Signaling events leading to the curative effect of cystatin on experimental visceral leishmaniasis: Involvement of ERK1/2, NF-κB and JAK/STAT pathways

Cystatin C Deficiency Increases LPS-Induced Sepsis and NLRP3 Inflammasome Activation in Mice

Cystatin C is a potent cysteine protease inhibitor that plays an important role in various biological processes including cancer, cardiovascular diseases and neurodegenerative diseases. However, the role of CstC in inflammation is still unclear. In this study we demonstrated that cystatin C-deficient mice were significantly more sensitive to the lethal LPS-induced sepsis. We further showed increased caspase-11 gene expression and enhanced processing of pro-inflammatory cytokines IL-1β and IL-18 in CstC KO bone marrow-derived macrophages (BMDM) upon LPS and ATP stimulation. Pre-treatment of BMDMs with the cysteine cathepsin inhibitor E-64d did not reverse the effect of CstC deficiency on IL-1β processing and secretion, suggesting that the increased cysteine cathepsin activity determined in CstC KO BMDMs is not essential for NLRP3 inflammasome activation. The CstC deficiency had no effect on (mitochondrial) reactive oxygen species (ROS) generation, the MAPK signaling pathway or the secretion of anti-inflammatory cytokine IL-10. However, CstC-deficient BMDMs showed dysfunctional autophagy, as autophagy induction via mTOR and AMPK signaling pathways was suppressed and accumulation of SQSTM1/p62 indicated a reduced autophagic flux. Collectively, our study demonstrates that the excessive inflammatory response to the LPS-induced sepsis in CstC KO mice is dependent on increased caspase-11 expression and impaired autophagy, but is not associated with increased cysteine cathepsin activity.

Can We Harness Immune Responses to Improve Drug Treatment in Leishmaniasis?

Leishmaniasis is a vector-borne parasitic disease that has been neglected in priority for control and eradication of malaria, tuberculosis, and HIV/AIDS. Collectively, over one seventh of the world’s population is at risk of being infected with 0.7–1.2 million new infections reported annually. Clinical manifestations range from self-healing cutaneous lesions to fatal visceral disease. The first anti-leishmanial drugs were introduced in the 1950′s and, despite several shortcomings, remain the mainstay for treatment. Regardless of this and the steady increase in infections over the years, particularly among populations of low economic status, research on leishmaniasis remains under funded. This review looks at the drugs currently in clinical use and how they interact with the host immune response. Employing chemoimmunotherapeutic approaches may be one viable alternative to improve the efficacy of novel/existing drugs and extend their lifespan in clinical use.

Cystatin C regulates major histocompatibility complex-II-peptide presentation and extracellular signal-regulated kinase-dependent polarizing cytokine production by bone marrow-derived dendritic cells

Cystatin C is a ubiquitously expressed cysteine protease inhibitor that protects cells from either improper hydrolysis by endogenous proteases or pathogen growth/virulence by exogenous proteases. Although commonly used as a serum biomarker for evaluating renal function, cystatin C is associated with many immunological disorders under various pathophysiological conditions. How cystatin C affects immune cells, especially dendritic cells (DCs), however, is far from clear. In this study, we found that pharmacological treatment with or genetic overexpression of cystatin C in bone marrow-derived DCs (BMDCs) reduced their capacity to stimulate CD4⁺ T-cell proliferation, despite increased antigen uptake. This reduced capacity corresponded with reduced major histocompatibility complex-II presentation owing to diminished levels of the chaperon H2-DM in BMDCs. Instead of promoting proliferation, cystatin C promoted skewing of T cells toward proinflammatory T-helper (Th)1/Th17 differentiation. This was mediated by augmented extracellular signal-regulated kinase 1/2 mitogen-activated protein kinase phosphorylation in BMDCs, leading to secretion of polarizing cytokines, which in turn led to the Th deviation. Collectively, our study explained the cellular and molecular basis of how this protease inhibitor can regulate immune responses, namely by affecting BMDCs and their cytokine pathway. Our results might open up an avenue for the development of therapeutic agents for the treatment of cystatin C-related immunological diseases.

