Calprotectin is a contributor to and potential therapeutic target for vascular calcification in chronic kidney disease

Vascular calcification is an important risk factor for cardiovascular (CV) mortality in patients with chronic kidney disease (CKD). It is also a complex process involving osteochondrogenic differentiation of vascular smooth muscle cells (VSMCs) and abnormal deposition of minerals in the vascular wall. In an observational, multicenter European study, including 112 patients with CKD from Spain and 171 patients on dialysis from France, we used serum proteome analysis and further validation by ELISA to identify calprotectin, a circulating damage-associated molecular pattern protein, as being independently associated with CV outcome and mortality. This was confirmed in an additional cohort of 170 patients with CKD from Sweden, where increased serum calprotectin concentrations correlated with increased vascular calcification. In primary human VSMCs and mouse aortic rings, calprotectin exacerbated calcification. Treatment with paquinimod, a calprotectin inhibitor, as well as pharmacological inhibition of the receptor for advanced glycation end products and Toll-like receptor 4 inhibited the procalcifying effect of calprotectin. Paquinimod also ameliorated calcification induced by the sera of uremic patients in primary human VSMCs. Treatment with paquinimod prevented vascular calcification in mice with chronic renal failure induced by subtotal nephrectomy and in aged apolipoprotein E-deficient mice as well. These observations identified calprotectin as a key contributor of vascular calcification, and increased circulating calprotectin was strongly and independently associated with calcification, CV outcome, and mortality in patients with CKD. Inhibition of calprotectin might therefore be a promising strategy to prevent vascular calcification in patients with CKD.

Mapping of the amniotic fluid proteome of fetuses with congenital anomalies of the kidney and urinary tract identifies plastin 3 as a protein involved in glomerular integrity

Congenital anomalies of the kidney and the urinary tract (CAKUT) are the first cause of chronic kidney disease in childhood. Several genetic and environmental origins are associated with CAKUT, but most pathogenic pathways remain elusive. Considering the amniotic fluid (AF) composition as a proxy for fetal kidney development, we analyzed the AF proteome from non-severe CAKUT (n = 19), severe CAKUT (n = 14), and healthy control (n = 22) fetuses using LC-MS/MS. We identified 471 significant proteins that discriminated the three AF groups with 81% precision. Among them, eight proteins independent of gestational age (CSPG4, LMAN2, ENDOD1, ANGPTL2, PRSS8, NGFR, ROBO4, PLS3) were associated with both the presence and the severity of CAKUT. Among those, five were part of a protein-protein interaction network involving proteins previously identified as being potentially associated with CAKUT. The actin-bundling protein PLS3 (plastin 3) was the only protein displaying a gradually increased AF abundance from control, via non-severe, to severe CAKUT. Immunohistochemistry experiments showed that PLS3 was expressed in the human fetal as well as in both the fetal and the postnatal mouse kidney. In zebrafish embryos, depletion of PLS3 led to a general disruption of embryonic growth including reduced pronephros development. In postnatal Pls3-knockout mice, kidneys were macroscopically normal, but the glomerular ultrastructure showed thickening of the basement membrane and fusion of podocyte foot processes. These structural changes were associated with albuminuria and decreased expression of podocyte markers including Wilms' tumor-1 protein, nephrin, and podocalyxin. In conclusion, we provide the first map of the CAKUT AF proteome that will serve as a reference for future studies. Among the proteins strongly associated with CAKUT, PLS3 did surprisingly not specifically affect nephrogenesis but was found as a new contributor in the maintenance of normal kidney function, at least in part through the control of glomerular integrity. © 2021 The Pathological Society of Great Britain and Ireland. Published by John Wiley & Sons, Ltd.

The low affinity p75 neurotrophin receptor is down-regulated in congenital anomalies of the kidney and the urinary tract: Possible involvement in early nephrogenesis

Congenital Anomalies of the Kidney and of the Urinary Tract (CAKUT) cover a broad range of disorders including abnormal kidney development caused by defective nephrogenesis. Here we explored the possible involvement of the low affinity p75 neurotrophin receptor (p75NTR) in CAKUT and nephrogenesis. In mouse, p75NTR was highly expressed in fetal kidney, located within cortical early nephrogenic bodies, and decreased rapidly after birth. In human control fetal kidney, p75NTR was also located within the early nephrogenic bodies as well as in the mature glomeruli, presumably in the mesangium. In CAKUT fetal kidneys, the kidney cortical structure and the localization of p75NTR were often disorganized, and quantification of p75NTR in amniotic fluid revealed a significant reduction in CAKUT compared to control. Finally, invalidation of p75NTR in zebrafish embryo with an antisense morpholino significantly altered pronephros development. Our results indicate that renal p75NTR is altered in CAKUT fetuses, and could participate to early nephrogenesis.

