Keeping the Balance Right

Exploring Single-cell RNA sequencing as a decision-making tool in the clinical management of Fuchs' Endothelial Corneal Dystrophy

Single-cell RNA sequencing (scRNA-seq) has enabled the identification of novel gene signatures and cell heterogeneity in numerous tissues and diseases. Here we review the use of this technology for Fuchs' Endothelial Corneal Dystrophy (FECD). FECD is the most common indication for corneal endothelial transplantation worldwide. FECD is challenging to manage because it is genetically heterogenous, can be autosomal dominant or sporadic, and progress at different rates. Single-cell RNA sequencing has enabled the discovery of several FECD subtypes, each with associated gene signatures, and cell heterogeneity. Current FECD treatments are mainly surgical, with various Rho kinase (ROCK) inhibitors used to promote endothelial cell metabolism and proliferation following surgery. A range of emerging therapies for FECD including cell therapies, gene therapies, tissue engineered scaffolds, and pharmaceuticals are in preclinical and clinical trials. Unlike conventional disease management methods based on clinical presentations and family history, targeting FECD using scRNA-seq based precision-medicine has the potential to pinpoint the disease subtypes, mechanisms, stages, severities, and help clinicians in making the best decision for surgeries and the applications of therapeutics. In this review, we first discuss the feasibility and potential of using scRNA-seq in clinical diagnostics for FECD, highlight advances from the latest clinical treatments and emerging therapies for FECD, integrate scRNA-seq results and clinical notes from our FECD patients and discuss the potential of applying alternative therapies to manage these cases clinically.

The roles of RGS proteins in cardiometabolic disease

G protein-coupled receptors (GPCRs) are the most prominent receptors on the surface of the cell and play a central role in the regulation of cardiac and metabolic functions. GPCRs transmit extracellular stimuli to the interior of the cells by activating one or more heterotrimeric G proteins. The duration and intensity of G protein-mediated signalling are tightly controlled by a large array of intracellular mediators, including the regulator of G protein signalling (RGS) proteins. RGS proteins selectively promote the GTPase activity of a subset of Gα subunits, thus serving as negative regulators in a pathway-dependent manner. In the current review, we summarise the involvement of RGS proteins in cardiometabolic function with a focus on their tissue distribution, mechanisms of action and dysregulation under various disease conditions. We also discuss the potential therapeutic applications for targeting RGS proteins in treating cardiometabolic conditions and current progress in developing RGS modulators. LINKED ARTICLES: This article is part of a themed issue Therapeutic Targeting of G Protein-Coupled Receptors: hot topics from the Australasian Society of Clinical and Experimental Pharmacologists and Toxicologists 2021 Virtual Annual Scientific Meeting. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.14/issuetoc.

Redox regulation of the immune response

The immune-inflammatory response is associated with increased nitro-oxidative stress. The aim of this mechanistic review is to examine: (a) the role of redox-sensitive transcription factors and enzymes, ROS/RNS production, and the activity of cellular antioxidants in the activation and performance of macrophages, dendritic cells, neutrophils, T-cells, B-cells, and natural killer cells; (b) the involvement of high-density lipoprotein (HDL), apolipoprotein A1 (ApoA1), paraoxonase-1 (PON1), and oxidized phospholipids in regulating the immune response; and (c) the detrimental effects of hypernitrosylation and chronic nitro-oxidative stress on the immune response. The redox changes during immune-inflammatory responses are orchestrated by the actions of nuclear factor-κB, HIF1α, the mechanistic target of rapamycin, the phosphatidylinositol 3-kinase/protein kinase B signaling pathway, mitogen-activated protein kinases, 5' AMP-activated protein kinase, and peroxisome proliferator-activated receptor. The performance and survival of individual immune cells is under redox control and depends on intracellular and extracellular levels of ROS/RNS. They are heavily influenced by cellular antioxidants including the glutathione and thioredoxin systems, nuclear factor erythroid 2-related factor 2, and the HDL/ApoA1/PON1 complex. Chronic nitro-oxidative stress and hypernitrosylation inhibit the activity of those antioxidant systems, the tricarboxylic acid cycle, mitochondrial functions, and the metabolism of immune cells. In conclusion, redox-associated mechanisms modulate metabolic reprogramming of immune cells, macrophage and T helper cell polarization, phagocytosis, production of pro- versus anti-inflammatory cytokines, immune training and tolerance, chemotaxis, pathogen sensing, antiviral and antibacterial effects, Toll-like receptor activity, and endotoxin tolerance.

