A role for fatty acid binding proteins in airway immune responses

The airway epithelium plays a critical role in the pathogenesis of asthma. It forms the primary defense against inhaled exogenous substances and is also a source of diverse inflammatory mediators such as cytokines, chemokines, cell adhesion molecules and other products that regulate airway physiology. Epithelial cells also aid in the clearance of tissue leukocytes, by serving as a gateway for transepithelial migration of leukocytes into the lung lumen. The central role of epithelium in controlling leukocyte recruitment and egress, led to the identification of molecules regulated in bronchial epithelium during inflammatory responses. One of the molecules highly regulated in airway epithelial cells by the Th2 cytokines IL-4 and IL-13 was the metabolism related lipid chaperone, fatty acid binding protein 5 (FABP5, also named mal1). mal1 plays a role in metabolic homeostasis, and lack of FABP5 moderately protects mice from atherosclerosis and insulin resistance. Of all of the FABPs, mal1 shows the most striking association with epithelial cell expression, although the functional relevance of this is unclear. With the use of immunised mal1-deficient mice, hybridomas that secreted specific mal1 antibodies were successfully generated. These antibodies were crucial in determining mal1 function during asthma pathogenesis. Using mal1-deficient mice in an allergic airway inflammation model, leukocyte clearance via egress to the lung lumen was almost completely dependent on mal1 function. In addition, leukocyte clearance was enhanced by treatment of wild-type mice with C16:1n7-palmitoleate, a mal1-regulated lipokine that affects metabolic homeostasis. mal1 affected the expression of one of the main epithelial cell adhesion molecules, E-Cadherin, which is necessary for tight junction formation and a main regulator of leukocyte transepithelial migration. Transepithelial migration of leukocytes in vitro was impeded by mal1 deficiency, in an E-Cadherin and PPAR-γ dependent manner. In addition to the immune functions of mal1 another FABP, aP2, was also found to regulate immune responses. aP2 mediated type 1 antibody and cytokine production which enhanced the protection of aP2-deficient mice against viral infection. However, the up-regulation of these responses exacerbated inflammation during K/BxN arthritis. These results provide a cellular and molecular role for mal1 in epithelial cell function, and suggest a new avenue to explore connections between metabolism and inflammatory disease

Semicarbazide-sensitive amine oxidase inhibition ameliorates albuminuria and glomerulosclerosis but does not improve tubulointerstitial fibrosis in diabetic nephropathy.

Semicarbazide-sensitive amine oxidase (SSAO) is an enzyme with a unique dual function in controlling inflammation as well as reactive oxygen species (ROS) generation. We have demonstrated benefit of SSAO inhibition in acute kidney fibrosis. However the function of SSAO in chronic kidney disease (CKD) and diabetic kidney disease (DKD) is yet to be determined. We aimed to assess the effectiveness of a SSAO inhibitor (SSAOi; PXS-4728A) as an antifibrotic agent using a diabetic model of CKD. Diabetic mice were treated with SSAOi for 24 weeks and outcomes compared with untreated diabetic mice and telmisartan treated animals as a standard of care comparator. Extracellular matrix markers, fibronectin and oxidative stress, were downregulated in diabetic mice treated with SSAOi compared with untreated diabetic mice. Expression of the pan-leukocyte marker CD45 was also supressed by SSAOi. SSAO inhibition in diabetic mice resulted in a significant reduction in glomerulosclerosis and associated albuminuria compared to untreated diabetic mice. However, the effect of SSAO inhibition was less obvious in the tubulointerstitial compartment than in the glomeruli. Therefore, SSAO may be a potential target for diabetic glomerulosclerosis

Chlamydia muridarum lung infection in infants alters hematopoietic cells to promote allergic airway disease in mice

