Influence of periostin-positive cell-specific Klf5 deletion on aortic thickening in DOCA-salt hypertensive mice

Chronic hypertension causes vascular remodeling that is associated with an increase in periostin- (postn) positive cells, including fibroblasts and smooth muscle cells. Krüppel-like factor (KLF) 5, a transcription factor, is also observed in vascular remodeling; however, it is unknown what role KLF5 plays in postn-positive cells during vascular remodeling induced by deoxycorticosterone-acetate (DOCA) salt. We used postn-positive cell-specific Klf5-deficient mice (Klf5^PostnKO: Klf5^flox/flox; Postn^Cre/-) and wild-type mice (WT: Klf5^flox/flox; Postn^-/-). We implanted a DOCA pellet and provided drinking water containing 0.9% NaCl for 8 weeks. The DOCA-salt treatment induced hypertension in both genotypes, as observed by increases in systolic blood pressure. In WT animals, DOCA-salt treatment increased the aortic medial area compared with the non-treated controls. Similarly, Tgfb1 was overexpressed in the aortas of the DOCA-salt treated WT mice compared with the controls. Immunofluorescence staining revealed that fibroblast-specific protein 1 (FSP1)⁺-α smooth muscle actin (αSMA)⁺ myofibroblasts exist in the medial area of the WT aortas after DOCA-salt intervention. Importantly, these changes were not observed in the Klf5^PostnKO animals. In conclusion, the results of this study suggest that the presence of KLF5 in postn-positive cells contributes to the pathogenesis of aortic thickening induced by DOCA-salt hypertension.

Periostin as a multifunctional modulator of the wound healing response

During tissue healing, the dynamic and temporal alterations required for effective repair occur in the structure and composition of the extracellular matrix (ECM). Matricellular proteins (MPs) are a group of diverse non-structural ECM components that bind cell surface receptors mediating interactions between the cell and its microenviroment, effectively regulating adhesion, migration, proliferation, signaling, and cell phenotype. Periostin (Postn), a pro-fibrogenic secreted glycoprotein, is defined as an MP based on its expression pattern and regulatory roles during development and healing and in disease processes. Postn consists of a typical signal sequence, an EMI domain responsible for binding to fibronectin, four tandem fasciclin-like domains that are responsible for integrin binding, and a C-terminal region in which multiple splice variants originate. This review focuses specifically on the role of Postn in wound healing and remodeling, an area of intense research during the last 10 years, particularly as related to skin healing and myocardium post-infarction. Postn interacts with cells through various integrin pairs and is an essential downstream effector of transforming growth factor-β superfamily signaling. Across various tissues, Postn is associated with the pro-fibrogenic process: specifically, the transition of fibroblasts to myofibroblasts, collagen fibrillogenesis, and ECM synthesis. Although the complexity of Postn as a modulator of cell behavior in tissue healing is only beginning to be elucidated, its expression is clearly a defining event in moving wound healing through the proliferative and remodeling phases.

Bone Morphogenetic Protein Signaling Is Required for Aortic Valve Calcification

OBJECTIVE

Calcific aortic valve disease (CAVD) is the most prevalent type of heart valve disease, affecting ≈2% of the US population. CAVD is characterized by the presence of calcific nodules, resulting in aortic valve (AoV) stenosis; however, the underlying mechanisms driving disease remain unknown. Studies of human diseased AoV provide initial evidence that bone morphogenetic protein (BMP) signaling, essential for normal bone formation, is activated during CAVD. Mice deficient in Klotho, an FGF23 transmembrane coreceptor, exhibit premature aging and develop AoV calcific nodules as occurs in human CAVD. The role of BMP signaling in the development of CAVD was examined in porcine aortic valve interstitial cells (VICs) and Klotho(-/-) mice.

APPROACH AND RESULTS

We show that activation of BMP signaling, as indicated by pSmad1/5/8 expression, precedes and later localizes with AoV calcification in Klotho(-/-) mice. In addition, cellular and extracellular matrix changes resembling features of normal bone formation are accompanied by increased osteochondrogenic gene induction in calcified Klotho(-/-) AoV. Likewise, osteogenic media treatment of porcine VICs results in BMP pathway activation, increased osteochondrogenic gene induction, and formation of calcific nodules in vitro. We demonstrate that genetic inactivation of the BMP type IA receptor in Klotho(-/-) aortic VICs, as well as BMP pathway inhibition of osteogenic media-treated aortic VICs in vitro, results in the inhibition of AoV calcification.

CONCLUSIONS

BMP signaling and osteochondrogenic gene induction are active in calcified Klotho(-/-) AoV in vivo and calcified porcine aortic VICs in vitro. Importantly, BMP signaling is required for the development of AoV calcification in vitro and in vivo.

Mechanisms of Specificity for Hox Factor Activity

Metazoans encode clusters of paralogous Hox genes that are critical for proper development of the body plan. However, there are a number of unresolved issues regarding how paralogous Hox factors achieve specificity to control distinct cell fates. First, how do Hox paralogs, which have very similar DNA binding preferences in vitro, drive different transcriptional programs in vivo? Second, the number of potential Hox binding sites within the genome is vast compared to the number of sites bound. Hence, what determines where in the genome Hox factors bind? Third, what determines whether a Hox factor will activate or repress a specific target gene? Here, we review the current evidence that is beginning to shed light onto these questions. In particular, we highlight how cooperative interactions with other transcription factors (especially PBC and HMP proteins) and the sequences of cis-regulatory modules provide a basis for the mechanisms of Hox specificity. We conclude by integrating a number of the concepts described throughout the review in a case study of a highly interrogated Drosophila cis-regulatory module named “The Distal-less Conserved Regulatory Element” (DCRE).

Targeted Ablation of Periostin-Expressing Activated Fibroblasts Prevents Adverse Cardiac Remodeling in Mice

RATIONALE

Activated cardiac fibroblasts (CF) are crucial players in the cardiac damage response; excess fibrosis, however, may result in myocardial stiffening and heart failure development. Inhibition of activated CF has been suggested as a therapeutic strategy in cardiac disease, but whether this truly improves cardiac function is unclear.

OBJECTIVE

To study the effect of CF ablation on cardiac remodeling.

METHODS AND RESULTS

We characterized subgroups of murine CF by single-cell expression analysis and identified periostin as the marker showing the highest correlation to an activated CF phenotype. We generated bacterial artificial chromosome-transgenic mice allowing tamoxifen-inducible Cre expression in periostin-positive cells as well as their diphtheria toxin-mediated ablation. In the healthy heart, periostin expression was restricted to valvular fibroblasts; ablation of this population did not affect cardiac function. After chronic angiotensin II exposure, ablation of activated CF resulted in significantly reduced cardiac fibrosis and improved cardiac function. After myocardial infarction, ablation of periostin-expressing CF resulted in reduced fibrosis without compromising scar stability, and cardiac function was significantly improved. Single-cell transcriptional analysis revealed reduced CF activation but increased expression of prohypertrophic factors in cardiac macrophages and cardiomyocytes, resulting in localized cardiomyocyte hypertrophy.

CONCLUSIONS

Modulation of the activated CF population is a promising approach to prevent adverse cardiac remodeling in response to angiotensin II and after myocardial infarction.

Initial Suppression of Transforming Growth Factor-β Signaling and Loss of TGFBI Causes Early Alveolar Structural Defects Resulting in Bronchopulmonary Dysplasia

Septation of the gas-exchange saccules of the morphologically immature mouse lung requires regulated timing, spatial direction, and dosage of transforming growth factor (TGF)-β signaling. We found that neonatal hyperoxia acutely initially diminished saccular TGF-β signaling coincident with alveolar simplification. However, sustained hyperoxia resulted in a biphasic response and subsequent up-regulation of TGF-β signaling, ultimately resulting in bronchopulmonary dysplasia. Significantly, we found that the TGF-β-induced matricellular protein (TGFBI) was similarly biphasically altered in response to hyperoxia. Moreover, genetic ablation revealed that TGFBI was required for normal alveolar structure and function. Although the phenotype was not neonatal lethal, Tgfbi-deficient lungs were morphologically abnormal. Mutant septal tips were stunted, lacked elastin-positive tips, exhibited reduced proliferation, and contained abnormally persistent alveolar α-smooth muscle actin myofibroblasts. In addition, Tgfbi-deficient lungs misexpressed TGF-β-responsive follistatin and serpine 1, and transiently suppressed myofibroblast platelet-derived growth factor α differentiation marker. Finally, despite normal lung volume, Tgfbi-null lungs displayed diminished elastic recoil and gas exchange efficiency. Combined, these data demonstrate that initial suppression of the TGF-β signaling apparatus, as well as loss of key TGF-β effectors (like TGFBI), underlies early alveolar structural defects, as well as long-lasting functional deficits routinely observed in chronic lung disease of infancy patients. These studies underline the complex (and often contradictory) role of TGF-β and indicate a need to design studies to associate alterations with initial appearance of phenotypical changes suggestive of bronchopulmonary dysplasia.

