Ontogeny of the intrarenal kallikrein-kinin system: proposed role in renal development

Ontogeny of bradykinin B1 receptors in the mouse kidney

Kinins are vasoactive peptides that stimulate two G-protein coupled bradykinin receptors (B1R and B2R). B2R-knockout mice are salt sensitive and develop renal dysgenesis and hypertension if salt stressed during embryogenesis. B1R-knockout mice, on the other hand, are protected from inflammation and fibrosis. This study examined the spatiotemporal expression of B1R during renal organogenesis. The segmental nephron identity of B1R immunoreactivity was determined by costaining with markers of the collecting duct (Dolichos biflorus), proximal tubule (Dolichos tetraglonus), and nephron progenitors (Pax2). At E14.5, the B1R was confined to few cells in the metanephric mesenchyme. Abundance of B1R increased progressively during development. On E17.5, B1R was enriched in differentiating proximal tubular cells and by postnatal day 1, B1R was clearly expressed on the luminal aspect of the proximal tubule. Quantitative real-time PCR revealed that the levels of B1R mRNA more than double during renal maturation. We conclude that 1) B1R expression correlates closely with nephron maturation; 2) lack of B1R in nephron progenitors suggests that B1R is unlikely to play a role in early nephrogenesis; and 3) enrichment of B1R in maturing proximal tubule suggests a potential role for this receptor in terminal differentiation of the proximal nephron.

Kinin-B2 receptor expression and activity during differentiation of embryonic rat neurospheres

Neural progenitor cells were isolated from rat fetal telencephalon and proliferate as neurospheres in the presence of EGF, FGF-2, and heparin. In the absence of these growth factors, neurospheres differentiate into neurons, astrocytes, and oligodendrocytes. Using an embryonal carcinoma cell line as in vitro differentiation model, we have already demonstrated the presence of an autocrine loop system between kinin-B2 receptor activity and secretion of its ligand bradykinin (BK) as prerequisites for final neuronal differentiation (Martins et al., J Biol Chem 2005; 280: 19576-19586). The aim of this study was to verify the activity of the kallikrein-kinin system (KKS) during neural progenitor cell differentiation. Immunofluorescence studies and flow cytometry analysis revealed increases in glial fibrillary acidic protein and beta-3 tubulin expression and decrease in the number of nestin-positive cells along neurospheres differentiation, indicating the transition of neural progenitor cells to astrocytes and neurons. Kinin-B2 receptor expression and activity, secretion of BK into the medium, and presence of high-molecular weight kininogen suggest the participation of the KKS in neurosphere differentiation. Functional kinin-B2 receptors and BK secretion indicate an autocrine loop during neurosphere differentiation to neurons, astrocytes, and oligodendrocytes, reflecting events occurring during early brain development.

Neuronal differentiation of P19 embryonal carcinoma cells modulates kinin B2 receptor gene expression and function

Kinins are vasoactive oligopeptides generated upon proteolytic cleavage of low and high molecular weight kininogens by kallikreins. These peptides have a well established signaling role in inflammation and homeostasis. Nevertheless, emerging evidence suggests that bradykinin and other kinins are stored in the central nervous system and may act as neuromediators in the control of nociceptive response. Here we show that the kinin-B2 receptor (B2BKR) is differentially expressed during in vitro neuronal differentiation of P19 cells. Following induction by retinoic acid, cells form embryonic bodies and then undergo neuronal differentiation, which is complete after 8 and 9 days. Immunochemical staining revealed that B2BKR protein expression was below detection limits in nondifferentiated P19 cells but increased during the course of neuronal differentiation and peaked on days 8 and 9. Measurement of [Ca(2+)](i) in the absence and presence of bradykinin showed that most undifferentiated cells are unresponsive to bradykinin application, but following differentiation, P19 cells express high molecular weight neurofilaments, secrete bradykinin into the culture medium, and respond to bradykinin application with a transient increase in [Ca(2+)](i). However, inhibition of B2BKR activity with HOE-140 during early differentiation led to a decrease in the size of embryonic bodies formed. Pretreatment of differentiating P19 cells with HOE-140 on day 5 resulted in a reduction of the calcium response induced by the cholinergic agonist carbamoylcholine and decreased expression levels of M1-M3 muscarinic acetylcholine receptors, indicating crucial functions of the B2BKR during neuronal differentiation.

