运动介导microRNAs调控骨代谢的研究进展

运动改善骨代谢,促进骨骼生长发育,缓解骨量流失的作用已被广泛证实。在骨代谢中,微小RNA(microRNAs,miRNAs)广泛参与骨髓间充质干细胞、成骨细胞及破骨细胞等骨组织细胞的增殖及分化,通过靶向作用于相关成骨因子或骨吸收因子调控骨形成与骨吸收之间的平衡,在骨代谢的调控中发挥重要作用。近年的研究表明,调控miRNAs是运动或机械应力促进骨代谢正平衡的途径之一,运动能够诱导骨骼中miRNAs差异表达,进而调控相关成骨因子或骨吸收因子的表达,进一步加强运动的促成骨效应。本综述总结了运动介导miRNAs调控骨代谢的相关研究进展,为骨质疏松的运动防治提供理论基础。     

淫羊藿苷治疗骨质疏松的研究进展

淫羊藿是中医常用的治疗骨质疏松的药物,其主要有效成分是多糖和黄酮类化合物具有补肾壮阳、祛风除湿、强筋健骨等功效。近年来研究表明,淫羊藿苷不仅可以促进骨髓间充质干细胞和成骨细胞的骨形成活性,而且能够抑制破骨细胞的分化成熟,具有较强的抗骨质疏松活性。本文从骨髓间充质干细胞、成骨细胞、破骨细胞及其代谢物雌激素样作用等方面综述淫羊藿苷治疗骨质疏松的研究进展,为后续研究与临床应用奠定基础。     

调控软骨形成的信号通路及相关因子在骨髓间充质干细胞骨向分化中的作用*

骨髓间充质干细胞是一类具有自我复制和多向分化潜能的成体干细胞,可以通过定向诱导分化为成骨细胞、软骨细胞、脂肪细胞等,是目前骨再生医学和细胞治疗研究最多的理想种子细胞。在骨缺损的修复过程中,骨髓间充质干细胞内成软骨相关基因表达升高进而分化为软骨细胞,后期随着成骨细胞和破骨细胞的形成及血管长入,软骨基质逐步降解并被骨基质所替换。软骨细胞参与了骨缺损前期的修复过程,调控软骨形成的信号通路及相关因子不仅调控骨髓间充质干细胞成软骨细胞分化,同时在成骨细胞分化过程中也发挥着重要的作用。对调控软骨形成的信号通路及相关因子在骨髓间充质干细胞骨向分化中的调控作用和研究现状进行了总结,以期为临床寻找更好的治疗骨缺损的方法提供理论依据和研究方向。     

miRNAs在破骨细胞中的研究进展

破骨细胞起源于造血干细胞,是体内一种负责骨吸收的骨特异性多核细胞,在骨代谢平衡的调控中起着重要作用。破骨细胞的分化形成及功能活性异常可引起一系列临床疾病,而其分化形成过程受到多种因子的调控,近年来越来越多研究聚焦于miRNAs对破骨细胞分化形成过程的调控作用。因此,本文主要对影响破骨细胞分化形成的相关miRNAs进行综述,为后续相关研究提供参考。     

Wnt 信号通路与骨髓间充质干细胞成骨之间的关系

Wnt信号通路是由Wnts诱发的一系列相互作用的分子组成。Wnt信号对骨髓间充质干细胞的影响在所有研究中均证实有明显作用,其可调节干细胞增殖、分化及凋亡。研究表明,抑制Wnt信号通路转导可使成骨细胞分化进程受阻,从而抑制骨形成;若诱导Wnt家族成员表达则可使成骨细胞特异性基因表达增加,促进骨形成。本文就Wnt信号通路的作用过程及其与骨髓间充质干细胞成骨诱导的关系做一综述。     

机械牵张力对成骨细胞及骨髓间充质干细胞的作用

牵张成骨过程与通常的骨愈合过程有明显的不同,可以将其解读为牵张和成骨两个方面.骨髓间充质干细胞在一定的条件下可以分化为成骨细胞,而成骨细胞是骨改建的主要效应细胞.作用在两骨段的牵张力促进或激发了成骨细胞和骨髓间充质干细胞的增殖和分化从而实现骨的再生.近年来,关于牵张成骨过程中骨组织的超微结构变化的研究已经相对明了,在力学机制尚未完全明确.本文综述了牵张力对成骨细胞和骨髓间充质干细胞的增殖和分化方面的影响.     

