periostin null mice exhibit dwarfism, incisor enamel defects, and an early-onset periodontal disease-like phenotype

TGF-ß1 and FAK regulate periostin expression in PDL fibroblasts

Recently identified as a key component of the murine periodontal ligament (PDL), periostin has been implicated in the regulation of collagen fibrillogenesis and fibroblast differentiation. We investigated whether periostin protein is expressed in the human PDL in situ and the mechanisms regulating periostin expression in PDL fibroblasts in vitro. With immunohistochemistry, periostin protein was identified in the PDL, with expression lower in teeth with reduced occlusal loading. In vitro application of uniaxial cyclic strain to PDL fibroblasts elevated periostin mRNA levels, depending on the age of the patient. Treatment with transforming growth factor-beta1 (TGF-β1) also significantly increased periostin mRNA levels, an effect attenuated by focal adhesion kinase (FAK) inhibition. FAK-null fibroblasts contained no detectable periostin mRNA, even after stimulation with cyclic strain. In conclusion, periostin protein is strongly expressed in the human PDL. In vitro, periostin mRNA levels are modulated by cyclic strain as well as TGF-β1 via FAK-dependent pathways.

Apatite microtopographies instruct signaling tapestries for progenitor-driven new attachment of teeth

Dimension and structure of extracellular matrix surfaces have powerful influences on cell shape, adhesion, and gene expression. Here we show that natural tooth root topographies induce integrin-mediated extracellular matrix signaling cascades in tandem with cell elongation and polarization to generate physiological periodontium-like tissues. In this study we replanted surface topography instructed periodontal progenitors into rat alveolar bone sockets for 8 and 16 weeks, resulting in complete reattachment of tooth roots to the surrounding alveolar bone with a periodontal fiber apparatus closely matching physiological controls along the entire root surface. Displacement studies and biochemical analyses confirmed that progenitor-based engineered periodontal tissues were similar to control teeth and uniquely derived from preimplantation green fluorescent protein (GFP)-labeled progenitors. Together, these studies illustrate the capacity of natural extracellular surface topographies to instruct progenitor cell populations to fully regenerate complex cellular and structural morphologies of tissues once lost to disease. We suggest that our strategy could be used for the replantation of teeth lost due to trauma or as a novel approach for tooth replacement using tooth-shaped replicas.

Development of a new ELISA for serum periostin: evaluation of growth-related changes and bisphosphonate treatment in mice

Periostin is a gamma-carboxyglutamic acid protein preferentially expressed in periosteum and bone mesenchymal stem cells. Lack of a precise assay for measuring circulating levels impairs the investigation of its biological significance. We developed a new ELISA and studied changes of periostin levels both locally at the bone site and systemically in circulating blood during growth and after bisphosphonate-induced inhibition of bone remodeling in the mouse. The ELISA we developed is based on an affinity-purified polyclonal antibody that was raised against the C-terminal sequence of mouse periostin. Reproducibility, repeatability, precision, and accuracy tests met standards of acceptance. Serum periostin and levels of the bone turnover markers osteocalcin, PINP, CTX-I, and TRAP5b were measured in (1) 4-, 6-, 8-, 10-, and 12-week-old wild-type female Balb/c mice and (2) adult ovariectomized female Balb/c mice treated with zoledronic acid or vehicle. Serum periostin decreased during growth and stabilized from 8 weeks and older, its levels correlating with bone turnover markers. Immunohistochemistry in bones from different growth stages showed that periostin localized specifically at the sites of endochondral and intramembranous ossification, especially at the periosteal envelopes. Zoledronic acid induced a marked decrease in bone remodeling markers but did not alter serum periostin levels or periostin immunostaining pattern. The novel ELISA is highly specific and allows accurate and precise measurements of serum periostin levels in mice.

Dilated capillaries, disorganized collagen fibers and differential gene expression in periodontal ligaments of hypomorphic fibrillin-1 mice

The periodontal ligaments (PDLs) are soft connective tissue between the cementum covering the tooth root surface and alveolar bone. PDLs are composed of collagen and elastic system fibers, blood vessels, nerves, and various types of cells. Elastic system fibers are generally formed by elastin and microfibrils, but PDLs are mainly composed of the latter. Compared with the well-known function of collagen fibers to support teeth, little is known about the role of elastic system fibers in PDLs. To clarify their role, we examined PDLs of mice under-expressing fibrillin-1 (mgR mice), which is one of the major microfibrillar proteins. The PDLs of homozygous mgR mice showed one-quarter of the elastic system fibers of wild-type (WT) mice. A close association between the elastic system fibers and the capillaries was noted in WT, homozygous and heterozygous mgR mice. Interestingly, capillaries in PDLs of homozygous mice were dilated or enlarged compared with those of WT mice. A comparable level of type I collagen, which is the major collagen in PDLs, was expressed in PDL-cells of mice with three genotypes. However, multi-oriented collagen fiber bundles with a thinner appearance were noted in homozygous mice, whereas well-organized collagen fiber bundles were seen in WT mice. Moreover, there was a marked decrease in periostin expression, which is known to regulate the fibrillogenesis and crosslinking of collagen. These observations suggest that the microfibrillar protein, fibrillin-1, is indispensable for normal tissue architecture and gene expression of PDLs.

Periostin promotes ovarian cancer angiogenesis and metastasis

OBJECTIVE

Perostin (PN) has been found to be overexpressed in a variety of human malignancies including ovarian cancer. In the present study, we investigated PN expression status in a large cohort of ovarian tumors with the focus on biological influence of PN related on ovarian tumor angiogenesis and metastasis.

METHODS

PN expression was determined by cDNA microarray, PN northern blot and PN IHC tissue array analyses. Exogenous PN expression in ovarian cancer cells OVCAR-3 and OV2008 were achieved through retroviral transfection and confirmed by PN western blot and ELISA. The effects of exogenous PN expression on tumor angiogenesis and metastatic growth were accessed in orthotopic mouse models. The in vitro cell adhesion, migration and invasion assays were performed to investigate the potential mechanisms involved in PN's in vivo effects.

RESULTS

PN was frequently overexpressed in ovarian tumors. Higher PN levels significantly correlated with clinical late stages (III/IV) and cancer recurrence. PN was produced by engineered PN-overexpressing cells at levels comparable to that of A2780 cells, an ovarian carcinoma cell line with endogenous PN expression. PN overexpression did not change cell growth rates in vitro; however it significantly promoted intraperitoneal tumor metastatic growth in immunodeficient mice, which was associated with increased tumor angiogenesis and decreased tumor cell apoptosis. In vitro purified PN promoted cell adhesion, migration, and invasion of both human umbilical endothelial cells (HUVECs) and/or ovarian cancer cells.

CONCLUSIONS

Our data indicate PN plays a critical role in both ovarian tumor angiogenesis and metastasis. Thus PN may represent a clinically effective new target for therapy of ovarian cancer.

Roles of epithelial cell-derived periostin in TGF-beta activation, collagen production, and collagen gel elasticity in asthma

Periostin is considered to be a matricellular protein with expression typically confined to cells of mesenchymal origin. Here, by using in situ hybridization, we show that periostin is specifically up-regulated in bronchial epithelial cells of asthmatic subjects, and in vitro, we show that periostin protein is basally secreted by airway epithelial cells in response to IL-13 to influence epithelial cell function, epithelial-mesenchymal interactions, and extracellular matrix organization. In primary human bronchial epithelial cells stimulated with periostin and epithelial cells overexpressing periostin, we reveal a function for periostin in stimulating the TGF-beta signaling pathway in a mechanism involving matrix metalloproteinases 2 and 9. Furthermore, conditioned medium from the epithelial cells overexpressing periostin caused TGF-beta-dependent secretion of type 1 collagen by airway fibroblasts. In addition, mixing recombinant periostin with type 1 collagen in solution caused a dramatic increase in the elastic modulus of the collagen gel, indicating that periostin alters collagen fibrillogenesis or cross-linking and leads to stiffening of the matrix. Epithelial cell-derived periostin in asthma has roles in TGF-beta activation and collagen gel elasticity in asthma.

