Bone marrow Schwann cells induce hematopoietic stem cell hibernation

How the bone microenvironment shapes the pre-metastatic niche and metastasis

The bone is a frequent metastatic site, with changes in the mineralized bone and the bone marrow milieu that can also prime other sites for metastasis by educating progenitor cells to support metastatic spread. Stromal and immune populations cooperatively maintain the organizationally complex bone niches and are dysregulated in the presence of a distant primary tumor and metastatic disease. Interrogating the bone niches that facilitate metastatic spread using innovative technologies holds the potential to aid in preventing metastasis in and mediated by the bone. Here, we review recent advances in bone niche biology and its adaptations in the context of cancer.

Schwann Cells as Orchestrators of Nerve Repair: Implications for Tissue Regeneration and Pathologies

Peripheral nerves exist in a stable state in adulthood providing a rapid bidirectional signaling system to control tissue structure and function. However, following injury, peripheral nerves can regenerate much more effectively than those of the central nervous system (CNS). This multicellular process is coordinated by peripheral glia, in particular Schwann cells, which have multiple roles in stimulating and nurturing the regrowth of damaged axons back to their targets. Aside from the repair of damaged nerves themselves, nerve regenerative processes have been linked to the repair of other tissues and de novo innervation appears important in establishing an environment conducive for the development and spread of tumors. In contrast, defects in these processes are linked to neuropathies, aging, and pain. In this review, we focus on the role of peripheral glia, especially Schwann cells, in multiple aspects of nerve regeneration and discuss how these findings may be relevant for pathologies associated with these processes.

Cholangiocarcinoma Malignant Traits Are Promoted by Schwann Cells through TGFβ Signaling in a Model of Perineural Invasion

The term cholangiocarcinoma (CCA) defines a class of epithelial malignancies originating from bile ducts. Although it has been demonstrated that CCA patients with perineural invasion (PNI) have a worse prognosis, the biological features of this phenomenon are yet unclear. Our data show that in human intrahepatic CCA specimens with documented PNI, nerve-infiltrating CCA cells display positivity of the epithelial marker cytokeratin 7, lower with respect to the rest of the tumor mass. In an in vitro 3D model, CCA cells move towards a peripheral nerve explant allowing contact with Schwann cells (SCs) emerging from the nerve. Here, we show that SCs produce soluble factors that favor the migration, invasion, survival and proliferation of CCA cells in vitro. This effect is accompanied by a cadherin switch, suggestive of an epithelial-mesenchymal transition. The influence of SCs in promoting the ability of CCA cells to migrate and invade the extracellular matrix is hampered by a specific TGFβ receptor 1 (TGFBR1) antagonist. Differential proteomic data indicate that the exposure of CCA cells to SC secreted factors induces the upregulation of key oncogenes and the concomitant downregulation of some tumor suppressors. Taken together, these data concur in identifying SCs as possible promoters of a more aggressive CCA phenotype, ascribing a central role to TGFβ signaling in regulating this process.

Ecological insights into hematopoiesis regulation: unraveling the influence of gut microbiota

The gut microbiota constitutes a vast ecological system within the human body, forming a mutually interdependent entity with the host. In recent years, advancements in molecular biology technologies have provided a clearer understanding of the role of the gut microbiota. They not only influence the local immune status and metabolic functions of the host's intestinal tract but also impact the functional transformation of hematopoietic stem cells (HSCs) through the gut-blood axis. In this review, we will discuss the role of the gut microbiota in influencing hematopoiesis. We analyze the interactions between HSCs and other cellular components, with a particular emphasis on the direct functional regulation of HSCs by the gut microbiota and their indirect influence through cellular components in the bone marrow microenvironment. Additionally, we propose potential control targets for signaling pathways triggered by the gut microbiota to regulate hematopoietic function, filling crucial knowledge gaps in the development of this research field.

Lessons from early life: understanding development to expand stem cells and treat cancers

Haematopoietic stem cell (HSC) self-renewal is a process that is essential for the development and homeostasis of the blood system. Self-renewal expansion divisions, which create two daughter HSCs from a single parent HSC, can be harnessed to create large numbers of HSCs for a wide range of cell and gene therapies, but the same process is also a driver of the abnormal expansion of HSCs in diseases such as cancer. Although HSCs are first produced during early embryonic development, the key stage and location where they undergo maximal expansion is in the foetal liver, making this tissue a rich source of data for deciphering the molecules driving HSC self-renewal. Another equally interesting stage occurs post-birth, several weeks after HSCs have migrated to the bone marrow, when HSCs undergo a developmental switch and adopt a more dormant state. Characterising these transition points during development is key, both for understanding the evolution of haematological malignancies and for developing methods to promote HSC expansion. In this Spotlight article, we provide an overview of some of the key insights that studying HSC development have brought to the fields of HSC expansion and translational medicine, many of which set the stage for the next big breakthroughs in the field.

