Biomedical subjects

Jun Chen

Publications and source records attributed to Jun Chen.

At least 19 recordsLinked to original sources

PubMed2026

Prognostic value and immune landscape implications of using a novel homologous recombination repair pathway signature in prostate cancer: A retrospective cohort study.

ObjectiveAlthough the homologous recombination repair (HRR) pathway plays a critical role in the treatment of prostate cancer, its prognostic value remains incompletely understood. This study aimed to identify HRR pathway-related biomarkers with clinical utility for prognosis prediction and treatment guidance.MethodsWe analyzed genomic data from The Cancer Genome Atlas and Chinese patients with prostate cancer in a retrospective cohort study using a comprehensive multiomics approach to characterize a novel HRR-related prognostic signature and its immune implications.ResultsIn the Chinese cohort, 25.6% of the patients exhibited homologous recombination deficiency scores >42, whereas 27.3% carried ≥1 HRR gene mutation. We established a prognostic HRR signature (homologous recombination deficiency score >32, HRR gene mutations, and Signature 3) associated with poor outcomes. Compared with The Cancer Genome Atlas data, the Chinese cohort demonstrated a higher prevalence of HRR signature. Patients with HRR signatures demonstrated significantly increased genomic instability markers, including segment number, alteration burden, aneuploidy score, and intratumor heterogeneity. The HRR signature was associated with higher neoantigen load but reduced T cell receptor (TCR) evenness. Immunologically, HRR-positive tumors were associated with computationally inferred immune profiles suggestive of reduced immune activity, characterized by depletion of T-helper 17 cell; downregulation of TLR4/PDCD1LG2 expression; and upregulation of ARG1, IFNG, KIR2DL3, and CXCL9. However, these findings are descriptive and require experimental validation.ConclusionOur findings identify a clinically relevant HRR signature that warrants investigation as a potential predictive biomarker for prostate cancer prognosis and treatment response. This biomarker provides new insights for personalized therapy and may help optimize patient outcomes.

Humans↗

PubMed2026

Comprehensive evaluation of new sequencer T20 and well-established T7 with 507 human samples.

The DNBSEQ-T20×2 (T20) sequencer, developed by MGI Tech, enables cost-effective human whole-genome sequencing (WGS) at 30× coverage for less than $100 per genome. Here, we evaluate the sequencing performance and data quality of the T20 platform by benchmarking it against the established DNBSEQ-T7 (T7) sequencer using 507 samples derived from blood (N = 75), stool (N = 242), and saliva (N = 190). The T20 exhibited lower sequencing quality metrics compared with the T7, with Q20 scores of 95.76%-95.83% and Q30 scores of 87.25%-87.40%, compared with 97.81%-97.93% and 93.26%-93.60%, respectively, for T7 data. Quality differences were more evident toward the end of reads, and PCR-free libraries sequenced on the T20 showed similar reductions in quality scores. The median empirical base error rate estimated from 102 ZymoBIOMICS samples was 0.33%. The T20 demonstrated comparable coverage uniformity to the T7 and showed high concordance in microbiome composition analysis, with a median Bray-Curtis dissimilarity of 0.02. Variant calling performance was highly consistent between the two platforms. Among variants with non-missing genotype calls on both platforms, 94.92% of SNPs and 87.20% of InDels showed concordant genotypes between T20 and T7. Overall, the T20 delivers reliable sequencing accuracy and reproducibility for large-scale genomic and microbiome studies, providing a cost-effective alternative for high-throughput sequencing applications.

Metagenomics↗

PubMed2026

Nrsn1-Smarcc1 Coupling Regulates Neural Stem Cell Differentiation and Chronic-phase Recovery After Ischemic Stroke.

