Very small embryonic/epiblast-like stem cells: a missing link to support the germ line hypothesis of cancer development?

Misconceptions Thrive in the Field of Cancer as Technological Advances Continue to Confuse Stem Cell Biology

Despite the huge thrust on targeted therapies, cancer survival rates have not improved and both cancer incidence and fatalities continue to rise globally. There is no consensus on how cancer initiates and two contrasting views were published in 2024 regarding cancer initiation. Based on the premise that no stem cells exist in tissues like liver, lungs, and pancreas but they are still affected by cancer; it was suggested that somatic cells dedifferentiate and undergo 'paligenosis' to initiate cancer. The second view discussed that tissue-resident, very small embryonic-like stem cells (VSELs) are vulnerable to extrinsic/intrinsic insults and their dysfunctions initiate cancer. The present article examines the underlying technical reasons that have led to these conflicting views. Scientists have struggled to detect quiescent cancer stem cells (CSCs) that survive chemotherapy, and radiotherapy and escape immunotherapy, cause recurrence and eventually therapeutic resistance leading to death. Lineage tracing studies fail to detect quiescent, acyclic stem cells and instead, the role of actively dividing LGR5+ cells was highlighted for tumor initiation, growth, and metastasis. Similarly, technologies like flow cytometry, and single-cell RNAseq, widely used to comprehend cancer biology, provide insights into cell populations present in abundance. Our article reviews why VSELs/CSCs in the pancreas have remained elusive despite employing advanced technologies, and the critique can be generalized to multiple other organs. This understanding is crucial as it will help to develop better therapeutic strategies for cancer, offer early detection when cancer is a weak disease, and pave the path for prevention over treatment.

Very small embryonic-like stem cells (VSELs) on the way for potential applications in regenerative medicine

Evidence has accumulated that adult tissues contain a population of early development stem cells capable of differentiating across germ layers into various types of cells. Our group purified these rare cells, naming them very small embryonic-like stem cells (VSELs). With their broad differentiation potential, VSELs have emerged as a new candidate population for clinical applications. This advancement is now possible due to our recent development of a model for ex vivo expansion of these rare cells. Importantly, no evidence suggests that VSELs, isolated from adult tissues, can form teratomas. In this review paper, we update current research on these cells reported in our laboratory as well as in those of several independent investigators.

In Vitro models of leukemia development: the role of very small leukemic stem-like cells in the cellular transformation cascade

Recent experimental findings indicate that cancer stem cells originate from transformed very small embryonic-like stem cells. This finding represents an essential advancement in uncovering the processes that drive the onset and progression of cancer. In continuously growing cell lines, for the first time, our team's follow-up research on leukemia, lung cancer, and healthy embryonic kidney cells revealed stages that resembles very small precursor stem cells. This review explores the origin of leukemic stem-like cells from very small leukemic stem-like cells establish from transformed very small embryonic-like stem cells. We explore theoretical model of acute myeloid leukemia initiation and progresses through various stages, as well basing the HL60 cell line, present its hierarchical stage development in vitro, highlighting the role of these very small precursor primitive stages. We also discuss the potential implications of further research into these unique cellular stages for advancing leukemia and cancer treatment and prevention.

Very small embryonic-like stem cells have the potential to win the three-front war on tissue damage, cancer, and aging

The concept of dedifferentiation and reprogramming of mature somatic cells holds much promise for the three-front "war" against tissue damage, cancer, and aging. It was hoped that reprogramming human somatic cells into the induced pluripotent state, along with the use of embryonic stem cells, would transform regenerative medicine. However, despite global efforts, clinical applications remain a distant dream, due to associated factors such as genomic instability, tumorigenicity, immunogenicity, and heterogeneity. Meanwhile, the expression of embryonic (pluripotent) markers in multiple cancers has baffled the scientific community, and it has been suggested that somatic cells dedifferentiate and "reprogram" into the pluripotent state in vivo to initiate cancer. It has also been suggested that aging can be reversed by partial reprogramming in vivo. However, better methods are needed; using vectors or Yamanaka factors in vivo, for example, is dangerous, and many potential anti-aging therapies carry the same risks as those using induced pluripotent cells, as described above. The present perspective examines the potential of endogenous, pluripotent very small embryonic-like stem cells (VSELs). These cells are naturally present in multiple tissues; they routinely replace diseased tissue and ensure regeneration to maintain life-long homeostasis, and they have the ability to differentiate into adult counterparts. Recent evidence suggests that cancers initiate due to the selective expansion of epigenetically altered VSELs and their blocked differentiation. Furthermore, VSEL numbers have been directly linked to lifespan in studies of long- and short-lived transgenic mice, and VSEL dysfunction has been found in the ovaries of aged mice. To conclude, a greater interest in VSELs, with their potential to address all three fronts of this war, could be the "light at the end of the tunnel."

Altered Biology of Testicular VSELs and SSCs by Neonatal Endocrine Disruption Results in Defective Spermatogenesis, Reduced Fertility and Tumor Initiation in Adult Mice

Reproductive health of men has declined in recent past with reduced sperm count and increased incidence of infertility and testicular cancers mainly attributed to endocrine disruption in early life. Present study aims to evaluate whether testicular stem cells including very small embryonic-like stem cells (VSELs) and spermatogonial stem cells (SSCs) get affected by endocrine disruption and result in pathologies in adult life. Effect of treatment on mice pups with estradiol (20 μg on days 5-7) and diethylstilbestrol (DES, 2 μg on days 1-5) was studied on VSELs, SSCs and spermatogonial cells in adult life. Treatment affected spermatogenesis, tubules in Stage VIII & sperm count were reduced along with reduction of meiotic (4n) cells and markers (Prohibitin, Scp3, Protamine). Enumeration of VSELs by flow cytometry (2-6 μm, 7AAD-, LIN-CD45-SCA-1+) and qRT-PCR using specific transcripts for VSELs (Oct-4a, Sox-2, Nanog, Stella, Fragilis), SSCs (tOct-4, Gfra-1, Gpr-125) and early germ cells (Mvh, Dazl) showed several-fold increase but transition from c-Kit negative to c-Kit positive spermatogonial cells was blocked on D100 after treatment. Transcripts specific for apoptosis (Bcl2, Bax) remained unaffected but tumor suppressor (p53) and epigenetic regulator (NP95) transcripts showed marked disruption. 9 of 10 mice exposed to DES showed tumor-like changes. To conclude, endocrine disruption resulted in a tilt towards excessive self-renewal of VSELs (leading to testicular cancer after DES treatment) and blocked differentiation (reduced numbers of c-Kit positive cells, meiosis, sperm count and fertility). Understanding the underlying basis for infertility and cancer initiation from endogenous stem cells through murine modelling will hopefully improve human therapies in future.

