Leptin synergistically enhances an extracellular matrix-degrading gingival fibroblast phenotype

Objectives: Obese individuals and patients with type 2 diabetes have an increased risk of periodontitis. Obesity and diabetes are also associated with elevated circulating levels of leptin, a hormone which also has pro-inflammatory effects. Human gingival fibroblasts (HGFs) secrete matrix metalloproteinases (MMPs) which mediate extracellular matrix degradation in response to inflammatory signals; however, the effect of leptin on these processes is unknown. Our objective was, therefore, to investigate the effect of leptin in regulating the production of MMP-1 and MMP-3 in primary HGFs and to identify the signalling pathways that may be involved.

Methods: HGFs isolated from gingival tissue were stimulated with leptin (0.1-10 μg/ml), the pro-inflammatory cytokines interleukin-1α (IL-1α)(0.05 ng/ml) and oncostatin M (OSM)(5 ng/ml), and the Toll-like receptor agonist pam2CSK4 (50 ng/ml). MMP production was assessed by real-time RT-PCR and ELISA. Intracellular signalling pathway activation was determined by Western blotting.

Results: Leptin (p<0.001), IL-1α (p<0.05) and OSM (p<0.05) significantly increased the production of MMP-1 mRNA and protein by HGFs compared to unstimulated cells, while only leptin significantly (p<0.001) increased MMP-3 production. Leptin and IL-1α synergistically increased MMP-1 (p<0.001) and MMP-3 (p<0.05) production in HGF cultures above that observed following IL-1α or leptin stimulation alone whilst OSM had no such activity. Similarly, pam2CSK4 and leptin synergistically enhanced MMP-1 mRNA and protein production by HGFs (p<0.01). Leptin and IL-1α increased Erk1/2 and JNK phosphorylation in HGFs, while pam2CSK4 induced p38 phosphorylation. HGFs stimulated with OSM, but not leptin, induced STAT1 and STAT3 tyrosine phosphorylation.

Conclusion: Leptin synergistically enhances MMP-1 and MMP-3 production by HGFs in the presence of IL-1α and pam2CSK4, and increases ERK and JNK activity. These findings support a mechanistic role for leptin in enhancing the degradation of gingival extracellular matrix during inflammation.