Human mesenchymal stem cell derived osteoblasts degrade organic bone matrix in vitro by matrix metalloproteinases

Assessment of the Biocompatibility Ability and Differentiation Capacity of Mesenchymal Stem Cells on Biopolymer/Gold Nanocomposites

This study assessed the biocompatibility of two types of nanogold composites: fibronectin-gold (FN-Au) and collagen-gold (Col-Au). It consisted of three main parts: surface characterization, in vitro biocompatibility assessments, and animal models. To determine the structural and functional differences between the materials used in this study, atomic force microscopy, Fourier-transform infrared spectroscopy, and ultraviolet-visible spectrophotometry were used to investigate their surface topography and functional groups. The F-actin staining, proliferation, migration, reactive oxygen species generation, platelet activation, and monocyte activation of mesenchymal stem cells (MSCs) cultured on the FN-Au and Col-Au nanocomposites were investigated to determine their biological and cellular behaviors. Additionally, animal biocompatibility experiments measured capsule formation and collagen deposition in female Sprague-Dawley rats. The results showed that MSCs responded better on the FN-Au and Col-AU nanocomposites than on the control (tissue culture polystyrene) or pure substances, attributed to their incorporation of an optimal Au concentration (12.2 ppm), which induced significant surface morphological changes, nano topography cues, and better biocompatibility. Moreover, neuronal, endothelial, bone, and adipose tissues demonstrated better differentiation ability on the FN-Au and Col-Au nanocomposites. Nanocomposites have a crucial role in tissue engineering and even vascular grafts. Finally, MSCs were demonstrated to effectively enhance the stability of the endothelial structure, indicating that they can be applied as promising alternatives to clinics in the future.

3D bioprinting of human mesenchymal stem cells-laden hydrogels incorporating MXene for spontaneous osteodifferentiation

Contemporary advances in three-dimensional (3D) bioprinting technologies have enabled the fabrication of tailored live 3D tissue mimetics. Furthermore, the development of advanced bioink materials has been highlighted to accurately reproduce the composition of a native extracellular matrix and mimic the intrinsic properties of laden cells. Recent research has shown that MXene is one of promising nanobiomaterials with osteogenic activity for bone grafts and scaffolds due to its unique atomic structure of three titanium layers between two carbon layers. In this study, the MXene-incorporated gelatin methacryloyl (GelMA) and hyaluronic acid methacryloyl (HAMA) (i.e., GelMA/HAMA-MXene) bioinks were prepared to explore if they have the potential to enable the spontaneous osteodifferentiation of human mesenchymal stem cells (hMSCs) when the hMSCs-laden GelMA/HAMA-MXene bioinks were 3D printed. The physicochemical and rheological characteristics of the GelMA/HAMA-MXene hydrogels were proven to be unprecedentedly favorable supportive matrices suited for the growth and survival of hMSCs. Furthermore, hMSCs were shown to spontaneously differentiate into osteoblasts within GelMA-HAMA/MXene composites to provide favorable microenvironments for osteogenesis. Therefore, our results suggest that the remarkable biofunctional advantages of the MXene-incorporated GelMA/HAMA bioink can be utilized in a wide range of strategies for the development of effective scaffolds in bone tissue regeneration.

Neonatal Porcine Germ Cells Dedifferentiate and Display Osteogenic and Pluripotency Properties

Gonocytes are progenitors of spermatogonial stem cells in the neonatal testis. We have previously shown that upon culturing, neonatal porcine gonocytes and their colonies express germ cell and pluripotency markers. The objectives of present study were to investigate in vitro trans-differentiation potential of porcine gonocytes and their colonies into cells from three germinal layers, and to assess pluripotency of cultured gonocytes/colonies in vivo. For osteogenic and tri-lineage differentiation, cells were incubated in regular culture media for 14 and 28 days, respectively. Cells were cultured for an additional 14 days for osteogenic differentiation or 7 days for differentiation into derivates of the three germinal layers. Osteogenic differentiation of cells and colonies was verified by Alizarin Red S staining and tri-lineage differentiation was confirmed using immunofluorescence and gene expression analyses. Furthermore, upon implantation into recipient mice, the cultured cells/colonies developed teratomas expressing markers of all three germinal layers. Successful osteogenic differentiation from porcine germ cells has important implications for bone regeneration and matrix formation studies. Hence, gonocytes emerge as a promising source of adult pluripotent stem cells due to the ability to differentiate into all germinal layers without typical biosafety risks associated with viral vectors or ethical implications.

Network Pharmacology Integrated with Molecular Docking Explores the Mechanisms of Naringin against Osteoporotic Fracture by Regulating Oxidative Stress

Naringin (NG), as the most abundant component of Drynariae Rhizoma (Chinese name: Gusuibu), has been proved to be an antioxidant flavonoid on promoting osteoporotic fracture (OF) healing, but relevant research is scanty on the underlying mechanisms. We adopted target prediction, protein-protein interaction (PPI) analysis, Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis, and molecular docking to establish a system pharmacology database of NG against OF. Totally 105 targets of naringin were obtained, including 26 common targets with OF. A total of 415 entries were obtained through GO Biological Process enrichment analysis (P < 0.05), and 37 entries were obtained through KEGG pathway enrichment analysis with seven signaling pathways included (P < 0.05), which were primarily concerned with p53, IL-17, TNF, estrogen, and PPAR signaling pathways. According to the results of molecular docking, naringin is all bound in the active pockets of the core targets with 3-9 hydrogen bonds through some connections such as hydrophobic interactions, Pi-Pi stacked interactions, and salt bridge, demonstrating that naringin binds tightly to the core targets. In general, naringin may treat OF through multiple targets and multiple pathways via regulating oxidative stress, etc. Notably, it is first reported that NG may regulate osteoclast differentiation and oxidative stress through the expression of the core targets so as to treat OF.

Osteosarcoma and Metastasis Associated Bone Degradation-A Tale of Osteoclast and Malignant Cell Cooperativity

Cancer-induced bone degradation is part of the pathological process associated with both primary bone cancers, such as osteosarcoma, and bone metastases originating from, e.g., breast, prostate, and colon carcinomas. Typically, this includes a cancer-dependent hijacking of processes also occurring during physiological bone remodeling, including osteoclast-mediated disruption of the inorganic bone component and collagenolysis. Extensive research has revealed the significance of osteoclast-mediated bone resorption throughout the course of disease for both primary and secondary bone cancer. Nevertheless, cancer cells representing both primary bone cancer and bone metastasis have also been implicated directly in bone degradation. We will present and discuss observations on the contribution of osteoclasts and cancer cells in cancer-associated bone degradation and reciprocal modulatory actions between these cells. The focus of this review is osteosarcoma, but we will also include relevant observations from studies of bone metastasis. Additionally, we propose a model for cancer-associated bone degradation that involves a collaboration between osteoclasts and cancer cells and in which both cell types may directly participate in the degradation process.

