Helical buckling of actin inside filopodia generates traction

Cells can interact with their surroundings via filopodia, which are membrane protrusions that extend beyond the cell body. Filopodia are essential during dynamic cellular processes like motility, invasion, and cell–cell communication. Filopodia contain cross-linked actin filaments, attached to the surrounding cell membrane via protein linkers such as integrins. These actin filaments are thought to play a pivotal role in force transduction, bending, and rotation. We investigated whether, and how, actin within filopodia is responsible for filopodia dynamics by conducting simultaneous force spectroscopy and confocal imaging of F-actin in membrane protrusions. The actin shaft was observed to periodically undergo helical coiling and rotational motion, which occurred simultaneously with retrograde movement of actin inside the filopodium. The cells were found to retract beads attached to the filopodial tip, and retraction was found to correlate with rotation and coiling of the actin shaft. These results suggest a previously unidentified mechanism by which a cell can use rotation of the filopodial actin shaft to induce coiling and hence axial shortening of the filopodial actin bundle.Tubular membrane remodeling driven by the actin cytoskeleton plays a major role in both pathogenesis and in a healthy immune response. For instance, invadopodia, podosomes, and filopodia are crucial for invasion and migration of cells (1). Filopodia are thin (100 to 300 nm), tube-like, actin-rich structures that function as “antennae” or “tentacles” that cells use to probe and interact with their microenvironment (2–4). Such structures have been studied in vitro using model systems where the point-like 3D contacts with the extracellular matrix (ECM) have been mimicked by using optically trapped dielectric particles, functionalized with relevant ligands. These model systems allow for mechanical and visual control over filopodial dynamics and have significantly advanced the understanding of cellular mechanosensing (5).Extraction of membrane tubes, using optical trapping, has been used to investigate mechanical properties of the membrane–cytoskeleton system (6–10), or membrane cholesterol content (11), and has revealed important insight into the mechanism that peripheral proteins use to shape membranes (12). Motivated by the pivotal role of F-actin in the mechanical behavior of filopodia and other cellular protrusions, special focus has been on revealing the presence of F-actin within extracted membrane tubes (1, 13–16). However, apart from a single study (9), fluorescent visualization of the F-actin was achieved by staining and fixation of the cells, and literature contains conflicting results regarding the presence or absence of actin in membrane tubes pulled from living cells (8, 11, 17).Filopodia in living cells have the ability to rotate and bend by a so-far unknown mechanism (13, 18–20). For instance, filopodia have been reported to exhibit sharp kinks in neuronal cells (21–23) and macrophages (6). These filopodial kinks have been observed both for surface-attached filopodia (23) as well as for filopodia that were free to rotate in three dimensions (6, 19).Other filaments such as DNA and bacterial flagella are common examples of structures that shorten and bend in response to torsional twist. Filopodia have previously been shown to have the ability to rotate by a mechanism that exists at their base (18, 19) and could have the ability to twist in presence of a frictional force. Rotation of the actin shaft results in friction with the surrounding filopodial membrane, and hence torsional energy can be transferred to the actin shaft. The myosin-Vb motor has been found to localize at the base of filopodia in neurite cells and to be critical for rotational movement of the filopodia; however, inhibition of myosin-Vc did not affect the rotation (19).Here, we reveal how actin filaments can simultaneously rotate and helically bend within cellular membrane tubes obtained by elongation of preexisting filopodia by an optically trapped bead. Simultaneous force measurements and confocal visualization reveal how the actin transduces a force as it rotates and retracts. After ∼100 s, the force exerted by the filopodium starts to exhibit pulling events reflecting transient contact between the actin and the tip region of the filopodium, which is attached to the optically trapped bead. We show that helical bending and rotation of the actin shaft (defined as the visible part of the actin) occurs simultaneously with movement of actin coils inside filopodia, which can occur concomitantly with a traction force exerted at the tip. The velocity of the coils depends on their location along the tube, thus indicating that retrograde flow is not the only mechanism driving the motion. Our data, and accompanying calculations, show that the rotation of the actin shaft, and the resulting torsional twist energy accumulated in the actin shaft, can contribute to shortening and bending of the actin shaft in conjunction with a retrograde flow.     

