Cell-to-cell communication--periodontal regeneration.

BACKGROUND Although regenerative treatment options are available, periodontal regeneration is still regarded as insufficient and unpredictable. AIM This review article provides scientific background information on the animated 3D film Cell-to-Cell Communication - Periodontal Regeneration. RESULTS Periodontal regeneration is understood as a recapitulation of embryonic mechanisms. Therefore, a thorough understanding of cellular and molecular mechanisms regulating normal tooth root development is imperative to improve existing and develop new periodontal regenerative therapies. However, compared to tooth crown and earlier stages of tooth development, much less is known about the development of the tooth root. The formation of root cementum is considered the critical element in periodontal regeneration. Therefore, much research in recent years has focused on the origin and differentiation of cementoblasts. Evidence is accumulating that the Hertwig's epithelial root sheath (HERS) has a pivotal role in root formation and cementogenesis. Traditionally, ectomesenchymal cells in the dental follicle were thought to differentiate into cementoblasts. According to an alternative theory, however, cementoblasts originate from the HERS. What happens when the periodontal attachment system is traumatically compromised? Minor mechanical insults to the periodontium may spontaneously heal, and the tissues can structurally and functionally be restored. But what happens to the periodontium in case of periodontitis, an infectious disease, after periodontal treatment? A non-regenerative treatment of periodontitis normally results in periodontal repair (i.e., the formation of a long junctional epithelium) rather than regeneration. Thus, a regenerative treatment is indicated to restore the original architecture and function of the periodontium. Guided tissue regeneration or enamel matrix proteins are such regenerative therapies, but further improvement is required. As remnants of HERS persist as epithelial cell rests of Malassez in the periodontal ligament, these epithelial cells are regarded as a stem cell niche that can give rise to new cementoblasts. Enamel matrix proteins and members of the transforming growth factor beta (TGF-ß) superfamily have been implicated in cementoblast differentiation. CONCLUSION A better knowledge of cell-to-cell communication leading to cementoblast differentiation may be used to develop improved regenerative therapies to reconstitute periodontal tissues that were lost due to periodontitis.

Successful transnasal delivery of stem cells in a rat model of perinatal hypoxic-ischemic brain injury

OBJECTIVE: New routes for cell transplantation into the brain need to be explored as intracerebral or intrathecal applications have a high risk to cause damage to the central nervous system. It has been hypothesized that transnasally administrated cells bypass the blood-brain barrier and migrate along the olfactory neural route into the brain and cerebrospinal fluid. Our goal is to confirm this hypothesis by transnasally administrating Wharton’s Jelly mesenchymal stem cells (WJ-MSC) and neural progenitor cells (NPC) to perinatal rats in a model of hypoxic-ischemic brain injury. STUDY DESIGN: Four-day-old Wistar rat pups, previously brain-damaged by combined hypoxic-ischemic and inflammatory insult, either received WJ-MSC or green fluorescent protein-expressing NPC: The heads of the rat pups were immobilized and 3 ml drops containing the cells (50’000 cells/ml) were placed on one nostril allowing it to be snorted. This procedure was repeated twice, alternating right to left nostril with an interval of one minute between administrations. The rat pups received a total of 600’000 cells. Animals were sacrificed 24h, 48h or 7 days after the application of the cells. Fixed brains were collected, embedded in paraffin and sectioned. RESULTS: Transplanted cells were found in the layers of the olfactory bulb (OB), the cerebral cortex, thalamus and the hippocampus. The amount of cells was highest in the OB. Animals treated with transnasally delivered stem cells showed significantly decreased gliosis compared to untreated animals. CONCLUSION: Our data show that transnasal delivery of WJ-MSC and NPC to the newborn brain after perinatal brain damage is successful. The cells not only migrate the brain, but also decrease scar formation and improve neurogenesis. Therefore, the non-invasive intranasal delivery of stem cells to the brain may be the preferred method for stem cell treatment of perinatal brain damage and should be preferred in future clinical trials.

In vitro analysis of osteogenic inhibition in non-union spinal fusion caused by nucleus pulposus cells.

