Activation of α7nAChR Promotes Diabetic Wound Healing by Suppressing AGE-Induced TNF-α Production

Diabetes frequently presents accumulation of advanced glycation end products (AGEs), which might induce excessive TNF-alpha production from macrophages to cause impaired wound healing. Recent studies have shown that activation of alpha 7 nicotinic acetylcholine receptor (alpha 7nAChR) on macrophages efficiently suppressed TNF-alpha synthesis. The aim of this study was to investigate the accumulation of AGEs in the wounds and determine whether PNU282987, an alpha 7nAChR agonist, can improve wound repair by inhibiting AGE-mediated TNF-alpha production in a streptozotocin (STZ)-induced diabetic mouse model. Animals were assigned into four groups: wounded control group, wounded diabetic group, wounded diabetic group treated intraperitoneally with PNU282987, or wounded diabetic group treated intraperitoneally with vehicle. Compared with the non-diabetic control mice, the diabetic mice exhibited delayed wound healing that was characterized by elevated accumulation of AGEs, increased TNF-alpha level and macrophage infiltration, and decreased fibroblast number and collagen deposition at the late stage of repair. Besides, macrophages of diabetic wounds showed expression of alpha 7nAChR. During late repair, PNU282987 treatment of diabetic mice significantly reduced the level of TNF-alpha, accelerated wound healing, and elevated fibroblast number and collagen deposition. To investigate the cellular mechanism of these observations, RAW 264.7 cells, a macrophage cell line, were incubated with AGEs in the presence or absence of PNU282987. TNF-alpha production from AGE-stimulated macrophages was significantly decreased by PNU282987 in a dose-dependent manner. Furthermore, PNU282987 significantly inhibited AGE-induced nuclear factor-kappa B (NF-kappa B) activation and receptor for AGE (RAGE) expression. These results strongly suggest that activating alpha 7nAChR can promote diabetic wound healing by suppressing AGE-induced TNF-alpha production, which may be closely associated with the blockage of NF-kappa B activation in macrophages.