Influence of the Cytoplasmic Domains of Aquaporin-4 on Water Conduction and Array Formation

Phosphorylation of Ser180 in cytoplasmic loop D has been shown to reduce the water permeability of aquaporin (AQP) 4, the predominant water channel in the brain. However, when the structure of the S180D mutant (AQP4M23S180D), which was generated to mimic phosphorylated Ser180, was determined to 2.8 Å resolution using electron diffraction patterns, it showed no significant differences from the structure of the wild-type channel. High-resolution density maps usually do not resolve protein regions that are only partially ordered, but these can sometimes be seen in lower-resolution density maps calculated from electron micrographs. We therefore used images of two-dimensional crystals and determined the structure of AQP4M23S180D at 10 Å resolution. The features of the 10-Å density map are consistent with those of the previously determined atomic model; in particular, there were no indications of any obstruction near the cytoplasmic pore entrance. In addition, water conductance measurements, both in vitro and in vivo, show the same water permeability for wild-type and mutant AQP4M23, suggesting that the S180D mutation neither reduces water conduction through a conformational change nor reduces water conduction by interacting with a protein that would obstruct the cytoplasmic channel entrance. Finally, the 10-Å map shows a cytoplasmic density in between four adjacent tetramers that most likely represents the association of four N termini. This finding supports the critical role of the N terminus of AQP4 in the stabilization of orthogonal arrays, as well as their interference through lipid modification of cysteine residues in the longer N-terminal isoform.     

The high viscosity encountered during freezing in glycerol solutions: effects on cryopreservation

The objective of this study was to determine the viscosity of the residual unfrozen solution that cells are exposed to during freezing in the presence of glycerol and use this to interpret some key aspects of cryopreservation. The viscosity of the glycerol-water binary system exceeded 1000 cP at -40 degrees C, whilst the viscosity of the ternary system, glycerol-water-NaCl, exceeded 100,000 cP at -55 degrees C. The effect of these high viscosities on the diffusion of water at a constant temperature during freezing and during cooling at different linear rates has been estimated. At rates of cooling faster than 100 degrees C min(-1) the diffusion distance during freezing was calculated to be less than 15 microm. Validation of the diffusion calculations was confirmed by examination of the ultrastructure of the freeze concentrated matrix in samples prepared at a range of cooling rates. At a critical rate of cooling, water diffusion becomes limited by the high viscosity and two phenomena, of relevance to cryobiology, occur: (1) the composition of the freeze concentrated matrix around cells deviates from that of the equilibrium phase diagram; and (2) the osmotic loss of water from cells is restricted. These factors are of particular relevance to an understanding of the response of cells such as spermatozoa, red blood cells, and bacteria cooled rapidly with glycerol as cryoprotectant.     

Continuity of interpersonal violence between Nubian communities

Modern communities affiliated with the same culture have been shown to experience comparable levels of interpersonal violence, no matter what their size. It was hypothesized that a similar relationship would exist among ancient rural and urban people, but that accident-related trauma may be more prominent among rural dwellers due to their activity base. Through an analysis of antemortem trauma, this investigation contrasted the injury profile of Nubian adult villagers (N = 55) from the Kerma period (2500-1750 BC) to that of their urban neighbors (N = 223) at Kerma (2050-1500 BC). The injury pattern associated with interpersonal violence (cranial injury, direct-force ulna fractures, and multiple injuries) was similar between the two samples, as hypothesized. The rural group sustained significantly more nonviolence-related injuries that suggested occupational or environmental influences. The more severe cranial injuries observed among urban people are attributed to a preference for more lethal hand-wielded objects that may have accompanied increasing local tensions and incursions into Egypt during the 17th Dynasty.     

Immunolocalization of myostatin (GDF-8) following musculoskeletal injury and the effects of exogenous myostatin on muscle and bone healing

The time course and cellular localization of myostatin expression following musculoskeletal injury are not well understood; therefore, the authors evaluated the temporal and spatial localization of myostatin during muscle and bone repair following deep penetrant injury in a mouse model. They then used hydrogel delivery of exogenous myostatin in the same injury model to determine the effects of myostatin exposure on muscle and bone healing. Results showed that a "pool" of intense myostatin staining was observed among injured skeletal muscle fibers 12-24 hr postsurgery and that myostatin was also expressed in the soft callus chondrocytes 4 days following osteotomy. Hydrogel delivery of 10 or 100 μg/ml recombinant myostatin decreased fracture callus cartilage area relative to total callus area in a dose-dependent manner by 41% and 80% (p<0.05), respectively, compared to vehicle treatment. Myostatin treatment also decreased fracture callus total bone volume by 30.6% and 38.8% (p<0.05), with the higher dose of recombinant myostatin yielding the greatest decrease in callus bone volume. Finally, exogenous myostatin treatment caused a significant dose-dependent increase in fibrous tissue formation in skeletal muscle. Together, these findings suggest that early pharmacological inhibition of myostatin is likely to improve the regenerative potential of both muscle and bone following deep penetrant musculoskeletal injury.     

Induced electric field and current density patterns in bone fractures

We have used the low frequency solver of the computer program SEMCAD‐X to model the induced electric field and current density patterns in simple models of a fractured femur embedded off‐center in cylindrical muscle tissue; a 1 cm fracture gap is filled with callus. The model is exposed to a 1 kHz, 1 mT sinusoidal magnetic field. The frequency chosen is typical of the major Fourier components of many waveforms used to stimulate fracture healing using pulsed magnetic fields; the intensity is also a typical level. Models include fractures perpendicular to the bone and at an angle from the perpendicular, each exposed to a field applied parallel to the bone or parallel to either of the two axes perpendicular to it. We find that all directions of applied magnetic fields produce essentially parallel induced electric fields and current densities through the plane of the callus, but that a magnetic field applied parallel to the bone induces considerably higher fields and currents than the same strength field applied in either perpendicular direction. Because investigations of pulsed‐field devices, including modeling of induced fields and currents, peaked more than a decade ago, this is the first application to our knowledge of the current capabilities of computer modeling systems to biological systems at low frequencies. Bioelectromagnetics 33:585–593, 2012. © 2012 Wiley Periodicals, Inc.     

