LIN28 coordinately promotes nucleolar/ribosomal functions and represses the 2C-like transcriptional program in pluripotent stem cells

LIN28 is an RNA binding protein with important roles in early embryo development, stem cell differentiation/reprogramming, tumorigenesis and metabolism. Previous studies have focused mainly on its role in the cytosol where it interacts with Let-7 microRNA precursors or mRNAs, and few have addressed LIN28's role within the nucleus. Here, we show that LIN28 displays dynamic temporal and spatial expression during murine embryo development. Maternal LIN28 expression drops upon exit from the 2-cell stage, and zygotic LIN28 protein is induced at the forming nucleolus during 4-cell to blastocyst stage development, to become dominantly expressed in the cytosol after implantation. In cultured pluripotent stem cells (PSCs), loss of LIN28 led to nucleolar stress and activation of a 2-cell/4-cell-like transcriptional program characterized by the expression of endogenous retrovirus genes. Mechanistically, LIN28 binds to small nucleolar RNAs and rRNA to maintain nucleolar integrity, and its loss leads to nucleolar phase separation defects, ribosomal stress and activation of P53 which in turn binds to and activates 2C transcription factor Dux. LIN28 also resides in a complex containing the nucleolar factor Nucleolin (NCL) and the transcriptional repressor TRIM28, and LIN28 loss leads to reduced occupancy of the NCL/TRIM28 complex on the Dux and rDNA loci, and thus de-repressed Dux and reduced rRNA expression. Lin28 knockout cells with nucleolar stress are more likely to assume a slowly cycling, translationally inert and anabolically inactive state, which is a part of previously unappreciated 2C-like transcriptional program. These findings elucidate novel roles for nucleolar LIN28 in PSCs, and a new mechanism linking 2C program and nucleolar functions in PSCs and early embryo development.

Metformin activates chaperone-mediated autophagy and improves disease pathologies in an Alzheimer disease mouse model

Chaperone-mediated autophagy (CMA) is a lysosome-dependent selective degradation pathway implicated in the pathogenesis of cancer and neurodegenerative diseases. However, the mechanisms that regulate CMA are not fully understood. Here, using unbiased drug screening approaches, we discover Metformin, a drug that is commonly the first medication prescribed for type 2 diabetes, can induce CMA. We delineate the mechanism of CMA induction by Metformin to be via activation of TAK1-IKKα/β signaling that leads to phosphorylation of Ser85 of the key mediator of CMA, Hsc70, and its activation. Notably, we find that amyloid-beta precursor protein (APP) is a CMA substrate and that it binds to Hsc70 in an IKKα/β-dependent manner. The inhibition of CMA-mediated degradation of APP enhances its cytotoxicity. Importantly, we find that in the APP/PS1 mouse model of Alzheimer's disease (AD), activation of CMA by Hsc70 overexpression or Metformin potently reduces the accumulated brain Aβ plaque levels and reverses the molecular and behavioral AD phenotypes. Our study elucidates a novel mechanism of CMA regulation via Metformin-TAK1-IKKα/β-Hsc70 signaling and suggests Metformin as a new activator of CMA for diseases, such as AD, where such therapeutic intervention could be beneficial.

Changes of bacterial spectrum and drug resistance in patients with posttraumatic bone infection / 中华创伤杂志

Objective To investigate the bacterial spectrum and drug resistance of bone infection after multiple hospitalizations.Methods A retrospective case series study was conducted on 95 patients with bone infection due to injuries admitted in the General Hospital of Shenyang Military Area from January 2009 to December 2016.There were 76 males and 34 females,with an average age of 47 years (range,17-94 years).Bacterial culture and drug sensitivity tests were performed in 246 specimens of the infection secretions and infected tissues.The bacterial species and drug resistance data of all the specimens were statistically analyzed.The numbers and ratios of Gram-positive bacteria and Gram negative bacteria were counted according to the changes of hospitalization frequency,and the changes of drug resistance of Staphylococcus aureus after repeated hospitalizations were also recorded.Results A total of 110 pathogenic bacteria were isolated,and mixed infection was found in 19％ of the bacteria.There were 61 Gram-positive bacteria (55.5％),including 35 Staphylococcus aureus [seven methicillin-resistant staphylococcus (MRSA) strains],accounting for 57％ of Gram-positive strains.Other Gram positive bacteria were mainly Enterococcus faecalis and Staphylococcus epidermidis.There were 48 Gram-negative bacteria (43.6％),including 12 Pseudomonas aeruginosa strains,accounting for 25％ of Gram-negative strains,nine Klebsiella pneumoniae strains,accounting for 19％ of the Gramnegative strains.Staphylococcus aureus had a resistance rate to penicillin of 82％,and the major Gram positive bacteria (Staphylococcus aureus,Enterococcus faecalis,Staphylococcus epidermidis) were all highly sensitive to vancomycin and linezolid.The major Gram-negative bacteria (Pseudomonas aeruginosa,Klebsiella pneumoniae,Escherichia coli,Acinetobacter baumannii) were highly resistant to the second generation of cephalosporins and were sensitive to carbapenem antibiotics.In 95 bone infection patients,the ratio of Gram positive bacteria to Gram negative bacteria increased from 0.98 at the first admission to 3 after repeated hospitalizations,and the ratio change was statistically significant (P ＜0.05).After multiple hospitalizations,the drug resistance of Staphylococcus aureus to gentamicin,ciprofloxacin,levofloxacin,and tetracycline increased gradually.The resistance rate to penicillin was even up to 100％.Conclusions The mixed infection of bone infection is common,among which Staphylococcus aureus and Staphylococcus epidermidis are the main Gram-positive pathogenic bacteria,Pseudomonas aeruginosa and Klebsiella pneumoniae are the main Gram negative pathogenic bacteria.The proportion of Gram-positive bacteria infection increased after multiple hospitalizations and became the major pathogenic bacteria.Penicillin should be avoided in the treatment of Staphylococcus aureus infection in multiple hospitalizations,and gentamicin and ciprofloxacin should be used with caution.Vancomycin or linezolid which is more sensitive is a better option.

Clinical curative effect analysis of Masquelet technique for treatment of infected single-bone defect of forearm / 局解手术学杂志

Objective To evaluate the clinical curative effect of Masquelet technique in treatment of infected single-bone defect of forearm.Methods The clinical data of 18 cases of forearm bone defect caused by bone infection in our department from January 2011 to June 2016 were retrospectively analyzed.All the patients received standard treatment of Masquelet technique with two stage.Radical debridement,bone defect filling with antibiotic PMMA bone cement, and internal fixation were accomplished at the first stage, and treatment of bone defect with autologous iliac bone graft were accomplished at the second stage after 6 to 8 weeks at the end of the first stage.The infection control,fracture healing and complications of the 18 patients were observed.Results There was no complications such as infection recurrence,bone resorption,plate screw loosening occured.The functional recovery of 18 cases in this group was evaluated according to the Anderson evaluation scale.The results were excellent in 9 cases,satisfactory in 6 cases,unsatisfactory in 3 cases,and no failure.The satisfactory rate was 83.33%.Conclusion Controlling infection with local release of antibiotics from PMMA bone cement implantation through Masquelet technique, inducing autogenous membrane structure in the bone defect area,and then transplanting autologous cancellous bone for bone defect reconstruction repair treatment are effective in the treatment of infected single-bone defect of forearm.