Decorin suppresses tumor lymphangiogenesis: A mechanism to curtail cancer progression

The complex interplay between malignant cells and the cellular and molecular components of the tumor stroma is a key aspect of cancer growth and development. These tumor-host interactions are often affected by soluble bioactive molecules such as proteoglycans. Decorin, an archetypical small leucine-rich proteoglycan primarily expressed by stromal cells, affects cancer growth in its soluble form by interacting with several receptor tyrosine kinases (RTK). Overall, decorin leads to a context-dependent and protracted cessation of oncogenic RTK activity by attenuating their ability to drive a prosurvival program and to sustain a proangiogenic network. Through an unbiased transcriptomic analysis using deep RNAseq, we identified that decorin down-regulated a cluster of tumor-associated genes involved in lymphatic vessel (LV) development when systemically delivered to mice harboring breast carcinoma allografts. We found that Lyve1 and Podoplanin, two established markers of LVs, were markedly suppressed at both the mRNA and protein levels, and this suppression correlated with a significant reduction in tumor LVs. We further identified that soluble decorin, but not its homologous proteoglycan biglycan, inhibited LV sprouting in an ex vivo 3D model of lymphangiogenesis. Mechanistically, we found that decorin interacted with vascular endothelial growth factor receptor 3 (VEGFR3), the main lymphatic RTK, and its activity was required for the decorin-mediated block of lymphangiogenesis. Finally, we identified that Lyve1 was in part degraded via decorin-evoked autophagy in a nutrient- and energy-independent manner. These findings implicate decorin as a biological factor with antilymphangiogenic activity and provide a potential therapeutic agent for curtailing breast cancer growth and metastasis.

A role for decorin in improving motor deficits after traumatic brain injury

Traumatic brain injury (TBI) is the leading cause of death and disability due to injury worldwide. Extracellular matrix (ECM) remodeling is known to significantly contribute to TBI pathophysiology. Glycosaminoglycans, which are long-chain, variably sulfated polysaccharides abundant within the ECM, have previously been shown to be substantially altered after TBI. In this study, we sought to delineate the dynamics of glycosaminoglycan alterations after TBI and discover the precise biologic processes responsible for observed glycosaminoglycan changes after injury. We performed state-of-the art mass spectrometry on brain tissues isolated from mice after TBI or craniotomy-alone. We observed dynamic changes in glycosaminoglycans at Day 1 and 7 post-TBI, with heparan sulfate, chondroitin sulfate, and hyaluronan remaining significantly increased after a week vis-à-vis craniotomy-alone tissues. We did not observe appreciable changes in circulating glycosaminoglycans in mice after experimental TBI compared to craniotomy-alone nor in patients with TBI and severe polytrauma compared to control patients with mild injuries, suggesting increases in injury site glycosaminoglycans are driven by local synthesis. We subsequently performed an unbiased whole genome transcriptomics analysis on mouse brain tissues 7 days post-TBI and discovered a significant induction of hyaluronan synthase 2, glypican-3, and decorin. The functional role of decorin after injury was further examined through multimodal behavioral testing comparing wild-type and Dcn-/- mice. We discovered that genetic ablation of Dcn led to an overall negative effect of TBI on function, exacerbating motor impairments after TBI. Collectively, our results provide a spatiotemporal characterization of post-TBI glycosaminoglycan alterations in the brain ECM and support an important adaptive role for decorin upregulation after TBI.

Global impact of proteoglycan science on human diseases

In this comprehensive review, we will dissect the impact of research on proteoglycans focusing on recent developments involved in their synthesis, degradation, and interactions, while critically assessing their usefulness in various biological processes. The emerging roles of proteoglycans in global infections, specifically the SARS-CoV-2 pandemic, and their rising functions in regenerative medicine and biomaterial science have significantly affected our current view of proteoglycans and related compounds. The roles of proteoglycans in cancer biology and their potential use as a next-generation protein-based adjuvant therapy to combat cancer is also emerging as a constructive and potentially beneficial therapeutic strategy. We will discuss the role of proteoglycans in selected and emerging areas of proteoglycan science, such as neurodegenerative diseases, autophagy, angiogenesis, cancer, infections and their impact on mammalian diseases.

Emilin2 fosters vascular stability by promoting pericyte recruitment

Angiogenesis, the formation of the new blood vessels from pre-existing vasculature, is an essential process occurring under both normal and pathological conditions, such as inflammation and cancer. This complex process is regulated by several cytokines, growth factors and extracellular matrix components modulating endothelial cell and pericyte function. In this study, we discovered that the extracellular matrix glycoprotein Elastin Microfibril Interfacer 2 (Emilin2) plays a prominent role in pericyte physiology. This work was originally prompted by the observations that tumor-associated vessels from Emilin2-/- mice display less pericyte coverage, impaired vascular perfusion, and reduced drug efficacy, suggesting that Emilin2 could promote vessel maturation and stabilization affecting pericyte recruitment. We found that Emilin2 affects different mechanisms engaged in pericyte recruitment and vascular stabilization. First, human primary endothelial cells challenged with recombinant Emilin2 synthesized and released ∼ 2.1 and 1.2 folds more PDGF-BB and HB-EGF, two cytokines known to promote pericyte recruitment. We also discovered that Emilin2, by directly engaging α5β1 and α6β1 integrins, highly expressed in pericytes, served as an adhesion substrate and haptotactic stimulus for pericytes. Moreover, Emilin2 evoked increased NCadherin expression via the sphingosine-1-phosphate receptor, leading to enhanced vascular stability by fostering interconnection between endothelial cells and pericytes. Finally, restoring pericyte coverage in melanoma and ovarian tumor vessels developed in Emilin2-/- mice improved drug delivery to the tumors. Collectively, our results implicate Emilin2 as a prominent regulator of pericyte function and suggest that Emilin2 expression could represent a promising maker to predict the clinical outcome of patients with melanoma, ovarian, and potentially other forms of cancer.

Decorin suppresses tumor lymphangiogenesis: A mechanism to curtail cancer progression

The complex interplay between malignant cells and the cellular and molecular components of the tumor stroma is a key aspect of cancer growth and development. These tumor-host interactions are often affected by soluble bioactive molecules such as proteoglycans. Decorin, an archetypical small leucine-rich proteoglycan primarily expressed by stromal cells, affects cancer growth in its soluble form by interacting with several receptor tyrosine kinases (RTK). Overall, decorin leads to a context-dependent and protracted cessation of oncogenic RTK activity by attenuating their ability to drive a pro-survival program and to sustain a pro-angiogenic network. Through an unbiased transcriptomic analysis using deep RNAseq, we discovered that decorin downregulated a cluster of tumor-associated genes involved in lymphatic vessel development when systemically delivered to mice harboring breast carcinoma allografts. We found that Lyve1 and Podoplanin, two established markers of lymphatic vessels, were markedly suppressed at both the mRNA and protein levels and this suppression correlated with a significant reduction in tumor lymphatic vessels. We further discovered that soluble decorin, but not its homologous proteoglycan biglycan, inhibited lymphatic vessel sprouting in an ex vivo 3D model of lymphangiogenesis. Mechanistically, we found that decorin interacted with VEGFR3, the main lymphatic RTK, and its activity was required for the decorin-mediated block of lymphangiogenesis. Finally, we discovered that Lyve1 was in part degraded via decorin-evoked autophagy in a nutrient- and energy-independent manner. These findings implicate decorin as a new biological factor with anti-lymphangiogenic activity and provide a potential therapeutic agent for curtailing breast cancer growth and metastasis.

Progranulin and EGFR modulate RYK (Receptor like Tyrosine Kinase) sorting and stability in mesothelioma cells

Progranulin is a growth factor with pro-tumorigenic activity. We recently demonstrated that in mesothelioma progranulin regulates cell migration, invasion, adhesion, and in vivo tumor formation by modulating a complex signaling network involving multiple receptor tyrosine kinase (RTK)s. Progranulin biological activity relies on EGFR and RYK, a co-receptor of the Wnt signaling pathway, which are both required for progranulin-induced downstream signaling. However, the molecular mechanism regulating the functional interaction among progranulin, EGFR and RYK are not known. In this study we demonstrated that progranulin directly interacted with RYK by specific ELISA (K_D=0.67). Using immunofluorescence and proximity ligation assay we further discovered that progranulin and RYK colocalized in mesothelioma cells in distinct vesicular compartments. Notably, progranulin-dependent downstream signaling was sensitive to endocytosis inhibitors, suggesting that it could depend on RYK or EGFR internalization. We discovered that progranulin promoted RYK ubiquitination and endocytosis preferentially through caveolin-1-enriched pathways, and modulated RYK stability. Interestingly, we also showed that in mesothelioma cells RYK complexes with the EGFR, contributing to the regulation of RYK stability. Collectively, our results suggest a complex regulation of RYK trafficking/activity in mesothelioma cells, a process that is concurrently regulated by exogenous soluble progranulin and EGFR.

