Src homology 2 domain-containing inositol 5-phosphatase 1 deficiency leads to a spontaneous allergic inflammation in the murine lung

SHIP-1 affects herpetic simplex keratitis prognosis by mediating CD4+ T lymphocytes migration through PI3K signaling and transcription factor KLF2 in the cornea

Herpetic simplex keratitis (HSK) mainly represents an immune cell-mediated, and more specifically, CD4⁺ T cell-orchestrated inflammatory response to virus invasion. The virus in infected corneas could be easily inhibited or hidden in the trigeminal ganglion using antiviral drugs, but the immune-related inflammation will last for a long time and lead to significant complications. In the present study, we found that the subconjunctival injection of SHIP-1 activator AQX1125 in mouse HSK model alleviated the corneal inflammatory and angiogenic responses, as well as promoted quicker recovery of the cornea, with significantly fewer infiltration of CD4⁺ T lymphocytes. Furthermore, using primary CD4⁺ T lymphocytes, we observed that by modulating PI3K signaling and the expression of transcription factors KLF2 and CCR7, SHIP-1 could significantly influence the migration of lymphocytes toward CCL19 and 21, which are the "exit cues" for cells to emigrate from inflammatory sites. Thus, we propose that the pharmacological SHIP-1 activation represents a new potential therapeutic approach to control HSK lesions, and its function on the CCR7-CCL19/21 biological axis may be a novel underlying mechanism for its anti-inflammatory action.

Selective deletion of SHIP-1 in hematopoietic cells in mice leads to severe lung inflammation involving ILC2 cells

Src homology 2 domain-containing inositol 5-phosphatase 1 (SHIP-1) regulates the intracellular levels of phosphotidylinositol-3, 4, 5-trisphosphate, a phosphoinositide 3-kinase (PI3K) product. Emerging evidence suggests that the PI3K pathway is involved in allergic inflammation in the lung. Germline or induced whole-body deletion of SHIP-1 in mice led to spontaneous type 2-dominated pulmonary inflammation, demonstrating that SHIP-1 is essential for lung homeostasis. However, the mechanisms by which SHIP-1 regulates lung inflammation and the responsible cell types are still unclear. Deletion of SHIP-1 selectively in B cells, T cells, dendritic cells (DC) or macrophages did not lead to spontaneous allergic inflammation in mice, suggesting that innate immune cells, particularly group 2 innate lymphoid cells (ILC2 cells) may play an important role in this process. We tested this idea using mice with deletion of SHIP-1 in the hematopoietic cell lineage and examined the changes in ILC2 cells. Conditional deletion of SHIP-1 in hematopoietic cells in Tek-Cre/SHIP-1 mice resulted in spontaneous pulmonary inflammation with features of type 2 immune responses and airway remodeling like those seen in mice with global deletion of SHIP-1. Furthermore, when compared to wild-type control mice, Tek-Cre/SHIP-1 mice displayed a significant increase in the number of IL-5/IL-13 producing ILC2 cells in the lung at baseline and after stimulation by allergen Papain. These findings provide some hints that PI3K signaling may play a role in ILC2 cell development at baseline and in response to allergen stimulation. SHIP-1 is required for maintaining lung homeostasis potentially by restraining ILC2 cells and type 2 inflammation.

SHIP-1 Regulates Phagocytosis and M2 Polarization Through the PI3K/Akt-STAT5-Trib1 Circuit in Pseudomonas aeruginosa Infection

SHIP-1 is an inositol phosphatase that hydrolyzes phosphatidylinositol 3-kinase (PI3K) products and negatively regulates protein kinase B (Akt) activity, thereby modulating a variety of cellular processes in mammals. However, the role of SHIP-1 in bacterial-induced sepsis is largely unknown. Here, we show that SHIP-1 regulates inflammatory responses during Gram-negative bacterium Pseudomonas aeruginosa infection. We found that infected-SHIP-1-/- mice exhibited decreased survival rates, increased inflammatory responses, and susceptibility owing to elevated expression of PI3K than wild-type (WT) mice. Inhibiting SHIP-1 via siRNA silencing resulted in lipid raft aggregates, aggravated oxidative damage, and bacterial burden in macrophages after PAO1 infection. Mechanistically, SHIP-1 deficiency augmented phosphorylation of PI3K and nuclear transcription of signal transducer and activator of transcription 5 (STAT5) to induce the expression of Trib1, which is critical for differentiation of M2 but not M1 macrophages. These findings reveal a previously unrecognized role of SHIP-1 in inflammatory responses and macrophage homeostasis during P. aeruginosa infection through a PI3K/Akt-STAT5-Trib1 axis.

SHIP-1, a target of miR-155, regulates endothelial cell responses in lung fibrosis

Src Homology 2-containing Inositol Phosphatase-1 (SHIP-1) is a target of miR-155, a pro-inflammatory factor. Deletion of the SHIP-1 gene in mice caused spontaneous lung inflammation and fibrosis. However, the role and function of endothelial miR-155 and SHIP-1 in lung fibrosis remain unknown. Using whole-body miR-155 knockout mice and endothelial cell-specific conditional miR-155 (VEC-Cre-miR-155 or VEC-miR-155) or SHIP-1 (VEC-SHIP-1) knockout mice, we assessed endothelial-mesenchymal transition (EndoMT) and fibrotic responses in bleomycin (BLM) induced lung fibrosis models. Primary mouse lung endothelial cells (MLEC) and human umbilical vein endothelial cells (HUVEC) with SHIP-1 knockdown were analyzed in TGF-β1 or BLM, respectively, induced fibrotic responses. Fibrosis and EndoMT were significantly reduced in miR-155KO mice and changes in EndoMT markers in MLEC after TGF-β1 stimulation confirmed the in vivo findings. Furthermore, lung fibrosis and EndoMT responses were reduced in VEC-miR-155 mice but significantly enhanced in VEC-SHIP-1 mice after BLM challenge. SHIP-1 knockdown in HUVEC cells resulted in enhanced EndoMT induced by BLM. Meanwhile, these changes involved the PI3K/AKT, JAK/STAT3, and SMAD/STAT signaling pathways. These studies demonstrate that endothelial miR-155 plays an important role in fibrotic responses in the lung through EndoMT. Endothelial SHIP-1 is essential in controlling fibrotic responses and SHIP-1 is a target of miR-155. Endothelial cells are an integral part in lung fibrosis.

Regulation of hematopoietic cell signaling by SHIP-1 inositol phosphatase: growth factors and beyond

SHIP-1 is a hematopoietic-specific inositol phosphatase activated downstream of a multitude of receptors including those for growth factors, cytokines, antigen, immunoglobulin and toll-like receptor agonists where it exerts inhibitory control. While it is constitutively expressed in all immune cells, SHIP-1 expression is negatively regulated by the inflammatory and oncogenic micro-RNA miR-155. Knockout mouse studies have shown the importance of SHIP-1 in various immune cell subsets and have revealed a range of immune-mediated pathologies that are engendered due to loss of SHIP-1's regulatory activity, impelling investigations into the role of SHIP-1 in human disease. In this review, we provide an overview of the literature relating to the role of SHIP-1 in hematopoietic cell signaling and function, we summarize recent reports that highlight the dysregulation of the SHIP-1 pathway in cancers, autoimmune disorders and inflammatory diseases, and lastly we discuss the importance of SHIP-1 in restraining myeloid growth factor signaling.

Granulocyte-CSF links destructive inflammation and comorbidities in obstructive lung disease

Chronic obstructive pulmonary disease (COPD) is an incurable inflammatory lung disease that afflicts millions of people worldwide, and it is the fourth leading cause of death. Systemic comorbidities affecting the heart, skeletal muscle, bone, and metabolism are major contributors to morbidity and mortality. Given the surprising finding in large prospective clinical biomarker studies that peripheral white blood cell count is more closely associated with disease than inflammatory biomarkers, we probed the role of blood growth factors. Using the SHIP-1-deficient COPD mouse model, which manifests a syndrome of destructive lung disease and a complex of comorbid pathologies, we have identified a critical and unexpected role for granulocyte-CSF (G-CSF) in linking these conditions. Deletion of G-CSF greatly reduced airway inflammation and lung tissue destruction, and attenuated systemic inflammation, right heart hypertrophy, loss of fat reserves, and bone osteoporosis. In human clinical translational studies, bronchoalveolar lavage fluid of patients with COPD demonstrated elevated G-CSF levels. These studies suggest that G-CSF may play a central and unforeseen pathogenic role in COPD and its complex comorbidities, and identify G-CSF and its regulators as potential therapeutic targets.

