Facial development and type III collagen RNA expression: concurrent repression in the osteopetrotic (Toothless,tl) rat and rescue after treatment with colony-stimulating factor-1

Fibulin-5 deficiency causes developmental defect of premaxillary bone in mice

Craniofacial sutures govern the shape of the craniofacial skeleton during postnatal development. The differentiation of suture mesenchymal cells to osteoblasts is precisely regulated in part by signaling through cell surface receptors that interact with extracellular proteins. Here we report that fibulin-5, a key extracellular matrix protein, is important for craniofacial skeletal development in mice. Fibulin-5 is deposited as a fibrous matrix in cranial neural crest-derived mesenchymal tissues, including craniofacial sutures. Fibulin-5-null mice show decreased premaxillary bone outgrowth during postnatal stages. While premaxillo-maxillary suture mesenchymal cells in fibulin-5-null mice were capable of differentiating into osteoblasts, suture cells in mutant mice were less proliferative. Our study provides the first evidence that fibulin-5 is indispensable for the regulation of facial suture mesenchymal cell proliferation required for craniofacial skeletal morphogenesis.

Disheveled hair and ear (Dhe), a spontaneous mouse Lmna mutation modeling human laminopathies

Background

Investigations of naturally-occurring mutations in animal models provide important insights and valuable disease models. Lamins A and C, along with lamin B, are type V intermediate filament proteins which constitute the proteinaceous boundary of the nucleus. LMNA mutations in humans cause a wide range of phenotypes, collectively termed laminopathies. To identify the mutation and investigate the phenotype of a spontaneous, semi-dominant mutation that we have named Disheveled hair and ear (Dhe), which causes a sparse coat and small external ears in heterozygotes and lethality in homozygotes by postnatal day 10.

Findings

Genetic mapping identified a point mutation in the Lmna gene, causing a single amino acid change, L52R, in the coiled coil rod domain of lamin A and C proteins. Cranial sutures in Dhe/+ mice failed to close. Gene expression for collagen types I and III in sutures was deficient. Skulls were small and disproportionate. Skeletons of Dhe/+ mice were hypomineralized and total body fat was deficient in males. In homozygotes, skin and oral mucosae were dysplastic and ulcerated. Nuclear morphometry of cultured cells revealed gene dose-dependent blebbing and wrinkling.

Conclusion

Dhe mice should provide a useful new model for investigations of the pathogenesis of laminopathies.

Temporal evolution of gene expression in rat carotid artery following balloon angioplasty

The success of vascular intervention including angioplasty, stenting, and arterial bypass remains limited by negative remodeling resulted in lumen restenosis. This study was to characterize the global transcription profile reflecting concurrent events along arterial remodeling and neointima formation in a rat carotid artery balloon-injury model. Expression profiling of injured and control common carotid arteries on days 4, 7, 14 post-injury that mark the major pathohistological progression stages of neointimal formation were recorded on high-density oligonucleotide arrays. A subset of genes from microarray-based data was further studied using quantitative real time RT-PCR and in situ hybridization with sequential arterial samples from days 1 to 28 post-injury. The gene-encoded proteins were validated with Western blot. Besides temporal induction of a large cluster of genes over-represented by cell proliferation and macromolecule metabolism gene ontology categories, a fast-evolving inflammation could be demonstrated by the induction of Tgfb and other anti-inflammatory genes (e.g., C1qtnf3 (C1q and tumor necrosis factor related protein 3 (predicted))) and a shift from type 1 to 2 helper T cell response. The most significant signature of the induced neointimal profile is enrichment of genes functionally related to angiogenesis and extracellular matrix (ECM) remodeling (e.g., Spp1 (secreted phosphoprotein 1), CD44 (CD44 antigen), and Cxcl12 (chemokine (C-X-C motif) ligand 12 (stromal cell-derived factor 1)). Some of the genes represent stress-responsive mesenchymal stromal cell cytokines. This study highlighted mesenchymal stromal cell cytokines-driven inflammatory extracellular matrix remodeling, as target processes for potential clinical therapeutic intervention.

The extracellular matrix environment in suture morphogenesis and growth

Sutures are the major bone growth sites of the craniofacial skeleton and form in response to developmental approximation of and interaction between two opposing osteogenic fronts. Premature obliteration of these craniofacial bone growth sites or craniosynostosis results in compensatory growth at other bone growth sites, with concomitant craniofacial dysmorphology. While much is now known about the growth and transcriptional factor regulation of suture formation and maintenance, little about the nature of the extracellular environment within sutures and their surrounding bones has been described. This review elucidates the nature of the sutural extracellular matrix and its role in mediating suture maintenance and growth through the regulation of cellular and biomechanical signaling.

