Roles of the kallikrein/kinin system in the adaptive immune system

Role of kinin receptors in skin pigmentation

Previous studies have shown that all kinin system is constitutively expressed in the normal and inflamed skin, with a potential role in both physiological and pathological processes. However, the understanding regarding the involvement of the kinin system in skin pigmentation and pigmentation disorders remains incomplete. In this context, the present study was designed to determine the role of kinins in the Monobenzone (MBZ)-induced vitiligo-like model. Our findings showed that MBZ induces higher local skin depigmentation in kinin receptors knockout mice (KOB1R, KOB2R and KOB1B2R) than in wild type (WT). Remarkably, lower levels of melanin content and reduced ROS generation were detected in KOB1R and KOB2R mice treated with MBZ. In addition, both KOB1R and KOB2R show increased dermal cell infiltrate in vitiligo-like skin, when compared to WT-MBZ. Additionally, lack of B1R was associated with greater skin accumulation of IL-4, IL-6, and IL-17 by MBZ, while KOB1B2R presented lower levels of TNF and IL-1. Of note, the absence of both kinin B1 and B2 receptors demonstrates a protective effect by preventing the increase in polymorphonuclear and mononuclear cell infiltrations, as well as inflammatory cytokine levels induced by MBZ. In addition, in vitro assays confirm that B1R and B2R agonists increase intracellular melanin synthesis, while bradykinin significantly enhanced extracellular melanin levels and proliferation of B16F10 cells. Our findings highlight that the lack of kinin receptors caused more severe depigmentation in the skin, as well as genetic deletion of both B1/B2 receptors seems to be linked with changes in levels of constitutive melanin levels, suggesting the involvement of kinin system in crucial skin pigmentation pathways.

Delayed plasma kallikrein inhibition fosters post-stroke recovery by reducing thrombo-inflammation

Activation of the kallikrein-kinin system promotes vascular leakage, inflammation, and neurodegeneration in ischemic stroke. Inhibition of plasma kallikrein (PK) - a key component of the KKS - in the acute phase of ischemic stroke has been reported to reduce thrombosis, inflammation, and damage to the blood-brain barrier. However, the role of PK during the recovery phase after cerebral ischemia is unknown. To this end, we evaluated the effect of subacute PK inhibition starting from day 3 on the recovery process after transient middle artery occlusion (tMCAO). Our study demonstrated a protective effect of PK inhibition by reducing infarct volume and improving functional outcome at day 7 after tMCAO. In addition, we observed reduced thrombus formation in cerebral microvessels, fewer infiltrated immune cells, and an improvement in blood-brain barrier integrity. This protective effect was facilitated by promoting tight junction reintegration, reducing detrimental matrix metalloproteinases, and upregulating regenerative angiogenic markers. Our findings suggest that PK inhibition in the subacute phase might be a promising approach to accelerate the post-stroke recovery process.

Serping1 associated with α-synuclein increase in colonic smooth muscles of MPTP-induced Parkinson's disease mice

Patients with Parkinson's disease (PD) have gastrointestinal motility disorders, which are common non-motor symptoms. However, the reasons for these motility disorders remain unclear. Increased alpha-synuclein (α-syn) is considered an important factor in peristalsis dysfunction in colonic smooth muscles in patients with PD. In this study, the morphological changes and association between serping1 and α-syn were investigated in the colon of the 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-induced chronic PD model. Increased serping1 and α-syn were noted in the colon of the PD model, and decreased serping1 also induced a decrease in α-syn in C2C12 cells. Serping1 is a major regulator of physiological processes in the kallikrein-kinin system, controlling processes including inflammation and vasodilation. The kinin system also comprises bradykinin and bradykinin receptor 1. The factors related to the kallikrein-kinin system, bradykinin, and bradykinin receptor 1 were regulated by serping1 in C2C12 cells. The expression levels of bradykinin and bradykinin receptor 1, modulated by serping1 also increased in the colon of the PD model. These results suggest that the regulation of increased serping1 could alleviate Lewy-type α-synucleinopathy, a characteristic of PD. Furthermore, this study could have a positive effect on the early stages of PD progression because of the perception that α-syn in colonic tissues is present prior to the development of PD motor symptoms.

