Susceptibility to metanephric apoptosis in bradykinin B2 receptor null mice via the p53-Bax pathway

The Kallikrein-Kinin System: A Novel Mediator of IL-17-Driven Anti-Candida Immunity in the Kidney

The incidence of life-threatening disseminated Candida albicans infections is increasing in hospitalized patients, with fatalities as high as 60%. Death from disseminated candidiasis in a significant percentage of cases is due to fungal invasion of the kidney, leading to renal failure. Treatment of candidiasis is hampered by drug toxicity, the emergence of antifungal drug resistance and lack of vaccines against fungal pathogens. IL-17 is a key mediator of defense against candidiasis. The underlying mechanisms of IL-17-mediated renal immunity have so far been assumed to occur solely through the regulation of antimicrobial mechanisms, particularly activation of neutrophils. Here, we identify an unexpected role for IL-17 in inducing the Kallikrein (Klk)-Kinin System (KKS) in C. albicans-infected kidney, and we show that the KKS provides significant renal protection in candidiasis. Microarray data indicated that Klk1 was upregulated in infected kidney in an IL-17-dependent manner. Overexpression of Klk1 or treatment with bradykinin rescued IL-17RA-/- mice from candidiasis. Therapeutic manipulation of IL-17-KKS pathways restored renal function and prolonged survival by preventing apoptosis of renal cells following C. albicans infection. Furthermore, combining a minimally effective dose of fluconazole with bradykinin markedly improved survival compared to either drug alone. These results indicate that IL-17 not only limits fungal growth in the kidney, but also prevents renal tissue damage and preserves kidney function during disseminated candidiasis through the KKS. Since drugs targeting the KKS are approved clinically, these findings offer potential avenues for the treatment of this fatal nosocomial infection.

Kallikrein-related peptidases (KLKs) and the hallmarks of cancer

The kallikrein-related peptidases (KLKs) represent the largest family of serine proteases within the human genome and are expressed in various tissues. Although they regulate several important physiological functions, KLKs have also been implicated in numerous pathophysiological processes, including cancer. Growing evidence describing the deregulation of KLK expression and secretion, as well as activation in various malignancies, has uncovered their potential as mediators of cancer progression, biomarkers of disease and as candidate therapeutic targets. The diversity of signalling pathways and proteolytic cascades involving KLKs and their downstream targets appears to affect cancer biology through multiple mechanisms, including those related to the hallmarks of cancer. The aim of this review is to provide an update on the importance of KLK-driven molecular pathways in relation to cancer cell traits associated with the hallmarks of cancer and to highlight their potential in personalized therapeutics.

Genome-wide analysis of gestational gene-environment interactions in the developing kidney

The G protein-coupled bradykinin B2 receptor (Bdkrb2) plays an important role in regulation of blood pressure under conditions of excess salt intake. Our previous work has shown that Bdkrb2 also plays a developmental role since Bdkrb2(-/-) embryos, but not their wild-type or heterozygous littermates, are prone to renal dysgenesis in response to gestational high salt intake. Although impaired terminal differentiation and apoptosis are consistent findings in the Bdkrb2(-/-) mutant kidneys, the developmental pathways downstream of gene-environment interactions leading to the renal phenotype remain unknown. Here, we performed genome-wide transcriptional profiling on embryonic kidneys from salt-stressed Bdkrb2(+/+) and Bdkrb2(-/-) embryos. The results reveal significant alterations in key pathways regulating Wnt signaling, apoptosis, embryonic development, and cell-matrix interactions. In silico analysis reveal that nearly 12% of differentially regulated genes harbor one or more Pax2 DNA-binding sites in their promoter region. Further analysis shows that metanephric kidneys of salt-stressed Bdkrb2(-/-) have a significant downregulation of Pax2 gene expression. This was corroborated in Bdkrb2(-/-);Pax2(GFP+/tg) mice, demonstrating that Pax2 transcriptional activity is significantly repressed by gestational salt-Bdkrb2 interactions. We conclude that gestational gene (Bdkrb2) and environment (salt) interactions cooperate to impact gene expression programs in the developing kidney. Suppression of Pax2 likely contributes to the defects in epithelial survival, growth, and differentiation in salt-stressed BdkrB2(-/-) mice.

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 regulation of apoptosis in kidney development: implications for nephron number and pattern?

