Sensory Stimulation of the Triceps Surae Muscle Complex Modulates Spinal Reflex Responses-A Comparison between Tapotement Massage and Repetitive Peripheral Magnetic Stimulation (rPMS).

BACKGROUND: The reduction of muscular hypertonia is important in the treatment of various diseases or rehabilitation. This study aims to test the efficacy of a 5 Hz mechanical muscle stimulation (tapotement massage) in comparison to a 5 Hz repetitive peripheral magnetic stimulation (rPMS) on the neuromuscular reflex response. METHODS: In a randomized control trial, 15 healthy volunteers were administered with either 5 Hz rPMS, tapotement massage, or rPMS sham stimulation. The posterior tibial nerve was stimulated with rPMS and sham stimulation. The Achilles tendon was exposed to a mechanically applied high-amplitude 5 Hz repetitive tendon tapotement massage (rTTM). The tendon reflex (TR) was measured for the spinal response of the soleus muscle. RESULTS: After rPMS, there was a reduction of the TR response (-9.8%, p ≤ 0.034) with no significant changes after sham stimulation. Likewise, TR decreased significantly (-17.4%, p ≤ 0.002) after Achilles tendon tapotement intervention. CONCLUSIONS: These findings support the hypothesis that both afferent 5 Hz sensory stimulations contributed to a modulation within the spinal and/or supraspinal circuits, which resulted in a reduction of the spinal reflex excitability. The effects could be beneficial for patients with muscle hypertonia and could improve the functional results of rehabilitation programs.

Behavioral Effects of Repetitive Transcranial Magnetic Stimulation in Disorders of Consciousness: A Systematic Review and Meta-Analysis.

Traumatic brain injury, cardiac arrest, intracerebral hemorrhage, and ischemic stroke may cause disorders of consciousness (DoC). Repetitive transcranial magnetic stimulation (rTMS) has been used to promote the recovery of disorders of consciousness (DoC) patients. In this meta-analysis, we examined whether rTMS can relieve DoC patient symptoms. We searched through journal articles indexed in PubMed, the Web of Science, Embase, Scopus, and the Cochrane Library until 20 April 2023. We assessed whether studies used rTMS as an intervention and reported the pre- and post-rTMS coma recovery scale-revised (CRS-R) scores. A total of 207 patients from seven trials were included. rTMS significantly improved the recovery degree of patients; the weighted mean difference (WMD) of the change in the CRS-R score was 1.89 (95% confidence interval (CI): 1.39-2.39; p < 0.00001) in comparison with controls. The subgroup analysis showed a significant improvement in CRS-R scores in rTMS over the dorsolateral prefrontal cortex (WMD = 2.24; 95% CI: 1.55-2.92; p < 0.00001; I2 = 31%) and the primary motor cortex (WMD = 1.63; 95% CI: 0.69-2.57; p = 0.0007; I2 = 14%). Twenty-hertz rTMS significantly improved CRS-R scores in patients with DoC (WMD = 1.61; 95% CI: 0.39-2.83; p = 0.010; I2 = 31%). Furthermore, CRS-R scores in rTMS over 20 sessions significantly improved (WMD = 1.75; 95% CI: 0.95-2.55; p < 0.0001; I2 = 12%). rTMS improved the symptoms of DoC patients; however, the available evidence remains limited and inadequate.

Ski Mountaineering-Scientific Knowledge of This New Olympic Sport: A Narrative Review.

ABSTRACT: Ski mountaineering (skimo) has been accepted as a new sport for the 2026 Milan-Cortina Olympics. The equipment used in this competitive ski mountaineering varies from leisure ski mountaineering equipment mainly in one point: the minimal weight. At the elite athlete level, skimo demands both maximal endurance performance and a high-intensity anaerobic capacity for the sprint and vertical races. Race time significantly correlates to V˙O2max, body mass index and racing gear mass. Available literature only rarely comments on competitive skimo injuries. Injuries are not only due to falls in downhill skiing but also can result from external hazards, such as avalanches and cold. The high training load of athletes in combination with a low body weight, low body fat, and exposure to cold cause high rates of respiratory infections in athletes. The inclusion of skimo into the Olympic program is expected to result in certain changes, such as higher training loads for the athletes and increased scientific interest into training methods.

