Secreted frizzled related-protein 2 (Sfrp2) deficiency decreases adult skeletal stem cell function in mice

In a previous transcriptomic study of human bone marrow stromal cells (BMSCs, also known as bone marrow-derived "mesenchymal stem cells"), SFRP2 was highly over-represented in a subset of multipotent BMSCs (skeletal stem cells, SSCs), which recreate a bone/marrow organ in an in vivo ectopic bone formation assay. SFRPs modulate WNT signaling, which is essential to maintain skeletal homeostasis, but the specific role of SFRP2 in BMSCs/SSCs is unclear. Here, we evaluated Sfrp2 deficiency on BMSC/SSC function in models of skeletal organogenesis and regeneration. The skeleton of Sfrp2-deficient (KO) mice is overtly normal; but their BMSCs/SSCs exhibit reduced colony-forming efficiency, reflecting low SSC self-renewal/abundancy. Sfrp2 KO BMSCs/SSCs formed less trabecular bone than those from WT littermates in the ectopic bone formation assay. Moreover, regeneration of a cortical drilled hole defect was dramatically impaired in Sfrp2 KO mice. Sfrp2-deficient BMSCs/SSCs exhibited poor in vitro osteogenic differentiation as measured by Runx2 and Osterix expression and calcium accumulation. Interestingly, activation of the Wnt co-receptor, Lrp6, and expression of Wnt target genes, Axin2, C-myc and Cyclin D1, were reduced in Sfrp2-deficient BMSCs/SSCs. Addition of recombinant Sfrp2 restored most of these activities, suggesting that Sfrp2 acts as a Wnt agonist. We demonstrate that Sfrp2 plays a role in self-renewal of SSCs and in the recruitment and differentiation of adult SSCs during bone healing. SFRP2 is also a useful marker of BMSC/SSC multipotency, and a factor to potentially improve the quality of ex vivo expanded BMSC/SSC products.

Lineage-specific differentiation of osteogenic progenitors from pluripotent stem cells reveals the FGF1-RUNX2 association in neural crest-derived osteoprogenitors

Human pluripotent stem cells (hPSCs) can provide a platform to model bone organogenesis and disease. To reflect the developmental process of the human skeleton, hPSC differentiation methods should include osteogenic progenitors (OPs) arising from three distinct embryonic lineages: the paraxial mesoderm, lateral plate mesoderm, and neural crest. Although OP differentiation protocols have been developed, the lineage from which they are derived, as well as characterization of their genetic and molecular differences, has not been well reported. Therefore, to generate lineage-specific OPs from human embryonic stem cells and human induced pluripotent stem cells, we employed stepwise differentiation of paraxial mesoderm-like cells, lateral plate mesoderm-like cells, and neural crest-like cells toward their respective OP subpopulation. Successful differentiation, confirmed through gene expression and in vivo assays, permitted the identification of transcriptomic signatures of all three cell populations. We also report, for the first time, high FGF1 levels in neural crest-derived OPs-a notable finding given the critical role of fibroblast growth factors (FGFs) in osteogenesis and mineral homeostasis. Our results indicate that FGF1 influences RUNX2 levels, with concomitant changes in ERK1/2 signaling. Overall, our study further validates hPSCs' power to model bone development and disease and reveals new, potentially important pathways influencing these processes.

In Vivo Formation of Stable Hyaline Cartilage by Naïve Human Bone Marrow Stromal Cells with Modified Fibrin Microbeads

Osteoarthritic and other types of articular cartilage defects never heal on their own. Medicinal and surgical approaches are often ineffective, and the supply of autologous chondrocytes for tissue engineering is very limited. Bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) have been suggested as an adequate cell source for cartilage reconstruction. However, the majority of studies employing BMSCs for cartilage tissue engineering have used BMSCs predifferentiated into cartilage prior to implantation. This strategy has failed to achieve formation of stable, hyaline-like cartilage, resistant to hypertrophy in vivo. We hypothesized that in vitro predifferentiation of BMSCs is not necessary when cells are combined with an adequate scaffold that supports the formation of stable cartilage in vivo. In this study, naïve (undifferentiated) human BMSCs were attached to dehydrothermally crosslinked stable fibrin microbeads (FMBs) without and with other scaffolds and implanted subcutaneously into immunocompromised mice. Optimal formation of abundant, hypertrophy-resistant, ectopic hyaline-like cartilage was achieved when BMSCs were attached to FMBs covalently coated with hyaluronic acid. The cartilage that was formed was of human origin and was stable for at least 28 weeks in vivo. Stem Cells Translational Medicine 2019;8:586-592.

