PDE4D and PDE3B orchestrate distinct cAMP microdomains in 3T3-L1 adipocytes

Area of Science:

• Adipocyte biology
• Cell signaling
• Lipid metabolism

Background:

• Lipolysis is regulated by cAMP/PKA signaling and counter-regulated by hormones like insulin and FGF1 via PDEs.
• Spatial compartmentalization of cAMP signaling in adipocytes is known but distinct pools are under-investigated.
• Understanding cAMP dynamics around lipid droplets (LDs) is crucial for lipolysis research.

Purpose of the Study:

• Investigate if FGF1/PDE4D and insulin/PDE3B pathways regulate distinct cAMP microdomains for antilipolytic actions.
• Determine the role of subcellular cAMP pools in lipolysis regulation by PDEs and antilipolytic hormones.

Main Methods:

• Utilized EPAC1-based FRET cAMP biosensors localized to the cytoplasm and plasma membrane.
• Developed a novel LD-associated cAMP biosensor by fusing perilipin-1 to the EPAC1 probe.
• Studied living cells to evaluate cAMP pool regulation.

Main Results:

• Identified distinct cAMP pools surrounding LDs, separate from cytoplasmic cAMP and resistant to PDE inhibition.
• PDE4D demonstrated a stronger effect on all investigated cAMP pools compared to PDE3B.
• FGF1 primarily inhibited plasma membrane cAMP, while insulin targeted cytoplasmic cAMP pools.

Conclusions:

• Discovery of LD-associated cAMP highlights greater cAMP signaling compartmentalization in adipocytes.
• FGF1 and insulin utilize distinct pathways to regulate cAMP, indicating non-uniform antilipolytic signaling.
• Refined understanding of lipolysis regulation through distinct cAMP microdomains and hormone actions.