Cardiovascular GPCR regulation by regulator of G protein signaling proteins

G protein-coupled receptors (GPCRs) play pivotal roles in regulation of cardiovascular homeostasis across all vertebrate species, including humans. In terms of normal cellular function, termination of GPCR signaling via the heterotrimeric G proteins is equally (if not more) important to its stimulation. The Regulator of G protein Signaling (RGS) protein superfamily are indispensable for GPCR signaling cessation at the cell membrane, and thus, for cellular control of GPCR signaling and function. Perturbations in both activation and termination of G protein signaling underlie many examples of cardiovascular dysfunction and heart disease pathogenesis. Despite the plethora of over 30 members comprising the mammalian RGS protein superfamily, each member interacts with a specific set of second messenger pathways and GPCR types/subtypes in a tissue/cell type-specific manner. An increasing number of studies over the past two decades have provided compelling evidence for the involvement of various RGS proteins in physiological regulation of cardiovascular GPCRs and, consequently, also in the pathophysiology of several cardiovascular ailments. This chapter summarizes the current understanding of the functional roles of RGS proteins as they pertain to cardiovascular, i.e., heart, blood vessel, and platelet GPCR function, with a particular focus on their implications for chronic heart failure pathophysiology and therapy.

Dual loss of regulator of G protein signaling 2 and 5 exacerbates ventricular myocyte arrhythmias and disrupts the fine-tuning of Gi/o signaling

AIMS

Cardiac contractility, essential to maintaining proper cardiac output and circulation, is regulated by G protein-coupled receptor (GPCR) signaling. Previously, the absence of regulator of G protein signaling (RGS) 2 and 5, separately, was shown to cause G protein dysregulation, contributing to modest blood pressure elevation and exaggerated cardiac hypertrophic response to pressure-overload. Whether RGS2 and 5 redundantly control G protein signaling to maintain cardiovascular homeostasis is unknown. Here we examined how the dual absence of RGS2 and 5 (Rgs2/5 dbKO) affects blood pressure and cardiac structure and function.

METHODS AND RESULTS

We found that Rgs2/5 dbKO mice showed left ventricular dilatation at baseline by echocardiography. Cardiac contractile response to dobutamine stress test was sex-dependently reduced in male Rgs2/5 dbKO relative to WT mice. When subjected to surgery-induced stress, male Rgs2/5 dbKO mice had 75% mortality within 72-96 h after surgery, accompanied by elevated baseline blood pressure and decreased cardiac contractile function. At the cellular level, cardiomyocytes (CM) from Rgs2/5 dbKO mice showed augmented Ca²⁺ transients and increased incidence of arrhythmia without augmented contractile response to electrical field stimulation (EFS) and activation of β-adrenergic receptors (βAR) with isoproterenol. Dual loss of Rgs2 and 5 suppressed forskolin-induced cAMP production, which was restored by G_i/o inactivation with pertussis toxin that also reduced arrhythmogenesis during EFS or βAR stimulation. Cardiomyocyte NCX and PMCA mRNA expression was unaffected in Rgs2/5 dbKO male mice. However, there was an exaggerated elevation of EFS-induced cytoplasmic Ca²⁺ in the presence of SERCA blockade with thapsigargin.

CONCLUSIONS

We conclude that RGS2 and 5 promote normal ventricular rhythm by coordinating their regulatory activity towards G_i/o signaling and facilitating cardiomyocyte calcium handling.

Hepatic stellate cells in the injured liver: Perspectives beyond hepatic fibrosis

