[Show abstract][Hide abstract] ABSTRACT: Elevated interleukin-4 (IL-4) levels are associated with cardiac fibrosis in hypertension and heart failure in both patients and experimental animals. We hypothesized that chronically elevated IL-4 induces cardiac fibrosis, resulting in a predisposition of the heart to angiotensin II-induced damage. Wild-type Balb/c (WT, high circulating IL-4) and IL-4-deficient Balb/c mice (IL-4(-/-)) were used. WT mice exhibited cardiac fibrosis (evidenced by an increase in expression of procollagen genes/interstitial collagen fraction), enlarged left ventricle chamber, and declined cardiac function associated with a greater number of mast cells and macrophages in the heart compared with IL-4(-/-). In contrast, IL-4(-/-) mice had normal cardiac architecture/function while showing a 57.9% reduction in heart interstitial collagen compared with WT, despite elevated proinflammatory cytokines in heart tissue. In response to angiotensin II administration, IL-4(-/-) had reduced interstitial myocardial fibrosis and were protected from developing dilated cardiomyopathy, which was seen in WT mice. This was associated with increased macrophage infiltration into the hearts of WT mice, despite a similar degree of hypertension and increased cardiac transforming growth factor-β1 in both groups. In vitro data demonstrated that IL-4 upregulates procollagen genes and stimulates collagen production in mouse cardiac fibroblasts. This process is mediated by signal transducer and activator of transcription 6 signaling pathway via IL-4 receptor alpha. This study not only establishes a causal relationship between IL-4 and cardiac fibrosis/dysfunction, but also reveals a critical role for IL-4 in angiotensin II-induced cardiac damage. IL-4 could serve as an additional target for the treatment of cardiac fibrosis.
[Show abstract][Hide abstract] ABSTRACT: Thick ascending limbs reabsorb 30% of the filtered NaCl load. Nitric oxide (NO) produced by NO synthase 3 (NOS3) inhibits NaCl transport by this segment. In contrast, chronic angiotensin II (Ang II) infusion increases net thick ascending limb transport. NOS3 activity is regulated by changes in expression and phosphorylation at threonine 495 (T495) and serine 1177 (S1177), inhibitory and stimulatory sites respectively. We hypothesized that NO production by thick ascending limbs is impaired by chronic Ang II-infusion, due to reduced NOS3 expression, increased phosphorylation of T495 and decreased phosphorylation of S1177. Rats were infused with 200 ng/kg/min Ang II or vehicle for 1 and 5 days. Ang II infusion for 5 days decreased NOS3 expression by 40 ± 12% (p < 0.007; n = 6) and increased T495 phosphorylation by 147 ± 26 % (p < 0.008; n = 6). One-day Ang-II infusion had no significant effect. NO production in response to endothelin-1 was blunted in thick ascending limbs from Ang II-infused animals (Ang II -0.01 ± 0.06 AFU/min vs. 0.17 ± 0.02 AFU/min in controls; p<0.01). This was not due to endothelin-1 receptor expression. Phosphatidylinositol 3,4,5-triphosphate (PIP3)-induced NO production was also reduced in Ang II-infused rats (Ang II -0.07 ± 0.06 AFU/min vs. 0.13 ± 0.04 AFU/min in controls; p<0.03), and this correlated with an impaired ability of PIP3 to increase S1177 phosphorylation. We conclude that in Ang II-induced hypertension NO production by thick ascending limbs is impaired due to decreased NOS3 expression and altered phosphorylation.-
No preview · Article · Nov 2014 · American journal of physiology. Renal physiology
[Show abstract][Hide abstract] ABSTRACT: Objective:
Inflammation has been proposed as a key component in the development of hypertension and cardiac remodeling associated with different cardiovascular diseases. However, the role of the proinflammatory cytokine interleukin-6 in the chronic stage of hypertension is not well defined. Here, we tested the hypothesis that deletion of interleukin-6 protects against the development of hypertension, cardiac inflammation, fibrosis, remodeling and dysfunction induced by high salt diet and angiotensin II (Ang II).
Male C57BL/6J and interleukin-6-knock out (KO) mice were implanted with telemetry devices for blood pressure (BP) measurements, fed a 4% NaCl diet, and infused with either vehicle or Ang II (90 ng/min per mouse subcutaneously) for 8 weeks. We studied BP and cardiac function by echocardiography at baseline, 4 and 8 weeks.
Myocyte cross-sectional area (MCSA), macrophage infiltration, and myocardial fibrosis were also assessed. BP increased similarly in both strains when treated with Ang II and high salt (Ang II-high salt); however, C57BL/6J mice developed a more severe decrease in left ventricle ejection fraction, fibrosis, and macrophage infiltration compared with interleukin-6-KO mice. No differences between strains were observed in MCSA, capillary density and MCSA to capillary density ratio.
