Involvement of Syk protein tyrosine kinase in LPS-induced responses in macrophages

Identification of new drugs to counteract anti-spike IgG-induced hyperinflammation in severe COVID-19

Previously, we and others have shown that SARS-CoV-2 spike-specific IgG antibodies play a major role in disease severity in COVID-19 by triggering macrophage hyperactivation, disrupting endothelial barrier integrity, and inducing thrombus formation. This hyperinflammation is dependent on high levels of anti-spike IgG with aberrant Fc tail glycosylation, leading to Fcγ receptor hyperactivation. For development of immune-regulatory therapeutics, drug specificity is crucial to counteract excessive inflammation whereas simultaneously minimizing the inhibition of antiviral immunity. We here developed an in vitro activation assay to screen for small molecule drugs that specifically counteract antibody-induced pathology. We identified that anti-spike-induced inflammation is specifically blocked by small molecule inhibitors against SYK and PI3K. We identified SYK inhibitor entospletinib as the most promising candidate drug, which also counteracted anti-spike-induced endothelial dysfunction and thrombus formation. Moreover, entospletinib blocked inflammation by different SARS-CoV-2 variants of concern. Combined, these data identify entospletinib as a promising treatment for severe COVID-19.

TLR4 phosphorylation at tyrosine 672 activates the ERK/c-FOS signaling module for LPS-induced cytokine responses in macrophages

TLRs engage numerous adaptor proteins and signaling molecules, enabling a complex series of post-translational modifications (PTMs) to mount inflammatory responses. TLRs themselves are post-translationally modified following ligand-induced activation, with this being required to relay the full spectrum of proinflammatory signaling responses. Here, we reveal indispensable roles for TLR4 Y672 and Y749 phosphorylation in mounting optimal LPS-inducible inflammatory responses in primary mouse macrophages. LPS promotes phosphorylation at both tyrosine residues, with Y749 phosphorylation being required for maintenance of total TLR4 protein levels and Y672 phosphorylation exerting its pro-inflammatory effects more selectively by initiating ERK1/2 and c-FOS phosphorylation. Our data also support a role for the TLR4-interacting membrane proteins SCIMP and the SYK kinase axis in mediating TLR4 Y672 phosphorylation to permit downstream inflammatory responses in murine macrophages. The corresponding residue in human TLR4 (Y674) is also required for optimal LPS signaling responses. Our study, thus, reveals how a single PTM on one of the most widely studied innate immune receptors orchestrates downstream inflammatory responses.

Emerging roles of tyrosine kinases in hepatic inflammatory diseases and therapeutic opportunities

Inflammation has been convicted of causing and worsening many liver diseases like acute liver failure, fibrosis, cirrhosis, fatty liver and liver cancer. Pattern recognition receptors (PRRs) like TLRs 4 and 9 localized on resident or recruited immune cells are well known cellular detectors of pathogen and damage-associated molecular patterns (PAMPs/DAMPs). Stimulation of these receptors generates the sterile and non-sterile inflammatory responses in the liver. When these responses are repeated, there will be a sustained liver injury that may progress to fibrosis and its outcomes. Crosstalk between inflammatory/fibrogenic-dependent streams and certain tyrosine kinases (TKs) has recently evolved in the context of hepatic diseases. Because of TKs increasing importance, their role should be elucidated to highlight effective approaches to manage the diverse liver disorders. This review will give a brief overview of types and functions of some TKs like BTK, JAKs, Syk, PI3K, Src and c-Abl, as well as receptors for TAM, PDGF, EGF, VEGF and HGF. It will then move to discuss the roles of these TKs in the regulation of the proinflammatory, fibrogenic and tumorigenic responses in the liver. Lastly, the therapeutic opportunities for targeting TKs in hepatic inflammatory disorders will be addressed. Overall, this review sheds light on the diverse TKs that have substantial roles in hepatic disorders and potential therapeutics modulating their activity.