Background Viral and bacterial respiratory tract infections in early-life are linked to the development of allergic airway inflammation and asthma. However, the mechanisms involved are not well understood. We have previously shown that neonatal and infant, but not adult, chlamydial lung infections in mice permanently alter inflammatory phenotype and physiology to increase the severity of allergic airway disease by increasing lung interleukin (IL)-13 expression, mucus hyper-secretion and airway hyper-responsiveness. This occurred through different mechanisms with infection at different ages. Neonatal infection suppressed inflammatory responses but enhanced systemic dendritic cell:T-cell IL-13 release and induced permanent alterations in lung structure (i.e., increased the size of alveoli). Infant infection enhanced inflammatory responses but had no effect on lung structure. Here we investigated the role of hematopoietic cells in these processes using bone marrow chimera studies. Methodology/Principal Findings Neonatal (<24-hours-old), infant (3-weeks-old) and adult (6-weeks-old) mice were infected with C. muridarum. Nine weeks after infection bone marrow was collected and transferred into recipient age-matched irradiated naïve mice. Allergic airway disease was induced (8 weeks after adoptive transfer) by sensitization and challenge with ovalbumin. Reconstitution of irradiated naïve mice with bone marrow from mice infected as neonates resulted in the suppression of the hallmark features of allergic airway disease including mucus hyper-secretion and airway hyper-responsiveness, which was associated with decreased IL-13 levels in the lung. In stark contrast, reconstitution with bone marrow from mice infected as infants increased the severity of allergic airway disease by increasing T helper type-2 cell cytokine release (IL-5 and IL-13), mucus hyper-secretion, airway hyper-responsiveness and IL-13 levels in the lung. Reconstitution with bone marrow from infected adult mice had no effects. Conclusions These results suggest that an infant chlamydial lung infection results in long lasting alterations in hematopoietic cells that increases the severity of allergic airway disease in later-life

Protection against Nippostrongylus brasiliensis infection in mice is independent of GM-CSF

Granulocyte macrophage-colony stimulating factor (GM-CSF) is a cytokine with the capacity to promote inflammation in a wide variety of infectious and inflammatory diseases. These conditions include allergic airway inflammation, which is driven by T-helper 2 (Th2) cells. Because of the importance of Th2 cells in parasite infections, we have investigated the role of GM-CSF in mice infected with the nematode Nippostrongylus brasiliensis. The effect of primary and secondary infection was investigated in mice lacking functional genes for GM-CSF (CSF2 genes) (DGM-CSF mice), and in mice lacking the cytokine receptor common b chain (Db mice), the latter being unable to signal in response to GM-CSF and interleukin (IL)-5. DGM-CSF mice showed no significant defect in parasite immunity, measured by larval numbers in the lungs, worm numbers in the intestine or egg numbers in the faeces, in either primary or secondary infection. By contrast, the Db mice showed increased parasite burden, with higher numbers of lung larvae after secondary infection and higher numbers of intestinal worms and faecal eggs after both primary and secondary infection. Unexpectedly, there were increased numbers of circulating eosinophils in the DGM-CSF mice, associated with significantly reduced larval numbers in the lungs. These results indicate that GM-CSF is redundant in protection against N.brasiliensis infection, and that the increased susceptibility of Db mice to infection is likely to be attributed to the lack of IL-5 signalling in these mice. The results suggest that clinical use of agents that neutralise GM-CSF may not be associated with increased risk of parasite infection.Doris S.C. Shim, Heidi C. Schilter, Michelle L. Knott, Ranni A. Almeida, Robert P. Short, Charles R. Mackay, Lindsay A. Dent and William A. Sewel

Regulation of inflammatory responses by gut microbiota and chemoattractant receptor GPR43

The immune system responds to pathogens by a variety of pattern recognition molecules such as the Toll-like receptors (TLRs), which promote recognition of dangerous foreign pathogens. However, recent evidence indicates that normal intestinal microbiota might also positively influence immune responses, and protect against the development of inflammatory diseases(1,2). One of these elements may be short-chain fatty acids (SCFAs), which are produced by fermentation of dietary fibre by intestinal microbiota. A feature of human ulcerative colitis and other colitic diseases is a change in 'healthy' microbiota such as Bifidobacterium and Bacteriodes(3), and a concurrent reduction in SCFAs4. Moreover, increased intake of fermentable dietary fibre, or SCFAs, seems to be clinically beneficial in the treatment of colitis(5-9). SCFAs bind the G-protein-coupled receptor 43 (GPR43, also known as FFAR2)(10,11), and here we show that SCFA-GPR43 interactions profoundly affect inflammatory responses. Stimulation of GPR43 by SCFAs was necessary for the normal resolution of certain inflammatory responses, because GPR43-deficient (Gpr43(-/-)) mice showed exacerbated or unresolving inflammation in models of colitis, arthritis and asthma. This seemed to relate to increased production of inflammatory mediators by Gpr43(-/-) immune cells, and increased immune cell recruitment. Germ-free mice, which are devoid of bacteria and express little or no SCFAs, showed a similar dysregulation of certain inflammatory responses. GPR43 binding of SCFAs potentially provides a molecular link between diet, gastrointestinal bacterial metabolism, and immune and inflammatory responses

Characterization of AAD in bone marrow chimeras.

