Tissue kallikrein elicits cardioprotection by direct kinin b2 receptor activation independent of kinin formation

KLK8 modulates macrophage function following myocardial infarction by promoting the paracrine of epidermal growth factor from cardiac fibroblasts

AIMS

Tissue kallikrein-related peptidase 8 (KLK8) plays a significant role in the regulation of cardiac remodeling following myocardial infarction (MI). However, the impact of KLK8 on macrophage (MΦ) function in the context of MI remains to be elucidated.

MATERIALS AND METHODS

MI was induced through the ligation of the left anterior descending coronary artery for a duration of 1 h, followed by reperfusion. The morphological and molecular alterations in the heart were assessed at 24 h and 14 days post-ischemic injury. Adult rat cardiac fibroblasts and bone marrow-derived macrophages were employed to explore the underlying molecular mechanisms in vitro.

KEY FINDINGS

In the acute phase of MI (24 h post-MI), KLK8 was observed to diminish the inflammatory response and mitigate tissue damage within the ischemic ventricle. Conversely, during the reparative phase of MI (14 days post-MI), KLK8 was found to enhance the accumulation of the M2 MΦs, elevate pro-fibrotic factors, and intensify cardiac fibrosis. The in vitro analysis revealed that KLK8 did not exert a direct effect on MΦs; rather, it facilitated the paracrine secretion of epidermal growth factor (EGF) from the cardiac fibroblasts. This EGF may play a role in inhibiting the pro-inflammatory activation of the MΦs and promoting their polarization towards the M2 phenotype under conditions of inflammatory stress.

SIGNIFICANCE

In summary, KLK8 modulates MΦ function through the paracrine of EGF derived from cardiac fibroblasts, which may have implications for cardiac injury and remodeling following MI.

Tissue kallikrein-related peptidase8 accentuates cardiac fibrosis after myocardial ischemia-reperfusion injury via regulation of cardiac fibroblasts

AIMS

Tissue kallikrein-related peptidase8 (KLK8) has been found to mitigate acute myocardial ischemia-reperfusion (IR) injury. However, the effect of KLK8 on cardiac remodeling in response to IR injury has not been determined.

MATERIALS AND METHODS

KLK8 overexpressing transgenic rat (KLK8-TG) was used as the animal model. IR injury was induced by ligating the left anterior descending coronary artery for 1 h and subsequent reperfusion. The functional and morphological changes of the heart were examined 14 days after the injury. Neonatal rat cardiac fibroblasts (CFs) were used to investigate the molecular mechanisms in vitro.

KEY FINDINGS

KLK8 overexpression enhanced cardiac diastolic dysfunction, fibrosis, and hypertrophy after IR injury, indicating that KLK8 accentuated cardiac remodeling in response to IR injury. Moreover, KLK8 overexpression increased epidermal growth factor (EGF) release and promoted the phosphorylation of EGF receptor (EGFR) and ERK1/2 in the heart after IR injury. It was interesting to find that both EGFR antagonist (AG 1478) and MEK inhibitor (PD98059) attenuated the KLK8-induced proliferation and activation of CFs in vitro, indicating that EGFR signaling might mediate the pro-fibrotic action of KLK8.

SIGNIFICANCE

KLK8 plays a crucial role in cardiac remodeling after myocardial infarction. KLK8 accentuates cardiac fibrosis after IR injury, possibly mediated by EGFR signaling in CFs.

Sexual Dimorphism in the Expression of Cardiac and Hippocampal Renin-Angiotensin and Kallikrein–Kinin Systems in Offspring from Mice Exposed to Alcohol during Gestation

Prenatal alcohol exposure (PAE) impairs fetal development. Alcohol consumption was shown to modulate the renin–angiotensin system (RAS). This study aimed to analyze the effects of PAE on the expression of the renin–angiotensin system (RAS) and kallikrein–kinin system (KKS) peptide systems in the hippocampus and heart of mice of both sexes. C57Bl/6 mice were exposed to alcohol during pregnancy at a concentration of 10% (v/v). On postnatal day 45 (PN45), mouse hippocampi and left ventricles (LV) were collected and processed for messenger RNA (mRNA) expression of components of the RAS and KKS. In PAE animals, more pronounced expression of AT1 and ACE mRNAs in males and a restored AT2 mRNA expression in females were observed in both tissues. In LV, increased AT2, ACE2, and B2 mRNA expressions were also observed in PAE females. Furthermore, high levels of H2O2 were observed in males from the PAE group in both tissues. Taken together, our results suggest that modulation of the expression of these peptidergic systems in PAE females may make them less susceptible to the effects of alcohol.

Decreased Tissue Kallikrein Levels and the Risk of Ischemic Stroke: A Community-Based Cross-Sectional Study in China

Aim

Tissue kallikrein (TK) exerts protective effects on cardiac cerebrovascular diseases (CCVDs). Changes in TK level in plasma are associated with ischemic stroke and coronary artery disease (CAD); however, a causal correlation could not be established. Therefore, we investigated the association between TK levels and CCVDs in a community-based cross-sectional study in China.

Methods

A total of 6043 subjects (4242 men and 1801 women) were enrolled in this community-based cross-sectional study. Then, TK levels were measured using an enzyme-linked immunosorbent assay kit. Multivariate linear regression model and logistic regression were used to assess the correlations between TK levels and CCVDs. Subsequently, the receiver operating characteristic (ROC) curve was drawn to assess the value of TK level in evaluating the risk of ischemic stroke. Finally, the influence of various medications was evaluated on TK levels.

Results

The TK level was significantly lower in subjects with ischemic stroke (P < 0.001) and hypertension (P < 0.001) and negatively associated with ischemic stroke (P < 0.001) but not associated with hypertension, coronary heart disease, and diabetes compared to the traditional risk factors. The diagnostic accuracy for ischemic stroke, as quantified by the area under the curve, was 0.892 (95% CI, 0.884–0.900) for TK level, deeming it as a promising assessment tool. Moreover, no appreciable influence of various drugs therapy was found in TK levels (P = 0.222) except for those taking antilipemic agents.

Conclusion

TK is a strong and independent endogenous protective factor against ischemic stroke in the Chinese population and could be a promising biomarker for the risk of ischemic stroke.

Pretreatment of cardiac progenitor cells with bradykinin attenuates H2O2-induced cell apoptosis and improves cardiac function in rats by regulating autophagy

Background

Previous studies have demonstrated that human cardiac c-Kit⁺ progenitor cells (hCPCs) can effectively improve ischemic heart disease. However, the major challenge in applying hCPCs to clinical therapy is the low survival rate of graft hCPCs in the host heart, which limited the benefit of transplanted hCPCs. Bradykinin (BK) is a principal active agent of the tissue kinin-kallikrein system. Our previous studies have highlighted that BK mediated the growth and migration of CPCs by regulating Ca²⁺ influx. However, the protective effect of BK on CPCs, improvement in the survival rate of BK-pretreated hCPCs in the infarcted heart, and the related mechanism remain elusive.

Methods

HCPCs were treated with H₂O₂ to induce cell apoptosis and autophagy, and different concentration of BK was applied to rescue the H₂O₂-induced injury detected by MTT assay, TUNEL staining, flow cytometry, western blotting, and mitoSOX assays. The role of autophagy in the anti-apoptotic effect of BK was chemically activated or inhibited using the autophagy inducer, rapamycin, or the inhibitor, 3-methyladenine (3-MA). To explore the protective effect of BK on hCPCs, 3-MA or BK-pretreated hCPCs were transplanted into the myocardial infarcted rats. An echocardiogram was used to determine cardiac function, H&E and Masson staining were employed to assess pathological characteristics, HLA gene expression was quantified by qRT-PCR, and immunostaining was applied to examine neovascularization using confocal microscopy.