Periostin is a collagen associated bone matrix protein regulated by parathyroid hormone

Periostin is a 90 kDa secreted protein, originally identified in murine osteoblast-like cells, with a distribution restricted to collagen-rich tissues and certain tumors. In this paper, we first analyzed the expression of periostin mRNA and protein in human fetal osteoblasts (hFOB) and human osteosarcoma (hOS) cell lines by RT real-time PCR and Western blot, respectively. The hFOB 1.19 and three hOS (MHM, KPDXM and Eggen) showed highly variable periostin mRNA levels and protein. Second, we showed that the expression of periostin mRNA was inversely related to the cells' abilities to differentiate and mineralize. Then, we investigated the regulation of periostin mRNA in hFOB after siRNA treatment and in mouse primary osteoblasts (mOB) treated with PTH. Knock-down of periostin mRNA, down-regulated PTHrP, but did not affect the expression of other important markers of differentiation such as RUNX2. In addition, periostin mRNA was transiently up-regulated in osteoblasts by PTH. Finally, the localization of periostin and its partially co-localization with collagen 1a1 mRNA and protein was studied in mouse embryos and postnatal pups using in situ hybridization and immunohistochemistry, respectively. In conclusion, the present study provides novel observations related to the expression, distribution and regulation of periostin in bone cells and extracellular matrix.

Periostin, a cell adhesion molecule, facilitates invasion in the tumor microenvironment and annotates a novel tumor-invasive signature in esophageal cancer

Human squamous cell cancers are the most common epithelially derived malignancies. One example is esophageal squamous cell carcinoma (ESCC), which is associated with a high mortality rate that is related to a propensity for invasion and metastasis. Here, we report that periostin, a highly expressed cell adhesion molecule, is a key component of a novel tumor-invasive signature obtained from an organotypic culture model of engineered ESCC. This tumor-invasive signature classifies with human ESCC microarrays, underscoring its utility in human cancer. Genetic modulation of periostin promotes tumor cell migration and invasion as revealed in gain-of-loss and loss-of-function experiments. Inhibition of epidermal growth factor receptor signaling and restoration of wild-type p53 function were each found to attenuate periostin, suggesting the interdependence of two common genetic alterations with periostin function. Collectively, our studies reveal periostin as an important mediator of ESCC tumor invasion and they indicate that organotypic (three-dimensional) culture can offer an important tool to discover novel biological effectors in cancer.

Role of matricellular proteins in cardiac tissue remodeling after myocardial infarction

After onset of myocardial infarction (MI), the left ventricle (LV) undergoes a continuum of molecular, cellular, and extracellular responses that result in LV wall thinning, dilatation, and dysfunction. These dynamic changes in LV shape, size, and function are termed cardiac remodeling. If the cardiac healing after MI does not proceed properly, it could lead to cardiac rupture or maladaptive cardiac remodeling, such as further LV dilatation and dysfunction, and ultimately death. Although the precise molecular mechanisms in this cardiac healing process have not been fully elucidated, this process is strictly coordinated by the interaction of cells with their surrounding extracellular matrix (ECM) proteins. The components of ECM include basic structural proteins such as collagen, elastin and specialized proteins such as fibronectin, proteoglycans and matricellular proteins. Matricellular proteins are a class of non-structural and secreted proteins that probably exert regulatory functions through direct binding to cell surface receptors, other matrix proteins, and soluble extracellular factors such as growth factors and cytokines. This small group of proteins, which includes osteopontin, thrombospondin-1/2, tenascin, periostin, and secreted protein, acidic and rich in cysteine, shows a low level of expression in normal adult tissue, but is markedly upregulated during wound healing and tissue remodeling, including MI. In this review, we focus on the regulatory functions of matricellular proteins during cardiac tissue healing and remodeling after MI.

Homeobox genes d11-d13 and a13 control mouse autopod cortical bone and joint formation

The molecular mechanisms that govern bone and joint formation are complex, involving an integrated network of signaling pathways and gene regulators. We investigated the role of Hox genes, which are known to specify individual segments of the skeleton, in the formation of autopod limb bones (i.e., the hands and feet) using the mouse mutant synpolydactyly homolog (spdh), which encodes a polyalanine expansion in Hoxd13. We found that no cortical bone was formed in the autopod in spdh/spdh mice; instead, these bones underwent trabecular ossification after birth. Spdh/spdh metacarpals acquired an ovoid shape and developed ectopic joints, indicating a loss of long bone characteristics and thus a transformation of metacarpals into carpal bones. The perichondrium of spdh/spdh mice showed abnormal morphology and decreased expression of Runt-related transcription factor 2 (Runx2), which was identified as a direct Hoxd13 transcriptional target. Hoxd11-/-Hoxd12-/-Hoxd13-/- triple-knockout mice and Hoxd13-/-Hoxa13+/- mice exhibited similar but less severe defects, suggesting that these Hox genes have similar and complementary functions and that the spdh allele acts as a dominant negative. This effect was shown to be due to sequestration of other polyalanine-containing transcription factors by the mutant Hoxd13 in the cytoplasm, leading to their degradation. These data indicate that Hox genes not only regulate patterning but also directly influence bone formation and the ossification pattern of bones, in part via Runx2.

Trigenic neural crest-restricted Smad7 over-expression results in congenital craniofacial and cardiovascular defects

Smad7 is a negative regulator of TGFbeta superfamily signaling. Using a three-component triple transgenic system, expression of the inhibitory Smad7 was induced via doxycycline within the NCC lineages at pre- and post-migratory stages. Consistent with its role in negatively regulating both TGFbeta and BMP signaling in vitro, induction of Smad7 within the NCC significantly suppressed phosphorylation levels of both Smad1/5/8 and Smad2/3 in vivo, resulting in subsequent loss of NCC-derived craniofacial, pharyngeal and cardiac OFT cushion cells. At the cellular level, increased cell death was observed in pharyngeal arches. However, cell proliferation and NCC-derived smooth muscle differentiation were unaltered. NCC lineage mapping demonstrated that cardiac NCC emigration and initial migration were not affected, but subsequent colonization of the OFT was significantly reduced. Induction of Smad7 in post-migratory NCC resulted in interventricular septal chamber septation defects, suggesting that TGFbeta superfamily signaling is also essential for cardiac NCC at post-migratory stages to govern normal cardiac development. Taken together, the data illustrate that tightly regulated TGFbeta superfamily signaling plays an essential role during craniofacial and cardiac NCC colonization and cell survival in vivo.

Fasciclin-like arabinogalactan proteins: specialization for stem biomechanics and cell wall architecture in Arabidopsis and Eucalyptus

The ancient cell adhesion fasciclin (FAS) domain is found in bacteria, fungi, algae, insects and animals, and occurs in a large family of fasciclin-like arabinogalactan proteins (FLAs) in higher plants. Functional roles for FAS-containing proteins have been determined for insects, algae and vertebrates; however, the biological functions of the various higher-plant FLAs are not clear. Expression of some FLAs has been correlated with the onset of secondary-wall cellulose synthesis in Arabidopsis stems, and also with wood formation in the stems and branches of trees, suggesting a biological role in plant stems. We examined whether FLAs contribute to plant stem biomechanics. Using phylogenetic, transcript abundance and promoter-GUS fusion analyses, we identified a conserved subset of single FAS domain FLAs (group A FLAs) in Eucalyptus and Arabidopsis that have specific and high transcript abundance in stems, particularly in stem cells undergoing secondary-wall deposition, and that the phylogenetic conservation appears to extend to other dicots and monocots. Gene-function analyses revealed that Arabidopsis T-DNA knockout double mutant stems had altered stem biomechanics with reduced tensile strength and a reduced tensile modulus of elasticity, as well as altered cell-wall architecture and composition, with increased cellulose microfibril angle and reduced arabinose, galactose and cellulose content. Using materials engineering concepts, we relate the effects of these FLAs on cell-wall composition with stem biomechanics. Our results suggest that a subset of single FAS domain FLAs contributes to plant stem strength by affecting cellulose deposition, and to the stem modulus of elasticity by affecting the integrity of the cell-wall matrix.

Gene replacement strategies to test the functional redundancy of basic helix-loop-helix transcription factor

Basic helix-loop-helix (bHLH) transcription factors control developmental decisions for a wide range of embryonic cell types. Hand1 and Hand2 are closely related bHLH proteins that control cardiac, craniofacial, and limb development. Within the developing heart, Hand1 expression becomes restricted predominantly to the left ventricle, whereas Hand2 becomes restricted predominantly to the left ventricle, for which findings have shown each Hand factor to be necessary for normal chamber formation. Forced overexpression of Hand1 throughout the early developing heart induces abnormal interventricular septal development, with resulting pathogenesis of congenital heart defects. To investigate the potential transcriptional mechanisms involved in heart morphogenesis by Hand2, this study used a replacement targeting approach to knock Hand2 into the Hand1 locus and ectopically express one copy of Hand2 within the endogenous Hand1 expression domain in the developing hearts of transgenic mice. The findings show that high-percentage Hand1 ( Hand2 ) chimeras die at birth and exhibit a range of congenital heart defects. These findings suggest that Hand factors may act via unique transcriptional mechanisms mediated by bHLH factor partner choice, supporting the notion that alterations of Hand factor stoichiometry may be as deleterious to normal heart morphogenesis as Hand factor loss of function.

