The intracrine hypothesis: an update

Role of angiotensin II in cellular entry and replication of dengue virus

Previous studies have demonstrated the relevance of several soluble molecules in the pathogenesis of dengue. In this regard, a possible role for angiotensin II (Ang II) in the pathophysiology of dengue has been suggested by the observation of a blockade of Ang II in patients with dengue, increased expression of molecules related to Ang II production in the plasma of dengue patients, increased expression of circulating cytokines and soluble molecules related to the action of Ang II, and an apparent relationship between DENV, Ang II effects, and miRNAs. In addition, in ex vivo experiments, the blockade of Ang II AT1 receptor and ACE-1 (angiotensin converting enzyme 1), both of which are involved in Ang II production and its function, inhibits infection of macrophages by DENV, suggesting a role of Ang II in viral entry or in intracellular viral replication of the virus. Here, we discuss the possible mechanisms of Ang II in the entry and replication of DENV. Ang II has the functions of increasing the expression of DENV entry receptors, creation of clathrin-coated vesicles, and increasing phagocytosis, all of which are involved in DENV entry. This hormone also modulates the expression of the Rab5 and Rab7 proteins, which are important in the endosomal processing of DENV during viral replication. This review summarizes the data related to the possible involvement of Ang II in the entry of DENV into cells and its replication.

Angiotensin II and post-streptococcal glomerulonephritis

BACKGROUND

Post-streptococcal glomerulonephritis (PSGN) is a consequence of the infection by group A beta-hemolytic streptococcus. During this infection, various immunological processes generated by streptococcal antigens are triggered, such as the induction of antibodies and immune complexes. This activation of the immune system involves both innate and acquired immunity. The immunological events that occur at the renal level lead to kidney damage with chronic renal failure as well as resolution of the pathological process (in most cases). Angiotensin II (Ang II) is a molecule with vasopressor and pro-inflammatory capacities, being an important factor in various inflammatory processes. During PSGN some events are defined that make Ang II conceivable as a molecule involved in the inflammatory processes during the disease.

CONCLUSION

This review is focused on defining which reported events would be related to the presence of this hormone in PSGN.

Angiotensin II and dengue

Dengue is a disease caused by a flavivirus that is transmitted principally by the bite of an Aedes aegypti mosquito and represents a major public-health problem. Many studies have been carried out to identify soluble factors that are involved in the pathogenesis of this infection. Cytokines, soluble factors, and oxidative stress have been reported to be involved in the development of severe disease. Angiotensin II (Ang II) is a hormone with the ability to induce the production of cytokines and soluble factors related to the inflammatory processes and coagulation disorders observed in dengue. However, a direct involvement of Ang II in this disease has not been demonstrated. This review primarily summarizes the pathophysiology of dengue, the role of Ang II in various diseases, and reports that are highly suggestive of the involvement of this hormone in dengue.

Angiotensin II and human obesity. A narrative review of the pathogenesis

Angiotensin II (Ang II) is a hormone and the main effector of the renin-angiotensin system (RAS). This peptide has crucial pathophysiologi-cal effects on hypertension, cardiac hypertrophy, endothelial proliferation, in-flammation and tissue remodelling through G protein-coupled receptors. The pro-inflammatory role of Ang II has been reported in various inflammatory pro-cesses. Obesity is linked to a chronic inflammatory process which in turn is the cause of some of its morbidities. Ang II is related to the comorbidities related to the comorbidities of obesity, which include alterations in the heart, kid-ney, hypertension and coagulation. In this regard, activation of AT1 receptors by Ang II can induce an inflammatory process mediated by the transcription factor NF-kB, triggering inflammation in various systems that are related to the comorbidities observed in obesity. The aim of this review was to highlight the pro-inflammatory effects of Ang II and the alterations induced by this hor-mone in various organs and systems in obesity. The search was done since 1990 through Medline, EMBASE and PubMed, using the keywords: angiotensin II; an-giotensin II, obesity; angiotensin II, kidney, obesity; angiotensin II, coagulation, obesity; angiotensin II, inflammation, obesity; angiotensin II, adipose tissue, obesity; angiotensin II, hypertension, obesity; angiotensin II, insulin resistance, obesity; angiotensin II, adiponectin, leptin, obesity; angiotensin II, COVID-19, obesity. Angiotensin II through its interaction with its AT1 receptor, can induce alterations in diverse systems that are related to the comorbidities observed in obesity. Therapeutic strategies to decrease the production and action of Ang II could improve the clinical conditions in individuals with obesity.

APC mutations in human colon lead to decreased neuroendocrine maturation of ALDH+ stem cells that alters GLP-2 and SST feedback signaling: Clue to a link between WNT and retinoic acid signalling in colon cancer development