Quest for Pan-Cancer Diagnosis/Prognosis Ends with HrC Test Measuring Oct4A in Peripheral Blood

Cancer is a devastating disease whose incidence has increased in recent times and early detection can lead to effective treatment. Existing detection tools suffer from low sensitivity and specificity, and are high cost, invasive and painful procedures. Cancers affecting different tissues, ubiquitously express embryonic markers including Oct-4A, whose expression levels have also been correlated to staging different types of cancer. Cancer stem cells (CSCs) that initiate cancer are possibly the 'transformed' and pluripotent very small embryonic-like stem cells (VSELs) that also express OCT-4A. Excessive self-renewal of otherwise quiescent, pluripotent VSELs in normal tissues possibly initiates cancer. In an initial study on 120 known cancer patients, it was observed that Oct-4A expression in peripheral blood correlated well with the stage of cancer. Based on these results, we developed a proprietary HrC scale wherein fold change of OCT-4A was linked to patient status - it is a numerical scoring system ranging from non-cancer (0-2), inflammation (>2-6), high-risk (>6-10), stage I (>10-20), stage II (>20-30), stage III (>30-40), and stage IV (>40) cancers. Later the scale was validated on 1000 subjects including 500 non-cancer and 500 cancer patients. Ten case studies are described and show (i) HrC scale can detect cancer, predict and monitor treatment outcome (ii) is superior to evaluating circulating tumor cells and (iii) can also serve as an early biomarker. HrC method is a novel breakthrough, non-invasive, blood-based diagnostic tool that can detect as well as classify solid tumors, hematological malignancies and sarcomas, based on their stage.

THE "-OMAS" and "-OPIAS": Targeted and Philosophical Considerations Regarding Hamartomas, Choristomas, Teratomas, Ectopias, and Heterotopias in Pediatric Otorhinolaryngologic Pathology

The spectrum of "developmental" lesions that occur in the head and neck predominantly congenital in origin and arising at birth and/or discovered in childhood is broad and fascinating. These have been grouped into categories such as "ectopias", "heterotopias", "hamartomas", and "choristomas". On a philosophical and consequently systematic level, these lesions, mostly benign tumors seem to lack a true understanding of the pathogenetic foundation on which to base a more unified taxonomic designation. In this review, we will consider some of these select tumors as they represent syndromic associations (nasal chondromesenchymal hamartoma and DICER1 syndrome), the lingual choristoma from the perspective of its nomenclature and classification, lesions with ectopic meningothelial elements, and teratomas and the enigmatic "hairy polyp" in reference to a broader discussion of pathogenesis and pluripotent cells in the head and neck. A consistent thread will be how these lesions are designated with some final thoughts on future directions regarding the investigation of their pathogenesis and taxonomic nomenclature.

The dualistic origin of human tumors

Life starts with a zygote, which is formed by the fusion of a haploid sperm and egg. The formation of a blastomere by cleavage division (nuclear division without an increase in cell size) is the first step in embryogenesis, after the formation of the zygote. Blastomeres are responsible for reprogramming the parental genome as a new embryonic genome for generation of the pluripotent stem cells which then differentiate by Waddington's epigenetic landscape to create a new life. Multiple authors over the past 150 years have proposed that tumors arises from development gone awry at a point within Waddington's landscape. Recent discoveries showing that differentiated somatic cells can be reprogrammed into induced pluripotent stem cells, and that somatic cell nuclear transfer can be used to successfully clone animals, have fundamentally reshaped our understanding of tumor development and origin. Differentiated somatic cells are plastic and can be induced to dedifferentiate into pluripotent stem cells. Here, I review the evidence that suggests somatic cells may have a previously overlooked endogenous embryonic program that can be activated to dedifferentiate somatic cells into stem cells of various potencies for tumor initiation. Polyploid giant cancer cells (PGCCs) have long been observed in cancer and were thought originally to be nondividing. Contrary to this belief, recent findings show that stress-induced PGCCs divide by endoreplication, which may recapitulate the pattern of cleavage-like division in blastomeres and lead to dedifferentiation of somatic cells by a programmed process known as "the giant cell cycle", which comprise four distinct but overlapping phases: initiation, self-renewal, termination and stability. Depending on the intensity and type of stress, different levels of dedifferentiation result in the formation of tumors of different grades of malignancy. Based on these results, I propose a unified dualistic model to demonstrate the origin of human tumors. The tenet of this model includes four points, as follows. 1. Tumors originate from a stem cell at a specific developmental hierarchy, which can be achieved by dualistic origin: dedifferentiation of the zygote formed by two haploid gametes (sexual reproduction) via the blastomere during normal development, or transformation from damaged or aged mature somatic cells via a blastomere-like embryonic program (asexual reproduction). 2. Initiation of the tumor begins with a stem cell that has uncoupled the differentiation from the proliferation program which results in stem cell maturation arrest. 3. The developmental hierarchy at which stem cells arrest determines the degree of malignancy: the more primitive the level at which stem cells arrest, the greater the likelihood of the tumor being malignant. 4. Environmental factors and intrinsic genetic or epigenetic alterations represent the risk factors or stressors that facilitate stem cell arrest and somatic cell dedifferentiation. However, they, per se, are not the driving force of tumorigenesis. Thus, the birth of a tumor can be viewed as a triad that originates from a stem cell via dedifferentiation through a blastomere or blastomere-like program, which then differentiates along Waddington's landscape, and arrests at a developmental hierarchy. Blocking the PGCC-mediated dedifferentiation process and inducing their differentiation may represent a novel alternative approach to eliminate the tumor occurrence and therapeutic resistance.