In conclusion, absence of interleukin -6 did not alter the development of Ang II-high salt-induced hypertension and cardiac hypertrophy, but it prevented the development of cardiac dysfunction, myocardial inflammation, and fibrosis. This indicates that interleukin-6 plays an important role in hypertensive heart damage but not in the development of hypertension.
Full-text · Article · Oct 2014 · Journal of Hypertension
[Show abstract][Hide abstract] ABSTRACT: Thymosin β4 (Tβ4) promotes cell survival, angiogenesis, tissue regeneration and reduces inflammation. Cardiac rupture after myocardial infarction (MI) is mainly the consequence of excessive regional inflammation, whereas cardiac dysfunction after MI results from a massive cardiomyocyte loss and cardiac fibrosis. It is possible that Tβ4 reduces incidence of cardiac rupture post-MI via anti-inflammatory actions and that it decreases adverse cardiac remodeling and improves cardiac function by promoting cardiac cell survival and cardiac repair. C57BL/6 mice were subjected to MI and treated with either vehicle or Tβ4 (1.6 mg/kg/day i.p. via osmotic minipump) for 7 days or 5 weeks. Mice were assessed for 1) cardiac remodeling and function by echocardiography; 2) inflammatory cell infiltration, capillary density, myocyte apoptosis and interstitial collagen fraction (ICF) histopathologically; 3) gelatinolytic activity by in situ zymography; and 4) expression of intercellular adhesion molecule-1 (ICAM-1) and p53 by immunoblot. Tβ4 reduced cardiac rupture that was associated with decrease in the numbers of infiltrating inflammatory cells and apoptotic myocytes, decrease in gelatinolytic activity and ICAM-1 and p53 expression, as well as the increase in the numbers of CD31-positive cells. Five-week treatment with Tβ4 ameliorated left ventricular dilation, improved cardiac function, and markedly reduced ICF and increased capillary density. In murine model of acute MI, Tβ4 not only decreased mortality rate as a result of cardiac rupture but also significantly improved cardiac function after MI. Thus the use of Tβ4 could be explored as an alternative therapy in preventing cardiac rupture and restoring cardiac function in patients with MI.
[Show abstract][Hide abstract] ABSTRACT: The afferent arteriole (Af-Art) controls glomerular capillary pressure, an important determinant of glomerular injury. Af-Art myogenic response is mediated by ATP, and ATP signaling is in turn mediated by 20-HETE. Dahl salt-sensitive rats (Dahl SS) have decreased renal 20-HETE production. We hypothesized that Dahl SS have an impaired myogenic response and constrictor response to ATP, due to decreased 20-HETE. Af-Arts from Dahl SS or Dahl salt resistant rats (Dahl SR) were microdissected and perfused. When myogenic response was induced by increasing Af-Art perfusion pressure from 60 to 140 mmHg, luminal Af-Art diameter decreased in Dahl SR but not in Dahl SS (-3.1±0.8 vs. 0.5±0.8 µm, P<0.01). The 20-HETE antagonist 20-HEDE (10(-6)M) blocked the myogenic response in Dahl SR but had no effect in Dahl SS. Addition of a subconstrictor concentration of 20-HETE (but not a subconstrictor concentration of norepinephrine) restored the myogenic response in Dahl SS. We then perfused Af-Arts at 60 mmHg and tested the effects of the ATP analog α,β-methylene-ATP (10-6M). Maximum ATP-induced constriction was attenuated in Dahl SS compared to Dahl SR (1.5±0.5 vs. 7.4±0.8 µm, P<0.001). 20-HEDE attenuated ATP-induced Af-Art constriction in Dahl SR but not in Dahl SS, and consequently, ATP-induced constriction was no longer different between strains. In conclusion, Dahl SS have an impaired myogenic response and ATP-induced Af-Art constriction due to a decrease in Af-Art 20-HETE. The impaired myogenic responses may contribute to the nephrosclerosis that develops in Dahl SS.
