Mixing states and secondary formation processes of organic nitrogen-containing single particles in Guangzhou, China.

Organic nitrogen (ON) compounds play a significant role in the light absorption of brown carbon and the formation of organic aerosols, however, the mixing state, secondary formation processes, and influencing factors of ON compounds are still unclear. This paper reports on the mixing state of ON-containing particles based on measurements obtained using a high-performance single particle aerosol mass spectrometer in January 2020 in Guangzhou. The ON-containing particles accounted for 21% of the total detected single particles, and the particle count and number fraction of the ON-containing particles were two times higher at night than during the day. The prominent increase in the content of ON-containing particles with the enhancement of NOx mainly occurred at night, and accompanied by high relative humidity and nitrate, which were associated with heterogeneous reactions between organics and gaseous NOx and/or NO3 radical. The synchronous decreases in ON-containing particles and the mass absorption coefficient of water-soluble extracts at 365 nm in the afternoon may be associated with photo-bleaching of the ON species in the particles. In addition, the positive matrix factorization analysis found five factors dominated the formation processes of ON particles, and the nitrate factor (33%) mainly contributed to the production of ON particles at night. The results of this study provide unique insights into the mixing states and secondary formation processes of the ON-containing particles.

One-pot magnetic field induced formation of Fe3O4/C composite microrods with enhanced lithium storage capability.

One-dimensional Fe3O4/C composite microrods are synthesized via a facile one-pot solvothermal reaction in the presence of an external magnetic field. When evaluated as an anode material for lithium ion batteries, these Fe3O4/C microrods manifest high specific capacity and excellent cycling performance.

Influence of ozone pollution on the mixing state and formation of oxygenated organics containing single particles.

The formation and aging processes of oxygenated organic molecules (OOMs) are important for understanding the formation mechanisms of secondary organic aerosols (SOAs) in the field. In this study, we investigated the mixing states of OOM particles by identifying several oxygenated species along with the distributions of secondary organic carbon (SOC) during both clean and ozone (O3)-polluted periods in July and September of 2022 in Guangzhou, China. OOM-containing particles accounted for 57 % and 49 % of the total detected single particles in July and September, respectively. Most of the OOM particles were internally mixed with sulfate and nitrate, while elemental carbon and hydrocarbon species were absent. Despite the higher SOC/OC ratio in September (81 %) than it in July (72 %), comparative investigations of the mass spectra, diurnal patterns, and distributions of OOM particles revealed the same composition and aging states of OOMs in two O3 pollution periods. As the O3 concentration increased from the clean to the polluted periods, the ratio of SOC to OC increased along with the relative abundance of secondary OOM particles among total OOM particles. In contrast, the relative abundance of OC-type OOM particles gradually decreased, indicating the conversion of hydrocarbon species into OOMs as the SOC/OC ratio increased. Both the bulk analysis of SOC from filter measurement and the mixing states of OOM particles suggested that OOM production and degree of oxidation were higher in the O3-polluted periods than in the clean periods. These results elucidate the effects of O3 pollution on the OOM formation process and offer new perspectives for the joint investigation of SOA production based on filter sampling and single-particle measurements.

Long-Term Observation of Mixing States and Sources of Vanadium-Containing Single Particles from 2020 to 2021 in Guangzhou, China.

The distribution of vanadium (V) in aerosols is commonly used to track ship exhaust emissions, yet the atmospheric abundance of V has been greatly reduced due to the implementation of a clean fuel policy. Recent research mainly discussed the chemical compositions of ship-related particles during specific events, yet few studies focus on the long-term changes of V in the atmosphere. In this study, a single-particle aerosol mass spectrometer was used to measure V-containing particles from 2020 to 2021 in Huangpu Port in Guangzhou, China. The long-term trend of the particle counts of V-containing particles declined annually, but the relative abundance of V-containing particles in the total single particles increased in summer due to the influence of ship emissions. Positive matrix factorization revealed that in June and July 2020, 35.7% of the V-containing particles were from ship emissions, followed by dust and industrial emissions. Furthermore, more than 80% of the V-containing particles were found mixing with sulfate and 60% of the V-containing particles were found mixing with nitrate, suggesting that the majority of the V-containing particles were secondary particles processed during the transport of ship emissions to urban areas. Compared with the small changes in the relative abundance of sulfate in the V-containing particles, the relative abundance of nitrate exhibited clear seasonal variations, with a high abundance in winter. This may have been due to the increased production of nitrate from high concentrations of precursors and a suitable chemical environment. For the first time, the long-term trends of V-containing particles in two years are investigated to demonstrate changes in their mixing states and sources after the clean fuel policy, and to suggest the cautious application of V as an indicator of ship emissions.