Results

The in vitro results showed that BK suppressed H₂O₂-induced hCPCs apoptosis and ROS production in a concentration-dependent manner by promoting pAkt and Bcl-2 expression and reducing cleaved caspase 3 and Bax expression. Moreover, BK restrained the H₂O₂-induced cell autophagy by decreasing LC3II/I, Beclin1, and ATG5 expression and increasing P62 expression. In the in vivo experiment, the transplanted BK- or 3-MA-treated hCPCs were found to be more effectively improved cardiac function by decreasing cardiomyocyte apoptosis, inflammatory infiltration, and myocardial fibrosis, and promoting neovascularization in the infarcted heart, compared to untreated-hCPCs or c-kit^- cardiomyocytes (CPC^- cells).

Conclusions

Our present study established a new method to rescue transplanted hCPCs in the infarcted cardiac area via regulating cell apoptosis and autophagy of hCPCs by pretreatment with BK, providing a new therapeutic option for heart failure.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02503-6.

The Rationale of Neprilysin Inhibition in Prevention of Myocardial Ischemia-Reperfusion Injury during ST-Elevation Myocardial Infarction

During the last three decades, timely myocardial reperfusion using either thrombolytic therapy or primary percutaneous intervention (pPCI) has allowed amazing improvements in outcomes with a more than halving in 1-year ST-elevation myocardial infarction (STEMI) mortality. However, mortality and left ventricle (LV) remodeling remain substantial in these patients. As such, novel therapeutic interventions are required to reduce myocardial infarction size, preserve LV systolic function, and improve survival in reperfused-STEMI patients. Myocardial ischemia-reperfusion injury (MIRI) prevention represents the main goal to reach in order to reduce STEMI mortality. There is currently no effective therapy for MIRI prevention in STEMI patients. A significant reason for the weak and inconsistent results obtained in this field may be the presence of multiple, partially redundant, mechanisms of cell death during ischemia-reperfusion, whose relative importance may depend on the conditions. Therefore, it is always more recognized that it is important to consider a "multi-targeted cardioprotective therapy", defined as an additive or synergistic cardioprotective agents or interventions directed to distinct targets with different timing of application (before, during, or after pPCI). Given that some neprilysin (NEP) substrates (natriuretic peptides, angiotensin II, bradykinin, apelins, substance P, and adrenomedullin) exert a cardioprotective effect against ischemia-reperfusion injury, it is conceivable that antagonism of proteolytic activity by this enzyme may be considered in a multi-targeted strategy for MIRI prevention. In this review, by starting from main pathophysiological mechanisms promoting MIRI, we discuss cardioprotective effects of NEP substrates and the potential benefit of NEP pharmacological inhibition in MIRI prevention.

Human tissue kallikrein in the treatment of acute ischemic stroke

Acute ischemic stroke (AIS) remains a major cause of death and disability throughout the world. The most severe form of stroke results from large vessel occlusion of the major branches of the Circle of Willis. The treatment strategies currently available in western countries for large vessel occlusion involve rapid restoration of blood flow through removal of the offending blood clot using mechanical or pharmacological means (e.g. tissue plasma activator; tPA). This review assesses prospects for a novel pharmacological approach to enhance the availability of the natural enzyme tissue kallikrein (KLK1), an important regulator of local blood flow. KLK1 is responsible for the generation of kinins (bradykinin and kallidin), which promote local vasodilation and long-term vascularization. Moreover, KLK1 has been used clinically as a direct treatment for multiple diseases associated with impaired local blood flow including AIS. A form of human KLK1 isolated from human urine is approved in the People's Republic of China for subacute treatment of AIS. Here we review the rationale for using KLK1 as an additional pharmacological treatment for AIS by providing the biochemical mechanism as well as the human clinical data that support this approach.

Bifunctional ligands of the bradykinin B2 and B1 receptors: An exercise in peptide hormone plasticity

Kinins are the small and fragile hydrophilic peptides related to bradykinin (BK) and derived from circulating kininogens via the action of kallikreins. Kinins bind to the preformed and widely distributed B₂ receptor (B₂R) and to the inducible B₁ receptor (B₁R). B₂Rs and B₁Rs are related G protein coupled receptors that possess natural agonist ligands of nanomolar affinity (BK and Lys BK for B₂Rs, Lys-des-Arg⁹-BK for B₁R). Decades of structure-activity exploration have resulted in the production of peptide analogs that are antagonists, one of which is clinically used (the B₂R antagonist icatibant), and also non-peptide ligands for both receptor subtypes. The modification of kinin receptor ligands has made them resistant to extracellular or endosomal peptidases and/or produced bifunctional ligands, defined as agonist or antagonist peptide ligands conjugated with a chemical fluorophore (emitting in the whole spectrum, from the infrared to the ultraviolet), a drug-like moiety, an epitope, an isotope chelator/carrier, a cleavable sequence (thus forming a pro-drug) and even a fused protein. Dual molecular targets for specific modified peptides may be a source of side effects or of medically exploitable benefits. Biotechnological protein ligands for either receptor subtype have been produced: they are enhanced green fluorescent protein or the engineered peroxidase APEX2 fused to an agonist kinin sequence at their C-terminal terminus. Antibodies endowed with pharmacological actions (agonist, antagonist) at B₂R have been reported, though not monoclonal antibodies. These findings define classes of alternative ligands of the kinin receptor of potential therapeutic and diagnostic value.

Therapeutic modulation of tissue kallikrein expression

The kallikrein kinin system has cardioprotective actions and mediates in part the cardioprotection produced by angiotensin converting enzyme inhibitors and angiotensin type 1 receptor blockers. Additional approaches to exploit the cardioprotective effects of the kallikrein kinin system include the administration of tissue kallikrein and kinin receptor agonists. The renin inhibitor aliskiren was recently shown to increase cardiac tissue kallikrein expression and bradykinin levels, and to reduce myocardial ischemia-reperfusion injury by bradykinin B2 receptor- and angiotensin AT2 receptor-mediated mechanisms. Thus, aliskiren represents a prototype drug for the modulation of tissue kallikrein expression for therapeutic benefit.

Moving Past Anti-VEGF: Novel Therapies for Treating Diabetic Retinopathy

Diabetic retinopathy is the leading cause of blindness in working age adults, and is projected to be a significant future health concern due to the rising incidence of diabetes. The recent advent of anti-vascular endothelial growth factor (VEGF) antibodies has revolutionized the treatment of diabetic retinopathy but a significant subset of patients fail to respond to treatment. Accumulating evidence indicates that inflammatory cytokines and chemokines other than VEGF may contribute to the disease process. The current review examines the presence of non-VEGF cytokines in the eyes of patients with diabetic retinopathy and highlights mechanistic pathways in relevant animal models. Finally, novel drug targets including components of the kinin-kallikrein system and emerging treatments such as anti-HPTP (human protein tyrosine phosphatase) β antibodies are discussed. Recognition of non-VEGF contributions to disease pathogenesis may lead to novel therapeutics to enhance existing treatments for patients who do not respond to anti-VEGF therapies.

Kallikrein-related peptidase 8 is expressed in myocardium and induces cardiac hypertrophy

The tissue kallikrein-related peptidase family (KLK) is a group of trypsin- and chymotrypsin-like serine proteases that share a similar homology to parent tissue kallikrein (KLK1). KLK1 is identified in heart and has anti-hypertrophic effects. However, whether other KLK family members play a role in regulating cardiac function remains unknown. In the present study, we demonstrated for the first time that KLK8 was expressed in myocardium. KLK8 expression was upregulated in left ventricle of cardiac hypertrophy models. Both intra-cardiac adenovirus-mediated and transgenic-mediated KLK8 overexpression led to cardiac hypertrophy in vivo. In primary neonatal rat cardiomyocytes, KLK8 knockdown inhibited phenylephrine (PE)-induced cardiomyocyte hypertrophy, whereas KLK8 overexpression promoted cardiomyocyte hypertrophy via a serine protease activity-dependent but kinin receptor-independent pathway. KLK8 overexpression increased epidermal growth factor (EGF) production, which was blocked by the inhibitors of serine protease. EGF receptor (EGFR) antagonist and EGFR knockdown reversed the hypertrophy induced by KLK8 overexpression. KLK8-induced cardiomyocyte hypertrophy was also significantly decreased by blocking the protease-activated receptor 1 (PAR1) or PAR2 pathway. Our data suggest that KLK8 may promote cardiomyocyte hypertrophy through EGF signaling- and PARs-dependent but a kinin receptor-independent pathway. It is implied that different KLK family members can subtly regulate cardiac function and remodeling.

