Differential roles of MAPK kinases MKK3 and MKK6 in osteoclastogenesis and bone loss

Oxyresveratrol attenuates bone resorption by inhibiting the mitogen-activated protein kinase pathway in ovariectomized rats

BACKGROUND

Bone is continuously produced by osteoblasts and resorbed by osteoclasts to maintain homeostasis. Impaired bone resorption by osteoclasts causes bone diseases such as osteoporosis and arthritis. Most pharmacological treatment of osteoporosis focuses on inhibiting osteoclast differentiation, often to restore osteoclast/osteoclast balance. However, recent osteoporosis treatments have various side effects. According to a recent study, resveratrol, known as a stilbenoid family, is known to increase bone density, and the osteoclast inhibitory effect was confirmed using oxyresveratrol, a stilbenoid family. Here, we investigated the effect of oxyresveratrol on osteoclast differentiation and an ovariectomized mouse model.

METHODS

Mouse leukemia monocyte/macrophage cell line RAW 264.7 was treated with oxyresveratrol, and cell cytotoxicity was confirmed by measuring MTT assay. Tartrate-resistant acid phosphatase (TRAP), an enzyme marker for osteoclasts, was confirmed by staining. In addition, osteoclast differentiation markers and MAPK-related markers were confirmed at the mRNA level and protein expression. The effect of oxyresveratrol was confirmed using ovariectomized mice. Deoxypyridinoline (DPD) was measured using mouse urine and TRAP activity was observed using serum. Bone mineral density was also measured using Micro-CT.

RESULTS

The polyphenol oxyresveratrol inhibited receptor activator of nuclear factor kappa-Β ligand (RANKL)-induced osteoclast differentiation of RAW 264.7 cells. Furthermore, oxyresveratrol inhibited TRAP activity and actin-ring formation. Moreover, oxyresveratrol suppressed the phosphorylation of the RANKL-induced mitogen-activated protein kinases (MAPKs) p38, JNK, and ERK and significantly reduced the expression of bone differentiation markers (NFATc1, cathepsin K, and TRAP).

CONCLUSION

Oxyresveratrol inhibits osteoclast differentiation via MAPK and increases bone density in ovariectomized rats, suggesting it has therapeutic potential for bone diseases such as osteoporosis. We confirmed the osteoporosis prevention effect of OR in Raw 264.7 cells, and future studies should confirm the effect of OR using rat bone marrow-derived cells.

Loureirin B downregulates osteoclast differentiation of bone marrow macrophages by targeting the MAPK signaling pathway

Excessive absorption of osteoclasts will break the balance between osteoclasts and osteoblasts, leading to bone loss, decreased bone density, and increased bone fragility. We have shown that Loureirin B (LrB) can inhibit osteoclasts. In this study, we demonstrated the targeting-inhibitory mechanism of LrB acting on osteoclast precursor. Using SPR, HPLC and MALDI-TOF-MS to capture and analyze the target protein of Loureirin B in bone marrow macrophages (BMMs), we used this method to detect all target proteins that LrB acts on BMMs, and analyzed the distribution and enrichment rate of the target protein by DAVID enrichment analysis. Ledock molecular docking was used to detect the binding of LrB. We used Western Blot for verification. The target proteins of LrB acting on BMMs were Serpine1, Atp6ap1, Dvl1, Rhd, Fzd2, MAPK1, MAP2K2, MAPK3 and so on. MAPK1, MAP2K2 and MAPK3 were the most relevant. LrB treatment attenuated the expression of phosphorylated JNK and p38 kinases of the MAPK signaling pathway. Our research further confirmed that LrB affects the MAPK signaling pathway in BMMs, thereby inhibiting the differentiation of BMMs into osteoclasts. This discovery can confirm the mechanism by which LrB acts on BMMs.