Neonatal McCune-Albright Syndrome: A Unique Syndromic Profile With an Unfavorable Outcome

Somatic gain‐of‐function mutations of GNAS cause a spectrum of clinical phenotypes, ranging from McCune‐Albright syndrome (MAS) to isolated disease of bone, endocrine glands, and more rarely, other organs. In MAS, a syndrome classically characterized by polyostotic fibrous dysplasia (FD), café‐au‐lait (CAL) skin spots, and precocious puberty, the heterogenity of organ involvement, age of onset, and clinical severity of the disease are thought to reflect the variable size and the random distribution of the mutated cell clone arising from the postzygotic mutation. We report a case of neonatal MAS with hypercortisolism and cholestatic hepatobiliary dysfunction in which bone changes indirectly emanating from the disease genotype, and distinct from FD, led to a fatal outcome. Pulmonary embolism of marrow and bone fragments secondary to rib fractures was the immediate cause of death. Ribs, and all other skeletal segments, were free of changes of typical FD and fractures appeared to be the result of a mild‐to‐moderate degree of osteopenia. The mutated allele was abundant in the adrenal glands and liver, but not in skin, muscle, and fractured ribs, where it could only be demonstrated using a much more sensitive PNA hybridization probe‐based FRET (Förster resonance energy transfer) technique. Histologically, bilateral adrenal hyperplasia and cholestatic disease matched the abundant disease genotype in the adrenals and liver. Based on this case and other sporadic reports, it appears that gain‐of‐function mutations of GNAS underlie a unique syndromic profile in neonates characterized by CAL skin spots, hypercortisolism, hyperthyroidism, hepatic and cardiac dysfunction, and an absence (or latency) of FD, often with a lethal outcome. Taken together, our and previous cases highlight the phenotypic severity and the diagnostic and therapeutic challenges of MAS in neonates. Furthermore, our case specifically points out how secondary bone changes, unrelated to the direct impact of the mutation, may contribute to the unfavorable outcome of very early‐onset MAS. © 2018 The Authors JBMR Plus published by Wiley Periodicals, Inc. on behalf of American Society for Bone and Mineral Research.

Molecular profile of clonal strains of human skeletal stem/progenitor cells with different potencies

Bone marrow stromal cells (BMSCs, also known as bone marrow-derived mesenchymal stem cells) are fibroblastic reticular cells, a subset of which is composed of multipotent skeletal stem cells (SSCs). SSCs/BMSCs are able to recreate a bone/marrow organ in vivo. To determine differences between clonogenic multipotent SSCs and similarly clonogenic but non-multipotent BMSCs, we established single colony-derived strains (SCDSs, initiated by individual Colony Forming Unit-Fibroblasts) and determined their differentiation capacity by vivo transplantation. In this series of human SCDSs (N=24), 20.8% formed fibrous tissue (F), 66.7% formed bone (B), and 12.5% formed a bone/marrow organ, and thus were multipotent (M). RNA isolated from 12 SCDSs just prior to transplantation was analyzed by microarray. Although highly similar, there was variability from one SCDS to another, and SCDSs did not strictly segregate into the three functional groups (F, B or M) by unsupervised hierarchical clustering. We then compared 3 F-SCDSs to 3 M-SCDSs that did segregate. Genes associated with skeletogenesis, osteoblastogeneis, hematopoiesis, and extracellular matrix were over-represented in M-SCDSs compared with F-SCDSs. These results highlight the heterogeneity of SSCs/BMSCs, even between functionally similar SCDSs, but also indicate that differences can be detected that may shed light on the character of the SSC.

