Intracrine action of angiotensin II in mesangial cells: subcellular distribution of angiotensin II receptor subtypes AT1 and AT2

Activation of Pannexin-1 channels causes cell dysfunction and damage in mesangial cells derived from angiotensin II-exposed mice

Chronic kidney disease (CKD) is a prevalent health concern associated with various pathological conditions, including hypertensive nephropathy. Mesangial cells are crucial in maintaining glomerular function, yet their involvement in CKD pathogenesis remains poorly understood. Recent evidence indicates that overactivation of Pannexin-1 (Panx1) channels could contribute to the pathogenesis and progression of various diseases. Although Panx1 is expressed in the kidney, its contribution to the dysfunction of renal cells during pathological conditions remains to be elucidated. This study aimed to investigate the impact of Panx1 channels on mesangial cell function in the context of hypertensive nephropathy. Using an Ang II-infused mouse model and primary mesangial cell cultures, we demonstrated that in vivo exposure to Ang II sensitizes cultured mesangial cells to show increased alterations when they are subjected to subsequent in vitro exposure to Ang II. Particularly, mesangial cell cultures treated with Ang II showed elevated activity of Panx1 channels and increased release of ATP. The latter was associated with enhanced basal intracellular Ca2+ ([Ca2+]i) and increased ATP-mediated [Ca2+]i responses. These effects were accompanied by increased lipid peroxidation and reduced cell viability. Crucially, all the adverse impacts evoked by Ang II were prevented by the blockade of Panx1 channels, underscoring their critical role in mediating cellular dysfunction in mesangial cells. By elucidating the mechanisms by which Ang II negatively impacts mesangial cell function, this study provides valuable insights into the pathogenesis of renal damage in hypertensive nephropathy.

Effect of extracellular vesicles derived from induced pluripotent stem cells on mesangial cells underwent a model of fibrosis in vitro

The fibrogenic process plays a significant pathophysiological role in the progression of chronic kidney disease. Inhibition of the renin-angiotensin system (RAS) is one strategy to delay disease progression but does not reverse established fibrosis. In this context, induced pluripotent stem cells (iPSCs) have been considered an alternative due to their regenerative potential. iPSCs exert their effects through paracrine signaling, which releases specific biomolecules into the extracellular environment, either directly or within extracellular vesicle (EVs), that can reach target cells. This study aims to evaluate the potential beneficial effects of iPSC-derived EVs (EV-iPSCs) in an in vitro model of fibrosis using mouse mesangial cells (MMCs) stimulated with TGF-β. EV-iPSCs were obtained by differentially ultracentrifuging iPSCs culture medium. MMCs were stimulated with 5 ng/mL of TGF-β and simultaneously treated with or without EV-iPSCs for 24 h. Markers of inflammation, fibrosis, and RAS components were assessed using RT-PCR, western blotting, and immunofluorescence. Under TGF-β stimulus, MMCs exhibited increased expression of inflammation markers, RAS components, and fibrosis. However, these changes were mitigated in the presence of EV-iPSCs. EV-iPSCs effectively reduced inflammation, RAS activation, and fibrogenesis in this fibrosis model involving mesangial cells, suggesting their potential as a strategy to reduce glomerular sclerosis.

The Angiotensin AT2 Receptor: From a Binding Site to a Novel Therapeutic Target

Discovered more than 30 years ago, the angiotensin AT2 receptor (AT2R) has evolved from a binding site with unknown function to a firmly established major effector within the protective arm of the renin-angiotensin system (RAS) and a target for new drugs in development. The AT2R represents an endogenous protective mechanism that can be manipulated in the majority of preclinical models to alleviate lung, renal, cardiovascular, metabolic, cutaneous, and neural diseases as well as cancer. This article is a comprehensive review summarizing our current knowledge of the AT2R, from its discovery to its position within the RAS and its overall functions. This is followed by an in-depth look at the characteristics of the AT2R, including its structure, intracellular signaling, homo- and heterodimerization, and expression. AT2R-selective ligands, from endogenous peptides to synthetic peptides and nonpeptide molecules that are used as research tools, are discussed. Finally, we summarize the known physiological roles of the AT2R and its abundant protective effects in multiple experimental disease models and expound on AT2R ligands that are undergoing development for clinical use. The present review highlights the controversial aspects and gaps in our knowledge of this receptor and illuminates future perspectives for AT2R research. SIGNIFICANCE STATEMENT: The angiotensin AT2 receptor (AT2R) is now regarded as a fully functional and important component of the renin-angiotensin system, with the potential of exerting protective actions in a variety of diseases. This review provides an in-depth view of the AT2R, which has progressed from being an enigma to becoming a therapeutic target.