Loading-related regulation of gene expression in bone in the contexts of estrogen deficiency, lack of estrogen receptor alpha and disuse

Loading-related changes in gene expression in resident cells in the tibia of female mice in the contexts of normality (WT), estrogen deficiency (WT-OVX), absence of estrogen receptor alpha (ERalpha(-/-)) and disuse due to sciatic neurectomy (WT-SN) were established by microarray. Total RNA was extracted from loaded and contra-lateral non-loaded tibiae at selected time points after a single, short period of dynamic loading sufficient to engender an osteogenic response. There were marked changes in the expression of many genes according to context as well as in response to loading within those contexts. In WT mice at 3, 8, 12 and 24 h after loading the expression of 642, 341, 171 and 24 genes, respectively, were differentially regulated compared with contra-lateral bones which were not loaded. Only a few of the genes differentially regulated by loading in the tibiae of WT mice have recognized roles in bone metabolism or have been linked previously to osteogenesis (Opn, Sost, Esr1, Tgfb1, Lrp1, Ostn, Timp, Mmp, Ctgf, Postn and Irs1, BMP and DLX5). The canonical pathways showing the greatest loading-related regulation were those involving pyruvate metabolism, mitochondrial dysfunction, calcium-induced apoptosis, glycolysis/gluconeogenesis, aryl hydrocarbon receptor and oxidative phosphorylation. In the tibiae from WT-OVX, ERalpha(-/-) and WT-SN mice, 440, 439 and 987 genes respectively were differentially regulated by context alone compared to WT. The early response to loading in tibiae of WT-OVX mice involved differential regulation compared to their contra-lateral non-loaded pair of fewer genes than in WT, more down-regulation than up-regulation and a later response. This was shared by WT-SN. In tibiae of ERalpha(-/-) mice, the number of genes differentially regulated by loading was markedly reduced at all time points. These data indicate that in resident bone cells, both basal and loading-related gene expression is substantially modified by context. Many of the genes differentially regulated by the earliest loading-related response were primarily involved in energy metabolism and were not specific to bone.

Periostin shows increased evolutionary plasticity in its alternatively spliced region

Background

Periostin (POSTN) is a secreted extracellular matrix protein of poorly defined function that has been related to bone and heart development as well as to cancer. In human and mouse, it is known to undergo alternative splicing in its C-terminal region, which is devoid of known protein domains. Differential expression of periostin, sometimes of specific splicing isoforms, is observed in a broad range of human cancers, including breast, pancreatic, and colon cancer. Here, we combine genomic and transcriptomic sequence data from vertebrate organisms to study the evolution of periostin and particularly of its C-terminal region.

Results

We found that the C-terminal part of periostin is markedly more variable among vertebrates than the rest of periostin in terms of exon count, length, and splicing pattern, which we interpret as a consequence of neofunctionalization after the split between periostin and its paralog transforming growth factor, beta-induced (TGFBI). We also defined periostin's sequential 13-amino acid repeat units - well conserved in teleost fish, but more obscure in higher vertebrates - whose secondary structure is predicted to be consecutive beta strands. We suggest that these beta strands may mediate binding interactions with other proteins through an extended beta-zipper in a manner similar to the way repeat units in bacterial cell wall proteins have been reported to bind human fibronectin.

Conclusions

Our results, obtained with the help of the increasingly large collection of complete vertebrate genomes, document the evolutionary plasticity of periostin's C-terminal region, and for the first time suggest a basis for its functional role.

The matricellular protein periostin is required for sost inhibition and the anabolic response to mechanical loading and physical activity

Periostin (gene Postn) is a secreted extracellular matrix protein involved in cell recruitment and adhesion and plays an important role in odontogenesis. In bone, periostin is preferentially expressed in the periosteum, but its functional significance remains unclear. We investigated Postn(-/-) mice and their wild type littermates to elucidate the role of periostin in the skeletal response to moderate physical activity and direct axial compression of the tibia. Furthermore, we administered a sclerostin-blocking antibody to these mice in order to demonstrate the influence of sustained Sost expression in their altered bone phenotypes. Cancellous and cortical bone microarchitecture as well as bending strength were altered in Postn(-/-) compared with Postn(+/+) mice. Exercise and axial compression both significantly increased bone mineral density and trabecular and cortical microarchitecture as well as biomechanical properties of the long bones in Postn(+/+) mice by increasing the bone formation activity, particularly at the periosteum. These changes correlated with an increase of periostin expression and a consecutive decrease of Sost in the stimulated bones. In contrast, mechanical stimuli had no effect on the skeletal properties of Postn(-/-) mice, where base-line expression of Sost levels were higher than Postn(+/+) and remained unchanged following axial compression. In turn, the concomitant injection of sclerostin-blocking antibody rescued the bone biomechanical response in Postn(-/-) mice. Taken together, these results indicate that the matricellular periostin protein is required for Sost inhibition and thereby plays an important role in the determination of bone mass and microstructural in response to loading.

Origin of cardiac fibroblasts and the role of periostin

Cardiac fibroblasts are the most populous nonmyocyte cell type within the mature heart and are required for extracellular matrix synthesis and deposition, generation of the cardiac skeleton, and to electrically insulate the atria from the ventricles. Significantly, cardiac fibroblasts have also been shown to play an important role in cardiomyocyte growth and expansion of the ventricular chambers during heart development. Although there are currently no cardiac fibroblast-restricted molecular markers, it is generally envisaged that the majority of the cardiac fibroblasts are derived from the proepicardium via epithelial-to-mesenchymal transformation. However, still relatively little is known about when and where the cardiac fibroblasts cells are generated, the lineage of each cell, and how cardiac fibroblasts move to reside in their final position throughout all four cardiac chambers. In this review, we summarize the present understanding regarding the function of Periostin, a useful marker of the noncardiomyocyte lineages, and its role during cardiac morphogenesis. Characterization of the cardiac fibroblast lineage and identification of the signals that maintain, expand and regulate their differentiation will be required to improve our understanding of cardiac function in both normal and pathophysiological states.

Incorporation of tenascin-C into the extracellular matrix by periostin underlies an extracellular meshwork architecture

Extracellular matrix (ECM) underlies a complicated multicellular architecture that is subjected to significant forces from mechanical environment. Although various components of the ECM have been enumerated, mechanisms that evolve the sophisticated ECM architecture remain to be addressed. Here we show that periostin, a matricellular protein, promotes incorporation of tenascin-C into the ECM and organizes a meshwork architecture of the ECM. We found that both periostin null mice and tenascin-C null mice exhibited a similar phenotype, confined tibial periostitis, which possibly corresponds to medial tibial stress syndrome in human sports injuries. Periostin possessed adjacent domains that bind to tenascin-C and the other ECM protein: fibronectin and type I collagen, respectively. These adjacent domains functioned as a bridge between tenascin-C and the ECM, which increased deposition of tenascin-C on the ECM. The deposition of hexabrachions of tenascin-C may stabilize bifurcations of the ECM fibrils, which is integrated into the extracellular meshwork architecture. This study suggests a role for periostin in adaptation of the ECM architecture in the mechanical environment.

Progesterone and interferon tau-regulated genes in the ovine uterine endometrium: identification of periostin as a potential mediator of conceptus elongation

During early pregnancy in ruminants, progesterone (P4) and interferon tau (IFNT) act on the endometrium to regulate genes hypothesized to be important for conceptus development and implantation. The present study was conducted to verify several candidate genes (actin α-2, smooth muscle, aorta (ACTA2), collagen, type III, α-1 (COL3A1), periostin (POSTN), secreted protein acidic cysteine-rich (SPARC), S100 calcium-binding protein A2 (S100A2),STAT5Aand transgelin (TAGLN)) regulated by pregnancy, P4, and/or IFNT in the endometrium determined using a custom ovine cDNA array.S100A2mRNA was detected primarily in endometrial epithelia and conceptuses.S100A2mRNA increased in endometrial epithelia from days 10 to 16 in cyclic ewes and from days 10 to 14 in pregnant ewes and declined thereafter. The abundance ofS100A2mRNA was less in endometrial luminal epithelium of IFNT-infused ewes receiving P4. Expression ofCOL3A1, SPARC, ACTA2, andTAGLNwas independent of pregnancy, P4, or IFNT.POSTNmRNA was detected primarily in compact stroma of intercaruncular and caruncular endometria, but not in the conceptus. EndometrialPOSTNmRNA increased between days 12 and 14 in pregnant but not cyclic ewes, andPOSTNmRNA was more abundant in uterine stroma of ewes treated with P4. POSTN protein was detected in uterine flushings of pregnant ewes and found to mediate attachment and stimulate migration of ovine trophectoderm cellsin vitro. These results support the ideas that POSTN and S100A2 are regulated by P4and IFNT respectively, and that POSTN is involved in conceptus elongation during early pregnancy.