APC mutations drive human colorectal cancer (CRC) development. A major contributing factor is colonic stem cell (SC) overpopulation. But, the mechanism has not been fully identified. A possible mechanism is the dysregulation of neuroendocrine cell (NEC) maturation by APC mutations because SCs and NECs both reside together in the colonic crypt SC niche where SCs mature into NECs. So, we hypothesized that sequential inactivation of APC alleles in human colonic crypts leads to progressively delayed maturation of SCs into NECs and overpopulation of SCs. Accordingly, we used quantitative immunohistochemical mapping to measure indices and proportions of SCs and NECs in human colon tissues (normal, adenomatous, malignant), which have different APC-zygosity states. In normal crypts, many cells staining for the colonic SC marker ALDH1 co-stained for chromogranin-A (CGA) and other NEC markers. In contrast, in APC-mutant tissues from familial adenomatous polyposis (FAP) patients, the proportion of ALDH+ SCs progressively increased while NECs markedly decreased. To explain how these cell populations change in FAP tissues, we used mathematical modelling to identify kinetic mechanisms. Computational analyses indicated that APC mutations lead to: 1) decreased maturation of ALDH+ SCs into progenitor NECs (not progenitor NECs into mature NECs); 2) diminished feedback signaling by mature NECs. Biological experiments using human CRC cell lines to test model predictions showed that mature GLP-2R+ and SSTR1+ NECs produce, via their signaling peptides, opposing effects on rates of NEC maturation via feedback regulation of progenitor NECs. However, decrease in this feedback signaling wouldn't explain the delayed maturation because both progenitor and mature NECs are depleted in CRCs. So the mechanism for delayed maturation must explain how APC mutation causes the ALDH+ SCs to remain immature. Given that ALDH is a key component of the retinoic acid (RA) signaling pathway, that other components of the RA pathway are selectively expressed in ALDH+ SCs, and that exogenous RA ligands can induce ALDH+ cancer SCs to mature into NECs, RA signaling must be attenuated in ALDH+ SCs in CRC. Thus, attenuation of RA signaling explains why ALDH+ SCs remain immature in APC mutant tissues. Since APC mutation causes increased WNT signaling in FAP and we found that sequential inactivation of APC in FAP patient tissues leads to progressively delayed maturation of colonic ALDH+ SCs, the hypothesis is developed that human CRC evolves due to an imbalance between WNT and RA signaling.

The role of the brain renin-angiotensin system (RAS) in mild traumatic brain injury (TBI)

There is considerable interest in traumatic brain injury (TBI) induced by repeated concussions suffered by athletes in sports, military personnel from combat-and non-combat related activities, and civilian populations who suffer head injuries from accidents and domestic violence. Although the renin-angiotensin system (RAS) is primarily a systemic cardiovascular regulatory system that, when dysregulated, causes hypertension and cardiovascular pathology, the brain contains a local RAS that plays a critical role in the pathophysiology of several neurodegenerative diseases. This local RAS includes receptors for angiotensin (Ang) II within the brain parenchyma, as well as on circumventricular organs outside the blood-brain-barrier. The brain RAS acts primarily via the type 1 Ang II receptor (AT₁R), exacerbating insults and pathology. With TBI, the brain RAS may contribute to permanent brain damage, especially when a second TBI occurs before the brain recovers from an initial injury. Agents are needed that minimize the extent of injury from an acute TBI, reducing TBI-mediated permanent brain damage. This review discusses how activation of the brain RAS following TBI contributes to this damage, and how drugs that counteract activation of the AT₁R including AT₁R blockers (ARBs), renin inhibitors, angiotensin-converting enzyme (ACE) inhibitors, and agonists at type 2 Ang II receptors (AT₂) and at Ang (1-7) receptors (Mas) can potentially ameliorate TBI-induced brain damage.

A proposed mechanism for the Berecek phenomenon with implications for cardiovascular reprogramming

Berecek et al reported in the 1990s that when spontaneously hypertensive rat (SHR) mating pairs were treated with captopril and the resulting pups were continued on the drug for 2 months followed by drug discontinuation, the pups did not develop full blown hypertension, and the cardiovascular structural changes associated with hypertension in SHR were mitigated. The offspring of the pups also displayed diminished hypertension and structural changes, suggesting that the drug therapy produced a heritable amelioration of the SHR phenotype. This observation is reviewed. The link between cellular renin angiotensin systems and epigenetic histone modification is explored, and a mechanism responsible for the observation is proposed. In any case, the observations of Berecek are sufficiently intriguing and biologically important to merit re-exploration and definitive explanation. Equally important is determining the role of renin angiotensin systems in epigenetic modification.

Growth hormone - past, present and future

Growth hormone (GH) research and its clinical application for the treatment of growth disorders span more than a century. During the first half of the 20th century, clinical observations and anatomical and biochemical studies formed the basis of the understanding of the structure of GH and its various metabolic effects in animals. The following period (1958-1985), during which pituitary-derived human GH was used, generated a wealth of information on the regulation and physiological role of GH - in conjunction with insulin-like growth factors (IGFs) - and its use in children with GH deficiency (GHD). The following era (1985 to present) of molecular genetics, recombinant technology and the generation of genetically modified biological systems has expanded our understanding of the regulation and role of the GH-IGF axis. Today, recombinant human GH is used for the treatment of GHD and various conditions of non-GHD short stature and catabolic states; however, safety concerns still accompany this therapeutic approach. In the future, new therapeutics based on various components of the GH-IGF axis might be developed to further improve the treatment of such disorders. In this Review, we describe the history of GH research and clinical use with a particular focus on disorders in childhood.

Role of intracellular angiotensin II

It has become clear that the vasoactive peptide angiotensin II, like other so-called intracrines, can act in the intracellular space. Evidence has accumulated indicating that such angiotensin II activity can be upregulated in disease states and cause pathology. Indeed, other intracrines appear to be involved in disease pathogenesis as well. At the same time, nitric oxide, potentially a cell protective factor, has been shown to be upregulated by intracellular angiotensin II. Recently data have been developed indicating that other potentially protective factors are directly upregulated at neuronal nuclei by angiotensin II. This led to the suggestion that intracellular angiotensin II is cell protective and not pathological. Here, the data on both sides of this issue and a possible resolution are discussed. In summary, there is evidence for both protective and pathological actions of intracellular angiotensin, just as there is abundant evidence derived from whole animal physiology to indicate that angiotensin-driven signaling cascades, including angiotensin II type 2 receptor- and Mas receptor-mediated events, can mitigate the effects of the angiotensin II/angiotensin II type 1 receptor axis (25). This mitigation does not negate the physiological and pathological importance of angiotensin II/angiotensin II type 1 receptor action but does expand our understanding of the workings of both intracellular and extracellular angiotensin II.

