Mammalian target of rapamycin (mTOR) orchestrates the defense program of innate immune cells

Area of Science:

• Immunology
• Cellular Biology
• Molecular Signaling

Background:

• The mammalian target of rapamycin (mTOR) is a key regulator of cellular growth, metabolism, and stress responses.
• Its role in innate immune defense mechanisms, particularly Toll-like receptor (TLR) signaling, remains largely unexplored.

Purpose of the Study:

• To investigate the involvement of mTOR in the innate immune response triggered by TLRs.
• To elucidate the molecular mechanisms by which mTOR influences immune cell function and cytokine production.

Main Methods:

• Utilized phosphoinositide 3-kinase/Akt signaling pathway analysis to study mTOR activation.
• Investigated the physical association of mTOR with MyD88 scaffold protein.
• Assessed the activation of interferon regulatory factors (IRFs) and caspase-1.
• Measured cytokine levels (IL-1beta, type I IFN) and animal survival in response to endotoxin.

Main Results:

• TLR activation stimulates mTOR through the phosphoinositide 3-kinase/Akt pathway.
• mTOR interacts with MyD88, facilitating the activation of IRF-5 and IRF-7, crucial for pro-inflammatory and type I IFN gene expression.
• Contrary to expectations, mTOR inactivation exacerbated lethality in endotoxin-induced shock, associated with elevated IL-1beta levels.
• Mechanistically, mTOR was found to suppress caspase-1 activation, thereby limiting the release of bioactive IL-1beta.

Conclusions:

• mTOR is an essential component of pattern recognition receptor (PRR) signaling pathways in innate immunity.
• mTOR orchestrates the innate immune cell defense program by modulating transcription factors and cytokine release.
• The study reveals a complex role for mTOR in innate immunity, highlighting its function in suppressing excessive inflammation via IL-1beta inhibition.