The many facets of the matricelluar protein periostin during cardiac development, remodeling, and pathophysiology

Periostin is a member of a growing family of matricellular proteins, defined by their ability to interact with components of the extracellular milieu, and with receptors at the cell surface. Through these interactions, periostin has been shown to play a crucial role as a profibrogenic molecule during tissue morphogenesis. Tissues destined to become fibrous structures are dependent on cooperative interactions between periostin and its binding partners, whereas in its absence, these structures either totally or partially fail to become mature fibrous entities. Within the heart, fibrogenic differentiation is required for normal tissue maturation, remodeling and function, as well as in response to a pathological myocardial insult. In this review, aspects related to the function of periostin during cardiac morphogenesis, remodeling and pathology are summarized.

Vitamin K, an example of triage theory: is micronutrient inadequacy linked to diseases of aging?

The triage theory posits that some functions of micronutrients (the approximately 40 essential vitamins, minerals, fatty acids, and amino acids) are restricted during shortage and that functions required for short-term survival take precedence over those that are less essential. Insidious changes accumulate as a consequence of restriction, which increases the risk of diseases of aging. For 16 known vitamin K-dependent (VKD) proteins, we evaluated the relative lethality of 11 known mouse knockout mutants to categorize essentiality. Results indicate that 5 VKD proteins that are required for coagulation had critical functions (knockouts were embryonic lethal), whereas the knockouts of 5 less critical VKD proteins [osteocalcin, matrix Gla protein (Mgp), growth arrest specific protein 6, transforming growth factor beta-inducible protein (Tgfbi or betaig-h3), and periostin] survived at least through weaning. The VKD gamma-carboxylation of the 5 essential VKD proteins in the liver and the 5 nonessential proteins in nonhepatic tissues sets up a dichotomy that takes advantage of the preferential distribution of dietary vitamin K1 to the liver to preserve coagulation function when vitamin K1 is limiting. Genetic loss of less critical VKD proteins, dietary vitamin K inadequacy, human polymorphisms or mutations, and vitamin K deficiency induced by chronic anticoagulant (warfarin/coumadin) therapy are all linked to age-associated conditions: bone fragility after estrogen loss (osteocalcin) and arterial calcification linked to cardiovascular disease (Mgp). There is increased spontaneous cancer in Tgfbi mouse knockouts, and knockdown of Tgfbi causes mitotic spindle abnormalities. A triage perspective reinforces recommendations of some experts that much of the population and warfarin/coumadin patients may not receive sufficient vitamin K for optimal function of VKD proteins that are important to maintain long-term health.

Lack of periostin leads to suppression of Notch1 signaling and calcific aortic valve disease

The Postn gene encodes protein periostin. During embryonic development, it is highly expressed in the outflow tract (OFT) endocardial cushions of the developing heart, which give rise to several structures of the mature heart including the aortic valve. Periostin was previously implicated in osteoblast differentiation, cancer metastasis, and tooth and bone development, but its role in cardiac OFT development is unclear. To elucidate the role that periostin plays in the developing heart we analyzed cardiac OFT phenotype in mice after deletion of the Postn gene. We found that lack of periostin in the embryonic OFT leads to ectopic expression of the proosteogenic growth factor pleiotrophin (Ptn) and overexpression of delta-like 1 homolog (Dlk1), a negative regulator of Notch1, in the distal (prevalvular) cushions of the OFT. This resulted in suppression of Notch1 signaling, strong induction of the central transcriptional regulator of osteoblast cell fate Runx2, upregulation of osteopontin and osteocalcin expression, and subsequent calcification of the aortic valve. Our data suggest that periostin represses a default osteogenic program in the OFT cushion mesenchyme and promotes differentiation along a fibrogenic lineage. Lack of periostin causes derepression of the osteogenic potential of OFT mesenchymal cells, calcium deposition, and calcific aortic valve disease. These results establish periostin as a key regulator of OFT endocardial cushion mesenchymal cell fate during embryonic development.

Molecular genetics of ameloblast cell lineage

Late tooth morphogenesis is characterized by a series of events that determine crown morphogenesis and the histodifferentiation of epithelial cells into enamel-secreting ameloblasts and of mesenchymal cells into dentin-secreting odontoblasts. Functional ameloblasts are tall, columnar, polarized cells that synthesize and secrete a number of enamel-specific proteins. After depositing the full thickness of enamel matrix, ameloblasts shrink in size and regulate enamel maturation. Amelogenesis imperfecta (AI) is a heterogeneous group of inherited defects in enamel formation. Clinically, AI presents as a spectrum of enamel malformations that are categorized as hypoplastic, hypocalcified, or hypomaturation types, based upon the thickness and hardness of the enamel. The different types of AI are inherited, either as X-linked, autosomal-dominant, or autosomal-recessive traits. Recently, several gene mutations have been identified to cause the subtypes of AI. How these genes, however, coordinate their function to control amelogenesis is not understood. In this review, we discuss the role of genes that play definitive role on the determination of ameloblast cell fate and life cycle based on studies in transgenic animals.

The KK-Periome database for transcripts of periodontal ligament development

The periodontal ligament (PDL) is a strong connective tissue that surrounds the tooth root, absorbs occlusal forces, and functions as a sense organ. PDL originated from dental follicle (DF), which possessed mesenchymal progenitors in the developing tooth germ. However, as specific marker genes for PDL and DF are currently unavailable, the molecular mechanisms of PDL development are yet to be clarified. To facilitate the identification of such genes, we have previously established a transcriptome database of the human PDL (the KK-Periome database) and screened for specific genes expressed during PDL development. Initial screening of the database revealed two marker genes for distinguishing DF and PDL. The KK-Periome database thus appears to offer a useful resource for investigating genes involved in PDL development.

The multifaceted role of periostin in tumorigenesis

Periostin, also called osteoblast-specific factor 2 (OSF-2), is a member of the fasciclin family and a disulfide-linked cell adhesion protein that has been shown to be expressed preferentially in the periosteum and periodontal ligaments, where it acts as a critical regulator of bone and tooth formation and maintenance. Furthermore, periostin plays an important role in cardiac development. Recent clinical evidence has also revealed that periostin is involved in the development of various tumors, such as breast, lung, colon, pancreatic, and ovarian cancers. Periostin interacts with multiple cell-surface receptors, most notably integrins, and signals mainly via the PI3-K/Akt and other pathways to promote cancer cell survival, epithelial-mesenchymal transition (EMT), invasion, and metastasis. In this review, aspects related to the function of periostin in tumorigenesis are summarized.

Extracellular matrix-mediated differentiation of periodontal progenitor cells

The periodontal ligament (PDL) is a specialized connective tissue that connects the surface of the tooth root with the bony tooth socket. The healthy PDL harbors stem cell niches and extracellular matrix (ECM) microenvironments that facilitate periodontal regeneration. During periodontal disease, the PDL is often compromised or destroyed, reducing the life-span of the tooth. In order to explore new approaches toward the regeneration of diseased periodontal tissues, we have tested the effect of periodontal ECM signals, fibroblast growth factor 2 (FGF2), connective tissue growth factor (CTGF), and the cell adhesion peptide Arg-Gly-Asp (RGD) on the differentiation of two types of periodontal progenitor cells, PDL progenitor cells (PDLPs) and dental follicle progenitor cells (DFCs). Our studies documented that CTGF and FGF2 significantly enhanced the expression of collagens I & III, biglycan and periostin in tissue engineered regenerates after 4 weeks compared to untreated controls. Specifically, CTGF promoted mature PDL-like tissue regeneration as demonstrated by dense periostin localization in collagen fiber bundles. CTGF and FGF2 displayed synergistic effects on collagen III and biglycan gene expression, while effects on mineralization were antagonistic to each other: CTGF promoted while FGF2 inhibited mineralization in PDL cell cultures. Incorporation of RGD peptides in hydrogel matrices significantly enhanced attachment, spreading, survival and mineralization of the encapsulated DFCs, suggesting that RGD additives might promote the use of hydrogels for periodontal mineralized tissue engineering. Together, our studies have documented the effect of three key components of the periodontal ECM on the differentiation of periodontal progenitor populations.

Differential global and extra-cellular matrix focused gene expression patterns between normal and glaucomatous human lamina cribrosa cells

PURPOSE

Marked extracellular matrix (ECM) remodeling occurs in the human optic nerve head in primary open angle glaucoma (POAG). The glial fibrillary acid protein (GFAP) negative lamina cribrosa cell may play an important role in this remodeling process. We report the first study of global and ECM-focused gene transcription differentials between GFAP-negative lamina cribrosa (LC) cells from normal and POAG human donors.