Connectivity mapping of glomerular proteins identifies dimethylaminoparthenolide as a new inhibitor of diabetic kidney disease

While blocking the renin angiotensin aldosterone system (RAAS) has been the main therapeutic strategy to control diabetic kidney disease (DKD) for many years, 25-30% of diabetic patients still develop the disease. In the present work we adopted a systems biology strategy to analyze glomerular protein signatures to identify drugs with potential therapeutic properties in DKD acting through a RAAS-independent mechanism. Glomeruli were isolated from wild type and type 1 diabetic (Ins2Akita) mice treated or not with the angiotensin-converting enzyme inhibitor (ACEi) ramipril. Ramipril efficiently reduced the urinary albumin/creatine ratio (ACR) of Ins2Akita mice without modifying DKD-associated renal-injuries. Large scale quantitative proteomics was used to identify the DKD-associated glomerular proteins (DKD-GPs) that were ramipril-insensitive (RI-DKD-GPs). The raw data are publicly available via ProteomeXchange with identifier PXD018728. We then applied an in silico drug repurposing approach using a pattern-matching algorithm (Connectivity Mapping) to compare the RI-DKD-GPs's signature with a collection of thousands of transcriptional signatures of bioactive compounds. The sesquiterpene lactone parthenolide was identified as one of the top compounds predicted to reverse the RI-DKD-GPs's signature. Oral treatment of 2 months old Ins2Akita mice with dimethylaminoparthenolide (DMAPT, a water-soluble analogue of parthenolide) for two months at 10 mg/kg/d by gavage significantly reduced urinary ACR. However, in contrast to ramipril, DMAPT also significantly reduced glomerulosclerosis and tubulointerstitial fibrosis. Using a system biology approach, we identified DMAPT, as a compound with a potential add-on value to standard-of-care ACEi-treatment in DKD.

Amniotic fluid peptides predict postnatal kidney survival in developmental kidney disease

Although a rare disease, bilateral congenital anomalies of the kidney and urinary tract (CAKUT) are the leading cause of end stage kidney disease in children. Ultrasound-based prenatal prediction of postnatal kidney survival in CAKUT pregnancies is far from accurate. To improve prediction, we conducted a prospective multicenter peptidome analysis of amniotic fluid spanning 140 evaluable fetuses with CAKUT. We identified a signature of 98 endogenous amniotic fluid peptides, mainly composed of fragments from extracellular matrix proteins and from the actin binding protein thymosin-β4. The peptide signature predicted postnatal kidney outcome with an area under the curve of 0.96 in the holdout validation set of patients with CAKUT with definite endpoint data. Additionally, this peptide signature was validated in a geographically independent sub-cohort of 12 patients (area under the curve 1.00) and displayed high specificity in non-CAKUT pregnancies (82 and 94% in 22 healthy fetuses and in 47 fetuses with congenital cytomegalovirus infection respectively). Change in amniotic fluid thymosin-β4 abundance was confirmed with ELISA. Knockout of thymosin-β4 in zebrafish altered proximal and distal tubule pronephros growth suggesting a possible role of thymosin β4 in fetal kidney development. Thus, recognition of the 98-peptide signature in amniotic fluid during diagnostic workup of prenatally detected fetuses with CAKUT can provide a long-sought evidence base for accurate management of the CAKUT disorder that is currently unavailable.

The protective effect of angiotensin converting enzyme inhibition in experimental renal fibrosis in mice is not mediated by bradykinin B2 receptor activation

Unilateral ureteral obstruction (UUO) is an animal model of accelerated renal tubulointerstitial fibrosis. We have recently shown, using this model, that mice lacking the bradykinin B2-receptor (B2-/- ) were more susceptible than control animals to the development of tubulointerstitial fibrosis. Angiotensin converting enzyme (ACE) inhibition slows down UUO-induced renal fibrosis. Since ACE-inhibition increases bradykinin and decreases angiotensin II concentrations we have verified if bradykinin is involved in the antifibrotic effects of ACE-inhibition using the UUO-model and B2-/- mice. Surprisingly, although ACE-inhibition significantly reduced renal fibrosis, no difference was observed between the degree of tubulointerstitial fibrosis, macrophage infiltration and cell proliferation between ACE-inhibitor treated B2+/+ and B2-/- mice suggesting the absence of a role of the B2-receptor in the antifibrotic effects of ACE-inhibition. This was confirmed at the level of bradykinin-induced activity of enzymes involved in the degradation of the extracellular matrix. However in both mouse strains, ACE-inhibitors were more efficient than AT1 receptor antagonists.