Insights into the different mixing states and formation processes of amine-containing single particles in Guangzhou, China.

The formation processes of particulate amines are closely related to their emission sources and secondary reactions, which can be revealed through the investigation of their real-time mixing states in individual particles. The mixing states of methylamine (MA)-, trimethylamine (TMA)-, and diethylamine (DEA)-containing particles were studied using a high-performance single particle aerosol mass spectrometer (HP-SPAMS) in Guangzhou, China, in January 2020. The sharp increase in TMA particles was found to be closely associated with the increase in the ambient relative humidity (RH), while the MA- and DEA-containing particles were not similarly influenced by the changes in the RH. The prominent enrichment of secondary oxygenated organics in DEA particles during the daytime was consistent with the active period of photochemistry, implying that the sharp decrease in DEA particles in the afternoon was likely due to photo-oxidation of the DEA. The number fraction (Nf) of DEA particles, the Nf of the nitrate in the DEA particles, and the abundance of nitrate increased as the NOx content all increased during the nighttime, suggesting that the formation of DEA·HNO3 salt was the dominant pathway of particulate DEA production. These results are consistent with our previous measurements in Nanjing, confirming the general and distinct mixing states of TMA and DEA particles. Positive matrix factorization analysis revealed that the total fraction of the more oxidized organics factor and the less oxidized organics factor were much higher in the DEA particles (26.9 %) than in the TMA particles (9 %), confirming the significant enrichment of oxygenated species in the DEA particles. The different mixing states of the amines revealed the unique response of each type of amine to the same atmospheric environment, and the prominent mixing states of the DEA with secondary oxygenated species suggest the potential role of DEA in tracing the evolution of organic aerosols.

5-HT2B-mediated serotonin activation in enterocytes suppresses colitis-associated cancer initiation and promotes cancer progression.

Rationale: Serotonin (5-hydroxytryptamine, 5-HT) is generally considered to be involved in colitis-associated cancer (CAC), but previous research has yielded inconsistent results regarding the effect of 5-HT on CAC. 5-HT2B is one of the receptors of 5-HT, and the receptor is expressed in intestinal epithelial cells (IECs). However, the functions of 5-HT2B in CAC remain unclear. Our work demonstrates the variable functions of 5-HT/5-HT2B signaling in the initiation and progression of CAC in mice. Methods: We constructed two types of mutant mice homozygous knockout of Htr2b, the gene encoding 5-HT2B, in IECs (Htr2bΔIEC and Htr2bΔIEC-ER) to study the role of 5-HT2B in AOM/DSS-induced CAC model. Inflammation was measured using the body weight, colon length, and colitis severity score, and by histologic analysis of colon tissues. Tumor severity was assessed by tumor quantity, load, and histologic analysis of colon tumor tissues. Results: In Htr2bΔIEC mice, AOM/DSS induced an enhancement of colitis and tumor severity. This process was due to the inhibition of TGF-ß/SMAD signaling pathway and activation of IL-6/STAT3 signaling pathway. IL-6 antibody treatment reversed the stimulating effect of Htr2b deletion on tumorigenesis. However, tumor severity decreased in Htr2bΔIEC-ER mice injected with tamoxifen on day 48 of AOM/DSS treatment. Knockout Akt1 eliminated the function of 5-HT in promoting tumor cells. Conclusion: Our work elucidates 5-HT/5-HT2B/TGF-ß signaling as a critical tumor suppressing axis during CAC initiation but as a promoter of cancer progression in the late-stage of CAC. Our findings provide a new understanding of the role of 5-HT in the initiation and progression of CAC, offering a new perspective on the long-standing debate on whether the 5-HT signal promotes or inhibits tumors.

