Definition of a Novel Pathway Centered on Lysophosphatidic Acid To Recruit Monocytes during the Resolution Phase of Tissue Inflammation.

Blood-derived monocytes remove apoptotic cells and terminate inflammation in settings as diverse as atherosclerosis and Alzheimer's disease. They express high levels of the proresolving receptor ALX/FPR2, which is activated by the protein annexin A1 (ANXA1), found in high abundance in inflammatory exudates. Using primary human blood monocytes from healthy donors, we identified ANXA1 as a potent CD14(+)CD16(-) monocyte chemoattractant, acting via ALX/FPR2. Downstream signaling pathway analysis revealed the p38 MAPK-mediated activation of a calcium independent phospholipase A2 with resultant synthesis of lysophosphatidic acid (LPA) driving chemotaxis through LPA receptor 2 and actin cytoskeletal mobilization. In vivo experiments confirmed ANXA1 as an independent phospholipase A2-dependent monocyte recruiter; congruently, monocyte recruitment was significantly impaired during ongoing zymosan-induced inflammation in AnxA1(-/-) or alx/fpr2/3(-/-) mice. Using a dorsal air-pouch model, passive transfer of apoptotic neutrophils between AnxA1(-/-) and wild-type mice identified effete neutrophils as the primary source of soluble ANXA1 in inflammatory resolution. Together, these data elucidate a novel proresolving network centered on ANXA1 and LPA generation and identify previously unappreciated determinants of ANXA1 and ALX/FPR2 signaling in monocytes.

Minocycline inhibits apoptotic cell death in a murine model of partial flap loss.

For breast reconstruction, the deep inferior epigastric perforator (DIEP) flap has become standard therapy. A feared complication is partial or even total flap loss. In a novel murine model of partial DIEP flap loss, the contribution of apoptotis to flap loss was investigated. The clinically available apoptosis-inhibiting compound minocycline was tested for its ability to reduce cell death. The effect of minocycline on cell proliferation was studied in cell cultures of breast carcinoma. In 12 mice, pedicled DIEP flaps were raised, which were subjected to 15 minutes of ischemia and 4 days of reperfusion. Six mice were treated with minocycline 2 hours before surgery and every 24 hours for 4 days. Apoptosis was revealed by injecting annexin A5 30 minutes before sacrifice. Annexin A5 binds to phosphatidylserines, which are expressed on the cell membrane during apoptotis. Prior to sacrifice, necrosis was measured using planimetry. Minocycline reduced cell death after 4 days from 35.9% (standard deviation = 10.6) to 13.9% (standard deviation = 8.0; P < 0.05). Apoptosis, as shown by annexin A5 binding in nontreated animals, was abundant. Minocycline did not influence tumor growth in cell cultures of human breast cancer. Minocycline treatment leads to increased DIEP flap viability in mice. This study widens the perspective in the improvement of free flap survival in patients.