cAMP cascade (PKA, Epac, adenylyl cyclase, Gi, and phosphodiesterases) regulates myelin phagocytosis mediated by complement receptor-3 and scavenger receptor-AI/II in microglia and macrophages.
The removal by phagocytosis of degenerated myelin is central for repair in Wallerian degeneration that follows traumatic injury to axons and in autoimmune demyelinating diseases (e.g., multiple sclerosis). We tested for roles played by the cAMP cascade in the regulation of myelin phagocytosis mediated by complement receptor-3 (CR3/MAC-1) and scavenger receptor-AI/II (SRAI/II) separately and combined in mouse microglia and macrophages. Components of the cAMP cascade tested are cAMP, adenylyl cyclase (AC), Gi, protein kinase A (PKA), exchange protein directly activated by cAMP (Epac), and phosphodiesterases (PDE). PKA inhibitors H-89 and PKI(14-22) amide inhibited phagocytosis at normal operating cAMP levels (i.e., those occurring in the absence of reagents that alter cAMP levels), suggesting activation of phagocytosis through PKA at normal cAMP levels. Phagocytosis was inhibited by reagents that elevate endogenous cAMP levels to above normal: Gi-inhibitor Pertussis toxin (PTX), AC activator Forskolin, and PDE inhibitors IBMX and Rolipram. Phagocytosis was inhibited also by cAMP analogues whose addition mimics abnormal elevations in endogenous cAMP levels: nonselective 8-bromo-cAMP, PKA-specific 6-Benz-cAMP, and Epac-specific 8-CPT-2'-O-Me-cAMP, suggesting that abnormal high cAMP levels inhibit phagocytosis through PKA and Epac. Altogether, observations suggest a dual role for cAMP and PKA in phagocytosis: activation at normal cAMP levels and inhibition at higher. Furthermore, a balance between Gi-controlled cAMP production by AC and cAMP degradation by PDE maintains normal operating cAMP levels that enable efficient phagocytosis.
Makranz
Chen
C
Department of Anatomy and Cell Biology, Hebrew University-Hadassah Medical Schooland the Eric Roland Center for Neurodegenerative Diseases, Jerusalem, Israel.
Cohen
Goni
G
Reichert
Fanny
F
Kodama
Tatsuhiko
T
Rotshenker
Shlomo
S
D000111:Acetylcysteine / Q000031:analogs & derivatives / Q000378:metabolism; D000262:Adenylyl Cyclases / Q000235:genetics / Q000378:metabolism; D000818:Animals; D002478:Cells, Cultured; D000242:Cyclic AMP / Q000502:physiology*; D017868:Cyclic AMP-Dependent Protein Kinases / Q000235:genetics / Q000378:metabolism; D004797:Enzyme-Linked Immunosorbent Assay; D004917:Erythromycin / Q000031:analogs & derivatives / Q000378:metabolism; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000235:genetics / Q000378:metabolism; D007202:Indicators and Reagents; D016177:Macrophage-1 Antigen / Q000235:genetics / Q000378:metabolism*; D008264:Macrophages / Q000502:physiology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D017628:Microglia / Q000502:physiology*; D009186:Myelin Sheath / Q000502:physiology*; D010587:Phagocytosis / Q000502:physiology*; D010727:Phosphoric Diester Hydrolases / Q000235:genetics / Q000378:metabolism; D051117:Scavenger Receptors, Class A / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction / Q000502:physiology
D007202:Indicators and Reagents; D016177:Macrophage-1 Antigen; D051117:Scavenger Receptors, Class A; D004917:Erythromycin; C057513:erythromycin propionate-N-acetylcysteinate; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D010727:Phosphoric Diester Hydrolases; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; D000262:Adenylyl Cyclases; D000111:Acetylcysteine