SIRT1 and Stress Suppress Regulatory T Cells

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Is it actually our stressful lives that are setting the stage for inflammatory bowel disease?
This week on TIBDI: Human stem cell transplantation redefines T cell repertoires, SIRT1 blocks the development of induced regulatory T cells, and stress sets the stage for intestinal inflammation.

Stem Cell Transplantation Wipes CD4+ T cell Memory

Human stem cell transplantation (HSCT) is a potential treatment for severe cases of inflammatory bowel disease (IBD). One way that HSCT works is by resetting the adaptive immune system. However, few studies have looked in depth at changes in the T cell repertoires. Dr. Paolo Muraro from the Imperial College of London has now addressed this question. In a HSCT trial for multiple sclerosis (MS) patients, he and his team used high-throughput sequencing to assess T cell receptor changes in 24 patients. They found that CD4+ and CD8+ T cells responded differently to HSCT. The patients’ CD4+ T cells were redefined and had a new repertoire of clones, while the CD8+ T cells reflected pre-HSCT clones. Resetting CD4+ T cells could be one reason why that HSCT is also successful for IBD.

SIRT1 Suppresses Suppressor Induction

Regulatory T cells (Tregs) are known to be important in IBD, and work from animal models shows that they can regulate the severity of symptoms. Previous work by Dr. Tatiana Akimova and her colleagues at the Children’s Hospital of Philadelphia demonstrated a connection between SIRT1 and Tregs. To investigate this more in induced Tregs, they used SIRT1 deficient cells in the T cell transfer model of colitis. Loss of SIRT1 increased the induction of Tregs and effectively attenuated colitis development. This result was mirrored in dextran sodium sulfate colitis using an inhibitor of SIRT1 (EX-527). It will be interesting in the future to see if targeting SIRT1 will work in a therapeutic setting.

Stress Hinders Regulatory T Cells

Most IBD patients are quite aware that stress plays a role in their disease progression. However, the connection between stress and IBD remains shaky. Dr. Wei Wu of Tongji University considered that the missing link could be Treg function. To test this concept, they stressed mice and investigated the Tregs both in vitro and in vivo. Tregs from stressed mice were unable to function as normal, and some expressed IL-17 and TNFα. Prolactin, a stress mediator, mediated this change via dendritic cells. Stressed mice were highly susceptible to colitis, however, blocking prolactin reduced colitis. The authors feel that stress and prolactin set the stage for IBD development by the conversion of Tregs from effective suppressors to harmful pro-inflammatory T cells.

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