ABSTRACT
BACKGROUND: All-trans retinoic acid (ATRA) is an ideal therapy for acute promyelocytic leukemia, which can induce promyelocytes to differentiate to mature granulocytes. However, differentiation syndrome is still a high risk for the patients undergoing ATRA therapy. Occurrence of this complication is closely related with cellular morphology change and expression and function of cellular adhesion molecules, especially selectin and integrin families. OBJECTIVE: To reveal rolling adhesion behavior and mechanical mechanism of ATRA treated HL-60 cells on the substrate coated with E-selectin under different fluid shear forces. METHODS: Using the equipment of parallel plate flow chamber, untreated and ATRA treated HL-60 cells were driven to roll on E-selectin-coated substrate. The mean rolling velocity and mean stop time were calculated. Here, the HL-60 cells were incubated in the medium containing 1×10-6mol/L ATRA for 0, 48, 72, 96 hours. The substrates were captured with 40 μg/L E-selectin overnight and the shear stresses were set to 0.02, 0.04, 0.06 Pa. RESULTS AND CONCLUSION: The velocity of untreated/treated HL-60 cells decreased firstly and then increased with monotonously increasing shear stress. On the contrary, the mean stop time and factional stop time increased firstly and then decreased. Therefore, we deduced that the flow enhanced rolling adhesion was regulated by the catch bond for the HL-60 cells rolling on E-selectin under flow. On the other side, rolling velocities decreased under the same shear stress even if treated with or without ATRA, and the mean stop time and factional stop time increased inversely, which further illustrate the rolling velocity is mainly regulated by stop time.
ABSTRACT
Objective To filter the noises in the experimental data of parallel plate flow chamber for observing more clearly the events occurring in the process of cell rolling adhesion and develop a new method to measure the elasticity of microvillus on cells based on the flow chamber experiment. Method The experiment of E-selectin regulated HL-60 cell rolling was performed by flow chamber system, and the data were denoised by wavelet analysis so that the high frequency thermal response signals were extracted from the data. Based on the equipartition theorem and equilibrium equations of tethered cell, the relationship between the cell microvillus spring constant and thermal fluctuations was constructed. Results Filtering noises from cell rolling time course by wavelet analysis, the events such as free rolling, slowing down, stopping and speeding up of rolling cell could be observed more easily; almost 80% of fluctuating energy of a rolling cell was involved in its high frequency fluctuation which was regarded as the thermal response of the cell to the Brown movement of water molecules, and the spring constant of microvillus on HL-60 cell was measured to be (13.7±7.4) μN/m at wall shear stress from 0.01～0.06 Pa. Conclusions The wavelet analysis can filter the thermal noises in cell rolling data of flow chamber experiment, and since the rigidity information of cell microvillus is involved in and can be extracted from the high frequency thermal fluctuation of the rolling cell, the parallel plate flow chamber experimental technique can be extended to measure the elasticity of microvillus on cells.