The canonical Wnt signaling pathway, in which ␤-catenin nuclear localization is a crucial step, plays an important role in osteoblast differentiation. Pin1, a prolyl isomerase, is also known as a key enzyme in osteogenesis. However, the role of Pin1 in canonical Wnt signal-induced osteoblast differentiation is poorly understood. We found that Pin1 deficiency caused osteopenia and reduction of ␤-catenin in bone lining cells. Similarly, Pin1 knockdown or treatment with Pin1 inhibitors strongly decreased the nuclear ␤-catenin level, TOP flash activity, and expression of bone marker genes induced by canonical Wnt activation and vice versa in Pin1 overexpression. Pin1 interacts directly with and isomerizes ␤-catenin in the nucleus. The isomerized ␤-catenin could not bind to nuclear adenomatous polyposis coli, which drives ␤-catenin out of the nucleus for proteasomal degradation, which consequently increases the retention of ␤-catenin in the nucleus and might explain the decrease of ␤-catenin ubiquitination. These results indicate that Pin1 could be a critical target to modulate ␤-catenin-mediated osteogenesis.

By using multiple satellite measurements, the changes of the aerosol optical depth (AOD) and nitrogen dioxide (NO2) over South Korea were investigated from January to March 2020 to evaluate the COVID-19 effect on the regional air quality. The NO2 decrease in South Korea was found but not significant, which indicates the effects of spontaneous social distancing under the maintenance of ordinary life. The AODs in 2020 were normally high in January, but they became lower starting from February. Since the atmosphere over Eastern Asia was unusually stagnant in January and February 2020, the AOD decrease in February 2020 clearly reveals the positive effect of the COVID-19. Considering the insignificant NO2 decrease in South Korea and the relatively long lifetime of aerosols, the AOD decrease in South Korea may be more attributed to the improvement of the air quality in neighboring countries. In March, regional atmosphere became well mixed and ventilated over South Korea, contributing to large enhancement of air quality. While the social activity was reduced after the COVID-19 outbreak, the regional meteorology should be also examined significantly to avoid the biased evaluation of the social impact on the change of the regional air quality.

This study investigated the various temporal (weekly, monthly, and inter-annual) variability of air pollutants (PM10, SO2, NO2, O3, CO) in seven megacities in South Korea (Seoul, Busan, Incheon, Daegu, Gwangju, Daejeon, and Ulsan). We found that the general decreasing trend of PM10, SO2, NO2, and CO. An exceptional pollutant is O3, showing a clear increasing trend consistently in all seven megacities. Seasonally PM10, SO2, NO2, and CO have the highest level in winter due to the large fossil-fuel combustion for the heating demand, but O3 shows the maximum peak in summer related to the intensified photochemistry. Based on the analysis for percentile values of air pollutants, we recognized that some patterns of air pollutants in Korean megacities are overlooked: O3 increase is not perfectly related to the NO2 pattern, somewhat high SO2 in the coastal cities, ambiguous weekly pattern on Monday (as a weekday) and Sunday (as a weekend). Through this comprehensive analysis of multiple air pollutants using the percentile values, the characteristic for various temporal change of air pollutants in Korean megacities can be better understood, and some useful ideas for the air quality control in the urban region can be also excavated.

No abstract