The Effect of MMP-2 Inhibitor 1 on Osteogenesis and Angiogenesis During Bone Regeneration

Bone regeneration is a popular research focus around the world. Recent studies have suggested that the formation of a vascular network as well as intrinsic osteogenic ability is important for bone regeneration. Here, we show for the first time that matrix metalloproteinase (MMP) 2 inhibitor 1 (MMP2-I1) has a positive role in the osteogenesis of human bone marrow mesenchymal stem cells (hBMSCs) and angiogenesis of human vascular endothelial cells (HUVECs). MMP2-I1 activated the p38/mitogen-activated protein kinase signaling pathway to promote the osteogenesis of hBMSCs, and promoted the angiogenesis of HUVECs via the hypoxia-inducible factor-1α signaling pathway. We also found that MMP2-I1 enhanced bone formation using a rat tibial defect model and prevented bone loss using an ovariectomy-induced mouse model of osteoporosis. Data from the mouse model demonstrated that MMP2-I1 generated more type H vessels (CD31^hiEmcn^hi) when preventing bone loss. These results provide important insights into the regulatory effects of MMP2-I1 on bone regeneration.

Remarkable migration propensity of dental pulp stem cells towards neurodegenerative milieu: An in vitro analysis

Stem cell therapy provides a ray of hope for treating neurodegenerative diseases (ND). Bone marrow mesenchymal stem cells (BM-MSC) were extensively investigated for their role in neuroregeneration. However, drawbacks like painful bone marrow extraction, less proliferation and poor CNS engraftment following systemic injections of BM-MSC prompt us to search for alternate/appropriate source of MSC for treating ND. In this context, dental pulp stem cells (DPSC) could be an alternative to BM-MSC as it possess both mesenchymal and neural characteristic features due to its origin from ectoderm, ease of isolation, higher proliferation index and better neuroprotection. A study on the migration potential of DPSC compared to BM-MSC in a neurodegenerative condition is warranted. Given the neural crest origin, we hypothesize that DPSC possess better migration towards neurodegenerative milieu as compared to BM-MSC. In this prospect, we investigated the migration potential of DPSC in an in vitro neurodegenerative condition. Towards this, transwell, Matrigel and chorioallantoic membrane (CAM) migration assays were carried-out by seeding hippocampal neurons in the lower chamber and treated with 300 μM kainic acid (KA) for 6 h to induce neurodegeneration. Subsequently, the upper chamber of transwell was loaded with DPSC/BM-MSC and their migration potential was assessed following 24 h of incubation. Our results revealed that the migration potential of DPSC/BM-MSC was comparable in non-degenerative condition. However, following injury the migration potential of DPSC towards the degenerating site was significantly higher as compared to BM-MSC. Furthermore, upon exposure of naïve DPSC/BM-MSCs to culture medium derived from neurodegenerative milieu resulted in significant upregulation of homing factors like SDF-1alpha, CXCR-4, VCAM-1, VLA-4, CD44, MMP-2 suggesting that the superior migration potential of DPSC might be due to prompt expression of homing factors in DPSC compared to BM-MSCs.

Mesenchymal Stem Cells Promote Tumor Progression via Inducing Stroma Remodeling on Rabbit VX2 Bladder Tumor Model

Background and aim: Mesenchymal stem cells (MSCs) are capable of impacting tumor progression but its role in tumor stroma remodeling still remains unclear. This present study was aimed to evaluate the potential function of MSCs on tumor stroma remodeling using rabbits VX2 bladder tumor model. Methods: The VX2 bladder tumor models were established by injecting mixed cell suspensions (10⁶ of VX2 tumor cells and 0/10⁶/10⁷ of autologous MSCs in group A, B, C, respectively) into the bladder mucosa using thirty male New Zealand white rabbits. The tumor volume was measured by ultrasound at the time points of 1st, 2nd, 3rd and 4th week after inoculation. At the end of the fourth week, the tumor tissue expressions of basic fibroblast growth factor (bFGF), transforming growth factor beta 1 (TGFβ-1), hepatocyte growth factor (HGF), matrix metalloproteinase 2 (MMP2) and matrix metalloproteinase 9 (MMP9) were determined using Real-time quantitative PCR and immunohistochemistry. Masson trichrome staining and Cy3-FITC double-labelled immunofluorescence staining were used to determine the MSCs distribution in tumor tissue in another two rabbits implanted with a cell suspension of 10⁶ VX2 tumor cells and 10⁶ autologous MSCs. Results: MSCs were homogeneously distributed in tumor tissues after 7 days of inoculation, which were not consistent with the distribution of tumor stroma. After 21 days of inoculation, MSCs have been integrated into tumor interstitial tissue and mainly distributed in the mesenchyma around the tumor nest. At the 1st, 2nd, 3rd and 4th week time point, tumor volume in group A < group B < group C, and the difference has statistical significance (all p<0.001).The relative mRNA and protein levels of bFGF, TGFβ-1 and HGF were significantly higher in group B and C compared with group A (all p<0.05), as well as the mRNA levels of bFGF, HGF were higher in group C than group B (p<0.05), and the protein levels of bFGF, TGFβ-1 were higher in group C than group B (p<0.05). The mRNA and protein levels of MMP2 were significantly higher in group B, C than group A (p<0.05). MMP9 was increasingly over expressed along with the growing amount of MSCs inoculated within tumor, both at the level of mRNA and protein (all p<0.05). Conclusion: MSCs participate in tumor stroma remodeling via inducing overexpression of some important growth factors and MMPs.

Mechanisms of mesenchymal stem cell correction of the impaired biomechanical properties of diabetic skin: The role of miR-29a

Diabetic skin has impaired wound healing properties following injury. We have further shown that diabetic skin has weakened biomechanical properties at baseline. We hypothesize that the biomechanical properties of diabetic skin decline during the progression of the diabetic phenotype, and that this decline is due to the dysregulation of miR-29a, resulting in decreased collagen content. We further hypothesize that treatment with mesenchymal stem cells (MSCs) may improve diabetic wound healing by correction of the dysregulated miR-29a expression. We analyzed the biomechanical properties, collagen gene expression, collagen protein production, and miR-29a levels in skin harvested from 6 to 18 week old mice during the development of the diabetic phenotype. We also examined the correction of these impairments by both MSC treatment and the inhibition of miR-29a. Diabetic skin demonstrated a progressive impairment of biomechanical properties, decreased collagen content, and increased miR-29a levels during the development of the diabetic phenotype. MSC treatment decreased miR-29a levels, increased collagen content, and corrected the impaired biomechanical properties of diabetic skin. Additionally, direct inhibition of miR-29a also increased collagen content in diabetic skin. This decline in the biomechanical properties of diabetic skin during the progression of diabetes may increase the susceptibility of diabetic skin to injury and miR-29a appears to play a key role in this process.