METHODS

GFAP-negative LC cell lines were generated from the optic nerve tissue of four normal (n=4) and four POAG (n=4) human donors. Using Affymetrix U133A arrays the transcriptional profile between the normal and diseased groups were compared. Bioinformatic analysis was performed using robust multichip average (RMA Express) and EASE/David. Real time TaqMan PCR and immunohistochemistry analyses were performed to validate the microarray data.

RESULTS

183 genes were upregulated by greater than 1.5 fold and 220 were down regulated by greater than 1.5 fold in the POAG LC cells versus normal controls. Upregulated genes in POAG LC cells included, transforming growth factor beta 1 (TGFbeta1), secreted acid protein cysteine rich (SPARC), periostin (POSTN), thrombospondin-1 (THBS1), cartilage linking protein-1 (CRTL-1), and collagen type I (COL1A1), collagen type V (COL5A1), and collagen type XI (COL11A1). Downregulated ECM genes in POAG included fibulin 1 (FBLN1), decorin (DCN), and collagen type XVIII (COL18A1). All TaqMan PCR validation assays were significant (*p<0.05) and consistent with the array data. Immunohistochemistry of one target (periostin) confirmed its differential expression at the protein level in POAG optic nerve head tissue compared with non-glaucomatous controls. Functional annotation and over-representation analysis identified ECM genes as a statistically over-represented class of genes in POAG LC cells compared with normal LC cells.

CONCLUSIONS

This study reports for the first time that POAG LC cells in-vitro demonstrate upregulated ECM and pro-fibrotic gene expression compared with normal LC cells. This may be a pathological characteristic of this cell type in POAG in-vivo. We believe that the LC cell may be a pivotal regulator of optic nerve head ECM remodeling in POAG and an attractive target for molecular therapeutic strategies in the future.

Periostin-like-factor in osteogenesis

Periostin-like-factor (PLF), an isoform related to Periostin, is expressed in bone, heart, and vascular smooth muscle cells. PLF was detected by immunostaining in mesenchymal cells in the periosteum and in osteoblasts lining trabecular bone, suggesting that PLF has a role in osteogenesis. PLF has a signal peptide and is also secreted from osteoblasts in vitro. To study the function of PLF in osteogenesis, we assessed the effect of PLF on osteoblast proliferation and differentiation in vitro and bone formation in vivo. First, to examine whether PLF regulates osteoblast proliferation in vitro, the CyQUANT cell proliferation assay was performed. PLF over-expression by adenovirus resulted in a significantly higher rate of cell proliferation compared to controls. This finding suggests that PLF promotes osteoblast proliferation in vitro. Second, to test whether PLF mediates osteoblast differentiation in vitro, differentiation markers of osteoblasts, were assessed, including alkaline phosphatase staining and activity, von Kossa staining and calcium deposition. Over-expression of PLF resulted in higher expression and activity of alkaline phosphatase and higher amounts of mineralization and calcium deposition compared to controls. These data suggest that PLF promotes osteoblast differentiation in vitro. Third, to investigate the role of PLF in bone formation in vivo, PLF adenovirus was injected into 6-week-old rat femur bone marrow. Over-expression of PLF resulted in increased bone formation within the marrow cavity. Lastly, in a model of fracture healing, PLF expression is robustly upregulated in callus osteoblasts at post-fracture days 7 and 14. Taken together, these findings suggests that PLF induces bone formation in vivo. We conclude that PLF stimulates bone formation in vivo possibly by promoting osteoblast proliferation and differentiation.

Prognostic significance of epithelial-mesenchymal and mesenchymal-epithelial transition protein expression in non-small cell lung cancer

PURPOSE

In carcinomas, invasive tumor growth is accompanied by desmoplastic stroma reaction and facilitated by epithelial-mesenchymal transition (EMT) of cancer cells. We investigated the prognostic significance of the EMT indicator proteins periostin and vimentin in comparison with versican, a putative indicator of the opposite mechanism mesenchymal-epithelial transition (MET), and to the desmoplasia proteins collagen and elastin in non-small cell lung cancer (NSCLC).

EXPERIMENTAL DESIGN

Tumor of 533 patients with surgically resected NSCLC was used for analysis of stromal and epithelial protein expression by immunohistochemistry (EMT-MET proteins) and Elastica van Gieson histochemical staining (collagen and elastin). A semiquantitative sum scoring system was done on three tissue microarrays.

RESULTS

Of the 533 patients, 48% had squamous cell carcinoma, 47% adenocarcinoma, and 5% adenosquamous carcinoma. High expression of periostin in either stroma or tumor epithelia, independently scored by two pathologists, correlated with male gender, higher stage, higher pT category, and larger tumor size, and in only stroma with tumor relapse. High expression of versican in either stroma or epithelia as well as of stromal collagen had fewer but concordant associations with advanced tumor and periostin, respectively. High expression of elastin was oppositely associated with less advanced disease. Associations of high vimentin were inconsistent (all P values < 0.05). High stromal periostin was found to be a prognostic factor for decreased progression-free survival on univariate analysis (P = 0.007).

CONCLUSIONS

Because up-regulation is frequently observed in the stromal and epithelial tumor compartment, EMT-MET indicator proteins may be integrated in progression models of NSCLC.

Evidence for a calcification process in the trabecular meshwork

The human trabecular meshwork (TM) expresses many genes that have been associated with physiological (bone, cartilage, teeth) and pathological (vascular systems, kidney) calcification. In particular, the TM highly expresses the inhibitor of calcification Matrix Gla (MGP) gene, which encodes a vitamin K-dependent protein that requires post-translational activation to inhibit the formation of calcium precipitates. TM cells have high activity of the activating gamma-carboxylase enzyme and produce active MGP. Silencing MGP increases the activity of alkaline phosphatase (ALP), an enzyme of the matrix vesicles and marker of calcification. Overexpressing MGP reduces the ALP activity induced by bone morphogenetic 2 (BMP2), a potent inducer of calcification. In this review we gathered evidence for the existence of a mineralization process in the TM. We selected twenty regulatory calcification genes, reviewed their functions in their original tissues and looked at their relative abundance in the TM by heat maps derived from existing microarrays. Although results are not yet fully conclusive and more experiments are needed, examining TM expression in the light of the calcification literature brings up many similarities. One such parallel is the role of mechanical forces in bone induction and the high levels of mineralization inhibitors found in the constantly mechanically stressed TM. During the next few years, examination of other calcification-related regulatory genes and pathways, as well as morphological examination of knockout animals, would help to elucidate the relevance of a calcification process to TM's overall function.

Periostin is essential for the integrity and function of the periodontal ligament during occlusal loading in mice

BACKGROUND

The ability of the periodontal ligament (PDL) to absorb and distribute forces is necessary for periodontal homeostasis. This adaptive response may be determined, in part, by a key molecule, periostin, which maintains the integrity of the PDL during occlusal function and inflammation. Periostin is primarily expressed in the PDL and is highly homologous to betaig-H3 (transforming growth factor-beta [TGF-beta] inducible gene). Cementum, alveolar bone, and the PDL of periostin-null mice dramatically deteriorate following tooth eruption. The purpose of this study was to determine the role of periostin in maintaining the functional integrity of the periodontium.

METHODS

The periodontia from periostin-null mice were characterized followed by unloading the incisors. The effect of substrate stretching on periostin expression was evaluated using a murine PDL cell line. Real-time reverse transcription-polymerase chain reaction was used to quantify mRNA levels of periostin and TGF-beta. TGF-beta1 neutralizing antibodies were used to determine whether the effects of substrate stretching on periostin expression are mediated through TGF-beta.

RESULTS

Severe periodontal defects were observed in the periostin-null mice after tooth eruption. The removal of masticatory forces in periostin-null mice rescue the periodontal defects. Periostin expression was increased in strained PDL cells by 9.2-fold at 48 hours and was preceded by a transient increase in TGF-beta mRNA in vitro. Elevation of periostin in response to mechanical stress was blocked by the addition of 2.5 ng/ml neutralizing antibody to TGF-beta1, suggesting that mechanical strain activates TGF-beta to have potential autocrine effects and to increase periostin expression.

CONCLUSION

Mechanical loading maintains sufficient periostin expression to ensure the integrity of the periodontium in response to occlusal load.