Directed differentiation of human induced pluripotent stem cells toward bone and cartilage: in vitro versus in vivo assays

The ability to differentiate induced pluripotent stem cells (iPSCs) into committed skeletal progenitors could allow for an unlimited autologous supply of such cells for therapeutic uses; therefore, we attempted to create novel bone-forming cells from human iPSCs using lines from two distinct tissue sources and methods of differentiation that we previously devised for osteogenic differentiation of human embryonic stem cells, and as suggested by other publications. The resulting cells were assayed using in vitro methods, and the results were compared with those obtained from in vivo transplantation assays. Our results show that true bone was formed in vivo by derivatives of several iPSC lines, but that the successful cell lines and differentiation methodologies were not predicted by the results of the in vitro assays. In addition, bone was formed equally well from iPSCs originating from skin or bone marrow stromal cells (also known as bone marrow-derived mesenchymal stem cells), suggesting that the iPSCs did not retain a "memory" of their previous life. Furthermore, one of the iPSC-derived cell lines formed verifiable cartilage in vivo, which likewise was not predicted by in vitro assays.

Denosumab treatment for fibrous dysplasia

Fibrous dysplasia (FD) is a skeletal disease caused by somatic activating mutations of the cyclic adenosine monophosphate (cAMP)-regulating protein, α-subunit of the Gs stimulatory protein (G(s) α). These mutations lead to replacement of normal bone by proliferative osteogenic precursors, resulting in deformity, fracture, and pain. Medical treatment has been ineffective in altering the disease course. Receptor activator of NF-κB ligand (RANKL) is a cell-surface protein involved in many cellular processes, including osteoclastogenesis, and is reported to be overexpressed in FD-like bone cells. Denosumab is a humanized monoclonal antibody to RANKL approved for treatment of osteoporosis and prevention of skeletal-related events from bone metastases. We present the case of a 9-year-old boy with severe FD who was treated with denosumab for a rapidly expanding femoral lesion. Immunohistochemical staining on a pretreatment bone biopsy specimen revealed marked RANKL expression. He was started on monthly denosumab, with an initial starting dose of 1 mg/kg and planned 0.25 mg/kg dose escalations every 3 months. Over 7 months of treatment he showed marked reduction in pain, bone turnover markers (BTMs), and tumor growth rate. Denosumab did not appear to impair healing of a femoral fracture that occurred while on treatment. With initiation of treatment he developed hypophosphatemia and secondary hyperparathyroidism, necessitating supplementation with phosphorus, calcium, and calcitriol. BTMs showed rapid and sustained suppression. With discontinuation there was rapid and dramatic rebound of BTMs with cross-linked C-telopeptide (reflecting osteoclast activity) exceeding pretreatment levels, accompanied by severe hypercalcemia. In this child, denosumab lead to dramatic reduction of FD expansion and FD-related bone pain. Denosumab was associated with clinically significant disturbances of mineral metabolism both while on treatment and after discontinuation. Denosumab treatment of FD warrants further study to confirm efficacy and determine potential morbidity, as well as to determine the mechanism of RANKL in the pathogenesis of FD and related bone marrow stromal cell diseases.

Mechanism of FGF23 processing in fibrous dysplasia

Fibroblast growth factor-23 (FGF23) is a phosphate- and vitamin D-regulating hormone derived from osteoblasts/osteocytes that circulates in both active (intact, iFGF23) and inactive (C-terminal, cFGF23) forms. O-glycosylation by O-glycosyl transferase N-acetylgalactosaminyltransferase 3 (ppGalNAcT3) and differential cleavage by furin have been shown to be involved in regulating the ratio of active to inactive FGF23. Elevated iFGF23 levels are observed in a number of hypophosphatemic disorders, such as X-linked, autosomal recessive, and autosomal dominant hypophosphatemic rickets, whereas low iFGF23 levels are found in the hyperphosphatemic disorder familial tumoral calcinosis/hyperphosphatemic hyperostosis syndrome. Fibrous dysplasia of bone (FD) is associated with increased total FGF23 levels (cFGF23 + iFGF23); however, classic hypophosphatemic rickets is uncommon. Our results suggest that it can be explained by increased FGF23 cleavage leading to an increase in inactive cFGF23 relative to active iFGF23. Given the fact that FD is caused by activating mutations in the small G-protein G(s) α that results in increased cyclic adenosine monophosphate (cAMP) levels, we postulated that there may be altered FGF23 cleavage in FD and that the mechanism may involve alterations in cAMP levels and ppGalNacT3 and furin activities. Analysis of blood specimens from patients with FD confirmed that the elevated total FGF23 levels are the result of proportionally increased cFGF23 levels, consistent with less glycosylation and enhanced cleavage by furin. Analysis of primary cell lines of normal and mutation-harboring bone marrow stromal cells (BMSCs) from patients with FD demonstrated that BMSCs harboring the causative G(s) α mutation had higher cAMP levels, lower ppGalNAcT3, and higher furin activity. These data support the model wherein glycosylation by ppGalNAcT3 inhibits FGF23 cleavage by furin and suggest that FGF23 processing is a regulated process that controls overall FGF23 activity in FD patients.