SHIP negatively regulates type II immune responses in mast cells and macrophages

SHIP is a hematopoietic-specific lipid phosphatase that dephosphorylates PI3K-generated PI(3,4,5)-trisphosphate. SHIP removes this second messenger from the cell membrane blunting PI3K activity in immune cells. Thus, SHIP negatively regulates mast cell activation downstream of multiple receptors. SHIP has been referred to as the "gatekeeper" of mast cell degranulation as loss of SHIP dramatically increases degranulation or permits degranulation in response to normally inert stimuli. SHIP also negatively regulates Mϕ activation, including both pro-inflammatory cytokine production downstream of pattern recognition receptors, and alternative Mϕ activation by the type II cytokines, IL-4, and IL-13. In the SHIP-deficient (SHIP-/- ) mouse, increased mast cell and Mϕ activation leads to spontaneous inflammatory pathology at mucosal sites, which is characterized by high levels of type II inflammatory cytokines. SHIP-/- mast cells and Mϕs have both been implicated in driving inflammation in the SHIP-/- mouse lung. SHIP-/- Mϕs drive Crohn's disease-like intestinal inflammation and fibrosis, which is dependent on heightened responses to innate immune stimuli generating IL-1, and IL-4 inducing abundant arginase I. Both lung and gut pathology translate to human disease as low SHIP levels and activity have been associated with allergy and with Crohn's disease in people. In this review, we summarize seminal literature and recent advances that provide insight into SHIP's role in mast cells and Mϕs, the contribution of these cell types to pathology in the SHIP-/- mouse, and describe how these findings translate to human disease and potential therapies.

AQX-1125, small molecule SHIP1 activator inhibits bleomycin-induced pulmonary fibrosis

BACKGROUND AND PURPOSE

The phosphatase SHIP1 negatively regulates the PI3K pathway, and its predominant expression within cells of the haematopoietic compartment makes SHIP1 activation a novel strategy to limit inflammatory signalling generated through PI3K. AQX-1125 is the only clinical-stage, orally administered, SHIP1 activator. Here, we demonstrate the prophylactic and therapeutic effects of AQX-1125, in a mouse model of bleomycin-induced lung fibrosis.

EXPERIMENTAL APPROACH

For prophylactic evaluation, AQX-1125 (3, 10 or 30 mg·kg^-1 ·d^-1 , p.o.) or dexamethasone (1 mg·kg^-1 ·d^-1 , i.p.) were given to CD-1 mice starting 3 days before intratracheal administration of bleomycin (0.1 IU per mouse) and continued daily for 7 or 21 days. Therapeutic potentials of AQX-1125 (3, 10 or 30 mg·kg^-1 ·d^-1 , p.o.) or pirfenidone (90 mg·kg^-1 ·d^-1 , p.o.) were assessed by initiating treatment 13 days after bleomycin instillation and continuing until day 28.

KEY RESULTS

Given prophylactically, AQX-1125 (10 and 30 mg·kg^-1 ) reduced histopathological changes in lungs, 7 and 21 days following bleomycin-induced injury. At the same doses, AQX-1125 reduced the number of total leukocytes, neutrophil activity, TGF-β immunoreactivity and soluble collagen in lungs. Administered therapeutically, AQX-1125 (10 and 30 mg·kg^-1 ) improved lung histopathology, cellular infiltration and reduced lung collagen content. At 30 mg·kg^-1 , the effects of AQX-1125 were similar to those of pirfenidone (90 mg·kg^-1 ) with corresponding improvements in disease severity.

CONCLUSIONS AND IMPLICATIONS

AQX-1125 prevented bleomycin-induced lung injury during the inflammatory and fibrotic phases. AQX-1125, given therapeutically, modified disease progression and improved survival, as effectively as pirfenidone.

Regulation of immune cell signaling by SHIP1: A phosphatase, scaffold protein, and potential therapeutic target

The phosphoinositide phosphatase SHIP is a critical regulator of immune cell activation. Despite considerable study, the mechanisms controlling SHIP activity to ensure balanced cell activation remain incompletely understood. SHIP dampens BCR signaling in part through its association with the inhibitory coreceptor Fc gamma receptor IIB, and serves as an effector for other inhibitory receptors in various immune cell types. The established paradigm emphasizes SHIP's inhibitory receptor-dependent function in regulating phosphoinositide 3-kinase signaling by dephosphorylating the phosphoinositide PI(3,4,5)P₃ ; however, substantial evidence indicates that SHIP can be activated independently of inhibitory receptors and can function as an intrinsic brake on activation signaling. Here, we integrate historical and recent reports addressing the regulation and function of SHIP in immune cells, which together indicate that SHIP acts as a multifunctional protein controlled by multiple regulatory inputs, and influences downstream signaling via both phosphatase-dependent and -independent means. We further summarize accumulated evidence regarding the functions of SHIP in B cells, T cells, NK cells, dendritic cells, mast cells, and macrophages, and data suggesting defective expression or activity of SHIP in autoimmune and malignant disorders. Lastly, we discuss the biological activities, therapeutic promise, and limitations of small molecule modulators of SHIP enzymatic activity.

Src Homology 2 Domain-Containing Inositol 5'-Phosphatase Ameliorates High Glucose-Induced Extracellular Matrix Deposition via the Phosphatidylinositol 3-Kinase/Protein Kinase B Pathway in Renal Tubular Epithelial Cells

A typical hallmark of diabetic kidney disease (DKD) is an excessive deposition of extracellular matrix (ECM) in the glomerulus and renal tubulointerstitium, leading to glomerulosclerosis and tubular interstitial fibrosis. Src homology 2 domain-containing inositol 5'-phosphatase (SHIP) is a negative regulator of the phosphatidylinositol 3-kinase/protein kinase B (PI3K/Akt) signaling. Here, we investigated the effect of SHIP on ECM deposition in diabetic mice and high glucose-stimulated human renal tubular epithelial cells (HK2 cells). The decreased SHIP and increased phospho-Akt (Ser 473, Thr 308) were found in the renal tubular cells of diabetic mice, which were accompanied by overexpression of transforming growth factor-β1 (TGF-β1), α-smooth muscle actin (α-SMA), and secreted collagen type 3 (Col 3) and a low expression of E-cadherin compared to that in normal mice. In vitro research revealed that high glucose-attenuated SHIP expression accompanied the activation of the PI3K/Akt signaling and ECM production. Knocking down SHIP in HK2 cells caused an increase in the levels of phospho-Akt (Ser 473), phospho-Akt (Thr 308), TGF-β1, α-SMA, and secreted Col 3 and a decrease in E-cadherin. Again, either the M90-SHIP plasmid or the PI3K/Akt pathway inhibitor LY294002 could significantly prevent the high glucose-induced increase in TGF-β1, α-SMA, and secreted Col 3 and decreased E-cadherin. Furthermore, we confirmed that inhibition of the TGF-β1 pathway with SB431542 blocked the effect of SHIP knockdown on ECM production in HK2 cells. In summary, our study suggests that decreased SHIP mediates high glucose-induced TGF-β1 upregulation and ECM deposition through activation of the PI3K/Akt pathway in renal tubular cells. J. Cell. Biochem. 118: 2271-2284, 2017. © 2017 Wiley Periodicals, Inc.