20 Hz Transcranial Alternating Current Stimulation Inhibits Observation-Execution-Related Motor Cortex Excitability.

The present study aimed to investigate the effect of transcranial alternating current stimulation (tACS) on the primary motor cortex (M1) during action observation, and subsequent action execution, on motor cortex excitability. The participants received tACS at 10 Hz or 20 Hz, or a sham stimulation over the left M1 for 10 min while they observed a video displaying a repeated button-tapping task using the right hand, and then performed an identical task with their right hand. Motor-evoked potential (MEP) amplitudes were measured before (T0) and after the action observation paired with tACS or a sham stimulation (T1), and after the performance of the action (T2). The results showed that MEPs were significantly reduced at time point T1 (p = 0.042, Cohen's d = 0.611) and T2 (p = 0.0003, Cohen's d = 0.852) in the 20 Hz tACS condition, in contrast with the sham stimulation. There was a significantly smaller MEP amplitude at time point T2 in the 20 Hz tACS condition, as compared to the 10 Hz tACS condition (p = 0.01, Cohen's d = 0.622), but the MEP amplitude did not significantly change at time point T1 between the 20 Hz and 10 Hz tACS conditions (p = 0.136, Cohen's d = 0.536). There were no significant differences at time point T1 and T2 between the 10 Hz tACS condition and the sham stimulation. We conclude that 20 Hz tACS during action observation inhibited motor cortex excitability and subsequently inhibited execution-related motor cortex excitability. The effects of tACS on task-related motor cortex excitability are frequency-dependent.

Comparing Different Filter-Parameter for Pre-Processing of Brain-Stimulation Evoked Motor Potentials.

BACKGROUND: Brain stimulation motor-evoked potentials (MEPs) are transient signals and not periodic signals, and thus, they differ significantly in their properties from classical surface electromyograms. Unsuitable pre-processing of MEPs due to inappropriate filter settings leads to distortions. Filtering of extensor carpi radialis MEPs with transient signal characteristics of 20 subjects was examined. The effects of a 1st-order Butterworth high-pass filter (HPF) with different cut-off frequencies 1 Hz, 20 Hz, 40 Hz, and 80 Hz and a 5 Hz Butterworth high-pass filter with degrees 1st, 2nd, 4th, 8th-order are investigated for the filter output. RESULTS: The filtering of the MEPs with an inappropriate filter setting led to distortions on the parameters peak-to-peak amplitudes of the MEP (MEPpp) and the absolute integral of the MEP (MEParea). The lowest distortions of all of the examined filter parameters were revealed after filtering with the lowest filter order and the lowest cut-off frequency. The 1st-order 1 Hz HPF calculation results in a difference of -0.53% (p < 0.001) for the MEPpp and -1.94% (p < 0.001) for the MEParea. SIGNIFICANCE: Reproducibility is a major concern in science, including brain stimulation research. Only the filtering of the MEPs with appropriate filter settings led to mostly undistorted MEPs.

Hangboard training in advanced climbers: A randomized controlled trial.

Improving climbing performance strongly depends upon effective training methods. Hangboard training is one of the most popular approaches to increase finger and forearm strength. Training protocols are based on maximizing weight or minimizing edges. We aimed to evaluate which of these protocols was superior. We prospectively analyzed 30 intermediate to advanced climbing athletes [Union Internationale des Associations d'Alpinisme (UIAA) VI-VIII] and randomized them into three groups: control group C (Control, normal climbing training), hangboard group HE (Hang endurance, grips to hold for a determined time decreased every week), and hangboard group HW (Hang weight, + 1.25 kg weight were added each week to hold for a determined time). As endpoints, we measured the grip strength before and after an 8-week training protocol in seven different pinches. Over the 8-week training period, HW hangboard training significantly improved the climbers' grip strength compared to C [p = 0.032, effect size (ES) 0.36]. Maximizing weight improved the strength in I/II + III, I/II + III + IV and fist significantly. HW was superior compared to C in terms of grip strength improvement in three out of seven pinches and overall grip strength. The overall changes in the HE group did not differ significantly from the C group. An 8-week training protocol with increasing weights (HW) significantly improved overall grip strength more than a regular climbing training without the use of a hangboard.