TNF-α Plus IL-1β Induces Opposite Regulation of Cx43 Hemichannels and Gap Junctions in Mesangial Cells through a RhoA/ROCK-Dependent Pathway

Connexin 43 (Cx43) is expressed in kidney tissue where it forms hemichannels and gap junction channels. However, the possible functional relationship between these membrane channels and their role in damaged renal cells remains unknown. Here, analysis of ethidium uptake and thiobarbituric acid reactive species revealed that treatment with TNF-α plus IL-1β increases Cx43 hemichannel activity and oxidative stress in MES-13 cells (a cell line derived from mesangial cells), and in primary mesangial cells. The latter was also accompanied by a reduction in gap junctional communication, whereas Western blotting assays showed a progressive increase in phosphorylated MYPT (a target of RhoA/ROCK) and Cx43 upon TNF-α/IL-1β treatment. Additionally, inhibition of RhoA/ROCK strongly antagonized the TNF-α/IL-1β-induced activation of Cx43 hemichannels and reduction in gap junctional coupling. We propose that activation of Cx43 hemichannels and inhibition of cell-cell coupling during pro-inflammatory conditions could contribute to oxidative stress and damage of mesangial cells via the RhoA/ROCK pathway.

The Receptor AT1 Appears to Be Important for the Maintenance of Bone Mass and AT2 Receptor Function in Periodontal Bone Loss Appears to Be Regulated by AT1 Receptor

A large number of experimental studies has demonstrated that angiotensin II (Ang II) is involved in key events of the inflammatory process. This study aimed to evaluate the role of Ang II type 1 (AT1) and Ang II type 2 (AT2) receptors on periodontitis. Methods: Experimental periodontitis was induced by placing a 5.0 nylon thread ligature around the second upper left molar of AT1 mice, no-ligature or ligature (AT1-NL and AT1-L), AT2 (AT2-NL or AT2-L) and wild type (WT-NL or L). Alveolar bone loss was scanned using Micro-CT. Cytokines, peptides and enzymes were analyzed from gingival tissues by Elisa and RT-PCR. Results: The blockade of AT1 receptor resulted in bone loss, even in healthy animals. Ang II receptor blockades did not prevent linear bone loss. Ang II and Ang 1-7 levels were significantly increased in the AT2-L (p < 0.01) group compared to AT2-NL and AT1-L. The genic expression of the Mas receptor was significantly increased in WT-L and AT2-L compared to (WT-NL and AT2-NL, respectively) and in AT1-L. Conclusions: Our data suggest that the receptor AT1 appears to be important for the maintenance of bone mass. AT2 receptor molecular function in periodontitis appears to be regulated by AT1.

An ACE2/Mas-related receptor MrgE axis in dopaminergic neuron mitochondria

ACE2 plays a pivotal role in the balance between the pro-oxidative pro-inflammatory and the anti-oxidative anti-inflammatory arms of the renin-angiotensin system. Furthermore, ACE2 is the entry receptor for SARS-CoV-2. Clarification of ACE2-related mechanisms is crucial for the understanding of COVID-19 and other oxidative stress and inflammation-related processes. In rat and monkey brain, we discovered that the intracellular ACE2 and its products Ang 1–7 and alamandine are highly concentrated in the mitochondria and bind to a new mitochondrial Mas-related receptor MrgE (MrgE) to produce nitric oxide. We found MrgE expressed in neurons and glia of rodents and primates in the substantia nigra and different brain regions. In the mitochondria, ACE2 and MrgE expressions decreased and NOX4 increased with aging. This new ACE2/MrgE/NO axis may play a major role in mitochondrial regulation of oxidative stress in neurons, and possibly other cells. Therefore, dysregulation of the mitochondrial ACE2/MrgE/NO axis may play a major role in neurodegenerative processes of dopaminergic neurons, where mitochondrial dysfunction and oxidative stress play a crucial role. Since ACE2 binds SARS-CoV-2 spike protein, the mitochondrial ACE2/MrgE/NO axis may also play a role in SARS-CoV-2 cellular effects.

