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Bone remodeling is a complex process that must be precisely controlled to maintain a healthy life. We show here that filamin-binding LIM protein 1 (FBLP-1, also known as migfilin), a kindlin- and filamin-binding focal adhesion protein, is essential for proper control of bone remodeling. Genetic inactivation of FBLIM1 (the gene encoding FBLP-1) in mice resulted in a severe osteopenic phenotype. Primary FBLP-1 null bone marrow stromal cells (BMSCs) exhibited significantly reduced extracellular matrix adhesion and migration compared with wild type BMSCs. Loss of FBLP-1 significantly impaired the growth and survival of BMSCs in vitro and decreased the number of osteoblast (OB) progenitors in bone marrow and OB differentiation in vivo. Furthermore, the loss of FBLP-1 caused a dramatic increase of osteoclast (OCL) differentiation in vivo. The level of receptor activator of nuclear factor κB ligand (RANKL), a key regulator of OCL differentiation, was markedly increased in FBLP-1 null BMSCs. The capacity of FBLP-1 null bone marrow monocytes (BMMs) to differentiate into multinucleated OCLs in response to exogenously supplied RANKL, however, was not different from that of WT BMMs. Finally, we show that a loss of FBLP-1 promotes activating phosphorylation of ERK1/2. Inhibition of ERK1/2 activation substantially suppressed the increase of RANKL induced by the loss of FBLP-1. Our results identify FBLP-1 as a key regulator of bone homeostasis and suggest that FBLP-1 functions in this process through modulating both the intrinsic properties of OB/BMSCs (i.e., BMSC-extracellular matrix adhesion and migration, cell growth, survival, and differentiation) and the communication between OB/BMSCs and BMMs (i.e., RANKL expression) that controls osteoclastogenesis.

Activating transcription factor 4 (ATF4) is a critical transcription factor for osteoblast (OBL) function and bone formation; however, a direct role in osteoclasts (OCLs) has not been established. Here, we targeted expression of ATF4 to the OCL lineage using the Trap promoter or through deletion of Atf4 in mice. OCL differentiation was drastically decreased in Atf4-/- bone marrow monocyte (BMM) cultures and bones. Coculture of Atf4-/- BMMs with WT OBLs or a high concentration of RANKL failed to restore the OCL differentiation defect. Conversely, Trap-Atf4-tg mice displayed severe osteopenia with dramatically increased osteoclastogenesis and bone resorption. We further showed that ATF4 was an upstream activator of the critical transcription factor Nfatc1 and was critical for RANKL activation of multiple MAPK pathways in OCL progenitors. Furthermore, ATF4 was crucial for M-CSF induction of RANK expression on BMMs, and lack of ATF4 caused a shift in OCL precursors to macrophages. Finally, ATF4 was largely modulated by M-CSF signaling and the PI3K/AKT pathways in BMMs. These results demonstrate that ATF4 plays a direct role in regulating OCL differentiation and suggest that it may be a therapeutic target for treating bone diseases associated with increased OCL activity.

Gene delivery into MSCs (mesenchymal stem cells) has great promise for gene therapy, and lentiviral transduction has recently been shown to be a highly efficient method for gene delivery. Our previous studies indicated that the umbilical cord is a new source of MSCs; however, it was unclear whether the UC-MSCs (umbilical-cord-derived MSCs) would retain their characteristics after LV (lentivirus)-mediated gene transduction. The aim of the present study is to investigate the feasibility of transducing UC-MSCs with lentiviral vectors and to determine whether these transduced stem cells would retain their ability to differentiate into different lineages. Herein, we demonstrate that the percentage of EGFP (enhanced green fluorescent protein)-positive cells increased with the MOI (multiplicity of infection) and the number of transduction cycles. In addition, we observed that the transduced MSCs were capable of differentiating into adipogenic and osteogenic lineages expressing lineage-specific genes while maintaining high EGFP expression levels. In their undifferentiated state, the UC-MSCs continued to express both the transgene [EGFP or TNF (tumour necrosis factor)-Tumstatin] and stem cell markers such as Oct-4, Nanog, BMI-1 and nucleostemin. The presence of exogenous antitumour molecule-coding gene integration was verified by PCR and RT-PCR (reverse transcription-PCR) and also by immunohistochemistry. It was also shown that TNF-Tumstatin that can be secreted by MSCs has a cytotoxic effect on prostate cancer cells in vitro. These findings suggest that lentiviral transduction may be used to deliver therapeutic genes to human UC-MSCs and this may have a wide range of applications in gene therapy.

