The Effect of Porphyromonas gingivalis Lipopolysaccharide (LPS) on Rat Brain Microglia Classical and Alternative Activation in vitro: MMP-9 generation
Background: The putative association between periodontal disease (PD), a chronic inflammatory disease affecting 64% of adults 65 years and older, and neuroinflammation, a condition which involves microglia, a cell of the brain innate immune system, remains relatively unexplored. We recently reported that lipopolysaccharide (LPS) of Porphyromonas gingivalis (Pg), a pathogenic bacteria implicated in periodontitis activates both classical (M1-type) and alternative (M2-type) activation of neonatal rat microglia (BMG) and concomitant release of superoxide anion, thromboxane B2, cytokines, and chemokines (Toxicological Sciences Supplement, 150 (1), Abstract # 2974, 2017). We hypothesized that classical activated microglia might also release the pro-inflammatory matrix metalloproteinase-9 (MMP-9).
Methods: P. gingivalis LPS (Pg LPS) was purchased from InvivoGen (San Diego, CA). E. coli LPS (Ec LPS) 026:B6 (from Difco Lab, Detroit, MI) was used as a positive control. BMG were isolated from neonatal rats, and treated in vitro with either Pg LPS or Ec LPS, in a concentration-dependent manner, for 18 hours at 35.9°C. BMG were identified by confocal microscopy using the surface marker CD11b/c. Matrix metalloproteinase-9 was determined with a rat total MMP-9 DuoSet ELISA kit (R&D Systems).
Results: Statistically significant and concentration-dependent release of pro-inflammatory MMP-9 was observed at > than 1ng/mL Ec LPS and 105 ng/mL Pg LPS.
Conclusions: Our results provide support for our working hypothesis, because Pg LPS stimulated BMGs to release pro-inflammatory MMP-9 in a time- and concentration-dependent manner. Thus, our current observations extend our studies on the effect of Pg LPS on rat brain microglia activation and contribute to further characterize both periodontitis, and the role of BMG in neuroinflammation and potential neurodegeneration.