NSUN2-Mediated m5C Methylation Impairs Endometrial Receptivity.

Impaired endometrial decidualization is the primary cause of recurrent implantation failure (RIF). RNA methylation modification, especially NSUN family mediated m5C, is crucial for various physiological events, such as maternal-to-zygotic transition, gametogenesis, embryonic development, organismal lifespan, and cell cycle. However, the regulatory mechanisms between NSUN family mediated m5C modification and RIF remain unknown. We acquired NSUN2 expression data of 15 human endometrium samples at proliferative and secretory stages from reproductive cell atlas. The overall pattern of m5C sites and genes was elucidated through m5C-BS-seq, whereas the overall m5C levels in different groups were revealed by dot blot assay. BrdU and western blotting assays were carried out to evaluate the role of NSUN2 in proliferation and autophagy. The effects of NSUN2-mediated m5C modification on embryo attachment were evaluated by an in vitro model of a confluent monolayer of Ishikawa cells cocultured with BeWo spheroids, and its downstream targets were evaluated by real-time reverse-transcription PCR and western blotting in Ishikawa cells. The molecular mechanism for NSUN2 regulating its downstream targets' expression was determined by Cut&Tag and coimmunoprecipitation assays. NSUN2 was increased in SOX9+ cells and widespread in epithelial cell type at the proliferative stage by previous single-cell RNA sequencing data. NSUN2 overexpression (NSUN2OE) in the Ishikawa cell line elevated m5C levels and promoted cell proliferation and autophagy. NSUN2OE reduced attachment efficiency of BeWo cell spheres. Overexpressed NSUN2 was found to increase STAT1 and MMP14 mRNA expressions by inducing exon skipping. NSUN2 interacted with CLDN4 through m5C modification, and NSUN2OE or NSUN2 knockdown resulted in a similar variation tendency of CLDN4. Overexpression of NSUN2 increased CLDN4 H3K9ac modification by downregulating SIRT4 expression at the protein level, leading to the upregulation of CLDN4 mRNA expression. Our results uncovered a novel intricate regulatory mechanism between NSUN2-mediated m5C and RIF and suggested a potential new therapeutic strategy for RIF.

Increased Expression of PDGFA Is Associated With Poor Prognosis and Immune Infiltration in Head and Neck Squamous Cell Carcinoma.

BACKGROUND: Platelet-derived growth factor A (PDGFA) has been shown to be upregulated in several tumors, contributing to their malignant phenotypes. However, its expression and function in head and neck squamous cell carcinoma (HNSC) are not clearly understood. Thus, we aimed to evaluate this issue using bioinformatic analyses and primary experimental validation. METHODS: The expression of PDGFA was analyzed using popular bio-databases and further validated by RT-PCR and immunohistochemical staining. Survival analyses were then performed. The association between PDGFA expression levels and immune cell infiltration in the immune microenvironment was assessed. RESULTS: PDGFA has been found to be significantly upregulated in a variety of cancers, including HNSC, and increased PDGFA expression may be an independent prognostic factor associated with immune cell infiltration in HNSC. CONCLUSION: Overexpression of PDGFA in HNSC is significantly associated with poor prognosis and immune cell infiltration in the tumor microenvironment (TME). PDGFA has potential as a molecular indicator for diagnosis, prognosis, and immune processes in HNSC.

Femtosecond laser direct writing multilayer chiral waveplates with minimal linear birefringence.

Chirality transfer from femtosecond laser direct writing in achiral transparent materials mainly originates from the interplay between anisotropic nanogratings and mechanical stress with non-parallel and non-perpendicular (oblique) neutral axes. Yet, the laser fabrication simultaneously induces non-negligible linear birefringence. For precise manipulation of circular polarization properties, as well as to unlock the full functionality, we report here a geometry-inspired multilayer method for direct writing of chiral waveplates with minimal linear birefringence. We perform a theoretical analysis of both circular and linear properties response for different multilayer configurations and achieve strong circular birefringence of up to -2.25 rad with an extinction ratio of circular birefringence to total linear birefringence of up to 5.5 dB at 550 nm. Our strategy enables the precise control of circular properties and provides a facile platform for chiral device exploration with almost no linear property existence.