Conditional expression of endorepellin in the tumor vasculature attenuates breast cancer growth, angiogenesis and hyaluronan deposition

The tumor stroma of most solid malignancies is characterized by a pathological accumulation of pro-angiogenic and pro-tumorigenic hyaluronan driving tumorigenesis and metastatic potential. Of all three hyaluronan synthase isoforms, HAS2 is the primary enzyme that promotes the build-up of tumorigenic HA in breast cancer. Previously, we discovered that endorepellin, the angiostatic C-terminal fragment of perlecan, evokes a catabolic mechanism targeting endothelial HAS2 and hyaluronan via autophagic induction. To explore the translational implications of endorepellin in breast cancer, we created a double transgenic, inducible Tie2CreERT2;endorepellin(ER)Ki mouse line that expresses recombinant endorepellin specifically from the endothelium. We investigated the therapeutic effects of recombinant endorepellin overexpression in an orthotopic, syngeneic breast cancer allograft mouse model. First, adenoviral delivery of Cre evoking intratumor expression of endorepellin in ERKi mice suppressed breast cancer growth, peritumor hyaluronan and angiogenesis. Moreover, tamoxifen-induced expression of recombinant endorepellin specifically from the endothelium in Tie2CreERT2;ERKi mice markedly suppressed breast cancer allograft growth, hyaluronan deposition in the tumor proper and perivascular tissues, and tumor angiogenesis. These results provide insight into the tumor suppressing activity of endorepellin at the molecular level and implicate endorepellin as a promising cancer protein therapy that targets hyaluronan in the tumor microenvironment.

Progranulin Oncogenic Network in Solid Tumors

Progranulin is a pleiotropic growth factor with important physiological roles in embryogenesis and maintenance of adult tissue homeostasis. While-progranulin deficiency is associated with a broad range of pathological conditions affecting the brain, such as frontotemporal dementia and neuronal ceroid lipofuscinosis, progranulin upregulation characterizes many tumors, including brain tumors, multiple myeloma, leiomyosarcoma, mesothelioma and epithelial cancers such as ovarian, liver, breast, bladder, adrenal, prostate and kidney carcinomas. The increase of progranulin levels in tumors might have diagnostic and prognostic significance. In cancer, progranulin has a pro-tumorigenic role by promoting cancer cell proliferation, migration, invasiveness, anchorage-independent growth and resistance to chemotherapy. In addition, progranulin regulates the tumor microenvironment, affects the function of cancer-associated fibroblasts, and modulates tumor immune surveillance. However, the molecular mechanisms of progranulin oncogenic function are not fully elucidated. In bladder cancer, progranulin action relies on the activation of its functional signaling receptor EphA2. Notably, more recent data suggest that progranulin can also modulate a functional crosstalk between multiple receptor-tyrosine kinases, demonstrating a more complex and context-dependent role of progranulin in cancer. Here, we will review what is currently known about the function of progranulin in tumors, with a focus on its molecular mechanisms of action and regulation.

Corneal injury is associated with stromal and vascular alterations within cranial dura mater

The cornea and cranial dura mater share sensory innervation. This link raises the possibility that pathological impulses mediated by corneal injury may be transmitted to the cranial dura, trigger dural perivascular/connective tissue nociceptor responses, and induce vascular and stromal alterations affecting dura mater blood and lymphatic vessel functionality. In this study, using a mouse model, we demonstrate for the first time that two weeks after the initial insult, alkaline injury to the cornea leads to remote pathological changes within the coronal suture area of the dura mater. Specifically, we detected significant pro-fibrotic changes in the dural stroma, as well as vascular remodeling characterized by alterations in vascular smooth muscle cell (VSMC) morphology, reduced blood vessel VSMC coverage, endothelial cell expression of the fibroblast specific protein 1, and significant increase in the number of podoplanin-positive lymphatic sprouts. Intriguingly, the deficiency of a major extracellular matrix component, small leucine-rich proteoglycan decorin, modifies both the direction and the extent of these changes. As the dura mater is the most important route for the brain metabolic clearance, these results are of clinical relevance and provide a much-needed link explaining the association between ophthalmic conditions and the development of neurodegenerative diseases.

Complexity of progranulin mechanisms of action in mesothelioma

BACKGROUND

Mesothelioma is an aggressive disease with limited therapeutic options. The growth factor progranulin plays a critical role in several cancer models, where it regulates tumor initiation and progression. Recent data from our laboratories have demonstrated that progranulin and its receptor, EphA2, constitute an oncogenic pathway in bladder cancer by promoting motility, invasion and in vivo tumor formation. Progranulin and EphA2 are expressed in mesothelioma cells but their mechanisms of action are not well defined. In addition, there are no data establishing whether the progranulin/EphA2 axis is tumorigenic for mesothelioma cells.

METHODS

The expression of progranulin in various mesothelioma cell lines derived from all major mesothelioma subtypes was examined by western blots on cell lysates, conditioned media and ELISA assays. The biological roles of progranulin, EphA2, EGFR, RYK and FAK were assessed in vitro by immunoblots, human phospho-RTK antibody arrays, pharmacological (specific inhibitors) and genetic (siRNAs, shRNAs, CRISPR/Cas9) approaches, motility, invasion and adhesion assays. In vivo tumorigenesis was determined by xenograft models. Focal adhesion turnover was evaluated biochemically using focal adhesion assembly/disassembly assays and immunofluorescence analysis with focal adhesion-specific markers.

RESULTS

In the present study we show that progranulin is upregulated in various mesothelioma cell lines covering all mesothelioma subtypes and is an important regulator of motility, invasion, adhesion and in vivo tumor formation. However, our results indicate that EphA2 is not the major functional receptor for progranulin in mesothelioma cells, where progranulin activates a complex signaling network including EGFR and RYK. We further characterized progranulin mechanisms of action and demonstrated that progranulin, by modulating FAK activity, regulates the kinetic of focal adhesion disassembly, a critical step for cell motility.

CONCLUSION

Collectively, our results highlight the complexity of progranulin oncogenic signaling in mesothelioma, where progranulin modulate functional cross-talks between multiple RTKs, thereby suggesting the need for combinatorial therapeutic approaches to improve treatments of this aggressive disease.

Decorin evokes reversible mitochondrial depolarization in carcinoma and vascular endothelial cells

Decorin, a small leucine-rich proteoglycan with multiple biological functions, is known to evoke autophagy and mitophagy in both endothelial and cancer cells. Here, we investigated the effects of soluble decorin on mitochondrial homeostasis using live cell imaging and ex vivo angiogenic assays. We discovered that decorin triggers mitochondrial depolarization in triple-negative breast carcinoma, HeLa, and endothelial cells. This bioactivity was mediated by the protein core in a time- and dose-dependent manner and was specific for decorin insofar as biglycan, the closest homolog, failed to trigger depolarization. Mechanistically, we found that the bioactivity of decorin to promote depolarization required the MET receptor and its tyrosine kinase. Moreover, two mitochondrial interacting proteins, mitostatin and mitofusin 2, were essential for downstream decorin effects. Finally, we found that decorin relied on the canonical mitochondrial permeability transition pore to trigger tumor cell mitochondrial depolarization. Collectively, our study implicates decorin as a soluble outside-in regulator of mitochondrial dynamics.

Abstract 97: Mechanisms of action and regulation of the progranulin/EphA2 axis in mesothelioma

Mesothelioma is an aggressive tumor with very poor prognosis. The limited availability of therapeutic options for mesothelioma patients suggests the need for a better understanding of mesothelioma biology and the identification of novel therapeutic targets. Progranulin is a pluripotent growth factor whose dysregulation is implicated in several human pathologies including cancer. The pro-tumorigenic activity of progranulin depends on the activation of its functional receptor EphA2. Indeed, in bladder cancer, progranulin promotes EphA2 phosphorylation at Ser897 and triggers EphA2 oncogenic action resulting in increased tumor cell migration, invasion and in vivo tumor growth. Both progranulin and EphA2 are expressed in mesothelioma, with progranulin promoting tumor angiogenesis in a VEGF-independent manner and EphA2 being often mutated or overexpressed. However, in mesothelioma, the potential functional interaction between progranulin and EphA2 is unexplored. Using a panel of mesothelioma cell lines covering all mesothelioma subtypes, we observed increased levels of phosphorylated EphA2 at Ser897 when compared to immortalized normal mesothelial cells, and the levels of phosphorylation positively correlated with progranulin expression. Progranulin-dependent activation of EphA2 in mesothelioma cells promoted the activation of the MAPK and AKT pathways and ERK1/2-dependent EphA2 phosphorylation at Ser897. Transient depletion of progranulin by siRNA approaches as well as GRN gene knock-out by CRISP/Cas9 strategies in mesothelioma cells reduced the activation of the AKT signaling pathway and inhibited the migratory and invasive capabilities of progranulin-depleted cells when compared to parental cells, suggesting that the progranulin/EphA2 axis is oncogenic in mesothelioma. However, EphA2 genetic ablation resulted in an increased basal activation of AKT and MAPK and in progranulin-evoked EphA2-independet AKT/MAPK activation, indicating that alternative membrane receptors might compensate for EphA2 loss and sustain progranulin action in mesothelioma. Using several pharmacological and genetic approaches, we uncovered a role for EGFR and FAK in compensating for EphA2 loss by triggering progranulin-dependent oncogenic signaling in mesothelioma, highlighting a complex functional cross-talk between EphA2, EGFR and FAK in mediating progranulin-dependent tumorigenesis. Thus, these results suggest the need for combinatorial therapeutic approaches to blunt progranulin oncogenic action in mesothelioma.

