NO signaling and S-nitrosylation regulate PTEN inhibition in neurodegeneration

<p>Abstract</p> <p>Background</p> <p>The phosphatase PTEN governs the phosphoinositide 3-kinase (PI3K)/Akt signaling pathway which is arguably the most important pro-survival pathway in neurons. Recently, PTEN has also been implicated in multiple important CNS functions such as neuronal differentiation, plasticity, injury and drug addiction. It has been reported that loss of PTEN protein, accompanied by Akt activation, occurs under excitotoxic conditions (stroke) as well as in Alzheimer's (AD) brains. However the molecular signals and mechanism underlying PTEN loss are unknown.</p> <p>Results</p> <p>In this study, we investigated redox regulation of PTEN, namely S-nitrosylation, a covalent modification of cysteine residues by nitric oxide (NO), and H₂O₂-mediated oxidation. We found that S-nitrosylation of PTEN was markedly elevated in brains in the early stages of AD (MCI). Surprisingly, there was no increase in the H₂O₂-mediated oxidation of PTEN, a modification common in cancer cell types, in the MCI/AD brains as compared to normal aged control. Using several cultured neuronal models, we further demonstrate that S-nitrosylation, in conjunction with NO-mediated enhanced ubiquitination, regulates both the lipid phosphatase activity and protein stability of PTEN. S-nitrosylation and oxidation occur on overlapping and distinct Cys residues of PTEN. The NO signal induces PTEN protein degradation via the ubiquitin-proteasome system (UPS) through NEDD4-1-mediated ubiquitination.</p> <p>Conclusion</p> <p>This study demonstrates for the first time that NO-mediated redox regulation is the mechanism of PTEN protein degradation, which is distinguished from the H₂O₂-mediated PTEN oxidation, known to only inactivate the enzyme. This novel regulatory mechanism likely accounts for the PTEN loss observed in neurodegeneration such as in AD, in which NO plays a critical pathophysiological role.</p

Critical role of ASCT2-mediated amino acid metabolism in promoting leukaemia development and progression

Amino acid (AA) metabolism is involved in diverse cellular functions, including cell survival and growth, however it remains unclear how it regulates normal hematopoiesis versus leukemogenesis. Here, we report that knockout of Slc1a5 (ASCT2), a transporter of neutral AAs, especially glutamine, results in mild to moderate defects in bone marrow and mature blood cell development under steady state conditions. In contrast, constitutive or induced deletion of Slc1a5 decreases leukemia initiation and maintenance driven by the oncogene MLL-AF9 or Pten deficiency. Survival of leukemic mice is prolonged following Slc1a5 deletion, and pharmacological inhibition of ASCT2 also decreases leukemia development and progression in xenograft models of human acute myeloid leukemia. Mechanistically, loss of ASCT2 generates a global effect on cellular metabolism, disrupts leucine influx and mTOR signaling, and induces apoptosis in leukemic cells. Given the substantial difference in reliance on ASCT2-mediated AA metabolism between normal and malignant blood cells, this in vivo study suggests ASCT2 as a promising therapeutic target for the treatment of leukemia

Prolonged drought regulates the silage quality of maize (Zea mays L.): Alterations in fermentation microecology

Prolonged drought stress caused by global warming poses a tremendous challenge to silage production of maize. Drought during maize growth and development resulted in altered micro-environment for silage fermentation. How fermentation of silage maize responds to moisture scales remains uncharted territory. In this research, Maize water control trials were conducted and the silage quality and microbial community of drought-affected maize were determined. The results showed that drought stress significantly reduced the dry matter but increased root-to-shoot ratio, soluble sugar and malonaldehyde content in maize. Before fermentation, the crude protein, crude ash and acid detergent fiber contents were significantly increased but the ether extract content was decreased under drought. The crude protein and acid detergent fiber were significantly decreased in the drought affected group after fermentation. Furthermore, water stress at maize maturity stage greatly reduced the number of total bacteria in silage fermentation but increased the proportion of the lactobacillus and lactic acid content of silage. Drought stress alters the microbial ecosystem of the fermentation process and reconstitutes the diversity of the bacterial community and its metabolites. This study provides a theoretical basis for the study of changes in silage fermentation as affected by abiotic stresses

Anatomic predictor of severe prosthesis malposition following transcatheter aortic valve replacement with self- expandable Venus-A Valve among pure aortic regurgitation: A multicenter retrospective study

BackgroundTranscatheter aortic valve replacement (TAVR) in the treatment of patients with pure native aortic valve regurgitation (NAVR) has been based on the “off-label” indications, while the absence of aortic valve calcification and difficulty in anchoring was found to significantly increase the risk of prosthesis malposition. The aim of this study was to explore the anatomical predictors of severe prosthesis malposition following TAVR with the self-expandable Venus-A Valve among patients with NAVR.MethodsA total of 62 patients with NAVR who underwent TAVR with Venus-A Valve at four Chinese clinical centers were retrospectively observed. The clinical features, aortic multidetector computed tomography (MDCT) data, and clinical outcomes were compared between non-/mild malposition and severe malposition groups. Univariate logistic regression analysis was used to identify the risk factors of severe prosthesis malposition, and the receiver operating characteristic (ROC) curve was used to explore the predictive value of the risk factors.ResultsValve migration to ascending aortic direction occurred in 1 patient, and the remaining 61 patients (including 19 severe malposition cases and 42 non-/mild malposition cases) were included in the analysis. The diameter and height of the sinotubular junction (STJ) and STJ cover index (STJCI, calculated as 100%*STJ diameter/nominal prosthesis crown diameter) were all greater in the severe malposition group (all p &lt; 0.05). Logistic regression showed that STJ diameter (OR = 1.23, 95% CI 1.04–1.47, p = 0.017), STJ height (OR = 1.24, 95% CI 1.04–1.47, p = 0.017), and STJCI (OR = 1.08, 95% CI 1.01–1.16, p = 0.032) were potential predictors for severe prosthesis malposition. The area under the ROC curve was 0.72 (95% CI 0.58–0.85, p = 0.008) for STJ diameter, 0.70 (95% CI 0.55–0.86, p = 0.012) for STJ height, and 0.69 (95% CI 0.55–0.83, p = 0.017) for STJCI, respectively. The cutoff value was 33.2 mm for STJ diameter (sensitivity was 84.2% and specificity was 65.8%), 24.1 mm for STJ height (sensitivity was 57.9% and specificity was 87.8%), and 81.0% for STJCI (sensitivity was 68.4% and specificity was 68.3%), respectively.ConclusionLarger and higher STJ, as well as greater STJ to valve crown diameter ratio, may help identify patients at high risk for severe prosthesis malposition among patients with NAVR undergoing TAVR with Venus-A prosthesis valve