The Effects of Serping1 siRNA in α-Synuclein Regulation in MPTP-Induced Parkinson's Disease

Our understanding of the gastrointestinal system in the pathophysiology of Parkinson's disease (PD) has grown considerably over the last two decades. Patients with PD experience notable gastrointestinal symptoms, including constipation. In this study, the effects of knocked-down serping1, associated with the contraction and relaxation of smooth muscle and inflammation responses, by applying the serping1 siRNA were investigated in 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-induced PD mice in an α-syn change aspect. In the result, serping1 expression was knocked down by the treatment of serping1 siRNA, and decreased serping1 induced the decrease α-syn in the colon. Furthermore, the changes in α-syn aggregation were also examined in the brain, and alleviated α-syn aggregation was also observed in an serping1 siRNA treatment group. The results indicated that serping1 siRNA could ease synucleinopathy related to the gastrointestinal system in PD. This study also raises the possibility that serping1 siRNA could alleviate α-syn aggregation in striatum and substantia nigra regions of the brain.

Exhaled biomarkers in adults with non-productive cough

BACKGROUND

Chronic cough is a common condition but disease mechanisms are not fully understood. Our aim was to study respiratory biomarkers from the small airways in individuals with non-productive cough.

METHODS

A cohort of 107 participants answered detailed questionnaires, performed spirometry, exhaled NO measurement, impulse oscillometry, gave blood samples and particles in exhaled air (PEx) samples. Current smokers (N = 38) were excluded. A total of 14 participants reported non-productive cough (cases). A total of 55 participants reported no cough (control group). PEx samples, containing exhaled particles derived from small airways, were collected and analysed with the SOMAscan proteomics platform.

RESULTS

Participants with non-productive cough had similar age, sex, BMI, and inflammation markers in blood tests, as participants without cough. The proteomics analysis found 75 proteins significantly altered among participants with chronic cough compared to controls, after adjusting for sex and investigator performing the PExA measurement (all with p-value < 0.05 and q-value ≤ 0.13, thereof 21 proteins with a q-value < 0.05). These proteins were mostly involved in immune and inflammatory responses, complement and coagulation system, but also tight junction proteins and proteins involved in neuroinflammatory responses.

CONCLUSIONS

This exploratory study on proteomics of exhaled particles among individuals with chronic cough found alterations in relative abundance of 75 proteins. The proteins identified are implicated in both pathways known to be implicated in cough, but also potentially new pathways. Further studies are needed to explore the importance of these findings.

Bradykinin receptor-1 activation induces inflammation and increases the permeability of human brain microvascular endothelial cells

Neuroinflammatory disorders such as Alzheimer's and Parkinson's diseases are characterised by chronic inflammation and loss of vascular integrity. Bradykinin 1 receptor (B1R) activation has been implicated in many neuroinflammatory diseases, but the contribution of B1R to inflammation and vascular breakdown is yet to be determined. As a result, the present study evaluated the effect of B1R stimulation using Des-Arg-9-BK on the cytokine profile and junctional properties of human cerebral microvascular endothelial cells (hCMVECs). Results showed that stimulation of B1R receptors increased secretion of pro-inflammatory cytokines, interleukin-6 (IL-6), IL-8, intracellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and monocyte chemoattractant protein-1 (MCP-1), but decreased the expression of vascular endothelial growth factor (VEGF), a cytokine and growth factor required for maintenance of the vasculature. B1R stimulation also resulted in the loss of occludin expression at tight junctions with no change in VE-cadherin expression. There was also a significant increase in permeability to Evans blue albumin, suggesting an increase of vascular permeability. Taken together, these results suggest that B1R activation that occurs in neuroinflammatory diseases may contribute to both the inflammation and loss of blood-brain barrier integrity that is characteristic of these diseases.