Ataxia telangiectasia mutated in cardiac fibroblasts regulates doxorubicin-induced cardiotoxicity

AIMS

Doxorubicin (Dox) is a potent anticancer agent that is widely used in the treatment of a variety of cancers, but its usage is limited by cumulative dose-dependent cardiotoxicity mainly due to oxidative damage. Ataxia telangiectasia mutated (ATM) kinase is thought to play a role in mediating the actions of oxidative stress. Here, we show that ATM in cardiac fibroblasts is essential for Dox-induced cardiotoxicity.

METHODS AND RESULTS

ATM knockout mice showed attenuated Dox-induced cardiotoxic effects (e.g. cardiac dysfunction, apoptosis, and mortality). As ATM was expressed and activated predominantly in cardiac fibroblasts, fibroblast-specific Atm-deleted mice (Atm(fl/fl);Postn-Cre) were generated to address cell type-specific effects, which showed that the fibroblast is the key lineage mediating Dox-induced cardiotoxicity through ATM. Mechanistically, ATM activated the Fas ligand, which subsequently regulated apoptosis in cardiomyocytes at later stages. Therapeutically, a potent and selective inhibitor of ATM, KU55933, when administered systemically was able to prevent Dox-induced cardiotoxicity.

CONCLUSION

ATM-regulated effects within cardiac fibroblasts are pivotal in Dox-induced cardiotoxicity, and antagonism of ATM and its functions may have potential therapeutic implications.

Definitive Hematopoiesis in the Yolk Sac Emerges from Wnt-Responsive Hemogenic Endothelium Independently of Circulation and Arterial Identity

Adult-repopulating hematopoietic stem cells (HSCs) emerge in low numbers in the midgestation mouse embryo from a subset of arterial endothelium, through an endothelial-to-hematopoietic transition. HSC-producing arterial hemogenic endothelium relies on the establishment of embryonic blood flow and arterial identity, and requires β-catenin signaling. Specified prior to and during the formation of these initial HSCs are thousands of yolk sac-derived erythro-myeloid progenitors (EMPs). EMPs ensure embryonic survival prior to the establishment of a permanent hematopoietic system, and provide subsets of long-lived tissue macrophages. While an endothelial origin for these HSC-independent definitive progenitors is also accepted, the spatial location and temporal output of yolk sac hemogenic endothelium over developmental time remain undefined. We performed a spatiotemporal analysis of EMP emergence, and document the morphological steps of the endothelial-to-hematopoietic transition. Emergence of rounded EMPs from polygonal clusters of Kit(+) cells initiates prior to the establishment of arborized arterial and venous vasculature in the yolk sac. Interestingly, Kit(+) polygonal clusters are detected in both arterial and venous vessels after remodeling. To determine whether there are similar mechanisms regulating the specification of EMPs with other angiogenic signals regulating adult-repopulating HSCs, we investigated the role of embryonic blood flow and Wnt/β-catenin signaling during EMP emergence. In embryos lacking a functional circulation, rounded Kit(+) EMPs still fully emerge from unremodeled yolk sac vasculature. In contrast, canonical Wnt signaling appears to be a common mechanism regulating hematopoietic emergence from hemogenic endothelium. These data illustrate the heterogeneity in hematopoietic output and spatiotemporal regulation of primary embryonic hemogenic endothelium.

Quantitative hopanoid analysis enables robust pattern detection and comparison between laboratories

Hopanoids are steroid-like lipids from the isoprenoid family that are produced primarily by bacteria. Hopanes, molecular fossils of hopanoids, offer the potential to provide insight into environmental transitions on the early Earth, if their sources and biological functions can be constrained. Semiquantitative methods for mass spectrometric analysis of hopanoids from cultures and environmental samples have been developed in the last two decades. However, the structural diversity of hopanoids, and possible variability in their ionization efficiencies on different instruments, have thus far precluded robust quantification and hindered comparison of results between laboratories. These ionization inconsistencies give rise to the need to calibrate individual instruments with purified hopanoids to reliably quantify hopanoids. Here, we present new approaches to obtain both purified and synthetic quantification standards. We optimized 2-methylhopanoid production in Rhodopseudomonas palustris TIE-1 and purified 2Me-diplopterol, 2Me-bacteriohopanetetrol (2Me-BHT), and their unmethylated species (diplopterol and BHT). We found that 2-methylation decreases the signal intensity of diplopterol between 2 and 34% depending on the instrument used to detect it, but decreases the BHT signal less than 5%. In addition, 2Me-diplopterol produces 10× higher ion counts than equivalent quantities of 2Me-BHT. Similar deviations were also observed using a flame ionization detector for signal quantification in GC. In LC-MS, however, 2Me-BHT produces 11× higher ion counts than 2Me-diplopterol but only 1.2× higher ion counts than the sterol standard pregnane acetate. To further improve quantification, we synthesized tetradeuterated (D4) diplopterol, a precursor for a variety of hopanoids. LC-MS analysis on a mixture of (D4)-diplopterol and phospholipids showed that under the influence of co-eluted phospholipids, the D4-diplopterol internal standard quantifies diplopterol more accurately than external diplopterol standards. These new quantitative approaches permit meaningful comparisons between studies, allowing more accurate hopanoid pattern detection in both laboratory and environmental samples.

Distinct Sources of Hematopoietic Progenitors Emerge before HSCs and Provide Functional Blood Cells in the Mammalian Embryo

Hematopoietic potential arises in mammalian embryos before adult-repopulating hematopoietic stem cells (HSCs). At embryonic day 9.5 (E9.5), we show the first murine definitive erythro-myeloid progenitors (EMPs) have an immunophenotype distinct from primitive hematopoietic progenitors, maturing megakaryocytes and macrophages, and rare B cell potential. EMPs emerge in the yolk sac with erythroid and broad myeloid, but not lymphoid, potential. EMPs migrate to the fetal liver and rapidly differentiate, including production of circulating neutrophils by E11.5. Although the surface markers, transcription factors, and lineage potential associated with EMPs overlap with those found in adult definitive hematopoiesis, they are present in unique combinations or proportions that result in a specialized definitive embryonic progenitor. Furthermore, we find that embryonic stem cell (ESC)-derived hematopoiesis recapitulates early yolk sac hematopoiesis, including primitive, EMP, and rare B cell potential. EMPs do not have long-term potential when transplanted in immunocompromised adults, but they can provide transient adult-like RBC reconstitution.

Modulation of cardiac fibrosis by Krüppel-like factor 6 through transcriptional control of thrombospondin 4 in cardiomyocytes

AIMS

Krüppel-like factors (KLFs) are a family of transcription factors which play important roles in the heart under pathological and developmental conditions. We previously identified and cloned Klf6 whose homozygous mutation in mice results in embryonic lethality suggesting a role in cardiovascular development. Effects of KLF6 on pathological regulation of the heart were investigated in the present study.

METHODS AND RESULTS

Mice heterozygous for Klf6 resulted in significantly diminished levels of cardiac fibrosis in response to angiotensin II infusion. Intriguingly, a similar phenotype was seen in cardiomyocyte-specific Klf6 knockout mice, but not in cardiac fibroblast-specific knockout mice. Microarray analysis revealed increased levels of the extracellular matrix factor, thrombospondin 4 (TSP4), in the Klf6-ablated heart. Mechanistically, KLF6 directly suppressed Tsp4 expression levels, and cardiac TSP4 regulated the activation of cardiac fibroblasts to regulate cardiac fibrosis.

