HIF-1α Regulates the Palatal Wound Healing Through M1/M2 Macrophage Reprogramming

Objectives: Patients with cleft palate often develop growth impairment and narrow collapse in the mid-facial region after primary surgery due to wound contraction and scar formation. It has been previously postulated that the blood flow in the wound scar is known to be decreased compared to the surrounding area of the wound closure. Hypoxia inducible factor-1α (HIF-1α), a key programmer of metabolism in inflammatory cells, is known to trigger macrophages recruitment and activation. However, the regulation of M1/M2 macrophage in palatal wound healing within HIF-1a deficient condition remains unclear. The purpose of this study was to investigate the role of HIF-1α in the palatal wound healing through reprogramming mechanism of M1/M2 macrophage.
Methods: HIF-1α heterozygous (HIF-1α HET) mice (n=35) and its wildtype (WT) littermates (n=35) were used. Wounding preparation of palatal tissue and histological analyses were performed to assess the wound closure. RNA isolation from palatal tissue surrounding wound area were carried out to examine the expression of inflammatory cytokines. Immunoblot analysis was used to detect the M1/M2 protein expression in palatal wound area. Immunohistochemical analysis underwent to analyze M1/M2 macrophage infiltration in the wound area.
Results: Histological analysis revealed delayed palatal wound closure in HIF-1α HET mice than in WT littermates, with a greater gap at day 5 after wounding. Lower levels of collagen type I, macrophage inflammatory protein-1α (MIP-1α), and monocyte chemoattractant protein-1 (MCP-1) were detected in the palatal tissue at day 5 after wounding. Furthermore, the immunohistochemical and immunoblot analyses in palatal wound area showed decreased infiltration and expression of M1 (iNOS, TNF-α) and M2 macrophage markers (Arginase-1, CD163) in HIF-1α HET mice compared to its WT littermates at day 5 after wounding.
Conclusions: It is concluded that HIF-1α signaling pathway plays an important role in the palatal wound healing through the regulation of M1/M2 macrophage.