Preview · Article · Jul 2014 · American journal of physiology. Renal physiology
[Show abstract][Hide abstract] ABSTRACT: Increasing Na delivery to epithelial Na channels (ENaC) in the connecting tubule (CNT) dilates the afferent arteriole (Af-Art), a process we call connecting tubule glomerular feedback (CTGF). We hypothesize that aldosterone sensitizes CTGF via a nongenomic mechanism that stimulates CNT ENaC via the aldosterone receptor GPR30. Rabbit Af-Arts and their adherent CNTs were microdissected and simultaneously perfused. Two consecutive CTGF curves were elicited by increasing luminal NaCl in the CNT. During the control period, the concentration of NaCl that elicited a half-maximal response (EC50) was 37.0±2.0 mmol/L; addition of aldosterone 10-8 mol/L to the CNT lumen caused a left-shift (decrease) in EC50 to 19.3±1.3 mmol/L (P=0.001 vs. Control; n=6). Neither the transcription inhibitor actinomycin D (control EC50=34.7±1.9 mmol/L; aldosterone+actinomycin D EC50=22.6±1.6 mmol/L; n=6; P < 0.001) nor the translation inhibitor cycloheximide (control EC50=32.4±4.3 mmol/L; aldosterone+cycloheximide EC50=17.4±3.3 mmol/L; n=6; P < 0.001) prevented the effect of aldosterone. The aldosterone antagonist eplerenone prevented the sensitization of CTGF by aldosterone (control EC50=33.2±1.7 mmol/L; aldosterone+eplerenone EC50=33.5±1.3 mmol/L; n=7). The GPR30 receptor blocker G-36 blocked the sensitization of CTGF by aldosterone (aldosterone EC50=16.5±1.9 mmol/L; aldosterone+G-36 EC50=29.0±2.1 mmol/L; n=7; P < 0.001). Finally, we found that the sensitization of CTGF by aldosterone was mediated, at least in part, by the sodium/hydrogen exchanger (NHE). We conclude that aldosterone in the CNT lumen sensitizes CTGF via a nongenomic effect involving GPR30 receptors and NHE. Sensitized CTGF induced by aldosterone may contribute to renal damage by increasing Af-Art dilation and glomerular capillary pressure (glomerular barotrauma).
Preview · Article · Jun 2014 · American journal of physiology. Renal physiology
[Show abstract][Hide abstract] ABSTRACT: The activation of angiotensin II type 2 receptor (AT2R) has been considered cardioprotective. However, there are controversial findings regarding the role of overexpressing AT2R in the heart. Using transgenic mice with different levels of AT2R gene overexpression in the heart (1, 4, or 9 copies of the AT2R transgene: Tg(1), Tg(4), or Tg(9)), we studied the effect of AT2R overexpression on left ventricular remodeling and dysfunction post-myocardial infarction (MI). Tg(1), Tg(4), Tg(9), and their wild-type littermates were divided into (1) sham MI, (2) MI plus vehicle, and (3) MI plus AT2R antagonist. Treatments were started 4 weeks after MI and continued for 8 weeks. AT2R protein and mRNA expression in the heart was significantly increased in transgenic mice, and the increase positively correlated with copies of the transgene. AT1R protein and mRNA expression remained unchanged in Tg(1) and Tg(4) but slightly increased in Tg(9) mice. Systolic blood pressure and cardiac phenotypes did not differ among strains under basal conditions. MI caused myocardial hypertrophy, interstitial fibrosis, ventricular dilatation, and dysfunction associated with increased protein expression of Nox2 and transforming growth factor β1. These pathological responses were diminished in Tg(1) and Tg(4) mice. Moreover, the protective effects of AT2R were abolished by AT2R antagonist and also absent in Tg(9) mice. We thus conclude that whether overexpression of AT2R is beneficial or detrimental to the heart is largely dependent on expression levels and possibly via regulations of Nox2 and transforming growth factor β1 signaling pathways.
[Show abstract][Hide abstract] ABSTRACT: P311 is an 8-kDa intracellular protein that is highly conserved across species and is expressed in the nervous system as well as in vascular and visceral smooth muscle cells. P311-null (P311-/-) mice display learning and memory defects, but alterations in their vasculature have not been previously described. Here we report that P311-/- mice are markedly hypotensive with accompanying defects in vascular tone and VSMC contractility. Functional abnormalities in P311-/- mice resulted from decreased total and active levels of TGF-β1, TGF-β2, and TGF-β3 that arise as a specific consequence of decreased translation. Vascular hypofunctionality was fully rescued in vitro and in vivo by exogenous TGF-β1-TGF-β3. Conversely, P311-transgenic (P311TG) mice had elevated levels of TGF-β1-TGF-β3 and subsequent hypertension. Consistent with findings attained in mouse models, arteries recovered from hypertensive human patients displayed increased P311 expression. Thus, we identified P311 as the first protein known to modulate TGF-β translation and the first pan-regulator of TGF-β expression under steady-state conditions. Together, our findings point to P311 as a critical blood pressure regulator and establish a potential link between P311 expression and the development of hypertensive disease.