Theme paper: Part of this paper was originally presented at the joint meetings of the 16th International Congress of the International Society of Fibrinolysis and Proteolysis (ISFP) and the 17th International Fibrinogen Workshop of the International Fibrinogen Research Society (IFRS) held in Munich, Germany, September, 2002.

Systems biology combining human- and animal-data miRNA and mRNA data identifies new targets in ureteropelvic junction obstruction

Background

Although renal fibrosis and inflammation have shown to be involved in the pathophysiology of obstructive nephropathies, molecular mechanisms underlying evolution of these processes remain undetermined. In an attempt towards improved understanding of obstructive nephropathy and improved translatability of the results to clinical practice we have developed a systems biology approach combining omics data of both human and mouse obstructive nephropathy.

Results

We have studied in parallel the urinary miRNome of infants with ureteropelvic junction obstruction and the kidney tissue miRNome and transcriptome of the corresponding neonatal partial unilateral ureteral obstruction (UUO) mouse model. Several hundreds of miRNAs and mRNAs displayed changed abundance during disease. Combination of miRNAs in both species and associated mRNAs let to the prioritization of five miRNAs and 35 mRNAs associated to disease. In vitro and in vivo validation identified consistent dysregulation of let-7a-5p and miR-29-3p and new potential targets, E3 ubiquitin-protein ligase (DTX4) and neuron navigator 1 (NAV1), potentially involved in fibrotic processes, in obstructive nephropathy in both human and mice that would not be identified otherwise.

Conclusions

Our study is the first to correlate a mouse model of neonatal partial UUO with human UPJ obstruction in a comprehensive systems biology analysis. Our data revealed let-7a and miR-29b as molecules potentially involved in the development of fibrosis in UPJ obstruction via the control of DTX4 in both man and mice that would not be identified otherwise.

Electronic supplementary material

The online version of this article (doi:10.1186/s12918-017-0411-7) contains supplementary material, which is available to authorized users.

miRNAs in urine: a mirror image of kidney disease?

miRNAs are short non-coding RNAs that control post-transcriptional regulation of gene expression. They are found ubiquitously in tissue and body fluids and participate in the pathogenesis of many diseases. Due to these characteristics and their stability, miRNAs could serve as biomarkers of different pathologies of the kidney. Urine is a non-invasive reservoir of molecules, especially indicative of the urinary system. In this review, we focus on urinary miRNAs and their potential to serve as biomarkers in kidney disease. Past studies show that urinary miRNAs correlate with renal dysfunctions and with processes involved in the pathophysiology. However, these studies also stress the need for future research focusing on large-scale studies to confirm the usability of urinary miRNAs as diagnostic and/or prognostic markers of different kidney diseases in clinical practice.

Kinin B1 receptor antagonism is equally efficient as angiotensin receptor 1 antagonism in reducing renal fibrosis in experimental obstructive nephropathy, but is not additive

Background: Renal tubulointerstitial fibrosis is the pathological hallmark of chronic kidney disease (CKD). Currently, inhibitors of the renin–angiotensin system (RAS) remain the sole therapy in human displaying antifibrotic properties. Further antifibrotic molecules are needed. We have recently reported that the delayed blockade of the bradykinin B1 receptor (B1R) reduced the development of fibrosis in two animal models of renal fibrosis. The usefulness of new drugs also resides in outperforming the gold standards and eventually being additive or complementary to existing therapies.

Methods: In this study we compared the efficacy of a B1R antagonist (B1Ra) with that of an angiotensin type 1 receptor antagonist (AT1a) in the unilateral ureteral obstruction (UUO) model of renal fibrosis and determined whether bi-therapy presented higher efficacy than any of the drugs alone.

Results: B1R antagonism was as efficient as the gold-standard AT1a treatment. However, bitherapy did not improve the antifibrotic effects at the protein level. We sought for the reason of the absence of this additive effect by studying the expression of a panel of genes involved in the fibrotic process. Interestingly, at the molecular level the different drugs targeted different players of fibrosis that, however, in this severe model did not result in improved reduction of fibrosis at the protein level.

Conclusions: As the B1R is induced specifically in the diseased organ and thus potentially displays low side effects it might be an interesting alternative in cases of poor tolerability to RAS inhibitors.

