Exogenous nitric oxide enhances calcification in embryonic stem cell-derived osteogenic cultures

The FOXO signaling axis displays conjoined functions in redox homeostasis and stemness

Previous views of reactive oxygen species (ROS) depicted them as harmful byproducts of metabolism as uncontrolled levels of ROS can lead to DNA damage and cell death. However, recent studies have shed light into the key role of ROS in the self-renewal or differentiation of the stem cell. The interplay between ROS levels, metabolism, and the downstream redox signaling pathways influence stem cell fate. In this review we will define ROS, explain how they are generated, and how ROS signaling can influence transcription factors, first and foremost forkhead box-O transcription factors, that shape not only the cellular redox state, but also stem cell fate. Now that studies have illustrated the importance of redox homeostasis and the role of redox signaling, understanding the mechanisms behind this interplay will further shed light into stem cell biology.

Is There a Governing Role of Osteocytes in Bone Tissue Regeneration?

PURPOSE OF REVIEW

Bone regeneration plays an important role in contemporary clinical treatment. Bone tissue engineering should result in successful bone regeneration to restore congenital or acquired bone defects in the human skeleton. Osteocytes are thought to have a governing role in bone remodeling by regulating osteoclast and osteoblast activity, and thus bone loss and formation. In this review, we address the so far largely unknown role osteocytes may play in bone tissue regeneration.

RECENT FINDINGS

Osteocytes release biochemical signaling molecules involved in bone remodeling such as prostaglandins, nitric oxide, Wnts, and insulin-like growth factor-1 (IGF-1). Treatment of mesenchymal stem cells in bone tissue engineering with prostaglandins (e.g., PGE₂, PGI₂, PGF_2α), nitric oxide, IGF-1, or Wnts (e.g., Wnt3a) improves osteogenesis. This review provides an overview of the functions of osteocytes in bone tissue, their interaction with other bone cells, and their role in bone remodeling. We postulate that osteocytes may have a pivotal role in bone regeneration as well, and consequently that the bone regeneration process may be improved effectively and rapidly if osteocytes are optimally used and stimulated.

Supplement of nitric oxide through calcium carbonate-based nanoparticles contributes osteogenic differentiation of mouse embryonic stem cells

This study investigated the delivery of S-nitrosothiol (GSNO) as a nitric oxide (NO) donor loaded into calcium carbonate-based mineralized nanoparticles (GSNO-MNPs) to regulate cell signaling pathways for the osteogenic differentiation of mouse embryonic stem cells (ESCs). GSNO-MNPs were prepared by an anionic block copolymer template-mediated calcium carbonate (CaCO₃) mineralization process in the presence of GSNO. GSNO-MNPs were spherical and had a narrow size distribution. GSNO was stably loaded within the MNPs without denaturation. TEM analysis also demonstrated the localization of GSNO-MNPs within membrane-bound structures in the cell, indicating the successful introduction of GSNO-MNPs into the cytosol of ESCs. Intracellular levels of NO and cGMP were significantly increased upon treatment with GSNO-MNPs, compared with the control group. When cells were exposed to GSNO-MNPs, the effects of nanoparticles on cell viability were not statistically significant. GSNO-MNPs treatment increased ALP activity assay and intracellular calcium levels. Real-time RT-PCR also revealed highly increased expression levels of the osteogenic target genes ALP, osteocalcin (OCN), and osterix (OSX) in GSNO-MNP-treated ESCs. The protein levels of OSX and Runt-related transcription factor 2 (RUNX2) showed similar patterns of expression based on real-time RT-PCR. These results indicate that GSNO-MNPs influenced the osteogenic differentiation of ESCs. Transcriptome profiling identified several significantly enriched and involved biological networks, such as RAP1, RAS, PI3K-AKT, and MAPK signaling pathways. These findings suggest that GSNO-MNPs can modulate osteogenic differentiation in ESCs via complex molecular pathways.

Lysed Erythrocyte Membranes Promote Vascular Calcification

BACKGROUND

Intraplaque hemorrhage promotes atherosclerosis progression, and erythrocytes may contribute to this process. In this study we examined the effects of red blood cells on smooth muscle cell mineralization and vascular calcification and the possible mechanisms involved.

METHODS

Erythrocytes were isolated from human and murine whole blood. Intact and lysed erythrocytes and their membrane fraction or specific erythrocyte components were examined in vitro using diverse calcification assays, ex vivo by using the murine aortic ring calcification model, and in vivo after murine erythrocyte membrane injection into neointimal lesions of hypercholesterolemic apolipoprotein E-deficient mice. Vascular tissues (aortic valves, atherosclerotic carotid artery specimens, abdominal aortic aneurysms) were obtained from patients undergoing surgery.