CONCLUSION

Our present studies on the cardiac function of KLF6 show a new mechanism whereby cardiomyocytes regulate cardiac fibrosis through transcriptional control of the extracellular matrix factor, TSP4, which, in turn, modulates activation of cardiac fibroblasts.

In situ hybridization (both radioactive and nonradioactive) and spatiotemporal gene expression analysis

Section in situ hybridization using either radioactive or nonradioactive labeled cDNA probes is an invaluable technique that enables the investigator to detect and localize mRNA expression within tissue sections and cells. Here, we describe the labeling of (35)S-UTP radioactive and nonradioactive digoxigenin probes, preparation of tissue sections, hybridization, and washing of non-hybridized probes, followed by the detection of radioactive signals via dipping in nuclear emulsion and the immunohistochemical and subsequent colorimetric detection of nonradioactive signals.

Loss of periostin/OSF-2 in ErbB2/Neu-driven tumors results in androgen receptor-positive molecular apocrine-like tumors with reduced Notch1 activity

INTRODUCTION

Periostin (Postn) is a secreted cell adhesion protein that activates signaling pathways to promote cancer cell survival, angiogenesis, invasion, and metastasis. Interestingly, Postn is frequently overexpressed in numerous human cancers, including breast, lung, colon, pancreatic, and ovarian cancer.

METHODS

Using transgenic mice expressing the Neu oncogene in the mammary epithelium crossed into Postn-deficient animals, we have assessed the effect of Postn gene deletion on Neu-driven mammary tumorigenesis.

RESULTS

Although Postn is exclusively expressed in the stromal fibroblasts of the mammary gland, Postn deletion does not affect mammary gland outgrowth during development or pregnancy. Furthermore, we find that loss of Postn in the mammary epithelium does not alter breast tumor initiation or growth in mouse mammary tumor virus (MMTV)-Neu expressing mice but results in an apocrine-like tumor phenotype. Surprisingly, we find that tumors derived from Postn-null animals express low levels of Notch protein and Hey1 mRNA but increased expression of androgen receptor (AR) and AR target genes. We show that tumor cells derived from wild-type animals do not proliferate when transplanted in a Postn-null environment but that this growth defect is rescued by the overexpression of active Notch or the AR target gene prolactin-induced protein (PIP/GCDFP-15).

CONCLUSIONS

Together our data suggest that loss of Postn in an ErbB2/Neu/HER2 overexpression model results in apocrine-like tumors that activate an AR-dependent pathway. This may have important implications for the treatment of breast cancers involving the therapeutic targeting of periostin or Notch signaling.

Periostin contributes to epidermal hyperplasia in psoriasis common to atopic dermatitis

BACKGROUND

Epidermal hyperplasia is a histological hallmark observed in both atopic dermatitis (AD) and psoriasis, although the clinical features and the underlying immunological disorders of these diseases are different. We previously showed that periostin, a matricellular protein, plays a critical role in epidermal hyperplasia in AD, using a mouse model and a 3-dimensional organotypic coculture system. In this study, we explore the hypothesis that periostin is involved in epidermal hyperplasia in psoriasis.

METHODS

To examine expression of periostin in psoriasis patients, we performed immunohistochemical analysis on skin biopsies from six such patients. To investigate periostin's role in the pathogenesis of psoriasis, we evaluated periostin-deficient mice in a psoriasis mouse model induced by topical treatment with imiquimod (IMQ).

RESULTS

Periostin was substantially expressed in the dermis of all investigated psoriasis patients. Epidermal hyperplasia induced by IMQ treatment was impaired in periostin-deficient mice, along with decreased skin swelling. However, upon treatment with IMQ, periostin deficiency did not alter infiltration of inflammatory cells such as neutrophils; production of IL-17, -22, or -23; or induction/expansion of IL-17- and IL-22-producing group 3 innate lymphoid cells.

CONCLUSIONS

Periostin plays an important role during epidermal hyperplasia in IMQ-induced skin inflammation, independently of the IL-23-IL-17/IL-22 axis. Periostin appears to be a mediator for epidermal hyperplasia that is common to AD and psoriasis.

Persistent Noggin arrests cardiomyocyte morphogenesis and results in early in utero lethality

BACKGROUND

Multiple bone morphogenetic protein (BMP) genes are expressed in the developing heart from the initiation to late-differentiation stages, and play pivotal roles in cardiovascular development. In this study, we investigated the requirement of BMP activity in heart development by transgenic over-expression of extracellular BMP antagonist Noggin.

RESULTS

Using Nkx2.5-Cre to drive lineage-restricted Noggin within cardiomyocyte progenitors, we show persistent Noggin arrests cardiac development at the linear heart stage. This is coupled with a significantly reduced cell proliferation rate, subsequent cardiomyocyte programmed cell death and reduction of downstream intracellular pSMAD1/5/8 expression. Noggin mutants exhibit reduced heartbeat which likely results in subsequent fully penetrant in utero lethality. Significantly, confocal and electron micrographic examination revealed considerably fewer contractile elements, as well as a lack of maturation of actin-myosin microfilaments. Molecular analysis demonstrated that ectopic Noggin-expressing regions in the early heart's pacemaker region, failed to express the potassium/sodium hyperpolarization-activated cyclic nucleotide-gated channel 4 (Hcn4), resulting in an overall decrease in Hcn4 levels.

CONCLUSIONS

Combined, our results reveal a novel role for BMP signaling in the progression of heart development from the tubular heart stage to the looped stage by means of regulation of proliferation and promotion of maturation of the in utero heart's contractile apparatus and pacemaker.

Ectopic Noggin in a Population of Nfatc1 Lineage Endocardial Progenitors Induces Embryonic Lethality

The initial heart is composed of a myocardial tube lined by endocardial cells. The TGFβ superfamily is known to play an important role, as BMPs from the myocardium signal to the overlying endocardium to create an environment for EMT. Subsequently, BMP and TGFβ signaling pathways synergize to form primitive valves and regulate myocardial growth. In this study, we investigated the requirement of BMP activity by transgenic over-expression of extracellular BMP antagonist Noggin. Using Nfatc1^Cre to drive lineage-restricted Noggin within the endocardium, we show that ectopic Noggin arrests cardiac development in E10.5-11 embryos, resulting in small hearts which beat poorly and die by E12.5. This is coupled with hypoplastic endocardial cushions, reduced trabeculation and fewer mature contractile fibrils in mutant hearts. Moreover, Nfatc1^Cre-mediated diphtheria toxin fragment-A expression in the endocardium resulted in genetic ablation and a more severe phenotype with lethality at E11 and abnormal linear hearts. Molecular analysis demonstrated that endocardial Noggin resulted in a specific alteration of TGFβ/BMP-mediated signal transduction, in that, both Endoglin and ALK1 were downregulated in mutant endocardium. Combined, these results demonstrate the cell-autonomous requirement of the endocardial lineage and function of unaltered BMP levels in facilitating endothelium-cardiomyocyte cross-talk and promoting endocardial cushion formation.

Loss of β-catenin promotes chondrogenic differentiation of aortic valve interstitial cells

OBJECTIVE

The Wnt/β-catenin signaling pathway has been implicated in human heart valve disease and is required for early heart valve formation in mouse and zebrafish. However, the specific functions of Wnt/β-catenin signaling activity in heart valve maturation and maintenance in adults have not been determined previously.

APPROACH AND RESULTS

Here, we show that Wnt/β-catenin signaling inhibits Sox9 nuclear localization and proteoglycan expression in cultured chicken embryo aortic valves. Loss of β-catenin in vivo in mice, using Periostin(Postn)Cre-mediated tissue-restricted loss of β-catenin (Ctnnb1) in valvular interstitial cells, leads to the formation of aberrant chondrogenic nodules and induction of chondrogenic gene expression in adult aortic valves. These nodular cells strongly express nuclear Sox9 and Sox9 downstream chondrogenic extracellular matrix genes, including Aggrecan, Col2a1, and Col10a1. Excessive chondrogenic proteoglycan accumulation and disruption of stratified extracellular matrix maintenance in the aortic valve leaflets are characteristics of myxomatous valve disease. Both in vitro and in vivo data demonstrate that the loss of Wnt/β-catenin signaling leads to increased nuclear expression of Sox9 concomitant with induced expression of chondrogenic extracellular matrix proteins.