Discectomy and spinal fusion is the gold standard for spinal surgery to relieve pain. However, fusion can be hindered for yet unknown reasons that lead to non-fusions with pseudo-arthrosis. Clinical observations indicate that presence of residual intervertebral disc (IVD) tissue might hinder the ossification. We hypothesize that BMP-antagonists are constantly secreted by IVD cells and potentially prevent the ossification process. Furthermore, L51P, the engineered BMP2 variant, stimulates osseo-induction of bone marrow-derived mesenchymal stem cells (MSC) by antagonizing BMP-inhibitors. Human MSCs, primary nucleus pulposus (NPC) and annulus pulposus cells (AFC) were isolated and expanded in monolayer cultures up to passage 3. IVD cells were seeded in 1.2% alginate beads (4Mio/mL) and separated by culture inserts from MSCs. MSCs were kept in 1:control medium, 2:osteogenic medium±alginate beads, 3:osteogenic medium+NPC (±L51P) and 4:osteogenic medium+AFC (±L51P) for 21 days. Relative gene expression of bone-related genes, alkaline phosphatase assay and histological staining were performed. Osteogenesis of MSCs was hindered as shown by reduced alizarin red staining in the presence of NPC. No such inhibition was observed if co-cultured with alginate only or in the presence of AFC. The results were confirmed on the RNA and protein level. Addition of L51Pto the co- cultures, however, induced mineralization of MSCs in presence of NPC. We demonstrated that NPC secrete BMP-antagonists that prevent osteogenesis of MSCs and L51P can antagonize BMP-antagonists and induce bone formation.

Cell cycle reactivation of cochlear progenitor cells in neonatal FUCCI mice by a GSK3 small molecule inhibitor.

Due to the lack of regenerative capacity of the mammalian auditory epithelium, sensory hair cell loss results in permanent hearing deficit. Nevertheless, a population of tissue resident stem/progenitor cells has been recently described. Identification of methods to trigger their activity could lead to exploitation of their potential therapeutically. Here we validate the use of transgenic mice reporting cell cycle progression (FUCCI), and stemness (Lgr5-GFP), as a valuable tool to identify regulators of cell cycle re-entry of supporting cells within the auditory epithelium. The small molecule compound CHIR99021 was used to inhibit GSK3 activity. This led to a significant increase in the fraction of proliferating sphere-forming cells, labeled by the FUCCI markers and in the percentage of Lgr5-GFP + cells, as well as a selective increase in the fraction of S-G2-M cells in the Lgr5 + population. Using whole mount cultures of the organ of Corti we detected a statistically significant increment in the fraction of proliferating Sox2 supporting cells after CHIR99021 treatment, but only rarely appearance of novel MyoVIIa+/Edu + hair cells. In conclusion, these tools provide a robust mean to identify novel regulators of auditory organ regeneration and to clarify the contribution of stem cell activity.

Tyrosine kinase inhibitor-induced CD70 expression mediates drug resistance in leukemia stem cells by activating Wnt signaling.

In chronic myelogenous leukemia (CML), oncogenic BCR-ABL1 activates the Wnt pathway, which is fundamental for leukemia stem cell (LSC) maintenance. Tyrosine kinase inhibitor (TKI) treatment reduces Wnt signaling in LSCs and often results in molecular remission of CML; however, LSCs persist long term despite BCR-ABL1 inhibition, ultimately causing disease relapse. We demonstrate that TKIs induce the expression of the tumor necrosis factor (TNF) family ligand CD70 in LSCs by down-regulating microRNA-29, resulting in reduced CD70 promoter DNA methylation and up-regulation of the transcription factor specificity protein 1. The resulting increase in CD70 triggered CD27 signaling and compensatory Wnt pathway activation. Combining TKIs with CD70 blockade effectively eliminated human CD34(+) CML stem/progenitor cells in xenografts and LSCs in a murine CML model. Therefore, targeting TKI-induced expression of CD70 and compensatory Wnt signaling resulting from the CD70/CD27 interaction is a promising approach to overcoming treatment resistance in CML LSCs.

