Profilin Expression Is Regulated by Bone Morphogenetic Protein (BMP) in Osteoblastic Cells

PFN1 Gene Polymorphisms and the Bone Mineral Density Response to Alendronate Therapy in Postmenopausal Chinese Women with Low Bone Mass

Purpose

Alendronate is a widely used anti-osteoporotic drug. PFN1 gene is a newly identified early-onset Paget’s disease pathogenic gene. The purpose of this study is to study whether the genetic variations in this gene affect the clinical efficacy of alendronate in postmenopausal Chinese women with low bone mass.

Patients and Methods

Seven single nucleotide polymorphisms in PFN1 gene were genotyped. A total of 500 postmenopausal women with osteoporosis or osteopenia were included. All participants were treated with weekly alendronate 70 mg for 12 months. A total of 466 subjects completed the follow-up. Bone mineral density (BMD) of lumbar spine, femoral neck and total hip were measured at baseline and after treatment.

Results

After 12 months of treatment, the BMD of lumbar spine, femoral neck and total hip all increased significantly (all P < 0.001), with an average increase of 4.72 ± 5.31%, 2.08 ± 4.45%, and 2.42 ± 3.46%, respectively. At baseline, there were no significant differences in BMD at lumbar spine, femoral neck and total hip between different genotype groups (P > 0.05). We failed to identify any significant association between the genotypes or haplotypes of PFN1 and the BMD response to alendronate therapy.

Conclusion

Genetic polymorphisms of PFN1 may not be a major contributor to the therapeutic response to alendronate treatment in Chinese women with low bone mass.

Metastatic Prostate Cancer Cells Secrete Methylglyoxal-Derived MG-H1 to Reprogram Human Osteoblasts into a Dedifferentiated, Malignant-like Phenotype: A Possible Novel Player in Prostate Cancer Bone Metastases

Bone metastases from prostate cancer (PCa) result from a complex cross-talk between PCa cells and osteoblasts (OB). Thus, targeting this interplay has become an attractive strategy to interfere with PCa bone dissemination. The agents currently used in clinical trials have proved ineffective, boosting research to identify additional mechanisms that may be involved in this two-directional talk. Here, we investigated whether and how 5-hydro-5-methylimidazolone (MG-H1), a specific methylglyoxal (MG)-derived advanced glycation end product (AGE), was a novel player in the dialogue between PCa and OB to drive PCa bone metastases. Conditioned medium from osteotropic PC3 PCa cells, pre-treated or not with a specific MG scavenger, was administrated to human primary OB and cell morphology, mesenchymal trans-differentiation, pro-osteogenic determinants, PCa-specific molecules, and migration/invasion were studied by phase-contrast microscopy, real-time PCR, western blot and specific assays, respectively. We found that PC3 cells were able to release MG-H1 that, by binding to the receptor for AGEs (RAGE) on OB, reprogrammed them into a less-differentiate phenotype, endowed with some PCa-specific molecular features and malignant properties, in a mechanism involving reactive oxidative species (ROS) production and NF-kB pathway activation. These findings provide novel insights into the mechanisms of PCa osteoblastic metastases and foster in vivo research toward new therapeutic strategies interfering with PCa/OB cross-talk.

Profilin: many facets of a small protein

Profilin is a ubiquitously expressed protein well known as a key regulator of actin polymerisation. The actin cytoskeleton is involved in almost all cellular processes including motility, endocytosis, metabolism, signal transduction and gene transcription. Hence, profilin's role in the cell goes beyond its direct and essential function in regulating actin dynamics. This review will focus on the interactions of Profilin 1 and its ligands at the plasma membrane, in the cytoplasm and the nucleus of the cells and the regulation of profilin activity within those cell compartments. We will discuss the interactions of profilin in cell signalling pathways and highlight the importance of the cell context in the multiple functions that this small essential protein has in conjunction with its role in cytoskeletal organisation and dynamics. We will review some of the mechanisms that control profilin expression and the implications of changed expression of profilin in the light of cancer biology and other pathologies.

Comparative proteomics analysis of microvesicles in human serum for the evaluation of osteoporosis

Osteoporosis is an emerging health issue worldwide. Due to the decrease of bone mineral density and the deterioration of skeletal microarchitecture, osteoporosis could lead to increased bone fragility and higher fracture risk. Since lack of specific symptoms, novel serum proteomic indicators are urgently needed for the evaluation of osteoporosis. Microvesicles (MVs) are important messengers widely present in body fluids and have emerged as novel targets for the diagnosis of multiple diseases. In this study, MVs were successfully isolated from human serum and comprehensively characterized. Comparative proteomics analysis revealed differential MVs protein profiling in normal subjects, osteopenia patients, and osteoporosis patients. In total, about 200 proteins were identified and quantified from serum MVs, among which 19 proteins were upregulated (fold change >2) and five proteins were downregulated (fold change <0.5) in osteopenia group and osteoporosis group when compared with the normal group. Three protein candidates were selected for initial verification, including Vinculin, Filamin A, and Profilin 1. Profilin 1 was further pre-validated in an independent sample set, which could differentiate osteoporosis group from osteopenia group and normal group (p < 0.05). Our data collectively demonstrate that serum MVs proteome can be valuable indicators for the evaluation and diagnostics of bone loss disease.

