The occludin and ZO-1 complex, defined by small angle X-ray scattering and NMR, has implications for modulating tight junction permeability

Tight junctions (TJs) are dynamic cellular structures that are critical for compartmentalizing environments within tissues and regulating transport of small molecules, ions, and fluids. Phosphorylation-dependent binding of the transmembrane protein occludin to the structural organizing protein ZO-1 contributes to the regulation of barrier properties; however, the details of their interaction are controversial. Using small angle X-ray scattering (SAXS), NMR chemical shift perturbation, cross-saturation, in vitro binding, and site-directed mutagenesis experiments. we define the interface between the ZO-1 PDZ3-SH3-U5-GuK (PSG) and occludin coiled-coil (CC) domains. The interface is comprised of basic residues in PSG and an acidic region in CC. Complex formation is blocked by a peptide (REESEEYM) that corresponds to CC residues 468-475 and includes a previously uncharacterized phosphosite, with the phosphorylated version having a larger effect. Furthermore, mutation of E470 and E472 reduces cell border localization of occludin. Together, these results localize the interaction to an acidic region in CC and a predominantly basic helix V within the ZO-1 GuK domain. This model has important implications for the phosphorylation-dependent regulation of the occludin:ZO-1 complex.     

Complexity of chromatin folding is captured by the strings and binders switch model

Chromatin has a complex spatial organization in the cell nucleus that serves vital functional purposes. A variety of chromatin folding conformations has been detected by single-cell imaging and chromosome conformation capture-based approaches. However, a unified quantitative framework describing spatial chromatin organization is still lacking. Here, we explore the “strings and binders switch” model to explain the origin and variety of chromatin behaviors that coexist and dynamically change within living cells. This simple polymer model recapitulates the scaling properties of chromatin folding reported experimentally in different cellular systems, the fractal state of chromatin, the processes of domain formation, and looping out. Additionally, the strings and binders switch model reproduces the recently proposed “fractal–globule” model, but only as one of many possible transient conformations.     

Evaluation of an anorganic bovine-derived mineral with P-15 hydrogel bone graft: preliminary study in a rabbit cranial bone model

Objectives: The present investigation aimed to assess the bone‐regenerative potential of two formulations of anorganic bovine‐derived mineral bound to a P‐15 (ABM/P‐15) bone graft – the particulate and the hydrogel forms – in a delayed healing rabbit cranial defect model. Material and methods: Ten adult male New Zealand White rabbits were used to create two 8 mm transcortical cranial defects per rabbit and each one received randomly the test material (ABM/P‐15 carboxymethyl cellulose (CMC)‐hydrogel graft), the standard control material (ABM/P‐15 particulate graft) or remained empty as a negative control. The defects were allowed to heal for 2 and 4 weeks. Qualitative and quantitative histological outcomes were assessed on undecalcified sections. Results: In the defects grafted with the test material, at both time points, there was a marked random migration of the bone substitute particles. As a consequence, the space maintenance provision was lost and new bone formation was reduced compared with the control particulate graft material. The histomorphometric analysis showed that the control material attained better results, with an average of 13.8 ± 1.9% and 18.2 ± 4.4% of new bone at 2 and 4 weeks, compared with 8.5 ± 2.4% and 13 ± 2.9% for the test material. These differences were significant at 2 weeks (P≤0.05), but not at 4 weeks (P>0.05). Additionally, there was a significant difference in the total area of mineralized tissue (new bone plus particles), favoring the standard control over the test material: 43.2 ± 14.4% vs. 14.2 ± 5.3% at 2 weeks and 56.9 ± 4.2% vs. 24.2 ± 9.6% at 4 weeks, respectively. Conclusions: The test ABM/P‐15 CMC‐hydrogel graft material behaved in this animal model by migration of the graft particles, what determined an unpredictable osseoconduction and, consequently, a decreased quality and quantity of bone regeneration as compared with the osseopromotive behavior exhibited by the standard particulate form of the ABM/P‐15 control graft. It is therefore suggested to restrain the application of the hydrogel graft form in non‐contained anatomical bone defects.     