Three-dimensional culture and characterization of mononuclear cells from human bone marrow

BACKGROUND AIMS The diverse phenotypic changes and clinical and economic disadvantages associated with the monolayer expansion of bone marrow-derived mesenchymal stromal cells (MSCs) have focused attention on the development of one-step intraoperative cells therapies and homing strategies. The mononuclear cell fraction of bone marrow, inclusive of discrete stem cell populations, is not well characterized, and we currently lack suitable cell culture systems in which to culture and investigate the behavior of these cells. METHODS Human bone marrow-derived mononuclear cells were cultured within fibrin for 2 weeks with or without fibroblast growth factor-2 supplementation. DNA content and cell viability of enzymatically retrieved cells were determined at days 7 and 14. Cell surface marker profiling and cell cycle analysis were performed by means of multi-color flow cytometry and a 5-ethynyl-2'-deoxyuridine incorporation assay, respectively. RESULTS Total mononuclear cell fractions, isolated from whole human bone marrow, was successfully cultured in fibrin gels for up to 14 days under static conditions. Discrete niche cell populations including MSCs, pericytes and hematopoietic stem cells were maintained in relative quiescence for 7 days in proportions similar to that in freshly isolated cells. Colony-forming unit efficiency of enzymatically retrieved MSCs was significantly higher at day 14 compared to day 0; and in accordance with previously published works, it was fibroblast growth factor-2-dependant. CONCLUSIONS Fibrin gels provide a simple, novel system in which to culture and study the complete fraction of bone marrow-derived mononuclear cells and may support the development of improved bone marrow cell-based therapies.

Bloodstream infection in paediatric cancer centres--leukaemia and relapsed malignancies are independent risk factors.

UNLABELLED In a prospective multicentre study of bloodstream infection (BSI) from November 01, 2007 to July 31, 2010, seven paediatric cancer centres (PCC) from Germany and one from Switzerland included 770 paediatric cancer patients (58% males; median age 8.3 years, interquartile range (IQR) 3.8-14.8 years) comprising 153,193 individual days of surveillance (in- and outpatient days during intensive treatment). Broviac catheters were used in 63% of all patients and Ports in 20%. One hundred forty-two patients (18%; 95% CI 16 to 21%) experienced at least one BSI (179 BSIs in total; bacteraemia 70%, bacterial sepsis 27%, candidaemia 2%). In 57%, the BSI occurred in inpatients, in 79% after conventional chemotherapy. Only 56 % of the patients showed neutropenia at BSI onset. Eventually, patients with acute lymphoblastic leukaemia (ALL) or acute myeloblastic leukaemia (AML), relapsed malignancy and patients with a Broviac faced an increased risk of BSI in the multivariate analysis. Relapsed malignancy (16%) was an independent risk factor for all BSI and for Gram-positive BSI. CONCLUSION This study confirms relapsed malignancy as an independent risk factor for BSIs in paediatric cancer patients. On a unit level, data on BSIs in this high-risk population derived from prospective surveillance are not only mandatory to decide on empiric antimicrobial treatment but also beneficial in planning and evaluating preventive bundles. WHAT IS KNOWN • Paediatric cancer patients face an increased risk of nosocomial bloodstream infections (BSIs). • In most cases, these BSIs are associated with the use of a long-term central venous catheter (Broviac, Port), severe and prolonged immunosuppression (e.g. neutropenia) and other chemotherapy-induced alterations of host defence mechanisms (e.g. mucositis). What is New: • This study is the first multicentre study confirming relapsed malignancy as an independent risk factor for BSIs in paediatric cancer patients. • It describes the epidemiology of nosocomial BSI in paediatric cancer patients mainly outside the stem cell transplantation setting during conventional intensive therapy and argues for prospective surveillance programmes to target and evaluate preventive bundle interventions.

Extracellular Iron is a Modulator of the Differentiation of Osteoclast Lineage Cells.

