Effect of position-specific single-point mutations and biophysical characterization of amyloidogenic peptide fragments identified from lattice corneal dystrophy patients.

Corneal stromal dystrophies are a group of genetic disorders that may be caused by mutations in the transforming growth factor ß-induced (TGFBI) gene which results in the aggregation and deposition of mutant proteins in various layers of the cornea. The type of amino acid substitution dictates the age of onset, anatomical location of the deposits, morphological features of deposits (amyloid, amorphous powder or a mixture of both forms) and the severity of disease presentation. It has been suggested that abnormal turnover and aberrant proteolytic processing of the mutant proteins result in the accumulation of insoluble protein deposits. Using mass spectrometry, we identified increased abundance of a 32 amino acid-long peptide in the 4th fasciclin-like domain-1 (FAS-1) domain of transforming growth factor ß-induced protein (amino acid 611-642) in the amyloid deposits of the patients with lattice corneal dystrophies (LCD). In vitro studies demonstrated that the peptide readily formed amyloid fibrils under physiological conditions. Clinically relevant substitution (M619K, N622K, N622H, G623R and H626R) of the truncated peptide resulted in profound changes in the kinetics of amyloid formation, thermal stability of the amyloid fibrils and cytotoxicity of fibrillar aggregates, depending on the position and the type of the amino acid substitution. The results suggest that reduction in the overall net charge, nature and position of cationic residue substitution determines the amyloid aggregation propensity and thermal stability of amyloid fibrils.

The familial Alzheimer's disease APPV717I mutation alters APP processing and Tau expression in iPSC-derived neurons.

Alzheimer's disease (AD) is a complex neurodegenerative disorder characterized by extracellular plaques containing amyloid ß (Aß)-protein and intracellular tangles containing hyperphosphorylated Tau protein. Here, we describe the generation of inducible pluripotent stem cell lines from patients harboring the London familial AD (fAD) amyloid precursor protein (APP) mutation (V717I). We examine AD-relevant phenotypes following directed differentiation to forebrain neuronal fates vulnerable in AD. We observe that over differentiation time to mature neuronal fates, APP expression and levels of Aß increase dramatically. In both immature and mature neuronal fates, the APPV717I mutation affects both ß- and γ-secretase cleavage of APP. Although the mutation lies near the γ-secretase cleavage site in the transmembrane domain of APP, we find that ß-secretase cleavage of APP is elevated leading to generation of increased levels of both APPsß and Aß. Furthermore, we find that this mutation alters the initial cleavage site of γ-secretase, resulting in an increased generation of both Aß42 and Aß38. In addition to altered APP processing, an increase in levels of total and phosphorylated Tau is observed in neurons with the APPV717I mutation. We show that treatment with Aß-specific antibodies early in culture reverses the phenotype of increased total Tau levels, implicating altered Aß production in fAD neurons in this phenotype. These studies use human neurons to reveal previously unrecognized effects of the most common fAD APP mutation and provide a model system for testing therapeutic strategies in the cell types most relevant to disease processes.

Hierarchical mechanisms build the DNA-binding specificity of FUSE binding protein.

The far upstream element (FUSE) binding protein (FBP), a single-stranded nucleic acid binding protein, is recruited to the c-myc promoter after melting of FUSE by transcriptionally generated dynamic supercoils. Via interactions with TFIIH and FBP-interacting repressor (FIR), FBP modulates c-myc transcription. Here, we investigate the contributions of FBP's 4 K Homology (KH) domains to sequence selectivity. EMSA and missing contact point analysis revealed that FBP contacts 4 separate patches spanning a large segment of FUSE. A SELEX procedure using paired KH-domains defined the preferred subsequences for each KH domain. Unexpectedly, there was also a strong selection for the noncontacted residues between these subsequences, showing that the contact points must be optimally presented in a backbone that minimizes secondary structure. Strategic mutation of contact points defined in this study disabled FUSE activity in vivo. Because the biological specificity of FBP is tuned at several layers: (i) accessibility of the site; (ii) supercoil-driven melting; (iii) presentation of unhindered bases for recognition; and (iv) modular interaction of KH-domains with cognate bases, the FBP-FIR system and sequence-specific, single-strand DNA binding proteins in general are likely to prove versatile tools for adjusting gene expression.

GAGA factor and the TFIID complex collaborate in generating an open chromatin structure at the Drosophila melanogaster hsp26 promoter.

The upstream regulatory region of the Drosophila melanogaster hsp26 gene includes two DNase I-hypersensitive sites (DH sites) that encompass the critical heat shock elements. This chromatin structure is required for heat shock-inducible expression and depends on two (CT)n*(GA)n elements bound by GAGA factor. To determine whether GAGA factor alone is sufficient to drive formation of the DH sites, we have created flies with an hsp26/lacZ transgene wherein the entire DNA segment known to interact with the TFIID complex has been replaced by a random sequence. The replacement results in a loss of heat shock-inducible hsp26 expression and drastically diminishes nuclease accessibility in the chromatin of the regulatory region. Chromatin immunoprecipitation experiments show that the decrease in TFIID binding does not reduce GAGA factor binding. In contrast, the loss of GAGA factor binding resulting from (CT)n mutations decreases TFIID binding. These data suggest that both GAGA factor and TFIID are necessary for formation of the appropriate chromatin structure at the hsp26 promoter and predict a regulatory mechanism in which GAGA factor binding precedes and contributes to the recruitment of TFIID.

Clinical predictors of length of stay in adults with congenital heart disease.

