Cell shape, cytoskeletal mechanics, and cell cycle control in angiogenesis

Capillary endothelial cells can be switched between growth and differentiation by altering cell-extracellular matrix interactions and thereby, modulating cell shape. Studies were carried out to determine when cell shape exerts its growth-regulatory influence during cell cycle progression and to explore the role of cytoskeletal structure and mechanics in this control mechanism. When G₀-synchronized cells were cultured in basic fibroblast growth factor (FGF)-containing defined medium on dishes coated with increasing densities of fibronectin or a synthelic integrin ligand (RGD-containing peptide), cell spreading, nuclear extention, and DNA synthesis all increased in parallel. To determine the minimum time cells must be adherent and spread on extracellular matrix (ECM) to gain entry into S phase, cells were removed with trypsin or induced to retract using cytochalasin D at different times after plating. Both approaches revealed that cells must remain extended for approximately 12–15 h and hence, most of G₁, in order to enter S phase. After this restriction point was passed, normally ‘anchorage-dependent’ endothelial cells turned on DNA synthesis even when round and in suspension. The importance of actin-containing microfilaments in shape-dependent growth control was confirmed by culturing cells in the presence of cytochalasin D (25–1000 ng ml⁻¹): dose-dependent inhibition of cell spreading, nuclear extension, and DNA synthesis resulted. In contrast, induction of microtubule disassembly using nocodazole had little effect on cell or nuclear spreading and only partially inhibited DNA synthesis. Interestingly, combination of nocodazole with a suboptimal dose of cytochalasin D (100 ng ml⁻¹) resulted in potent inhibition of both spreading and growth, suggesting that microtubules are redundant structural elements which can provide critical load-bearing functions when microfilaments are partially compromised. Similar synergism between nocodazole and cytochalasin D was observed when cytoskeletal stiffness was measured directly in living cells using magnetic twisting cytometry. These results emphasize the importance of matrix-dependent changes in cell and nuclear shape as well as higher order structural interactions between different cytoskeletal filament systems for control of capillary cell growth during angiogenesis.     

Human osteoblasts from younger normal and osteoporotic donors show differences in proliferation and TGFβ-release in response to cyclic strain

Mechanical stimulation of bone tissue by physical activity stimulates bone formation in normal bone and may attenuate bone loss of osteoporotic patients. However, altered responsiveness of osteoblasts in osteoporotic bone to mechanical stimuli may contribute to osteoporotic bone involution. The purpose of the present study was to investigate whether osteoblasts from osteoporotic patients and normal donors show differences in proliferation and TGFβ production in responses to cyclic strain. Human osteoblasts isolated from collagenase-treated bone explants of 10 osteoporotic patients (average age 70 ± 6 yr) and 8 normal donors (average age 54 ± 10 yr) were plated into elastic rectangular silicone dishes. Subconfluent cultures were stimulated by cyclic strain (1%, 1 Hz) in an electromechanical cell stretching apparatus at three consecutive days for each 30 min. The cultures were assayed for proliferation, alkaline phosphatase activity and TGFβ release in each three parallel cultures. In all experiments, osteoblasts grown in the same elastic dishes but without mechanical stimulation served as controls. Significant differences between stimulated cultures and unstimulated controls were determined by a paired two-tailed Wilcoxon test. In comparison to the unstimulated controls, osteoblasts from normal donors significantly increased proliferation (p = 0.025) and TGFβ secretion (p = 0.009) into the conditioned culture medium. In contrast, osteoblasts from osteoporotic donors failed to increase both proliferation (p > 0.05) and TGFβ release (p > 0.05) in response to cyclic strain. Alkaline phosphatase activity was not significantly affected (p > 0.05) in normal as well as osteoporotic bone derived osteoblasts.