Application of human iPSC-derived macrophages in a miniaturized high-content-imaging-based efferocytosis assay

Macrophages play a pivotal role in drug discovery due to their key regulatory functions in health and disease. Overcoming the limited availability and donor variability of human monocyte-derived macrophages (MDMs), human induced pluripotent stem cell (iPSC)-derived macrophages (IDMs) could provide a promising tool for both disease modeling and drug discovery. To access large numbers of model cells for medium- to high-throughput application purposes, an upscaled protocol was established for differentiation of iPSCs into progenitor cells and subsequent maturation into functional macrophages. These IDM cells resembled MDMs both with respect to surface marker expression and phago- as well as efferocytotic function. A statistically robust high-content-imaging assay was developed to quantify the efferocytosis rate of IDMs and MDMs allowing for measurements both in the 384- and 1536-well microplate format. Validating the applicability of the assay, inhibitors of spleen tyrosine kinase (Syk) were shown to modulate efferocytosis in IDMs and MDMs with comparable pharmacology. The miniaturized cellular assay with the upscaled provision of macrophages opens new routes to pharmaceutical drug discovery in the context of efferocytosis-modulating substances.

Amurensin H, a Derivative From Resveratrol, Ameliorates Lipopolysaccharide/Cigarette Smoke-Induced Airway Inflammation by Blocking the Syk/NF-κB Pathway

Amurensin H, a resveratrol dimer derived from Vitis amurensis Rupr, has several biological effects, including anti-inflammatory and antioxidant activities. Studies have found that amurensin H attenuated asthma-like allergic airway inflammation. However, its protective activity on chronic obstructive pulmonary disease (COPD) airway inflammation is not fully explored. The present study used a lipopolysaccharide (LPS)/cigarette smoke-induced mice model and an LPS-stimulated THP-1-derived macrophages model to measure the lung tissue's morphology changes. The results showed that amurensin H ameliorated the histological inflammatory alterations in the lung tissues, leading to a decrease in the expression of interleukin 6 (IL-6), IL-17A, tumor necrosis factor α (TNF-α), and interferon γ in bronchoalveolar lavage fluid. Amurensin H also significantly inhibited the release of IL-1β, IL-6, IL-8, and TNF-α in LPS-stimulated THP-1-derived macrophages. Furthermore, amurensin H markedly inhibited the expressions of p-Syk, nuclear factor κB (NF-κB), and p-NF-κB both in vivo and in vitro. Results from cotreatment with Syk inhibitor BAY61-3606 and NF-κB inhibitor BAY11-7082 in vitro revealed that amurensin H's protective effect against airway inflammation could be due partly to the inhibition of the Syk/NF-κB pathway. These findings suggest that amurensin H shows therapeutic effects on COPD airway inflammation, and inhibiting the Syk/NF-κB pathway might be part of its underlying mechanisms.

Microglia in Retinal Degeneration

The retina is a complex tissue with multiple cell layers that are highly ordered. Its sophisticated structure makes it especially sensitive to external or internal perturbations that exceed the homeostatic range. This necessitates the continuous surveillance of the retina for the detection of noxious stimuli. This task is mainly performed by microglia cells, the resident tissue macrophages which confer neuroprotection against transient pathophysiological insults. However, under sustained pathological stimuli, microglial inflammatory responses become dysregulated, often worsening disease pathology. In this review, we provide an overview of recent studies that depict microglial responses in diverse retinal pathologies that have degeneration and chronic immune reactions as key pathophysiological components. We also discuss innovative immunomodulatory therapy strategies that dampen the detrimental immunological responses to improve disease outcome.

