STAC2 negatively regulates osteoclast formation by targeting the RANK signaling complex

A Dual-Function CD47-Targeting Nano-Drug Delivery System Used to Regulate Immune and Anti-Inflammatory Activities in the Treatment of Atherosclerosis

Atherosclerosis is a primary contributor to cardiovascular disease. Current studies have highlighted the association between the immune system, particularly immune cells, and atherosclerosis, although treatment options and clinical trials remain scarce. Immunotherapy for cardiovascular disease is still in its infancy. Bruton's tyrosine kinase (BTK), widely expressed in various immune cells, represents a promising therapeutic target for atherosclerosis by modulating the anti-inflammatory function of immune cells. This study introduces a polydopamine-based nanocarrier system to deliver the BTK inhibitor, ibrutinib, to atherosclerotic plaques with an active targeting property via an anti-CD47 antibody. Leveraging polydopamine's pH-sensitive reversible disassembly, the system offers responsive, controlled release within the pathologic microenvironment. This allows precise and efficient ibrutinib delivery, concurrently inhibiting the activation of the NF-κB pathway in B cells and the NLRP3 inflammasome in macrophages within the plaques. This treatment also modulates both the immune cell microenvironment and inflammatory conditions in atherosclerotic lesions, thereby conveying promising therapeutic effects for atherosclerosis in vivo. This strategy also provides a novel option for atherosclerosis treatment.

The histone methyltransferase ASH1L protects against bone loss by inhibiting osteoclastogenesis

Absent, small, or homeotic1-like (ASH1L) is a histone lysine methyltransferase that generally functions as a transcriptional activator in controlling cell fate. So far, its physiological relevance in bone homeostasis and osteoclast differentiation remains elusive. Here, by conditional deleting Ash1l in osteoclast progenitors of mice, we found ASH1L deficiency resulted in osteoporosis and potentiation of osteoclastogenesis in vivo and in vitro. Mechanistically, ASH1L binds the promoter of the Src homology 3 and cysteine-rich domain 2 (Stac2) and increases the gene's transcription via histone 3 lysine 4 (H3K4) trimethylation modification, thus augmenting the STAC2's protection against receptor activator of nuclear factor kB ligand (RANKL)-initiated inflammation during osteoclast formation. Collectively, we demonstrate the first piece of evidence to prove ASH1L as a critical checkpoint during osteoclastogenesis. The work sheds new light on our understanding about the biological function of ASH1L in bone homeostasis, therefore providing a valuable therapeutic target for the treatment of osteoporosis or inflammatory bone diseases.

Modulation of fracture healing by senescence-associated secretory phenotype (SASP): a narrative review of the current literature

The senescence-associated secretory phenotype (SASP) is a generic term for the secretion of cytokines, such as pro-inflammatory factors and proteases. It is a crucial feature of senescent cells. SASP factors induce tissue remodeling and immune cell recruitment. Previous studies have focused on the beneficial role of SASP during embryonic development, wound healing, tissue healing in general, immunoregulation properties, and cancer. However, some recent studies have identified several negative effects of SASP on fracture healing. Senolytics is a drug that selectively eliminates senescent cells. Senolytics can inhibit the function of senescent cells and SASP, which has been found to have positive effects on a variety of aging-related diseases. At the same time, recent data suggest that removing senescent cells may promote fracture healing. Here, we reviewed the latest research progress about SASP and illustrated the inflammatory response and the influence of SASP on fracture healing. This review aims to understand the role of SASP in fracture healing, aiming to provide an important clinical prevention and treatment strategy for fracture. Clinical trials of some senolytics agents are underway and are expected to clarify the effectiveness of their targeted therapy in the clinic in the future. Meanwhile, the adverse effects of this treatment method still need further study.

