STIM1 regulates acidic Ca2+ store refilling by interaction with SERCA3 in human platelets

Area of Science:

• Cellular Biology
• Hematology
• Biochemistry

Background:

• Calcium (Ca2+) mobilization is vital for cellular functions, including platelet activation.
• Platelets store releasable Ca2+ in acidic organelles, with the sarcoendoplasmic reticulum Ca2+-ATPase-3 (SERCA3) pump refilling these stores.
• Stromal interaction molecule 1 (STIM1) acts as a Ca2+ sensor for intracellular Ca2+ stores and regulates platelet function.

Purpose of the Study:

• To investigate the role of STIM1 in the refilling of acidic Ca2+ stores in platelets.
• To determine the interaction between STIM1 and SERCA3 during Ca2+ store refilling.
• To examine the impact of type 2 diabetes on STIM1-SERCA3 interaction and Ca2+ store refilling in platelets.

Main Methods:

• Platelet stimulation with thrombin or thapsigargin/ionomycin to induce Ca2+ store depletion and refilling.
• Electrotransfection of platelets with anti-STIM1 antibody to disrupt STIM1 function.
• Measurement of Ca2+ store refilling using remobilization assays with 2,5-di-(t-butyl)-1,4-hydroquinone (TBHQ).
• Assessment of STIM1 and SERCA3 interaction via co-localization or co-immunoprecipitation techniques.

Main Results:

• Anti-STIM1 antibody significantly reduced acidic Ca2+ store refilling.
• Platelet stimulation led to a transient increase in STIM1 and SERCA3 interaction, peaking at 30 seconds.
• This STIM1-SERCA3 coupling was abolished by anti-STIM1 antibody.
• The STIM1-SERCA3 interaction and Ca2+ reuptake into acidic stores were reduced in platelets from type 2 diabetic patients.

Conclusions:

• STIM1 is essential for acidic Ca2+ store refilling in platelets, likely by sensing Ca2+ and regulating SERCA3 activity.
• Impaired STIM1-SERCA3 interaction and reduced Ca2+ store refilling in type 2 diabetes may contribute to increased cytosolic Ca2+ and platelet hyperactivity.
• These findings highlight a novel mechanism linking STIM1, SERCA3, and Ca2+ homeostasis in platelet function and its dysregulation in diabetes.