Modeling human skeletal development using human pluripotent stem cells.

Chondrocytes and osteoblasts differentiated from induced pluripotent stem cells (iPSCs) will provide insights into skeletal development and genetic skeletal disorders and will generate cells for regenerative medicine applications. Here, we describe a method that directs iPSC-derived sclerotome to chondroprogenitors in 3D pellet culture then to articular chondrocytes or, alternatively, along the growth plate cartilage pathway to become hypertrophic chondrocytes that can transition to osteoblasts. Osteogenic organoids deposit and mineralize a collagen I extracellular matrix (ECM), mirroring in vivo endochondral bone formation. We have identified gene expression signatures at key developmental stages including chondrocyte maturation, hypertrophy, and transition to osteoblasts and show that this system can be used to model genetic cartilage and bone disorders.

XBP1-Independent UPR Pathways Suppress C/EBP-ß Mediated Chondrocyte Differentiation in ER-Stress Related Skeletal Disease.

Schmid metaphyseal chondrodysplasia (MCDS) involves dwarfism and growth plate cartilage hypertrophic zone expansion resulting from dominant mutations in the hypertrophic zone collagen, Col10a1. Mouse models phenocopying MCDS through the expression of an exogenous misfolding protein in the endoplasmic reticulum (ER) in hypertrophic chondrocytes have demonstrated the central importance of ER stress in the pathology of MCDS. The resultant unfolded protein response (UPR) in affected chondrocytes involved activation of canonical ER stress sensors, IRE1, ATF6, and PERK with the downstream effect of disrupted chondrocyte differentiation. Here, we investigated the role of the highly conserved IRE1/XBP1 pathway in the pathology of MCDS. Mice with a MCDS collagen X p.N617K knock-in mutation (ColXN617K) were crossed with mice in which Xbp1 was inactivated specifically in cartilage (Xbp1CartΔEx2), generating the compound mutant, C/X. The severity of dwarfism and hypertrophic zone expansion in C/X did not differ significantly from ColXN617K, revealing surprising redundancy for the IRE1/XBP1 UPR pathway in the pathology of MCDS. Transcriptomic analyses of hypertrophic zone cartilage identified differentially expressed gene cohorts in MCDS that are pathologically relevant (XBP1-independent) or pathologically redundant (XBP1-dependent). XBP1-independent gene expression changes included large-scale transcriptional attenuation of genes encoding secreted proteins and disrupted differentiation from proliferative to hypertrophic chondrocytes. Moreover, these changes were consistent with disruption of C/EBP-ß, a master regulator of chondrocyte differentiation, by CHOP, a transcription factor downstream of PERK that inhibits C/EBP proteins, and down-regulation of C/EBP-ß transcriptional co-factors, GADD45-ß and RUNX2. Thus we propose that the pathology of MCDS is underpinned by XBP1 independent UPR-induced dysregulation of C/EBP-ß-mediated chondrocyte differentiation. Our data suggest that modulation of C/EBP-ß activity in MCDS chondrocytes may offer therapeutic opportunities.

Recurrent dominant mutations affecting two adjacent residues in the motor domain of the monomeric kinesin KIF22 result in skeletal dysplasia and joint laxity.

Spondyloepimetaphyseal dysplasia with joint laxity, leptodactylic type (lepto-SEMDJL, aka SEMDJL, Hall type), is an autosomal dominant skeletal disorder that, in spite of being relatively common among skeletal dysplasias, has eluded molecular elucidation so far. We used whole-exome sequencing of five unrelated individuals with lepto-SEMDJL to identify mutations in KIF22 as the cause of this skeletal condition. Missense mutations affecting one of two adjacent amino acids in the motor domain of KIF22 were present in 20 familial cases from eight families and in 12 other sporadic cases. The skeletal and connective tissue phenotype produced by these specific mutations point to functions of KIF22 beyond those previously ascribed functions involving chromosome segregation. Although we have found Kif22 to be strongly upregulated at the growth plate, the precise pathogenetic mechanisms remain to be elucidated.

