Multiscale modelling of Potts shunt as a potential palliative treatment for suprasystemic idiopathic pulmonary artery hypertension: a paediatric case study

Biomechanics and Modeling in Mechanobiology - Potts shunt (PS) was suggested as palliation for patients with suprasystemic pulmonary arterial hypertension (PAH) and right ventricular (RV) failure....     

Kinetics of basic fibroblast growth factor binding to its receptor and heparan sulfate proteoglycan: a mechanism for cooperactivity.

Basic fibroblast growth factor (bFGF) binds to cell surface receptor (CSR) proteins and to heparan sulfate proteoglycans (HSPG). On the basis of equilibrium dissociation constants (Kd), the CSR has been considered a "high-affinity" binding site and HSPG a "low-affinity" site. We measured the apparent individual on and off rate constants (kon and koff) for bFGF binding to these two sites on intact cells and to each class of binding site in the absence of the other. While the kon's for CSR and HSPG on intact cells were not statistically different (konC = 2.27 x 10(8) M-1 min-1; konH = 0.90 x 10(8) M-1 min-1), the koff for the HSPG was 22.7-fold greater than that for the CSR (koffC = 0.003 min-1; koffH = 0.68 min-1). Thus, the difference in Kd's appears to result from the faster rate at which bFGF is released from the HSPG sites compared to the CSR. The kon's for isolated CSR and HSPG, and the koff for isolated HSPG, did not differ significantly from those for intact cells konC = 2.50 x 10(8) M-1 min-1; konH = 0.92 x 10(8) M-1 min-1; koffH = 0.095 min-1). However, the off rate for isolated CSR (koffC = 0.048 min-1) was statistically indistinguishable from the off rate for HSPG and 16-fold greater than the off rate for CSR on intact cells. The "high-affinity" binding of bFGF to intact cells probably refers only to a complex of bFGF with both CSR and HSPG, and not to the CSR alone.     

'Sloughing-off' of heterochromatin in Werner's syndrome cells during high-temperature phosphate incubation

Previous investigations of cells undergoing rapid division revealed the presence of heterochromatic 'dots' in chromosomes as well as numerous chromocentres in interphase nuclei. Such structures were seen in human embryonic cells, as well as cells from organisms capable of regeneration, and cells from various malignancies. Cells with a reduced capacity for reproduction were found to be virtually devoid of nuclear chromocentres and chromosome dots after incubation in phosphate buffer at high temperature. The lack of heterochromatin in such cells (Werner's syndrome) thereby explained their reduced capacity for cell division and the resultant rapid rate of aging in individuals afflicted. Re-examination of such slides containing these cells revealed that chromocentres and chromosome dots were present initially, but the incubation process resulted in a 'sloughing-off' of such structures. The incubation process left these heterochromatic structures intact in malignant and control cells, inferring a link between cell proliferation and stable intact heterochromatin. These findings implicate heterochromatin as the object of the purported chromosomal instability factor characteristic of Werner's syndrome. The loss of heterochromatin did not result in chromosome breakage, suggesting that heterochromatin may not be an integral part of chromosome structure, but rather a surface feature or covering.     

Expression Profiling of a Genetic Animal Model of Depression Reveals Novel Molecular Pathways Underlying Depressive-Like Behaviours

Background

The Flinders model is a validated genetic rat model of depression that exhibits a number of behavioural, neurochemical and pharmacological features consistent with those observed in human depression.

Principal Findings

In this study we have used genome-wide microarray expression profiling of the hippocampus and prefrontal/frontal cortex of Flinders Depression Sensitive (FSL) and control Flinders Depression Resistant (FRL) lines to understand molecular basis for the differences between the two lines. We profiled two independent cohorts of Flinders animals derived from the same colony six months apart, each cohort statistically powered to allow independent as well as combined analysis. Using this approach, we were able to validate using real-time-PCR a core set of gene expression differences that showed statistical significance in each of the temporally distinct cohorts, representing consistently maintained features of the model. Small but statistically significant increases were confirmed for cholinergic (chrm2, chrna7) and serotonergic receptors (Htr1a, Htr2a) in FSL rats consistent with known neurochemical changes in the model. Much larger gene changes were validated in a number of novel genes as exemplified by TMEM176A, which showed 35-fold enrichment in the cortex and 30-fold enrichment in hippocampus of FRL animals relative to FSL.

Conclusions

These data provide significant insights into the molecular differences underlying the Flinders model, and have potential relevance to broader depression research.     

The influence of spatial pulsed magnetic field application on neuropathic pain after tibial nerve transection in rat

The purpose of the study was to examine the influence of the spatial variable magnetic field (induction: 150–300?µT, 80–150?µT, 20–80?µT; frequency 40?Hz) on neuropathic pain after tibial nerve transection. The experiments were carried out on 64 male Wistar C rats. The exposure of animals to magnetic field was performed 1?d/20?min., 5?d/week, for 28?d. Behavioural tests assessing the intensity of allodynia and sensitivity to mechanical and thermal stimuli were conducted 1?d prior to surgery and 3, 7, 14, 21 and 28?d after the surgery. The extent of autotomy was examined. Histological and immunohistochemical analysis was performed. The use of extremely low-frequency magnetic fields of minimal induction values (20–80?µT/40?Hz) decreased pain in rats after nerve transection. The nociceptive sensitivity of healthy rats was not changed following the exposition to the spatial magnetic field of the low frequency. The results of histological and immunohistochemical investigations confirm those findings. Our results indicate that extremely low-frequency magnetic field may be useful in the neuropathic pain therapy.     

