The intramembrane protease Sppl2a is required for B cell and DC development and survival via cleavage of the invariant chain

The protease Sppl2a cleaves the N-terminal fragment of invariant chain (CD74) and is required for efficient B cell development and function.B cell development requires tight regulation to allow for the generation of a diverse repertoire while preventing the development of autoreactive cells. We report, using N-ethyl-N-nitrosourea (ENU)–induced mutagenesis, the identification of a mutant mouse (chompB) with a block in early B cell development. The blockade occurs after the transitional 1 (T1) stage and leads to a decrease in mature B cell subsets and deficits in T cell–dependent antibody responses. Additionally, chompB mice have decreases in myeloid dendritic cells (DCs). The mutation was mapped to the intramembrane protease signal peptide peptidase-like 2a (Sppl2a), a gene not previously implicated in immune cell development. Proteomic analysis identified the invariant chain (CD74) as a key substrate of Sppl2a and suggests that regulated intramembrane proteolysis of CD74 by Sppl2a contributes to B cell and DC survival. Moreover, these data suggest that modulation of Sppl2a may be a useful therapeutic strategy for treatment of B cell dependent autoimmune disorders

Evolutionary connectionism: algorithmic principles underlying the evolution of biological organisation in evo-devo, evo-eco and evolutionary transitions

The mechanisms of variation, selection and inheritance, on which evolution by natural selection depends, are not fixed over evolutionary time. Current evolutionary biology is increasingly focussed on understanding how the evolution of developmental organisations modifies the distribution of phenotypic variation, the evolution of ecological relationships modifies the selective environment, and the evolution of reproductive relationships modifies the heritability of the evolutionary unit. The major transitions in evolution, in particular, involve radical changes in developmental, ecological and reproductive organisations that instantiate variation, selection and inheritance at a higher level of biological organisation. However, current evolutionary theory is poorly equipped to describe how these organisations change over evolutionary time and especially how that results in adaptive complexes at successive scales of organisation (the key problem is that evolution is self-referential, i.e. the products of evolution change the parameters of the evolutionary process). Here we first reinterpret the central open questions in these domains from a perspective that emphasises the common underlying themes. We then synthesise the findings from a developing body of work that is building a new theoretical approach to these questions by converting well-understood theory and results from models of cognitive learning. Specifically, connectionist models of memory and learning demonstrate how simple incremental mechanisms, adjusting the relationships between individually-simple components, can produce organisations that exhibit complex system-level behaviours and improve the adaptive capabilities of the system. We use the term “evolutionary connectionism” to recognise that, by functionally equivalent processes, natural selection acting on the relationships within and between evolutionary entities can result in organisations that produce complex system-level behaviours in evolutionary systems and modify the adaptive capabilities of natural selection over time. We review the evidence supporting the functional equivalences between the domains of learning and of evolution, and discuss the potential for this to resolve conceptual problems in our understanding of the evolution of developmental, ecological and reproductive organisations and, in particular, the major evolutionary transitions

Inhibition of the inositol kinase Itpkb augments calcium signaling in lymphocytes and reveals a novel strategy to treat autoimmune disease

Emerging approaches to treat immune disorders target positive regulatory kinases downstream of antigen receptors with small molecule inhibitors. Here we provide evidence for an alternative approach in which inhibition of the negative regulatory inositol kinase Itpkb in mature T lymphocytes results in enhanced intracellular calcium levels following antigen receptor activation leading to T cell death. Using Itpkb conditional knockout mice and LMW Itpkb inhibitors these studies reveal that Itpkb through its product IP4 inhibits the Orai1/Stim1 calcium channel on lymphocytes. Pharmacological inhibition or genetic deletion of Itpkb results in elevated intracellular Ca2+ and induction of FasL and Bim resulting in T cell apoptosis. Deletion of Itpkb or treatment with Itpkb inhibitors blocks T-cell dependent antibody responses in vivo and prevents T cell driven arthritis in rats. These data identify Itpkb as an essential mediator of T cell activation and suggest Itpkb inhibition as a novel approach to treat autoimmune disease

Inositol 1,4,5-trisphosphate 3-kinase B is a negative regulator of BCR signaling that controls B cell selection and tolerance induction.