Blockade of the kinin B1 receptor ameloriates glomerulonephritis

Severe inflammation characterizes rapidly progressive glomerulonephritides, and expression of the kinin B1 receptor (B1R) associates with inflammation. Delayed B1R blockade reduces renal inflammation in a model of unilateral ureteral obstruction, but whether B1R modulates the pathophysiology of glomerulonephritides is unknown. Here, we observed an association of B1R protein expression and inflammation, in both glomeruli and the renal interstitium, in biopsies of patients with glomerulonephritides, Henoch-Schönlein purpura nephropathy, and ANCA-associated vasculitis. In the nephrotoxic serum-induced glomerulonephritis model, we observed upregulation of the B1R receptor; treatment with a B1R antagonist beginning 2 weeks after the onset of disease reduced both glomerular and tubular lesions and improved renal function. B1R blockade reduced renal chemokine expression and macrophage accumulation. Collectively, our data demonstrate that blockade of the kinin B1R has significant potential for the treatment of glomerulonephritis.

Delayed treatment with plasminogen activator inhibitor-1 decoys reduces tubulointerstitial fibrosis

We examined the capacity of delayed inhibition of plasminogen activator inhibitor-1 (PAI-1) to reduce tubulointerstitial fibrosis induced by unilateral ureteral obstruction (UUO) in mice. Small peptides mimicking parts of urokinase (uPA) and tissular plasminogen activator (tPA) and serving as decoy molecules for PAI-1 were administered daily during the late stages (3 to 8 days) of UUO. Treatment with PAI-1 decoys reduced interstitial deposition of fibronectin, collagen III and collagen IV without changes in macrophage and myofibroblast infiltration. Interestingly, while PAI-1 activity was reduced and the combined uPA and tPA activity was increased, the antifibrotic effect was obtained without modification of plasmin activity but with increased of hepatocyte growth factor (HGF) expression. We show for the first time that treatment with small PAI-1 decoy peptides reduces established tubulointerstitial fibrosis. This protective effect probably resulted from increased degradation of the extracellular matrix by an HGF dependent mechanism.

Delayed blockade of the kinin B1 receptor reduces renal inflammation and fibrosis in obstructive nephropathy

Renal fibrosis is the common histological feature of advanced glomerular and tubulointerstitial disease leading to end-stage renal disease (ESRD). However, specific antifibrotic therapies to slow down the evolution to ESRD are still absent. Because persistent inflammation is a key event in the development of fibrosis, we hypothesized that the proinflammatory kinin B1 receptor (B1R) could be such a new target. Here we show that, in the unilateral ureteral obstruction model of renal fibrosis, the B1R is overexpressed and that delayed treatment with an orally active nonpeptide B1R antagonist blocks macrophage infiltration, leading to a reversal of the level of renal fibrosis. In vivo bone marrow transplantation studies as well as in vitro studies on renal cells show that part of this antifibrotic mechanism of B1R blockade involves a direct effect on resident renal cells by inhibiting chemokine CCL2 and CCL7 expression. These findings suggest that blocking the B1R is a promising antifibrotic therapy.

LPA1 receptor activation promotes renal interstitial fibrosis

Tubulointerstitial fibrosis in chronic renal disease is strongly associated with progressive loss of renal function. We studied the potential involvement of lysophosphatidic acid (LPA), a growth factor-like phospholipid, and its receptors LPA(1-4) in the development of tubulointerstitial fibrosis (TIF). Renal fibrosis was induced in mice by unilateral ureteral obstruction (UUO) for up to 8 d, and kidney explants were prepared from the distal poles to measure LPA release into conditioned media. After obstruction, the extracellular release of LPA increased approximately 3-fold. Real-time reverse transcription PCR (RT-PCR) analysis demonstrated significant upregulation in the expression of the LPA(1) receptor subtype, downregulation of LPA3, and no change of LPA2 or LPA4. TIF was significantly attenuated in LPA1 (-/-) mice compared to wild-type littermates, as measured by expression of collagen III, alpha-smooth muscle actin (alpha-SMA), and F4/80. Furthermore, treatment of wild-type mice with the LPA1 antagonist Ki16425 similarly reduced fibrosis and significantly attenuated renal expression of the profibrotic cytokines connective tissue growth factor (CTGF) and transforming growth factor beta (TGFbeta). In vitro, LPA induced a rapid, dose-dependent increase in CTGF expression that was inhibited by Ki16425. In conclusion, LPA, likely acting through LPA1, is involved in obstruction-induced TIF. Therefore, the LPA1 receptor might be a pharmaceutical target to treat renal fibrosis.