Human Tissue Kallikrein Activity in Angiographically Documented Chronic Stable Coronary Artery Disease

Background

Human tissue kallikrein (hK1) is a key enzyme in the kallikrein–kinin system (KKS). hK1-specific amidase activity is reduced in urine samples from hypertensive and heart failure (HF) patients. The pathophysiologic role of hK1 in coronary artery disease (CAD) remains unclear.

Objective

To evaluate hK1-specific amidase activity in the urine of CAD patients

Methods

Sixty-five individuals (18–75 years) who underwent cardiac catheterism (CATH) were included. Random midstream urine samples were collected immediately before CATH. Patients were classified in two groups according to the presence of coronary lesions: CAD (43 patients) and non-CAD (22 patients). hK1 amidase activity was estimated using the chromogenic substrate D-Val-Leu-Arg-Nan. Creatinine was determined using Jaffé’s method. Urinary hK1-specific amidase activity was expressed as µM/(min · mg creatinine) to correct for differences in urine flow rates.

Results

Urinary hK1-specific amidase activity levels were similar between CAD [0.146 µM/(min ·mg creatinine)] and non-CAD [0.189 µM/(min . mg creatinine)] patients (p = 0.803) and remained similar to values previously reported for hypertensive patients [0.210 µM/(min . mg creatinine)] and HF patients [0.104 µM/(min . mg creatinine)]. CAD severity and hypertension were not observed to significantly affect urinary hK1-specific amidase activity.

Conclusion

CAD patients had low levels of urinary hK1-specific amidase activity, suggesting that renal KKS activity may be reduced in patients with this disease.

Human urine kininogenase attenuates balloon-induced intimal hyperplasia in rabbit carotid artery through transforming growth factor β1/Smad2/3 signaling pathway

OBJECTIVE

Effective treatments against restenosis after percutaneous transluminal angioplasty and stenting are largely lacking. Human tissue kallikrein gene transfer has been shown to be able to attenuate neointima formation induced by balloon catheter. As a tissue kallikrein in vivo, human urinary kininogenase (HUK) is widely used to prevent ischemia-reperfusion injury. However, the effects of HUK on neointima formation have not been explored. We therefore investigated whether HUK could alleviate balloon catheter-induced intimal hyperplasia in rabbits fed with high-fat diets.

METHODS

The effects of HUK on neointima and atherosclerosis formation were analyzed by hematoxylin-eosin staining and immunohistochemical staining in balloon-injured carotid arteries of rabbits. Local inflammatory response was evaluated by detecting the gene expression of tumor necrosis factor α and interleukin 1β with real-time quantitative polymerase chain reaction plus the invasion of macrophages with immunohistochemical staining. Western blotting was employed to investigate the effects of HUK on activities of endothelial nitric oxide synthase (eNOS), transforming growth factor β1 (TGF-β1), and Smad signaling pathway. The long-term effect of HUK on intimal hyperplasia of the injured carotid artery was assessed by angiography.

RESULTS

Quantitative image analysis showed that intravenous administration of HUK for 14 days significantly decreased the intimal areas and intima area/media area ratios (day 14, 54% decrease in intimal area and 58% decrease in intima area/media area ratios; day 28, 63% and 85%). Significant decreases were also noted in macrophage foam cell-positive area after 7-day or 14-day administration of HUK (day 7, 69% decrease in intimal area and 78% decrease in media area; day 14, 79% and 60%; day 28, 68% and 44%). Actin staining for smooth muscle cells in neointima at 2 months showed similar results (vascular smooth muscle cell-positive area of neointima, 28.21% ± 5.58% vs 43.78% ± 8.36%; P < .05). Real-time quantitative polymerase chain reaction or Western blot analysis showed that HUK reduced expression of tumor necrosis factor α, interleukin 1β, TGF-β1, and p-Smad2/3 but increased the expression of p-eNOS. Angiography analysis showed that 14-day administration of HUK significantly decreased the degree of stenosis (26.8% ± 7.1% vs 47.9% ± 5.7%; P < .01) at 2 months after balloon injury.

CONCLUSIONS

Our results indicate that HUK is able to attenuate atherosclerosis formation and to inhibit intimal hyperplasia by downregulating TGF-β1 expression and Smad2/3 phosphorylation, upregulating eNOS activity. HUK may be a potential therapeutic agent to prevent stenosis after vascular injury.

Activation of membrane-bound proteins and receptor systems: a link between tissue kallikrein and the KLK-related peptidases

The 15 members of the kallikrein-related serine peptidase (KLK) family have diverse tissue-specific expression profiles and roles in a range of cellular processes, including proliferation, migration, invasion, differentiation, inflammation and angiogenesis that are required in both normal physiology as well as pathological conditions. These roles require cleavage of a range of substrates, including extracellular matrix proteins, growth factors, cytokines as well as other proteinases. In addition, it has been clear since the earliest days of KLK research that cleavage of cell surface substrates is also essential in a range of KLK-mediated cellular processes where these peptidases are essentially acting as agonists and antagonists. In this review we focus on these KLK-regulated cell surface receptor systems including bradykinin receptors, proteinase-activated receptors, as well as the plasminogen activator, ephrins and their receptors, and hepatocyte growth factor/Met receptor systems and other plasma membrane proteins. From this analysis it is clear that in many physiological and pathological settings KLKs have the potential to regulate multiple receptor systems simultaneously; an important issue when these peptidases and substrates are targeted in disease.

Tissue kallikrein is required for the cardioprotective effect of cyclosporin A in myocardial ischemia in the mouse

Clinical and experimental studies suggest that pharmacological postconditioning with Cyclosporin A (CsA) reduces infarct size in cardiac ischemia and reperfusion. CsA interacts with Cyclophilin D (CypD) preventing opening of the mitochondrial permeability transition pore (mPTP). Tissue kallikrein (TK) and its products kinins are involved in cardioprotection in ischemia. CypD knockout mice are resistant to the cardioprotective effects of both CsA and kinins suggesting common mechanisms of action. Using TK gene knockout mice, we investigated whether the kallikrein-kinin system is involved in the cardioprotective effect of CsA. Homozygote and heterozygote TK deficient mice (TK(-/-), TK(+/-)) and wild type littermates (TK(+/+)) were subjected to cardiac ischemia-reperfusion with and without CsA postconditioning. CsA reduced infarct size in TK(+/+) mice but had no effect in TK(+/-) and TK(-/-) mice. Cardiac mitochondria isolated from TK(-/-) mice had indistinguishable basal oxidative phosphorylation and calcium retention capacity compared to TK(+/+) mice but were resistant to CsA inhibition of mPTP opening. TK activity was documented in mouse heart and rat cardiomyoblasts mitochondria. By proximity ligation assay TK was found in close proximity to the mitochondrial membrane proteins VDAC and Tom22, and CypD. Thus, partial or total deficiency in TK induces resistance to the infarct size reducing effect of CsA in cardiac ischemia in mice, suggesting that TK level is a critical factor for cardioprotection by CsA. TK is required for the mitochondrial action of CsA and may interact with CypD. Genetic variability in TK activity has been documented in man and may influence the cardioprotective effect of CsA.

