Examination of signal transduction pathway of stimulated B1 and B2 kinin receptors; MAP kinase pathway to AP-1 translocation in HEK 293 cells

Kinin B1 receptor modulates glucose homeostasis and physical exercise capacity by altering adrenal catecholamine synthesis and secretion

Our group has shown in several papers that kinin B1 receptor (B1R) is involved in metabolic adaptations, mediating glucose homeostasis and interfering in leptin and insulin signaling. Since catecholamines are involved with metabolism management, we sought to evaluate B1R role in catecholamine synthesis/secretion. Using B1R global knockout mice, we observed increased basal epinephrine content, accompanied by decreased hepatic glycogen content and increased glucosuria. When these mice were challenged with maximal intensity exercise, they showed decreased epinephrine and norepinephrine response, accompanied by disturbed glycemic responses to effort and poor performance. This phenotype was related to alterations in adrenal catecholamine synthesis: increased basal epinephrine concentration and reduced norepinephrine content in response to exercise, as well decreased gene expression and protein content of tyrosine hydroxylase and decreased gene expression of dopamine beta hydroxylase and kinin B2 receptor. We conclude that the global absence of B1R impairs catecholamine synthesis, interfering with glucose metabolism at rest and during maximal exercise.

Attenuation of pulmonary ACE2 activity impairs inactivation of des-Arg9 bradykinin/BKB1R axis and facilitates LPS-induced neutrophil infiltration

Angiotensin-converting enzyme 2 (ACE2) is a terminal carboxypeptidase with important functions in the renin-angiotensin system and plays a critical role in inflammatory lung diseases. ACE2 cleaves single-terminal residues from several bioactive peptides such as angiotensin II. However, few of its substrates in the respiratory tract have been identified, and the mechanism underlying the role of ACE2 in inflammatory lung disease has not been fully characterized. In an effort to identify biological targets of ACE2 in the lung, we tested its effects on des-Arg⁹ bradykinin (DABK) in airway epithelial cells on the basis of the hypothesis that DABK is a biological substrate of ACE2 in the lung and ACE2 plays an important role in the pathogenesis of acute lung inflammation partly through modulating DABK/bradykinin receptor B1 (BKB1R) axis signaling. We found that loss of ACE2 function in mouse lung in the setting of endotoxin inhalation led to activation of the DABK/BKB1R axis, release of proinflammatory chemokines such as C-X-C motif chemokine 5 (CXCL5), macrophage inflammatory protein-2 (MIP2), C-X-C motif chemokine 1 (KC), and TNF-α from airway epithelia, increased neutrophil infiltration, and exaggerated lung inflammation and injury. These results indicate that a reduction in pulmonary ACE2 activity contributes to the pathogenesis of lung inflammation, in part because of an impaired ability to inhibit DABK/BKB1R axis-mediated signaling, resulting in more prompt onset of neutrophil infiltration and more severe inflammation in the lung. Our study identifies a biological substrate of ACE2 within the airways, as well as a potential new therapeutic target for inflammatory diseases.

Functional overexpression and characterization of human bradykinin subtype 2 receptor in insect cells using the baculovirus system

Bradykinin exerts its actions via binding to B1 and B2 receptors (B1R and B2R), which are members of G protein-coupled receptor superfamily. B2R is constitutively expressed in a variety of cells such as endothelial cells, vascular smooth muscle cells, and cardiomyocytes and it is an important drug target for the treatment of cardiovascular disorders. During this study, the human B2R was functionally overexpressed in insect cells using the baculovirus expression system. The maximum expression level in Sf9 cells under optimized condition was 10 pmol/mg. This corresponds to approximately 0.25 mg active receptor per liter culture. The recombinant receptor showed high affinity for its endogenous ligand bradykinin, similar to the B2R expressed in native tissues. Functional coupling of the recombinant receptor to the endogenous G alpha(s) protein was demonstrated via cAMP release assay upon agonist stimulation. Confocal laser scanning microscopy and immunogold-labeling experiment revealed that the recombinant B2R was mainly localized intracellularly and only a minor fraction of the recombinant receptor reached the plasma membrane. To our knowledge, this is the first report of high level expression of recombinant B2R in insect cells and provides a way for large scale production and structural characterization of this receptor.

