Characterization of the 5'-flanking region of the rat AJ18 gene

Gene Expression Profiling of Muscle Stem Cells Identifies Novel Regulators of Postnatal Myogenesis

Skeletal muscle growth and regeneration require a population of muscle stem cells, the satellite cells, located in close contact to the myofiber. These cells are specified during fetal and early postnatal development in mice from a Pax3/7 population of embryonic progenitor cells. As little is known about the genetic control of their formation and maintenance, we performed a genome-wide chronological expression profile identifying the dynamic transcriptomic changes involved in establishment of muscle stem cells through life, and acquisition of muscle stem cell properties. We have identified multiple genes and pathways associated with satellite cell formation, including set of genes specifically induced (EphA1, EphA2, EfnA1, EphB1, Zbtb4, Zbtb20) or inhibited (EphA3, EphA4, EphA7, EfnA2, EfnA3, EfnA4, EfnA5, EphB2, EphB3, EphB4, EfnBs, Zfp354c, Zcchc5, Hmga2) in adult stem cells. Ephrin receptors and ephrins ligands have been implicated in cell migration and guidance in many tissues including skeletal muscle. Here we show that Ephrin receptors and ephrins ligands are also involved in regulating the adult myogenic program. Strikingly, impairment of EPHB1 function in satellite cells leads to increased differentiation at the expense of self-renewal in isolated myofiber cultures. In addition, we identified new transcription factors, including several zinc finger proteins. ZFP354C and ZCCHC5 decreased self-renewal capacity when overexpressed, whereas ZBTB4 increased it, and ZBTB20 induced myogenic progression. The architectural and transcriptional regulator HMGA2 was involved in satellite cell activation. Together, our study shows that transcriptome profiling coupled with myofiber culture analysis, provides an efficient system to identify and validate candidate genes implicated in establishment/maintenance of muscle stem cells. Furthermore, tour de force transcriptomic profiling provides a wealth of data to inform for future stem cell-based muscle therapies.

Prediction of osteoporosis candidate genes by computational disease-gene identification strategy

Osteoporosis is a complex disease with a strong genetic component. To date, more than 20 genome-wide linkage scans across multiple populations have been launched to hunt for osteoporosis susceptibility genes. Some significant or suggestive chromosomal regions of linkage to bone mineral density have been identified and replicated in genome-wide linkage screens. However, identification of key candidate genes within these confirmed regions is challenging. We used five freely available bioinformatics tools (Prioritizer, GeneSeeker, PROSPECTR and SUSPECTS, Disease Gene Prediction, and Endeavor) to analyze the 13 well-replicated osteoporosis susceptibility loci: 1p36, 1q21-25, 2p22-24, 3p14-25, 4q25-34, 6p21, 7p14-21, 11q14-25, 12q23-24, 13q14-34, 20p12, 2q24-32, and 5q12-21. Pathways and regulatory network analyses were performed using the Ingenuity Pathways Analysis (IPA) software. We identified a subset of most likely candidate osteoporosis susceptibility genes that are largely involved in transforming growth factor (TGF)-beta signaling, granulocyte-macrophage colony-stimulating factor (GM-CSF) signaling, axonal guidance signaling, peroxisome proliferator-activated receptor (PPAR) signaling, and Wnt/beta-catenin signaling pathway. Six nonoverlapping networks were generated by IPA 5.0 from 88 out of the 91 candidate genes. The list of most likely candidate genes and the associated pathway identified will assist researchers in prioritizing candidate disease genes for further empirical analysis and understanding the pathogenesis of osteoporosis.

The effect of retinoic acid on a zinc finger transcription factor, AJ18, during differentiation of a rat clonal preosteoblastic cell line, ROB-C20, into osteoblasts

OBJECTIVE

A zinc finger type transcription factor, AJ18, is thought to be a negative regulator of osteoblast differentiation, but its expression mechanism is not fully understood. Retinoic acid (RA) is a metabolite of vitamin A and involves the proliferation and differentiation in a variety of cells. To verify the effect of RA on osteoblast differentiation, AJ18 expression level was examined using a rat clonal preosteoblastic cell line, ROB-C20 (C20).