The role of microRNA-15b in the impaired angiogenesis in diabetic wounds

The impairment in diabetic wound healing represents a significant clinical problem. Decreased angiogenesis is thought to play a central role in the pathogenesis of this impairment. We have previously shown that treatment of diabetic murine wounds with mesenchymal stem cells can improve healing, but the mechanisms are not completely defined. MicroRNA-15b (miR-15b) has been implicated in the regulation of the angiogenic response. We hypothesized that abnormal miR-15b expression may contribute to the impaired angiogenesis observed in impaired diabetic wound healing. To test this hypothesis, we examined the expression of miR-15b and its target genes in diabetic and nondiabetic mice before and after injury. MiR-15b expression was significantly up-regulated in diabetic mouse wounds during the wound healing response. Increased miR-15b levels also closely correlated with decreased gene expression of its proangiogenic target genes. Furthermore, the correction of the diabetic wound healing impairment with mesenchymal stem cell treatment was associated with a significant decrease in miR-15b expression level and increased gene expression of its proangiogenic target genes. These results provide the first evidence that increased expression of miR-15b in diabetic wounds in response to injury may, in part, be responsible for the abnormal angiogenic response seen in diabetic wounds and may contribute to the observed wound healing impairment.

Effect of 17β-estradiol on mediators involved in mesenchymal stromal cell trafficking in cell therapy of diabetes

BACKGROUND AIMS

Mesenchymal stromal cells (MSCs) have shown great promise for cell therapy of a wide range of diseases such as diabetes. However, insufficient viability of transplanted cells reaching to damaged tissues has limited their potential therapeutic effects. Expression of estrogen receptors on stem cells may suggest a role for 17β-estradiol (E2) in regulating some functions in these cells. There is evidence that E2 enhances homing of stem cells. Induction of hypoxia-inducible factor-1α (HIF-1α) by E2 and the profound effect of HIF-1α on migration of cells have previously been demonstrated. We investigated the effect of E2 on major mediators involved in trafficking and subsequent homing of MSCs both in vitro and in vivo in diabetic rats.

METHODS

E2 has been selected to improve the poor migration capacity of MSCs toward sites of injury. MSCs were incubated with different concentrations of E2 for varying periods of time to investigate whether estradiol treatment could be effective to enhance the efficiency of MSC transplantation.

RESULTS

E2 significantly enhanced the viability of the cells that were blocked by ICI 182,780 (estrogen receptor antagonist). E2 also increased HIF-1α, CXC chemokine receptor 4 and C-C chemokine receptor 2 protein and messenger RNA levels measured by Western blot and reverse transcription-polymerase chain reaction. The enzymatic activity of matrix metalloproteinase 2 and metalloproteinase 9 was elevated in E2-treated cells through the use of gelatin zymography. Finally, the improved migration capacity of E2-treated MSCs was evaluated with the use of a Boyden chamber and in vivo migration assays.

CONCLUSIONS

Our data support that conditioning of MSCs with E2 promotes migration of cells in cultured MSCs in vitro and in a diabetic rat model in vivo through regulation of major mediators of cell trafficking.

Human bone marrow mesenchymal stem cells induce collagen production and tongue cancer invasion

Tumor microenvironment (TME) is an active player in carcinogenesis and changes in its composition modify cancer growth. Carcinoma-associated fibroblasts, bone marrow-derived multipotent mesenchymal stem cells (BMMSCs), and inflammatory cells can all affect the composition of TME leading to changes in proliferation, invasion and metastasis formation of carcinoma cells. In this study, we confirmed an interaction between BMMSCs and oral tongue squamous cell carcinoma (OTSCC) cells by analyzing the invasion progression and gene expression pattern. In a 3-dimensional myoma organotypic invasion model the presence of BMMSCs inhibited the proliferation but increased the invasion of OTSCC cells. Furthermore, the signals originating from OTSCC cells up-regulated the expression of inflammatory chemokines by BMMSCs, whereas BMMSC products induced the expression of known invasion linked molecules by carcinoma cells. Particularly, after the cell-cell interactions, the chemokine CCL5 was abundantly secreted from BMMSCs and a function blocking antibody against CCL5 inhibited BMMSC enhanced cancer invasion area. However, CCL5 blocking antibody did not inhibit the depth of invasion. Additionally, after exposure to BMMSCs, the expression of type I collagen mRNA in OTSCC cells was markedly up-regulated. Interestingly, also high expression of type I collagen N-terminal propeptide (PINP) in vivo correlated with the cancer-specific mortality of OTSCC patients, whereas there was no association between cancer tissue CCL5 levels and the clinical parameters. In conclusion, our results suggest that the interaction between BMMSC and carcinoma cells induce cytokine and matrix molecule expression, of which high level of type I collagen production correlates with the prognosis of OTSCC patients.

Three-dimensional hMSC motility within peptide-functionalized PEG-based hydrogels of varying adhesivity and crosslinking density

Human mesenchymal stem cell (hMSC) migration and recruitment play a critical role during bone fracture healing. Within the complex three-dimensional (3-D) in vivo microenvironment, hMSC migration is regulated through a myriad of extracellular cues. Here, we use a thiol-ene photopolymerized hydrogel to recapitulate structural and bioactive inputs in a tunable manner to understand their role in regulating 3-D hMSC migration. Specifically, peptide-functionalized poly(ethylene glycol) hydrogels were used to encapsulate hMSC while varying the crosslinking density, from 0.18±0.02 to 1.60±0.04 mM, and the adhesive ligand density, from 0.001 to 1.0 mM. Using live-cell videomicroscopy, migratory cell paths were tracked and fitted to a Persistent Random Walk model. It was shown that hMSC migrating through the lowest crosslinking density and highest adhesivity had more sustained polarization, higher migrating speeds (17.6±0.9 μm h(-1)) and higher cell spreading (elliptical form factor=3.9±0.2). However, manipulation of these material properties did not significantly affect migration persistence. Further, there was a monotonic increase in cell speed and spreading with increasing adhesivity that showed a lack of the biphasic trend seen in 2-D cell migration. Immunohistochemistry showed well-formed actin fibers and β1 integrin staining at the ends of stress fibers. This thiol-ene platform provides a highly tunable substrate to characterize 3-D hMSC migration that can be applied as an implantable cell carrier platform or for the recruitment of endogenous hMSC in vivo.

