Foxp3-mediated blockage of ryanodine receptor 2 underlies contact-based suppression by regulatory T cells

Area of Science:

• Immunology
• Cell Biology
• Molecular Biology

Background:

• Regulatory T cells (Tregs) are crucial for maintaining immune homeostasis.
• The precise mechanisms by which Tregs suppress immune responses, particularly through indirect inhibition of dendritic cells (DCs), are under intense investigation.
• A universally applicable effector mechanism controlled by the transcription factor forkhead box P3 (Foxp3) has not been identified.

Purpose of the Study:

• To investigate the role of Foxp3 in Treg-mediated immune suppression.
• To identify the molecular targets and pathways regulated by Foxp3 in Tregs.
• To elucidate the contribution of calcium signaling to Treg function.

Main Methods:

• Investigated the interaction between Foxp3 and ryanodine receptor 2 (RyR2) gene expression.
• Analyzed the impact of reduced RyR2 on calcium (Ca2+) oscillations in Tregs.
• Assessed the effect of RyR2 deficiency on T cell disengagement from DCs and DC antigen presentation.
• Evaluated the immune suppressive capacity of RyR2-deficient CD4+ T cells in various disease models (viral infection, asthma, hypersensitivity, colitis, tumor development).
• Studied the rescue of autoimmunity in scurfy mice by Ryr2-deficient CD4+ T cells in the absence of Foxp3.

Main Results:

• Foxp3 was found to inhibit the transcription of the ER Ca2+-release channel ryanodine receptor 2 (RyR2).
• Reduced RyR2 expression led to diminished basal Ca2+ oscillations in Tregs.
• This reduction in Ca2+ oscillations impaired m-calpain activity, hindering T cell disengagement from DCs and resulting in persistent blockage of DC antigen presentation.
• RyR2 deficiency rendered CD4+ T cells immune suppressive, mimicking Foxp3+ Tregs in various disease contexts.
• Ryr2-deficient CD4+ T cells rescued systemic autoimmunity in Foxp3-deficient scurfy mice.

Conclusions:

• Foxp3-mediated inhibition of Ca2+ signaling via RyR2 represents a central effector mechanism of Treg immune suppression.
• The RyR2 pathway is critical for Treg function in preventing excessive immune responses.
• Targeting the Foxp3-RyR2-Ca2+ axis could offer novel therapeutic strategies for immune-related disorders.