Serum response factor orchestrates nascent sarcomerogenesis and silences the biomineralization gene program in the heart

Our conditional serum response factor (SRF) knockout, Srf (Cko), in the heart-forming region blocked the appearance of rhythmic beating myocytes, one of the earliest cardiac defects caused by the ablation of a cardiac-enriched transcription factor. The appearance of Hand1 and Smyd1, transcription and chromatin remodeling factors; Acta1, Acta2, Myl3, and Myom1, myofibril proteins; and calcium-activated potassium-channel gene activity (KCNMB1), the channel protein, were powerfully attenuated in the Srf(CKO) mutant hearts. A requisite role for combinatorial cofactor interactions with SRF, as a major determinant for regulating the appearance of organized sarcomeres, was shown by viral rescue of SRF-null ES cells with SRF point mutants that block cofactor interactions. In the absence of SRF genes associated with biomineralization, GATA-6, bone morphogenetic protein 4 (BMP4), and periostin were strongly up-regulated, coinciding with the down regulation of many SRF dependent microRNA, including miR1, which exerted robust silencer activity over the induction of GATA-6 leading to the down regulation of BMP4 and periostin.

Periostin, a novel marker of intramembranous ossification, is expressed in fibrous dysplasia and in c-Fos-overexpressing bone lesions

Fibrous dysplasia is a benign bone disease caused by a mutation in the gene for the stimulatory guanine nucleotide-binding protein Gs alpha, leading to high cyclic adenosine monophosphate levels. Histologically, fibrous dysplasia is characterized by the production of fibrous tissue accompanied by the deposition of ectopic type I collagen and other bone-associated extracellular matrix proteins, as well as by irregular woven intramembranous bone onto which type I collagen-containing Sharpey fibers are often attached. Fibrous dysplasia is also characterized by high expression of c-Fos/c-Jun, known targets for cyclic adenosine monophosphate signaling. In this study, we examined the expression of the bone-related extracellular matrix protein, periostin, and its known receptor, integrin alpha v beta 3 (CD51/61), in normal bones as well as in fibrous dysplasia. Immunohistochemistry and in situ hybridization studies revealed that periostin was expressed in the extracellular matrix during intramembranous but not endochondral ossification, as well as in the fibrous component of fibrous dysplasia; and all cells adjacent to periostin-positive regions expressed CD51/61. Importantly, periostin was abundantly localized to Sharpey fibers. To investigate the contribution of c-Fos, we examined transgenic mice overexpressing c-fos, which develop sclerotic lesions closely resembling those found in fibrous dysplasia. In all lesions, transformed osteoblasts expressed high levels of periostin, whereas normal osteoblasts did not. Our results show that periostin is a novel marker for intramembranous ossification, and is a good candidate as a diagnostic tool and/or a therapeutic target in fibrous dysplasia. Moreover, the Gs alpha-cyclic adenosine monophosphate-c-Fos pathway might represent one mechanism of periostin up-regulation in fibrous dysplasia, resulting in altered collagen fibrillogenesis characteristic of this disease.

Aryl hydrocarbon receptor-mediated down-regulation of sox9b causes jaw malformation in zebrafish embryos

Exposure to environmental contaminants can disrupt normal development of the early vertebrate skeleton. 2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) impairs craniofacial skeletal development across many vertebrate species, and its effects are especially prominent in early life stages of fish. TCDD activates the aryl hydrocarbon receptor, a transcription factor that mediates most if not all TCDD responses. We investigated the transcriptional response in the developing zebrafish jaw after TCDD exposure using DNA microarrays. Zebrafish larvae were exposed to TCDD at 96 h after fertilization, and jaw cartilage tissue was harvested for microarray analysis at 1, 2, 4, and 12 h after exposure. Numerous chondrogenic transcripts were misregulated by TCDD in the jaw. Comparison of transcripts altered by TCDD in jaw with transcripts altered in embryonic heart showed that the transcriptional responses in the jaw and the heart were strikingly different. Sox9b, a critical chondrogenic transcription factor, was the most significantly reduced transcript in the jaw. We hypothesized that the TCDD reduction of sox9b expression plays an integral role in affecting the formation of the embryonic jaw. Morpholino knockdown of sox9b expression demonstrated that partial reduction of sox9b expression alone was sufficient to produce a TCDD-like jaw phenotype. Loss of a single copy of the sox9b gene in sox9b(+/-) heterozygotes increased sensitivity to jaw malformation by TCDD. Finally, embryos injected with sox9b mRNA and then exposed to TCDD blocked TCDD-induced jaw toxicity in approximately 14% of sox9b-injected embryos. These results suggest that reduced sox9b expression in TCDD-exposed zebrafish embryos contributes to jaw malformation.

Functional role of periostin in development and wound repair: implications for connective tissue disease

Integrity of the extracellular matrix (ECM) is essential for maintaining the normal structure and function of connective tissues. ECM is secreted locally by cells and organized into a complex meshwork providing physical support to cells, tissues, and organs. Initially thought to act only as a scaffold, the ECM is now known to provide a myriad of signals to cells regulating all aspects of their phenotype from morphology to differentiation. Matricellular proteins are a class of ECM related molecules defined through their ability to modulate cell-matrix interactions. Matricellular proteins are expressed at high levels during development, but typically only appear in postnatal tissue in wound repair or disease, where their levels increase substantially. Members of the CCN family, tenascin-C, osteopontin, secreted protein acidic rich in cysteine (SPARC), bone sialoprotein, thrombospondins, and galectins have all been classed as matricellular proteins. Periostin, a 90 kDa secreted homophilic cell adhesion protein, was recently added to matricellular class of proteins based on its expression pattern and function during development as well as in wound repair. Periostin is expressed in connective tissues including the periodontal ligament, tendons, skin and bone, and is also prominent in neoplastic tissues, cardiovascular disease, as well as in connective tissue wound repair. This review will focus on the functional role of periostin in tissue physiology. Fundamentally, it appears that periostin influences cell behaviour as well as collagen fibrillogenesis, and therefore exerts control over the structural and functional properties of connective tissues in both health and disease. Periostin is a novel matricellular protein with close homology to Drosophila fasciclin 1. In this review, the functional role of periostin is discussed in the context of connective tissue physiology, in development, disease, and wound repair.

Characterization of Apin, a secreted protein highly expressed in tooth-associated epithelia

We previously reported expression of a protein by enamel organ (EO) cells in rat incisors, originally isolated from the amyloid of Pindborg odontogenic tumors called Apin. The aim of the present study was to further characterize the Apin gene and its protein in various species, assess tissue specificity, and clarify its localization within the EO. Northern blotting and RT-PCR revealed that expression of Apin was highest in the EO and gingiva, moderate in nasal and salivary glands, and lowest in the epididymis. The protein sequences deduced from the cloned cDNA for rat, mouse, pig, and human were aligned together with those obtained from four other mammal genomes. Apin is highly conserved in mammals but is absent in fish, birds, and amphibians. Comparative SDS-PAGE analyses of the protein obtained from bacteria, transfected cells, and extracted from EOs all indicated that Apin is post-translationally modified, a finding consistent with the presence of predicted sites for phosphorylation and O-linked glycosylation. In rodent incisors, Apin was detected only in the ameloblast layer of the EO, starting at post-secretory transition and extending throughout the maturation stage. Intense labeling was visible over the Golgi region as well as on the apices of ameloblasts abutting the enamel matrix. Apin was also immunodetected in epithelial cells of the gingiva which bind it to the tooth surface (junctional epithelium). The presence of Apin at cell-tooth interfaces suggests involvement in adhesive mechanisms active at these sites, but its presence among other epithelial tissues indicates Apin likely possesses broader physiological roles.

An absence of Twist1 results in aberrant cardiac neural crest morphogenesis

The basic helix-loop-helix transcription factor Twist1 plays an essential role in mesenchymal cell populations during embryonic development and in pathological disease. Remodeling of the cardiac outflow tract (OFT) into the functionally separate aortic arch and pulmonary trunk is dependent upon the dynamic, coordinated contribution of multiple mesenchymal cell populations. Here, we report that Twist1(-/-) mice exhibit OFTs that contain amorphic cellular nodules within their OFT endocardial cushions. The nodular mesenchyme expresses the related bHLH factors Hand1 and Hand2, but reduced levels of the normal cushion marker Periostin. Lineage mapping confirms that nodule cells are exclusively of cardiac neural crest origin (cNCC), and are not ectopic cardiomyocytes or smooth muscle cells. These studies also reveal a delay in cNCC colonization of the OFT cushions. Furthermore, these mapping studies uncover nodules in the pharyngeal arches, and identify Twist1(-/-) neural crest cell defects within the dorsal neural tube, which exhibits an expanded domain of Wnt1-Cre-lineage marked cells. Together, these data support a model where Twist1 is required both for proper cNCC delamination, and for emigration from the dorsal neural tube and along cNCC migration pathways. Within the Twist1(-/-) neural crest cell populations that do emigrate to the OFT, a Hand-expressing subpopulation displays defective maturation, tracking, and, presumably, cell-cell adhesion, further compromising cNCC morphogenesis.