Gene expression profiling in the remnant kidney model of wild type and kinin B1 and B2 receptor knockout mice

Angiotensin-converting enzyme inhibitors are the most efficient pharmacologic agents to delay the development of end-stage renal disease (ESRD). This is a multipharmacologic approach that inhibits angiotensin II formation while increasing kinin concentrations. Considerable attention has been focused on the role of decreased angiotensin II levels; however, the role of increased kinin levels is gaining in interest. Kinins affect cellular physiology by interacting with one of two receptors being the more inducible B1 and the more constitutive B2 receptors. This study utilizes the mouse remnant kidney of 20 weeks duration as a model of ESRD. Whole mouse genome microarrays were used to evaluate gene expression in the remnant kidneys of wild type, B1 and B2 receptor knockout animals. The microarray data indicate that gene families involved in vascular damage, inflammation, fibrosis, and proteinuria were upregulated, whereas gene families involved in cell growth, metabolism, lipid, and protein biosynthesis were downregulated in the remnant kidneys. Interestingly, the microarray analyses coupled to histological evaluations are suggestive of a possible protective role of kinins operating through the B2 receptor subtype in this model of renal disease. The results highlight the potential of microarray technology for unraveling complex mechanisms contributing to chronic renal failure.

IGFBP-1 inhibits EGF mitogenic activity in cultured endometrial stromal cells

The properties of the insulin-like growth factor-binding proteins (IGFBP-1 to 6) are not limited to modulation of IGF actions. IGFBP-1, which shares an Arg-Gly-Asp (RGD) motif in its C-terminal domain, modulates cell motility by binding to integrin alpha5beta1. The cross-talks between integrins and growth factor receptor signalling pathways are extensively documented, particularly in the case of the epidermal growth factor receptor (EGFR). However, whether IGFBP-1 can modulate growth factor signalling through its interaction with integrin alpha5beta1 has not yet been studied. As EGF is involved in the decidualisation of endometrial stromal cells (ESCs) and as decidualised ESCs are a source of IGFBP-1, we investigated if IGFBP-1 can modulate EGF effects on ESCs. RGD- and IGF-independent inhibition of EGF mitogenic activity and EGFR signalling by IGFBP-1 were demonstrated in ESC primary cultures, A431, cells and in mouse fibroblasts lacking IGF receptors.

Renal gene expression profiling using kinin B1 and B2 receptor knockout mice reveals comparable modulation of functionally related genes

The kinin B2 receptor, which is constitutively expressed in a large number of tissues, mediates most of the known effects of bradykinin (BK). Normally undetectable in healthy tissues, the B1 receptor is strongly over-expressed under pathological conditions. BK is an important mediator in renal homeostasis and is mainly known for its natriuretic and vasodilatory effects. Recent data evidenced a role for BK in many other biological processes, such as apoptosis, development, extracellular matrix regulation and angiogenesis. In a first step to better understand how BK and its receptors could be involved in such a large variety of biological effects, we used microarray analysis to identify, under physiological conditions, the global renal gene expression profile in mice lacking either the kinin B1 or B2 receptor. Microarray experiments were performed using Agilent Mouse Oligonucleotide Microarrays (21 000 genes/microarray). Interestingly, there was a considerable number of mostly downregulated genes in both BK null mouse models compared with wild-type mice. Furthermore, a number of genes that are known to be implicated in renal physiology and/or pathology were differentially expressed in the BK null mice, which is indicative of the important role of both BK receptors in renal function.

The protective effect of angiotensin converting enzyme inhibition in experimental renal fibrosis in mice is not mediated by bradykinin B2 receptor activation

Unilateral ureteral obstruction (UUO) is an animal model of accelerated renal tubulointerstitial fibrosis. We have recently shown, using this model, that mice lacking the bradykinin B2-receptor (B2(-/-)) were more susceptible than control animals to the development of tubulointerstitial fibrosis. Angiotensin converting enzyme (ACE) inhibition slows down UUO-induced renal fibrosis. Since ACE-inhibition increases bradykinin and decreases angiotensin II concentrations we have verified if bradykinin is involved in the antifibrotic effects of ACE-inhibition using the UUO-model and B2(-/-) mice. Surprisingly, although ACE-inhibition significantly reduced renal fibrosis, no difference was observed between the degree of tubulointerstitial fibrosis, macrophage infiltration and cell proliferation between ACE-inhibitor treated B2(+/+) and B2(-/-) mice suggesting the absence of a role of the B2-receptor in the antifibrotic effects of ACE-inhibition. This was confirmed at the level of bradykinin-induced activity of enzymes involved in the degradation of the extracellular matrix. However in both mouse strains, ACE-inhibitors were more efficient than AT1 receptor antagonists.