Isoliensinine Suppresses Osteoclast Formation Through NF-κB Signaling Pathways and Relieves Ovariectomy-Induced Bone Loss

Osteoporosis is among the major contributors of pathologic fracture in postmenopausal women, which is caused by the bone metabolic disorder owing to the over-activation of osteoclasts. Inhibition of osteoclast differentiation and maturation has become a mainstream research interest in the prevention of osteoporosis. Isoliensinine (Iso) is a dibenzyl isoquinoline alkaloid with antioxidant, anti-inflammatory, and anti-cancer activities. However, whether it can be used as a potential treatment for osteoporosis remains undiscovered. Here, we investigated whether Iso might suppress the differentiation of osteoclasts in vitro and in vivo to play an anti-osteoporosis role. Our results showed that Iso inhibits the formation of mature multinuclear osteoclasts induced by RANKL, the bone resorption, and the osteoclast-specific genes expression by blocking the nuclear translocation of NF-κB p65, and the effect was in a dosage-dependent way. Furthermore, we investigated the therapeutic effect of Iso on osteoporosis in ovariectomized (OVX) mice. We found that Iso attenuated bone loss in the OVX mice and significantly promoted BS, Conn. DN, Tb.Th, TB.N, and BV/TV Index. All in all, Iso showed a prominent effect of osteoclast inhibition, with great promise for treating osteoporosis.

Extraction and characterization of matrix protein from pacific oyster (Crassostrea gigs) shell and its anti-osteoporosis properties in vitro and in vivo

Matrix protein is a kind of secretory protein that regulates the biomineralization of the bivalve shell. In this study, a water-soluble matrix protein (WSMP) from Pacific oysters (Crassostrea gigs) shell was isolated, and its structure was analyzed in detail, in addition to its anti-osteoporosis activity in vitro and in vivo. Results showed that WSMP was an acidic protein with an apparent molecular mass of 47 and 79 kDa and contained a glycoprotein structure. In vitro, the reduction of Tartrate-resistant acid phosphatase (TRAP) and deoxypyridinoline (DPD) indicated that osteoclast activity was inhibited compared with the model group. Moreover, the increased osteocalcin (OCN) and BMD levels suggested that the high osteoblast activity and bone mineralization was improved. SEM analysis of the femur showed that there were fewer bone pits in experimental groups, which was consistent with the above results. In vivo, WSMP promoted the expression of alkaline phosphatase (ALP) and osteogenic differentiation factor BMP-2 in osteoblasts. In addition, the activity of osteoclasts was inhibited by regulating the process of osteoclast differentiation induced by RANKL. Both in vitro and in vivo studies showed that WSMP could promote osteogenesis and inhibit osteoclast absorption, thus demonstrating their potential applications in osteoporosis.

[Zoledronate regulates osteoclast differentiation and bone resorption in high glucose through p38 MAPK pathway]

OBJECTIVE

To investigate the effect of zoledronate (ZOL) on osteoclast differentiation and bone resorption under high glucose, and the regulation mechanism of p38 mitogen activated kinase (p38 MAPK) signaling pathway in this process.

METHODS

RAW264.7 cells were divided into four groups: low group, high group, low+ZOL group and high+ZOL group after induced into osteoclasts. Cell proliferation activity was determined by MTT assay. The migration of RAW264.7 cells were examined Optical microscopy. Immunofluorescence microscopy was used to observe the cytoskeleton and sealing zones of osteoclasts. After adding group 5: high + ZOL + SB203580 group, trap staining was used to identify the number of positive osteoclasts in each group. The number and area of resorption lacunae were observed by SEM. The mRNA and protein expression of osteoclast related factors were detected by real-time PCR and Western blotting.

RESULTS

The cells in the 5 groups showed similar proliferative activity. High glucose promoted the migration of RAW264.7 cells (P < 0.05), inhibited the clarity of cytoskeleton and the formation of sealing zones in the osteoclasts. Exposure to high glucose significantly lowered the expressions of p38 MAPK, p-p38 MAPK, NFATc1, CTSK and TRAP, and inhibited osteoclast differentiation and bone absorption (P < 0.05). Treatment with ZOL obviously suppressed the migration ability of RAW264.7 cells, further reduced the clarity of the cytoskeleton, inhibited the formation of sealing zones of the osteoclasts, lowered the expressions of p38 MAPK, p-p38 MAPK, NFATc1, CTSK, and TRAP (P < 0.05), and inhibited osteoclast differentiation and bone absorption. Treatment with SB203580 obviously inhibited osteoclast differentiation and bone resorption and the expressions of P38 MAPK, p-p38 MAPK, NFATc1, CTSK and TRAP (P < 0.05).

CONCLUSIONS

High glucose inhibits osteoclast differentiation and bone resorption. ZOL inhibits osteoclast differentiation and bone resorption in high-glucose conditions by regulating p38 MAPK pathway, which can be a new pathway for ZOL to regulate diabetic osteoporosis.