Single nucleotide polymorphisms of the genes IL-2, IL-2RB, and JAK3 in patients with cutaneous leishmaniasis caused by Leishmania (V.) guyanensis in Manaus, Amazonas, Brazil

Leishmaniasis is a disease caused by intracellular protozoan parasites of the genus Leishmania. In endemic areas, only a portion of exposed subjects develops cutaneous leishmaniasis (CL), suggesting that the genetic inheritance of the host plays a vital role in both resistance and susceptibility to the disease. Interleukin-2 (IL-2) is a cytokine that plays a central role in the regulation of the immune response in infection through the axis IL-2/IL-2R (receptor) complex, triggering a series of intracellular events, among which the signaling of Janus kinase/signal transducers and activators of transcription (JAK-STAT). The present study aimed at verifying the possible relationship between single nucleotide polymorphism (s) (SNP s) in the genes IL-2, IL-2RB, and JAK3 in subjects with CL caused by Leishmania guyanensis in the city of Manaus, state of Amazonas, Brazil. 820 patients with CL and 850 healthy subjects (control group) coming from the same endemic areas as the patients were examined. The SNPs -2425G/A (rs4833248) and -330 T/G (rs2069762), located in the IL-2 gene promoter region, seem to influence the expression of the gene and the SNP +10558G/A (rs1003694) and +13295T/C (rs3212760) located in the 3rd intron of the IL-2RB gene and the 13th intron of the JAK3 gene, respectively, were studied by PCR-RFLP. Genotypes and alleles frequencies were obtained by direct counting. For the comparison between the two groups, the χ2 test with OR (odds ratio) and the 95% confidence interval (CI) were used. Similar genotypes and alleles frequencies for the different SNPs were observed in both patients with CL and healthy controls. Comparison of genotypic and allelic frequency between patients with CL and healthy subjects did not show any difference. These polymorphisms do not predict susceptibility to, or protection against the development of CL caused by L. guyanensis in the Amazonas.

Involvement of cystatin C in immunity and apoptosis

As an abundantly expressed cysteine protease inhibitor widely distributed in the organisms, cystatin C is involved in various physiological processes. Due to its relatively small molecular weight and easy detection, cystatin C is commonly used as a measure for glomerular filtration rate. In pathological conditions, however, growing evidences suggest that cystatin C is associated with various immune responses against either exogenous or endogenous antigens, which ultimately result in inflammatory autoimmune diseases or tumor development if not properly controlled. Thus the fluctuation of cystatin C levels might have more clinical implications than a reflection of kidney functions. Here, we summarize the latest development of studies on the pathophysiological functions of cystatin C, with focus on its immune regulatory roles at both cellular and molecular levels including antigen presentation, secretion of cytokines, synthesis of nitric oxide, as well as apoptosis. Finally, we discuss the clinical implications and therapeutic potentials of what this predominantly expressed protease inhibitor can bring to us.

Salivary Tick Cystatin OmC2 Targets Lysosomal Cathepsins S and C in Human Dendritic Cells

To ensure successful feeding tick saliva contains a number of inhibitory proteins that interfere with the host immune response and help to create a permissive environment for pathogen transmission. Among the potential targets of the salivary cystatins are two host cysteine proteases, cathepsin S, which is essential for antigen- and invariant chain-processing, and cathepsin C (dipeptidyl peptidase 1, DPP1), which plays a critical role in processing and activation of the granule serine proteases. Here, the effect of salivary cystatin OmC2 from Ornithodoros moubata was studied using differentiated MUTZ-3 cells as a model of immature dendritic cells of the host skin. Following internalization, cystatin OmC2 was initially found to inhibit the activity of several cysteine cathepsins, as indicated by the decreased rates of degradation of fluorogenic peptide substrates. To identify targets, affinity chromatography was used to isolate His-tagged cystatin OmC2 together with the bound proteins from MUTZ-3 cells. Cathepsins S and C were identified in these complexes by mass spectrometry and confirmed by immunoblotting. Furthermore, reduced increase in the surface expression of MHC II and CD86, which are associated with the maturation of dendritic cells, was observed. In contrast, human inhibitor cystatin C, which is normally expressed and secreted by dendritic cells, did not affect the expression of CD86. It is proposed that internalization of salivary cystatin OmC2 by the host dendritic cells targets cathepsins S and C, thereby affecting their maturation.