Cancer from the perspective of stem cells and misappropriated tissue regeneration mechanisms

Tumorigenesis can be considered as pathologically misappropriated tissue regeneration. In this review we will address some unresolved issues that support this concept. First, we will address the issue of the identity of cancer-initiating cells and the presence of cancer stem cells in growing tumors. We will also ask are there rare and distinct populations of cancer stem cells in established tumor cell lines, or are all of the cells cancer stem cells? Second, the most important clinical problem with cancer is its metastasis, and here a challenging question arises: by employing radio-chemotherapy for tumor treatment, do we unintentionally create a prometastatic microenvironment in collateral organs? Specifically, many factors upregulated in response to radio-chemotherapy-induced injury may attract highly migratory cancer cells that survived initial treatment. Third, what is the contribution of normal circulating stem cells to the growing malignancy? Do circulating normal stem cells recognize a tumor as a hypoxia-damaged tissue that needs vascular and stromal support and thereby contribute to tumor expansion? Fourth, is it reasonable to inhibit only one prometastatic ligand-receptor axis when cancer stem cells express several receptors for several chemotactic factors that may compensate for inhibition of the targeted receptor? Fifth, since most aggressive cancer cells mimic early-development stem cells, which properties of embryonic stem cells are retained in cancer cells? Would it be reasonable to inhibit cancer cell signaling pathways involved in the migration and proliferation of embryonic stem cells? We will also briefly address some new players in cancerogenesis, including extracellular microvesicles, bioactive phospholipids, and extracellular nucleotides.

Co-expression of Piwil2/Piwil4 in nucleus indicates poor prognosis of hepatocellular carcinoma

Purpose

This study aimed to explore the localization and expression of P-element-induced wimpy testis-like 2 (piwil2)/Piwil4 in hepatocellular carcinoma (HCC) tissues, and analyze the correlation between co-expression pattern and prognosis of HCC.

Results

Piwil2 showed 100% positive expression in the cell nucleus, with the intensity higher than in the cytoplasm. Piwil4 showed a lower intensity of expression in the cell nucleus than in the cytoplasm. The molecular chaperone Piwil2/Piwil4 had four co-expression patterns: nuclear co-expression, nuclear and cytoplasmic co-expression, cytoplasmic co-expression, and non-coexpression. The survival rate and the overall survival sequentially increased. The prognostic phenotype of the nuclear co-expression of Piwil2/Piwil4 was worse than that of non-coexpression, and the intracellular localization and expression of Piwil2 and Piwil4 were not significantly different.

Methods

HCC pathological tissue samples with follow-up information (90 cases) and 2 normal control liver tissues were collected and made into a 92-site microarray. The expression of Piwil2 and Piwil4 was detected using the immunofluorescence double staining method. The differences in the expression and location of Piwil2 and Piwil4 in tumor cells were explored, and the influence of such differences on the long-term survival rate of HCC was studied using Kaplan-Meier survival curve and log-rank test. The clinical staging was analyzed according to the HCC international TNM staging criteria.

Conclusions

The nuclear co-expression of Piwil2/Piwil4 indicated that patients with HCC had a worse prognostic phenotype. The molecular chaperone Piwil2/Piwil4 seems promising as a molecular marker for prognosis judgment; a single marker (Piwil2/Piwil4) cannot be used for prognosis judgment.

The effect of long-term lithium treatment of bipolar disorder on stem cells circulating in peripheral blood

OBJECTIVES

To investigate the effect of long-term lithium treatment on very small embryonic-like stem cells (VSELs), haematopoietic stem cells (HSCs), mesenchymal stem cells (MSCs) and endothelial progenitor cells (EPCs) circulating in peripheral blood (PB), in bipolar disorder (BD).

METHODS

The study included 15 BD patients (aged 55 ± 6 years) treated with lithium for 8-40 years (mean 16 years), 15 BD patients (aged 53 ± 7 years) with duration of illness >10 years, who had never received lithium, and 15 healthy controls (aged 50 ± 5 years). The VSELs, HSCs, MSCs and EPCs were measured by flow cytometric analysis.

RESULTS

In BD subjects not taking lithium the number of CD34⁺VSELs was significantly higher, and MSCs and EPCs numerically higher, than in control subjects and the number of CD34⁺VSELs correlated with the duration of illness. In lithium-treated patients these values were similar to controls and the number of CD34⁺VSELs correlated negatively with the duration of lithium treatment and serum lithium concentration.

CONCLUSIONS

Long-term treatment with lithium may suppress the activation of regenerative processes by reducing the number of VSELs circulating in PB. These cells, in BD patients not treated with lithium, may provide a new potential biological marker of the illness and its clinical progress.

Pituitary sex hormones enhance the pro‑metastatic potential of human lung cancer cells by downregulating the intracellular expression of heme oxygenase‑1

We report that human lung cancer cell lines express functional receptors for pituitary sex hormones (SexHs) and respond to stimulation by follicle‑stimulating hormone (FSH), luteinizing hormone (LH), and prolactin (PRL). Expression of these receptors has also been confirmed in patient lung cancer samples at the mRNA level. Stimulation of human lung cancer cell lines with FSH, LH, or PRL stimulated migration and chemotaxis, and some cell lines responded by enhanced proliferation. Moreover, priming of human lung cancer cells by exposing them to pituitary SexHs resulted in enhanced seeding efficiency of injected human lung cancer cells into bone marrow, liver, and lungs in an immunodeficient mouse model. The chemotaxis of lung cancer cell lines corresponded with the activity of heme oxygenase‑1 (HO‑1), as stimulation of these cells by FSH, LH, and PRL downregulated its expression in a p38 MAPK‑dependent manner. Moreover, while downregulation of HO‑1 by the small‑molecule inhibitor tin protoporphyrin (SnPP) promoted migration, upregulation of HO‑1 by the small‑molecule activator cobalt protoporphyrin (CoPP) showed the opposite effect. Based on this finding, we propose that pituitary SexHs play a significant role in the pathogenesis of lung cancer, particularly when the blood level of FSH increases due to gonadal dysfunction with advanced age. Finally, we propose that upregulation of HO‑1 expression by a small‑molecule activator may be effective in controlling SexH‑induced cell migration in lung cancer.