Pharmacological effects of recombinant human tissue kallikrein on bradykinin B2 receptors

Tissue kallikrein (KLK-1), a serine protease, initiates the release of bradykinin (BK)-related peptides from low-molecular weight kininogen. KLK-1 and the BK B₂ receptor (B₂R) mediate beneficial effects on the progression of type 2 diabetes and renal disease, but the precise role of KLK-1 independent of its kinin-forming activity remains unclear. We used DM199, a recombinant form of human KLK-1, along with the isolated human umbilical vein, a robust bioassay of the B₂R, to address the previous claims that KLK-1 directly binds to and activates the human B₂R, with possible receptor cleavage. DM199 (1–10 nmol/L) contracted the isolated vein via the B₂R, but in a tachyphylactic, kinin-dependent manner, without desensitization of the tissue to exogenously added BK. In binding experiments with recombinant N-terminally tagged myc-B₂Rs expressed in HEK 293a cells, DM199 displaced [³H]BK binding from the rabbit myc-B₂R, but not from the human or rat myc-B₂Rs. No evidence of myc-B₂R degradation by immunoblot analysis was apparent following treatment of these 3 myc-B₂R constructs with DM199 (30 min, ≤10 nmol/L). In HEK 293 cells stably expressing rabbit B₂R-GFP, DM199 (11–108 pmol/L) elicited signaling-dependent endocytosis and reexpression, while a higher concentration (1.1 nmol/L) induced a partially irreversible endocytosis of the construct (microscopy), paralleled by the appearance of free GFP in cells (immunoblotting, indicative of incomplete receptor down-regulation). The pharmacology of DM199 at relevant concentrations (<10 nmol/L) is essentially based on the activity of locally generated kinins. Binding to and mild down-regulation of the B₂R is possibly a species-dependent idiosyncratic response to DM199.

Autoimmune diabetes is suppressed by treatment with recombinant human tissue Kallikrein-1

The kallikrein-kinin system (KKS) comprises a cascade of proteolytic enzymes and biogenic peptides that regulate several physiological processes. Over-expression of tissue kallikrein-1 and modulation of the KKS shows beneficial effects on insulin sensitivity and other parameters relevant to type 2 diabetes mellitus. However, much less is known about the role of kallikreins, in particular tissue kallikrein-1, in type 1 diabetes mellitus (T1D). We report that chronic administration of recombinant human tissue kallikrein-1 protein (DM199) to non-obese diabetic mice delayed the onset of T1D, attenuated the degree of insulitis, and improved pancreatic beta cell mass in a dose- and treatment frequency-dependent manner. Suppression of the autoimmune reaction against pancreatic beta cells was evidenced by a reduction in the relative numbers of infiltrating cytotoxic lymphocytes and an increase in the relative numbers of regulatory T cells in the pancreas and pancreatic lymph nodes. These effects may be due in part to a DM199 treatment-dependent increase in active TGF-beta1. Treatment with DM199 also resulted in elevated C-peptide levels, elevated glucagon like peptide-1 levels and a reduction in dipeptidyl peptidase-4 activity. Overall, the data suggest that DM199 may have a beneficial effect on T1D by attenuating the autoimmune reaction and improving beta cell health.

Novel role of kallistatin in vascular repair by promoting mobility, viability, and function of endothelial progenitor cells

Background

Kallistatin exerts pleiotropic activities in inhibiting inflammation, apoptosis, and oxidative stress in endothelial cells. Because endothelial progenitor cells (EPCs) play a significant role in vascular repair, we investigated whether kallistatin contributes to vascular regeneration by enhancing EPC migration and function.

Methods and Results

We examined the effect of endogenous kallistatin on circulating EPCs in a rat model of vascular injury and the mechanisms of kallistatin on EPC mobility and function in vitro. In deoxycorticosterone acetate–salt hypertensive rats, we found that kallistatin depletion augmented glomerular endothelial cell loss and diminished circulating EPC number, whereas kallistatin gene delivery increased EPC levels. In cultured EPCs, kallistatin significantly reduced tumor necrosis factor‐α–induced apoptosis and caspase‐3 activity, but kallistatin's effects were blocked by phosphoinositide 3‐kinase inhibitor (LY294002) and nitric oxide (NO) synthase inhibitor (l‐NAME). Kallistatin stimulated the proliferation, migration, adhesion and tube formation of EPCs; however, kallistatin's actions were abolished by LY294002, l‐NAME, endothelial NO synthase–small interfering RNA, constitutively active glycogen synthase kinase‐3β, or vascular endothelial growth factor antibody. Kallistatin also increased Akt, glycogen synthase kinase‐3β, and endothelial NO synthase phosphorylation; endothelial NO synthase, vascular endothelial growth factor, and matrix metalloproteinase‐2 synthesis and activity; and NO and vascular endothelial growth factor levels. Kallistatin's actions on phosphoinositide 3‐kinase–Akt signaling were blocked by LY294002, l‐NAME, and anti–vascular endothelial growth factor antibody.

Conclusions

Endogenous kallistatin plays a novel role in protection against vascular injury in hypertensive rats by promoting the mobility, viability, and vasculogenic capacity of EPCs via enhancing NO and vascular endothelial growth factor levels through activation of phosphoinositide 3‐kinase–Akt signaling. Kallistatin therapy may be a promising approach in the treatment of vascular diseases.

Preclinical characterization of recombinant human tissue kallikrein-1 as a novel treatment for type 2 diabetes mellitus

Modulation of the kallikrein-kinin system (KKS) has been shown to have beneficial effects on glucose homeostasis and several other physiological responses relevant to the progression of type 2 diabetes mellitus (T2D). The importance of bradykinin and its receptors in mediating these responses is well documented, but the role of tissue kallikrein-1, the protease that generates bradykinin insitu, is much less understood. We developed and tested DM199, recombinant human tissue kallikrein-1 protein (rhKLK-1), as a potential novel therapeutic for T2D. Hyperinsulinemic-euglycemic clamp studies suggest that DM199 increases whole body glucose disposal in non-diabetic rats. Single-dose administration of DM199 in obese db/db mice and ZDF rats, showed an acute, dose-dependent improvement in whole-body glucose utilization. Sub-acute dosing for a week in ZDF rats improved glucose utilization, with a concomitant rise in fasting insulin levels and HOMA1-%B scores. After cessation of sub-acute dosing, fasting blood glucose levels were significantly lower in ZDF rats during a drug wash-out period. Our studies show for the first time that DM199 administration results in acute anti-hyperglycemic effects in several preclinical models, and demonstrate the potential for further development of DM199 as a novel therapeutic for T2D.

Bradykinin-forming components in Kuwaiti patients with type 2 diabetes

Diabetes is the most common risk factor in inducing hypertension, nephropathy and retinopathy. The bradykinin (BK)-forming system has been proposed to protect cardiovascular and renal functions. We therefore evaluated urinary active and proactive kallikrein, total kininogen, plasma tissue kallikrein, plasma creatinine, plasma glucose and plasma HbA1c in newly diagnosed untreated type 2 diabetic patients and healthy subjects. In diabetic patients, urinary and plasma tissue kallikrein concentrations were significantly increased. In addition, plasma prekallikrein levels were also significantly higher. However, urinary kininogen values were significantly reduced in diabetic patients when compared with healthy subjects. This is the first investigation among Kuwaiti Arab patients with type 2 diabetes showing abnormal activities in the BK-forming system. High levels of plasma prekallikrein may be a risk factor for developing high blood pressure as well as nephropathy. The urinary and plasma tissue kallikrein concentrations were higher in diabetic patients, which could indicate the hyperactivities of these components, and may result in increased levels of plasma glucose to induce diabetes. Furthermore, the urinary kininogen levels were reduced in diabetic patients. These alterations might reflect the utilization of urinary kininogen to form BK, a potent inflammatory agent. However, this hypothesis needs further investigation.