A Reassessment of the Pathophysiology of Progressive Cardiorenal Disorders

Heart failure and chronic renal diseases are usually progressive and only partially amenable to therapy. These disorders can be the sequelae of hypertension or worsened by hypertension. They are associated with the tissue up-regulation of multiple peptides, many of which are capable of acting within the cell interior. This article proposes that these peptides, intracrines, can form self-sustaining regulatory loops that can spread through heart or kidney, producing progressive disease. Moreover, mineralocorticoid activation seems capable of amplifying some of these peptide networks. This view suggests an expanded explanation of the pathogenesis of progressive cardiorenal disease and suggests new approaches to treatment.

Studies of intracellular angiotensin II

Many extracellular signaling proteins act within their cells of synthesis and/or in target cells after internalization. This type of action is called intracrine and it plays a role in diverse biological processes. The mechanisms of intracrine intracellular action are becoming clear thanks to the application of modern techniques of molecular biology. Here, progress in this area is reviewed. In particular the intracrine biology of angiotensin II is discussed.

A possible mechanism for the progression of chronic renal disease and congestive heart failure

Chronic neurologic diseases such as Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis, as well as various forms of chronic renal disease and systolic congestive heart failure, are among the most common progressive degenerative disorders encountered in medicine. Each disease follows a nearly relentless course, albeit at varying rates, driven by progressive cell dysfunction and drop-out. The neurologic diseases are characterized by the progressive spread of disease-causing proteins (prion-like proteins) from cell to cell. Recent evidence indicates that cell autonomous renin angiotensin systems operate in heart and kidney, and it is known that functional intracrine proteins can also spread between cells. This then suggests that certain progressive degenerative cardiovascular disorders such as forms of chronic renal insufficiency and systolic congestive heart failure result from dysfunctional renin angiotensin system intracrine action spreading in kidney or myocardium.

Altered glutamyl-aminopeptidase activity and expression in renal neoplasms

Background

Advances in the knowledge of renal neoplasms have demonstrated the implication of several proteases in their genesis, growth and dissemination. Glutamyl-aminopeptidase (GAP) (EC. 3.4.11.7) is a zinc metallopeptidase with angiotensinase activity highly expressed in kidney tissues and its expression and activity have been associated wtih tumour development.

Methods

In this prospective study, GAP spectrofluorometric activity and immunohistochemical expression were analysed in clear-cell (CCRCC), papillary (PRCC) and chromophobe (ChRCC) renal cell carcinomas, and in renal oncocytoma (RO). Data obtained in tumour tissue were compared with those from the surrounding uninvolved kidney tissue. In CCRCC, classic pathological parameters such as grade, stage and tumour size were stratified following GAP data and analyzed for 5-year survival.

Results

GAP activity in both the membrane-bound and soluble fractions was sharply decreased and its immunohistochemical expression showed mild staining in the four histological types of renal tumours. Soluble and membrane-bound GAP activities correlated with tumour grade and size in CCRCCs.

Conclusions

This study suggests a role for GAP in the neoplastic development of renal tumours and provides additional data for considering the activity and expression of this enzyme of interest in the diagnosis and prognosis of renal neoplasms.

Altered peptidase activities in thyroid neoplasia and hyperplasia

Background. Papillary thyroid carcinoma (PTC), follicular thyroid adenoma (FTA), and thyroid nodular hyperplasia (TNH) are the most frequent diseases of the thyroid gland. Previous studies described the involvement of dipeptidyl-peptidase IV (DPPIV/CD26) in the development of thyroid neoplasia and proposed it as an additional tool in the diagnosis/prognosis of these diseases. However, very little is known about the involvement of other peptidases in neoplastic and hyperplastic processes of this gland. Methods. The catalytic activity of 10 peptidases in a series of 30 PTC, 10 FTA, and 14 TNH was measured fluorimetrically in tumour and nontumour adjacent tissues. Results. The activity of DPPIV/CD26 was markedly higher in PTC than in FTA, TNH, and nontumour tissues. Aspartyl aminopeptidase (AspAP), alanyl aminopeptidase (AlaAP), prolyl endopeptidase, pyroglutamyl peptidase I, and aminopeptidase B activities were significantly increased in thyroid neoplasms when compared to nontumour tissues. AspAP and AlaAP activities were also significantly higher in PTC than in FTA and TNH. Conclusions. These data suggest the involvement of DPPIV/CD26 and some cytosolic peptidases in the neoplastic development of PTC and FTA. Further studies will help to define the possible clinical usefulness of AlaAP and AspAP in the diagnosis/prognosis of thyroid neoplasms.