Chemokine and chemokine receptor expression during colony stimulating factor-1-induced osteoclast differentiation in the toothless osteopetrotic rat: a key role for CCL9 (MIP-1gamma) in osteoclastogenesis in vivo and in vitro

Osteoclasts differentiate from hematopoietic precursors under systemic and local controls. Chemokines and receptors direct leukocyte traffic throughout the body and may help regulate site-specific bone resorption. We investigated bone gene expression in vivo during rapid osteoclast differentiation induced by colony-stimulating factor 1 (CSF-1) in Csf1-null toothless (tl/tl) rats. Long-bone RNA from CSF-1-treated tl/tl rats was analyzed by high-density microarray over a time course. TRAP (tartrate-resistant acid phosphatase)-positive osteoclasts appeared on day 2, peaked on day 4, and decreased slightly on day 6, as marrow space was expanding. TRAP and cathepsin K mRNA paralleled the cell counts. We examined all chemokine and receptor mRNAs on the arrays. CCL9 was strongly induced and peaked on day 2, as did its receptor, CCR1, and regulatory receptors c-Fms (CSF-1 receptor) and RANK (receptor activator of nuclear factor kappaB). Other chemokines and receptors showed little or no significant changes. In situ hybridization and immunohistochemistry revealed CCL9 in small, immature osteoclasts on day 2 and in mature cells at later times. Anti-CCL9 antibody inhibited osteoclast differentiation in culture and significantly suppressed the osteoclast response in CSF-1-treated tl/tl rats. While various chemokines have been implicated in osteoclastogenesis in vitro, this first systematic analysis of chemokines and receptors during osteoclast differentiation in vivo highlights the key role of CCL9 in this process.

Tgf-beta1, Tgf-beta2, Tgf-beta3 and Msx2 expression is elevated during frontonasal suture morphogenesis and during active postnatal facial growth

OBJECTIVES

It is hypothesized that regulation of facial suture morphogenesis is similar to that of cranial sutures, with expression of similar regulatory molecules, governing suture formation and patency. The present study was designed to characterize the morphology of the frontonasal (FN) suture of the rat at different developmental stages and to investigate the presence and temporal-spatial expression of transforming growth factor-beta 1 (Tgf-beta1), Tgf-beta2, Tgf-beta3 and Msx2 mRNA within these structures.

SETTING AND SAMPLE POPULATION

The Department of Biomedical Sciences at Texas A&M University System Health Science Center, Baylor College of Dentistry, Dallas, TX USA. Histological sections and RNA isolated from FN suture tissues of Sprague-Dawley rats, aged embryonic day 16 through postnatal day 20.

METHOD

Sections were examined after immunohistochemical staining. Gene expression was determined by densitometric analysis of RT-PCR products run on agarose gels.

RESULTS

FN sutures develop slightly later than cranial sutures and show increased complexity over time when compared to cranial sutures. FN sutures were closely associated with the nasal capsular cartilage, with intervening layers of perichondrium and periosteum. The pattern of expression of Tgf-betas within the FN suture tissues was similar to that seen in the cranial sutures. However, mRNA and protein of the Tgf-betas were differentially expressed over time compared to cranial sutures. In FN sutures, Tgf-beta mRNA levels were elevated both during the period of suture morphogenesis and during active bone growth from the suture in the early postnatal period. Msx2 mRNA expression was elevated in both the prenatal and postnatal periods, similar to Tgf-beta mRNA expression.

CONCLUSION

Tgf-beta and Msx2 are present in facial sutures similar to cranial sutures, but are differentially expressed over time, perhaps reflecting different bone growth rates from these sutures.

The osteopetrotic mutation toothless (tl) is a loss-of-function frameshift mutation in the rat Csf1 gene: Evidence of a crucial role for CSF-1 in osteoclastogenesis and endochondral ossification

The toothless (tl) mutation in the rat is a naturally occurring, autosomal recessive mutation resulting in a profound deficiency of bone-resorbing osteoclasts and peritoneal macrophages. The failure to resorb bone produces severe, unrelenting osteopetrosis, with a highly sclerotic skeleton, lack of marrow spaces, failure of tooth eruption, and other pathologies. Injections of CSF-1 improve some, but not all, of these. In this report we have used polymorphism mapping, sequencing, and expression studies to identify the genetic lesion in the tl rat. We found a 10-base insertion near the beginning of the open reading of the Csf1 gene that yields a truncated, nonfunctional protein and an early stop codon, thus rendering the tl rat CSF-1(null). All mutants were homozygous for the mutation and all carriers were heterozygous. No CSF-1 transcripts were identified in rat mRNA that would avoid the mutation via alternative splicing. The biology and actions of CSF-1 have been elucidated by many studies that use another naturally occurring mutation, the op mouse, in which a single base insertion also disrupts the reading frame. The op mouse has milder osteoclastopenia and osteopetrosis than the tl rat and recovers spontaneously over the first few months of life. Thus, the tl rat provides a second model in which the functions of CSF-1 can be studied. Understanding the similarities and differences in the phenotypes of these two models will be important to advancing our knowledge of the many actions of CSF-1.

Procollagen-derived biomarkers in malignant ascites of ovarian cancer. Independent prognosticators for progression-free interval and survival

OBJECTIVE

Matrix formation is a hallmark of solid tumor biology. Circulating antigens of structural matrix proteins should reflect this fact, yet are subject to systemic variables. We propose that if measured regionally, in a cancer-induced extravascular fluid pool such as malignant ascites of ovarian cancer, the same antigens retain their conceptual advantage as surrogate markers for tumor biology.

