Delineating Zinc Influx Mechanisms during Platelet Activation

Area of Science:

• Hematology
• Cellular Physiology
• Biochemistry

Background:

• Platelets release zinc (Zn²⁺) during hemostasis.
• Extracellular zinc ([Zn²⁺]_o) activates platelets via influx into the cytosol.
• Mechanisms of Zn²⁺ influx into platelets were previously unknown.

Purpose of the Study:

• To elucidate the mechanisms of extracellular zinc ([Zn²⁺]_o) influx into platelets.
• To investigate the role of zinc influx in platelet activation and signaling.
• To identify the specific channels and pathways involved in zinc entry.

Main Methods:

• Measured intracellular zinc ([Zn²⁺]_i) using fluozin-3, fluorometry, and flow cytometry.
• Assessed platelet activation via light transmission aggregometry.
• Detected phosphoproteins using Western blotting.
• Investigated the role of TRP channels, NCX, ZIP7, Orai1, and IP₃R.

Main Results:

• [Zn²⁺]_o influx and platelet activation were blocked by inhibiting the sodium/calcium exchanger (NCX), TRP channels, and ZIP7.
• Cation store depletion regulated Zn²⁺ influx, indicating a store-operated pathway (SOZE).
• [Zn²⁺]_o stimulation led to phosphorylation of PKC substates, MLC, and β3 integrin.
• Platelet activation induced ZIP7 phosphorylation and subsequent Zn²⁺ influx via Orai1, ZIP7, or IP₃R pathways.

Conclusions:

• Platelets detect and respond to extracellular zinc ([Zn²⁺]_o) through influx via TRP channels and the NCX exchanger.
• Platelet activation involves ZIP7 externalization, regulating further zinc influx.
• Increased intracellular zinc ([Zn²⁺]_i) activates cation-dependent enzymes, impacting thrombosis and hemostasis.