Stroke remains a leading cause of long-term neurological disability worldwide, largely due to irreversible neuronal loss and the limited regenerative capacity of the adult mammalian brain. Neural stem cells (NSCs) in the adult brain possess the potential to generate new neurons after injury, yet the molecular mechanisms regulating their neuronal differentiation following ischemic insult remain incompletely understood. Here, integrating single-cell multi-omics analyses with spatial transcriptomics, we systematically delineated cell type-specific spatiotemporal dynamics in the striatum of a mouse model of ischemia-reperfusion injury. We identified Neurensin 1 (Nrsn1) as a gene markedly upregulated during NSC-derived neuronal differentiation in the recovery phase. Mechanistically, Foxa2 directly activates Nrsn1 transcription, whereas Nrsn1 promotes neuronal differentiation by facilitating the nuclear translocation of the chromatin-remodeling factor Smarcc1 in vitro. In vivo, both endogenous NSCs and transplanted NSCs overexpressing Nrsn1 significantly enhanced neuronal regeneration and improved functional recovery in mice subjected to middle cerebral artery occlusion and reperfusion (MCAO/R). Collectively, these findings identify Nrsn1 as a key regulator of NSC neuronal differentiation and uncover a Nrsn1-Smarcc1 coupling mechanism that promotes neural regeneration after ischemic brain injury, highlighting a potential molecular target for strategies aimed at enhancing post-stroke recovery.

Foxa2↗

PubMed2026

Stage shift, histological differentiation, and survival patterns of lung squamous cell carcinoma versus adenocarcinoma in low-dose CT screening.

BACKGROUND: Whether LDCT-associated stage shift translates into similar survival patterns across lung cancer histologies remains uncertain. We compared stage shift, histological differentiation, tumor characteristics, and survival between lung squamous cell carcinoma (LUSC) and adenocarcinoma (LUAD) in the National Lung Screening Trial. METHODS: Among participants diagnosed with LUSC or LUAD, stage distribution and histological differentiation were compared between LDCT and chest X-ray (CXR) arms. Survival among diagnosed cases was measured from randomization. Multivariable models tested screening arm-by-histology interactions. Screen-detected LDCT tumors were compared by histology. RESULTS: During 6.5 years of median follow-up, 498 LUAD and 249 LUSC cases were diagnosed in the LDCT arm, and 374 and 212, respectively, were diagnosed in the CXR arm. LDCT was associated with higher odds of stage I disease for LUAD (adjusted odds ratio [aOR], 2.48; 95% CI 1.88-3.28) and LUSC (aOR, 1.71; 95% CI 1.17-2.48), without significant interaction (P = 0.116). LDCT was associated with lower hazard of lung cancer-specific death among diagnosed LUAD cases (adjusted hazard ratio [aHR], 0.54; 95% CI 0.43-0.66), but not among diagnosed LUSC cases (aHR, 1.04; 95% CI 0.78-1.39; P for interaction<0.001). LUSC had lower screening sensitivity, more frequent detection in annual screening rounds, greater prediagnostic tumor size increase, and fewer well-differentiated stage I tumors than LUAD. CONCLUSION: LDCT was associated with stage shift for both subtypes, but favorable survival patterns among diagnosed cases were mainly observed for LUAD. Lower screening sensitivity, greater prediagnostic tumor size increase, and poorer histological differentiation may help explain why stage shift did not translate into similar survival patterns for LUSC. TRIAL REGISTRATION: ClinicalTrials.gov, NCT00047385.

Humans↗

PubMed2026

Recombinant Human Thrombopoietin Reduces the Need for Platelet Transfusion in Patients With Chronic Liver Disease and Thrombocytopenia.

Chronic liver disease (CLD)-related thrombocytopenia can limit the feasibility of invasive procedures. Recombinant human thrombopoietin (rhTPO) has demonstrated a favorable safety profile without hepatotoxicity. We evaluated the efficacy and safety of rhTPO in patients with CLD-related thrombocytopenia who were undergoing elective invasive procedures. In this multicenter, randomized (2:1), double-blind, placebo-controlled phase III trial, 120 adult Chinese patients with CLD-related thrombocytopenia (platelet count < 50 × 109/L) received rhTPO (n = 80) or placebo (n = 40) once daily for up to 5 or 7 days. The primary endpoint was the proportion of patients with sustained platelet counts ≥ 50 × 109/L from 24 h before invasive procedure to 7 days post-procedure, without requiring emergency bleeding management. The primary endpoint was achieved by 85.0% of patients in the rhTPO group versus 12.5% in the placebo group (p < 0.0001). Preoperatively, platelet counts ≥ 50 × 109/L were achieved in 92.5% and 20.0% of patients in the rhTPO and placebo groups, respectively (p < 0.0001). Platelet transfusion was avoided in 92.5% of rhTPO-treated patients versus 25.0% of placebo-treated patients (p < 0.0001). The median duration of platelet counts ≥ 50 × 109/L was significantly longer with rhTPO than with placebo (21.0 vs. 3.0 days, p = 0.0007). Treatment-related treatment-emergent adverse events (TEAEs) occurred in 12.5% of patients in both the rhTPO and placebo groups. No treatment-related serious adverse events were reported. Overall, rhTPO was effective and well tolerated in patients with CLD-related thrombocytopenia and may represent a viable therapeutic option for those undergoing elective invasive procedures. Trial Registration: www.chinadrugtrials.org.cn: number CTR20230919.