<p>Bone marrow from adult naïve BALB/c mice was adoptively transferred into age-matched irradiated, naïve mice. Eight weeks later, after bone marrow reconstitution, chimeras were subjected to Ova-induced AAD and the development of AAD was assessed. (<b>A</b>) Transpulmonary resistance, (<b>B</b>) dynamic compliance, (<b>C</b>) mucus secreting cell (MSCs) within 100 µM of basement membrane (BM) in the airways, and Ova-specific (<b>D</b>) IL-5 and (<b>E</b>) IL-13 release from re-stimulated MLN cell culture supernatants. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042588#s3" target="_blank">Results</a> are represented as mean ± SEM. n = 6–8, from two independent experiments of 3–4 mice. *P&lt;0.05 compared to non-allergic (Chimera + Sham) control. ND = not detected.</p

<i>C. muridarum</i> lung infection in infants, but not neonates, alters hematopoietic cells to increase AHR during AAD.

<p>BALB/c mice were infected with <i>C. muridarum</i> or sham inoculated (vehicle) as neonates, infants or adults. Nine weeks after infection bone marrow was extracted and adoptively transferred into age-matched, irradiated naïve mice. Eight weeks after bone marrow reconstitution, chimeras were subjected to Ova-induced AAD and the development of AAD was assessed. Transpulmonary resistance at the maximal dose of methacholine administered (10 mg/mL) in (<b>A</b>) neonate, (<b>B</b>) infant and (<b>C</b>) adult bone marrow chimeras. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042588#s3" target="_blank">Results</a> are represented as mean ± SEM. n = 6–8, from two independent experiments of 3–4 mice. Age-matched controls were run in parallel with every experiment. *P&lt;0.05 compared to un-infected allergic (Vehicle Chimera + Ova) controls.</p

<i>C. muridarum</i> lung infection in infants, but not neonates, alters hematopoietic cells to increase IL-13 in the lung during AAD.

<p>BALB/c mice were infected with <i>C. muridarum</i> or sham inoculated (vehicle) as neonates, infants or adults. Nine weeks after infection bone marrow was extracted and adoptively transferred into age-matched, irradiated naïve mice. Eight weeks after bone marrow reconstitution, chimeras were subjected to Ova-induced AAD and the development of AAD was assessed. IL-13 protein in lung homgenates (<b>A</b>) neonate, (<b>B</b>) infant and (<b>C</b>) adult bone marrow chimeras. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042588#s3" target="_blank">Results</a> are represented as mean ± SEM. n = 6–8, from two independent experiments of 3–4 mice. Age-matched controls were run in parallel with every experiment. *P&lt;0.05 compared to un-infected allergic (Vehicle Chimera + Ova) controls.</p

<i>C. muridarum</i> lung infection in infants, but not neonates, alters hematopoietic cells to increase Th2 cytokine release from MLN cells.

<p>BALB/c mice were infected with <i>C. muridarum</i> or sham inoculated (Vehicle) as neonates, infants or adults. Nine weeks after infection bone marrow was extracted and adoptively transferred into age-matched irradiated, naïve mice. Eight weeks after bone marrow reconstitution, chimeras were subjected to Ova-induced AAD and the development of AAD was assessed. Ova-induced (<b>A–C</b>) IL-5 and (<b>D–F</b>) IL-13 release in MLN cell cultures from neonate, infant and adult bone marrow chimeras. <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0042588#s3" target="_blank">Results</a> are represented as mean ± SEM. n = 6–8, from two independent experiments of 3–4 mice. Age-matched controls were run in parallel with every experiment. *P&lt;0.05 compared to un-infected allergic (Vehicle Chimera + Ova) controls.</p