Role of intron 1 in smooth muscle alpha-actin transcriptional regulation in activated mesangial cells in vivo

Cooperative action of APJ and α1A-adrenergic receptor in vascular smooth muscle cells induces vasoconstriction

The apelin receptor (APJ), a receptor for apelin and elabela/apela, induces vasodilation and vasoconstriction in blood vessels. However, the prolonged effects of increased APJ-mediated signalling, involving vasoconstriction, in smooth muscle cells have not been fully characterized. Here, we investigated the vasoactive effects of APJ gain of function under the control of the smooth muscle actin (SMA) gene promoter in mice. Transgenic overexpression of APJ (SMA-APJ) conferred sensitivity to blood pressure and vascular contraction induced by apelin administration in vivo. Interestingly, ex vivo experiments showed that apelin markedly increased the vasoconstriction of isolated aorta induced by noradrenaline (NA), an agonist for α- and β-adrenergic receptors, or phenylephrine, a specific agonist for α1-adrenergic receptor (α1-AR). In addition, intracellular calcium influx was augmented by apelin with NA in HEK293T cells expressing APJ and α1A-AR. To examine the cooperative action of APJ and α1A-AR in the regulation of vasoconstriction, we developed α1A-AR deficient mice using a genome-editing technique, and then established SMA-APJ/α1A-AR-KO mice. In the latter mouse line, aortic vasoconstriction induced by a specific agonist for α1A-AR, A-61603, were significantly less than in SMA-APJ mice. These results suggest that the APJ-enhanced response requires α1A-AR to contract vessels coordinately.

Human Smooth Muscle α-Actin Promoter Drives Cre Recombinase Expression in the Cranial Suture in Addition to Smooth Muscle Cell

Tissue-specific gene deletion by the Cre-loxp system is a powerful tool to investigate the roles of specific genes. To determine the specificity and efficiency of the Cre-mediated recombination under the control of the human smooth muscle alpha-actin promoter, we mated SMalphaA-Cre mice and R26R reporter mice. Cre-mediated recombination was observed in visceral and vascular smooth muscle cells. Partial recombination was also found in heart and musculoskeletal connective tissues. Highly efficient recombination was found in cranial sutures. Hence, we propose that SMalphaA-Cre mice are good tool for conditionally deleting gene function in the cranial suture in addition to smooth muscle cells.

Effect of the absence of interleukin-12 on mesangial proliferative glomerulonephritis induced by habu snake venom

BACKGROUND

Interleukin-12 (IL12) participates in the pathophysiology of various experimental types of progressive glomerulonephritis, but its role in acute mesangial glomerulonephritis (AMG) induced by habu snake venom (HSV) has not been determined. This study aims to evaluate the effect of the absence of IL12 on AMG induced by HSV.

METHODS

AMG was induced in IL12 knockout (IL12-/-) and C57Bl/6 (IL12+/+) mice by a single i.v. administration of HSV. Vehicle was used in control animals. Mice were studied after 3, 7, and 14 days (D3, D7, and D14).

RESULTS

After treatment with HSV, IL12+/+ and -/- mice developed focal glomerular lesions, but groups of both lineages showed no statistical difference concerning albuminuria, serum creatinine, histopathology, number of cells by glomerular tuft, and glomerular tuft area. Compared to IL12+/+ mice, IL12-/- mice showed lower scores of glomerular desmin expression on D7 [1.55 (1.32; 1.65) vs. 1.12 (1.07; 1.22); p < 0.01] and D14 [1.60 (1.55; 1.75) vs. 1.20 (1.15; 1.20); p < 0.001], respectively, and lower scores of glomerular alpha-SMA expression on D14 [0.30 (0.21; 0.38) vs. 0.16 (0.26; 0.36); p < 0.001], respectively.

CONCLUSION

The absence of IL12 reduced the activity of mesangial cells, but did not modify the course of HSV-induced AMG in mice.

