The mechanisms behind decreased internalization of angiotensin II type 1 receptor

Angiotensin II constricts mouse iliac arteries: possible mechanism for aortic aneurysms

Abdominal aortic aneurysms (AAA) result from maladaptive remodeling of the vascular wall and reduces structural integrity. Angiotensin II (AngII) infusion has become a standard laboratory model for studying AAA initiation and progression. We determined the different vasoactive responses of various mouse arteries to Ang II. Ex vivo isometric tension analysis was conducted on 18-week-old male C57BL/6 mice (n = 4) brachiocephalic arteries (BC), iliac arteries (IL), and abdominal (AA) and thoracic aorta (TA). Arterial rings were mounted between organ hooks, gently stretched and an AngII dose response was performed. Rings were placed in 4% paraformaldehyde for immunohistochemistry analysis to quantify peptide expression of angiotensin type 1 (AT1R) and 2 receptors (AT2R) in the endothelium, media, and adventitia. Results from this study demonstrated vasoconstriction responses in IL were significantly higher at all AngII doses when compared to BC, and TA and AA responses (maximum constriction-IL: 68.64 ± 5.47% vs. BC: 1.96 ± 1.00%; TA: 3.13 ± 0.16% and AA: 2.75 ± 1.77%, p < 0.0001). Expression of AT1R was highest in the endothelium of IL (p < 0.05) and in the media and (p < 0.05) adventitia (p < 0.05) of AA. In contrast, AT2R expression was highest in endothelium (p < 0.05), media (p < 0.01, p < 0.05) and adventitia of TA. These results suggest that mouse arteries display different vasoactive responses to AngII, and the exaggerated response in IL arteries may play a role during AAA development.

G Protein-Biased Agonists for Intracellular Angiotensin Receptors Promote Collagen Secretion in Myofibroblasts

Photoactivatable ligands remain valuable tools to study the spatiotemporal aspects of cellular signaling. However, the synthesis, handling, and biological validation of such compounds remain challenging, especially when dealing with peptides. We report an optimized synthetic strategy, where laborious preparation of dimethoxy-nitrobenzyl-tyrosine building blocks was replaced by direct functionalization of amino acid side chains while peptides remained coupled to resin, reducing both preparation time and cost. Our caged peptides were designed to investigate cellular responses mediated by intracellular angiotensin II receptors (iATR) upon interaction with known biased and unbiased ligands. The pathophysiological roles of iATRs remain poorly understood, and we sought to develop ligands to explore this. Initial validation showed that our caged ligands undergo rapid photolysis and produced functionally active peptides upon UV exposure. We also show, for the first time, that different biased ligands (β-arrestin- vs G protein-biased analogues) evoked distinct responses when uncaged in adult rat myofibroblasts. Intracellularly targeted versions of Ang II (unbiased) or G protein-biased analogues (TRV055, TRV056) were more effective than β-arrestin-biased Ang II analogues (SI, TRV026, and TRV27) in inducing collagen secretion, suggesting a divergent role in regulating the fibrotic response.

Endocytosis and signaling of angiotensin II type 1 receptor

A vasoactive octapeptide angiotensin II (Ang II) hormone is the key regulator of the renin-angiotensin system (RAS). It binds with the two different plasma membrane receptors like angiotensin II type 1 (AT1) and type 2 (AT2) and consequence various biological responses occur. Further, AT1 has two subtypes such as AT1A and AT1B. These angiotensin receptors are classified to be G protein-coupled receptors (GPCRs). The main constituent of RAS is the AT1 receptor (AT1R), and its activation, signal transduction, and regulation have been extensively studied. After Ang II stimulation, the ligand-receptor complexes internalized and trafficked through the early endosome, recycling endosome, and some receptors skipped the recycling endosome and trafficked to the lysosome for metabolic degradation. Moreover, some short sequence motifs located in the carboxyl-terminus (CT) of the receptor play a vital role in the internalization, phosphorylation, subcellular trafficking, signaling, and desensitization. Furthermore, in endocytosis, the various proteins interact with the CT region of the receptor. This chapter highlights the basic mechanism of AT1 receptor internalization, trafficking and signaling in both physiological and pathophysiological conditions.

