Physiological levels of fluid shear stress modulate vascular function through TRPV4 sparklets

Area of Science:

• Cardiovascular Physiology
• Endothelial Cell Biology
• Calcium Signaling

Background:

• Endothelial calcium (Ca2+) signaling is crucial for vasodilation.
• Transient Receptor Potential Vanilloid 4 (TRPV4) channels mediate Ca2+ influx ('sparklets') in response to stimuli.
• The role of fluid shear stress (FSS) in initiating TRPV4 sparklets and vasodilation is not fully understood.

Purpose of the Study:

• To determine the range of FSS that induces TRPV4 sparklets.
• To investigate the mechanisms of FSS-induced vasodilation mediated by TRPV4 channels.
• To elucidate the role of Ca2+ signaling in regulating vascular function under FSS.

Main Methods:

• Ca2+ imaging in intact small mesenteric arteries using a GCaMP2(TRPV4-KO) mouse model.
• High-speed confocal microscopy to observe Ca2+ signals under varying FSS levels (4-8 dyne/cm2 and >8 dyne/cm2).
• Analysis of TRPV4 channel clustering and downstream signaling pathways.

Main Results:

• Increased local Ca2+ signals (sparklets) observed in endothelium under 4-8 dyne/cm2 FSS.
• Global Ca2+ influx occurred at FSS >8 dyne/cm2.
• TRPV4 channels function as four-channel clusters to mediate sparklets under specific FSS.
• Ca2+ influx hyperpolarized endothelial and smooth muscle cells via IK and SK channels, causing vasodilation.

Conclusions:

• Specific FSS levels activate endothelial TRPV4 channels, initiating Ca2+ sparklets.
• These sparklets trigger a signaling cascade involving IK/SK channels, leading to endothelium-dependent vasodilation.
• TRPV4-mediated Ca2+ signaling is a key mechanism in regulating vascular tone in response to blood flow.