Humans↗

PubMed2026

Safety and efficacy of recombinant botulinum toxin type A (Eveotox®) in patients with post-stroke upper limb spasticity: Results from a Phase Ib/II clinical trial.

Upper limb spasticity is a common and disabling complication of stroke. Botulinum toxin type A (BoNT-A) is widely used for focal spasticity treatment, but naturally derived products may present limitations related to immunogenicity and manufacturing variability. Recombinant botulinum toxin type A, produced by genetic engineering without complexing proteins, may provide improved product consistency. This Ib/II study evaluated the safety, tolerability, and preliminary efficacy of recombinant botulinum toxin type A in adults with post-stroke upper limb spasticity. This multicenter, seamless Ib/II clinical study included an open-label dose-escalation Ib phase and a randomized, double-blind, placebo-controlled II phase. Adult patients with post-stroke upper limb spasticity received a single intramuscular injection of recombinant botulinum toxin type A or placebo. The primary endpoint in Phase II was the change from baseline in the Modified Ashworth Scale (MAS) score of the primary target muscle group at Week 4. Secondary endpoints included MAS and Tardieu scale changes in individual muscle groups, Disability Assessment Scale (DAS), Physician's Global Assessment (PGA), and immunogenicity. The Ib phase showed improvements in MAS, DAS, and PGA, indicating an early efficacy signal. In Phase II, recombinant botulinum toxin type A produced a significant reduction in MAS score of the primary target muscle group at Week 4 compared with placebo, with effects sustained through Week 12. At Week 4, the PGA score in the Eveotox® group showed a statistically significant improvement compared with the placebo group. While MAS and PGA scores showed significant improvement, DAS functional scores did not differ statistically from the placebo group at week 4. The treatment was generally well tolerated, and low incidence of antibodies were observed. Recombinant botulinum toxin type A was safe and effective in reducing post-stroke upper limb spasticity after a single administration. These results support further Phase III clinical evaluation.

Humans↗

PubMed2025

Plasma metabolites mediate the causal relationship between gut microbiota and erectile dysfunction: insights from Mendelian randomization study.

BACKGROUND: While the relationship between gut microbiota and erectile dysfunction (ED) has been reported, the specific pathways involved remain unclear. AIM: This study aims to investigate the causal relationship between gut microbiota and ED, and to identify the potential role of plasma metabolites as mediators. METHODS: Utilizing aggregated genome-wide association study (GWAS) data, a comprehensive two-sample Mendelian randomization (MR) analysis was performed involving 196 gut microbiota taxa, 1400 plasma metabolites and ED. Causal relationships between gut microbiota, plasma metabolites and ED were explored. In addition, mediation analysis was applied to identify the pathway from gut microbiota to ED mediated by plasma metabolites. OUTCOMES: This study reveals that plasma metabolites act as mediators regulating the influence of gut microbiota on ED. RESULTS: MR analysis identified causal relationships between six gut microbial taxa and ED, with Butyrivibrio increasing the risk of ED, while Alistipes, Prevotella 9, Dialister, Marvinbryantia, and LachnospiraceaeUCG010 exhibited protective effects. Additionally, 45 plasma metabolites demonstrated causal associations with ED. Finally, mediation analysis revealed four mediation relationships. Sensitivity analysis indicated no heterogeneity or pleiotropy in this study. CLINICAL IMPLICATIONS: Modulating gut microbiota or targeting specific metabolites may offer new therapeutic approaches for ED, highlighting the potential for microbiome-based interventions. STRENGTHS AND LIMITATIONS: The MR approach and large-scale GWAS data provide robust causal evidence, but the findings are limited by their focus on European populations and lack of experimental validation. Further studies are needed to confirm these mechanisms in diverse cohorts and functional models. CONCLUSION: This study establishes a causal link between gut microbiota, plasma metabolites, and ED, identifying specific microbial taxa and metabolites as key contributors to ED risk. The mediating role of plasma metabolites highlights potential therapeutic strategies, such as probiotics or dietary interventions targeting harmful metabolites.

