Mast cell chymase protects against acute ischemic kidney injury by limiting neutrophil hyperactivation and recruitment.

Here we investigated the role of murine mast cell protease 4 (MCPT4), the functional counterpart of human mast cell chymase, in an experimental model of renal ischemia reperfusion injury, a major cause of acute kidney injury. MCPT4-deficient mice had worsened kidney function compared to wildtype mice. MCPT4 absence exacerbated pathologic neutrophil infiltration in the kidney and increased kidney myeloperoxidase expression, cell death and necrosis. In kidneys with ischemia reperfusion injury, when compared to wildtype mice, MCPT4-deficient mice showed increased surface expression of adhesion molecules necessary for leukocyte extravasation including neutrophil CD162 and endothelial cell CD54. In vitro, human chymase mediated the cleavage of neutrophil expressed CD162 and also CD54, P- and E-Selectin expressed on human glomerular endothelial cells. MCPT4 also dampened systemic neutrophil activation after renal ischemia reperfusion injury as neutrophils expressed more CD11b integrin and produced more reactive oxygen species in MCPT4-deficient mice. Accordingly, after renal injury, neutrophil migration to an inflammatory site distal from the kidney was increased in MCPT4-deficient versus wildtype mice. Thus, contrary to the described overall aggravating role of mast cells, one granule-released mediator, the MCPT4 chymase, exhibits a potent anti-inflammatory function in renal ischemia reperfusion injury by controlling neutrophil extravasation and activation thereby limiting associated damage.

Mutation in IL36RN impairs the processing and regulatory function of the interleukin-36-receptor antagonist and is associated with DITRA syndrome.

The identification of loss-of-function mutations of the IL36RN gene encoding the interleukin-36 receptor antagonist (IL-36Ra) in generalized pustular psoriasis (GPP) emphasized the key role of this pathway in skin innate immunity and systemic inflammation. It has been previously shown in vitro that removal of the N-terminal amino acid IL36Ra (M1) is critical to its biological activity, but the in vivo contribution of this processing remains unknown. We report herein a new homozygous (c4G>T, pV2F) missense IL36RN mutation segregating in a family with three GPP-affected patients. The V2F mutation does not alter IL-36Ra protein expression but was devoid of any antagonist activity. Mass spectrometry showed that the V2F IL-36Ra mutant retains its first N-terminal methionine. These results provide the first in vivo demonstration that removal of N-terminal methionine of native IL-36Ra is a mandatory step to reach optimal antagonist activity and to prevent sustained skin and systemic inflammation in humans.

Mast Cells and MCPT4 Chymase Promote Renal Impairment after Partial Ureteral Obstruction.

Obstructive nephropathy constitutes a major cause of pediatric renal progressive disease. The mechanisms leading to disease progression are still poorly understood. Kidney fibrotic lesions are reproduced using a model of partial unilateral ureteral obstruction (pUUO) in newborn mice. Based on data showing significant mast cell (MC) infiltration in patients, we investigated the role of MC and murine MCPT4, a MC-released chymase, in pUUO using MC- (Wsh/sh), MCPT4-deficient (Mcpt4-/-), and wild-type (WT) mice. Measurement of kidney length and volume by magnetic resonance imaging (MRI) as well as postmortem kidney weight revealed hypotrophy of operated right kidneys (RKs) and compensatory hypertrophy of left kidneys. Differences between kidneys were major for WT, minimal for Wsh/sh, and intermediate for Mcpt4-/- mice. Fibrosis development was focal and increased only in WT-obstructed kidneys. No differences were noticed for local inflammatory responses, but serum CCL2 was significantly higher in WT versus Mcpt4-/- and Wsh/sh mice. Alpha-smooth muscle actin (αSMA) expression, a marker of epithelial-mesenchymal transition (EMT), was high in WT, minimal for Wsh/sh, and intermediate for Mcpt4-/- RK. Supernatants of activated MC induced αSMA in co-culture experiments with proximal tubular epithelial cells. Our results support a role of MC in EMT and parenchyma lesions after pUUO involving, at least partly, MCPT4 chymase. They confirm the importance of morphologic impairment evaluation by MRI in pUUO.

The function of mast cells in autoimmune glomerulonephritis.

Immune-mediated glomerulonephritis is caused by deposition of immune complexes on the glomerular basement membrane or of autoantibodies directed against the glomerular basement membrane. Depositions lead to an inflammatory response that can ultimately destroy renal function and lead to chronic kidney disease. However, the pathological processes leading to the development of renal injury and disease progression remain poorly understood. To investigate the mechanisms of disease development in glomerulonephritis various animal models have been developed, which include as the most popular one the induction of glomerulonephritis by the injection of heterologous antibodies directed to the glomerular basement membrane. The role of mast cells and mast cell-derived mediators has been evaluated in these models. In this chapter we describe the methods that allow to set up and study the disease parameters of immune-mediated glomerulonephritis development.