Cystatin C peptidomimetic derivative with antimicrobial properties as a potential compound against wound infections

A peptidomimetic called A20 (Cystapep 1) structurally based upon the N-terminal fragment of human cystatin C is known to have strong antibacterial properties. A20 is characterized by high activity against several bacterial strains often isolated from infected wounds, including methicillin-resistant S. aureus (MRSA). In this work we wanted to explore the therapeutic potential of A20 in the treatment of wound infections. We examined, cytotoxicity, allergenicity and impact of A20 on the proliferation and viability of human keratinocytes. Furthermore, the previously described antimicrobial action of A20has been confirmed here with reference strains of bacteria and extended by several other species. The A20 was highly active against Gram-positive bacteria with minimal inhibitory (MIC) and minimal bactericidal concentrations (MBC) between 8 and 128μg/mL. A20 did not affect proliferation of primary human keratinocytes in concentrations up to 50μg/mL. At the same time, it did not activate Peripheral Blood Mononuclear Cells (PBMCs), including basophils or neutrophils in vitro. Interestingly A20 was found to display immunomodulatory functions as it influences the production of Th2 cytokines (IL-4 and IL-13) by activated PBMCs. It was also resistant to degradation for at least 48h in human plasma. The results indicate that A20 is effective against the multiantibiotic-resistant bacteria and has a high safety profile, which makes it a promising antimicrobial drug candidate.

Activity of a novel sulfonamide compound 2-nitro-N-(pyridin-2-ylmethyl)benzenesulfonamide against Leishmania donovani

New treatments for visceral leishmaniasis, caused by Leishmania donovani, are needed to overcome sustained toxicity, cost, and drug resistance. The aim of this study was to evaluate the therapeutic effects of 2-nitro-N-(pyridin-2-ylmethyl)benzenesulfonamide (2NB) against promastigote and amastigote forms of L. donovani and examine its effect in combination with amphotericin B (AmB) against AmB-resistant clinical isolates. Effects were assessed against extracellular promastigotes in vitro and intracellular amastigotes in L. donovani-infected macrophages. Levels of inducible nitric oxide and Th1 and Th2 cytokines were measured in infected 2NB-treated macrophages, and levels of reactive oxygen species and NO were measured in 2NB-treated macrophages. 2NB was active against promastigotes and intracellular amastigotes with 50% inhibitory concentration values of 38.5±1.5 µg/mL and 86.4±2.4 µg/mL, respectively. 2NB was not toxic to macrophages. Parasite titer was reduced by >85% in infected versus uninfected macrophages at a 2NB concentration of 120 µg/mL. The parasiticidal activity was associated with increased levels of Th1 cytokines, NO, and reactive oxygen species. Finally, 2NB increased the efficacy of AmB against AmB-resistant L. donovani. These results demonstrate 2NB to be an antileishmanial agent, opening up a new avenue for the development of alternative chemotherapies against visceral leishmaniasis.

Leishmania molecules that mediate intracellular pathogenesis

Parasites of the Leishmania genus are the causative agents of a complex disease called leishmaniasis. Many activities of infected cells including their responses to a range of stimuli are modulated by Leishmania parasites. This review will profile some of the parasite molecules that target host cell processes for which there has been recent progress.

The curative effect of fucoidan on visceral leishmaniasis is mediated by activation of MAP kinases through specific protein kinase C isoforms

Fucoidan can cure both antimony-sensitive and antimony-resistant visceral leishmaniasis through immune activation. However, the signaling events underlying this cellular response remain uncharacterized. The present study reveals that fucoidan induces activation of p38 and ERK1/2 and NF-κB DNA binding in both normal and Leishmania donovani-infected macrophages, as revealed by western blotting and electrophoretic mobility shift assay (EMSA), respectively. Pharmacological inhibition of p38, ERK1/2 or the NF-κB pathway markedly attenuated fucoidan-induced pro-inflammatory cytokine synthesis and inducible nitric oxide synthase (iNOS) gene transcription, resulting in a reduction of parasite clearance. To decipher the underlying mechanism of fucoidan-mediated parasite suppression, the expression and functionality of various protein kinase C (PKC) isoforms were evaluated by immunoblotting and enzyme activity assay. Fucoidan elicited an increase in expression and activity of PKC-α, -βI and -βII isoforms in infected macrophages. Functional knockdown of PKC-α and -β resulted in downregulation of p38 and ERK1/2, along with a marked reduction of IL-12 and TNF-α production in fucoidan-treated infected macrophages. Collectively, these results suggest that the curative effect of fucoidan is mediated by PKC-dependent activation of the mitogen-activated protein kinase (MAPK)/NF-κB pathway, which ultimately results in the production of nitric oxide (NO) and disease-resolving pro-inflammatory cytokines.