Nicotine reduced MMP-9 expression in the primary porcine tenocytes exposed to cyclic stretch

Nicotine is one of the major chemical components of the cigarette smoke, which has been known as a risk factor for tendon ruptures including rotator cuff tears. This study investigated the effect of nicotine on tenocytes under cyclic-stretched condition. Particularly, we focused on the morphologic changes of tenocytes and their expression of MMPs. Primary porcine tenocytes were obtained from the infraspinatus tendon. The cells were cultured on elastic chambers under static or cyclic-stretched condition for 24 h in the existence of nicotine (0, 1, 10, and 100 µM). Cell shape, gene expression of collagen type I and III, MMPs (-1, -2, -3, -9, and -13) and TIMPs (-1, -2, and -3) and enzyme activity of MMP-9 were analyzed using immunohistochemistry, RT-PCR, and zymography. Tenocytes exposed to nicotine represented significantly decreased gene expressions in MMP-9 (p < 0.001) and TIMP-3 (p < 0.05) under the cyclic stretch. Enzymatic activity of MMP-9 was also reduced by nicotine exposure in a dose-dependent manner (p < 0.001). The down-regulation of MMP and TIMP expression by nicotine shown in our in vitro experiment might deteriorate normal metabolism of the tendon. These mechanisms might affect the mechanical properties of the extracellular matrix of the rotator cuff tendon.

The role of microRNA-146a in the pathogenesis of the diabetic wound-healing impairment: correction with mesenchymal stem cell treatment

The impairment in diabetic wound healing represents a significant clinical problem. Chronic inflammation is thought to play a central role in the pathogenesis of this impairment. We have previously shown that treatment of diabetic murine wounds with mesenchymal stem cells (MSCs) can improve healing, but the mechanisms are not completely defined. MicroRNA-146a (miR-146a) has been implicated in regulation of the immune and inflammatory responses. We hypothesized that abnormal miRNA-146a expression may contribute to the chronic inflammation. To test this hypothesis, we examined the expression of miRNA-146a and its target genes in diabetic and nondiabetic mice at baseline and after injury. MiR-146a expression was significantly downregulated in diabetic mouse wounds. Decreased miR-146a levels also closely correlated with increased gene expression of its proinflammatory target genes. Furthermore, the correction of the diabetic wound-healing impairment with MSC treatment was associated with a significant increase in the miR-146a expression level and decreased gene expression of its proinflammatory target genes. These results provide the first evidence that decreased expression of miR-146a in diabetic wounds in response to injury may, in part, be responsible for the abnormal inflammatory response seen in diabetic wounds and may contribute to wound-healing impairment.

Extracellular matrix remodeling: the common denominator in connective tissue diseases. Possibilities for evaluation and current understanding of the matrix as more than a passive architecture, but a key player in tissue failure

Increased attention is paid to the structural components of tissues. These components are mostly collagens and various proteoglycans. Emerging evidence suggests that altered components and noncoded modifications of the matrix may be both initiators and drivers of disease, exemplified by excessive tissue remodeling leading to tissue stiffness, as well as by changes in the signaling potential of both intact matrix and fragments thereof. Although tissue structure until recently was viewed as a simple architecture anchoring cells and proteins, this complex grid may contain essential information enabling the maintenance of the structure and normal functioning of tissue. The aims of this review are to (1) discuss the structural components of the matrix and the relevance of their mutations to the pathology of diseases such as fibrosis and cancer, (2) introduce the possibility that post-translational modifications (PTMs), such as protease cleavage, citrullination, cross-linking, nitrosylation, glycosylation, and isomerization, generated during pathology, may be unique, disease-specific biochemical markers, (3) list and review the range of simple enzyme-linked immunosorbent assays (ELISAs) that have been developed for assessing the extracellular matrix (ECM) and detecting abnormal ECM remodeling, and (4) discuss whether some PTMs are the cause or consequence of disease. New evidence clearly suggests that the ECM at some point in the pathogenesis becomes a driver of disease. These pathological modified ECM proteins may allow insights into complicated pathologies in which the end stage is excessive tissue remodeling, and provide unique and more pathology-specific biochemical markers.

The involvement of oxidants and NF-κB in cytokine-induced MMP-9 synthesis by bone marrow-derived osteoprogenitor cells

OBJECTIVE AND DESIGN

The activity of immune cells affects the balance between bone mineralization and resorption carried out by the opposing actions of osteoblasts and osteoclasts, respectively. This study was aimed at determining the possible interaction between inflammatory conditions and collagen type I degrading MMP (mainly MMP-2 and MMP-9) synthesis and secretion in rat osteoprogenitors.

MATERIALS AND METHODS

The study was performed using primary rat bone marrow-derived osteoprogenitors during their advanced osteogenesis. Biochemical, immunohistochemical, and molecular biology techniques were used to investigate the influence of pro-inflammatory cytokines on MMP-2 and MMP-9 synthesis and secretion in osteoprogenitors.

RESULTS

Results indicated that both synthesis and secretion of MMPs (MMP-1, -2, -8, -9, and -13) were significantly induced after pro-inflammatory cytokine treatments, except MMP-2, whose levels remained unchanged. NF-κB (nuclear factor kappa-light chain enhancer of activated B cells) inhibition assays showed that induced MMP-9 secretion by inflammatory cytokines was mediated by activation of NF-κB via the classical pathway and that oxidants play a significant role in this signal transduction pathway. In contrast, no such effect was observed for synthesis of MMP-2.

CONCLUSIONS

These results indicate the possibility that inflammatory processes may trigger osteoblasts to absorb bone by secreting elevated levels of MMPs capable of degrading collagen type I, especially MMP-9 which is upregulated due to increased NF-κB transcription activity.

Bioprocess forces and their impact on cell behavior: implications for bone regeneration therapy

Bioprocess forces such as shear stress experienced during routine cell culture are considered to be harmful to cells. However, the impact of physical forces on cell behavior is an area of growing interest within the tissue engineering community, and it is widely acknowledged that mechanical stimulation including shear stress can enhance osteogenic differentiation. This paper considers the effects of bioprocess shear stress on cell responses such as survival and proliferation in several contexts, including suspension-adapted cells used for recombinant protein and monoclonal antibody manufacture, adherent cells for therapy in suspension, and adherent cells attached to their growth substrates. The enhanced osteogenic differentiation that fluid flow shear stress is widely found to induce is discussed, along with the tissue engineering of mineralized tissue using perfusion bioreactors. Recent evidence that bioprocess forces produced during capillary transfer or pipetting of cell suspensions can enhance osteogenic responses is also discussed.