Over the last two decades, our understanding of the pathological role of hepatic stellate cells (HSCs) in fibrotic liver disease has increased dramatically. As HSCs are identified as the principal collagen-producing cells in the injured liver, several experimental and clinical studies have targeted HSCs to treat liver fibrosis. However, HSCs also play a critical role in developing nonfibrotic liver diseases such as cholestasis, portal hypertension, and hepatocellular carcinoma (HCC). Therefore, this review exclusively focuses on the role of activated HSCs beyond hepatic fibrosis. In cholestasis conditions, elevated bile salts and bile acids activate HSCs to secrete collagen and other extracellular matrix products, which cause biliary fibrosis and cholangitis. In the chronically injured liver, autocrine and paracrine signaling from liver sinusoidal endothelial cells activates HSCs to induce portal hypertension via endothelin-1 release. In the tumor microenvironment (TME), activated HSCs are the major source of cancer-associated fibroblasts (CAF). The crosstalk between activated HSC/CAF and tumor cells is associated with tumor cell proliferation, migration, metastasis, and chemoresistance. In TME, activated HSCs convert macrophages to tumor-associated macrophages and induce the differentiation of dendritic cells (DCs) and monocytes to regulatory DCs and myeloid-derived suppressor cells, respectively. This differentiation, in turn, increases T cells proliferation and induces their apoptosis leading to reduced immune surveillance in TME. Thus, HSCs activation in chronically injured liver is a critical process involved in the progression of cholestasis, portal hypertension, and liver cancer.

Residue-level determinants of RGS R4 subfamily GAP activity and specificity towards the Gi subfamily

The structural basis for the GTPase-accelerating activity of regulators of G protein signaling (RGS) proteins, as well as the mechanistic basis for their specificity in interacting with the heterotrimeric (αβγ) G proteins they inactivate, is not sufficiently understood at the family level. Here, we used biochemical assays to compare RGS domains across the RGS family and map those individual residues that favorably contribute to GTPase-accelerating activity, and those residues responsible for attenuating RGS domain interactions with Gα subunits. We show that conserved interactions of RGS residues with both the Gα switch I and II regions are crucial for RGS activity, while the reciprocal effects of "modulatory" and "disruptor" residues selectively modulate RGS activity. Our results quantify how specific interactions between RGS domains and Gα subunits are set by a balance between favorable RGS residue interactions with particular Gα switch regions, and unfavorable interactions with the Gα helical domain.

Identification and validation of the miRNA-mRNA regulatory network in fetoplacental arterial endothelial cells of gestational diabetes mellitus

Gestational diabetes mellitus (GDM) increases the risk of fetal heart malformations, though little is known about the mechanism of hyperglycemia-induced heart malformations. Thus, we aimed to reveal the global landscape of miRNAs and mRNAs in GDM-exposed fetoplacental arterial endothelial cells (dAECs) and establish regulatory networks for exploring the pathophysiological mechanism of fetal heart malformations in maternal hyperglycemia. Gene Expression Omnibus (GEO) datasets were used, and identification of differentially expressed miRNAs (DEMs) and genes (DEGs) in GDM was based on a previous sequencing analysis of dAECs. A miRNA-mRNA network containing 20 DEMs and 65 DEGs was established using DEMs altered in opposite directions to DEGs. In an in vivo study, we established a streptozotocin-induced pregestational diabetes mellitus (PGDM) mouse model and found the fetal cardiac wall thickness in different regions to be dramatically increased in the PGDM grouValidation of DEMs and DEGs in the fetal heart showed significantly upregulated expression of let-7e-5p, miR-139-5p and miR-195-5p and downregulated expression of SGOL1, RRM2, RGS5, CDK1 and CENPA. In summary, we reveal the miRNA-mRNA regulatory network related to fetal cardiac development disorders in offspring, which may shed light on the potential molecular mechanisms of fetal cardiac development disorders during maternal hyperglycemia.

Endothelial dysfunction in neuroprogressive disorders-causes and suggested treatments

BACKGROUND

Potential routes whereby systemic inflammation, oxidative stress and mitochondrial dysfunction may drive the development of endothelial dysfunction and atherosclerosis, even in an environment of low cholesterol, are examined.

MAIN TEXT

Key molecular players involved in the regulation of endothelial cell function are described, including PECAM-1, VE-cadherin, VEGFRs, SFK, Rho GEF TRIO, RAC-1, ITAM, SHP-2, MAPK/ERK, STAT-3, NF-κB, PI3K/AKT, eNOS, nitric oxide, miRNAs, KLF-4 and KLF-2. The key roles of platelet activation, xanthene oxidase and myeloperoxidase in the genesis of endothelial cell dysfunction and activation are detailed. The following roles of circulating reactive oxygen species (ROS), reactive nitrogen species and pro-inflammatory cytokines in the development of endothelial cell dysfunction are then described: paracrine signalling by circulating hydrogen peroxide, inhibition of eNOS and increased levels of mitochondrial ROS, including compromised mitochondrial dynamics, loss of calcium ion homeostasis and inactivation of SIRT-1-mediated signalling pathways. Next, loss of cellular redox homeostasis is considered, including further aspects of the roles of hydrogen peroxide signalling, the pathological consequences of elevated NF-κB, compromised S-nitrosylation and the development of hypernitrosylation and increased transcription of atherogenic miRNAs. These molecular aspects are then applied to neuroprogressive disorders by considering the following potential generators of endothelial dysfunction and activation in major depressive disorder, bipolar disorder and schizophrenia: NF-κB; platelet activation; atherogenic miRs; myeloperoxidase; xanthene oxidase and uric acid; and inflammation, oxidative stress, nitrosative stress and mitochondrial dysfunction.

