Suppression by Ghrelin ofPorphyromonas gingivalis-Induced Constitutive Nitric Oxide Synthase S-Nitrosylation and Apoptosis in Salivary Gland Acinar Cells

Bronislaw L Slomiany,Amalia Slomiany

doi:10.1155/2010/643642

Abstract

Oral mucosal inflammatory responses to periodontopathic bacterium, P. gingivalis, and its key virulence factor, LPS, are characterized by a massive rise in epithelial cell apoptosis and the disturbances in NO signaling pathways. Here, we report that the LPS-induced enhancement in rat sublingual salivary gland acinar cell apoptosis and NO generation was associated with the suppression in constitutive nitric oxide synthase (cNOS) activity and a marked increase in the activity of inducible nitric oxide synthase (iNOS). We demonstrate that the detrimental effect of the LPS on cNOS was manifested by the enzyme protein S-nitrosylation, that was susceptible to inhibition by iNOS inhibitor, 1400 W. Further, we show that a peptide hormone, ghrelin, countered the LPS-induced changes in apoptosis and cNOS activity. This effect of ghrelin was reflected in the decrease in cNOS S-nitrosylation and the increase in phosphorylation. Our findings imply that P. gingivalis-induced disturbances in the acinar cell NO signaling pathways result from upregulation in iNOS-derived NO that causes cNOS S-nitrosylation that interferes with its activation through phosphorylation. We also show that ghrelin protection against P. gingivalis-induced disturbances involves cNOS activation associated with a decrease in its S-nitrosylation and the increase in phosphorylation.

Highlights

Nitric oxide is a multifunctional, short-lived signaling molecule that plays an important role in a variety of regulatory pathways that are of significance to cellular survival, integrity maintenance, and the modulation of inflammatory responses to bacterial infection [1,2,3]
To examine the role of NO generated by constitutive nitric oxide synthase (cNOS) and inducible nitric oxide synthase (iNOS) isozyme systems in propagation of apoptogenic processes induced by periodontopathic bacterium, P. gingivalis, we employed rat sublingual salivary gland acinar cells exposed to the bacterium key virulence factor, LPS
DNA fragmentation assay in conjunction with the measurements of NO, we demonstrated that P. gingivalis LPS caused a dose-dependent increase in the acinar cell apoptosis and NO production, which at 100 ng/mL LPS reached respective values of 6.7- and 15.1-fold over that of controls (Figure 1)

Summary

Introduction

Nitric oxide is a multifunctional, short-lived signaling molecule that plays an important role in a variety of regulatory pathways that are of significance to cellular survival, integrity maintenance, and the modulation of inflammatory responses to bacterial infection [1,2,3]. A low level of NO generated by membraneassociated cNOS appears to access a pool of substrates that are of importance to maintenance of normal physiological functions, including the regulation of apoptogenic signal propagation [3,4,5]. There are recent reports that cNOS enzyme protein S-nitrosylation at the critical zinctetrathiolate cysteine residues leads to a transient inhibition of cNOS activity [11, 12].

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Conclusion