DESIGN

Confluent C20 cells were treated with or without RA (10(-6)M) for several days. Northern, real time RT-PCR and Western blotting analyses were performed to examine AJ18 expression pattern in gene and protein levels. To identify the active promoter sequence of AJ18 gene, luciferase assay was designed. Furthermore, the effect of overexpressed AJ18 in C20 cells on alkaline phosphatase (ALP) mRNA expression and its activity was compared with that of RA-treated cells.

RESULTS

RA increased the expression of AJ18 mRNA from 2 to 13 days as well as its protein production. However, no significant changes of Runx2 mRNA expression and undetectable osterix mRNA expression were observed in C20 cells treated with or without RA. Luciferase assay showed increases in promoter activities in some constructs of 5'-flanking region of AJ18 gene in RA-treated C20 cells. On the other hand, RA decreases enzymatic activity and mRNA expression level of ALP, but mRNA expression levels of bone sialoprotein and osteocalcin were not altered. Interestingly, reduced ALP activity and its mRNA expression level were detected in exogenous AJ18-overexpressing C20 cells.

CONCLUSIONS

This study supports the hypothesis that RA may restrict to the differentiation of C20 cells into mature osteoblasts via inductive AJ18 expression with activation of multiple signal pathways.

Low-intensity pulsed ultrasound stimulates osteogenic differentiation in ROS 17/2.8 cells

There have been no studies investigating the effects of the mechanical stimulation provided by Low-intensity pulsed ultrasound (LIPUS) treatment on periodontal disease accompanying bone loss. LIPUS is known to accelerate mineralization and bone regeneration, but the precise cellular mechanism is unclear. Here, we investigated the effect of LIPUS on osteogenesis by examining the effect of LIPUS stimulation on cell proliferation, alkaline phosphatase (ALPase) activity, osteogenesis-related gene expression, and mineralized nodule formation in a rat osteosarcoma cell line. The cells were cultured in medium with or without the addition of LIPUS stimulation. The ultrasound signal consisted of 1.5 MHz at an intensity of 30 mW/cm(2) for 20 min for all cultures. LIPUS stimulation did not affect the rate of cell proliferation. ALPase activity was increased at day 7 of culture after LIPUS stimulation. Real-time PCR analysis indicated that LIPUS significantly increased the expression of mRNA for the transcription factors Runx2, Msx2, Dlx5, and Osterix and for bone sialoprotein, whereas the mRNA expression of AJ18 was significantly reduced. The mineralized nodule formation and the calcium content in mineralized nodules were markedly increased on day 14 of culture after LIPUS stimulation. Our study demonstrates that LIPUS stimulation directly affects osteogenic cells, leading to mineralized nodule formation. In view of the widespread use of LIPUS for the clinical therapy of periodontal disease, it is likely that LIPUS has an important influence on key functional activities of osteoblasts in alveolar bone.

Autoregulatory mechanism of Runx2 through the expression of transcription factors and bone matrix proteins in multipotential mesenchymal cell line, ROB-C26

Runx2 is essential for osteoblast differentiation and gene expression of bone matrix proteins, however, little is known about the mechanism regulating its activity. In this study, the role of Runx2 on gene expression of transcription factors, AJ18, Msx2, and Dlx5, was examined in vitro. It is known that AJ18 and Msx2 act as repressors to inhibit activity of Runx2, whereas Dlx5 promotes its activity. An expression vector inserted Runx2 cDNA was transiently overexpressed in a rat multipotential mesenchymal cell line, ROB-C26 (C26). Real time reverse transcription-PCR analysis showed that, in exogenous Runx2-overexpressing C26 cells (C26-Rx), AJ18 expression increased 1.8-fold, Msx2 expression increased 3.0-fold, and Dlx5 expression increased 2.7-fold compared to the cells transfected with vector alone (C26-Co). Luciferase assay also showed that, in C26-Rx, AJ18 promoter activity increased 2.1-fold compared to C26-Co. Furthermore, gene expression of alkaline phosphatase (ALP) and bone matrix proteins including type I collagen (Col1), osteocalcin (OC), osteopontin (OPN), and matrix Gla protein (MGP) was examined. In C26-Rx, MGP expression increased 1.8-fold, and OPN expression increased 1.4-fold compared to C26-Co. However, no significant difference in Col1, ALP, and OC expressions was detected between C26-Rx and C26-Co. These results suggest that the existence of autoregulatory feed back loops, which inhibit Runx2 activity through the interaction of AJ18, Dlx5, and Msx2 cooperating with that of MGP and OPN, interferes with the differentiation of C26 cells toward mature osteoblasts.

