G protein-coupled receptor APJ and its ligand apelin act downstream of Cripto to specify embryonic stem cells toward the cardiac lineage through extracellular signal-regulated kinase/p70S6 kinase signaling pathway

RATIONALE

Pluripotent stem cells represent a powerful model system to study the early steps of cardiac specification for which the molecular control is largely unknown. The EGF-CFC (epidermal growth factor-Cripto/FRL-1/Cryptic) Cripto protein is essential for cardiac myogenesis in embryonic stem cells (ESCs).

OBJECTIVE

Here, we study the role of apelin and its G protein-coupled receptor, APJ, as downstream targets of Cripto both in vivo and in ESC differentiation.

METHODS AND RESULTS

Gain-of-function experiments show that APJ suppresses neuronal differentiation and restores the cardiac program in Cripto(-/-) ESCs. Loss-of-function experiments point for a central role for APJ/apelin in the gene regulatory cascade promoting cardiac specification and differentiation in ESCs. Remarkably, we show for the first time that apelin promotes mammalian cardiomyogenesis via activation of mitogen-activated protein kinase/p70S6 through coupling to a Go/Gi protein.

CONCLUSIONS

Together our data provide evidence for a previously unrecognized function of APJ/apelin in the Cripto signaling pathway governing mesoderm patterning and cardiac specification in mammals.

Nanoalgosomes: Introducing extracellular vesicles produced by microalgae

Cellular, inter-organismal and cross kingdom communication via extracellular vesicles (EVs) is intensively studied in basic science with high expectation for a large variety of bio-technological applications. EVs intrinsically possess many attributes of a drug delivery vehicle. Beyond the implications for basic cell biology, academic and industrial interests in EVs have increased in the last few years. Microalgae constitute sustainable and renewable sources of bioactive compounds with a range of sectoral applications, including the formulation of health supplements, cosmetic products and food ingredients. Here we describe a newly discovered subtype of EVs derived from microalgae, which we named nanoalgosomes. We isolated these extracellular nano-objects from cultures of microalgal strains, including the marine photosynthetic chlorophyte Tetraselmis chuii, using differential ultracentrifugation or tangential flow fractionation and focusing on the nanosized small EVs (sEVs). We explore different biochemical and physical properties and we show that nanoalgosomes are efficiently taken up by mammalian cell lines, confirming the cross kingdom communication potential of EVs. This is the first detailed description of such membranous nanovesicles from microalgae. With respect to EVs isolated from other organisms, nanoalgosomes present several advantages in that microalgae are a renewable and sustainable natural source, which could easily be scalable in terms of nanoalgosome production.

Role of the EGF-CFC gene cripto in cell differentiation and embryo development

The EGF-CFC proteins have been recently recognized as a novel family of extracellular factors required during early vertebrate development. Cripto is the founder member of the EGF-CFC family initially related to the epidermal growth factor (EGF); its expression is increased in human colon, gastric, pancreatic and lung carcinoma and in different types of both mouse and human breast carcinomas. Genetic studies in the mouse have established an essential role of cripto in the formation and correct positioning of the anterior-posterior axis. Furthermore, the absence of cripto results in a defective precardiac mesoderm, unable to differentiate into functional cardiomyocytes. Although mouse and human Cripto have been shown to activate the ras/raf/MAP kinase pathway in mammary epithelial cell lines, genetic evidence in Zebrafish has been provided for a relationship between the EGF-CFC proteins and Nodal, a member of the transforming growth factor family. Here we review the biological role of cripto in development and differentiation, pointing out recent findings on the biochemical interactions of Cripto, Nodal and Activin-like receptors.

Anterior neural plate regionalization in cripto null mutant mouse embryos in the absence of node and primitive streak

The relation between the role of the organizer at the gastrula stage and the activity of earlier signals in the specification, maintenance, and regionalization of the developing brain anlage is still controversial. Mouse embryos homozygous for null mutation in the cripto gene die at about 9.0 days postcoitum (d.p.c.) and fail to gastrulate and to form the node (the primary organizer). Here, we study the presence and the distribution of anterior neural plate molecular domains in cripto null mutants. We demonstrate that, in cripto(-/-) embryos, the main prosencephalic and mesencephalic regions are present and that they assume the correct topological organization. The identity of the anterior neural domains is maintained in mutant embryos at 8.5 d.p.c., as well as in mutant explants dissected at 8.5 d.p.c. and cultured in vitro for 24 h. Our data imply the existence of a stable neural regionalization of anterior character inside the cripto(-/-) embryos, despite the failure in both the gastrulation process and node formation. These results suggest that, in mouse embryos, the specification of the anterior neural identities can be maintained without an absolute requirement for the embryonic mesoderm and the node.

