Activation of cardiac fibroblasts and their differentiation into myofibroblasts is a key event in the progression of cardiac fibrosis that leads to end-stage heart failure. Apelin, an ...adipocyte-derived factor, exhibits a number of cardioprotective properties; however, whether apelin is involved in cardiac fibroblast activation and myofibroblast formation remains unknown. The aim of this study was to determine the effects of apelin in activated cardiac fibroblasts, the potential related mechanisms and impact on cardiac fibrotic remodelling process.
In vitro experiments were performed in mouse cardiac fibroblasts obtained from normal and pressure-overload hearts. Pretreatment of naive cardiac fibroblasts with apelin (1-100 nM) inhibited Transforming growth factor-β (TGF-β)-mediated expression of the myofibroblast marker α-smooth muscle actin (α-SMA) and collagen production. Furthermore, apelin decreased the spontaneous collagen production in cardiac fibroblasts isolated from hearts after aortic banding. Knockdown strategy and pharmacological inhibition revealed that prevention of collagen accumulation by apelin was mediated by a reduction in sphingosine kinase 1 (SphK1) activity. In vivo studies using the aortic banding model indicated that pretreatment with apelin attenuated the development of myocardial fibrotic remodelling and inhibited cardiac SphK1 activity and α-SMA expression. Moreover, administration of apelin 2 weeks after aortic banding prevented cardiac remodelling by inhibiting myocyte hypertrophy, cardiac fibrosis, and ventricular dysfunction.
Our data provide the first evidence that apelin inhibits TGF-β-stimulated activation of cardiac fibroblasts through a SphK1-dependent mechanism. We also demonstrated that the administration of apelin during the phase of reactive fibrosis prevents structural remodelling of the myocardium and ventricular dysfunction. These findings may have important implications for designing future therapies for myocardial performance during fibrotic remodelling, affecting the clinical management of patients with progressive heart failure.
Abstract
Background
Chromosomes are subdivided spatially to delimit long-range interactions into topologically associating domains (TADs). TADs are often flanked by chromatin insulators and ...transcription units that may participate in such demarcation. Remarkably, single-cell Drosophila TAD units correspond to dynamic heterochromatin nano-compartments that can self-assemble. The influence of insulators on such dynamic compartmentalization remains unclear. Moreover, to what extent heterochromatin domains are fully compartmentalized away from active genes remains unclear from Drosophila to human.
Results
Here, we identify H3K27me3 micro-domains genome-wide in Drosophila, which are attributed to the three-dimensional spreading of heterochromatin marks into euchromatin. Whereas depletion of insulator proteins increases H3K27me3 spreading locally, across heterochromatin borders, it concomitantly decreases H3K27me3 levels at distant micro-domains discrete sites. Quantifying long-range interactions suggests that random interactions between heterochromatin TADs and neighbor euchromatin cannot predict the presence of micro-domains, arguing against the hypothesis that they reflect defects in self-folding or in insulating repressive TADs. Rather, micro-domains are predicted by specific long-range interactions with the TAD borders bound by insulator proteins and co-factors required for looping. Accordingly, H3K27me3 spreading to distant sites is impaired by insulator mutants that compromise recruitment of looping co-factors. Both depletions and insulator mutants significantly reduce H3K27me3 micro-domains, deregulating the flanking genes.
Conclusions
Our data highlight a new regulatory mode of H3K27me3 by insulator-based long-range interactions controlling distant euchromatic genes.
Activation of heterotrimeric G proteins by their cognate seven transmembrane domain receptors is believed to involve conformational changes propagated from the receptor to the G proteins. However, ...the nature of these changes remains unknown. We monitored the conformational rearrangements at the interfaces between receptors and G proteins and between G protein subunits by measuring bioluminescence resonance energy transfer between probes inserted at multiple sites in receptor-G protein complexes. Using the data obtained for the alpha(2A)AR-G alpha(i1) beta1gamma2 complex and the available crystal structures of G alpha(i1) beta1gamma2, we propose a model wherein agonist binding induces conformational reorganization of a preexisting receptor-G protein complex, leading the G alpha-G betagamma interface to open but not dissociate. This conformational change may represent the movement required to allow nucleotide exit from the G alpha subunit, thus reflecting the initial activation event.