Citation Format: Elisa Ventura, Simone Buraschi, Stephen J. Williams, Antonino Belfiore, Renato V. Iozzo, Antonio Giordano, Andrea Morrione. Mechanisms of action and regulation of the progranulin/EphA2 axis in mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 97.

Decorin regulates collagen fibrillogenesis during corneal wound healing in mouse in vivo

A characteristic rigid spatial arrangement of collagen fibrils in the stroma is critical for corneal transparency. This unique organization of collagen fibrils in corneal stroma can be impacted by the presence and interactions of proteoglycans and extracellular matrix (ECM) proteins in a corneal microenvironment. Earlier studies revealed that decorin, a leucine-rich proteoglycan in stroma, regulates keratocyte-collagen matrix assembly and wound healing in the cornea. This study investigated the role of decorin in the regulation of stromal fibrillogenesis and corneal transparency in vivo employing a loss-of-function genetic approach using decorin null (dcn^-/-) and wild type (dcn^+/+) mice and a standard alkali-injury model. A time-dependent ocular examinations with Slit lamp microscope in live animals assessed corneal clarity, haze, and neovascularization levels in normal and injured eyes. Morphometric changes in normal and injured dcn^+/+ and dcn^-/- corneas, post-euthanasia, were analyzed with Masson's Trichrome and Periodic Acid-Schiff (PAS) histology evaluations. The ultrastructure changes in all corneas were investigated with transmission electron microscopy (TEM). Injury to eye produced clinically relevant corneal haze and neovascularization in dcn^-/- and dcn^+/+ mice while corneas of uninjured eyes remained clear and avascular. A clinically significant haze and neovascularization appeared in injured dcn^-/- corneas compared to the dcn^+/+ corneas at day 21 post-injury and not at early tested times. Histological examinations revealed noticeably abnormal morphology and compromised collagen levels in injured dcn^-/- corneas compared to the injured/normal dcn^+/+ and uninjured dcn^-/- corneas. TEM analysis exhibited remarkably uneven collagen fibrils size and distribution in the stroma with asymmetrical organization and loose packing in injured dcn^-/- corneas than injured/normal dcn^+/+ and uninjured dcn^-/- corneas. The minimum and maximum inter-fibril distances were markedly irregular in injured dcn^-/- corneas compared to all other corneas. Together, results of clinical, histological, and ultrastructural investigations in a genetic knockout model suggested that decorin influenced stromal fibrillogenesis and transparency in healing cornea.

Oncosuppressive roles of decorin through regulation of multiple receptors and diverse signaling pathways

Decorin is a stromal-derived prototype member of the small leucine-rich proteoglycan gene family. In addition to its functions as a regulator of collagen fibrillogenesis and TGF-β activity soluble decorin acts as a pan-receptor tyrosine kinase (RTK) inhibitor. Decorin binds to various RTKs including EGFR HER2 HGFR/Met VEGFR2 TLR and IGFR. Although the molecular mechanism for the action of decorin on these receptors is not entirely elucidated overall decorin evokes transient activation of these receptors with suppression of downstream signaling cascades culminating in growth inhibition followed by their physical downregulation via caveosomal internalization and degradation. In the case of Met decorin leads to decreased β-catenin signaling pathway and growth suppression. As most of these RTKs are responsible for providing a growth advantage to cancer cells the result of decorin treatment is oncosuppression. Another decorin-driven mechanism to restrict cancer growth and dissemination is by impeding angiogenesis via vascular endothelial growth factor receptor 2 (VEGFR2) and the concurrent activation of protracted endothelial cell autophagy. In this review we will dissect the multiple roles of decorin in cancer biology and its potential use as a next-generation protein-based adjuvant therapy to combat cancer.

The Role of Decorin Proteoglycan in Mitophagy

Simple Summary

The eminent rise of extracellular matrix constituents, chiefly hailing from the proteoglycan gene family, has revolutionized our understanding of how intracellular catabolism is regulated at the intersection of autophagy and breast cancer. In this review, we examine the mechanisms of decorin, a small leucine-rich proteoglycan, as it relates to autophagy and mitochondrial autophagy (mitophagy). In each case, decorin signals via a unique cell surface receptor tyrosine kinase to evoke autophagy (VEGFR2) or mitophagy (MET receptor) that converges on a novel tumor suppressor gene. The downstream function of either Peg3 or mitostatin in response to decorin manifests as potent means to subdue breast cancer development and progression.

Abstract

Proteoglycans are emerging as critical regulators of intracellular catabolism. This rise in prominence has transformed our basic understanding and alerted us to the existence of non-canonical pathways, independent of nutrient deprivation, that potently control the autophagy downstream of a cell surface receptor. As a member of the small leucine-rich proteoglycan gene family, decorin has single-handedly pioneered the connection between extracellular matrix signaling and autophagy regulation. Soluble decorin evokes protracted endothelial cell autophagy via Peg3 and breast carcinoma cell mitophagy via mitostatin by interacting with VEGFR2 or the MET receptor tyrosine kinase, respectively. In this paper, we give a mechanistic perspective of the vital factors underlying the nutrient-independent, SLRP-dependent programs utilized for autophagic and/or mitophagic progression in breast cancer. Future protein therapies based on decorin (or fellow proteoglycan members) will represent a quantum leap forward in transforming autophagic progression into a powerful tool to control intracellular cell catabolism from the outside.

Novel regulatory roles of small leucine-rich proteoglycans in remodeling of the uterine cervix in pregnancy

The cervix undergoes rapid and dramatic shifts in collagen and elastic fiber structure to achieve its disparate physiological roles of competence during pregnancy and compliance during birth. An understanding of the structure-function relationships of collagen and elastic fibers to maintain extracellular matrix (ECM) homeostasis requires an understanding of the mechanisms executed by non-structural ECM molecules. Small-leucine rich proteoglycans (SLRPs) play key functions in biology by affecting collagen fibrillogenesis and regulating enzyme and growth factor bioactivities. In the current study, we evaluated collagen and elastic fiber structure-function relationships in mouse cervices using mice with genetic ablation of decorin and/or biglycan genes as representative of Class I SLRPs, and lumican gene representative of Class II SLRP. We identified structural defects in collagen fibril and elastic fiber organization in nonpregnant mice lacking decorin, or biglycan or lumican with variable resolution of defects noted during pregnancy. The severity of collagen and elastic fiber defects was greater in nonpregnant mice lacking both decorin and biglycan and defects were maintained throughout pregnancy. Loss of biglycan alone reduced tissue extensibility in nonpregnant mice while loss of both decorin and biglycan manifested in decreased rupture stretch in late pregnancy. Collagen cross-link density was similar in the Class I SLRP null mice as compared to wild-type nonpregnant and pregnant controls. A broader range in collagen fibril diameter along with an increase in mean fibril spacing was observed in the mutant mice compared to wild-type controls. Collectively, these findings uncover functional redundancy and hierarchical roles of Class I and Class II SLRPs as key regulators of cervical ECM remodeling in pregnancy. These results expand our understating of the critical role SLRPs play to maintain ECM homeostasis in the cervix.

Extracellular matrix guidance of autophagy: a mechanism regulating cancer growth

The extracellular matrix (ECM) exists as a dynamic network of biophysical and biochemical factors that maintain tissue homeostasis. Given its sensitivity to changes in the intra- and extracellular space, the plasticity of the ECM can be pathological in driving disease through aberrant matrix remodelling. In particular, cancer uses the matrix for its proliferation, angiogenesis, cellular reprogramming and metastatic spread. An emerging field of matrix biology focuses on proteoglycans that regulate autophagy, an intracellular process that plays both critical and contextual roles in cancer. Here, we review the most prominent autophagic modulators from the matrix and the current understanding of the cellular pathways and signalling cascades that mechanistically drive their autophagic function. We then critically assess how their autophagic functions influence tumorigenesis, emphasizing the complexities and stage-dependent nature of this relationship in cancer. We highlight novel emerging data on immunoglobulin-containing and proline-rich receptor-1, heparanase and thrombospondin 1 in autophagy and cancer. Finally, we further discuss the pro- and anti-autophagic modulators originating from the ECM, as well as how these proteoglycans and other matrix constituents specifically influence cancer progression.