SHIP, a novel factor to ameliorate extracellular matrix accumulation via suppressing PI3K/Akt/CTGF signaling in diabetic kidney disease

Tubular interstitial extracellular matrix accumulation, which plays a key role in the pathogenesis and progression of diabetic kidney disease (DKD), is believed to be mediated by activation of PI3K/Akt signal pathway. However, it is still not clear whether SH2 domain-containing inositol 5'-phosphatase (SHIP), known as a negative regulator of PI3K/Akt pathway is also involved in extracellular matrix metabolism of diabetic kidney. In the present study, decreased SHIP and increased phospho-Akt (Ser 473, Thr 308) were found in renal tubular cells of diabetic mice accompanied by overexpression of connective tissue growth factor (CTGF) and extracellular matrix deposition versus normal mice. Again, high glucose attenuated SHIP expression in a time-dependent manner, concomitant with activation of PI3K/Akt signaling and extracellular matrix production in human renal proximal tubular epithelial cells (HK2) cultured in vitro, which was significantly prevented by transfection of M90-SHIP vector. Furthermore, in vivo delivery of rAd-INPP5D vector (SHIP expression vector) via intraperitoneal injection in diabetic mice increased SHIP expression by 3.36 times followed by 65.26%, 70.38% and 46.71% decreases of phospho-Akt (Ser 473), phospho-Akt (Thr 308) and CTGF expression versus diabetic mice receiving rAd-EGFP vector. Meanwhile, increased renal extracellular matrix accumulation of diabetic mice was also inhibited with intraperitoneal injection of rAd-INPP5D vector. These above data suggested that overexpression of SHIP might be a potent method to lessen renal extracellular matrix accumulation via inactivation of PI3K/Akt pathway and suppression of CTGF expression in DKD.

SHIP represses lung inflammation and inhibits mammary tumor metastasis in BALB/c mice

SH2-containing-inositol-5'-phosphatase (SHIP) is a negative regulator of the phosphatidylinositol-3-kinase pathway in hematopoietic cells and limits the development of leukemias and lymphomas. The potential role of SHIP in solid tumor development and metastasis remains unknown. While SHIP restricts the aberrant development of myeloid cells in C57BL/6 mice, there are conflicting reports regarding the effect of SHIP deletion in BALB/c mice with important consequences for determining the influence of SHIP in different model tumor systems. We generated SHIP-/- BALB/c mice and challenged them with syngeneic non-metastatic 67NR or metastatic 4T1 mammary tumors. We demonstrate that SHIP restricts the development, alternative-activation, and immunosuppressive function of myeloid cells in tumor-free and tumor-bearing BALB/c mice. Tumor-free SHIP-/- BALB/c mice exhibited pulmonary inflammation, myeloid hyperplasia, and M2-polarized macrophages and this phenotype was greatly exacerbated by 4T1, but not 67NR, tumors. 4T1-bearing SHIP-/- mice rapidly lost weight and died from necrohemorrhagic inflammatory pulmonary disease, characterized by massive infiltration of pulmonary macrophages and myeloid-derived suppressor cells that were more M2-polarized and immunosuppressive than wild-type cells. Importantly, while SHIP loss did not affect primary tumor growth, 4T1-bearing SHIP-/- mice had 7.5-fold more metastatic tumor cells in their lungs than wild-type mice, consistent with the influence of immunosuppressive myeloid cells on metastatic growth. Our findings identify the hematopoietic cell-restricted protein SHIP as an intriguing target to influence the development of solid tumor metastases, and support development of SHIP agonists to prevent the accumulation of immunosuppressive myeloid cells and tumor metastases in the lungs to improve treatment of metastatic breast cancer.

Chitin-Induced Airway Epithelial Cell Innate Immune Responses Are Inhibited by Carvacrol/Thymol

Chitin is produced in large amounts by fungi, insects, and other organisms and has been implicated in the pathogenesis of asthma. Airway epithelial cells are in direct contact with environmental particles and serve as the first line of defense against inhaled allergens and pathogens. The potential contributions of airway epithelial cells to chitin-induced asthma remain poorly understood. We hypothesized that chitin directly stimulates airway epithelial cells to release cytokines that promote type 2 immune responses and to induce expression of molecules which are important in innate immune responses. We found that chitin exposure rapidly induced the expression of three key type 2-promoting cytokines, IL-25, IL-33 and TSLP, in BEAS-2B transformed human bronchial epithelial cells and in A549 and H292 lung carcinoma cells. Chitin also induced the expression of the key pattern recognition receptors TLR2 and TLR4. Chitin induced the expression of miR-155, miR-146a and miR-21, each of which is known to up-regulate the expression of pro-inflammatory cytokines. Also the expression of SOCS1 and SHIP1 which are known targets of miR-155 was repressed by chitin treatment. The monoterpene phenol carvacrol (Car) and its isomer thymol (Thy) are found in herbal essential oils and have been shown to inhibit allergic inflammation in asthma models. We found that Car/Thy inhibited the effects of chitin on type 2-promoting cytokine release and on the expression of TLRs, SOCS1, SHIP1, and miRNAs. Car/Thy could also efficiently reduce the protein levels of TLR4, inhibit the increase in TLR2 protein levels in chitin plus Car/Thy-treated cells and increase the protein levels of SHIP1 and SOCS1, which are negative regulators of TLR-mediated inflammatory responses. We conclude that direct effects of chitin on airway epithelial cells are likely to contribute to allergic airway diseases like asthma, and that Car/Thy directly inhibits epithelial cell pro-inflammatory responses to chitin.

The adaptor protein insulin receptor substrate 2 inhibits alternative macrophage activation and allergic lung inflammation

Insulin receptor substrate 2 (IRS2) is an adaptor protein that becomes tyrosine-phosphorylated in response to the cytokines interleukin-4 (IL-4) and IL-13, which results in activation of the phosphoinositide 3-kinase (PI3K)-Akt pathway. IL-4 and IL-13 contribute to allergic lung inflammation. To examine the role of IRS2 in allergic disease, we evaluated the responses of IRS2-deficient (IRS2(-/-)) mice. Unexpectedly, loss of IRS2 resulted in a substantial increase in the expression of a subset of genes associated with the generation of alternatively activated macrophages (AAMs) in response to IL-4 or IL-13 in vitro. AAMs secrete factors that enhance allergic responses and promote airway remodeling. Moreover, compared to IRS2(+/+) mice, IRS2(+/-) and IRS2(-/-) mice developed enhanced pulmonary inflammation, accumulated eosinophils and AAMs, and exhibited airway and vascular remodeling upon allergen stimulation, responses that partially depended on macrophage-intrinsic IRS2 signaling. Both in unstimulated and IL-4-stimulated macrophages, lack of IRS2 enhanced phosphorylation of Akt and ribosomal S6 protein. Thus, we identified a critical inhibitory loop downstream of IRS2, demonstrating an unanticipated and previously unrecognized role for IRS2 in suppressing allergic lung inflammation and remodeling.

Targeting miR-155 to Treat Experimental Scleroderma

Scleroderma is a refractory autoimmune skin fibrotic disorder. Alterations of microRNAs in lesional skin could be a new approach to treating the disease. Here, we found that expression of miR-155 was up regulated in lesional skin tissue from patients with either systemic or localized scleroderma, and correlated with fibrosis area. Then we demonstrated the potential of miR-155 as a therapeutic target in pre-clinical scleroderma models. MiR-155^−/− mice were resistant to bleomycin induced skin fibrosis. Moreover, topical antagomiR-155 could effectively treat mice primed with subcutaneous bleomycin. In primary skin fibroblast, miR-155 silencing could inhibit collagen synthesis function, as well as signaling intensity of two pro-fibrotic pathways, Wnt/β-catenin and Akt, simultaneously. We further showed that miR-155 could regulate the two pathways via directly targeting casein kinase 1α (CK1α) and Src homology 2-containing inositol phosphatase-1 (SHIP-1), as previous reports. Mice with miR-155 knockout or topical antagomir-155 treatment showed inhibited Wnt/β-catenin and Akt signaling in skin upon bleomycin challenge. Together, our data suggest the potential of miR-155 silencing as a promising treatment for dermal fibrosis, especially in topical applications.

