Effects of 5-aza-2´-deoxycytidine on primary human chondrocytes from osteoarthritic patients.

Chondrocytes, comparable to many cells from the connective tissue, dedifferentiate and end up in a similar fibroblastoid cell type, marked by the loss of the specific expression pattern. Here, chondrocytes isolated from osteoarthritic (OA) patients were investigated. The OA chondrocytes used in this work were not affected by the loss of specific gene expression upon cell culture. The mRNA levels of known cartilage markers, such as SOX5, SOX6, SOX9, aggrecan and proteoglycan 4, remained unchanged. Since chondrocytes from OA and healthy tissue show different DNA methylation patterns, the underlying mechanisms of cartilage marker maintenance were investigated with a focus on the epigenetic modification by DNA methylation. The treatment of dedifferentiated chondrocytes with the DNA methyltransferase inhibitor 5-aza-2´-deoxycytidine (5-aza-dC) displayed no considerable impact on the maintenance of marker gene expression observed in the dedifferentiated state, while the chondrogenic differentiation capacity was compromised. On the other hand, the pre-cultivation with 5-aza-dC improved the osteogenesis and adipogenesis of OA chondrocytes. Contradictory to these effects, the DNA methylation levels were not reduced after treatment for four weeks with 1 µM 5-aza-dC. In conclusion, 5-aza-dC affects the differentiation capacity of OA chondrocytes, while the global DNA methylation level remains stable. Furthermore, dedifferentiated chondrocytes isolated from late-stage OA patients represent a reliable cell source for in vitro studies and disease models without the need for additional alterations.

Emulating the early phases of human tooth development in vitro.

Functional in vitro models emulating the physiological processes of human organ formation are invaluable for future research and the development of regenerative therapies. Here, a developmentally inspired approach is pursued to reproduce fundamental steps of human tooth organogenesis in vitro using human dental pulp cells. Similar to the in vivo situation of tooth initiating mesenchymal condensation, a 3D self-organizing culture was pursued resulting in an organoid of the size of a human tooth germ with odontogenic marker expression. Furthermore, the model is capable of epithelial invagination into the condensed mesenchyme, mimicking the reciprocal tissue interactions of human tooth development. Comprehensive transcriptome analysis revealed activation of well-studied as well as rather less investigated signaling pathways implicated in human tooth organogenesis, such as the Notch signaling. Early condensation in vitro revealed a shift to the TGFß signal transduction pathway and a decreased RhoA small GTPase activity, connected to the remodeling of the cytoskeleton and actin-mediated mechanotransduction. Therefore, this in vitro model of tooth development provides a valuable model to study basic human developmental mechanisms.

3-Iodothyronamine Activates a Set of Membrane Proteins in Murine Hypothalamic Cell Lines.

3-Iodothyronamine (3-T1AM) is an endogenous thyroid hormone metabolite. The profound pharmacological effects of 3-T1AM on energy metabolism and thermal homeostasis have raised interest to elucidate its signaling properties in tissues that pertain to metabolic regulation and thermogenesis. Previous studies identified G protein-coupled receptors (GPCRs) and transient receptor potential channels (TRPs) as targets of 3-T1AM in different cell types. These two superfamilies of membrane proteins are largely expressed in tissue which influences energy balance and metabolism. As the first indication that 3-T1AM virtually modulates the function of the neurons in hypothalamus, we observed that intraperitoneal administration of 50 mg/kg bodyweight of 3-T1AM significantly increased the c-FOS activation in the paraventricular nucleus (PVN) of C57BL/6 mice. To elucidate the underlying mechanism behind this 3-T1AM-induced signalosome, we used three different murine hypothalamic cell lines, which are all known to express PVN markers, GT1-7, mHypoE-N39 (N39) and mHypoE-N41 (N41). Various aminergic GPCRs, which are the known targets of 3-T1AM, as well as numerous members of TRP channel superfamily, are expressed in these cell lines. Effects of 3-T1AM on activation of GPCRs were tested for the two major signaling pathways, the action of Gαs/adenylyl cyclase and Gi/o. Here, we demonstrated that this thyroid hormone metabolite has no significant effect on Gi/o signaling and only a minor effect on the Gαs/adenylyl cyclase pathway, despite the expression of known GPCR targets of 3-T1AM. Next, to test for other potential mechanisms involved in 3-T1AM-induced c-FOS activation in PVN, we evaluated the effect of 3-T1AM on the intracellular Ca2+ concentration and whole-cell currents. The fluorescence-optic measurements showed a significant increase of intracellular Ca2+ concentration in the three cell lines in the presence of 10 µM 3-T1AM. Furthermore, this thyroid hormone metabolite led to an increase of whole-cell currents in N41 cells. Interestingly, the TRPM8 selective inhibitor (10 µM AMTB) reduced the 3-T1AM stimulatory effects on cytosolic Ca2+ and whole-cell currents. Our results suggest that the profound pharmacological effects of 3-T1AM on selected brain nuclei of murine hypothalamus, which are known to be involved in energy metabolism and thermoregulation, might be partially attributable to TRP channel activation in hypothalamic cells.

