Sirtuin-1 in immunotherapy: A Janus-headed target

Sirtuin-1 (Sirt1), a member of the NAD-dependent sirtuin family of histone/protein deacetylases (HDAC), is an important target for immunotherapy due to its role in deacetylating the transcription factors Foxp3 and thymic retinoid acid receptor related orphan receptor gamma (ROR gamma t). Sirt1 inhibition can increase Foxp3 acetylation and promote the production and functions of Foxp3(+) T-regulatory (Treg) cells, whereas the acetylation of ROR gamma t decreases its transcriptional activity DNA binding and decreases the differentiation of proinflammatory Th17 cells. Pharmacologic inhibitors of Sirt1 increase allograft survival and decrease autoimmune colitis and experimental allergic encephalomyelitis. However, in contrast to its role in T cells, Sirt1 has anti-inflammatory effects in myeloid cells, and, context dependent, in Th17 cells. Here, inhibition of Sirt1 can have proinflammatory effects. In addition to effects arising from the central role of Sirt1 in cellular metabolism and NAD-dependent reactions, such proinflammatory effects further complicate the potential of Sirt1 for therapeutic immunosuppression. This review aims to reconcile the opposing literature on pro- and anti-inflammatory effects of Sirt1, provides an overview of the role of Sir1 in the immune system, and discusses the pros and cons associated with inhibiting Sirt1 for control of inflammation and immune responses.