Differentiation of bone marrow-derived stage-specific embryonic antigen 1 positive pluripotent stem cells into male germ cells

Studies published in recent years have changed the outlook on sterility and germ cell development by producing gametes from stem cells. In present study, a novel approach on differentiation of bone marrow-derived stage-specific embryonic antigen 1 positive (SSEA-1⁺ ) pluripotent stem cells into male germ cells has been addressed. SSEA-1⁺ stem cells were separated from murine bone marrow using magnetic-activated cell sorting (MACS) system and propagated on a feeder layer cells. To evaluate the pluripotency characteristic of the purified cells, they were differentiated toward cells of three germ layers. Later the SSEA-1⁺ stem cells were induced to differentiate along male germ cell lineage with retinoic acid. Flowcytometric analysis of SSEA-1⁺ stem cells revealed purity of about 62% which increased to 91% after cultivation over feeder cells. Expression of specific transcripts of Oct4, SSEA-1, Nanog, Dppa3, fragilis, Rex-1, SOX-2, and alkaline-phosphatase and immunofluorescence evaluation of Oct4 and SSEA-1 expression showed the differentiation of purified stem cells toward the cells of three germ layers. Differentiation potential of purified cells was positively evidenced by expression markers specific for primordial germ cells, spermatogonial stem cells and spermatogonia including Mvh, fragilis, Dppa3, Stra8, DAZL, Piwil2, β1, and α6-integrins as well as meiotic-specific marker SYCP3. Our results showed that SSEA-1⁺ pluripotent stem cells are able to differentiate into male germ cells. The results of the present study are encouraging enough to merit further investigation, provide a new hope for those suffering from infertility and introduce a novel platform for research on germ cell development.

Does it make sense to target one tumor cell chemotactic factor or its receptor when several chemotactic axes are involved in metastasis of the same cancer?

The major problem with cancer progression and anti-cancer therapy is the inherent ability of cancer cells to migrate and establish distant metastases. This ability to metastasize correlates with the presence in a growing tumor of cells with a more malignant phenotype, which express certain cancer stem cell markers. The propensity of malignant cells to migrate and their resistance to radio-chemotherapy somewhat mimics the properties of normal developmentally early stem cells that migrate during organogenesis in the developing embryo. In the past, several factors, including cell migration-promoting cytokines, chemokines, growth factors, bioactive lipids, extracellular nucleotides, and even H(+) ions, were found to influence the metastasis of cancer cells. This plethora of pro-migratory factors demonstrates the existence of significant redundancy in the chemoattractants for cancer cells. In spite of this obvious fact, significant research effort has been dedicated to demonstrating the crucial involvement of particular pro-metastatic factor-receptor axes and the development of new drugs targeting one receptor or one chemoattractant. Based on our own experience working with a model of metastatic rhabdomyosarcoma as well as the work of others, in this review we conclude that targeting a single receptor-ligand pro-metastatic axis will not effectively prevent metastasis and that we should seek other more effective therapeutic options.

Endogenous, very small embryonic-like stem cells: critical review, therapeutic potential and a look ahead

BACKGROUND

Both pluripotent very small embryonic-like stem cells (VSELs) and induced pluripotent stem (iPS) cells were reported in 2006. In 2012, a Nobel Prize was awarded for iPS technology whereas even today the very existence of VSELs is not well accepted. The underlying reason is that VSELs exist in low numbers, remain dormant under homeostatic conditions, are very small in size and do not pellet down at 250-280g. The VSELs maintain life-long tissue homeostasis, serve as a backup pool for adult stem cells and are mobilized under stress conditions. An imbalance in VSELs function (uncontrolled proliferation) may result in cancer.

SEARCH METHODS

The electronic database 'Medline/Pubmed' was systematically searched with the subject heading term 'very small embryonic-like stem cells'.

OBJECTIVE AND RATIONALE

The most primitive stem cells that undergo asymmetric cell divisions to self-renew and give rise to progenitors still remain elusive in the hematopoietic system and testes, while the presence of stem cells in ovary is still being debated. We propose to review the available literature on VSELs, the methods of their isolation and characterization, their ontogeny, how they compare with embryonic stem (ES) cells, primordial germ cells (PGCs) and iPS cells, and their role in maintaining tissue homeostasis. The review includes a look ahead on how VSELs will result in paradigm shifts in basic reproductive biology.

OUTCOMES

Adult tissue-specific stem cells including hematopoietic, spermatogonial, ovarian and mesenchymal stem cells have good proliferation potential and are indeed committed progenitors (with cytoplasmic OCT-4), which arise by asymmetric cell divisions of pluripotent VSELs (with nuclear OCT-4). VSELs are the most primitive stem cells and postulated to be an overlapping population with the PGCs. Rather than migrating only to the gonads, PGCs migrate and survive in various adult body organs throughout life as VSELs. VSELs express both pluripotent and PGC-specific markers and are epigenetically and developmentally more mature compared with ES cells obtained from the inner cell mass of a blastocyst-stage embryo. As a result, VSELs readily differentiate into three embryonic germ layers and spontaneously give rise to both sperm and oocytes in vitro. Like PGCs, VSELs do not divide readily in culture, nor produce teratoma or integrate in the developing embryo. But this property of being relatively quiescent allows endogenous VSELs to survive various kinds of toxic insults. VSELs that survive oncotherapy can be targeted to induce endogenous regeneration of non-functional gonads. Transplanting healthy niche (mesenchymal) cells have resulted in improved gonadal function and live births.