USP7 Inhibits Osteoclastogenesis via Dual Effects of Attenuating TRAF6/TAK1 Axis and Stimulating STING Signaling

Ubiquitination is a reversible post-translational modification implicated in cell differentiation, homeostasis, and organ development. Several deubiquitinases (DUBs) decrease protein ubiquitination through the hydrolysis of ubiquitin linkages. However, the role of DUBs in bone resorption and formation is still unclear. In this study, we identified DUB ubiquitin-specific protease 7 (USP7) as a negative regulator of osteoclast formation. USP7 combines with tumor necrosis factor receptor-associated factor 6 (TRAF6) and inhibits its ubiquitination by impairing the Lys63-linked polyubiquitin chain. Such impairment leads to the suppression of receptor activator of NF-κB ligand (RANKL)-mediated nuclear factor-κB (NF-κB) and mitogen-activated protein kinases (MAPKs) activation without affecting TRAF6 stability. USP7 also protects the stimulator of interferon genes (STING) against degradation, inducing interferon-β (IFN-β) expression in osteoclast formation, thereby inhibiting osteoclastogenesis cooperatively with the classical TRAF6 pathway. Furthermore, USP7 inhibition accelerates osteoclast differentiation and bone resorption both in vitro and in vivo. Contrarily, USP7 overexpression impairs osteoclast differentiation and bone resorption in vitro and in vivo. Additionally, in ovariectomy (OVX) mice, USP7 levels are lower than those in sham-operated mice, suggesting that USP7 plays a role in osteoporosis. Altogether, our data reveal the dual effect of USP7-mediated TRAF6 signal transduction and USP7-mediated protein degradation of STING in osteoclast formation.

Brevilin A inhibits RANKL-induced osteoclast differentiation and bone resorption

Brevilin A (BA) is the primary component of Centipeda minima, which is widely used in Chinese traditional medicine. The anti-inflammatory and anti-tumor properties of BA have been established; however, its function in bone metabolism is not well understood. This study revealed that concentrations of BA below 1.0 µM did not inhibit the proliferation of bone marrow macrophages but did impede the differentiation and bone resorption activity of osteoclasts. Furthermore, BA suppressed the expression of osteoclast-specific genes Mmp9, Acp5, Dc-stamp, Ctsk, and Atp6v0d2. In addition, mTOR, ERK, and NFATc1 activation in bone marrow macrophages were suppressed by BA. As a whole, BA blocks the mTOR and ERK signaling pathways, which is responsible for the development and activity of osteoclasts, and the resorption of bone.

Annexin A3 accelerates osteoclast differentiation by promoting the level of RANK and TRAF6

Annexin A3 (ANXA3), a member of Annexin family, is reported to mediate membrane transport and cancer development. However, the effect of ANXA3 on osteoclast formation and bone metabolism is still unclear. In this study, we found that knockdown of ANXA3 can significantly inhibit receptor activator of nuclear factor-κB ligand (RANKL)-induced osteoclast formation through NF-κB signaling. ANXA3 downregulation abrogated the expression of osteoclast-specific genes, including Acp5, Mmp9 and Ctsk in osteoclast precursors. Moreover, lentiviral of shRNA against ANXA3 reversed the bone loss in osteoporosis using ovariectomized mice model. Mechanistically, we found that ANXA3 directly bound to RANK and TRAF6 to accelerate osteoclast differentiation by promoting their transcription and limiting degradation. In conclusion, we propose a fundamentally novel RANK-ANXA3-TRAF6 complex to effectively modulate the formation and differentiation of osteoclast to manipulate bone metabolism. The ANXA3-targeted therapeutic strategy may provide new insight for bone degrading-related diseases prevention and treatment.

Molecular interactions of STAC proteins with skeletal muscle dihydropyridine receptor and excitation‐contraction coupling

Excitation‐contraction coupling (ECC) is the physiological process in which an electrical signal originating from the central nervous system is converted into muscle contraction. In skeletal muscle tissue, the key step in the molecular mechanism of ECC initiated by the muscle action potential is the cooperation between two Ca²⁺ channels, dihydropyridine receptor (DHPR; voltage‐dependent L‐type calcium channel) and ryanodine receptor 1 (RyR1). These two channels were originally postulated to communicate with each other via direct mechanical interactions; however, the molecular details of this cooperation have remained ambiguous. Recently, it has been proposed that one or more supporting proteins are in fact required for communication of DHPR with RyR1 during the ECC process. One such protein that is increasingly believed to play a role in this interaction is the SH3 and cysteine‐rich domain‐containing protein 3 (STAC3), which has been proposed to bind a cytosolic portion of the DHPR α_1S subunit known as the II–III loop. In this work, we present direct evidence for an interaction between a small peptide sequence of the II–III loop and several residues within the SH3 domains of STAC3 as well as the neuronal isoform STAC2. Differences in this interaction between STAC3 and STAC2 suggest that STAC3 possesses distinct biophysical features that are potentially important for its physiological interactions with the II–III loop. Therefore, this work demonstrates an isoform‐specific interaction between STAC3 and the II–III loop of DHPR and provides novel insights into a putative molecular mechanism behind this association in the skeletal muscle ECC process.