Cripto promotes A-P axis specification independently of its stimulatory effect on Nodal autoinduction

The EGF-CFC gene cripto governs anterior-posterior (A-P) axis specification in the vertebrate embryo. Existing models suggest that Cripto facilitates binding of Nodal to an ActRII-activin-like kinase (ALK) 4 receptor complex. Cripto also has a crucial function in cellular transformation that is independent of Nodal and ALK4. However, how ALK4-independent Cripto pathways function in vivo has remained unclear. We have generated cripto mutants carrying the amino acid substitution F78A, which blocks the Nodal-ALK4-Smad2 signaling both in embryonic stem cells and cell-based assays. In cripto(F78A/F78A) mouse embryos, Nodal fails to expand its own expression domain and that of cripto, indicating that F78 is essential in vivo to stimulate Smad-dependent Nodal autoinduction. In sharp contrast to cripto-null mutants, cripto(F78A/F78A) embryos establish an A-P axis and initiate gastrulation movements. Our findings provide in vivo evidence that Cripto is required in the Nodal-Smad2 pathway to activate an autoinductive feedback loop, whereas it can promote A-P axis formation and initiate gastrulation movements independently of its stimulatory effect on the canonical Nodal-ALK4-Smad2 signaling pathway.

Isolation of extracellular vesicles from microalgae: towards the production of sustainable and natural nanocarriers of bioactive compounds

Biophysical and biochemical characterisation of microalgae-derived extracellular vesicles.

Characterization of the functional properties of the neuroectoderm in mouse Cripto(-/-) embryos showing severe gastrulation defects

During development of the mammalian embryo, there is a complex relation between formation of the mesoderm and the neuroectoderm. In mouse, for example, the role of the node and its mesendoderm derivatives in anterior neural specification is still debated. Mouse Cripto(-/-) embryos could potentially help settle this debate because they lack almost all embryonic endoderm and mesoderm, including the node and its derivatives. In the present paper, we show that Cripto(-/-) embryos can still form functional neural stem cells that are able to differentiate and maintain a neural phenotype both in vivo and in vitro. These data suggest that signals emanating from the mesoderm and endoderm might not be essential for the formation and differentiation of neural stem cells. However, we use grafting experiments to show that the Cripto(-/-) isthmus (the secondary organizer located at the midbrain-hindbrain boundary) loses its inductive ability. We further show that the Cripto(-/-)isthmus expresses lower amounts of the isthmic signalling molecule, Fgf8. Since nearby tissues remain competent to respond to exogenously added Fgf8, this reduction in Fgf8 levels in the Cripto(-/-) isthmus is the potential cause of the loss of patterning ability in graft experiments. Overall, we interpret our data to suggest that the mammalian node and primitive streak are essential for the development of the regional identities that control the specification and formation of the secondary organizers within the developing brain.

A Novel Localization in Human Large Extracellular Vesicles for the EGF-CFC Founder Member CRIPTO and Its Biological and Therapeutic Implications

Tumor growth and metastasis strongly rely on cell–cell communication. One of the mechanisms by which tumor cells communicate involves the release and uptake of lipid membrane encapsulated particles full of bioactive molecules, called extracellular vesicles (EVs). EV exchange between cancer cells may induce phenotype changes in the recipient cells. Our work investigated the effect of EVs released by teratocarcinoma cells on glioblastoma (GBM) cells. EVs were isolated by differential centrifugation and analyzed through Western blot, nanoparticle tracking analysis, and electron microscopy. The effect of large EVs on GBM cells was tested through cell migration, proliferation, and drug-sensitivity assays, and resulted in a specific impairment in cell migration with no effects on proliferation and drug-sensitivity. Noticeably, we found the presence of the EGF-CFC founder member CRIPTO on both small and large EVs, in the latter case implicated in the EV-mediated negative regulation of GBM cell migration. Our data let us propose a novel route and function for CRIPTO during tumorigenesis, highlighting a complex scenario regulating its effect, and paving the way to novel strategies to control cell migration, to ultimately improve the prognosis and quality of life of GBM patients.

Cripto haploinsufficiency affects in vivo colon tumor development

Colorectal cancer is one of the most common and aggressive cancers arising from alterations in various signaling pathways, such as the WNT, RAS-MAPK, PI3K and transforming growth factor-β (TGF-β) pathways. Cripto (also called Teratocarcinoma-derived growth factor), the original member of the vertebrate EGF-CFC family, plays a key role in all of these pathways and is deeply involved in early embryo development and cancer progression. The role of Cripto in colon and breast cancer, in particular, has been investigated, as it is still not clearly understood. In this article, we provide the first in vivo functional evidence of a role of Cripto in colon cancer development. We analyzed the effect of Cripto haploinsufficiency on colon tumor formation by treating Cripto heterozygous mice with the colonotropic carcinogen azoxymethane (AOM). Of note, in our model system, Cripto haploinsufficiency increased tumorigenesis. Moreover, we revealed a correlation between the differential AOM response found in wt and Cripto⁺/⁻ mice and the expression levels of glucose regulated protein-78 (Grp78), a heat shock protein required for Cripto signaling pathways. We hypothesize that the balance between Cripto and Grp78 expression levels might be crucial in cancer development and may account for the increased tumorigenesis in Cripto heterozygous mice. In summary, our results highlight the heterogeneous effect of Cripto on tumorigenesis and the consequent high level of complexity in the Cripto regulatory pathway, whose imbalance causes tumors.