WIDER IMPLICATIONS

Being quiescent, VSELs possibly do not accumulate genomic (nuclear or mitochondrial) mutations and thus may be ideal endogenous, pluripotent stem cell candidates for regenerative and reproductive medicine. The presence of VSELs in adult gonads and the fact that they survive oncotherapy may obviate the need to bank gonadal tissue for fertility preservation prior to oncotherapy. VSELs and their ability to undergo spermatogenesis/neo-oogenesis in the presence of a healthy niche will help identify newer strategies toward fertility restoration in cancer survivors, delaying menopause and also enabling aged mothers to have better quality eggs.

Expression of Cancer Testis Antigens in Colorectal Cancer: New Prognostic and Therapeutic Implications

Background. While cancer/testis antigens (CTAs) are restricted in postnatal tissues to testes and germ line-derived cells, their role in cancer development and the clinical significance of their expression still remain to be better defined. Objective. The aim of this study was to investigate the level of CTA expression in colon samples from patients with colorectal cancer (CRC) in relation to patient clinical status. Methods. Forty-five patients with newly diagnosed colorectal cancer were included in the study. We selected a panel of 18 CTAs that were previously detected in CRC as well as some new gene candidates, and their expression was detected at the mRNA level by employing RQ-PCR. Additionally, we evaluated CTA expression in three colon cancer cell lines (CL-188, HTB-39, and HTB-37) after exposure to the DNA methylation-modifying drug 5-azacytidine. Results. We report that 6 out of 18 (33%) CTAs tested (MAGEA3, OIP5, TTK, PLU1, DKKL1, and FBXO39) were significantly (p < 0.05) overexpressed in tumor tissue compared with healthy colon samples isolated from the same patients. Conclusions. Moreover, we found that MAGEA3, PLU-1, and DKKL expression positively correlated with disease progression, evaluated according to the Dukes staging system. Finally, 5-azacytidine exposure significantly upregulated expression of CTAs on CRC cells, which indicates that this demethylation agent could be employed therapeutically to enhance the immune response against tumor cells.

Vitamin D3 stimulates embryonic stem cells but inhibits migration and growth of ovarian cancer and teratocarcinoma cell lines

BACKGROUND

Deficiency in Vitamin D3 (cholecalciferol) may predispose to some malignancies, including gonadal tumors and in experimental models vitamin D3 has been proven to inhibit the growth of cancer cells. To learn more about the potential role of vitamin D3 in cancerogenesis, we evaluated the expression and functionality of the vitamin D receptor (VDR) and its role in metastasis of ovarian cancer cells and of murine and human teratocarcinoma cell lines.

METHODS

In our studies we employed murine embrynic stem cells (ESD3), murine (P19) and human (NTERA-2) teratocarcimona cells lines, human ovarian cancer cells (A2780) as well as purified murine and human purified very small embryonic like stem cells (VSELs). We evaluated expression of Vitamin D3 receptor (VDR) in these cells as well as effect of vitamin D3 exposure on cell proliferation and migration.

RESULTS

We here provide also more evidence for the role of vitamin D3 in germline-derived malignancies, and this evidence supports the proposal that vitamin D3 treatment inhibits growth and metastatic potential of several germline-derived malignancies. We also found that the ESD3 murine immortalized embryonic stem cell line and normal, pluripotent, germline-marker-positive very small embryonic-like stem cells (VSELs) isolated from adult tissues are stimulated by vitamin D3, which suggests that vitamin D3 affects the earliest stages of embryogenesis.

CONCLUSIONS

We found that however all normal and malignant germ-line derived cells express functional VDR, Vitamin D3 differently affects their proliferation and migration. We postulate that while Vitamin D3 as anticancer drug inhibits proliferation of malignant cells, it may protect normal stem cells that play an important role in development and tissue/organ regeneration.

Making gametes from pluripotent stem cells--a promising role for very small embryonic-like stem cells

The urge to have one's own biological child supersedes any desire in life. Several options have been used to obtain gametes including pluripotent stem cells (embryonic ES and induced pluripotent iPS stem cells); gonadal stem cells (spermatogonial SSCs, ovarian OSCs stem cells), bone marrow, mesenchymal cells and fetal skin. However, the field poses a huge challenge including inefficient existing protocols for differentiation, epigenetic and genetic changes associated with extensive in vitro manipulation and also ethical/regulatory constraints. A tremendous leap in the field occurred using mouse ES and iPS cells wherein they were first differentiated into epiblast-like cells and then primordial germ cell-like cells. These on further development produced sperm, oocytes and live offspring (had associated genetic problems). Evidently differentiating pluripotent stem cells into primordial germ cells (PGCs) remains a major bottleneck. Against this backdrop, we propose that a novel population of pluripotent stem cells termed very small embryonic-like stem cells (VSELs) may serve as an alternative, potential source of autologus gametes, keeping in mind that they are indeed PGCs surviving in adult mammalian ovaries and testes. Both VSELs and PGCs are pluripotent, relatively quiescent because of epigenetic modifications of parentally imprinted genes loci like Igf2-H19 and KCNQ1p57, share several markers like Stella, Fragilis, Mvh, Dppa2, Dppa4, Sall4, Blimp1 and functional receptors. VSELs are localized in the basement membrane of seminiferous tubules in testis and in the ovary surface epithelium. Ovarian stem cells from mouse, rabbit, sheep, marmoset and humans (menopausal women and those with premature ovarian failure) spontaneously differentiate into oocyte-like structures in vitro with no additional requirement of growth factors. Thus a more pragmatic option to obtain autologus gametes may be the pluripotent VSELs and if we could manipulate them in vivo - existing ethical and epigenetic/genetic concerns associated with in vitro culture may also be minimized. The field of oncofertility may undergo a sea-change and existing strategies of cryopreservation of gametes and gonadal tissue for fertility preservation in cancer patients will necessitate a revision. However, first the scientific community needs to arrive at a consensus about VSELs in the gonads and then work towards exploiting their potential.

