Inhibition of histone deacetylase 6 improves long-term survival in a lethal septic model

Sepsis, a systemic inflammatory response syndrome caused by severe infection, is still a tremendous burden for health-care systems and results in more than 225,000 deaths annually in the United States1. No pharmacological agents have been shown to effectively change the outcomes2. Acetylation of histone is an important epigenetic mechanism that governs amplitude of the immune signaling by controlling the chromatin structure, accessibility of transcription factors to DNA, and gene transcription. Regulation of this process needs the opposing actions of two families of enzymes: histone acetyltransferases (HATs) and histone deacetylases (HDACs). It is found that dysregulated HDAC activity is linked to the pathogenesis of inflammatory and autoimmune diseases3. So far, 18 HDAC isoforms have been identified in humans and mice and grouped into four classes 4. Classical HDACs (class I, II and IV) are Zn2+ dependent hydrolases, while the class III sirtuins are NAD+-dependent. Class I HDACs (HDAC1, 2, 3 and 8) play a role in cell survival and proliferation. Class II HDACs, subdivided into class IIa (HDAC4, 5, 7 and 9) and IIb (HDAC6 and 10) based on domain organization 5, may have tissue-specific roles 6. Recently, HDAC6 has become an important target for anti-cancer drug development, and inhibition of HDAC6 was also shown to have therapeutic potential to ameliorate injury of central nervous system7. MS-275 is a HDAC class I inhibitor with selectivity for HDAC1, 2, and 3. Tubastatin A is a newly synthesized selective inhibitor of HDAC class IIb with high selectivity for HDAC6 8. Suberoylanilide hydroxamic acid (SAHA, vorinostat) is a broad-spectrum histone deacetylase inhibitor (HDACI) with a selectivity for HDAC1, 2, 3 and 6 9. Our laboratory has previously demonstrated that administration of SAHA improves survival in rodent models of lipopolysaccharided (LPS)-induced endotoxemia and cecal ligation and puncture (CLP)-induced septic shock 10, 11. However, this HDACI was also found to increase host susceptibility to bacterial infection due to cell apoptosis 12. We hypothesized that targeting different HDACs could have different effect on animal survival in a mouse model of cecal ligation and puncture (CLP)-induced sepsis. In the present study, we first determined that inhibitor of HDAC6 (Tubastatin A) rather than that of HDAC1, 2, and 3 significantly prolonged animal lives in the CLP model. We then assessed impact of HDAC6 inhibition on production of some key pro-inflammatory cytokines, organ (liver) injury, and immune cell apoptosis. Our findings suggested that selective inhibition of HDAC6 has a substantial advantage for sepsis treatment.