CONCLUSIONS

β-Catenin limits Sox9 nuclear localization and inhibits chondrogenic differentiation during valve development and in adult aortic valve homeostasis.

Pax3 expression enhances PDGF-B-induced brainstem gliomagenesis and characterizes a subset of brainstem glioma

High-grade Brainstem Glioma (BSG), also known as Diffuse Intrinsic Pontine Glioma (DIPG), is an incurable pediatric brain cancer. Increasing evidence supports the existence of regional differences in gliomagenesis such that BSG is considered a distinct disease from glioma of the cerebral cortex (CG). In an effort to elucidate unique characteristics of BSG, we conducted expression analysis of mouse PDGF-B-driven BSG and CG initiated in Nestin progenitor cells and identified a short list of expression changes specific to the brainstem gliomagenesis process, including abnormal upregulation of paired box 3 (Pax3). In the neonatal mouse brain, Pax3 expression marks a subset of brainstem progenitor cells, while it is absent from the cerebral cortex, mirroring its regional expression in glioma. Ectopic expression of Pax3 in normal brainstem progenitors in vitro shows that Pax3 inhibits apoptosis. Pax3-induced inhibition of apoptosis is p53-dependent, however, and in the absence of p53, Pax3 promotes proliferation of brainstem progenitors. In vivo, Pax3 enhances PDGF-B-driven gliomagenesis by shortening tumor latency and increasing tumor penetrance and grade, in a region-specific manner, while loss of Pax3 function extends survival of PDGF-B-driven;p53-deficient BSG-bearing mice by 33%. Importantly, Pax3 is regionally expressed in human glioma as well, with high PAX3 mRNA characterizing 40% of human BSG, revealing a subset of tumors that significantly associates with PDGFRA alterations, amplifications of cell cycle regulatory genes, and is exclusive of ACVR1 mutations. Collectively, these data suggest that regional Pax3 expression not only marks a novel subset of BSG but also contributes to PDGF-B-induced brainstem gliomagenesis.

A murine model of neurofibromatosis type 2 that accurately phenocopies human schwannoma formation

Neurofibromatosis type 2 (NF2) is an autosomal dominant genetic disorder resulting from germline mutations in the NF2 gene. Bilateral vestibular schwannomas, tumors on cranial nerve VIII, are pathognomonic for NF2 disease. Furthermore, schwannomas also commonly develop in other cranial nerves, dorsal root ganglia and peripheral nerves. These tumors are a major cause of morbidity and mortality, and medical therapies to treat them are limited. Animal models that accurately recapitulate the full anatomical spectrum of human NF2-related schwannomas, including the characteristic functional deficits in hearing and balance associated with cranial nerve VIII tumors, would allow systematic evaluation of experimental therapeutics prior to clinical use. Here, we present a genetically engineered NF2 mouse model generated through excision of the Nf2 gene driven by Cre expression under control of a tissue-restricted 3.9kbPeriostin promoter element. By 10 months of age, 100% of Postn-Cre; Nf2(flox/flox) mice develop spinal, peripheral and cranial nerve tumors histologically identical to human schwannomas. In addition, the development of cranial nerve VIII tumors correlates with functional impairments in hearing and balance, as measured by auditory brainstem response and vestibular testing. Overall, the Postn-Cre; Nf2(flox/flox) tumor model provides a novel tool for future mechanistic and therapeutic studies of NF2-associated schwannomas.

Abstract 332: Loss of beta-catenin Leads to Induction of a Chondrogenic Phenotype in Adult Mouse Heart Aortic Valves

Objectives: Altered Wnt/beta-catenin signaling has been implicated in human heart valve disease; however, a causal relation has not been established. This study is aimed at determining the role of Wnt/beta-catenin signaling in adult valve homeostasis and disease. In endochondral bone development, Wnt/beta-catenin signaling inhibits early chondrogenesis and promotes osteogenesis. Therefore, we hypothesize that loss of Wnt/beta-catenin signaling promotes chondrogenic differentiation of valvular interstitial cells (VICs) resembling myxomatous valve disease.

Methods & Results: Periostin (Postn)Cre was used for conditional loss of beta-catenin (Ctnnb1) specifically in VICs in mice. PostnCre is active in valve mesenchymal progenitors by embryonic day (E)13.5, therefore bypassing requirements for beta-catenin in endothelial-to-mesenchymal transition and endocardial cushion formation. Histology of adult heart valves was analyzed by Masson’s Trichrome and Movat’s Pentachrome staining, and the expression of extracellular matrix (ECM) genes was examined at both mRNA and protein level. Heart valve development appears normal at both fetal and neonatal stages with loss of beta-catenin. However proteoglycan-rich nodules form in adult aortic valves (AoVs) lacking beta-catenin at 3 months with 100% penetrance. These nodular cells are enlarged and express nuclear Sox9 and chondrogenic ECM genes, including Aggrecan, Collagen type 2 (Col1) and Col10, reminiscent of hypertrophic cartilage. Fibrillar collagens 1 and 3, as well as Versican, are excluded from the nodules, accompanied by abnormal ECM deposition throughout the AoV leaflets. Likewise, treatment of cultured porcine aortic VICs with the Wnt pathway inhibitor XAV also induces Aggrecan and Col2 gene expression in vitro. This work demonstrates that beta-catenin is required for the maintenance of normal ECM deposition and composition in adult mice, and, therefore, is indispensible for adult heart valve homeostasis.

Conclusions: We have demonstrated that beta-catenin is a key factor in maintaining normal valve ECM organization in adult AoV. In the absence of beta-catenin, VICs are susceptible to chondrogenic differentiation related to myxomatous valve disease.

The role of periostin in tissue remodeling across health and disease

Periostin, also termed osteoblast-specific factor 2, is a matricellular protein with known functions in osteology, tissue repair, oncology, cardiovascular and respiratory systems, and in various inflammatory settings. However, most of the research to date has been conducted in divergent and circumscribed areas meaning that the overall understanding of this intriguing molecule remains fragmented. Here, we integrate the available evidence on periostin expression, its normal role in development, and whether it plays a similar function during pathologic repair, regeneration, and disease in order to bring together the different research fields in which periostin investigations are ongoing. In spite of the seemingly disparate roles of periostin in health and disease, tissue remodeling as a response to insult/injury is emerging as a common functional denominator of this matricellular molecule. Periostin is transiently upregulated during cell fate changes, either physiologic or pathologic. Combining observations from various conditions, a common pattern of events can be suggested, including periostin localization during development, insult and injury, epithelial-mesenchymal transition, extracellular matrix restructuring, and remodeling. We propose mesenchymal remodeling as an overarching role for the matricellular protein periostin, across physiology and disease. Periostin may be seen as an important structural mediator, balancing appropriate versus inappropriate tissue adaption in response to insult/injury.

Cardiogenic genes expressed in cardiac fibroblasts contribute to heart development and repair

RATIONALE

Cardiac fibroblasts are critical to proper heart function through multiple interactions with the myocardial compartment, but appreciation of their contribution has suffered from incomplete characterization and lack of cell-specific markers.

OBJECTIVE

To generate an unbiased comparative gene expression profile of the cardiac fibroblast pool, identify and characterize the role of key genes in cardiac fibroblast function, and determine their contribution to myocardial development and regeneration.

METHODS AND RESULTS

High-throughput cell surface and intracellular profiling of cardiac and tail fibroblasts identified canonical mesenchymal stem cell and a surprising number of cardiogenic genes, some expressed at higher levels than in whole heart. While genetically marked fibroblasts contributed heterogeneously to interstitial but not cardiomyocyte compartments in infarcted hearts, fibroblast-restricted depletion of one highly expressed cardiogenic marker, T-box 20, caused marked myocardial dysmorphology and perturbations in scar formation on myocardial infarction.

CONCLUSIONS

The surprising transcriptional identity of cardiac fibroblasts, the adoption of cardiogenic gene programs, and direct contribution to cardiac development and repair provoke alternative interpretations for studies on more specialized cardiac progenitors, offering a novel perspective for reinterpreting cardiac regenerative therapies.