Vortex soliton oscillation in a mode-locked laser based on broadband long-period fiber grating.

Optical vortex beams (OVBs) have attracted much attention in diverse applications and spatiotemporal mode locking for optical soliton formation. In this Letter, a compact mode-locked (ML) vortex fiber laser is demonstrated based on a broadband long-period fiber grating near the dispersion turnaround point, where the group velocities between the core modes of ${{\rm LP}_{01}}$ and ${{\rm LP}_{11}}$ in a two-mode fiber are matched. The OVB pulses with first-order orbital angular momentum are oscillated through broadband mode conversion inside the cavity. The time-stretch dispersive Fourier transform method is also employed for the observation of vortex soliton buildup dynamics. The study of vortex soliton oscillation motivates the development towards controlling vortex modes in the ML fiber lasers.

Dynamic vortex mode-switchable erbium-doped Brillouin laser pumped by high-order mode.

We experimentally demonstrated that the transversal vortex modes of an all-fiber erbium-doped Brillouin laser can be dynamically switched by using the high-order mode (HOM) of Brillouin pump (BP), which is used to achieve the oscillation of HOM inside the ring cavity. Core-mode conversion in a few-mode fiber (FMF) between the fundamental mode and HOM is obtained by cascading an acoustically induced fiber grating (AIFG) and a mode selection coupler (MSC) operating at the same wavelength region. Through frequency shift keying (FSK) modulation of the AIFG signal, the output transversal modes can be switched dynamically between LP01 and vortex modes, and the measured purities of output HOM are more than 82%. Moreover, the output Brillouin wavelength can also be tuned via altering the input wavelength of BP and the resonant response of AIFG. We have achieved HOM Brillouin-shifted laser output within the wavelength band from 1545-1560 nm. The output linewidth of the proposed Brillouin laser is less than 4 kHz.

Exosomal miRNA-17-5p derived from human umbilical cord mesenchymal stem cells improves ovarian function in premature ovarian insufficiency by regulating SIRT7.

Premature ovarian insufficiency (POI) is clinically irreversible in women aged over 40 years. Although numerous studies have demonstrated satisfactory outcomes of mesenchymal stem cell therapy, the underlying therapeutic mechanism remains unclear. Exosomes were collected from the culture medium of human umbilical cord mesenchymal stem cells (hUMSCs) and assessed by electron microscopy and Western blot (WB) analysis. Then, exosomes were added to the culture medium of cyclophosphamide (CTX)-damaged human granulosa cells (hGCs), and the mixture was injected into the ovaries of CTX-induced POI model mice before detection of antiapoptotic and apoptotic gene expression. Next, the microRNA expression profiles of hUMSC-derived exosomes (hUMSC-Exos) were detected by small RNA sequencing. The ameliorative effect of exosomal microRNA-17-5P (miR-17-5P) was demonstrated by miR-17-5P knockdown before assessment of ovarian phenotype and function, reactive oxygen species (ROS) levels and SIRT7 expression. Finally, SIRT7 was inhibited or overexpressed by RNA interference or retrovirus transduction, and the protein expression of PARP1, γH2AX, and XRCC6 was analyzed. The ameliorative effect of hUMSC-Exos on POI was validated. Our results illustrated that hUMSC-Exos restored ovarian phenotype and function in a POI mouse model, promoted proliferation of CTX-damaged hGCs and ovarian cells, and alleviated ROS accumulation by delivering exosomal miR-17-5P and inhibiting SIRT7 expression. Moreover, our findings elucidated that miR-17-5P repressed PARP1, γH2AX, and XRCC6 by inhibiting SIRT7. Our findings suggest a critical role for exosomal miR-17-5P and its downstream target mRNA SIRT7 in hUMSC transplantation therapy. This study indicates the promise of exosome-based therapy for POI treatment.

CiRS-126 inhibits proliferation of ovarian granulosa cells through targeting the miR-21-PDCD4-ROS axis in a polycystic ovarian syndrome model.