Indoor Bouldering-A Prospective Injury Evaluation.

INTRODUCTION: Bouldering has become a sport of growing interest, but little prospective evidence exists about injury proportions and patterns. The purpose of this study was to prospectively evaluate the cause of injuries sustained during indoor bouldering, proportion of affected body location, and injury severity. METHODS: Proportions and patterns of injury among German-speaking indoor boulderers were evaluated prospectively in an explorative cohort study. Participants completed a baseline questionnaire assessing anthropometric data and sport-specific potential preventive and risk factors, followed by monthly injury questionnaires including injury location and injury severity over a period of 12 mo. RESULTS: Out of 507 boulderers, 222 (44%) sustained 305 injuries. Of those, 78% (n=238) were classified as Union Internationale de Associations d'Alpinisme (UIAA) 1, 19% (n=57) as UIAA 2, and 3% (n=10) as UIAA 3. Injuries of the upper extremities accounted for 63% (n=191) of all injuries. Injuries of the lower extremities accounted for 23% (n=71) but were more often classified as UIAA≥2 (P=0.0071; odds ratio [OR] 2.23; 95% CI 1.23-4.04) and were more often caused by falling (P=0.0005; OR 2.92; 95% CI 1.57-5.42) and jumping off the wall (P<0.0001; OR 4.39; 95% CI 2.25-8.56) than injuries of other body locations. There was no statistically significant protective effect of the evaluated potential preventive measures. Participants who used heavily downturned climbing shoes had a higher risk of sustaining a UIAA ≥2 injury (P=0.0034; OR 2.58; 95% CI 1.34-4.95). CONCLUSIONS: Injuries in indoor bouldering are common. Lower extremity injuries are associated with higher injury severity. Preventive measures need to be established to reduce bouldering injuries, especially during falls and landings.

Multimodal Sensorimotor Integration of Visual and Kinaesthetic Afferents Modulates Motor Circuits in Humans.

Optimal motor control requires the effective integration of multi-modal information. Visual information of movement performed by others even enhances potentials in the upper motor neurons through the mirror-neuron system. On the other hand, it is known that motor control is intimately associated with afferent proprioceptive information. Kinaesthetic information is also generated by passive, external-driven movements. In the context of sensory integration, it is an important question how such passive kinaesthetic information and visually perceived movements are integrated. We studied the effects of visual and kinaesthetic information in combination, as well as isolated, on sensorimotor integration, compared to a control condition. For this, we measured the change in the excitability of the motor cortex (M1) using low-intensity Transcranial magnetic stimulation (TMS). We hypothesised that both visual motoneurons and kinaesthetic motoneurons enhance the excitability of motor responses. We found that passive wrist movements increase the motor excitability, suggesting that kinaesthetic motoneurons do exist. The kinaesthetic influence on the motor threshold was even stronger than the visual information. Moreover, the simultaneous visual and passive kinaesthetic information increased the cortical excitability more than each of them independently. Thus, for the first time, we found evidence for the integration of passive kinaesthetic- and visual-sensory stimuli.

Morphological dependent effect of cell-free formed supramolecular fibronectin on cellular activities.

Fibrillar fibronectin (FFN), an active form of fibronectin (FN), plays important roles in various cellular processes. Our goal is to investigate effect of FFN morphology on cellular behaviors. Plasma FN at two concentrations was cross-linked into FFN by dialysis against 2 M urea followed by morphological analysis under Scanning Electron Microscopy. To evaluate effect of FFN morphology, fibroblasts were cultured on FN or different FFNs. Fibroblast behaviors including adhesion, spreading, and migration were evaluated. Our data showed that FN fibrillogenesis was dependent on FN concentration. At high concentrations (0.75 mg/mL), large FFN approximately 2.167 + 0.875 µm in diameter were formed with attached nodular structures and rough surface. In contrast, smooth surface FFN fibrils with diameter of 1.886 + 0.412 µm were formed from FN at 0.25 mg/mL. Cellular assays revealed morphological dependent biological effects of different FFNs. Fibroblast separately adhered to native FN and remained spherical while on FFN, cells attached with higher quantity and showed spreading morphology. A synergistic ligand interaction of integrin α5ß1 and αvß3 was observed in cell adhering on FFN. Cell migration results showed that large FFN decreased migration rate while small FFN did not. Taken together, our data draws new attention towards controlling biological function of FN by its fibrillar structure.