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ACE2 products Ang1-7 and alamandine (Ala) highly concentrate in brain mitochondria.

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Ang1-7 and Ala bind to mitochondrial Mas-related receptor MrgE producing nitric oxide.

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ACE2/MrgE may play a major role in mitochondrial function and oxidative stress.

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Clarification of ACE2-related mechanisms is also crucial for understanding COVID-19.

Reference genes for mesangial cell and podocyte qPCR gene expression studies under high-glucose and renin-angiotensin-system blocker conditions

BACKGROUND

Real-time PCR remains currently the gold standard method for gene expression studies. Identification of the best reference gene is a key point in performing high-quality qPCR, providing strong support for results, and performing as a source of bias when inappropriately chosen. Mesangial cells and podocytes, as essential cell lines to study diabetic kidney disease (DKD) physiopathology, demand accurate analysis of the reference genes used thus far to enhance the validity of gene expression studies, especially regarding high glucose (HG) and DKD treatments, with angiotensin II receptor blockers (e.g., losartan) being the most commonly used. This study aimed to evaluate the suitability and define the most stable reference gene for mesangial cell and podocyte studies of an in vitro DKD model of disease and its treatment.

METHODS

Five software packages (RefFinder, NormFinder, GeNorm, Bestkeeper, and DataAssist) and the comparative ΔCt method were selected to analyze six different candidate genes: HPRT, ACTB, PGAM-1, GAPDH, PPIA, and B2M. RNA was extracted, and cDNA was synthesized from immortalized mouse mesangial cells and podocytes cultured in 4 groups: control (n = 5; 5 mM glucose), mannitol (n = 5; 30 mM, as osmotic control), HG (n = 5; 30 mM glucose), and HG + losartan (n = 5; 30 mM glucose and 10-4 mM losartan). Real-time PCR was performed according to MIQE guidelines.

RESULTS

We identified that the use of 2 genes was the best combination for qPCR normalization for both mesangial cells and podocytes. For mesangial cells, the combination of HPRT and ACTB presented higher stability values. For podocytes, HPRT and GAPDH showed the best results.

CONCLUSION

This analysis provides support for the use of HPRT and ACTB as reference genes in mouse mesangial cell studies of gene expression via real-time PCR, while for podocytes, HPRT and GAPDH should be chosen.

AT1 and AT2 Receptor Knockout Changed Osteonectin and Bone Density in Mice in Periodontal Inflammation Experimental Model

BACKGROUND

The aim of this study was to evaluate the role of AT1 and AT2 receptors in a periodontal inflammation experimental model.

METHODS

Periodontal inflammation was induced by LPS/Porphyromonas gingivalis. Maxillae, femur, and vertebra were scanned using Micro-CT. Maxillae were analyzed histopathologically, immunohistochemically, and by RT-PCR.

RESULTS

The vertebra showed decreased BMD in AT1 H compared with WT H (p < 0.05). The femur showed increased Tb.Sp for AT1 H and AT2 H, p < 0.01 and p < 0.05, respectively. The Tb.N was decreased in the vertebra (WT H-AT1 H: p < 0.05; WT H-AT2 H: p < 0.05) and in the femur (WT H-AT1 H: p < 0.01; WT H-AT2 H: p < 0.05). AT1 PD increased linear bone loss (p < 0.05) and decreased osteoblast cells (p < 0.05). RANKL immunostaining was intense for AT1 PD and WT PD (p < 0.001). OPG was intense in the WT H, WT PD, and AT2 PD when compared to AT1 PD (p < 0.001). AT1 PD showed weak immunostaining for osteocalcin compared with WT H, WT PD, and AT2 PD (p < 0.001). AT1 H showed significantly stronger immunostaining for osteonectin in fibroblasts compared to AT2 H (p < 0.01).

CONCLUSION

AT1 receptor knockout changed bone density, the quality and number of bone trabeculae, decreased the number of osteoblast cells, and increased osteonectin in fibroblasts.