Polycystic ovarian syndrome (PCOS) is considered to be one of the most prevalent endocrine disorders affecting women of reproductive age. CiRS-126, an innovative circular microRNA, has previously been proven to be a promising miR-21 sponge. However, a proper understanding of the impact of ciRS-126 on PCOS is needed. Circular RNA (CiRS) profiles were initially evaluated in ovarian cortex samples obtained from 18 women with PCOS as well from 9 women without PCOS. Insulin-induced ovarian granulosa cells isolated from mice were utilized for the functional study. CiRS microarray analysis and quantitative real-time PCR indicated that ciRs-126 expression was downregulated while miR-21 expression was upregulated in PCOS samples and insulin-induced granulosa cells as compared with non-PCOS samples and non-insulin-induced granulosa cells. Furthermore, ectopic overexpression of ciRS-126 was associated with a reduction in proliferation and increased apoptosis in insulin-treated granulosa cells. Meanwhile, bioinformatic prediction and the results of the dual-luciferase reporter assay indicated the presence of consecutive binding in the ciRS-126-miR-21-programmed cell death protein 4 (PDCD4) axis. Moreover, overexpression of miR-21 blocked ciRS-126 repression of proliferation and triggered the death of insulin-induced granulosa cells. Excessive PDCD4 expression counteracted the influence of miR-21 on cell death and proliferation. The data indicated that PDCD4 played a regulatory role in ROS generation, which is reportedly involved in apoptosis. Therefore, ciRS-126 reduction in PCOS granulosa cells targeted the miR-21-PDCD4 axis to reduce proliferation and promote apoptosis. CiRS-126 shows potential as a promising predictor of clinical outcome as well as a therapeutic target in PCOS.

The fragmentation patterns of maternal plasma cell-free DNA and its applications in non-invasive prenatal testing.

The discovery of cell-free DNA (cfDNA) in maternal plasma has opened up new promises for the development of non-invasive prenatal testing (NIPT). Application of cfDNA in NIPT of fetus diseases and abnormalities is restricted by the low amount of fetal DNA molecules in maternal plasma. Fetus-derived cfDNA in maternal plasma are shorter than maternal DNA, thus leveraging the maternal and fetus-derived cfDNA molecules size difference has become a novel and more accurate method for NIPT. However, multiple biological properties such as size distribution of plasma DNA, proportion of fetal-derived DNA and methylation levels in maternal plasma across different gestational ages still remain largely unknown. Further insights into the size distribution and fragmentation pattern of circulating plasma cfDNA will shed light on the origin and fragmentation mechanisms of cfDNA during physiological and pathological processes in prenatal diseases and enhance our ability to take the advantage of plasma cfDNA as a molecular diagnostic tool. In the review, we start by summarizing the research techniques for the determination of the fragmentation profiles of cfDNA in maternal plasma. We then summarize the main progress and findings in size profiles of maternal plasma cfDNA and cffDNA. Finally, we discuss the potential diagnostic applications of plasma cfDNA size profiling.

Sequencing shorter cfDNA fragments improves the fetal DNA fraction in noninvasive prenatal testing.