A mosaic activating mutation in AKT1 associated with the Proteus syndrome

BACKGROUND

The Proteus syndrome is characterized by the overgrowth of skin, connective tissue, brain, and other tissues. It has been hypothesized that the syndrome is caused by somatic mosaicism for a mutation that is lethal in the nonmosaic state.

METHODS

We performed exome sequencing of DNA from biopsy samples obtained from patients with the Proteus syndrome and compared the resultant DNA sequences with those of unaffected tissues obtained from the same patients. We confirmed and extended an observed association, using a custom restriction-enzyme assay to analyze the DNA in 158 samples from 29 patients with the Proteus syndrome. We then assayed activation of the AKT protein in affected tissues, using phosphorylation-specific antibodies on Western blots.

RESULTS

Of 29 patients with the Proteus syndrome, 26 had a somatic activating mutation (c.49G→A, p.Glu17Lys) in the oncogene AKT1, encoding the AKT1 kinase, an enzyme known to mediate processes such as cell proliferation and apoptosis. Tissues and cell lines from patients with the Proteus syndrome harbored admixtures of mutant alleles that ranged from 1% to approximately 50%. Mutant cell lines showed greater AKT phosphorylation than did control cell lines. A pair of single-cell clones that were established from the same starting culture and differed with respect to their mutation status had different levels of AKT phosphorylation.

CONCLUSIONS

The Proteus syndrome is caused by a somatic activating mutation in AKT1, proving the hypothesis of somatic mosaicism and implicating activation of the PI3K-AKT pathway in the characteristic clinical findings of overgrowth and tumor susceptibility in this disorder. (Funded by the Intramural Research Program of the National Human Genome Research Institute.).

In vivo bone formation by progeny of human embryonic stem cells

The derivation of osteogenic cells from human embryonic stem cells (hESCs) or from induced pluripotent stem cells for bone regeneration would be a welcome alternative to the use of adult stem cells. In an attempt to promote hESC osteogenic differentiation, cells of the HSF-6 line were cultured in differentiating conditions in vitro for prolonged periods of time ranging from 7 to 14.5 weeks, followed by in vivo transplantation into immunocompromised mice in conjunction with hydroxyapatite/tricalcium phosphate ceramic powder. Twelve different medium compositions were tested, along with a number of other variables in culture parameters. In differentiating conditions, HSF-6-derived cells demonstrated an array of diverse phenotypes reminiscent of multiple tissues, but after a few passages, acquired a more uniform, fibroblast-like morphology. Eight to 16 weeks post-transplantation, a group of transplants revealed the formation of histologically proven bone of human origin, including broad areas of multiple intertwining trabeculae, which represents by far the most extensive in vivo bone formation by the hESC-derived cells described to date. Knockout-Dulbecco's modified Eagle's medium-based media with fetal bovine serum, dexamethasone, and ascorbate promoted more frequent bone formation, while media based on α-modified minimum essential medium promoted teratoma formation in 12- to 20-week-old transplants. Transcription levels of pluripotency-related (octamer binding protein 4, Nanog), osteogenesis-related (collagen type I, Runx2, alkaline phosphatase, and bone sialoprotein), and chondrogenesis-related (collagen types II and X, and aggrecan) genes were not predictive of either bone or teratoma formation. The most extensive bone was formed by the strains that, following 4 passages in monolayer conditions, were cultured for 23 to 25 extra days on the surface of hydroxyapatite/tricalcium phosphate particles, suggesting that coculturing of hESC-derived cells with osteoconductive material may increase their osteogenic potential. While none of the conditions tested in this study, and elsewhere, ensured consistent bone formation by hESC-derived cells, our results may elucidate further directions toward the construction of bone on the basis of hESCs or an individual's own induced pluripotent stem cells.