Returning to Climb after Epiphyseal Finger Stress Fracture.

The number of youth participating in rock climbing has increased over the years. Finger stress epiphyseal fractures are the most common injury among youth climbers. These injuries tend to occur around puberty because this is when the physis is most vulnerable to injury. Additionally, it has been found that intensive finger training (campus boarding, a previously known risk factor for epiphyseal fractures) during adolescence can lead to early-onset osteoarthritis of the hand up to a decade later. There is currently a lack of a return-to-climb protocol for youth climbers following a repetitive stress epiphyseal fracture. Because of this gap in the literature, our purpose was to create a structured return-to-play protocol specific to youth climbers who sustained an epiphyseal fracture to the finger. By establishing these guidelines, medical professionals and coaches may be able to guide their athlete to gradually and safely return to sport.

Neuromuscular Properties of the Human Wrist Flexors as a Function of the Wrist Joint Angle.

The joint angle dependence of voluntary activation and twitch properties has been investigated for several human skeletal muscles. However, although they play a key role for hand function and possess a unique neural control compared to muscles surrounding other joint complexes, little is known about the wrist flexors innervated by the median nerve. Therefore, isometric voluntary and electrically evoked contractions of the wrist flexors were analyzed at three wrist joint angles (extension: -30°, neutral: 0°, flexion: 30°) to quantify the joint angle dependence of (i) voluntary activation (assessed via peripheral nerve stimulation and electromyography [EMG]), (ii) unpotentiated twitch torques, and (iii) potentiated twitch torques. Maximum voluntary torque was lower in extension compared to neutral and flexion. Although voluntary activation was generally high, data indicate that voluntary activation of the wrist flexors innervated by the median nerve was lower and the antagonist·agonist-1 EMG ratio was higher with the wrist joint in flexion compared to extension. Peak twitch torque, rate of twitch torque development, and twitch half-relaxation time increased, whereas electromechanical delay decreased from flexion to extension for the unpotentiated twitch torques. Activity-induced potentiation partly abolished these differences and was higher in short than long wrist flexors. Different angle-dependent excitatory and inhibitory inputs to spinal and supraspinal centers might be responsible for the altered activation of the investigated wrist muscles. Potential mechanisms were discussed and might have operated conjointly to increase stiffness of the flexed wrist joint. Differences in twitch torque properties were probably related to angle-dependent alterations in series elastic properties, actin-myosin interaction, Ca2+ sensitivity, and phosphorylation of myosin regulatory light chains. The results of the present study provide valuable information about the contribution of neural and muscular properties to changes in strength capabilities of the wrist flexors at different wrist joint angles. These data could help to understand normal wrist function, which is a first step in determining mechanisms underlying musculoskeletal disorders and in giving recommendations for the restoration of musculoskeletal function after traumatic or overuse injuries.

Repetitive Peripheral Magnetic Nerve Stimulation (rPMS) as Adjuvant Therapy Reduces Skeletal Muscle Reflex Activity.

