A Study Of DEHP Exacerbates Allergic Asthma By Affecting Macrophage Polarization

Background: Allergic asthma is still a major global problem in public health and medicine.House dust mite(HDM)is one of the most common allergen sources associated with allergic airway diseases in most parts of the world.In the past two decades,environmental pollution caused by industrialization and urbanization has intensified.Polycyclic aromatic hydrocarbons(PAHs)and phthalates(PAEs)in environmental pollutants may cause high incidence of asthma and other allergic diseases.However,the causal relationship between environmental pollutants and the onset of asthma has not yet been established,and its mechanism of action remains obscure.Dioctyl phthalate(DEHP),one of the most common phthalates,is widely available worldwide.DEHP is often used as a plasticizer in polyvinyl chloride(PVC).Because it does not chemically combine with PVC,it often leaks and migrates to indoor air,atmosphere,and drinking water.DEHP used in food packaging is also present in different foods.Oral exposure is the main route of human exposure to phthalates in the living environment.Inhalation exposure and skin exposure are the main modes of occupational exposure to human phthalates.DEHP is easily metabolized into monoethylhexyl phthalate(MEHP)in the body and exerts a toxic effect.Epidemiological studies have shown a significant positive correlation between DEHP exposure and allergic asthma,especially in children with allergic asthma.Allergic asthma is not only characterized by an imbalance of Th1/Th2 immune response,but also by imbalances of various immune cells including macrophages.Although the function of M2-type macrophages is not fully understood,these cells are believed to promote a Th2 immune response.Studies have reported that the number of M2 macrophages in asthma patients is related to the severity of asthma symptoms and promotes the Th2 inflammatory response in allergic asthma.Objective: A mouse model was used to simulate long-term low-dose human exposure to DEHP,and to investigate whether DEHP affects M2 polarization of lung macrophages through the PPARγ signaling pathway and aggravates Th2 allergic response.The mechanism of MEHP’s effect on macrophages was explored.Methods:(1)A DEHP-exposed murine model of allergic asthma was established,and asthma-related indicators were detected,such as mouse airway hyperresponsiveness,cytokines and cell composition of alveolar lavage fluid,serum HDM-specific Ig E,lung tissue sections,Tregs of spleen cells and oxidative stress in lung tissues.(2)A mouse allergic asthma model was established,and the number and proportion of M2 macrophages in the lungs of mice was calculated.Some indicators were detected,such as the lung tissue transcription factor of PPARγ and Arg1 expression levels.(3)Cell experiments were used to observe the effects of MEHP on bone marrow-derived macrophages(BMDMs)M1/M2 polarization.(4)PPARγ gene expression was inhibited to investigate whether Arg1 expression was dependent by PPARγ.(5)Chromatin Immunoprecipitation(CHIP)test was performed to validate the binding of PPARγ to Arg1,Fizz1,and Ym1 promoter.(6)MEHP stimulated M2 macrophages were co-cultured with CD4~+T cells to investigate the polarization of T cells.Results:(1)DEHP exposure significantly aggravated allergic asthma in mice sensitized by HDM,including exacerbated airway hyperresponsiveness and lung tissue damage,elevated serum Ig E levels,increased eosinophils in alveolar lavage fluid,and augmented IL4,IL5,IL13 inflammatory factor levels;(2)DEHP exposure led to an increase in the proportion and number of M2 macrophages in the lungs of mice,and elevated PPARγ and Arg1 in lung tissue;(3)MEHP promoted BMDMs to polarize to M2 type Macrophages and was dependent on PPARγ activation;(4)MEHP could up-regulate the expression of the transcription factor PPARγ,and PPARγ bound to the Arg1,Fizz1,and Ym1 gene promoters to increase the corresponding gene expression to promote macrophage M2 polarization;(4)MEHP stimulated M2 macrophages.CD4~+T cells co-cultured with M2 macrophages were polarized toward a CD4~+IL4+cells phenotype,suggesting MEHP promoted macrophages M2 polarization and up-regulated the proportion of Th2 cells to aggravate allergic asthma.