In the present study, we investigated the therapeutic potential of mesenchymal stem cells (MSCs) in a rat acute renal failure (ARF) model and explored the possible in vivo and in vitro mechanisms of action. Rat and human MSCs were isolated from bone marrow. After being co-cultured with injured kidney tissues in trans-well dishes in vitro, the rat MSCs became rounded renal tubular epithelial-like cells, and highly expressed renal markers such as cytokeratin 18 (CK18) and aquaporin-1 (AQP1). Human MSCs were infused into rats with ARF, and techniques of microscopy, histology, PCR, RT-PCR and fluorescence in situ hybridization were used to characterize the MSCs after transplantation. We found that there were more exogenous human MSCs localized to injured kidney tissues. The kidney recovery rate in the transplanted MSC group was higher than in the control group. Genes associated with human renal tubular epithelial cells such as AQP1 and parathyroid hormone receptor 1 were detected. These findings suggest that the injured kidney tissue induced rat and human MSCs to differentiate into renal tubular epithelial-like cells in vitro and in vivo, and exogenous human MSCs can home specifically to injured regions and efficiently cure rat ARF. These results demonstrate that cell therapy has potential as a novel intervention in ARF.

Abstract: Mesenchymal stem cells (MSCs) have been identified in and isolated from numerous human tissues. The characteristics of mesenchymal stem cells, including their plasticity, the secretion of cytokines, and their low immunogenicity, contribute to their therapeutic potential. It has recently been reported that MSCs are also involved in tumorigenesis and its prognosis. Here, we present the first report of MSC-like cells isolated from human gastric cancer tissues. In our study, gastric cancer-derived MSC-like cells (hGC-MSCs) were isolated from 13 out of 20 cancer tissue samples. Their characteristics, including their morphology, surface antigens, specific gene expression, and differentiation potential, were similar to those of MSCs derived from human bone marrow (hBM-MSCs) but different from gastric cancer cells. The existence of MSC-like cells in gastric cancer tissues suggests that they may be potential targets for cancer therapy and provides an experimental foundation for investigating their role in the initiation and progression of gastric cancers. [Copyright &y& Elsevier]

Activating transcription factor 4 (ATF4) is a critical transcription factor for osteoblast (OBL) function and bone formation; however, a direct role in osteoclasts (OCLs) has not been established. Here, we targeted expression of ATF4 to the OCL lineage using the Trap promoter or through deletion of Atf4 in mice. OCL differentiation was drastically decreased in Atf4-/- bone marrow monocyte (BMM) cultures and bones. Coculture of Atf4-/- BMMs with WT OBLs or a high concentration of RANKL failed to restore the OCL differentiation defect. Conversely, Trap-Atf4-tg mice displayed severe osteopenia with dramatically increased osteoclastogenesis and bone resorption. We further showed that ATF4 was an upstream activator of the critical transcription factor Nfatc1 and was critical for RANKL activation of multiple MAPK pathways in OCL progenitors. Furthermore, ATF4 was crucial for M-CSF induction of RANK expression on BMMs, and lack of ATF4 caused a shift in OCL precursors to macrophages. Finally, ATF4 was largely modulated by M-CSF signaling and the PI3K/AKT pathways in BMMs. These results demonstrate that ATF4 plays a direct role in regulating OCL differentiation and suggest that it may be a therapeutic target for treating bone diseases associated with increased OCL activity. [ABSTRACT FROM AUTHOR]