Transcriptional regulation of the rat bradykinin B2 receptor gene: identification of a silencer element

Kinins are involved in a variety of physiological and pathophysiological processes related to cardiovascular homeostasis, inflammation, blood flow, and nociception. Under physiological conditions, the bradykinin B2 (BKB2) receptor is constitutively expressed and mediates most of kinins' actions. However, the mechanisms regulating BKB2 receptor gene expression are still poorly understood. In this study, 4.6 kilobases of the 5'-flanking region from the rat BKB2 receptor gene were sequenced, and computer analysis revealed several sites for transcriptional factors. Nine promoter mutants were cloned in luciferase reporter gene vectors and transfected in NG108-15 cells and rat aorta vascular smooth muscle cells (VSMCs), showing several positive and negative regulatory elements. A classical silencer with 56 base pairs (bp) caused a decrease in reporter gene activity in NG108-15 cells and VSMCs and was able to inhibit the thymidine kinase promoter. Using electrophoretic mobility shift assay and surface plasmon resonance assay, protein-DNA interactions in the silencer region were determined and specific sets of protein-silencer complexes were detected in both cell types. More intense complexes were observed in the central 21 bp of the silencer and mutation in a putative SRE-1 site strongly impaired the protein-DNA binding. Down-regulation of the BKB2 receptor population in NG108-15 cells promoted by N(6), 2'-O-dibutyryladenosine 3':5'-cyclic monophosphate was paralleled by an increase in the amount of nuclear proteins bound to the silencer sequence showing an inverse relationship between protein-silencer complexes and the transcription of the BKB2 receptor gene. In summary, these data highlight the cell-specific regulation of the BKB2 receptor and the importance of a silencer element present in the regulatory region of the gene.

Temporal and tissue-specific expression of kallikrein (Klk) genes and identification of a novel Klk messenger ribonucleic acid transcript during early development in the mouse

The kallikreins are a multigene family of serine proteases that act on a diverse number of substrates, including several growth factors and extracellular matrix (ECM) glycoproteins and proteinases. Recently, this family has been implicated in the process of early development and embryo implantation. In this study, we used reverse transcription-polymerase chain reaction with gene-specific primers and Southern hybridization to elucidate the temporal and tissue-specific expression patterns of the mouse kallikreins Klk1, Klk3, Klk5, Klk9, and Klk21 during early development in the embryo, uterus, and decidua. We observed the expression of Klk1 (tissue kallikrein), Klk3 (gamma-nerve growth factor), Klk9 (epidermal growth factor-binding protein), and Klk21 in the early conceptus (until the 2-cell stage). Only Klk21 continued to be expressed in the blastocyst until Day 7.5 of pregnancy. Expression of Klk9 reappeared at Day 7.5 and was consistently detected until Day 11, the last day studied; Klk1 was again expressed in the embryo from Day 9.5, with decreased levels by Day 11. In contrast, in the uterus or decidua, there was no expression of Klk1 until Day 7.5, when mRNA transcripts were abundant; transcripts then decreased in the Day 9.5 and Day 11 uterus. Expression of Klk21 in the uterus and decidua displayed a similar pattern but was detected at much lower levels. Interestingly, a novel Klk21-like mRNA was also detected in uterine tissue samples but not in embryonic samples; Klk3, Klk5, and Klk9 were not consistently expressed in the uterus or decidua over this time. This is the first report of the expression of specific kallikreins during early development. The distinct gene- and tissue-specific expression patterns presented in this study, in conjunction with the well-characterized roles of kallikreins in regulation of protein activation, ECM degradation, and proliferative events, suggests the involvement of the kallikrein gene family during early development.