Celotno besedilo
Dostopno za:
DOBA, IJS, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
The localization of condensin along chromosomes is crucial for their accurate segregation in anaphase. Condensin is enriched at telomeres but how and for what purpose had remained elusive. Here, we ...show that fission yeast condensin accumulates at telomere repeats through the balancing acts of Taz1, a core component of the shelterin complex that ensures telomeric functions, and Mit1, a nucleosome remodeler associated with shelterin. We further show that condensin takes part in sister-telomere separation in anaphase, and that this event can be uncoupled from the prior separation of chromosome arms, implying a telomere-specific separation mechanism. Consistent with a cis-acting process, increasing or decreasing condensin occupancy specifically at telomeres modifies accordingly the efficiency of their separation in anaphase. Genetic evidence suggests that condensin promotes sister-telomere separation by counteracting cohesin. Thus, our results reveal a shelterin-based mechanism that enriches condensin at telomeres to drive in cis their separation during mitosis.
We have investigated the mechanisms whereby α2B-adrenergic receptor (α2B-AR) promotes MAPK activation in a clone of the renal tubular cell line, LLC-PK1, transfected with the rat nonglycosylated ...α2-AR gene. Treatment of LLC-PK1-α2Bwith UK14304 or dexmedetomidine caused arachidonic acid (AA) release and ERK2 phosphorylation. AA release was abolished by prior treatment of the cells with pertussis toxin, quinacrine, or methyl arachidonyl fluorophosphonate but not by the addition of the MEK inhibitor U0126. The effects of α2-agonists on MAPK phosphorylation were mimicked by cell exposure to exogenous AA. On the other hand, quinacrine abolished the effects of UK14304, but not of AA, suggesting that AA released through PLA2 is responsible for MAPK activation by α2B-AR. The effects of α2-agonists or AA were PKC-independent and were attenuated by indomethacin and nordihydroguaiaretic acid. Treatment with batimastat, CRM 197, or tyrphostin AG1478 suppressed MAPK phosphorylation promoted by α2-agonist or AA. Furthermore, conditioned culture medium from UK14304-treated LLC-PK1-α2B induced MAPK phosphorylation in wild-type LLC-PK1. Based on these data, we propose a model whereby activation of MAPK by α2B-AR is mediated through stimulation of PLA2, AA release, generation of AA derivatives, activation of matrix metalloproteinases, release of heparin-binding EGF-like growth factor, transactivation of epidermal growth factor receptor, and recruitment of Shc. Whether this pathway is particular to α2B-AR and LLC-PK1 or whether it can be extended to other cell types and/or other G-protein-coupled receptors remains to be established.
Background and Purpose
Phenelzine is an antidepressant drug known to increase the risk of hypertensive crisis when dietary tyramine is not restricted. However, this MAO inhibitor inhibits other ...enzymes not limited to the nervous system. Here we investigated if its antiadipogenic and antilipogenic effects in cultured adipocytes could contribute to decreased body fat in vivo, without unwanted hypertensive or cardiovascular effects.
Experimental Approach
Mice were fed a standard chow and given 0.028% phenelzine in drinking water for 12 weeks. Body composition was determined by NMR. Cardiovascular dysfunction was assessed by heart rate variability analyses and by evaluation of cardiac oxidative stress markers. MAO activity, hydrogen peroxide release and triacylglycerol turnover were assayed in white adipose tissue (WAT), alongside determination of glucose and lipid circulating levels.
Key Results
Phenelzine‐treated mice exhibited lower body fat content, subcutaneous WAT mass and lipid content in skeletal muscles than control, without decreased body weight gain or food consumption. A modest alteration of cardiac sympathovagal balance occurred without depressed aconitase activity. In WAT, phenelzine impaired the lipogenic but not the antilipolytic actions of insulin, MAO activity and hydrogen peroxide release. Phenelzine treatment lowered non‐fasting blood glucose and phosphoenolpyruvate carboxykinase expression. In vitro, high doses of phenelzine decreased both lipolytic and lipogenic responses in mouse adipocytes.
Conclusion and Implications
As phenelzine reduced body fat content without affecting cardiovascular function in mice, it may be of benefit in the treatment of obesity‐associated complications, with the precautions of use recommended for antidepressant therapy.
OBJECTIVE:Sparse data are available on renal consequences of hemorrhagic shock in mice. This study aimed to extend the current knowledge on functional and morphologic renal impact of hemorrhagic ...shock in mice and to determine its ability to stand as an accurate model of acute kidney injury.
