A novel microRNA targeting HDAC5 regulates osteoblast differentiation in mice and contributes to primary osteoporosis in humans

Recent highlights on bone stem cells: a report from Bone Stem Cells 2009, and not only…

The use of stem cells has opened new prospects for the treatment of orthopaedic conditions characterized by large bone defects. However, many issues still exist to which answers are needed before routine, large-scale application becomes possible. Bone marrow stromal cells (MSC), which are clonogenic, multipotential precursors present in the bone marrow stroma, are generally employed for bone regeneration. Stem cells with multilineage differentiation similar to MSC have also been demonstrated in adipose tissue, peripheral blood, umbilical cord and amniotic fluid. Each source presents its own advantages and drawbacks. Unfortunately, no unique surface antigen is expressed by MSC, and this hampers simple MSC enrichment from heterogeneous populations. MSC are identified through a combination of physical, morphological and functional assays. Different in vitro and in vivo models have been described for the research on bone stem cells. These models should predict the in vivo bone healing capacity of MSC and if the induced osteogenesis is similar to the physiological one. Although stem cells offer an exciting possibility of a renewable source of cells and tissues for replacement, orthopaedic applications often represent case reports whereas controlled randomized trials are still lacking. Further biological aspects of bone stem cells should be elucidated and a general consensus on the best models, protocols and proper use of scaffolds and growth factors should be achieved.

A program of microRNAs controls osteogenic lineage progression by targeting transcription factor Runx2

Lineage progression in osteoblasts and chondrocytes is stringently controlled by the cell-fate-determining transcription factor Runx2. In this study, we directly addressed whether microRNAs (miRNAs) can control the osteogenic activity of Runx2 and affect osteoblast maturation. A panel of 11 Runx2-targeting miRNAs (miR-23a, miR-30c, miR-34c, miR-133a, miR-135a, miR-137, miR-204, miR-205, miR-217, miR-218, and miR-338) is expressed in a lineage-related pattern in mesenchymal cell types. During both osteogenic and chondrogenic differentiation, these miRNAs, in general, are inversely expressed relative to Runx2. Based on 3'UTR luciferase reporter, immunoblot, and mRNA stability assays, each miRNA directly attenuates Runx2 protein accumulation. Runx2-targeting miRNAs differentially inhibit Runx2 protein expression in osteoblasts and chondrocytes and display different efficacies. Thus, cellular context contributes to miRNA-mediated regulation of Runx2. All Runx2-targeting miRNAs (except miR-218) significantly impede osteoblast differentiation, and their effects can be reversed by the corresponding anti-miRNAs. These findings demonstrate that osteoblastogenesis is limited by an elaborate network of functionally tested miRNAs that directly target the osteogenic master regulator Runx2.

MicroRNA biogenesis and regulation of bone remodeling

MicroRNAs (miRNAs) are key post-transcriptional regulators of gene expression. This review will highlight our current understanding of miRNA biogenesis and mechanisms of action, and will summarize recent work on the role of miRNAs, including the miR-29 family, in bone remodeling. These studies represent the first steps in demonstrating the importance of miRNAs in the control of osteoblast and osteoclast differentiation and function. An in-depth understanding of the roles of these regulatory RNAs in the skeleton will be critical for the development of new therapeutics aimed at treating bone loss and perhaps facilitating fracture repair.

Common variants in a novel gene, FONG on chromosome 2q33.1 confer risk of osteoporosis in Japanese

Osteoporosis is a common disease characterized by low bone mass, decreased bone quality and increased predisposition to fracture. Genetic factors have been implicated in its etiology; however, the specific genes related to susceptibility to osteoporosis are not entirely known. To detect susceptibility genes for osteoporosis, we conducted a genome-wide association study in Japanese using ∼270,000 SNPs in 1,747 subjects (190 cases and 1,557 controls) followed by multiple levels of replication of the association using a total of ∼5,000 subjects (2,092 cases and 3,114 controls). Through these staged association studies followed by resequencing and linkage disequilibrium mapping, we identified a single nucleotide polymorphism (SNP), rs7605378 associated with osteoporosis. (combined P = 1.51×10⁻⁸, odds ratio = 1.25). This SNP is in a previously unknown gene on chromosome 2q33.1, FONG. FONG is predicted to encode a 147 amino-acid protein with a formiminotransferase domain in its N-terminal (FTCD_N domain) and is ubiquitously expressed in various tissues including bone. Our findings would give a new insight into osteoporosis etiology and pathogenesis.