Mendelian randomization↗

PubMed2025

Composition-on-composition regression analysis for multi-omics integration of metagenomic data.

MOTIVATION: Compositional data are frequently encountered in many disciplines, such as in next-generation sequencing experiments widely used in biomedical studies. Regression analysis with compositional data as either responses or predictors has been well studied. However, when both responses and predictors are compositional, the inventory of analysis tools is surprisingly limited, especially in the high-dimensional setting. Among the few existing methods, most of them rely on a log-ratio transformation to move compositional data from the simplex to real numbers. Yet, a serious weakness of these methods is their failure to handle the substantial fraction of zeroes observed in data collected from next-generation sequencing experiments. RESULTS: To investigate associations between two high-dimensional multi-omics compositions, we propose a composition-on-composition (COC) regression analysis method which does not require log-ratio transformations and hence can handle zeroes in the data. To account for high dimensionality, we estimate regression coefficients using a penalized estimation equation approach. Finally, inference procedures for COC regression are also proposed. Superior performance of COC is demonstrated through both comprehensive numerical simulations and case studies. AVAILABILITY AND IMPLEMENTATION: Source R codes to implement COC method is available at https://github.com/nrios4/COC.

Regression Analysis↗

PubMed2025

Exploring biosynthetic potential of the endophytic Penicillium turbatum BLH34 using whole-genome sequence analysis and molecular networking.

An in-depth genomic and metabolomic investigation was conducted on the endophytic fungus Penicillium turbatum BLH34, isolated from Macleaya cordata. Hybrid sequencing (Illumina-Nanopore) generated a high-quality 27.9 Mb genome (GC 48.6%) encoding 9798 proteins, with functional annotation linking 5350 genes to the NCBI non-redundant database and 3404 to KEGG pathways. AntiSMASH analysis uncovered 35 biosynthetic gene clusters (BGCs), 23 of which lacked homology to known pathways, highlighting BLH34's potential for novel metabolite discovery. Molecular networking (GNPS) and LC-MS/MS identified 19 specialised metabolites, including antimicrobial polyketides. Bioassays demonstrated potent inhibition against Staphylococcus aureus (36 mm), Bacillus subtilis (28 mm) and Escherichia coli (24 mm), underscoring its pharmaceutical relevance.

Penicillium↗

PubMed2025

The R203M and D377Y mutations of the nucleocapsid protein promote SARS-CoV-2 infectivity by impairing RIG-I-mediated antiviral signaling.

The viral protein mutations can modify virus-host interactions during virus evolution, and thus alter the extent of infection or pathogenicity. Studies indicate that nucleocapsid (N) protein of SARS-CoV-2 participates in viral genome assembly, intracellular signal regulation and immune interference. However, its biological function in viral evolution is not well understood. SARS-CoV-2 N protein mutations were analyzed in Delta, Omicron, and original strains. Two mutations with a methionine (M) residue at site 203 and a tyrosine (Y) residue at site 377 of the N protein were found in Delta strain but not in Omicron and original strains, and promoted SARS-CoV-2 infection therein. Those mutations, R203M and D377Y, enhanced the inhibitory impact of N protein on the impairment of RIG-I-mediated antiviral signaling, such as IRF3 phosphorylation and IFN-β activation. The viral RNA-binding activity of N protein was promoted by these mutations, effectively attenuating the recognition and interaction of RIG-I with viral RNA compared to the original or other variants. The R203M/D377Y mutations thus enhanced the suppressive activity of the N protein on RIG-I-mediated interferon induction both in vitro and in vivo, which in turn promoted viral replication. This study helps to understand the variability of SARS-CoV-2 in regulating host immunity.

SARS-CoV-2↗

PubMed2024

L3MBTL1, a polycomb protein, promotes Osimertinib acquired resistance through epigenetic regulation of DNA damage response in lung adenocarcinoma.