Targeting myofibroblasts in model systems of fibrosis by an artificial alpha-smooth muscle-actin promoter hybrid

Myofibroblasts are the main cell types producing extracellular matrix proteins in a variety of fibrotic diseases. Therefore, they are useful targets for studies of intracellular communication and gene therapeutical approaches in scarring diseases. An artificial promoter containing the -702 bp regulatory sequence of the alpha-smooth muscle actin (SMA) gene linked to the first intron enhancer sequence of the beta-actin gene and the beta-globin intron-exon junction was constructed and tested for myofibroblast-dependent gene expression using the green fluorescent protein as a reporter. Reporter expression revealed myofibroblast-specific function in hepatic and renal myofibroblasts, in vitro. In addition, differentiation-dependent activation of the SMA-beta-actin promoter hybrid was shown after induction of myofibroblastic features in mesangial cells by stretching treatment. Furthermore, wound healing experiments with SMA-beta-actin promoter reporter mice demonstrated myofibroblast-specific action, in vivo. In conclusion, the -702 bp regulatory region of the SMA promoter linked to enhancing beta-actin and beta-globin sequences benefits from its small size and is suggested as a promising tool to target myofibroblasts as the crucial cell type in various scarring processes.

ERCC4 associated with breast cancer risk: a two-stage case-control study using high-throughput genotyping

The failure of linkage studies to identify further high-penetrance susceptibility genes for breast cancer points to a polygenic model, with more common variants having modest effects on risk, as the most likely candidate. We have carried out a two-stage case-control study in two European populations to identify low-penetrance genes for breast cancer using high-throughput genotyping. Single-nucleotide polymorphisms (SNPs) were selected across preselected cancer-related genes, choosing tagSNPs and functional variants where possible. In stage 1, genotype frequencies for 640 SNPs in 111 genes were compared between 864 breast cancer cases and 845 controls from the Spanish population. In stage 2, candidate SNPs identified in stage 1 (nominal P < 0.01) were tested in a Finnish series of 884 cases and 1,104 controls. Of the 10 candidate SNPs in seven genes identified in stage 1, one (rs744154) on intron 1 of ERCC4, a gene belonging to the nucleotide excision repair pathway, was associated with recessive protection from breast cancer after adjustment for multiple testing in stage 2 (odds ratio, 0.57; Bonferroni-adjusted P = 0.04). After considering potential functional SNPs in the region of high linkage disequilibrium that extends across the entire gene and upstream into the promoter region, we concluded that rs744154 itself could be causal. Although intronic, it is located on the first intron, in a region that is highly conserved across species, and could therefore be functionally important. This study suggests that common intronic variation in ERCC4 is associated with protection from breast cancer.

Smooth muscle alpha-actin deficiency in myofibroblasts leads to enhanced renal tissue fibrosis

Myofibroblasts are a major source of proinflammatory cytokines and extracellular matrix in progressive tissue fibrosis leading to chronic organ failure. Myofibroblasts are characterized by de novo expression of smooth muscle alpha-actin (SMalphaA), which correlates with the extent of disease progression, although their exact role is unknown. In vitro cultured myofibroblasts from kidney of SMalphaA knock-out mice demonstrate significantly more prominent cell motility, proliferation, and type-I procollagen expression than those of wild-type myofibroblasts. These pro-fibrotic properties are suppressed by adenovirus-mediated SMalphaA re-expression, accompanied by down-regulation of focal adhesion proteins. In interstitial fibrosis model, tissue fibrosis area, proliferating interstitial cell number, and type-I procollagen expression are enhanced under SMalphaA deficiency. In mesangioproliferative glomerulonephritis model, cell proliferation in the mesangial area is also enhanced in SMalphaA knock-out mice. Adenoviral SMalphaA introduction into renal interstitium obviously ameliorates tissue fibrosis in interstitial fibrosis model. These results indicate that SMalphaA suppresses the pro-fibrotic properties of myofibroblasts, highlighting the significance of smooth muscle-related proteins in moderating chronic organ fibrosis under pathological conditions.

Smooth muscle-specific dystrophin expression improves aberrant vasoregulation in mdx mice

Duchenne muscular dystrophy (DMD) is a fatal X-linked muscle-wasting disease caused by mutations of the gene encoding the cytoskeletal protein dystrophin. Therapeutic options for DMD are limited because the pathogenetic mechanism by which dystrophin deficiency produces the clinical phenotype remains obscure. Recent reports of abnormal alpha-adrenergic vasoregulation in the exercising muscles of DMD patients and in the mdx mouse, an animal model of DMD, prompted us to hypothesize that the dystrophin-deficient smooth muscle contributes to the vascular and dystrophic phenotypes of DMD. To test this, we generated transgenic mdx mice that express dystrophin only in smooth muscle (SMTg/mdx). We found that alpha-adrenergic vasoconstriction was markedly attenuated in the contracting hindlimbs of C57BL/10 wild-type mice, an effect that was mediated by nitric oxide (NO) and was severely impaired in the mdx mice. SMTg/mdx mice showed an intermediate phenotype, with partial restoration of the NO-dependent modulation of alpha-adrenergic vasoconstriction in active muscle. In addition, the elevated serum creatine kinase levels observed in mdx mice were significantly reduced in SMTg/mdx mice. This is the first report of a functional role of dystrophin in vascular smooth muscle.