Very small embryonic-like stem cells as a novel developmental concept and the hierarchy of the stem cell compartment

Our current understanding of stem cells suffers from a lack of precision, as the stem cell compartment is a broad continuum between early stages of development and adult postnatal tissues, and it is not fully understood how this transition occurs. The definition of stem cell pluripotency is adapted from embryology and excludes the possibility that some early-development stem cells with pluri- and/or multipotential differentiation potential may reside in postnatal tissues in a dormant state in which they are protected from uncontrolled proliferation and thus do not form teratomas or have the ability to complement blastocyst development. We will discuss the concept that a population of very small embryonic-like stem cells (VSELs) could be a link between early-development stages and adult stem cell compartments and reside in a quiescent state in adult tissues. The epigenetic mechanism identified that changes expression of certain genes involved in insulin/insulin-like growth factor signaling (IIS) in VSELs, on the one hand, keeps these cells quiescent in adult tissues and, on the other hand, provides a novel view of the stem cell compartment, IIS, tissue/organ rejuvenation, aging, and cancerogenesis.

Expression of the erythropoietin receptor by germline-derived cells - further support for a potential developmental link between the germline and hematopoiesis

BACKGROUND

Expressing several markers of migrating primordial germ cells (PGCs), the rare population of quiescent, bone marrow (BM)-residing very small embryonic-like stem cells (VSELs) can be specified like PGCs into hematopoietic stem/progenitor cells (HSPCs). These two properties of VSELs support the possibility of a developmental origin of HSPCs from migrating PGCs.

METHODS

To address a potential link between VSELs and germ line cells we analyzed by RT-PCR and FACS expression of erythropoietin receptor (EpoR) on murine bone marrow- and human umbilical cord blood-derived VSELs, murine and human teratocarcinoma cell lines and human ovarian cancer cells. A proper gating strategy and immunostaining excluded from FACS analysis potential contamination by erythroblasts. Furthermore, the transwell chemotaxis assays as well as adhesion and signaling studies were performed to demonstrate functionality of erythropoietin - EpoR axes on these cells.

RESULTS

We report here that murine and human VSELs as well as murine and human teratocarcinoma cell lines and ovarian cancer cell lines share a functional EpoR.

CONCLUSIONS

Our data provide more evidence of a potential developmental link between germline cells, VSELs, and HSCs and sheds more light on the developmental hierarchy of the stem cell compartment in adult tissues.

Very small embryonic-like stem cells (VSELs) represent a real challenge in stem cell biology: recent pros and cons in the midst of a lively debate

The concept that adult tissue, including bone marrow (BM), contains early-development cells with broader differentiation potential has again been recently challenged. In response, we would like to review the accumulated evidence from several independent laboratories that adult tissues, including BM, harbor a population of very rare stem cells that may cross germ layers in their differentiation potential. Thus, the BM stem cell compartment hierarchy needs to be revisited. These dormant, early-development cells that our group described as very small embryonic-like stem cells (VSELs) most likely overlap with similar populations of stem cells that have been identified in adult tissues by other investigators as the result of various experimental strategies and have been given various names. As reported, murine VSELs have some pluripotent stem cell characteristics. Moreover, they display several epiblast/germline markers that suggest their embryonic origin and developmental deposition in adult BM. Moreover, at the molecular level, changes in expression of parentally imprinted genes (for example, Igf2-H19) and resistance to insulin/insulin-like growth factor signaling (IIS) regulates their quiescent state in adult tissues. In several emergency situations related to organ damage, VSELs can be activated and mobilized into peripheral blood, and in appropriate animal models they contribute to tissue organ/regeneration. Interestingly, their number correlates with lifespan in mice, and they may also be involved in some malignancies. VSELs have been successfully isolated in several laboratories; however, some investigators experience problems with their isolation.

An intensified systemic trafficking of bone marrow-derived stem/progenitor cells in patients with pancreatic cancer

Various experimental studies indicate potential involvement of bone marrow (BM)-derived stem cells (SCs) in malignancy development and progression. In this study, we comprehensively analysed systemic trafficking of various populations of BM-derived SCs (BMSCs), i.e., mesenchymal, haematopoietic, endothelial stem/progenitor cells (MSCs, HSCs, EPCs respectively), and of recently discovered population of very small embryonic/epiblast-like SCs (VSELs) in pancreatic cancer patients. Circulating CD133⁺/Lin⁻/CD45⁻/CD34⁺ cells enriched for HSCs, CD105⁺/STRO-1⁺/CD45⁻ cells enriched for MSCs, CD34⁺/KDR⁺/CD31⁺/CD45⁻ cells enriched for EPCs and small CXCR4⁺CD34⁺CD133⁺ subsets of Lin⁻CD45⁻ cells that correspond to VSELs were enumerated and sorted from blood samples derived from 29 patients with pancreatic cancer, and 19 healthy controls. In addition, plasma levels of stromal-derived factor-1 (SDF-1), growth/inhibitory factors and sphingosine-1-phosphate (S1P; chemoattractants for SCs), as well as, of complement cascade (CC) molecules (C3a, C5a and C5b-9/membrane attack complex – MAC) were measured. Higher numbers of circulating VSELs and MSCs were detected in pancreatic cancer patients (P < 0.05 and 0.01 respectively). This trafficking of BMSCs was associated with significantly elevated C5a (P < 0.05) and C5b-9/MAC (P < 0.005) levels together with S1P concentrations detected in plasma of cancer patients, and seemed to be executed in a SDF-1 independent manner. In conclusion, we demonstrated that in patients with pancreatic cancer, intensified peripheral trafficking of selected populations of BMSCs occurs. This phenomenon seems to correlate with systemic activation of the CC, hepatocyte growth factor and S1P levels. In contrast to previous studies, we demonstrate herein that systemic SDF-1 levels do not seem to be linked with increased mobilization of stem cells in patients with pancreatic cancer.