Suberoylanilide hydroxamic acid (SAHA; vorinostat) causes bone loss by inhibiting immature osteoblasts

Histone deacetylase (Hdac) inhibitors are used clinically to treat cancer and epilepsy. Although Hdac inhibition accelerates osteoblast maturation and suppresses osteoclast maturation in vitro, the effects of Hdac inhibitors on the skeleton are not understood. The purpose of this study was to determine how the pan-Hdac inhibitor, suberoylanilide hydroxamic acid (SAHA; a.k.a. vorinostat or Zolinza(TM)) affects bone mass and remodeling in vivo. Male C57BL/6J mice received daily SAHA (100mg/kg) or vehicle injections for 3 to 4weeks. SAHA decreased trabecular bone volume fraction and trabecular number in the distal femur. Cortical bone at the femoral midshaft was not affected. SAHA reduced serum levels of P1NP, a bone formation marker, and also suppressed tibial mRNA levels of type I collagen, osteocalcin and osteopontin, but did not alter Runx2 or osterix transcripts. SAHA decreased histological measures of osteoblast number but interestingly increased indices of osteoblast activity including mineral apposition rate and bone formation rate. Neither serum (TRAcP 5b) nor histological markers of bone resorption were affected by SAHA. P1NP levels returned to baseline in animals which were allowed to recover for 4weeks after 4weeks of daily SAHA injections, but bone density remained low. In vitro, SAHA suppressed osteogenic colony formation, decreased osteoblastic gene expression, induced cell cycle arrest, and caused DNA damage in bone marrow-derived adherent cells. Collectively, these data demonstrate that bone loss following treatment with SAHA is primarily due to a reduction in osteoblast number. Moreover, these decreases in osteoblast number can be attributed to the deleterious effects of SAHA on immature osteoblasts, even while mature osteoblasts are resistant to the harmful effects and demonstrate increased activity in vivo, indicating that the response of osteoblasts to SAHA is dependent upon their differentiation state. These studies suggest that clinical use of SAHA and other Hdac inhibitors to treat cancer, epilepsy or other conditions may potentially compromise skeletal structure and function.

MicroRNA-138 regulates osteogenic differentiation of human stromal (mesenchymal) stem cells in vivo

Elucidating the molecular mechanisms that regulate human stromal (mesenchymal) stem cell (hMSC) differentiation into osteogenic lineage is important for the development of anabolic therapies for treatment of osteoporosis. MicroRNAs (miRNAs) are short, noncoding RNAs that act as key regulators of diverse biological processes by mediating translational repression or mRNA degradation of their target genes. Here, we show that miRNA-138 (miR-138) modulates osteogenic differentiation of hMSCs. miRNA array profiling and further validation by quantitative RT-PCR (qRT-PCR) revealed that miR-138 was down-regulated during osteoblast differentiation of hMSCs. Overexpression of miR-138 inhibited osteoblast differentiation of hMSCs in vitro, whereas inhibition of miR-138 function by antimiR-138 promoted expression of osteoblast-specific genes, alkaline phosphatase (ALP) activity, and matrix mineralization. Furthermore, overexpression of miR-138 reduced ectopic bone formation in vivo by 85%, and conversely, in vivo bone formation was enhanced by 60% when miR-138 was antagonized. Target prediction analysis and experimental validation by luciferase 3' UTR reporter assay confirmed focal adhesion kinase, a kinase playing a central role in promoting osteoblast differentiation, as a bona fide target of miR-138. We show that miR-138 attenuates bone formation in vivo, at least in part by inhibiting the focal adhesion kinase signaling pathway. Our findings suggest that pharmacological inhibition of miR-138 by antimiR-138 could represent a therapeutic strategy for enhancing bone formation in vivo.

Histone deacetylases in skeletal development and bone mass maintenance

The skeleton is a multifunctional and regenerative organ. Dynamic activities within the bone microenvironment necessitate and instigate rapid and temporal changes in gene expression within the cells (osteoclasts, osteoblasts, and osteocytes) responsible for skeletal maintenance. Regulation of gene expression is controlled, in part, by histone deacetylases (Hdacs), which are intracellular enzymes that directly affect chromatin structure and transcription factor activity. Key roles for several Hdacs in bone development and biology have been elucidated though in vitro and in vivo models. Recent findings suggest that clinical usage of small molecule Hdac inhibitors for conditions like epilepsy, bipolar disorder, cancer, and a multitude of other ailments may have unintended effects on bone cell populations. Here we review the progress that has been made in the last decade in understanding how Hdacs contribute to bone development and maintenance.

