RESUMO
Based on panel data from 210 prefecture-level cities in China from 2003 to 2021, this study employs the Time-Varying Differences-in-Differences (Time-Varying DID) approach to systematically examine the impact of smart city construction on pollution emissions and its underlying mechanisms. Additionally, the Propensity Score Matching-Differences-in-Differences method is employed for further validation. The research findings indicate that Smart City Construction (SCC) significantly reduces urban Volume of Sewage Discharge (VSD), sulfur dioxide emissions (SO2), and Emissions of Fumes and Dust (EFD), thereby mitigating pollution emissions (PE) and enhancing environmental quality. Mechanism analysis reveals that SCC achieves these effects through scale effects, structural effects, and technological effects. City heterogeneity analysis shows that provincial capital cities exhibit a stronger suppression effect on pollution emissions compared to non-provincial capital cities. Moreover, cities with lower levels of education attainment demonstrate a stronger ability to curb pollution emissions, while larger cities exhibit a more pronounced impact on mitigating pollution emissions. The marginal contributions of this study mainly consist of three aspects: Firstly, it enriches the literature on environmental impact factors by assessing, for the first time, the influence of SCC on PE. Secondly, a comprehensive approach is employed, integrating VSD, EFD, SO2 data, and economic and pollution data at the city level. Time-Varying DID is used to evaluate the policy effects of SCC. Finally, the study analyzes the impact mechanisms of SCC policy on environmental emissions from various perspectives.
RESUMO
OBJECTIVE: To study the effects of different calcium ion concentrations on epithelial mesenchymal transformation (EMT) of human peritoneal mesothelial cell (HPMC) via endoplasmic reticulum stress (ERS). METHODS: HPMC cell line HMrSV5 was cultured in vitro and treated in groups. The cells in the control group, high calcium group 1, and high calcium group 2 were treated with medium containing calcium ion concentrations of 1.25, 1.75, and 2.25 mmol/L, respectively. The solvent control group was treated with medium containing 1.25 mmol/L physiological calcium ion concentration and 0.1% dimethyl sulfoxide (DMSO), the high calcium+solvent group was treated with medium containing 2.25 mmol/L calcium ion concentration and 0.1% DMSO, the high calcium+4-phenylbutyric acid (4-PBA) group was treated with medium containing 2.25 mmol/L calcium ion concentration and 1 mmol/L ERS inhibitor 4-PBA, and each group was treated for 48 hours. Morphological changes of cells in each group were observed under light microscope. The expressions of epithelial cell phenotype marker zonula occluden-1 (ZO-1) and mesenchymal cell phenotype marker α-smooth muscle actin (α-SMA) in the cells were observed by immunofluorescence staining. The expressions of EMT marker genes E-cadherin, ZO-1, α-SMA and Vimentin were detected by fluorescence quantitative polymerase chain reaction (PCR). The expressions of ERS marker proteins phosphorylated protein kinase R-like endoplasmic reticulum kinase (p-PERK), phosphorylated eukaryotic initiation factor 2α (p-eIF2α), transcription activating factor 4 (ATF4) and C/EBP homologous protein (CHOP) were detected by Western blotting. RESULTS: Compared with the control group, the morphology of HMrSV5 cells became slender and fibrotic, the fluorescence intensity of ZO-1 increased, and the fluorescence intensity of α-SMA decreased in high calcium 1 and high calcium 2 groups, indicating that the cells transformed from epithelial cells to mesenchyme cells. The mRNA expressions of E-cadherin and ZO-1 were significantly decreased, while the mRNA expressions of α-SMA and Vimentin and the protein expressions of p-PERK, p-eIF2α, ATF4 and CHOP were significantly increased, moreover, the expressions of the above marker genes or proteins in the high calcium 2 group was more obvious than those in the high calcium 1 group [E-cadherin mRNA (2-ΔΔCt): 0.53±0.05 vs. 0.75±0.09, ZO-1 mRNA (2-ΔΔCt): 0.42±0.06 vs. 0.69±0.06, α-SMA mRNA (2-ΔΔCt): 1.81±0.16 vs. 1.32±0.14, Vimentin mRNA (2-ΔΔCt): 2.05±0.22 vs. 1.48±0.16, p-PERK protein (p-PERK/ß-actin): 0.81±0.09 vs. 0.59±0.06, p-eIF2α protein (p-eIF2α/ß-actin): 0.87±0.10 vs. 0.50±0.06, ATF4 protein (ATF4/ß-actin): 0.93±0.10 vs. 0.72±0.06, CHOP protein (CHOP/ß-actin): 0.79±0.09 vs. 0.46±0.04, all P < 0.05]. Compared with the solvent control group, the morphological changes of cells, the expressions of EMT marker genes and ERS marker proteins after high calcium ion concentration of 2.25 mmol/L were consistent with those in the high calcium 2 group than control group. Compared with the high calcium+solvent group, the cell morphology recovered the characteristics of polygonal and pebble-like epithelial cells in the high calcium+4-PBA group, the fluorescence intensity of ZO-1 increased, the fluorescence intensity of α-SMA decreased, and the mRNA expressions of E-cadherin and ZO-1 in the cells were significantly increased [E-cadherin mRNA (2-ΔΔCt): 0.86±0.09 vs. 0.57±0.04, ZO-1 mRNA (2-ΔΔCt): 0.81±0.06 vs. 0.48±0.05, both P < 0.05], the mRNA expressions of α-SMA and Vimentin and the protein expressions of p-PERK, p-eIF2α, ATF4 and CHOP were significantly decreased [α-SMA mRNA (2-ΔΔCt): 1.21±0.13 vs. 1.77±0.15, Vimentin mRNA (2-ΔΔCt): 1.30±0.14 vs. 1.94±0.20, p-PERK protein (p-PERK/ß-actin): 0.38±0.04 vs. 0.92±0.11, p-eIF2α protein (p-eIF2α/ß-actin): 0.34±0.05 vs. 1.05±0.13, ATF4 protein (ATF4/ß-actin): 0.57±0.06 vs. 0.97±0.11, CHOP protein (CHOP/ß-actin): 0.51±0.04 vs. 0.90±0.12, all P < 0.05]. CONCLUSIONS: High calcium ion concentrations of 1.75 mmol/L and 2.25 mmol/L promote EMT of HPMC via activating ERS.