Endosomal receptor kinetics determine the stability of intracellular growth factor signalling complexes

There is an emerging paradigm that growth factor signalling continues in the endosome and that cell response to a growth factor is defined by the integration of cell surface and endosomal events. As activated receptors in the endosome are exposed to a different set of binding partners, they probably elicit differential signals compared with when they are at the cell surface. As such, complete appreciation of growth factor signalling requires understanding of growth factor-receptor binding and trafficking kinetics both at the cell surface and in endosomes. Growth factor binding to surface receptors is well characterized, and endosomal binding is assumed to follow surface kinetics if one accounts for changes in pH. Yet, specific binding kinetics within the endosome has not been examined in detail. To parse the factors governing the binding state of endosomal receptors we analysed a whole-cell mathematical model of epidermal growth factor receptor trafficking and binding. We discovered that the stability of growth factor-receptor complexes within endosomes is governed by three primary independent factors: the endosomal dissociation constant, total endosomal volume and the number of endosomal receptors. These factors were combined into a single dimensionless parameter that determines the endosomal binding state of the growth factor-receptor complex and can distinguish different growth factors from each other and different cell states. Our findings indicate that growth factor binding within endosomal compartments cannot be appreciated solely on the basis of the pH-dependence of the dissociation constant and that the concentration of receptors in the endosomal compartment must also be considered.     

Kangaroo Rats Remodel Burrows in Response to Seasonal Changes in Environmental Conditions

Burrow architecture enhances important animal functions such as food storage, predator avoidance, and thermoregulation. Occupants may be able to maximize fitness by remodeling burrows in response to seasonal changes in climate and predation risk. My objective was to examine how banner‐tailed kangaroo rats (Dipodomys spectabilis) modify the number of burrow entrances in response to seasonal conditions. For 3 yr, I monitored fluctuations in number of burrow entrances in kangaroo rat mounds. Individual kangaroo rats continually remodeled mounds in response to seasonal conditions. Compared to summer, mounds in winter had approximately 50% fewer entrances and plugged entrances were common. Monthly differences in number of entrances were closely linked with seasonal changes in soil temperature and precipitation. Number of entrances decreased as soil temperature and precipitation declined. Changes in burrow entrances likely reflect seasonal differences in the relative importance of burrow functions. Fewer burrow entrances during winter would create a warmer microclimate by reducing convective heat loss in mounds, resulting in thermoregulatory savings for occupants. During the summer, thermoregulatory costs of kangaroo rats are low, but risk of seed cache spoilage and predation from snakes increases. Adding burrow entrances after large summer rainfall events would increase the evaporation rate within mounds, reducing spoilage of seed caches. More burrow entrances would also reduce predation risk in the summer by providing additional escape routes.     

Localization during development of alternatively spliced forms of cytotactin mRNA by in situ hybridization

Cytotactin, an extracellular glycoprotein found in neural and nonneural tissues, influences a variety of cellular phenomena, particularly cell adhesion and cell migration. Northern and Western blot analysis and in situ hybridization were used to determine localization of alternatively spliced forms of cytotactin in neural and nonneural tissues using a probe (CT) that detected all forms of cytotactin mRNA, and one (VbVc) that detected two of the differentially spliced repeats homologous to the type III repeats of fibronectin. In the brain, the levels of mRNA and protein increased from E8 through E15 and then gradually decreased until they were barely detectable by P3. Among the three cytotactin mRNAs (7.2, 6.6, and 6.4 kb) detected in the brain, the VbVc probe hybridized only to the 7.2-kb message. In isolated cerebella, the 220-kD polypeptide and 7.2-kb mRNA were the only cytotactin species present at hatching, indicating that the 220-kD polypeptide is encoded by the 7.2-kb message that contains the VbVc alternatively spliced insert. In situ hybridization showed cytotactin mRNA in glia and glial precursors in the ventricular zone throughout the central nervous system. In all regions of the nervous system, cytotactin mRNAs were more transient and more localized than the polypeptides. For example, in the radial glia, cytotactin mRNA was observed in the soma whereas the protein was present externally along the glial fibers. In the telencephalon, cytotactin mRNAs were found in a narrow band at the edge of a larger region in which the protein was wide-spread. Hybridization with the VbVc probe generally overlapped that of the CT probe in the spinal cord and cerebellum, consistent with the results of Northern blot analysis. In contrast, in the outermost tectal layers, differential hybridization was observed with the two probes. In nonneural tissues, hybridization with the CT probe, but not the VbVc probe, was detected in chondroblasts, tendinous tissues, and certain mesenchymal cells in the lung. In contrast, hybridization with both probes was observed in smooth muscle and lung epithelium. Both epithelium and mesenchyme expressed cytotactin mRNA in varying combinations: in the choroid plexus, only epithelial cells expressed cytotactin mRNA; in kidney, only mesenchymal cells; and in the lung, both of these cell types contained cytotactin mRNA. These spatiotemporal changes during development suggest that the synthesis of the various alternatively spliced cytotactin mRNAs is responsive to tissue-specific local signals and prompt a search for functional differences in the various molecular forms of the protein.