CONCLUSIONS

Finally, on the basis of the above molecular mechanisms, details are given of potential treatment options for mitigating endothelial cell dysfunction and activation in neuroprogressive disorders.

Regulator of G-Protein Signaling 5 Maintains Brain Endothelial Cell Function in Focal Cerebral Ischemia

Background

Regulator of G‐protein signaling 5 (RGS5) is a negative modulator of G‐protein–coupled receptors. The role of RGS5 in brain endothelial cells is not known. We hypothesized that RGS5 in brain microvascular endothelial cells may be an important mediator of blood‐brain barrier function and stroke severity after focal cerebral ischemia.

Methods and Results

Using a transient middle cerebral artery occlusion model, we found that mice with global and endothelial‐specific deletion of Rgs5 exhibited larger cerebral infarct size, greater neurological motor deficits, and increased brain edema. In our in vitro models, we observed increased G_q activity and elevated intracellular Ca²⁺ levels in brain endothelial cells. Furthermore, the loss of endothelial RGS5 leads to decreased endothelial NO synthase expression and phosphorylation, relocalization of endothelial tight junction proteins, and increased cell permeability. Indeed, RGS5 deficiency leads to increased Rho‐associated kinase and myosin light chain kinase activity, which were partially reversed in our in vitro model by pharmacological inhibition of G_q, metabotropic glutamate receptor 1, and ligand‐gated ionotropic glutamate receptor.

Conclusions

Our findings indicate that endothelial RGS5 plays a novel neuroprotective role in focal cerebral ischemia. Loss of endothelial RGS5 leads to hyperresponsiveness to glutamate signaling pathways, enhanced Rho‐associated kinase– and myosin light chain kinase–mediated actin‐cytoskeleton reorganization, endothelial dysfunction, tight junction protein relocalization, increased blood‐brain barrier permeability, and greater stroke severity. These findings suggest that preservation of endothelial RGS5 may be an important therapeutic strategy for maintaining blood‐brain barrier integrity and limiting the severity of ischemic stroke.

Regulator of G Protein Signaling 2 Facilitates Uterine Artery Adaptation During Pregnancy in Mice

Background Decreased uterine blood flow is known to contribute to pregnancy complications such as gestational hypertension and preeclampsia. Previously, we showed that the loss of regulator of G protein signaling 2 ( RGS 2), a GTP ase activating protein for G_q/11 and G_i/o class G proteins, decreases uterine blood flow in the nonpregnant state in mice. Here, we examined the effects of the absence of RGS 2 and 5 on uterine blood flow and uterine vascular structure and function at early, mid, and late gestation, as well as peripartum period in mice. Methods and Results Abdominal Doppler ultrasonography was performed on adult female wild-type, Rgs2^-/-, and Rgs5^-/- mice at pre-pregnancy, gestational days 10, 15, and 18, and postpartum day 3. Uterine artery structure and function were also assessed by vessel myograph studies. At mid-pregnancy, uterine blood flow decreased in both Rgs2^-/- and Rgs5^-/- mice, whereas resistive index increased only in Rgs2^-/- mice. In uterine arteries from wild-type mice, mRNA expression of RGS 2 and 4 increased, whereas RGS 5 expression remained elevated at mid-pregnancy. These changes in gene expression were unique to uterine arteries because they were absent in mesenteric arteries and the aorta of wild-type mice. In Rgs2^-/- mice, uterine artery medial cross-sectional area and G protein-coupled receptor-mediated vasoconstriction increased in mid-pregnancy, implicating a role for RGS 2 in structural and functional remodeling of uterine arteries during pregnancy. In contrast, RGS 5 absence increased vasoconstriction only in the peripartum period. Conclusions These data together indicate that RGS 2 plays a critical role in the structural and functional remodeling of uterine arteries to impact uterine blood flow during pregnancy. Targeting the signaling pathway regulated by RGS 2 may therefore be a therapeutic strategy for ameliorating utero-placental perfusion disorders during pregnancy.