METHODS

In malignant ascites obtained at staging laparatomy of 35 women with ovarian cancer, the protein-normalized levels of the C-terminal propeptide of procollagen type I (pnPICP) and the N-terminal propeptide of procollagen type III (pnPIIINP) were determined. Using univariate and multivariate analysis, we examined these parameters, their (pnPIIINP/pnPICP) quotient, and clinical criteria (FIGO stage, age, residual tumor, histology, and tumor grade) for impact on progression-free interval and survival.

RESULTS

The absolute level of pnPIIINP was the single most powerful independent factor impacting on survival, its P value being distinctly below (P = 0.0005 vs 0.003) and its risk ratio distinctly above (15 vs 2.5) residual tumor after debulking surgery. The relative level of pnPIIINP, i.e. (pnPIIINP / pnPICP), impacted on the likelihood of recurrence even more than residual tumor. By Kaplan-Meier analysis, cutoff values for the absolute or relative pnPIIINP level significantly discriminated patients with shortened survival or progression-free interval, respectively.

CONCLUSIONS

Since malignant ovarian epithelium itself forms collagen type III, and since collagen type III is a solid-phase regulator of angiogenesis, we propose that ascitic pnPIIINP is a fluid-phase indicator for angiogenic activity in ovarian cancer and thus represents a tumor virulence index.

Mutation of macrophage colony stimulating factor (Csf1) causes osteopetrosis in the tl rat

Osteopetrosis results from a heterogeneous group of congenital bone diseases that display inadequate osteoclastic bone resorption. We recently mapped tl (toothless), a mutation that causes osteopetrosis in rats, to a genetic region predicted to include the rat Csf1 gene. In this study, we sequenced the coding sequence of the rat Csf1 gene to determine if a mutation in Csf1 could be responsible for the tl phenotype. Sequencing revealed a 10-base insertion in the coding sequence of mutant animals that produces a frameshift and generates a stop codon early in the mutant Csf1 coding sequence. The 41 amino acid polypeptide predicted to be produced from the Csf1 promoter would have only the first nine amino acids of the wild-type rat protein. These data suggest that osteopetrosis develops in tl/tl rats because they cannot produce functional mCsf, a growth factor required for osteoclast differentiation and activation.

A new protein expressed in bone marrow cells and osteoblasts with implication in osteoblast recruitment

To study osteoblast recruitment from bone marrow cells, a rat femur cDNA library was screened by in situ hybridization for novel mRNA sequences that are frequently expressed in both marrow cells and osteoblasts. One isolated clone, called RP59, is described here. Northern blots indicated two bands of 2.6 and 2.8 kb in femur and spleen, tissues containing high amounts of immature mesenchymal cells, and no or little expression in other tissues. The cDNA sequence revealed a reading frame for a repetitive protein composed of arrays of 14-mers and phased phosphorylation sites. Antisera versus RP59 detected a single band of 90 kDa by Western blotting of femur extract. Immunohistochemistry indicated strong RP59 presence in the cytoplasm of bone marrow cells and weaker presence in nuclei of osteoblasts. Intermediate stages were found between strongly labeled, round, free bone marrow cells and weaker labeled, fibroblast-like young osteoblasts associated with bone matrix. These data indicated that marrow cells with high RP59 content were recruited into growing bone tissue. RP59 may help to study the transition of bone marrow cell to osteoblast in more detail.

Cranial sutures as intramembranous bone growth sites

Intramembranous bone growth is achieved through bone formation within a periosteum or by bone formation at sutures. Sutures are formed during embryonic development at the sites of approximation of the membranous bones of the craniofacial skeleton. They serve as the major sites of bone expansion during postnatal craniofacial growth. For sutures to function as intramembranous bone growth sites, they need to remain in an unossified state, yet allow new bone to be formed at the edges of the overlapping bone fronts. This process relies on the production of sufficient new bone cells to be recruited into the bone fronts, while ensuring that the cells within the suture remain undifferentiated. Unlike endochondral growth plates, which expand through chondrocyte hypertrophy, sutures do not have intrinsic growth potential. Rather, they produce new bone at the sutural edges of the bone fronts in response to external stimuli, such as signals arising from the expanding neurocranium. This process allows growth of the cranial vault to be coordinated with growth of the neurocranium. Too little or delayed bone growth will result in wide-open fontanels and suture agenesis, whereas too much or accelerated bone growth will result in osseous obliteration of the sutures or craniosynostosis. Craniosynostosis in humans, suture fusion in animals, and induced suture obliteration in vitro has been associated with mutations or alterations in expression of several transcription factors, growth factors, and their receptors. Much of the data concerning signaling within sutures has been garnered from research on cranial sutures; hence, only the cranial sutures will be discussed in detail in this review. This review synthesizes classic descriptions of suture growth and pathology with modern molecular analysis of genetics and cell function in normal and abnormal suture morphogenesis and growth in a unifying hypothesis. At the same time, the reader is reminded of the importance of the suture as an intramembranous bone growth site.