Osteoclasts originate from the hematopoietic stem cell and share a differentiation pathway with the cells of the monocyte/macrophage lineages. Development and activation of osteoclasts, and as a consequence regulation of bone resorption, depend on two growth factors: macrophage colony-stimulating factor and receptor activator of NF-κB ligand. Furthermore, cell development and activity are modulated by a microenvironment composed of cytokines and growth factors and of the extracellular matrix. Membrane transporters are a means for cells to interact with their environment. Within this study, the expression of proteins regulating cellular iron homeostasis in osteoclast-like cells grown from bone marrow-derived progenitors was compared to the expression of this set of proteins by monocyte/macrophage lineage cells. In differentiating osteoclasts, levels of transcripts encoding transferrin receptor 1 and divalent metal transporter 1 (Slc11A2) were increased, while levels of transcripts encoding ferroportin (Slc40A1) and natural resistance-associated macrophage protein 1 (Slc11A1) were decreased. Supplementation of the culture media with exogenous iron led to an increase in the proliferation of osteoclast progenitor cells and to the expression of a macrophage-like phenotype, while the development of osteoclasts was reduced. Upon transfer of mature OC onto a CaP substrate, iron depletion of the medium with the Fe(3+)-chelator Deferoxamine Mesylate decreased CaP dissolution by ~30 %, which could be restored by addition of exogenous iron. During the 24 h of the assay, no effects were observed on total TRAP activity. The data demonstrate transcriptional regulation of the components of cellular iron transporters during OC development and suggests that iron homeostasis may contribute to fine-tuning of the RANKL-induced OC development.

Cell Competition During Growth and Regeneration

Tissue growth and regeneration are autonomous, stem-cell-mediated processes in which stem cells within the organ self-renew and differentiate to create new cells, leading to new tissue. The processes of growth and regeneration require communication and interplay between neighboring cells. In particular, cell competition, which is a process in which viable cells are actively eliminated by more competitive cells, has been increasingly implicated to play an important role. Here, we discuss the existing literature regarding the current landscape of cell competition, including classical pathways and models, fitness fingerprint mechanisms, and immune system mechanisms of cell competition. We further discuss the clinical relevance of cell competition in the physiological processes of tissue growth and regeneration, highlighting studies in clinically important disease models, including oncological, neurological, and cardiovascular diseases.

Angiopoietin-1 receptor Tie2 distinguishes multipotent differentiation capability in bovine coccygeal nucleus pulposus cells.

BACKGROUND The intervertebral disc (IVD) has limited self-healing potential and disc repair strategies require an appropriate cell source such as progenitor cells that could regenerate the damaged cells and tissues. The objective of this study was to identify nucleus pulposus-derived progenitor cells (NPPC) and examine their potential in regenerative medicine in vitro. METHODS Nucleus pulposus cells (NPC) were obtained from 1-year-old bovine coccygeal discs by enzymatic digestion and were sorted for the angiopoietin-1 receptor Tie2. The obtained Tie2- and Tie2+ fractions of cells were differentiated into osteogenic, adipogenic, and chondrogenic lineages in vitro. Colony-forming units were prepared from both cell populations and the colonies formed were analyzed and quantified after 8 days of culture. In order to improve the preservation of the Tie2+ phenotype of NPPC in monolayer cultures, we tested a selection of growth factors known to have stimulating effects, cocultured NPPC with IVD tissue, and exposed them to hypoxic conditions (2 % O2). RESULTS After 3 weeks of differentiation culture, only the NPC that were positive for Tie2 were able to differentiate into osteocytes, adipocytes, and chondrocytes as characterized by calcium deposition (p < 0.0001), fat droplet formation (p < 0.0001), and glycosaminoglycan content (p = 0.0095 vs. Tie2- NPC), respectively. Sorted Tie2- and Tie2+ subpopulations of cells both formed colonies; however, the colonies formed from Tie2+ cells were spheroid in shape, whereas those from Tie2- cells were spread and fibroblastic. In addition, Tie2+ cells formed more colonies in 3D culture (p = 0.011) than Tie2- cells. During expansion, a fast decline in the fraction of Tie2+ cells was observed (p < 0.0001), which was partially reversed by low oxygen concentration (p = 0.0068) and supplementation of the culture with fibroblast growth factor 2 (FGF2) (p < 0.0001). CONCLUSIONS Our results showed that the bovine nucleus pulposus contains NPPC that are Tie2+. These cells fulfilled formally progenitor criteria that were maintained in subsequent monolayer culture for up to 7 days by addition of FGF2 or hypoxic conditions. We propose that the nucleus pulposus represents a niche of precursor cells for regeneration of the IVD.