Neuroprotective effects of SMAds in a rat model of cerebral ischemia/reperfusion

Previous studies have shown that up-regulation of transforming growth factor β1 results in neuroprotective effects. However, the role of the transforming growth factor β1 downstream molecule, SMAD2/3, following ischemia/reperfusion remains unclear. Here, we investigated the neuroprotective effects of SMAD2/3 by analyzing the relationships between SMAD2/3 expression and cell apoptosis and inflammation in the brain of a rat model of cerebral ischemia/reperfusion. Levels of SMAD2/3 mRNA were up-regulated in the ischemic penumbra 6 hours after cerebral ischemia/reperfusion, reached a peak after 72 hours and were then decreased at 7 days. Phos- phorylated SMAD2/3 protein levels at the aforementioned time points were consistent with the mRNA levels. Over-expression of SMAD3 in the brains of the ischemia/reperfusion model rats via delivery of an adeno-associated virus containing the SMAD3 gene could reduce tumor ne- crosis factor-a and interleukin-lβ mRNA levels, down-regulate expression of the pro-apoptotic gene, capase-3, and up-regulate expression of the anti-apoptotic protein, Bcl-2. The SMAD3 protein level was negatively correlated with cell apoptosis. These findings indicate that SMAD3 exhibits neuroprotective effects on the brain after ischemia/reperfusion through anti-inflamma- tory and anti-apoptotic pathways.

Cortical neurogenesis in adult rats after ischemic brain injury: most new neurons fail to mature

The present study examines the hypothesis that endogenous neural progenitor cells isolated from the neocortex of ischemic brain can differentiate into neurons or glial cells and contribute to neural regeneration. We performed middle cerebral artery occlusion to establish a model of cerebral ischemia/reperfusion injury in adult rats. Immunohistochemical staining of the cortex 1, 3, 7, 14 or 28 days after injury revealed that neural progenitor cells double-positive for nestin and sox-2 appeared in the injured cortex 1 and 3 days post-injury, and were also positive for glial ifbrillary acidic protein. New neurons were labeled using bromodeoxyuridine and different stages of maturity were identiifed using doublecortin, microtubule-associated protein 2 and neuronal nuclei antigen immunohistochemistry. Immature new neurons coexpressing doublecortin and bromodeoxyuridine were observed in the cortex at 3 and 7 days post-injury, and semi-mature and mature new neurons double-positive for microtubule-associated protein 2 and bromode-oxyuridine were found at 14 days post-injury. A few mature new neurons coexpressing neuronal nuclei antigen and bromodeoxyuridine were observed in the injured cortex 28 days post-injury. Glial ifbrillary acidic protein/bromodeoxyuridine double-positive astrocytes were also found in the injured cortex. Our ifndings suggest that neural progenitor cells are present in the damaged cortex of adult rats with cerebral ischemic brain injury, and that they differentiate into astrocytes and immature neurons, but most neurons fail to reach the mature stage.

The reversal of surface air temperature anomalies in China between early and late winter 2021/2022:Observations and predictions

During winter of 2021/2022,the temperature in China is characterized by a warm-to-cold transition,and the average temperature anomaly in February 2022 is−1.6℃,the coldest February in 2013-2022.We revealed the circulation regimes and physical mechanisms associated with this reversal event and demonstrated the advantage of a regional model downscaling over the use of the global model alone in predicting.In early winter,the warm anomalies are mainly related to an anomalous anticyclonic system downstream of a PNA-like(Pacific-North America)Rossby-wave train induced by La Niña.In late winter,due to the circulation response to the central Pacific warming and negative tropical Indian Ocean Dipole(TIOD),two‘−+−’Rossby-wave trains from high latitudes and the tropical Indian Ocean jointly lead to an anomalous cyclonic system in China.Meanwhile,an anticyclonic blocking system on the northern side of Baikal brings strong and cold air to China.These two systems together cause a significant drop in surface air temperature anomaly in China during the late winter.The Beijing Climate Center climate system model(BCC_CSM1.1 m)can essentially predict this temperature reversal in China about five months in advance.However,the reversal amplitude is weaker due to warm deviations over the tropical Pacific Ocean and equatorial Indian Ocean.Using dynamic downscaling,a regional Climate-Weather Research and Forecasting(CWRF)model correctly predicts the cold SAT anomalies in late winter 2021/2022.The regional model depicts more realistic circulation patterns in East Asia;the anomalous cyclonic system in Inner Mongolia accompanied by the northerly anomalies contribute to a lower-than-normal SAT over China.This study reveals the cooperative effect of wave trains from high latitudes and the tropics on the subseasonal temperature reversal and demonstrates a possible solution to improve the forecast skill by dynamic downscaling according to precise characterization of local surface information.

Winter extreme precipitation over the Tibetan Plateau influenced by Arctic sea ice on interdecadal timescale

The Tibetan Plateau(TP)and the Arctic are the most sensitive regions to global climate change.However,the interdecadal varibility of winter extreme precipitation over the TP and its linkage with Arctic sea ice are still unclear.In this study,the characteristics and mechisnems of the TP extreme precipitation(TPEP)influenced by Arctic sea ice on interdecadal timescale are studied based on the daily precipitation,monthly sea ice concentration and ERA5 reanalysis data from 1980 to 2018.We found that the dominant mode of the TPEP in winter mostly exhibits a uniform spatial variation on the interdecadal timescale,with an opposite weak variation in the southeastern TP,and the Arctic sea ice concentration(SIC)before 2002 are larger than that after 2003.The interdecadal variation of TPEP is affected by two teleconnection wave trains regulated by the Barents and Kara Sea ice.In the light ice years,a remarkable positive geopotential height(HGT)anomaly appears over the Barents-Kara Sea and a remarkable negative HGT anomaly is located over the Lake Baikal.Two wave trains originating over the Barents-Kara Sea can be observed.The southern branch forms a wave train through the North Atlantic along the subtropical westerly jet stream,showing a‘+-+-+'pattern of HGT anomalies from Arctic to the TP.Negative HGT anomaly controls the western TP,which creates dynamic and water vapor conditions for the TPEP.The northern branch forms a wave train through the Lake Baikal and the southeast of the TP,showing a‘+-+'HGT anomaly distribution.Positive HGT anomaly controls the southeastern TP,which is not conducive to precipitation in the region.When the SIC in the Barents-Kara Sea increases,the situation is opposite.The above analysis also reveals the reason for the difference in the east-west distribution of the TPEP.