Nanomedicine for the treatment of diabetes-associated cardiovascular diseases and fibrosis

Cardiomyopathy and fibrosis are the main causes of heart failure in diabetes patients. For therapeutic purposes, a delivery system is required to enhance antidiabetic drug efficacy and specifically target profibrotic pathways in cardiomyocytes. Nanoparticles (NPs) have distinct advantages, including biocompatibility, bioavailability, targeting efficiency, and minimal toxicity, which make them ideal for antidiabetic treatment. In this review, we overview the latest information on the pathogenesis of cardiomyopathy and fibrosis in diabetes patients. We summarize how NP applications improve insulin and liraglutide efficacy and their sustained release upon oral administration. We provide a comprehensive review of the results of NP clinical trials in diabetes patients and of animal studies investigating the effects of NP-mediated anti-fibrotic treatments. Collectively, the application of advanced NP delivery systems in the treatment of cardiomyopathy and fibrosis in diabetes patients is a promising and innovative therapeutic strategy.

The intracellular renin-angiotensin system: Friend or foe. Some light from the dopaminergic neurons

The renin-angiotensin system (RAS) is one of the oldest hormone systems in vertebrate phylogeny. RAS was initially related to regulation of blood pressure and sodium and water homeostasis. However, local or paracrine RAS were later identified in many tissues, including brain, and play a major role in their physiology and pathophysiology. In addition, a major component, ACE2, is the entry receptor for SARS-CoV-2. Overactivation of tissue RAS leads several oxidative stress and inflammatory processes involved in aging-related degenerative changes. In addition, a third level of RAS, the intracellular or intracrine RAS (iRAS), with still unclear functions, has been observed. The possible interaction between the intracellular and extracellular RAS, and particularly the possible deleterious or beneficial effects of the iRAS activation are controversial. The dopaminergic system is particularly interesting to investigate the RAS as important functional interactions between dopamine and RAS have been observed in the brain and several peripheral tissues. Our recent observations in mitochondria and nucleus of dopaminergic neurons may clarify the role of the iRAS. This may be important for the developing of new therapeutic strategies, since the effects on both extracellular and intracellular RAS must be taken into account, and perhaps better understanding of COVID-19 cell mechanisms.

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.

Angiotensin receptor subtypes regulate adipose tissue renewal and remodelling

Obesity is often associated with high systemic and local renin-angiotensin system (RAS) activity in adipose tissue. Adipose-derived mesenchymal stem/stromal cells (ADSCs), responsible for adipose tissue growth upon high-fat diet, express multiple angiotensin II receptor isoforms, including angiotensin II type 1 receptor (AT₁ R), angiotensin II type 2 receptor (AT₂ R), Mas and Mas-related G protein-coupled receptor D. Although AT₁ R is expressed on most ADSCs, other angiotensin receptors are co-expressed on a small subpopulation of the cells, a phenomenon that results in a complex response pattern. Following AT₁ R activation, the effects are transient due to rapid receptor internalisation. This short-lived effect can be prevented by heteromerisation with AT₂ R, a particularly important strategy for the regulation of ADSC differentiation and secretory activity. Heteromeric AT₂ R might be especially important for the generation of thermogenic beige adipocytes. This review summarises current data regarding the regulation of adipose tissue renewal and particularly ADSC adipogenic differentiation and secretory activity by RAS, with an emphasis on AT₂ R and its effects. We reveal a new scheme that implicates AT₂ R into the regulation of ADSC hormonal sensitivity.

Intracrine Endorphinergic Systems in Modulation of Myocardial Differentiation

A wide variety of peptides not only interact with the cell surface, but govern complex signaling from inside the cell. This has been referred to as an "intracrine" action, and the orchestrating molecules as "intracrines". Here, we review the intracrine action of dynorphin B, a bioactive end-product of the prodynorphin gene, on nuclear opioid receptors and nuclear protein kinase C signaling to stimulate the transcription of a gene program of cardiogenesis. The ability of intracrine dynorphin B to prime the transcription of its own coding gene in isolated nuclei is discussed as a feed-forward loop of gene expression amplification and synchronization. We describe the role of hyaluronan mixed esters of butyric and retinoic acids as synthetic intracrines, controlling prodynorphin gene expression, cardiogenesis, and cardiac repair. We also discuss the increase in prodynorphin gene transcription and intracellular dynorphin B afforded by electromagnetic fields in stem cells, as a mechanism of cardiogenic signaling and enhancement in the yield of stem cell-derived cardiomyocytes. We underline the possibility of using the diffusive features of physical energies to modulate intracrinergic systems without the needs of viral vector-mediated gene transfer technologies, and prompt the exploration of this hypothesis in the near future.