Polyphosphate, Zn2+ and high molecular weight kininogen modulate individual reactions of the contact pathway of blood clotting

BACKGROUND

Inorganic polyphosphate modulates the contact pathway of blood clotting, which is implicated in thrombosis and inflammation. Polyphosphate polymer lengths are highly variable, with shorter polymers (approximately 60-100 phosphates) secreted from human platelets, and longer polymers (up to thousands of phosphates) in microbes. We previously reported that optimal triggering of clotting via the contact pathway requires very long polyphosphates, although the impact of shorter polyphosphate polymers on individual proteolytic reactions of the contact pathway was not interrogated.

OBJECTIVES AND METHODS

We conducted in vitro measurements of enzyme kinetics to investigate the ability of varying polyphosphate sizes, together with high molecular weight kininogen and Zn2+ , to mediate four individual proteolytic reactions of the contact pathway: factor XII autoactivation, factor XII activation by kallikrein, prekallikrein activation by factor XIIa, and prekallikrein autoactivation.

RESULTS

The individual contact pathway reactions were differentially dependent on polyphosphate length. Very long-chain polyphosphate was required to support factor XII autoactivation, whereas platelet-size polyphosphate significantly accelerated the activation of factor XII by kallikrein, and the activation of prekallikrein by factor XIIa. Intriguingly, polyphosphate did not support prekallikrein autoactivation. We also report that high molecular weight kininogen was required only when kallikrein was the enzyme (ie, FXII activation by kallikrein), whereas Zn2+ was required only when FXII was the substrate (ie, FXII activation by either kallikrein or FXIIa). Activation of prekallikrein by FXIIa required neither Zn2+ nor high molecular weight kininogen.

CONCLUSIONS

Platelet polyphosphate and Zn2+ can promote subsets of the reactions of the contact pathway, with implications for a variety of disease states.

Activation of the Kinin B1 Receptor by Its Agonist Reduces Melanoma Metastasis by Playing a Dual Effect on Tumor Cells and Host Immune Response

Metastatic melanoma is an aggressive type of skin cancer leading half of the patients to death within 8–10 months after diagnosis. Kinins are peptides that interact with B1 and B2 receptors playing diverse biological roles. We investigated whether treatment with B1 receptor agonist, des-Arg⁹-bradykinin (DABK), has effects in lung metastasis establishment after melanoma induction in mice. We found a lower number of metastatic colonies in lungs of DABK-treated mice, reduced expression of vascular cell adhesion molecule 1 (VCAM-1), and increased CD8⁺T-cell recruitment to the metastatic area compared to animals that did not receive treatment. To understand whether the effects of DABK observed were due to the activation of the B1 receptor in the tumor cells or in the host, we treated wild-type (WT) and kinin B1 receptor knockout (B1^−/−) mice with DABK. No significant differences in the number of melanoma colonies established in lungs were seen between WT and B1^−/−mice; however, B1^−/−mice presented higher VCAM-1 expression and lower CD8⁺T-cell infiltration. In conclusion, we believe that activation of kinin B1 receptor by its agonist in the host stimulates the immune response more efficiently, promoting CD8⁺T-cell recruitment to the metastatic lungs and interfering in VCAM-1 expression. Moreover, treatment with DABK reduced establishment of metastatic colonies by mainly acting on tumor cells; hence, this study brings insights to explore novel approaches to treat metastatic melanoma targeting the B1 receptor.