DESIGN:In vivo study.
SETTING:University research unit.
SUBJECTS:C57/Bl6 mice.
INTERVENTIONS:A model of controlled hemorrhagic shock was adapted to determine the renal impact of hemorrhagic shock in mice.
MEASUREMENTS AND MAIN RESULTS:Renal functions and kidney morphology were followed up from 3 hrs to 21 days after hemorrhagic shock. When prolonged up to 2 hrs, hypotension (35 mm Hg mean arterial blood pressure) induced by temporary blood removal was responsible for an early and lasting increase in hypoxia-inducible factor-1α and kidney-inducible molecule-1 gene expression that paralleled acute tubular necrosis and renal failure. Two-hr hypotension induced an important but reversible decrease in glomerular filtration rate up to 6 days after hemorrhagic shock. Other renal dysfunctions included a renal loss of sodium, assessed by the increase in sodium excretion, and a decrease in urine concentration that persists up to day 21. Tissular damages prevailed in the outer medulla 2 days after hemorrhagic shock, being maximal at day 6. At day 21, renal healing was associated with epithelial recovery and a significant interstitial fibrosis.
CONCLUSIONS:Our data indicate that apparent recovery of renal function after acute kidney injury can mask persisting dysfunctions and tissular damages that could predispose to chronic kidney disease. Prolonged hemorrhagic shock in mice closely mimics renal effects induced by similar situation in humans, thus providing a useful tool to investigate pathophysiological mechanisms and protection strategies against acute kidney injury in situations such as hemorrhagic shock.
Tyramine is naturally occurring in food and induces pressor responses. Low-tyramine diets are recommended for patients treated with MAO inhibitors to avoid the fatal hypertensive crisis sadly known ...as “cheese effect”. Hence, tyramine intake is suspected to have toxicological consequences in humans, while its administration to type 1 diabetic rodents has been reported to improve glucose tolerance. We investigated in mice whether prolonged tyramine ingestion could alter glucose homeostasis, insulin sensitivity, adipose tissue physiology or cardiovascular functions. Tyramine was added at 0.04 or 0.14 % in the drinking water since this was estimated to increase by 10- to 40-fold the spontaneous tyramine intake of control mice fed a standard diet. Ten to 12 weeks of such tyramine supplementation did not influence body weight gain, adiposity or food consumption. Both doses (reaching approx. 300 and 1100 μmol tyramine/kg bw/day) decreased nonfasting blood glucose but did not modify glucose tolerance or fasting levels of glucose, insulin or circulating lipids. Blood pressure was not increased in tyramine-drinking mice, while only the higher tested dose moderately increased heart rate without change in its variability. Markers of cardiac tissue injury or oxidative stress remained unaltered, except an increased hydrogen peroxide production in heart preparations. In isolated adipocytes, tyramine inhibited lipolysis similarly in treated and control groups, as did insulin. The lack of serious adverse cardiovascular effects of prolonged tyramine supplementation in normoglycemic mice together with the somewhat insulin-like effects found on adipose cells should lead to reconsider favourably the risk/benefit ratio of the intake of this dietary amine.
Dietary cholesterol absorption contributes to a large part of the circulating cholesterol. However, the mechanism of sterol intestinal uptake is not clearly elucidated. Scavenger receptor class B ...type I (SR-BI), major component in the control of cholesterol homeostasis, is expressed in the intestine, but its role in this organ remains unclear. We have generated transgenic mice overexpressing SR-BI primarily in the intestine by using the mouse SR-BI gene under the control of intestinal specific “apoC-III enhancer coupled with apoA-IV promoter.” We found SR-BI overexpression with respect to the natural protein along the intestine and at the top of the villosities. After a meal containing 14Ccholesterol and 3Htriolein, SR-BI transgenic mice presented a rise in intestinal absorption of both lipids that was not due to a defect in chylomicron clearance nor to a change in the bile flow or the bile acid content. Nevertheless, SR-BI transgenic mice showed a decrease of total cholesterol but an increase of triglyceride content in plasma without any change in the high density lipoprotein apoA-I level. Thus, we described for the first time a functional role in vivo for SR-BI in cholesterol but also in triglyceride intestinal absorption.
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