OBJECTIVE: Length of stay (LOS) is a major driver of inpatient care costs. To date, few studies have investigated risk factors associated with increased LOS in patients with adult congenital heart disease (ACHD). In the present work, we sought to address this knowledge gap. METHODS: We conducted an analysis of the State Inpatient Databases from Arkansas, California, Florida, Hawaii, Nebraska and New York. We analysed data on admissions in patients with ACHD and constructed a series of hierarchical regression models to identify the clinical factors having the greatest effects on LOS. RESULTS: We identified 99 103 inpatient hospitalisations meeting criteria for inclusion. Diagnoses associated with the longest LOS were septicaemia (LOS=14.2 days in patients atrial septal defect, and 11.7 days among all other ACHD) and pericarditis, endocarditis and myocarditis (LOS=13.6 days and 10.0 days, respectively). When separated by underlying anatomy, the variables most consistently associated with longer LOS were bacterial infection, complications of surgeries or medical care, acute renal disease and anaemia. CONCLUSIONS: In the present study, we identified risk factors associated with longer LOS in ACHD. These data may be used to identify at-risk patients for targeted intervention to decrease LOS and thereby cost.

Contemporary Hospitalization Rate Among Adults With Complex Congenital Heart Disease.

BACKGROUND: Adults with congenital heart disease are hospitalized at increasing rates in the Western world. Identification of rates of and risk factors for hospitalization is essential for research and improving patient outcomes. METHODS: We conducted a single-center retrospective analysis of patients with a primary diagnosis of tetralogy of Fallot (TOF), transposition of the great arteries (both d- and l-transposition of the great arteries [TGAs]), or single ventricle (SV). We investigated the rates of mortality, annual hospitalization, and patient-specific risk factors for unplanned cardiac hospitalization. RESULTS: Adult patients with complex congenital heart disease are hospitalized at a rate four to eight times greater than the general US population (P < .001). In addition, there are significant differences between the rates of hospitalization in TOF and TGA (0.39 and 0.41 hospitalizations per patient-year, respectively) and SV (0.72 hospitalizations per patient-year). The majority of excess hospitalizations in the study group were due to cardiac disease (P < .001 for all three groups). Risk factors for unplanned cardiac hospitalization in TOF included pulmonary atresia, depressed left ventricular and right ventricular ejection fraction, and smoking; in TGA, they included Ebstein malformation, surgeries other than primary repair, noncardiac diagnoses, atrial arrhythmias, atrioventricular nodal block, left ventricular ejection fraction, and smoking; and in SV, they included atrial arrhythmias and cyanosis. CONCLUSIONS: Patients born with complex congenital heart disease are hospitalized far more frequently than the general US population, primarily for cardiac-related illness. Future research should focus on confirming the present findings and on identification of strategies to improve outcomes in this growing group of patients.

Predicative Factors for Corneal Endothelial Cell Migration.

PURPOSE: To characterize the effects of Descemet's stripping, Rho-associated protein kinase inhibitor Y-27632, and donor age on endothelial migration in human corneas maintained in ex vivo culture. METHODS: Twenty-eight cadaveric human corneas underwent ex vivo culture in either standard or Y-27632-supplemented culture medium for 14 days. The posterior surface of each cornea was manipulated to create two types of wounds: scratched wound--corneal endothelial cells (CECs) were denuded from the Descemet's membrane (DM) to leave behind a bare but intact DM; and peeled wound--both the DM and overlying CECs were stripped to leave behind bare corneal stroma. Endothelial migration was assessed via Trypan blue staining. Morphologic traits of CECs were assessed via Alizarin red microscopy and scanning electron microscopy. RESULTS: The CECs migrated preferentially over scratched wounds compared with peeled wounds. Y-27632 supplementation accelerated endothelial migration over scratched wounds. Endothelial migration decreased with advanced donor age for both wound types, regardless of exposure to Y-27632. Y-27632 supplementation resulted in a less rapid decline in endothelial migration for donors older than 50 years of age for scratched surfaces. Greater cell density and hexagonality was observed over scratched wounds compared with peeled wounds, regardless of Y-27632 supplementation. CONCLUSIONS: The presence of an intact DM, Y-27632 supplementation, and young donor age are factors that promote endothelial migration in an ex vivo human cornea culture model. The negative effect of age on endothelial migration can be mitigated by the presence of an intact DM and Y-27632 supplementation.

NELF and DSIF cause promoter proximal pausing on the hsp70 promoter in Drosophila.

NELF and DSIF collaborate to inhibit elongation by RNA polymerase IIa in extracts from human cells. A multifaceted approach was taken to investigate the potential role of these factors in promoter proximal pausing on the hsp70 gene in Drosophila. Immunodepletion of DSIF from a Drosophila nuclear extract reduced the level of polymerase that paused in the promoter proximal region of hsp70. Depletion of one NELF subunit in salivary glands using RNA interference also reduced the level of paused polymerase. In vivo protein-DNA cross-linking showed that NELF and DSIF associate with the promoter region before heat shock. Immunofluorescence analysis of polytene chromosomes corroborated the cross-linking result and showed that NELF, DSIF, and RNA polymerase IIa colocalize at the hsp70 genes, small heat shock genes, and many other chromosomal locations. Finally, following heat shock induction, DSIF and polymerase but not NELF were strongly recruited to chromosomal puffs harboring the hsp70 genes. We propose that NELF and DSIF cause polymerase to pause in the promoter proximal region of hsp70. The transcriptional activator, HSF, might cause NELF to dissociate from the elongation complex. DSIF continues to associate with the elongation complex and could serve a positive role in elongation.