Influence of high glucose on mesangial cell-derived exosome composition, secretion and cell communication

Mesangial cells stimulated with high glucose (HG) exhibit increased intracellular angiotensin II (AngII) synthesis that is correlated with the upregulation of AngII target genes, such as profibrotic cytokines. The intracrine effects of AngII can be mediated by several molecules transferred to other cells via exosomes (Exos), which play a key role in cellular communication under many physiological and pathological conditions. The aim of this study was to investigate the effects of exosomes derived from HG-stimulated human mesangial cells (HG-HMCs) on normal unstimulated HMCs. Exosomes from HMCs (C-Exos) and HG-HMCs (HG-Exos) were obtained from cell culture supernatants. HMCs were incubated with C-Exos or HG-Exos. HG stimulus induced a change in the amount but not the size of Exos. Both C-Exos and HG-Exos contained angiotensinogen and renin, but no angiotensin converting enzyme was detected. Compared with HMCs treated with C-Exos, HMCs treated with HG-Exos presented higher levels of fibronectin, angiotensinogen, renin, AT₁ and AT₂ receptors, indicating that HG-Exos modified the function of normal HMCs. These results suggest that the intercellular communication through Exos may have pathophysiological implications in the diabetic kidney.

Significance of intranuclear angiotensin-II type 2 receptor in oral squamous cell carcinoma

The renin-angiotensin system (RAS) is implicated in the maintenance of blood pressure and in many other biological processes including tumorigenesis and metastasis formation. Angiotensin-II (A-II) type 2 receptor (AGTR2) seems to be involved in different types of cancer; its role, however, is still unclear. Here, we investigated the role of RAS, and specifically that of AGTR2, in oral squamous cell carcinoma (OSCC) progression. AGTR2 has opposite effect on vasodilation and blood pressure compared to AGTR1. In 23 OSCCs, we found that the AGTR1/AGTR2 mRNA ratio was inversely associated with disease progression, while nuclear AGTR2 positivity was associated with disease progression. In the human OSCC cell lines HSC3 and HSC4, AGTR1 was associated with proliferation and invasion, while AGTR2 was associated with anti-apoptosis and anti-oxidative stress. Levels of nuclear AGTR2 confirmed by subcellular fractionation increased in hypoxic and hyperglycemic conditions, in which apoptosis and oxidative stress were suppressed and the redox status altered to reduction. Accumulation of nuclear AGTR2 by inhibition of extranuclear transportation decreased apoptosis and increased proliferation and invasion in HSC3 cells. Intratumoral angiotensin-II (but not serum angiotensin-II) levels were associated with stage and nuclear AGTR2 positivity. In OSCC cell lines, intracellular angiotensin-II was produced by themselves. Notably, losartan, an angiotensin receptor blocker, inhibited intracellular angiotensin-II production and AGTR2 nuclear localization to enhance the antitumoral effect of 5-FU in an OSCC tumor model. While the precise role of nuclear AGTR2 requires further examination, these data suggest that the intracellular angiotensin system might be a significant target for OSCC.

Bone marrow-derived mesenchymal stromal cell: what next?

Bone marrow mesenchymal stromal cell (MSC) is a potential alternative in regenerative medicine and has great potential in many pathologic conditions including kidney disease. Although most of the studies demonstrate MSC efficiency, the regenerative potential may not be efficient in all diseases and patients. Stem cell feasibility is modified by donor characteristics as gender, age, diet, and health status, producing both positive and negative results. The conditioning of MSC can potentiate its effects and modify its culture medium (CM). In current practices, the cell-free treatment is gaining notable attention, while MSC-conditioned CM is being applied and studied in many experimental diseases, including, but not limited to, certain kidney diseases. This may be the next step for clinical trials. Studies in stem cell CM have focused mainly on extracellular vesicles, nucleic acids (mRNA and microRNA), lipids, and proteins presented in this CM. They mediate regenerative effects of MSC in a harmonic manner. In this review, we will analyze the regenerative potential of MSC and its CM as well as discuss some effective techniques for modifying its fractions and improving its therapeutic potential. CM fractions may be modified by hypoxic conditions, inflammation, lipid exposition, and protein growth factors. Other possible mechanisms of action of stem cells are also suggested. In the future, the MSC paracrine effect may be modified to more closely meet each patient’s needs.