Periostin, a member of a novel family of vitamin K-dependent proteins, is expressed by mesenchymal stromal cells

The modification of glutamic acid residues to gamma-carboxyglutamic acid (Gla) is a post-translational modification catalyzed by the vitamin K-dependent enzyme gamma-glutamylcarboxylase. Despite ubiquitous expression of the gamma-carboxylation machinery in mammalian tissues, only 12 Gla-containing proteins have so far been identified in humans. Because bone tissue is the second most abundant source of Gla-containing proteins after the liver, we sought to identify Gla proteins secreted by bone marrow-derived mesenchymal stromal cells (MSCs). We used a proteomics approach to screen the secretome of MSCs with a combination of two-dimensional gel electrophoresis and tandem mass spectrometry. The most abundant Gla-containing protein secreted by MSCs was identified as periostin, a previously unrecognized gamma-carboxylated protein. In silico amino acid sequence analysis of periostin demonstrated the presence of four consensus gamma-carboxylase recognition sites embedded within fasciclin-like protein domains. The carboxylation of periostin was confirmed by immunoprecipitation and purification of the recombinant protein. Carboxylation of periostin could be inhibited by warfarin in MSCs, demonstrating its dependence on the presence of vitamin K. We were able to demonstrate localization of carboxylated periostin to bone nodules formed by MSCs in vitro, suggesting a role in extracellular matrix mineralization. Our data also show that another fasciclin I-like protein, betaig-h3, contains Gla. In conclusion, periostin is a member of a novel vitamin K-dependent gamma-carboxylated protein family characterized by the presence of fasciclin domains. Furthermore, carboxylated periostin is produced by bone-derived cells of mesenchymal lineage and is abundantly found in mineralized bone nodules in vitro.

Fluoride at non-toxic dose affects odontoblast gene expression in vitro

Elevated fluoride intake may lead to local tissue disturbances, known as fluorosis. Towards an understanding of this effect, fluoride-induced molecular responses were analyzed in MO6-G3 cultured odontoblasts cells. NaF at 1mM changed expression of genes implicated in tissue formation and growth, without affecting cell proliferation or inducing stress factor RNAs. Up to 1mM NaF, DNA accumulation was not inhibited, whereas at 3mM, cells detached from their support and did not proliferate. Intracellular structures, characterized by EM, were normal up to 1mM, but at 3mM, necrotic features were evident. No sign of apoptotic transformation appeared at any NaF concentration. Fluoride-sensitive genes were identified by microarray analysis; expression levels of selected RNAs were determined by conventional and real-time RT-PCR. At 1mM fluoride, RNAs encoding the extracellular matrix proteins asporin and fibromodulin, and the cell membrane associated proteins periostin and IMT2A were 10-fold reduced. RNA coding for signaling factor TNF-receptor 9 was diminished to one-third, whereas that for the chemokine Scya-5 was enhanced 2.5-fold. These RNAs are present in vivo in tooth forming cells. This was demonstrated by in situ hybridization and RT-PCR on RNA from dissected tissue samples; for the presence and functioning of fibromodulin in dentin matrix, a more comprehensive study has earlier been performed by others [Goldberg, M., Septier, D., Oldberg, A., Young, M.F., Ameye, L.G., 2006. Fibromodulin deficient mice display impaired collagen fibrillogenesis in predentin as well as altered dentin mineralization and enamel formation. J. Histochem. Cytochem. 54, 525-537]. Expression of most other RNA species, in particular of stress factor coding RNAs, was not altered. It was concluded that fluoride could influence the transcription pattern without inducing cell stress or apoptosis. In odontoblasts in vivo, aberrant expression of these fluoride-sensitive genes may impair the formation of the extracellular matrix and influence cell communication, with the possible consequence of fluorotic patterns of normal and deviant dentin.

Epicardium-derived cells in development of annulus fibrosis and persistence of accessory pathways

BACKGROUND

The developmental mechanisms underlying the persistence of myocardial accessory atrioventricular pathways (APs) that bypass the annulus fibrosis are mainly unknown. In the present study, we investigated the role of epicardium-derived cells (EPDCs) in annulus fibrosis formation and the occurrence of APs.

METHODS AND RESULTS

EPDC migration was mechanically inhibited by in ovo microsurgery in quail embryos. In ovo ECGs were recorded in wild-type (n=12) and EPDC-inhibited (n=12) hearts at Hamburger-Hamilton (HH) stages 38 to 42. Subsequently, in these EPDC-inhibited hearts (n=12) and in additional wild-type hearts (n=45; HH 38-42), ex ovo extracellular electrograms were recorded. Electrophysiological data were correlated with differentiation markers for cardiomyocytes (MLC2a) and fibroblasts (periostin). In ovo ECGs showed significantly shorter PR intervals in EPDC-inhibited hearts (45+/-10 ms) than in wild-type hearts (55+/-8 ms, 95% CI 50 to 60 ms, P=0.030), whereas the QRS durations were significantly longer in EPDC-inhibited hearts (29+/-14 versus 19+/-2 ms, 95% CI 18 to 21 ms, P=0.011). Furthermore, ex ovo extracellular electrograms (HH 38-42) displayed base-first ventricular activation in 44% (20/45) of wild-type hearts, whereas in all EPDC-inhibited hearts (100%, 12/12), the ventricular base was activated first (P<0.001). Small periostin- and MLC2a-positive APs were found mainly in the posteroseptal region of both wild-type and EPDC-inhibited hearts. Interestingly, in all (n=10) EPDC-inhibited hearts, additional large periostin-negative and MLC2a-positive APs were found in the right and left lateral free wall coursing through marked isolation defects in the annulus fibrosis until the last stages of embryonic development.

CONCLUSIONS

EPDCs play an important role in annulus fibrosis formation. EPDC outgrowth inhibition may result in marked defects in the fibrous annulus with persistence of large APs, which results in ventricular preexcitation on ECG. These APs may provide a substrate for postnatally persistent reentrant arrhythmias.

Multipotent mesenchymal stromal cells obtained from diverse human tissues share functional properties and gene-expression profile with CD146+ perivascular cells and fibroblasts

OBJECTIVE

The relationship of multipotent mesenchymal stromal cells (MSC) with pericytes and fibroblasts has not been established thus far, although they share many markers of primitive marrow stromal cells and the osteogenic, adipogenic, and chondrogenic differentiation potentials.

MATERIALS AND METHODS

We compared MSCs from adult or fetal tissues, MSC differentiated in vitro, fibroblasts and cultures of retinal pericytes obtained either by separation with anti-CD146 or adhesion. The characterizations included morphological, immunophenotypic, gene-expression profile, and differentiation potential.

RESULTS

Osteogenic, adipocytic, and chondrocytic differentiation was demonstrated for MSC, retinal perivascular cells, and fibroblasts. Cell morphology and the phenotypes defined by 22 markers were very similar. Analysis of the global gene expression obtained by serial analysis of gene expression for 17 libraries and by reverse transcription polymerase chain reaction of 39 selected genes from 31 different cell cultures, revealed similarities among MSC, retinal perivascular cells, and hepatic stellate cells. Despite this overall similarity, there was a heterogeneous expression of genes related to angiogenesis, in MSC derived from veins, artery, perivascular cells, and fibroblasts. Evaluation of typical pericyte and MSC transcripts, such as NG2, CD146, CD271, and CD140B on CD146 selected perivascular cells and MSC by real-time polymerase chain reaction confirm the relationship between these two cell types. Furthermore, the inverse correlation between fibroblast-specific protein-1 and CD146 transcripts observed on pericytes, MSC, and fibroblasts highlight their potential use as markers of this differentiation pathway.

CONCLUSION

Our results indicate that human MSC and pericytes are similar cells located in the wall of the vasculature, where they function as cell sources for repair and tissue maintenance, whereas fibroblasts are more differentiated cells with more restricted differentiation potential.