MECHANISMS OF COMBINED ACTION OF ACE INHIBITORS AND CALCIUM ANTAGONISTS IN ARTERIAL HYPERTENSION

This review presents the modern views on the effectiveness of water-soluble angiotensin-converting enzyme (ACE) antagonists and calcium antagonists (CA), as monotherapy or as fixed-dose combination therapy, in the treatment of arterial hypertension (AH). The results of the X-ray structural analysis of crystal ACE-lisinopril complexes suggest a highly selective, strong inhibitory effect of lisinopril on various ACE forms of the hormonal renin-angiotensin-aldosterone system and tissue renin-angiotensin systems. The association between specific action mechanisms and therapeutic effects in hypertension is analysed for a third-generation CA amlodipine. The benefits of a fixed-dose combination medication Ekvator (amlodipine 5 mg plus lisinopril 10 mg) in hypertension are described, including its synergetic protective effects. 

The impact of peptidase activity on clear cell renal cell carcinoma survival

Several studies have proposed that protease expression and activity may have a predictive value in the survival of clear cell renal cell carcinoma (CCRCC). Most efforts on this issue have been focused on the analysis of matrix metalloproteinases (MMP) and very little on the role of other proteases, such as peptidases. The catalytic activity of 9 peptidases (APN, APB, ASP, CAP, DPP-IV, NEP/CD10, PEP, PGI, and PSA) was quantified by fluorometric methods in a series of 79 CCRCC patients, and the results obtained were analyzed for survival (Kaplan-Meier curves, log-rank test, and Cox multivariate analysis). CCRCC patients with higher activity levels of membrane-bound APN and soluble APN, DPP-IV, and CAP had significantly shorter 5-yr survival rates than those with lower levels. By contrast, higher soluble APB activity significantly correlated with longer survival. Our data suggest the involvement of peptidases in the biological aggressiveness of CCRCC and support the usefulness of measuring these proteases to assess the prognosis of patients with CCRCC.

Hepassocin regulates cell proliferation of the human hepatic cells L02 and hepatocarcinoma cells through different mechanisms

Hepassocin (HPS) is a specific mitogenic active factor for hepatocytes, and inhibits growth by overexpression in hepatocellular carcinoma (HCC) cells. However, the mechanism of HPS regulation on growth of liver-derived cells still remains largely unknown. In this study, we found that HPS was expressed and secreted into the extracellular medium in cultured L02 human hepatic cells; conditional medium of L02 cells promoted proliferation of L02 cells and this activity could be blocked by anti-HPS antibody. Moreover, we identified the presence of receptor for HPS on L02 cells and HepG2 human hepatoma cells. Overproduction of truncated HPS, which signal peptide was deleted, significantly inhibited the proliferation of HCC cells and induced cell cycle arrest. These findings suggest that HPS promotes hepatic cell line L02 cells proliferation via an autocrine mechanism and inhibits HCC cells proliferation by an intracrine pathway.

The anorexigenic cytokine ciliary neurotrophic factor stimulates POMC gene expression via receptors localized in the nucleus of arcuate neurons

Ciliary neurotrophic factor (CNTF) is a neural cytokine that reduces appetite and body weight when administrated to rodents or humans. We have demonstrated recently that the level of CNTF in the arcuate nucleus (ARC), a key hypothalamic region involved in food intake regulation, is positively correlated with protection against diet-induced obesity. However, the comprehension of the physiological significance of neural CNTF action was still incomplete because CNTF lacks a signal peptide and thus may not be secreted by the classical exocytosis pathways. Knowing that CNTF distribution shares similarities with that of its receptor subunits in the rat ARC, we hypothesized that CNTF could exert a direct intracrine effect in ARC cells. Here, we demonstrate that CNTF, together with its receptor subunits, translocates to the cell nucleus of anorexigenic POMC neurons in the rat ARC. Furthermore, the stimulation of hypothalamic nuclear fractions with CNTF induces the phosphorylation of several signaling proteins, including Akt, as well as the transcription of the POMC gene. These data strongly suggest that intracellular CNTF may directly modulate POMC gene expression via the activation of receptors localized in the cell nucleus, providing a novel plausible mechanism of CNTF action in regulating energy homeostasis.

Properties of antibodies to a synthetic peptide representing an epitope shared by receptors of the type I cytokine family

Previous works from our laboratory demonstrated that the monoclonal antibody (MAb) called R7B4 is directed to an epitope shared by various receptors corresponding to the type I cytokine receptor family, containing the common motif WSXWS or the homologous F(Y)GEFS. Later a consensus peptide significantly recognized by the MAb was identified and synthesized (sequence HGYWSEWSPE). In the present work, an homologous of the consensus sequence (HHGYWSEWSPE) was conjugated to PADRE adjuvant to produce Ab that could simulate theMAb activity, that is, acting as hormone and/or cytokine antagonists. The covalently conjugated peptide-PADRE was a better immunogen than the consensus peptide alone according to the reactivity of sera from C57BL/6 immunized mice and, besides, no Ab to PADRE were detected. Furthermore, Ab to consensus peptide elicited after peptide-PADRE inoculation into mice behaved as immunomodulatory agents, since they improved the humoral response to a foreign antigen (in this case ovalbumin). In addition, the Ab inhibited the in vitro proliferation of various cell lines, mainly cells derived from human and mouse breast cancer. Thus, immunization with the conjugate peptide-PADRE prepared under the experimental conditions described herein originated immunomodulatory Ab that, in the future, could be tested in some pathological conditions.

Intracardiac intracellular angiotensin system in diabetes

The renin-angiotensin system (RAS) has mainly been categorized as a circulating and a local tissue RAS. A new component of the local system, known as the intracellular RAS, has recently been described. The intracellular RAS is defined as synthesis and action of ANG II intracellularly. This RAS appears to differ from the circulating and the local RAS, in terms of components and the mechanism of action. These differences may alter treatment strategies that target the RAS in several pathological conditions. Recent work from our laboratory has demonstrated significant upregulation of the cardiac, intracellular RAS in diabetes, which is associated with cardiac dysfunction. Here, we have reviewed evidence supporting an intracellular RAS in different cell types, ANG II's actions in cardiac cells, and its mechanism of action, focusing on the intracellular cardiac RAS in diabetes. We have discussed the significance of an intracellular RAS in cardiac pathophysiology and implications for potential therapies.