Curative effect of 18β-glycyrrhetinic acid in experimental visceral leishmaniasis depends on phosphatase-dependent modulation of cellular MAP kinases

We earlier showed that 18β-glycyrrhetinic acid (GRA), a pentacyclic triterpenoid from licorice root, could completely cure visceral leishmaniasis in BALB/c mouse model. This was associated with induction of nitric oxide and proinflammatory cytokine production through the up regulation of NF-κB. In the present study we tried to decipher the underlying cellular mechanisms of the curative effect of GRA. Analysis of MAP kinase pathways revealed that GRA caused strong activation of p38 and to a lesser extent, ERK in bone marrow-derived macrophages (BMDM). Almost complete abrogation of GRA-induced cytokine production in presence of specific inhibitors of p38 and ERK1/2 confirmed the involvement of these MAP kinases in GRA-mediated responses. GRA induced mitogen- and stress-activated protein kinase (MSK1) activity in a time-dependent manner suggested that GRA-mediated NF-κB transactivation is mediated by p38, ERK and MSK1 pathway. As kinase/phosphatase balance plays an important role in modulating infection, the effect of GRA on MAPK directed phosphatases (MKP) was studied. GRA markedly reduced the expression and activities of three phosphatases, MKP1, MKP3 and protein phosphatase 2A (PP2A) along with a substantial reduction of p38 and ERK dephosphorylation in infected BMDM. Similarly in the in vivo situation, GRA treatment of L. donovani-infected BALB/c mice caused marked reduction of spleen parasite burden associated with concomitant decrease of individual phosphatase levels. However, activation of kinases also played an important role as the protective effect of GRA was significantly abrogated by pharmacological inhibition of p38 and ERK pathway. Curative effect of GRA may, therefore, be associated with restoration of proper cellular kinase/phosphatase balance, rather than modulation of either kinases or phosphatases.

Expression of IL-10-triggered STAT3-dependent IL-4Rα is required for induction of arginase 1 in visceral leishmaniasis

Although enhanced macrophage-specific arginase activity is directly related to increased parasite burden in cutaneous leishmaniasis (CL), the regulation and precise role of arginase in the disease outcome of visceral leishmaniasis (VL) has yet to be explored. As in CL, BALB/c mice infected with Leishmania donovani showed increased levels of arginase in acute infection. Arginase 1 is the major isoform associated with infection and while the IL-4-induced arginase pathway is operative in CL, IL-10 plays a crucial role in modulating arginase activity in VL, although a synergism with IL-4 is required. IL-10, in combination with IL-4, regulated both in vivo and ex vivo arginase 1 induction in a STAT6 and C/EBPβ-dependent fashion. Further investigation toward the cause of such synergism suggests that induction of a STAT3-dependent IL-10-mediated cascade in VL triggers the expression and surface localization of the IL-4 receptor alpha (IL-4Rα) which, in turn, enhances IL-4 responsiveness toward STAT6 and C/EBPβ-dependent signaling for arginase 1. This could also offer a mechanistic explanation for the fact that, in spite of the low level of IL-4 in VL, enhanced IL-4-Rα expression by IL-10 might markedly amplify IL-4-mediated arginase 1 signaling and provide a possible mechanism for synergistic induction of arginase 1.

A helminth immunomodulator exploits host signaling events to regulate cytokine production in macrophages