Asian summer monsoon responses to the change of land‒sea thermodynamic contrast in a warming climate:CMIP6 projections

It is of practical significance to use the updated Coupled Model Intercomparison Project Phase 6(CMIP6)models to study the impact of changes in land‒sea thermodynamic contrast(TC)on the Asian summer monsoon under different scenarios and to compare the similarities and differences of the impact mechanisms between different monsoon regions.In this study,we investigated future changes of the Asian summer monsoon under four Shared Socioeconomic Pathway(SSP)scenarios using 19 CMIP6 models.The intensity of the South Asian summer monsoon(SASM)is projected to decrease by 2.6%,6.3%,10.1%,and 11.1%,while the East Asian summer monsoon(EASM)intensity is projected to increase by 4.6%,7.9%,7.4%,and 9.8%until the end of the 21st century for SSP126,SSP245,SSP370,and SSP585 scenarios,respectively.Moreover,summer precipitation in Asia is projected to increase remarkably in 2015-2099 under all four scenarios.The inconsistent warming trends over the Tibetan Plateau(TP),Northwest Pacific,and tropical Indian Ocean would greatly impact the monsoon circulations.The upper-troposphere warming trend over the surrounding oceans is remarkably greater than that over the TP,while the near-surface warming trend over the surrounding oceans is smaller than that over the TP.The decrease of upper-troposphere TC between the TP and tropical Indian Ocean results in a weakening of the SASM circulation.The enhancement of the lower-troposphere TC between the TP and Northwest Pacific would strengthen the EASM circulation.Moisture budget analysis shows that the water-vapor would increase in the future,which would thermodynamically enhance summer precipitation through the anomalous vertical moisture transport associated with mean flow.The strengthening of the meridional circulation of the EASM would increase monsoon precipitation,while the weakening of zonal circulation of the SASM would dynamically reduce South Asian summer precipitation.

Evaluation of multidimensional simulations of summer air temperature in China from CMIP5 to CMIP6 by the BCC models: From trends to modes

To determine whether the capability of the CMIP6 version of Beijing Climate Center(BCC)models(BCC-ESMI and BCC-CSM2-MR)in simulating China summer surface air temperature(SAT)has improved,we presented a multidimensional evaluation of the summer SAT in China including the trends,modes,and influencing factors.Critical comparisons are also made with the results of CMIP5(BCC-CSM1.1 and BCC-CSMl.lm).In general,the CMIP6,especially BCC-CSM2-MR,has smaller deviations in the trends,the means,the mutations,the maximum centers,the variances,and the spatial patterns of the dominant modes from observatio relative to those of CMIP5.However,the BCC CMIP6 models still underestimate the SAT variation in the Qinghai-Tibetan Plateau and the northeastern regions of China,and the performance is unsatisfactory with respect to the physical drivers of the dominant modes.Importantly,all the BCC models can capture the spatio-temporal characteristics of the first mode well and can,in general,characterize the spatial pattern of the second mode,but none of the models perform well in the principal component of the second mode(PC2)due to the low performance with respect to the interannual variation of PC2.Furthermore,the factors influencing the leading two modes are evaluated.The two CMIP6 can simulate better the Northern Hemisphere subtropical high northern boundary affecting the first mode.Another factor,the Asia polar vortex area,can only be simulated better by two low-resolution models(BCC-CSM1.1 and BCC-ESM I).For the second mode,all four models simulate the influence of Asian zonal circulation well,but poorly simulate that of the southern Indian Ocean dipole due to a large deviation in the Indian Ocean surface temperature.

The extreme Northeast China cold vortex activities in the late spring of 2021 and possible causes involved

Record-breaking numbers of Northeast China cold vortex(NCCV)occurred during the late spring(April-May)of 2021,which provided favorable background for more severe convection weather(such as hailstorm and tornado)happened and struck Jiangsu and Hubei provinces,China,causing heavy casualties and property losses.To better understand the possible causes of extremely abnormal NCCV activities,the external forcing and dynamical analysis was conducted.The results show that the extreme NCCV activity is regulated by the preceding sea surface temperature(SST)anomalies in the tropical Pacific,the snow conditions over the Tibetan Plateau,and the wave-mean flow interaction over the Eurasian continent.During the preceding autumn and winter in 2020,a moderate La Niña event occurred over the tropical Pacific,which triggered the Pacific-North America teleconnection pattern(PNA)like wave train and further dispersed the Rossby wave energy downstream along the mid-latitude westerly jet,forming a zonal wave train over the Eurasian continent.Moreover,the second minimum snow depth was recorded over the southeastern Tibetan Plateau during the boreal winter of 2020/2021,which induced a concurrent local anomalous anticyclone and a cyclone over northeast Asia in the following spring.Finally,the anomalous circulation is capable of achieving energy from the mean state through barotropic energy conversion and strengthening the downstream wave train accordingly.This study highlights the joint impacts of external forcings and internal atmospheric processes on the NCCV activity.