The role of type 1 and type 2 5'-deiodinase in the pathophysiology of the 3,5,3'-triiodothyronine toxicosis of McCune-Albright syndrome

CONTEXT

McCune-Albright syndrome (MAS) is caused by mutations in GNAS (most often R201C or R201H) leading to constitutive cAMP signaling and multiple endocrine dysfunctions, including morphological and functional thyroid involvement.

OBJECTIVE

The objective of the study was to characterize the clinical and molecular features of the MAS-associated thyroid disease in a large cohort of patients.

DESIGN

This was a retrospective analysis.

SETTING

The study was conducted at the National Institutes of Health Clinical Center.

PATIENTS

The study included 100 consecutive MAS patients.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURE

Functional and morphological evaluation of the thyroid was measured. Ex vivo experiments were performed on MAS thyroid samples to study the effects of the GNAS mutations on the 5'-deiodinases. Reconstitution experiments in HEK-293 cells were performed to study the effects of GNAS mutations on the type-2 5'-deiodinase.

RESULTS

Fifty-four patients had abnormal thyroid ultrasound findings. This group, compared with patients without abnormal findings, had higher T(3) to T(4) ratio, indicating an elevated 5'-deiodinase activity. Thyroid samples from MAS subjects, compared with normal tissue, showed a significant increase in both type 1 (D1) and type 2 (D2) 5'-deiodinase activity (D1 control 5.9 +/- 4.5 vs. MAS 41.7 +/- 26.8 fmol/min.mg, P < 0.001; D2 control 28.3 +/- 13.8 vs. MAS 153.1 +/- 43.7 fmol/min.mg, P < 0.001). Compared with cells transfected with the wild-type R201 allele, the basal transcriptional activity of the D2 promoter was significantly increased in both mutants (C and H) (R 10733 +/- 2855, vs. C 18548 +/- 4514, vs. H 19032 +/- 4410 RLU +/- SD, P < 0.001).

CONCLUSION

Thyroid pathology is a common occurrence in MAS. Consistent with the molecular etiology of the disease, the shift in T(3) to T(4) ratio is at least in part secondary to a cAMP-mediated intrathyroidal activation of D2 and to elevated D1 activity.

GNAS transcripts in skeletal progenitors: evidence for random asymmetric allelic expression of Gs alpha

Activating mutations of the Gsalpha gene, encoded by the guanine nucleotide-binding protein, alpha stimulating (GNAS) locus located on chromosome 20q13, underlie different clinical phenotypes characterized by skeletal lesions [fibrous dysplasia (FD) of bone], extraskeletal diseases (mainly endocrine hyperfunction and skin hyperpigmentation) and variable combinations thereof [the McCune-Albright syndrome (MAS)]. This clinical heterogeneity is commonly assumed to reflect the post-zygotic origin of the mutation. However, the pattern of imprinting of the Gsalpha gene in some human post-natal tissues suggests that parental-dependent epigenetic mechanisms may also play a role in the phenotypic effect of the mutated GNAS genotype. FD lesions are generated by mutated clonogenic osteoprogenitors that reside, along with their normal counterparts, in FD bone marrow stroma. We analyzed the allelic expression pattern of Gsalpha and other GNAS alternative transcripts in the progeny of normal and mutated clonogenic stromal cells isolated in vitro from a series of informative FD/MAS patients. We report here for the first time that the two Gsalpha alleles are unequally expressed in both normal and FD-mutated stromal clones. However, in contrast to imprinting, the ratio of Gsalpha allelic expression is randomly established in different clones from the same patient. This result suggests that a parental-independent modulation of Gsalpha expression occurs in clonogenic osteoprogenitor cells and, at the single cell level, may impact on the severity of an FD lesion. Furthermore, we show that normal and mutated clonogenic stromal cells express GNAS alternative transcripts other than the common Gsalpha, some of which may be relevant to the development of FD.

Monostotic fibrous dysplasia of the proximal femur and liposclerosing myxofibrous tumor: which one is which?

Clinical, histological, and genetic studies of two cases of isolated fibro-osseous lesions of the femur in adults show the overlap between monostotic fibrous dysplasia (MFD) of the proximal femur and the so-called liposclerosing myxofibrous tumor. The two cases highlight how the incomplete understanding of the natural history of MFD may result in diagnostic pitfalls or incorrect classification of individual lesions.