BACKGROUND: Sequencing cell-free DNA in maternal plasma is an effective noninvasive prenatal testing technique that has been used in fetal aneuploidy screening worldwide. However, its clinical application is limited by the low fetal fraction (<4%) of cell-free DNA in many singleton pregnancies, which usually results in screen failures or no calls. In addition, dizygotic twin contributions of cell-free DNA into the maternal circulation can vary by 2-fold, complicating the quantitative diagnosis of fetal aneuploidy. OBJECTIVE: We performed semiconductor sequencing of shorter fragments (107-145 bp) of circulating cell-free DNA to improve the fetal DNA fraction at lower uniquely mapped reads (1-8.5 MB) to reduce the probability of no calls. STUDY DESIGN: We identified 2903 plasma samples from pregnant women, including 86 dizygotic twin pregnancy, that were collected at a single prenatal diagnostic center between October 2015 and July 2018. Size-selection noninvasive prenatal testing for fetal aneuploidy was applied to 2817 plasma samples (1409 male and 1408 female fetuses) and 86 dizygotic twins using noninvasive prenatal testing with and without size selection. Shorter fragment size was the key factor affecting fetal fraction in multivariable linear regression models as well as to validate the accuracy of the size selection for noninvasive prenatal testing. RESULTS: Analysis of 1409 male fetuses by multivariable linear regression showed that maternal age, body mass index, number of pregnancies, average cell-free DNA size, maternal plasma cell-free DNA concentration, library concentration, and multiple gestation were negatively correlated with fetal fraction. Conversely, gestational age and uniquely mapped reads were positively correlated with fetal fraction. Compared with ≤120 bp cell-free DNA fragments, mean fetal fraction differences were -3.57% (95% confidence interval, -5.95% to -1.19%), for 121-130 bp, -9.52% (95% confidence interval, -11.89% to -7.14%) for 131-140 bp, and -14.47% (95% confidence interval, -18.37% to -10.58%) for ≥141 bp (Ptrend < .0001). These results were statistically significant after multivariable adjustments in models for fetal fraction. Meanwhile, results from 86 dizygotic twins showed that the size selection increased the fetal fraction by ∼3.2-fold, with 98.8% of samples reaching a fetal fraction >10%. Improved detection accuracy was also achieved. CONCLUSION: Sequencing shorter cell-free DNA fragments is a reasonable strategy to reduce the probability of no calls results because of low fetal fraction and should be recommended to pregnant subjects.

Analysis of genome-wide in cell free DNA methylation: progress and prospect.

DNA methylation is an important epigenetic marker that affects gene expression. Cell-free DNA methylation detection is a promising approach as abnormal distribution of DNA methylation is one of the hallmarks of many cancers and methylation changes occur early during carcinogenesis. This review summarizes the existing literature and reviews on the detection methods based on next generation sequencing for DNA methylation. The review also discusses the feasibility of detecting cfDNA methylation and the latest progress.

Dynamic mode-switchable optical vortex beams using acousto-optic mode converter.

We propose a dynamic scheme to realize mode-switchable generation of LP11a/b modes and ±1-order orbital angular momentum (OAM) modes simultaneously, which are induced by an acoustically induced fiber grating driven by radio frequency modulation. LP11a/b mode degeneration in a few-mode fiber is induced by the geometric irregularity of optical fibers. A dual-wavelength resonance of mode coupling from LP01 to LP11a/b modes is found based on the combined effects of optical and acoustic birefringence. Within the configuration of continuous-wave intra-cavity laser output, we experimentally demonstrate a fast-switchable generation of LP11a/b modes and optical vortex beams with ±1-order OAM at a switching speed up to 4.3 kHz. This approach has potential applications in mode-division multiplexing, particle manipulation, stimulated emission depletion microscopy, and quantum information science.

miRNA in plasma exosome is stable under different storage conditions.

Exosomes are small membrane-bound vesicles secreted by most cell types. Exosomes contain various functional proteins, mRNAs and microRNAs (miRNAs) that could be used for diagnostic and therapeutic purposes. How we should store the samples before RNA isolation and whether those long term stored samples could be used for circulating RNA investigation because of RNase is unknown. The aim of the study was to determine the stability of circulating miRNA in exosomes and plasma. Exosomes were isolated from plasma samples by using ExoQuick Precipitation methods. RNA was extracted from exosomes and the corresponding plasma samples with a Qiagen miRNeasy Mini kit. The concentration of RNA was measured by a Qubit® RNA HS Assay Kit, and quantitative PCR was used for individual miRNA expression level detection. Results showed that exosomal miRNA showed extra stability under different storage conditions and no significant influence on plasma miRNA, except for short term storage at 4 °C. It is thus indicated that exosome miRNAs can be good biomarkers based on their stability under various storage conditions.

Tiaogan Bushen Xiaoji Formula Enhances the Sensitivity of Estrogen Receptor- Positive Breast Cancer to Tamoxifen by Inhibiting the TGF-ß/SMAD Pathway.