CD11b immunophenotyping identifies inflammatory profiles in the mouse and human lungs

The development of easily accessible tools for human immunophenotyping to classify patients into discrete disease endotypes is advancing personalized therapy. However, no systematic approach has been developed for the study of inflammatory lung diseases with often complex and highly heterogeneous disease etiologies. We have devised an internally standardized flow cytometry approach that can identify parallel inflammatory alveolar macrophage phenotypes in both the mouse and human lungs. In mice, lung innate immune cell alterations during endotoxin challenge, influenza virus infection, and in two genetic models of chronic obstructive lung disease could be segregated based on the presence or absence of CD11b alveolar macrophage upregulation and lung eosinophilia. Additionally, heightened alveolar macrophage CD11b expression was a novel feature of acute lung exacerbations in the SHIP-1(-/-) model of chronic obstructive lung disease, and anti-CD11b antibody administration selectively blocked inflammatory CD11b(pos) but not homeostatic CD11b(neg) alveolar macrophages in vivo. The identification of analogous profiles in respiratory disease patients highlights this approach as a translational avenue for lung disease endotyping and suggests that heterogeneous innate immune cell phenotypes are an underappreciated component of the human lung disease microenvironment.

Lineage-specific regulation of allergic airway inflammation by the lipid phosphatase Src homology 2 domain-containing inositol 5-phosphatase (SHIP-1)

BACKGROUND

Inpp5d (Src homology 2 domain-containing inositol-5-phosphatase [Ship1])-deficient mice experience spontaneous airway inflammation and have enhanced sensitivity to allergen-induced airway inflammation.

OBJECTIVE

We hypothesized that lineage-specific deletion of Ship1 expression in cells known to be crucial for adaptive TH2 responses would uncover distinct roles that could either positively or negatively regulate susceptibility to allergic airway inflammation (AAI).

METHODS

Ship1 expression was deleted in B cells, T cells, or dendritic cells (DCs), and the resulting Ship1(ΔB cell), Ship1(ΔT cell), Ship1(ΔDC), or Ship1(F/F) (wild-type) control mice were evaluated in a model of house dust mite (HDM)-induced AAI.

RESULTS

Unlike germline panhematopoietic Ship1 deletion, deletion of Ship1 selectively in either the B-cell, T-cell, or DC lineages did not result in spontaneous airway inflammation. Strikingly, although loss of Ship1 in the B-cell lineage did not affect HDM-induced AAI, loss of Ship1 in either of the T-cell or DC lineages protected mice from AAI by skewing the typical TH2 immune response toward a TH1 response.

CONCLUSIONS

Although panhematopoietic deletion of Ship1 leads to spontaneous lung inflammation, selective deletion of Ship1 in T cells or DCs impairs the formation of an adaptive TH2 response and protects animals from HDM-induced AAI.

Periostin is required for maximal airways inflammation and hyperresponsiveness in mice

BACKGROUND

Periostin, a secreted extracellular matrix protein, has been localized to deposits of subepithelial fibrosis in asthmatic patients, and periostin levels have been linked to increases in IL-13.

OBJECTIVE

We hypothesized that periostin is required for airway inflammatory responses to a physiologic aeroallergen, house dust mite (HDM).

METHODS

We studied F4-F6 B6;129-Postn(tm1Jmol)/J wild-type (Postn(+/+)) and null (Postn(-/-)) mice, as well as C57BL/6 mice treated with either IgM or OC-20 periostin neutralizing antibody. Mice were exposed to 5 doses of HDM intranasally over a 16-day period.

RESULTS

HDM increased airways responsiveness in Postn(+/+) but not Postn(-/-) mice. In addition, HDM-treated C57BL/6 mice injected with OC-20 had lower airways responsiveness than HDM-treated mice injected with IgM. Compared with Postn(+/+) mice, Postn(-/-) mice showed decreases in HDM-induced inflammation and mucous metaplasia, as well as reduced IL-4, IL-25, CD68, Gob5, and periostin mRNA expression. OC-20 antibody produced similar results. HDM exposure increased periostin expression in the airway epithelium, subepithelium, smooth muscle and inflammatory cells. OC-20 blocked the HDM-induced IgE response, and T cells incubated with dendritic cells (DCs) from Postn(-/-) mice or treated with OC-20 showed deficient DNA synthesis and IL-13 responses compared with T cells incubated with wild-type DCs. Finally, adoptive transfer of bone marrow-derived DCs from Postn(+/+) mice was sufficient to promote allergic responses in F6 Postn(-/-) littermates.

CONCLUSIONS

In mice, periostin is required for maximal airways hyperresponsiveness and inflammation after HDM sensitization and challenge. Periostin is required for maximal HDM-induced T-cell responses.

SHIP-1 deficiency in the myeloid compartment is insufficient to induce myeloid expansion or chronic inflammation

SHIP-1 has an important role in controlling immune cell function through its ability to downmodulate PI3K signaling pathways that regulate cell survival and responses to stimulation. Mice deficient in SHIP-1 display several chronic inflammatory phenotypes including antibody-mediated autoimmune disease, Crohn's disease-like ileitis and a lung disease reminiscent of chronic obstructive pulmonary disease. The ileum and lungs of SHIP-1-deficient mice are infiltrated at an early age with abundant myeloid cells and the mice have a limited lifespan primarily thought to be due to the consolidation of lungs with spontaneously activated macrophages. To determine whether the myeloid compartment is the key initiator of inflammatory disease in SHIP-1-deficient mice, we examined two independent strains of mice harboring myeloid-restricted deletion of SHIP-1. Contrary to expectations, conditional deletion of SHIP-1 in myeloid cells did not result in consolidating pneumonia or segmental ileitis typical of germline SHIP-1 deficiency. In addition, other myeloid cell abnormalities characteristic of germline loss of SHIP-1, including flagrant splenomegaly and enhanced myelopoiesis, were absent in mice lacking SHIP-1 in myeloid cells. This study indicates that the spontaneous inflammatory disease characteristic of germline SHIP-1 deficiency is not initiated solely by LysM-positive myeloid cells but requires the simultaneous loss of SHIP-1 in other hematolymphoid lineages.

Characterization of AQX-1125, a small-molecule SHIP1 activator: Part 2. Efficacy studies in allergic and pulmonary inflammation models in vivo

BACKGROUND

The efficacy of AQX-1125, a small-molecule SH2-containing inositol-5'-phosphatase 1 (SHIP1) activator and clinical development candidate, is investigated in rodent models of inflammation.

EXPERIMENTAL APPROACH

AQX-1125 was administered orally in a mouse model of passive cutaneous anaphylaxis (PCA) and a number of rodent models of respiratory inflammation including: cigarette smoke, LPS and ovalbumin (OVA)-mediated airway inflammation. SHIP1 dependency of the AQX-1125 mechanism of action was investigated by comparing the efficacy in wild-type and SHIP1-deficient mice subjected to an intrapulmonary LPS challenge.

RESULTS

AQX-1125 exerted anti-inflammatory effects in all of the models studied. AQX-1125 decreased the PCA response at all doses tested. Using bronchoalveolar lavage (BAL) cell counts as an end point, oral or aerosolized AQX-1125 dose dependently decreased the LPS-mediated pulmonary neutrophilic infiltration at 3-30 mg kg⁻¹ and 0.15-15 μg kg⁻¹ respectively. AQX-1125 suppressed the OVA-mediated airway inflammation at 0.1-10 mg kg⁻¹. In the smoke-induced airway inflammation model, AQX-1125 was tested at 30 mg kg⁻¹ and significantly reduced the neutrophil infiltration of the BAL fluid. AQX-1125 (10 mg kg⁻¹) decreased LPS-induced pulmonary neutrophilia in wild-type mice but not in SHIP1-deficient mice.

CONCLUSIONS

The SHIP1 activator, AQX-1125, suppresses leukocyte accumulation and inflammatory mediator release in rodent models of pulmonary inflammation and allergy. As shown in the mouse model of LPS-induced lung inflammation, the efficacy of the compound is dependent on the presence of SHIP1. Pharmacological SHIP1 activation may have clinical potential for the treatment of pulmonary inflammatory diseases.

