The nitric oxide donor sodium nitroprusside inhibits mineralization in ATDC5 cells

ABCC6 prevents ectopic mineralization seen in pseudoxanthoma elasticum by inducing cellular nucleotide release

Pseudoxanthoma elasticum (PXE) is an autosomal recessive disease characterized by progressive ectopic mineralization of the skin, eyes, and arteries, for which no effective treatment exists. PXE is caused by inactivating mutations in the gene encoding ATP-binding cassette sub-family C member 6 (ABCC6), an ATP-dependent efflux transporter present mainly in the liver. Abcc6(-/-) mice have been instrumental in demonstrating that PXE is a metabolic disease caused by the absence of an unknown factor in the circulation, the presence of which depends on ABCC6 in the liver. Why absence of this factor results in PXE has remained a mystery. Here we report that medium from HEK293 cells overexpressing either human or rat ABCC6 potently inhibits mineralization in vitro, whereas medium from HEK293 control cells does not. Untargeted metabolomics revealed that cells expressing ABCC6 excrete large amounts of nucleoside triphosphates, even though ABCC6 itself does not transport nucleoside triphosphates. Extracellularly, ectonucleotidases hydrolyze the excreted nucleoside triphosphates to nucleoside monophosphates and inorganic pyrophosphate (PPi), a strong inhibitor of mineralization that plays a pivotal role in several mineralization disorders similar to PXE. The in vivo relevance of our data are demonstrated in Abcc6(-/-) mice, which had plasma PPi levels <40% of those found in WT mice. This study provides insight into how ABCC6 affects PXE. Our data indicate that the factor that normally prevents PXE is PPi, which is provided to the circulation in the form of nucleoside triphosphates via an as-yet unidentified but ABCC6-dependent mechanism.

Embryonic stem cell-like cells derived from adult human testis

BACKGROUND

Given the significant drawbacks of using human embryonic stem (hES) cells for regenerative medicine, the search for alternative sources of multipotent cells is ongoing. Studies in mice have shown that multipotent ES-like cells can be derived from neonatal and adult testis. Here we report the derivation of ES-like cells from adult human testis.

METHODS

Testis material was donated for research by four men undergoing bilateral castration as part of prostate cancer treatment. Testicular cells were cultured using StemPro medium. Colonies that appeared sharp edged and compact were collected and subcultured under hES-specific conditions. Molecular characterization of these colonies was performed using RT-PCR and immunohistochemistry. (Epi)genetic stability was tested using bisulphite sequencing and karyotype analysis. Directed differentiation protocols in vitro were performed to investigate the potency of these cells and the cells were injected into immunocompromised mice to investigate their tumorigenicity.

RESULTS

In testicular cell cultures from all four men, sharp-edged and compact colonies appeared between 3 and 8 weeks. Subcultured cells from these colonies showed alkaline phosphatase activity and expressed hES cell-specific genes (Pou5f1, Sox2, Cripto1, Dnmt3b), proteins and carbohydrate antigens (POU5F1, NANOG, SOX2 and TRA-1-60, TRA-1-81, SSEA4). These ES-like cells were able to differentiate in vitro into derivatives of all three germ layers including neural, epithelial, osteogenic, myogenic, adipocyte and pancreatic lineages. The pancreatic beta cells were able to produce insulin in response to glucose and osteogenic-differentiated cells showed deposition of phosphate and calcium, demonstrating their functional capacity. Although we observed small areas with differentiated cell types of human origin, we never observed extensive teratomas upon injection of testis-derived ES-like cells into immunocompromised mice.

CONCLUSIONS

Multipotent cells can be established from adult human testis. Their easy accessibility and ethical acceptability as well as their non-tumorigenic and autogenic nature make these cells an attractive alternative to human ES cells for future stem cell therapies.