RESULTS

The membrane fraction of lysed, but not intact human erythrocytes promoted mineralization of human arterial smooth muscle cells in culture, as shown by Alizarin red and van Kossa stain and increased alkaline phosphatase activity, and by increased expression of osteoblast-specific transcription factors (eg, runt-related transcription factor 2, osterix) and differentiation markers (eg, osteopontin, osteocalcin, and osterix). Erythrocyte membranes dose-dependently enhanced calcification in murine aortic rings, and extravasated CD235a-positive erythrocytes or Perl iron-positive signals colocalized with calcified areas or osteoblast-like cells in human vascular lesions. Mechanistically, the osteoinductive activity of lysed erythrocytes was localized to their membrane fraction, did not involve membrane lipids, heme, or iron, and was enhanced after removal of the nitric oxide (NO) scavenger hemoglobin. Lysed erythrocyte membranes enhanced calcification to a similar extent as the NO donor diethylenetriamine-NO, and their osteoinductive effects could be further augmented by arginase-1 inhibition (indirectly increasing NO bioavailability). However, the osteoinductive effects of erythrocyte membranes were reduced in human arterial smooth muscle cells treated with the NO scavenger 2-phenyl-4,4,5,5-tetramethylimidazoline-1-oxyl 3-oxide or following inhibition of NO synthase or the NO receptor soluble guanylate cyclase. Erythrocytes isolated from endothelial NO synthase-deficient mice exhibited a reduced potency to promote calcification in the aortic ring assay and after injection into murine vascular lesions.

CONCLUSIONS

Our findings in cells, genetically modified mice, and human vascular specimens suggest that intraplaque hemorrhage with erythrocyte extravasation and lysis promotes osteoblastic differentiation of smooth muscle cells and vascular lesion calcification, and also support a role for erythrocyte-derived NO.

Exogenous nitric oxide stimulates the odontogenic differentiation of rat dental pulp stem cells

Nitric oxide (NO) is thought to play a pivotal regulatory role in dental pulp tissues under both physiological and pathological conditions. However, little is known about the NO functions in dental pulp stem cells (DPSCs). We examined the direct actions of a spontaneous NO gas-releasing donor, NOC-18, on the odontogenic capacity of rat DPSCs (rDPSCs). In the presence of NOC-18, rDPSCs were transformed into odontoblast-like cells with long cytoplasmic processes and a polarized nucleus. NOC-18 treatment increased alkaline phosphatase activity and enhanced dentin-like mineralized tissue formation and the expression levels of several odontoblast-specific genes, such as runt related factor 2, dentin matrix protein 1 and dentin sialophosphoprotein, in rDPSCs. In contrast, carboxy-PTIO, a NO scavenger, completely suppressed the odontogenic capacity of rDPSCs. This NO-promoted odontogenic differentiation was activated by tumor necrosis factor-NF-κB axis in rDPSCs. Further in vivo study demonstrated that NOC-18-application in a tooth cavity accelerated tertiary dentin formation, which was associated with early nitrotyrosine expression in the dental pulp tissues beneath the cavity. Taken together, the present findings indicate that exogenous NO directly induces the odontogenic capacity of rDPSCs, suggesting that NO donors might offer a novel host DPSC-targeting alternative to current pulp capping agents in endodontics.

Bone biomaterials and interactions with stem cells

Bone biomaterials play a vital role in bone repair by providing the necessary substrate for cell adhesion, proliferation, and differentiation and by modulating cell activity and function. In past decades, extensive efforts have been devoted to developing bone biomaterials with a focus on the following issues: (1) developing ideal biomaterials with a combination of suitable biological and mechanical properties; (2) constructing a cell microenvironment with pores ranging in size from nanoscale to submicro- and microscale; and (3) inducing the oriented differentiation of stem cells for artificial-to-biological transformation. Here we present a comprehensive review of the state of the art of bone biomaterials and their interactions with stem cells. Typical bone biomaterials that have been developed, including bioactive ceramics, biodegradable polymers, and biodegradable metals, are reviewed, with an emphasis on their characteristics and applications. The necessary porous structure of bone biomaterials for the cell microenvironment is discussed, along with the corresponding fabrication methods. Additionally, the promising seed stem cells for bone repair are summarized, and their interaction mechanisms with bone biomaterials are discussed in detail. Special attention has been paid to the signaling pathways involved in the focal adhesion and osteogenic differentiation of stem cells on bone biomaterials. Finally, achievements regarding bone biomaterials are summarized, and future research directions are proposed.

Angiotensin (1-7) ameliorates the structural and biochemical alterations of ovariectomy-induced osteoporosis in rats via activation of ACE-2/Mas receptor axis

The local and systemic renin angiotensin system (RAS) influences the skeletal system micro-structure and metabolism. Studies suggested angiotensin 1-7 (Ang(1-7)) as the beneficial RAS molecule via Mas receptor activation. This study examines the function of Ang(1-7) in bone micro-architecture and metabolism in an ovariectomized (OVX) rodent model of osteoporosis. OVX rats showed structural and bone metabolic degeneration in parallel with suppressed expressions of the angiotensin converting enzyme-2 (ACE-2)/Ang(1-7)/Mas components. The infusion of Ang(1-7) markedly alleviated the altered bone metabolism and significantly enhanced both trabecular (metaphyseal) and cortical (metaphyseal-diaphyseal) morphometry. Urinary and bones minerals were also improved in OVX rats by Ang(1-7). The infusion of the heptapeptide enhanced ACE-2/Mas receptor expressions, while down-regulated AngII, ACE, and AngII type-1 receptor (AT1R) in OVX animals. Moreover, Ang(1-7) markedly improved osteoprotegerin (OPG) and lowered receptor activator NF-κB ligand (RANKL) expressions. The defensive properties of Ang(1-7) on bone metabolism, structure and minerals were considerably eradicated after blockage of Mas receptor with A-779. Ang(1-7)-induced up-regulated ACE-2/Ang(1-7)/Mas cascade and OPG expressions were abolished and the expressions of ACE/AngII/AT1R and RANKL were provoked by A-779. These findings shows for the first time the novel valuable therapeutic role of Ang(1-7) on bone health and metabolism through the ACE-2/Mas cascade.