Lessons from in vitro studies and a related intracellular angiotensin II transgenic mouse model

In the classical renin-angiotensin system, circulating ANG II mediates growth stimulatory and hemodynamic effects through the plasma membrane ANG II type I receptor, AT1. ANG II also exists in the intracellular space in some native cells, and tissues and can be upregulated in diseases, including hypertension and diabetes. Moreover, intracellular AT1 receptors can be found associated with endosomes, nuclei, and mitochondria. Intracellular ANG II can function in a canonical fashion through the native receptor and also in a noncanonical fashion through interaction with alternative proteins. Likewise, the receptor and proteolytic fragments of the receptor can function independently of ANG II. Participation of the receptor and ligand in alternative intracellular pathways may serve to amplify events that are initiated at the plasma membrane. We review historical and current literature relevant to ANG II, compared with other intracrines, in tissue culture and transgenic models. In particular, we describe a new transgenic mouse model, which demonstrates that intracellular ANG II is linked to high blood pressure. Appreciation of the diverse, pleiotropic intracellular effects of components of the renin-angiotensin system should lead to alternative disease treatment targets and new therapies.

Activity of soluble aminopeptidase A and dipeptidyl peptidase IV and membrane-bound aminopeptidase B and pyroglutamyl peptidase I in adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis

OBJECTIVE

To analyze soluble and membrane-bound peptidase activities in the tonsils and adenoids removed from patients with adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis.

METHODS

A total of 48 tissue samples from patients undergoing adenoidectomy and tonsillectomy for adenoid hyperplasia, tonsillar hyperplasia or chronic tonsillitis were analyzed. The catalytic activity of a pool of peptidases in the soluble (dipeptidyl peptidase IV, aminopeptidase A, aminopeptidase N and cystinyl aminopeptidase) and membrane-bound (prolyl endopeptidase, aspartyl aminopeptidase, aminopeptidase B and pyroglutamyl peptidase I) fractions was measured fluorometrically.

RESULTS

The activity of membrane-bound aminopeptidase B was higher in cases of chronic tonsillitis and adenoid hyperplasia than in tonsillar hyperplasia, p=0.004. Soluble dipeptidyl peptidase IV and membrane-bound pyroglutamyl peptidase I were found to be more active in tissues from male chronic tonsillitis tissues, p<0.05, while membrane-bound aminopeptidase B activity was higher in tissues of females with tonsillar hyperplasia, p<0.001. In the case of chronic tonsillitis, soluble aminopeptidase A was found to have a higher level of activity in tissues from children than those from adults, p=0.005.

CONCLUSIONS

Our results suggest a potential role of soluble aminopeptidase A, soluble dipeptidyl peptidase IV, membrane-bound aminopeptidase B and membrane-bound pyroglutamyl peptidase I in the pathobiology of adenoid hyperplasia, tonsillar hyperplasia and chronic tonsillitis that is differently regulated as a function of gender. These finfings may modify in the future the clinical approach to these diseases.

Uptake and metabolism of the novel peptide angiotensin-(1-12) by neonatal cardiac myocytes

Background

Angiotensin-(1–12) [Ang-(1–12)] functions as an endogenous substrate for the productions of Ang II and Ang-(1–7) by a non-renin dependent mechanism. This study evaluated whether Ang-(1–12) is incorporated by neonatal cardiac myocytes and the enzymatic pathways of ¹²⁵I-Ang-(1–12) metabolism in the cardiac myocyte medium from WKY and SHR rats.

Methodology/Principal Findings

The degradation of ¹²⁵I-Ang-(1–12) (1 nmol/L) in the cultured medium of these cardiac myocytes was evaluated in the presence and absence of inhibitors for angiotensin converting enzymes 1 and 2, neprilysin and chymase. In both strains uptake of ¹²⁵I-Ang-(1–12) by myocytes occurred in a time-dependent fashion. Uptake of intact Ang-(1–12) was significantly greater in cardiac myocytes of SHR as compared to WKY. In the absence of renin angiotensin system (RAS) enzymes inhibitors the hydrolysis of labeled Ang-(1–12) and the subsequent generation of smaller Ang peptides from Ang-(1–12) was significantly greater in SHR compared to WKY controls. ¹²⁵I-Ang-(1–12) degradation into smaller Ang peptides fragments was significantly inhibited (90% in WKY and 71% in SHR) in the presence of all RAS enzymes inhibitors. Further analysis of peptide fractions generated through the incubation of Ang-(1–12) in the myocyte medium demonstrated a predominant hydrolytic effect of angiotensin converting enzyme and neprilysin in WKY and an additional role for chymase in SHR.

Conclusions/Significance

These studies demonstrate that neonatal myocytes sequester angiotensin-(1–12) and revealed the enzymes involved in the conversion of the dodecapeptide substrate to biologically active angiotensin peptides.