Alteration in Rab11-mediated endocytic trafficking of LDL receptor contributes to angiotensin II-induced cholesterol accumulation and injury in podocytes

Objectives

Exposure of podocytes to angiotensin II (Ang II) enhances the abundance of the cell surface glycoprotein, low‐density lipoprotein receptor (LDLR) and promotes significant changes in the cellular cholesterol content. Recent investigation provides evidence that the small GTPase Rab11 is involved in the regulation of LDLR, but the exact mechanisms remain unknown. In this study, the role of Rab11 in post‐transcriptional regulation of LDLR was evaluated to investigate potential mechanisms of podocyte cholesterol dysregulation in chronic kidney disease.

Materials and Methods

Cholesterol content, LDLR and Rab11 expression were assessed in podocytes from Ang II‐infused mice. In vitro, the intracellular localization of LDLR was detected under different conditions. Rab11 expression was modulated and we then explored the effect of anti‐lipid cytotoxicity by detecting LDLR expression and trafficking, cholesterol content and apoptosis in podocytes.

Results

Cholesterol accumulation, upregulated expression of LDLR and Rab11 were discovered in podocytes from Ang II‐infused mice. Ang II enhanced the co‐precipitation of LDLR with Rab11 and accelerated the endocytic recycling of LDLR to the plasma membrane. Additionally, silencing Rab11 promoted lysosomal degradation of LDLR and alleviated Ang II‐induced cholesterol accumulation and apoptosis in podocytes. Conversely, overexpression of Rab11 or inhibition of lysosomal degradation up‐regulated the abundance of LDLR and aggravated podocyte cholesterol deposition.

Conclusions

Rab11 triggers the endocytic trafficking and recycling of LDLR; overactivation of this pathway contributes to Ang II‐induced podocyte cholesterol accumulation and injury.

A NanoBiT assay to monitor membrane proteins trafficking for drug discovery and drug development

Internalization of membrane proteins plays a key role in many physiological functions; however, highly sensitive and versatile technologies are lacking to study such processes in real-time living systems. Here we describe an assay based on bioluminescence able to quantify membrane receptor trafficking for a wide variety of internalization mechanisms such as GPCR internalization/recycling, antibody-mediated internalization, and SARS-CoV2 viral infection. This study represents an alternative drug discovery tool to accelerate the drug development for a wide range of physiological processes, such as cancer, neurological, cardiopulmonary, metabolic, and infectious diseases including COVID-19.

Membrane protein trafficking is monitored using split nanoluciferase. Receptor internalization leads to complementation on the early endosome and a bioluminescent response, and is applied to receptor internalization/recycling, antibody-mediated internalization and SARS-CoV2 entry.

Phosphorylation of meprin β controls its cell surface abundance and subsequently diminishes ectodomain shedding

Meprin β is a zinc-dependent metalloprotease exhibiting a unique cleavage specificity with strong preference for acidic amino acids at the cleavage site. Proteomic studies revealed a diverse substrate pool of meprin β including the interleukin-6 receptor (IL-6R) and the amyloid precursor protein (APP). Dysregulation of meprin β is often associated with pathological conditions such as chronic inflammation, fibrosis, or Alzheimer's disease (AD). The extracellular regulation of meprin β including interactors, sheddases, and activators has been intensively investigated while intracellular regulation has been barely addressed in the literature. This study aimed to analyze C-terminal phosphorylation of meprin β with regard to cell surface expression and proteolytic activity. By immunoprecipitation of endogenous meprin β from the colon cancer cell line Colo320 and subsequent LC-MS analysis, we identified several phosphorylation sites in its C-terminal region. Here, T694 in the C-terminus of meprin β was the most preferred residue after phorbol 12-myristate 13-acetate (PMA) stimulation. We further demonstrated the role of protein kinase C (PKC) isoforms for meprin β phosphorylation and identified the involvement of PKC-α and PKC-β. As a result of phosphorylation, the meprin β activity at the cell surface is reduced and, consequently, the extent of substrate cleavage is diminished. Our data indicate that this decrease of the surface activity is caused by the internalization and degradation of meprin β.

Blocking FcγRIIB in Smooth Muscle Cells Reduces Hypertension

[Figure: see text].