High expression of MKK3 is associated with worse clinical outcomes in African American breast cancer patients

BACKGROUND

African American women experience a twofold higher incidence of triple-negative breast cancer (TNBC) and are 40% more likely to die from breast cancer than women of other ethnicities. However, the molecular bases for the survival disparity in breast cancer remain unclear, and no race-specific therapeutic targets have been proposed. To address this knowledge gap, we performed a systematic analysis of the relationship between gene mRNA expression and clinical outcomes determined for The Cancer Genome Atlas (TCGA) breast cancer patient cohort.

METHODS

The systematic differential analysis of mRNA expression integrated with the analysis of clinical outcomes was performed for 1055 samples from the breast invasive carcinoma TCGA PanCancer cohorts. A deep learning fully-convolutional model was used to determine the association between gene expression and tumor features based on breast cancer patient histopathological images.

RESULTS

We found that more than 30% of all protein-coding genes are differentially expressed in White and African American breast cancer patients. We have determined a set of 32 genes whose overexpression in African American patients strongly correlates with decreased survival of African American but not White breast cancer patients. Among those genes, the overexpression of mitogen-activated protein kinase kinase 3 (MKK3) has one of the most dramatic and race-specific negative impacts on the survival of African American patients, specifically with triple-negative breast cancer. We found that MKK3 can promote the TNBC tumorigenesis in African American patients in part by activating of the epithelial-to-mesenchymal transition induced by master regulator MYC.

CONCLUSIONS

The poor clinical outcomes in African American women with breast cancer can be associated with the abnormal elevation of individual gene expression. Such genes, including those identified and prioritized in this study, could represent new targets for therapeutic intervention. A strong correlation between MKK3 overexpression, activation of its binding partner and major oncogene MYC, and worsened clinical outcomes suggests the MKK3-MYC protein-protein interaction as a new promising target to reduce racial disparity in breast cancer survival.

MKK3 sustains cell proliferation and survival through p38DELTA MAPK activation in colorectal cancer

Colorectal cancer (CRC) is one of the most common malignant tumors worldwide and understanding its underlying molecular mechanisms is crucial for the development of therapeutic strategies. The mitogen-activated protein kinase-kinase 3 (MKK3) is a specific activator of p38 MAP kinases (p38 MAPKs), which contributes to the regulation of several cellular functions, such as proliferation, differentiation, apoptosis as well as response to drugs. At present, the exact MKK3/p38 MAPK pathway contribution in cancer is heavily debated because of its pleiotropic function. In this work, we retrospectively explored the prognostic and pathobiologic relevance of MKK3 in a cohort of CRC patients and assessed MKK3 molecular functions in a panel of CRC lines and colonocytes primary cultures. We found increased MKK3 levels in late-stage CRC patients which correlated with shorter overall survival. Herein, we report that the MKK3 targeting by inducible RNA interference univocally exerts antitumor effects in CRC lines but not in primary colonocytes. While MKK3 depletion per se affects growth and survival by induction of sustained autophagy and death in some CRC lines, it potentiates response to chemotherapeutic drug 5-fluorouracil (5-FU) in all of the tested CRC lines in vitro. Here, we demonstrate for the first time that in CRC the MKK3 specifically activates p38delta MAPK isoform to sustain prosurvival signaling and that such effect is exacerbated upon 5-FU challenge. Indeed, p38delta MAPK silencing recapitulates MKK3 depletion effects in CRC cells in vitro and in vivo. Overall, our data identified a molecular mechanism through which MKK3 supports proliferation and survival signaling in CRC, further supporting MKK3 as a novel and extremely attractive therapeutic target for the development of promising strategies for the management of CRC patients.

Cervus and cucumis peptides ameliorates bone erosion in experimental arthritis by inhibiting osteoclastogenesis

OBJECTIVE

Rheumatoid arthritis is an autoimmune disease characterised by inflammation and bone loss, leading to joint destruction and deformity. The cervus and cucumis polypeptide (CCP) injection, one of the traditional Chinese medicine injections combined extracts from deer horn and sweet melon seeds, is widely used to treat arthritis and bone fracture in China. The present study investigated the therapeutic efficacy and mechanism of CCP on pathological immune cells and bone homoeostasis in rodent experimental arthritis.