The Trace Amine-Associated Receptor 1 Agonist 3-Iodothyronamine Induces Biased Signaling at the Serotonin 1b Receptor.

Trace amine-associated receptors (TAARs) belong to the class A G-protein-coupled receptors (GPCR) and are evolutionary related to aminergic receptors. TAARs have been identified to mediate effects of trace amines. TAAR1 signaling is mainly mediated via activation of the Gs/adenylyl cyclase pathway. In addition to classical trace amines, TAAR1 can also be activated by the thyroid hormone derivative 3-iodothyronamine (3-T1AM). Pharmacological doses of 3-T1AM induced metabolic and anapyrexic effects, which might be centrally mediated in the hypothalamus in rodents. However, the observed anapyrexic effect of 3-T1AM persists in Taar1 knock-out mice which raises the question whether further GPCRs are potential targets for 3-T1AM and mediate the observed physiological effect. Anapyrexia has been observed to be related to action on aminergic receptors such as the serotonin receptor 1b (5-HT1b). This receptor primarily activates the Gi/o mediated pathway and PLC signaling through the Gßγ of Gi/o. Since the expression profiles of TAAR1 and 5-HT1b overlap, we questioned whether 3-T1AM may activate 5-HT1b. Finally, we also evaluated heteromerization between these two GPCRs and tested signaling under co-expressed conditions. In this study, we showed, that 3-T1AM can induce Gi/o signaling through 5-HT1b in a concentration of 10 µM. Strikingly, at 5-HT1b the ligand 3-T1AM only activates the Gi/o mediated reduction of cAMP accumulation, but not PLC activation. Co-stimulation of 5-HT1b by both ligands did not lead to additive or synergistic signaling effects. In addition, we confirmed the capacity for heteromerization between TAAR1 and 5-HT1b. Under co-expression of TAAR1 and HTR1b, 3-T1AM action is only mediated via TAAR1 and activation of 5-HT1b is abrogated. In conclusion, we found evidence for 5-HT1b as a new receptor target for 3-T1AM, albeit with a different signaling effect than the endogenous ligand. Altogether, this indicates a complex interrelation of signaling effects between the investigated GPCRs and respective ligands.

Bone marrow-on-a-chip: Long-term culture of human haematopoietic stem cells in a three-dimensional microfluidic environment.

Multipotent haematopoietic stem and progenitor cells (HSPCs) are the source for all blood cell types. The bone marrow stem cell niche in which the HSPCs are maintained is known to be vital for their maintenance. Unfortunately, to date, no in vitro model exists that accurately mimics the aspects of the bone marrow niche and simultaneously allows the long-term culture of HSPCs. In this study, a novel three-dimensional coculture model is presented, based on a hydroxyapatite coated zirconium oxide scaffold, comprising of human mesenchymal stromal cells (MSCs) and cord blood derived HSPCs, enabling successful HSPC culture for a time span of 28 days within the microfluidic multiorgan chip. The HSPCs were found to stay in their primitive state (CD34+ CD38- ) and capable of granulocyte, erythrocyte, macrophage, megakaryocyte colony formation. Furthermore, a microenvironment was formed bearing molecular and structural similarity to the in vivo bone marrow niche containing extracellular matrix and signalling molecules known to play an important role in HSPC homeostasis. Here, a novel human in vitro bone marrow model is presented for the first time, capable of long-term culture of primitive HSPCs in a microfluidic environment.

Estrogenicity of novel phase I and phase II metabolites of zearalenone and cis-zearalenone.

Zearalenone and its cis-isomer, cis-zearalenone, are nonsteroidal mycotoxins that elicit an estrogenic response upon binding to the estrogen receptor. This study compares the estrogenicity of eleven congeners including novel metabolites as 15-OH-zearalenone, zearalenone-14-sulfate, α-cis-zearalenol and ß-cis-zearalenol using the E-Screen assay. Overall, a change in the configuration from trans to cis retains significant estrogenic activity. In contrast, alterations of the aromatic moiety including hydroxylation and sulfation showed a markedly decreased estrogenicity when compared to zearalenone.

Growth and differentiation factor 3 induces expression of genes related to differentiation in a model of cancer stem cells and protects them from retinoic acid-induced apoptosis.

Misexpression of growth factors, particularly those related to stem cell-like phenotype, is often observed in several cancer types. It has been found to influence parameters of disease progression like cell proliferation, differentiation, maintenance of undifferentiated phenotype and modulation of the immune system. GDF3 is a TGFB family member associated with pluripotency and differentiation during embryonic development that has been previously reported to be re-expressed in a number of cancer types. However, its role in tumor development and progression has not been clarified yet. In this study we decipher the role of GDF3 in an in vitro model of cancer stem cells, NCCIT cells. By classical approach to study protein function combined with high-throughput technique for transcriptome analysis and differentiation assays we evaluated GDF3 as a potential therapeutic target. We observed that GDF3 robustly induces a panel of genes related to differentiation, including several potent tumor suppressors, without impacting the proliferative capacity. Moreover, we report for the first time the protective effect of GDF3 against retinoic acid-induced apoptosis in cells with stem cell-like properties. Our study implies that blocking of GDF3 combined with retinoic acid-treatment of solid cancers is a compelling direction for further investigations, which can lead to re-design of cancer differentiation therapies.