Effects of Artemisia annua L. Essential Oil on Osteoclast Differentiation and Function Induced by RANKL

Objective

This study aimed to assess the main components of Artemisia annua L. essential oil (AEO) and determine their effect on the proliferation and differentiation of RAW264.7 cells induced by receptor activator for nuclear factor-ligand (RANKL) in vitro. Then, we tried to explain part of the function of its possible mechanisms.

Materials and Methods

Essential oil was extracted from Artemisia annua L. Osteoclasts were induced in vitro by RANKL in mouse RAW264.7 cells. The experimental group was treated with different concentrations of AEO, while the control group was not treated with AEO. CCK8 was used to detect osteoclast proliferation. The osteoclasts were stained with TRAP. Western blot was used to detect protein in the MAPK pathway and the NF-κB pathway after treatment with different concentrations of AEO. RT-PCR was used to determine the expression of osteoclast-related mRNA in cells.

Results

The GC-MS analysis was used to obtain the main components of AEO, including camphor, borneol, camphor, borneol, terpinen-4-ol, p-cymene, eucalyptol, deoxyartemisinin, and artemisia ketone. The CCK8 results showed that the AEO volume ratio of 1 : 4000, 1 : 5000, and 1 : 6000 did not affect the proliferation of RAW264.7 cells. However, TRAP staining showed that AEO decreased osteoclast formation. Western blot results showed that the expression of protein TRAF6, p-p38, p-ERK, p-p65, and NFATc1 decreased in the MAPK pathway and the NF-κB pathway affected by AEO. Furthermore, RT-PCR results showed that the expression of osteoclast resorption-related mRNAs (MMP-9, DC-STAMP, TRAP, and CTSK) and osteoclast differentiation-related mRNAs (OSCAR, NFATc1, c-Src, and c-Fos) also decreased in the experimental group.

Conclusions

AEO inhibits osteoclast differentiation in vitro, probably by reducing TRAF6 activation, acting on the MAPK pathway and NF-κB pathway, and inhibiting the expression of osteoclast-related genes.

CYT387, a JAK-Specific Inhibitor Impedes Osteoclast Activity and Oophorectomy-Induced Osteoporosis via Modulating RANKL and ROS Signaling Pathways

Osteoclasts are of hematopoietic lineage and have the ability to degrade mineralized bone tissues. Abnormalities in osteoclastic activity under certain pathological conditions are common in bone diseases such as osteoporosis, osteosclerosis, and arthritis. Although many kinds of drugs are currently used to treat osteoporosis, they have obvious adverse reactions and limitations. CYT387 is a new small-molecule Janus kinase (JAK) inhibitor involved in hematopoiesis, immune modulation, fertility, lactation, and embryonic development. However, it has remained unclear whether CYT387 functionally impacts osteoclast formation. Our study demonstrated through osteoclast formation assay in vitro, that the use of CYT387 is a potential drug candidate for treating osteoclast-associated bone disease. The effects of CYT387 on osteoclast formation, bone resorption, NFATc1 activation, and especially intracellular ROS levels were investigated in vitro. Further, we examined the preclinical prospects of CYT387 using an oophorectomy (OVX) mouse model of osteoporosis with its anti-osteoclast activity in vivo. On the whole, this study shows that CYT387 holds promise for treating osteoclast-related bone illnesses including osteoporosis.