These findings suggest a different responsiveness to 1% cyclic strain of osteoblasts isolated from normal and osteoporotic bone that could be influenced by both the disease of osteoporosis and the higher average age of the osteoporotic patient group. While osteoblasts from osteoporotic donors failed to increase proliferation and TGFβ release under the chosen mechanical strain regimen that stimulated both parameters in normal osteoblasts, it is possible that some other strain regimen would provide more effective stimulation of osteoporotic cells.     

Discrete and reversible vacuole-like dilations induced by osmomechanical perturbation of neurons

In cultured Lymnaea stagnalis neurons, osmolarity increases (upshocks) rapidly elicited large membranous dilations that could be dislodged and pushed around inside the cell with a microprobe. Subsequent osmolarity decreases (downshocks) caused these vacuole-like dilations (VLDs) to disappear. Additional upshock/downshock perturbations resulted in repeated appearance/disappearance (formation/reversal) of VLDs at discrete sites. Confocal microscopy indicated that VLDs formed as invaginations of the substrate-adherent surface of the neuron: extracellular rhodamine-dextran entered VLDs as they formed and was expelled during reversal. Our standard VLD-inducing perturbation was: 2–4 min downshock to distilled water, upshock to normal saline. However, a wide range of other osmotic perturbations (involving osmolarities up to 3.5x normal, perturbations with or without Ca²⁺, replacement of ions by sucrose) were also used. We concluded that mechanical, not chemical, aspects of the osmo-mechanical shocks drove the VLD formation and reversal dynamics and that extracellular Ca²⁺ was not required.Following a standard perturbation, VLDs grew from invisible to their full diameter (>10 m) in just over a minute. Over the next 0.5–3 hr in normal saline, neurons recovered. Recovery eliminated any visible VLDs and was accompanied by cytoplasmic turmoil around the VLDs. Recovery was prevented by cytochalasin B, brefeldin A and N-ethylmaleimide but not by nocodazole. In striking contrast, these drugs did not prevent repeated VLD formation and reversal in response to standard osmo-mechanical perturbations; VLD disappearance during reversal and during recovery are different.The osmo-mechanical changes that elicited VLDs may, in an exaggerated fashion, mimic tension changes in extending and retracting neuntes. In this context we postulate: (a) the trafficking or disposition of membrane between internal stores and plasma membrane is mechano sensitive, (b) normally, this mechanosensitivity provides an on demand system by which neurons can accommodate stretch/release perturbations and control cell shape but, (c) given sudden extreme mechanical stimuli, it yields VLDs. Present address: Biology Department, Washington University, St Louis, MO 63130-4899This work was supported by NSERC of Canada research grants to CEM and to LRM. CR was the recipient of a postdoctoral fellowship from the Ministere francais de la Recherche et de l'Espace. We thank J-M. Trifaro for the use of his image processing equipment.     

Cortical remodeling data are affected by sampling location

It has been argued that techniques for estimating adult ageat-death from cortical histology are deleteriously affected by sampling location. This study uses nine complete femoral midshaft cross-sections to test the effect of sampling site on measurement of a standard histological variable, percent remodeled bone. Circumferential periosteal fields from four anatomically defined locations (anterior, posterior, medial, lateral) and four mechanically defined locations (maximum and minimum moments of area) were evaluated. Locations deviating from the periosteal surface toward the endosteal surface were also compared. Significant differences were found for both location and field placement. The anatomical axes exhibited greater variability than the mechanical axes, in particular the anterior location, a standard sampling site for age-at-death estimation techniques. More endosteal fields tended to show elevated levels of percent remodeled bone. This study demonstrates that circumferential and radial sampling locations are important considerations in deriving and applying predictive equations based on cortical remodeling. © 1995 Wiley-Liss, Inc.     