Post-translational modifications of the extracellular matrix are key events in cancer progression: opportunities for biochemical marker development

The aim of this review is to discuss the potential usefulness of a novel class of biochemical markers, designated neoepitopes. Neoepitopes are post-translational modifications (PTMs) of proteins and are derived by processes, such as protease cleavage, citrullination, nitrosylation, glycosylation and isomerization. Each PTM results from a specific local physiological or pathobiological process. Identification of each modification to a tissue-specific protein may reveal a unique disease-specific biochemical marker. During cancer metastasis, the host tissue is extensively degraded and replaced by cancer-associated extracellular matrix (ECM) proteins. Furthermore, severe cellular stress and inflammation, caused by cancer, results in generation of PTMs, which will be distributed throughout the ECM. This gives rise to release of protein-specific fragments to the circulation. Here we highlight the importance of remodeling of the ECM in cancer and the generation of PTMs, which may be cancer specific and reflect disease progression; thus having potential for biochemical marker development.

Divergent upstream osteogenic events contribute to the differential modulation of MG63 cell osteoblast differentiation by MMP-1 (collagenase-1) and MMP-13 (collagenase-3)

Previously we showed that MMP-1 (collagenase-1) and MMP-13 (collagenase-3) differentially regulate the expression of osteoblastic markers in a heterogenous population of primary human periodontal ligament cells. The mechanisms for these differential responses are not known, but may result from divergence in regulation of early osteogenic transcription factors. The purpose of this study was to elucidate where in the hierarchy of osteoblast-specific transcription factors and markers the differences in MMP-1- and -13-mediated regulation of osteoblastic differentiation arise. We found that the overexpression of MMP-1 resulted in significant decreases in BMP-2, Dlx5, AP, OP and BSP and increases in TGF-β1 and MSX2. In contrast, MMP-13 overexpression resulted in significant decreases in Runx2, OP and BSP, and increases in TGF-β1, MSX2 and OC. The knockdown of MMP-1 caused significant increases in all osteoblastic markers. MMP-13 knockdown produced significant increases only in TGF-β1, MSX2 and Osx, but decreases in Runx2 and OC. Suppression of both MMPs together resulted in significant increases of all osteoblastic markers except Runx2. MMP-1 had a more robust and generalized effect in regulating osteoblast transcription factors and markers than MMP-13. Finally, of the markers and transcription factors assayed, Runx2 is the most early stage transcription factor induced by suppression of MMP-1, while Osx and MSX2 are the most early stage transcription factors regulated by MMP-13. These data show that MMP-1's and -13's differential regulation of osteoblastic markers in MG63 cells likely results from their modulation of divergent signaling pathways involved in osteoblastic differentiation.

The performance of human mesenchymal stem cells encapsulated in cell-degradable polymer-peptide hydrogels

Thiol-ene photopolymerization offers a unique platform for the formation of peptide-functionalized poly(ethylene glycol) hydrogels and the encapsulation, culture and differentiation of cells. Specifically, this photoinitiated polymerization scheme occurs at neutral pH and can be controlled both spatially and temporally. Here, we have encapsulated human mesenchymal stem cells (hMSCs) in matrix metalloproteinase (MMP) degradable and cell-adhesive hydrogels using thiol-ene photopolymerization. We find that hMSCs survive equally well in this system, regardless of MMP-degradability. When hMSCs are encapsulated in these cell-degradable hydrogels, they survive and are able to proliferate. In classic hMSC differentiation medias, hMSCs locally remodel their microenvironment and take on characteristic morphologies; hMSCs cultured in growth or osteogenic differentiation media are less round, as measured by elliptical form factor, and are smaller than hMSCs cultured in chondrogenic or adipogenic differentiation media. In addition, hMSCs encapsulated in completely cell-degradable hydrogels and cultured in osteogenic, chondrogenic, or adipogenic differentiation media generally express increased levels of specific differentiation markers as compared to cells in hydrogels that are not cell-degradable. These studies demonstrate the ability to culture and differentiate hMSCs in MMP-degradable hydrogels polymerized via a thiol-ene reaction scheme and that increased cell-mediated hydrogel degradability facilitates directed differentiation of hMSCs.

Matrix metalloproteinases as master regulators of the vicious cycle of bone metastasis

Bone remodeling is a delicate balancing act between the bone matrix synthesizing osteoblasts and bone resorbing osteoclasts. Active bone metastases typically subvert this process to generate lesions that are comprised of extensive areas of pathological osteogenesis and osteolysis. The resultant increase in bone matrix remodeling enhances cytokine/growth factor bioavailability thus creating a vicious cycle that stimulates tumor progression. Given the extent of matrix remodeling occurring in the tumor-bone microenvironment, the expression of matrix metalloproteinases (MMPs) would be expected, since collectively they have the ability to degrade all components of the extracellular matrix (ECM). However, in addition to being "matrix bulldozers", MMPs control the bioavailability and bioactivity of factors such as RANKL and TGFβ that have been described as crucial for tumor-bone interaction, thus implicating MMPs as key regulators of the vicious cycle of bone metastases.

Local communication on and within bone controls bone remodeling

Bone remodeling is required for healthy calcium homeostasis and for repair of damage occurring with stress and age. Osteoclasts resorb bone and osteoblasts form bone. These processes normally occur in a tightly regulated sequence of events, where the amount of formed bone equals the amount of resorbed bone, thereby restoring the removed bone completely. Osteocytes are the third cell type playing an essential role in bone turnover. They appear to regulate activation of bone remodeling, and they exert both positive and negative regulation on both osteoclasts and osteoblasts. In this review, we consider the intricate communication between these bone cells in relation to bone remodeling, reviewing novel data from patients with mutations rendering different cell populations inactive, which have shown that these interactions are more complex than originally thought. We highlight the high probability that a detailed understanding of these processes will aid in the development of novel treatments for bone metabolic disorders, i.e. we discuss the possibility that bone resorption can be attenuated pharmacologically without a secondary reduction in bone formation.

Overexpression of cathepsin K accelerates the resorption cycle and osteoblast differentiation in vitro

Bone resorption is a multistep process including osteoclast attachment, cytoskeletal reorganization, formation of four distinct plasma membrane domains, and matrix demineralization and degradation followed by cell detachment. The present study describes the intracellular mechanisms by which overexpression of cathepsin K in osteoclasts results in enhanced bone resorption. Osteoclasts and bone marrow-derived osteoclast and osteoblast precursors were isolated from mice homozygous (UTU17(+/+)) and negative for the transgene locus. Cells cultured on bovine cortical bone slices were analyzed by fluorescence and confocal laser scanning microscopy, and bone resorption was studied by measurements of biochemical resorption markers, morphometry, and FESEM. Excessive cathepsin K protein and enzyme activity were microscopically observed in various intracellular vesicles and in the resorption lacunae of cathepsin K-overexpressing osteoclasts. The number of cathepsin K-containing vesicles in UTU17(+/+) osteoclasts was highly increased, and co-localization with markers for the biosynthetic and transcytotic pathways was observed throughout the cytoplasm. As a functional consequence of cathepsin K overexpression, biochemical resorption markers were increased in culture media of UTU17(+/+) osteoclasts. Detailed morphometrical analysis of the erosion in bone slices indicated that the increased biosynthesis of cathepsin K was sufficient to accelerate the osteoclastic bone resorption cycle. Cathepsin K overexpression also enhanced osteogenesis and induced the formation of exceptionally small, actively resorbing osteoclasts from their bone marrow precursors in vitro. The present study describes for the first time how enhancement in one phase of the osteoclastic resorption cycle also stimulates its other phases and further demonstrate that tight control and temporal coupling of mesenchymal and hematopoietic bone cells in this multistep process.