Phosphoproteomics of Mycobacterium-host interaction and inspirations for novel measures against tuberculosis

Tuberculosis caused by Mycobacterium tuberculosis (Mtb) remains a tremendous global public health concern. Deciphering the biology of the pathogen and its interaction with host can inspire new measures against tuberculosis. Phosphorylation plays versatile and important role in the pathogen and host physiology, such as virulence, signaling and immune response. Proteome-wide phosphorylation of Mtb and its infected host cells, namely phosphoproteome, can inform the post-translational modification of the interaction network between the pathogen and the host, key targets for novel antibiotics. We summarized the phosphoproteome of Mtb, as well as the host, focusing on potential application for new measures against tuberculosis.

Oroxin B Attenuates Ovariectomy-Induced Bone Loss by Suppressing Osteoclast Formation and Activity

Background

Osteoclasts are the major players in bone resorption and have always been studied in the prevention and treatment of osteoporosis. Previous studies have confirmed that a variety of flavonoids inhibit osteoporosis and improve bone health mainly through inhibiting osteoclastogenesis. Oroxin B (OB) is a flavonoid compound extracted from traditional Chinese herbal medicine Oroxylum indicum (L.) Vent, exerts potent antitumor and anti-inflammation effect, but its effect on osteoclastogensis remains unknown.

Methods

We comprehensively evaluated the effect of OB on the formation and function of osteoclasts and the underling mechanism by bone marrow-derived macrophage in vitro. In vivo, we used mice ovariectomized model to verify the protective effect of OB.

Results

OB was found to inhibit osteoclast formation and bone resorption function in vitro, in a dose-dependent manner and the increased osteoclastic-related genes induced by RANKL (NFATc1, c-fos, cathepsin K, RANK, MMP9 and TRAP) were also attenuated following OB treatment. Mechanistical investigation showed OB abrogated the increased phosphorylation level of MAPK and NF-κB pathway, and diminished the expression of the vital transcription factors for osteoclastogenesis. OB also prevented ovariectomy (OVX)-induced bone loss by inhibiting osteoclast formation and activity in mice.

Conclusion

Our study demonstrated that OB may act as an anti-osteoporosis agent by inhibiting osteoclast maturation and attenuating bone resorption.

TRPV6 is a potential regulator of bone resorption in bone loss induced by estrogen deficiency

The precise effect of estrogen (E2) on osteoclast function is still poorly understood. The aim of this study was to investigate the potential role of transient receptor potential vanilloid 6 (TRPV6) in E2-mediated osteoclast function and to characterize the relevant underlying mechanisms. Here, we found that Trpv6 is drastically decreased in ovariectomy operation animals and the administration of E2 results in an increased expression of Trpv6 in osteoclasts. In contrast, Trpv6 depletion significantly blocked the inhibitory effects of E2 on bone resorption activity, and silencing Trpv6 alleviated E2-induced osteoclast apoptosis. In addition, we found that E2 regulates the transcription of Trpv6 through ERα, by interacting with C/EBPβ and NF-κB. Chip assay analysis indicated that C/EBPβ regulates Trpv6 transcription by binding to Trpv6 promoter fragments −1,866 nt to −1,761 nt and −2,685 nt to −2,580 nt, whereas NF-κB binds to the −953 nt to −851 nt region. We conclude that TRPV6 has a significant effect on E2-mediated osteoclast function.

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E2 induces Trpv6 expression in osteoclasts

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TRPV6 was involved in the effect of E2-mediated osteoclast function

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E2 regulates the transcription of Trpv6 through Erα in osteoclasts

Plastrum testudinis extract suppresses osteoclast differentiation via the NF-κB signaling pathway and ameliorates senile osteoporosis

ETHNOPHARMACOLOGICAL RELEVANCE

Plastrum testudinis (PT) is a kind of single traditional Chinese medicine that can tonify kidney and strengthen bone. Plastrum testudinis extract (PTE) has been approved to promote the osteogenic differentiation of bone marrow-derived mesenchymal stem cells in vitro. However, the mechanism by which PTE reduces osteoclast differentiation has not yet been reported.

AIM OF THE STUDY

To explore the potential of PTE as a therapeutic treatment for bone loss caused by senile osteoporosis (SOP).

MATERIALS AND METHODS

We evaluated whether PTE could inhibit RANKL-induced osteoclast differentiation both in vitro and in vivo, and investigated PTE-induced phenotypes of human peripheral blood monocytes.