Catalase deficiency renders remnant kidneys more susceptible to oxidant tissue injury and renal fibrosis in mice

BACKGROUND

Catalase is one of the important antioxidant enzymes regulating the levels of intracellular hydrogen peroxide and hydroxyl radical. The effect of catalase deficiency on progressive renal fibrosis has not been fully elucidated.

METHODS

Homozygous acatalasemic mutant mice (C3H/AnLCs(b)Cs(b)) and control wild-type mice (C3H/AnLCs(a)Cs(a)) were subjected to 5/6 nephrectomy. The functional and morphological alterations of the remnant kidneys, including tubulointerstitial fibrosis, epithelial to mesenchymal transition (EMT), peroxidation, antioxidant enzyme activity, and gene expression of EMT-related molecules were compared between the two groups at 6, 12, and 18 weeks after 5/6 nephrectomy.

RESULTS

The 5/6 nephrectomy resulted in albuminuria, decreased renal function, and tubulointerstitial fibrosis with accumulation of type I and type IV collagens in the remnant kidneys of both mouse groups. However, the degree of these changes was significantly higher in acatalasemic mice after 5/6 nephrectomy as compared with wild-type mice until week 18. EMT, a crucial phenotypic alteration of tubular epithelial cells, was observed in acatalasemic mice by electron microscopy and was associated with upregulation of EMT-related alpha-smooth muscle actin (alpha-SMA), transforming growth factor-beta1 (TGF-beta1), connective tissue growth factor (CTGF), and fibroblast specific protein-1 (FSP-1) gene expression. Significant increases in the tubulointerstitial deposition of lipid peroxidation products, including 4-hydroxy-2-nonenal and urinary excretion of 8-hydroxy-2'- deoxyguanosine were observed in the acatalasemic mice after 5/6 nephrectomy as compared with the wild-type mice. Glomerular sclerosis developed after tubulointerstitial injury in acatalasemic mice. The level of catalase activity remained low in the remnant kidneys of acatalasemic mice until week 18 without compensatory up-regulation of glutathione peroxidase or superoxide dismutase (SOD) activity. Finally, supplementation of a SOD mimetic tempol did not prevent peroxidation and tubulointerstitial fibrosis in the acatalasemic remnant kidneys.

CONCLUSION

These findings indicate that acatalasemia exacerbates renal oxidant tissue injury and sensitizes remnant kidneys to EMT and progressive renal fibrosis. This study suggests a central role for catalase in the defense against oxidant-mediated renal fibrosis.

Disruption of glomerular cell-cell and cell-matrix interactions in hydrocarbon nephropathy

Environmental chemicals play an etiological role in greater than 50% of idiopathic glomerular diseases. The present studies were conducted to define mechanisms of renal cell-specific hydrocarbon injury. Female rats were given 10 mg/kg benzo(a)pyrene (BaP) once a week for 16 wk. Progressive elevations in total urinary protein, protein/creatinine ratios, and microalbuminuria were observed in rats treated with BaP for up to 16 wk. The nephropathic response involved early reductions in mesangial cell numbers and fibronectin levels by 8 wk, coupled to transient increases in podocyte cellularity. Changes in podocyte numbers subsided by 16 wk and correlated with rebound increases in mesangial cell numbers and fibronectin levels, along with increased α-smooth muscle actin and Cu/Zn superoxide dismutase and fusion of podocyte foot processes. In culture, mesangial cells were more sensitive than podocytes to hydrocarbon injury and expressed higher levels of inducible aryl hydrocarbon hydroxylase activity. Naïve mesangial cells exerted a strong inhibitory influence on podocyte proliferation under both direct and indirect coculture conditions, and this response involved a mesangial cell-derived matrix that selectively inhibited podocyte proliferation. These findings indicate that hydrocarbon nephropathy in rats involves disruption of glomerular cell-cell and cell-matrix interactions mediated by deposition of a mesangial cell-derived growth-inhibitory matrix that regulates podocyte proliferation.