Tradeoffs between hydraulic efficiency and mechanical strength in the stems of four co-occurring species of chaparral shrubs

Possible tradeoffs between efficiency of water transport and mechanical strength were examined in stems of two congeneric pairs of co-occurring chaparral shrubs. First, since previously published results indicated that Adenostoma sparsifolium (Rosaceae) had greater specific conductivity (k _s or hydraulic conductivity per xylem transverse area) than A. fasciculatum, it was hypothesized that A. sparsifolium would have greater vessel lumen area per square millimeter of xylem area, and less mechanical strength, than A. fasciculatum. Secondly, since Ceanothus megacarpus (Rhamnaceae) is a non-sprouter (unable to sprout from the root crown following fire or other major disturbance) whereas C. spinosus is a sprouter and thus able to form new stems following disturbance, it was hypothesized that C. megacarpus would have greater mechanical strength, but lower k _s, than C. spinosus. Both hypotheses were supported. Based upon computer-aided image analyses, A. sparsifolum had significantly higher mean and maximum vessel diameters (16.4, 40.5 vs. 14.6, 35.7 μm), a 34% greater percent vessel lumen area, and a two-fold greater measured and theoretical k _s than A. fasciculatum. This corresponded to 14% lower stem density (wet weight/volume) and less mechanical strength, with a 37% lower modulus of elasticity (MOE) and a 30% lower modulus of rupture (MOR) than A. fasciculatum. Similarly, C.␣spinosus had a significantly higher maximum vessel diameter (52.7 vs. 41.8 μm) and a 92% higher theoretical k _s (and 43% higher measured k _s) than C. megacarpus. This corresponded to a 9% lower stem density and 20% lower MOR than for C. megacarpus. Thus, at least within these two congeneric pairs of chaparral shrubs growing together in the same habitat, there may be tradeoffs between mechanical strength and conductive efficiency of the stem xylem which correspond to differences in transport physiology and life history traits of sprouter versus non-sprouter species.     

针刺疗法联合穴位贴敷对急性呼吸衰竭机械通气患者血气分析指标、膈肌功能及炎症免疫指标的影响

摘要 目的：观察穴位贴敷、针刺疗法联合治疗对急性呼吸衰竭机械通气患者血气分析指标、膈肌功能及炎症免疫指标的影响。方法：选择2021年11月～2022年12月期间在安徽中医药大学附属六安医院接受治疗的92例急性呼吸衰竭机械通气患者,按照随机数字表法将患者分为对照组（常规治疗,46例）和研究组（对照组的基础上增加针刺疗法联合穴位贴敷治疗,46例）。对比两组血气分析指标、膈肌功能、炎症免疫指标及胃肠功能,同时记录两组并发症发生率。结果：研究组撤机前氧合指数（OI）、pH、动脉血氧分压（PaO2）高于对照组,动脉血二氧化碳分压（PaCO₂）低于对照组（P<0.05）。研究组撤机前右侧膈肌呼气末厚度（Tdi-ee）、吸气末厚度（Tdi-ei）、膈肌增厚分数（TFdi）低于对照组（P<0.05）。研究组撤机前超敏C反应蛋白（hs-CRP）、降钙素原（PCT）、白细胞计数（WBC）低于对照组,CD4⁺高于对照组（P<0.05）。研究组撤机前胃肠功能评分低于对照组（P<0.05）。两组并发症发生率组间对比无统计学差异（P>0.05）。结论：针刺疗法联合穴位贴敷在改善急性呼吸衰竭机械通气患者的血气分析指标、膈肌功能、炎症免疫指标中的应用价值较好。     

