Mechanics of Vorticella Contraction

Vorticella convallaria is one of a class of fast-moving organisms that can traverse its body size in less than a millisecond by rapidly coiling a slender stalk anchoring it to a nearby surface. The stalk houses a fiber called the spasmoneme, which winds helically within the stalk and rapidly contracts in response to calcium signaling. We have developed a coupled mechanical-chemical model of the coiling process, accounting for the coiling of the elastic stalk and the binding of calcium to the protein spasmin. Simulations of the model describe the contraction and recovery processes quantitatively. The stalk-spasmoneme system is shown to satisfy geometric constraints, which explains why the cell body sometimes rotates during contraction. The shape of the collapsing and recovering stalk bounds its effective bending stiffness. Simulations suggest that recovery from the contracted state is driven by the stalk at a rate controlled by dissociation of calcium from spasmin.     

Variation in E- and Z-guggulsterones of Commiphora wightii

The seasonal and geographical variations in guggulsterone content in oleo-gum resin have been examined in order to determine the optimum collection time and to identify suitable locations for large-scale cultivation of Commiphora wightii. The results clearly showed that E- and Z-guggulsterones varied significantly on seasonal basis. A higher guggulsterone concentration was observed during summer (May–July) and this was lower during winter (November–March). A wide variation in guggulsterone content was also observed in the different geographical regions in Rajasthan. The southern part of the state produced the lowest guggulsterone (< 1.19%) whereas the central, northern and western regions had higher yields (1.87–2.76%). The guggulsterone yield exhibited a positive correlation with annual rainfall between 15 and 55 cm and declined in the regions with higher rainfall (> 60 cm). Plants with high guggulsterone content can be utilized for mass multiplication and genetic improvement.     

Abattoir-sourced isolated ileum from Gallus gallus domesticus as an experimental tool

A study was undertaken to determine the longevity of active muscarinic receptors on abattoir-sourced isolated ileum preparations from Gallus gallus domesticus, with a view to using the tissue as an experimental tool for functional response assays in laboratory experiments. A concentration-response curve for acetylcholine (1-256 μM) was plotted, in the presence and absence of 1, 3 and 6 nM atropine. In a second experiment, unknown concentrations of acetylcholine samples were determined by using an interpolation method. In this experiment, four sample concentrations were used and the calculated values were found to be almost equal to the actual values. Finally, an experiment was carried out to elucidate the effects of post-sacrifice time on the contractile response of the tissue. The results showed that the tissue maintained considerable contractile response at the 6-hour post-sacrifice time-point. Competitive antagonistic activity was observed between acetylcholine and atropine on the chicken ileum, and the pA2 value was calculated to be 9.21 by using an Arunlakshana-Schild plot. The results suggest that isolated ileum preparations of Gallus gallus domesticus, obtained from a meat abattoir, can be used as a basic experimental tool for bioassays in routine laboratory experiments. However, its potential as a research tool still needs to be confirmed.     

Device Thrombogenicity Emulator (DTE) − Design optimization methodology for cardiovascular devices: A study in two bileaflet MHV designs

Patients who receive prosthetic heart valve (PHV) implants require mandatory anticoagulation medication after implantation due to the thrombogenic potential of the valve. Optimization of PHV designs may facilitate reduction of flow-induced thrombogenicity and reduce or eliminate the need for post-implant anticoagulants. We present a methodology entitled Device Thrombogenicty Emulator (DTE) for optimizing the thrombo-resistance performance of PHV by combining numerical and experimental approaches. Two bileaflet mechanical heart valves (MHV) designs, St. Jude Medical (SJM) and ATS, were investigated by studying the effect of distinct flow phases on platelet activation. Transient turbulent and direct numerical simulations (DNS) were conducted, and stress loading histories experienced by the platelets were calculated along flow trajectories. The numerical simulations indicated distinct design dependent differences between the two valves. The stress loading waveforms extracted from the numerical simulations were programmed into a hemodynamic shearing device (HSD), emulating the flow conditions past the valves in distinct ‘hot-spot’ flow regions that are implicated in MHV thrombogenicity. The resultant platelet activity was measured with a modified prothrombinase assay, and was found to be significantly higher in the SJM valve, mostly during the regurgitation phase. The experimental results were in excellent agreement with the calculated platelet activation potential. This establishes the utility of the DTE methodology for serving as a test bed for evaluating design modifications for achieving better thrombogenic performance for such devices.     

Lysophosphatidic acid acyltransferase β (LPAATβ) promotes the tumor growth of human osteosarcoma

Background

Osteosarcoma is the most common primary malignancy of bone with poorly characterized molecular pathways important in its pathogenesis. Increasing evidence indicates that elevated lipid biosynthesis is a characteristic feature of cancer. We sought to investigate the role of lysophosphatidic acid acyltransferase β (LPAATβ, aka, AGPAT2) in regulating the proliferation and growth of human osteosarcoma cells. LPAATβ can generate phosphatidic acid, which plays a key role in lipid biosynthesis as well as in cell proliferation and survival. Although elevated expression of LPAATβ has been reported in several types of human tumors, the role of LPAATβ in osteosarcoma progression has yet to be elucidated.