Background: The resistance to endocrine therapy can lead to recurrence and metastasis of breast cancer (BC), affecting the survival period. Tiaogan Bushen Xiaoji (TGBSXJ) Formula, a traditional Chinese medicine (TCM) decoction, has been widely used in the treatment of estrogen receptor-positive (ER+) BC. However, the underlying mechanism of TGBSXJ Formula in ER+BC treatment has not been totally elucidated. Methods: Network pharmacology (NP) and RNA sequencing were used to predict the candidate ingredients and explore the potential targets of TGBSXJ Formula. Then, the results of NP and RNA sequencing were investigated by in vitro experiments. Results: Active ingredients of TGBSXJ Formula mainly included Mangiferin, Rutin, Anemarrhena asphodeloides saponin BII, Ganoderic acid A and Acacetin, etc. A protein-protein interaction (PPI) network was created based on the active ingredients of TGBSXJ Formula and target genes of ER+ BC, in which TGF-ß, MMP2 and SMAD3 were defined as the hub genes. In vitro experiments showed that TGBSXJ Formula significantly inhibited the viability, colony ability and migration of ER+ BC cells, and significantly increased the sensitivity to TAM. Western blot analysis showed that TGBSXJ Formula significantly downregulated TGF-ß, E-cadherin, MMP2, MMP9, N-cadherin, p-Smad2 and p-Smad3 in ER+ BC cells. Conclusion: TGBSXJ Formula increases the sensitivity of ER+ BC cells to TAM by inhibiting the TGF-ß/Smad signaling pathway.

A low-cost, low-input method establishment for m6A MeRIP-seq.

N6-methyladenosine (m6A) is a highly prevalent modification found in mammal mRNA molecules that plays a crucial role in the regulation of cellular function. m6A RNA immunoprecipitation sequencing (MeRIP-seq) has been frequently used in transcriptomics research to identify the location of m6A. MABE572 (Millipore) is the most widely utilized and efficient anti-m6A antibody for MeRIP-seq. However, due to the high dose and price of this antibody, which has also been taken off the market, we discovered that CST's anti-m6A antibody can be used instead of MABE572 to map the m6A transcriptome. In the present study, we performed different concentrations of the CST anti-m6A antibodies with the corresponding initiation RNA of HEK293T cells, 2.5 µg antibody with 1 µg total RNA, 1.25 µg antibody with 0.5 µg total RNA, and 1.25 µg antibody with 0.1 µg total RNA. By comparing the m6A peak calling, enriched motifs, alternative splicing events, and nuclear transcripts modified by m6A between the CST and Millipore libraries, it was found that the CST library presented similar data to Millipore, even at incredibly low doses. The volume and cost of antibodies are significantly reduced by this refined MeRIP-seq using CST antibody, making it convenient to map future large-scale sample m6A methylation.

Construction and assessment of an angiogenesis-related gene signature for prognosis of head and neck squamous cell carcinoma.

OBJECTIVE: Angiogenesis-associated genes (AAGs) play a critical role in cancer patient survival. However, there are insufficient reports on the prognostic value of AAGs in head and neck squamous cell carcinoma (HNSC). Therefore, this study aimed to investigate the correlation between AAG expression levels and survival in HNSC patients, explore the predictive value of signature genes and lay the groundwork for future in-depth research. METHODS: Relevant data for HNSC were obtained from the databases. AAGs-associated signature genes linked to prognosis were screened to construct a predictive model. Further analysis was conducted to determine the functional correlation of the signature genes. RESULTS: The signature genes (STC1, SERPINA5, APP, OLR1, and PDGFA) were used to construct prognostic models. Patients were divided into high-risk and low-risk groups based on the calculated risk scores. Survival analysis showed that patients in the high-risk group had a significantly lower overall survival than those in the low-risk group (P < 0.05). Therefore, this prognostic model was an independent prognostic factor for predicting HNSC. In addition, patients in the low-risk group were more sensitive to multiple anti-cancer drugs. Functional correlation analysis showed a good correlation between the characteristic genes and HNSC metastasis, invasion, and angiogenesis. CONCLUSION: This study established a new prognostic model for AAGs and may guide the selection of therapeutic agents for HNSC. These genes have important functions in the tumor microenvironment; it also provides a valuable resource for the future clinical trials investigating the relationship between HNSC and AAGs.