388 Haemodynamic arterial changes in heart failure: a proposed new paradigm of heart and vessels failure. The Copernican revolution?

Aims

Although heart failure (HF) is one of the most common conditions affecting the heart, little attention has been placed on the role of arteries in contributing to the progression of this disease. We sought to determine the haemodynamic change of arteries in HF patients subdivided according to left ventricular ejection fraction. The major goal was to establish the active compensatory role of arteries in HF.

Methods and results

Using sphygmography, we systematically studied a cohort of 228 HF patients and 52 healthy controls. We focused on the common carotid as the main elastic artery and the posterior tibial as the main muscular artery (Figure 1). Moreover, we categorized the three HF groups, HFrEF, HFmrEF, HFpEF, into two subgroups (A and B) according to the presence or absence of HF signs at baseline. We discovered that all the parameters of measured arterial kinetics, i.e. work, power, acceleration, and speed, were significantly increased (P < 0.001 by one-way ANOVA) in the groups without HF signs. In contrast, all the arterial kinetics parameters were significantly reduced (P < 0.001) in the groups exhibiting HF signs. Similar results were obtained in both types of arteries and were consistently observed across all the three different types of HF, although with some differences in magnitude. Finally, we discovered that HFpEF patients exhibited more compromised arterial function vis-à-vis HFrEF patients [Figure 2: Patients disposition (Top) and quantification of arterial kinetics and haemodynamic parameters (Down) from the common carotid artery (A) and the posterior tibial artery (B)].

Conclusions

We provide the first documentation of an active compensatory role of arteries during HF. Mechanistically, we explain these findings by a dual activity of large arteries accomplished via an active propulsive work and a concurrent haemodynamic suction. These underestimated arterial functions partially compensate for the heart dysfunction in HF, underlining a key interplay between the heart and the vessels. We propose a new paradigm that we define as ‘heart and vessels failure’ that explicitly focuses on both heart and vessels’ interaction during the progression of HF.

The Role of Decorin and Biglycan Signaling in Tumorigenesis

The complex and adaptive nature of malignant neoplasm constitute a major challenge for the development of effective anti-oncogenic therapies. Emerging evidence has uncovered the pivotal functions exerted by the small leucine-rich proteoglycans, decorin and biglycan, in affecting tumor growth and progression. In their soluble forms, decorin and biglycan act as powerful signaling molecules. By receptor-mediated signal transduction, both proteoglycans modulate key processes vital for tumor initiation and progression, such as autophagy, inflammation, cell-cycle, apoptosis, and angiogenesis. Despite of their structural homology, these two proteoglycans interact with distinct cell surface receptors and thus modulate distinct signaling pathways that ultimately affect cancer development. In this review, we summarize growing evidence for the complex roles of decorin and biglycan signaling in tumor biology and address potential novel therapeutic implications.

Multimerin-2 orchestrates the cross-talk between endothelial cells and pericytes: A mechanism to maintain vascular stability

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The ECM Multimerin-2 is a substrate for pericyte adhesion.

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The recruitment of pericytes leads to enhanced Multimerin-2 expression by endothelial cells.

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Multimerin-2 induces the expression of important cytokines both in endothelial cells and pericytes.

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The deposition of Multimerin-2 is key for the endothelial cell/pericyte crosstalk required for the establishment of vascular stability.

Tumor angiogenesis is vital for the growth and development of various solid cancers and as such is a valid and promising therapeutic target. Unfortunately, the use of the currently available anti-angiogenic drugs increases the progression-free survival by only a few months. Conversely, targeting angiogenesis to prompt both vessel reduction and normalization, has been recently viewed as a promising approach to improve therapeutic efficacy. As a double-edged sword, this line of attack may on one side halt tumor growth as a consequence of the reduction of nutrients and oxygen supplied to the tumor cells, and on the other side improve drug delivery and, hence, efficacy. Thus, it is of upmost importance to better characterize the mechanisms regulating vascular stability. In this context, recruitment of pericytes along the blood vessels is crucial to their maturation and stabilization. As the extracellular matrix molecule Multimerin-2 is secreted by endothelial cells and deposited also in juxtaposition between endothelial cells and pericytes, we explored Multimerin-2 role in the cross-talk between the two cell types. We discovered that Multimerin-2 is an adhesion substrate for pericytes. Interestingly, and consistent with the notion that Multimerin-2 is a homeostatic molecule deposited in the later stages of vessel formation, we found that the interaction between endothelial cells and pericytes promoted the expression of Multimerin-2. Furthermore, we found that Multimerin-2 modulated the expression of key cytokines both in endothelial cells and pericytes. Collectively, our findings posit Multimerin-2 as a key molecule in the cross-talk between endothelial cells and pericytes and suggest that the expression of this glycoprotein is required to maintain vascular stability.

Differentiated activities of decorin and biglycan in the progression of post-traumatic osteoarthritis

OBJECTIVE

To delineate the activities of decorin and biglycan in the progression of post-traumatic osteoarthritis (PTOA).

DESIGN

Three-month-old inducible biglycan (BgniKO) and decorin/biglycan compound (Dcn/BgniKO) knockout mice were subjected to the destabilization of the medial meniscus (DMM) surgery to induce PTOA. The OA phenotype was evaluated by assessing joint structure and sulfated glycosaminoglycan (sGAG) staining via histology, surface collagen fibril nanostructure and calcium content via scanning electron microscopy, tissue modulus via atomic force microscopy-nanoindentation, as well as subchondral bone structure and meniscus ossification via micro-computed tomography. Outcomes were compared with previous findings in the inducible decorin (DcniKO) knockout mice.

RESULTS

In the DMM model, BgniKO mice developed similar degree of OA as the control (0.44 [-0.18 1.05] difference in modified Mankin score), different from the more severe OA phenotype observed in DcniKO mice (1.38 [0.91 1.85] difference). Dcn/BgniKO mice exhibited similar histological OA phenotype as DcniKO mice (1.51 [0.97 2.04] difference vs control), including aggravated loss of sGAGs, salient surface fibrillation and formation of osteophyte. Meanwhile, Dcn/BgniKO mice showed further cartilage thinning than DcniKO mice, resulting in the exposure of underlying calcified tissues and aberrantly high surface modulus. BgniKO and Dcn/BgniKO mice developed altered subchondral trabecular bone structure in both Sham and DMM groups, while DcniKO and control mice did not.

CONCLUSION

In PTOA, decorin plays a more crucial role than biglycan in regulating cartilage degeneration, while biglycan is more important in regulating subchondral bone structure. The two have distinct activities and modest synergy in the pathogenesis of PTOA.

Hemodynamic arterial changes in heart failure: a proposed new paradigm of "Heart and Vessels Failure (HVF)"

BACKGROUND

Although heart failure (HF) is one of the most common conditions affecting the heart, little attention has been placed on the role of arteries in contributing to the progression of this disease. We sought to determine the hemodynamic change of arteries in HF patients subdivided according to left ventricular ejection fraction. The major goal was to establish the active compensatory role of arteries in HF.

METHODS

Using sphygmography, we systematically studied a cohort of 228 HF patients and 52 healthy controls. We focused on the common carotid as the main elastic artery and the posterior tibial as the main muscular artery. Moreover, we categorized the three HF groups, HFrEF, HFmrEF, HFpEF, into two subgroups (A and B) according to the presence or absence of HF signs at baseline.

RESULTS

We discovered that all the parameters of measured arterial kinetics, i.e., work, power, acceleration, and speed, were significantly increased (p<0.001 by one-way ANOVA) in the groups without HF signs. In contrast, all the arterial kinetics parameters were significantly reduced (p<0.001) in the groups exhibiting HF signs. Similar results were obtained in both types of arteries and were consistently observed across all the three different types of HF, although with some differences in magnitude. Finally, we discovered that HFpEF patients exhibited more compromised arterial function vis-à-vis HFrEF patients.

CONCLUSIONS

We provide the first documentation of an active compensatory role of arteries during HF. Mechanistically, we explain these findings by a dual activity of large arteries accomplished via an active propulsive work and a concurrent hemodynamic suction. These underestimated arterial functions partially compensate for the heart dysfunction in HF, underlining a key interplay between the heart and the vessels. We propose a new paradigm that we define as "heart and vessels failure" that explicitly focuses on both heart and vessels' interaction during the progression of HF.