Collagen cross-linking but not collagen amount associates with elevated filling pressures in hypertensive patients with stage C heart failure: potential role of lysyl oxidase

We investigated whether the quality of myocardial collagen associates with elevated left-sided filling pressures in 38 hypertensive patients with stage C chronic heart failure. Filling pressures were assessed invasively measuring pulmonary capillary wedge pressure. Left ventricular chamber stiffness constant was calculated from the deceleration time of the early mitral filling wave. The fraction of myocardial volume occupied by total collagen tissue and collagen type I fibers was assessed histomorphologically. The degree of collagen cross-linking (CCL), which determines the formation of insoluble stiff collagen, was assessed by colorimetric and enzymatic procedures. The expression of lysyl oxidase (LOX), which regulates CCL, was assessed by Western blot. Compared with patients with normal pulmonary capillary wedge pressure (≤12 mm Hg; n=16), patients with elevated pulmonary capillary wedge pressure (>12 mm Hg; n=22) exhibited increases of left ventricular chamber stiffness constant, fraction of myocardial volume occupied by total collagen tissue, fraction of myocardial volume occupied by collagen type I fibers, CCL, insoluble stiff collagen, and LOX. Pulmonary capillary wedge pressure was correlated with left ventricular chamber stiffness constant (r=0.639; P<0.001), insoluble stiff collagen (r=0.474; P<0.005), CCL (r=0.625; P<0.001), and LOX (r=0.410; P<0.05) in all of the patients but not with fraction of myocardial volume occupied by total collagen tissue or fraction of myocardial volume occupied by collagen type I fibers. In addition, CCL was correlated with insoluble stiff collagen (r=0.612; P<0.005), LOX (r=0.538; P<0.01), left ventricular chamber stiffness constant (r=0.535; P<0.005), peak filling rate (r=-0.343; P<0.05), ejection fraction (r=-0.430; P<0.01), and amino-terminal propeptide of brain natriuretic peptide (r=0.421; P<0.05) in all of the patients. These associations were independent of confounding factors. These findings indicate that, in hypertensive patients with stage C heart failure, it is only the quality of collagen (ie, degree of cross-linking) that associates with elevated filling pressures. It is suggested that LOX-mediated excessive CCL facilitates the increase in left ventricular stiffness with the resulting elevation of filling pressures in these patients.     

Red blood cell distribution width adds prognostic value for outpatients with chronic heart failure

Introduction and objectives

Red blood cell distribution width has emerged as a new prognostic biomarker in cardiovascular diseases. Its additional value in risk stratification of patients with chronic heart failure has not yet been established.

Methods

A total of 698 consecutive outpatients with chronic heart failure were studied (median age 71 years [interquartile range, 62-77], 63% male, left ventricular ejection fraction 40 [14]%). On inclusion, the red cell distribution width was measured and clinical, biochemical, and echocardiographic variables were recorded. The median follow-up period was 2.5 years [interquartile range 1.2-3.7].

Results

A total of 211 patients died and 206 required hospitalization for decompensated heart failure. Kaplan-Meier analysis showed an increase in the probability of death and hospitalization for heart failure with red cell distribution width quartiles (log rank, P<.001). A ROC analysis identified a red cell distribution width of 15.4% as the optimal cut-off point for a significantly higher risk of death (P<.001; hazard ratio=2.63; 95% confidence interval, 2.01-3.45) and hospitalization for heart failure (P<.001; hazard ratio=2.37; 95% confidence interval, 1.80-3.13). This predictive value was independent of other covariates, and regardless of the presence or not of anaemia. Importantly, the addition of red cell distribution width to the clinical risk model for the prediction of death or hospitalization for heart failure at 1 year had a significant integrated discrimination improvement of 33% (P<.001) and a net reclassification improvement of 10.3% (P=.001).

Conclusions

Red cell distribution width is an independent risk marker and adds prognostic information in outpatients with chronic heart failure. These findings suggest that this biological measurement should be included in the management of these patients.Full English text available from:www.revespcardiol.org