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61.
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《Journal of lipid research》2017,58(5):962-973
SM is a fundamental component of mammalian cell membranes that contributes to mechanical stability, signaling, and sorting. Its production involves the transfer of phosphocholine from phosphatidylcholine onto ceramide, a reaction catalyzed by SM synthase (SMS)1 in the Golgi and SMS2 at the plasma membrane. Mammalian cells also synthesize trace amounts of the SM analog, ceramide phosphoethanolamine (CPE), but the physiological relevance of CPE production is unclear. Previous work revealed that SMS2 is a bifunctional enzyme producing both SM and CPE, whereas a closely related enzyme, SMS-related protein (SMSr)/SAMD8, acts as a monofunctional CPE synthase in the endoplasmic reticulum. Using domain swapping and site-directed mutagenesis on enzymes expressed in defined lipid environments, we here identified structural determinants that mediate the head group selectivity of SMS family members. Notably, a single residue adjacent to the catalytic histidine in the third exoplasmic loop profoundly influenced enzyme specificity, with Glu permitting SMS-catalyzed CPE production and Asp confining the enzyme to produce SM. An exchange of exoplasmic residues with SMSr proved sufficient to convert SMS1 into a bulk CPE synthase. This allowed us to establish mammalian cells that produce CPE rather than SM as the principal phosphosphingolipid and provide a model of the molecular interactions that impart catalytic specificity among SMS enzymes. 相似文献
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Claudia Tresoldi Elena Bianchi Alessandro Filippo Pellegata Gabriele Dubini Sara Mantero 《Computer methods in biomechanics and biomedical engineering》2017,20(10):1077-1088
The in vitro replication of physiological mechanical conditioning through bioreactors plays a crucial role in the development of functional Small-Caliber Tissue-Engineered Blood Vessels. An in silico scaffold-specific model under pulsatile perfusion provided by a bioreactor was implemented using a fluid-structure interaction (FSI) approach for viscoelastic tubular scaffolds (e.g. decellularized swine arteries, DSA). Results of working pressures, circumferential deformations, and wall shear stress on DSA fell within the desired physiological range and indicated the ability of this model to correctly predict the mechanical conditioning acting on the cells-scaffold system. Consequently, the FSI model allowed us to a priori define the stimulation pattern, driving in vitro physiological maturation of scaffolds, especially with viscoelastic properties. 相似文献
65.
The Shule River Basin is an ecologically fragile area in arid zone. To understand the state of land eco-security, the Environment-Economic-Society model was applied to build a land eco-security evaluation index system in the Shule River Basin. An entropy-weighted and matter-element model was built for eco-security evaluation from 2005 to 2014. Principal component analysis was used to quantitatively study the limiting factors of land ecological security. The result showed: the direction of development of the state of land eco-security in the Shule River Basin from 2005 to 2014 was characterized by “unsafe (No4) → safe (No1),” and presented an upward trend. The land eco-security status during 2005–2007 was in the “Unsafe” state and the state changed to “Critical Safe” in 2008–2009, “Safer” in 2010–2011, but “Safe” in 2012–2014. The key factors that affected land eco-security in the Shule River Basin were Per Capita Arable Land, Forest Cover Rate, Per Capita Water Resources, Water Production Modulus, the Tertiary Industry Output Value, and GDP Ratio and Water Consumption. Among them, Forest Cover Rate and Water Production Modulus had the greatest impact, with principal component loads of up to 0.973 and 0.968, respectively. The result of this study is expected to serve as reference and support for the conservation and management of Shule River Basin to ensure sustainable development. 相似文献
66.
Evan P. Tanner R. Dwayne Elmore Samuel D. Fuhlendorf Craig. A. Davis David K. Dahlgren Jeremy P. Orange 《Global Change Biology》2017,23(5):1832-1846
Two fundamental issues in ecology are understanding what influences the distribution and abundance of organisms through space and time. While it is well established that broad‐scale patterns of abiotic and biotic conditions affect organisms’ distributions and population fluctuations, discrete events may be important drivers of space use, survival, and persistence. These discrete extreme climatic events can constrain populations and space use at fine scales beyond that which is typically measured in ecological studies. Recently, a growing body of literature has identified thermal stress as a potential mechanism in determining space use and survival. We sought to determine how ambient temperature at fine temporal scales affected survival and space use for a ground‐nesting quail species (Colinus virginianus; northern bobwhite). We modeled space use across an ambient temperature gradient (ranging from ?20 to 38 °C) through a maxent algorithm. We also used Andersen–Gill proportional hazard models to assess the influence of ambient temperature‐related variables on survival through time. Estimated available useable space ranged from 18.6% to 57.1% of the landscape depending on ambient temperature. The lowest and highest ambient temperature categories (35 °C, respectively) were associated with the least amount of estimated useable space (18.6% and 24.6%, respectively). Range overlap analysis indicated dissimilarity in areas where Colinus virginianus were restricted during times of thermal extremes (range overlap = 0.38). This suggests that habitat under a given condition is not necessarily a habitat under alternative conditions. Further, we found survival was most influenced by weekly minimum ambient temperatures. Our results demonstrate that ecological constraints can occur along a thermal gradient and that understanding the effects of these discrete events and how they change over time may be more important to conservation of organisms than are average and broad‐scale conditions as typically measured in ecological studies. 相似文献
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Landscapes are continually changing due to numerous assaults, including habitat alteration, anthropogenic disturbances, and climate change. Understanding how species will respond to these changes is of critical importance for conservation and management. Mechanistic models, such as biophysical models (BPMs), are an increasingly popular tool to predict how local population dynamics or species’ distributions may be altered in response to environmental and climate changes. By mechanistically modeling relationships between environmental conditions, physiology and behavior, it is possible to make accurate predictions about how species may respond. However, BPMs are often difficult to implement due to lack of appropriate, species-specific data that is biologically realistic or relevant. In this study, we present a BPM for the salamander Plethodon jordani and assess how adding more biological realism has potential to alter model predictions about annual energy budgets. Additionally, we conducted local and global sensitivity analyses to evaluate the importance of accurately specifying model parameter values and functional relationships. We found that the addition of biological realism resulted in greater model complexity as well as substantially different estimates of energy balance. Correct parameterization of biophysical models is also critical, as small changes in parameter values can result in disproportionately large changes in downstream model estimates. Our model highlights the overall importance of using ecologically relevant and specific data for input parameters, as well as careful assessment of parameter sensitivity. We encourage researchers to be aware of the data they are using to parameterize BPMs, and urge the collection of system-specific data that is relevant in spatial and temporal scale. We also recommend greater and more transparent use of sensitivity analyses to provide a better understanding of the model, as well as greater confidence in model predictions. 相似文献
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目的 观察植物乳杆菌YXCC-1和嗜酸乳杆菌YXCC-2对小鼠急性溃疡性结肠炎（UC）的疗效。方法 对这两株菌进行体外模拟胃肠环境抗性研究,并进行动物实验。采用DSS诱导的小鼠急性UC模型,将60只小鼠随机分为4组,分别为空白对照组、DSS模型组、YXCC-1组和YXCC-2组,每组15只,观察小鼠治疗前后一般情况,计算小鼠组织学损伤评分以及观察组织学病理改变。结果 菌株YXCC-1、YXCC-2有一定的耐酸、耐胆盐能力,在人工肠液环境下能较好存活;灌胃菌株发酵液可显著降低UC小鼠DAI水平,明显改善结肠组织损伤。结论 植物乳杆菌YXCC-1、嗜酸乳杆菌YXCC-2发酵液对小鼠溃疡性结肠炎有治疗作用,且两者疗效相当。 相似文献