Phagosomal Malfunction of Neutrophils Leads to Periodontitis in LAMP-2 Deficiency

Objectives: The limiting membrane of the lysosomal compartment is important for phagosome maturation. Lysosome-associated membrane protein (LAMP-2)is a highly glycosylated protein abundant in the lysosomal membrane. This study was undertaken to determine the role of LAMP-2 in neutrophil functioning and host-defense against periodontal infection. Methods: LAMP-2-deficient mice were generated as previously described (Tanaka et al, Nature 2000). Knockout mice and wildtype littermates were maintained in a conventional facility. For antibiotic treatment selected mice received amoxicillin in the drinking water. Neutrophils from 2- to 4-mo old wild-type and LAMP-2-deficient animals were isolated and co-cultured with E. Coli and A. Actinomycetemcomitans bacteria to study phagocytosis and bacterial killing capacity. For microscopic observation of molar periodontium, mice were killed between 7 wk and 12 mo after birth. Upper and lower jaws were processed for MicroCT, light and electron microscopy. Sections were subjected to image analysis. Data were analyzed by Student's t test. Results: In the knockout animals - but not in wildtype littermates - signs of natural periodontitis were already observed 7 wk after birth. Extensive accumulation of bacterial plaque was noted along all tooth surfaces. Gingival inflammation, alveolar bone resorption, loss of connective tissue attachment, apical migration of junctional epithelium, and pathological migration of molars were recorded in the knockouts. The inflammatory lesions were dominated by neutrophils. Systemic treatment with antibiotics prevented periodontal pathology. Isolated neutrophils from LAMP-2-deficient mice showed an accumulation of autophagic vacuoles and a reduced bacterial killing capacity. Latex bead and bacterial feeding experiments showed a reduced ability of phagosomes to acquire an acidic pH, suggesting impaired fusion of late endosomes-lysosomes with phagosomes. Conclusions: This study underlines the importance of LAMP-2 for the maturation of phagosomes in neutrophils and underscores the requirement of lysosomal fusion events to provide sufficient antimicrobial activity in neutrophils, which is needed to prevent periodontal disease.