Normalization of wall shear stress as a physiological mechanism for regulating maternal uterine artery expansive remodeling during pregnancy

Outward remodeling of the maternal uterine circulation during pregnancy is essential for normal uteroplacental perfusion and pregnancy outcome. The physiological mechanism by which this process is regulated is unknown; we hypothesized that it involved the normalization of wall shear stress (WSS). Pregnant Sprague-Dawley rats underwent unilateral ligation of the main uterine artery and vein at the cervical end of the uterus on gestational day 10, thus restricting inflow/outflow of blood into that uterine horn to a single point at the ovarian end; the contralateral sham-operated side provided an internal control. This procedure alters uterine hemodynamics by increasing WSS, since the entire uterine horn is supplied by one rather than two vessels. Arterial diameter and blood flow velocity values were measured by intravital ultrasonographic pulse-wave Doppler on gestational day 20 and used to calculate WSS. Although both ovarian artery lumen diameter and blood velocity increased, WSS was similar in both horns. These data support the concept that increased WSS secondary to hemochorial placentation is the primary physiological stimulus for uterine vascular remodeling and that its normalization may be the primary mechanism that regulates the extent of arterial circumferential growth required to maintain placental perfusion. We further hypothesize that shallow spiral artery invasion, such as occurs in preeclampsia, limits the increase in upstream shear stress and results in attenuated remodeling and placental under-perfusion.

Plasticity of the Maternal Vasculature During Pregnancy

Maternal cardiovascular changes during pregnancy include an expansion of plasma volume, increased cardiac output, decreased peripheral resistance, and increased uteroplacental blood flow. These adaptations facilitate the progressive increase in uteroplacental perfusion that is required for normal fetal growth and development, prevent the development of hypertension, and provide a reserve of blood in anticipation of the significant blood loss associated with parturition. Each woman's genotype and phenotype determine her ability to adapt in response to molecular signals that emanate from the fetoplacental unit. Here, we provide an overview of the major hemodynamic and cardiac changes and then consider regional changes in the splanchnic, renal, cerebral, and uterine circulations in terms of endothelial and vascular smooth muscle cell plasticity. Although consideration of gestational disease is beyond the scope of this review, aberrant signaling and/or maternal responsiveness contribute to the etiology of several common gestational diseases such as preeclampsia, intrauterine growth restriction, and gestational diabetes.

Enhanced Vascular Smooth Muscle Calcium Sensitivity and Loss of Endothelial Vasodilator Influence Contribute to Myogenic Tone Development in Rat Radial Uterine Arteries during Gestation

Uterine artery myogenic tone (MT) develops during pregnancy in hemochorial placentates such as rats and humans. The physiological reason for its appearance is not clear, and we reasoned that it may be a late pregnancy (LP) event in preparation for controlling hemorrhage during parturition. We also hypothesized that gestational increases in RhoA-induced vascular smooth muscle (VSM) calcium sensitivity are contributory and occur under the tonic influence of nitric oxide (NO). Second-order pre-placental radial arteries from early-pregnant (day 12, n = 5), mid-pregnant (day 16, n = 5) and LP (day 20, n = 20) rats were used in combination with arteriography, VSM calcium measurements, pharmacological RHO/Rho-associated protein kinase (ROCK) and nitric oxide synthase (NOS) inhibition, and Western blotting. A subgroup of LP animals (LP + LN; n = 5) treated with L-NAME from gestational days 10 to 20 were used to determine the effects of NOS inhibition on MT and RhoA expression. MT was evident throughout pregnancy, but its expression in pressurized vessels was masked by endothelial NO-induced vasodilation during early gestation. RhoA protein expression was upregulated in LP and attenuated by in vivo NOS inhibition (as was MT). In vitro RHO/ROCK inhibition decreased MT in a concentration-dependent manner without reducing VSM calcium. In summary, pressure-dependent uterine artery tone increases with gestational age due to a combination of RhoA-mediated increases in VSM calcium sensitivity and a loss of endothelial NO influence.