Apoptosis is essential to remodel developing structures and eliminate superfluous cells in a controlled manner during normal development, and continues to be an important component of tissue remodeling and regeneration during an organism's lifespan, or as a response to injury. This mini review will discuss recent studies that have provided insights into the roles of apoptosis in the determination of nephron number and pattern, during normal and abnormal kidney development. The regulation of congenital nephron endowment has implications for risk of chronic kidney disease in later life, whereas abnormalities in nephron pattern are associated with congenital anomalies of the kidney and urinary tract (the leading cause of renal disease in children). Tight regulation of apoptosis is required in normal renal morphogenesis, although many questions remain regarding the regulation of apoptosis by genetic, epigenetic, and environmental factors, in addition to the functional requirement of different components of the apoptotic pathway.

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.

p53 family in development

The p53 family network is a unique cellular processor that integrates information from various pathways and determines cellular choices between proliferation, replication arrest/repair, differentiation, senescence, or apoptosis. The most studied role of the p53 family is the regulation of stress response and tumor suppression. By removing damaged cells from the proliferating pool, p53 family members preserve the integrity of the genome. In addition to this well recognized role, recent data implicate the p53 protein family in a broader role of controlling cell proliferation, differentiation and death. Members of the p53 protein family with opposing activity perform coordination of these processes. Imbalance of p53 protein family may contribute to a significant proportion of congenital developmental abnormalities in humans.

Bradykinin B2 receptor null mice harboring a Ser23-to-Ala substitution in the p53 gene are protected from renal dysgenesis

A physiological cross talk operates between the tumor suppressor protein p53 and the bradykinin B2 receptor (BdkrB2) during renal organogenesis. Thus, although BdkrB2 is a target for p53-mediated transcriptional activation, BdkrB2 is required to restrict p53 proapoptotic activity. We previously demonstrated that BdkrB2(-/-) embryos exposed to gestational salt stress develop renal dysgenesis as a result of p53-mediated apoptosis of nephron progenitors and repression of the terminal differentiation program. Compared with wild-type kidneys, BdkrB2(-/-) express abnormally high levels of the Checkpoint kinase (Chk1), which activates p53 via Ser23 phosphorylation. To define the functional relevance of p53S23 phosphorylation, we generated a compound strain of BdkrB2(-/-) mice harboring a homozygous Ser23-to-Ala (S23A) mutation in the p53 gene by crossing BdkrB2(-/-) with p53S23A knockin mice. Unlike salt-stressed BdkrB2(-/-) pups, which exhibit renal dysgenesis, homozygous S23A;BdkrB2(-/-) littermates are protected and have normal renal development. Heterozygous S23A;BdkrB2(-/-) mice have an intermediate phenotype. The p53-S23A substitution was associated with amelioration of apoptosis and restored markers of nephrogenesis and tubulogenesis. Real-time quantitative RT-PCR of terminal differentiation genes demonstrated that the S23A substitution restored normal expression patterns of aquaporin-2, Na-Cl cotransporter, Na-K-2Cl cotransporter, Na-bicarbonate cotransporter, and Sglt1. We conclude that p53 phosphorylation on Ser23 is an essential step in the signaling pathway mediating the susceptibility of BdkrB2(-/-) mutants to renal dysgenesis.

Downregulation of Spry-1, an inhibitor of GDNF/Ret, causes angiotensin II-induced ureteric bud branching

Mutations of genes in the renin-angiotensin system are associated with congenital abnormalities of the kidney and urinary tract. The major signaling pathway for branching morphogenesis during kidney development is the c-Ret receptor tyrosine kinase whose ligand is GDNF and whose downstream target is Wnt11. We determined whether angiotensin II, an inducer of ureteric bud branching in vitro, influences the GDNF/c-Ret/Wnt11 pathway. Mouse metanephroi were grown in the presence or absence of angiotensin II or an angiotensin type 1 receptor (AT1R) antagonist and gene expression was measured by whole mount in situ hybridization. Angiotensin II induced the expression of c-Ret and Wnt11 in ureteric bud tip cells. GDNF, a Wnt11-regulated gene expressed in the mesenchyme, was also upregulated by angiotensin II but this downregulated Spry1, an endogenous inhibitor of Ret tyrosine kinase activity in an AT1R-dependent manner. Angiotensin II also decreased Spry1 mRNA levels in cultured ureteric bud cells. Exogenous angiotensin II preferentially stimulated ureteric bud tip cell proliferation in vivo while AT1R blockade increased cell apoptosis. Our findings suggest AT1R-mediated inhibition of the Spry1 gene increases c-Ret tyrosine kinase activity leading to upregulation of its downstream target Wnt11. Enhanced Wnt11 expression induces GDNF in adjacent mesenchyme causing focal bursts of ureteric bud tip cell proliferation, decreased tip cell apoptosis and branching.