Preview · Article · Oct 2013 · The Journal of clinical investigation
[Show abstract][Hide abstract] ABSTRACT: Connecting tubule glomerular feedback (CTGF) is a mechanism in which Na reabsorption in the connecting tubule (CNT) causes afferent arteriole (Af-Art) dilation. CTGF is mediated by eicosanoids, including prostaglandins and epoxyeicosatrienoic acids; however, their exact nature and source remain unknown. We hypothesized that during CTGF, the CNT releases prostaglandin E2, which binds its type 4 receptor (EP4) and dilates the Af-Art. Rabbit Af-Arts with the adherent CNT intact were microdissected, perfused, and preconstricted with norepinephrine. CTGF was elicited by increasing luminal NaCl in the CNT from 10 to 80 mmol/L. We induced CTGF with or without the EP4 receptor blocker ONO-AE3-208 added to the bath in the presence of the epoxyeicosatrienoic acid synthesis inhibitor MS-PPOH. ONO-AE3-208 abolished CTGF (control, 9.4±0.5; MS-PPOH+ONO-AE3-208, -0.6±0.2 μm; P<0.001; n=6). To confirm these results, we used a different, specific EP4 blocker, L161982 (10(-5) mol/L), that also abolished CTGF (control, 8.5±0.9; MS-PPOH+L161982, 0.8±0.4 μm; P<0.001; n=6). To confirm that the eicosanoids that mediate CTGF are released from the CNT rather than the Af-Art, we first disrupted the Af-Art endothelium with an antibody and complement. Endothelial disruption did not affect CTGF (7.9±0.9 versus 8.6±0.6 μm; P=NS; n=7). We then added arachidonic acid to the lumen of the CNT while maintaining zero NaCl in the perfusate. Arachidonic acid caused dose-dependent dilation of the attached Af-Art (from 8.6±1.2 to 15.3±0.7 μm; P<0.001; n=6), and this effect was blocked by ONO-AE3-208 (10(-7) mol/L). We conclude that during CTGF, the CNT releases prostaglandin E2, which acts on EP4 on the Af-Art inducing endothelium-independent dilation.
[Show abstract][Hide abstract] ABSTRACT: In Dahl salt-sensitive rats (Dahl SS), glomerular capillary pressure increases in response to high salt intake and this is accompanied by significant glomerular injury compared with spontaneously hypertensive rats with similar blood pressure. Glomerular capillary pressure is controlled mainly by afferent arteriolar resistance, which is regulated by the vasoconstrictor tubule glomerular feedback (TGF) and the vasodilator connecting TGF (CTGF). We hypothesized that Dahl SS have a decreased TGF response and enhanced TGF resetting compared with spontaneously hypertensive rats, and that these differences are attributable in part to an increase in CTGF. In vivo, using micropuncture we measured stop-flow pressure (a surrogate of glomerular capillary pressure). TGF was calculated as the maximal decrease in stop-flow pressure caused by increasing nephron perfusion, TGF resetting as the attenuation in TGF induced by high salt diet, and CTGF as the difference in TGF response before and during CTGF inhibition with benzamil. Compared with spontaneously hypertensive rats, Dahl SS had (1) lower TGF responses in normal (6.6±0.1 versus 11.0±0.2 mm Hg; P<0.001) and high-salt diets (3.3±0.1 versus 10.1±0.3 mm Hg; P<0.001), (2) greater TGF resetting (3.3±0.1 versus 1.0±0.3 mm Hg; P<0.001), and (3) greater CTGF (3.4±0.4 versus 1.2±0.1 mm Hg; P<0.001). We conclude that Dahl SS have lower TGF and greater CTGF than spontaneously hypertensive rats, and that CTGF antagonizes TGF. Furthermore, CTGF is enhanced by a high-salt diet and contributes significantly to TGF resetting. Our findings may explain in part the increase in vasodilatation, glomerular capillary pressure, and glomerular damage in SS hypertension during high salt intake.
