Expression of the Components of the Renin-Angiotensin System in Venous Malformation

Insights Into Vascular Anomalies, Cancer, and Fibroproliferative Conditions: The Role of Stem Cells and the Renin-Angiotensin System

Cells exhibiting embryonic stem cell (ESC) characteristics have been demonstrated in vascular anomalies (VAs), cancer, and fibroproliferative conditions, which are commonly managed by plastic surgeons and remain largely unsolved. The efficacy of the mTOR inhibitor sirolimus, and targeted therapies that block the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways in many types of cancer and VAs, further supports the critical role of ESC-like cells in the pathogenesis of these conditions. ESC-like cells in VAs, cancer, and fibroproliferative conditions express components of the renin-angiotensin system (RAS) – a homeostatic endocrine signaling cascade that regulates cells with ESC characteristics. ESC-like cells are influenced by the Ras/BRAF/MEK/ERK1/2 and PI3KCA/AKT/mTOR pathways, which directly regulate cellular proliferation and stemness, and interact with the RAS at multiple points. Gain-of-function mutations affecting these pathways have been identified in many types of cancer and VAs, that have been treated with targeted therapies with some success. In cancer, the RAS promotes tumor progression, treatment resistance, recurrence, and metastasis. The RAS modulates cellular invasion, migration, proliferation, and angiogenesis. It also indirectly regulates ESC-like cells via its direct influence on the tissue microenvironment and by its interaction with the immune system. In vitro studies show that RAS inhibition suppresses the hallmarks of cancer in different experimental models. Numerous epidemiological studies show a reduced incidence of cancer and improved survival outcomes in patients taking RAS inhibitors, although some studies have shown no such effect. The discovery of ESC-like cells that express RAS components in infantile hemangioma (IH) underscores the paradigm shift in the understanding of its programmed biologic behavior and accelerated involution induced by β-blockers and angiotensin-converting enzyme inhibitors. The findings of SOX18 inhibition by R-propranolol suggests the possibility of targeting ESC-like cells in IH without β-adrenergic blockade, and its associated side effects. This article provides an overview of the current knowledge of ESC-like cells and the RAS in VAs, cancer, and fibroproliferative conditions. It also highlights new lines of research and potential novel therapeutic approaches for these unsolved problems in plastic surgery, by targeting the ESC-like cells through manipulation of the RAS, its bypass loops and converging signaling pathways using existing low-cost, commonly available, and safe oral medications.

Expression of Cathepsins B, D, and G in Extracranial Arterio-Venous Malformation

Objectives: We have previously identified a population of cells that expressed stemness-associated markers in extracranial arterio-venous malformation (AVM) and demonstrated expression of cathepsins B, D, and G on embryonic stem cell (ESC)-like populations in other vascular anomalies. This study investigated the expression of cathepsins B, D, and G, and their localization in relation to this primitive population in extracranial AVM.

Methods: Immunohistochemical staining was performed on AVM tissue samples from 13 patients to demonstrate expression of cathepsins B, D, and G. Western blotting was performed on four AVM tissue samples and three AVM-derived primary cell lines to confirm protein expression of cathepsins B and D proteins. RT-qPCR was performed on three AVM-derived primary cell lines to demonstrate transcript expression of cathepsins B, D, and G. Enzymatic activity assays were performed on three AVM-derived primary cell lines to investigate if cathepsins B and D were active. Localization of the cathepsins was investigated using immunofluorescence dual-staining of the cathepsins with the ESC markers OCT4 and SOX2, and mast cells marker chymase on two of the 13 AVM tissue samples.

Results: Immunohistochemical staining demonstrated expression of cathepsins B, D, and G in all 13 AVM tissue samples. Western blotting showed expression of cathepsins B and D proteins in all four AVM tissue samples and all three AVM-derived primary cell lines. RT-qPCR demonstrated transcripts of cathepsins B, D, and G in all three AVM-derived primary cell lines. Enzymatic activity assays showed that cathepsins B and D were active. Immunofluorescence staining showed expression of cathepsins B and D on the OCT4+/SOX2+ endothelium and media of the lesional vessels and cells within the stroma in AVM nidus. Cathepsin G was expressed on the chymase+ phenotypic mast cells.

Conclusions: This study demonstrated the novel finding of the expression of cathepsins B, D, and G in AVM. Cathepsins B and D were expressed by the primitive population, and cathepsin G was localized to mast cells, within the AVM nidus.

Stemness-Associated Markers Are Expressed in Extracranial Arteriovenous Malformation

Objectives: Arteriovenous malformation (AVM) consists of a nidus with poorly formed low-resistance vessels in place of a functional capillary network. The role of somatic mutations in embryonic stem cells (ESCs) and vascular anomalies and the presence of primitive populations in vascular anomalies led us to investigate the presence of a primitive population in extracranial AVM.

