Cardiac valves arise from endocardial cushions, specialized regions of the developing heart that are formed by an endothelial-to-mesenchymal cell transdifferentiation. Whether and to what extent this transdifferentiation is retained in mature heart valves is unknown. Herein we show that endothelial cells from mature valves can transdifferentiate to a mesenchymal phenotype. Using induction of alpha-smooth muscle actin (alpha-SMA), an established marker for this process, two distinct pathways of transdifferentiation were identified in clonally derived endothelial cell populations isolated from ovine aortic valve leaflets. alpha-SMA expression was induced by culturing clonal endothelial cells in medium containing either transforming growth factor-beta or low levels of serum and no basic fibroblast growth factor. Cells induced to express alpha-SMA exhibited markedly increased migration in response to platelet-derived growth factor-BB, consistent with a mesenchymal phenotype. A population of the differentiated cells co-expressed CD31, an endothelial marker, along with alpha-SMA, as seen by double-label immunofluorescence. Similarly, this co-expression of endothelial markers and alpha-SMA was detected in a subpopulation of cells in frozen sections of aortic valves, suggesting the transdifferentiation may occur in vivo. Hence, the clonal populations of valvular endothelial cells described here provide a powerful in vitro model for dissecting molecular events that regulate valvular endothelium.

Human AC133 antigen, also called CD133, was recently identified as a hematopoietic stem cell marker. However, the molecular structure and function of this protein has remained unclear. Here we cloned and identified a novel isoform of AC133, which we named AC133-2. In comparison to the reported AC133 cDNA, which is referred to herein as AC133-1, a small exon of 27 nucleotides is deleted in AC133-2 by alternative mRNA splicing. Similar to the previously characterized AC133 antigen, recombinant AC133-2 expressed in 293 cells was glycosylated and transported to plasma membrane. AC133-2 mRNA was found predominant in a variety of human fetal tissue, adult tissues, and several carcinomas. In contrast, AC133-1 mRNA was more prominent in fetal brain and adult skeletal muscle but was not detected in fetal liver and kidney, adult pancreas, kidney, and placenta, suggesting different roles for the two isoforms in fetal development and mature organ homeostasis. Here, we demonstrate that AC133-2 is the isoform expressed on hematopoietic stem cells derived from fetal liver, bone marrow, and peripheral blood. The results indicate that AC133-2, not AC133-1, has been the cell surface antigen recognized by anti-AC133 monoclonal antibodies that are used for isolation of hematopoietic stem cells. To further investigate its expression in other stem cell populations, we found that AC133-2 co-expressed with ␤ 1 integrin in the basal layer of human neonatal epidermis. AC133-2 ؉ /␤ 1 integrin ؉ cells proliferated and differentiated in culture, which coincided with a loss of AC133-2 and gain in a terminal differentiation marker involucrin. Taken together, these results suggest that AC133-2 is expressed in multiple stem cell niches and may provide a means to isolate specific stem cell subpopulations from human tissues.Human AC133 antigen is a glycoprotein with a molecular mass of ϳ120 kDa. Based on its predicted amino acid sequence, AC133 contains an extracellular N terminus, two large extracellular loops, five transmembrane domains, two small cysteine-rich cytoplasmic loops, and a cytoplasmic C terminus (1). AC133 antigen was first detected on CD34 bright hematopoietic stem cells using a monoclonal antibody (mAb) 1 named clone AC133 that was raised against human CD34 ϩ cells (2). AC133 antigen has since been widely used to facilitate the analysis and isolation of hematopoietic primitive cells (3-5). Subsequently, Peichev et al. (6) showed that endothelial progenitor cells co-express AC133 antigen and the endothelial cell-specific receptor kinase-insert domain-containing acceptor (KDR) in subpopulations of CD34 ϩ cells derived from fetal liver, bone marrow, cord blood, and peripheral blood (6, 7). Recently, human central nervous system stem cells were also reported to express AC133 antigen (8). A characteristic feature of this protein is its rapid down-regulation during cell differentiation (7, 9), which makes it a unique cell surface marker for the identification and isolation of stem cells and progenitor cells.A structural and sequence-r...

Objective To examine the accessibility of absolute risk in articles reporting ratio measures in leading medical journals. Participants 222 articles based on study designs in which absolute risks were directly calculable (61 randomised trials, 161 cohort studies). Main outcome measure Accessibility of the absolute risks underlying the first ratio measure in the abstract. Results 68% of articles (150/222) failed to report the underlying absolute risks for the first ratio measure in the abstract (range 55 − 81% across the journals). Among these articles, about half did report the underlying absolute risks elsewhere in the article (text, table, or figure) but half did not report them anywhere. Absolute risks were more likely to be reported in the abstract for randomised trials compared with cohort studies (62% v 21%; relative risk 3.0, 95% confidence interval 2.1 to 4.2) and for studies reporting crude compared with adjusted ratio measures (62% v 21%; relative risk 3.0, 2.1 to 4.3). Conclusion Absolute risks are often not easily accessible in articles reporting ratio measures and sometimes are missing altogether-this lack of accessibility can easily exaggerate readers' perceptions of benefit or harm.