[Show abstract][Hide abstract] ABSTRACT: We previously reported that N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP) reduces fibrosis and inflammation (macrophages and mast cells). However, it is not known whether Ac-SDKP decreases collagen cross-linking and lymphocyte infiltration; lymphocytes modulate both collagen cross-linking and extracellular matrix formation in hypertension. Thus, we hypothesized that 1) in angiotensin (Ang) II-induced hypertension, Ac-SDKP prevents increases in cross-linked and total collagen by down-regulating lysyl oxidase (LOX), the enzyme responsible for cross-linking, and 2) these effects are associated with decreased a) pro-fibrotic cytokine TGF-β and b) the pro-inflammatory transcription factor nuclear factor κB (NFκB), and c) CD4+/CD8+ lymphocyte infiltration. We induced hypertension in rats by infusing Ang II either alone or combined with Ac-SDKP for 3 weeks. While Ac-SDKP failed to lower blood pressure or left ventricular hypertrophy, it did prevent Ang II-induced increases in 1) cross-linked and total collagen, 2) LOX mRNA expression and LOXL1 protein, 3) TGF-β expression, 4) nuclear translocation of NFκB, 5) CD4+/CD8+ lymphocyte infiltration and 6) CD68+ macrophages infiltration. In addition, we found a positive correlation between CD4+ infiltration and LOXL1 expression. In conclusion, the effect of Ac-SDKP on collagen cross-linking and total collagen may be due to reduced TGF-β1, LOXL1 and lymphocyte and macrophages infiltration, and its effect on inflammation could be due to lower NFκB.
[Show abstract][Hide abstract] ABSTRACT: Previously, we found thymosin β4 (Tβ4) is upregulated in glomerulosclerosis and required for angiotensin II-induced expression of plasminogen activator inhibitor-1 (PAI-1) in glomerular endothelial cells. Tβ4 has beneficial effects in dermal and corneal wound healing and heart disease, yet its effects in kidney disease are unknown. Here we studied renal fibrosis in wild-type and PAI-1 knockout mice following unilateral ureteral obstruction to explore the impact of Tβ4 and its prolyl oligopeptidase tetrapeptide degradation product, N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), in renal fibrosis. Additionally, we explored interactions of Tβ4 with PAI-1. Treatment with Ac-SDKP significantly decreased fibrosis in both wild-type and PAI-1 knockout mice, as observed by decreased collagen and fibronectin deposition, fewer myofibroblasts and macrophages, and suppressed profibrotic factors. In contrast, Tβ4 plus a prolyl oligopeptidase inhibitor significantly increased fibrosis in wild-type mice. Tβ4 alone also promoted repair and reduced late fibrosis in wild-type mice. Importantly, both profibrotic effects of Tβ4 plus the prolyl oligopeptidase inhibitor, and late reparative effects of Tβ4 alone, were absent in PAI-1 knockout mice. Thus, Tβ4 combined with prolyl oligopeptidase inhibition is consistently profibrotic, but by itself has antifibrotic effects in late-stage fibrosis, while Ac-SDKP has consistent antifibrotic effects in both early and late stages of kidney injury. These effects of Tβ4 are dependent on PAI-1.Kidney International advance online publication, 5 June 2013; doi:10.1038/ki.2013.209.
Full-text · Article · Jun 2013 · Kidney International
[Show abstract][Hide abstract] ABSTRACT: Myocardial matrix turnover involves a dynamic balance between collagen synthesis and degradation, which is regulated by matrix metalloproteinases (MMPs). N-acetyl-Ser-Asp-Lys-Pro (Ac-SDKP) is a small peptide that inhibits cardiac inflammation and fibrosis. However, its role in MMP regulation is not known. Thus, we hypothesized that Ac-SDKP promotes MMP activation in cardiac fibroblasts and decreases collagen deposition via this mechanism. To that end, we tested the effects of Ac-SDKP on interleukin-1β (IL-1β; 5 ng/ml)-stimulated adult rat cardiac fibroblasts. We measured total collagenase activity, MMP-2, MMP-9, and MMP-13 expressions, and activity along with their inhibitors, tissue inhibitor of metalloproteinase (TIMP)-1 and TIMP-2. In order to examine the effects of Ac-SDKP on the signaling pathway that controls MMP transcription, we also measured nuclear factor-κB (NFκB) and p42/44 mitogen-activated protein kinase (MAPK) activation. Ac-SDKP did not alter collagenase or gelatinase activity in cardiac fibroblasts under basal conditions, but blunted the IL-1β-induced increase in total collagenase activity. Similarly, Ac-SDKP normalized the IL-1β-mediated increase in MMP-2 and MMP-9 activities and MMP-13 expression. Inhibition of MMPs by Ac-SDKP was associated with increased TIMP-1 and TIMP-2 expressions. Collagen production was not affected by Ac-SDKP, IL-1β, or a combination of both agents. Ac-SDKP blocked IL-1β-induced p42/44 phosphorylation and NFκB activation in cardiac fibroblasts. We concluded that the Ac-SDKP-inhibited collagenase expression and activation was associated with increased expression of TIMP-1 and TIMP-2. These pharmacological effects of Ac-SDKP may be linked to the inhibition of MAPK and NFκB pathway.
No preview · Article · May 2013 · Pflügers Archiv - European Journal of Physiology