Methods: Extracranial AVM tissue samples from 12 patients were stained for stemness-associated markers OCT4, SOX2, NANOG, KLF4, and c-MYC using immunohistochemical staining. In situ hybridization (ISH) was performed on six tissue samples to determine transcript expression. Western blotting and RT-qPCR were performed on two AVM-derived primary cell lines to determine protein and transcript expression of these markers, respectively. Immunofluorescence staining was performed on two tissue samples to investigate marker co-localization.

Results: Immunohistochemical staining demonstrated the expression of OCT4, SOX2, KLF4, and c-MYC on the endothelium and media of lesional vessels and cells within the stroma of the nidus in all 12 AVM tissue samples. ISH and RT-qPCR confirmed transcript expression of all five markers. Western blotting showed protein expression of all markers except NANOG. Immunofluorescence staining demonstrated an OCT4+/SOX2+/KLF4+/c-MYC+ population within the endothelium and media of the lesional vessels and cells within the stroma of the AVM nidus.

Conclusions: Our findings may suggest the presence of a primitive population within the AVM nidus. Further investigation may lead to novel therapeutic targeting of this population.

Cell Populations Expressing Stemness-Associated Markers in Vascular Anomalies

Treatment of vascular anomalies (VAs) is mostly empirical and, in many instances unsatisfactory, as the pathogeneses of these heterogeneous conditions remain largely unknown. There is emerging evidence of the presence of cell populations expressing stemness-associated markers within many types of vascular tumors and vascular malformations. The presence of these populations in VAs is supported, in part, by the observed clinical effect of the mTOR inhibitor, sirolimus, that regulates differentiation of embryonic stem cells (ESCs). The discovery of the central role of the renin-angiotensin system (RAS) in regulating stem cells in infantile hemangioma (IH) provides a plausible explanation for its spontaneous and accelerated involution induced by β-blockers and ACE inhibitors. Recent work on targeting IH stem cells by inhibiting the transcription factor SOX18 using the stereoisomer R(+) propranolol, independent of β-adrenergic blockade, opens up exciting opportunities for novel treatment of IH without the β-adrenergic blockade-related side effects. Gene mutations have been identified in several VAs, involving mainly the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways. Existing cancer therapies that target these pathways engenders the exciting possibility of repurposing these agents for challenging VAs, with early results demonstrating clinical efficacy. However, there are several shortcomings with this approach, including the treatment cost, side effects, emergence of treatment resistance and unknown long-term effects in young patients. The presence of populations expressing stemness-associated markers, including transcription factors involved in the generation of induced pluripotent stem cells (iPSCs), in different types of VAs, suggests the possible role of stem cell pathways in their pathogenesis. Components of the RAS are expressed by cell populations expressing stemness-associated markers in different types of VAs. The gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways interact with different components of the RAS, which may influence cell populations expressing stemness-associated markers within VAs. The potential of targeting these populations by manipulating the RAS using repurposed, low-cost and commonly available oral medications, warrants further investigation. This review presents the accumulating evidence demonstrating the presence of stemness-associated markers in VAs, their expression of the RAS, and their interaction with gene mutations affecting the PI3K/AKT/mTOR and/or the Ras/RAF/MEK/ERK pathways, in the pathogenesis of VAs.

β-blocker therapy for infantile hemangioma

INTRODUCTION

Fifteen percent of proliferating infantile hemangioma (IH) require intervention because of the threat to function or life, ulceration, or tissue distortion. Propranolol is the mainstay treatment for problematic proliferating IH. Other β-blockers and angiotensin-converting enzyme (ACE) inhibitors have been explored as alternative treatments.

AREAS COVERED

The demonstration of a hemogenic endothelium origin of IH, with a neural crest phenotype and multi-lineage differentiation capacity, regulated by the renin-angiotensin system, underscores its programmed biologic behavior and accelerated involution induced by propranolol, other β-blockers and ACE inhibitors. We review the indications, dosing regimens, duration of treatment, efficacy and adverse effects of propranolol, and therapeutic alternatives including oral atenolol, acebutolol, nadolol, intralesional propranolol injections, topical propranolol and timolol, and oral captopril.

EXPERT OPINION

Improved understanding of the biology of IH provides insights into the mechanism of action underscoring its accelerated involution induced by propranolol, other β-blockers and ACE inhibitors. More research is required to understand the optimal dosing and duration, efficacy and safety of these alternative therapies. Recent demonstration of propranolol's actions mediated by non-β-adrenergic isomer R-propranolol on stem cells, offers an immense opportunity to harness the efficacy of β-blockers to induce accelerated involution of IH, while mitigating their β-adrenergic receptor-mediated adverse effects.