Identification of miRNomes in human liver and hepatocellular carcinoma reveals miR-199a/b-3p as therapeutic target for hepatocellular carcinoma

The full scale of human miRNome in specific cell or tissue, especially in cancers, remains to be determined. An in-depth analysis of miRNomes in human normal liver, hepatitis liver, and hepatocellular carcinoma (HCC) was carried out in this study. We found nine miRNAs accounted for ∼88.2% of the miRNome in human liver. The third most highly expressed miR-199a/b-3p is consistently decreased in HCC, and its decrement significantly correlates with poor survival of HCC patients. Moreover, miR-199a/b-3p can target tumor-promoting PAK4 to suppress HCC growth through inhibiting PAK4/Raf/MEK/ERK pathway both in vitro and in vivo. Our study provides miRNomes of human liver and HCC and contributes to better understanding of the important deregulated miRNAs in HCC and liver diseases.

A Runx2/miR-3960/miR-2861 regulatory feedback loop during mouse osteoblast differentiation

Our recent study showed that miR-2861 promotes osteoblast differentiation by targeting histone deacetylase 5, resulting in increased runt-related transcription factor 2 (Runx2) protein production. Here we identified another new microRNA (miRNA) (miR-3960) that played a regulatory role in osteoblast differentiation through a regulatory feedback loop with miR-2861. miR-3960 and miR-2861 were found clustered at the same loci. miR-3960 was transcribed during bone morphogenic protein 2 (BMP2)-induced osteogenesis of ST2 stromal cells. Overexpression of miR-3960 promoted BMP2-induced osteoblastogenesis. However, the inhibition of miR-3960 expression attenuated the osteoblastogenesis. Homeobox A2 (Hoxa2), a repressor of Runx2 expression, was confirmed to be a target of miR-3960. Electrophoretic mobility shift assay and chromatin immunoprecipitation experiments confirmed that Runx2 bound to the promoter of the miR-3960/miR-2861 cluster. Furthermore, overexpression of Runx2 induced miR-3960/miR-2861 transcription, and block of Runx2 expression attenuated BMP2-induced miR-3960/miR-2861 transcription. Here we report that miR-3960 and miR-2861, transcribed together from the same miRNA polycistron, both function in osteoblast differentiation through a novel Runx2/miR-3960/miR-2861 regulatory feedback loop. Our findings provide new insights into the roles of miRNAs in osteoblast differentiation.

Epigenetic mechanisms in inflammation

Epigenetic modifications occur in response to environmental changes and play a fundamental role in gene expression following environmental stimuli. Major epigenetic events include methylation and acetylation of histones and regulatory factors, DNA methylation, and small non-coding RNAs. Diet, pollution, infections, and other environmental factors have profound effects on epigenetic modifications and trigger susceptibility to diseases. Despite a growing body of literature addressing the role of the environment on gene expression, very little is known about the epigenetic pathways involved in the modulation of inflammatory and anti-inflammatory genes. This review summarizes the current knowledge about epigenetic control mechanisms during the inflammatory response.

The role of microRNAs in self-renewal and differentiation of mesenchymal stem cells

MicroRNAs (miRNAs) are short non-coding RNAs involved in post-trascriptional regulation of gene expression and diverse biological activities. They are crucial for self-renewal and behavior of embryonic stem cells, but their role in mesenchymal stem cells has been poorly understood. Recently emerging evidence suggests that miRNAs are closely involved in controlling key steps of mesenchymal stem cell differentiation into certain cell lineages. This review focuses on miRNAs identified recently that regulate mesenchymal stem cell differentiation and other activities.

