Extracellular signal-regulated kinase activation and endothelin-1 production in human endothelial cells exposed to vibration

Abstract

Hand-arm vibration syndrome is a vascular disease of occupational origin and a form of secondary Raynaud's phenomenon. Chronic exposure to hand-held vibrating tools may cause endothelial injury. This study investigates the biomechanical forces involved in the transduction of fluid vibration in the endothelium. Human endothelial cells were exposed to direct vibration and rapid low-volume fluid oscillation. Rapid low-volume fluid oscillation was used to simulate the effects of vibration by generating defined temporal gradients in fluid shear stress across an endothelial monolayer. Extracellular signal-regulated kinase (ERK1/2) phosphorylation and endothelin-1 (ET-1) release were monitored as specific biochemical markers for temporal gradients and endothelial response, respectively. Both vibrational methods were found to phosphorylate ERK1/2 in a similar pattern. At a fixed frequency of fluid oscillation where the duration of each pulse cycle remained constant, ERK1/2 phosphorylation increased with the increasing magnitude of the applied temporal gradient. However, when the frequency of flow oscillation was increased (thus decreasing the duration of each pulse cycle), ERK1/2 phosphorylation was attenuated across all temporal gradient flow profiles. Fluid oscillation significantly stimulated ET-1 release compared to steady flow, and endothelin-1 was also attenuated with the increase in oscillation frequency. Taken together, these results show that both the absolute magnitude of the temporal gradient and the frequency/duration of each pulse cycle play a role in the biomechanical transduction of fluid vibrational forces in endothelial cells. Furthermore, this study reports for the first time a link between the ERK1/2 signal transduction pathway and transmission of vibrational forces in the endothelium.

Figure 1. Activation of ERK1/2 in HUVEC after 10 min of direct platform vibration

For 1g at 30 Hz n = 5, and for 2g at 30 Hz n = 6. All values are means ±s.e.m.*Significant difference from sham control (P < 0.05). ^†Positive linear trend.

Figure 2. Activation of ERK1/2 as a function of the magnitude of the temporal gradient

A, diagrammatic representation comparing the low (grey line) and high (black line) temporal gradient flow profiles. The magnitude of the peak amplitudes is not to scale. B, low temporal gradient flow profile (70 Pa s⁻¹; n = 6), and high temporal gradient flow profile (930 Pa s⁻¹; n = 8). All values are means ± s.e.m.*Significant difference from sham control (P < 0.05). ^†Positive linear trend.

Figure 3. Activation of ERK1/2 as a function of the frequency of flow oscillation

A, diagrammatic representation of three oscillation frequencies for a given temporal gradient flow profile. For a given flow profile, the black line represents the lowest frequency, the white line represents the middle frequency, and the grey line represents the highest frequency. Absolute frequency and magnitude of the peak amplitudes are not to scale. B, low temporal gradient flow profile (70 Pa s⁻¹; n = 6; left panel), and high temporal gradient flow profile (930 Pas⁻¹; n = 8; right panel). Sham control = 100%. All values are means ±s.e.m. All values are significantly greater than sham control, except for 70 Pa s⁻¹ at 8 Hz. *Significant difference between frequencies within the same profile. ^†Significant difference between profiles at the same frequency.

Figure 4. Activation of ERK1/2 at a fixed frequency and matched peak amplitudes between three temporal gradient flow profiles

A, diagrammatic representation comparing the low (grey line), intermediate (white line) and high (black line) temporal gradient flow profiles. At 1 Hz fluid flow (forward or reverse) is continuous throughout the low profile cycle. Small lag times between the forward and reverse components of flow are required in order to match both frequency and peak amplitude in the intermediate and high profiles. The magnitude of the peak amplitudes and pulse widths is not to scale. B, low temporal gradient flow profile (60 Pa s⁻¹; n = 12), intermediate temporal gradient flow profile (240 Pa s⁻¹; n = 10), and high temporal gradient flow profile (720 Pa s⁻¹; n = 12). All values are means ±s.e.m. All values are significantly greater than sham control, except for 720 Pa s⁻¹. *Significant difference between treatments.

Figure 5. Endothelial production of ET-1 is enhanced by flow oscillation

Steady fluid shear stress was devoid of temporal gradients (n = 7). For 4 and 8 Hz n = 7, for 12 Hz n = 10. All values are means ±s.e.m.*Significant difference from steady fluid shear stress.