转位皮瓣联合异体巩膜植入治疗外伤性下睑缺损

目的 探讨不同转位皮瓣联合异体巩膜植入在外伤性下睑缺损的临床效果.方法 选择因外伤致下睑全层缺损程度大于1/2,导致眼睑闭合不全,下睑呈退缩状态＞2mm的8例,采用不同部位的转位皮瓣代替下睑前层,异体巩膜植入和分离的残留穹窿结膜代替下睑后层,从而矫正缺损的下睑.结果 随访12 ～24个月,全部病例异体巩膜血管化,无溶解和排斥现象,皮肤活性好,下睑缘位于角膜下缘或稍高,无巩膜暴露,l例轻度下睑外翻,外观形态基本正常.结论 对于外伤所致大于1/2的下睑全层缺损,异体巩膜植入联合转位皮瓣治疗是一种有效方法.     

青光眼引流阀植入术与小梁切除术对巩膜扣带术后难治性青光眼疗效

目的 评价Ahmed青光眼引流阀植入术与小梁切除术在巩膜扣带术后难治性青光眼治疗中的疗效比较.方法 接受滤过手术的巩膜扣带术后难治性青光眼41例(41眼).其中Ahmed青光眼引流阀植入术19例(阀门组),小梁切除术22例(小梁组).分析两组术后1年内的成功率、眼压降幅、视力、并发症和合并用药情况.结果 12个月阀门组的成功率为63.16％;小梁组为31.82％.阀门组成功率显著高于小梁组(X2=4.027,P=0.0427).阀门组术后12个月眼压均值为(16.5 ±4.9)mm Hg;小梁组术后12个月为(19.8 ±4.3)mm Hg.阀门组眼压显著低于小梁组(t=2.1102,P=0.0427).两组术后视力变化、并发症及合并青光眼药物使用情况均无差异.结论 Ahmed青光眼引流阀植入术较之小梁切除术,具有更为持久的降眼压作用和相似的安全性,是治疗巩膜扣带术后难治性青光眼的有效方法 .     

巩膜扣带术联合超声乳化治疗孔源性视网膜脱离合并白内障

目的 探讨巩膜扣带术联合晶状体超声乳化治疗孔源性视网膜脱离合并白内障的手术操作技巧及其效果.方法 回顾性分析巩膜扣带术联合晶状体超声乳化治疗的孔源性视网膜脱离合并白内障29例(29眼)其中同期后房型人工晶状体植入25眼.术中联合玻璃体腔注入六氟乙烷(C2F6)8眼,注入滤过空气1眼.手术后随访3～24个月.对视力、人工晶状体位置、视网膜复位情况及手术并发症等进行了临床观察.结果 所有病例术中眼底检查满意,均发现裂孔.随访期末视力提高者22眼,占75.86％(其中提高2行以上者16眼占55.17％);视力不变者7眼,占24.14％.随访期内28眼视网膜完全复位(96.55％),1眼视网膜未完全复位(3.45％).所有病例人工晶状体无明显偏位,术中术后无严重并发症发生.结论 巩膜扣带术联合晶状体超声乳化治疗孔源性视网膜脱离合并白内障既可免除患者二次手术的痛苦,又可使视网膜脱离及时复位,有助于恢复较好的视功能.     

不放液巩膜扣带术联合玻璃体腔注气治疗孔源性视网膜脱离的分析

目的 探讨不放液巩膜扣带术联合玻璃体腔注气治疗孔源性视网膜脱离的效果.方法 回顾性分析65例(65只眼)孔源性视网膜脱离行不放液巩膜扣带术联合玻璃体腔消毒空气注射患者的临床资料,分析视网膜复位率、视网膜下液吸收情况、术后视力、主要并发症等.随访时间2周至1年.结果 视网膜复位63例,手术成功率96.92％,49例视网膜下液在3天内吸收,占77.78％,术后视力进步者50例,占79.36％,主要并发症为术后高眼压和玻璃体混浊.结论 在掌握好手术适应证的情况下,不放液巩膜扣带术联合玻璃体腔注气是治疗孔源性视网膜脱离的有效方法,患者术后恢复快,手术并发症较少.     