Background: The reduction of muscle hypertonia and spasticity, as well as an increase in mobility, is an essential prerequisite for the amelioration of physiotherapeutical treatments. Repetitive peripheral magnetic nerve stimulation (rPMS) is a putative adjuvant therapy that improves the mobility of patients, but the underlying mechanism is not entirely clear. Methods: Thirty-eight participants underwent either an rPMS treatment (N = 19) with a 5 Hz stimulation protocol in the posterior tibial nerve or sham stimulation (N = 19). The stimulation took place over 5 min. The study was conducted in a pre-test post-test design with matched groups. Outcome measures were taken at the baseline and after following intervention. Results: The primary outcome was a significant reduction of the reflex activity of the soleus muscle, triggered by a computer-aided tendon-reflex impact. The pre-post differences of the tendon reflex response activity were -23.7% (P < 0.001) for the treatment group. No significant effects showed in the sham stimulation group. Conclusion: Low-frequency magnetic stimulation (5 Hz rPMS) shows a substantial reduction of the tendon reflex amplitude. It seems to be an effective procedure to reduce muscular stiffness, increase mobility, and thus, makes the therapeutic effect of neuro-rehabilitation more effective. For this reason, the 5 Hz rPMS treatment might have the potential to be used as an adjuvant therapy in the rehabilitation of gait and posture control in patients suffering from limited mobility due to spasticity. The effect observed in this study should be investigated conjoined with the presented method in patients with impaired mobility due to spasticity.

Modulating Observation-Execution-Related Motor Cortex Activity by Cathodal Transcranial Direct Current Stimulation.

The aim of this randomized sham-controlled study was to examine the impact of cathodal transcranial direct current stimulation (ctDCS) of the primary motor cortex (M1) during movement observation on subsequent execution-related motor cortex activity. Thirty healthy participants received sham or real ctDCS (1 mA) over the left M1 for 10 minutes, respectively. The participants observed a video showing repeated button pressing tasks of the right hand during the sham or real ctDCS, followed by performance of these tasks by the right hand. Motor-evoked potentials (MEP) were recorded from the resting right first dorsal interosseous muscle before movement observation during the sham or real ctDCS, immediately after observation of actions, and after subsequent movement execution. The results of the ANOVA showed a significant main effect on the group (F1,28 = 4.60, p = 0.041) and a significant interaction between time and the group (F2,56 = 5.34, p = 0.008). As revealed by respective post hoc tests, ctDCS induced a significant reduction of MEP amplitudes in connection with movement observation (p = 0.026, Cohen's d = 0.861) and after subsequent movement execution (p = 0.018, Cohen's d = 0.914) in comparison with the sham stimulation. It is concluded that ctDCS during movement observation was effective in terms of modulating motor cortex excitability. Moreover, it subsequently influenced execution-related motor cortex activity. This indicates a possible application for rehabilitative treatment in syndromes with pathologically enhanced cortical activity.

Interaction Between Transcranial Random Noise Stimulation and Observation-Execution Matching Activity Promotes Motor Cortex Excitability.

Pathways of the human mirror neuron system are activated during both, action observation and action execution, including lateralized activation of respective areas, as shown by observed right-or left-hand actions. Here, we investigated whether execution-dependent motor cortex excitability is affected by prior interaction between transcranial random noise stimulation (tRNS) and action observation. Sham or real tRNS (1 mA) was applied for 10-min over the left primary motor cortex during action observation. In the main experiments, participants received sham or real tRNS while they watched a video showing repeated tapping tasks, involving either the right-hand (Experiment 1, congruent action observation), or a mirror-reversed video showing the same performance (Experiment 2), followed by action execution of the right-hand. In control Experiments 1-3, participants received real tRNS while observing a perceptual sequence, watching a landscape picture, or observing the left-hand performing the action (the sequence was identical to Experiment 1), followed by action execution of the right-hand. In control Experiment 4, participants received real tRNS during congruent action observation, and then took 6-min rest. Motor-evoked potentials (MEP) were recorded before action observation, a perceptual sequence or a landscape picture, immediately after, and after action execution, or an interval of 6-min, dependent on the respective experimental condition. MEPs in the right first dorsal interosseous muscle increased significantly after real tRNS combined with congruent action observation, and after action execution compared to the sham session in Experiment 1 and control experiments. We conclude that prior interaction between real tRNS and action observation of mirror-matched movements modulates subsequent execution-dependent motor cortex excitability.

The rheology of batch and continuously prepared gluten-free bread dough in oscillatory and capillary shear flow.

