Calcium signalling during chemotaxis

Area of Science:

• Cell Biology
• Immunology
• Biochemistry

Background:

• Eosinophils are crucial immune cells involved in inflammatory responses.
• Chemotaxis, the directed movement of cells towards a chemical attractant, is fundamental to immune cell function.
• Calcium ions (Ca2+) are known secondary messengers in cellular signaling pathways.

Purpose of the Study:

• To investigate the specific role of Ca2+ in the chemotaxis of newt eosinophils.
• To elucidate the mechanisms by which Ca2+ gradients are established and maintained during directed cell migration.
• To understand the involvement of inositol 1,4,5-trisphosphate (InsP3) and 1,2-diacyl-sn-glycerol (DAG) in regulating Ca2+ signaling during chemotaxis.

Main Methods:

• Utilized fluorescent indicators and digital imaging microscopy to monitor intracellular Ca2+ concentration ([Ca2+]i).
• Employed microinjection of heparin to block Ca2+ signals and caged InsP3 to study InsP3-mediated Ca2+ release.
• Investigated the effects of DAG and protein kinase C (PKC) on Ca2+ signaling.

Main Results:

• Cytoplasmic Ca2+ concentration ([Ca2+]i) rises before eosinophil polarization in response to chemoattractant.
• [Ca2+]i gradients (high at the tail, low at the front) are observed in polarized cells, with transient increases preceding changes in direction.
• Ca2+ signals are dependent on internal Ca2+ stores released by InsP3 and are modulated by DAG, likely via PKC.
• InsP3-responsive Ca2+ stores are concentrated near the nucleus and microtubule-organizing center, and InsP3 acts as a global secondary messenger.

Conclusions:

• Ca2+ signaling is essential for eosinophil polarization and locomotion during chemotaxis.
• Stable [Ca2+] gradients during migration result from the localization of InsP3-sensitive Ca2+ stores.
• Reorientation of [Ca2+] gradients is mediated by the interplay between InsP3-induced Ca2+ release and DAG/PKC-mediated local inhibition of Ca2+ influx.