Postpartum Persistence of Maternal Uterine Vascular Gestational Adaptation in Rodents

Although pregnancy has long-lasting consequences for maternal vascular health, little is known about vascular changes postpartum (PP). Focusing on the uterine circulation, which undergoes unique structural and functional adaptation during gestation, we hypothesized that most pregnancy-induced changes would return to baseline PP, with minimal hysteresis. Large (main; MUA) and small (segmental; SUA) uterine arteries from adult Sprague Dawley rats (n = 42) were evaluated 1 and 4 weeks PP (1PP, 4PP) and compared with those of late-pregnant (LP, day 21) and age-matched non-pregnant (NP) animals. Some comparisons were extended to mesenteric arteries to evaluate differences between reproductive and systemic vessels. Pregnancy-induced axial elongation regressed > 80% 1PP in MUAs and SUAs, although some minimal hysteresis remained 4PP. Circumferential growth was slower to regress, with no reductions in lumen diameter or media thickness 1PP; values returned to (MUA) or approached (SUA) NP values by 4PP. Changes in vascular smooth muscle cell cross-sectional area-a measure of hypertrophy-paralleled those in lumen diameter. Mesenteric and uterine artery compliance diverged during gestation, and continued to do so PP. Decreased MUA compliance 4PP was supported by an increased collagen:elastin ratio. Adrenergic sensitivity increased in uterine, and decreased in mesenteric arteries during pregnancy, and returned to NP values 4PP in both types of vessels. MUA α-1 adrenoceptor expression tracked along with sensitivity. Thus, postpartum adaptation varies by both parameter and vessel type. While many parameters regressed postpartum, alterations in compliance did not, suggesting that matrix changes may have long-term consequences for maternal vascular function and health.

Pregnancy-Induced Physiologic Adaptation of the Abdominal Aorta Is Associated with Changes in Gene Expression and Genomic Methylation

BACKGROUND/AIMS

Ten-eleven translocation 2 (Tet2), a DNA demethylase enzyme, has been identified as a master epigenetic regulator of vascular smooth muscle cell plasticity. We hypothesized that pregnancy will induce significant adaptive changes in aortic biomechanics that correlate with the Tet family gene expression.

METHODS

Abdominal aortas from pregnant and nonpregnant mice were dissected and cannulated. Intraluminal pressure was adjusted using a pressure-servo system while using a video dimension analyzer to measure the lumen diameter. Quantitative polymerase chain reaction and immunoblot was used to analyze the expression of Tet genes. Global genomic methylation was assessed with the luminometric methylation assay.

RESULTS

Compared to the nonpregnant (NP, 706 ± 8 µm) control group, the aortic luminal diameter was significantly increased in both E18.5 (836 ± 14 µm) and PP30 (889 ± 16 µm) mice. Distensibility was reduced in E18.5 (90 ± 4%) mice and returned to NP values (108 ± 2%) in PP30 (108 ± 3%) mice. Tet2 transcription decreased at the beginning of pregnancy and subsequently increased in late gestation, inversely corresponding to changes in global methylation.

CONCLUSION

Physiologic changes in the aorta were accompanied by changes in gene expression and genomic methylation, suggesting an epigenetic component to maternal vascular remodeling during pregnancy.

The Piezo1 cation channel mediates uterine artery shear stress mechanotransduction and vasodilation during rat pregnancy