成骨细胞的分化调控

骨组织中有两类参与调控骨代谢过程的细胞,成骨细胞负责造骨,破骨细胞负责溶骨。在一些骨相关疾病(如骨质疏松、骨相关肿瘤)发病过程中,造骨和溶骨失去平衡,这种失衡与破骨细胞和成骨细胞的数量异常及功能失调都有关,所以对成骨细胞分化机制的研究也是十分必要的。目前,已经有大量的文献表明,成骨细胞分化机制复杂,受许多激素、细胞因子以及一些小分子化合物的调控和影响,如骨形态发生蛋白(BMP)、Wnts等。     

黄芩总黄酮及黄芩苷对大鼠成骨细胞及破骨细胞活性的研究

为观察黄芩总黄酮及黄芩苷对新生大鼠成骨细胞及破骨细胞活性影响,给SD大鼠灌胃给药3 d后取含药血清,分离成骨细胞及破骨细胞体外培养,MTT法检测成骨细胞活性,AKP检测成骨细胞分化程度,用骨吸收陷窝数量评价破骨细胞活性。结果表明,与对照组相比,含黄芩总黄酮及黄芩苷血清剂量依赖性地促进成骨细胞增殖;其通过促进成骨细胞的增殖和分化,抑制破骨细胞的活性,对临床骨质疏松的防治具有积极意义。     

DNA甲基化与骨代谢调节及骨质疏松症研究进展

骨质疏松症的根本病因是由于多种因素导致成骨细胞介导的骨形成与破骨细胞介导的骨吸收过程之间的负平衡,引起骨质进行性丢失,骨密度降低,骨脆性增加,进而导致骨折风险增加。越来越多的研究表明,DNA甲基化可通过调控相关基因表达调节成骨细胞/破骨细胞的分化与功能,进而影响骨形成/骨吸收平衡,介导骨质疏松症的发生、发展。现主要阐述DNA甲基化与骨代谢调节和骨质疏松症之间的关系,并对相关研究进展进行综述。     

铁过载与骨质疏松的关系

近来研究表明,铁过载与骨质疏松有密切的关系。遗传性血色素沉着症和地中海贫血症等铁代谢紊乱的疾病患者中都伴随有不同程度的骨质疏松现象。另外,长期在轨飞行环境下,航天员出现机体铁沉积现象,同时,骨丢失情况十分严重,每月的骨丢失量约与地面上绝经后妇女每年的骨丢失量相当。铁水平升高能够抑制成骨细胞的分化,降低成骨细胞功能,成骨能力下降,骨形成受到抑制。铁沉积的同时,能够促进破骨细胞活性,增强骨吸收的能力,造成机体骨量减少,导致骨质疏松。铁调素能够作用于成骨细胞,随着铁调素剂量的增加,成骨细胞中与骨形成相关的基因表达量明显升高。铁调素还能作用于破骨细胞,促进破骨细胞的分化。在预防和治疗骨质疏松方面,有实验证明,铁螯合剂和铁调素都有治疗骨质疏松的作用。利用铁调素调节机体铁代谢平衡,降低铁过载程度,为日后临床治疗骨质疏松提供了理论支持。     

Calcineurin/NFAT signaling in osteoblasts regulates bone mass

Development and repair of the vertebrate skeleton requires the precise coordination of bone-forming osteoblasts and bone-resorbing osteoclasts. In diseases such as osteoporosis, bone resorption dominates over bone formation, suggesting a failure to harmonize osteoclast and osteoblast function. Here, we show that mice expressing a constitutively nuclear NFATc1 variant (NFATc1(nuc)) in osteoblasts develop high bone mass. NFATc1(nuc) mice have massive osteoblast overgrowth, enhanced osteoblast proliferation, and coordinated changes in the expression of Wnt signaling components. In contrast, viable NFATc1-deficient mice have defects in skull bone formation in addition to impaired osteoclast development. NFATc1(nuc) mice have increased osteoclastogenesis despite normal levels of RANKL and OPG, indicating that an additional NFAT-regulated mechanism influences osteoclastogenesis in vivo. Calcineurin/NFATc signaling in osteoblasts controls the expression of chemoattractants that attract monocytic osteoclast precursors, thereby coupling bone formation and bone resorption. Our results indicate that NFATc1 regulates bone mass by functioning in both osteoblasts and osteoclasts.     

Pseudogene PTENP1 sponges miR-214 to regulate the expression of PTEN to modulate osteoclast differentiation and attenuate osteoporosis