METHODS

The effects of CCP (4 mg/kg and 2 mg/kg) on clinical arthritis symptoms, bone erosion, proinflammatory cytokines and pathological immune cells induced by complete Freund's adjuvant was evaluated in male Sprague-Dawley rats. The impacts of CCP (2 mg/kg) on joint erythema and swelling, production of pathogenic antibodies and the proportion of inflammatory cells were assessed in collagen-induced arthritis (CIA) in DBA/1J mice. Regulation of osteoclastogenesis by CCP was observed in the murine macrophage-like RAW264.7 cells treated with receptor activator of nuclear factor-κB ligand (RANKL) and macrophage colony-stimulating factor (M-CSF).

RESULTS

CCP administration significantly prevented disease progression in both adjuvant-induced arthritis (AIA) rats and CIA mice. The therapeutic benefits were accompanied by reduction of paw oedema, reversed bone destruction, decreased pathological changes and osteoclast numbers in joints in AIA rats, as well as attenuated clinical manifestation and autoantibodies production in CIA mice. Meanwhile, in vitro supplemented of CCP concentration dependently inhibited RANKL/M-CSF-induced osteoclast differentiation, without showing cytotoxicity in RAW264.7 cells. Further, the presence of CCP dampened the augmented downstream signalling transduction as well as activation of osteoclast-specific genes and transcription factors induced by RANKL/M-CSF in RAW264.7 cells.

CONCLUSION

Our study suggested that the therapeutic effects of CCP in experimental arthritis could be attributed to its intervention on RANKL-induced osteoclastogenesis signalling pathway in osteoclast precursor cells.

Inhibition of Osteoclastogenesis by Thioredoxin-Interacting Protein-Derived Peptide (TN13)

Overactivated osteoclasts lead to many bone diseases, including osteoporosis and rheumatoid arthritis. The p38 MAPK (p38) is an essential regulator of the receptor activator of nuclear factor-κB ligand (RANKL)-mediated osteoclastogenesis and bone loss. We previously reported TAT conjugated thioredoxin-interacting protein-derived peptide (TAT-TN13) as an inhibitor of p38 in hematopoietic stem cells (HSCs). Here, we examined the role of TAT-TN13 in the differentiation and function of osteoclasts. TAT-TN13 significantly suppressed RANKL-mediated differentiation of RAW 264.7 cells and bone marrow macrophages (BMMs) into osteoclasts. TAT-TN13 also inhibited the RANKL-induced activation of NF-κB and nuclear factor of activated T-cells cytoplasmic 1 (NFATc1), leading to the decreased expression of osteoclast-specific genes, including tartrate-resistant acid phosphatase (TRAP) and Cathepsin K. Additionally, TAT-TN13 treatment protected bone loss in ovariectomized (OVX) mice. Taken together, these results suggest that TAT-TN13 inhibits osteoclast differentiation by regulating the p38 and NF-κB signaling pathway; thus, it may be a useful agent for preventing or treating osteoporosis.

Roles of Mitogen-Activated Protein Kinases in Osteoclast Biology

Bone undergoes continuous remodeling, which is homeostatically regulated by concerted communication between bone-forming osteoblasts and bone-degrading osteoclasts. Multinucleated giant osteoclasts are the only specialized cells that degrade or resorb the organic and inorganic bone components. They secrete proteases (e.g., cathepsin K) that degrade the organic collagenous matrix and establish localized acidosis at the bone-resorbing site through proton-pumping to facilitate the dissolution of inorganic mineral. Osteoporosis, the most common bone disease, is caused by excessive bone resorption, highlighting the crucial role of osteoclasts in intact bone remodeling. Signaling mediated by mitogen-activated protein kinases (MAPKs), including extracellular signal-regulated kinase (ERK), c-Jun N-terminal kinase (JNK), and p38, has been recognized to be critical for normal osteoclast differentiation and activation. Various exogenous (e.g., toll-like receptor agonists) and endogenous (e.g., growth factors and inflammatory cytokines) stimuli contribute to determining whether MAPKs positively or negatively regulate osteoclast adhesion, migration, fusion and survival, and osteoclastic bone resorption. In this review, we delineate the unique roles of MAPKs in osteoclast metabolism and provide an overview of the upstream regulators that activate or inhibit MAPKs and their downstream targets. Furthermore, we discuss the current knowledge about the differential kinetics of ERK, JNK, and p38, and the crosstalk between MAPKs in osteoclast metabolism.

