Extracellular CIRP Induces Calpain Activation in Neurons via PLC-IP₃-Dependent Calcium Pathway

Area of Science:

• Neuroscience
• Molecular Biology
• Biochemistry

Background:

• Abnormal calcium homeostasis, calpain activation, and Cdk5 hyperactivation are implicated in neurodegenerative diseases.
• Extracellular cold-inducible RNA-binding protein (eCIRP) is known to induce Cdk5 activation via p25.

Purpose of the Study:

• To elucidate the molecular mechanism by which eCIRP regulates calcium signaling and calpain.
• To investigate the role of eCIRP in p25 generation and subsequent Cdk5 activation.

Main Methods:

• Utilized Neuro 2a (N2a) and HT22 cells to study eCIRP's effects on calpain activity, calpastatin levels, and p25 generation.
• Employed calpain inhibition (calpeptin), calpain 1 silencing, and specific inhibitors (Compound 23, U73122, xestospongin-C) to dissect the signaling pathway.
• Measured intracellular calcium ([Ca2+]i) levels and assessed the involvement of endoplasmic reticulum (ER) calcium release and phospholipase C (PLC) signaling.

Main Results:

• eCIRP increased calpain activity and decreased calpastatin in N2a cells, an effect attenuated by calpeptin.
• eCIRP upregulated cytosolic calpain 1, and its silencing reduced eCIRP-induced p25.
• eCIRP stimulated Ca2+ release from ER stores via an IL-6Rα/PLC/IP3 pathway, increasing cytosolic free Ca2+ in HT22 cells.

Conclusions:

• eCIRP triggers Ca2+ release from ER stores through an IL-6Rα/PLC/IP3-dependent pathway.
• This mechanism underlies eCIRP-induced p25 generation and Cdk5 hyperactivation.
• The findings reveal a novel molecular pathway linking eCIRP to neurodegeneration.