Exercise training can prevent cardiac hypertrophy induced by sympathetic hyperactivity with modulation of kallikrein-kinin pathway and angiogenesis

Sympathetic hyperactivity induces adverse effects in myocardial. Recent studies have shown that exercise training induces cardioprotection against sympathetic overload; however, relevant mechanisms of this issue remain unclear. We analyzed whether exercise can prevent pathological hypertrophy induced by sympathetic hyperactivity with modulation of the kallikrein-kinin and angiogenesis pathways. Male Wistar rats were assigned to non-trained group that received vehicle; non-trained isoproterenol treated group (Iso, 0.3 mg kg(-1) day-(1)); and trained group (Iso+Exe) which was subjected to sympathetic hyperactivity with isoproterenol. The Iso rats showed hypertrophy and myocardial dysfunction with reduced force development and relaxation of muscle. The isoproterenol induced severe fibrosis, apoptosis and reduced myocardial capillary. Interestingly, exercise blunted hypertrophy, myocardial dysfunction, fibrosis, apoptosis and capillary decreases. The sympathetic hyperactivity was associated with high abundance of ANF mRNA and β-MHC mRNA, which was significantly attenuated by exercise. The tissue kallikrein was augmented in the Iso+Exe group, and kinin B1 receptor mRNA was increased in the Iso group. Moreover, exercise induced an increase of kinin B2 receptor mRNA in myocardial. The myocardial content of eNOS, VEGF, VEGF receptor 2, pAkt and Bcl-2 were increased in the Iso+Exe group. Likewise, increased expression of pro-apoptotic Bad in the Iso rats was prevented by prior exercise. Our results represent the first demonstration that exercise can modulate kallikrein-kinin and angiogenesis pathways in the myocardial on sympathetic hyperactivity. These findings suggest that kallikrein-kinin and angiogenesis may have a key role in protecting the heart.

Tissue kallikrein mediates pro-inflammatory pathways and activation of protease-activated receptor-4 in proximal tubular epithelial cells

Tissue kallikrein (KLK1) expression is up-regulated in human diabetic kidney tissue and induced by high glucose (HG) in human proximal tubular epithelial cells (PTEC). Since the kallikrein-kinin system (KKS) has been linked to cellular inflammatory process in many diseases, it is likely that KLK1 expression may mediate the inflammatory process during the development of diabetic nephropathy. In this study, we explored the role of KLK1 in tubular pro-inflammatory responses under the diabetic milieu. Recombinant KLK1 stimulated the production of inflammatory cytokines in PTEC via the activation of p42/44 and p38 MAPK signaling pathways. Molecular knockdown of endogenous KLK1 expression by siRNA transfection in PTEC attenuated advanced glycation end-products (AGE)-induced IL-8 and ICAM-1 productions in vitro. Interestingly, exposure of PTEC to KLK1 induced the expression of protease-activated receptors (PARs). There was a 2.9-fold increase in PAR-4, 1.4-fold increase in PAR-1 and 1.2-fold increase in PAR-2 mRNA levels. Activation of PAR-4 by a selective agonist was found to elicit the pro-inflammatory and pro-fibrotic phenotypes in PTEC while blockade of the receptor by specific antagonist attenuated high glucose-induced IL-6, CCL-2, CTGF and collagen IV expression. Calcium mobilization by the PAR-4 agonist in PTEC was desensitized by pretreatment with KLK1. Consistent with these in vitro findings, there was a markedly up-regulation of tubular PAR-4 expression in human diabetic renal cortical tissues. Together, these results suggest that up-regulation of KLK1 in tubular epithelial cells may mediate pro-inflammatory pathway and PAR activation during diabetic nephropathy and provide a new therapeutic target for further investigation.

Tissue kallikrein-kinin therapy in hypertension and organ damage

Tissue kallikrein is a serine proteinase that cleaves low molecular weight kininogen to produce kinin peptides, which in turn activate kinin receptors to trigger multiple biological functions. In addition to its kinin-releasing activity, tissue kallikrein directly interacts with the kinin B2 receptor, protease-activated receptor-1, and gamma-epithelial Na channel. The tissue kallikrein-kinin system (KKS) elicits a wide spectrum of biological activities, including reducing hypertension, cardiac and renal damage, restenosis, ischemic stroke, and skin wound injury. Both loss-of-function and gain-of-function studies have shown that the KKS plays an important endogenous role in the protection against health pathologies. Tissue kallikrein/kinin treatment attenuates cardiovascular, renal, and brain injury by inhibiting oxidative stress, apoptosis, inflammation, hypertrophy, and fibrosis and promoting angiogenesis and neurogenesis. Approaches that augment tissue kallikrein-kinin activity might provide an effective strategy for the treatment of hypertension and associated organ damage.

Genetic manipulation and genetic variation of the kallikrein-kinin system: impact on cardiovascular and renal diseases

Genetic manipulation of the kallikrein-kinin system (KKS) in mice, with either gain or loss of function, and study of human genetic variability in KKS components which has been well documented at the phenotypic and genomic level, have allowed recognizing the physiological role of KKS in health and in disease. This role has been especially documented in the cardiovascular system and the kidney. Kinins are produced at slow rate in most organs in resting condition and/or inactivated quickly. Yet the KKS is involved in arterial function and in renal tubular function. In several pathological situations, kinin production increases, kinin receptor synthesis is upregulated, and kinins play an important role, whether beneficial or detrimental, in disease outcome. In the setting of ischemic, diabetic or hemodynamic aggression, kinin release by tissue kallikrein protects against organ damage, through B2 and/or B1 bradykinin receptor activation, depending on organ and disease. This has been well documented for the ischemic or diabetic heart, kidney and skeletal muscle, where KKS activity reduces oxidative stress, limits necrosis or fibrosis and promotes angiogenesis. On the other hand, in some pathological situations where plasma prekallikrein is inappropriately activated, excess kinin release in local or systemic circulation is detrimental, through oedema or hypotension. Putative therapeutic application of these clinical and experimental findings through current pharmacological development is discussed in the chapter.

The kallikrein-kinin system in experimental Chagas disease: a paradigm to investigate the impact of inflammatory edema on GPCR-mediated pathways of host cell invasion by Trypanosoma cruzi

Chronic chagasic myocarditis (CCM) depends on Trypanosoma cruzi persistence in the myocardium. Studies of the proteolytic mechanisms governing host/parasite balance in peripheral sites of T. cruzi infection revealed that tissue culture trypomastigotes (TCTs) elicit inflammatory edema and stimulate protective type-1 effector T cells through the activation of the kallikrein-kinin system. Molecular studies linked the proinflammatory phenotype of Dm28c TCTs to the synergistic activities of tGPI, a lipid anchor that functions as a Toll-like receptor 2 (TLR2) ligand, and cruzipain, a kinin-releasing cysteine protease. Analysis of the dynamics of inflammation revealed that TCTs activate innate sentinel cells via TLR2, releasing CXC chemokines, which in turn evoke neutrophil/CXCR2-dependent extravasation of plasma proteins, including high molecular weight kininogen (HK), in parasite-laden tissues. Further downstream, TCTs process surface bound HK, liberating lysyl-BK (LBK), which then propagates inflammatory edema via signaling of endothelial G-protein-coupled bradykinin B₂ receptors (BK₂R). Dm28 TCTs take advantage of the transient availability of infection-promoting peptides (e.g., bradykinin and endothelins) in inflamed tissues to invade cardiovascular cells via interdependent signaling of BKRs and endothelin receptors (ETRs). Herein we present a space-filling model whereby ceramide-enriched endocytic vesicles generated by the sphingomyelinase pathway might incorporate BK₂R and ETRs, which then trigger Ca²⁺-driven responses that optimize the housekeeping mechanism of plasma membrane repair from cell wounding. The hypothesis predicts that the NF-κB-inducible BKR (BK₁R) may integrate the multimolecular signaling platforms forged by ceramide rafts, as the chronic myocarditis progresses. Exploited as gateways for parasite invasion, BK₂R, BK₁R, ET_AR, ET_BR, and other G protein-coupled receptor partners may enable persistent myocardial parasitism in the edematous tissues at expense of adverse cardiac remodeling.

Plasma tissue kallikrein level is negatively associated with incident and recurrent stroke: a multicenter case-control study in China

OBJECTIVE

Tissue kallikrein (TK) cleaves kininogen to produce the potent bioactive compounds kinin and bradykinin, which lower blood pressure and protect the heart, kidneys, and blood vessels. Reduction in TK levels is associated with cardiovascular disease and diabetes in animal models. In this study, we investigated the association of TK levels with event-free survival over 5 years in Chinese first-ever stroke patients.