Identification of miR-708-5p in peripheral blood monocytes: Potential marker for postmenopausal osteoporosis in Mexican-Mestizo population

IMPACT STATEMENT

This is the first study in which hsa-miR-708-5p has been identified in peripheral blood monocytes (osteoclast precursors) and associated with postmenopausal osteoporosis through small RNA-Sequencing, in an Admixed Mexican Mestizo population. By conducting in silico and bioinformatic analyzes, we identified target genes and important signaling pathways involved in bone metabolism pointing hsa-miR-708-5p as a candidate marker for osteoporosis in Mexican population. These approaches provide a landscape of the post-transcriptional regulation, which can be useful for the management of postmenopausal osteoporosis along with the potential use of microRNAs as markers for its early detection.

Insights of Crosstalk between p53 Protein and the MKK3/MKK6/p38 MAPK Signaling Pathway in Cancer

TP53 is universally recognized as a pivotal protein in cell-cycle fate and apoptotic induction and, unsurprisingly, it is one of the most commonly hijacked control mechanisms in cancer. Recently, the kinase MKK3 emerged as a potential therapeutic target in different types of solid tumor being linked to mutant p53 gain-of-function. In this review, we summarize the delicate relationship among p53 mutational status, MKK3/MKK6 and the downstream activated master kinase p38MAPK, dissecting a finely-tuned crosstalk, in a potentially cell-context dependent scenario that urges towards a deeper characterization of the different molecular players involved in this signaling cascade and their interactions.

Relationship between osteogenesis and angiogenesis in ovariectomized osteoporotic rats after exercise training

To reveal the role of exercise training in regulating osteogenesis and angiogenesis in rats after ovariectomy (OVX), then further examine the relationship between osteoporosis (OP) and local blood supply. Ninety-six rats were randomly assigned to OVX, OVX + exercise (OVX + Exe), sham operation (CON), and sham + exercise (CON + Exe) groups. Bone mineral density (BMD) was determined by dual-energy X-ray absorptiometer (DXA). Microarchitecture and angiogenesis of the femoral condyles were measured by micro-cumputed tomography (micro-CT). The femoral artery was separated for evaluating the vasodilation and endothelial nitric oxide synthase (eNOS) gene expression.BMD was markedly lower in the OVX than CON and CON + Exe groups. The trabecular bone integrity was better in the OVX + Exe than OVX group, but BMD showed no significant difference. The bone parameters indicated OP characteristics in rats after OVX, parts of them were relatively improved after exercise training. Acetylcholine-induced vessel vasodilation was enhanced by exercise training, but blocked by a NOS inhibitor. eNOS gene expression in femoral vessels showed a downward trend after OVX, and a upward trend in CON group, but seemed not to be affected by exercise training. Angiogenesis in the femur was lower in the OVX group than the CON group, but substantially better in the OVX + Exe than OVX group. Exercise training enhancing acetylcholine-induced femoral artery vasodilation and bone angiogenesis improve the blood supply of bone to facilitate osteogenesis in the OP site and therefore delay the progression of OP after menopause.

Roles of Wnt3a and Dkk1 in experimental periodontitis

Background/purpose

Periodontitis is an inflammatory, destructive disease caused by periodontal bacteria, and its molecular mechanism remains unclear. The aims of this study are to evaluate the expressions of Wnt3a and Dkk1 in experimental periodontitis (EP) and preliminarily explore their roles in periodontal diseases.

Materials and methods

A total of 64 six-week-old male Sprague–Dawley rats were randomly divided into a normal group and an EP group. The EP group was prepared by using silk ligature combined with intraoral bacteria inoculation. To assess the periodontal inflammation and bone destruction extent, hematoxylin and eosin staining and tartrate-resistant acid phosphatase staining was performed 2 weeks, 4 weeks, and 6 weeks after the modeling, respectively, and immunohistochemistry and enzyme-linked immunosorbent assay were also performed to detect the changes of Wnt3a and Dkk1 in periodontal tissue and plasma.

Results

Wnt3a expression was significantly decreased in the EP group when compared with the normal group (P < 0.05). Meanwhile, Dkk1 expression was significantly increased in the EP group when compared with the normal group (P < 0.05).