Background aimsOsteoporosis (OP) is a common bone metabolic disease with a high incidence. Our study aimed to explore the pseudogene PTENP1/miR-214/PTEN axis to modulate the osteoclast differentiation in osteoporosis.MethodsPatients with osteoporosis were recruited in our study, and RANKL-induced osteoclast differentiation and ovariectomy-induced osteoporosis mouse model were established in vitro and in vivo, respectively.ResultsPseudogene PTENP1 and PTEN were significantly down-regulated and miR-214 was up-regulated in osteoporosis patients. In addition, overexpression of PTENP1 or silence of miR-214 inhibited the expression levels of osteoclast specific markers and osteoclast differentiation induced by RANKL. Overexpression of PTENP1 or silence of miR-214 also inhibited the levels of phosphorylation of PI3K and AKT, p65 nuclear translocation, IκBα degradation and the expression level of NFATc1. AlsoSilence of PTENP1 or overexpression of miR-214 induced the osteoclast differentiation under normal physiological condition. Pseudogene PTENP1 sponged miR-214 to regulate the expression of PTEN.ConclusionsIn an ovariectomy-induced osteoporosis mouse model, obvious pathological changes in bone tissues were found, and bone marrow mononuclear cells in this group were more likely to differentiate into osteoclasts. Therefore, pseudogene PTENP1 sponged miR-214 to regulate the expression of PTEN to inhibit osteoclast differentiation and attenuate osteoporosis by suppressing the PI3K/AKT/NF-κB signaling pathway.     

New insights into the epigenetics of osteoporosis

Osteoporosis is characterized by reduced bone formation and accumulation of adipocytes in the bone marrow compartment. The decrease in bone mass results from an imbalance between osteoclast-mediated bone resorption and osteoblast-mediated bone formation. The deficiency of bone cells to replace the resorpted bone can be due to a preferential differentiation of bone marrow stromal cells into adipocytes at the expense of osteoblasts. Consequently, the processes that control the differentiation of osteoclasts, osteoblasts and adipocytes play a crucial role in bone metabolism. It is known that epigenetic mechanisms are critical regulator of the differentiation programs for cell fate and moreover are subject to changes during aging. Here, we summarize recent findings on the role of epigenetics in the modulation of mechanisms that may be associated with osteoporosis. In particular, we focus on disturbances in the bone remodeling process described in human studies that address the epigenetic regulation of the osteoblast/adipocyte balance.     

Retracted: Long non-coding RNA MEG3 silencing and microRNA-214 restoration elevate osteoprotegerin expression to ameliorate osteoporosis by limiting TXNIP

Studies have shown that long non-coding RNA (lncRNA) MEG3 plays a key role in osteoporosis (OP), but its regulatory mechanism is somewhat incompletely clear. Here, we intend to probe into the mechanism of MEG3 on OP development by modulating microRNA-214 (miR-214) and thioredoxin-interacting protein (TXNIP). Rat models of OP were established. MEG3, miR-214 and TXNIP mRNA expression in rat femoral tissues were detected, along with TXNIP, OPG and RANKL protein expression. BMD, BV/TV, Tb.N and Tb.Th in tissue samples were measured. Ca, P and ALP contents in rat serum were also determined. Primary osteoblasts were isolated and cultured. Viability, COL-I, COL-II and COL-Χ mRNA expression, PCNA, cyclin D1, OCN, RUNX2 and osteolix protein expresion, ALP content and activity, and mineralized nodule area of rat osteoblasts were further detected. Dual-luciferase reporter gene and RNA-pull down assays verified the targeting relationship between MEG3, miR-214 and TXNIP. MEG3 and TXNIP were up-regulated while miR-214 was down-regulated in femoral tissues of OP rats. MEG3 silencing and miR-214 overexpression increased BMD, BV/TV, Tb.N, Tb.Th, trabecular bone area, collagen area and OPG expression, and down-regulated RANKL of femoral tissues in OP rats. MEG3 silencing and miR-214 overexpression elevated Ca and P and reduced ALP in OP rat serum, elevated osteoblast viability, differentiation ability, COL-I and COL-Χ expression and ALP activity, and reduced COL-II expression of osteoblasts. MEG3 specifically bound to miR-214 to regulate TXNIP. MEG3 silencing and miR-214 overexpression promote proliferation and differentiation of osteoblasts in OP by down-regulating TXNIP, which further improves OP.     

Arbutin ameliorates glucocorticoid-induced osteoporosis through activating autophagy in osteoblasts

Chronic long-term glucocorticoid use causes osteoporosis partly by interrupting osteoblast homeostasis and exacerbating bone loss. Arbutin, a natural hydroquinone glycoside, has been reported to have biological activities related to the differentiation of osteoblasts and osteoclasts. However, the role and underlying mechanism of arbutin in glucocorticoid-induced osteoporosis are elusive. In this study, we demonstrated that arbutin administration ameliorated osteoporotic disorders in glucocorticoid dexamethasone (Dex)-induced mouse model, including attenuating the loss of bone mass and trabecular microstructure, promoting bone formation, suppressing bone resorption, and activating autophagy in bone tissues. Furthermore, Dex-stimulated mouse osteoblastic MC3T3-E1 cells were treated with arbutin. Arbutin treatment rescued Dex-induced repression of osteoblast differentiation and mineralization, the downregulation of osteogenic gene expression, reduced autophagic marker expression, and decreased autophagic puncta formation. The application of autophagy inhibitor 3-MA decreased autophagy, differentiation, and mineralization of MC3T3-E1 cells triggered by arbutin. Taken together, our findings suggest that arbutin treatment fends off glucocorticoid-induced osteoporosis, partly through promoting differentiation and mineralization of osteoblasts by autophagy activation.     