METHODS

We conducted a case-control study with 1,268 stroke patients (941 cerebral infarction, 327 cerebral hemorrhage) and 1,210 controls. Plasma TK levels were measured with an enzyme-linked immunosorbent assay. We used logistic regression and Cox proportional hazards models to assess the relationship between TK levels and risk of first-time or recurrent stroke.

RESULTS

Plasma TK levels were significantly lower in stroke patients (0.163 ± 0.064mg/l vs 0.252 ± 0.093mg/l, p < 0.001), especially those with ischemic stroke. After adjustment for traditional risk factors, plasma TK levels were negatively associated with the risk of first-ever stroke (odds ratio [OR], 0.344; 95% confidence interval [CI], 0.30-0.389; p < 0.001) and stroke recurrence and positively associated with event-free survival during 5 years of follow-up (relative risk, 0.82; 95% CI, 0.74-0.90; p < 0.001). Compared with the first quartile of plasma TK levels, the ORs for first-ever stroke patients were as follows: second quartile, 0.77 (95% CI, 0.56-1.07); third quartile, 0.23 (95% CI, 0.17-0.32); fourth quartile, 0.04 (95% CI, 0.03-0.06).

INTERPRETATION

Lower plasma TK levels are independently associated with first-ever stroke and are an independent predictor of recurrence after an initial stroke.

Tissue kallikrein promotes prostate cancer cell migration and invasion via a protease-activated receptor-1-dependent signaling pathway

We recently demonstrated that tissue kallikrein (TK) promotes keratinocyte migration through activation of protease-activated receptor-1 (PAR(1)) and transactivation of the epi-dermal growth factor receptor (EGFR). In this study, we investigated the potential role of PAR(1) in mediating the effect of TK on cancer cell migration, invasion and proliferation. Our results show that TK promotes DU145 prostate cancer cell migration in a concentration-dependent manner, but has no effect on A549 lung cancer cells. Active TK markedly increases DU145 cell migration and invasion, which are blocked by aprotinin but minimally affected by icatibant; kinin treatment has little effect. TK-induced cell migration and invasion are abolished by inhibition of PAR(1) using a pharmacological inhibitor or RNA interference. The effect of TK on cell migration and invasion are also blocked by inhibitors of protein kinase C, c-Src, matrix metalloproteinase, EGFR and extracellular signal-regulated kinase (ERK). Moreover, TK stimulates ERK phosphorylation, which is inhibited by an EGFR antagonist. Additionally, TK but not kinin stimulates DU145 cell proliferation through activation of the kinin B2 receptor, but not PAR(1) and EGFR. These results indicate differential signaling pathways mediated by TK in promoting prostate cancer cell migration and invasion via PAR(1) activation, and proliferation via kinin B2 receptor stimulation.

Tissue kallikrein is essential for invasive capacity of circulating proangiogenic cells

RATIONALE

Homing of proangiogenic cells (PACs) is guided by chemoattractants and requires proteases to disrupt the extracellular matrix. The possibility that PAC recruitment involves an interaction between proteases and chemotactic factor receptors remains largely unexplored.

OBJECTIVE

To determine the role of human tissue kallikrein (hK1) in PAC invasion and its dependency on kinin receptor signaling.

METHODS AND RESULTS

Human mononuclear cells (MNCs) and culture-selected PACs express and release mature hK1 protein. HK1 gene (KLK1) silencing reduced PACs migratory, invasive, and proangiogenic activities. KLK1-knockout mouse bone marrow-derived MNCs showed similar impairments and were unable to support reparative angiogenesis in a mouse model of peripheral ischemia. Conversely, adenovirus-mediated KLK1 (Ad.KLK1) gene transfer enhanced PAC-associated functions, whereas the catalytically inactive variant R53H-KLK1 was ineffective. HK1-induced effects are mediated by a kinin B(2) receptor (B(2)R)-dependent mechanism involving inducible nitric oxide synthase and metalloproteinase-2 (MMP2). Lower hK1 protein levels were observed in PACs from type 2 diabetic (T2D) patients, whereas KLK1 mRNA levels were similar to those of healthy subjects, suggesting a post-transcriptional defect. Furthermore, B(2)R is normally expressed on T2D-PACs but remains uncoupled from downstream signaling. Importantly, whereas Ad.KLK1 alone could not restore T2D-PAC invasion capacity, combined KLK1 and B(2)R expression rescued the diabetic phenotype.

CONCLUSIONS

This study reveals new interactive components of the PACs invasive machinery, acting via protease- and kinin receptor-dependent mechanisms.

Kinin B1 receptor enhances the oxidative stress in a rat model of insulin resistance: outcome in hypertension, allodynia and metabolic complications

Background

Kinin B₁ receptor (B₁R) is induced by the oxidative stress in models of diabetes mellitus. This study aims at determining whether B₁R activation could perpetuate the oxidative stress which leads to diabetic complications.

Methods and Findings

Young Sprague-Dawley rats were fed with 10% D-Glucose or tap water (controls) for 8–12 weeks. A selective B₁R antagonist (SSR240612) was administered acutely (3–30 mg/kg) or daily for a period of 7 days (10 mg/kg) and the impact was measured on systolic blood pressure, allodynia, protein and/or mRNA B₁R expression, aortic superoxide anion (O₂^•−) production and expression of superoxide dismutase (MnSOD) and catalase. SSR240612 reduced dose-dependently (3–30 mg/kg) high blood pressure in 12-week glucose-fed rats, but had no effect in controls. Eight-week glucose-fed rats exhibited insulin resistance (HOMA index), hypertension, tactile and cold allodynia and significant increases of plasma levels of glucose and insulin. This was associated with higher aortic levels of O₂^•−, NADPH oxidase activity, MnSOD and catalase expression. All these abnormalities including B₁R overexpression (spinal cord, aorta, liver and gastrocnemius muscle) were normalized by the prolonged treatment with SSR240612. The production of O₂^•− in the aorta of glucose-fed rats was also measured in the presence and absence of inhibitors (10–100 µM) of NADPH oxidase (apocynin), xanthine oxidase (allopurinol) or nitric oxide synthase (L-NAME) with and without Sar[D-Phe⁸]des-Arg⁹-BK (20 µM; B₁R agonist). Data show that the greater aortic O₂^•− production induced by the B₁R agonist was blocked only by apocynin.

Conclusions

Activation of kinin B₁R increased O₂^•− through the activation of NADPH oxidase in the vasculature. Prolonged blockade of B₁R restored cardiovascular, sensory and metabolic abnormalities by reducing oxidative stress and B₁R gene expression in this model.

Kallistatin attenuates endothelial apoptosis through inhibition of oxidative stress and activation of Akt-eNOS signaling

Kallistatin is a regulator of vascular homeostasis capable of controlling a wide spectrum of biological actions in the cardiovascular and renal systems. We previously reported that kallistatin inhibited intracellular reactive oxygen species formation in cultured cardiac and renal cells. The present study was aimed to investigate the role and mechanisms of kallistatin in protection against oxidative stress-induced vascular injury and endothelial cell apoptosis. We found that kallistatin gene delivery significantly attenuated aortic superoxide formation and glomerular capillary loss in hypertensive DOCA-salt rats. In cultured endothelial cells, kallistatin suppressed TNF-α-induced cellular apoptosis, and the effect was blocked by the pharmacological inhibition of phosphatidylinositol 3-kinase and nitric oxide synthase (NOS) and by the knockdown of endothelial NOS (eNOS) expression. The transduction of endothelial cells with adenovirus expressing dominant-negative Akt abolished the protective effect of kallistatin on endothelial apoptosis and caspase activity. In addition, kallistatin inhibited TNF-α-induced reactive oxygen species formation and NADPH oxidase activity, and these effects were attenuated by phosphatidylinositol 3-kinase and NOS inhibition. Kallistatin also prevented the induction of Bim protein and mRNA expression by oxidative stress. Moreover, the downregulation of forkhead box O 1 (FOXO1) and Bim expression suppressed TNF-α-mediated endothelial cell death. Furthermore, the antiapoptotic actions of kallistatin were accompanied by Akt-mediated FOXO1 and eNOS phosphorylation, as well as increased NOS activity. These findings indicate a novel role of kallistatin in the protection against vascular injury and oxidative stress-induced endothelial apoptosis via the activation of Akt-dependent eNOS signaling.