Cartilage oligomeric matrix protein (COMP) forms part of the connective tissue of normal human hair follicles.

Hair follicle cycling is driven by epithelial-mesenchymal interactions (EMI), which require extracellular matrix (ECM) modifications to control the crosstalk between key epithelial- and mesenchymal-derived growth factors and cytokines. The exact roles of these ECM modifications in hair cycle-associated EMI are still unknown. Here, we used differential microarray analysis of laser capture-microdissected human scalp hair follicles (HF) to identify new ECM components that distinguish fibroblasts from the connective tissue sheath (CTS) from those of the follicular dermal papilla (DP). These analyses provide the first evidence that normal human CTS fibroblasts are characterized by the selective in situ-transcription of cartilage oligomeric matrix protein (COMP). Following this up on the protein level, COMP was found to be hair cycle-dependent, suggesting critical role in this process: COMP is expressed during telogen and early anagen at regions of EMI and is degraded during catagen (only the CTS adjacent to the bulge remains COMP+ during catagen). Notably, COMP gene expression in vitro suggests direct correlation with the expression of TGFß2 in CTS fibroblasts. This raises the question whether COMP expression undergoes regulation by transforming growth factor, beta (TGFß) signalling. The intrafollicular COMP expression suggests to be functionally important and deserves further scrutiny in hair biology as indicated by the fact that altered COMP expression might be associated with scant fine hair in the case of some chondrodysplasia and scleroderma patients. Together these results reveal for the first time that COMP is part of the ECM and suggests its important role in normal human HF biology.

Follistatin antagonizes transforming growth factor-beta3-induced epithelial-mesenchymal transition in vitro: implications for murine palatal development supported by microarray analysis.

Epithelial-mesenchymal transition (EMT) is involved in normal embryonic development as well as in tumor progression and invasiveness. This process is also known to be a crucial step in palatogenesis during fusion of the bi-lateral palatal processes. Disruption of this step results in a cleft palate, which is among the most frequent birth defects in humans. A number of genes and encoded proteins have been shown to play a role in this developmental stage. The central role is attributed to the cytokine transforming growth factor-beta3 (TGF-beta3), which is expressed in the medial edge epithelium (MEE) already before the fusion process. The MEE covers the tips of the growing palatal shelves and eventually undergoes EMT or programmed cell death (apoptosis). TGF-beta3 is described to induce EMT in embryonic palates. With regard to the early expression of this molecule before the fusion process, it is not well understood which mechanisms prevent the TGF-beta3 producing epithelial cells from undergoing differentiation precociously. We used the murine palatal fusion to study the regulation of EMT. Specifically, we analyzed the MEE for the expression of known antagonists of TGF-beta molecules using in situ hybridization and detected the gene coding for Follistatin to be co-expressed with TGF-beta3. Further, we could show that Follistatin directly binds to TGF-beta3 and that it completely blocks TGF-beta3-induced EMT of the normal murine mammary gland (NMuMG) epithelial cell line in vitro. In addition, we analyzed the gene expression profile of NMuMG cells during TGF-beta3-induced EMT by microarray hybridization, detecting strong changes in the expression of apoptosis-regulating genes.

Initiation of mesenchymal condensation in alginate hollow spheres--a useful model for understanding cartilage repair?

A promising strategy for the regeneration of degenerated cartilage tissue structure in osteoarthritic joints is the use of mesenchymal precursor cells. These cells can be triggered to undergo differentiation into functional active chondrocytes resulting in newly synthesized cartilage. Because chondrogenic differentiation is initiated by the step of mesenchymal condensation in vitro, it is of great interest to fully characterize the first lineage specific step in vitro. Therefore, a modified culture system was developed which mimics the process in vitro and may finally help to identify the key factors that are essential for the induction of chondrogenic differentiation in vivo. Compared to other established 3D culture systems like alginate beads and micromass cultures, the use of alginate hollow spheres bears the advantage to analyze different phases of cell aggregation starting from a single cell suspension of previously isolated and expanded human primary cells of mesenchymal origin.

Expression of Fgf and Tgfbeta signaling related genes during embryonic endochondral ossification.

Disturbed fibroblast growth factor (Fgf) and transforming growth factor beta (Tgfbeta) signaling lead to a variety of human skeletal disorders. To reveal the possible function and interaction of these signaling systems we have started to analyze the expression patterns of signaling factors, antagonists, receptors and transducers of these pathways in forelimbs of mouse embryos and compared them to the expression of established markers including Ihh. In addition to defining their expression domains in the developing bone, our study identified new subpopulations of chondrocytes characterized by the expression of distinct combinations of markers.