A functional outside-in signaling network of proteoglycans and matrix molecules regulating autophagy

Proteoglycans and selected extracellular matrix constituents are emerging as intrinsic and critical regulators of evolutionarily conversed, intracellular catabolic pathways. Often, these secreted molecules evoke sustained autophagy in a variety of cell types, tissues, and model systems. The unique properties of proteoglycans have ushered in a paradigmatic shift to broaden our understanding of matrix-mediated signaling cascades. The dynamic cellular pathway controlling autophagy is now linked to an equally dynamic and fluid signaling network embedded in a complex meshwork of matrix molecules. A rapidly emerging field of research encompasses multiple matrix-derived candidates, representing a menagerie of soluble matrix constituents including decorin, biglycan, endorepellin, endostatin, collagen VI and plasminogen kringle 5. These matrix constituents are pro-autophagic and simultaneously anti-angiogenic. In contrast, perlecan, laminin α2 chain, and lumican have anti-autophagic functions. Mechanistically, each matrix constituent linked to intracellular catabolic events engages a specific cell surface receptor that often converges on a common core of the autophagic machinery including AMPK, Peg3 and Beclin 1. We consider this matrix-evoked autophagy as non-canonical given that it occurs in an allosteric manner and is independent of nutrient availability or prevailing bioenergetics control. We propose that matrix-regulated autophagy is an important outside-in signaling mechanism for proper tissue homeostasis that could be therapeutically leveraged to combat a variety of diseases.

The functional role of decorin in corneal neovascularization in vivo

Our earlier decorin (Dcn) gene overexpression studies found that the targeted Dcn gene transfer into the cornea inhibited corneal angiogenesis in vivo using a rabbit model. In this study, we tested the hypothesis that anti-angiogenic effects of decorin in the cornea are mediated by alterations in a normal physiologic balance of pro- and anti-angiogenic factors using decorin deficient (Dcn^-/-) and wild type (Dcn^+/+) mice. Corneal neovascularization (CNV) in Dcn^-/- and Dcn^+/+ mice was produced with a standard chemical injury technique. The clinical progression of CNV in mice was monitored with stereo- and slit-lamp microscopes, and histopathological hematoxylin and eosin (H&E) staining. Protein and mRNA expression of pro- and anti-angiogenic factors in the cornea were evaluated using immunofluorescence and quantitative real-time PCR, respectively. Slit-lamp clinical eye examinations revealed significantly more CNV in Dcn^-/- mice than the Dcn^+/+ mice post-injury (p < 0.05) and AAV5-Dcn gene therapy significantly reduced CNV in Dcn^-/- mice compered to no AAV5-Dcn gene therapy controls (p < 0.001). H&E-stained corneal sections exhibited morphology with several neovessels in injured corneas of the Dcn^-/- mice than the Dcn^+/+ mice. Immunofluorescence of corneal sections displayed significantly higher expression of α-smooth muscle actin (α-SMA) and endoglin proteins in Dcn^-/- mice than Dcn^+/+ mice (p < 0.05). Quantitative real-time PCR found significantly increased mRNA levels of pro-angiogenic factors endoglin (2.53-fold; p < 0.05), Vegf (2.47-fold; p < 0.05), and Pecam (2.14-fold; p < 0.05) and anti-angiogenic factor Vegfr2 (1.56-fold; p < 0.05) in the normal cornea of the Dcn^-/- mice than the Dcn^+/+ mice. Furthermore, neovascularized Dcn^-/- mice corneas showed greater increase in mRNA expression of pro-angiogenic factors endoglin (4.58-fold; p < 0.0001), Vegf (4.16-fold; p < 0.0001), and Pdgf (2.15-fold; p < 0.0001) and reduced expression of anti-angiogenic factors Ang2 (0.12-fold; p < 0.05), Timp1 (0.22-fold; p < 0.05), and Vegfr2 (0.67-fold; p > 0.05) compared to neovascularized Dcn^+/+ mice corneas. These gene deficience studies carried with transgenic Dcn^-/- mice revealed decorin's role in influencing a physiologic balance between pro-and anti-angiogenic factors in the normal and injured cornea. We infer that the functional deletion of Dcn promotes irregular corneal repair and aggravates CNV.

miR-21 Plays a Dual Role in Tumor Formation and Cytotoxic Response in Breast Tumors

Simple Summary

miR-21 is an oncogenic microRNA that has been associated with breast tumor growth and metastasis in vitro and is also noted to be upregulated by cytotoxic stressors in model systems and in breast cancer patients who have undergone radiation. In the present study, our findings demonstrate the novel role of miR-21 in vivo for breast cancer initiation and metastases, and in sensitizing tumor cells to cytotoxic therapy by upregulating the FAS/FASL signaling pathway.

Abstract

Breast cancer (BrCa) relies on specific microRNAs to drive disease progression. Oncogenic miR-21 is upregulated in many cancers, including BrCa, and is associated with poor survival and treatment resistance. We sought to determine the role of miR-21 in BrCa tumor initiation, progression and treatment response. In a triple-negative BrCa model, radiation exposure increased miR-21 in both primary tumor and metastases. In vitro, miR-21 knockdown decreased survival in all BrCa subtypes in the presence of radiation. The role of miR-21 in BrCa initiation was evaluated by implanting wild-type miR-21 BrCa cells into genetically engineered mouse models where miR-21 was intact, heterozygous or globally ablated. Tumors were unable to grow in the mammary fat pads of miR-21^−/− mice, and grew in ~50% of miR-21^+/− and 100% in miR-21^+/+ mice. The contribution of miR-21 to progression and metastases was tested by crossing miR-21^−/− mice with mice that spontaneously develop BrCa. The global ablation of miR-21 significantly decreased the tumorigenesis and metastases of BrCa, while sensitizing tumors to radio- and chemotherapeutic agents via Fas/FasL-dependent apoptosis. Therefore, targeting miR-21 alone or in combination with various radio or cytotoxic therapies may represent novel and efficacious therapeutic modalities for the future treatment of BrCa patients.

A novel ocular function for decorin in the aqueous humor outflow

Primary open-angle glaucoma, a neurodegenerative disorder characterized by degeneration of optic nerve axons, is a frequent cause of vision loss and blindness worldwide. Several randomized multicenter studies have identified intraocular pressure as the major risk factor for its development, caused by an increased outflow resistance to the aqueous humor within the trabecular meshwork. However, the molecular mechanism for increased outflow resistance in POAG has not been fully established. One of the proposed players is the pro-fibrotic transforming growth factor (TGF)-β2, which is found in higher amounts in the aqueous humor of patients with POAG. In this study we elucidated the role of decorin, a small leucine-rich proteoglycan and known antagonist of TGF-β, in the region of aqueous humor outflow tissue. Utilizing decorin deficient mice, we discovered that decorin modulated TGF-β signaling in the canonical outflow pathways and the lack of decorin in vivo caused an increase in intraocular pressure. Additionally, the Dcn^-/- mice showed significant loss of optic nerve axons and morphological changes in the glial lamina, typical features of glaucoma. Moreover, using human trabecular meshwork cells we discovered that soluble decorin attenuated TGF-β2 mediated synthesis and expression of typical downstream target genes including CCN2/CTGF, FN and COL IV.  Finally, we found a negative reciprocal regulation of decorin and TGF-β, with a dramatic downregulation of decorin in the canonical outflow pathways of patients with primary open-angle glaucoma. Collectively, our results indicate that decorin plays an important role in the pathogenesis of primary open-angle glaucoma and offers novel perspectives in the treatment of this serious disease.

Angiostatic cues from the matrix: Endothelial cell autophagy meets hyaluronan biology

The extracellular matrix encompasses a reservoir of bioactive macromolecules that modulates a cornucopia of biological functions. A prominent body of work posits matrix constituents as master regulators of autophagy and angiogenesis and provides molecular insight into how these two processes are coordinated. Here, we review current understanding of the molecular mechanisms underlying hyaluronan and HAS2 regulation and the role of soluble proteoglycan in affecting autophagy and angiogenesis. Specifically, we assess the role of proteoglycan-evoked autophagy in regulating angiogenesis via the HAS2-hyaluronan axis and ATG9A, a novel HAS2 binding partner. We discuss extracellular hyaluronan biology and the post-transcriptional and post-translational modifications that regulate its main synthesizer, HAS2. We highlight the emerging group of proteoglycans that utilize outside-in signaling to modulate autophagy and angiogenesis in cancer microenvironments and thoroughly review the most up-to-date understanding of endorepellin signaling in vascular endothelia, providing insight into the temporal complexities involved.

