Amino-acid sensing and degrading pathways in immune regulation

Abstract Indoleamine 2,3-dioxygenases (IDOs) − belonging in the heme dioxygenase family and degrading tryptophan − are responsible for the de novo synthesis of nicotinamide adenine dinucleotide (NAD + ). As such, they are expressed by a variety of invertebrate and vertebrate species. In mammals, IDO1 has remarkably evolved to expand its functions, so to become a prominent homeostatic regulator, capable of modulating infection and immunity in multiple ways, including local tryptophan deprivation, production of biologically active tryptophan catabolites, and non-enzymatic cell-signaling activity. Much like IDO1, arginase 1 (Arg1) is an immunoregulatory enzyme that catalyzes the degradation of arginine. Here, we discuss the possible role of amino-acid degradation as related to the evolution of the immune systems and how the functions of those enzymes are linked by an entwined pathway selected by phylogenesis to meet the newly arising needs imposed by an evolving environment

Allosteric modulation of metabotropic glutamate receptor 4 activates IDO1-dependent, immunoregulatory signaling in dendritic cells

Metabotropic glutamate receptor 4 (mGluR4) possesses immune modulatory properties in vivo, such that a positive allosteric modulator (PAM) of the receptor confers protection on mice with relapsing-remitting experimental autoimmune encephalomyelitis (RR-EAE). ADX88178 is a newly-developed, one such mGluR4 modulator with high selectivity, potency, and optimized pharmacokinetics. Here we found that application of ADX88178 in the RR-EAE model system converted disease into a form of mild-yet chronic-neuroinflammation that remained stable for over two months after discontinuing drug treatment. In vitro, ADX88178 modulated the cytokine secretion profile of dendritic cells (DCs), increasing production of tolerogenic IL-10 and TGF-β. The in vitro effects required activation of a Gi-independent, alternative signaling pathway that involved phosphatidylinositol-3-kinase (PI3K), Src kinase, and the signaling activity of indoleamine 2,3-dioxygenase 1 (IDO1). A PI3K inhibitor as well as small interfering RNA targeting Ido1-but not pertussis toxin, which affects Gi protein-dependent responses-abrogated the tolerogenic effects of ADX88178-conditioned DCs in vivo. Thus our data indicate that, in DCs, highly selective and potent mGluR4 PAMs such as ADX88178 may activate a Gi-independent, long-lived regulatory pathway that could be therapeutically exploited in chronic autoimmune diseases such as multiple sclerosis

A Relay Pathway between Arginine and Tryptophan Metabolism Confers Immunosuppressive Properties on Dendritic Cells

Arginase 1 (Arg1) and indoleamine 2,3-dioxygenase 1\ua0(IDO1) are immunoregulatory enzymes catalyzing the degradation of L-arginine and L-tryptophan, respectively, resulting in local amino acid deprivation. In addition, unlike Arg1, IDO1 is also endowed with non-enzymatic signaling activity in dendritic cells (DCs). Despite considerable knowledge of their individual biology, no integrated functions of Arg1 and IDO1 have been reported yet. We found that IDO1 phosphorylation and consequent activation of IDO1 signaling in DCs was strictly dependent on prior expression of Arg1 and Arg1-dependent production of polyamines. Polyamines, either produced by DCs or released by bystander Arg1+ myeloid-derived suppressor cells, conditioned DCs toward an IDO1-dependent, immunosuppressive phenotype via activation of the Src kinase, which has IDO1-phosphorylating activity. Thus our data indicate that Arg1 and IDO1 are linked by an entwined pathway in immunometabolism and that their joint modulation could represent an important target for effective immunotherapy in several disease settings

Relationship between functions and intracellular localization of the immune checkpoint target indoleamine 2,3-dioxygenase 1

Indoleamine 2,3-dioxygenase (IDO1), a tryptophan catabolizing enzyme, is recognized as an authentic regulator of immunity in several physiopathologic conditions. In cancer, IDO1 can either be expressed directly by the tumor cells themselves, or induced indirectly in host antigen presenting cells by the tumor and its expression has been associated with a worse clinical outcome in a variety of cancers, such as melanoma, ovarian cancer, and colorectal cancer. This consideration has driven to the definition of IDO1 as an investigational immune checkpoint target and to the development of several IDO1 inhibitors, some of which have entered clinical evaluation. Its mechanisms of action as an immune regulator, is composite and involves tryptophan deprivation and production of immunosuppressive metabolites (kynurenines). We recently demonstrated that IDO1 also acts as a signal-transducing molecule, independently of its enzymic function. In particular, in a microenvironment dominated by TGF-?, we found that IDO1 is involved in intracellular signaling events responsible for the self-amplification and maintenance of a stably regulatory phenotype in plasmacytoid dendritic cells (pDCs), a DC subset. In the literature, IDO1 has been described as a protein with a cytoplasmic localization. However, no thorough analysis of modifications of this localization in different conditions has been performed so far

