Rex Sun

Th2 Cytokine-Induced Alterations in Intestinal Smooth Muscle Function Depend on Alternatively Activated Macrophages

BACKGROUND & AIMS Enteric nematode infection induces a strong type 2 T helper cell (Th2) cytokine response characterized by increased infiltration of various immune cells, including macrophages. The role of these immune cells in host defense against nematode infection remains poorly defined. The present study investigated the role of macrophages and the arginase pathway in nematode-induced changes in intestinal smooth muscle function and worm expulsion. METHODS Mice were infected with Nippostrongylus brasiliensis and treated with clodronate-containing liposome to deplete macrophages or given S-(2-boronoethyl)-I-cysteine in drinking water to inhibit arginase activity. Segments of intestinal smooth muscle were suspended in organ baths to determine responses to acetylcholine, 5-hydroxytryptamine, or nerve stimulation. The phenotype of macrophages was monitored by measuring mRNA expression of the specific molecular markers by real-time polymerase chain reaction or viewed by immunofluorescence staining. RESULTS Infection increased the infiltration of macrophages and up-regulation alternatively activated macrophage markers by a mechanism dependent on interleukin-4 (IL-4) or interleukin-13 (IL-13) activation of signal transducer and activator of transcription 6. Elimination of alternatively activated macrophages blocked smooth muscle hypercontractility and the increased smooth muscle thickness, and impaired worm expulsion. In addition, specific inhibition of arginase activity interfered with smooth muscle contractility, but only partially affected the protective immunity of the host. CONCLUSIONS These data show that the phenotype of macrophages is determined by the local immune environment and that alternatively activated macrophages play a major role in the effects of Th2 cytokines, IL-4 and IL-13, on intestinal smooth muscle function.

Critical Role of IL-25 in Nematode Infection-Induced Alterations in Intestinal Function

IL-25 (IL-17E) is a member of the IL-17 cytokine family. IL-25–deficient mice exhibit impaired Th2 immunity against nematode infection, implicating IL-25 as a key component in mucosal immunity. The sources of IL-25 and mechanisms responsible for the induction of Th2 immunity by IL-25 in the gastrointestinal tract remain poorly understood. There is also little information on the regulation of IL-25 during inflammation or its role in gut function. In the current study, we investigated the regulation of IL-25 during Nippostrongylus brasiliensis infection and the contribution of IL-25 to the infection-induced alterations in intestinal function. We found that epithelial cells, but not immune cells, are the major source of IL-25 in the small intestine. N. brasiliensis infection-induced upregulation of IL-25 depends upon IL-13 activation of STAT6. IL-25−/− mice had diminished intestinal smooth muscle and epithelial responses to N. brasiliensis infection that were associated with an impaired Th2 protective immunity. Exogenous IL-25 induced characteristic changes similar to those after nematode infection but was unable to restore the impaired host immunity against N. brasiliensis infection in IL-13−/− mice. These data show that IL-25 plays a critical role in nematode infection-induced alterations in intestinal function that are important for host protective immunity, and IL-13 is the major downstream Th2 cytokine responsible for the IL-25 effects.

Macrophages as IL-25/IL-33-Responsive Cells Play an Important Role in the Induction of Type 2 Immunity

Type 2 immunity is essential for host protection against nematode infection but is detrimental in allergic inflammation or asthma. There is a major research focus on the effector molecules and specific cell types involved in the initiation of type 2 immunity. Recent work has implicated an important role of epithelial-derived cytokines, IL-25 and IL-33, acting on innate immune cells that are believed to be the initial sources of type 2 cytokines IL-4/IL-5/IL-13. The identities of the cell types that mediate the effects of IL-25/IL-33, however, remain to be fully elucidated. In the present study, we demonstrate that macrophages as IL-25/IL-33-responsive cells play an important role in inducing type 2 immunity using both in vitro and in vivo approaches. Macrophages produced type 2 cytokines IL-5 and IL-13 in response to the stimulation of IL-25/IL-33 in vitro, or were the IL-13-producing cells in mice administrated with exogenous IL-33 or infected with Heligmosomoides bakeri. In addition, IL-33 induced alternative activation of macrophages primarily through autocrine IL-13 activating the IL-4Rα-STAT6 pathway. Moreover, depletion of macrophages attenuated the IL-25/IL-33-induced type 2 immunity in mice, while adoptive transfer of IL-33-activated macrophages into mice with a chronic Heligmosomoides bakeri infection induced worm expulsion accompanied by a potent type 2 protective immune response. Thus, macrophages represent a unique population of the innate immune cells pivotal to type 2 immunity and a potential therapeutic target in controlling type 2 immunity-mediated inflammatory pathologies.

