The Wnt/β-catenin signaling pathway has emerged as a key regulator in bone development and bone homeostasis. Loss-of-function mutations in the Wnt co-receptor LRP5 result in osteoporosis and "activating" mutations in LRP5 result in high bone mass. Dickkopf-1 (DKK1) is a secreted Wnt inhibitor that binds LRP5 and LRP6 during embryonic development, therefore it is expected that a decrease in DKK1 will result in an increase in Wnt activity and a high bone mass phenotype. Dkk1 −/− knockout mice are embryonic lethal, but mice with hypomorphic Dkk1 d (doubleridge) alleles that express low amounts of Dkk1 are viable. In this study we generated an allelic series by crossing Dkk1 +/− and Dkk1 +/d mice resulting in the following genotypes with decreasing Dkk1 expression levels: +/+, +/d, +/− and d/−. Using μCT imaging we scanned dissected left femora and calvariae from eight week old mice (n=60). We analyzed the distal femur to represent trabecular bone and the femur diaphysis for cortical endochondral bone. A region of the parietal bones was used to analyze intramembranous bone of the calvaria. We found that trabecular bone volume is increased in Dkk1 mutant mice in a manner that is inversely proportional to the level of Dkk1 expression. Trabeculae number and thickness were significantly higher in the low Dkk1 expressing genotypes from both female and male mice. Similar results were found in cortical bone with an increase in cortical thickness and cross sectional area of the femur diaphysis that correlated with lower Dkk1 expression. No consistent differences were found in the calvaria measurements. Our results indicate that the progressive Dkk1 reduction increases trabecular and cortical bone mass and that even a 25% reduction in Dkk1 expression could produce significant increases in trabecular bone volume fraction. Thus DKK1 is a negative regulator of normal bone homeostasis in vivo. Our study suggests that manipulation of DKK1 function or expression may have therapeutic significance for the treatment of low bone mass disorders.

Pericytes are essential to vascularization, but the purification and characterization of pericytes remain unclear. Smooth muscle actin alpha (alpha-SMA) is one marker [corrected] of pericytes. The aim of this study is to purify the alpha-SMA positive cells from bone marrow and study the characteristics of these cells and the interaction between alpha-SMA positive cells and endothelial cells. The bone marrow stromal cells were harvested from alpha-SMA-GFP transgenic mice, and the alpha-SMA-GFP positive cells were sorted by FACS. The proliferative characteristics and multilineage differentiation ability of the alpha-SMA-GFP positive cells were tested. A 3-D culture model was then applied to test their vascularization by loading alpha-SMA-GFP positive cells and endothelial cells on collagen-fibronectin gel. Results demonstrated that bone marrow stromal cells are mostly alpha-SMA-GFP positive cells which are pluripotent, and these cells expressed alpha-SMA during differentiation. The alpha-SMA-GFP positive cells could stimulate the endothelial cells to form tube-like structures and subsequently robust vascular networks in 3-D culture. In conclusion, the bone marrow derived pluripotent cells include [corrected] pericytes and can contribute to vascularization.

Stem cell factor (SCF) is the pleiotropic ligand for the tyrosine kinase receptor, c-kit. Ligand and receptor are usually expressed in different cell types, and binding of SCF to c-kit promotes cell proliferation, differentiation, and recruitment of progenitor cells in various biologic systems. However, the localization of these two molecules in cells of the oral cavity has not been systematically examined. We investigated the expression of SCF and c-kit in human dental pulp (HDP) cells as well as in human gingival fibroblasts (HGF). Both alternatively spliced isoforms of SCF were detected (through reverse transcription-polymerase chain reaction) in RNA obtained from the two cell types. Western analysis established that both cell types express SCF and/or c-kit, whereas flow cytometry demonstrated distinct cell populations expressing only the ligand (SCF), only the receptor (c-kit), or co-expressing the two. HDP cultures showed higher soluble SCF (sSCF) production associated with faster cell growth, as compared with HGF cultures. In both cell types, however, sSCF levels appeared to increase as a result of in vitro aging and/or differentiation.

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Spermatogenesis is a series of complex events involving a delicate balance between cell proliferation and cell differentiation. Aggregation of chromatins and epigenetic modifications play a vital role in spermatogenesis via regulation of molecular pathways to maintain testicular homeostasis. These epigenetic mechanisms consist of histone modification, chromatin remodelling, DNA methylation and miRNA, etc., which reportedly are critical players in spermatogenesis. One such mechanism involves regulation of oxidative stress in the male reproductive system. The fact that testicular cells contain plenty of unsaturated fatty acids and undergo division at a high rate makes spermatogenic cells highly susceptible to oxidative insult leading to deleterious effect on spermatozoa, which may culminate in infertility in men. Although the correlation between ROS‐mediated oxidative stress and epigenetic alterations has been indicated, research in this regard is still in infancy. Further, the fact that environmental and life style factors are critical determinants of spermatogenic potential indicates the importance of epigenetic regulation of key molecular events in spermatogenesis. Therefore, the current review aims to discuss the ROS‐induced epigenetic deregulation of the molecular mechanism(s) involved in spermatogenesis.

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