Atomic-level differences between brain parenchymal- and cerebrovascular-seeded Aß fibrils.

Alzheimer's disease is characterized by neuritic plaques, the main protein components of which are ß-amyloid (Aß) peptides deposited as ß-sheet-rich amyloid fibrils. Cerebral Amyloid Angiopathy (CAA) consists of cerebrovascular deposits of Aß peptides; it usually accompanies Alzheimer's disease, though it sometimes occurs in the absence of neuritic plaques, as AD also occurs without accompanying CAA. Although neuritic plaques and vascular deposits have similar protein compositions, one of the characteristic features of amyloids is polymorphism, i.e., the ability of a single pure peptide to adopt multiple conformations in fibrils, depending on fibrillization conditions. For this reason, we asked whether the Aß fibrils in neuritic plaques differed structurally from those in cerebral blood vessels. To address this question, we used seeding techniques, starting with amyloid-enriched material from either brain parenchyma or cerebral blood vessels (using meninges as the source). These amyloid-enriched preparations were then added to fresh, disaggregated solutions of Aß to make replicate fibrils, as described elsewhere. Such fibrils were then studied by solid-state NMR, fiber X-ray diffraction, and other biophysical techniques. We observed chemical shift differences between parenchymal vs. vascular-seeded replicate fibrils in select sites (in particular, Ala2, Phe4, Val12, and Gln15 side chains) in two-dimensional 13C-13C correlation solid-state NMR spectra, strongly indicating structural differences at these sites. X-ray diffraction studies also indicated that vascular-seeded fibrils displayed greater order than parenchyma-seeded fibrils in the "side-chain dimension" (~ 10 Å reflection), though the "hydrogen-bond dimensions" (~ 5 Å reflection) were alike. These results indicate that the different nucleation conditions at two sites in the brain, parenchyma and blood vessels, affect the fibril products that get formed at each site, possibly leading to distinct pathophysiological outcomes.

Functional Grading of a Transversely Isotropic Hyperelastic Model with Applications in Modeling Tricuspid and Mitral Valve Transition Regions.

Surgical simulators and injury-prediction human models require a combination of representative tissue geometry and accurate tissue material properties to predict realistic tool-tissue interaction forces and injury mechanisms, respectively. While biological tissues have been individually characterized, the transition regions between tissues have received limited research attention, potentially resulting in inaccuracies within simulations. In this work, an approach to characterize the transition regions in transversely isotropic (TI) soft tissues using functionally graded material (FGM) modeling is presented. The effect of nonlinearities and multi-regime nature of the TI model on the functional grading process is discussed. The proposed approach has been implemented to characterize the transition regions in the leaflet (LL), chordae tendinae (CT) and the papillary muscle (PM) of porcine tricuspid valve (TV) and mitral valve (MV). The FGM model is informed using high resolution morphological measurements of the collagen fiber orientation and tissue composition in the transition regions, and deformation characteristics predicted by the FGM model are numerically validated to experimental data using X-ray diffraction imaging. The results indicate feasibility of using the FGM approach in modeling soft-tissue transitions and has implications in improving physical representation of tissue deformation throughout the body using a scalable version of the proposed approach.

Ultrastructural Location and Interactions of the Immunoglobulin Receptor Binding Sequence within Fibrillar Type I Collagen.

Collagen type I is a major constituent of animal bodies. It is found in large quantities in tendon, bone, skin, cartilage, blood vessels, bronchi, and the lung interstitium. It is also produced and accumulates in large amounts in response to certain inflammations such as lung fibrosis. Our understanding of the molecular organization of fibrillar collagen and cellular interaction motifs, such as those involved with immune-associated molecules, continues to be refined. In this study, antibodies raised against type I collagen were used to label intact D-periodic type I collagen fibrils and observed with atomic force microscopy (AFM), and X-ray diffraction (XRD) and immunolabeling positions were observed with both methods. The antibodies bind close to the C-terminal telopeptide which verifies the location and accessibility of both the major histocompatibility complex (MHC) class I (MHCI) binding domain and C-terminal telopeptide on the outside of the collagen fibril. The close proximity of the C-telopeptide and the MHC1 domain of type I collagen to fibronectin, discoidin domain receptor (DDR), and collagenase cleavage domains likely facilitate the interaction of ligands and receptors related to cellular immunity and the collagen-based Extracellular Matrix.