A microRNA expression signature of osteoclastogenesis

MicroRNAs (miRs) are small noncoding RNAs that principally function in the spatiotemporal regulation of protein translation in animal cells. Although emerging evidence suggests that some miRs play important roles in osteoblastogenesis and skeletal homeostasis, much less is known in osteoclastogenesis. Here, we show that receptor activator of nuclear factor κB ligand (RANKL)-induced osteoclastogenesis is mediated by miR-21. MiR-21 was identified as an miR expression signature of RANKL-induced osteoclastogenesis that down-regulates programmed cell death 4 (PDCD4) protein levels. Diminished PDCD4 removes a repression from c-Fos, a critical transcription factor for osteoclastogenesis and osteoclast-specific downstream target genes. In addition, RANKL-induced c-Fos up-regulates miR-21 gene expression. Bone marrow-derived monocyte/macrophage precursors deficient of DiGeorge syndrome critical region gene 8, an RNA binding protein associated with miR biogenesis, and Dicer, an endoribonuclease in the RNaseIII family associated with miR biogenesis, possessed significantly decreased miR-21 levels and increased PDCD4 protein levels so that RANKL-induced osteoclastogenesis was impaired in those cells. However, forced expression of miR-21 rescued osteoclast development because of down-regulation of PDCD4 protein expression levels. Thus, our studies provide a new molecular mechanism, including a positive feedback loop of c-Fos/miR-21/PDCD4, regulating osteoclastogenesis.

Estrogen receptor α36 mediates a bone-sparing effect of 17β-estrodiol in postmenopausal women

Recently, a membrane-based estrogen receptor (ER), ER-α36, was identified and cloned that transduces membrane-initiated estrogen signaling such as activation of the mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) signaling pathway. Here we show that the postmenopausal level of estradiol (E2) induces mitogenic, antiapoptotic, and antiosteogenic effects and proapoptotic effects in postmenopausal osteoblasts and osteoclasts with high levels of ER-α36 expression, respectively. We also found that ER-α36 mediated the effects of postmenopausal-level E(2) on proliferation, apoptosis, and differentiation of osteoblasts through transient activation of the MAPK/ERK pathway, whereas ER-α36-mediated postmenopausal-level E(2) induces apoptosis of osteoclasts through prolonged activation of the MAPK/ERK pathway with the involvement of reactive oxygen species. We also show that the levels of ER-α36 expression in bone are positively associated with bone mineral density but negatively associated with bone biochemical markers in postmenopausal women. Thus the higher levels of ER-α36 expression are required for preserving bone mass in postmenopausal and menopausal women who become osteoporotic if ER-α36-mediated activities are dysregulated.

Hdac-mediated control of endochondral and intramembranous ossification

Histone deacetylases (Hdacs) remove acetyl groups (CH3CO-) from ε-amino groups in lysine residues within histones and other proteins. This posttranslational (de) modification alters protein stability, protein-protein interactions, and chromatin structure. Hdac activity plays important roles in the development of all organs and tissues, including the mineralized skeleton. Bone is a dynamic tissue that forms and regenerates by two processes: endochondral and intramembranous ossification. Chondrocytes and osteoblasts are responsible for producing the extracellular matrices of skeletal tissues. Several Hdacs contribute to the molecular pathways and chromatin changes that regulate tissue-specific gene expression during chondrocyte and osteoblast specification, maturation, and terminal differentiation. In this review, we summarize the roles of class I and class II Hdacs in chondrocytes and osteoblasts. The effects of small molecule Hdac inhibitors on the skeleton are also discussed.

MicroRNAs, epigenetics and disease

Epigenetics is defined as the heritable chances that affect gene expression without changing the DNA sequence. Epigenetic regulation of gene expression can be through different mechanisms such as DNA methylation, histone modifications and nucleosome positioning. MicroRNAs are short RNA molecules which do not code for a protein but have a role in post-transcriptional silencing of multiple target genes by binding to their 3' UTRs (untranslated regions). Both epigenetic mechanisms, such as DNA methylation and histone modifications, and the microRNAs are crucial for normal differentiation, development and maintenance of tissue-specific gene expression. These mechanisms also explain how cells with the same DNA content can differentiate into cells with different functions. Changes in epigenetic processes can lead to changes in gene function, cancer formation and progression, as well as other diseases. In the present chapter we will mainly focus on microRNAs and methylation and their implications in human disease, mainly in cancer.