巩膜外垫压联合视网膜激光光凝治疗硅油眼视网膜脱离的临床分析

目的研究巩膜外垫压手术联合视网膜激光光凝对硅油眼视网膜脱离的治疗效果。方法回顾性分析2009年1月一2012年1月,用巩膜外垫压联合视网膜光凝手术治疗36例硅油眼视网膜脱离的视网膜复位效果。结果全部患者均顺利完成巩膜外垫压手术及随后的视网膜激光光凝,行巩膜外放液5只眼,手术中未发生视网膜嵌顿、眼内出血和眼压显著升高等并发症;手术后1周视网膜复位21只眼（58．33％）,剩下15只眼1个月后复位7只眼（19．44％）,视网膜脱离总复位率为28只眼（77．77％）;未复位8只眼（22．23％）,改用玻璃体切割手术方式,视网膜成功复位;6个月后取出硅油,随访6个月视网膜无脱离或者脱离范围增加;手术后眼压≥30mmHg（11mmHg=0．133kPa）3只眼,≥20mmHg7只眼,对症治疗1周后眼压均恢复到正常范围。结论巩膜外垫压联合视网膜激光光凝治疗硅油眼视网膜脱离,手术简单,复位率高,可为硅油眼视网膜脱离首选手术方式,对于巩膜外垫压手术失败和复杂的硅油眼视网膜脱离,应当选择玻璃体切割手术方式。     

卵磷脂络合碘对视网膜脱离复位术后低视力患者视网膜功能和形态的影响

目的探讨卵磷脂络合碘对视网膜脱离（RD）术后视网膜功能和黄斑部视网膜形态的干预效果。方法采用前瞻随机对照研究的方法将50例（50眼）RD术后患者分为卵磷脂络合碘组和对照组；应用视网膜电图（ERG）和光学相干断层扫描（OCT）方法观察术后1、2、4、8周视网膜功能和形态的改变。结果对照组和用药组的年龄、视力和病程匹配。与术后第1周ERGb波比较，用药组第2周ERGb波即有显著的改变，而对照组延迟到第8周。OCT检查表明，用药组黄斑部视网膜厚度在术后第4周明显改善，而对照组为术后第8周。术后第8周用药组患者的最佳矫正视力与对照组的差异有统计学意义（P〈0．01）。结论卵磷脂络合碘可在一定程度上促进RD术后视功能的改变。     

异体巩膜羊膜移植治疗义眼台暴露

目的：探讨以异体巩膜联合羊膜移植治疗羟基磷灰石义眼台植入后义眼台暴露的方法。方法：用钻磨器将暴露的羟基磷灰石义眼台打磨平滑，用异体巩膜和羊膜覆盖义眼台的暴露区。治疗10例，术后进行随访观察5－19月。结果：10例中9例术后8周结膜完全愈合，安装义眼后外观满意；1例后1周巩膜羊膜植片融解脱落，2周后取出义眼台。结论：异体巩膜联合羊膜移植治疗羟基磷灰石义眼台植入后暴露是效果良好的治疗方法。     

Hardness evaluation of penile prostheses

AIM: This work investigates the hardness and buckling force of penile prostheses to further understand the rigidity of penile prostheses before and after implantation. METHODS: Evaluated herein are four prosthetic samples (three inflatable, one semi-rigid), five real prostheses (one inflatable, four semi-rigid), and one prosthesis after implantation. The hardness is measured with a Shore Durimeter by pressing the tester's indentor to the surface of the specimen. A volunteer with inflatable prosthesis implantation is evaluated with respect to penile hardness versus various numbers of pumping. The buckling force of the prosthesis is also determined by a push-pull gauge and a specially designed sampling table. RESULTS: Results in this study demonstrate that although the inflatable prosthesis could only be pumped to a certain amount of hardness, hardness and buckling force correlate well with each other. After reaching the hardness limit, prostheses can even be pumped a further few times. However, continuous pumping only puts more tension on the prosthetic material without increasing hardness and could induce mechanical failure of the prosthesis. Results also indicate that the buckling force decreases with increasing length of the semirigid prostheses, and increases when the prosthesis has a larger diameter. CONCLUSION: This mechanical measurement of rigidity in penile prostheses could provide more information to clinicians about the penile prosthesis before surgical implantation, and to patients about prosthesis usage after implantation.     

Massive Exudative Retinal and Choroidal Detachments Following Scleral Buckling Surgery

Three aphakic male patients underwent successful scleral buckling surgery for unilateral rhegmatogenous retinal detachment. Within a two-week postoperative period, each developed severe ocular pain with massive exudative retinal and choroidal detachments resembling recurrent rhegmatogenous or traction retinal detachment or implant infection. Systemic prednisone therapy resulted in prompt resolution of ocular pain and reabsorption of subretinal and suprachoroidal fluid. It is important to recognize this uncommon postoperative syndrome so that proper medical therapy may be initiated and unnecessary additional retinal or vitreous surgery can be avoided.