Similar rates but different modes of sequence evolution in introns and at exonic silent sites in rodents: evidence for selectively driven codon usage

In mammals divergence at fourfold degenerate sites in codons (K(4)) and intronic sequence (K(i)) are both used to estimate the mutation rate, under the supposition that both evolve neutrally. Does it matter which of these we use? Using either class of sequence can be defended because (1) K(4) is the same as K(i) (at least in rodents) and (2) there is no selectively driven codon usage (hence no systematic selection on third sites). Here we re-examine these findings using 560 introns (for 136 genes) in the mouse-rat comparison, aligned by eye and using a new maximum likelihood protocol. We find that the rate of evolution at fourfold sites and at intronic sites is similar in magnitude, but only after eliminating putatively constrained sites from introns (first introns and sites flanking intron-exon junctions). Any approximate congruence between the two rates is not, however, owing to an underlying similarity in the mode of sequence evolution. Some dinucleotides are hypermutable and differently abundant in exons and introns (e.g., CpGs). More importantly, after controlling for relative abundance, all dinucleotides starting with A or T are more prevalent in mismatches in exons than in introns, whereas C-starting dinucleotides (except CG) are more common in introns. Although C content at intronic sites is lower than at flanking fourfold sites, G content is similar, demonstrating that there exists a strong strand-specific preference for C nucleotides that is unique to exons. Transcription-coupled mutational processes and biased gene conversion cannot explain this, as they should affect introns and flanking exons equally. Therefore, by elimination, we propose this to be strong evidence for selectively driven codon usage in mammals.

Therapeutic effect of all-trans retinoic acid on rats with anti-GBM antibody glomerulonephritis

BACKGROUND

All-trans retinoic acid (ATRA) has antiproliferative and anti-inflammatory effects and is currently used in the treatment of leukemia and dermatologic diseases. We tested the therapeutic potential of ATRA on anti-glomerular basement membrane (GBM) glomerulonephritis rats.

METHODS

Glomerulonephritis was induced in male Wistar-Kyoto rats on day 0 by an intravenous injection of antirat GBM antibody. On day 14 after the induction of anti-GBM glomerulonephritis, some rats were sacrificed (N = 5). Another 10 rats were divided into two groups: the vehicle group (N = 5) and the ATRA treated group (N = 5). ATRA was orally administrated from day 14 to day 27 after disease induction. Blood pressure, body weight, urinary protein excretion, and blood chemistry was determined on days 1, 14, 21, and 27. Kidney samples were obtained on day 28. The kidneys were examined with periodic acid-Schiff staining (PAS) and immunohistochemistry using antibodies against the proliferative cell nuclear antigen (PCNA), rat monocyte and macrophage (ED-1), and alpha-smooth muscle actin (alpha-SMA). Glomerular RNA was extracted from isolated glomeruli, and reverse transcription (RT) followed by polymerase chain reaction (PCR) was performed.

RESULTS

ATRA administration produced a 55% reduction of proteinuria in glomerulonephritis rats. Light microscopic analysis revealed severe necrosis/crescent formation (>50% of the glomerulus) affecting 34% of glomeruli in vehicle rats, whereas ATRA treatment reduced the glomeruli showing severe change to 14%. ATRA also significantly reduced PCNA-positive cells, ED-1-positive cells and alpha-SMA-positive area in the glomeruli. RT-PCR analyses revealed that a wide variety of genes including inflammation related [tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta), and CCAAT enhancer-binding protein delta (C/EBPdelta)], cell proliferation-related [platelet-derived growth factor (PDGF)] and fibrosis-related [transforming growth factor-beta1 (TGF-beta1), type I collagen, and alpha-SMA) genes were suppressed in the glomeruli of ATRA-treated rats.

CONCLUSION

ATRA administration significantly reduced severe necrosis/crescent formation and urinary protein excretion in glomerulonephritis rats. Suppression of a wide variety of gene expression may partly explain the mechanism of ATRA's antiproliferative and anti-inflammatory effects. These data suggest a novel therapeutic application of ATRA toward glomerulonephritis.