Inositol polyphosphate phosphatases in human disease

Phosphoinositide signalling molecules interact with a plethora of effector proteins to regulate cell proliferation and survival, vesicular trafficking, metabolism, actin dynamics and many other cellular functions. The generation of specific phosphoinositide species is achieved by the activity of phosphoinositide kinases and phosphatases, which phosphorylate and dephosphorylate, respectively, the inositol headgroup of phosphoinositide molecules. The phosphoinositide phosphatases can be classified as 3-, 4- and 5-phosphatases based on their specificity for dephosphorylating phosphates from specific positions on the inositol head group. The SAC phosphatases show less specificity for the position of the phosphate on the inositol ring. The phosphoinositide phosphatases regulate PI3K/Akt signalling, insulin signalling, endocytosis, vesicle trafficking, cell migration, proliferation and apoptosis. Mouse knockout models of several of the phosphoinositide phosphatases have revealed significant physiological roles for these enzymes, including the regulation of embryonic development, fertility, neurological function, the immune system and insulin sensitivity. Importantly, several phosphoinositide phosphatases have been directly associated with a range of human diseases. Genetic mutations in the 5-phosphatase INPP5E are causative of the ciliopathy syndromes Joubert and MORM, and mutations in the 5-phosphatase OCRL result in Lowe's syndrome and Dent 2 disease. Additionally, polymorphisms in the 5-phosphatase SHIP2 confer diabetes susceptibility in specific populations, whereas reduced protein expression of SHIP1 is reported in several human leukaemias. The 4-phosphatase, INPP4B, has recently been identified as a tumour suppressor in human breast and prostate cancer. Mutations in one SAC phosphatase, SAC3/FIG4, results in the degenerative neuropathy, Charcot-Marie-Tooth disease. Indeed, an understanding of the precise functions of phosphoinositide phosphatases is not only important in the context of normal human physiology, but to reveal the mechanisms by which these enzyme families are implicated in an increasing repertoire of human diseases.

Inhibition of PI3K signaling spurs new therapeutic opportunities in inflammatory/autoimmune diseases and hematological malignancies

The phosphoinositide 3-kinase/mammalian target of rapamycin/protein kinase B (PI3K/mTOR/Akt) signaling pathway is central to a plethora of cellular mechanisms in a wide variety of cells including leukocytes. Perturbation of this signaling cascade is implicated in inflammatory and autoimmune disorders as well as hematological malignancies. Proteins within the PI3K/mTOR/Akt pathway therefore represent attractive targets for therapeutic intervention. There has been a remarkable evolution of PI3K inhibitors in the past 20 years from the early chemical tool compounds to drugs that are showing promise as anticancer agents in clinical trials. The use of animal models and pharmacological tools has expanded our knowledge about the contribution of individual class I PI3K isoforms to immune cell function. In addition, class II and III PI3K isoforms are emerging as nonredundant regulators of immune cell signaling revealing potentially novel targets for disease treatment. Further complexity is added to the PI3K/mTOR/Akt pathway by a number of novel signaling inputs and feedback mechanisms. These can present either caveats or opportunities for novel drug targets. Here, we consider recent advances in 1) our understanding of the contribution of individual PI3K isoforms to immune cell function and their relevance to inflammatory/autoimmune diseases as well as lymphoma and 2) development of small molecules with which to inhibit the PI3K pathway. We also consider whether manipulating other proximal elements of the PI3K signaling cascade (such as class II and III PI3Ks or lipid phosphatases) are likely to be successful in fighting off different immune diseases.

Interleukin-4- and interleukin-13-mediated alternatively activated macrophages: roles in homeostasis and disease

The macrophage, a versatile cell type prominently involved in host defense and immunity, assumes a distinct state of alternative activation in the context of polarized type 2 immune responses such as allergic inflammation and helminth infection. This alternatively activated phenotype is induced by the canonical type 2 cytokines interleukin (IL)-4 and IL-13, which mediate expression of several characteristic markers along with a dramatic shift in macrophage metabolic pathways that influence surrounding cells and tissues. We discuss recent advances in the understanding of IL-4- and IL-13-mediated alternatively activated macrophages and type 2 immune responses; such advances have led to an expanded appreciation for functions of these cells beyond immunity, including maintenance of physiologic homeostasis and tissue repair.

Dok adaptors play anti-inflammatory roles in pulmonary homeostasis

Asthma is a chronic inflammatory disease of the lung with airflow obstruction and bronchospasm, characterized by pulmonary eosinophilia, airway remodeling, increased airway hyperresponsiveness to environmental stimuli, and excessive Th2-type cytokine production. Recent studies indicate that crosstalk between the innate and adaptive immune systems is crucial for this disease. We and others have showed that the Dok (downstream of tyrosine kinases) family adaptors, Dok-1, Dok-2, and Dok-3, play essential roles in negative regulation of a wide variety of signaling pathways in both innate and adaptive immunities. Here, histopathology and bronchoalveolar lavage fluid (BALF) cellularity showed spontaneous pulmonary inflammation in Dok-1-/- Dok-2-/- Dok-3-/- (TKO) mice, but not in Dok-1-/- Dok-2-/- or Dok-3-/- mice, with hallmarks of asthma, including eosinophilia, goblet cell hyperplasia, and subepithelial fibrosis. Consistently, TKO mice, but not the other mutants, showed increased airway hyperresponsiveness to methacholine inhalation. In addition, Th2-type cytokine concentrations in BALF were increased in TKO mice. These findings provide strong evidence that Dok-1, Dok-2, and Dok-3 cooperatively play critical anti-inflammatory roles in lung homeostasis.

Loss-of-function of inositol polyphosphate-4-phosphatase reversibly increases the severity of allergic airway inflammation

Inositol polyphosphate phosphatases regulate the magnitude of phosphoinositide-3 kinase signalling output. Although inositol polyphosphate-4-phosphatase is known to regulate phosphoinositide-3 kinase signalling, little is known regarding its role in asthma pathogenesis. Here we show that modulation of inositol polyphosphate-4-phosphatase alters the severity of asthma. Allergic airway inflammation in mice led to calpain-mediated degradation of inositol polyphosphate-4-phosphatase. In allergic airway inflammation models, preventing inositol polyphosphate-4-phosphatase degradation by inhibiting calpain activity, or overexpression of inositol polyphosphate-4-phosphatase in mouse lungs, led to attenuation of the asthma phenotype. Conversely, knockdown of inositol polyphosphate-4-phosphatase severely aggravated the allergic airway inflammation and the asthma phenotype. Interestingly, inositol polyphosphate-4-phosphatase knockdown in lungs of naive mice led to spontaneous airway hyper-responsiveness, suggesting that inositol polyphosphate-4-phosphatase could be vital in maintaining the lung homeostasis. We suggest that inositol polyphosphate-4-phosphatase has an important role in modulating inflammatory response in asthma, and thus, uncover a new understanding of the complex interplay between inositol signalling and asthma, which could provide alternative strategies in asthma management.

The role of SHIP in the development and activation of mouse mucosal and connective tissue mast cells

Although SHIP is a well-established suppressor of IgE plus Ag-induced degranulation and cytokine production in bone marrow-derived mast cells (BMMCs), little is known about its role in connective tissue (CTMCs) or mucosal (MMCs) mast cells. In this study, we compared SHIP's role in the development as well as the IgE plus Ag and TLR-induced activation of CTMCs, MMCs, and BMMCs and found that SHIP delays the maturation of all three mast cell subsets and, surprisingly, that it is a positive regulator of IgE-induced BMMC survival. We also found that SHIP represses IgE plus Ag-induced degranulation of all three mast cell subsets and that TLR agonists do not trigger their degranulation, whether SHIP is present or not, nor do they enhance IgE plus Ag-induced degranulation. In terms of cytokine production, we found that in MMCs and BMMCs, which are poor producers of TLR-induced cytokines, SHIP is a potent negative regulator of IgE plus Ag-induced IL-6 and TNF-α production. Surprisingly, however, in splenic or peritoneal derived CTMCs, which are poor producers of IgE plus Ag-induced cytokines, SHIP is a potent positive regulator of TLR-induced cytokine production. Lastly, cell signaling and cytokine production studies with and without LY294002, wortmannin, and PI3Kα inhibitor-2, as well as with PI3K p85α(-/-) BMMCs and CTMCs, are consistent with SHIP positively regulating TLR-induced cytokine production via an adaptor-mediated pathway while negatively regulating IgE plus Ag-induced cytokine production by repressing the PI3K pathway.