Conclusion

The expression of Wnt3a and Dkk1 was well correlated with EP. It is suggested that Wnt3a and Dkk1 may be involved in periodontal diseases.

p38α MAPK regulates proliferation and differentiation of osteoclast progenitors and bone remodeling in an aging-dependent manner

Bone mass is determined by the balance between bone formation, carried out by mesenchymal stem cell-derived osteoblasts, and bone resorption, carried out by monocyte-derived osteoclasts. Here we investigated the potential roles of p38 MAPKs, which are activated by growth factors and cytokines including RANKL and BMPs, in osteoclastogenesis and bone resorption by ablating p38α MAPK in LysM+monocytes. p38α deficiency promoted monocyte proliferation but regulated monocyte osteoclastic differentiation in a cell-density dependent manner, with proliferating p38α^−/− cultures showing increased differentiation. While young mutant mice showed minor increase in bone mass, 6-month-old mutant mice developed osteoporosis, associated with an increase in osteoclastogenesis and bone resorption and an increase in the pool of monocytes. Moreover, monocyte-specific p38α ablation resulted in a decrease in bone formation and the number of bone marrow mesenchymal stem/stromal cells, likely due to decreased expression of PDGF-AA and BMP2. The expression of PDGF-AA and BMP2 was positively regulated by the p38 MAPK-Creb axis in osteoclasts, with the promoters of PDGF-AA and BMP2 having Creb binding sites. These findings uncovered the molecular mechanisms by which p38α MAPK regulates osteoclastogenesis and coordinates osteoclastogenesis and osteoblastogenesis.

miR-434-3p and DNA hypomethylation co-regulate eIF5A1 to increase AChRs and to improve plasticity in SCT rat skeletal muscle

Acetylcholine receptors (AChRs) serve as connections between motor neurons and skeletal muscle and are essential for recovery from spinal cord transection (SCT). Recently, microRNAs have emerged as important potential biotherapeutics for several diseases; however, whether miRNAs operate in the modulation of AChRs remains unknown. We found increased AChRs numbers and function scores in rats with SCT; these increases were reduced following the injection of a eukaryotic translation initiation factor 5A1 (eIF5A1) shRNA lentivirus into the hindlimb muscle. Then, high-throughput screening for microRNAs targeting eIF5A1 was performed, and miR-434-3p was found to be robustly depleted in SCT rat skeletal muscle. Furthermore, a highly conserved miR-434-3p binding site was identified within the mRNA encoding eIF5A1 through bioinformatics analysis and dual-luciferase assay. Overexpression or knockdown of miR-434-3p in vivo demonstrated it was a negative post-transcriptional regulator of eIF5A1 expression and influenced AChRs expression. The microarray-enriched Gene Ontology (GO) terms regulated by miR-434-3p were muscle development terms. Using a lentivirus, one functional gene (map2k6) was confirmed to have a similar function to that of miR-434-3p in GO terms. Finally, HRM and MeDIP-PCR analyses revealed that DNA demethylation also up-regulated eIF5A1 after SCT. Consequently, miR-434-3p/eIF5A1 in muscle is a promising potential biotherapy for SCI repair.

Ablation of p38α MAPK Signaling in Osteoblast Lineage Cells Protects Mice From Bone Loss Induced by Estrogen Deficiency

Estrogen deficiency causes bone loss by increasing the number of bone-resorbing osteoclasts. Selective p38α MAPK inhibitors prevent bone-wasting effects of estrogen withdrawal but implicated mechanisms remain to be identified. Here, we show that inactivation of the p38α-encoding gene in osteoblast lineage cells with the use of an osteocalcin-cre transgene protects mice from ovariectomy-induced bone loss (a murine model of postmenopausal osteoporosis). Ovariectomy fails to induce bone loss, increase bone resorption, and stimulate receptor activator of nuclear factor κB ligand and IL-6 expression in mice lacking p38α in osteoblasts and osteocytes. Finally, TNFα or IL-1, which are osteoclastogenic cytokines overproduced in the bone marrow under estrogen deficiency, can activate p38α signaling in osteoblasts, but those cytokines cannot enhance Rankl and Il6 expressions or increase osteoclast formation in p38a-deficient osteoblast cultures. These findings demonstrate that p38α MAPK signaling in osteoblast lineage cells mediates ovariectomy-induced bone loss by up-regulating receptor activator of nuclear factor κB ligand and IL-6 production.