The effect of IL-1α on the expression of matrix metalloproteinases, plasminogen activators, and their inhibitors in osteoblastic ROS 17/2.8 cells

Interleukin-1 (IL-1) plays key roles in altering bone matrix turnover. This turnover is regulated by matrix metalloproteinases (MMPs), tissue inhibitor of matrix metalloproteinases (TIMPs), and the plasminogen activation system, including tissue-type plasminogen activator (tPA), urokinase-type plasminogen activator (uPA) , and plasminogen activator inhibitor type-1 (PAI-1). In this study, we examined the effect of IL-1alpha on the expression of the MMPs, TIMPs, tPA, uPA, and PAI-1 genes in osteoblasts derived from the rat osteosarcoma cell line ROS 17/2.8. The cells were cultured in alpha-minimum essential medium containing 10% fetal bovine serum with 0 or 100 U/ml of IL-1alpha for up to 14 days. The levels of MMPs, TIMPs, uPA, tPA, and PAI-1 expression were estimated by determining the mRNA levels using real-time RT-PCR and by determining protein levels using ELISA. In IL-1alpha cultures, the expression levels of MMP-1, -2, -3, -13, and -14 exceeded that of the control through day 14 of culture, and the expression of MMPs increased markedly from the proliferative to the later stages of culture. The TIMP-1, -2, and -3 expression levels increased from the initial to the proliferative stages of culture. The expression of tPA increased greatly during the proliferative stage of culture, and uPA expression increased throughout the culture period, increasing markedly from the proliferative to the later stages of culture. In contrast, PAI-1 expression decreased in the presence of IL-1alpha through day 14. These results suggest that IL-1alpha stimulate bone matrix turnover by increasing MMPs, tPA, and uPA production and decreasing PAI-1 production by osteoblasts, and incline the turnover to the resolution.

Identification of the DNA binding element of the human ZNF333 protein

ZNF 333 is a new and sole gene containing two KRAB domains which has been identified currently. It is a member of subfamilies of zinc finger gene complex which had been localized on chromosome 19p13.1. The ZNF333 gene mainly encodes a 75.5 kDa protein which contains 10 zinc finger domains. Using the methods of random oligonucleotide selection assay, electromobility gel shift assay and luciferase activity assay, we found that ZNF333 recognized the specific DNA core binding sequence ATAAT. Moreover, these data indicated that the KRAB domain of ZNF333 really has the ability of transcriptional repression.

Zinc finger transcription factors in skeletal development

Cellular and molecular processes that regulate the development of skeletal tissues resemble those required for regeneration. Given the prevalence of degenerative skeletal disorders in an increasingly aging population, the molecular mechanisms of skeletal development must be understood in detail if novel strategies are to be developed in regenerative medicine. Research in this area over the past decade has revealed that cell differentiation is largely controlled at the level of gene transcription, which in turn is regulated by transcription factors. Transcription factors usually recognize and bind to specific DNA sequences in the promoter of target genes via characteristic DNA-binding domains. Although the gene family containing C2H2 zinc fingers as DNA-binding motifs is the largest family of transciptional regulators, with several hundred individual members in mammals, only a small but increasing number of zinc finger genes have been implicated in bone, cartilage, or tooth development. These zinc finger proteins (ZFPs) contain multiple structural motifs that require zinc to maintain their structural integrity and function. Interestingly, zinc deficiency is known to result in skeletal growth retardation and has been identified as a risk factor in the pathogenesis of osteoporosis. This review attempts to summarize our current state of knowledge regarding the role of ZFPs in the molecular regulation of skeletogenesis.