During mammalian pregnancy, the uterine circulation must undergo substantial vasodilation and growth to maintain sufficient uteroplacental perfusion. Although we and others have shown that nitric oxide (NO) is a key mediator of these processes, the mechanisms that augment uterine artery NO signaling during gestation have not been identified. We hypothesized that Piezo1, a recently discovered cation channel, may be involved in the process of shear stress mechanotransduction, as other studies have shown that it is both mechanosensitive and linked to NO production. Surprisingly, there are no studies on Piezo1 in the uterine circulation. Our aims in the present study were to determine whether this novel channel is 1) present in uterine arteries, 2) regulated by gestation, 3) functionally relevant (able to elicit rises in intracellular Ca²⁺ concentration and vasodilation), and 4) linked to NO. Immunohistochemistry confirmed that Piezo1 is present in uterine arteries, primarily but not exclusively in endothelial cells. Western blot analysis showed that its protein expression was elevated during gestation. In pressurized main uterine arteries, pharmacological activation of Piezo1 by Yoda1 produced near maximal vasodilation and was associated with significant increases in intracellular Ca²⁺ concentration in endothelial cell sheets. Shear stress induced by intraluminal flow produced reversible vasodilations that were inhibited >50% by GsMTx-4, a Piezo1 inhibitor, and by N^ω-nitro-l-arginine methyl ester/ N^ω-nitro-l-arginine, inhibitors of NO synthase. These findings are the first to implicate a functional role for Piezo1 in the uterine circulation as a mechanosensor of endothelial shear stress. Moreover, our data demonstrate that Piezo1 activation leads to vasodilation via NO and indicate that its molecular expression is upregulated during pregnancy. NEW & NOTEWORTHY This is the first study to highlight Piezo1 in the uterine circulation. As a potentially important endothelial mechanosensor of shear stress, Piezo1 may be linked to mechanisms that support increased uteroplacental perfusion during pregnancy. Listen to this article's corresponding podcast at https://ajpheart.podbean.com/e/piezo1-mechanotransduction-in-the-uterine-circulation/ .

Venoarterial communication mediates arterial wall shear stress-induced maternal uterine vascular remodeling during pregnancy

Although expansive remodeling of the maternal uterine circulation during pregnancy is essential for maintaining uteroplacental perfusion and normal fetal growth, the underlying physiological mechanisms are not well understood. Using a rat model, surgical approaches were used to alter uterine hemodynamics and wall shear stress (WSS) to evaluate the effects of WSS and venoarterial communication (e.g., transfer of placentally derived growth signals from postplacental veins to preplacental arteries) on gestational uterine vascular remodeling. Changes in WSS secondary to ligation of the cervical but not the ovarian end of the main uterine artery and vein provoked significant expansive remodeling at the opposite end of both vessels, but only in pregnant animals. The ≈50% increase in lumen diameter (relative to the contralateral horn) was associated with an upregulation of total endothelial nitric oxide (NO) synthase expression and was abolished by in vivo NO synthase inhibition with N-nitro-l-arginine methyl ester. Complete removal of a venous segment adjacent to the uterine artery to eliminate local venous influences significantly attenuated the WSS-induced remodeling by about one-half ( P < 0.05). These findings indicate that, during pregnancy, 1) increased WSS stimulates uterine artery growth via NO signaling and 2) the presence of an adjacent vein is required for arterial remodeling to fully occur. NEW & NOTEWORTHY This study provides the first in vivo evidence for the importance of venous influences on arterial growth within the uteroplacental circulation.

Altered Endothelial Nitric Oxide Signaling as a Paradigm for Maternal Vascular Maladaptation in Preeclampsia

PURPOSE OF REVIEW

The goal of this review is to present the newest insights into what we view as a central failure of cardiovascular adaptation in preeclampsia (PE) by focusing on one clinically significant manifestation of maternal endothelial dysfunction: nitric oxide signaling. The etiology, symptoms, and current theories of the PE syndrome are described first, followed by a review of the available evidence, and underlying causes of reduced endothelial nitric oxide (NO) signaling in PE.

RECENT FINDINGS

PE maladaptations include, but are not limited to, altered physiological stimulatory inputs (e.g., estrogen; VEGF/PlGF; shear stress) and substrates (L-Arg; ADMA), augmented placental secretion of anti-angiogenic and inflammatory factors such as sFlt-1 and Eng, changes in eNOS (polymorphisms, expression), and reduced bioavailability of NO secondary to oxidative stress. PE is a complex obstetrical syndrome that is associated with maternal vascular dysfunction. Diminished peripheral endothelial vasodilator influence in general, and of NO signaling specifically, are key in driving disease progression and severity.

ADAR1 enhances HTLV-1 and HTLV-2 replication through inhibition of PKR activity

Background

The role of innate immunity in general and of type I interferon (IFN-I) in particular in HTLV-1 pathogenesis is still a matter of debate. ADAR1-p150 is an Interferon Stimulated Gene (ISG) induced by IFN-I that can edit viral RNAs. We therefore investigated whether it could play the role of an anti-HTLV factor.