A framework for estimating the fixation time of an advantageous allele in stepping-stone models

Determining how population subdivision increases the fixation time of an advantageous allele is an important problem in evolutionary genetics as this influences many processes. Here, I lay out a framework for calculating the fixation time of a positively selected allele in a subdivided population, as a function of the number of demes present, the migration rate between them and the manner in which they are connected. Using this framework, it becomes clear that a beneficial allele's fixation time is significantly reduced through migration continuously introducing copies of the allele into a newly colonized subpopulation, increasing its frequency within these demes. The effect that migration has on allele frequency needs to be explicitly taken into account to produce a realistic estimate of fixation time. This behaviour is most prominent when demes are arranged on a two-dimensional torus, in comparison with populations where demes are arranged in a circle. This is because each subpopulation is connected to several neighbours over a torus, so that there are multiple paths that an allele can take in order to fix. As a consequence, some demes experience a greater influx and efflux of migrants than others. Analytical results are found to be very accurate when compared to stochastic simulations, and are generally robust if there are a large number of demes, or if the allele is weakly selected for.     

Mesenchymal stem cells show radioresistance in vivo

Irradiation impacts on the viability and differentiation capacity of tissue‐borne mesenchymal stem cells (MSC), which play a pivotal role in bone regeneration. As a consequence of radiotherapy, bones may develop osteoradionecrosis. When irradiating human bone‐derived MSC in vitro with increasing doses, the cells’ self‐renewal capabilities were greatly reduced. Mitotically stalled cells were still capable of differentiating into osteoblasts and pre‐adipocytes. As a large animal model comparable to the clinical situation, pig mandibles were subjected to fractionized radiation of 2 χ 9 Gy within 1 week. This treatment mimics that of a standardized clinical treatment regimen of head and neck cancer patients irradiated 30 χ 2 Gy. In the pig model, fractures which had been irradiated, showed delayed osseous healing. When isolating MSC at different time points post‐irradiation, no significant changes regarding proliferation capacity and osteogenic differentiation potential became apparent. Therefore, pig mandibles were irradiated with a single dose of either 9 or 18 Gy in vivo, and MSC were isolated immediately afterwards. No significant differences between the untreated and 9 Gy irradiated bone with respect to proliferation and osteogenic differentiation were unveiled. Yet, cells isolated from 18 Gy irradiated specimens exhibited a reduced osteogenic differentiation capacity, and during the first 2 weeks proliferation rates were greatly diminished. Thereafter, cells recovered and showed normal proliferation behaviour. These findings imply that MSC can effectively cope with irradiation up to high doses in vivo. This finding should thus be implemented in future therapeutic concepts to protect regenerating tissue from radiation consequences.     

Pilon 骨折的分型与治疗进展

本文回顾了Pilon骨折的诊断、分型及治疗发展,Pilon骨折特点是高能量损伤累及踝关节负重关节面的胫骨远端骨折,常伴有腓骨骨折和下胫腓关节分离。20世纪中期Pilon骨折被认为无法通过内固定进行治疗,公认的方法是通过骨牵引使关节早期模造获得关节功能的恢复。20世纪后期随着AO理论的深入研究,学术界广泛认同所有关节内骨折的理想治疗方法是解剖复位、坚强固定和早期活动。此后,随着内固定技术的发展及骨科BO理论的出现,目前普遍认为Pilon骨折的治疗应遵循的原则是:1.寻求骨折稳固和软组织完整之间的一种平衡;2.不以牺牲局部软组织血供来强求达到坚强固定。     

Simulation of fracture healing incorporating mechanoregulation of tissue differentiation and dispersal/proliferation of cells

Modelling the course of healing of a long bone subjected to loading has been the subject of several investigations. These have succeeded in predicting the differentiation of tissues in the callus in response to a static mechanical load and the diffusion of biological factors. In this paper an approach is presented which includes both mechanoregulation of tissue differentiation and the diffusion and proliferation of cell populations (mesenchymal stem cells, fibroblasts, chondrocytes, and osteoblasts). This is achieved in a three-dimensional poroelastic finite element model which, being poroelastic, can model the effect of the frequency of dynamic loading. Given the number of parameters involved in the simulation, a parameter variation study is reported, and final parameters are selected based on comparison with an in vivo experiment. The model predicts that asymmetric loading creates an asymmetric distribution of tissues in the callus, but only for high bending moments. Furthermore the frequency of loading is predicted to have an effect. In conclusion, a numerical algorithm is presented incorporating both mechanoregulation and evolution of cell populations, and it proves capable of predicting realistic difference in bone healing in a 3D fracture callus.     

关节镜下逆行交锁髓内钉治疗股骨远端骨折36例分析

目的:探讨关节镜下逆行交锁髓内钉治疗股骨远端骨折的疗效、特点及其必要性.方法:采用关节镜下逆行交锁髓内钉进行手术治疗36例股骨远端骨折.结果:36例中膝关节内病损17例,经随访6个月至2年,平均10月,膝关节活动度90°～140°,平均125°.骨折愈合时间3～9个月,平均6个月.结论:关节镜引导下逆行交锁髓内钉治疗股骨远端骨折,同时对膝关节内损伤或病变明确诊断并进行相应处理,避免漏诊,手术时间短,最大限度地保留了膝关节的解剖与功能的完整性,对膝关节损伤小,值得推广.