Assessment of inhibited alveolar-capillary membrane structural development and function in bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease of extreme prematurity and is defined clinically by dependence on supplemental oxygen due to impaired gas exchange. Optimal gas exchange is dependent on the development of a sufficient surface area for diffusion. In the mammalian lung, rapid acquisition of distal lung surface area is accomplished in neonatal and early adult life by means of vascularization and secondary septation of distal lung airspaces. Extreme preterm birth interrupts secondary septation and pulmonary capillary development and ultimately reduces the efficiency of the alveolar-capillary membrane. Although pulmonary health in BPD infants rapidly improves over the first few years, persistent alveolar-capillary membrane dysfunction continues into adolescence and adulthood. Preventative therapies have been largely ineffective, and therapies aimed at promoting normal development of the air-blood barrier in infants with established BPD remain largely unexplored. The purpose of this review will be: (1) to summarize the histological evidence of aberrant alveolar-capillary membrane development associated with extreme preterm birth and BPD, (2) to review the clinical evidence assessing the long-term impact of BPD on alveolar-capillary membrane function, and (3) to discuss the need to develop and incorporate direct measurements of functional gas exchange into clinically relevant animal models of inhibited alveolar development.

Inhibition of periostin expression protects against the development of renal inflammation and fibrosis

Increased renal expression of periostin, a protein normally involved in embryonic and dental development, correlates with the decline of renal function in experimental models and patient biopsies. Because periostin has been reported to induce cell differentiation, we investigated whether it is also involved in the development of renal disease and whether blocking its abnormal expression improves renal function and/or structure. After unilateral ureteral obstruction in wild-type mice, we observed a progressive increase in the expression and synthesis of periostin in the obstructed kidney that associated with the progression of renal lesions. In contrast, mice lacking the periostin gene showed less injury-induced interstitial fibrosis and inflammation and were protected against structural alterations. This protection was associated with a preservation of the renal epithelial phenotype. In vitro, administration of TGF-β to renal epithelial cells increased the expression of periostin several-fold, leading to subsequent loss of the epithelial phenotype. Furthermore, treatment of these cells with periostin increased the expression of collagen I and stimulated the phosphorylation of FAK, p38, and ERK 42/44. In vivo delivery of antisense oligonucleotides to inhibit periostin expression protected animals from L-NAME-induced renal injury. These data strongly suggest that periostin mediates renal disease in response to TGF-β and that blocking periostin may be a promising therapeutic strategy against the development of CKD.

Neurofibromin-deficient myeloid cells are critical mediators of aneurysm formation in vivo

BACKGROUND

Neurofibromatosis type 1 (NF1) is a genetic disorder resulting from mutations in the NF1 tumor suppressor gene. Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity in circulating hematopoietic and vascular wall cells, which are critical for maintaining vessel wall homeostasis. NF1 patients have evidence of chronic inflammation resulting in the development of premature cardiovascular disease, including arterial aneurysms, which may manifest as sudden death. However, the molecular pathogenesis of NF1 aneurysm formation is unknown.

METHOD AND RESULTS

With the use of an angiotensin II-induced aneurysm model, we demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) enhanced aneurysm formation with myeloid cell infiltration and increased oxidative stress in the vessel wall. Using lineage-restricted transgenic mice, we show that loss of a single Nf1 allele in myeloid cells is sufficient to recapitulate the Nf1(+/-) aneurysm phenotype in vivo. Finally, oral administration of simvastatin or the antioxidant apocynin reduced aneurysm formation in Nf1(+/-) mice.

CONCLUSION

These data provide genetic and pharmacological evidence that Nf1(+/-) myeloid cells are the cellular triggers for aneurysm formation in a novel model of NF1 vasculopathy and provide a potential therapeutic target.

Periostin promotes renal cyst growth and interstitial fibrosis in polycystic kidney disease

In renal cystic diseases, sustained enlargement of fluid-filled cysts is associated with severe interstitial fibrosis and progressive loss of functioning nephrons. Periostin, a matricellular protein, is highly overexpressed in cyst-lining epithelial cells of autosomal-dominant polycystic disease kidneys (ADPKD) compared with normal tubule cells. Periostin accumulates in situ within the matrix subjacent to ADPKD cysts, binds to αVβ3 and αVβ5 integrins, and stimulates the integrin-linked kinase to promote cell proliferation. We knocked out periostin (Postn) in pcy/pcy mice, an orthologous model of nephronophthisis type 3, to determine whether periostin loss reduces PKD progression in a slowly progressive model of renal cystic disease. At 20 weeks of age, pcy/pcy:Postn(-/-) mice had a 34% reduction in kidney weight/body weight, a reduction in cyst number and total cystic area, a 69% reduction in phosphorylated S6, a downstream component of the mTOR pathway, and fewer proliferating cells in the kidneys compared with pcy/pcy:Postn(+/+) mice. The pcy/pcy Postin knockout mice also had less interstitial fibrosis with improved renal function at 20 weeks and significantly longer survival (51.4 compared with 38.0 weeks). Thus, periostin adversely modifies the progression of renal cystic disease by promoting cyst epithelial cell proliferation, cyst enlargement, and interstitial fibrosis, all contributing to the decline in renal function and premature death.

Origin, development, and differentiation of cardiac fibroblasts

Cardiac fibroblasts are the most abundant cell in the mammalian heart. While they have been historically underappreciated in terms of their functional contributions to cardiac development and physiology, they and their activated form, myofibroblasts, are now known to play key roles in both development and disease through structural, paracrine, and electrical interactions with cardiomyocytes. The lack of specific markers for fibroblasts currently convolutes the study of this dynamic cell lineage, but advances in marker analysis and lineage mapping technologies are continuously being made. Understanding how to best utilize these tools, both individually and in combination, will help to elucidate the functional significance of fibroblast-cardiomyocyte interactions in vivo. Here we review what is currently known about the diverse roles played by cardiac fibroblasts and myofibroblasts throughout development and periods of injury with the intent of emphasizing the duality of their nature. This article is part of a Special Issue entitled "Myocyte-Fibroblast Signalling in Myocardium ".

Periostin deficiency increases bone damage and impairs injury response to fatigue loading in adult mice

Bone damage removal and callus formation in response to fatigue loading are essential to prevent fractures. Periostin (Postn) is a matricellular protein that mediates adaptive response of cortical bone to loading. Whether and how periostin influences damage and the injury response to fatigue remains unknown. We investigated the skeletal response of Postn(-/-) and Postn(+/+) mice after fatigue stimulus by axial compression of their tibia. In Postn(+/+) mice, cracks number and surface (CsNb, CsS) increased 1h after fatigue, with a decrease in strength compared to non-fatigued tibia. At 15 days, CsNb had started to decline, while CtTV and CtBV increased in fatigued vs non-fatigued tibia, reflecting a woven bone response that was present in 75% of the fatigued bones. Cortical porosity and remodelling also prominently increased in the fatigued tibia of Postn(+/+) mice. At 30 days, paralleling a continuous removal of cortical damage, strength of the fatigued tibia was similar to the non-fatigue tibia. In Postn(-/-) mice, cracks were detectable even in the absence of fatigue, while the amount of collagen crosslinks and tissue hardness was decreased compared to Postn(+/+). Fatigue significantly increased CsNb and CsS in Postn(-/-), but was not associated with changes in CtTV and CtBV, as only 16% of the fatigued bones formed some woven bone. Cortical porosity and remodelling did not increase either after fatigue in Postn(-/-), and the level of damage remained high even after 30 days. As a result, strength remained compromised in Postn(-/-) mice. Contrary to Postn(+/+), which osteocytic lacunae showed a change in the degree of anisotropy (DA) after fatigue, Postn(-/-) showed no DA change. Hence periostin appears to influence bone materials properties, damage accumulation and repair, including local modeling/remodeling processes in response to fatigue. These observations suggest that the level of periostin expression could influence the propensity to fatigue fractures.