Smad3 mediates transforming growth factor-beta-induced alpha-smooth muscle actin expression

Transforming growth factor-beta (TGF-beta)-induced alpha-smooth muscle actin (ASMA) expression is a key indicator of myofibroblast differentiation from fibroblasts. Recent studies suggest that a TGF-beta control element is important in the regulation of the ASMA gene promoter by TGF-beta. In this study, the role of Smad3, a key component of the Smad pathway that mediates TGF-beta signaling in regulation of ASMA gene expression, is investigated. All members of the Smad family were expressed in rat lung fibroblasts, and Smad3 expression was elevated upon TGF-beta 1 treatment. Transfection with a Smad3-expressing plasmid markedly increased Smad3 and ASMA protein expression, whereas transfection with an antisense Smad3 plasmid suppressed Smad3 and ASMA expression. Similar effects were noted when the cloned rat ASMA promoter-luciferase reporter gene construct was used to monitor transcriptional activation of the ASMA gene. Electrophoretic mobility shift assays and DNA affinity precipitation indicated Smad3 binding to at least two regions of the promoter containing CAGA motifs, termed Smad3-binding elements (SBEs). Mutation of one of the SBEs decreased promoter activity significantly, indicative of a functional role for this SBE. Taken together, these findings suggest a role for Smad3 in TGF-beta regulation of ASMA gene expression in myofibroblast differentiation.

Mycophenolic acid antagonizes the activation of cultured human mesangial cells

BACKGROUND

Activation of mesangial cells is observed in several forms of chronic renal disease, and in culture conditions upon stimulation by fetal calf serum (FCS), or agonists such as transforming growth factor beta (TGF-beta). Mycophenolate mofetil (MMF), the precursor of mycophenolic acid (MPA), is currently used in organ transplantation and has been shown to be protective in clinical and experimental glomerulonephritis. This study assessed the effects of MPA on markers of human mesangial cells (HMC) activation.

METHODS

Primary cultures of HMC and of an immortalized HMC clone (IP15 cells characterized in this report) were stimulated either by FCS or by TGF-beta, and treated by MPA at clinically relevant concentrations (1 to 10 micromol/L) for 24 hours to 14 days. HMC proliferation, smooth muscle alpha-actin (SMA), collagen type I alpha-1 chain (coll I) and fibronectin synthesis were used as markers of HMC phenotypic activation.

RESULTS

Exposure of HMC to MPA inhibited proliferation induced by FCS without cytotoxicity. MPA counteracted the stimulatory effects of FCS and TGF-beta on coll I mRNA and protein and fibronectin protein. SMA expression was increased upon exposure to MPA, without cell hypertrophy.

CONCLUSION

Treatment of cultured HMC with MPA inhibited mesangial cell proliferation and matrix production induced by stimulation with either FCS or TGF-beta. Such mechanisms may contribute to the favorable effects of treatment using mycophenolate mofetil in chronic fibrotic kidney diseases, including chronic allograft rejection.

Growth and decline of introns

To gauge the processes that might direct the length of introns, I studied the balance of indels (insertions or deletions, determined using Alu and LINE1 retroposon repeats) and the density of these repeats in the introns of the human genome. The indel balance is biased in favour of deletions and correlated with the divergence of repeats. At fixed repeat divergence, the indel bias correlated with the intron size: the shorter the intron, the more deletions were favoured over insertions. This correlation with the intron size was stronger than with the gene-wide or isochore-wide parameters. The density of repeats (the number of repeats in a unit of intron length) correlated positively with the intron size. Thus, quite different mechanisms, the indel bias and the integration and/or persistence of retroposons, act in the same direction in regards to intron size, which suggests selection for the size of individual introns.

Angiotensin II type 2 receptor overexpression activates the vascular kinin system and causes vasodilation

Angiotensin II (Ang II) is a potent vasopressor peptide that interacts with 2 major receptor isoforms - AT1 and AT2. Although blood pressure is increased in AT2 knockout mice, the underlying mechanisms remain undefined because of the low levels of expression of AT2 in the vasculature. Here we overexpressed AT2 in vascular smooth muscle (VSM) cells in transgenic (TG) mice. Aortic AT1 was not affected by overexpression of AT2. Chronic infusion of Ang II into AT2-TG mice completely abolished the AT1-mediated pressor effect, which was blocked by inhibitors of bradykinin type 2 receptor (icatibant) and nitric oxide (NO) synthase (L-NAME). Aortic explants from TG mice showed greatly increased cGMP production and diminished Ang II-induced vascular constriction. Removal of endothelium or treatment with icatibant and L-NAME abolished these AT2-mediated effects. AT2 blocked the amiloride-sensitive Na(+)/H(+) exchanger, promoting intracellular acidosis in VSM cells and activating kininogenases. The resulting enhancement of aortic kinin formation in TG mice was not affected by removal of endothelium. Our results suggest that AT2 in aortic VSM cells stimulates the production of bradykinin, which stimulates the NO/cGMP system in a paracrine manner to promote vasodilation. Selective stimulation of AT2 in the presence of AT1 antagonists is predicted to have a beneficial clinical effect in controlling blood pressure.