Adult Stem Cells in Hibernation: Future Perspectives of Space Travel

Space traveling is imperative for mankind in the future. Expectedly, hibernation will become an option for space traveler to overcome the endless voyage. With regard to some of the studies pointed out that during hibernation, muscle will undergo atrophy and meantime neurogenesis will reduce, these obstacles were frequently related with stem cell regeneration. Thus, investigation on whether hibernation will lead to dysfunction of stem cell becomes an important issue. By going through four main systems in this article, such as, hematopoietic system, skeletal muscle system, central nervous system and orthopedic system, we are expecting that stem cells regeneration capacity will be affected by hibernation. To date, these researches are majorly the read-out from short term or seasonal hibernating mammals. Proposing and creating a simulated long-term hibernation animal model is turning essential for the further investigation on the effect of longer period of hibernation to human stem cells.

tRNA‑derived small RNAs: A novel class of small RNAs in human hypertrophic scar fibroblasts

tRNA-derived small RNAs (tsRNAs) have been shown to play regulatory roles in many physiological and pathological processes. However, their roles in hypertrophic scars remain unclear. The present study investigated differentially expressed tsRNAs in human hypertrophic scar fibroblasts and normal skin fibroblasts via high-throughput sequencing. Several dysregulated tsRNAs were validated by reverse transcription-quantitative polymerase chain reaction (RT-qPCR). Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment, target prediction, coexpression networks and competing endogenous RNA (ceRNA) networks were evaluated to discover the principal functions of significantly differentially expressed tsRNAs. In total, 67 differentially expressed tsRNAs were detected, of which 27 were upregulated and 40 downregulated in hyper-trophic scar fibroblasts. The GO analysis indicated that the dysregulated tsRNAs are associated with numerous biological functions, including 'nervous system development', 'cell adhesion', 'focal adhesion', 'protein binding', 'angiogenesis' and 'actin binding'. KEGG pathway analysis revealed that the most altered pathways include 'Ras signaling pathway', 'Rap1 signaling pathway' and 'cGMP-PKG signaling pathway'. The target genes of the differentially expressed tsRNAs participate in several signaling pathways important for scar formation. The results of RT-qPCR were consistent with those of sequencing. MicroRNA (miR)-29b-1-5p was identified as a target of tsRNA-23678 and was downregulated in hypertrophic scar fibroblasts, constituting a negative regulatory factor for scar formation. Furthermore, tsRNA-23761 acted as a ceRNA and bound to miR-3135b to regulate the expression of miR-3135b targets, including angiotensin-converting enzyme. Collectively, these findings reveal that tsRNAs are differentially expressed in human hypertrophic scar fibroblasts, and may contribute to the molecular mechanism and treatment of hypertrophic scars.

Schwann cell plasticity-roles in tissue homeostasis, regeneration, and disease

How tissues are maintained over a lifetime and repaired following injury are fundamental questions in biology with a disruption to these processes underlying pathologies such as cancer and degenerative disorders. It is becoming increasingly clear that each tissue has a distinct mechanism to maintain homeostasis and respond to injury utilizing different types of stem/progenitor cell populations depending on the insult and/or with a contribution from more differentiated cells that are able to dedifferentiate to aid tissue regeneration. Peripheral nerves are highly quiescent yet show remarkable regenerative capabilities. Remarkably, there is no evidence for a classical stem cell population, rather all cell-types within the nerve are able to proliferate to produce new nerve tissue. Co-ordinating the regeneration of this tissue are Schwann cells (SCs), the main glial cells of the peripheral nervous system. SCs exist in architecturally stable structures that can persist for the lifetime of an animal, however, they are not postmitotic, in that following injury they are reprogrammed at high efficiency to a progenitor-like state, with these cells acting to orchestrate the nerve regeneration process. During nerve regeneration, SCs show little plasticity, maintaining their identity in the repaired tissue. However, once free of the nerve environment they appear to exhibit increased plasticity with reported roles in the repair of other tissues. In this review, we will discuss the mechanisms underlying the homeostasis and regeneration of peripheral nerves and how reprogrammed progenitor-like SCs have broader roles in the repair of other tissues with implications for pathologies such as cancer.