Suppression of bone formation by osteoclastic expression of semaphorin 4D

Most of the currently available drugs for osteoporosis inhibit osteoclastic bone resorption; only a few drugs promote osteoblastic bone formation. It is thus becoming increasingly necessary to identify the factors that regulate bone formation. We found that osteoclasts express semaphorin 4D (Sema4D), previously shown to be an axon guidance molecule, which potently inhibits bone formation. The binding of Sema4D to its receptor Plexin-B1 on osteoblasts resulted in the activation of the small GTPase RhoA, which inhibits bone formation by suppressing insulin-like growth factor-1 (IGF-1) signaling and by modulating osteoblast motility. Sema4d-/- mice, Plxnb1-/- mice and mice expressing a dominant-negative RhoA specifically in osteoblasts showed an osteosclerotic phenotype due to augmented bone formation. Notably, Sema4D-specific antibody treatment markedly prevented bone loss in a model of postmenopausal osteoporosis. Thus, Sema4D has emerged as a new therapeutic target for the discovery and development of bone-increasing drugs.     

Lactoferrin and bone; structure-activity relationships.

The maintenance of the mechanical integrity of the skeleton depends on bone remodeling, the well-coordinated balance between bone formation by osteoblasts and bone resorption by osteoclasts. The coupled action of osteoblasts and osteoclasts is regulated by the action of many local and circulating hormones and factors as well as central regulation by a neurological mechanism. We have previously shown that lactoferrin can promote bone growth. At physiological concentrations, lactoferrin potently stimulates the proliferation and differentiation of primary osteoblasts and acts as a survival factor. Lactoferrin also affects osteoclasts, potently inhibiting their formation. In vivo, local injection of lactoferrin results in substantial increases in bone formation and bone area. In a critical bone-defect model in vivo, lactoferrin was also seen to promote bone growth. The mitogenic effect of lactoferrin in osteoblast-like cells is mediated mainly through low-density lipoprotein-receptor protein-1 (LRP1), a member of the low-density lipoprotein-receptor-related proteins that are primarily known as endocytic receptors; however, LRP1 is not necessary for the anti-apoptotic actions of lactoferrin. Lactoferrin also induces the activation of p42/44 mitogen-activated protein kinase (MAPK) signalling and the PI3-kinase-dependent phosphorylation of Akt in osteoblasts. In this study, we examined other properties of lactoferrin and the way they affect osteogenic activity. The degree of glycosylation, iron-binding, and the structure-activity relationships indicate that lactoferrin maintains osteogenic activity in deglycosylated, holo, and apo forms, and in with various small fragments of the molecule. These data suggest that lactoferrin signals through more than 1 membrane-bound receptor to produce its anabolic skeletal effects, and that it signals through diverse pathways. We conclude that lactoferrin might have a physiological role in bone growth and healing and a potential therapeutic role as an anabolic factor in osteoporosis.     

Toddaculin,Isolated from of Toddalia asiatica (L.) Lam., Inhibited Osteoclastogenesis in RAW 264 Cells and Enhanced Osteoblastogenesis in MC3T3-E1 Cells

Osteoporosis with bone loss is widely recognized as a major health problem. Bone homeostasis is maintained by balancing bone formation and bone resorption. The imbalance caused by increased bone resorption over bone formation can lead to various bone-related diseases such as osteoporosis and rheumatoid arthritis. Osteoclasts are the principal cells responsible for bone resorption and the main targets of anti-resorptive therapies. However, excessive inhibition of osteoclast differentiation may lead to inhibition of osteoblast differentiation. Therefore, it is important to screen for new compounds capable of inhibiting bone resorption and enhancing bone formation. Toddalia asiatica (L.) Lam. has been utilized traditionally for medicinal purposes such as the treatment of rheumatism. Currently, the extract is considered to be a good source of pharmacological agents for the treatment of bone-related diseases, but the active compounds have yet to be identified. We investigated whether toddaculin, derived from Toddalia asiatica (L.) Lam., affects both processes by inhibiting bone resorption and enhancing bone formation. Towards this end, we used pre-osteoclastic RAW 264 cells and pre-osteoblastic MC3T3-E1 cells. We found that toddaculin not only inhibited the differentiation of osteoclasts via activation of the NF-κB, ERK 1/2, and p38 MAPK signaling pathways, but it also induced differentiation and mineralization of osteoblasts by regulating differentiation factors. Thus, toddaculin might be beneficial for the prevention and treatment of osteoporosis.