Omentin inhibits osteoblastic differentiation of calcifying vascular smooth muscle cells through the PI3K/Akt pathway

Arterial calcification is positively associated with visceral adiposity, but the mechanisms remain unclear. Omentin is a novel adipokine that is selectively expressed in visceral adipose tissue. The levels of circulating omentin are decreased in obesity, and they correlate negatively with waist circumference. This study investigated the effects of omentin on the osteoblastic differentiation of calcifying vascular smooth muscle cells (CVSMCs), a subpopulation of aortic smooth muscle cells putatively involved in vascular calcification. Omentin inhibited mRNA expression of alkaline phosphatase (ALP) and osteocalcin; omentin also suppressed ALP activity, osteocalcin protein production, and the matrix mineralization. Furthermore, omentin selectively activated phosphatidylinositol 3-kinase (PI3K) downstream effector Akt. Moreover, inhibition of PI3K or Akt activation reversed the effects of omentin on ALP activity and the matrix mineralization. The present results demonstrate for the first time that omentin can inhibit osteoblastic differentiation of CVSMCs via PI3K/Akt signaling pathway, suggesting that the lower omentin levels in obese (specially visceral obese) subjects contribute to the development of arterial calcification, and omentin plays a protective role against arterial calcification.

No association between LRP5 gene polymorphisms and bone and obesity phenotypes in Chinese male-offspring nuclear families

AIM

To investigate the effect of low-density lipoprotein receptor-related protein 5 (LRP5) gene polymorphisms on bone and obesity phenotypes in young Chinese men.

METHODS

A total of 1244 subjects from 411 Chinese nuclear families were genotyped by using the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) technique at the Q89R, N740N, and A1330V sites in the LRP5 gene. Bone mineral density (BMD) in the lumbar spine and the hip, total fat mass and total lean mass were measured using dual-energy X-ray absorptiometry. The association between LRP5 gene polymorphisms and peak BMD, body mass index (BMI), total fat mass, total lean mass and percentage of fat mass was assessed using a quantitative transmission disequilibrium test (QTDT).

RESULTS

No significant within-family associations were found between genotypes or haplotypes of the LRP5 gene and peak BMD, BMI, total fat mass, total lean mass and percentage of fat mass. The 1000 permutations that were subsequently simulated were in agreement with these within-family association results.

CONCLUSION

Our results suggest that common polymorphic variations of the LRP5 gene do not influence peak bone mass acquisition and obesity phenotypes in young Chinese men.

A network connecting Runx2, SATB2, and the miR-23a~27a~24-2 cluster regulates the osteoblast differentiation program

Induced osteogenesis includes a program of microRNAs (miRs) to repress the translation of genes that act as inhibitors of bone formation. How expression of bone-related miRs is regulated remains a compelling question. Here we report that Runx2, a transcription factor essential for osteoblastogenesis, negatively regulates expression of the miR cluster 23a∼27a∼24-2. Overexpression, reporter, and chromatin immunoprecipitation assays established the presence of a functional Runx binding element that represses expression of these miRs. Consistent with this finding, exogenous expression of each of the miRs suppressed osteoblast differentiation, whereas antagomirs increased bone marker expression. The biological significance of Runx2 repression of this miR cluster is that each miR directly targets the 3' UTR of SATB2, which is known to synergize with Runx2 to facilitate bone formation. The findings suggest Runx2-negative regulation of multiple miRs by a feed-forward mechanism to cause derepression of SATB2 to promote differentiation. We find also that miR-23a represses Runx2 in the terminally differentiated osteocyte, representing a feedback mechanism to attenuate osteoblast maturation. We provide direct evidence for an interdependent relationship among transcriptional inhibition of the miR cluster by Runx2, translational repression of Runx2 and of SATB2 by the cluster miRs during progression of osteoblast differentiation. Furthermore, miR cluster gain of function (i.e., inhibition of osteogenesis) is rescued by the exogenous expression of SATB2. Taken together, we have established a regulatory network with a central role for the miR cluster 23a∼27a∼24-2 in both progression and maintenance of the osteocyte phenotype.

MicroRNAs as regulators of differentiation and cell fate decisions

Unique expression domains, targets, and gain- and loss-of-function phenotypes of particular microRNAs have important implications for directed differentiation of stem cell populations and suppression of undesired cell types. We discuss this emerging topic, in part using muscle differentiation as a paradigm, and highlight common themes and unique modalities by which microRNAs exert their lineage-promoting or differentiation effects on multiple tissues.