Sensitive and specific method for detecting G protein-coupled receptor mRNAs

G protein-coupled receptors (GPCRs) mediate effects of extracellular signaling molecules in all the body's cells. These receptors are encoded by scarce mRNAs; therefore, detecting their transcripts with conventional microarrays is difficult. We present a method based on multiplex PCR and array detection of amplicons to assay GPCR gene expression with as little as 1 mug of total RNA, and using it, we profiled three human bone marrow stromal cell (BMSC) lines.

Pegvisomant for the treatment of gsp-mediated growth hormone excess in patients with McCune-Albright syndrome

CONTEXT

GH excess affects approximately 20% of the patients with McCune-Albright syndrome (MAS). MAS is caused by sporadic, postzygotic, activating mutations in the GNAS gene, which codes for the cAMP-regulating protein, G(s)alpha (gsp oncogene). These same mutations are found in approximately one third of the sporadic cases of acromegaly.

OBJECTIVE

We examined efficacy of the GH receptor antagonist, pegvisomant, in controlling gsp oncogene-mediated GH excess and skeletal disease (fibrous dysplasia of bone) associated with MAS.

SETTING AND PATIENTS

Five MAS patients with GH excess were treated with 20 mg/d sc injection of pegvisomant for 12 wk in a randomized, double-blind, placebo-controlled crossover study at the National Institutes of Health.

MAIN OUTCOME MEASURES

The primary measure of efficacy was normalization of IGF-I. Secondary outcome measures were reduction in serum IGF binding protein-3 (IGFBP-3), improvement of fatigue and sweating, and reduction in markers of bone metabolism and bone pain.

RESULTS

Combined mean changes in serum IGF-I at 6 and 12 wk were -236.4 ng/ml (53%, P < 0.005) and -329.8 ng/ml (62%, P < 0.001), respectively. IGFBP-3 decreased by 0.8 mg/liter (24%, P < 0.01) and 2.9 mg/liter (37%, P < 0.005), respectively. There were no significant changes in signs and symptoms of acromegaly or markers of bone metabolism and bone pain, nor was there a significant change in pituitary size. Retrospective comparison of the degree of control achieved with pegvisomant vs. other medications (long-acting octreotide +/- dopamine agonist) in the same group showed that the two regimens were similarly effective.

CONCLUSIONS

Pegvisomant effectively reduced IGF-I and IGFBP-3 levels in gsp-mediated GH excess but had no effect on fibrous dysplasia.

A novel technique based on a PNA hybridization probe and FRET principle for quantification of mutant genotype in fibrous dysplasia/McCune-Albright syndrome

Somatic mutations are present in various proportions in numerous developmental pathologies. Somatic activating missense mutations of the GNAS gene encoding the Gs(alpha) protein have previously been shown to be the cause of fibrous dysplasia of bone (FD)/McCune-Albright syndrome (MAS). Because in MAS patients, tissues as diverse as melanocytes, gonads and bone are affected, it is generally accepted that the GNAS mutation in this disease must have occurred early in development. Interestingly, it has been shown that the development of an active FD lesion may require both normal and mutant cells. Studies of the somatic mosaic states of FD/MAS and many other somatic diseases need an accurate method to determine the ratio of mutant to normal cells in a given tissue. A new method for quantification of the mutant:normal ratio of cells using a PNA hybridization probe-based FRET technique was developed. This novel technique, with a linear sensitivity of 2.5% mutant alleles, was used to detect the percentage mutant cells in a number of tissue and cell culture samples derived from FD/MAS lesions and could easily be adapted for the quantification of mutations in a large spectrum of diseases including cancer.

FGF-23 in fibrous dysplasia of bone and its relationship to renal phosphate wasting

FGF-23, a novel member of the FGF family, is the product of the gene mutated in autosomal dominant hypophosphatemic rickets (ADHR). FGF-23 has been proposed as a circulating factor causing renal phosphate wasting not only in ADHR (as a result of inadequate degradation), but also in tumor-induced osteomalacia (as a result of excess synthesis by tumor cells). Renal phosphate wasting occurs in approximately 50% of patients with McCune-Albright syndrome (MAS) and fibrous dysplasia of bone (FD), which result from postzygotic mutations of the GNAS1 gene. We found that FGF-23 is produced by normal and FD osteoprogenitors and bone-forming cells in vivo and in vitro. In situ hybridization analysis of FGF-23 mRNA expression identified "fibrous" cells, osteogenic cells, and cells associated with microvascular walls as specific cellular sources of FGF-23 in FD. Serum levels of FGF-23 were increased in FD/MAS patients compared with normal age-matched controls and significantly higher in FD/MAS patients with renal phosphate wasting compared with those without, and correlated with disease burden bone turnover markers commonly used to assess disease activity. Production of FGF-23 by FD tissue may play an important role in the renal phosphate-wasting syndrome associated with FD/MAS.