Advanced Methodology and Preliminary Measurements of Molecular and Mechanical Properties of Heart Valves under Dynamic Strain.

Mammalian heart valves are soft tissue assemblies with multi-scale material properties. This is because they are constructs comprising both muscle and non-contractile extracellular matrix proteins (such as collagens and proteoglycans) and transition regions where one form of tissue structure becomes another, significantly different form. The leaflets of the mitral and tricuspid valves are connected to chordae tendinae which, in turn, bind through papillary muscles to the cardiac wall of the ventricle. The transition regions between these tissue subsets are complex and diffuse. Their material composition and mechanical properties have not been previously described with both micro and nanoscopic data recorded simultaneously, as reported here. Annotating the mechanical characteristics of these tissue transitions will be of great value in developing novel implants, improving the state of the surgical simulators and advancing robot-assisted surgery. We present here developments in multi-scale methodology that produce data that can relate mechanical properties to molecular structure using scanning X-ray diffraction. We correlate these data to corresponding tissue level (macro and microscopic) stress and strain, with particular emphasis on the transition regions and present analyses to indicate points of possible failure in these tissues.

A structural prospective for collagen receptors such as DDR and their binding of the collagen fibril.

The structure of the collagen fibril surface directly effects and possibly assists the management of collagen receptor interactions. An important class of collagen receptors, the receptor tyrosine kinases of the Discoidin Domain Receptor family (DDR1 and DDR2), are differentially activated by specific collagen types and play important roles in cell adhesion, migration, proliferation, and matrix remodeling. This review discusses their structure and function as it pertains directly to the fibrillar collagen structure with which they interact far more readily than they do with isolated molecular collagen. This prospective provides further insight into the mechanisms of activation and rational cellular control of this important class of receptors while also providing a comparison of DDR-collagen interactions with other receptors such as integrin and GPVI. When improperly regulated, DDR activation can lead to abnormal cellular proliferation activities such as in cancer. Hence how and when the DDRs associate with the major basis of mammalian tissue infrastructure, fibrillar collagen, should be of keen interest.

X-ray diffraction reveals blunt-force loading threshold for nanoscopic structural change in ex vivo neuronal tissues.

An ex vivo blunt-force loading experiment is reported that may, in the future, provide insight into the molecular structural changes occurring in load-induced conditions such as traumatic brain injury (TBI). TBI appears to manifest in changes in multiple structures and elements within the brain and nervous system. Individuals with a TBI may suffer from cognitive and/or behavioral impairments which can adversely affect their quality of life. Information on the injury threshold of tissue loading for mammalian neurons is critical in the development of a quantified neuronal-level dose-response model. Such a model could aid in the discovery of enhanced methods for TBI detection, treatment and prevention. Currently, thresholds of mechanical load leading to direct force-coupled nanostructural changes in neurons are unknown. In this study, we make use of the fact that changes in the structure and periodicity of myelin may indicate neurological damage and can be detected with X-ray diffraction (XRD). XRD allows access to a nanoscopic resolution range not readily achieved by alternative methods, nor does the experimental methodology require chemical sample fixation. In this study, XRD was used to evaluate the affects of controlled mechanical loading on myelin packing structure in ex vivo optic nerve samples. By using a series of crush tests on isolated optic nerves a quantified baseline for mechanical load was found to induce changes in the packing structure of myelin. To the authors' knowledge, this is the first report of its kind.