Immunomodulation in stem cell differentiation into neurons and brain repair

Immunomodulators regulate stem cell activity at all stages of development as well as during adulthood. Embryonic stem cell (ESC) proliferation as well as neurogenic processes during embryonic development are controlled by factors of the immune system. We review here immunophenotypic expression patterns of  different stem cell types, including ESC, neural (NSC) and tissue-specific mesenchymal stem cells (MSC), and focus on immunodulatory properties of these cells. Immune and inflammatory responses, involving actions of cytokines as well as toll-like receptor (TLR) signaling are known to affect the differentiation capacity of NSC and MSC. Secretion of pro- and anti-inflammatory messengers by MSC have been observed as the consequence of TLR and cytokine activation and promotion of differentiation into specified phenotypes. As result of augmented differentiation capacity, stem cells secrete angiogenic factors including vascular endothelial growth factor, resulting in multifactorial actions in tissue repair. Immunoregulatory properties of tissue specific adult stem cells are put into the context of possible clinical applications.

What have we learned about the kallikrein-kinin and renin-angiotensin systems in neurological disorders?

The kallikrein-kinin system (KKS) is an intricate endogenous pathway involved in several physiological and pathological cascades in the brain. Due to the pathological effects of kinins in blood vessels and tissues, their formation and degradation are tightly controlled. Their components have been related to several central nervous system diseases such as stroke, Alzheimer’s disease, Parkinson’s disease, multiple sclerosis, epilepsy and others. Bradykinin and its receptors (B1R and B2R) may have a role in the pathophysiology of certain central nervous system diseases. It has been suggested that kinin B1R is up-regulated in pathological conditions and has a neurodegenerative pattern, while kinin B2R is constitutive and can act as a neuroprotective factor in many neurological conditions. The renin angiotensin system (RAS) is an important blood pressure regulator and controls both sodium and water intake. AngII is a potent vasoconstrictor molecule and angiotensin converting enzyme is the major enzyme responsible for its release. AngII acts mainly on the AT1 receptor, with involvement in several systemic and neurological disorders. Brain RAS has been associated with physiological pathways, but is also associated with brain disorders. This review describes topics relating to the involvement of both systems in several forms of brain dysfunction and indicates components of the KKS and RAS that have been used as targets in several pharmacological approaches.

Immune regulation of multiple sclerosis

Multiple sclerosis (MS) is considered a prototype inflammatory autoimmune disorder of the central nervous system (CNS). The etiology of this disease remains unknown, but an interplay between as yet unidentified environmental factors and susceptibility genes appears most likely. In consequence, these factors trigger a cascade, involving an inflammatory response within the CNS that results in demyelination, oligodendrocyte death, axonal damage, gliosis, and neurodegeneration. How these complex traits translate into the clinical presentation of the disease is a focus of ongoing research. The central hypothesis is that T lymphocytes with receptors for CNS myelin components are driving the disease. The initial activation of autoreactive lymphocytes is thought to take place in the systemic lymphoid organs, most likely through molecular mimickry or nonspecifically through bystander activation. These autoreactive lymphocytes can migrate to the CNS where they become reactivated upon encountering their target antigen, initiating an autoimmune inflammatory attack. This ultimately leads to demyelination and axonal damage. This chapter focuses on the role of T and B lymphocytes in the immunopathogenesis of MS.

Kinin-mediated inflammation in neurodegenerative disorders

The mediatory role of kinins in both acute and chronic inflammation within nervous tissues has been widely described. Bradykinin, the major representative of these bioactive peptides, is one of a few mediators of inflammation that directly stimulates afferent nerves due to the broad expression of specific kinin receptors in cell types in these tissues. Moreover, kinins may be delivered to a site of injury not only after their production at the endothelium surface but also following their local production through the enzymatic degradation of kininogens at the surface of nerve cells. A strong correlation between inflammatory processes and neurodegeneration has been established. The activation of nerve cells, particularly microglia, in response to injury, trauma or infection initiates a number of reactions in the neuronal neighborhood that can lead to cell death after the prolonged action of inflammatory substances. In recent years, there has been a growing interest in the effects of kinins on neuronal destruction. In these studies, the overexpression of proteins involved in kinin generation or of kinin receptors has been observed in several neurologic disorders including neurodegenerative diseases such Alzheimer's disease and multiple sclerosis as well as disorders associated with a deficiency in cell communication such as epilepsy. This review is focused on recent findings that provide reliable evidence of the mediatory role of kinins in the inflammatory responses associated with different neurological disorders. A deeper understanding of the role of kinins in neurodegenerative diseases is likely to promote the future development of new therapeutic strategies for the control of these disorders. An example of this could be the prospective use of kinin receptor antagonists.