Osteoclastogenesis in fibrous dysplasia of bone: in situ and in vitro analysis of IL-6 expression

Fibrous dysplasia of bone (FD) is caused by somatic mutations of the GNAS1 gene, which lead to constitutive activation of adenylyl cyclase and overproduction of cAMP in osteogenic cells. Previous in vitro studies using nonclonal, heterogeneous strains of FD-derived cells suggested that IL-6 might play a critical role in promoting excess osteoclastogenesis in FD. In this study, we investigated IL-6 expression in FD in situ and its relationship to the actual patterns of osteoclastogenesis within the abnormal tissue. We found that osteoclastogenesis is not spatially restricted to bone surfaces in FD but occurs to a large extent ectopicly in the fibrous tissue, where stromal cells diffusely express IL-6 mRNA and exhibit a characteristic cell morphology. We also observed specific expression of IL-6 mRNA in a proportion of osteoclasts, suggesting that an autocrine/paracrine loop may contribute to osteoclastogenesis in vivo in FD, as in some other bone diseases, including Paget's disease. We also generated homogeneous, clonally derived strains of wild-type and GNAS1-mutated stromal cells from the same individual, parent FD lesions. In this way, we could show that mutated stromal cells produce IL-6 at a basal magnitude and rate that are significantly higher than in the cognate wild-type cells. Conversely, wild-type cells respond to db-cAMP with a severalfold increase in magnitude and rate of IL-6 production, whereas mutant strains remain essentially unresponsive. Our data establish a direct link between GNAS1 mutations in stromal cells and IL-6 production but also define the complexity of the role of IL-6 in regulating osteoclastogenesis in FD in vivo. Here, patterns of osteoclastogenesis and bone resorption reflect not only the cell-autonomous effects of GNAS1 mutations in osteogenic cells (including IL-6 production) but also the local and systemic context to which non-osteogenic cells, local proportions of wild-type vs mutated cells, and systemic hormones contribute.

FGF-23 in fibrous dysplasia of bone and its relationship to renal phosphate wasting

FGF-23, a novel member of the FGF family, is the product of the gene mutated in autosomal dominant hypophosphatemic rickets (ADHR). FGF-23 has been proposed as a circulating factor causing renal phosphate wasting not only in ADHR (as a result of inadequate degradation), but also in tumor-induced osteomalacia (as a result of excess synthesis by tumor cells). Renal phosphate wasting occurs in approximately 50% of patients with McCune-Albright syndrome (MAS) and fibrous dysplasia of bone (FD), which result from postzygotic mutations of the GNAS1 gene. We found that FGF-23 is produced by normal and FD osteoprogenitors and bone-forming cells in vivo and in vitro. In situ hybridization analysis of FGF-23 mRNA expression identified "fibrous" cells, osteogenic cells, and cells associated with microvascular walls as specific cellular sources of FGF-23 in FD. Serum levels of FGF-23 were increased in FD/MAS patients compared with normal age-matched controls and significantly higher in FD/MAS patients with renal phosphate wasting compared with those without, and correlated with disease burden bone turnover markers commonly used to assess disease activity. Production of FGF-23 by FD tissue may play an important role in the renal phosphate-wasting syndrome associated with FD/MAS.