RGS5 rs4657251 polymorphism is associated with small vessel occlusion stroke in Taiwan Han Chinese

BACKGROUND

The regulator of G-protein signaling protein 5 (RGS5) has been demonstrated to play a role in regulating blood pressure and cardiovascular function. Studies have shown that RGS5 polymorphisms exhibit susceptibility to hypertension. However, no study has yet been performed among stroke patients.

METHODS

To evaluate whether RGS5 rs4657251 is a susceptibility gene for stroke, we performed a case-control association study involving 714 large-artery atherosclerosis (LAA) patients, 383 small vessel occlusion (SVO) patients, 401 hypertensive intracranial hemorrhages (HICH), and 626 controls. The RGS5 rs4657251 polymorphism was analyzed through polymerase chain reaction.

RESULTS

The TC genotype was significantly higher in the SVO group compared with that in the control group (odds ratio [OR] = 1.34, 95% confidence interval [CI] = 1.02-1.76, p = 0.035). In addition, the dominant phenotype (TC + CC vs TT) was also significantly different between the SVO and the control groups (OR = 1.31, 95% CI = 1.01-1.70, p = 0.046). However, no association was found between RGS5 rs4657251 and LAA an HICH. After adjustment with gender, diabetes, smoking, cholesterol and low-density lipoprotein levels, RGS5 rs4657251 polymorphism remained an independent risk factor for SVO (OR = 1.49; 95% CI = 1.12-1.98) but not for LAA or HICH.

CONCLUSION

Our findings, obtained among Taiwan Han Chinese subjects, provide the first evidence that RGS5 rs4657251 polymorphism is an independent risk factor for SVO.

Human cytomegalovirus promoting endothelial cell proliferation by targeting regulator of G-protein signaling 5 hypermethylation and downregulation

Interactions between human cytomegalovirus (HCMV) infection and environmental factors can increase susceptibility to essential hypertension (EH). Although endothelial dysfunction is the initial factor of EH, the epigenetic mechanisms through which HCMV infection induces endothelial cell dysfunction are poorly understood. Here, we evaluated whether HCMV regulated endothelial cell function and assessed the underlying mechanisms. Microarray analysis in human umbilical vein endothelial cells (HUVECs) treated with HCMV AD169 strain in the presence of hyperglycemia and hyperlipidemia revealed differential expression of genes involved in hypertension. Further analyses validated that the regulator of G-protein signaling 5 (RGS5) gene was downregulated in infected HUVECs and showed that HCMV infection promoted HUVEC proliferation, whereas hyperglycemia and hyperlipidemia inhibited HUVEC proliferation. Additionally, treatment with decitabine (DAC) and RGS5 reversed the effects of HCMV infection on HUVEC proliferation, but not triggered by hyperglycemia and hyperlipidemia. In summary, upregulation of RGS5 may be a promising treatment for preventing HCMV-induced hypertension.

Tumor Vessel Normalization: A Window to Enhancing Cancer Immunotherapy

Hostile microenvironment produced by abnormal blood vessels, which is characterized by hypoxia, low pH value and increasing interstitial fluid pressure, would facilitate tumor progression, metastasis, immunosuppression and anticancer treatments resistance. These abnormalities are the result of the imbalance of pro-angiogenic and anti-angiogenic factors (such as VEGF and angiopoietin 2, ANG2). Prudent use of anti-angiogenesis drugs would normalize these aberrant tumor vessels, resulting in a transient window of vessel normalization. In addition, use of cancer immunotherapy including immune checkpoint blockers when vessel normalization is achieved brings better outcomes. In this review, we sum up the advances in the field of understanding and application of the concept of tumor vessels normalization window to treat cancer. Moreover, we also outline some challenges and opportunities ahead to optimize the combination of anti-angiogenic agents and immunotherapy, leading to improve patients' outcomes.