Genes, mutations, and human inherited disease at the dawn of the age of personalized genomics

The number of reported germline mutations in human nuclear genes, either underlying or associated with inherited disease, has now exceeded 100,000 in more than 3,700 different genes. The availability of these data has both revolutionized the study of the morbid anatomy of the human genome and facilitated "personalized genomics." With approximately 300 new "inherited disease genes" (and approximately 10,000 new mutations) being identified annually, it is pertinent to ask how many "inherited disease genes" there are in the human genome, how many mutations reside within them, and where such lesions are likely to be located? To address these questions, it is necessary not only to reconsider how we define human genes but also to explore notions of gene "essentiality" and "dispensability."Answers to these questions are now emerging from recent novel insights into genome structure and function and through complete genome sequence information derived from multiple individual human genomes. However, a change in focus toward screening functional genomic elements as opposed to genes sensu stricto will be required if we are to capitalize fully on recent technical and conceptual advances and identify new types of disease-associated mutation within noncoding regions remote from the genes whose function they disrupt.

MicroRNA-208 modulates BMP-2-stimulated mouse preosteoblast differentiation by directly targeting V-ets erythroblastosis virus E26 oncogene homolog 1

MicroRNAs (miRs) represent a class of endogenous approximately 18-25 nucleotide RNAs that regulate gene expression through translational repression by binding to a target mRNA. These miRs regulate several biological functions, such as cell growth, cell differentiation, carcinogenesis, and so on. In a previous report, we have indicated that miR-141 and -200a act as preosteoblast differentiation modulators. In the present study, using microRNA array and in silico analyses, we found that miR-208 is closely involved in preosteoblast differentiation by partially regulating the expression of Ets1 (V-ets erythroblastosis virus E26 oncogene homolog 1), which transactivates osteopontin, runt-related transcription factor 2, parathyroid hormone-related protein, and type I procollagen. Furthermore, the enforced expression of mature miR-208 in murine preosteoblast in MC3T3-E1 cells or primary osteoblast cells remarkably attenuated BMP-2-induced preosteoblast differentiation. In addition, we determined that Ets1 is a target gene of miR-208 by using a sensor luciferase reporter assay. Taken together, these results suggest that the down-regulation of miR-208 in BMP-2-stimulated osteoblast differentiation is an important part of the regulatory machinery involved in early osteogenesis.

miR-29 modulates Wnt signaling in human osteoblasts through a positive feedback loop

Differentiation of human mesenchymal stem cells into osteoblasts is controlled by extracellular cues. Canonical Wnt signaling is particularly important for maintenance of bone mass in humans. Post-transcriptional regulation of gene expression, mediated by microRNAs, plays an essential role in the control of osteoblast differentiation. Here, we find that miR-29a is necessary for human osteoblast differentiation, and miR-29a is increased during differentiation in the mesenchymal precursor cell line hFOB1.19 and in primary cultures of human osteoblasts. Furthermore, the promoter of the expressed sequence tag containing the human miR-29a gene is induced by canonical Wnt signaling. This effect is mediated, at least in part, by two T-cell factor/LEF-binding sites within the proximal promoter. Furthermore, we show that the negative regulators of Wnt signaling, Dikkopf-1 (Dkk1), Kremen2, and secreted frizzled related protein 2 (sFRP2), are direct targets of miR-29a. Endogenous protein levels for these Wnt antagonists are increased in cells transfected with synthetic miR-29a inhibitor. In contrast, transfection with miR-29a mimic decreases expression of these antagonists and potentiates Wnt signaling. Overall, we demonstrate that miR-29 and Wnt signaling are involved in a regulatory circuit that can modulate osteoblast differentiation. Specifically, canonical Wnt signaling induces miR-29a transcription. The subsequent down-regulation of key Wnt signaling antagonists, Dkk1, Kremen2, and sFRP2, by miR-29a potentiates Wnt signaling, contributing to a gene expression program important for osteoblast differentiation. This novel regulatory circuit provides additional insight into how microRNAs interact with signaling molecules during osteoblast differentiation, allowing for fine-tuning of intricate cellular processes.