Role of kinin B1 and B2 receptors in the development of pilocarpine model of epilepsy

The tissue sclerosis found in epilepsy of limbic origin is characterized by shrunken gliotic hippocampus, granule cell loss in the dentate gyrus and extensive pyramidal cell loss in Ammon's horn. Evidence has indicated that sprouting of dentate granule cell axons into the inner molecular layer of the dentate gyrus is related to hyperexcitability. Trying to understand the role of kinin B1 and B2 receptors in the physiopathology of temporal lobe epilepsy (TLE), the present work was delineated to study the development of the epilepsy model induced by pilocarpine in B1 and B2 knockout mice (B1KO and B2KO, respectively). Behavior parameters, cell death and mossy fiber sprouting were analyzed. B1KO mice showed increased latency for the first seizure, associated to a decreased frequency of spontaneous seizures, when compared with wild-type mice. In addition, B1KO mice showed less cell death in all hippocampal formation associated to a reduced grade of mossy fiber sprouting. Furthermore, B2KO mice presented minor duration of the silent period and an increased frequency of spontaneous seizures, when compared with wild-type mice. B2KO and their control lineage showed similar pattern of cell death in the hippocampus, which was very intense when compared with saline-treated animals. The mossy fiber sprouting was also increased in B2KO mice, when compared to wild-type mice and saline-treated animals. Taken together, these data suggest a deleterious effect for kinin B1 receptor and a protective effect for kinin B2 receptor during the development of the temporal lobe epilepsy.

Host stromal bradykinin B2 receptor signaling facilitates tumor-associated angiogenesis and tumor growth

We evaluated the significance of the host kallikrein-kinin system in tumor angiogenesis and tumor growth using two rodent models genetically deficient in a kallikrein-kinin system. Inoculation of Walker 256 carcinoma cells into the s.c. tissues of the back of normal Brown Norway Kitasato rats (BN-Ki rats) resulted in the rapid development of solid tumors with marked angiogenesis. By contrast, in kininogen-deficient Brown Norway Katholiek rats (BN-Ka rats), which cannot generate intrinsic bradykinin (BK), the weights of the tumors and the extent of angiogenesis were significantly less than those in BN-Ki rats. Daily administration of B(2) receptor antagonists significantly reduced angiogenesis and tumor weights in BN-Ki rats to levels similar to those in BN-Ka rats but did not do so in BN-Ka rats. Angiogenesis and tumor growth were significantly suppressed in B(2) receptor knockout mice bearing sarcoma 180 compared with their wild-type counterparts. Immunoreactive vascular endothelial growth factor (VEGF) was localized in Walker tumor stroma more extensively in BN-Ki rats than in BN-Ka rats, although immunoreactive B(2) receptor also was detected in the stroma to the same extent in both types of rats. Cultured stromal fibroblasts isolated from BN-Ki rats and BN-Ka rats produced VEGF in response to BK (10(-8)-10(-6) m), and this stimulatory effect of BK was abolished with a B(2) receptor antagonist, Hoe140 (10(-5) m). These results suggest that BK generated from kininogens supplied from the host may facilitate tumor-associated angiogenesis and tumor growth by stimulating stromal B(2) signaling to up-regulate VEGF production mainly in fibroblasts.

The synthesis and distribution of the kinin B1 and B2 receptors are modified in the hippocampus of rats submitted to pilocarpine model of epilepsy

Kinins, a special class of polypeptides, are represented by bradykinin (BK), kallidin (Lys-BK), as well as their metabolites. The biological actions of these polypeptides binding on their receptors (B1 and B2) have been related to inflammation process, cytokines action, glutamate release and prostaglandins production. Usually, kinin B1 receptor is not expressed at a significant level under physiologic conditions in most tissues, but its expression is induced by injury, or upon exposure in vivo or in vitro to pro-inflammatory mediators. The kinin B2 receptor subtype is constitutively and widely expressed throughout the central and peripheral nervous system. These data raise the possibility for de novo expression of those receptors during the temporal lobe epilepsy (TLE), which has been related to cell death, gliosis and hippocampal reorganization. To correlate kinin system and TLE, adult male Wistar rats were submitted to pilocarpine model of epilepsy. The hippocampi were removed 6 h, 5 and 60 days after status epilepticus (SE) onset. The collected tissues were used to study the expression of kinin B1 and B2 mRNA receptors, using Real-Time PCR. Immunohistochemistry assay was also employed to visualize kinin B1 and B2 distribution in the hippocampus. The results show increased kinin B1 and B2 mRNA levels during acute, silent and chronic periods and changes in the kinin B1 and B2 receptors distribution. In addition, the immunoreactivity against kinin B1 receptor was increased mainly during the silent period, where neuron clusters of could be visualized. The kinin B2 receptor immunoreactivity also showed augmentation but mainly during the acute and silent periods. Our results suggest that kinin B1 and B2 receptors play an important role in the epileptic phenomena.