Parental imprinting regulates insulin-like growth factor signaling: a Rosetta Stone for understanding the biology of pluripotent stem cells, aging and cancerogenesis

In recent years, solid evidence has accumulated that insulin-like growth factor-1 (IGF-1) and 2 (IGF-2) regulate many biological processes in normal and malignant cells. Recently, more light has been shed on the epigenetic mechanisms regulating expression of genes involved in IGF signaling (IFS) and it has become evident that these mechanisms are crucial for initiation of embryogenesis, maintaining the quiescence of pluripotent stem cells deposited in adult tissues (for example, very-small embryonic-like stem cells), the aging process, and the malignant transformation of cells. The expression of several genes involved in IFS is regulated at the epigenetic level by imprinting/methylation within differentially methylated regions (DMRs), which regulate their expression from paternal or maternal chromosomes. The most important role in the regulation of IFS gene expression is played by the Igf-2-H19 locus, which encodes the autocrine/paracrine mitogen IGF-2 and the H19 gene, which gives rise to a non-coding RNA precursor of several microRNAs that negatively affect cell proliferation. Among these, miR-675 has recently been demonstrated to downregulate expression of the IGF-1 receptor. The proper imprinting of DMRs at the Igf-2-H19 locus, with methylation of the paternal chromosome and a lack of methylation on the maternal chromosome, regulates expression of these genes so that Igf-2 is transcribed only from the paternal chromosome and H19 (including miR-675) only from the maternal chromosome. In this review, we will discuss the relevance of (i) proper somatic imprinting, (ii) erasure of imprinting and (iii) loss of imprinting within the DMRs at the Igf-2-H19 locus to the expression of genes involved in IFS, and the consequences of these alternative patterns of imprinting for stem cell biology.

The negative effect of prolonged somatotrophic/insulin signaling on an adult bone marrow-residing population of pluripotent very small embryonic-like stem cells (VSELs)

It is well known that attenuated insulin/insulin-like growth factor signaling (IIS) has a positive effect on longevity in several animal species, including mice. Here, we demonstrate that a population of murine pluripotent very small embryonic-like stem cells (VSELs) that reside in bone marrow (BM) is protected from premature depletion during aging by intrinsic parental gene imprinting mechanisms and the level of circulating insulin-like growth factor-I (IGF-I). Accordingly, an increase in the circulating level of IGF-I, as seen in short-lived bovine growth hormone (bGH)-expressing transgenic mice, which age prematurely, as well as in wild-type animals injected for 2 months with bGH, leads to accelerated depletion of VSELs from bone marrow (BM). In contrast, long-living GHR-null or Ames dwarf mice, which have very low levels of circulating IGF-I, exhibit a significantly higher number of VSELs in BM than their littermates at the same age. However, the number of VSELs in these animals decreases after GH or IGF-I treatment. These changes in the level of plasma-circulating IGF-I corroborate with changes in the genomic imprinting status of crucial genes involved in IIS, such as Igf-2-H19, RasGRF1, and Ig2R. Thus, we propose that a chronic increase in IIS contributes to aging by premature depletion of pluripotent VSELs in adult tissues.

High male chimerism in the female breast shows quantitative links with cancer

Clinical observations suggest that pregnancy provides protection against cancer. The mechanisms involved, however, remain unclear. Fetal cells are known to enter the mother's circulation during pregnancy and establish microchimerism. We investigated if pregnancy-related embryonic/fetal stem cell integration plays a role in breast cancer. A high-sensitivity Y-chromosome assay was developed to trace male allogeneic cells (from male fetus) in females. Fixed-embedded samples (n = 206) from both normal and breast cancer patients were screened for microchimerism. The results were combined with matching clinicopathological and histological parameters and processed statistically. The results show that in our samples (182 informative) more than half of healthy women (56%) carried male cells in their breast tissue for decades (n = 68), while only one out of five in the cancer sample pool (21%) (n = 114) (odds ratio = 4.75, CI at 95% 2.34-9.69; p = 0.0001). The data support the notion that a biological link may exist between chimerism and tissue-integrity. The correlation, however, is non-linear, since male microchimerism in excess ("hyperchimerism") is also involved in cancer. The data suggest a link between hyperchimerism and HER2-type cancers, while decreased chimerism ("hypochimerism") associates with ER/PR-positive (luminal-type) breast cancers. Chimerism levels that correlate with protection appear to be non-random and share densities with the mammary progenitor components of the stem cell lineage in the breast. The results suggest that protection may involve stem/progenitor level interactions and implicate novel quantitative mechanisms in chimerism biology.

Very small embryonic-like stem cells: implications in reproductive biology

The most primitive germ cells in adult mammalian testis are the spermatogonial stem cells (SSCs) whereas primordial follicles (PFs) are considered the fundamental functional unit in ovary. However, this central dogma has recently been modified with the identification of a novel population of very small embryonic-like stem cells (VSELs) in the adult mammalian gonads. These stem cells are more primitive to SSCs and are also implicated during postnatal ovarian neo-oogenesis and primordial follicle assembly. VSELs are pluripotent in nature and characterized by nuclear Oct-4A, cell surface SSEA-4, and other pluripotent markers like Nanog, Sox2, and TERT. VSELs are considered to be the descendants of epiblast stem cells and possibly the primordial germ cells that persist into adulthood and undergo asymmetric cell division to replenish the gonadal germ cells throughout life. Elucidation of their role during infertility, endometrial repair, superovulation, and pathogenesis of various reproductive diseases like PCOS, endometriosis, cancer, and so on needs to be addressed. Hence, a detailed review of current understanding of VSEL biology is pertinent, which will hopefully open up new avenues for research to better understand various reproductive processes and cancers. It will also be relevant for future regenerative medicine, translational research, and clinical applications in human reproduction.

Gonadotropin treatment augments postnatal oogenesis and primordial follicle assembly in adult mouse ovaries?

BACKGROUND

Follicle stimulating hormone (FSH) exerts action on both germline and somatic compartment in both ovary and testis although FSH receptors (FSHR) are localized only on the somatic cells namely granulosa cells of growing follicles and Sertoli cells in the seminiferous tubules. High levels of FSH in females are associated with poor ovarian reserve, ovarian hyper stimulation syndrome etc. and at the same time FSH acts as a survival factor during in vitro organotypic culture of ovarian cortical strips. Thus a further understanding of FSH action on the ovary is essential. We have earlier reported presence of pluripotent very small embryonic-like stem cells (VSELs express Oct-4A in addition to other pluripotent markers) and their immediate descendants 'progenitors' ovarian germ stem cells (OGSCs express Oct-4B in addition to other germ cell markers) in ovarian surface epithelium (OSE) in various mammalian species including mice, rabbit, monkey, sheep and human. Present study was undertaken to investigate the effect of pregnant mare serum gonadotropin (PMSG) on adult mice ovaries with a focus on VSELs, OGSCs, postnatal oogenesis and primordial follicle assembly.