Asymmetric Dimethylarginine does not Predict Early Access Events in Hemodialysis Patients with Brachiocephalic Fistula Access.

BACKGROUND: Vascular access for hemodialysis is best provided by an arteriovenous fistula (AVF). AVF fail primarily because of neointimal hyperplasia. Asymmetric dimethlyarginine (ADMA) is a naturally occurring analogue of L-arginine, which is elevated in renal failure and impairs endothelial cell function. ADMA inhibits nitric oxide synthetase, leading to impaired nitric oxide production and contributing to the development of neointimal hyperplasia. ADMA was measured at the time of AVF placement to evaluate associations with access failure. METHODS: ADMA was measured at the time of brachiocephalic access placement. Patients were followed for up to 12 months with end-points of access thrombosis or venous stenosis. RESULTS: Sixty patients with primary brachiocephalic fistulas were included in the study cohort. The median value for ADMA drawn at the time of AVF creation was 3.1 µmol/L. ADMA was not significantly associated with early thrombosis or venous stenosis events (P>0.05). CONCLUSION: Preoperative ADMA levels, as a surrogate for endothelial cell dysfunction and predictor of adverse access event (thrombosis or stenosis), were not associated with subsequent access events Future studies that identify markers of endothelial cell dysfunction are warranted.

Molecular and ultrastructural studies of a fibrillar collagen from octocoral (Cnidaria).

We report here the biochemical, molecular and ultrastructural features of a unique organization of fibrillar collagen extracted from the octocoral Sarcophyton ehrenbergi Collagen, the most abundant protein in the animal kingdom, is often defined as a structural component of extracellular matrices in metazoans. In the present study, collagen fibers were extracted from the mesenteries of S. ehrenbergi polyps. These fibers are organized as filaments and further compacted as coiled fibers. The fibers are uniquely long, reaching an unprecedented length of tens of centimeters. The diameter of these fibers is 9±0.37 µm. The amino acid content of these fibers was identified using chromatography and revealed close similarity in content to mammalian type I and II collagens. The ultrastructural organization of the fibers was characterized by means of high-resolution microscopy and X-ray diffraction. The fibers are composed of fibrils and fibril bundles in the range of 15 to 35 nm. These data indicate a fibrillar collagen possessing structural aspects of both types I and II collagen, a highly interesting and newly described form of fibrillar collagen organization.

Morphometric and histological parameters in veins of diabetic patients undergoing brachiocephalic fistula placement.

Diabetic patients with end-stage renal failure have higher rates of arteriovenous failures when compared with nondiabetics. The aim was to compare differences in indicators of vascular remodeling and endothelial dysfunction in veins of patients with or without diabetes at the time of surgical placement. In this prospective observational trial, vein samples were collected from patients when a brachiocephalic fistula was created. Morphometric measurements and extent of fibrosis were determined using Image J software. Histological analysis, for the presence of myofibroblasts and level of endothelial nitric oxide synthase, was performed by immunohistochemical staining and scored in semi-quantitative manner. Asymmetric dimethylarginine was determined at the time of access placement. Comparison of diabetics and nondiabetics was performed using Wilcoxon rank sum and Fisher's exact tests. Eighteen patients were included; 10 were diabetics. There was a significant difference in the measurement of vein area between groups, with diabetic vein samples having larger luminal area of average 832,001.18 µm(2) (317,582.17-3,695,670.36, P = 0.04). The maximal intimal to medial thickness ratio was higher in diabetic vein samples (0.71 vs. 0.24, P = 0.03) along with statistically significant higher maximal intimal thickness (312.12 vs. 115.14 µm, P = 0.03). There is a significant difference in vascular wall remodeling between diabetics and nondiabetics at the level of the cephalic vein at the time of brachiocephalic placement. The unexpected finding of significantly larger luminal area in diabetic veins could be a major factor positively affecting brachiocephalic outcomes in otherwise impaired remodeling in this patient population.