Loss of bradykinin signaling does not accelerate the development of cardiac dysfunction in type 1 diabetic akita mice

Bradykinin signaling has been proposed to play either protective or deleterious roles in the development of cardiac dysfunction in response to various pathological stimuli. To further define the role of bradykinin signaling in the diabetic heart, we examined cardiac function in mice with genetic ablation of both bradykinin B1 and B2 receptors (B1RB2R(-/-)) in the context of the Akita model of insulin-deficient type 1 diabetes (Ins2(Akita/+)). In 5-month-old diabetic and nondiabetic, wild-type and B1RB2R(-/-) mice, in vivo cardiac contractile function was determined by left-ventricular (LV) catheterization and echocardiography. Reactive oxygen species levels were measured by 2'-7'-dichlorofluorescein diacetate fluorescence. Mitochondrial function and ATP synthesis were determined in saponin-permeabilized cardiac fibers. LV systolic pressure and the peak rate of LV pressure rise and decline were decreased with diabetes but did not deteriorate further with loss of bradykinin signaling. Wall thinning and reduced ejection fractions in Akita mouse hearts were partially attenuated by B1RB2R deficiency, although other parameters of LV function were unaffected. Loss of bradykinin signaling did not increase fibrosis in Ins2(Akita/+) diabetic mouse hearts. Mitochondrial dysfunction was not exacerbated by B1RB2R deficiency, nor was there any additional increase in tissue levels of reactive oxygen species. Thus, loss of bradykinin B2 receptor signaling does not abrogate the previously reported beneficial effect of inhibition of B1 receptor signaling. In conclusion, complete loss of bradykinin expression does not worsen cardiac function or increase myocardial fibrosis in diabetes.

Tissue kallikrein in cardiovascular, cerebrovascular and renal diseases and skin wound healing

Tissue kallikrein (KLK1) processes low-molecular weight kininogen to produce vasoactive kinins, which exert biological functions via kinin receptor signaling. Using various delivery approaches, we have demonstrated that tissue kallikrein through kinin B2 receptor signaling exhibits a wide spectrum of beneficial effects by reducing cardiac and renal injuries, restenosis and ischemic stroke, and by promoting angiogenesis and skin wound healing, independent of blood pressure reduction. Protection by tissue kallikrein in oxidative organ damage is attributed to the inhibition of apoptosis, inflammation, hypertrophy and fibrosis. Tissue kallikrein also enhances neovascularization in ischemic heart and limb. Moreover, tissue kallikrein/kinin infusion not only prevents but also reverses kidney injury, inflammation and fibrosis in salt-induced hypertensive rats. Furthermore, there is a wide time window for kallikrein administration in protection against ischemic brain infarction, as delayed kallikrein infusion for 24 h after cerebral ischemia in rats is effective in reducing neurological deficits, infarct size, apoptosis and inflammation. Importantly, in the clinical setting, human tissue kallikrein has been proven to be effective in the treatment of patients with acute brain infarction when injected within 48 h after stroke onset. Finally, kallikrein promotes skin wound healing and keratinocyte migration by direct activation of protease-activated receptor 1.

Human urinary kallidinogenase suppresses cerebral inflammation in experimental stroke and downregulates nuclear factor-kappaB

The purpose of this study is to investigate the possible mechanism and the neuroprotective effect of human urinary kallidinogenase (HUK) in cerebral ischemia. The mouse middle cerebral artery occlusion (MCAO) model was used. Mice were treated with HUK (20 PNAU/g per day, intravenous) or saline as control, from the beginning of reperfusion to 72 h. Neurological deficits, infarct size, and BWC were measured at 6, 24, 48, and 72 h after MCAO, respectively. Pathological changes of brain were observed by TUNEL assay. Inflammatory factors were measured by real-time PCR and western blotting. Activation of MAPKs, Akt, and nuclear factor-kappaB (NF-kappaB) was detected by western blotting. Our results indicated that HUK significantly improved neurofunction, decreased infarct size, and suppressed edema, as well as inflammatory mediators as compared with the vehicle group. Furthermore, HUK inhibited the NF-kappaB pathway and activated the MAPK/ERK pathway in this neuroprotection.

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.

Blockade of endogenous tissue kallikrein aggravates renal injury by enhancing oxidative stress and inhibiting matrix degradation

Levels of tissue kallikrein (TK) are significantly lower in the urine of patients with kidney failure, and TK expression is specifically diminished in rat kidney after recovery from ischemia-reperfusion injury. In this study, we investigated the functional consequence of blocking endogenous TK activity in a rat model of chronic kidney disease. Inhibition of endogenous TK levels for 10 days by neutralizing TK antibody injection in DOCA-salt rats caused a significant increase in blood urea nitrogen and urinary protein levels, and a decrease in creatinine clearance. Kidney sections from anti-TK antibody-treated rats displayed a marked rise in tubular dilation and protein cast accumulation as well as glomerular sclerosis and size. TK blockade also increased inflammatory cell infiltration, myofibroblast and collagen accumulation, and collagen fraction volume. Elevated renal inflammation and fibrosis by anti-TK antibody were associated with increased expression of tumor necrosis factor-alpha, intercellular adhesion molecule-1, tissue inhibitor of metalloproteinase-2 (TIMP-2), and plasminogen activator inhibitor-1 (PAI-1). Moreover, the detrimental effect of TK blockade resulted in reduced nitric oxide (NO) levels as well as increased serum lipid peroxidation, renal NADH oxidase activity, and superoxide formation. In cultured proximal tubular cells, TK inhibited angiotensin II-induced superoxide production and NADH oxidase activity via NO formation. In addition, TK markedly increased matrix metalloproteinase-2 activity with a parallel reduction of TIMP-2 and PAI-1 synthesis. These findings indicate that endogenous TK has the propensity to preserve kidney structure and function in rats with chronic renal disease by inhibiting oxidative stress and activating matrix degradation pathways.

Angiotensin I-converting enzyme inhibitors are allosteric enhancers of kinin B1 and B2 receptor function

The beneficial effects of angiotensin I-converting enzyme (ACE) inhibitors go beyond the inhibition of ACE to decrease angiotensin (Ang) II or increase kinin levels. ACE inhibitors also affect kinin B1 and B2 receptor (B1R and B2R) signaling, which may underlie some of their therapeutic usefulness. They can indirectly potentiate the actions of bradykinin (BK) and ACE-resistant BK analogs on B2Rs to elevate arachidonic acid and NO release in laboratory experiments. Studies indicate that ACE inhibitors and some Ang metabolites increase B2R functions as allosteric enhancers by inducing a conformational change in ACE. This is transmitted to B2Rs via heterodimerization with ACE on the plasma membrane of cells. ACE inhibitors are also agonists of the B1R, at a Zn-binding sequence on the second extracellular loop that differs from the orthosteric binding site of the des-Arg-kinin peptide ligands. Thus, ACE inhibitors act as direct allosteric B1R agonists. When ACE inhibitors enhance B2R and B1R signaling, they augment NO production. Enhancement of B2R signaling activates endothelial NO synthase, yielding a short burst of NO; activation of B1Rs results in a prolonged high output of NO by inducible NO synthase. These actions, outside inhibiting peptide hydrolysis, may contribute to the pleiotropic therapeutic effects of ACE inhibitors in various cardiovascular disorders.