Abstract 290: Haemogenic Endocardium Contribute To Definitive Hematopoiesis During Cardiogenesis

The circulatory system is the first functional organ system that develops during mammalian life. Accumulating evidences suggest that cardiac and endocardial cells can arise from a single common progenitor cell during mammalian cardiogenesis. Notably, these early cardiac progenitors express multiple hematopoietic transcription factors, consistent with previous reports. Indeed, a close relationship among cardiac, endocardial and hematopoietic lineages has been suggested in fly, zebrafish, and embryonic stem cell in vitro differentiation models. However, it is unclear when, where and how this hematopoietic gene program is in operation during in vivo mammalian cardiogenesis. Hematopoietic colony assay suggests that mouse heart explants generate myeloids and erythroids in the absence of circulation, suggesting that the heart tube is a de novo site for the definitive hematopoiesis. Lineage tracing revealed that putative cardiac-derived Nkx2-5+/Isl1+ endocardial cells give rise to CD41+ hematopoietic progenitors that contribute to definitive hematopoiesis in vivo and ex vivo during embryogenesis earlier than in the AGM region. Furthermore, Nkx2-5 and Isl1 are both required for the hemogenic activity of the endocardium. Together, identification of Nkx2-5/Isl1-dependent hemogenic endocardial cells (1) adds hematopoietic component in the cardiogenesis lineage tree, (2) changes the long-held dogma that AGM is the only major source of definitive hematopoiesis in the embryo proper, and (3) represents phylogenetically conserved fundamental mechanism of cardio-vasculo-hematopoietic differentiation pathway during the development of circulatory system.

Fkbp1a controls ventricular myocardium trabeculation and compaction by regulating endocardial Notch1 activity

Trabeculation and compaction of the embryonic myocardium are morphogenetic events crucial for the formation and function of the ventricular walls. Fkbp1a (FKBP12) is a ubiquitously expressed cis-trans peptidyl-prolyl isomerase. Fkbp1a-deficient mice develop ventricular hypertrabeculation and noncompaction. To determine the physiological function of Fkbp1a in regulating the intercellular and intracellular signaling pathways involved in ventricular trabeculation and compaction, we generated a series of Fkbp1a conditional knockouts. Surprisingly, cardiomyocyte-restricted ablation of Fkbp1a did not give rise to the ventricular developmental defect, whereas endothelial cell-restricted ablation of Fkbp1a recapitulated the ventricular hypertrabeculation and noncompaction observed in Fkbp1a systemically deficient mice, suggesting an important contribution of Fkbp1a within the developing endocardia in regulating the morphogenesis of ventricular trabeculation and compaction. Further analysis demonstrated that Fkbp1a is a novel negative modulator of activated Notch1. Activated Notch1 (N1ICD) was significantly upregulated in Fkbp1a-ablated endothelial cells in vivo and in vitro. Overexpression of Fkbp1a significantly reduced the stability of N1ICD and direct inhibition of Notch signaling significantly reduced hypertrabeculation in Fkbp1a-deficient mice. Our findings suggest that Fkbp1a-mediated regulation of Notch1 plays an important role in intercellular communication between endocardium and myocardium, which is crucial in controlling the formation of the ventricular walls.

Periostin downregulation is an early marker of inhibited neonatal murine lung alveolar septation

BACKGROUND

Extreme preterm birth exposes the saccular lung to multiple teratogens, which ultimately retard alveolar development. Specifically, therapeutic high level oxygen supplementation adversely affects the premature lungs and results in blunted alveolarization. Prolonged hyperoxic lung injury has previously been shown to upregulate the matricellular protein Periostin (Postn) and stimulate ectopic accumulation of alpha smooth muscle actin (αSMA) myofibroblasts. Therapies that promote lung septation are lacking largely due to a lack of reliable early biomarkers of injury. Thus, we determined if Postn expression correlated with the initial appearance of myofibroblasts in the saccular lung and was required for early alveolar development.

METHODS

Lung development in C57BL/6J mice following room-air (RA, 21%-O₂) or continuous hyperoxia (85%-O₂) from birth (P0) through postnatal day P14 was correlated with Postn and αSMA expression. Alveolarization in Postn knockout mice exposed to room-air, 60%-, and 85%-O₂ was also examined.

RESULTS

Postn was widely expressed in distal lung septa through P2 to P4 and peak expression coincided with accumulation of saccular myofibroblasts. Initially, 85%-O₂ prematurely downregulated Postn and αSMA expression and suppressed proliferation before the first evidence of distal lung simplification at P4. By P14, chronic 85%-O₂ resulted in secondary upregulation of Postn and αSMA in blunted septa. Myofibroblast differentiation and alveolar development was unaffected in Postn null mice and acute 85%-O₂ exposure equally inhibited septal formation in Postn null and wild-type littermates.

CONCLUSION

Postn expression is tightly correlated with the presence of αSMA-myofibroblasts and is a novel early biomarker of acutely inhibited alveolar septation during a crucial window of lung development.

Cardiac outflow tract anomalies

The mature outflow tract (OFT) is, in basic terms, a short conduit. It is a simple, although vital, connection situated between contracting muscular heart chambers and a vast embryonic vascular network. Unfortunately, it is also a focal point underlying many multifactorial congenital heart defects (CHDs). Through the use of various animal models combined with human genetic investigations, we are beginning to comprehend the molecular and cellular framework that controls OFT morphogenesis. Clear roles of neural crest cells (NCC) and second heart field (SHF) derivatives have been established during OFT formation and remodeling. The challenge now is to determine how the SHF and cardiac NCC interact, the complex reciprocal signaling that appears to be occurring at various stages of OFT morphogenesis, and finally how endocardial progenitors and primary heart field (PHF) communicate with both these colonizing extra-cardiac lineages. Although we are beginning to understand that this dance of progenitor populations is wonderfully intricate, the underlying pathogenesis and the spatiotemporal cell lineage interactions remain to be fully elucidated. What is now clear is that OFT alignment and septation are independent processes, invested via separate SHF and cardiac neural crest (CNC) lineages. This review will focus on our current understanding of the respective contributions of the SHF and CNC lineage during OFT development and pathogenesis.

Haemogenic endocardium contributes to transient definitive haematopoiesis

Haematopoietic cells arise from spatiotemporally restricted domains in the developing embryo. Although studies of non-mammalian animal and in vitro embryonic stem cell models suggest a close relationship among cardiac, endocardial and haematopoietic lineages, it remains unknown whether the mammalian heart tube serves as a haemogenic organ akin to the dorsal aorta. Here we examine the haemogenic activity of the developing endocardium. Mouse heart explants generate myeloid and erythroid colonies in the absence of circulation. Haemogenic activity arises from a subset of endocardial cells in the outflow cushion and atria earlier than in the aorta-gonad-mesonephros region, and is transient and definitive in nature. Interestingly, key cardiac transcription factors, Nkx2-5 and Isl1, are expressed in and required for the haemogenic population of the endocardium. Together, these data suggest that a subset of endocardial/endothelial cells serve as a de novo source for transient definitive haematopoietic progenitors.

Periostin contributes to the pathogenesis of atopic dermatitis by inducing TSLP production from keratinocytes

BACKGROUND

Atopic dermatitis (AD) is a chronic inflammatory skin disease where Th2-type immune responses are dominant. Keratinocytes persistently secrete proinflammatory cytokines and chemokines, amplifying Th2-type responses in AD. We have recently reported that periostin, an extracellular matrix protein induced by Th2 cytokines, plays a critical role in AD. In the present study, we have further investigated the characteristics of our allergen-induced AD model mice and the role of periostin in the pathogenesis of AD.

METHODS

The ears of C57BL/6 mice, BALB/c mice, and Rag-2-/- γ(c)-/- mice (BALB/c background) were epicutaneously sensitized repeatedly with HDM. Mice were analyzed after the final sensitization. To examine the direct role of periostin, we reconstituted skin in vitro by coculture of keratinocytes with wild-type or periostin-deficient fibroblasts.

RESULTS

Epicutaneous sensitization with HDM induced AD-like phenotypes and accumulation of periostin in dermis in C57BL/6 mice but not in Rag-2-/- γ(c)-/- mice. In vitro organotypic coculture systems revealed that periostin promoted survival and proliferation of keratinocytes and directly induced production of thymic stromal lymphopoietin (TSLP).