Characterization of gsp-mediated growth hormone excess in the context of McCune-Albright syndrome

McCune-Albright syndrome (MAS) is a disorder characterized by the triad of café-au-lait skin pigmentation, polyostotic fibrous dysplasia of bone, and hyperfunctioning endocrinopathies, including GH excess. The molecular etiology of the disease is postzygotic activating mutations of the GNAS1 gene product, G(s)alpha. The term gsp oncogene has been assigned to these mutations due to their association with certain neoplasms. The aim of this study was to estimate the prevalence of GH excess in MAS, characterize the clinical and endocrine manifestations, and describe the response to treatment. Fifty-eight patients with MAS were screened, and 22 with stigmata of acromegaly and/or elevated GH or IGF-I underwent oral glucose tolerance testing. Twelve patients (21%) had GH excess, based on failure to suppress serum GH on oral glucose tolerance test, and underwent a TRH test, serial GH sampling from 2000-0800 h, and magnetic resonance imaging of the sella. We found that vision and hearing deficits were more common in patients with GH excess (4 of 12, 33%) than those without (2 of 56, 4%). Of interest, patients with a history of precocious puberty and GH excess who had reached skeletal maturity achieved normal adult height despite a history of early epiphyseal fusion. All 9 patients tested had an increase in serum GH after TRH, 11 of 12 (92%) had hyperprolactinemia, and all 8 tested had detectable or elevated nighttime GH levels. Pituitary adenoma was detected in 4 of 12 (33%) patients. All patients with elevated IGF-I levels were treated with cabergoline (7 patients), long-acting octreotide (LAO; 8 patients), or a combination of cabergoline and LAO (4 patients). In six of the seven patients (86%) treated with cabergoline, serum IGF-I decreased, but not to the normal range. In the eight patients treated with LAO alone, IGF-I decreased, and, in four, returned to the normal range. The remaining 4 patients were treated with a combination of cabergoline and LAO. For them, symptoms of GH excess diminished, and IGF-I decreased further, but did not enter the normal range. GH excess is common in MAS and results in a distinct clinical phenotype characterized by inappropriately normal stature, TRH responsiveness, prolactin cosecretion, small or absent pituitary tumors, a consistent but inadequate response to treatment with cabergoline, and an intermediate response to LAO.

Stem cell properties of human dental pulp stem cells

In this study, we characterized the self-renewal capability, multi-lineage differentiation capacity, and clonogenic efficiency of human dental pulp stem cells (DPSCs). DPSCs were capable of forming ectopic dentin and associated pulp tissue in vivo. Stromal-like cells were reestablished in culture from primary DPSC transplants and re-transplanted into immunocompromised mice to generate a dentin-pulp-like tissue, demonstrating their self-renewal capability. DPSCs were also found to be capable of differentiating into adipocytes and neural-like cells. The odontogenic potential of 12 individual single-colony-derived DPSC strains was determined. Two-thirds of the single-colony-derived DPSC strains generated abundant ectopic dentin in vivo, while only a limited amount of dentin was detected in the remaining one-third. These results indicate that single-colony-derived DPSC strains differ from each other with respect to their rate of odontogenesis. Taken together, these results demonstrate that DPSCs possess stem-cell-like qualities, including self-renewal capability and multi-lineage differentiation.

Gnathodiaphyseal dysplasia: a syndrome of fibro-osseous lesions of jawbones, bone fragility, and long bone bowing

We report an unusual generalized skeletal syndrome characterized by fibro-osseous lesions of the jawbones with a prominent psammomatoid body component, bone fragility, and bowing/sclerosis of tubular bones. The case fits with the emerging profile of a distinct syndrome with similarities to previously reported cases, some with an autosomal dominant inheritance and others sporadic. We suggest that the syndrome be named gnathodiaphyseal dysplasia. The patient had been diagnosed previously with polyostotic fibrous dysplasia (PFD) elsewhere, but further clinical evaluation, histopathological study, and mutation analysis excluded this diagnosis. In addition to providing a novel observation of an as yet poorly characterized syndrome, the case illustrates the need for stringent diagnostic criteria for FD. The jaw lesions showed fibro-osseous features with the histopathological characteristics of cemento-ossifying fibroma, psammomatoid variant. This case emphasizes that the boundaries between genuine GNAS1 mutation-positive FD and other fibro-osseous lesions occurring in the jawbones should be kept sharply defined, contrary to a prevailing tendency in the literature. A detailed pathological study revealed previously unreported features of cemento-ossifying fibroma, including the participation of myofibroblasts and the occurrence of psammomatoid bodies and aberrant mineralization, within the walls of blood vessels. Transplantation of stromal cells grown from the lesion into immunocompromised mice resulted in a close mimicry of the native lesion, including the sporadic formation of psammomatoid bodies, suggesting an intrinsic abnormality of bone-forming cells.