Fine Particulate Matter Promoted Myocardial Hypoxia Injury Via The Regulation Of Oxygen Sensor Mediated-Anaerobic Energy Metabolism

Objective:Particulate matter（PM）,as an important component of air pollution,is one of the independent risk factors of cardiovascular disease.Ischemic heart disease（IHD）is the second most serious cardiovascular disease in our country.Numerous epidemiological studies have indicated that PM exposure is closely related to the increased incidence and mortality of IHD.However,little is known about the specific mechanism by which PM induces IHD.Myocardial energy metabolism regulated by oxygen sensors plays a pivotal role in the progression of IHD.Our previous studies have found that PM exposure leads to energy metabolism disorder of myocardial cells.But whether PM affects the energy metabolism regulated by oxygen sensors and its mode of action remains unclear.This study focuses on oxygen sensor mediating myocardial anaerobic energy metabolism to elucidate the toxic mechanism of PM-induced myocardial ischemia-hypoxic injury.Methods:Based on the mice exposed to real ambient PM for four months,H&E,TUNEL,and immunohistochemical staining were adopted to analyze the changes in myocardial histopathological structure,injury,and hypoxia.Meanwhile,the hypoxia-ischemia cellular model was established and the protein expressions of hypoxia inducible factor-1alpha（HIF-1α）,bax,and cleaved-caspase3 were analyzed to clarify the influence of PM_2.5on myocardial cellular hypoxia and injury.In order to clarify the effect of PM_2.5 on myocardial cellular energy metabolism（i.e.,fatty acidβ-oxidation,tricarboxylic acid cycle,and glycolysis）at the basic hypoxia-ischemia condition,the related product content,enzymatic activity,and regulatory gene expression were determined by kit and q RT-PCR.Subsequently,the pivotal role of HIF-1αin the PM_2.5 induced myocardial cellular energy metabolism changes and hypoxia injury was investigated by the co-exposure of inhibitor of HIF-1α（YC-1）and PM_2.5.Finally,the database analysis was used and the regulation of oxygen sensors（i.e.,PHD2 and FIH1）on HIF-1αwere analyzed by the Western Blot,co-immunoprecipitation,and immunofluorescence to comprehensively elucidate the mechanism of PM_2.5regulating HIF-1α.Results:The four months exposure of mice in the real ambient PM exposure system could induce hypertrophy of myocardial right ventricular free wall,increase myocardial injury,myocardial apoptosis rate and expression of HIF-1α.Meanwhile,the non-cytotoxic dose of PM_2.5 exposure promoted the myocardial hypoxia and increased injury at the basic hypoxia-ischemia condition,indicating that PM could induce myocardial hypoxia and injury.Further analysis showed that PM_2.5 exposure promoted the remodeling of myocardial energy metabolism at the basic hypoxia-ischemia condition,such as increased glycolysis（up-regulated Glut1,LDHA,and PKM gene expression,and increased content of lactate and pyruvate）,down-regulation of fatty acidβ-oxidation（down-regulated CPT1 gene expression）and TCA cycle（down-regulated CS and OGDH gene expression,and decreased MDH enzyme activity）,and decreased total ATP content.Follow-up results of PM exposure in YC-1 pretreated cells showed inhibited remodeling of myocardial energy metabolism and further alleviated hypoxia and injury,which verified that the important role of upregulated HIF-1αin PM_2.5 exacerbated myocardial energy metabolism remodeling and hypoxia injury.The in-depth mechanism study using database analysis revealed that the protein ubiquitin degradation pathway was the main functional pathway of PM_2.5 exposure regulating HIF-1α,and PM_2.5down-regulated the expression of ubiquitin protein.Further analysis on the regulatory role of oxygen sensors（PHD2 and FIH1）revealed that PM_2.5reduced the binding of HIF-1αwith PHD2,protein level of OH-HIF-1αand ubiquitin protease levels,accounting for elevated HIF-1α.Simultaneously,PM_2.5 declined FIH1expression,thus promoting HIF-1αtranslocation to the nucleus and the transcriptional function.Conclusions:Focusing on the anaerobic energy metabolism mediated by oxygen sensors,our study found for the first time that PM can promote myocardial hypoxia and anaerobic energy metabolism by inhibiting the regulatory of oxygen sensors（i.e.,PHD2 and FIH1）on the stability and function of HIF-1α,which finally lead to the aggravated myocardial hypoxia injury.This study provided new perspectives and key data for the study of the mechanisms of cardiovascular injury due to particulate matter exposure.