The SH2-domain of SHIP1 interacts with the SHIP1 C-terminus: impact on SHIP1/Ig-α interaction

The SH2-containing inositol 5'-phosphatase, SHIP1, negatively regulates signal transduction from the B cell antigen receptor (BCR). The mode of coupling between SHIP1 and the BCR has not been elucidated so far. In comparison to wild-type cells, B cells expressing a mutant IgD- or IgM-BCR containing a C-terminally truncated Ig-α respond to pervanadate stimulation with markedly reduced tyrosine phosphorylation of SHIP1 and augmented activation of protein kinase B. This indicates that SHIP1 is capable of interacting with the C-terminus of Ig-α. Employing a system of fluorescence resonance energy transfer in S2 cells, we can clearly demonstrate interaction between the SH2-domain of SHIP1 and Ig-α. Furthermore, a fluorescently labeled SH2-domain of SHIP1 translocates to the plasma membrane in an Ig-α-dependent manner. Interestingly, whereas the SHIP1 SH2-domain can be pulled-down with phospho-peptides corresponding to the immunoreceptor tyrosine-based activation motif (ITAM) of Ig-α from detergent lysates, no interaction between full-length SHIP1 and the phosphorylated Ig-α ITAM can be observed. Further studies show that the SH2-domain of SHIP1 can bind to the C-terminus of the SHIP1 molecule, most probably by inter- as well as intra-molecular means, and that this interaction regulates the association between different forms of SHIP1 and Ig-α.

T-cell subset regulation in atopy

Presentation of processed allergen by antigen-presenting cells to T-helper (Th) lymphocytes, which is influenced costimulatory signals, cytokines, chemokines, and regulatory T cells (Tregs), determines the development of different types of T-cell immunity. The discovery of Tregs revolutionized the primary concepts of immune regulation interpreted within the framework of a binary Th1/Th2 paradigm. Tregs play a central role in the maintenance of peripheral homeostasis, the establishment of controlled immune responses, and the inhibition of allergen-specific effector cells. Recently, some other T-cell subsets appeared, including Th17 and Th9 cells, which control local tissue inflammation through upregulation of proinflammatory cytokines and chemokines. This review aims to discuss our understanding of the T-cell subset reciprocal interaction in atopy.

Genetic segregation of inflammatory lung disease and autoimmune disease severity in SHIP-1-/- mice

Alternatively activated M2 macrophages are implicated as both regulators and agents of lung disease, but their control is poorly understood. SHIP-1 is a 5' inositol phosphatase that negatively regulates the PI3K signaling pathway implicated in inflammation. SHIP-1-deficient mice have defects in hematopoiesis and B cell development, and die prematurely due to consolidation of lungs with M2-skewed macrophages. SHIP-1 is thought to restrain M2 macrophage polarization, with deregulated M2 skewing coinciding with severe lung disease in SHIP-1-deficient mice. To determine the influence of genetic background on the lung phenotype in SHIP-1(-/-) mice, we backcrossed the SHIP-1 null mutation onto C57BL/6 (Th2-resistant) and BALB/c (Th2-prone) backgrounds. Remarkably, we found that inflammatory lung disease was severe in C57.SHIP-1(-/-) mice, but absent in BALB.SHIP-1(-/-) mice. C57.SHIP-1(-/-), but not BALB.SHIP-1(-/-) mice had greatly increased myeloid progenitors, myeloid hyperplasia, markedly enhanced numbers of activated alveolar macrophages, and elevated amounts of Th2 and proinflammatory cytokines in bronchoalveolar lavage fluid and serum, suggesting that deregulated cytokine production induced disease. C57.SHIP-1(-/-) mice also developed severe B cell-dependent autoimmune disease, which was markedly attenuated on the BALB/c background. These data demonstrate that, contrary to current concepts, loss of SHIP-1 alone is not sufficient to cause lung inflammation, with disease only manifest on a permissive genetic background. This finding questions the nature of the lung disease in SHIP-1(-/-) mice, suggesting that its M2 classification is not strictly correct. Future identification of disease-promoting loci might reveal determinants of comorbid lung disease and autoimmunity and uncover potentially useful therapeutic targets.

Inhibitor and activator: dual functions for SHIP in immunity and cancer

SHIP1 is at the nexus of intracellular signaling pathways in immune cells that mediate bone marrow (BM) graft rejection, production of inflammatory and immunosuppressive cytokines, immunoregulatory cell formation, the BM niche that supports development of the immune system, and immune cancers. This review summarizes how SHIP participates in normal immune physiology or the pathologies that result when SHIP is mutated. This review also proposes that SHIP can have either inhibitory or activating roles in cell signaling that are determined by whether signaling pathways distal to PI3K are promoted by SHIP's substrate (PI(3,4,5)P(3) ) or its product (PI(3,4)P(2) ). This review also proposes the "two PIP hypothesis" that postulates that both SHIP's product and its substrate are necessary for a cancer cell to achieve and sustain a malignant state. Finally, due to the recent discovery of small molecule antagonists and agonists for SHIP, this review discusses potential therapeutic settings where chemical modulation of SHIP might be of benefit.

Role of SHIP-1 in the adaptive immune responses to aeroallergen in the airway

Background

Th2-dominated inflammatory response in the airway is an integral component in the pathogenesis of allergic asthma. Accumulating evidence supports the notion that the phosphoinositide 3-kinase (PI3K) pathway is involved in the process. We previously reported that SHIP-1, a negative regulator of the PI3K pathway, is essential in maintaining lung immunohomeostasis, potentially through regulation of innate immune cells. However, the function of SHIP-1 in adaptive immune response in the lung has not been defined. We sought to determine the role of SHIP-1 in adaptive immunity in response to aeroallergen stimulation in the airway.

Methodology/Principal Findings

SHIP-1 knockout (SHIP-1^−/−) mice on BALB/c background were immunized with ovalbumin (OVA) plus aluminum hydroxide, a strong Th2-inducing immunization, and challenged with OVA. Airway and lung inflammation, immunoglobulin response, Th2 cytokine production and lymphocyte response were analyzed and compared with wild type mice. Even though there was mild spontaneous inflammation in the lung at baseline, SHIP-1^−/− mice showed altered responses, including less cell infiltration around the airways but more in the parenchyma, less mucus production, decreased Th2 cytokine production, and diminished serum OVA-specific IgE, IgG1, but not IgG2a. Naïve and OVA sensitized SHIP-1^−/− T cells produced a lower amount of IL-4. In vitro differentiated SHIP-1^−/− Th2 cells produced less IL-4 compared to wild type Th2 cells upon T cell receptor stimulation.

Conclusions/Significance

These findings indicate that, in contrast to its role as a negative regulator in the innate immune cells, SHIP-1 acts as a positive regulator in Th2 cells in the adaptive immune response to aeroallergen. Thus any potential manipulation of SHIP-1 activity should be adjusted according to the specific immune response.

Role of SHIP in cancer

The SH2-containing inositol-5'-phosphatase, SHIP (or SHIP1), is a hematopoietic-restricted phosphatidylinositide phosphatase that translocates to the plasma membrane after extracellular stimulation and hydrolyzes the phosphatidylinositol-3-kinase-generated second messenger PI-3,4,5-P(3) to PI-3,4-P(2). As a result, SHIP dampens down PI-3,4,5-P(3)-mediated signaling and represses the proliferation, differentiation, survival, activation, and migration of hematopoietic cells. There are multiple lines of evidence suggesting that SHIP may act as a tumor suppressor during leukemogenesis and lymphomagenesis. Because of its ability to skew macrophage progenitors toward M1 macrophages and naïve T cells toward T helper 1 and T helper 17 cells, SHIP may play a critical role in activating the immune system to eradicate solid tumors. In this review, we will discuss the role of SHIP in hematopoietic cells and its therapeutic potential in terms of suppressing leukemias and lymphomas and manipulating the immune system to combat cancer.

