Time-Course Statistical Evaluation of Intercellular Adhesion Maturation by Femtosecond Laser Impulse

The maturation of intercellular adhesion is an essential process for establishing the signal transduction network in living cells. Although the maturation is naturally considered to enhance the signal transduction, the relationship between the signal transduction and the maturation process has not been revealed in detail using time-course data. Here, using a coculture of mast cells and neurites, differences in maturation between individual cells were estimated as a function of the adhesion strength by our original single-cell measurement method utilizing a laser-induced impulsive force. When an intense femtosecond laser is focused into a culture medium under a microscope, shock and stress waves are generated at the laser focal point that exert an impulsive force on individual cells. In our method, this impulse is used to break the adhesion between a mast cell and a neurite. The magnitude of the impulse is then quantified by a local force-measurement system utilizing an atomic force microscope, and the adhesion strength is estimated from the threshold of the impulse required to break the adhesion. The measurement is conducted within 1 min/cell, and thus, data on the individual differences of the adhesion strength can be obtained within only a few hours. Coculturing of neurites and mast cells for 4 h resulted in a specific adhesion that was stronger than the nonspecific adhesions between the substrate and mast cells. In the time-course investigation, we identified two distinct temporal patterns of adhesion: 1) the strength at 24 h was the same as the initial strength; and 2) the strength increased threefold from baseline and became saturated within 24 h. Based on these results, the distribution of CADM1 adhesion molecules in the neurites was suggested to be inhomogeneous, and the relationship between adhesion maturation and the signal-transduction process was considered.