Human lung fibroblasts express multiple means for enhanced activity of bradykinin receptor pathways

Molecular profiling reveals diversity of stress signal transduction cascades in highly penetrant Alzheimer's disease human skin fibroblasts

The serious and growing impact of the neurodegenerative disorder Alzheimer's disease (AD) as an individual and societal burden raises a number of key questions: Can a blanket test for Alzheimer's disease be devised forecasting long-term risk for acquiring this disorder? Can a unified therapy be devised to forestall the development of AD as well as improve the lot of present sufferers? Inflammatory and oxidative stresses are associated with enhanced risk for AD. Can an AD molecular signature be identified in signaling pathways for communication within and among cells during inflammatory and oxidative stress, suggesting possible biomarkers and therapeutic avenues? We postulated a unique molecular signature of dysfunctional activity profiles in AD-relevant signaling pathways in peripheral tissues, based on a gain of function in G-protein-coupled bradykinin B2 receptor (BKB2R) inflammatory stress signaling in skin fibroblasts from AD patients that results in tau protein Ser hyperphosphorylation. Such a signaling profile, routed through both phosphorylation and proteolytic cascades activated by inflammatory and oxidative stresses in highly penetrant familial monogenic forms of AD, could be informative for pathogenesis of the complex multigenic sporadic form of AD. Comparing stimulus-specific cascades of signal transduction revealed a striking diversity of molecular signaling profiles in AD human skin fibroblasts that express endogenous levels of mutant presenilins PS-1 or PS-2 or the Trisomy 21 proteome. AD fibroblasts bearing the PS-1 M146L mutation associated with highly aggressive AD displayed persistent BKB2R signaling plus decreased ERK activation by BK, correctible by gamma-secretase inhibitor Compound E. Lack of these effects in the homologous PS-2 mutant cells indicates specificity of presenilin gamma-secretase catalytic components in BK signaling biology directed toward MAPK activation. Oxidative stress revealed a JNK-dependent survival pathway in normal fibroblasts lost in PS-1 M146L fibroblasts. Complex molecular profiles of signaling dysfunction in the most putatively straightforward human cellular models of AD suggest that risk ascertainment and therapeutic interventions in AD as a whole will likely demand complex solutions.

Mechanisms regulating the expression, self-maintenance, and signaling-function of the bradykinin B2 and B1 receptors

Bradykinin (BK) is a potent short-lived effector belonging to a class of peptides known as kinins. It participates in inflammatory and vascular regulation and processes including angioedema, tissue permeability, vascular dilation, and smooth muscle contraction. BK exerts its biological effects through the activation of the bradykinin B2 receptor (BKB2R) which is G-protein-coupled and is generally constitutively expressed. Upon binding, the receptor is activated and transduces signal cascades which have become paradigms for the actions of the Galphai and Galphaq G-protein subunits. Following activation the receptor is then desensitized, endocytosed, and resensitized. The bradykinin B1 (BKB1R) is a closely related receptor. It is activated by desArg(10)-kallidin or desArg(9)-BK, metabolites of kallidin and BK, respectively. This receptor is induced following tissue injury or after treatment with bacterial endotoxins such as lipopolysacharide or cytokines such as interleukin-1 or tumor necrosis factor-alpha. In this review we will summarize the BKB2R and BKB1R mediated signal transduction pathways. We will then emphasize the relevance of key residues and domains of the intracellular regions of the BKB2R as they relate to modulating its function (signal transduction) and self-maintenance (desensitization, endocytosis, and resensitization). We will examine the features of the BKB1R gene promoter and its mRNA as these operate in the expression and self-maintenance of this inducible receptor. This communication will not cover areas discussed in earlier reviews pertaining to the actions of peptide analogs. For these we refer you to earlier reviews (Regoli and Barabé, 1980, Pharmacol Rev 32:1-46; Regoli et al., 1990, J Cardiovasc Pharmacol 15(Suppl 6):S30-S38; Regoli et al., 1993, Can J Physiol Pharmacol 71:556-557; Marceau, 1995, Immunopharmacology 30:1-26; Regoli et al., 1998, Eur J Pharmacol 348:1-10).

Pharmacological characterization of bradykinin B1 and B2 receptors in IMR-90 and INT-407 human cell lines using a microphysiometer

1. In the present study, we used a microphysiometer to measure bradykinin-induced acidification responses in IMR-90, a human lung fibroblast cell line, and INT-407, a human colonic epithelial cell line. Furthermore, we investigated the effect of 24 h exposure of transforming growth factor (TGF)-alpha on the bradykinin response in INT-407 cells. 2. Bradykinin (0.1-100 nmol/L) was potent in producing acidification responses in IMR-90 cells (pEC50 8.79+/-0.13; Hill slope 0.96+/-0.04) and INT-407 cells (pEC50 8.90+/-0.04; Hill slope 1.00+/-0.07). These responses were competitively antagonized by the bradykinin B2 receptor antagonist icatibant in both IMR-90 cells (apparent pKB = 8.54+/-0.15; Hill slope = 1.09+/-0.13 and 1.66+/-0.26 in the absence and presence of 10 nmol/L icatibant, respectively) and INT-407 cells (pKB = 8.12+/-0.07 (3, 10 and 30 nmol/L icatibant); Hill slope = 1.06+/-0.04). However, the bradykinin B1 receptor antagonist des-Arg9Leu8-bradykinin (3 micromol/L) had no effect on the bradykinin responses. 3. The non-peptide bradykinin B2 receptor antagonist FR173657 selectively antagonized bradykinin-induced acidification responses in INT-407 cells in a competitive manner (pKB = 8.76+/-0.10; Hill slope = 0.92+/-0.05) at lower concentrations (1 and 3 nmol/L) but in an insurmountable manner at higher concentrations (10 nmol/L; Hill slope = 1.04+/-0.09). This compound, at concentrations of 10 and 100 nmol/L (Hill slope = 1.38+/-0.15), also proved to be an insurmountable antagonist in IMR-90 cells. 4. The bradykinin B1 receptor selective agonist Lys0des-Arg10-bradykinin (0.1 nmol/L to 0.1 micromol/L) failed to produce acidification responses in IMR-90 cells, even after 24 h pre-incubation with bacterial lipopolysaccharide (0.1 microg/mL). 5. A 24 h pre-incubation of INT-407 cells with TGF-alpha (1, 10 and 100 ng/mL) caused a significant concentration-dependent decrease in maximal bradykinin response without affecting the pEC50. 6. In addition to this study being the first to use a microphysiometer to characterize bradykinin B2 receptors in cultured IMR-90 human lung fibroblast cells and INT-407 human colonic epithelial cells, we also showed that pre-incubation of INT-407 cells with TGF-alpha caused a significant decrease in maximal acidification response mediated by bradykinin B2 receptors.