The role of oxidative stress in the pathogenesis of asthma

Oxidative stress plays a critical role in the pathogenesis of asthma. To effectively control oxidative stress in asthmatics, it is important to investigate the precise intracellular mechanism by which the development of immunity, rather than immune tolerance and progression of airway inflammation, is induced. In this article, we suggest that protein tyrosine phosphatases, as intracellular negative regulators, and intracellular antioxidant enzymes such as peroxiredoxins can be regulated by oxidative stress during intracellular signaling.

In vivo regulation of the allergic response by the IL-4 receptor alpha chain immunoreceptor tyrosine-based inhibitory motif

BACKGROUND

Signaling by IL-4 and IL-13 through the IL-4 receptor alpha chain (IL-4Ralpha) plays a critical role in the pathology of allergic diseases. The IL-4Ralpha is endowed with an immunoreceptor tyrosine-based inhibitory motif (ITIM) centered on tyrosine 709 (Y709) in the cytoplasmic domain that binds a number of regulatory phosphatases. The function of the ITIM in the in vivo regulation of IL-4 receptor signaling remains unknown.

OBJECTIVE

We sought to determine the in vivo function of the IL-4Ralpha ITIM by using mice in which the ITIM was inactivated by mutagenesis of the tyrosine Y709 residue into phenylalanine (F709).

METHODS

F709 ITIM mutant mice were derived by means of knock-in mutagenesis. Activation of intracellular signaling cascades by IL-4 and IL-13 was assessed by means of intracellular staining of phosphorylated signaling intermediates and gene expression analysis. In vivo responses to allergic sensitization were assessed by using models of allergic airway inflammation.

RESULTS

The F709 mutation increased signal transducer and activator of transcription 6 phosphorylation by IL-4 and, disproportionately, by IL-13. This was associated with exaggerated T(H)2 polarization, enhanced alternative macrophage activation by IL-13, augmented basal and antigen-induced IgE responses, and intensified allergen-induced eosinophilic airway inflammation and hyperreactivity.

CONCLUSIONS

These results point to a physiologic negative regulatory role for the Y709 ITIM in signaling through IL-4Ralpha, especially by IL-13.

SHIP is required for dendritic cell maturation

Although several groups have investigated the role of SHIP in macrophage (M) development and function, SHIP's contribution to the generation, maturation, and innate immune activation of dendritic cells (DCs) is poorly understood. We show herein that SHIP negatively regulates the generation of DCs from bone marrow precursors in vitro and in vivo, as illustrated by the enhanced expansion of DCs from SHIP(-/-) GM-CSF cultures, as well as increased numbers of DCs in the spleens of SHIP-deficient mice. Interestingly, however, these SHIP(-/-) DCs display a relatively immature phenotype and secrete substantially lower levels of IL-12 after TLR ligand stimulation than wild type DCs. This, in turn, leads to a dramatically reduced stimulation of Ag-specific T cell proliferation and Th1 cell responses in vitro and in vivo. This immature phenotype of SHIP(-/-) DCs could be reversed with the PI3K inhibitors LY294002 and wortmannin, suggesting that SHIP promotes DC maturation by reducing the levels of the PI3K second messenger phosphatidylinositol-3,4,5-trisphosphate. These results are consistent with SHIP being a negative regulator of GM-CSF-derived DC generation but a positive regulator of GM-CSF-derived DC maturation and function.

SHP-1 deficient mast cells are hyperresponsive to stimulation and critical in initiating allergic inflammation in the lung

Phosphatase Src homology region 2 domain-containing phosphatase 1 (SHP-1)-deficient mice display an allergic asthma phenotype that is largely IL-13 and STAT6 dependent. The cell types responsible for the Th2 phenotype have not been identified. We hypothesized that SHP-1 deficiency leads to mast cell dysregulation and increased production and release of mediators and Th2 cytokines, leading to the allergic asthma phenotype. We examined SHP-1 regulation of mast cell differentiation, survival, and functional responses to stimulation using bone marrow-derived mast cells from viable motheaten (mev) mice. We assessed pulmonary phenotypical changes in mev mice on the mast cell-deficient Kit(W-Sh) genetic background. The results showed that SHP-1 deficiency led to increased differentiation and survival, but reduced proliferation, of mast cells. SHP-1-deficient mast cells produced and released increased amounts of mediators and Th2 cytokines IL-4 and -13 spontaneously and in response to H(2)O(2), LPS, and Fc epsilonI cross-linking, involving c-Kit-dependent and -independent processes. The Fc epsilonRI signaling led to binding of SHP-1 to linker for activation of T cells 2 and enhanced linker for activation of T cells 2 phosphorylation in mev bone marrow-derived mast cells. Furthermore, the number of mast cells in the lung tissue of mev mice was increased and mast cell production and release of Th2 cytokines were distinctly increased upon Fc epsilonRI stimulation. When backcrossed to the Kit(W-Sh) background, mev mice had markedly reduced pulmonary inflammation and Th2 cytokine production. These findings demonstrate that SHP-1 is a critical regulator of mast cell development and function and that SHP-1-deficient mast cells are able to produce increased Th2 cytokines and initiate allergic inflammatory responses in the lung.

Maladaptation of critical cellular functions in asthma: bioinformatic analysis

Small maladaptations in cellular response to environmental stressors may underlie diseases like asthma. However, genomewide transcriptional profile comparisons between case and controls only highlight the quantitatively largest changes. Critical cellular homeostatic pathways may be upregulated modestly during normal adaptation to stress but insufficiently during disease. To discover such pathways in asthma, we utilized public information on differential response of primary bronchial epithelial cells from asthmatic or normal subjects to stressors like ozone and viral infections. Genes that were upregulated by stressor conditions in normal cells but were relatively downregulated in cells from asthmatic subjects were selected for further analysis. Either a stringent selection based on quantitative criterion or a nonstringent selection followed by network-based analysis was used. At the individual gene level, decay accelerating factor-1 (DAF-1, CD55) was identified and selected for validation. In a mouse model of allergic airway inflammation (AAI) resembling asthma, protein expression of CD55 was reduced compared with normal mice and returned to normal upon resolution of the allergic response. This was consistent with our finding of relative downregulation of CD55 in asthmatic compared with normal subjects. Interestingly, at a network level, the results pointed to possible abnormalities in the inositol signaling pathway, a critical cell signaling mechanism. In the mouse model of AAI, we found downregulation of inositol polyphosphate 4 phosphatase A (INPP4A), a critical member of the inositol signaling pathway. This and previous genetic evidence supports a role for inositol signaling abnormalities in asthma. In summary, logic-gated hypothesis-free exploration of published data sets may be valuable in discovery of novel disease-associated pathways.

The inhibitory Fc gamma IIb receptor dampens TLR4-mediated immune responses and is selectively up-regulated on dendritic cells from rheumatoid arthritis patients with quiescent disease

Rheumatoid arthritis (RA) is a common autoimmune disease leading to profound disability and premature death. Although a role for FcgammaRs and TLRs is accepted, their precise involvement remains to be elucidated. FcgammaRIIb is an inhibitory FcR important in the maintenance of tolerance. We hypothesized that the inhibitory FcgammaRIIb inhibits TLR responses on monocyte-derived dendritic cells (DC) and serves as a counterregulatory mechanism to dampen inflammation, and we surmised that this mechanism might be defective in RA. The expression of the inhibitory FcgammaRIIb was found to be significantly higher on DCs from RA patients having low RA disease activity in the absence of treatment with antirheumatic drugs. The expression of activating FcgammaRs was similarly distributed among all RA patients and healthy controls. Intriguingly, only DCs with a high expression of FcgammaRIIb were able to inhibit TLR4-mediated secretion of proinflammatory cytokines when stimulated with immune complexes. In addition, when these DCs were coincubated with the combination of a TLR4 agonist and immune complexes, a markedly inhibited T cell proliferation was apparent, regulatory T cell development was promoted, and T cells were primed to produce high levels of IL-13 compared with stimulation of the DCs with the TLR4 agonist alone. Blocking FcgammaRIIb with specific Abs fully abrogated these effects demonstrating the full dependence on the inhibitory FcgammaRIIb in the induction of these phenomena. This TLR4-FcgammaRIIb interaction was shown to dependent on the PI3K and Akt pathway.