CONCLUSIONS

Our results suggest that periostin exacerbates the pathogenesis of AD through TSLP production from keratinocytes.

Heterozygous inactivation of the Nf1 gene in myeloid cells enhances neointima formation via a rosuvastatin-sensitive cellular pathway

Mutations in the NF1 tumor suppressor gene cause Neurofibromatosis type 1 (NF1). Neurofibromin, the protein product of NF1, functions as a negative regulator of Ras activity. Some NF1 patients develop cardiovascular disease, which represents an underrecognized disease complication and contributes to excess morbidity and mortality. Specifically, NF1 patients develop arterial occlusion resulting in tissue ischemia and sudden death. Murine studies demonstrate that heterozygous inactivation of Nf1 (Nf1(+/-)) in bone marrow cells enhances neointima formation following arterial injury. Macrophages infiltrate Nf1(+/-) neointimas, and NF1 patients have increased circulating inflammatory monocytes in their peripheral blood. Therefore, we tested the hypothesis that heterozygous inactivation of Nf1 in myeloid cells is sufficient for neointima formation. Specific ablation of a single copy of the Nf1 gene in myeloid cells alone mobilizes a discrete pro-inflammatory murine monocyte population via a cell autonomous and gene-dosage dependent mechanism. Furthermore, lineage-restricted heterozygous inactivation of Nf1 in myeloid cells is sufficient to reproduce the enhanced neointima formation observed in Nf1(+/-) mice when compared with wild-type controls, and homozygous inactivation of Nf1 in myeloid cells amplified the degree of arterial stenosis after arterial injury. Treatment of Nf1(+/-) mice with rosuvastatin, a stain with anti-inflammatory properties, significantly reduced neointima formation when compared with control. These studies identify neurofibromin-deficient myeloid cells as critical cellular effectors of Nf1(+/-) neointima formation and propose a potential therapeutic for NF1 cardiovascular disease.

Periostin, a matricellular protein, accelerates cutaneous wound repair by activating dermal fibroblasts

Cutaneous wound repair is a highly ordered and well-coordinated process involving various cell lineages and many molecular effectors. Cell-matrix interactions through integrin molecules provide key signals important for wound repair. Periostin is a matricellular protein that may provide signals important during tissue development and remodelling by interacting with several integrin molecules, via the phosphatidylinositol 3-kinase/Akt and MAP kinase pathways. In this study, we examined the role of periostin in the process of cutaneous wound repair using periostin-deficient mice and by analysing the effects of periostin on dermal fibroblasts. We first determined the expression profile and localization of periostin in a well-characterized wound repair model mice. Periostin was robustly deposited in the granulation tissues beneath the extended epidermal wound edges and at the dermal-epidermal junctions in wounded mice. Moreover, periostin-deficient mice exhibited delayed in vivo wound repair, which could be improved by direct administration of exogenous periostin. In vitro analyses revealed that loss of periostin impaired proliferation and migration of dermal fibroblasts, but exogenous supplementation or enforced periostin expression enhanced their proliferation. Combined, these results demonstrate that periostin accelerates the process of cutaneous wound repair by activating fibroblasts.

Regulation of beta catenin signaling and parathyroid hormone anabolic effects in bone by the matricellular protein periostin

Periostin (Postn) is a matricellular protein preferentially expressed by osteocytes and periosteal osteoblasts in response to mechanical stimulation and parathyroid hormone (PTH). Whether and how periostin expression influences bone anabolism, however, remains unknown. We investigated the skeletal response of adult Postn −/− and Postn +/+ mice to intermittent PTH. Compared with Postn +/+ , Postn −/− mice had a lower bone mass, cortical bone volume, and strength response to PTH. PTH-stimulated bone-forming indices were all significantly lower in Postn −/− mice, particularly at the periosteum. Furthermore, in vivo stimulation of Wnt-β-catenin signaling by PTH, as evaluated in TOPGAL reporter mice, was inhibited in the absence of periostin ( TOPGAL;Postn −/− mice). PTH stimulated periostin and inhibited MEF2C and sclerostin (Sost) expression in bone and osteoblasts in vitro. Recombinant periostin also suppressed Sost expression, which was mediated through the integrin αVβ3 receptor, whereas periostin-blocking antibody prevented inhibition of MEF2C and Sost by PTH. In turn, administration of a Sost-blocking antiboby partially restored the PTH-mediated increase in bone mass in Postn −/− mice. In addition, primary osteoblasts from Postn −/− mice showed a lower proliferation, mineralization, and migration, both spontaneously and in response to PTH. Osteoblastic gene expression levels confirmed a defect of Postn −/− osteoblast differentiation with and without PTH, as well as an increased osteoblast apoptosis in the absence of periostin. These data elucidate the complex role of periostin on bone anabolism, through the regulation of Sost, Wnt-β-catenin signaling, and osteoblast differentiation.

The dynamic role of cardiac fibroblasts in development and disease

Cardiac fibroblasts are the most abundant cell in the mammalian heart. While they have been historically overlooked in terms of functional contributions to development and physiology, cardiac fibroblasts are now front and center. They are currently recognized as key protagonists during both normal development and cardiomyopathy disease, and work together with cardiomyocytes through paracrine, structural, and potentially electrical interactions. However, the lack of specific biomarkers and fibroblast heterogeneous nature currently convolutes the study of this dynamic cell lineage; though, efforts to advance marker analysis and lineage mapping technologies are ongoing. These tools will help elucidate the functional significance of fibroblast-cardiomyocyte interactions in vivo and delineate the dynamic nature of normal and pathological cardiac fibroblasts. Since therapeutic promise lies in understanding the interface between developmental biology and the postnatal injury response, future studies to understand the divergent roles played by cardiac fibroblasts both in utero and following cardiac insult are essential.

Periostin promotes chronic allergic inflammation in response to Th2 cytokines

Allergic inflammation triggered by exposure of an allergen frequently leads to the onset of chronic inflammatory diseases such as atopic dermatitis (AD) and bronchial asthma. The mechanisms underlying chronicity in allergic inflammation remain unresolved. Periostin, a recently characterized matricellular protein, interacts with several cell surface integrin molecules, providing signals for tissue development and remodeling. Here we show that periostin is a critical mediator for the amplification and persistence of allergic inflammation using a mouse model of skin inflammation. Th2 cytokines IL-4 and IL-13 stimulated fibroblasts to produce periostin, which interacted with αv integrin, a functional periostin receptor on keratinocytes, inducing production of proinflammatory cytokines, which consequently accelerated Th2-type immune responses. Accordingly, inhibition of periostin or αv integrin prevented the development or progression of allergen-induced skin inflammation. Thus, periostin sets up a vicious circle that links Th2-type immune responses to keratinocyte activation and plays a critical role in the amplification and chronicity of allergic skin inflammation.

Adult Langerhans cells derive predominantly from embryonic fetal liver monocytes with a minor contribution of yolk sac-derived macrophages

Langerhans cells (LCs) are the dendritic cells (DCs) of the epidermis, forming one of the first hematopoietic lines of defense against skin pathogens. In contrast to other DCs, LCs arise from hematopoietic precursors that seed the skin before birth. However, the origin of these embryonic precursors remains unclear. Using in vivo lineage tracing, we identify a first wave of yolk sac (YS)-derived primitive myeloid progenitors that seed the skin before the onset of fetal liver hematopoiesis. YS progenitors migrate to the embryo proper, including the prospective skin, where they give rise to LC precursors, and the brain rudiment, where they give rise to microglial cells. However, in contrast to microglia, which remain of YS origin throughout life, YS-derived LC precursors are largely replaced by fetal liver monocytes during late embryogenesis. Consequently, adult LCs derive predominantly from fetal liver monocyte-derived cells with a minor contribution of YS-derived cells. Altogether, we establish that adult LCs have a dual origin, bridging early embryonic and late fetal myeloid development.