ULK1 phosphorylates Exo70 to suppress breast cancer metastasis.

Increased expression of protein kinase ULK1 was reported to negatively correlate with breast cancer metastasis. Here we report that ULK1 suppresses the migration and invasion of human breast cancer cells. The suppressive effect is mediated through direct phosphorylation of Exo70, a key component of the exocyst complex. ULK1 phosphorylation inhibits Exo70 homo-oligomerization as well as its assembly to the exocyst complex, which are needed for cell protrusion formation and matrix metalloproteinases secretion during cell invasion. Reversely, upon growth factor stimulation, Exo70 is phosphorylated by ERK1/2, which in turn suppresses its phosphorylation by ULK1. Together, our study identifies Exo70 as a substrate of ULK1 that inhibits cancer metastasis, and demonstrates that two counteractive regulatory mechanisms are well orchestrated during tumor cell invasion.

Berberine decelerates glucose metabolism via suppression of mTOR­dependent HIF­1α protein synthesis in colon cancer cells.

Hyperactivated glucose uptake and glycolytic metabolism are considered as a hallmark of cancer. Berberine, a natural alkaloid with tumor­selective anticancer effects, has been shown to promote glucose uptake in metabolic tissues and cells. However, whether and how berberine regulates the glucose metabolism of cancer cells are still poorly understood. In the present study, we revealed that berberine, which suppressed the growth of colon cancer cell lines HCT116 and KM12C, greatly inhibited the glucose uptake and the transcription of glucose metabolic genes, GLUT1, LDHA and HK2 in these two cell lines as assessed by RT­qPCR. A mechanistic study further indicated that the protein expression but not mRNA transcription of HIF­1α, a well­known transcription factor critical for dysregulated cancer cell glucose metabolism, was dramatically inhibited in berberine­treated colon cancer cell lines. Using western blot analysis, this regulation appears to occur via protein synthesis but not protein stability as blockade of HIF­1α protein degradation by hypoxia mimic desferrioxamine (DFX) or proteasome inhibitor MG132 did not affect berberine's effect. In addition, mTOR signaling previously reported to regulate HIF­1α protein synthesis was further found to be suppressed by berberine. Taken together, our results indicated that berberine inhibits overactive glucose metabolism of colon cancer cells via suppressing mTOR­depended HIF­1α protein synthesis, which provided not only a novel mechanism involved in berberine's tumor­specific toxicity but also a theoretical basis for the development of berberine for colon cancer treatment.

Exo70 is transcriptionally up-regulated by hepatic nuclear factor 4α and contributes to cell cycle control in hepatoma cells.

Exo70, a member of the exocyst complex, is involved in cell exocytosis, migration, invasion and autophagy. However, the expression regulation and function of Exo70 in hepatocellular carcinoma are still poorly understood. In this study, we found Exo70 expression in human hepatoma cells was greatly reduced after knocking down hepatic nuclear factor 4α (HNF4α), the most important and abundant transcription factor in liver. This regulation occurred at the transcriptional level but not post-translational level. HNF4α transactivated Exo70 promoter through directly binding to the HNF4α-response element in this promoter. Cell cycle analysis further revealed that down-regulation of HNF4α and Exo70 was essential to berberine-stimulated G2/M cell cycle arrest in hepatoma cells. Moreover, knocking down either Exo70 or HNF4α induced G2/M phase arrest of hepatoma cells. Exo70 acted downstream of HNF4α to stimulate G2/M transition via increasing Cdc2 expression. Together, our results identify Exo70 as a novel transcriptional target of HNF4α to promote cell cycle progression in hepatoma, thus provide a basis for the development of therapeutic strategies for hepatocellular carcinoma.