SHIP1 is a repressor of mast cell hyperplasia, cytokine production, and allergic inflammation in vivo

SHIP1 inhibits immune receptor signaling through hydrolysis of the PI3K product phosphatidylinositol 3,4,5-trisphosphate, forming phosphatidylinositol 3,4-bisphosphate. In mast cells, SHIP1 represses FcepsilonRI- and cytokine-mediated activation in vitro, but little is known regarding the function of SHIP1 in mast cells in vivo or the susceptibility of Ship1(-/-) mice to mast cell-associated diseases. In this study, we found that Ship1(-/-) mice have systemic mast cell hyperplasia, increased serum levels of IL-6, TNF, and IL-5, and heightened anaphylactic response. Further, by reconstituting mast cell-deficient mice with Ship1(+/+) or Ship1(-/-) mast cells, we found that the above defects were due to loss of SHIP1 in mast cells. Additionally, we found that mice reconstituted with Ship1(-/-) mast cells suffered worse allergic asthma pathology than those reconstituted with Ship1(+/+) mast cells. In summary, our data show that SHIP1 represses allergic inflammation and mast cell hyperplasia in vivo and exerts these effects specifically in mast cells.

The role of the inositol polyphosphate 5-phosphatases in cellular function and human disease

Phosphoinositides are membrane-bound signalling molecules that regulate cell proliferation and survival, cytoskeletal reorganization and vesicular trafficking by recruiting effector proteins to cellular membranes. Growth factor or insulin stimulation induces a canonical cascade resulting in the transient phosphorylation of PtdIns(4,5)P(2) by PI3K (phosphoinositide 3-kinase) to form PtdIns(3,4,5)P(3), which is rapidly dephosphorylated either by PTEN (phosphatase and tensin homologue deleted on chromosome 10) back to PtdIns(4,5)P(2), or by the 5-ptases (inositol polyphosphate 5-phosphatases), generating PtdIns(3,4)P(2). The 5-ptases also hydrolyse PtdIns(4,5)P(2), forming PtdIns4P. Ten mammalian 5-ptases have been identified, which share a catalytic mechanism similar to that of the apurinic/apyrimidinic endonucleases. Gene-targeted deletion of 5-ptases in mice has revealed that these enzymes regulate haemopoietic cell proliferation, synaptic vesicle recycling, insulin signalling, endocytosis, vesicular trafficking and actin polymerization. Several studies have revealed that the molecular basis of Lowe's syndrome is due to mutations in the 5-ptase OCRL (oculocerebrorenal syndrome of Lowe). Futhermore, the 5-ptases SHIP [SH2 (Src homology 2)-domain-containing inositol phosphatase] 2, SKIP (skeletal muscle- and kidney-enriched inositol phosphatase) and 72-5ptase (72 kDa 5-ptase)/Type IV/Inpp5e (inositol polyphosphate 5-phosphatase E) are implicated in negatively regulating insulin signalling and glucose homoeostasis in specific tissues. SHIP2 polymorphisms are associated with a predisposition to insulin resistance. Gene profiling studies have identified changes in the expression of various 5-ptases in specific cancers. In addition, 5-ptases such as SHIP1, SHIP2 and 72-5ptase/Type IV/Inpp5e regulate macrophage phagocytosis, and SHIP1 also controls haemopoietic cell proliferation. Therefore the 5-ptases are a significant family of signal-modulating enzymes that govern a plethora of cellular functions by regulating the levels of specific phosphoinositides. Emerging studies have implicated their loss or gain of function in human disease.

New insights into mechanisms of immunoregulation in 2007

Substantial progress in understanding the mechanisms of immune regulation in allergic diseases and asthma has been made during the last year. In asthma, rhinitis, and atopic dermatitis the immune system is activated by allergens, autoantigens, and components of superimposed infectious agents. Immune regulation in the lymphatic organs and in the tissue has an important role in the control and suppression of allergic disease in all stages of the inflammatory process, such as cell migration to tissues, cells gaining an inflammatory and tissue-destructive phenotype in the tissues, and their interaction with resident tissue cells to augment the inflammation. After the discovery of regulatory T cells, the importance of their unique suppressive capacity was strongly emphasized for the suppression of effector T-cell responses. However, it seems that all 3 subsets of effector T(H)1, T(H)2, and T(H)17 cells, as well as regulatory T cells, regulate each other at the level of transcription, major cytokines, and surface molecules. This review highlights key advances in immune regulation that were published in the Journal of Allergy and Clinical Immunology.

Endotyping asthma: new insights into key pathogenic mechanisms in a complex, heterogeneous disease

Clinical asthma is very widely assumed to be the net result of excessive inflammation driven by aberrant T-helper-2 (Th2) immunity that leads to inflamed, remodelled airways and then functional derangement that, in turn, causes symptoms. This notion of disease is actually poorly supported by data, and there are substantial discrepancies and very poor correlation between inflammation, damage, functional impairment, and degree of symptoms. Furthermore, this problem is compounded by the poor understanding of the heterogeneity of clinical disease. Failure to recognise and discover the underlying mechanisms of these major variants or endotypes of asthma is, arguably, the major intellectual limitation to progress at present. Fortunately, both clinical research and animal models are very well suited to dissecting the cellular and molecular basis of disease endotypes. This approach is already suggesting entirely novel pathways to disease-eg, alternative macrophage specification, steroid refractory innate immunity, the interleukin-17-regulatory T-cell axis, epidermal growth factor receptor co-amplification, and Th2-mimicking but non-T-cell, interleukins 18 and 33 dependent processes that can offer unexpected therapeutic opportunities for specific patient endotypes.

The multiple roles of phosphoinositide 3-kinase in mast cell biology

Mast cells play a central role in the initiation of inflammatory responses associated with asthma and other allergic disorders. Receptor-mediated mast cell growth, differentiation, homing to their target tissues, survival and activation are all controlled, to varying degrees, by phosphoinositide-3-kinase (PI3K)-driven pathways. It is not fully understood how such diverse responses can be differentially regulated by PI3K. However, recent studies have provided greater insight into the mechanisms that control, and those that are controlled by, different PI3K subunit isoforms in mast cells. In this review, we discuss how PI3K influences the mast cell processes described above. Furthermore, we describe how different mast cell receptors use alternative isoforms of PI3K for these functions and discuss potential downstream targets of these isoforms.

The inositol phosphatase SHIP controls Salmonella enterica serovar Typhimurium infection in vivo

The SH2 domain-containing inositol 5'-phosphatase, SHIP, negatively regulates various hematopoietic cell functions and is critical for maintaining immune homeostasis. However, whether SHIP plays a role in controlling bacterial infections in vivo remains unknown. Salmonella enterica causes human salmonellosis, a disease that ranges in severity from mild gastroenteritis to severe systemic illness, resulting in significant morbidity and mortality worldwide. The susceptibility of ship(+/+) and ship(-/-) mice and bone marrow-derived macrophages to S. enterica serovar Typhimurium infection was compared. ship(-/-) mice displayed an increased susceptibility to both oral and intraperitoneal serovar Typhimurium infection and had significantly higher bacterial loads in intestinal and systemic sites than ship(+/+) mice, indicating a role for SHIP in the gut-associated and systemic pathogenesis of serovar Typhimurium in vivo. Cytokine analysis of serum from orally infected mice showed that ship(-/-) mice produce lower levels of Th1 cytokines than do ship(+/+) animals at 2 days postinfection, and in vitro analysis of supernatants taken from infected bone marrow-derived macrophages derived to mimic the in vivo ship(-/-) alternatively activated (M2) macrophage phenotype correlated with these data. M2 macrophages were the predominant population in vivo in both oral and intraperitoneal infections, since tissue macrophages within the small intestine and peritoneal macrophages from ship(-/-) mice showed elevated levels of the M2 macrophage markers Ym1 and Arginase 1 compared to ship(+/+) cells. Based on these data, we propose that M2 macrophage skewing in ship(-/-) mice contributes to ineffective clearance of Salmonella in vivo.