Syk inhibitor R406 downregulates inflammation in an in vitro model of Pseudomonas aeruginosa infection

As Pseudomonas aeruginosa infections are characterized by strong inflammation of infected tissues, anti-inflammatory therapies in combination with antibiotics have been considered for the treatment of associated diseases. Syk tyrosine kinase is an important regulator of inflammatory responses, and its specific inhibition was explored as a therapeutic option in several inflammatory conditions; however, this has not been studied in bacterial infections. We used a model of in vitro infection of human monocytic cell line THP-1 and lung epithelial cell line H292 with both wild-type and flagella-deficient mutant of P. aeruginosa strain K, as well as with clinical isolates from cystic fibrosis patients, to study the effect of a small molecule Syk inhibitor R406 on inflammatory responses induced by this pathogen. One-hour pretreatment of THP-1 cells with 10 μmol/L R406 resulted in a significant downregulation of the expression of the adhesion molecule ICAM-1, pro-inflammatory cytokines TNF-α and IL-1β, and phosphorylated signaling proteins ERK2, JNK, p-38, and IκBα, as well as significantly decreased TNF-α release by infected H292 cells. The results suggest that Syk is involved in the regulation of inflammatory responses to P. aeruginosa, and R406 may potentially be useful in dampening the damage caused by severe inflammation associated with this infection.

Oligonucleotide Therapy for Obstructive and Restrictive Respiratory Diseases

Inhaled oligonucleotide is an emerging therapeutic modality for various common respiratory diseases, including obstructive airway diseases like asthma and chronic obstructive pulmonary disease (COPD) and restrictive airway diseases like idiopathic pulmonary fibrosis (IPF). The advantage of direct accessibility for oligonucleotide molecules to the lung target sites, bypassing systemic administration, makes this therapeutic approach promising with minimized potential systemic side effects. Asthma, COPD, and IPF are common chronic respiratory diseases, characterized by persistent airway inflammation and dysregulated tissue repair and remodeling, although each individual disease has its unique etiology. Corticosteroids have been widely prescribed for the treatment of asthma, COPD, and IPF. However, the effectiveness of corticosteroids as an anti-inflammatory drug is limited by steroid resistance in severe asthma, the majority of COPD cases, and pulmonary fibrosis. There is an urgent medical need to develop target-specific drugs for the treatment of these respiratory conditions. Oligonucleotide therapies, including antisense oligonucleotide (ASO), small interfering RNA (siRNA), and microRNA (miRNA) are now being evaluated both pre-clinically and clinically as potential therapeutics. The mechanisms of action of ASO and siRNA are highly target mRNA specific, ultimately leading to target protein knockdown. miRNA has both biomarker and therapeutic values, and its knockdown by a miRNA antagonist (antagomir) has a broader but potentially more non-specific biological outcome. This review will compile the current findings of oligonucleotide therapeutic targets, verified in various respiratory disease models and in clinical trials, and evaluate different chemical modification approaches to improve the stability and potency of oligonucleotides for the treatment of respiratory diseases.

Inhibition of spleen tyrosine kinase as treatment of postoperative ileus

OBJECTIVE

Intestinal inflammation resulting from manipulation-induced mast cell activation is a crucial mechanism in the pathophysiology of postoperative ileus (POI). Recently it has been shown that spleen tyrosine kinase (Syk) is involved in mast cell degranulation. Therefore, we have evaluated the effect of the Syk-inhibitor GSK compound 143 (GSK143) as potential treatment to shorten POI.

DESIGN

In vivo: in a mouse model of POI, the effect of the Syk inhibitor (GSK143) was evaluated on gastrointestinal transit, muscular inflammation and cytokine production. In vitro: the effect of GSK143 and doxantrazole were evaluated on cultured peritoneal mast cells (PMCs) and bone marrow derived macrophages.

RESULTS

In vivo: intestinal manipulation resulted in a delay in gastrointestinal transit at t=24 h (Geometric Center (GC): 4.4 ± 0.3). Doxantrazole and GSK143 significantly increased gastrointestinal transit (GC doxantrazole (10 mg/kg): 7.2 ± 0.7; GSK143 (1 mg/kg): 7.6 ± 0.6), reduced inflammation and prevented recruitment of immune cells in the intestinal muscularis. In vitro: in PMCs, substance P (0-90 μM) and trinitrophenyl (0-4 μg/ml) induced a concentration-dependent release of β-hexosaminidase. Pretreatment with doxantrazole and GSK143 (0.03-10 μM) concentration dependently blocked substance P and trinitrophenyl induced β-hexosaminidase release. In addition, GSK143 was able to reduce cytokine expression in endotoxin-treated bone marrow derived macrophages in a concentration-dependent manner.

