The Expression of PDK1 is Decreased in Neutrophils from LAPsubjects

Objective:

Localized Aggressive Periodontitis (LAP) is associated with altered neutrophil function including decreased chemotaxis, enhanced superoxide generation and various signal transduction abnormalities. Activation of the phosphatidylinositol-3 kinase (PI3K) pathway is a crucial mechanism regulating chemotaxis, cell growth, differentiation, superoxide generation, and apoptosis. Phosphoinositide dependent kinase 1 (PDK1) activates PI3K signaling. In this study, we have focused on the expression of PDK1 in neutrophils from LAP or healthy subjects and we have investigated fMLP-induced Akt phosphorylation that is downstream of PDK1 signaling.

Methods:

Human neutrophils were isolated from peripheral blood of LAP (n=19) and matched healthy subjects (n=19). Protein and mRNA expression were monitored by Western blotting and Real-time quantitative PCR, respectively. Protein phosphorylation was analyzed by Western blotting using phospho-specific antibodies.

Results:

PDK1 expression at both mRNA and protein levels was significantly decreased in LAP neutrophils compared to neutrophils for age-, race-, and gender-matched controls (p<0.05; 30%). There was no change in the expression of PI3K-p110γ and PI3K-p110δ (upstream to PDK1) levels in LAP neutrophils. Likewise, expression of Akt (downstream to PDK1) was similar between LAP and control neutrophils at protein level. In response to fMLP (100 nM, 1 min) stimulation, phosphorylation of Akt (Thr308) was reduced in LAP neutrophils, while Akt phosphorylation at Ser473 was unchanged.

Conclusions:

Collectively, the data suggest that expression and activity of PDK1 are decreased in neutrophils from LAP. Reduction of PDK1 may underlie the functional alternations observed in neutrophils such as decreased chemotaxis and increased superoxide. Supported by USPHS grants DE16191 and RR00533.