Focus on the p38 MAPK signaling pathway in bone development and maintenance

The p38 mitogen-activated protein kinase (MAPK) signaling pathway can be activated in response to a wide range of extracellular signals. As a consequence, it can generate many different biological effects that depend on the stimulus and on the activated cell type. Therefore, this pathway has been found to regulate many aspects of tissue development and homeostasis. Recent work with the aid of genetically modified mice has highlighted the physiological functions of this pathway in skeletogenesis and postnatal bone maintenance. In this review, emphasis is given to the roles of the p38 MAPK pathway in chondrocyte, osteoblast and osteoclast biology. In particular, we describe the molecular mechanisms of p38 MAPK activation and downstream targets. The requirement of this pathway in physiological bone development and homeostasis is demonstrated by the ability of p38 MAPK to regulate master transcription factors controlling geneses and functions of chondrocytes, osteoblasts and osteoclasts.

A de novo 1.58 Mb deletion, including MAP2K6 and mapping 1.28 Mb upstream to SOX9, identified in a patient with Pierre Robin sequence and osteopenia with multiple fractures

Defects of long-range regulatory elements of dosage-sensitive genes represent an under-recognized mechanism underlying genetic diseases. Haploinsufficiency of SOX9, the gene essential for development of testes and differentiation of chondrocytes, results in campomelic dysplasia, a skeletal malformation syndrome often associated with sex reversal. Chromosomal rearrangements with breakpoints mapping up to 1.6 Mb up- and downstream to SOX9, and disrupting its distant cis-regulatory elements, have been described in patients with milder forms of campomelic dysplasia, Pierre Robin sequence, and sex reversal. We present an ∼1.58 Mb deletion mapping ∼1.28 Mb upstream to SOX9 that encompasses its putative long-range cis-regulatory element(s) and MAP2K6 in a patient with Pierre Robin sequence and osteopenia with multiple fractures. Low bone mass panel testing using massively parallel sequencing of 23 nuclear genes, including COL1A1 and COL1A2 was negative. Based on the previous mouse model of Map2k6, suggesting that Sox9 is likely a downstream target of the p38 MAPK pathway, and our previous chromosome conformation capture-on-chip (4C) data showing potential interactions between SOX9 promoter and MAP2K6, we hypothesize that deletion of MAP2K6 might have affected SOX9 expression and contributed to our patient's phenotype.

Osteoclast derivation from mouse bone marrow

Osteoclasts are highly specialized cells that are derived from the monocyte/macrophage lineage of the bone marrow. Their unique ability to resorb both the organic and inorganic matrices of bone means that they play a key role in regulating skeletal remodeling. Together, osteoblasts and osteoclasts are responsible for the dynamic coupling process that involves both bone resorption and bone formation acting together to maintain the normal skeleton during health and disease. As the principal bone-resorbing cell in the body, changes in osteoclast differentiation or function can result in profound effects in the body. Diseases associated with altered osteoclast function can range in severity from lethal neonatal disease due to failure to form a marrow space for hematopoiesis, to more commonly observed pathologies such as osteoporosis, in which excessive osteoclastic bone resorption predisposes to fracture formation. An ability to isolate osteoclasts in high numbers in vitro has allowed for significant advances in the understanding of the bone remodeling cycle and has paved the way for the discovery of novel therapeutic strategies that combat these diseases. Here, we describe a protocol to isolate and cultivate osteoclasts from mouse bone marrow that will yield large numbers of osteoclasts.

Dietary Polyphenols, Berries, and Age-Related Bone Loss: A Review Based on Human, Animal, and Cell Studies

Bone loss during aging has become an increasing public health concern as average life expectancy has increased. One of the most prevalent forms of age-related bone disease today is osteoporosis in which the body slows down bone formation and existing bone is increasingly being resorbed by the body to maintain the calcium balance. Some causes of this bone loss can be attributed to dysregulation of osteoblast and osteoclast activity mediated by increased oxidative stress through the aging process. Due to certain serious adverse effects of the currently available therapeutic agents that limit their efficacy, complementary and alternative medicine (CAM) has garnered interest as a natural means for the prevention of this debilitating disease. Natural antioxidant supplementation, a type of CAM, has been researched to aid in reducing bone loss caused by oxidative stress. Naturally occurring polyphenols, such as anthocyanins rich in berries, are known to have anti-oxidative properties. Several studies have been reviewed to determine the impact polyphenol intake-particularly that of berries-has on bone health. Studies reveal a positive association of high berry intake and higher bone mass, implicating berries as possible inexpensive alternatives in reducing the risk of age related bone loss.