Mast cell chymase protects against renal fibrosis in murine unilateral ureteral obstruction.

Mast cell release of chymase is important in tissue remodeling and may participate in inflammation leading to fibrosis and organ failure. Here we analyzed the function of chymase in unilateral ureteral obstruction, an established accelerated model of renal tubulointerstitial fibrosis. Mice deficient in mouse mast cell protease 4 (mMCP4), the functional counterpart of human chymase, had increased obstruction-induced fibrosis when compared to wild-type mice indicating a protective effect of mMCP4. Engraftment of mast cell-deficient Kit(Wsh/Wsh) mice with wild type, but not mMCP4-deficient mast cells, restored protection confirming the role of mMCP4. Kidneys of mMCP4-deficient mice had higher levels of renal tubular damage, interstitial fibrosis, collagen deposition, increased α-smooth muscle actin, and decreased E-cadherin expression compared to the kidneys of wild-type mice. Further analysis showed an elevated inflammatory response in mMCP4-deficient mice with increased levels of kidney-infiltrating macrophages and T cells and local profibrotic TGF-ß1 and CCL2. Granulated and degranulated mast cells and mMCP4 were mainly found in the kidney capsule, respectively, before and after ureteral obstruction. Analysis of mMCP4 substrates showed that it mediates its anti-fibrotic actions by degrading interstitial deposits of fibronectin, a known promoter of inflammatory cell infiltration and adhesion. Thus, mast cell released mMCP4 has anti-fibrotic potential in acutely induced obstructive nephropathy.

Mast cells as cellular sensors in inflammation and immunity.

Mast cells are localized in tissues. Intense research on these cells over the years has demonstrated their role as effector cells in the maintenance of tissue integrity following injury produced by infectious agents, toxins, metabolic states, etc. After stimulation they release a sophisticated array of inflammatory mediators, cytokines, and growth factors to orchestrate an inflammatory response. These mediators can directly initiate tissue responses on resident cells, but they have also been shown to regulate other infiltrating immune cell functions. Research in recent years has revealed that the outcome of mast cell actions is not always detrimental for the host but can also limit disease development. In addition, mast cell functions highly depend on the physiological context in the organism. Depending on the genetic background, strength of the injurious event, the particular microenvironment, mast cells direct responses ranging from pro- to anti-inflammatory. It appears that they have evolved as cellular sensors to discern their environment in order to initiate an appropriate physiological response either aimed to favor inflammation for repair or at the contrary limit the inflammatory process to prevent further damage. Like every sophisticated machinery, its dysregulation leads to pathology. Given the broad distribution of mast cells in tissues this also explains their implication in many inflammatory diseases.

Mouse mast cell protease-4 deteriorates renal function by contributing to inflammation and fibrosis in immune complex-mediated glomerulonephritis.

Mast cells exert protective effects in experimental antiglomerular basement membrane-induced glomerulonephritis (GN), yet the responsible mediators have not been identified. In this study, we investigated the role of mouse mast cell protease (mMCP)-4, the functional homolog of human chymase, using mMCP-4-deficient mice. Compared with wild type animals, mMCP-4-deficient mice exhibited lower proteinuria, blood creatinine, and blood urea nitrogen levels, indicating an aggravating role of mMCP-4. Kidney histology confirmed less severe renal damage in mMCP-4-deficient mice with reduced deposits, glomerular and interstitial cellularity, and fibrosis scores. High amounts of mMCP-4 were detected in renal capsules, but not in the whole kidney, from wild type mice. Its expression in renal capsules was markedly decreased after GN induction, suggesting that locally released enzyme by degranulated mast cells could contribute to the functional and physiopathological hallmarks of GN. Supporting a proinflammatory role, glomerular and interstitial macrophage and T cell infiltration, levels of proinflammatory TNF and MCP-1 mRNA, and the expression of the profibrotic peptide angiotensin II together with type I collagen were markedly downregulated in kidneys of mMCP-4-deficient mice. We conclude that mMCP-4 chymase, contrary to the global anti-inflammatory action of mast cells, aggravates GN by promoting kidney inflammation. These results highlight the complexity of mast cell-mediated inflammatory actions and suggest that chymase inhibition may represent a novel therapeutic target in GN.

Histamine H(3) receptor-mediated signaling protects mice from cerebral malaria.