使用机械通气联合限制性液体复苏对重度颅脑损伤患者的急救效果及对远期认知功能影响

摘要 目的：探讨使用机械通气联合限制性液体复苏对重度颅脑损伤患者的急救效果及对远期认知功能影响。方法：选取我院2020年1月到2022年12月急诊收治的90例重度颅脑损伤患者作为研究对象,应用随机数字表法将所有患者分为观察组与对照组,每组45例。所有患者均采取常规重型颅脑损伤治疗,对照组患者在损伤后立即给予机械通气,并采取常规液体复苏措施进行治疗。观察组在损伤后立即给予机械通气,并采取限制性液体复苏治疗,对比两组患者急救效果,急救治疗前与急救治疗后1 h的血气指标变化情况,急救治疗前与急救治疗后1 d的血尿素氮（BUN）、血清肌酐（Scr）、乳酸、肌酸激酶（CK）相关生化指标表达水平,最后分别在患者苏醒时、术后3 d、6 d、10 d检测两组患者S100B蛋白与褪黑素表达水平。结果：观察组患者苏醒时间、说话时间、总输液量以及死亡率明显低于对照组,观察组GOS评分明显高于对照组（P＜0.05）;治疗前两组患者血氧饱和度（SpO₂）、动脉血二氧化碳分压（PaCO₂）水平对比无明显差异（P＞0.05）,治疗后,对照组SpO₂水平降低,观察组无明显变化,两组患者PaCO₂水平均降低,且观察组低于对照组（P＜0.05）;治疗前两组患者BUN、Scr、乳酸、CK相关指标表达水平对比无明显差异（P＞0.05）,治疗后对照组患者CK水平升高,观察组无明显变化,且观察组明显低于对照组,BUN、Scr、乳酸水平均降低,且观察组明显低于对照组（P＜0.05）;两组患者苏醒时S100B 蛋白、褪黑素对比无明显差异（P＞0.05）,术后3 d、6 d、10 d S100B 蛋白明显降低,且观察组低于对照组,术后3 d、6 d、10 d褪黑素明显升高,观察组高于对照组（P＜0.05）。结论：使用机械通气联合限制性液体复苏能够提升重度颅脑损伤患者的急救效果,降低患者死亡率,且能够及时改善患者血氧饱和度、动脉血二氧化碳分压相关血气指标水平,减轻对患者心功能、肾功能带来的损伤,同时能够降低对患者神经功能产生的损伤情况。     

Auxin-induced cell elongation and cell wall changes

It has been well known that auxin induces cell elongation through its effect on modifications of the cell wall. The present review will discuss cell wall modifications, physical and biochemical, as the background of the former, based on the experimental results from our laboratory and from others, with the historical background. Discussions will particularly put stress on the auxin effect on the cell wall in terms of the following studies, namely, (1) measurements of the mechanical property of the cell wall, and (2) biochemical studies on the polysaccharide molecules of the cell wall. This article is dedicated to Professor Anton N.J. Heyn for his 85th birthday.     

热处理对水洞沟遗址石器原料力学性能的影响

宁夏水洞沟遗址的发现首次证实了旧石器时代东亚古人类的热处理行为。本文通过压缩实验和XRD(X射线衍射)检测,对宁夏水洞沟遗址区采集的白云岩石料热处理前后的力学性能进行了定量研究。结果表明,经过450℃热处理的白云岩石料材质更加均匀,硅质含量减小、钙质含量增加,抗压强度下降31%,最大应变提高27%,在应力-应变曲线上出现了明显的锯齿状波动现象。这些变化降低了打击石料所需的力度,使石料易于产生多次开裂,不容易发生一次性灾变破坏,为古人类调整打击点、打击方向和力度创造了机会,从而降低了打制难度,提高了石器的制作质量和效率。     

Rotational model for nematic phase stability of fluorinated phenylbicyclohexane liquid crystals

A mechanical molecular rotation model for liquid crystal (LC) systems is employed to evaluate phase transition temperature of fluorinated phenylbicyclohexane isomeric LC compounds. Results show that when a fluorine atom is substituted along the molecular long axis, an LC molecule acquires high rotational speed and its rotation becomes stable, thereby resulting in a better thermal stability of the nematic phase. A novel explanation is proposed for the behavior of the nematic-isotropic phase of the LC system when a heavy atom is substituted along the molecular long axis. Figure Molecular conformation of fluorinated bicyclohexylphenyl compounds. . The fluorine atoms are substituted in different positions 2, 3, 4, and 5 of the phenyl ring, respectively. The axis expresses molecular long rotation axis.