Expression and regulation of periostin/OSF-2 gene in rat uterus and human endometrium

Periostin/OSF2 is a ligand for alphavbeta3 and alphavbeta5 integrins and activates the Akt/PKB pathway. Recent reports of periostin/OSF2 gene disrupted mice indicate that periostin/OSF-2 plays an important role in implantation. Quantitative RT-PCR revealed that the expression of periostin/OSF-2 mRNA in rat uteri was reduced to approximately 10% at 12 h after 17beta-estradiol (E2) injection, but was not changed after progesterone (P) injection. RT-PCR revealed the expression of periostin/OSF-2 in human endometrium, cultured human endometrial stromal cells (ESCs), and cultured human endometrial epithelial cells. In ESCs, the expression of periostin/OSF-2 mRNA was reduced to approximately 50% at 6 h after E2 treatment. The amount of periostin/OSF2 mRNA in human endometrium significantly increased during mid-proliferative and early secretory phases of menstrual cycle, and decreased during late-proliferative, mid-secretory and late secretory phases. The expression of periostin/OSF2 mRNA significantly decreased in ESCs decidualized by treatment with E2 and P for 7 and 11 days. By immunohistochemistry, the expression of periostin/OSF-2 was strongly detected in endometrial stromal cells during early proliferative, mid-proliferative and early secretory phases, and was strongly detected in endometrial epithelial cells during late secretory phase. This study demonstrated that the expression of periostin/OSF-2 is regulated by ovarian steroid hormones in rat uterus and human endometrium.

Periostin is required for maturation and extracellular matrix stabilization of noncardiomyocyte lineages of the heart

The secreted periostin protein, which marks mesenchymal cells in endocardial cushions following epithelial-mesenchymal transformation and in mature valves following remodeling, is a putative valvulogenesis target molecule. Indeed, periostin is expressed throughout cardiovascular morphogenesis and in all 4 adult mice valves (annulus and leaflets). Additionally, periostin is expressed throughout the fibrous cardiac skeleton and endocardial cushions in the developing heart but is absent from both normal and/or pathological mouse cardiomyocytes. Periostin (peri(lacZ)) knockout mice exhibit viable valve disease, with neonatal lethality in a minority and latent disease with leaflet abnormalities in the viable majority. Surviving peri(lacZ)-null leaflets are truncated, contain ectopic cardiomyocytes and smooth muscle, misexpress the cartilage proteoglycan aggrecan, demonstrate disorganized matrix stratification, and exhibit reduced transforming growth factor-beta signaling. Neonatal peri(lacZ) nulls that die (14%) display additional defects, including leaflet discontinuities, delamination defects, and deposition of acellular extracellular matrix. Assessment of collagen production, 3D lattice formation ability, and transforming growth factor-beta responsiveness indicate periostin-deficient fibroblasts are unable to support normal valvular remodeling and establishment of a mature cardiac skeleton. Furthermore, pediatric stenotic bicuspid aortic valves that have lost normal extracellular matrix trilaminar stratification have greatly reduced periostin. This suggests that loss of periostin results in inappropriate differentiation of mesenchymal cushion cells and valvular abnormalities via a transforming growth factor-beta-dependent pathway during establishment of the mature heart. Thus, peri(lacZ) knockouts provide a new model of viable latent valve disease.

Periostin expression by epicardium-derived cells is involved in the development of the atrioventricular valves and fibrous heart skeleton

The epicardium is embryologically formed by outgrowth of proepicardial cells over the naked heart tube. Epicardium-derived cells (EPDCs) migrate into the myocardium, contributing to myocardial architecture, valve development, and the coronary vasculature. Defective EPDC formation causes valve malformations, myocardial thinning, and coronary defects. In the atrioventricular (AV) valves and the fibrous heart skeleton isolating atrial from ventricular myocardium, EPDCs colocalize with periostin, a matrix molecule involved in remodeling. We investigated whether proepicardial outgrowth inhibition affected periostin expression and how this related to development of the AV valves and fibrous heart skeleton. Periostin expression by epicardium and EPDCs was confirmed in vitro in primary cultures of human and quail EPDCs. Disturbing EPDC formation in quail embryos reduced periostin expression in the endocardial cushions and AV junction. Disturbed fibrous tissue development resulted in AV myocardial connections reflected by preexcitation electrocardiographic patterns. We conclude that EPDCs are local producers of periostin. Disturbance of EPDC formation results in decreased cardiac periostin levels and hampers the development of fibrous tissue in AV junction and the developing AV valves. The resulting cardiac anomalies might link to Wolff-Parkinson White syndrome with persistent AV myocardial connections.

Periostin regulates atrioventricular valve maturation

Cardiac valve leaflets develop from rudimentary structures termed endocardial cushions. These pre-valve tissues arise from a complex interplay of signals between the myocardium and endocardium whereby secreted cues induce the endothelial cells to transform into migratory mesenchyme through an endothelial to mesenchymal transformation (EMT). Even though much is currently known regarding the initial EMT process, the mechanisms by which these undifferentiated cushion mesenchymal tissues are remodeled "post-EMT" into mature fibrous valve leaflets remains one of the major, unsolved questions in heart development. Expression analyses, presented in this report, demonstrate that periostin, a component of the extracellular matrix, is predominantly expressed in post-EMT valve tissues and their supporting apparatus from embryonic to adult life. Analyses of periostin gene targeted mice demonstrate that it is within these regions that significant defects are observed. Periostin null mice exhibit atrial septal defects, structural abnormalities of the AV valves and their supporting tensile apparatus, and aberrant differentiation of AV cushion mesenchyme. Rescue experiments further demonstrate that periostin functions as a hierarchical molecular switch that can promote the differentiation of mesenchymal cells into a fibroblastic lineage while repressing their transformation into other mesodermal cell lineages (e.g. myocytes). This is the first report of an extracellular matrix protein directly regulating post-EMT AV valve differentiation, a process foundational and indispensable for the morphogenesis of a cushion into a leaflet.

BMP-2 induces cell migration and periostin expression during atrioventricular valvulogenesis

Atrioventricular (AV) endocardium transforms into the cushion mesenchyme, the primordia of the valves and membranous septa, through epithelial-mesenchymal transformation (EMT). While bone morphogenetic protein (BMP)-2 is known to be critical for AV EMT, the role of BMP-2 in post-EMT AV valvulogenesis remains to be elucidated. To find BMP signaling loops, we first localized Type I BMP receptors (BMPRs), BMPR-1A (ALK3), -1B (ALK6) and ALK2 in AV cushion mesenchyme in stage-24 chick embryos. Based on the BMP receptor expression pattern, we examined the functional roles of BMP-2 and BMP signaling in post-EMT valvulogenesis by using stage-24 AV cushion mesenchymal cell aggregates cultured on 3D-collagen gels. Exogenous BMP-2 or constitutively active (ca) BMPR-1B (ALK6)-virus treatments induced migration of the mesenchymal cells into the collagen gels, whereas noggin, an antagonist of BMPs, or dominant-negative (dn) BMPR-1 B (ALK6)-virus treatments reduced cell migration from the mesenchymal cell aggregates. Exogenous BMP-2 or caBMPR-1B (ALK6) treatments significantly promoted expression of an extracellular matrix (ECM) protein, periostin, a known valvulogenic matrix maturation mediator, at both mRNA and protein levels, whereas periostin expression was repressed by adding noggin or dnBMPR-1B (ALK6)-virus to the culture. Moreover, transcripts of Twist and Id1, which have been implicated in cell migration in embryogenesis and activation of the periostin promoter, were induced by BMP-2 but repressed by noggin in cushion mesenchymal cell cultures. These data provide evidence that BMP-2 and BMP signaling induce biological processes involved in early AV valvulogenesis, i.e. mesenchymal cell migration and expression of periostin, indicating critical roles for BMP signaling in post-EMT AV cushion tissue maturation and differentiation.

Immunolocalization of Periostin-like factor and Periostin during embryogenesis

Periostin-like factor (PLF) and Periostin are alternatively spliced mRNAs. Our findings are the first to show similarities and differences between PLF and Periostin location using isoform-specific antibodies. The differences in when and where they are present during mouse embryogenesis suggest that they may have different functions. Using immunostaining techniques, we observed that PLF was highly expressed at 12.5 days postconception (dpc) in the intermediate and outer zones of most brain regions, spinal cord, cranial and spinal nerves, and chondrocytes in developing bone and in the heart wall. By 16.5 dpc, PLF was also present in ameloblasts and odontoblasts in developing teeth, and by 19.5 dpc, PLF was present at low levels only in vagal nerve bundles, discrete white matter bundles in the brain, and chondrocytes of developing ribs. Periostin, on the other hand, was absent at 12.5 dpc from dorsal spinal cord and from cranial and spinal nerves. By 16.5 dpc, Periostin was present in many spinal nerves, but absent thereafter, and at 19.5 dpc, Periostin was present in chondrocytes in developing bone but not in neural tissues. The different spatial and temporal location of PLF and Periostin in cartilage and bone cells suggests different roles for these proteins in endochondral bone formation. The early expression of PLF in brain differentiation zones and in developing axon bundles and nerves suggests that it may facilitate axon growth.