In vitro osteoblast differentiation is negatively regulated by Hoxc8

miR-301a inhibits adipogenic differentiation of adipose-derived stromal vascular fractions by targeting HOXC8 in sheep

MicroRNAs (miRNAs) regulate adipogenic differentiation in stromal vascular fractions (SVFs) through post-transcriptional regulation of transcription factors and other functional genes. miR-301 and the homeobox C8 (HOXC8) gene are involved in lipid homeostasis; however, their roles in the adipogenic differentiation of ovine SVFs are unknown. Here, we explored the effects of miR-301 and HOXC8 on adipogenic differentiation in ovine SVFs and the regulatory role of miR-301a in HOXC8 expression. Additionally, we evaluated the effect of miR-301a and HOXC8 on the mRNA abundance of adipogenic markers and the ability of ovine SVFs to accumulate lipids. We found that miR-301a regulates adipogenic differentiation in ovine SVFs by directly targeting the 3'-untranslated region of HOXC8, resulting in significant downregulation of the HOXC8 mRNA and protein. Moreover, miR-301a overexpression suppressed adipogenic differentiation in ovine SVFs and significantly inhibited the expression of adipogenesis-related genes-including adiponectin, C/EBPα, PPARγ, and FABP4. Conversely, HOXC8 overexpression in ovine SVFs increased the accumulation of lipid droplets and remarkably promoted the expression of adipogenic markers. Taken together, our results indicate that miR-301a attenuates the adipogenic differentiation of ovine SVFs by targeting HOXC8. These findings improve our understanding of the mechanism of lipid accumulation and metabolism in sheep.

T-Box20 inhibits osteogenic differentiation in adipose-derived human mesenchymal stem cells: the role of T-Box20 on osteogenesis

Background

Skeletal development and its cellular function are regulated by various transcription factors. The T-box (Tbx) family of transcription factors have critical roles in cellular differentiation as well as heart and limbs organogenesis. These factors possess activator and/or repressor domains to modify the expression of target genes. Despite the obvious effects of Tbx20 on heart development, its impact on bone development is still unknown.

Methods

To investigate the consequence by forced Tbx20 expression in the osteogenic differentiation of human mesenchymal stem cells derived from adipose tissue (Ad-MSCs), these cells were transduced with a bicistronic lentiviral vector encoding Tbx20 and an enhanced green fluorescent protein.

Results

Tbx20 gene delivery system suppressed the osteogenic differentiation of Ad-MSCs, as indicated by reduction in alkaline phosphatase activity and Alizarin Red S staining. Consistently, reverse transcription-polymerase chain reaction analyses showed that Tbx20 gain-of-function reduced the expression levels of osteoblast marker genes in osteo-inductive Ad-MSCs cultures. Accordingly, Tbx20 negatively affected osteogenesis through modulating expression of key factors involved in this process.

Conclusion

The present study suggests that Tbx20 could inhibit osteogenic differentiation in adipose-derived human mesenchymal stem cells.

In vitro models for evaluation of periodontal wound healing/regeneration

Periodontal wound healing and regeneration are highly complex processes, involving cells, matrices, molecules and genes that must be properly choreographed and orchestrated. As we attempt to understand and influence these clinical entities, we need experimental models to mimic the various aspects of human wound healing and regeneration. In vivo animal models that simulate clinical situations of humans can be costly and cumbersome. In vitro models have been devised to dissect wound healing/regeneration processes into discrete, analyzable steps. For soft tissue (e.g. gingival) healing, in vitro models range from simple culture of cells grown in monolayers and exposed to biological modulators or physical effectors and materials, to models in which cells are 'injured' by scraping and subsequently the 'wound' is filled with new or migrating cells, to three-dimensional models of epithelial-mesenchymal recombination or tissue explants. The cells employed are gingival keratinocytes, fibroblasts or endothelial cells, and their proliferation, migration, attachment, differentiation, survival, gene expression, matrix production or capillary formation are measured. Studies of periodontal regeneration also include periodontal ligament fibroblasts or progenitors, osteoblasts or osteoprogenitors, and cementoblasts. Regeneration models measure cellular proliferation, attachment and migration, as well as gene expression, transfer and differentiation into a mineralizing phenotype and biomineralization. Only by integrating data from models on all levels (i.e. a single cell to the whole organism) can various critical aspects of periodontal wound healing/regeneration be fully evaluated.

