Paschall Christopher D, Guilford William H, Lawrence Michael B
Department of Biomedical Engineering, University of Virginia, Charlottesville, Virginia 22908, USA.
Biophys J. 2008 Feb 1;94(3):1034-45. doi: 10.1529/biophysj.106.098707. Epub 2007 Sep 21.
L-selectin-mediated leukocyte rolling has been proposed to require a high rate of bond formation compared to that of P-selectin to compensate for its much higher off-rate. To test this hypothesis, a microbead system was utilized to measure relative L-selectin and P-selectin bond formation rates on their common ligand P-selectin glycoprotein ligand-1 (PSGL-1) under shear flow. Using video microscopy, we tracked selectin-coated microbeads to detect the formation frequency of adhesive tether bonds. From velocity distributions of noninteracting and interacting microbeads, we observed that tether bond formation rates for P-selectin on PSGL-1 decreased with increasing wall shear stress, from 0.14 +/- 0.04 bonds/microm at 0.2 dyn/cm(2) to 0.014 +/- 0.003 bonds/microm at 1.0 dyn/cm(2). In contrast, L-selectin tether bond formation increased from 0.017 +/- 0.005 bonds/microm at 0.2 dyn/cm(2) to 0.031 +/- 0.005 bonds/microm at 1.0 dyn/cm(2). L-selectin tether bond formation rates appeared to be enhanced by convective transport, whereas P-selectin rates were inhibited. The transition force for the L-selectin catch-slip transition of 44 pN/bond agreed well with theoretical models (Pereverzev et al. 2005. Biophys. J. 89:1446-1454). Despite catch bond behavior, hydrodymanic shear thresholding was not detected with L-selectin beads rolling on PSGL-1. We speculate that shear flow generated compressive forces may enhance L-selectin bond formation relative to that of P-selectin and that L-selectin bonds with PSGL-1 may be tuned for the compressive forces characteristic of leukocyte-leukocyte collisions during secondary capture on the blood vessel wall. This is the first report, to our knowledge, comparing L-selectin and P-selectin bond formation frequencies in shear flow.
与P-选择素相比，L-选择素介导的白细胞滚动被认为需要更高的键形成速率，以补偿其更高的解离速率。为了验证这一假设，我们利用微珠系统在剪切流下测量L-选择素和P-选择素与其共同配体P-选择素糖蛋白配体-1（PSGL-1）的相对键形成速率。通过视频显微镜，我们追踪选择素包被的微珠以检测粘附系链键的形成频率。从非相互作用和相互作用微珠的速度分布中，我们观察到PSGL-1上P-选择素的系链键形成速率随壁面剪切应力的增加而降低，从0.2达因/平方厘米时的0.14±0.04个键/微米降至1.0达因/平方厘米时的0.014±0.003个键/微米。相比之下，L-选择素系链键的形成从0.2达因/平方厘米时的0.017±0.005个键/微米增加到1.0达因/平方厘米时的0.031±0.005个键/微米。L-选择素系链键的形成速率似乎因对流运输而增强，而P-选择素的速率则受到抑制。L-选择素捕获-滑移转变的转变力为44皮牛/键，与理论模型吻合良好（Pereverzev等人，2005年。《生物物理学杂志》89:1446 - 1454）。尽管存在捕获键行为，但在PSGL-1上滚动的L-选择素微珠未检测到流体动力学剪切阈值。我们推测，剪切流产生的压缩力可能相对于P-选择素增强L-选择素的键形成，并且L-选择素与PSGL-1的键可能针对血管壁二次捕获期间白细胞-白细胞碰撞的压缩力特性进行了调整。据我们所知，这是第一份比较剪切流下L-选择素和P-选择素键形成频率的报告。