Trigeminal nitric oxide synthase expression correlates with new bone formation during distraction osteogenesis

Nitric oxide synthase (NOS) has been reported to be involved with both bone healing and bone metabolism. The aim of this study was to test the null hypothesis that there is no correlation between new bone formation during mandibular distraction osteogenesis and NOS expression in the trigeminal ganglion of rats. Newly formed tissue during distraction osteogenesis and trigeminal NOS expression measured by the NADPH-diaphorase (NADPH-d) reaction were evaluated in 72 male Wistar rats by histomorphometric and histochemical methods. In animals submitted to 0.5 mm/day distraction osteogenesis, the percentage of bone tissue was higher in the basal area of the mandibles compared with the center and significantly increased through the experimental periods (P < 0.05). At the sixth postoperative week, the difference in bone formation between the continuous and acute distraction osteogenesis groups was the highest. Significant correlation between new bone formation by distraction osteogenesis and NADPH-d-reactive neurons was found, varying according to neuronal cell size (r = -0.6, P = 0.005, small cells strongly stained; r = 0.5, P = 0.018, large cells moderately stained). The results suggest that NOS may play a role in the bone healing process via neurogenic pathways, and the phenomenon seems to be neuronal cell morphotype-dependent. Further studies are now warranted to investigate the mechanistic link between the expression of trigeminal NOS and mandibular new bone formation by distraction osteogenesis.

Mechanistic roles of leptin in osteogenic stimulation in thoracic ligament flavum cells

Obesity is a risk factor for thoracic ossification of ligament flavum (TOLF) that is characterized by ectopic bone formation in the spinal ligaments. Hyperleptinemia is a common feature of obese people, and leptin, an adipocyte-derived cytokine with proliferative and osteogenic effects in several cell types, is believed to be an important factor in the pathogenesis of TOLF. However, how leptin might stimulate cell osteogenic differentiation in TOLF is not totally understood. We reported here that leptin-induced osteogenic effect in TOLF cells is associated with activation of signaling molecules STAT3, JNK, and ERK1/2 but not p38. Blocking STAT3 phosphorylation with a selective inhibitor, AG490, significantly abolished leptin-induced osteogenic differentiation of TOLF cells, whereas blocking ERK1/2 and JNK phosphorylation with their selective inhibitors PD98059 and SP600125, respectively, had only marginal effects. In addition, we showed that STAT3 interacted with Runt-related transcription factor 2 (Runx2) in the nucleus, and STAT3, Runx2, and steroid receptor coactivator steroid receptor coactivator-1 were components of the transcription complex recruited on Runx2 target gene promoters in response to leptin treatment. Our experiments identified STAT3, Runx2, and steroid receptor coactivator-1 as critical molecules in mediating leptin-stimulated cell osteogenesis in TOLF.

Iron ions derived from the nitric oxide donor sodium nitroprusside inhibit mineralization

Sodium nitroprusside (SNP) is a nitric oxide (NO) donor drug, which is therapeutically used as a vasodilating drug in heart transplantations. In our previous study it was found that SNP at a concentration of 100 microM inhibited mineralization in a cell culture system, indicating that the beneficial effects of this drug may also include inhibition of vascular calcification. The aim of this study was to investigate which bioactive compounds generated from SNP inhibit mineralization. ATDC5 cells were grown for 14 days and mineralization was induced by addition of 5 mM phosphate for 24 h. Mineralization was determined by staining precipitated calcium with an alizarin red stain. It was found that the NO donors S-nitrosoglutathione and S-nitroso-N-acetylpenicillamine were not able to inhibit mineralization and NO scavengers could not antagonize the inhibiting effect of SNP on mineralization. The iron chelator deferoxamine (200 microM) antagonized the inhibiting effect on mineralization mediated by SNP and ammonium iron sulfate inhibited mineralization in a dose-dependent manner (10-100 microM). Furthermore, iron ions (30 microM) were detected to be released from SNP in the cell culture. These data show that the iron moiety of sodium nitroprusside, rather than nitric oxide inhibits mineralization.