Analysis of correlation between blood biochemical indicators and bone mineral density of post-menopausal women

Osteoporosis is a degenerative disease of the skeletal system, and its major complication is fracture that severely influences the living quality of the middle-aged and the aged. The purpose of this study was to investigate the significance of sex hormones and some biochemical indicators related to bone metabolism in the genesis and development of osteoporosis. The plasma samples were collected from 244 post-menopausal women of Xi'an urban area, and their plasma contents of testosterone, estradiol, calcitonin, osteocalcin and N-terminal propeptide of type I procollagen were detected by ELISA. The activity of tartrate-resistant acid phosphatase was determined by spectrophotometric method, and the content of nitric oxide was measured by Griess method. Bone mineral density (BMD) in lumbar vertebrae (L1-L4) and hips was measured by QDR-2000 dual energy X-ray absorptiometry. The concentrations of the biochemical indicators were compared among the three groups (normal bone mass group, osteopenia group and osteoporosis group), and Pearson correlation analysis was used to verify the correlations between the indicators and BMD. The comparison results of blood biochemical indicators of BMD-based groups showed that the plasma contents of estradiol (P = 0.006), testosterone (P = 0.038) and calcitonin (P = 0.042) decreased more significantly in the osteoporosis group, but the content of osteocalcin (P = 0.008) increased significantly in osteoporosis group than those in the other groups. The correlation analysis between BMD of different parts and the blood biochemical indicators showed that there was a significant positive correlation between estradiol and the BMD of lumber vertebra (r = 0.200, P = 0.002), femoral neck (r = 0.160, P = 0.013), and great trochanter (r = 0.204, P = 0.001). Significant positive correlations between calcitonin and BMD of lumber vertebra (r = 0.166, P = 0.018) and femoral great trochanter (r = 0.152, P = 0.041), and between testosterone and BMD of femoral great trochanter (r = 0.158, P = 0.014) were also observed. In addition, there existed significant negative correlations between osteocalcin and BMD of lumber vertebra (r = -0.220, P = 0.001), femoral neck (r = -0.259, P < 0.000), and great trochanter (r = -0.221, P = 0.001), and between the activity of tartrate-resistant acid phosphatase and BMD of femoral great trochanter (r = -0.135, P = 0.037). The partial correlation analysis also showed that there were significant correlations between estradiol (r = 0.160, P = 0.014), calcitonin (r = 0.240, P = 0.013), osteocalcin (r = -0.226, P = 0.023) and BMD when the influence of age was excluded. The Pearson correlation analysis of biochemical indicators showed there were positive correlations between the contents of testosterone and calcitonin, testosterone and osteocalcin, calcitonin and osteocalcin, calcitonin and PINP, calcitonin and NO, osteocalcin and NO, and PINP and NO, but negative correlations between the contents of testosterone and PINP, estradiol and calcitonin, estradiol and osteocalcin, and estradiol and NO. The blood contents of sex hormones and calcitonin significantly influence BMD and osteoporosis development, and the increase of osteocalcin contents could be used as a biomarker to indicate the degree of osteoporosis in post-menopausal women.

MicroRNA-21 and microRNA-148a contribute to DNA hypomethylation in lupus CD4+ T cells by directly and indirectly targeting DNA methyltransferase 1

Systemic lupus erythematosus is a complex autoimmune disease caused by genetic and epigenetic alterations. DNA methylation abnormalities play an important role in systemic lupus erythematosus disease processes. MicroRNAs (miRNAs) have been implicated as fine-tuning regulators controlling diverse biological processes at the level of posttranscriptional repression. Dysregulation of miRNAs has been described in various disease states, including human lupus. Whereas previous studies have shown miRNAs can regulate DNA methylation by targeting the DNA methylation machinery, the role of miRNAs in aberrant CD4+ T cell DNA hypomethylation of lupus is unclear. In this study, by using high-throughput microRNA profiling, we identified that two miRNAs (miR-21 and miR-148a) overexpressed in CD4+ T cells from both patients with lupus and lupus-prone MRL/lpr mice, which promote cell hypomethylation by repressing DNA methyltransferase 1 (DNMT1) expression. This in turn leads to the overexpression of autoimmune-associated methylation-sensitive genes, such as CD70 and LFA-1, via promoter demethylation. Further experiments revealed that miR-21 indirectly downregulated DNMT1 expression by targeting an important autoimmune gene, RASGRP1, which mediated the Ras-MAPK pathway upstream of DNMT1; miR-148a directly downregulated DNMT1 expression by targeting the protein coding region of its transcript. Additionally, inhibition of miR-21 and miR-148a expression in CD4+ T cells from patients with lupus could increase DNMT1 expression and attenuate DNA hypomethylation. Together, our data demonstrated a critical functional link between miRNAs and the aberrant DNA hypomethylation in lupus CD4+ T cells and could help to develop new therapeutic approaches.