Parasitic Nematode-Induced Modulation of Body Weight and Associated Metabolic Dysfunction in Mouse Models of Obesity

ABSTRACT Obesity is associated with a chronic low-grade inflammation characterized by increased levels of proinflammatory cytokines that are implicated in disrupted metabolic homeostasis. Parasitic nematode infection induces a polarized Th2 cytokine response and has been explored to treat autoimmune diseases. We investigated the effects of nematode infection against obesity and the associated metabolic dysfunction. Infection of RIP2-Opa1KO mice or C57BL/6 mice fed a high-fat diet (HFD) with Nippostrongylus brasiliensis decreased weight gain and was associated with improved glucose metabolism. Infection of obese mice fed the HFD reduced body weight and adipose tissue mass, ameliorated hepatic steatosis associated with a decreased expression of key lipogenic enzymes/mediators, and improved glucose metabolism, accompanied by changes in the profile of metabolic hormones. The infection resulted in a phenotypic change in adipose tissue macrophages that was characterized by upregulation of alternative activation markers. Interleukin-13 (IL-13) activation of the STAT6 signaling pathway was required for the infection-induced attenuation of steatosis but not for improved glucose metabolism, whereas weight loss was attributed to both IL-13/STAT6-dependent and -independent mechanisms. Parasitic nematode infection has both preventive and therapeutic effects against the development of obesity and associated features of metabolic dysfunction in mice.

IL-13 Receptor α2 Regulates the Immune and Functional Response to Nippostrongylus brasiliensis Infection

IL-13 has a prominent role in host defense against the gastrointestinal nematode Nippostrongylus brasiliensis; however, the role of IL-13Rα2 in the immune and functional response to enteric infection is not known. In the current study, we investigated changes in smooth muscle and epithelial cell function as well as alterations in gene expression of IL-13 and IL-4 and their receptors using laser-capture microdissection of specific cell types in the small intestine of N. brasiliensis-infected mice. An infection-induced up-regulation of IL-13Rα2 gene expression was confined to smooth muscle and was dependent on STAT6 and IL-13, but not on IL-4. In contrast, expression of IL-13Rα1 was reduced, indicating that changes in IL-13α2 expression serve to limit the biological effects of IL-13. The increased availability of IL-13 in IL-13Rα2−/− mice resulted in marked changes in constitutive epithelial and smooth muscle function. In addition, maximal changes in smooth muscle hypercontractility and epithelial cell resistance peaked earlier after infection in IL-13Rα2−/− compared with wild-type mice. This did not coincide with an earlier Th2 immune response as expression of IL-4 and IL-13 was attenuated in IL-13Rα2−/− mice and worm expulsion was similar to that of wild-type mice. These data show that IL-13Rα2 plays an important role in nematode infection by limiting the availability of IL-13 during infection, thereby regulating both the immune and biological effects of IL-13.

Mechanisms of smooth muscle responses to inflammation

Background Inflammation‐induced changes in smooth muscle may be the consequence of changes in the properties of smooth muscle itself, in the control by nerves and hormones, in the microenvironment, or in the balance of constitutive or induced mediators. A general concept is that the specific characteristics and effects of inflammation can be linked to the nature of the infiltrate and the associated mediators, which are dictated predominantly by the immune environment. Inflammatory mediators may regulate smooth muscle function by directly acting on smooth muscle cells or, indirectly, through stimulation of the release of mediators from other cells. In addition, smooth muscle is not a passive bystander during inflammation and our knowledge of molecular signaling pathways that control smooth muscle function, and the contribution of the immune mechanisms to smooth muscle homeostasis, has expanded greatly in the last decade. Recent studies also demonstrated the relevance of extracellular proteases, of endogenous or exogenous origin, redox imbalance, or epigenetic mechanisms, to gastrointestinal dismotility and inflammation in the context of functional and organic disorders.