Expression of Cathepsins B, D, and G in Microcystic Lymphatic Malformation

Background: This study investigated the expression and localization of cathepsins B, D, and G in relationship to the embryonic stem cell (ESC)-like population we have previously identified in microcystic lymphatic malformation (mLM). Methods and Results: Immunohistochemical staining demonstrated expression of cathepsins B, D, and G in cervicofacial mLM tissue samples from 11 patients. Immunofluorescence staining of two representative mLM samples showed localization of cathepsins B and D to the OCT4+ and the c-MYC+ cells on the endothelium of lesional vessels and the stroma, while cathepsin G was localized to the OCT4+/tryptase+ cells within the stroma. Transcript expression of cathepsins B, D, and G was confirmed using reverse transcription quantitative polymerase chain reaction (RT-qPCR; n = 5). Western blotting (n = 3) performed on the mLM tissue samples revealed protein expression of cathepsins B and D, which were demonstrated to be enzymatically active using enzymatic activity assays. Conclusion: This study demonstrated expression of cathepsins B and D by the ESC-like cells on the endothelium of lesional vessels and the stroma, while cathepsin G was localized to the OCT4+ phenotypic mast cells within the stroma of mLM.

The (pro)renin receptor in health and disease

The (pro)renin receptor ((P)RR) was first identified as a single-transmembrane receptor in human kidneys and initially attracted attention owing to its potential role as a regulator of the tissue renin-angiotensin system (RAS). Subsequent studies found that the (P)RR is widely distributed in organs throughout the body, including the kidneys, heart, brain, eyes, placenta and the immune system, and has multifaceted functions in vivo. The (P)RR has roles in various physiological processes, such as the cell cycle, autophagy, acid-base balance, energy metabolism, embryonic development, T cell homeostasis, water balance, blood pressure regulation, cardiac remodelling and maintenance of podocyte structure. These roles of the (P)RR are mediated by its effects on important biological systems and pathways including the tissue RAS, vacuolar H⁺-ATPase, Wnt, partitioning defective homologue (Par) and tyrosine phosphorylation. In addition, the (P)RR has been reported to contribute to the pathogenesis of diseases such as fibrosis, hypertension, pre-eclampsia, diabetic microangiopathy, acute kidney injury, cardiovascular disease, cancer and obesity. Current evidence suggests that the (P)RR has key roles in the normal development and maintenance of vital organs and that dysfunction of the (P)RR is associated with diseases that are characterized by a disruption of the homeostasis of physiological functions.

Expression of Components of the Renin-Angiotensin System in Pyogenic Granuloma

Background: There is a growing body of research demonstrating expression of the renin-angiotensin system (RAS) by a putative embryonic stem cell (ESC)-like population within vascular anomalies. This study investigated the expression of components of the RAS in relation to the putative ESC-like population within pyogenic granuloma (PG) that we have recently reported.

Methods: PG samples from 14 patients were analyzed for the expression of components of the RAS: pro-renin receptor (PRR), angiotensin converting enzyme (ACE), angiotensin II receptor 1 (ATIIR1) and angiotensin II receptor 2 (ATIIR2), using 3,3-diaminobenzidine (DAB) immunohistochemical (IHC) staining. Immunofluorescence (IF) IHC staining was performed to localize these proteins on four of the PG samples. RT-qPCR was performed on two snap-frozen PG samples. Western blotting (WB) was performed on one snap-frozen PG sample and two PG-derived primary cell lines.

Results: DAB IHC staining demonstrated the expression of ACE, PRR, ATIIR1, and ATIIR2 in all 14 PG tissue samples. RT-qPCR analysis confirmed abundant mRNA transcripts for PRR, ACE, AIITR1 and ATIIR2, relative to the housekeeping gene. WB confirmed the presence of PRR, ATIIR1, and ACE in the PG tissue sample, and PRR and ATIIR1, in the PG-derived primary cell lines. IF IHC staining demonstrated the expression of PRR, ACE, ATIIR1 on the primitive population that expressed NANOG and SOX2 on the ERG⁺ endothelium of the microvessels within PG.

Conclusion: We have demonstrated the expression of PRR, ACE, and ATIIR1 by the putative the ESC-like population within PG.

Embryonic Stem Cell-like Population within Venous Malformation Expresses the Renin-Angiotensin System

Background

We have recently demonstrated the presence of a NANOG⁺/pSTAT3⁺/OCT4⁺/SOX2⁺/SALL4⁺/CD44⁺ embryonic stem cell (ESC)-like subpopulation localized to the endothelium and a NANOG⁺/pSTAT3⁺/SOX2⁺/CD44⁺ subpopulation outside of the endothelium, within subcutaneous VM (SCVM) and intramuscular VM (IMVM). We have also shown the expression of components of the renin-angiotensin system (RAS): (pro)renin receptor (PRR); angiotensin converting enzyme (ACE), angiotensin II receptor 1 (ATIIR1) and angiotensin II receptor 2 (ATIIR2), in both SCVM and IMVM. This study investigated whether the ESC-like subpopulations within SCVM and IMVM expressed the RAS.