Osimertinib is a third-generation epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor (EGFR-TKI) approved for patients with EGFR T790M resistance mutations as first- or second-line treatment of EGFR-positive patients. Resistance to Osimertinib will inevitably develop, and the underlying mechanisms are largely unknown. In this study, we discovered that acquired resistance to Osimertinib is associated with abnormal DNA damage response (DDR) in lung adenocarcinoma cells. We discovered that the polycomb protein Lethal(3) Malignant Brain Tumor-Like Protein 1 (L3MBTL1) regulates chromatin structure, thereby contributing to DDR and Osimertinib resistance. EGFR oncogene inhibition reduced L3MBTL1 ubiquitination while stabilizing its expression in Osimertinib-resistant cells. L3MBTL1 reduction and treatment with Osimertinib significantly inhibited DDR and proliferation of Osimertinib-resistant lung cancer cells in vitro and in vivo. L3MBTL1 binds throughout the genome and plays an important role in EGFR-TKI resistance. It also competes with 53BP1 for H4K20Me2 and inhibits the development of drug resistance in Osimertinib-resistant lung cancer cells in vitro and in vivo. Our findings suggest that L3MBTL1 inhibition is a novel approach to overcoming EGFR-TKI-acquired resistance.

Humans↗

PubMed2024

Risk relationship between inflammatory bowel disease and urolithiasis: A two-sample Mendelian randomization study.

BACKGROUND: The causal genetic relationship between common parenteral manifestations of inflammatory bowel disease (IBD) and urolithiasis remains unclear because their timing is difficult to determine. This study investigated the causal genetic association between IBD and urolithiasis using Mendelian randomization (MR) based on data from large population-based genome-wide association studies (GWASs). METHODS: A two-sample MR analysis was performed to assess the potential relationship between IBD and urolithiasis. Specific single nucleotide polymorphism data were obtained from GWASs, including IBD (n = 59957) and its main subtypes, Crohn's disease (CD) (n = 40266) and ulcerative colitis (UC) (n = 45975). Summarized data on urolithiasis (n = 218792) were obtained from different GWAS studies. A random-effects model was analyzed using inverse-variance weighting, MR-Egger, and weighted medians. RESULTS: Genetic predisposition to IBD and the risk of urolithiasis were significantly associated [odds ratio (OR), 1.04 (95% confidence interval [CI], 1.00-.08), P = 0.01]. Consistently, the weighted median method yielded similar results [OR, 1.06 (95% CI, 1.00-1.12), P = 0.02]. The MR-Egger method also demonstrated comparable findings [OR, 1.02 (95% CI, 0.96-1.08), P = 0.45]. Both funnel plots and MR-Egger intercepts indicated no directional pleiotropic effects between IBD and urolithiasis. CD was strongly associated with it in its subtype analysis [OR, 1.04 (95% CI, 1.01-1.07), P = 0.01], and UC was also causally associated with urolithiasis, although the association was not significant [OR, 0.99 (95% CI, 0.95-1.03), P = 0.71]. CONCLUSION: A unidirectional positive causal correlation was identified between IBD and urolithiasis, with varying degrees of association observed among the different subtypes of IBD. Recognizing the increased incidence of urolithiasis in patients with IBD is crucial in clinical practice. Early detection and surveillance of IBD, improved patient awareness, adoption of preventive strategies, and promotion of collaborative efforts among healthcare providers regarding treatment methodologies are vital for improving patient outcomes.

Humans↗

PubMed2007

Chromium accumulation by the hyperaccumulator plant Leersia hexandra Swartz.

Leersia hexandra Swartz (Gramineae), which occurs in Southern China, has been found to be a new chromium hyperaccumulator by means of field survey and pot-culture experiment. The field survey showed that this species had an extraordinary accumulation capacity for chromium. The maximum Cr concentration in the dry leaf matter was 2978 mg kg(-1) on the side of a pond near an electroplating factory. The average concentration of chromium in the leaves was 18.86 times as that in the pond sediment, and 297.41 times as that in the pond water. Under conditions of the nutrient solution culture, it was found that L. hexandra had a high tolerance and accumulation capacity to Cr(III) and Cr(VI). Under 60 mg l(-1) Cr(III) and 10 mg l(-1) Cr(VI) treatment, there was no significant decrease of biomass in the leaves of L. hexandra (p>0.05). The highest bioaccumulation coefficients of the leaves for Cr(III) and Cr(VI) were 486.8 and 72.1, respectively. However, L. hexandra had a higher accumulation capacity for Cr(III) than for Cr(VI). At the Cr(III) concentration of 10 mg l(-1) in the culture solution, the concentration of chromium in leaves was 4868 mg kg(-1), while at the same Cr(VI) concentration, the concentration of chromium in leaves was only 597 mg kg(-1). These results confirmed that L. hexandra is a chromium hyperaccumulator which grows rapidly with a great tolerance to Cr and broad ecological amplitude. This species could provide a new plant resource that explores the mechanism of Cr hyperaccumulation, and has potential for usage in the phytoremediation of Cr-contaminated soil and water.