Results

We demonstrate here that ADAR1 is also expressed in the absence of IFN stimulation in activated primary T-lymphocytes that are the natural target of this virus and in HTLV-1 or HTLV-2 chronically infected T-cells. ADAR1 expression is also increased in primary lymphocytes obtained from HTLV-1 infected individuals. We show that ADAR1 enhances HTLV-1 and HTLV-2 infection in T-lymphocytes and that this proviral effect is independent from its editing activity. ADAR1 expression suppresses IFN-α inhibitory effect on HTLV-1 and HTLV-2 and acts through the repression of PKR phosphorylation.

Discussion

This study demonstrates that two interferon stimulated genes, i.e. PKR and ADAR1 have opposite effects on HTLV replication in vivo. The balanced expression of those proteins could determine the fate of the viral cycle in the course of infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-014-0093-9) contains supplementary material, which is available to authorized users.

Alpha interferon restricts human T-lymphotropic virus type 1 and 2 de novo infection through PKR activation

Type I interferon (IFN-I) inhibits the replication of different viruses. However, the effect of IFN-I on the human T-lymphotropic virus type 1 (HTLV-1) viral cycle is controversial. Here, we investigated the consequences of IFN-α addition for different steps of HTLV-1 and HTLV-2 infection. We first show that alpha interferon (IFN-α) efficiently impairs HTLV-1 and HTLV-2 de novo infection in a T cell line and in primary lymphocytes. Using pseudotyped viruses expressing HTLV-1 envelope, we then show that cell-free infection is insensitive to IFN-α, demonstrating that the cytokine does not affect the early stages of the viral cycle. In contrast, intracellular levels of Gag, Env, or Tax protein are affected by IFN-α treatment in T cells, primary lymphocytes, or 293T cells transfected with HTLV-1 or HTLV-2 molecular clones, demonstrating that IFN-α acts during the late stages of infection. We show that IFN-α does not affect Tax-mediated transcription and acts at a posttranscriptional level. Using either small interfering RNA (siRNA) directed against PKR or a PKR inhibitor, we demonstrate that PKR, whose expression is induced by interferon, plays a major role in IFN-α-induced HTLV-1/2 inhibition. These results indicate that IFN-α has a strong repressive effect on the HTLV-1 and HTLV-2 viral cycle during de novo infection of cells that are natural targets of the viruses.

Metabolic conversion from co-existing ingredient leading to significant systemic exposure of Z-butylidenephthalide, a minor ingredient in Chuanxiong Rhizoma in rats

Pharmacokinetic (PK) study of medicinal herbs is a great challenge, because which component(s) is(are) the bioactive ingredients is largely unknown. Most of the reported PK studies of herbs focused on the major ingredients regardless of their in vivo bioactivities, while PK of components with low content in herbs is often ignored. The present study demonstrates how PK study can reveal potential importance of a low content ingredient to the herbal bioactivities using Z-butylidenephthalide (BuPh), a bioactive phthalide present in a significantly low quantity in medicinal herb Chuanxiong Rhizoma, as an example. PK of BuPh was investigated in rats using Chuanxiong extract, fraction containing BuPh and ligustilide, and pure BuPh, respectively. The results demonstrated that remarkable blood concentrations of BuPh were observed after administration of the herbal extract and its systemic exposure was significantly different between BuPh given in pure and mixed forms. More interestingly, AUC of BuPh via intake of fraction (9.3-fold) and extract (4.5-fold) was significantly greater than that obtained from pure BuPh, which was further evidenced to be mainly due to metabolic conversion from ligustilide, a major component in Chuanxiong. Our findings revealed that although it naturally occurred in low amount, BuPh reached significant systemic concentrations via metabolic conversion from ligustilide. Moreover, our results demonstrated that PK study is one of crucial and inevitable steps for revealing in vivo bioactive ingredients of herbal medicines, and such studies should be more appropriate to focus on in vivo profile of the ingredients co-existing in herbs rather than only studying them individually.