Reduced elasticity and high stickiness of gluten-free bread doughs are major issues regarding the industrial breadmaking process. In this work, we compared traditional batch mixing with a revised continuous extrusion process and extensively study the rheological properties of both doughs. Shear viscosities were measured offline with a capillary rheometer and inline at the extruder die over a large range of apparent shear rates. Data were corrected for entrance effects, wall slip and non-Newtonian flow behaviour. Good agreement between inline and offline measured viscosities were supplemented by amplitude and frequency sweep tests. The results highlight that this extrusion process fostered the production of gluten-free bread dough. We demonstrated that extrusion processing support the combined mixing, kneading, and moulding of gluten-free dough in one single unit. This fundamental study linked physical dough characterization with applied engineering and yielded the understanding and processing of corresponding products.

Leu33Pro (PlA) polymorphism of integrin beta3 modulates platelet Src pY418 and focal adhesion kinase pY397 phosphorylation in response to abnormally high shear stress.

OBJECTIVES: Shear stress can activate platelet integrin-mediated signaling that leads to shear-induced platelet aggregation (SIPA) and eventually contribute to acute myocardial infarction. The major platelet integrin αIIbß3 is polymorphic at residue 33 [Leu33Pro (PlA) polymorphism]. The Pro33 isoform has been shown to have a prothrombotic phenotype. In this work, we studied the impact of Leu33/Pro33 polymorphism on the shear-induced integrin-mediated Src and FAK activation in platelets. METHODS: Platelets of both genotypes were placed on immobilized fibrinogen or heat activated BSA and were exposed to physiological (500/s) or abnormally high (5000/s) shear rates for 2-10 min. Platelets after exposure to shear were analysed for Src pY418 and FAK pY397 activities. RESULTS: Whereas physiological shear stress does not affect platelet signaling, abnormally high-shear stress considerably elevates Src and FAK phosphorylation in both Pro33 and Leu33 platelets. Both under static and flow conditions, Pro33 platelets exhibited a significantly higher Src and FAK activities than Leu33 platelets. Interestingly, even in the absence of the αIIbß3-fibrinogen interaction, we could detect a shear-induced integrin-mediated signaling of Src and FAK in platelets. In parallel experiments in which platelets were pretreated with abciximab, an integrin αIIbß3 antagonist, activation of both kinases by shear was inhibited. CONCLUSION: Taken together, our data indicates an important role of αIIbß3 and shows that Leu33Pro polymorphism modulates the integrin-mediated Src and FAK signaling in platelets in response to shear stress.

Delivery of the second twin: influence of presentation on neonatal outcome, a case controlled study.

BACKGROUND: Spontaneous vaginal twin delivery after 32nd week of gestation is safe when first twin presenting cephalic. Aim of this study is to identify obstetric factors influencing the condition of second twin and to verify whether non-cephalic presentation and vaginal breech delivery of the second twin is safe. METHODS: This is a retrospective case controlled cohort study of 717 uncomplicated twin deliveries ≥32 + 0 weeks of gestation from 2005 to 2014 in two tertiary perinatal centers. Obstetric parameters were evaluated in three groups with descriptive, univariate logistic regression analysis for perinatal outcome of second twins. RESULTS: The three groups included twins delivered by elective cesarean section ECS (n = 277, 38.6%), by unplanned cesarean section UPC (n = 233, 32.5%) and vaginally (n = 207, 28.9%). Serious adverse fetal outcome is rare and we found no differences between the groups. Second twins after ECS had significant better umbilical artery UA pH (p < 0.001) and better Apgar compared to UPC (p = 0.002). Variables for a fetal population "at risk" for adverse neonatal outcome after vaginal delivery (UA pH < 7.20, Apgar 5´ < 9) were associated with higher gestational age (p = 0.001), longer twin-twin interval (p = 0.05) and vacuum extraction of twin A (p = 0.04). Non-cephalic presentation of second twins was not associated (UA pH < 7.20 OR 1.97, CI 95% 0.93-4.22, p = 0.07, Apgar 5´ < 9 OR 1.63, CI 95% 0.70-3.77, p = 0.25, Transfer to neonatal intermediate care unit p = 0.48). Twenty-one second twins (2,9%) were delivered by cesarean section following vaginal delivery of the first twin. Even though non-cephalic presentation was overrepresented in this subgroup, outcome variables were not significantly different compared to cephalic presentation. CONCLUSIONS: Even though elective cesarean means reduced stress for second twins this seems not to be clinically relevant. Non-cephalic presentation of the second twin does not significantly influence the perinatal outcome of the second twin but might be a risk factor for vaginal-cesarean birth.