CONCLUSIONS

The Syk inhibitor GSK143 reduces macrophage activation and mast cell degranulation in vitro. In addition, it inhibits manipulation-induced intestinal muscular inflammation and restores intestinal transit in mice. These findings suggest that Syk inhibition may be a new tool to shorten POI.

The tyrosine kinase Syk differentially regulates Toll-like receptor signaling downstream of the adaptor molecules TRAF6 and TRAF3

Toll-like receptors (TLRs) are a major family of pattern recognition receptors, and they play a crucial role in innate immune responses. Activation of TLR4 signaling at the plasma membrane by its ligand lipopolysaccharide (LPS) stimulates a proinflammatory pathway dependent on the E3 ubiquitin ligase TRAF6 (tumor necrosis factor receptor-associated factor 6) and the kinase TAK1 (transforming growth factor β-activated kinase 1), whereas TLR4 signaling at endosomes stimulates the production of type I interferons (IFNs) through a pathway that depends on TRAF3 and the kinase TBK1 (TANK-binding kinase-1). We found that the nonreceptor tyrosine kinase Syk partially mediated the endocytosis of TLR4, but it also played a dual role in TLR4-mediated signaling. LPS-dependent stimulation of TLR4 in Syk-deficient macrophages led to enhanced activation of TAK1 and increased production of proinflammatory cytokines compared to that in wild-type macrophages. In contrast, Syk-deficient macrophages exhibited decreased TLR4-dependent activation of TBK1 signaling and production of type I IFNs. We found that Syk was present in both TRAF6- and TRAF3-containing signaling complexes; however, the LPS-dependent, lysine 63-linked ubiquitination of TRAF6 and TRAF3 was oppositely regulated by Syk. We identified the domains of Syk that interacted with TRAF3, TRAF6, TAK1, and TBK1, factors activated by multiple TLRs, which suggests that Syk may act as a common regulator of various TLR responses. Together, our results demonstrate the opposing regulatory roles of Syk in TLR-mediated TRAF6 and TRAF3 signaling pathways, which suggests that Syk may fine-tune the innate immune response to lessen inflammation.

Mannose receptor and macrophage galactose-type lectin are involved in Bordetella pertussis mast cell interaction

Mast cells are crucial in the development of immunity against Bordetella pertussis, and the function of TLRs in this process has been investigated. Here, the interaction between mast cells and B. pertussis with an emphasis on the role of CLRs is examined. In this study, two CLRs, MGL and MR, were detected for the first time on the surface of mast cells. The involvement of MR and MGL in the stimulation of mast cells by heat-inactivated BP was investigated by the use of blocking antibodies and specific carbohydrate ligands. The cell wall LOS of BP was also isolated to explore its role in this interaction. Mast cells stimulated with heat-inactivated BP or BP LOS induced TNF-α, IL-6, and IFN-γ secretion, which was suppressed by blocking MR or MGL. Inhibition of CLRs signaling during BP stimulation affected the ability of mast cells to promote cytokine secretion in T cells but had no effect on the cell-surface expression of ICAM1. Blocking MR or MGL suppressed BP-induced NF-κB expression but not ERK phosphorylation. Syk was involved in the CLR-mediated activation of mast cells by BP. Bacterial recognition by immune cells has been predominantly attributed to TLRs; in this study, the novel role of CLRs in the BP-mast cell interaction is highlighted.

