Background:

Immune cells play a key role in regulating angiogenesis through the production and release of a wide range of pro-angiogenic mediators. As the AMP-activated protein kinase (AMPK) has been shown to positively regulate angiogenesis, we investigated the effect of deleting the AMPKα2 subunit in myeloid cells (LysM-AMPKα2) on macrophage and neutrophil function as well as on vascular repair.

Methods:

Wild-type and LysM-AMPKα2 mice were subjected to femoral artery ligation. The recovery of blood flow (laser Doppler), capillary density (immunohistochemistry) and immune cell infiltration (flow cytometry) were determined. To assess the role of AMPKα2 in myeloid cells, bone marrow monocytes were differentiated (in M-CSF) and polarized to M1 (IFN-γ and LPS) or M2 (IL-4 and IL-13) macrophages. Polymorphonuclear cells (PMN) were stimulated with LPS for 2 hours. Expression levels of cytokines and growth factors were analyzed using quantitative real time PCR.

Results:

Recovery of blood flow after hindlimb ischemia was significantly impaired (80%) in LysM-AMPKα2 versus the wild-type littermates. In addition, LysM-AMPKα2^-/- mice showed significantly reduced capillary density and decreased myeloid cell infiltration into the ligated limb. The deletion of the AMPKα2 subunit increased the mRNA expression levels of TNF-α, IL-1β and inducible nitric oxide synthase (iNOS) in macrophages and PMN. In contrast, the mRNA level of FIZZ-1, an M2 marker gene, and VEGF was decreased in macrophages and PMN from LysM-AMPKα2.

Conclusion:

Deletion of the AMPKα2 in the cells of the myeloid lineage almost abolished vascular repair after hindlimb ischemia. These results indicate that the AMPKa2 plays a crucial role in regulating the inflammatory state and angiogenic potential of myeloid cells.