Angiotensin II revisited: new roles in inflammation, immunology and aging

That the renin–angiotensin system (RAS) is involved in regulation of blood pressure, vasoconstriction, sodium intake and potassium excretion is well established. Studies in the last few years have however documented new roles for this molecule as a pro-inflammatory molecule and more recently as a possible pro-fibrotic agent that contributes to progressive deterioration of organ function in disease. Binding of Ang II to its receptors (in particular AT₁) mediates intracellular free radical generation that contributes to tissue damage by promoting mitochondrial dysfunction. Blocking Ang II signalling protects against neurodegenerative processes and promotes longevity in rodents. Altogether these findings open the unanticipated perspective for exploring Ang II signalling in therapeutic interventions in inflammatory diseases and aging-related tissue injury. This review extends from the discovery of Ang II and its implications in renal and cardiovascular physiology to cover the roles of the system in inflammation, tissue injury, autoimmunity, oxidative stress and aging.

The mitochondrial component of intracrine action

In recent years the actions of intracellular-acting, extracellular signaling proteins/peptides (intracrines) have become increasingly defined. General principles of intracrine action have been proposed. Mitochondria represent one locus of intracrine action, and thus far, angiotensin II, transforming growth factor-beta, growth hormone, atrial natriuretic peptide, Wnt 13, stanniocalcin, other renin-angiotensin system components, and vascular endothelial-derived growth factor, among others, have been shown to be mitochondria-localizing intracrines. The implications of this mitochondrial intracrine biology are discussed.

C-terminal processing of GABARAP is not required for trafficking of the angiotensin II type 1A receptor

OBJECTIVE

GABARAP, a small (117 aa) trafficking protein, binds to the C-terminal, cytoplasmic domain of rat angiotensin type-1A receptor (AT(1)R), the predominant effector of the octapeptide angiotensin II (Ang II) (Cook et al., Circ. Res. 2008;102:1539-47). The objectives of this study were to map the interaction domains of GABARAP and AT(1)R, to determine the effect of GABARAP association on AT(1)R signaling activity, and to determine the importance of post-translational processing of GABARAP on accumulation of AT(1)R on the plasma membrane and its signaling function.

RESULTS

Deletion analysis identified two regions within GABARAP necessary for interaction with AT(1)R in yeast two-hybrid assays: 1) a domain comprised of residues 32-51 that is nearly identical to that involved in binding and intracellular trafficking of the GABA(A) receptor and 2) a domain encompassing the C-terminal 21 aa. The GABARAP interaction domain of AT(1)R was delimited to the 15 aa immediately downstream of the last membrane spanning region. Overexpression of GABARAP in rat adrenal pheochromocytoma PC-12 cells increased the cell-surface expression of AT(1)R and Ang II-dependent activation of the cAMP signaling pathway. Residues within AT(1)R necessary for these responses were identified by mutational analysis. In PC-12 cells, GABARAP was constitutively and quantitatively cleaved at the C-terminus peptide bond and this cleavage was prevented by mutation of Gly(116). Wild-type GABARAP and the G116A mutant were, however, equally effective in stimulating AT(1)R surface expression and signaling activity.

CONCLUSIONS

GABARAP and AT(1)R interact through discrete domains and this association regulates the cell-surface accumulation and, consequently, ligand-induced function of the receptor. Unlike that observed with the GABA(A) receptor, this regulation is not dependent on C-terminal processing and modification of GABARAP.

Angiotensin-(1-7), Angiotensin-Converting Enzyme 2, and New Components of the Renin Angiotensin System

The discovery of angiotensin-(1-7) [Ang-(1-7)] in 1988 represented the first deviation from the traditional biochemical cascade of forming bioactive angiotensin peptides. Prior to that time, the biological actions of angiotensin II (Ang II) were being investigated as it relates to cardiovascular function, including hypertension, cardiac hypertrophy and failure, as well as biological actions in the brain and kidney. We now know that Ang II elicits a whole host of actions both within and outside of the cardiovascular system. Furthermore, the discovery of Ang-(1-7) by our laboratory was also the first indication of a biologically active angiotensin peptide that further studies revealed served to counter-balance the actions of Ang II. This chapter reviews the data demonstrating the role of the vasodepressor axis of the renin angiotensin system in the regulation of cardiovascular function and the new data that shows the existence of angiotensin-(1-12) as a novel alternate substrate for the production of angiotensin peptides. The ultimate role of this discovery, as well as the continuing elucidation of mechanisms pertaining to RAS physiology, will likely be clarified in the coming years, in hopes of improving the treatment of cardiovascular disease.

Senescence, apoptosis, and stem cell biology: the rationale for an expanded view of intracrine action

Some extracellular-signaling peptides also at times function within the intracellular space. We have termed these peptides intracrines and have argued that intracrine function is associated with a wide variety of peptides/proteins including hormones, growth factors, cytokines, enzymes, and DNA-binding proteins among others. Here we consider the possibility that intracrines participate in the related phenomena of senescence, apoptosis, and stem cell regulation of tissue biology. Based on this analysis, we also suggest that the concept of intracrine action be expanded to include possible regulatory peptide transfer via exosomes/microvesicles and possibly by nanotubes. Moreover, the process of microvesicular and nanotube transfer of peptides and other biologically relevant molecules, which we inclusively term laterality, is explored. These notions have potentially important therapeutic implications, including implications for the therapy of cardiovascular disease.

New insights into target organ involvement in hypertension

Hypertension and its sequelae are complex processes. Optimization of the care of the hypertensive patient requires not only attention to the regulation of arterial pressure but also attention to blunting the hypertension-related processes that lead to vascular disease. It is clear that the regulation of these processes is much more complex than previously understood. Here several new insights into the pathogenesis of hypertension-related vascular disease have been explored. While this review is not exhaustive, it does serve to point out the varied nature of the biologic processes that must be taken into account and it points to new avenues for the development of therapeutic agents.