Tetramethylpyrazine attenuates TNF-α-induced iNOS expression in human endothelial cells: Involvement of Syk-mediated activation of PI3K-IKK-IκB signaling pathways

Endothelial cells produce nitric oxide (NO) by activation of constitutive nitric oxide synthase (NOS) and transcription of inducible NO synthase (iNOS). We explored the effect of tetramethylpyrazine (TMP), a compound derived from chuanxiong, on tumor necrosis factor (TNF)-α-induced iNOS in human umbilical vein endothelial cells (HUVECs) and explored the signal pathways involved by using RT-PCR and Western blot. TMP suppressed TNF-α-induced expression of iNOS by inhibiting IκB kinase (IKK) phosphorylation, IκB degradation and nuclear factor κB (NF-κB) nuclear translocation, which were required for NO gene transcription. Exposure to wortmannin abrogated IKK/IκB/NF-κB-mediated iNOS expression, suggesting activation of such a signal pathway might be phosphoinositide-3-kinase (PI3K) dependent. Spleen tyrosine kinase (Syk) inhibitor piceatannol significantly inhibited NO production. Furthermore, piceatannol obviously suppressed TNF-α-induced IκB phosphorylation and the downstream NF-κB activation, suggesting that Syk is an upstream key regulator in the activation of PI3K/IKK/IκB-mediated signaling. TMP significantly inhibited TNF-α-induced phosphorylation of Syk and PI3K. Our data indicate that TMP might repress iNOS expression, at least in part, through its inhibitory effect of Syk-mediated PI3K phosphorylation in TNF-α-stimulated HUVECs.

HangAmDan-B, an ethnomedicinal herbal mixture, suppresses inflammatory responses by inhibiting Syk/NF-κB and JNK/ATF-2 pathways

HangAmDan-B (HAD-B) is a powdered mixture of eight ethnopharmacologically characterized folk medicines that is prescribed for solid masses and cancers in Korea. In view of the finding that macrophage-mediated inflammation is a pathophysiologically important phenomenon, we investigated whether HAD-B modulates inflammatory responses and explored the associated molecular mechanisms. The immunomodulatory activity of HAD-B in toll-like receptor-activated macrophages induced by lipopolysaccharide (LPS) was assessed by measuring nitric oxide (NO) and prostaglandin E(2) (PGE(2)) levels. To identify the specific transcription factors (such as nuclear factor [NF]-κB and signaling enzymes) targeted by HAD-B, biochemical approaches, including kinase assays and immunoblot analysis, were additionally employed. HAD-B suppressed the production of PGE(2) and NO in LPS-activated macrophages in a dose-dependent manner. Furthermore, the extract ameliorated HCl/EtOH-induced gastritis symptoms. Moreover, HAD-B significantly inhibited LPS-induced mRNA expression of inducible NO synthase and cyclooxygenase (COX)-2. Interestingly, marked inhibition of NF-κB and activating transcription factor was observed in the presence of HAD-B. Data from direct kinase assays and immunoblot analysis showed that HAD-B suppresses activation of the upstream signaling cascade involving spleen tyrosine kinase, Src, p38, c-Jun N-terminal kinase, and transforming growth factor β-activated kinase 1. Finally, kaempferol, but not quercetin or resveratrol was identified as a bioactive compound in HAD-B. Therefore, our results suggest that HAD-B possesses anti-inflammatory activity that contributes to its anticancer property.

Spleen tyrosine kinase regulates AP-1 dependent transcriptional response to minimally oxidized LDL

Oxidative modification of low-density lipoprotein (LDL) turns it into an endogenous ligand recognized by pattern-recognition receptors. We have demonstrated that minimally oxidized LDL (mmLDL) binds to CD14 and mediates TLR4/MD-2-dependent responses in macrophages, many of which are MyD88-independent. We have also demonstrated that the mmLDL activation leads to recruitment of spleen tyrosine kinase (Syk) to TLR4 and TLR4 and Syk phosphorylation. In this study, we produced a macrophage-specific Syk knockout mouse and used primary Syk(-/-) macrophages in our studies. We demonstrated that Syk mediated phosphorylation of ERK1/2 and JNK, which in turn phosphorylated c-Fos and c-Jun, respectively, as assessed by an in vitro kinase assay. c-Jun phosphorylation was also mediated by IKKε. c-Jun and c-Fos bound to consensus DNA sites and thereby completed an AP-1 transcriptional complex and induced expression of CXCL2 and IL-6. These results suggest that Syk plays a key role in TLR4-mediated macrophage responses to host-generated ligands, like mmLDL, with subsequent activation of an AP-1 transcription program.