In vivo bradykinin B2 receptor activation reduces renal fibrosis

Angiotensin-converting enzyme (ACE) inhibitors reduce the progression of various fibrotic renal diseases both in humans and in animal models. Unilateral ureteral obstruction (UUO) is an animal model of accelerated renal tubulointerstitial fibrosis that is attenuated by ACE inhibition. Although ACE inhibitors increase bradykinin concentrations in addition to their effect on angiotensin II formation, the role of bradykinin in renal fibrosis has not been studied. We show here that genetic ablation (B2(-/-) mice) or pharmacological blockade of the bradykinin B2 receptor increases UUO-induced interstitial fibrosis in mice, whereas transgenic rats expressing increased endogenous bradykinin show reduced UUO-induced interstitial fibrosis. The increased interstitial fibrosis in B2(-/-) mice was accompanied by a decreased activity of plasminogen activators (PAs) and metalloproteinase-2 (MMP-2), enzymes involved in ECM degradation, suggesting that the protective effects of bradykinin involve activation of a B2 receptor/PA/MMP-2 cascade. This ability of bradykinin to increase PA activity was confirmed in primary culture proximal tubular cells. Thus, in both mice and rats, bradykinin B2 receptor activation reduces renal tubulointerstitial fibrosis in vivo, most likely by increasing ECM degradation.

Induction of B1 receptors in streptozotocin diabetic rats: possible involvement in the control of hyperglycemia-induced glomerular Erk 1 and 2 phosphorylation

We investigated the effects of a 3-week treatment with various combinations of angiotensin-converting enzyme inhibitor (ACEI) and B1 and B2 bradykinin receptor (B1R and B2R) antagonists (B1A and B2A) and AT1 receptor antagonist on ERK 1 and 2 phosphorylation in isolated glomeruli from streptozotocin-treated diabetic rats (STZ rats). Body weight, glycemia, and blood pressure were monitored. The rats were divided into nine groups: (1) control; and groups 2-9 were STZ treated with (3) insulin, (4) ACEI, (5) ACEI + B1A, (6) ACEI + B2A, (7) B2A, (8) B1A, (9) AT1 antagonist. ERK 1 and 2 phosphorylation and expression of B1R and B2R were assessed by Western blot analysis. ERK 1 and 2 phosphorylation was higher in STZ rats; this activation was normalized by insulin and reduced by ACEI but not by AT1 antagonist. The reduction of ERK 1 and 2 phosphorylation by the ACEI was reversed by B1A and B2A. The induction of B1R was confirmed by increased expression of mRNA and B1 receptor protein. Since ERK 1 and 2 phosphorylation is an early event in the induction of matrix secretion and hyperproliferation associated with diabetic nephropathy, activation of B1R and B2R appears to be a useful pharmacological target in the management of this pathology.

Induction of functional bradykinin b(1)-receptors in normotensive rats and mice under chronic Angiotensin-converting enzyme inhibitor treatment

BACKGROUND

The physiological effects of ACE inhibitors may act in part through a kinin-dependent mechanism. We investigated the effect of chronic ACE-inhibitor treatment on functional kinin B(1)- and B(2)-receptor expression, which are the molecular entities responsible for the biological effects of kinins.

METHODS AND RESULTS

Rats were subjected to different 6-week treatments using various mixtures of the following agents: ACE inhibitor, angiotensin AT(1)-receptor antagonist, and B(1)- and B(2)-receptor antagonists. Chronic ACE inhibition induced both renal and vascular B(1)-receptor expression, whereas B(2)-receptor expression was not modified. Furthermore, with B(1)-receptor antagonists, it was shown that B(1)-receptor induction was involved in the hypotensive effect of ACE inhibition. Using microdissection, we prepared 10 different nephron segments and found ACE-inhibitor-induced expression of functional B(1)-receptors in all segments. ACE-inhibitor-induced B(1)-receptor induction involved homologous upregulation, because it was prevented by B(1)-receptor antagonist treatment. Finally, using B(2)-receptor knockout mice, we showed that ACE-inhibitor-induced B(1)-receptor expression was B(2)-receptor independent.

CONCLUSIONS

This study provides the first evidence that chronic ACE-inhibitor administration is associated with functional vascular and renal B(1)-receptor induction, which is involved in ACE-inhibitor-induced hypotension. The observed B(1)-receptor induction in the kidney might participate in the known renoprotective effects of ACE inhibition.

The glucocorticoid response element II is functionally homologous in rat and human insulin-like growth factor-binding protein-1 promoters