Methods

Formalin-fixed paraffin-embedded sections of two representative samples from each of the seven SCVM and seven IMVM patients included in our previous studies underwent dual immunofluorescence (IF) immunohistochemical (IHC) staining for ESC marker OCT4 or SOX2 with PRR, ACE, ATIIR1, and ATIIR2.

Results

IF IHC staining demonstrated the expression PRR by the OCT4⁺ cells on the endothelium and outside the endothelium in SCVM and IMVM. ACE was expressed by the SOX2⁺ cells, predominantly in the endothelium in SCVM and IMVM. ATIIR1 was expressed by the SOX2⁺ cells on the endothelium and outside the endothelium in SCVM and IMVM. ATIIR2 was expressed by the OCT4⁺ endothelium and outside the endothelium in SCVM and IMVM.

Conclusions

Components of the RAS are expressed by ESC-like subpopulations within both SCVM and IMVM. These primitive subpopulations may be a novel therapeutic target by manipulation of the RAS using existing medications.

Embryonic Stem Cell-Like Subpopulations in Venous Malformation

Background

Venous malformation (VM) consists of a network of ectatic anomalous thin-walled venous channels. A role for an activating TIE2 mutation in the development of the dilated luminal vessels in VM, and its proposed involvement of embryonic stem cells (ESCs), led us to investigate the expression of ESC markers in subcutaneous VM (SCVM) and intramuscular VM (IMVM).

Methods

Formalin-fixed paraffin-embedded sections of SCVM from seven patients and IMVM samples from seven patients were analyzed for the expression of Nanog, pSTAT3, OCT4, SOX2, SALL4, and CD44, using 3,3′-diaminobenzidine (DAB) immunohistochemical (IHC) staining. All these samples did not express lymphatic marker D2-40. NanoString mRNA analysis and RT-PCR were performed on snap-frozen samples of SCVM (n = 3) and IMVM (n = 3) from the respective original cohorts of patients included in DAB IHC staining. To confirm co-expression of two proteins, immunofluorescent (IF) IHC staining on two representative samples of IMVM and SCVM samples from the original cohorts of patients included for DAB IHC staining was performed.

Results

DAB IHC staining demonstrated expression of all of the above ESC markers in both SCVM and IMVM samples. IF IHC staining showed that these markers were localized to the endothelium within these lesions and that Nanog, pSTAT3, SOX2, and CD44 were also expressed by cells outside of the endothelium. NanoString mRNA analysis confirmed transcription activation of pSTAT3, OCT4, and CD44. RT-qPCR confirmed transcription activation of Nanog, SOX2, and SALL4.

Conclusion

Our findings support the presence of two ESC-like subpopulations, one within and one outside of the endothelium, of both SCVM and IMVM. Given that the endothelial ESC-like subpopulation expresses the more primitive marker, OCT4, it is exciting to speculate that they give rise to the non-endothelial subpopulation.

Efficient isolation and culture of endothelial cells from venous malformation using the Rho-associated protein kinase inhibitor Y27632

BACKGROUND

The investigation of primary cells from a pathological lesion can elucidate the pathogenesis of diseases, but, for vascular malformations in humans, such basic research is still stagnant, because the isolation and culture of vascular endothelial cells (ECs) is very difficult. To obtain a sufficient amount of ECs from venous malformation (VM) this study took advantage of a Rho-associated protein kinase inhibitor, Y27632, which had been used for the efficient procurement of primary keratinocytes.

METHODS

ECs were isolated and cultured from VM lesions, combining enzymatic digestion, cell sorting, and Y27632. The proliferative effect of Y27632 on ECs was examined by proliferation assay. The characteristics of the ECs cultured with Y27632 by EC marker expression and tube formation assay were also examined.

RESULTS

Y27632 enhanced the proliferation of ECs and elongated the senescence of the cells. The expression of specific markers of ECs such as von Willebrand factor, endothelin-1, and VE-cadherin, was confirmed in the cells cultured with Y27632. In a tube formation assay, the cells cultured with Y27632 showed higher tube formation ability compared to the cells cultured without Y27632, indicating that Y27632 promoted the angiogenic capability of ECs.

CONCLUSIONS

The protocol using Y27632 offers a new EC culture methodology and provides a new option for the biological investigation of vascular malformations. This new method will contribute to other types of vascular biology research as well.