ABSTRACT
Insulin resistance and hyperglycemia are risk factors for periodontitis and poor wound healing in diabetes, which have been associated with selective loss of insulin activation of the PI3K/Akt pathway in the gingiva. This study showed that insulin resistance in the mouse gingiva due to selective deletion of smooth muscle and fibroblast insulin receptor (SMIRKO mice) or systemic metabolic changes induced by a high-fat diet (HFD) in HFD-fed mice exacerbated periodontitis-induced alveolar bone loss, preceded by delayed neutrophil and monocyte recruitment and impaired bacterial clearance compared with their respective controls. The immunocytokines, CXCL1, CXCL2, MCP-1, TNFα, IL-1ß, and IL-17A, exhibited delayed maximal expression in the gingiva of male SMIRKO and HFD-fed mice compared with controls. Targeted overexpression of CXCL1 in the gingiva by adenovirus normalized neutrophil and monocyte recruitment and prevented bone loss in both mouse models of insulin resistance. Mechanistically, insulin enhanced bacterial lipopolysaccharide-induced CXCL1 production in mouse and human gingival fibroblasts (GFs), via Akt pathway and NF-κB activation, which were reduced in GFs from SMIRKO and HFD-fed mice. These results provided the first report that insulin signaling can enhance endotoxin-induced CXCL1 expression to modulate neutrophil recruitment, suggesting CXCL1 as a new therapeutic direction for periodontitis or wound healing in diabetes. ARTICLE HIGHLIGHTS: The mechanism for the increased risks for periodontitis in the gingival tissues due to insulin resistance and diabetes is unclear. We investigated how insulin action in gingival fibroblasts modulates the progression of periodontitis in resistance and diabetes. Insulin upregulated the lipopolysaccharide-induced neutrophil chemoattractant, CXCL1, production in gingival fibroblasts via insulin receptors and Akt activation. Enhancing CXCL1 expression in the gingiva normalized diabetes and insulin resistance-induced delays in neutrophils recruitment and periodontitis. Targeting dysregulation of CXCL1 in fibroblasts is potentially therapeutic for periodontitis and may also improve wound healing in insulin resistance and diabetes.