Decorin regulates cartilage pericellular matrix micromechanobiology

In cartilage tissue engineering, one key challenge is for regenerative tissue to recapitulate the biomechanical functions of native cartilage while maintaining normal mechanosensitive activities of chondrocytes. Thus, it is imperative to discern the micromechanobiological functions of the pericellular matrix, the ~ 2-4 µm-thick domain that is in immediate contact with chondrocytes. In this study, we discovered that decorin, a small leucine-rich proteoglycan, is a key determinant of cartilage pericellular matrix micromechanics and chondrocyte mechanotransduction in vivo. The pericellular matrix of decorin-null murine cartilage developed reduced content of aggrecan, the major chondroitin sulfate proteoglycan of cartilage and a mild increase in collagen II fibril diameter vis-à-vis wild-type controls. As a result, decorin-null pericellular matrix showed a significant reduction in micromodulus, which became progressively more pronounced with maturation. In alignment with the defects of pericellular matrix, decorin-null chondrocytes exhibited decreased intracellular calcium activities, [Ca²⁺]_i, in both physiologic and osmotically evoked fluidic environments in situ, illustrating impaired chondrocyte mechanotransduction. Next, we compared [Ca²⁺]_i activities of wild-type and decorin-null chondrocytes following enzymatic removal of chondroitin sulfate glycosaminoglycans. The results showed that decorin mediates chondrocyte mechanotransduction primarily through regulating the integrity of aggrecan network, and thus, aggrecan-endowed negative charge microenvironment in the pericellular matrix. Collectively, our results provide robust genetic and biomechanical evidence that decorin is an essential constituent of the native cartilage matrix, and suggest that modulating decorin activities could improve cartilage regeneration.

Transcriptomic profiling of fetal membranes of mice deficient in biglycan and decorin as a model of preterm birth†

Approximately, 25% of all preterm births are due to preterm premature rupture of membranes. Mice deficient in proteoglycans biglycan (Bgn) and decorin (Dcn) display abnormal fetal membranes and increased incidence of preterm birth. We conducted RNA-Seq to profile fetal membranes and identify molecular pathways that may lead to preterm birth in double knockout (DKO) mice (Bgn-/-; Dcn-/-) compared to wild-type (WT) at two different gestational stages, E12 and E18 (n = 3 in each group). 3264 transcripts were differentially regulated in E18 DKO vs. WT fetal membranes, and 96 transcripts differentially regulated in E12 DKO vs. WT fetal membranes (FDR < 0.05, log 2 FC ≥ 1). Differentially regulated transcripts in E18 DKO fetal membranes were significantly enriched for genes involved in cell cycle regulation, extracellular matrix-receptor interaction, and the complement cascade. Fifty transcripts involved in the cell cycle were altered in E18 DKO fetal membranes (40↓, 10↑, FDR < 0.05), including p21 and p57 (↑), and Tgfb2, Smad3, CycA, Cdk1, and Cdk2(↓). Thirty-one transcripts involved in the complement cascade were altered (11↓, 20↑, FDR < 0.05) in E18 DKO fetal membranes, including C1q, C2, and C3 (↑). Differentially expressed genes in the top three molecular pathways (1) showed evidence of negative or purifying selection, and (2) were significantly enriched (Z-score > 10) for transcription factor binding sites for Nr2f1 at E18. We propose that in DKO mice, cell cycle arrest results in lack of cell proliferation in fetal membranes, inability to contain the growing fetus, and preterm birth.

Proteoglycan-driven Autophagy: A Nutrient-independent Mechanism to Control Intracellular Catabolism

Proteoglycans are rapidly emerging as versatile regulators of intracellular catabolic pathways. This is predominantly achieved via the non-canonical induction of autophagy, a fundamentally and evolutionarily conserved eukaryotic pathway necessary for maintaining organismal homeostasis. Autophagy facilitated by either decorin, a small leucine-rich proteoglycan, or perlecan, a basement membrane heparan sulfate proteoglycan, proceeds independently of ambient nutrient conditions. We found that soluble decorin evokes endothelial cell autophagy and breast carcinoma cell mitophagy by directly interacting with vascular endothelial growth factor receptor 2 (VEGFR2) or the Met receptor tyrosine kinase, respectively. Endorepellin, a soluble, proteolytic fragment of perlecan, induces autophagy and endoplasmic reticulum stress within the vasculature, downstream of VEGFR2. These potent matrix-derived cues transduce key biological information via receptor binding to converge upon a newly discovered nexus of core autophagic machinery comprised of Peg3 (paternally expressed gene 3) for autophagy or mitostatin for mitophagy. Here, we give a mechanistic overview of the nutrient-independent, proteoglycan-driven programs utilized for autophagic or mitophagic progression. We propose that catabolic control of cell behavior is an underlying basis for proteoglycan versatility and may provide novel therapeutic targets for the treatment of human disease.

Decorin deficiency promotes epithelial-mesenchymal transition and colon cancer metastasis

The tumor microenvironment encompasses a complex cellular network that includes cancer-associated fibroblasts, inflammatory cells, neo-vessels, and an extracellular matrix enriched in angiogenic growth factors. Decorin is one of the main components of the tumor stroma, but it is not expressed by cancer cells. Lack of this proteoglycan correlates with down-regulation of E-cadherin and induction of β-catenin signaling. In this study, we investigated the role of a decorin-deficient tumor microenvironment in colon carcinoma progression and metastasis. We utilized an established model of colitis-associated cancer by administering Azoxymethane/Dextran sodium sulfate to adult wild-type and Dcn^-/- mice. We discovered that after 12 weeks, all the animals developed intestinal tumors independently of their genotype. However, the number of intestinal neoplasms was significantly higher in the Dcn^-/- microenvironment vis-à-vis wild-type mice. Mechanistically, we found that under unchallenged basal conditions, the intestinal epithelium of the Dcn^-/- mice showed a significant increase in the protein levels of epithelial-mesenchymal transition associated factors including Snail, Slug, Twist, and MMP2. In comparison, in the colitis-associated cancer evoked in the Dcn^-/- mice, we found that intercellular adhesion molecule 1 (ICAM-1) was also significantly increased, in parallel with epithelial-mesenchymal transition signaling pathway-related factors. Furthermore, a combined Celecoxib/decorin treatment revealed a promising therapeutic efficacy in treating human colorectal cancer cells, in decorin-deficient animals. Collectively, our results shed light on colorectal cancer progression and provide a protein-based therapy, i.e., treatment using recombinant decorin, to target the tumor microenvironment.

Autophagic degradation of HAS2 in endothelial cells: A novel mechanism to regulate angiogenesis

Hyaluronan plays a key role in regulating inflammation and tumor angiogenesis. Of the three transmembrane hyaluronan synthases, HAS2 is the main pro-angiogenic enzyme responsible for excessive hyaluronan production. We discovered that HAS2 was degraded in vascular endothelial cells via autophagy evoked by nutrient deprivation, mTOR inhibition, or pro-autophagic proteoglycan fragments endorepellin and endostatin. Using live-cell and super-resolution confocal microscopy, we found that protracted autophagy evoked a dynamic interaction between HAS2 and ATG9A, a key transmembrane autophagic protein. This regulatory axis of HAS2 degradation occurred in various cell types and species and in vivo upon nutrient deprivation. Inhibiting in vivo autophagic flux via chloroquine showed increased levels of HAS2 in the heart and aorta. Functionally, autophagic induction via endorepellin or mTOR inhibition markedly suppressed extracellular hyaluronan production in vascular endothelial cells and inhibited ex vivo angiogenic sprouting. Thus, we propose autophagy as a novel catabolic mechanism regulating hyaluronan production in endothelial cells and demonstrate a new link between autophagy and angiogenesis that could lead to potential therapeutic modalities for angiogenesis.

Mediation of Cartilage Matrix Degeneration and Fibrillation by Decorin in Post-traumatic Osteoarthritis

OBJECTIVE

To elucidate the role of decorin, a small leucine-rich proteoglycan, in the degradation of cartilage matrix during the progression of post-traumatic osteoarthritis (OA).

METHODS

Three-month-old decorin-null (Dcn^-/- ) and inducible decorin-knockout (Dcn^{i KO} ) mice were subjected to surgical destabilization of the medial meniscus (DMM) to induce post-traumatic OA. The OA phenotype that resulted was evaluated by assessing joint morphology and sulfated glycosaminoglycan (sGAG) staining via histological analysis (n = 6 mice per group), surface collagen fibril nanostructure via scanning electron microscopy (n = 4 mice per group), tissue modulus via atomic force microscopy-nanoindentation (n = 5 or more mice per group) and subchondral bone structure via micro-computed tomography (n = 5 mice per group). Femoral head cartilage explants from wild-type and Dcn^-/- mice were stimulated with the inflammatory cytokine interleukin-1β (IL-1β) in vitro (n = 6 mice per group). The resulting chondrocyte response to IL-1β and release of sGAGs were quantified.

RESULTS

In both Dcn^-/- and Dcn^{i KO} mice, the absence of decorin resulted in accelerated sGAG loss and formation of highly aligned collagen fibrils on the cartilage surface relative to the control (P < 0.05). Also, Dcn^-/- mice developed more salient osteophytes, illustrating more severe OA. In cartilage explants treated with IL-1β, loss of decorin did not alter the expression of either anabolic or catabolic genes. However, a greater proportion of sGAGs was released to the media from Dcn^-/- mouse explants, in both live and devitalized conditions (P < 0.05).