RESULTS

We found that PTE inhibited osteoclast differentiation and bone resorption in vitro in a concentration-dependent manner and that PTE treatment is most effective during the early stages of osteoclastogenesis. Moreover, we found that PTE could block the NF-κB signaling pathway in vitro, leading to the down-regulation of osteoclast-specific genes including C-FOS and NFATC1. The results from our in vivo mouse study suggest that PTE treatment suppresses osteoclast formation and mitigates bone loss caused by SOP. Notably, we also found that PTE inhibited RANKL-induced osteoclast differentiation in human peripheral blood monocytes.

CONCLUSION

Our results suggest that PTE treatment suppresses osteoclastogenesis and ameliorates bone loss caused by SOP by selectively blocking the nuclear translocation of NF-κB/p50.

Structure and function of STAC proteins: Calcium channel modulators and critical components of muscle excitation-contraction coupling

In skeletal muscle tissue, an intriguing mechanical coupling exists between two ion channels from different membranes: the L-type voltage-gated calcium channel (Ca_V1.1), located in the plasma membrane, and ryanodine receptor 1 (RyR1) located in the sarcoplasmic reticulum membrane. Excitable cells rely on Ca_vs to initiate Ca²⁺ entry in response to action potentials. RyRs can amplify this signal by releasing Ca²⁺ from internal stores. Although this process can be mediated through Ca²⁺ as a messenger, an overwhelming amount of evidence suggests that RyR1 has recruited Ca_V1.1 directly as its voltage sensor. The exact mechanisms that underlie this coupling have been enigmatic, but a recent wave of reports have illuminated the coupling protein STAC3 as a critical player. Without STAC3, the mechanical coupling between Ca_v1.1 and RyR1 is lost, and muscles fail to contract. Various sequence variants of this protein have been linked to congenital myopathy. Other STAC isoforms are expressed in the brain and may serve as regulators of L-type Ca_Vs. Despite the short length of STACs, several points of contacts have been proposed between them and Ca_Vs. However, it is currently unclear whether STAC3 also forms direct interactions with RyR1, and whether this modulates RyR1 function. In this review, we discuss the 3D architecture of STAC proteins, the biochemical evidence for their interactions, the relevance of these connections for functional modulation, and their involvement in myopathy.

In silico candidate variant and gene identification using inbred mouse strains

Mice are the most widely used animal model to study genotype to phenotype relationships. Inbred mice are genetically identical, which eliminates genetic heterogeneity and makes them particularly useful for genetic studies. Many different strains have been bred over decades and a vast amount of phenotypic data has been generated. In addition, recently whole genome sequencing-based genome-wide genotype data for many widely used inbred strains has been released. Here, we present an approach for in silico fine-mapping that uses genotypic data of 37 inbred mouse strains together with phenotypic data provided by the user to propose candidate variants and genes for the phenotype under study. Public genome-wide genotype data covering more than 74 million variant sites is queried efficiently in real-time to provide those variants that are compatible with the observed phenotype differences between strains. Variants can be filtered by molecular consequences and by corresponding molecular impact. Candidate gene lists can be generated from variant lists on the fly. Fine-mapping together with annotation or filtering of results is provided in a Bioconductor package called MouseFM. In order to characterize candidate variant lists under various settings, MouseFM was applied to two expression data sets across 20 inbred mouse strains, one from neutrophils and one from CD4⁺ T cells. Fine-mapping was assessed for about 10,000 genes, respectively, and identified candidate variants and haplotypes for many expression quantitative trait loci (eQTLs) reported previously based on these data. For albinism, MouseFM reports only one variant allele of moderate or high molecular impact that only albino mice share: a missense variant in the Tyr gene, reported previously to be causal for this phenotype. Performing in silico fine-mapping for interfrontal bone formation in mice using four strains with and five strains without interfrontal bone results in 12 genes. Of these, three are related to skull shaping abnormality. Finally performing fine-mapping for dystrophic cardiac calcification by comparing 9 strains showing the phenotype with eight strains lacking it, we identify only one moderate impact variant in the known causal gene Abcc6. In summary, this illustrates the benefit of using MouseFM for candidate variant and gene identification.