Sphingosine-1-Phosphate Regulates the Expression of Adherens Junction Protein E-Cadherin and Enhances Intestinal Epithelial Cell Barrier Function

BackgroundThe regulation of intestinal barrier permeability is important in the maintenance of normal intestinal physiology. Sphingosine-1-phosphate (S1P) has been shown to play a pivotal role in enhancing barrier function in several non-intestinal tissues. The current study determined whether S1P regulated function of the intestinal epithelial barrier by altering expression of E-cadherin, an important protein in adherens junctions.MethodsStudies were performed upon cultured differentiated IECs (IEC-Cdx2L1 line) using standard techniques.ResultsS1P treatment significantly increased levels of E-cadherin protein and mRNA in intestinal epithelial cells (IECs) and also led to E-cadherin localizing strongly to the cell–cell border. S1P also improved the barrier function as indicated by a decrease in 14C-mannitol paracellular permeability and an increase in transepithelial electrical resistance (TEER) in vitro.ConclusionsThese results indicate that S1P increases levels of E-cadherin, both in cellular amounts and at the cell–cell junctions, and leads to improved barrier integrity in cultured intestinal epithelial cells.

Role of enteric nerves in immune-mediated changes in protease-activated receptor 2 effects on gut function

Background  Protease‐activated receptors (PARs) are expressed on structural and immune cells. Control of initiation, duration, and magnitude of PAR effects is linked to the level of receptor expression, availability of proteases, and the intracellular signal transduction machinery. We investigated nematode infection‐induced changes in PAR2 expression and the impact on smooth muscle and epithelial responses to PAR2 agonists.

SerpinB2 Is Critical to Th2 Immunity against Enteric Nematode Infection

SerpinB2, a member of the serine protease inhibitor family, is expressed by macrophages and is significantly upregulated by inflammation. Recent studies implicated a role for SerpinB2 in the control of Th1 and Th2 immune responses, but the mechanisms of these effects are unknown. In this study, we used mice deficient in SerpinB2 (SerpinB2−/−) to investigate its role in the host response to the enteric nematode, Heligmosomoides bakeri. Nematode infection induced a STAT6-dependent increase in intestinal SerpinB2 expression. The H. bakeri–induced upregulation of IL-4 and IL-13 expression was attenuated in SerpinB2−/− mice coincident with an impaired worm clearance. In addition, lack of SerpinB2 in mice resulted in a loss of the H. bakeri–induced smooth muscle hypercontractility and a significant delay in infection-induced increase in mucosal permeability. Th2 immunity is generally linked to a CCL2-mediated increase in the infiltration of macrophages that develop into the alternatively activated phenotype (M2). In H. bakeri–infected SerpinB2−/− mice, there was an impaired infiltration and alternative activation of macrophages accompanied by a decrease in the intestinal CCL2 expression. Studies in macrophages isolated from SerpinB2−/− mice showed a reduced CCL2 expression, but normal M2 development, in response to stimulation of Th2 cytokines. These data demonstrate that the immune regulation of SerpinB2 expression plays a critical role in the development of Th2-mediated protective immunity against nematode infection by a mechanism involving CCL2 production and macrophage infiltration.

Role of Macrophages in the Altered Epithelial Function during a Type 2 Immune Response Induced by Enteric Nematode Infection

Parasitic enteric nematodes induce a type 2 immune response characterized by increased production of Th2 cytokines, IL-4 and IL-13, and recruitment of alternatively activated macrophages (M2) to the site of infection. Nematode infection is associated with changes in epithelial permeability and inhibition of sodium-linked glucose absorption, but the role of M2 in these effects is unknown. Clodronate-containing liposomes were administered prior to and during nematode infection to deplete macrophages and prevent the development of M2 in response to infection with Nippostrongylus brasiliensis. The inhibition of epithelial glucose absorption that is associated with nematode infection involved a macrophage-dependent reduction in SGLT1 activity, with no change in receptor expression, and a macrophage-independent down-regulation of GLUT2 expression. The reduced transport of glucose into the enterocyte is compensated partially by an up-regulation of the constitutive GLUT1 transporter consistent with stress-induced activation of HIF-1α. Thus, nematode infection results in a “lean” epithelial phenotype that features decreased SGLT1 activity, decreased expression of GLUT2 and an emergent dependence on GLUT1 for glucose uptake into the enterocyte. Macrophages do not play a role in enteric nematode infection-induced changes in epithelial barrier function. There is a greater contribution, however, of paracellular absorption of glucose to supply the energy demands of host resistance. These data provide further evidence of the ability of macrophages to alter glucose metabolism of neighboring cells.