Shear-dependent fibrillogenesis of fibronectin: Impact of platelet integrins and actin cytoskeleton.

Soluble plasma fibronectin (Fn) with its inactive compact structure requires unfolding to assemble into active fibrils, which play a role in hemostasis and thrombosis. Fn fibril assembly involves Fn binding to cell receptors, biomechanical coupling of Fn to the cytoskeleton by integrins, exposure of self-assembly sites via contractile cell forces, and elongation of fibrils by Fn polymerization. In this report, we investigated the effect of platelet integrins and actin cytoskeleton on conformational changes of Fn induced by shear. Plasma Fn, in the presence or absence of washed platelets, was exposed to dynamic shear simulating venous or arterial flow conditions. Platelet integrins (αIIbß3, αvß3, and α5ß1) were blocked by inhibitory antibodies to determine their contribution to shear-induced Fn fibrillogenesis. To examine the role of platelet cytoskeleton in Fn fibrillogenesis induced by shear, platelets were preincubated with cytoskeleton drugs, i. e jasplakinolide to stabilize actin or cytochalasin D to inhibit actin polymerization. Microscopic analyses demonstrated that flow and resulting shear stress over a broad range of physiological and pathological rates (50-5000 s-1) could induce conformational changes of plasma Fn. In addition, the formation of Fn fibrils is modulated by platelet integrins. In this respect, ß3 integrins play a dominant role in terms of Fn fibrillogenesis induced by shear. Disruption of the actin polymerization markedly diminished Fn unfolding and assembly. These observations lead to the conclusion that Fn-integrin ß3-cytoskeleton interaction is crucial for the assembly of plasma Fn matrix under flow conditions.

The human platelet antigen-1b (Pro33) variant of αIIbß3 allosterically shifts the dynamic conformational equilibrium of this integrin toward the active state.

Integrins are heterodimeric cell-adhesion receptors comprising α and ß subunits that transmit signals allosterically in both directions across the membrane by binding to intra- and extracellular components. The human platelet antigen-1 (HPA-1) polymorphism in αIIbß3 arises from a Leu → Pro exchange at residue 33 in the genu of the ß3 subunit, resulting in Leu33 (HPA-1a) or Pro33 (HPA-1b) isoforms. Although clinical investigations have provided conflicting results, some studies have suggested that Pro33 platelets exhibit increased thrombogenicity. Under flow-dynamic conditions, the Pro33 variant displays prothrombotic properties, characterized by increased platelet adhesion, aggregate/thrombus formation, and outside-in signaling. However, the molecular events underlying this prothrombotic phenotype have remained elusive. As residue 33 is located >80 Å away from extracellular binding sites or transmembrane domains, we hypothesized that the Leu → Pro exchange allosterically shifts the dynamic conformational equilibrium of αIIbß3 toward an active state. Multiple microsecond-long, all-atom molecular dynamics simulations of the ectodomain of the Leu33 and Pro33 isoforms provided evidence that the Leu → Pro exchange weakens interdomain interactions at the genu and alters the structural dynamics of the integrin to a more unbent and splayed state. Using FRET analysis of fluorescent proteins fused with αIIbß3 in transfected HEK293 cells, we found that the Pro33 variant in its resting state displays a lower energy transfer than the Leu33 isoform. This finding indicated a larger spatial separation of the cytoplasmic tails in the Pro33 variant. Together, our results indicate that the Leu → Pro exchange allosterically shifts the dynamic conformational equilibrium of αIIbß3 to a structural state closer to the active one, promoting the fully active state and fostering the prothrombotic phenotype of Pro33 platelets.