A three-dimensional assemblage of gingiva-derived mesenchymal stem cells and NO-releasing microspheres for improved differentiation

Stem cell therapy is an attractive approach to bone tissue regeneration. Nitric oxide (NO) has been reported to facilitate osteogenic differentiation of stem cells. To enhance osteogenic differentiation of gingiva-derived mesenchymal stem cells (GMSCs), we designed a method for in situ delivery of exogenous NO to these cells. A NO donor, polyethylenimine/NONOate, was incorporated into poly(lactic-co-glycolic acid) microspheres to deliver NO to the cells for an extended period of time under in vitro culture conditions. A hybrid aggregate of GMSCs and NO-releasing microspheres was prepared by the hanging drop technique. Confocal microscopy revealed homogeneous arrangement of the stem cells and microspheres in heterospheroids. Western blot analysis and live-dead imaging showed no significant change in cell viability. Importantly, the in situ delivery of NO within the heterospheroids enhanced osteogenic differentiation indicated by a 1.2-fold increase in alkaline phosphatase activity and an approximately 10% increase in alizarin red staining. In addition, a low dose of NO promoted proliferation of the GMSCs in this 3D system. Thus, delivery of the NO-releasing microsphers to induce differentiation of stem cells within this three dimensional system may be one of possible strategies to direct differentiation of a stem cell-based therapeutic agent toward a specific lineage.

Molecular control of nitric oxide synthesis through eNOS and caveolin-1 interaction regulates osteogenic differentiation of adipose-derived stem cells by modulation of Wnt/β-catenin signaling

Background

Nitric oxide (NO) plays a role in a number of physiological processes including stem cell differentiation and osteogenesis. Endothelial nitric oxide synthase (eNOS), one of three NO-producing enzymes, is located in a close conformation with the caveolin-1 (CAV-1^WT) membrane protein which is inhibitory to NO production. Modification of this interaction through mutation of the caveolin scaffold domain can increase NO release. In this study, we genetically modified equine adipose-derived stem cells (eASCs) with eNOS, CAV-1^WT, and a CAV-1^F92A (CAV-1^WT mutant) and assessed NO-mediated osteogenic differentiation and the relationship with the Wnt signaling pathway.

Methods

NO production was enhanced by lentiviral vector co-delivery of eNOS and CAV-1^F92A to eASCs, and osteogenesis and Wnt signaling was assessed by gene expression analysis and activity of a novel Runx2-GFP reporter. Cells were also exposed to a NO donor (NONOate) and the eNOS inhibitor, l-NAME.

Results

NO production as measured by nitrite was significantly increased in eNOS and CAV-1^F92A transduced eASCs +(5.59 ± 0.22 μM) compared to eNOS alone (4.81 ± 0.59 μM) and un-transduced control cells (0.91 ± 0.23 μM) (p < 0.05). During osteogenic differentiation, higher NO correlated with increased calcium deposition, Runx2, and alkaline phosphatase (ALP) gene expression and the activity of a Runx2-eGFP reporter. Co-expression of eNOS and CAV-1^WT transgenes resulted in lower NO production. Canonical Wnt signaling pathway-associated Wnt3a and Wnt8a gene expressions were increased in eNOS-CAV-1^F92A cells undergoing osteogenesis whilst non-canonical Wnt5a was decreased and similar results were seen with NONOate treatment. Treatment of osteogenic cultures with 2 mM l-NAME resulted in reduced Runx2, ALP, and Wnt3a expressions, whilst Wnt5a expression was increased in eNOS-delivered cells. Co-transduction of eASCs with a Wnt pathway responsive lenti-TCF/LEF-dGFP reporter only showed activity in osteogenic cultures co-transduced with a doxycycline inducible eNOS. Lentiviral vector expression of canonical Wnt3a and non-canonical Wnt5a in eASCs was associated with induced and suppressed osteogenic differentiation, respectively, whilst treatment of eNOS-osteogenic cells with the Wnt inhibitor Dkk-1 significantly reduced expressions of Runx2 and ALP.

Conclusions

This study identifies NO as a regulator of canonical Wnt/β-catenin signaling to promote osteogenesis in eASCs which may contribute to novel bone regeneration strategies.

Electronic supplementary material

The online version of this article (doi:10.1186/s13287-016-0442-9) contains supplementary material, which is available to authorized users.