Inositol 1,4,5-trisphosphate 3-kinase B (or Itpkb) converts inositol 1,4,5-trisphosphate to inositol 1,3,4,5-tetrakisphosphate upon Ag receptor activation and controls the fate and function of lymphocytes. To determine the role of Itpkb in B cell tolerance, Itpkb(-/-) mice were crossed to transgenic mice that express a BCR specific for hen egg lysozyme (IgHEL). B cells from Itpkb(-/-) IgHEL mice possess an anergic phenotype, hypoproliferate in response to cognate Ag, and yet they exhibit enhanced Ag-induced calcium signaling. In IgHEL transgenic mice that also express soluble HEL, lack of Itpkb converts anergy induction to deletion. These data establish Itpkb as a negative regulator of BCR signaling that controls the fate of developing B cells and tolerance induction

The intramembrane protease Sppl2a is required for B cell and DC development and survival via cleavage of the invariant chain

B cell development requires tight regulation to allow for the generation of a diverse repertoire while preventing the development of autoreactive cells. We report, using N-ethyl-N-nitrosourea (ENU)–induced mutagenesis, the identification of a mutant mouse (chompB) with a block in early B cell development. The blockade occurs after the transitional 1 (T1) stage and leads to a decrease in mature B cell subsets and deficits in T cell–dependent antibody responses. Additionally, chompB mice have decreases in myeloid dendritic cells (DCs). The mutation was mapped to the intramembrane protease signal peptide peptidase-like 2a (Sppl2a), a gene not previously implicated in immune cell development. Proteomic analysis identified the invariant chain (CD74) as a key substrate of Sppl2a and suggests that regulated intramembrane proteolysis of CD74 by Sppl2a contributes to B cell and DC survival. Moreover, these data suggest that modulation of Sppl2a may be a useful therapeutic strategy for treatment of B cell dependent autoimmune disorders

Discovery of the First Potent, Selective, and Orally Bioavailable Signal Peptide Peptidase-Like 2a (SPPL2a) Inhibitor Displaying Pronounced Immunomodulatory Effects In Vivo

Signal peptide peptidase-like 2a (SPPL2a) is an aspartic intramembrane protease which has recently been shown to play an important role in the development and function of antigen presenting cells such as B lymphocytes and dendritic cells. In this paper, we describe the discovery of the first selective and orally active SPPL2a inhibitor (<i>S</i>)-2-cyclopropyl-<i>N</i>1-((<i>S</i>)-5,11-dioxo-10,11-dihydro-1<i>H</i>,3<i>H</i>,5<i>H</i>-spiro­[benzo­[<i>d</i>]­pyrazolo­[1,2-<i>a</i>]­[1,2]­diazepine-2,1′-cyclopropan]-10-yl)-<i>N</i>4-(5-fluoro-2-methylpyridin-3-yl)­succinamide <b>40</b> (<b>SPL-707</b>). This compound shows adequate selectivity against the closely related enzymes γ-secretase and SPP and a good pharmacokinetic profile in mouse and rat. Compound <b>40</b> significantly inhibited processing of the SPPL2a substrate CD74/p8 fragment in rodents at doses ≤10 mg/kg b.i.d. po. Oral dosing of <b>40</b> for 11 days at ≥10 mg/kg b.i.d. recapitulated the phenotype seen in Sppl2a knockout (ko) and ENU mutant mice (reduced number of specific B cells and myeloid dendritic cells). Thus, we believe that SPPL2a represents an interesting and druggable pharmacological target, potentially providing a novel approach for the treatment of autoimmune diseases by targeting B cells and dendritic cells