Adrenergic Modulation of Hematopoiesis

Hematopoiesis produce every day billions of blood cells and takes place in the bone marrow (BM) by the proliferation and differentiation of hematopoietic stem cells (HSC). HSC are found mainly adjacent to the BM vascular sinusoids where endothelial cells and mesenchimal stromal cells promote HSC maintenance by producing a variety of factors. Other cell types that regulate HSC niches include sympathetic nerves, non-myelinating Schwann cells and a variety of mature hematopoietic cells such as macrophages, neutrophils, and megakaryocytes. This review will focus on the role of adrenergic signals, i.e. of catecholamines, in the regulation of the HSC niche. The available evidence is rather controversial possibly due to the fact that adrenergic receptors are expressed by many cellular components of the niche and also by the often neglected observation that catecholamines may be produced and released also by the BM cells themselves. In addition one has to consider that, physiologically, the sympathetic nervous system (SNS) activity follows a circadian rhythmicity as driven by the suprachiasmatic nucleus (SCN) of the hypothalamus but may be also activated by cognitive and non-cognitive environmental stimuli. The adrenergic modulation of hematopoiesis holds a considerable potential for pharmacological therapeutic approaches in a variety of hematopoietic disorders and for HSC transplantation however the complexity of the system demands further studies. Graphical Abstract Sympathetic nerve termini may release NE while mature BM cells may release norepinephrine (NE) and / or epinephrine (E). Both may bind to β-adrenergic receptor (AR) expressed in nestin+MSC in the hematopoietic stem cell (HSC) niche and regulate the physiological trafficking of HSC by modulating the expression of CXCL12 and SCF. Both NE and E may also activate Lin - c-Kit+ Sca-1+ (LKS) cell via another AR. In addition, NE may also signal to α1-AR expressed in pre-B cells which by TGF-β secretion might regulate proliferation of their lymphoid progenitors in an autocrine manner and/or inhibit myeloid progenitors.

How Schwann cells facilitate cancer progression in nerves

Recent studies have demonstrated a critical role for nerves in enabling tumor progression. The association of nerves with cancer cells is well established for a variety of malignant tumors, including pancreatic, prostate and the head and neck cancers. This association is often correlated with poor prognosis. A strong partnership between cancer cells and nerve cells leads to both cancer progression and expansion of the nerve network. This relationship is supported by molecular pathways related to nerve growth and repair. Peripheral nerves form complex tumor microenvironments, which are made of several cell types including Schwann cells. Recent studies have revealed that Schwann cells enable cancer progression by adopting a de-differentiated phenotype, similar to the Schwann cell response to nerve trauma. A detailed understanding of the molecular and cellular mechanisms involved in the regulation of cancer progression by the nerves is essential to design strategies to inhibit tumor progression.

A portable platform for stepwise hematopoiesis from human pluripotent stem cells within PET-reinforced collagen sponges

Various systems for differentiating hematopoietic cells from human pluripotent stem cells (PSCs) have been developed, although none have been fully optimized. In this report, we describe the development of a novel three-dimensional system for differentiating hematopoietic cells from PSCs using collagen sponges (CSs) reinforced with poly(ethylene terephthalate) fibers as a scaffold. PSCs seeded onto CSs were differentiated in a stepwise manner with appropriate cytokines under serum-free and feeder-free conditions. This process yielded several lineages of floating hematopoietic cells repeatedly for more than 1 month. On immunohistochemical staining, we detected CD34+ cells and CD45+ cells in the surface and cavities of the CS. Taking advantage of the portability of this system, we were able to culture multiple CSs together floating in medium, making it possible to harvest large numbers of hematopoietic cells repeatedly. Given these findings, we suggest that this novel three-dimensional culture system may be useful in the large-scale culture of PSC-derived hematopoietic cells.

Prospective isolation of resident adult human mesenchymal stem cell population from multiple organs

Mesenchymal stem/stromal cells (MSCs) have the potential to form colonies in culture and reside in adult tissues. Because MSCs have been defined using cells cultured in vitro, discrepancies have arisen between studies concerning their properties. There are also differences between populations obtained using different isolation methods. This review article focuses on recent developments in the identification of novel MSC markers for the in vivo localization and prospective isolation of human MSCs. The prospective isolation method described in this study represents an important strategy for the isolation of MSCs in a short period of time, and may find applications for regenerative medicine. Purified MSCs can be tailored according to their intended clinical therapeutic applications. Lineage tracing methods define the MSC phenotype and can be used to investigate the physiological roles of MSCs in vivo. These findings may facilitate the development of effective stem cell treatments.

The epigenetic/noncoding origin of tumor dormancy

Cancer stem cells (CSCs) have been implicated as the seeds of treatment resistance and metastasis, which are the most deadly features of a neoplasm. However, an unequivocal definition of the CSC phenotype is still missing. A common feature of normal and aberrant stem cells is their ability to enter a prolonged dormant state. Cancer dormancy is a key mechanism for treatment resistance and metastasis. Here we propose a unified definition of dormancy-competent CSCs (DCCs) as the neoplastic subpopulation that can plastically alternate periods of dormancy and rapid growth. Irreversible DNA mutations can hardly account for this versatile behavior, and based on emerging evidence we propose that cancer dormancy is a nongenetic disease driven by the flexible nature of the epigenetic/noncoding interactome.