Identification of a metallopeptidase with TOP-like activity in Paracoccidioides brasiliensis, with increased expression in a virulent strain

Paracoccidioidomycosis (PCM), caused by the pathogenic fungus Paracoccidioides brasiliensis, is a systemic mycosis with severe acute and chronic forms. The pathology of PCM is not completely understood, and the role of proteases in the infection is not clearly defined. In this report, we describe a metallopeptidase activity in P. brasiliensis total and cytosolic protein extracts similar to that of mammalian thimet oligopeptidase (TOP). The analogous enzyme was suggested by analysis of P. brasiliensis genome databank and by hydrolytic activity of the FRET peptide Abz-GFSPFRQ-EDDnp which was completely inhibited by o-phenanthrolin and significantly inhibited by the TOP inhibitor, JA-2. This activity was also partially inhibited by IgG purified from patients with PCM, but not from normal individuals. As shown by high-performance liquid chromatography (HPLC), the hydrolysis of bradykinin had the same pattern as that of mammalian TOP, and anti-mammalian TOP antibodies significantly inhibited fungal cytosolic peptidase activity. Moreover, anti-mammalian TOP antibodies recognized a component of 80 kDa on fungal cytosol. A P. brasiliensis virulent isolate showed higher gene expression and TOP-like peptidase activity than a non-virulent strain. The release of enzyme following fungal lysis would be consistent with host antibody production and may have a role in the pathogenesis, inflammation and further development of the mycosis.

Kinins in cardiac inflammation and regeneration: insights from ischemic and diabetic cardiomyopathy

The kallikrein-kinin system (KKS) is a system of vasoactive peptides, the kinins, involved in different aspects of remodeling, inflammation and angiogenesis. Kinins mediate their actions through two receptors, B1R and B2R. It is increasingly recognized that the KKS is involved in the inflammatory processes of the heart. Evidence shows that the B2R is beneficial in myocardial diseases, protecting from inflammation, fibrosis and apoptosis, while B1R shows a proinflammatory character contributing to the disease progression by increasing the production of cytokines and stimulating the migration of immune cells. Furthermore, novel important actions of the KKS and its receptors contribute to neovascularization and recruitment of endothelial progenitor cells in ischemic areas and endothelial dysfunction. The kinin receptors could therefore constitute potential therapeutic targets in the treatment of myocardial ischemia and diabetic cardiomyopathy.

Misfolded proteins activate factor XII in humans, leading to kallikrein formation without initiating coagulation

When blood is exposed to negatively charged surface materials such as glass, an enzymatic cascade known as the contact system becomes activated. This cascade is initiated by autoactivation of Factor XII and leads to both coagulation (via Factor XI) and an inflammatory response (via the kallikrein-kinin system). However, while Factor XII is important for coagulation in vitro, it is not important for physiological hemostasis, so the physiological role of the contact system remains elusive. Using patient blood samples and isolated proteins, we identified a novel class of Factor XII activators. Factor XII was activated by misfolded protein aggregates that formed by denaturation or by surface adsorption, which specifically led to the activation of the kallikrein-kinin system without inducing coagulation. Consistent with this, we found that Factor XII, but not Factor XI, was activated and kallikrein was formed in blood from patients with systemic amyloidosis, a disease marked by the accumulation and deposition of misfolded plasma proteins. These results show that the kallikrein-kinin system can be activated by Factor XII, in a process separate from the coagulation cascade, and point to a protective role for Factor XII following activation by misfolded protein aggregates.