Parenchymal pericytes are not the major contributor of extracellular matrix in the fibrotic scar after stroke in male mice

Scar formation after injury of the brain or spinal cord is a common event. While glial scar formation by astrocytes has been extensively studied, much less is known about the fibrotic scar, in particular after stroke. Platelet‐derived growth factor receptor ß‐expressing (PDGFRß⁺) pericytes have been suggested as a source of the fibrotic scar depositing fibrous extracellular matrix (ECM) proteins after detaching from the vessel wall. However, to what extent these parenchymal PDGFRß⁺ cells contribute to the fibrotic scar and whether targeting these cells affects fibrotic scar formation in stroke is still unclear. Here, we utilize male transgenic mice that after a permanent middle cerebral artery occlusion stroke model have a shift from a parenchymal to a perivascular location of PDGFRß⁺ cells due to the loss of regulator of G‐protein signaling 5 in pericytes. We find that only a small fraction of parenchymal PDGFRß⁺ cells co‐label with type I collagen and fibronectin. Consequently, a reduction in parenchymal PDGFRß⁺ cells by ca. 50% did not affect the overall type I collagen or fibronectin deposition after stroke. The redistribution of PDGFRß⁺ cells to a perivascular location, however, resulted in a reduced thickening of the vascular basement membrane and changed the temporal dynamics of glial scar maturation after stroke. We demonstrate that parenchymal PDGFRß⁺ cells are not the main contributor to the fibrotic ECM, and therefore targeting these cells might not impact on fibrotic scar formation after stroke.

Genetic Analysis of Rare Human Variants of Regulators of G Protein Signaling Proteins and Their Role in Human Physiology and Disease

Regulators of G protein signaling (RGS) proteins modulate the physiologic actions of many neurotransmitters, hormones, and other signaling molecules. Human RGS proteins comprise a family of 20 canonical proteins that bind directly to G protein-coupled receptors/G protein complexes to limit the lifetime of their signaling events, which regulate all aspects of cell and organ physiology. Genetic variations account for diverse human traits and individual predispositions to disease. RGS proteins contribute to many complex polygenic human traits and pathologies such as hypertension, atherosclerosis, schizophrenia, depression, addiction, cancers, and many others. Recent analysis indicates that most human diseases are due to extremely rare genetic variants. In this study, we summarize physiologic roles for RGS proteins and links to human diseases/traits and report rare variants found within each human RGS protein exome sequence derived from global population studies. Each RGS sequence is analyzed using recently described bioinformatics and proteomic tools for measures of missense tolerance ratio paired with combined annotation-dependent depletion scores, and protein post-translational modification (PTM) alignment cluster analysis. We highlight selected variants within the well-studied RGS domain that likely disrupt RGS protein functions and provide comprehensive variant and PTM data for each RGS protein for future study. We propose that rare variants in functionally sensitive regions of RGS proteins confer profound change-of-function phenotypes that may contribute, in newly appreciated ways, to complex human diseases and/or traits. This information provides investigators with a valuable database to explore variation in RGS protein function, and for targeting RGS proteins as future therapeutic targets.

Regulators of G protein signaling in cardiovascular function during pregnancy

G protein-coupled receptor signaling mechanisms are implicated in many aspects of cardiovascular control, and dysfunction of such signaling mechanisms is commonly associated with disease states. Investigators have identified a large number of regulator of G protein signaling (RGS) proteins that variously contribute to the modulation of intracellular second-messenger signaling kinetics. These many RGS proteins each interact with a specific set of second-messenger cascades and receptor types and exhibit tissue-specific expression patterns. Increasing evidence supports the contribution of RGS proteins, or their loss, in the pathogenesis of cardiovascular dysfunctions. This review summarizes the current understanding of the functional contributions of RGS proteins, particularly within the B/R4 family, in cardiovascular disorders of pregnancy including gestational hypertension, uterine artery dysfunction, and preeclampsia.

Ultrahigh-Resolution Optical Coherence Elastography Images Cellular-Scale Stiffness of Mouse Aorta

Cellular-scale imaging of the mechanical properties of tissue has helped to reveal the origins of disease; however, cellular-scale resolution is not readily achievable in intact tissue volumes. Here, we demonstrate volumetric imaging of Young's modulus using ultrahigh-resolution optical coherence elastography, and apply it to characterizing the stiffness of mouse aortas. We achieve isotropic resolution of better than 15 μm over a 1-mm lateral field of view through the entire depth of an intact aortic wall. We employ a method of quasi-static compression elastography that measures volumetric axial strain and uses a compliant, transparent layer to measure surface axial stress. This combination is used to estimate Young's modulus throughout the volume. We demonstrate differentiation by stiffness of individual elastic lamellae and vascular smooth muscle. We observe stiffening of the aorta in regulator of G protein signaling 5-deficient mice, a model that is linked to vascular remodeling and fibrosis. We observe increased stiffness with proximity to the heart, as well as regions with micro-structural and micro-mechanical signatures characteristic of fibrous and lipid-rich tissue. High-resolution imaging of Young's modulus with optical coherence elastography may become an important tool in vascular biology and in other fields concerned with understanding the role of mechanics within the complex three-dimensional architecture of tissue.