BACKGROUND: Histamine is a biogenic amine that has been shown to contribute to several pathological conditions, such as allergic conditions, experimental encephalomyelitis, and malaria. In humans, as well as in murine models of malaria, increased plasma levels of histamine are associated with severity of infection. We reported recently that histamine plays a critical role in the pathogenesis of experimental cerebral malaria (CM) in mice infected with Plasmodium berghei ANKA. Histamine exerts its biological effects through four different receptors designated H1R, H2R, H3R, and H4R. PRINCIPAL FINDINGS: In the present work, we explored the role of histamine signaling via the histamine H3 receptor (H3R) in the pathogenesis of murine CM. We observed that the lack of H3R expression (H3R(-/-) mice) accelerates the onset of CM and this was correlated with enhanced brain pathology and earlier and more pronounced loss of blood brain barrier integrity than in wild type mice. Additionally tele-methylhistamine, the major histamine metabolite in the brain, that was initially present at a higher level in the brain of H3R(-/-) mice was depleted more quickly post-infection in H3R(-/-) mice as compared to wild-type counterparts. CONCLUSIONS: Our data suggest that histamine regulation through the H3R in the brain suppresses the development of CM. Thus modulating histamine signaling in the central nervous system, in combination with standard therapies, may represent a novel strategy to reduce the risk of progression to cerebral malaria.

[Role of histamine and histamine receptors in the pathogenesis of malaria]. / Rôle de l'histamine et des récepteurs histaminiques dans la pathogenèse du paludisme.

A hallmark of the host response to Plasmodium parasite is an inflammatory reaction characterized by elevated histaminemia levels. Since histamine, which acts through four different receptors and which synthesis is under the control of the histidine decarboxylase (HDC), is endowed with pro-inflammatory and immunosuppressive activities, we hypothesized that this vaso-active amine may participe to malaria pathogenesis. Combining genetic and pharmacologic approaches by using H1R(-/-), H2R(-/-), H3R(-/-), HDC(-/-) mice and H1R, H2R-, and H3R-antagonists, respectively, we found that cerebral malaria-associated pathogenetic processes such as blood brain barrier disruption, and T lymphocyte sequestration to cerebral vascular endothelium in mice were associated with histamine production. The identification of this novel inflammatory pathway and its implication in Plasmodium infection may lead to novel strategies to manipulate the anti-Plasmodium immune response and may provide new therapeutic tools to alleviate malaria disease.

Inhibition of histamine-mediated signaling confers significant protection against severe malaria in mouse models of disease.

From the inoculation of Plasmodium sporozoites via Anopheles mosquito bites to the development of blood-stage parasites, a hallmark of the host response is an inflammatory reaction characterized by elevated histamine levels in the serum and tissues. Given the proinflammatory and immunosuppressive activities associated with histamine, we postulated that this vasoactive amine participates in malaria pathogenesis. Combined genetic and pharmacologic approaches demonstrated that histamine binding to H1R and H2R but not H3R and H4R increases the susceptibility of mice to infection with Plasmodium. To further understand the role of histamine in malaria pathogenesis, we used histidine decarboxylase-deficient (HDC(-/-)) mice, which are free of histamine. HDC(-/-) mice were highly resistant to severe malaria whether infected by mosquito bites or via injection of infected erythrocytes. HDC(-/-) mice displayed resistance to two lethal strains: Plasmodium berghei (Pb) ANKA, which triggers cerebral malaria (CM), and Pb NK65, which causes death without neurological symptoms. The resistance of HDC(-/-) mice to CM was associated with preserved blood-brain barrier integrity, the absence of infected erythrocyte aggregation in the brain vessels, and a lack of sequestration of CD4 and CD8 T cells. We demonstrate that histamine-mediated signaling contributes to malaria pathogenesis. Understanding the basis for these biological effects of histamine during infection may lead to novel therapeutic strategies to alleviate the severity of malaria.

Mast cell-dependent down-regulation of antigen-specific immune responses by mosquito bites.

While probing host skin to search for blood vessels, the female Anopheles mosquito delivers Plasmodium parasites in the presence of saliva. Saliva from various blood-feeding vectors which contains several pharmacologically active components is believed to facilitate blood feeding as well as parasite transmission to the host. Recently, we found that mosquito saliva has the capacity to activate dermal mast cells and to induce local inflammatory cell influx. Our main objective in the present work is to investigate whether saliva, through mosquito bites, controls the magnitude of Ag-specific immune responses and whether this control is dependent on the mast cell-mediated inflammatory response. Using a mast cell knockin mouse model, we found that mosquito bites consistently induced MIP-2 in the skin and IL-10 in draining lymph nodes, and down-regulate Ag-specific T cell responses by a mechanism dependent on mast cells and mediated by IL-10. Our results provide evidence for new mechanisms which may operate during Plasmodium parasite transmission by mosquito bites.