CONCLUSION

In post-traumatic OA, decorin delays the loss of fragmented aggrecan and fibrillation of cartilage surface, and thus, plays a protective role in ameliorating cartilage degeneration.

Endorepellin evokes an angiostatic stress signaling cascade in endothelial cells

Endorepellin, the C-terminal fragment of the heparan sulfate proteoglycan perlecan, influences various signaling pathways in endothelial cells by binding to VEGFR2. In this study, we discovered that soluble endorepellin activates the canonical stress signaling pathway consisting of PERK, eIF2α, ATF4, and GADD45α. Specifically, endorepellin evoked transient activation of VEGFR2, which, in turn, phosphorylated PERK at Thr980 Subsequently, PERK phosphorylated eIF2α at Ser51, upregulating its downstream effector proteins ATF4 and GADD45α. RNAi-mediated knockdown of PERK or eIF2α abrogated the endorepellin-mediated up-regulation of GADD45α, the ultimate effector protein of this stress signaling cascade. To functionally validate these findings, we utilized an ex vivo model of angiogenesis. Exposure of the aortic rings embedded in 3D fibrillar collagen to recombinant endorepellin for 2-4 h activated PERK and induced GADD45α vis à vis vehicle-treated counterparts. Similar effects were obtained with the established cellular stress inducer tunicamycin. Notably, chronic exposure of aortic rings to endorepellin for 7-9 days markedly suppressed vessel sprouting, an angiostatic effect that was rescued by blocking PERK kinase activity. Our findings unravel a mechanism by which an extracellular matrix protein evokes stress signaling in endothelial cells, which leads to angiostasis.

Complexity of matrix phenotypes

The extracellular matrix is engaged in an ever-evolving and elegant ballet of dynamic reciprocity that directly and bi-directionally regulates cell behavior. Homeostatic and pathophysiological changes in cell-matrix signaling cascades manifest as complex matrix phenotypes. Indeed, the extracellular matrix can be implicated in virtually every known human disease, thus, making it the most critical and dynamic "organ" in the human body. The overall goal of this Special Issue is to provide an accurate and inclusive functional definition that addresses the inherent complexity of matrix phenotypes. This goal is summarily achieved via a corpus of expertly written articles, reviews and original research, focused at answering this question empirically and fundamentally via state-of-the-art methods and research strategies.

Catabolic degradation of endothelial VEGFA via autophagy

Extracellular matrix-evoked angiostasis and autophagy within the tumor microenvironment represent two critical, but unconnected, functions of the small leucine-rich proteoglycan, decorin. Acting as a partial agonist of vascular endothelial growth factor 2 (VEGFR2), soluble decorin signals via the energy sensing protein, AMP-activated protein kinase (AMPK), in the autophagic degradation of intracellular vascular endothelial growth factor A (VEGFA). Here, we discovered that soluble decorin evokes intracellular catabolism of endothelial VEGFA that is mechanistically independent of mTOR, but requires an autophagic regulator, paternally expressed gene 3 (PEG3). We found that administration of autophagic inhibitors such as chloroquine or bafilomycin A1, or depletion of autophagy-related 5 (ATG5), results in accumulation of intracellular VEGFA, indicating that VEGFA is a basal autophagic substrate. Mechanistically, decorin increased the VEGFA clearance rate by augmenting autophagic flux, a process that required RAB24 member RAS oncogene family (RAB24), a small GTPase that facilitates the disposal of autophagic compartments. We validated these findings by demonstrating the physiological relevance of this process in vivo Mice starved for 48 h exhibited a sharp decrease in overall cardiac and aortic VEGFA that could be blocked by systemic chloroquine treatment. Thus, our findings reveal a unified mechanism for the metabolic control of endothelial VEGFA for autophagic clearance in response to decorin and canonical pro-autophagic stimuli. We posit that the VEGFR2/AMPK/PEG3 axis integrates the anti-angiogenic and pro-autophagic bioactivities of decorin as the molecular basis for tumorigenic suppression. These results support future therapeutic use of decorin as a next-generation protein therapy to combat cancer.

Deregulated expression of Elastin Microfibril Interfacer 2 (EMILIN2) in gastric cancer affects tumor growth and angiogenesis

Gastric cancer is a frequent human tumor and often a lethal disease. Targeted therapy for gastric carcinomas is far behind vis-à-vis other solid tumors, primarily because of the paucity of cancer-driving mutations that could be efficiently and specifically targeted by current therapy. Thus, there is a need to discover actionable pathways/proteins and new diagnostic and prognostic biomarkers. In this study, we explored the role of the extracellular matrix glycoprotein EMILIN2, Elastin Microfibril Interfacer 2, in a cohort of gastric cancer patients. We discovered that EMILIN2 expression was consistently suppressed in gastric cancer and high expression levels of this glycoprotein were linked to abnormal vascular density. Furthermore, we found that EMILIN2 had a dual effect on gastric carcinoma cells: on one hand, it decreased tumor cell proliferation by triggering apoptosis, and on the other hand, it evoked the production of a number of cytokines involved in angiogenesis and inflammation, such as IL-8. Collectively, our findings posit EMILIN2 as an important onco-regulator exerting pleiotropic effects on the gastric cancer microenvironment.

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EMILIN2 is localized in the gastric lamina propria and its expression is down-regulated in gastric cancer.

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High levels of EMILIN2 associate with elevated vascular density.

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EMILIN2 impairs the proliferation of gastric cancer cells by evoking apoptosis.

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Surprisingly, EMILIN2 triggers the expression of pro-angiogenic and pro-inflammatory cytokines.

Discoidin Domain Receptor 1 functionally interacts with the IGF-I system in bladder cancer

Bladder cancer is one of the most common and aggressive cancers and, regardless of the treatment, often recurs and metastasizes. Thus, a better understanding of the mechanisms regulating urothelial tumorigenesis is critical for the design and implementation of rational therapeutic strategies. We previously discovered that the IGF-IR axis is critical for bladder cancer cell motility and invasion, suggesting a possible role in bladder cancer progression. However, IGF-IR depletion in metastatic bladder cancer cells only partially inhibited anchorage-independent growth. Significantly, metastatic bladder cancer cells have decreased IGF-IR levels but overexpressed the insulin receptor isoform A (IR-A), suggesting that the latter may play a more prevalent role than the IGF-IR in bladder tumor progression. The collagen receptor DDR1 cross-talks with both the IGF-IR and IR in breast cancer, and previous data suggest a role of DDR1 in bladder cancer. Here, we show that DDR1 is expressed in invasive and metastatic, but not in papillary, non-invasive bladder cancer cells. DDR1 is phosphorylated upon stimulation with IGF-I, IGF-II, and insulin, co-precipitates with the IGF-IR, and the IR-A and transient DDR1 depletion severely inhibits IGF-I-induced motility. We further demonstrate that DDR1 interacts with Pyk2 and non-muscle myosin IIA in ligands-dependent fashion, suggesting that it may link the IGF-IR and IR-A to the regulation of F-actin cytoskeleton dynamics. Similarly to the IGF-IR, DDR1 is upregulated in bladder cancer tissues compared to healthy tissue controls. Thus, our findings provide the first characterization of the molecular cross-talk between DDR1 and the IGF-I system and could lead to the identification of novel targets for therapeutic intervention in bladder cancer. Moreover, the expression profiles of IGF-IR, IR-A, DDR1, and downstream effectors could serve as a novel biomarker signature with diagnostic and prognostic significance.

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We discovered that the collagen receptor DDR1 cross-talks with insulin growth factor I (IGF-I) signaling in bladder cancer

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DDR1 co-precipitates with the IGF-IR and the insulin receptor (IR), and is phosphorylated upon stimulation with IGF ligands

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This collagen receptor modulates IGF-I-evoked motility and anchorage-independent growth

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DDR1 complexes with Pyk2, myosin IIA, IGF-IR and/or IR and regulates actin dynamics

Decorin Regulates the Aggrecan Network Integrity and Biomechanical Functions of Cartilage Extracellular Matrix

Joint biomechanical functions rely on the integrity of cartilage extracellular matrix. Understanding the molecular activities that govern cartilage matrix assembly is critical for developing effective cartilage regeneration strategies. This study elucidated the role of decorin, a small leucine-rich proteoglycan, in the structure and biomechanical functions of cartilage. In decorin-null cartilage, we discovered a substantial reduction of aggrecan content, the major proteoglycan of cartilage matrix, and mild changes in collagen fibril nanostructure. This loss of aggrecan resulted in significantly impaired biomechanical properties of cartilage, including decreased modulus, elevated hydraulic permeability, and reduced energy dissipation capabilities. At the cellular level, we found that decorin functions to increase the retention of aggrecan in the neo-matrix of chondrocytes, rather than to directly influence the biosynthesis of aggrecan. At the molecular level, we demonstrated that decorin significantly increases the adhesion between aggrecan and aggrecan molecules and between aggrecan molecules and collagen II fibrils. We hypothesize that decorin plays a crucial structural role in mediating the matrix integrity and biomechanical functions of cartilage by providing physical linkages to increase the adhesion and assembly of aggrecan molecules at the nanoscale.