Characterization of human mesenchymal stem cell secretome at early steps of adipocyte and osteoblast differentiation

Background

It is well established that adipose tissue plays a key role in energy storage and release but is also a secretory organ and a source of stem cells. Among different lineages, stem cells are able to differentiate into adipocytes and osteoblasts. As secreted proteins could regulate the balance between both lineages, we aimed at characterizing the secretome of human multipotent adipose-derived stem cell (hMADS) at an early step of commitment to adipocytes and osteoblasts.

Results

A proteomic approach, using mono-dimensional electrophoresis and tandem mass spectrometry, allowed us to identify a total of 73 proteins at day 0 and day 3 of adipocyte and osteoblast differentiation. Analysis of identified proteins showed that 52 % corresponded to classical secreted proteins characterized by a signal peptide, that 37 % previously described in the extracellular compartment were devoid of signal peptide and that 11 % neither exhibited a signal peptide nor had been previously described extracellularly. These proteins were classified into 8 clusters according to their function. Quantitative analysis has been performed for 8 candidates: PAI-1, PEDF, BIGH3, PTX3, SPARC, ENO1, GRP78 and MMP2. Among them, PAI-1 was detected at day 0 and day 3 of osteoblast differentiation but never in adipocyte secretome. Furthermore we showed that PAI-1 mRNA was down-regulated in the bone of ovariectomized mice.

Conclusion

Given its regulation during the early events of hMADS cell differentiation and its status in ovariectomized mice, PAI-1 could play a role in the adipocyte/osteoblast balance and thus in bone diseases such as osteoporosis.

Exposure to pro-inflammatory cytokines upregulates MMP-9 synthesis by mesenchymal stem cells-derived osteoprogenitors

An intimate interplay exists between the bone and the immune system, which has been recently termed osteoimmunology. The activity of immune cells affects the intrinsic balance of bone mineralization and resorption carried out by the opposing actions of osteoblasts and osteoclasts. The aim of this study was to determine the possible interaction between inflammatory-induced conditions and matrix metalloproteinases-2,-9 (MMP-2,-9) synthesis and secretion by bone marrow-derived osteoprogenitor cells during advanced stages of osteogenesis. Rat bone marrow-derived mesenchymal stem cells (MSCs) were cultured in the presence of osteogenic supplements in order to direct the cells towards the osteogenic differentiation lineage. At the late stages of osteogenesis, assessed by histochemistry, immunohistochemistry and RT-PCR, cultures were exposed to pro-inflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 alpha (IL-1 alpha). Biochemical, histochemical and molecular biology techniques were used to discern the influence of pro-inflammatory cytokines on MMP-2,-9 synthesis and secretion. Results indicated that MMP-9 synthesis and secretion were significantly induced after exposure to the cytokines (TNF-alpha, IL-1 alpha) treatment, while MMP-2 levels remained unchanged. These results indicate that in response to inflammatory processes, osteoblasts, in addition to osteoclasts, can also be involved and contribute to the process of active bone resorption by secretion and activation of MMPs.

Microenvironmental changes during differentiation of mesenchymal stem cells towards chondrocytes

Chondrogenesis is a process involving stem-cell differentiation through the coordinated effects of growth/differentiation factors and extracellular matrix (ECM) components. Recently, mesenchymal stem cells (MSCs) were found within the cartilage, which constitutes a specific niche composed of ECM proteins with unique features. Therefore, we hypothesized that the induction of MSC differentiation towards chondrocytes might be induced and/or influenced by molecules from the microenvironment. Using microarray analysis, we previously identified genes that are regulated during MSC differentiation towards chondrocytes. In this study, we wanted to precisely assess the differential expression of genes associated with the microenvironment using a large-scale real-time PCR assay, according to the simultaneous detection of up to 384 mRNAs in one sample. Chondrogenesis of bone-marrow-derived human MSCs was induced by culture in micropellet for various periods of time. Total RNA was extracted and submitted to quantitative RT-PCR. We identified molecules already known to be involved in attachment and cell migration, including syndecans, glypicans, gelsolin, decorin, fibronectin, and type II, IX and XI collagens. Importantly, we detected the expression of molecules that were not previously associated with MSCs or chondrocytes, namely metalloproteases (MMP-7 and MMP-28), molecules of the connective tissue growth factor (CTGF); cef10/cyr61 and nov (CCN) family (CCN3 and CCN4), chemokines and their receptors chemokine CXC motif ligand (CXCL1), Fms-related tyrosine kinase 3 ligand (FlT3L), chemokine CC motif receptor (CCR3 and CCR4), molecules with A Disintegrin And Metalloproteinase domain (ADAM8, ADAM9, ADAM19, ADAM23, A Disintegrin And Metalloproteinase with thrombospondin type 1 motif ADAMTS-4 and ADAMTS-5), cadherins (4 and 13) and integrins (alpha4, alpha7 and beta5). Our data suggest that crosstalk between ECM components of the microenvironment and MSCs within the cartilage is responsible for the differentiation of MSCs into chondrocytes.

Role of matrix metalloproteinase 13 in both endochondral and intramembranous ossification during skeletal regeneration

Extracellular matrix (ECM) remodeling is important during bone development and repair. Because matrix metalloproteinase 13 (MMP13, collagenase-3) plays a role in long bone development, we have examined its role during adult skeletal repair. In this study we find that MMP13 is expressed by hypertrophic chondrocytes and osteoblasts in the fracture callus. We demonstrate that MMP13 is required for proper resorption of hypertrophic cartilage and for normal bone remodeling during non-stabilized fracture healing, which occurs via endochondral ossification. However, no difference in callus strength was detected in the absence of MMP13. Transplant of wild-type bone marrow, which reconstitutes cells only of the hematopoietic lineage, did not rescue the endochondral repair defect, indicating that impaired healing in Mmp13^−/− mice is intrinsic to cartilage and bone. Mmp13^−/− mice also exhibited altered bone remodeling during healing of stabilized fractures and cortical defects via intramembranous ossification. This indicates that the bone phenotype occurs independently from the cartilage phenotype. Taken together, our findings demonstrate that MMP13 is involved in normal remodeling of bone and cartilage during adult skeletal repair, and that MMP13 may act directly in the initial stages of ECM degradation in these tissues prior to invasion of blood vessels and osteoclasts.

