrafine particles less than 100 nm in diameter small enough to penetrate human lungs and pass through air-blood barriers to organs.Long-term exposures to PM2.5 are linked to acute lower respiratory infections,chronic obstructive pulmonary disease,stroke,ischemic heart attack and lung cancer.In 2013,the International Agency for Research on Cancer(IARC)classified air-borne particulate matter as a carcinogen.In 2016,air pollution was responsible for 7.5%of global deaths,in which China and India together account for nearly half of it.Toxicological studies have shown that PM2.5 particles induce cytotoxicity,immunotoxicity,oxidative stress and DNA damages in human cells.Inflammation is a crucial trigger for most PM2.5-induced diseases.However,although there are many studies on the toxic effects of PM2.5,due to the complexity of PM2.5 composition and its region-and time-dependence,very little is known about how different components contribute to PM2.s-induced overall inflammatory responses.Inflammation induction is orchestrated by sophisticated cell signaling networks involving various biomolecules such as proteins,DNA and RNA molecules.However,the involvement of non-coding RN As in PM2.5-induced inflammation is not well known.Noncoding RNAs are non-protein-coding transcripts.About 75-90%mammalian genomes are transcribed as noncoding RNAs.There is growing evidence that long noncoding RNAs(lncRNAs),which have more than 200 nucleotides in length,contribute to the regulation of gene expression in immune cells(such as macrophages,DCs,and epithelial cells).It is reported that lncRNA-Cox2 interacts with other proteins to alter the expression of NF-?B related genes.A IncRNA THRIL interacts with hnRNPL(heterogenous nuclear ribonucleoprotein L)and regulates the expression of tumor necrosis factor alpha(TNF-?)following the activation of toll-like receptor 2 in human monocytes.Our previous work has found that PM2.5 upregulated lncRNA LINC00341 in 16HBE cells and induced cell cycle arrest.However,PM2.5-induced non-coding RNAs involved in the regulation of inflammation and related epigenetic changes that regulate inflammation are not understood.Human bronchial epithelial(16HBE)cells participate in the initial interactions with inhaled PM2.5 particles and,therefore,induce early inflammatory responses.In this investigation,we use 16HBE as a cell model.By taking a reductionism approach we synthesized a carbon nanoparticle-based model PM2.5 library of 20 members with controlled loadings of pollutants either individually or in combination at environment relevant concentrations.We discovered that only carbon nanoparticle-Pb2+adducts,rather than free Pb2+,blank carbon nanoparticles or other pollutants/carbon adducts,induced inflammation in human bronchial cells by suppressing the expression of a novel long non-coding RNA lnc-PCK1-2:1.We also found that lnc-PCK1-2:1 routinely plays a regulatory role in inhibiting inflammation.This finding was further substantiated by varying Pb2+loadings on carbon nanoparticles and overexpressing lncPCK1-2:1.The success of this project opens an avenue for further elucidation of molecular mechanisms of PM2.5-induced inflammation and toxicity and understanding the role of non-coding RNAs in regulating cell function.