Macrophage Recruitment and Polarization During Collateral Vessel Remodeling in Murine Adipose Tissue

Abstract

Objective During autologous flap transplantation for reconstructive surgeries, plastic surgeons use a surgical pre-treatment strategy called “flap delay”, which entails ligating a feeding artery into an adipose tissue flap 10–14 days prior to transfer. It is believed that this blood flow alteration leads to vascular remodeling in the flap, resulting in better flap survival following transfer; however, the structural changes in the microvascular network are poorly understood. Here, we evaluate microvascular adaptations within adipose tissue in a murine model of flap delay. Methods and Results We used a murine flap delay model in which we ligated an artery supplying the inguinal fat pad. Although the extent of angiogenesis appeared minimal, significant diameter expansion of pre-existing collateral arterioles was observed. There was a 5-fold increase in recruitment of CX3CR1+ monocytes to ligated tissue, a 3-fold increase in CD68+/CD206+ macrophages in ligated tissue, a 40% increase in collateral vessel diameters supplying ligated tissue, and a 6-fold increase in the number of proliferating cells in ligated tissue. Conclusions Our study describes microvascular adaptations in adipose in response to altered blood flow and underscores the importance of macrophages. Our data supports the development of therapies that target macrophages in order to enhance vascular remodeling in flaps.

A MicroRNA93–Interferon Regulatory Factor-9–Immunoresponsive Gene-1–Itaconic Acid Pathway Modulates M2-Like Macrophage Polarization to Revascularize Ischemic Muscle

“…The ability of macrophages to favorably modulate these processes is dependent on their polarized state, especially in diseased tissue (19,9,17) . M2-like-macrophages play critical roles in inflammation resolution by secreting anti-inflammatory cytokines including IL-10, TGF-β that helps in tissue repair (38,39) and by secreting growth factors (40,41) that induces arteriogenesis and angiogenesis.…”

“…In experimental-PAD, monocyte/macrophage recruitment into the occluded vessel can induce a potent arteriogenic response (8,9,10) , however limited information is available on the role of macrophage activation state in regulating this process. Classically activated macrophages (M1-polarized) in response to lipopolysaccharide (LPS) and/or interferon-γ are pro-inflammatory and cytotoxic (11) and alternatively activated macrophages (M2-polarized), seen in response to IL-4 and IL-13, are anti-inflammatory and reparative (11) .…”

Arteriogenesis in murine adipose tissue is contingent on CD68+/CD206+ macrophages

“…Mice were euthanized via CO 2 asphyxiation 3 days postinjection to quantify the retention of injected Vybrant DiI‐labeled cells and the total number of macrophages present postinjection. The area of the inguinal fat pad surrounding the collateral vessel was harvested as previously described . Samples of the tissues that had been injected with Vybrant DiI‐labeled cells from each mouse (n=3) were divided into three small (~1 mm 3 ) pieces for immunostaining.…”

“…All samples were washed with PBS three times. Sample 1 was mounted on a gelatin‐coated slide and imaged immediately after PBS washing as described previously . Samples 2 and 3 were submerged in 100 μL of 5% mouse serum in 0.3% (volume/volume) Triton X‐100/PBS for 3 hours at room temperature to permeabilize and block the tissue.…”

“…A previously published murine model of flap delay was used for the following “ligated” and “sham” surgeries. Briefly, the epigastric artery, which feeds the subcutaneous inguinal fat pad, was isolated via blunt dissection.…”