METHODS

Ovaries were collected from adult mice during different stages of estrus cycle and after 2 and 7 days of PMSG (5 IU) treatment to study histo-architecture and expression for FSHR, pluripotent stem cells , meiosis and germ cell specific markers.

RESULTS

PMSG treatment resulted in increased FSHR and proliferation as indicated by increased FSHR and PCNA immunostaining in OSE and oocytes of primordial follicles (PF) besides the granulosa cells of large antral follicles. Small 1-2 regions of multilayered OSE invariably associated with a cohort of PF during estrus stage in control ovary were increased to 5-8 regions after PMSG treatment. This was associated with an increase in pluripotent transcripts (Oct-4A, Nanog), meiosis (Scp-3) and germ cells (Oct-4B, Mvh) specific markers. MVH showed positive immuno staining on germ cell nest-like clusters and at places primordial follicles appeared connected through oocytes.

CONCLUSIONS

The results of the present study show that gonadotropin (PMSG) treatment to adult mouse leads to increased pluripotent stem cell activity in the ovaries, associated with increased meiosis, appearance of several cohorts of PF and their assembly in close proximity of OSE. This was found associated with the presence of germ cell nests and cytoplasmic continuity of oocytes in PF. We have earlier reported that pluripotent ovarian stem cells in the adult mammalian ovary are the VSELs which give rise to slightly differentiated OGSCs. Thus we propose that gonadotropin through its action on pluripotent VSELs augments neo-oogenesis and PF assembly in adult mouse ovaries.

Adult murine bone marrow-derived very small embryonic-like stem cells differentiate into the hematopoietic lineage after coculture over OP9 stromal cells

OBJECTIVE

We recently identified a population of small Sca-1(+)/Lin(-)/CD45(-) cells in adult murine bone marrow that express several epiblast/germ line and pluripotent stem cell markers (e.g., Oct-4 and SSEA-4) that we named "very small embryonic-like stem cells" (VSELs). In this report, we test the hypothesis that VSELs can differentiate along the hemato/lymphopoietic lineage.

MATERIALS AND METHODS

Purified from bone marrow, VSELs were primed/cocultured over OP9 stroma cell line and subsequently tested in vitro and in vivo assays for their hematopoietic potential. In parallel, cells derived from VSELs were evaluated for expression of hematopoietic genes and surface markers.

RESULTS

Although we observed that freshly isolated VSELs do not exhibit in vitro and in vivo hematopoietic potential, they may, after coculture over OP9 stromal cells, differentiate along the hematopoietic lineage in a similar way as embryonic stem cells or inducible pluripotent stem cells. "OP9-primed," VSEL-derived cells acquired expression of several hemato/lymphopoiesis-specific genes and markers, gave rise to hematopoietic colonies in vitro, and protected lethally irradiated mice in both primary and secondary transplant models on transplantation. We also observed that, compared to hematopoietic stem/progenitor cells, VSELs are highly resistant to total body irradiation.

CONCLUSIONS

Based on these observations, we postulate that VSELs are the most primitive murine bone marrow-residing population of stem cells that have the potential to become specified into the hematopoietic lineage and may share some of the characteristics of long-term repopulating HSCs.

A novel insight into aging: are there pluripotent very small embryonic-like stem cells (VSELs) in adult tissues overtime depleted in an Igf-1-dependent manner?

Tissue and organ rejuvenation and senescence/aging are closely related to the function of stem cells. Recently, we demonstrated that a population of pluripotent Oct-4+ SSEA-1+Sca-1+Lin-CD45- very small embryonic-like stem cells (VSELs) resides in the adult murine bone marrow (BM) and other murine tissues. We hypothesize that these pluripotent stem cells play an important role in tissue/organ rejuvenation, and have demonstrated that their proliferation and potentially premature depletion is negatively controlled by epigenetic changes of some imprinted genes that regulate insulin factor signaling (Igf2-H19 locus, Igf2R and RasGRF1). Since the attenuation of insulin/insulin growth factor (Ins/Igf) signaling positively correlates with longevity, we propose, based on our experimental data, that gradual decrease in the number of VSELs deposited in adult tissues, which occurs throughout life in an Ins/Igf signaling-dependent manner is an important mechanism of aging. In contrast, a decrease in Ins/Igf stimulation of VSELs that extends the half life of these cells in adult organs would have a beneficial effect on life span. Our preliminary data in long-living Igf-1-signaling-deficient mice show that these animals possess a 3-4 times higher number of VSELs deposited in adult BM, lending support to this novel hypothesis.

Epiblast/germ line hypothesis of cancer development revisited: lesson from the presence of Oct-4+ cells in adult tissues

The morphology of several tumors mimics developmentally early tissues; tumors often express early developmental markers characteristic for the germ line lineage. Recently, our group identified a population of very small stem cells (SCs) in murine bone marrow (BM) and other adult organs that express several markers characteristic for epiblast/germ line-derived SCs. We named these rare cells "Very Small Embryonic/Epiblast-like Stem Cells (VSELs)." We hypothesized that these cells that express both epiblast and germ line markers are deposited during early gastrulation in developing tissues and organs and play an important role in the turnover of tissue-committed (TC) SCs. To support this, we envision that the germ line is not only the origin of SCs, but also remains as a scaffold or back-up for the SC compartment in adult life. Furthermore, we noticed that VSELs are protected from uncontrolled proliferation and teratoma formation by a unique DNA methylation pattern in some developmentally crucial imprinted genes, which show hypomethylation or erasure of imprints in paternally methylated genes and hypermethylation of imprints in the maternally methylated. In pathological situations, however, we hypothesize that VSELs could be involved in the development of several malignancies. Therefore, potential involvement of VSELs in cancerogenesis could support century-old concepts of embryonic rest- or germ line-origin hypotheses of cancer development. However, we are aware that this working hypothesis requires further direct experimental confirmation.