Metformin Promotes the Survival of Random-Pattern Skin Flaps by Inducing Autophagy via the AMPK-mTOR-TFEB signaling pathway

Abstract

Random-pattern skin flaps are widely used to close defects in reconstructive and plastic surgeries; however, they are vulnerable to necrosis, particularly in the distal portion of the flap. Here, we examined the effects of metformin on flap survival and the mechanisms underlying these effects. Following metformin treatment, the survival area, blood flow, and number of microvessels present in skin flaps were increased on postoperative day 7, whereas tissue edema was reduced. In addition, metformin promoted angiogenesis, inhibited apoptosis, relieved oxidative stress, and increased autophagy in areas of ischemia; these effects were reversed by autophagy inhibitors 3-methyladenine (3MA) or chloroquine (CQ). Either 3MA or CQ reversed the metformin-induced increase in flap viability. Moreover, metformin also activated the AMPK-mTOR-TFEB signaling pathway in ischemic areas. Inhibitions of AMPK via Compound C (CC) or AMPK shRNA adeno-associated virus (AAV) vector resulted in the downregulation of the AMPK-mTOR-TFEB signaling pathway and autophagy level in metformin-treated flaps. Taken together, our findings suggest that metformin improves the survival of random-pattern skin flaps by enhancing angiogenesis and suppressing apoptosis and oxidative stress. These effects result from increased autophagy mediated by activation of the AMPK-mTOR-TFEB signaling pathway.

Apelin/APJ‐Manipulated CaMKK/AMPK/GSK3β Signaling Works as an Endogenous Counterinjury Mechanism in Promoting the Vitality of Random‐Pattern Skin Flaps

“…By confirming that the blood vessels were amputated, separated flaps were inserted to the original position and sutured with a 7-0 nonabsorbable suture. The random skin area was equally separated into three zones from the pedicle to the distal: proximal (area I), intermediate (area II), and distal (area III) [ 3 , 9 ].…”

“…On day 3, day 5, and day 7, all mice were anesthetized and placed in a warm and quiet room, and the laser Doppler instrument (Moor Instruments, Axminster, UK) was used to scan mice in each group. The infrared Doppler scanning probe scanned the area of the skin flap to record the blood flow distribution as described in the previous literature [ 3 , 9 ]. Blood flow of the skin flap was visualized with the strong signal (green, yellow, and red shown in pictures) and quantified with Moor LDI Review software (ver 6.1; Moor Instruments).…”

“…A skin flap has been proven to be one of the most common and effective methods for wound repair in surgical practice. Random-pattern skin flap replantation is increasingly being selected to close large surficial tissue defects caused by various reasons such as trauma, cancer excisions, and congenital deformity corrective surgery [ 1 – 3 ]. Obviously, wound healing is a coordinated, complex process involving oxidative stress, inflammation, cell proliferation, cell migration, and angiogenesis [ 4 ].…”

“…During skin flap replantation, especially with the purpose of treating large-area wounds, blood supply interruption, oxidative stress, inflammation, and postoperative infection make the distal flap vulnerable to necrosis and to a great extent limit the clinical application of a random skin flap [ 5 – 8 ]. Blood supply recovery is a consequence of vascular stump's initiation, growth, and recanalization from the pedicle to the distal area [ 3 , 9 ]. During neovascularization, the ischemia-reperfusion injury (IRI) process is inevitable and necessary, in which effective and reasonable artificial intervention can greatly improve the survival of the skin flap by diminishing the accumulation of acute inflammatory cells [ 10 ] and suppressing oxidative stress [ 11 ].…”

Dual Roles of the AMP-Activated Protein Kinase Pathway in Angiogenesis

“…Furthermore, studies from the same group have demonstrated that LKB1/AMPK regulates angiogenesis in response to ischemic injury in hind limbs of mice [51,52]. Many of later studies have corroborated the positive role of AMPK in angiogenesis or protective effects on endothelial cells under such circumstances as hypoxia, ischemia, stroke, and oxidative stress, and in response to cytokines and pharmacological agents such as AICAR, metformin and statins [34,43,44,45,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69].…”