Extracellular β-NAD⁺ inhibits interleukin-1-induced matrix metalloproteinase-1 and -3 expression on human gingival fibroblasts

There is increasing evidence to show that extracellular β-nicotinamide adenine dinucleotide (β-NAD⁺) modulates various biological functions in inflammatory/immune regions. The aim of this study was to determine the effect of β-NAD⁺ on matrix metalloproteinase (MMP) expression on human gingival fibroblasts (hGF), the excess production of which leads to the matrix degradation associated with the pathological processes of periodontitis. The expression of MMP-1 and MMP-3 on hGF was determined by real-time polymerase chain reaction (PCR) and an enzyme-linked immunosorbent assay. The phosphorylated status of mitogen-activated protein (MAP) kinases, extracellular signal-regulated kinase 1/2 (ERK), c-Jun N-terminal kinase (JNK), and p38 and the expression of inhibitor κB (IκB)α were determined by Western blotting. β-NAD⁺ inhibited the expression of MMP-1 and MMP-3 triggered by IL-1α at gene and protein levels. β-NAD⁺ had no significant effect on the IL-1α-induced phosphorylation of ERK1/2, JNK, and p38 and also had no effect on the IL-1α-induced degradation of IκBα relative to the control, suggesting that inhibition by β-NAD⁺ was independent of the MAP kinase and the nuclear factor-κB signaling pathways. Transcripts of NAD⁺-metabolizing enzymes, such as NAD⁺-glycohydrolase, adenosine diphosphate (ADP)-ribosylcyclase, and ADP-ribosyltransferase, were expressed by hGF as assessed by RT-PCR. Experiments using α-NAD ⁺, which is not a substrate for ADP-ribosylcyclase or ADP-ribosyltransferase, revealed the possible contribution of NAD ⁺-glycohydrolase to the inhibition of MMP. This is consistent with the finding that ADP-ribose, an NAD⁺-metabolite by NAD ⁺-glycohydrolase, exhibited MMP inhibition similar to β-NAD ⁺. The present findings may provide an additional viewpoint to clarify a natural feedback mechanism during the inflammatory process in periodontal tissue.