MicroRNA variants as genetic determinants of bone mass

Single nucleotide polymorphisms (SNPs) are the most abundant genetic variants that contribute to the heritability of bone mass. MicroRNAs (miRNAs, miRs) are key post-transcriptional regulators that modulate the differentiation and function of skeletal cells by targeting multiple genes in the same or distinct signaling pathways. SNPs in miRNA genes and miRNA binding sites can alter miRNA abundance and mRNA targeting. This review describes the potential impact of miRNA-related SNPs on skeletal phenotype. Although many associations between SNPs and bone mass have been described, this review is limited to gene variants for which a function has been experimentally validated. SNPs in miRNA genes (miR-SNPs) that impair miRNA processing and alter the abundance of mature miRNA are discussed for miR-146a, miR-125a, miR-196a, miR-149 and miR-27a. SNPs in miRNA targeting sites (miR-TS-SNPs) that alter miRNA binding are described for the bone remodeling genes bone morphogenetic protein receptor 1 (Bmpr1), fibroblast growth factor 2 (Fgf2), osteonectin (Sparc) and histone deacetylase 5 (Hdac5). The review highlights two aspects of miRNA-associated SNPs: the mechanism for altering miRNA mediated gene regulation and the potential of miR-associated SNPs to alter osteoblast, osteoclast or chondrocyte differentiation and function. Given the polygenic nature of skeletal diseases like osteoporosis and osteoarthritis, validating the function of additional miRNA-associated SNPs has the potential to enhance our understanding of the genetic determinants of bone mass and predisposition to selected skeletal diseases.

A potential role of homeobox transcription factors in osteoarthritis

When a healthy joint progressively becomes osteoarthritic, the structures of the affected cartilage, bone and synovia undergo an initial phase of rearrangement. The exact molecular and cellular events occurring in this early osteoarthritic transition phase still remain elusive. Homeobox (Hox) genes encode for transcription factors that typically regulate limb morphogenesis and skeletal formation during development. More recently they were shown to be required for tissue remodelling and homeostasis in adults and to be modulated in a variety of pathologies. Here we present and discuss the hypothesis that dysregulation of specific Hox genes is associated with the onset and development of osteoarthritis (OA). Discovering mechanisms modulating Hox gene expression could not only provide important information in understanding OA pathology and its initiation, but also help to identify biomarkers reflecting the state of early OA. This knowledge would allow anticipating the time window for clinical treatment of the affected cartilage and assist in the development of innovative strategies to restore joint homeostasis, e.g., by cell or gene therapy.

Realizing the potential of gene-based molecular therapies in bone repair

A better understanding of osteogenesis at genetic and biochemical levels is yielding new molecular entities that can modulate bone regeneration and potentially act as novel therapies in a clinical setting. These new entities are motivating alternative approaches for bone repair by utilizing DNA-derived expression systems, as well as RNA-based regulatory molecules controlling the fate of cells involved in osteogenesis. These sophisticated mediators of osteogenesis, however, pose unique delivery challenges that are not obvious in deployment of conventional therapeutic agents. Viral and nonviral delivery systems are actively pursued in preclinical animal models to realize the potential of the gene-based medicines. This article will summarize promising bone-inducing molecular agents on the horizon as well as provide a critical review of delivery systems employed for their administration. Special attention was paid to synthetic (nonviral) delivery systems because they are more likely to be adopted for clinical testing because of safety considerations. We present a comparative analysis of dose-response relationships, as well as pharmacokinetic and pharmacodynamic features of various approaches, with the purpose of clearly defining the current frontier in the field. We conclude with the authors' perspective on the future of gene-based therapy of bone defects, articulating promising research avenues to advance the field of clinical bone repair.

HOXC8 inhibits androgen receptor signaling in human prostate cancer cells by inhibiting SRC-3 recruitment to direct androgen target genes

HOX (homeobox) genes encode homeodomain-containing transcription factors critical to development, differentiation, and homeostasis. Their dysregulation has been implicated in a variety of cancers. Previously, we showed that a subset of genes of the HOXC cluster is upregulated in primary prostate tumors, lymph node metastases, and malignant prostate cell lines. In the present study, we show that HOXC8 inhibits androgen receptor (AR)-mediated gene induction in LNCaP prostate cancer cells and HPr-1 AR, a nontumorigenic prostate epithelial cell line. Mechanistically, HOXC8 blocks the AR-dependent recruitment of the steroid receptor coactivators steroid receptor coactivator-3 (SRC-3), and CREB binding protein to the androgen-regulated prostate-specific antigen gene enhancer and inhibits histone acetylation of androgen-regulated genes. Inhibition of androgen induction by HOXC8 is reversed upon expression of SRC-3, a member of the SRC/p160 steroid receptor cofactor family. Coimmunoprecipitation studies show that HOXC8 expression inhibits the hormone-dependent interaction of AR and SRC-3. Finally, HOXC8 expression increases invasion in HPr-1 AR nontumorigenic cells. These data suggest a complex role for HOXC8 in prostate cancer, promoting invasiveness while inhibiting AR-mediated gene induction at androgen response element-regulated genes associated with differentiated function of the prostate. A greater understanding of HOXC8 actions in the prostate and its interactions with androgen signaling pathways may elucidate mechanisms driving the onset and progression of prostate cancer.