Effects of glucosamine on the tibial epiphyseal disk of ovariectomized rats: morphologic and morphometric analysis

OBJECTIVE

The aim of this study was to analyze the effect of glucosamine sulfate on the tibial epiphyseal disk of the ovariectomized rats.

METHODS

After ovariectomy (OVx), 28 female rats were randomly divided into 4 experimental groups with 7 animals each, treated as follows: OVx 21 - vehicle (NaCl 0.9%) 0.5 mL/day) for 21 days; OVx GS21 - 230 mg/kg/day glucosamine sulphate for 21 days; OVx 45 - treated with NaCl 0.9% as above for 45 days; and OVx - GS45230 mg/kg/day glucosamine sulphate for 45 days. Seven intact animals in the proestrous phase were used as controls (CG). Upon treatment completion, the animals were sacrificed and the left knee joint was dissected and prepared for histological analysis.

RESULTS

The percentage of remaining cartilage in new bone of the CG; that found in THE OVx GS45 group was significantly less than that of the OVx 21, OVx GS21, and OVx 45 groups. The percentage of trabecular bone in proestrous animals was the highest. The OVx GS45 group showed higher values compared with the other ovariectomized groups. These results were paralleled by the findings regarding the cells of the proliferative zone, since the CG had the highest values, and the values of the OVx GS45 group were greater than those of the OVx 21, OVx GS21, and OVx 45 groups.

CONCLUSION

Our studies suggested that glucosamine may stimulate tibial cartilage and bone growth after ovariectomy in rats.

Properties of the stromal cell in giant cell tumor of bone

The histiogenesis and mechanisms of bone destruction in giant cell tumor (GCT) of bone are not well understood. We asked whether the spindle-like stromal cells of GCT of bone exhibit osteoblastic properties, and whether the stromal cells produce active matrix-degrading proteases in vitro. We performed immunohistochemistry on 17 paraffin-embedded archival specimens with a pathologic diagnosis of GCT with monoclonal antibodies for the osteoblastic lineage markers osteopontin, osteonectin, and osteocalcin. The average staining grade for the 17 specimens was highest for osteonectin, followed by osteopontin, and osteocalcin. Primary cell cultures of GCT stromal cells were prepared from two fresh tumor specimens. Western blots were used on the cell lysates and media to detect osteocalcin precursor and the matrix-degrading proteases MMP-2 and MMP-9. We found the stromal cells in culture produce osteocalcin precursor, indicating osteoblastic lineage. The cells also express both the active and inactive isoforms of MMP-2 and MMP-9. Gelatinase assays confirmed the activity of the proteases in vitro. The spindle like stromal cells of GCT have characteristics of osteoblast progenitors and produce active matrix-degrading proteases. These cells may therefore play a central role in bone destruction.

Matrix metalloprotease activity is an essential link between mechanical stimulus and mesenchymal stem cell behavior

Progenitor cells are involved in the regeneration of the musculoskeletal system, which is known to be influenced by mechanical boundary conditions. Furthermore, matrix metalloproteases (MMPs) and tissue-specific inhibitors of metalloproteases (TIMPs) are crucial for matrix remodelling processes that occur during regeneration of bone and other tissues. This study has therefore investigated whether MMP activity affects mesenchymal stem cell (MSC) behavior and how MMP activity is influenced by the mechanical stimulation of these cells. Broad spectrum inhibition of MMPs altered the migration, proliferation, and osteogenic differentiation of MSCs. Expression analysis detected MMP-2, -3, -10, -11, -13, and -14, as well as TIMP-2, in MSCs at the mRNA and protein levels. Mechanical stimulation of MSCs led to an upregulation of their extracellular gelatinolytic activity, which was consistent with the increased protein levels seen for MMP-2, -3, -13, and TIMP-2. However, mRNA expression levels of MMPs/TIMPs showed no changes in response to mechanical stimulation, indicating an involvement of post-transcriptional regulatory processes such as alterations in MMP secretion or activation. One potential regulatory molecule might be the furin protease. Specific inhibition of MMP-2, -3, and -13 showed MMP-13 to be involved in osteogenic differentiation. The results of this study suggest that MSC function is controlled by MMP activity, which in turn is regulated by mechanical stimulation of cells. Thus, MMP/TIMP balance seems to play an essential role in transferring mechanical signals into MSC function. Disclosure of potential conflicts of interest is found at the end of this article.

Treatment of diabetic wounds with fetal murine mesenchymal stromal cells enhances wound closure

Diabetes impairs multiple aspects of the wound-healing response. Delayed wound healing continues to be a significant healthcare problem for which effective therapies are lacking. We have hypothesized that local delivery of mesenchymal stromal cells (MSC) at a wound might correct many of the wound-healing impairments seen in diabetic lesions. We treated excisional wounds of genetically diabetic (Db-/Db-) mice and heterozygous controls with either MSC, CD45(+) cells, or vehicle. At 7 days, treatment with MSC resulted in a decrease in the epithelial gap from 3.2 +/- 0.5 mm in vehicle-treated wounds to 1.3 +/- 0.4 mm in MSC-treated wounds and an increase in granulation tissue from 0.8 +/- 0.3 mm(2) to 2.4 +/- 0.6 mm(2), respectively (mean +/- SD, P < 0.04). MSC-treated wounds also displayed a higher density of CD31(+) vessels and exhibited increases in the production of mRNA for epidermal growth factor, transforming growth factor beta 1, vascular endothelial growth factor, and stromal-derived growth factor 1-alpha. MSC also demonstrated greater contractile ability than fibroblast controls in a collagen gel contraction assay. The effects of locally applied MSC are thus sufficient to improve healing in diabetic mice. Possible mechanisms of this effect include augmented local growth-factor production, improved neovascularization, enhanced cellular recruitment to wounds, and improved wound contraction.

Gene expression profiling of bone marrow stromal cells from juvenile, adult, aged and osteoporotic rats: with an emphasis on osteoporosis

PURPOSE

Osteoporosis is a multi-factorial, age-related disease with a complex etiology and mode of regulation involving a large numbers of genes. To better understand the possible relationships among genes, we fingerprinted genes in a rat model induced by ovariectomy to determine differences among osteoporotic, non-osteoporotic, aged and juvenile rats.