In vivo, insulin-like growth factor-binding protein-1 (IGFBP-1) modulates the IGFs' bioavailability and may contribute to their delivery to peripheral tissues. In rat and human hepatocytes, glucocorticoids stimulate IGFBP-1 gene transcription through homologous glucocorticoid response units (GRU). Transfection experiments have shown that one of these, GRU2 (nucleotide (nt) -121 to -85 and nt -111 to -74 in human and rat promoters, respectively), was on its own able to mediate the glucocorticoid response in rat but not in human species (Suwanichkul, A., Allander, S., Morris, S. L. & Powell, D. R. (1994) J. Biol. Chem. 269, 30835-30841, Goswami, R., Lacson, R., Yang, E., Sam, R. & Unterman, T. (1994) Endocrinology 134, 736-743, and Suh, D. S., Ooi, G. T. & Rechler, M. M. (1994) Mol. Endocrinol. 8, 794-805). A close comparison of GRU2 sequences has pointed out a C to A transition in the underlying GREII, which creates a GATC tetranucleotide in rat species. This tetranucleotide is submitted to adenosyl methylation (dam methylation) in most Escherichia coli bacterial strains, but not in eucaryotic cells. We showed (i) that on its own, the unmethylated rat GRU2 (propagated in dam E. coli strains) was inactive, as is the case for its human counterpart (nonsignificant glucocorticoid inductions, 1.48 +/- 0.23 and 1.7 +/- 0.35-fold in Chinese hamster ovary cells, respectively) and (ii) that its adenosyl methylation in standard dam+ bacterial strains yielded a functional GRU (6.5 +/- 1. 1 and 13.1 +/- 3.9-fold glucocorticoid inductions in Chinese hamster ovary and HepG2 cells, respectively). Transient transfection in HepG2 hepatoma cells clearly showed that the interaction of liver-enriched trans-acting factor(s) with the 5'-overlapping insulin response element does not enable the unmethylated rat GRU2 or the human GRU2 to become responsive to glucocorticoids (nonsignificant 2.21 +/- 0.48 and 1.20 +/- 0.06-fold induction, respectively). Furthermore, we have correlated these functional data with in vitro DNA-protein interaction studies: the dam methylated rat GREII displayed a 2.8-fold higher affinity for the glucocorticoid receptor than its unmethylated counterpart.

Stimulation of transcription in vitro from a liver-specific promoter by human glucocorticoid receptor (hGRalpha)

The rat tyrosine aminotransferase (TAT) gene is a liver-specific and glucocorticoid-inducible gene. Previous studies have shown that the TAT promoter (TAT0.35; nt -350 to +1) is able to sustain liver-specific gene expression both in transient transfection and in a transcription assay in vitro [Schweizer-Groyer, Groyer, Cadepond, Grange, Baulieu and Pictet (1994) Nucleic Acids Res. 22, 1583-1592]. Here we report that the basal transcriptional activity generated from TAT0.35 in the presence of crude liver nuclear extracts is enhanced by added human glucocorticoid receptor (hGRalpha), provided that TAT0.35 sequences were flanked (5') with a glucocorticoid responsive unit (GREII of the TAT gene, including its 5'-CCAAT flanking sequence). Two sources of hGRalpha were used: nuclear extracts prepared from Sf9 insect (Sf9-NEs) cells over-expressing hGRalpha, and hGRalpha from pRShGRalpha-transfected COS-7 cells, enriched by high-performance ion-exchange chromatography. The enhancement of transcription in vitro (1.5-4.5-fold) was dependent on the amount of added hGRalpha and independent of the nature (agonist or antagonist) of the ligand. Moreover, the hGRalpha-mediated stimulation of transcription was (i) dependent on GRE/progesterone response element (PRE) (it was inhibited by a 25-fold excess of GRE/PRE but not by a 100-fold excess of oestrogen response element) and (ii) receptor-dependent (Sf9-NEs prepared from uninfected Sf9 cells or from Sf9 cells infected with wild-type baculoviral DNA did not enhance transcription). Taken together, these experiments support the conclusions that in vitro the glucocorticoid receptor is able to enhance transcription from genomic, liver-specific, promoter sequences (those of the TAT gene), and that this enhancement of transcription from the liver-specific TAT0.35 promoter is dependent both on the glucocorticoid receptor and on the latter's interaction with its cognate response elements.

Multiple liver-enriched trans-acting factors interact with the glucocorticoid- (GRU) and cAMP-(CRU) responsive units within the h-IGFBP-1 promoter