Fluorescence intensity fluctuation analysis of receptor oligomerization in membrane domains

Fluorescence micrographs of the plasma membrane of cells expressing fluorescently labeled G protein-coupled receptors (GPCRs) often exhibit small clusters of pixels (or puncta) with intensities that are higher than those of the surrounding pixels. Although studies of GPCR interactions in uniform membrane areas abound, understanding the details of the GPCR interactions within such puncta as well as the nature of the membrane formations underlying the puncta is hampered by the lack of adequate experimental techniques. Here, we introduce an enhancement of a recently developed method termed fluorescence intensity fluctuation spectrometry, which permits analysis of protein-protein interactions within the puncta in live cell membranes. We applied the novel fluorescence intensity fluctuation data analysis protocol to previously published data from cells expressing human secretin receptors and determined that the oligomer size increases with receptor concentration and duration of treatment with cognate ligand, not only within uniform regions of the membrane (in agreement with previous publications) but also within the puncta. In addition, we found that the number density and fractional area of the puncta increased after treatment with ligand. This method could be applied for probing the evolution in the time of the chain of events that begins with ligand binding and continues with coated pits formation and receptor internalization for other GPCRs and, indeed, other membrane receptors in living cells.

Angiotensin Receptors Heterodimerization and Trafficking: How Much Do They Influence Their Biological Function?

G-protein–coupled receptors (GPCRs) are targets for around one third of currently approved and clinical prescribed drugs and represent the largest and most structurally diverse family of transmembrane signaling proteins, with almost 1000 members identified in the human genome. Upon agonist stimulation, GPCRs are internalized and trafficked inside the cell: they may be targeted to different organelles, recycled back to the plasma membrane or be degraded. Once inside the cell, the receptors may initiate other signaling pathways leading to different biological responses. GPCRs’ biological function may also be influenced by interaction with other receptors. Thus, the ultimate cellular response may depend not only on the activation of the receptor from the cell membrane, but also from receptor trafficking and/or the interaction with other receptors. This review is focused on angiotensin receptors and how their biological function is influenced by trafficking and interaction with others receptors.

A Practical Approach to Acute Postoperative Pain Management in Chronic Pain Patients

In the United States, more than 100 million people suffer from chronic pain. Among patients presenting for surgery, about one in four have chronic pain. Acute perioperative pain management in this population is challenging because many patients with chronic pain require long-term opioids for the management of this pain, which may result in tolerance, physical dependence, addiction, and opioid-induced hyperalgesia. These challenges are compounded by the ongoing opioid epidemic that has resulted in calls for a reduction in opioid use, with a concurrent increase in the number of patients with chronic opioid exposure presenting for surgery. This article aims to summarize practical considerations for acute postoperative pain management in patients with chronic pain conditions. A patient-centered acute pain management plan, including nonopioid analgesics, regional anesthesia, and careful selection of opioid medications, can lead to adequate analgesia and satisfaction with care. Also, a meticulous rotation from one opioid to another may decrease opioid requirement, increase analgesic effectiveness, and improve satisfaction with care.

Targeted Delivery of Recombinant Heat Shock Protein 27 to Cardiomyocytes Promotes Recovery from Myocardial Infarction

Ischemic heart disease, especially myocardial infarction (MI), is the leading cause of death worldwide. Apoptotic mechanisms are thought to play a significant role in cardiomyocyte death after MI. Increased production of heat shock proteins (Hsps) in cardiomyocytes is a normal response to promote tolerance and to reduce cell damage. Hsp27 is considered to be a therapeutic option for the treatment of ischemic heart disease due to its protective effects on hypoxia-induced apoptosis. Despite its antiapoptotic effects, the lack of strategies to deliver Hsp27 to the heart tissue in vivo limits its clinical applicability. In this study, we utilized an antibody against the angiotensin II type 1 (AT1) receptor, which is expressed immediately after ischemia/reperfusion in the heart of MI rats. To achieve cardiomyocyte-targeted Hsp27 delivery after ischemia/reperfusion, we employed the immunoglobulin-binding dimer ZZ, a modified domain of protein A, in conjunction with the AT1 receptor antibody. Using the AT1 receptor antibody, we achieved systemic delivery of ZZ-TAT-GFP fusion protein into the heart of MI rats. This approach enabled selective delivery of Hsp27 to cardiomyocytes, rescued cells from apoptosis, reduced the area of fibrosis, and improved cardiac function in the rat MI model, thus suggesting its applicability as a cardiomyocyte-targeted protein delivery system to inhibit apoptosis induced by ischemic injury.