Global comparative transcriptome analysis of cartilage formation in vivo.

BACKGROUND: During vertebrate embryogenesis the initial stages of bone formation by endochondral ossification involve the aggregation and proliferation of mesenchymal cells into condensations. Continued growth of the condensations and differentiation of the mesenchymal cells into chondrocytes results in the formation of cartilage templates, or anlagen, which prefigure the shape of the future bones. The chondrocytes in the anlagen further differentiate by undergoing a complex sequence of maturation and hypertrophy, and are eventually replaced by mineralized bone. Regulation of the onset of chondrogenesis is incompletely understood, and would be informed by comprehensive analyses of in vivo gene expression. RESULTS: Tibial and fibular pre-condensed mesenchyme was microdissected from mouse hind limbs at 11.5 dpc, and the corresponding condensations at 12.5 dpc and cartilage anlagen at 13.5 dpc. Total RNA was isolated, and cRNA generated by linear amplification was interrogated using mouse whole genome microarrays. Differential expression was validated by quantitative PCR for Agc1, Bmp8a, Col2a1, Fgfr4, Foxa3, Gdf5, Klf2, Klf4, Lepre1, Ncad, Sox11, and Trpv4. Further, independent validation of the microarray data was achieved by in situ hybridization to analyse the expression of Lepre1, Pcdh8, Sox11, and Trpv4 from 11.5 dpc to 13.5 dpc during mouse hind limb development. We found significant differential expression of 931 genes during these early stages of chondrogenesis. Of these, 380 genes were down-regulated and 551 up-regulated. Our studies characterized the expression pattern of gene families previously associated with chondrogenesis, such as adhesion molecules, secreted signalling molecules, transcription factors, and extracellular matrix components. Gene ontology approaches identified 892 differentially expressed genes not previously identified during the initiation of chondrogenesis. These included several Bmp, Gdf, Wnt, Sox and Fox family members. CONCLUSION: These data represent the first global gene expression profiling analysis of chondrogenic tissues during in vivo development. They identify genes for further study on their functional roles in chondrogenesis, and provide a comprehensive and important resource for future studies on cartilage development and disease.

Laser surface estimation for microwave breast imaging systems.

Microwave breast imaging techniques involve collecting measurements from a breast that is positioned in a scanner. While the patient interface typically includes a hole through which the breast is placed when the patient lies in the prone position, the exact location and shape of breast are not known. In this paper, we explore the addition of a laser sensor and associated algorithms in order to provide a rapid and accurate estimate of the breast surface location. We demonstrate that the laser is capable of estimating surfaces with improved accuracy compared to microwave measurements. The impact of accurate surface estimation on images is shown, and results obtained from human scans are presented.

Transcriptional profiling of chondrodysplasia growth plate cartilage reveals adaptive ER-stress networks that allow survival but disrupt hypertrophy.

Metaphyseal chondrodysplasia, Schmid type (MCDS) is characterized by mild short stature and growth plate hypertrophic zone expansion, and caused by collagen X mutations. We recently demonstrated the central importance of ER stress in the pathology of MCDS by recapitulating the disease phenotype by expressing misfolding forms of collagen X (Schmid) or thyroglobulin (Cog) in the hypertrophic zone. Here we characterize the Schmid and Cog ER stress signaling networks by transcriptional profiling of microdissected mutant and wildtype hypertrophic zones. Both models displayed similar unfolded protein responses (UPRs), involving activation of canonical ER stress sensors and upregulation of their downstream targets, including molecular chaperones, foldases, and ER-associated degradation machinery. Also upregulated were the emerging UPR regulators Wfs1 and Syvn1, recently identified UPR components including Armet and Creld2, and genes not previously implicated in ER stress such as Steap1 and Fgf21. Despite upregulation of the Chop/Cebpb pathway, apoptosis was not increased in mutant hypertrophic zones. Ultrastructural analysis of mutant growth plates revealed ER stress and disrupted chondrocyte maturation throughout mutant hypertrophic zones. This disruption was defined by profiling the expression of wildtype growth plate zone gene signatures in the mutant hypertrophic zones. Hypertrophic zone gene upregulation and proliferative zone gene downregulation were both inhibited in Schmid hypertrophic zones, resulting in the persistence of a proliferative chondrocyte-like expression profile in ER-stressed Schmid chondrocytes. Our findings provide a transcriptional map of two chondrocyte UPR gene networks in vivo, and define the consequences of UPR activation for the adaptation, differentiation, and survival of chondrocytes experiencing ER stress during hypertrophy. Thus they provide important insights into ER stress signaling and its impact on cartilage pathophysiology.