Angiotensin II Type 1 Receptor Mechanoactivation Involves RGS5 (Regulator of G Protein Signaling 5) in Skeletal Muscle Arteries: Impaired Trafficking of RGS5 in Hypertension

Studies suggest that arteriolar pressure-induced vasoconstriction can be initiated by GPCRs (G protein-coupled receptors), including the AT₁R (angiotensin II type 1 receptor). This raises the question, are such mechanisms regulated by negative feedback? The present studies examined whether RGS (regulators of G protein signaling) proteins in vascular smooth muscle cells are colocalized with the AT₁R when activated by mechanical stress or angiotensin II and whether this modulates AT₁R-mediated vasoconstriction. To determine whether activation of the AT₁R recruits RGS5, an in situ proximity ligation assay was performed in primary cultures of cremaster muscle arteriolar vascular smooth muscle cells treated with angiotensin II or hypotonic solution in the absence or presence of candesartan (an AT₁R blocker). Proximity ligation assay results revealed a concentration-dependent increase in trafficking/translocation of RGS5 toward the activated AT₁R, which was attenuated by candesartan. In intact arterioles, knockdown of RGS5 enhanced constriction to angiotensin II and augmented myogenic responses to increased intraluminal pressure. Myogenic constriction was attenuated to a higher degree by candesartan in RGS5 siRNA-transfected arterioles, consistent with RGS5 contributing to downregulation of AT₁R-mediated signaling. Further, translocation of RGS5 was impaired in vascular smooth muscle cells of spontaneously hypertensive rats. This is consistent with dysregulated (RGS5-mediated) AT₁R signaling that could contribute to excessive vasoconstriction in hypertension. In intact vessels, candesartan reduced myogenic vasoconstriction to a greater extent in spontaneously hypertensive rats compared with controls. Collectively, these findings suggest that AT₁R activation results in translocation of RGS5 toward the plasma membrane, limiting AT₁R-mediated vasoconstriction through its role in G_q/11 protein-dependent signaling.

Maternal Metabolism and Vascular Adaptation in Pregnancy: The PPAR Link

Current therapies for pregnancy-related hypertension and its complications remain inadequate, although an increasing role for maternal susceptibility is becoming evident. Systemic vascular dysfunction in response to imbalances in angiogenic, inflammatory, and constricting factors is implicated in the pathogenesis of gestational hypertension, and growing evidence now links these factors with maternal metabolism. In particular, the crucial role of peroxisome proliferator-activated receptors (PPARs) in maternal vascular adaptation provides further insights into how obesity and gestational diabetes may be linked to pregnancy-induced hypertension and preeclampsia. This is especially important given the rapidly growing prevalence of obesity during pregnancy, and highlights a new approach to treat pregnancy-related hypertension and its complications.

Ruminal expression of the NQO1, RGS5, and ACAT1 genes may be indicators of feed efficiency in beef steers

Ruminal genes differentially expressed in crossbred beef steers from USMARC with variation in gain and feed intake were identified in a previous study. Several of the genes identified with expression patterns differing between animals with high gain-low feed intake and low gain-high feed intake were evaluated in a separate, unrelated population of Angus × Hereford beef steers from the University of Wyoming that was classified to differ in residual feed intake (RFI). Of the 17 genes tested, two were differentially expressed by RFI class in the Angus × Hereford animals. These genes included NAD(P)H dehydrogenase, quinone 1 (NQO1; P = 0.0009) and regulator of G-protein signaling 5 (RGS5; P = 0.01). A third gene, acetyl-CoA acetyltransferase 1 (ACAT1; P = 0.06), displayed a trend toward association with RFI. These data suggest that some of the genes identified in a previous rumen transcriptome discovery study may have utility for identifying or selecting for animals with superior feed efficiency phenotypes across cattle breeds and populations.