Suppressed angiogenesis in kininogen-deficiencies

We investigated whether the kinin-generating system enhanced angiogenesis in chronic and proliferative granuloma and in tumor-surrounding stroma. In rat sponge implants, angiogenesis was gradually developed in normal Brown Norway Kitasato rats (BN-Ki). The development of angiogenesis was significantly suppressed in kininogen-deficient Brown Norway Katholiek rats (BN-Ka). The angiogenesis enhanced by basic fibroblast growth factor was also significantly less marked in BN-Ka than in BN-Ki. Naturally occurring angiogenesis was significantly suppressed by B(1) or B(2) antagonist. mRNA of vascular endothelial growth factor was more highly expressed in the granulation tissues in BN-Ki than in BN-Ka. Daily topical injections of aprotinin, but not of soy bean trypsin inhibitor, suppressed angiogenesis. Daily topical injections of low-molecular weight kininogen enhanced angiogenesis in BN-Ka. Topical injections of serum from BN-Ki, but not from BN-Ka, also facilitated angiogenesis in BN-Ka. FR190997, a nonpeptide mimic of bradykinin, promoted angiogenesis markedly, with concomitant increases in vascular endothelial growth factor mRNA. Angiogenesis in the granulation tissues around the implanted Millipore chambers containing Walker-256 cells was markedly more suppressed in BN-Ka than in BN-Ki. Our results suggest that endogenous kinin generated from the tissue kallikrein-kinin system enhances angiogenesis in chronic and proliferative granuloma and in the stroma surrounding a tumor. Thus, the agents for the kinin-generating system and/or kinin receptor signaling may become useful tools for controlling angiogenesis.

Regulation of MAP kinase activity by peptide receptor signalling pathway: paradigms of multiplicity

G protein-coupled receptors (GPCRs) can stimulate the mitogen-activated protein kinase (MAPK) cascade and thereby induce cellular proliferation like receptor tyrosine kinases (RTKs). Work over the past 5 years has established several models which reduce the links of G(i)-, G(q)-, and G(s)-coupled receptors to MAPK on few principle pathways. They include (i) Ras-dependent activation of MAPK via transactivation of RTKs such as the epidermal growth factor receptor (EGFR), (ii) Ras-independent MAPK activation via protein kinase C (PKC) that converges with the RTK signalling at the level of Raf, and (iii) activation as well as inactivation of MAPK via the cAMP/protein kinase A (PKA) pathway in dependency on the type of Raf. Most of these generalizing hypotheses are founded on experimental data obtained from expression studies and using a limited set of individual receptors. This review will compare these models with pathways to MAPK found for a great variety of peptide hormone and neuropeptide receptor subtypes in various cells. It becomes evident that under endogenous conditions, the transactivation pathway is less dominant as postulated, whereas pathways involving isoforms of PKC and, especially, phosphoinositide 3-kinase (PI-3K) appear to play a more important role as assumed so far. Highly cell-specific and unusual connections of signalling proteins towards MAPK, in particular tumour cells, might provide points of attacks for new therapeutic concepts.

Mediator caused induction of a human bradykinin B1 receptor minigene: participation of c-Jun in the process

The bradykinin B1 receptor (BKB1R) gene is expressed in selected tissues such as lung and kidney. In these tissues it is expressed at a very low level until induced by inflammatory mediators. Our aim has been to understand the mechanism of this regulatory process. A human BKB1R minigene was constructed. It contained a 1.8 kb promoter, the entire exon I, 1.5 kb of intron I, the entire exon II and intron II, and the luciferase gene as a reporter. Transient transfection of the minigene into SV40-transformed IMR90 cells (IMRSV) resulted in a promoter activity which was activated by the mediators, lipopolysaccharide and (LPS) desArg(10)-kallidin. In contrast, these mediators did not induce the activity of the 1.8 kb promoter construct alone. Thus, motifs exclusive of the promoter such as 5'-UTR and/or intron regions are required for mediator-induced expression of this gene. Promoter activities of both the minigene and the 1.8 kb promoter construct were enhanced in a dose-dependent manner upon cotransfection with c-Jun. Furthermore, cotransfecting c-Jun with the minigene achieved the maximal promoter activity with no further increase in response to mediators. Conversely, the induction of the minigene promoter activity by mediators was abolished upon cotransfection with a dominant negative mutant of c-Jun. Other experiments suggest that multiple AP-1 sites are interactive with the c-Jun upregulation of this gene. Taken together, these results point to c-Jun as a key intermediary in the activation of the expression of this gene by mediators. However, participation of motifs outside of the promoter are necessary to obtain this inducible expression.