Biodegradation, Environmental↗

PubMed2007

T-cell protein tyrosine phosphatase, distinctively expressed in activated-B-cell-like diffuse large B-cell lymphomas, is the nuclear phosphatase of STAT6.

Diffuse large B-cell lymphomas (DLBCLs) consist of clinically distinct subtypes: germinal center B-cell (GCB)-like and activated-B-cell (ABC)-like tumors, characterized by long and short survival, respectively. We reported distinct interleukin 4 (IL-4) responsiveness and STAT6 signaling in these DLBCL subtypes. Increased nuclear dephosphorylation of phospho-STAT6 (pSTAT6) was observed in ABC-like tumors, which exhibited a different expression profile of protein tyrosine phosphatases (PTPs). Among the differentially expressed PTPs, only T-cell PTP (TCPTP) localizes to the nucleus. Herein, we report that the elevated expression of TCPTP in ABC- versus GCB-like DLBCL tumors is not due to the distinct ontogeny of these neoplasms but rather may be an acquired feature of the tumors. Moreover, we report that STAT6 may serve as a physiological nuclear substrate for TCPTP. We demonstrate interactions between endogenous TCPTP and STAT6 and delineate the domains responsible for the interaction. Overexpression of TCPTP ameliorates IL-4-induced STAT6 phosphorylation and associated gene transcription, whereas knockdown of endogenous TCPTP results in increased IL-4-induced STAT6 signaling. Moreover, we report that TCPTP protein levels may be increased in response to IL-4 and that TCPTP may serve in a negative feedback loop for the suppression of IL-4-induced signaling. Taken together, these results identify TCPTP as a physiological regulator of STAT6 phosphorylation and suggest that specific increases in TCPTP expression in ABC-like DLBCLs may contribute to the different biological characteristics of these tumors.

Catalytic Domain↗

PubMed2007

Mild hypothermia diminishes oxidative DNA damage and pro-death signaling events after cerebral ischemia: a mechanism for neuroprotection.

Mild hypothermia, applied either during or soon after cerebral ischemia, has been shown to confer robust neuroprotection against brain injury in experimental stroke and in patients recovering from cardiac arrest. However, the mechanism underlying hypothermic neuroprotection is not completely understood. In this study, the effect of mild hypothermia on the induction of oxidative DNA damage, an early harmful event during post-ischemic reperfusion that triggers both necrotic and apoptotic cell death in the brain, was studied using the rat model of middle cerebral artery occlusion (MCAO) and reperfusion. Rats were subjected to 2-hr MCAO and reperfusion of various durations up to 3 days. Selective brain hypothermia (33 degrees C) was induced at the onset of ischemia and terminated at the beginning of reperfusion, and this significantly decreased infarct volume 72 hr later. Correlated with this protective effect, intraischemic mild hypothermia markedly attenuated the nuclear accumulations of several oxidative DNA lesions, including 8-oxodG, AP sites, and DNA single-strand breaks, after 2-hr MCAO. Consequently, harmful DNA damage-dependent signaling events, including NAD depletion, p53 activation, and mitochondrial translocation of PUMA and NOXA, were reduced during post-ischemic reperfusion in hypothermia-treated brains. These results suggest that the attenuation of oxidative DNA damage and DNA damage-triggered pro-death signaling events may be an important mechanism underlying the neuroprotective effect of mild hypothermia against ischemic brain injury.

Animals↗

PubMed2007

Impaired DNA repair via the base-excision repair pathway after focal ischemic brain injury: a protein phosphorylation-dependent mechanism reversed by hypothermic neuroprotection.

