Absence of Appl2 sensitizes endotoxin shock through activation of PI3K/Akt pathway

Area of Science:

• Immunology
• Molecular Biology
• Cell Signaling

Background:

• Adapter proteins adaptor protein containing pleckstrin homology domain, phosphotyrosine domain, and leucine zipper motif 1 (Appl1) and Appl2 are homologous and involved in signaling.
• Appl1 is known to regulate adiponectin signaling and insulin secretion.
• The physiological roles of Appl2 remain largely uncharacterized.

Purpose of the Study:

• To investigate the function of Appl2 in the context of sepsis shock.
• To elucidate the molecular mechanisms underlying Appl2's role in innate immunity.

Main Methods:

• Utilized Appl2 knockout (KO) mice to study sepsis shock.
• Stimulated macrophages with lipopolysaccharides (LPS) to assess cytokine production.
• Employed co-immunoprecipitation to identify protein interactions.
• Analyzed Akt and NF-κB phosphorylation levels.

Main Results:

• Appl2 KO mice displayed exacerbated endotoxin shock symptoms and increased pro-inflammatory cytokine production (TNF-α, IL-1β) upon LPS challenge.
• Deletion of Appl2 led to enhanced Akt and NF-κB phosphorylation in macrophages.
• Appl2 interacts with Appl1 and PI3K regulatory subunit p85α, forming a complex that inhibits Akt activation.
• Appl1 deficiency mirrored reduced Akt activation and cytokine production.

Conclusions:

• Appl2 acts as a critical negative regulator of the innate immune response.
• Appl2 inhibits the PI3K/Akt/NF-κB signaling pathway.
• Appl2 exerts its function by forming a complex with Appl1 and PI3K, thereby modulating immune responses during sepsis.