Three-dimensional scaffolds made of bioabsorbable polymeric constituents are currently being tested for use in tissue engineering of various tissues. A composite scaffold of poly-glycolic acid (PGA) non-woven mesh dip-coated in a 1% solution of poly-4-hydroxybutyrate (P4HB) was shown to be suitable as a scaffold for creation of tissue-engineered trileaflet pulmonic valve replacements in sheep [Hoerstrup, S.P., et al., Circulation 102(Suppl. 3), III44, 2000]. However, little is known about how cells seeded on PGA/P4HB respond in vitro to soluble factors supplied in the culture medium. To optimize tissue development in vitro, before implantation, we set out to develop quantitative biochemical assays to measure how cells seeded on PGA/P4HB respond to growth and differentiation factors. Herein we show that ovine aortic valvular endothelial cells and circulating endothelial progenitor cells (EPCs) seeded onto PGA/P4HB proliferate in response to vascular endothelial growth factor and transdifferentiate to a mesenchymal phenotype in response to transforming growth factor beta(1). Transdifferentiation from an endothelial to mesenchymal phenotype is a critical step during embryonic development of cardiac valves. Our results demonstrate that valvular endothelial cells and EPCs isolated from peripheral blood can recapitulate critical developmental steps on PGA/P4HB. These results demonstrate that PGA/P4HB provides a conducive environment for cellular proliferation, differentiation, and tissue development.

Clinical practice guidelines do not recommend systemic steroids in the treatment of acute respiratory tract infections (ARTIs). 1 While some studies have shown earlier symptom resolution with steroids given for pharyngitis, 2 clinical trials show no efficacy of systemic steroids for sinusitis 3 and bronchitis. 4 Adverse events can develop within 30 days of short-term steroid use, which raises concern about the safety of systemic steroids for ARTIs. 5 We conducted the present study to examine the frequency of steroid use for ARTIs in Louisiana and nationally and to examine factors associated with this clinical practice. Methods | Study Settings and Populations. We conducted a retrospective observational study of adults who had outpatient ambulatory care encounters that included an ARTI diagnosis (otitis, upper respiratory infection, sinusitis, pharyngitis, bronchitis, allergic rhinitis, influenza, and pneumonia) through Ochsner Health System primary care clinics in 2014 ("Health System") and as reported in the National Ambulatory Medical Care Survey (NAMCS) in 2012 to 2013. Asthma and chronic obstructive pulmonary disease (COPD) encounter diagnoses were not Editor's Note page 854

Background Evidence and guidelines do not support use of systemic steroids for acute respiratory tract infections (ARTIs), but such practice appears common. We aim to quantify such use and determine its predictors. Methods and findings We conducted a cohort study based on a large United States national commercial claims database, the IBM MarketScan, to identify patients aged 18-64 years with an ARTI diagnosis (acute bronchitis, sinusitis, pharyngitis, otitis media, allergic rhinitis, influenza, pneumonia, and unspecified upper respiratory infections) recorded in ambulatory visits from 2007 to 2016. We excluded those with systemic steroid use in the prior year and an extensive list of steroid-indicated conditions, including asthma, chronic obstructive pulmonary disease, and various autoimmune diseases. We calculated the proportion receiving systemic steroids within 7 days of the ARTI diagnosis and determined its significant predictors. We identified 9,763,710 patients with an eligible ARTI encounter (mean age 39.6, female 56.0%) and found 11.8% were prescribed systemic steroids (46.1% parenteral, 47.3% oral, 6.6% both). All ARTI diagnoses but influenza predicted receiving systemic steroids. There was high geographical variability: the adjusted odds ratio (aOR) of receiving parenteral steroids was 14.48 (95% confidence interval [CI] 14.23-14.72, p < 0.001) comparing southern versus northeastern US. The corresponding aOR was 1.68 (95% CI 1.66-1.69, p < 0.001) for oral steroids. Other positive predictors for prescribing included emergency department (ED) or urgent care settings (versus regular office), otolaryngologist/ED doctors (versus primary care), fewer comorbidities, and older patient age. There was an increasing trend from 2007 to 2016 (aOR 1.93 [95% CI 1.91-1.95] comparing 2016 to 2007, p < 0.001). Our findings are

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