Proteoglycan signaling in tumor angiogenesis and endothelial cell autophagy

The need for more effective cancer therapies is omnipresent as the ever-complex, and highly adaptive, mechanisms of tumor biology allow this disease to elude even the most stringent treatment options. The expanding field of proteoglycan signaling is enticing as a reservoir of potential drug targets and prospects for novel therapeutic strategies. The newest trend in proteoglycan biology is the interplay between extracellular signaling and autophagy fueled by the close link between autophagy and angiogenesis. Here we summarize the most current evidence surrounding proteoglycan signaling in both of these biological processes featuring the well-known suspects, decorin and perlecan, as well as other up-and-coming neophytes in this evolving signaling web.

Second-harmonic generation microscopy analysis reveals proteoglycan decorin is necessary for proper collagen organization in prostate

Collagen remodeling occurs in many prostate pathologies; however, the underlying structural architecture in both normal and diseased prostatic tissues is largely unexplored. Here, we use second-harmonic generation (SHG) microscopy to specifically probe the role of the proteoglycan decorin (Dcn) on collagen assembly in a wild type (wt) and Dcn null mouse (Dcn  -    /    -  ). Dcn is required for proper organization of collagen fibrils as it regulates size by forming an arch-like structure at the end of the fibril. We have utilized SHG metrics based on emission directionality (forward-backward ratio) and relative conversion efficiency, which are both related to the SHG coherence length, and found more disordered fibril organization in the Dcn  -    /    -  . We have also used image analysis readouts based on entropy, multifractal dimension, and wavelet transforms to compare the collagen fibril/fiber architecture in the two models, where all these showed that the Dcn  -    /    -   prostate comprised smaller and more disorganized collagen structures. All these SHG metrics are consistent with decreased SHG phase matching in the Dcn  -    /    -   and are further consistent with ultrastructural analysis of collagen in this model in other tissues, which show a more random distribution of fibril sizes and their packing into fibers. As Dcn is a known tumor suppressor, this work forms the basis for future studies of collagen remodeling in both malignant and benign prostate disease.

Dissecting the role of hyaluronan synthases in the tumor microenvironment

The tumor microenvironment is becoming a crucial factor in determining the aggressiveness of neoplastic cells. The glycosaminoglycan hyaluronan is one of the principal constituents of both the tumor stroma and the cancer cell surfaces, and its accumulation can dramatically influence patient survival. Hyaluronan functions are dictated by its ability to interact with several signaling receptors that often activate pro-angiogenic and pro-tumorigenic intracellular pathways. Although hyaluronan is a linear, non-sulfated polysaccharide, and thus lacks the ability of the other sulfated glycosaminoglycans to bind and modulate growth factors, it compensates for this by the ability to form hyaluronan fragments characterized by a remarkable variability in length. Here, we will focus on the role of both high and low molecular weight hyaluronan in controlling the hallmarks of cancer cells, including cell proliferation, migration, metabolism, inflammation, and angiogenesis. We will critically assess the multilayered regulation of HAS2, the most critical hyaluronan synthase, and its role in cancer growth, metabolism, and therapy.

Methods for Monitoring Matrix-Induced Autophagy

A growing body of research demonstrates modulation of autophagy by a variety of matrix constituents, including decorin, endorepellin, and endostatin. These matrix proteins are both pro-autophagic and anti-angiogenic. Here, we detail a series of methods to monitor matrix-induced autophagy and its concurrent effects on angiogenesis. We first discuss cloning and purifying proteoglycan fragment and core proteins in the laboratory and review relevant techniques spanning from cell culture to treatment with these purified proteoglycans in vitro and ex vivo. Further, we cover protocols in monitoring autophagic progression via morphological and microscopic characterization, biochemical western blot analysis, and signaling pathway investigation. Downstream angiogenic effects using in vivo approaches are then discussed using wild-type mice and the GFP-LC3 transgenic mouse model. Finally, we explore matrix-induced mitophagy via monitoring changes in mitochondrial DNA and permeability.

Matrix modeling and remodeling: A biological interplay regulating tissue homeostasis and diseases

The overall structure and architecture of the extracellular matrix undergo dramatic alterations in composition, form, and functionality over time. The stochasticity begins during development, essential for maintaining organismal homeostasis and is heavily implicated in many pathobiological states including fibrosis and cancer. Modeling and remodeling of the matrix is driven by the local cellular milieu and secreted and cell-associated components in a framework of dynamic reciprocity. This collection of expertly-written reviews aims to relay state-of-the-art information concerning the mechanisms of matrix modeling and remodeling in physiological development and disease.

Endorepellin remodels the endothelial transcriptome toward a pro-autophagic and pro-mitophagic gene signature

Regulation of autophagy by proteolytically cleaved fragments of heparan sulfate proteoglycans is a novel and current research focus in tumor biology. Endorepellin is the C-terminal angiostatic fragment of the heparan sulfate proteoglycan perlecan and induces autophagy in endothelial cells. To further investigate this property, we used NanoString, a digital PCR platform for measuring pre-defined transcripts in biological samples to analyze a custom subset of 95 autophagy-related genes in human umbilical vein endothelial cells treated with ultrapure human recombinant endorepellin. We discovered an endorepellin-evoked pro-autophagic and pro-mitophagic gene expression signatures, which included two coordinately up-regulated mitochondrial-associated genes encoding the E3 ubiquitin protein ligase Parkin and the tumor suppressor mitostatin. Induction of both proteins required the tyrosine kinase activity of vascular endothelial growth factor receptor 2 (VEGFR2). Furthermore, we discovered that endorepellin evoked mitochondrial depolarization in endothelial cells via a specific interaction between its two proximal LG1/2 domains and VEGFR2. We also found that following loss of membrane potential, mitostatin and parkin interact and that mitostatin associates with the established Parkin receptor mitofusin-2. In conclusion, we have identified a critical role for endorepellin in remodeling the autophagic transcriptome and influencing mitochondrial homeostasis.

Metabolic reprogramming of murine cardiomyocytes during autophagy requires the extracellular nutrient sensor decorin

The extracellular matrix is a master regulator of tissue homeostasis in health and disease. Here we examined how the small, leucine-rich, extracellular matrix proteoglycan decorin regulates cardiomyocyte metabolism during fasting in vivo First, we validated in Dcn ^-/- mice that decorin plays an essential role in autophagy induced by fasting. High-throughput metabolomics analyses of cardiac tissue in Dcn ^-/- mice subjected to fasting revealed striking differences in the hexosamine biosynthetic pathway resulting in aberrant cardiac O-β-N-acetylglycosylation as compared with WT mice. Functionally, Dcn ^-/- mice maintained cardiac function at a level comparable with nonfasted animals whereas fasted WT mice showed reduced ejection fraction. Collectively, our results suggest that reduced sensing of nutrient deprivation in the absence of decorin preempts functional adjustments of cardiac output associated with metabolic reprogramming.

Serglycin promotes breast cancer cell aggressiveness: Induction of epithelial to mesenchymal transition, proteolytic activity and IL-8 signaling

Serglycin is an intracellular proteoglycan that is expressed and constitutively secreted by numerous malignant cells, especially prominent in the highly-invasive, triple-negative MDA-MB-231 breast carcinoma cells. Notably, de novo expression of serglycin in low aggressive estrogen receptor α (ERα)-positive MCF7 breast cancer cells promotes an aggressive phenotype. In this study, we discovered that serglycin promoted epithelial to mesenchymal transition (EMT) in MCF7 cells as shown by increased expression of mesenchymal markers vimentin, fibronectin and EMT-related transcription factor Snail2. These phenotypic traits were also associated with the development of drug resistance toward various chemotherapy agents and induction of their proteolytic potential as shown by the increased expression of matrix metalloproteinases, including MMP-1, MMP-2, MMP-9, MT1-MMP and up-regulation of urokinase-type plasminogen activator. Knockdown of serglycin markedly reduced the expression of these proteolytic enzymes in MDA-MB-231 cells. In addition, serglycin expression was closely linked to a pro-inflammatory gene signature including the chemokine IL-8 in ERα-negative breast cancer cells and tumors. Notably, serglycin regulated the secretion of IL-8 in breast cancer cells independently of their ERα status and promoted their proliferation, migration and invasion by triggering IL-8/CXCR2 downstream signaling cascades including PI3K, Src and Rac activation. Thus, serglycin promotes the establishment of a pro-inflammatory milieu in breast cancer cells that evokes an invasive mesenchymal phenotype via autocrine activation of IL-8/CXCR2 signaling axis.