Periostin modulates myofibroblast differentiation during full-thickness cutaneous wound repair

The matricellular protein periostin is expressed in the skin. Although periostin has been hypothesized to contribute to dermal homeostasis and repair, this has not been directly tested. To assess the contribution of periostin to dermal healing, 6 mm full-thickness excisional wounds were created in the skin of periostin-knockout and wild-type, sex-matched control mice. In wild-type mice, periostin was potently induced 5-7 days after wounding. In the absence of periostin, day 7 wounds showed a significant reduction in myofibroblasts, as visualized by expression of α-smooth muscle actin (α-SMA) within the granulation tissue. Delivery of recombinant human periostin by electrospun collagen scaffolds restored α-SMA expression. Isolated wild-type and knockout dermal fibroblasts did not differ in in vitro assays of adhesion or migration; however, in 3D culture, periostin-knockout fibroblasts showed a significantly reduced ability to contract a collagen matrix, and adopted a dendritic phenotype. Recombinant periostin restored the defects in cell morphology and matrix contraction displayed by periostin-deficient fibroblasts in a manner that was sensitive to a neutralizing anti-β1-integrin and to the FAK and Src inhibitor PP2. We propose that periostin promotes wound contraction by facilitating myofibroblast differentiation and contraction.

Periostin, a matricellular protein, plays a role in the induction of chemokines in pulmonary fibrosis

Idiopathic pulmonary fibrosis (IPF) is a chronic, progressive, and usually fatal form of interstitial lung disease (ILD). The precise molecular mechanisms of IPF remain poorly understood. However, analyses of mice receiving bleomycin (BLM) as a model of IPF established the importance of preceding inflammation for the formation of fibrosis. Periostin is a recently characterized matricellular protein involved in modulating cell functions. We recently found that periostin is highly expressed in the lung tissue of patients with IPF, suggesting that it may play a role in the process of pulmonary fibrosis. To explore this possibility, we administered BLM to periostin-deficient mice, and they subsequently showed a reduction of pulmonary fibrosis. We next determined whether this result was caused by a decrease in the preceding recruitment of neutrophils and macrophages in the lungs because of the lower production of chemokines and proinflammatory cytokines. We performed an in vitro analysis of chemokine production in lung fibroblasts, which indicated that periostin-deficient fibroblasts produced few or no chemokines in response to TNF-α compared with control samples, at least partly explaining the lack of inflammatory response and, therefore, fibrosis after BLM administration to periostin-deficient mice. In addition, we confirmed that periostin is highly expressed in the lung tissue of chemotherapeutic-agent-induced ILD as well as of patients with IPF. Taking these results together, we conclude that periostin plays a unique role as an inducer of chemokines to recruit neutrophils and macrophages important in the process of pulmonary fibrosis in BLM-administered model mice. Our results suggest a therapeutic potential for periostin in IPF and drug-induced ILD.

Characterization of Pax3-expressing cells from adult blood vessels

We report expression of Pax3, an important regulator of skeletal muscle stem cell behaviour, in the brachial and femoral arteries of adult mice. In these contractile arteries of the limb, but not in the elastic arteries of the trunk, bands of GFP-positive cells were observed in Pax3(GFP/+) mice. Histological and biochemical examination of the vessels, together with clonal analysis after purification of Pax3-GFP-positive cells by flow cytometry, established their vascular smooth muscle identity. These blood-vessel-derived cells do not respond to inducers of other mesodermal cell types, such as bone, however, they can contribute to muscle fibre formation when co-cultured with skeletal muscle cells. This myogenic conversion depends on the expression of Pax3, but is rare and non-cell autonomous as it requires cell fusion. Myocardin, which promotes acquisition of a mature smooth muscle phenotype in these Pax3-GFP-positive cells, antagonises their potential for skeletal muscle differentiation. Genetic manipulation shows that myocardin is, however, positively regulated by Pax3, unlike genes for other myocardin-related factors, MRTFA, MRTFB or SRF. Expression of Pax3 overlaps with that reported for Msx2, which is required for smooth muscle differentiation of blood vessel-derived multipotent mesoangioblasts. These observations are discussed with respect to the origin and function of Pax3-expressing cells in blood vessels, and more general questions of cell fate determination and adult cell plasticity and reprogramming.

Aberrant signaling pathways of the lung mesenchyme and their contributions to the pathogenesis of bronchopulmonary dysplasia

Bronchopulmonary dysplasia (BPD) is a chronic lung disease in infants born extremely preterm, typically before 28 weeks' gestation, characterized by a prolonged need for supplemental oxygen or positive pressure ventilation beyond 36 weeks postmenstrual age. The limited number of autopsy samples available from infants with BPD in the postsurfactant era has revealed a reduced capacity for gas exchange resulting from simplification of the distal lung structure with fewer, larger alveoli because of a failure of normal lung alveolar septation and pulmonary microvascular development. The mechanisms responsible for alveolar simplification in BPD have not been fully elucidated, but mounting evidence suggests that aberrations in the cross-talk between growth factors of the lung mesenchyme and distal airspace epithelium have a key role. Animal models that recapitulate the human condition have expanded our knowledge of the pathology of BPD and have identified candidate matrix components and growth factors in the developing lung that are disrupted by conditions that predispose infants to BPD and interfere with normal vascular and alveolar morphogenesis. This review focuses on the deviations from normal lung development that define the pathophysiology of BPD and summarizes the various candidate mesenchyme-associated proteins and growth factors that have been identified as being disrupted in animal models of BPD. Finally, future areas of research to identify novel targets affected in arrested lung development and recovery are discussed.

Transforming growth factor beta signaling in adult cardiovascular diseases and repair

The majority of children with congenital heart disease now live into adulthood due to the remarkable surgical and medical advances that have taken place over the past half century. Because of this, adults now represent the largest age group with adult cardiovascular diseases. It includes patients with heart diseases that were not detected or not treated during childhood, those whose defects were surgically corrected but now need revision due to maladaptive responses to the procedure, those with exercise problems and those with age-related degenerative diseases. Because adult cardiovascular diseases in this population are relatively new, they are not well understood. It is therefore necessary to understand the molecular and physiological pathways involved if we are to improve treatments. Since there is a developmental basis to adult cardiovascular disease, transforming growth factor beta (TGFβ) signaling pathways that are essential for proper cardiovascular development may also play critical roles in the homeostatic, repair and stress response processes involved in adult cardiovascular diseases. Consequently, we have chosen to summarize the current information on a subset of TGFβ ligand and receptor genes and related effector genes that, when dysregulated, are known to lead to cardiovascular diseases and adult cardiovascular deficiencies and/or pathologies. A better understanding of the TGFβ signaling network in cardiovascular disease and repair will impact genetic and physiologic investigations of cardiovascular diseases in elderly patients and lead to an improvement in clinical interventions.

A protective role for periostin and TGF-β in IgE-mediated allergy and airway hyperresponsiveness

Background

The pathophysiology of asthma involves allergic inflammation and remodelling in the airway and airway hyperresponsiveness (AHR) to cholinergic stimuli, but many details of the specific underlying cellular and molecular mechanisms remain unknown. Periostin is a matricellular protein with roles in tissue repair following injury in both the skin and heart. It has recently been shown to be up-regulated in the airway epithelium of asthmatics and to increase active TGF-β. Though one might expect periostin to play a deleterious role in asthma pathogenesis, to date its biological role in the airway is unknown.

Objective

To determine the effect of periostin deficiency on airway responses to inhaled allergen.

Methods

In vivo measures of airway responsiveness, inflammation, and remodelling were made in periostin deficient mice and wild-type controls following repeated intranasal challenge with Aspergillus fumigatus antigen. In vitro studies of the effects of epithelial cell-derived periostin on murine T cells were also performed.

Results

Surprisingly, compared with wild-type controls, periostin deficient mice developed increased AHR and serum IgE levels following allergen challenge without differences in two outcomes of airway remodelling (mucus metaplasia and peribronchial fibrosis). These changes were associated with decreased expression of TGF-β1 and Foxp3 in the lungs of periostin deficient mice. Airway epithelial cell-derived periostin-induced conversion of CD4⁺ CD25⁻ cells into CD25⁺, Foxp3⁺ T cells in vitro in a TGF-β dependent manner.

Conclusions and Clinical Relevance

Allergen-induced increases in serum IgE and bronchial hyperresponsiveness are exaggerated in periostin deficient mice challenged with inhaled aeroallergen. The mechanism of periostin's effect as a brake on allergen-induced responses may involve augmentation of TGF-β-induced T regulatory cell differentiation.