Breakdown in immunological tolerance to self-antigens or uncontrolled inflammation results in autoimmune disorders. Dendritic cells (DCs) play an important role in regulating the balance between inflammatory and regulatory responses in the periphery. However, factors in the tissue microenvironment and the signaling networks critical for programming DCs to control chronic inflammation and promote tolerance are unknown. Here, we show that wnt ligand-mediated activation of β-catenin signaling in DCs is critical for promoting tolerance and limiting neuroinflammation. DC-specific deletion of key upstream (LRP5/6) or downstream mediators (β-catenin) of canonical wnt-signaling in mice exacerbated experimental autoimmune encephalomyelitis (EAE) pathology. Mechanistically, loss of LRP5/6-β-catenin-mediated signaling in DCs led to an increased Th1/ Th17 cell differentiation whereas reduced regulatory T cell response. This was due to increased production of pro-inflammatory cytokines and decreased production of anti-inflammatory cytokines such as IL-10 and IL-27 by DCs lacking LRP5/6-β-catenin signaling. Consistent with these findings, pharmacological activation of canonical wnt/β-catenin signaling delayed EAE onset and diminished CNS pathology. Thus, the activation of canonical wnt signaling in DCs limits effector T cell responses and represents a potential therapeutic approach to control autoimmune neuroinflammation.

At mucosal sites such as the intestine, the immune system launches robust immunity against invading pathogens while maintaining a state of tolerance to commensal flora and ingested food Ags. The molecular mechanisms underlying this phenomenon remain poorly understood. In this study, we report that signaling by GPR81, a receptor for lactate, in colonic dendritic cells and macrophages plays an important role in suppressing colonic inflammation and restoring colonic homeostasis. Genetic deletion of GPR81 in mice led to increased Th1/Th17 cell differentiation and reduced regulatory T cell differentiation, resulting in enhanced susceptibility to colonic inflammation. This was due to increased production of proinflammatory cytokines (IL-6, IL-1β, and TNF-α) and decreased expression of immune regulatory factors (IL-10, retinoic acid, and IDO) by intestinal APCs lacking GPR81. Consistent with these findings, pharmacological activation of GPR81 decreased inflammatory cytokine expression and ameliorated colonic inflammation. Taken together, these findings identify a new and important role for the GPR81 signaling pathway in regulating immune tolerance and colonic inflammation. Thus, manipulation of the GPR81 pathway could provide novel opportunities for enhancing regulatory responses and treating colonic inflammation.

The Wnt/β-catenin pathway is an evolutionarily conserved signaling pathway critical for several biological processes. An aberrant Wnt/β-catenin signaling is linked to several human diseases. Emerging studies have highlighted the regulatory role of the Wnt/β-catenin signaling pathway in normal physiological processes of parenchymal and hematopoietic cells. Recent studies have shown that the activation of Wnt/β-catenin pathway in dendritic cells (DCs) play a critical role in mucosal tolerance and suppression of chronic autoimmune pathologies. Alternatively, tumors activate Wnt/β-catenin pathway in DCs to induce immune tolerance and thereby evade antitumor immunity through suppression of effector T cell responses and promotion of regulatory T cell responses. Here, we review our work and current understanding of how Wnt/β-catenin signaling in DCs shapes the immune response in cancer and autoimmunity and discuss how Wnt/β-catenin pathway can be targeted for successful therapeutic interventions in various human diseases.

The tumor microenvironment (TME) contains high levels of the Wnt family of ligands, and aberrant Wnt-signaling occurs in many tumors. Past studies have been directed toward how the Wnt signaling cascade regulates cancer development, progression and metastasis. However, its effects on host antitumor immunity remain unknown. In this report, we show that Wnts in the TME condition dendritic cells (DCs) to a regulatory state and suppress host antitumor immunity. DC-specific deletion of Wnt co-receptors low-density lipoprotein receptor-related protein 5 and 6 (LRP5/6) in mice markedly delayed tumor growth and enhanced host antitumor immunity. Mechanistically, loss of LRP5/6-mediated signaling in DCs resulted in enhanced effector T cell differentiation and decreased regulatory T cell differentiation. This was due to increased production of pro-inflammatory cytokines and decreased production of IL-10, TGF-β1 and retinoic acid (RA). Likewise, pharmacological inhibition of the Wnts' interaction with its cognate co-receptors LRP5/6 and Frizzled (Fzd) receptors had similar effects on tumor growth and effector T cell responses. Moreover, blocking Wnt-signaling in DCs resulted in enhanced capture of tumor-associated antigens and efficient cross-priming of CD8 T cells. Hence, blocking the Wnt pathway represents a potential therapeutic to overcome tumor-mediated immune suppression and augment antitumor immunity.