Time course of decompensation after angiotensin II and high-salt diet in Balb/CJ mice suggests pulmonary hypertension-induced cardiorenal syndrome

The genetic background of a mouse strain determines its susceptibility to disease. C57BL/6J and Balb/CJ are two widely used inbred mouse strains that we found react dramatically differently to angiotensin II and high-salt diet (ANG II + Salt). Balb/CJ show increased mortality associated with anuria and edema formation while C57BL/6J develop arterial hypertension but do not decompensate and die. Clinical symptoms of heart failure in Balb/CJ mice gave the hypothesis that ANG II + Salt impairs cardiac function and induces cardiac remodeling in male Balb/CJ but not in male C57BL/6J mice. To test this hypothesis, we measured cardiac function using echocardiography before treatment and every day for 7 days during treatment with ANG II + Salt. Interestingly, pulsed wave Doppler of pulmonary artery flow indicated increased pulmonary vascular resistance and right ventricle systolic pressure in Balb/CJ mice, already 24 h after ANG II + Salt treatment was started. In addition, Balb/CJ mice showed abnormal diastolic filling indicated by reduced early and late filling and increased isovolumic relaxation time. Furthermore, Balb/CJ exhibited lower cardiac output compared with C57BL/6J even though they retained more sodium and water, as assessed using metabolic cages. Left posterior wall thickness increased during ANG II + Salt treatment but did not differ between the strains. In conclusion, ANG II + Salt treatment causes early restriction of pulmonary flow and reduced left ventricular filling and cardiac output in Balb/CJ, which results in fluid retention and peripheral edema. This makes Balb/CJ a potential model to study the adaptive capacity of the heart for identifying new disease mechanisms and drug targets.

Blood pressure control and impact on cardiovascular events in patients with type 2 diabetes mellitus: A critical analysis of the literature

High blood pressure in individuals with type2 diabetes mellitus increases the risk of cardiovascular events. The international management guidelines recommend starting pharmacological treatment with blood pressure values >140/90mmHg. However, there is no optimal cut-off point from which cardiovascular events can be reduced without causing adverse events. A blood pressure range of >130/80 to <140/90mmHg seems to be adequate. These values can be achieved through non-pharmacological (diet, exercise) and pharmacological interventions (using drugs that have been shown to reduce cardiovascular events). The choice of one or several drugs must be individualised, according to factors including, ethnicity, age, and associated comorbidities, among others.

Control of Blood Pressure and Cardiovascular Outcomes in Type 2 Diabetes

High blood pressure in patients with diabetes mellitus results in a significant increase in the risk of cardiovascular events and mortality. The current evidence regarding the impact of intervention on blood pressure levels (in accordance with a specific threshold) is not particularly robust. Blood pressure control is more difficult to achieve in patients with diabetes than in non-diabetic patients, and requires using combination therapy in most patients. Different management guidelines recommend initiating pharmacological therapy with values >140/90 mm/Hg; however, an optimal cut point for this population has not been established. Based on the available evidence, it appears that blood pressure targets will probably have to be lower than <140/90mmHg, and that values approaching 130/80mmHg should be recommended. Initial treatment of hypertension in diabetes should include drug classes demonstrated to reduce cardiovascular events; i.e., angiotensin converting-enzyme inhibitors, angiotensin receptor blockers, diuretics, or dihydropyridine calcium channel blockers. The start of therapy must be individualized in accordance with the patient's baseline characteristics, and factors such as associated comorbidities, race, and age, inter alia.

Dimerization of AT2 and Mas Receptors in Control of Blood Pressure

PURPOSE OF REVIEW

Angiotensin type 2 receptor (AT₂R) and receptor Mas (MasR) are part of the "protective arm" of the renin angiotensin system. Gene and pharmacological manipulation studies reveal that AT₂R and MasR are involved in natriuretic, vasodilatory, and anti-inflammatory responses and in lowering blood pressure in various animal models under normal and pathological conditions such as salt-sensitive hypertension, obesity, and diabetes. The scope of this review is to discuss co-localization and heterodimerization as potential molecular mechanisms of AT₂R- and MasR-mediated functions including antihypertensive activities.

RECENT FINDINGS

Accumulating evidences show that AT₂R and MasR are co-localized, make a heterodimer, and are functionally interdependent in producing their physiological responses. Moreover, ang-(1-7) preferably may be an AT₁R-biased agonist while acting as a MasR agonist. The physical interactions of AT₂R and MasR appear to be an important mechanism by which these receptors are involved in blood pressure regulation and antihypertensive activity. Whether heteromers of these receptors influence affinity or efficacy of endogenous or synthetic agonists remains a question to be considered.