Genetic variants modulating CRIPTO serum levels identified by genome-wide association study in Cilento isolates

Cripto, the founding member of the EGF-CFC genes, plays an essential role in embryo development and is involved in cancer progression. Cripto is a GPI-anchored protein that can interact with various components of multiple signaling pathways, such as TGF-β, Wnt and MAPK, driving different processes, among them epithelial-mesenchymal transition, cell proliferation, and stem cell renewal. Cripto protein can also be cleaved and released outside the cell in a soluble and still active form. Cripto is not significantly expressed in adult somatic tissues and its re-expression has been observed associated to pathological conditions, mainly cancer. Accordingly, CRIPTO has been detected at very low levels in the plasma of healthy volunteers, whereas its levels are significantly higher in patients with breast, colon or glioblastoma tumors. These data suggest that CRIPTO levels in human plasma or serum may have clinical significance. However, very little is known about the variability of serum levels of CRIPTO at a population level and the genetic contribution underlying this variability remains unknown. Here, we report the first genome-wide association study of CRIPTO serum levels in isolated populations (n = 1,054) from Cilento area in South Italy. The most associated SNPs (p-value<5*10-8) were all located on chromosome 3p22.1-3p21.3, in the CRIPTO gene region. Overall six CRIPTO associated loci were replicated in an independent sample (n = 535). Pathway analysis identified a main network including two other genes, besides CRIPTO, in the associated regions, involved in cell movement and proliferation. The replicated loci explain more than 87% of the CRIPTO variance, with 85% explained by the most associated SNP. Moreover, the functional analysis of the main associated locus identified a causal variant in the 5’UTR of CRIPTO gene which is able to strongly modulate CRIPTO expression through an AP-1-mediate transcriptional regulation.

Cripto gene has a fundamental role in embryo development and is also involved in cancer. The protein is bound to the cell membrane through an anchor, that can be cleaved, causing the secretion of the protein, in a still active form. In the adult, CRIPTO is detected at very low levels in normal tissues and in the blood, while its increase in both tissues and blood is associated to pathological conditions, mainly cancer. As other GPI linked proteins such as the carcinoembryonic antigen (CEA), one of the most used tumor markers, CRIPTO is able to reach the bloodstream. Therefore, CRIPTO represents a new promising biomarker and potential therapeutic target, and blood CRIPTO levels might be associated to clinical features. Here we examined the variability of blood CRIPTO levels at a population level (population isolates from the Cilento region in South Italy) and we investigated the genetic architecture underlying this variability. We reported the association of common genetic variants with the levels of CRIPTO protein in the blood and we identified a main locus on chromosome 3 and additional five associated loci. Moreover, through functional analyses, we were able to uncover the mechanism responsible for the variation in CRIPTO levels, which is a regulation mediated by the transcriptional factor AP-1.

Pathological and Therapeutic Significance of Tumor-Derived Extracellular Vesicles in Cancer Cell Migration and Metastasis

The infiltration of primary tumors and metastasis formation at distant sites strongly impact the prognosis and the quality of life of cancer patients. Current therapies including surgery, radiotherapy, and chemotherapy are limited in targeting the complex cell migration mechanisms responsible for cancer cell invasiveness and metastasis. A better understanding of these mechanisms and the development of new therapies are urgently needed. Extracellular vesicles (EVs) are lipid-enveloped particles involved in inter-tissue and inter-cell communication. This review article focuses on the impact of EVs released by tumor cells, specifically on cancer cell migration and metastasis. We first introduce cell migration processes and EV subtypes, and we give an overview of how tumor-derived EVs (TDEVs) may impact cancer cell migration. Then, we discuss ongoing EV-based cancer therapeutic approaches, including the inhibition of general EV-related mechanisms as well as the use of EVs for anti-cancer drug delivery, focusing on the harnessing of TDEVs. We propose a protein-EV shuttle as a route alternative to secretion or cell membrane binding, influencing downstream signaling and the final effect on target cells, with strong implications in tumorigenesis. Finally, we highlight the pitfalls and limitations of therapeutic EV exploitation that must be overcome to realize the promise of EVs for cancer therapy.