Methodology/Principal Findings

Endogenous expression of LPAATβ in osteosarcoma cell lines is analyzed by using semi-quantitative PCR and immunohistochemical staining. Adenovirus-mediated overexpression of LPAATβ and silencing LPAATβ expression is employed to determine the effect of LPAATβ on osteosarcoma cell proliferation and migration in vitro and osteosarcoma tumor growth in vivo. We have found that expression of LPAATβ is readily detected in 8 of the 10 analyzed human osteosarcoma lines. Exogenous expression of LPAATβ promotes osteosarcoma cell proliferation and migration, while silencing LPAATβ expression inhibits these cellular characteristics. We further demonstrate that exogenous expression of LPAATβ effectively promotes tumor growth, while knockdown of LPAATβ expression inhibits tumor growth in an orthotopic xenograft model of human osteosarcoma.

Conclusions/Significance

Our results strongly suggest that LPAATβ expression may be associated with the aggressive phenotypes of human osteosarcoma and that LPAATβ may play an important role in regulating osteosarcoma cell proliferation and tumor growth. Thus, targeting LPAATβ may be exploited as a novel therapeutic strategy for the clinical management of osteosarcoma. This is especially attractive given the availability of selective pharmacological inhibitors.     

Solution structure of the MAPK phosphatase PAC-1 catalytic domain. Insights into substrate-induced enzymatic activation of MKP

Inactivation of mitogen-activated protein kinases (MAPKs) by MAPK phosphatases (MKPs) is accomplished via substrate-induced activation of the latter enzymes; however, the structural basis for the underlying mechanism remains elusive. Here, we report the three-dimensional solution structure of the C-terminal phosphatase domain of the prototypical MKP PAC-1, determined when bound to phosphate. Structural and biochemical analyses reveal unique active site geometry of the enzyme important for binding to phosphorylated threonine and tyrosine of MAPK ERK2. Our study further demonstrates that the dynamic interaction between the N-terminal kinase binding domain and the C-terminal phosphatase domain of an MKP is directly coupled to MAPK-induced conformational change of the phosphatase active site, which is essential for eliciting its full enzymatic activity.     

Selectin-like kinetics and biomechanics promote rapid platelet adhesion in flow: the GPIb(alpha)-vWF tether bond

The ability of platelets to tether to and translocate on injured vascular endothelium relies on the interaction between the platelet glycoprotein receptor Ib alpha (GPIb(alpha)) and the A1 domain of von Willebrand factor (vWF-A1). To date, limited information exists on the kinetics that govern platelet interactions with vWF in hemodynamic flow. We now report that the GPIb(alpha)-vWF-A1 tether bond displays similar kinetic attributes as the selectins including: 1) the requirement for a critical level of hydrodynamic flow to initiate adhesion, 2) short-lived tethering events at sites of vascular injury in vivo, and 3) a fast intrinsic dissociation rate constant, k(0)(off) (3.45 +/- 0.37 s(-1)). Values for k(off), as determined by pause time analysis of transient capture/release events, were also found to vary exponentially (4.2 +/- 0.8 s(-1) to 7.3 +/- 0.4 s(-1)) as a function of the force applied to the bond (from 36 to 217 pN). The biological importance of rapid bond dissociation in platelet adhesion is demonstrated by kinetic characterization of the A1 domain mutation, I546V that is associated with type 2B von Willebrand disease (vWD), a bleeding disorder that is due to the spontaneous binding of plasma vWF to circulating platelets. This mutation resulted in a loss of the shear threshold phenomenon, a approximately sixfold reduction in k(off), but no significant alteration in the ability of the tether bond to resist shear-induced forces. Thus, flow dependent adhesion and rapid and force-dependent kinetic properties are the predominant features of the GPIb(alpha)-vWF-A1 tether bond that in part may explain the preferential binding of platelets to vWF at sites of vascular injury, the lack of spontaneous platelet aggregation in circulating blood, and a mechanism to limit thrombus formation.     

Enhanced photocatalytic activity of ceria-doped zinc oxide under UV illumination prepared via chemical precipitation

Transition metal oxide has emerged as one of the most potential candidates for environment remediation by utilizing solar energy through photocatalysis. This study compares the optical characteristics of zinc oxide (ZnO) and ceria-doped zinc oxide (CeZnO) nanoparticles synthesized through a facile chemical precipitation method without using any assistant catalyst. The present work investigates the consequences of ceria (cerium dioxide, CeO₂) intrusion on the photocatalytic activity of ZnO nanoparticles using methylene blue (MB) as a probe pollutant. The CeZnO showed an increase in photoactivity when compared to ZnO nanoparticles for degradation of MB in an aqueous solution under ultraviolet (UV) irradiance. The resulting heterojunction between ZnO and that of ceria enhances the charge separation efficiency showing a strong correlation between ZnO and CeO₂ heterojunction on the charge transfer mechanism across the interface.