In response to hormonal control, serum concentrations of insulin-like growth factor-binding protein-1 (IGFBP-1) may vary as much as 10-fold, owing to strict control of its gene's expression in hepatocytes. IGFBP-1 gene transcription is increased by glucocorticoids and cAMP and inhibited by insulin. The effect of insulin is dominant since it suppresses constitutive and both glucocorticoid- and cAMP-stimulated transcription. Close examination of the human (h)IGFBP-1 promoter sequences showed that the glucocorticoid (GRE, nt -88 to -102) and cAMP (CRE, nt -259 to -264) response elements are 5'-flanked by an A/T-rich imperfect palindrome (nt -102 to -117 and -265 to -285, respectively). These A/T-rich motifs are putative cis-elements for liver-enriched trans-acting factors. Competition experiments in electrophoretic mobility shift assay were carried out using rat liver nuclear extracts and a set of synthetic oligonucleotides designed from hIGFBP-1 Glucorticoid and cAMP Response Units (GRU and CRU), the rat transthyretin HNF3 cis-element and the "D-site' of the mouse albumin promoter. The nucleotide motifs located between nt -108 and -121 of the GRU, interacted with the HNF3 family of trans-acting factors (alpha, beta, gamma), whereas those encompassing nt -81 to -104 bound DBP and/or nuclear proteins sharing similar sequence specificity (i.e. from the C/EBP family of bZIP proteins). We have also shown that the hIGFBP-1-GRE binds glucocorticoid receptor homodimers. In the case of the CRU, the cis-elements located between nt -249 and -285 bound DBP and/or nuclear proteins sharing similar sequence specificities. In addition, the nucleotide stretch lying between nt -256 and -275 was able to interact with the HNF3 family of trans-acting factors. Our results support the view that the dominant inhibitory effect of insulin over glucocorticoid- and cAMP- enhanced transcription may be mediated by different target sequences located 5'- of the GRE and CRE. In both cases, the mechanism would involve the interplay of common trans-acting factor(s), some of which are liver-enriched [HNF3, DBP or C/EBP related bZIP proteins] with their cognate target sequence.

Direct protein sequencing of wheat mitochondrial ATP synthase subunit 9 confirms RNA editing in plants

RNA editing, a process that results in the production of RNA molecules having a nucleotide sequence different from that of the initial DNA template, has been demonstrated in several organisms using different biochemical pathways. Very recently RNA editing was described in plant mitochondria following the discovery that the sequence of certain wheat and Oenothera cDNAs is different from the nucleotide sequence of the corresponding genes. The main conversion observed was C to U, leading to amino acid changes in the deduced protein sequence when these modifications occurred in an open reading frame. In this communication we show the first attempt to isolate and sequence a protein encoded by a plant mitochondrial gene. Subunit 9 of the wheat mitochondrial ATP synthase complex was purified to apparent homogeneity and the sequence of the first 32 amino acid residues was determined. We have observed that at position 7 leucine was obtained by protein sequencing, instead of the serine predicted from the previously determined genomic sequence. Also we found phenylalanine at position 28 instead of a leucine residue. Both amino acid conversions, UCA (serine) to UUA (leucine) and CUC (leucine) to UUC (phenylalanine), imply a C to U change. Thus our results seem to confirm, at the protein level, the RNA editing process in plant mitochondria.

Hydroxylation of the thiophene ring by hepatic monooxygenases. Evidence for 5-hydroxylation of 2-aroylthiophenes as a general metabolic pathway using a simple UV-visible assay

The 5-hydroxylation of tienilic acid by rat liver microsomes was measured by a new, simple method involving the detection of 5-hydroxytienilic acid by UV-visible spectroscopy. This assay allowed continuous detection of this metabolite and could be easily used to determine the kinetic parameters of the reaction (Vmax and Km being respectively 1 +/- 0.2 nmol product formed/mg protein/min and 14 +/- 2 microM for liver microsomes from phenobarbital-treated rats). This activity was found to be dependent on NADPH and to be inhibited by CO, SKF 525A and metyrapone, indicating that it is dependent on cytochromes P-450. This UV-visible assay is based on intrinsic properties of 5-hydroxy 2-aroylthiophenes which exist as highly conjugated anions at physiological pH and exhibit large epsilon values around 390 nm. Its application to other 2-aroylthiophenes like suprofen, 2-parachlorobenzoylthiophene and a series of 2-aroylthiophenes with various substituents on the aroyl group showed that, in general, thiophene compounds bearing a 2-arylketo substituent appear to be hydroxylated at position 5 by rat liver microsomes. The kinetic parameters of the 5-hydroxylation of suprofen and 2-parachlorobenzoylthiophene by liver microsomes from phenobarbital-treated rats were determined and found to be similar to those for tienilic acid hydroxylation.

Evidence for a photoactivation of CO rebinding to fully reduced cytochrome c oxidase after low-temperature flash photolysis

Carbon monoxide rebinding to isolated fully reduced cytochrome c oxidase has been investigated by low-temperature, flash photolysis, dual-wavelength spectrometry. By using separately different wavelength pairs to monitor the liganding of CO to Fe a3 and by keeping all other experimental conditions identical, there has been singled out a photoactivation effect on CO rebinding. For instance, at 187 K, the rate constant of CO rebinding observed at 425-475 nm was twice that derived from the kinetic at 444-475 nm despite a rate constant of photodissociation about 10 times larger at 425-475 nm than at 444-475 nm. This new finding is discussed with respect to previous investigations under similar conditions.