Suppressive effects of methoxyflavonoids isolated from Kaempferia parviflora on inducible nitric oxide synthase (iNOS) expression in RAW 264.7 cells

ETHNOPHARMACOLOGICAL RELEVANCE

The rhizomes of Kaempferia parviflora Wall. ex Baker have been traditionally used in Thailand to treat abscesses, gout, and peptic ulcers.

AIM

Previously, we reported that the chloroform fraction of a Kaempferia parviflora extract had an inhibitory effect on rat paw-edema. In the present study, we isolated the constituents of this fraction and investigated the anti-inflammatory mechanism against nitric oxide (NO) production, tumor necrosis factor-α (TNF-α) and the expression of inducible nitric oxide synthase (iNOS) as well as phosphorylated extracellular signal-regulated kinase (p-ERK), and phosphorylated c-Jun N-terminal kinase (p-JNK). In addition, effects of trimethylapigenin (4) on the enzyme activities of protein kinases possibly leading to iNOS expression were examined to clarify the targets.

MATERIALS AND METHODS

The chloroform fraction was isolated using silica gel column chromatography and HPLC. Isolated compounds were tested against NO and TNF-α using RAW264.7 cells. Cytotoxicity and iNOS, p-ERK and p-JNK expression were also examined.

RESULTS

Three active components, 5,7-dimethoxyflavone (2), trimethylapigenin (4), and tetramethylluteolin (5), markedly inhibited the production of NO in lipopolysaccharide (LPS)-activated RAW264.7 cells. Compounds 2, 4, and 5 moderately inhibited production of TNF-α. Compounds 2, 4, and 5 strongly inhibited expression of iNOS mRNA and iNOS protein in a dose-dependent manner, but did not inhibit p-ERK or p-JNK protein expression. The most active compound, 4, did not inhibit the enzyme activity of inhibitor of κB kinases or mitogen-activated protein kinases, but inhibited that of spleen tyrosine kinase (SYK).

CONCLUSION

The mechanism responsible for the anti-inflammatory activity of methoxyflavonoids from the chloroform fraction of the rhizomes of Kaempferia parviflora is mainly the inhibition of iNOS expression, and the inhibition of SYK by 4 may be involved in the suppression of LPS-induced signaling in macrophages.

The oral spleen tyrosine kinase inhibitor fostamatinib attenuates inflammation and atherogenesis in low-density lipoprotein receptor-deficient mice

OBJECTIVE

Spleen tyrosine kinase (SYK) has come into focus as a potential therapeutic target in chronic inflammatory diseases, such as rheumatoid arthritis and asthma, as well as in B-cell lymphomas. SYK has also been involved in the signaling of immunoreceptors, cytokine receptors, and integrins. We therefore hypothesized that inhibition of SYK attenuates the inflammatory process underlying atherosclerosis and reduces plaque development.

METHODS AND RESULTS

Low-density lipoprotein receptor-deficient mice consuming a high-cholesterol diet supplemented with 2 doses of the orally available SYK inhibitor fostamatinib for 16 weeks showed a dose-dependent reduction in atherosclerotic lesion size by up to 59±6% compared with the respective controls. Lesions of fostamatinib-treated animals contained fewer macrophages but more smooth muscle cells and collagen-characteristics associated with more stable plaques in humans. Mechanistically, fostamatinib attenuated adhesion and migration of inflammatory cells and limited macrophage survival. Furthermore, fostamatinib normalized high-cholesterol diet -induced monocytosis and inflammatory gene expression.

