Oral Treponeme Surface Proteins Dampen Neutrophil Signaling and Function

Objectives: Periodontal disease affects 47% of the US population and is caused by dysbiosis of the oral biofilm, which in turn causes chronic inflammation and disrupts host cell functions, particularly neutrophils. The spirochetes Treponema denticola, Treponema maltophilum, and Treponema lecithinolyticum are strongly associated with severe periodontal disease. The major outer sheath protein (Msp) of T. denticola impairs neutrophil function by disruption of phosphoinositide signaling. T. maltophilum and T. lecithinolyticum have membrane proteins similar to Msp; MspA and MspTL respectively. Our objectives were to characterize the effect of MspA and MspTL on neutrophil function and examine their prevalence in cases of periodontal disease.
Methods: Saliva samples were collected from patients with (n=20) and without (n=5) periodontal disease and Treponema species identified by PCR. MspA and MspTL were identified in samples positive for T. maltophilum and T. lecithinolyticum, amplified by PCR, and regions of variation identified by sequencing. Murine bone marrow neutrophils were pretreated with recombinant Msp, MspA, or MspTL followed by exposure to chemoattractant stimulus. Rac1 activity (G-LISA Small G-protein Activation Assay) and neutrophil chemotaxis (transwell) were assessed.
Results: T. denticola, T. maltophilum, and T. lecithinolyticum were identified in 60%, 75%, and 25% of saliva samples from periodontal disease patients, respectively. MspA and MspTL inhibited Rac1 activity significantly more than Msp. MspA and MspTL both inhibit neutrophil chemotaxis as Msp does. There were two regions of sequence variation identified in MspA and one in MspTL.
Conclusions: The outer membrane proteins of T. maltophilum (MspA) and T. lecithinolyticum (MspTL) inhibit chemotaxis and Rac1 signaling in neutrophils. MspA and MspTL are detectable in saliva samples and sequence variation may cause functional differences. Understanding the relationship between Msp proteins and neutrophils provides important insight into how these bacteria survive and promote disease progression in the oral cavity.