Transplantation of olfactory ensheathing cells can alleviate neuroinflammatory responses in rats with trigeminal neuralgia.

Trigeminal neuralgia (TN) is a common form of facial pain, which primarily manifests as severe pain similar to facial acupuncture and electric shock. Olfactory ensheathing cells (OECs) are glial cells with high bioactivity; these cells are essential for the periodic regeneration of the olfactory nerve and have been utilized for the repair of nerve injuries. A member of the P2X receptor family, P2X7R, is an ion channel type receptor that has been confirmed to participate in various pain response processes. In this study, we transplanted OECs into trigeminal nerve-model rats with distal infraorbital nerve ligation to observe the therapeutic effect of transplanted OECs in rats. Additionally, we utilized the P2X7R-specific inhibitor brilliant blue G (BBG) to study the therapeutic mechanisms of cell transplantation. The facial mechanical pain threshold of these rats significantly increased following cell transplantation. The immunohistochemistry, immunoblotting, and RT-qPCR results demonstrated that the levels of P2X7R, (NOD)-like receptor protein-3 (NLRP3), nuclear factor-κB (NF-κB), interleukin (IL)-1ß, and IL-18 in the trigeminal ganglion of rats treated with OEC transplantation or BBG treatment were significantly lower than those in the injured group without treatment. Overall, our results demonstrate that OEC transplantation can alleviate TN in rats, and it can reduce the expression of P2X7R related inflammatory factors in TN rats, reducing neuroinflammatory response in TG.

Tailoring chiral optical properties by femtosecond laser direct writing in silica.

An object that possesses chirality, that is, having its mirror image not overlayed on itself by rotation and translation, can provide a different optical response to a left- or right-handed circular polarized light. Chiral nanostructures may exhibit polarization-selective optical properties that can be controlled for micro-to-nano optical element engineering. An attractive way to induce such complex nanostructures in three-dimension in glass is femtosecond laser direct writing. However, the mechanism of femtosecond laser induced chirality remains to be unveiled due to complex physical and chemical processes occurring during the ultrashort light-matter interaction. Here, a phenomenological model is proposed and is built on two-layers phase shifters to account for this laser-induced optical chirality in an initially achiral material (silica glass). This model is based on the observation that femtosecond laser induced nanogratings own two principal contributions to its aggregate birefringent response: a form and a stress-related one. By refining this formalism, a multilayer approach is developed to imprint on demand optical rotation. Values up to +/-60° at 550 nm within an optimal 80 µm thickness in silica glass are possible, corresponding to the highest value in a glass to date. These results provide new insights of circular-optical control in micro-nano optical manufacturing and open new opportunities for photonics applications.

ATP ion channel P2X purinergic receptors in inflammation response.

Different studies have confirmed that P2X purinergic receptors play a key role in inflammation. Activation of P2X purinergic receptors can release inflammatory cytokines and participate in the progression of inflammatory diseases. In an inflammatory microenvironment, cells can release a large amount of ATP to activate P2X receptors, open non-selective cation channels, activate multiple intracellular signaling, release multiple inflammatory cytokines, amplify inflammatory response. While P2X4 and P2X7 receptors play an important role in the process of inflammation. P2X4 receptor can mediate the activation of microglia involved in neuroinflammation, and P2X7 receptor can mediate different inflammatory cells to mediate the progression of tissue-wide inflammation. At present, the role of P2X receptors in inflammatory response has been widely recognized and affirmed. Therefore, in this paper, we discussed the role of P2X receptors-mediated inflammation. Moreover, we also described the effects of some antagonists (such as A-438079, 5-BDBD, A-804598, A-839977, and A-740003) on inflammation relief by antagonizing the activities of P2X receptors.

[Pollution Characteristics of PM2.5 Chemical Composition in Zhejiang Province].