CONCLUSIONS

We present the novel finding that the SYK inhibitor fostamatinib attenuates atherogenesis in mice. Our data identify SYK inhibition as a potentially fruitful antiinflammatory therapeutic strategy in atherosclerosis.

Psoralidin inhibits LPS-induced iNOS expression via repressing Syk-mediated activation of PI3K-IKK-IκB signaling pathways

Psoralidin has been reported to inhibit lipopolysaccharide (LPS)-induced nitric oxide (NO) production, but the mechanisms of the action remain unclear. Thus, the impact of psoralidin on signaling pathways known to be implicated in NO synthesis was explored in LPS-activated RAW264.7 macrophages by using RT-PCR and Western blotting. Consistent with NO inhibition, psoralidin suppressed LPS-induced expression of inducible NO synthase (iNOS) by abolishing IκB kinase (IKK) phosphorylation, IκB degradation and nuclear factor κB (NF-κB) nuclear translocation without effecting mitogen-activated protein kinases (MAPKs) phosphorylation. Exposure to wortmannin abrogated IKK/IκB/NF-κB-mediated iNOS expression, suggesting activation of such a signal pathway might also be phosphoinositide-3-kinase (PI3K) dependent. By using Src inhibitor PP2, Janus kinase 2 (JAK-2) inhibitor AG490, Bruton's tyrosine kinase (Btk) inhibitor LFM-A13 and spleen tyrosine kinase (Syk) inhibitor piceatannol, the results showed that piceatannol clearly repressed NO production more potently than the other inhibitors. Furthermore, piceatannol significantly repressed LPS-induced PI3K/Akt phosphorylation and the downstream IKK/IκB activation, suggesting that Syk is an upstream key regulator in the activation of PI3K/Akt-mediated signaling. In fact, transfection with siRNA targeting Syk obviously reduced iNOS expression. Interestingly, LPS-induced phosphorylations of Syk and PI3K-p85 were both significantly blunted by psoralidin treatment. The present results show that interfering with Syk-mediated PI3K phosphorylation might contribute to the NO inhibitory effect of psoralidin via blocking IKK/IκB signaling propagation in LPS-stimulated RAW 264.7 macrophages.

Spleen tyrosine kinases: biology, therapeutic targets and drugs

Spleen tyrosine kinase (Syk) is an intriguing protein tyrosine kinase involved in signal transduction in a variety of cell types, and its aberrant regulation is associated with different allergic disorders and antibody-mediated autoimmune diseases such as rheumatoid arthritis, asthma and allergic rhinitis. Syk also plays an important part in the uncontrolled growth of tumor cells, particularly B cells. For these reasons, Syk is considered one of the most interesting biological targets of the last decade, as proved by the great number of papers and patents published, and the possibility of treating these pathologies by means of Syk kinase inhibitors has led to a great interest from the pharmaceutical and biotech industry.

Identifying the functional part of heparin-binding protein (HBP) as a monocyte stimulator and the novel role of monocytes as HBP producers

Heparin-binding protein (HBP), an evolutionary ancient and biologically highly important molecule in inflammation, is an inactive serine protease due to mutations in the catalytic triad. The histidine (position 41) in the conserved sequence TAAHC is mutated to serine and this sequence (TAASC) plays a crucial role when HBP binds to monocytes. We synthesized a 20-44 HBP peptide, cyclicized by a sulphur bridge, which encompasses this amino acid and functions as full-length HBP. Using a human monocyte cell line, we have shown that lipopolysaccharide (LPS)-triggered secretion of IL-6 is enhanced up to 10-fold when full-length HBP or the peptide are present in low-to-moderate concentrations. A monoclonal antibody neutralizing HBP also neutralizes the peptide, indicating that the ligand for the HBP receptor is located near serine in position 41 on the HBP surface. A 'back mutated' 20-44 peptide (serine→histidine) has some, but not significant, stimulatory effect on monocytes. Normally, HBP production and release is ascribed to neutrophil granulocytes, but here we find that also monocytes secrete HBP when stimulated with LPS. Furthermore, a small amount of HBP can be demonstrated when monocytes are incubated in medium alone. Our efforts to identify a suggested HBP receptor on monocytes has failed so far.