Parasitic worms alter their host's immune system to diminish the inflammatory responses directed against them, using very efficient immunomodulating molecules. We have previously shown that the helminth immunomodulator cystatin (AvCystatin) profoundly reduces the progression of inflammatory diseases via modulation of macrophages. Here we elucidate the signaling events in macrophages triggered by AvCystatin. Labeled AvCystatin was predominantly taken up by macrophages and subsequently induced the phosphorylation of the mitogen-activated protein kinases (MAPK) ERK1/2 and p38. IL-10 expression induced by AvCystatin in macrophages was tyrosine kinase sensitive and dependent on activation of both MAP kinases, in clear contrast to expression of IL-12/23p40. In addition, phosphorylation of the transcription factors CREB and STAT3 was induced by AvCystatin and regulated by phospho-ERK. Chemical inhibition of phosphoinositide 3-kinase (PI3K) reduced AvCystatin-induced cytokine release; however, AKT, the downstream target of PI3K, was not activated following AvCystatin exposure. To characterize signaling elements involved in alteration of the macrophage phenotype we applied mathematical modeling. Experimental testing of the in silico generated hypotheses identified dual specificity phosphatase (DUSP) 1 and 2, as regulators in AvCystatin triggered macrophages in vitro and in vivo. In particular, DUSP1 was subsequently found to be responsible for regulation of ERK- and p38-phosphorylation and controlled the IL-10 expression in macrophages by AvCystatin. Thus, we show that AvCystatin exploits activation and deactivation pathways of MAP kinases to induce regulatory macrophages. This study provides insights into molecular mechanisms of macrophage manipulation by parasites and highlights the utility of mathematical modeling for the elucidation of regulatory circuits of immune cells.

Helminths have the ability to interfere with their host's immune response, thus downregulating inflammatory responses. We previously demonstrated the role of helminth infections or isolated helminth proteins in suppressing bystander immune responses in mouse models of allergy and colitis via a macrophage and IL-10 dependent mechanism. The current study elucidates the signaling events induced by the parasite immunomodulator AvCystatin, leading to alteration of the macrophage phenotype. AvCystatin was predominantly taken up by macrophages and induced cytokine production by phosphorylation of mitogen-activated protein kinases (MAPK) ERK1/2 and p38. To identify molecules involved in the regulation of IL-10 production we developed a mathematical model. In silico generated data suggested a negative feedback mechanism via deactivating ERK1/2 and p38. Ensuing experiments validated the model and revealed AvCystatin-induced dual specificity phosphatases (DUSPs) as negative regulators of MAPK activation and IL-10 expression in vitro and in vivo. Taken together, the nematode immunomodulator AvCystatin targets activating and deactivating pathways of MAPK to induce regulatory macrophages.

Cystatin cures visceral leishmaniasis by NF-κB-mediated proinflammatory response through co-ordination of TLR/MyD88 signaling with p105-Tpl2-ERK pathway

Cystatin could completely cure experimental visceral leishmaniasis by switching the differentiation of Th2 cells to Th1 type, as well as upregulating NO, and activation of NF-κB played a major role in these processes. Analysis of upstream signaling events revealed that TLR 2/4-mediated MyD88-dependent participation of IL-1R-activated kinase (IRAK)1, TNF receptor-associated factor (TRAF)6 and TGFβ-activated kinase (TAK)1 is essential to induce cystatin-mediated IκB kinase (IKK)/NF-κB activation in macrophages. Cystatin plus IFN-γ activated the IKK complex to induce phosphorylation-mediated degradation of p105, the physiological partner and inhibitor of the MEK kinase, tumor progression locus 2 (Tpl-2). Consequently, Tpl-2 was liberated from p105, thereby stimulating activation of the MEK/ERK MAPK cascade. Cystatin plus IFN-γ-induced IKK-β post-transcriptionally modified p65/RelA subunit of NF-κB by dual phosphorylation in infected phagocytic cells. IKK induced the phosphorylation of p65 directly on Ser-536 residue whereas phosphorylation on Ser 276 residue was by sequential activation of Tpl-2/MEK/ERK/MSK1. Collectively, the present study indicates that cystatin plus IFN-γ-induced MyD88 signaling may bifurcate at the level of IKK, leading to a divergent pathway regulating NF-κB activation by IκBα phosphorylation and by p65 transactivation through Tpl-2/MEK/ERK/MSK1.

Endolysosomal proteases and their inhibitors in immunity

The cellular endolysosomal compartment is dynamic, complex and incompletely understood. Its organelles and constituents vary between different cell types, but endolysosomal proteases are key components of this compartment in all cells. In immune cells, these proteases function in pathogen recognition and elimination, signal processing and cell homeostasis, and they are regulated by dedicated inhibitors. Pathogens can produce analogous proteases to subvert the host immune response. The balance in activity between a protease and its inhibitor can tune the immune response or cause damage as a result of mislocalized proteolysis. In this Review, we highlight recent developments in this area and emphasize the importance of studying the role of endolysosomal proteases, and their natural inhibitors, in the initiation and regulation of immune responses.