Isolated Anxa5+/Sca-1+ perivascular cells from mouse meningeal vasculature retain their perivascular phenotype in vitro and in vivo.

Pericytes are closely associated with endothelial cells, contribute to vascular stability and represent a potential source of mesenchymal progenitor cells. Using the specifically expressed annexin A5-LacZ fusion gene (Anxa5-LacZ), it became possible to isolate perivascular cells (PVC) from mouse tissues. These cells proliferate and can be cultured without undergoing senescence for multiple passages. PVC display phenotypic characteristics of pericytes, as they express pericyte-specific markers (NG2-proteoglycan, desmin, alphaSMA, PDGFR-beta). They also express stem cell marker Sca-1, whereas endothelial (PECAM), hematopoietic (CD45) or myeloid (F4/80, CD11b) lineage markers are not detectable. These characteristics are in common with the pericyte-like cell line 10T1/2. PVC also display a phagocytoic activity higher than 10T1/2 cells. During coculture with endothelial cells both cell types stimulate angiogenic processes indicated by an increased expression of PECAM in endothelial cells and specific deposition of basement membrane proteins. PVC show a significantly increased induction of endothelial specific PECAM expression compared to 10T1/2 cells. Accordingly, in vivo grafts of PVC aggregates onto chorioallantoic membranes of quail embryos recruit endothelial cells, get highly vascularized and deposit basement membrane components. These data demonstrate that isolated Anxa5-LacZ(+) PVC from mouse meninges retain their capacity for differentiation to pericyte-like cells and contribute to angiogenic processes.

Association between dependent smoking and a polymorphism in the tyrosine hydroxylase gene in a prospective population-based study of adolescent health.

This study reports pilot data on an association between tobacco dependence and a five-allele tetranucleotide repeat polymorphism in the first intron of the tyrosine hydroxylase (TH) gene. One hundred and twenty-six Australian adolescents who had participated in the Health in Transition Study (1993-1997), and who showed patterns of either dependent or nondependent smoking across four waves of data collection, consented to participation in the pilot study. The smoking status of those recruited was confirmed using a telephone-administered drug use questionnaire during 2000. Tobacco dependence was defined as smoking more than 6 days per week and more than 10 cigarettes per day during wave 5 (year 2000) and at least one prior wave ( n = 58). A second, more stringent phenotype included smoking within an hour of waking ( n = 37). The control group comprised adolescents who had used tobacco but had remained low-level social smokers across each wave of data ( n = 56). DNA was collected using a mouthwash procedure. Using the more strictly defined tobacco dependence phenotype, and after adjusting for sex, a significant protective association was found between the K4 allele and tobacco dependence (OR 0.27, 95% confidence interval [CI] 0.09, 0.82). No association was found using the liberal criteria of tobacco dependence (OR 0.51, 95% confidence interval [CI] 0.23, 1.2). These preliminary results replicate a previous association between tobacco use and the K4 allele of the TH gene (Lerman et al., 1997). The potential significance of including time to first cigarette in definitions of tobacco dependence and the possible role that these TH variants might play in tobacco dependence are discussed.