Proteins secreted by embryonic stem cells activate cardiomyocytes through ligand binding pathways

Human embryonic stem cells (hESC) underlie embryogenesis but paracrine signals associated with the process are unknown. This study was designed to 1) profile native proteins secreted by undifferentiated hESC and 2) determine their biological effects on primary neonatal cardiomyocytes. We utilized multi-analyte, immunochemical assays to characterize media conditioned by undifferentiated hESC versus unconditioned media. Expression profiling was performed on cardiomyocytes subjected to these different media conditions and altered transcripts were mapped to critical pathways. Thirty-two of 109 proteins were significantly elevated in conditioned media ranging in concentration from thrombospondin (57.2+/-5.0 ng/ml) to nerve growth factor (7.4+/-1.2pg/ml) and comprising chemokines, cytokines, growth factors, and proteins involved in cell adhesion and extracellular matrix remodeling. Conditioned media induced karyokinesis, cytokinesis and proliferation in mono- and binucleate cardiomyocytes. Pathway analysis revealed comprehensive activation of the ROCK 1 and 2 G-protein coupled receptor (GPCR) pathway associated with cytokinesis, and the RAS/RAF/MEK/ERK receptor tyrosine kinase (RTK) and JAK/STAT-cytokine pathway involved in cell cycle progression. These results provide a partial database of proteins secreted by pluripotent hESC that potentiate cell division in cardiomyocytes via a paracrine mechanism suggesting a potential role for these stem cell factors in cardiogenesis and cardiac repair.

A novel signaling pathway of tissue kallikrein in promoting keratinocyte migration: activation of proteinase-activated receptor 1 and epidermal growth factor receptor

Biological functions of tissue kallikrein (TK, KLK1) are mainly mediated by kinin generation and subsequent kinin B2 receptor activation. In this study, we investigated the potential role of TK and its signaling pathways in cultured human keratinocyte migration and in a rat skin wound healing model. Herein, we show that TK promoted cell migration and proliferation in a concentration- and time-dependent manner. Inactive TK or kinin had no significant effect on cell migration. Interestingly, cell migration induced by active TK was not blocked by icatibant or L-NAME, indicating an event independent of kinin B2 receptor and nitric oxide formation. TK's stimulatory effect on cell migration was inhibited by small interfering RNA for proteinase-activated receptor 1 (PAR(1)), and by PAR(1) inhibitor. TK-induced migration was associated with increased phosphorylation of epidermal growth factor receptor (EGFR) and extracellular signal-regulated kinase (ERK), which was blocked by inhibition of protein kinase C (PKC), Src, EGFR and ERK. TK-induced cell migration and EGFR phosphorylation were blocked by metalloproteinase (MMP) inhibitor, heparin, and antibodies against EGFR external domain, heparin-binding EGF-like growth factor (HB-EGF) and amphiregulin (AR). Local application of TK promoted skin wound healing in rats, whereas icatibant and EGFR inhibitor blocked TK's effect. Skin wound healing was further delayed by aprotinin and neutralizing TK antibody. This study demonstrates a novel role of TK in skin wound healing and uncovers new signaling pathways mediated by TK in promoting keratinocyte migration through activation of the PAR(1)-PKC-Src-MMP pathway and HB-EGF/AR shedding-dependent EGFR transactivation.

Cardioprotective effect of ornitho-kinin in an anesthetized, open-chest chicken model of acute coronary occlusion

The generation of bradykinin (BK; Arg-Pro-Pro-Gly-Phe-Ser-Pro-Phe-Arg) in blood and kallidin (Lys-BK) in tissues by the action of the kallikrein-kinin system has received little attention in non-mammalian vertebrates. In mammals, kallidin can be generated by the coronary endothelium and myocytes in response to ischemia, mediating cardioprotective events. The plasma of birds lacks two key components of the kallikrein-kinin system: the low molecular weight kininogen and a prekallikrein activator analogous to mammalian factor XII, but treatment with bovine plasma kallikrein generates ornitho-kinin [Thr6,Leu8]-BK. The possible cardioprotective effect of ornitho-kinin infusion was investigated in an anesthetized, open-chest chicken model of acute coronary occlusion. A branch of the left main coronary artery was reversibly ligated to produce ischemia followed by reperfusion, after which the degree of myocardial necrosis (infarct size as a percent of area at risk) was assessed by tetrazolium staining. The iv injection of a low dose of ornitho-kinin (4 microg/kg) reduced mean arterial pressure from 88 +/- 12 to 42 +/- 7 mmHg and increased heart rate from 335 +/- 38 to 402 +/- 45 bpm (N = 5). The size of the infarct was reduced by pretreatment with ornitho-kinin (500 microg/kg infused over a period of 5 min) from 35 +/- 3 to 10 +/- 2% of the area at risk. These results suggest that the physiological role of the kallikrein-kinin system is preserved in this animal model in spite of the absence of two key components, i.e., low molecular weight kininogen and factor XII.

Gene deletion of the kinin receptor B1 attenuates cardiac inflammation and fibrosis during the development of experimental diabetic cardiomyopathy

OBJECTIVE

Diabetic cardiomyopathy is associated with increased mortality in patients with diabetes. The underlying pathology of this disease is still under discussion. We studied the role of the kinin B1 receptor on the development of experimental diabetic cardiomyopathy.

RESEARCH DESIGN AND METHODS

We utilized B1 receptor knockout mice and investigated cardiac inflammation, fibrosis, and oxidative stress after induction of streptozotocin (STZ)-induced diabetes. Furthermore, the left ventricular function was measured by pressure-volume loops after 8 weeks of diabetes.

RESULTS

B1 receptor knockout mice showed an attenuation of diabetic cardiomyopathy with improved systolic and diastolic function in comparison with diabetic control mice. This was associated with a decreased activation state of the mitogen-activated protein kinase p38, less oxidative stress, as well as normalized cardiac inflammation, shown by fewer invading cells and no increase in matrix metalloproteinase-9 as well as the chemokine CXCL-5. Furthermore, the profibrotic connective tissue growth factor was normalized, leading to a reduction in cardiac fibrosis despite severe hyperglycemia in mice lacking the B1 receptor.

CONCLUSIONS

These findings suggest that the B1 receptor is detrimental in diabetic cardiomyopathy in that it mediates inflammatory and fibrotic processes. These insights might have useful implications on future studies utilizing B1 receptor antagonists for treatment of human diabetic cardiomyopathy.

Critical role of tissue kallikrein in vessel formation and maturation: implications for therapeutic revascularization

OBJECTIVE

Human Tissue Kallikrein (hKLK1) overexpression promotes an enduring neovascularization of ischemic tissue, yet the cellular mechanisms of hKLK1-induced arteriogenesis remain unknown. Furthermore, no previous study has compared the angiogenic potency of hKLK1, with its loss of function polymorphic variant, rs5515 (R53H), which possesses reduced kinin-forming activity.

METHODS AND RESULTS

Here, we demonstrate that tissue kallikrein knockout mice (KLK1-/-) show impaired muscle neovascularization in response to hindlimb ischemia. Gene-transfer of wild-type Ad.hKLK1 but not Ad.R53H-hKLK1 was able to rescue this defect. Similarly, in the rat mesenteric assay, Ad.hKLK1 induced a mature neovasculature with increased vessel diameter through kinin-B2 receptor-mediated recruitment of pericytes and vascular smooth muscle cells, whereas Ad.R53H-hKLK1 was ineffective. Moreover, hKLK1 but not R53H-hKLK1 overexpression in the zebrafish induced endothelial precursor cell migration and vascular remodeling. Furthermore, Ad.hKLK1 activates metalloproteinase (MMP) activity in normoperfused muscle and fails to promote reparative neovascularization in ischemic MMP9-/- mice, whereas its proarteriogenic action was preserved in ApoE-/- mice, an atherosclerotic model of impaired angiogenesis.

CONCLUSIONS

These results demonstrate the fundamental role of endogenous Tissue Kallikrein in vascular repair and provide novel information on the cellular and molecular mechanisms responsible for the robust arterialization induced by hKLK1 overexpression.