Toward a role for the acoustic field in cells interaction

Abstract

Nanoscale motility of cells is a fundamental phenomenon, closely associated with biological status and response to environmental solicitations, whose investigation has disclosed new perspectives for the comprehension of cell behavior and fate. To investigate intracellular interactions, we designed an experiment to monitor movements of clusters of neuroblastoma cells (SH-SY5Y) growing on a nanomechanical oscillator (nanomotion sensor) suspended few hundreds of microns over the surface of a Petri dish where other neuroblastoma cells are freely moving. We observed that the free-to-move cells feel the presence of cells on the nearby nanosensor (at a distance of up to 300 microns) and migrate toward them, even in presence of environmental hampering factors, such as medium microflows. The interaction is bidirectional since, as evidenced by nanomotion sensing, the cells on the sensor enhance their motion when clusters of freely moving cells approach. Considering the geometry and environmental context, our observations extend beyond what can be explained by sensing of chemical trackers, suggesting the presence of other physical mechanisms. We hypothesize that the acoustic field generated by cell vibrations can have a role in the initial recognition between distant clusters. Integrating our findings with a suitable wave propagation model, we show that mechanical waves produced by cellular activity have sufficient energy to trigger mechanotransduction in target cells hundreds of microns away. This interaction can explain the observed distance-dependent patterns of cellular migration and motion alteration. Our results suggest that acoustic fields generated by cells can mediate cell-cell interaction and contribute to signaling and communication.

Keywords: acoustic field; cell behavior; cell-cell interactions; mechanical waves; nanomotion sensor; neuroblastoma cell.

Figure 1

Sketch of the setup. The sensor is immersed in the growing medium in a Petri dish with an optical microscope collecting images. The sensor is bearing S-cell NB which are interacting (outward black and gray circles) with P-cells. These cells are aggregating and moving in the background following the medium flow (black arrow lines). Inset: Image of the setup as acquired through the optical microscope, with the sensor in foreground and the aggregated cells in focus on the background.

Figure 2

Aggregation tendency of P-cells. Panels a1–a2 and b1–b2: Two examples of NB cells which tend, over time, to aggregate to form larger clusters. In the foreground, the sensor bearing S-cells.

Figure 3

Dynamics of the interaction between P-cells and S-cells. The trajectories (series of black or red squares on the optical image) and displacement (corresponding a1–a2 and b1–b2 graphs) of a cell cluster over time. (A) Shows a cluster stopping near the S-cells (red squares with a larger square corresponding to the area of cell-cell interaction) and a nearby cluster which does not change its trajectory (black squares). (B) Shows two clusters stopping near the S-cells (red squares with larger squares and numbers corresponding to the areas of cell-cell interaction) and a nearby cluster which passes under the sensor but does not change its trajectory (black squares). The scale bar indicates 50 mm and the lighter variance curves indicate the error in the displacement measurements.

Figure 4

Cellular nanoscale vibration response of the S-cells to the nearby presence of the P-cells. (A) Nanomotion variance during an entire experiment, lasting more than 3 h. (B) Zoom in to highlight the behavior at lower variance values. Panels 1 to 4: Snapshots of interesting cell-cell interactions: the nanomotion variance increases according to the size and distance of the cluster of P-cells which have approached the sensor. (C) Typical amplitudes collected from the sensor in correspondence to zones 1 and 2 (right curve), zone 3 (center curve) and zone 4 (right curve).