As a key regulator of immune response,CD40 L is usually associated with chronic disease-related inflammation,autoimmune diseases and malignant diseases.Receptor recognition of platelet CD40 L is the initial event that...As a key regulator of immune response,CD40 L is usually associated with chronic disease-related inflammation,autoimmune diseases and malignant diseases.Receptor recognition of platelet CD40 L is the initial event that mediates platelet aggregation and leukocyte immune response.Unlike soluble CD40 L,the interaction between transmembrane platelet CD40 L and its receptors occurs within the cell junction surface,usually,in a physiological and pathological high blood flow shear stress environment.This two-dimensional reaction kinetics should be a mechano-chemical coupling process.In addition to its classical receptor CD40,CD40 L also binds to receptorα5β1,CD40 L can bind to the resting state of integrinα5β1,but the mechanical regulation mechanism of integrinα5β1 activation under fluid shear stress remains unclear.We assume that the force can promote CD40 L-inducedα5β1 activation.To check this hypothesis,we performed flow chamber experiment to investigate interaction of CD40 L andα5β1.In experiments,the bottom of the flow chamber is functionalized by a suitable concentration of CD40 L,and the fiber spheres of 6μm diameter was coated withα5β1.The selection of CD40 L concentration was based on the observation that as many tether events ofα5β1-coated spheres as possible were observed rather than stable adhesion events of these spheres.Theα5β1-coated sphere suspension was poured over the CD40 L-coated substrates in the flow chamber under different shear rates.A high-speed camera was used to observe and record tether events of fiber spheres at a rate of 100 frames per second.According to our affinity state transition model for integrin,the data were analyzed to obtain the rate of integrin activation and its mechanical regulation characteristics.Our results demonstrated that the interaction betweenα5β1 and CD40 L is biphasic force-dependent,showing mechano-chemical regulation mechanism of'Catch-slip bond'transition.The affinity jumping model was well fitted with the data obtained from flow chamber experiment at various wall shear stresses.We found that,CD40 L ligation-induced jumping ofα5β1 affinity state from low to medium(or high)one will occur within 0.5-1.0 second,resulting in prolonging of bond lifetimes.And,frequency distribution of the tether events number with tether lifetime under each force,exhibits obvious doublet peaks,one within 0.5-1 s and second within 1.5-2.5 s,indicating theα5β1 affinity state transform from low to high one.The probability distribution of the tether lifetime under different shear forces are not linear,and exists a turning point,which shows that the rate ofα5β1 dissociation from CD40 L is fast first,and then become slow,showing a force-induced conformation transformation of the integrinα5β1 from low affinity state to high affinity one.Our findings suggest that,the continuous force stimulation will quickly cause the affinity state change of integrinα5β1. The dissociation rate of theα5β1/CD40 L complex decreases first and then increases with wall shear stress,exhibiting a'Catch-slip bond'transformation of interaction betweenα5β1-CD40 L.This mechanical regulation mechanism exists in interaction of CD40 L not only toα5β1 at low affinity state but also to one at high affinity state.Our results should be useful in understanding the mechanical regulation mechanism of a5β1-CD40 L interaction-mediated cellular immune response and inflammatory processes.展开更多
基金supported by the National Natural Science Foundation of China ( 116272109, 11432006)
文摘As a key regulator of immune response,CD40 L is usually associated with chronic disease-related inflammation,autoimmune diseases and malignant diseases.Receptor recognition of platelet CD40 L is the initial event that mediates platelet aggregation and leukocyte immune response.Unlike soluble CD40 L,the interaction between transmembrane platelet CD40 L and its receptors occurs within the cell junction surface,usually,in a physiological and pathological high blood flow shear stress environment.This two-dimensional reaction kinetics should be a mechano-chemical coupling process.In addition to its classical receptor CD40,CD40 L also binds to receptorα5β1,CD40 L can bind to the resting state of integrinα5β1,but the mechanical regulation mechanism of integrinα5β1 activation under fluid shear stress remains unclear.We assume that the force can promote CD40 L-inducedα5β1 activation.To check this hypothesis,we performed flow chamber experiment to investigate interaction of CD40 L andα5β1.In experiments,the bottom of the flow chamber is functionalized by a suitable concentration of CD40 L,and the fiber spheres of 6μm diameter was coated withα5β1.The selection of CD40 L concentration was based on the observation that as many tether events ofα5β1-coated spheres as possible were observed rather than stable adhesion events of these spheres.Theα5β1-coated sphere suspension was poured over the CD40 L-coated substrates in the flow chamber under different shear rates.A high-speed camera was used to observe and record tether events of fiber spheres at a rate of 100 frames per second.According to our affinity state transition model for integrin,the data were analyzed to obtain the rate of integrin activation and its mechanical regulation characteristics.Our results demonstrated that the interaction betweenα5β1 and CD40 L is biphasic force-dependent,showing mechano-chemical regulation mechanism of'Catch-slip bond'transition.The affinity jumping model was well fitted with the data obtained from flow chamber experiment at various wall shear stresses.We found that,CD40 L ligation-induced jumping ofα5β1 affinity state from low to medium(or high)one will occur within 0.5-1.0 second,resulting in prolonging of bond lifetimes.And,frequency distribution of the tether events number with tether lifetime under each force,exhibits obvious doublet peaks,one within 0.5-1 s and second within 1.5-2.5 s,indicating theα5β1 affinity state transform from low to high one.The probability distribution of the tether lifetime under different shear forces are not linear,and exists a turning point,which shows that the rate ofα5β1 dissociation from CD40 L is fast first,and then become slow,showing a force-induced conformation transformation of the integrinα5β1 from low affinity state to high affinity one.Our findings suggest that,the continuous force stimulation will quickly cause the affinity state change of integrinα5β1. The dissociation rate of theα5β1/CD40 L complex decreases first and then increases with wall shear stress,exhibiting a'Catch-slip bond'transformation of interaction betweenα5β1-CD40 L.This mechanical regulation mechanism exists in interaction of CD40 L not only toα5β1 at low affinity state but also to one at high affinity state.Our results should be useful in understanding the mechanical regulation mechanism of a5β1-CD40 L interaction-mediated cellular immune response and inflammatory processes.