A Drosophila model of ALS reveals a partial loss of function of causative human PFN1 mutants

Mutations in the profilin 1 (PFN1) gene are causative for familial amyotrophic lateral sclerosis (fALS). However, it is still not fully understood how these mutations lead to neurodegeneration. To address this question, we generated a novel Drosophila model expressing human wild-type and ALS-causative PFN1 mutants. We show that at larval neuromuscular junctions (NMJ), motor neuron expression of wild-type human PFN1 increases the number of ghost boutons, active zone density, F-actin content, and the formation of filopodia. In contrast, the expression of ALS-causative human PFN1 mutants causes a less pronounced phenotype, suggesting a loss of function of these mutants in promoting NMJ remodeling. Importantly, expression of human PFN1 in motor neurons results in progressive locomotion defects and shorter lifespan in adult flies, while ALS-causative PFN1 mutants display a less toxic effect. In summary, our study provides evidence that PFN1 is important in regulating NMJ morphology and influences survival and locomotion in Drosophila. Furthermore, our results suggest ALS-causative human PFN1 mutants display a partial loss of function relative to wild-type hPFN1 that may contribute to human disease pathogenesis.

Osteogenic commitment and differentiation of human mesenchymal stem cells by low-intensity pulsed ultrasound stimulation

Low-intensity pulsed ultrasound (LIPUS) as an adjuvant therapy in in vitro and in vivo bone engineering has proven to be extremely useful. The present study aimed at investigating the effect of 30 mW/cm² LIPUS stimulation on commercially available human mesenchymal stem cells (hMSCs) cultured in basal or osteogenic medium at different experimental time points (7, 14, 21 days). The hypothesis was that LIPUS would improve the osteogenic differentiation of hMSC and guarantying the maintenance of osteogenic committed fraction, as demonstrated by cell vitality and proteomic analysis. LIPUS stimulation (a) regulated the balance between osteoblast commitment and differentiation by specific networks (activations of RhoA/ROCK signaling and upregulation of Ribosome constituent/Protein metabolic process, Glycolysis/Gluconeogenesis, RNA metabolic process/Splicing and Tubulins); (b) allowed the maintenance of a few percentage of osteoblast precursors (21 days CD73+/CD90+: 6%; OCT-3/4+/NANOG+/SOX2+: 10%); (c) induced the activation of osteogenic specific pathways shown by gene expression (early: ALPL, COL1A1, late: RUNX2, BGLAP, MAPK1/6) and related protein release (COL1a1, OPN, OC), in particular in the presence of osteogenic soluble factors able to mimic bone microenvironment. To summarize, LIPUS might be able to improve the osteogenic commitment of hMSCs in vitro, and, at the same time, enhance their osteogenic differentiation.

Profilin1 is expressed in osteocytes and regulates cell shape and migration

Osteocytes are the most abundant cells in bone and regulate bone metabolism in coordination with osteoblasts and osteoclasts. However, the molecules that control osteocytes are still incompletely understood. Profilin1 is an actin-binding protein that is involved in actin polymerization. Osteocytes possess characteristic dendritic process formed based on actin cytoskeleton. Here, we examined the expression of profilin1 and its function in osteocytes. Profilin1 mRNA was expressed in osteocytic MLO-Y4 cells and its levels were gradually increased along with the time in culture. With regard to functional aspect, knockdown of profilin1 by siRNA enhanced BMP-induced increase in alkaline phosphatase expression levels in MLO-Y4 cells. Profilin1 knockdown suppressed the levels of dendritic processes and migration of MLO-Y4 cells. Since aging causes an increase in ROS in the body, we further examined the effects of hydrogen peroxide on the expression of profilin1. Hydrogen peroxide treatment increased the levels of profilin1 mRNA in MLO-Y4 cells in contrast to the decline in alkaline phosphatase. Profilin1 was expressed not only in MLO-Y4cells but also in the primary cultures of osteocytes. Importantly, profilin1 mRNA levels in primary cultures of osteocytes were higher than those in primary cultures of osteoblasts. To examine in vivo role of profilin1 in osteocytes, profilin1 was conditionally knocked out by using DMP1-cre and profilin1 floxed mice. This conditional deletion of profilin1 specifically in osteocytes resulted in reduction in the levels of bone volume and bone mineral density. These data indicate that profilin1 is expressed in osteocytes and regulates cell shape, migration and bone mass.

Role of Periostin in Adhesion and Migration of Bone Remodeling Cells

Periostin is an extracellular matrix protein highly expressed in collagen-rich tissues subjected to continuous mechanical stress. Functionally, periostin is involved in tissue remodeling and its altered function is associated to numerous pathological processes. In orthodontics, periostin plays key roles in the maintenance of dental tissues and it is mainly expressed in those areas where tension or pressing forces are taking place. In this regard, high expression of periostin is essential to promote migration and proliferation of periodontal ligament fibroblasts. However little is known about the participation of periostin in migration and adhesion processes of bone remodeling cells. In this work we employ the mouse pre-osteoblastic MC3T3-E1 and the macrophage-like RAW 264.7 cell lines to overexpress periostin and perform different cell-based assays to study changes in cell behavior. Our data indicate that periostin overexpression not only increases adhesion capacity of MC3T3-E1 cells to different matrix proteins but also hampers their migratory capacity. Changes on RNA expression profile of MC3T3-E1 cells upon periostin overexpression have been also analyzed, highlighting the alteration of genes implicated in processes such as cell migration, adhesion or bone metabolism but not in bone differentiation. Overall, our work provides new evidence on the impact of periostin in osteoblasts physiology.