Renin-angiotensin system revisited

New components and functions of the renin-angiotensin system (RAS) are still being unravelled. The classical RAS as it looked in the middle 1970s consisted of circulating renin, acting on angiotensinogen to produce angiotensin I, which in turn was converted into angiotensin II (Ang II) by angiotensin-converting enzyme (ACE). Ang II, still considered the main effector of RAS was believed to act only as a circulating hormone via angiotensin receptors, AT1 and AT2. Since then, an expanded view of RAS has gradually emerged. Local tissue RAS systems have been identified in most organs. Recently, evidence for an intracellular RAS has been reported. The new expanded view of RAS therefore covers both endocrine, paracrine and intracrine functions. Other peptides of RAS have been shown to have biological actions; angiotensin 2-8 heptapeptide (Ang III) has actions similar to those of Ang II. Further, the angiotensin 3-8 hexapeptide (Ang IV) exerts its actions via insulin-regulated amino peptidase receptors. Finally, angiotensin 1-7 (Ang 1-7) acts via mas receptors. The discovery of another ACE2 was an important complement to this picture. The recent discovery of renin receptors has made our view of RAS unexpectedly complex and multilayered. The importance of RAS in cardiovascular disease has been demonstrated by the clinical benefits of ACE inhibitors and AT1 receptor blockers. Great expectations are now generated by the introduction of renin inhibitors. Indeed, RAS regulates much more and diverse physiological functions than previously believed.

Peptide hormones as developmental growth and differentiation factors

Peptide hormones, usually considered to be endocrine factors responsible for communication between tissues remotely located from each other, are increasingly being found to be synthesized in developing tissues, where they act locally. Several hormones are now known to be produced in developing tissues that are unrelated to the endocrine gland of origin in the adult. These hormones are synthesized locally, and are active as differentiation and survival factors, before the developing adult endocrine tissue becomes functional. There is increasing evidence for paracrine and/or autocrine actions for these factors during development, thus, placing them among the conventional growth and differentiation factors. We review the evidence for the view that thyroid hormones, growth hormone, prolactin, insulin, and parathyroid hormone-related protein are developmental growth and differentiation factors.

Cellular and subcellular distribution of rat brain prolyl oligopeptidase and its association with specific neuronal neurotransmitters

Prolyl oligopeptidase (POP) is a serine endopeptidase that hydrolyzes proline-containing peptides shorter than 30-mer. It has been suggested that POP is associated with cognitive functions and inositol 1,4,5-triphosphate (IP(3)) signaling. However, little is known about the distribution and physiological role of POP in the brain. We used immunohistochemistry to determine the cellular and subcellular distribution of POP in the rat brain. POP was specifically expressed in the glutamatergic pyramidal neurons of the cerebral cortex, particularly in the primary motor and somatosensory cortices, and also in the CA1 field of hippocampus. Purkinje cells of the cerebellum were also intensively immunostained for POP. Double immunofluorescence indicated that POP was present in the gamma-aminobutyric acid (GABA)ergic and cholinergic interneurons of the thalamus and cortex but not in the nigrostriatal dopaminergic neurons. POP did not colocalize with astrocytic markers in any part of the rat brain. We used postembedding immunoelectron microscopy to determine the distribution of POP at the subcellular level. POP was mainly present in neuronal cytosol and membranes, hardly at all in neuronal plasma membrane, but more extensively in intracellular membranes such as the rough endoplasmic reticulum and Golgi apparatus. Our findings point to a role for POP--evidently modifying neuropeptide levels--in excitatory and inhibitory neurotransmission in the central nervous system via glutamatergic, GABAergic, and cholinergic neurotransmission systems. Furthermore, according to our results, POP may be involved in thalamocortical neurotransmission, memory and learning functions of the hippocampal formation, and GABAergic regulation of voluntary movements. Subcellular distribution of POP points to a role in protein processing and secretion.

The physiological basis of intracrine stem cell regulation

Intracrine peptides and proteins participate in the regulation of adult and pleuripotential embryonic-like stem cells. Included among these factors are VEGF, dynorphin, the readthrough form of acetylcholinesterase, Oct3/4, Pdx-1, Pax-6, and high-mobility group protein B1, among others. In some cases, the establishment of intracrine feedback loops can be shown to be relevant to this regulation, consistent with previously proposed principles of intracrine action. Here the role of intracrines in stem cell regulation is reviewed, with particular attention to the intracrine regulation of cardiac stem cells. The reprogramming of cells to restore the pleuripotent phenotype and the possible role of stem/progenitor cells in neoplasia are also discussed.

The basis of an intracrine pharmacology

Intracrines are extracellular signaling peptide factors that can act in the intracellular space after either internalization or retention in the cells that synthesize them. They are structurally diverse and include hormones, growth factors, enzymes, DNA-binding proteins, and other peptide moieties. We have suggested principles of intracrine action and have applied those principles to forms of cellular and tissue differentiation, hormonal responsiveness, and memory. Moreover, recent findings make clear that some currently available pharmaceuticals act via the alteration of intracrine function. Thus, the beginnings of an intracrine pharmacology are at hand and we here review principles applicable to the design of such agents. The intracrine pharmacology of the renin-angiotensin system, angiogenesis, and stem cell development is discussed.