Hyperediting of human T-cell leukemia virus type 2 and simian T-cell leukemia virus type 3 by the dsRNA adenosine deaminase ADAR-1

RNA editing mediated by adenosine deaminases acting on RNA (ADARs) converts adenosine (A) to inosine (I) residues in dsRNA templates. While ADAR-1-mediated editing was essentially described for RNA viruses, the present work addresses the issue for two δ-retroviruses, human T-cell leukemia virus type 2 and simian T-cell leukemia virus type 3 (HTLV-2 and STLV-3). We examined whether ADAR-1 could edit HTLV-2 and STLV-3 virus genomes in cell culture and in vivo. Using a highly sensitive PCR-based method, referred to as 3DI-PCR, we showed that ADAR-1 could hypermutate adenosine residues in HTLV-2. STLV-3 hypermutation was obtained without using 3DI-PCR, suggesting a higher mutation frequency for this virus. Detailed analysis of the dinucleotide editing context showed preferences for 5' ArA and 5' UrA. In conclusion, the present observations demonstrate that ADAR-1 massively edits HTLV-2 and STLV-3 retroviruses in vitro, but probably remains a rare phenomenon in vivo.

Pharmacokinetics and metabolism of ligustilide, a major bioactive component in Rhizoma Chuanxiong, in the rat

Ligustilide is the most abundant bioactive ingredient in Rhizoma Chuanxiong, a Chinese medicinal herb commonly used for the treatment of cardiovascular ailments. The present study reported, for the first time, the pharmacokinetics of ligustilide, administered in its pure form and in an herbal extract, in rats. After i.v. administration of pure ligustilide, it was distributed extensively (V(d), 3.76 +/- 1.23 l/kg) and eliminated rapidly (t(1/2), 0.31 +/- 0.12 h). The i.v. clearance (CL) of ligustilide after Chuanxiong extract administration was significantly higher than that dosed in its pure form [CL, 20.35 +/- 3.05 versus 9.14 +/- 1.27 l/h/kg, p < 0.01; area under the curve (AUC), 0.79 +/- 0.10 versus 1.81 +/- 0.24 mg x h/l, p < 0.01], suggesting significant interaction between ligustilide and components present in the extract. Dose-dependent pharmacokinetics was observed after i.p. administration, and a significantly higher dose-normalized AUC (1.77 +/- 0.23 mg x h/l) at 52 mg/kg was obtained than that at 26 mg/kg (0.93 +/- 0.07 mg x h/l, p < 0.05). Oral bioavailability of ligustilide was low (2.6%), which was partly because of extensive first-pass metabolism in the liver. Seven metabolites of ligustilide were identified, and three of them were unequivocally characterized as butylidenephthalide, senkyunolide I, and senkyunolide H. These three compounds also occurred naturally in the herb and were reported to be bioactive.

Low Oral Bioavailability and Pharmacokinetics of Senkyunolide A, a Major Bioactive Component in Rhizoma Chuanxiong, in the Rat

The pharmacokinetics of senkyunolide A, one of the major bioactive ingredients in the traditional Chinese medicinal herb Rhizoma Chuanxiong, which is commonly used for the treatment of cardiovascular diseases, was studied in rats. After intravenous (IV) administration, senkyunolide A was extensively distributed (Vd/F: 6.74 +/- 0.73 L/kg) and rapidly eliminated from the plasma (CL/F: 7.20 +/- 0.48 L/h per kilogram and t1/2: 0.65 +/- 0.06 hr). Hepatic metabolism was suggested as the major route of senkyunolide A elimination as indicated by the results of in vitro S9 fraction study. After intraperitoneal (IP) administration, senkyunolide A exhibited dose-independent pharmacokinetics. The absorption after IP administration was rapid (Tmax: 0.04 +/- 0.01 hours), and the bioavailability was 75%. After oral administration, senkyunolide A was also absorbed rapidly (Tmax: 0.21 +/- 0.08 hours); however, its oral bioavailability was low (approximately 8%). The contributing factors were determined to be instability in the gastrointestinal tract (accounting for 67% of the loss) and hepatic first-pass metabolism (accounting for another 25%). Pharmacokinetics of senkyunolide A were unaltered when Chuanxiong extract was administered, which suggests that components in the extract have insignificant effects on senkyunolide A pharmacokinetics.