Bacteria degrade the specialized basal lamina of the junctional epithelium

Objectives: The junctional epithelium (JE)is a specialized portion of the gingiva that seals off the tooth supporting tissues from the oral environment. This relationship is achieved via a specialized basal lamina (sBL) which to date is known to comprise three unique proteins -AMTN, ODAM and SCPPPQ1- and Laminin-332. These interact to structure the supramolecular organization of this sBL and determine its adhesive capacity. Despite its critical and strategic importance and continued exposure to bacteria, little is known on the susceptibility of the sBL to bacterial activity.
Methods: The objective of this study was to evaluate the impact of various oral bacteria on the sBL using molecular biology and complementary imaging approaches.
Results: SDS-PAGE and western blot analysis with trypsin like proteases as well as incubation with Porphyromonas gingivalis revealed that all sBL constituents, except SCPPPQ1, were rapidly degraded. Mass spectrometry confirmed that SCPPPQ1 was not degraded. To observe the impact of P. gingivalis on the sBL network, we have incubated the bacteria on both a reconstituted and a native sBL and examined the outcome by atomic force microscopy and scanning electron microscopy (SEM). The bacteria destroyed the reconstituted supramolecular network in their vicinity creating a peripheral space around them. After two hours of exposure, SEM analysis of the native sBL revealed the presence of a shallow depression around the bacteria. After 6 h, the affected peri-bacterial area became deeper and cavitated, suggesting active degradation of the native sBL as well.
Conclusions: We show here for the first time that P. gingivalis, one of the major bacteria implicated in chronic periodontitis, and related enzymes can attack the individual components of the sBL as well as alter the supramolecular organization of this critical adhesive extracellular matrix. These results highlight the importance of the sBL in PD and open the door for new treatment paradigms.