Alteration in Ca2+ homeostasis by a trauma peptide

Area of Science:

• Immunology
• Cell Biology
• Biochemistry

Background:

• Post-injury inflammation generates immunosuppressive fibronectin peptides (FNDP).
• FNDP impair T-cell activation and proliferation.
• Elevated intracellular calcium ([Ca2+]i) inhibits T-cell activation.

Purpose of the Study:

• To quantify changes in [Ca2+]i after exposure to fibronectin degradation peptides (FNDP).
• To elucidate the mechanism by which FNDP affect calcium homeostasis in T-cells.
• To investigate the role of extracellular and intracellular calcium sources in FNDP-induced calcium changes.

Main Methods:

• Human peripheral blood lymphocytes (PBLs) were loaded with the calcium indicator FURA-2AM.
• PBLs were exposed to FNDP, and resting and sustained [Ca2+]i were measured.
• Experiments involved pretreatment with EDTA, calcium channel blockers (verapamil, nifedipine), and dantrolene; inositol triphosphate (IP3) levels were also assessed.

Main Results:

• FNDP exposure caused a 200-400% increase in [Ca2+]i at immunosuppressive doses.
• Verapamil and nifedipine partially inhibited [Ca2+]i influx (up to 50%), suggesting involvement of slow, voltage-independent calcium channels.
• EDTA blocked extracellular calcium influx but did not fully inhibit [Ca2+]i release, despite an 80% suppression of IP3.

Conclusions:

• The increase in [Ca2+]i following FNDP stimulation is primarily due to the release of calcium from intracellular stores.
• FNDP-induced calcium dysregulation contributes to T-cell dysfunction.
• Understanding this mechanism provides insight into immunosuppression during inflammation.