To investigate the seasonal and regional pollution characteristics of PM2.5 chemical composition in Zhejiang province, this study was based on manual sampling monitoring data from 11 sampling sites of four regions in Zhejiang province from October 1, 2019 to September 30, 2020. The results showed that during the observation period, the average ρ(PM2.5) of the four regions ranged from 34.3 µg·m-3 to 46.4 µg·m-3. The PM2.5 mass concentrations in the hinterland areas of western Zhejiang and northern Zhejiang were relatively high, 15.1% and 13.2% higher than the mean value, respectively. The PM2.5 mass concentrations in the coastal areas of eastern Zhejiang and southern Zhejiang were relatively low, 8.4% and 14.9% lower than the average, respectively. The seasonal characteristics showed a higher concentration in autumn and winter and lowest concentration in summer. The seasonal variation in PM2.5 mass concentration from autumn to spring was not obvious in southern Zhejiang, whereas in western Zhejiang, the PM2.5 mass concentration followed a descending sequence of autumn>winter>spring>summer. In northern Zhejiang and eastern Zhejiang, the trend was winter>autumn>spring>summer. During the observation period in the inland area, the ρ(PM2.5) of the scenic area, administrative area, residential area, and mixed area of commercial traffic and residents were (40.2±10.2), (46.3±9.6), (50.1±10.6), and (46.7±10.2) µg·m-3, respectively. The highest value of ρ(PM2.5) was in the residential area. During the sampling period in coastal areas, the ρ(PM2.5) of the cultural and entertainment area and mixed area of commercial traffic and residents were (27.4±5.8) µg·m-3and (37.2±5.6) µg·m-3, respectively. The contribution rates of organic matter (OM), NO3-, SO42-, NH4+, trace elements, and crustal matter in PM2.5were 26.4%, 15.4%, 12.4%, 9.0%, 7.1%, and 5.7%, respectively. The SNA, including SO42-, NO3-, and NH4+, contributed 36.8% in PM2.5. In terms of seasons, the contribution of OM to PM2.5 in autumn, spring, and summer was higher than that of other compositions, which accounted for 28.3%, 27.7%, and 26.3%, respectively. The contribution rate of NO3- in PM2.5 was the largest in winter, reaching 24.3%. In terms of spatial distribution, SNA contributed the most to PM2.5 in all regions, ranging from 32.8% to 39.7%, with the highest in northern Zhejiang and the lowest in southern Zhejiang. The SNA of all regions presented NO3->SO42->NH4+. Based on the backward trajectory clustering analysis, the main air sources of northern Zhejiang were the Yellow Sea-southern Jiangsu (autumn), northern Anhui (winter), East China Sea (spring), and western Jiangsu (summer) areas, with contribution rates of 38.11%, 35.28%, 37.46%, and 27.87%, respectively. The main air sources of western Zhejiang were the Yellow Sea-southern Jiangsu (autumn), southern Anhui (winter), eastern Zhejiang (spring), and northern Zhejiang (summer), with contribution rates of 38.11%, 37.50%, 46.55%, and 32.58%, respectively. The air of autumn, winter, spring, and summer in eastern Zhejiang were influenced by air masses from northern Hebei (36.07%), eastern Shandong (38.06%), East China Sea (30.17%), and southern Guangdong (34.43%), respectively. In autumn, winter, spring, and summer, southern Zhejiang was affected by air masses from the Yellow Sea (35.66%), northeast Anhui (34.44%), East China Sea (26.72%), and southern Fujian coast (35.00%), respectively. The regions in Zhejiang province showed large seasonal differences. The difference value between the maximum value of ρ(PM2.5) in the northwest and the lowest value in the southeast was 21.0 µg·m-3 and 20.5 µg·m-3 in autumn and winter, respectively; the difference values in spring and summer were 10.4 µg·m-3 and 6.1 µg·m-3. Thus, the northern air mass had a certain exogenous contribution to PM2.5 in autumn and winter in Zhejiang province. However, with the weakening of the northern air mass trajectory in spring and summer and the increasing contribution of the southern and east China Sea air mass to the air flow in Zhejiang province, PM2.5 pollution showed a trend of improvement.