METHODS

We applied genome wide cDNA microarray technology to analyze genes expressed in bone marrow mesenchymal stromal cells (BMSC) and compared non-osteoporotic adult vs. osteoporotic, non-osteoporotic adult vs. aged, and non-osteoporotic adult vs. juvenile. Rigorous statistical analysis of functional annotation (EASE program) identified over-represented biological and molecular functions with significant group wide changes (p< or =0.05). Some of the expressed genes were further confirmed by quantitative RT-PCR (reverse transcription-polymerase chain reaction).

RESULTS

Differences in gene expression were observed by identifying transcripts selected by t-test that were consistently changed by a minimum of two-fold. There were 195 transcripts that showed an increased expression and 109 transcripts that showed decreased expression relative to the osteoporotic condition. Of these, 75% transcripts were unknown gene products or ESTs (expressed sequence tag). A number of genes found in the aged and juvenile groups were not present in the osteoporotic rats. Functional clustering of the genes using the EASE bioinformatics program revealed that transcripts in osteoporosis were associated with signal transduction, lipid metabolism, protein metabolism, ionic and protein transport, neuropeptide and G protein signaling pathways. Although some of the genes have previously been shown to play a key role in osteoporosis, several genes were uniquely identified in this study and likely play a role in developing aged related osteoporosis that could have compelling implications in the development of new diagnostic strategies and therapeutics for osteoporosis.

CONCLUSIONS

These data suggest that osteoporosis is associated with changes of multiple novel gene expression and that numerous pathways could play important roles in osteoporosis pathogenesis.

The role of matrix metalloproteinases in the oral environment

This review focuses specifically on matrix metalloproteinases (MMPs) and their role in physiological and pathological extracellular matrix (ECM) remodeling and degradation processes in the oral environment. A group of enzymes capable of degrading almost all ECM proteins, MMPs contribute to both normal and pathological tissue remodeling. The expression of different MMPs may be upregulated in pathological conditions such as inflammation and tumor invasion. The balance between activated MMPs and tissue inhibitors of metalloproteinases (TIMPs) controls the extent of ECM remodeling. Prior to mineralization, MMPs may participate in the organization of enamel and dentin organic matrix, or they may regulate mineralization by controlling the proteoglycan turnover. There is evidence indicating that MMPs could be involved in the etiology of enamel fluorosis and amelogenesis imperfecta. They seem to play a part in dentinal caries progression, since they have a crucial role in dentin collagen breakdown in caries lesions. MMPs have been identified in pulpal and periapical inflammation and are strongly correlated with periodontal diseases, since they are the major players in collagen breakdown during periodontal tissue destruction. The use of MMP inhibitors could help the prevention and treatment of many MMP-related oral diseases.

Akt signaling regulates actin organization via modulation of MMP-2 activity during chondrogenesis of chick wing limb bud mesenchymal cells

Endochondral ossification is initiated by the differentiation of mesenchymal precursor cells to chondrocytes. This process is characterized by a strong interdependence of cell shape and cytoskeletal organization accompanying the onset of chondrogenic gene expression, but the molecular mechanisms mediating these interactions are not known. In this study, we hypothesized that the activation of matrix metalloproteinase (MMP)-2 would be involved in the reorganization of the actin cytoskeleton and that this would require an Akt-dependent signaling pathway in chick wing bud mesenchymal cells. The pharmacological inhibition of Akt signaling resulted in decreased glycosaminoglycan synthesis and reduced the level of active MMP-2, leading to suppressed cortical actin organization which is characteristic of differentiated chondrocytes. In addition, the exposure of cells to bafilomycin A1 reversed these chondro-inhibitory effects induced by inhibition of Akt signaling. In conclusion, our data indicate that Akt signaling is involved in the activation of MMP-2 and that this Akt-induced activation of MMP-2 is responsible for reorganization of the actin cytoskeleton into a cortical pattern with parallel rounding of chondrogenic competent cells.

MMP-2, MT1-MMP, and TIMP-2 are essential for the invasive capacity of human mesenchymal stem cells: differential regulation by inflammatory cytokines

Human mesenchymal stem cells (hMSCs) represent promising tools in various clinical applications, including the regeneration of injured tissues by endogenous or transplanted hMSCs. The molecular mechanisms, however, that control hMSC mobilization and homing which require invasion through extracellular matrix (ECM) barriers are almost unknown. We have analyzed bone marrow-derivedhMSCs and detected strong expression and synthesis of matrix metalloproteinase 2 (MMP-2), membrane type 1 MMP (MT1-MMP), tissue inhibitor of metalloproteinase 1 (TIMP-1), and TIMP-2. The ability of hMSCs to traverse reconstituted human basement membranes was effectively blocked in the presence of synthetic MMP inhibitors. Detailed studies by RNA interference revealed that gene knock-down of MMP-2, MT1-MMP, or TIMP-2 substantially impaired hMSC invasion, whereas silencing of TIMP-1 enhanced cell migration, indicating opposing roles of both TIMPs in this process. Moreover, the inflammatory cytokines TGF-beta1, IL-1beta, and TNF-alpha up-regulated MMP-2, MT1-MMP, and/or MMP-9 production in these cells, resulting in a strong stimulation of chemotactic migration through ECM, whereas the chemokine SDF-1alpha exhibited minor effects on MMP/TIMP expression and cell invasion. Thus, induction of specific MMP activity in hMSCs by inflammatory cytokines promotes directed cell migration across reconstituted basement membranes in vitro providing a potential mechanism in hMSC recruitment and extravasation into injured tissues in vivo.

Human osteoblasts produce cathepsin K

Healthy bone is a rigid yet living tissue that undergoes continuous remodeling. Osteoclasts resorb bone in the remodeling cycle. They secrete H(+)-ions and proteinases to dissolve bone mineral and degrade organic bone matrix, respectively. One of the main collagenolytic proteinase in osteoclasts is cathepsin K, a member of papain family cysteine proteinases. Recently, it has been shown that osteoblasts may contribute to organic matrix remodeling. We therefore investigated their ability to produce cathepsin K for this action. Trabecular bone samples were collected from patients operated due to a fracture of the femoral neck. Part of the bone was decalcified and the rest was used for cell isolation. Sections from the decalcified bone were immunostained with antibodies against cathepsin K. Isolated cells were characterized for their ability to form mineralized matrix and subsequently analyzed for their cathepsin K production by Western blotting and quantitative RT-PCR. Osteoblasts, bone lining cells and some osteocytes in situ showed cathepsin K immunoreactivity and osteoblast-like cells in vitro produced cathepsin K mRNA and released both 42 kDa pro- and 27 kDa processed cathepsin K to culture media. Osteoblastic cathepsin K may thus contribute to collagenous matrix maintenance and recycling of improperly processed collagen I. Whether osteoblastic cathepsin K synthesis has consequences in diseases characterized by abnormal bone matrix turnover remains to be investigated.