Emerging oligonucleotide therapies for asthma and chronic obstructive pulmonary disease

Chronic respiratory diseases such as asthma and chronic obstructive pulmonary disease (COPD) are disorders of the airways largely related to the presence of persistent inflammation. The approval of inhaled corticosteroids in the early 1970s pioneered a new age of therapy in treating chronic inflammatory airway diseases. This was the first time that an anti-inflammatory product was available to reduce the characteristic lung inflammation in airways and the associated obstruction, inflammation and hyper-responsiveness. Fast forward 40 years: corticosteroids are still an important therapeutic intervention; however, they exhibit limited use in moderate to severe asthma and COPD. Oligonucleotide therapies are an emerging class which include the antisense, the RNAi (siRNA and miRNA), the immunomodulatory, the aptamer and the decoy approaches. As these approaches are rather recent in the respiratory field, most are still early in development. Nevertheless, with limitations of current small molecule therapies and the hurdles faced with biologics, the use of oligonucleotides is relevant and the door is open to the development of this category of therapeutics. This review focuses on the major classes of oligonucleotides that are currently in late stage preclinical or clinical development for the treatment of asthma and COPD, and discusses the implications for their use as therapies for respiratory diseases.

RhoA GTPase activation by TLR2 and TLR3 ligands: connecting via Src to NF-kappa B

Rho GTPases are essential regulators of signaling networks emanating from many receptors involved in innate or adaptive immunity. The Rho family member RhoA controls cytoskeletal processes as well as the activity of transcription factors such as NF-kappaB, C/EBP, and serum response factor. The multifaceted host cell activation triggered by TLRs in response to soluble and particulate microbial structures includes rapid stimulation of RhoA activity. RhoA acts downstream of TLR2 in HEK-TLR2 and monocytic THP-1 cells, but the signaling pathway connecting TLR2 and RhoA is still unknown. It is also not clear if RhoA activation is dependent on a certain TLR adapter. Using lung epithelial cells, we demonstrate TLR2- and TLR3-triggered recruitment and activation of RhoA at receptor-proximal cellular compartments. RhoA activity was dependent on TLR-mediated stimulation of Src family kinases. Both Src family kinases and RhoA were required for NF-kappaB activation, whereas RhoA was dispensable for type I IFN generation. These results suggest that RhoA plays a role downstream of MyD88-dependent and -independent TLR signaling and acts as a molecular switch downstream of TLR-Src-initiated pathways.

Epithelial cell apoptosis and neutrophil recruitment in acute lung injury-a unifying hypothesis? What we have learned from small interfering RNAs

In spite of protective ventilatory strategies, Acute Lung Injury (ALI) remains associated with high morbidity and mortality. One reason for the lack of therapeutic options might be that ALI is a co-morbid event associated with a diverse family of diseases and, thus, may be the result of distinct pathological processes. Among them, activated neutrophil- (PMN-) induced tissue injury and epithelial cell apoptosis mediated lung damage represent two potentially important candidate pathomechanisms that have been put forward. Several approaches have been undertaken to test these hypotheses, with substantial success in the treatment of experimental forms of ALI. With this in mind, we will summarize these two current hypotheses of ALI briefly, emphasizing the role of apoptosis in regulating PMN and/or lung epithelial cell responses. In addition, the contribution that Fas-mediated inflammation may play as a potential biological link between lung cell apoptosis and PMN recruitment will be considered, as well as the in vivo application of small interfering RNA (siRNA) as a novel approach to the inhibition of ALI and its therapeutic implications.