Vaccination with (1-11)E2 in alum efficiently induces an antibody response to β-amyloid without affecting brain β-amyloid load and microglia activation in 3xTg mice

Immunization against β-amyloid (Aβ) is pursued as a possible strategy for the prevention of Alzheimer’s disease (AD). In clinical trials, Aβ 1–42 proved poorly immunogenic and caused severe adverse effects; therefore, safer and more immunogenic candidate vaccines are needed. Multimeric protein (1–11)E2 is able to induce an antibody response to Aβ, immunological memory, and IL-4 production, with no concomitant anti-Aβ T cell response. Antisera recognize Aβ oligomers, protofibrils, and fibrils. In this study, we evaluated the effect of prophylactic immunization with three doses of (1–11)E2 in alum in the 3xTg mouse model of AD. Immunization with (1–11)E2 efficiently induced anti-Aβ antibodies, but afforded no protection against Aβ accumulation and neuroinflammation. The identification of the features of the anti-Aβ immune response that correlate with the ability to prevent Aβ accumulation remains an open problem that deserves further investigation.

Dormancy and awakening of cancer cells: the extracellular vesicle-mediated cross-talk between Dr. Jekill and Mr. Hyde

Cancer cell dormancy is a reversible process whereby cancer cells enter a quiescent state characterized by cell cycle arrest, inhibition of cell migration and invasion, and increased chemoresistance. Because of its reversibility and resistance to treatment, dormancy is a key process to study, monitor, and interfere with, in order to prevent tumor recurrence and metastasis and improve the prognosis of cancer patients. However, to achieve this goal, further studies are needed to elucidate the mechanisms underlying this complex and dynamic dual process. Here, we review the contribution of extracellular vesicles (EVs) to the regulation of cancer cell dormancy/awakening, focusing on the cross-talk between tumor and non-tumor cells in both the primary tumor and the (pre-)metastatic niche. Although EVs are recognized as key players in tumor progression and metastasis, as well as in tumor diagnostics and therapeutics, their role specifically in dormancy induction/escape is still largely elusive. We report on the most recent and promising results on this topic, focusing on the EV-associated nucleic acids involved. We highlight how EV studies could greatly contribute to the identification of dormancy signaling pathways and a dormancy/early awakening signature for the development of successful diagnostic/prognostic and therapeutic approaches.

A decision-making tool for navigating extracellular vesicle research and product development

Due to their intercellular communication properties and involvement in a wide range of biological processes, extracellular vesicles (EVs) are increasingly being studied and exploited for different applications. Nevertheless, their complex nature and heterogeneity, as well as the challenges related to their purification and characterization procedures, require a cautious assessment of the qualitative and quantitative parameters that need to be monitored. This translates into a multitude of choices and putative solutions that any EV researcher must confront in both research and translational environments. In this respect, decision-making tools may help assess various options, weigh pros and cons, and ultimately arrive at a thought-out decision that considers both the best fit-to-source and fit-to-scope EV application(s). Here, we present a multi-criteria EV decision-making grid (EV-DMG) as a novel, efficient, customizable, and easy-to-use tool to support EV research and innovation. By identifying and weighing key assessment criteria for comparing distinct EV-based preparations and related processes, our EV-DMG may assist any EV community member in making informed, traceable, and reproducible decisions regarding the management of EV sources or samples. Ultimately, this EV-DMG may guide the adoption of the most suitable EV production and analytical pipelines for targeting a defined aim or application.

Challenges and Promise for Glioblastoma Treatment through Extracellular Vesicle Inquiry

Glioblastoma (GB) is a rare but extremely aggressive brain tumor that significantly impacts patient outcomes, affecting both duration and quality of life. The protocol established by Stupp and colleagues in 2005, based on radiotherapy and chemotherapy with Temozolomide, following maximum safe surgical resection remains the gold standard for GB treatment; however, it is evident nowadays that the extreme intratumoral and intertumoral heterogeneity, as well as the invasiveness and tendency to recur, of GB are not compatible with a routine and unfortunately ineffective treatment. This review article summarizes the main challenges in the search for new valuable therapies for GB and focuses on the impact that extracellular vesicle (EV) research and exploitation may have in the field. EVs are natural particles delimited by a lipidic bilayer and filled with functional cellular content that are released and uptaken by cells as key means of cell communication. Furthermore, EVs are stable in body fluids and well tolerated by the immune system, and are able to cross physiological, interspecies, and interkingdom barriers and to target specific cells, releasing inherent or externally loaded functionally active molecules. Therefore, EVs have the potential to be ideal allies in the fight against GB and to improve the prognosis for GB patients. The present work describes the main preclinical results obtained so far on the use of EVs for GB treatment, focusing on both the EV sources and molecular cargo used in the various functional studies, primarily in vivo. Finally, a SWOT analysis is performed, highlighting the main advantages and pitfalls of developing EV-based GB therapeutic strategies. The analysis also suggests the main directions to explore to realize the possibility of exploiting EVs for the treatment of GB.