Amino acid metabolism as drug target in autoimmune diseases

In mammals, amino acid metabolism has evolved to control immune responses. Autoimmune diseases are heterogeneous conditions that involve the breakdown of tolerogenic circuitries and consequent activation of autoreactive immune cells. Therefore, critical enzymes along amino acid degradative pathways may be hijacked to keep in check autoimmunity. We examined here current knowledge of indoleamine 2,3-dioxygenase 1 (IDO1) and arginase 1 (ARG1), the main enzymes catabolizing tryptophan and arginine, respectively, in organ-specific and systemic autoimmune diseases as well as in the development of autoantibodies to therapeutic proteins. At variance with neoplastic contexts, in which it is known to act as a pure immunosuppressive molecule, ARG1 exhibited a protective or pathogenetic profile, depending on the disease. In contrast, in several autoimmune conditions, the bulk of data indicated that drugs capable of potentiating IDO1 expression and activity may represent valuable therapeutic tools and that IDO1-based immunotherapeutic protocols could be more effective if tailored to the genetic profile of individual patients.This work was supported by the European Research Council (338954-DIDO and 780807-DIDO-MS, both to U.G.) and the Italian Ministry of Education, Universities, and Research (PRIN2015- 20155C2PP7 to C.V.). A.C. was supported by the Northern Portugal Regional Operational Programme (NORTE 2020), under the Portugal 2020 Partnership Agreement, through the European Regional Development Fund (FEDER) (NORTE-01-0145-FEDER-000013), and the Fundação para a Ciência e Tecnologia (FCT) (IF/00735/2014)

Class IA PI3Ks regulate subcellular and functional dynamics of IDO1

none35sìKnowledge of a protein's spatial dynamics at the subcellular level is key to understanding its function(s), interactions, and associated intracellular events. Indoleamine 2,3-dioxygenase 1 (IDO1) is a cytosolic enzyme that controls immune responses via tryptophan metabolism, mainly through its enzymic activity. When phosphorylated, however, IDO1 acts as a signaling molecule in plasmacytoid dendritic cells (pDCs), thus activating genomic effects, ultimately leading to long-lasting immunosuppression. Whether the two activities-namely, the catalytic and signaling functions-are spatially segregated has been unclear. We found that, under conditions favoring signaling rather than catabolic events, IDO1 shifts from the cytosol to early endosomes. The event requires interaction with class IA phosphoinositide 3-kinases (PI3Ks), which become activated, resulting in full expression of the immunoregulatory phenotype in vivo in pDCs as resulting from IDO1-dependent signaling events. Thus, IDO1's spatial dynamics meet the needs for short-acting as well as durable mechanisms of immune suppression, both under acute and chronic inflammatory conditions. These data expand the theoretical basis for an IDO1-centered therapy in inflammation and autoimmunity.noneAlberta Iacono , Andrea Pompa, Francesca De Marchis , Eleonora Panfili , Francesco A Greco , Alice Coletti , Ciriana Orabona , Claudia Volpi , Maria L Belladonna , Giada Mondanelli, Elisa Albini , Carmine Vacca , Marco Gargaro , Francesca Fallarino , Roberta Bianchi , Carine De Marcos Lousa , Emilia Mc Mazza , Silvio Bicciato , Elisa Proietti , Francesca Milano , Maria P Martelli , Ioana M Iamandii , Mariona Graupera Garcia-Mila , Judith Llena Sopena , Phillip Hawkins , Sabine Suire , Klaus Okkenhaug , Anne-Katrien Stark , Fabio Grassi , Michele Bellucci , Paolo Puccetti , Laura Santambrogio , Antonio Macchiarulo, Ursula Grohmann , Maria T PallottaIacono, Alberta; Pompa, Andrea; De Marchis, Francesca; Panfili, Eleonora; A Greco, Francesco; Coletti, Alice; Orabona, Ciriana; Volpi, Claudia; L Belladonna, Maria; Mondanelli, Giada; Albini, Elisa; Vacca, Carmine; Gargaro, Marco; Fallarino, Francesca; Bianchi, Roberta; De Marcos Lousa, Carine; Mc Mazza, Emilia; Bicciato, Silvio; Proietti, Elisa; Milano, Francesca; P Martelli, Maria; M Iamandii, Ioana; Graupera Garcia-Mila, Mariona; Llena Sopena, Judith; Hawkins, Phillip; Suire, Sabine; Okkenhaug, Klaus; Stark, Anne-Katrien; Grassi, Fabio; Bellucci, Michele; Puccetti, Paolo; Santambrogio, Laura; Macchiarulo, Antonio; Grohmann, Ursula; T Pallotta, Mari