Mechanisms of Disease: intracrine physiology in the cardiovascular system

The field of intracrine physiology attempts to codify the biological actions of intracrines--extracellular signaling proteins or peptides that also operate in the intracellular space, either because they are retained in their cells of synthesis or because they have been internalized by a target cell. Intracrines are structurally diverse; hormones, growth factors, DNA-binding proteins and enzymes can all display intracrine functionality. Here, we review the role of intracrines in the heart and vasculature, including the intracrine actions of renin-angiotensin-system components in cardiac pathology, dynorphin B in cardiac development, and a variety of factors in pathologic and therapeutic angiogenesis. We argue that principles of intracrine physiology can inform our understanding of important pathologic processes such as left ventricular hypertrophy, diabetic cardiomyopathy and arrythmogenesis, and can aid the development of more-effective therapeutic interventions in cardiovascular disease.

The intrarenal renin-angiotensin system: from physiology to the pathobiology of hypertension and kidney disease

In recent years, the focus of interest on the role of the renin-angiotensin system (RAS) in the pathophysiology of hypertension and organ injury has changed to a major emphasis on the role of the local RAS in specific tissues. In the kidney, all of the RAS components are present and intrarenal angiotensin II (Ang II) is formed by independent multiple mechanisms. Proximal tubular angiotensinogen, collecting duct renin, and tubular angiotensin II type 1 (AT1) receptors are positively augmented by intrarenal Ang II. In addition to the classic RAS pathways, prorenin receptors and chymase are also involved in local Ang II formation in the kidney. Moreover, circulating Ang II is actively internalized into proximal tubular cells by AT1 receptor-dependent mechanisms. Consequently, Ang II is compartmentalized in the renal interstitial fluid and the proximal tubular compartments with much higher concentrations than those existing in the circulation. Recent evidence has also revealed that inappropriate activation of the intrarenal RAS is an important contributor to the pathogenesis of hypertension and renal injury. Thus, it is necessary to understand the mechanisms responsible for independent regulation of the intrarenal RAS. In this review, we will briefly summarize our current understanding of independent regulation of the intrarenal RAS and discuss how inappropriate activation of this system contributes to the development and maintenance of hypertension and renal injury. We will also discuss the impact of antihypertensive agents in preventing the progressive increases in the intrarenal RAS during the development of hypertension and renal injury.

High-glucose-induced regulation of intracellular ANG II synthesis and nuclear redistribution in cardiac myocytes

The prevailing paradigm is that cardiac ANG II is synthesized in the extracellular space from components of the circulating and/or local renin-angiotensin system. The recent discovery of intracrine effects of ANG II led us to determine whether ANG II is synthesized intracellularly in neonatal rat ventricular myocytes (NRVM). NRVM, incubated in serum-free medium, were exposed to isoproterenol or high glucose in the absence or presence of candesartan, which was used to prevent angiotensin type 1 (AT1) receptor-mediated internalization of ANG II. ANG II was measured in cell lysates and the culture medium, which represented intra- and extracellularly synthesized ANG II, respectively. Isoproterenol increased ANG II concentration in cell lysates and medium of NRVM in the absence or presence of candesartan. High glucose markedly increased ANG II synthesis only in cell lysates in the absence and presence of candesartan. Western analysis showed increased intracellular levels of angiotensinogen, renin, and chymase in high-glucose-exposed cells. Confocal immunofluorocytometry confirmed the presence of ANG II in the cytoplasm and nucleus of high-glucose-exposed NRVM and along the actin filaments in isoproterenol-exposed cells. ANG II synthesis was dependent on renin and chymase in high-glucose-exposed cells and on renin and angiotensin-converting enzyme in isoproterenol-exposed cells. In summary, the site of ANG II synthesis, intracellular localization, and the synthetic pathway in NRVM are stimulus dependent. Significantly, NRVM synthesized and retained ANG II intracellularly, which redistributed to the nucleus under high-glucose conditions, suggesting a role for an intracrine mechanism in diabetic conditions.

The intracellular form of human MAGP1 elicits a complex and specific transcriptional response

Microfibril-associated glycoprotein-1 (MAGP1) is found associated with microfibrils in the extracellular matrix (ECM). In humans, MAGP1 is expressed as two alternatively spliced isoforms: MAGP1A, the extracellular microfibril-associated form; and MAGP1B, an exclusively intracellular isoform derived from the skipping of exon 3. The biological function of MAGP1B is unknown. We performed gene expression profiling to study the cellular response to MAGP1B using whole-genome genechips. We found that MAGP1B specifically induces the expression of genes linked to cell adhesion, motility, metabolism, gene expression, development and signal transduction. Versican, a gene product involved in the structure and functional regulation of the ECM, showed the highest up-regulation in response to MAGP1B. These studies suggest a dual role for MAGP1, with extracellular MAGP1A involved in ECM function, and intracellular MAGP1B modulating the expression of genes that function in cell adhesion, migration and control of ECM deposition.

The intracellular renin-angiotensin system: a new paradigm

More than a century after its discovery, the physiological implications of the renin-angiotensin system (RAS) continue to expand, with the identification of new components, functions and subsystems. These advancements have led to better management and understanding of a broad range of cardiovascular and metabolic disorders. The RAS has traditionally been viewed as a circulatory system, involved in the short-term regulation of volume and blood pressure homeostasis. Recently, local RASs have been described as regulators of chronic tissue effects. Most recently, studies have provided evidence of a complete, functional RAS within cells, described as an 'intracrine' or intracellular system. A more comprehensive understanding of the intracellular RAS provides for new strategies in system regulation and a more efficacious approach to the management of RAS-related diseases.