Cerebral ischemia and reperfusion induces rapid accumulation of oxidative DNA lesions in the brain, which, if not repaired promptly, may trigger cell death. The base-excision repair (BER) pathway is the main mechanism employed by neurons to repair various types of oxidative DNA damage. Recent studies have suggested that the cellular activity of BER is highly regulated (up- or down-regulated) after ischemic brain injury, and this regulation may contribute to the outcome of cell injury. The mechanism through which cellular BER is regulated in response to neuronal injury is currently poorly understood. In the present study, we have examined BER regulation in the rat model of focal ischemic brain injury induced by 2 hr of middle cerebral artery occlusion and 0-72 hr of reperfusion. As determined using cerebral nuclear extracts, focal ischemia resulted in a marked reduction in BER activities, including the overall BER activity, AP endonuclease activity and DNA polymerase-beta activity, indicating functional impairment of the BER pathway. BER reduction occurred as early as 0.5 hr after the onset of reperfusion. Thereafter, BER activity failed to recover, and there were persistent accumulations of apurinic/apyrimidinic abasic sites and DNA single-strand breaks in ischemic tissues. The reduction in BER during the early reperfusion phase (less than 6 hr) was not accompanied by any alterations in the levels of essential BER enzymes in brain extracts. However, increased serine- and threonine-specific phosphorylation was detected for both AP endonuclease and DNA polymerase-beta after ischemia, with the time course of serine phosphorylation closely correlated to that of changes in BER activity. Furthermore, dephosphorylation of nuclear extracts with alkaline phosphatase largely restored AP endonuclease and DNA polymerase-beta activities. Taking advantage of the neuroprotective effect of mild hypothermia (33 degrees C), which was induced in the brain during the first 2 hr of reperfusion, we found that the post-ischemic suppression of BER activity is a reversible event. Hypothermic treatment diminished the serine-specific phosphorylation of AP endonuclease and DNA polymerase-beta, promoted BER activities, and attenuated the levels of oxidative DNA lesions after ischemia. These results suggest that the functional impairment of the BER pathway after severe focal cerebral ischemia is due to the loss-of-function post-translational modifications of repair enzymes. Further investigations elucidating the precise mechanism underlying the post-translational regulation of BER enzymes may lead to novel therapeutic strategies for cerebral ischemia.

Animals↗

PubMed2006

Time-resolved photoluminescence characteristics of subnanometer ZnO clusters confined in the micropores of zeolites.

Subnanometric ZnO clusters confined in different micropore zeolites are studied by steady-state and nanosecond time-resolved photoluminescence (PL) spectroscopy. The microsecond-scale lifetime is observed at room temperature for ZnO clusters confined in zeolites, which is significantly different from that of macrocrystalline ZnO on the external surface of zeolites. The dependence of luminescence lifetime on the amount of ZnO in zeolites indicates that the electron-phonon interactions between the ZnO clusters and the zeolite host significantly affect the dynamic relaxation process of ZnO clusters. The long lifetime luminescence of ZnO clusters can be achieved by weakening the coupling of electronic transition to zeolites host phonons. The similar long-lived luminescence is obtained when dispersing ZnO clusters into the porous SiO2. It is suggested that encapsulating the semiconductor cluster in the porous support is a possible way to inhibit or to retard the electron-hole recombination.

Journal Article↗

PubMed2006

Synthesis, characterization, and electrochemical properties of Ag2V4O11 and AgVO3 1-D nano/microstructures.

We report on the synthesis, characterization, and electrochemical properties of Ag(2)V(4)O(11) nanowires, alpha-AgVO(3) microrods, and beta-AgVO(3) nanowires that were synthesized through a simple and facile low-temperature hydrothermal approach without any template or catalyst. It was found that by simply controlling the hydrothermal reaction parameters such as pH and dwell time, the transformation of alpha-AgVO(3) microrods to beta-AgVO(3) nanowires were readily achieved through a "ripening-splitting model" mechanism. Electrochemical measurements revealed that the as-prepared Ag(2)V(4)O(11) nanowires, alpha-AgVO(3) microrods, and beta-AgVO(3) nanowires exhibited high discharge capacities and excellent high-rate dischargeability. In particular, the beta-AgVO(3) nanowires have much higher capacity above 3 V than that of alpha-AgVO(3) microrods, Ag(2)V(4)O(11) nanowires, and commercial Ag(2)V(4)O(11) bulk. The mechanisms for electrochemical lithium intercalation of the AgVO(3) nanostructures were also discussed. It is anticipated that the novel Ag(2)V(4)O(11) and AgVO(3) one-dimensional nano/microstructures are promising cathode candidates in the application of primary lithium ion batteries for implantable cardioverter defibrillators (ICDs).

Journal Article↗