Presentation: Protein Deacetylase Inhibitors Suppress Inflammatory Cytokine Production by Human Macrophages and Induce Apoptosis (2007)

145 Protein Deacetylase Inhibitors Suppress Inflammatory Cytokine Production by Human Macrophages and Induce Apoptosis

Purpose: Histone hyperacetylation promotes inflammatory gene transcription, and depressed histone deacetylase (HDAC) activity in rheumatoid arthritis (RA) synovial tissue has been proposed to contribute to disease pathology (1). Counter-intuitively, HDAC inhibitors are protective in animal models of RA. The purpose of this study was to examine the effect of HDAC inhibitors on human macrophage activation and survival.
Methods: Human macrophages were generated by culture of healthy donor peripheral blood-derived monocytes in GM-CSF, or purified from RA patient synovial fluid. Macrophages were then incubated in medium alone, or in medium containing increasing concentrations of trichostatin A (TSA, HDAC inhibitor) or nicotinamide (NAD, inhibitor of NADPH-dependent non-histone deacetylases), in the absence or presence of IL-1beta or TNF-alpha stimulation. Apoptosis was assessed by Annexin V/propidium iodide staining and FACS analysis. Macrophage IL-6 production was measured by ELISA. Acetylation of cellular proteins was assessed by immunoblotting of macrophage lysates with anti-acetyl-lysine antibodies.
Results: Both TSA and NAD induced significant dose-dependent apoptosis in macrophages. Maximal apoptosis was observed at the highest dosages tested (TSA - 2 micromolar, 26% apoptosis, sem ± 3; NAD - 20 mM, 14% ± 2) as compared to control (5% ± 1; p< 0.001). RA SF macrophages were highly sensitive to apoptosis induced by TSA (90% ± 2) and NAD (95% ± 3). Unexpectedly, both TSA (0.25 micromolar) and NAD (10 mM) almost completely blocked TNF-induced IL-6 production in macrophages, at concentrations insufficient to induce apoptosis. Both TSA and NAD treatment was accompanied by rapid acetylation of non-histone proteins in macrophages.
Conclusions: Inhibition of HDAC and non-histone deacetylase activity in human macrophages promotes cellular apoptosis, and blocks rather than enhances inflammatory cytokine production. These effects may be mediated by hyperacetylation of non-histone proteins. Our results indicate that inhibition of HDAC activity may have therapeutic potential in RA.
This research was made possible by funding from the Dutch Arthritis Association.
(1) Huber LC et al (2007). Histone deacetylase/acetylase activity in total synovial tissue derived from rheumatoid arthritis and osteoarthritis patients. Arthritis Rheum 56:1087.

 A. Grabiec, None; S. Krausz, None; M.E. Sanders, None; D. Groot, None; P.P. Tak, None; K.A. Reedquist, None.