2-NPPA Mitigates Osteoclastogenesis via Reducing TRAF6-Mediated c-fos Expression

Excessive bone resorption leads to bone destruction in pathological bone diseases. Osteoporosis, which occurs when osteoclast-mediated bone resorption exceeds osteoblast-mediated bone synthesis, is regarded a global health challenge. Therefore, it is of great importance to identify agents that can regulate the activity of osteoclasts and prevent bone diseases mediated mainly by bone loss. We screened compounds for this purpose and found that 2-(2-chlorophenoxy)-N-[2-(4-propionyl-1piperazinyl) phenyl] acetamide (2-NPPA) exhibited a strong inhibitory effect on osteoclastogenesis. 2-NPPA suppressed the mRNA and protein expression of several osteoclast-specific markers and blocked the formation of mature osteoclasts, reducing the F-actin ring formation and bone resorption activity. In a cell signaling point of view, 2-NPPA exhibited a significant inhibitory effect on the phosphorylation of nuclear factor kappa-B (NF-κB) and c-fos expression in vitro and prevented ovariectomy-induced bone loss in vivo. These findings highlighted the potential of 2-NPPA as a drug for the treatment of bone loss-mediated disorders.

The calcium channel TRPV6 is a novel regulator of RANKL-induced osteoclastic differentiation and bone absorption activity through the IGF-PI3K-AKT pathway

Objectives

Calcium ion signals are important for osteoclast differentiation. Transient receptor potential vanilloid 6 (TRPV6) is a regulator of bone homeostasis. However, it was unclear whether TRPV6 was involved in osteoclast formation. Therefore, the aim of this study was to evaluate the role of TPRV6 in bone metabolism and to clarify its regulatory role in osteoclasts at the cellular level.

Materials and methods

Bone structure and histological changes in Trpv6 knockout mice were examined using micro‐computed tomography and histological analyses. To investigate the effects of Trpv6 on osteoclast function, we silenced or overexpressed Trpv6 in osteoclasts via lentivirus transfection, respectively. Osteoclast differentiation and bone resorption viability were measured by tartrate‐resistant acid phosphatase (TRAP) staining and pit formation assays. The expression of osteoclast marker genes, including cathepsin k, DC‐STAMP, Atp6v0d2 and TRAP, was measured by qRT‐PCR. Cell immunofluorescence and Western blotting were applied to explore the mechanisms by which the IGF‐PI3K‐AKT pathway was involved in the regulation of osteoclast formation and bone resorption by Trpv6.

Results

We found that knockout of Trpv6 induced osteoporosis and enhanced bone resorption in mice, but did not affect bone formation. Further studies showed that Trpv6, which was distributed on the cell membrane of osteoclasts, acted as a negative regulator for osteoclast differentiation and function. Mechanistically, Trpv6 suppressed osteoclastogenesis by decreasing the ratios of phosphoprotein/total protein in the IGF–PI3K–AKT signalling pathway. Blocking of the IGF–PI3K–AKT pathway significantly alleviated the inhibitory effect of Trpv6 on osteoclasts formation.

Conclusions

Our study confirmed the important role of Trpv6 in bone metabolism and clarified its regulatory role in osteoclasts at the cellular level. Taken together, this study may inspire a new strategy for the treatment of osteoporosis.

Landscape of Genome-Wide DNA Methylation of Colorectal Cancer Metastasis

Colorectal cancer is a heterogeneous disease caused by both genetic and epigenetics factors. Analysing DNA methylation changes occurring during colorectal cancer progression and metastasis formation is crucial for the identification of novel epigenetic markers of patient prognosis. Genome-wide methylation sequencing of paired samples of colon (normal adjacent, primary tumour and lymph node metastasis) showed global hypomethylation and CpG island (CGI) hypermethylation of primary tumours compared to normal. In metastasis we observed high global and non-CGI regions methylation, but lower CGI methylation, compared to primary tumours. Gene ontology analysis showed shared biological processes between hypermethylated CGIs in metastasis and primary tumours. After complementary analysis with The Cancer Genome Atlas (TCGA) cohort, FIGN, HTRA3, BDNF, HCN4 and STAC2 genes were found associated with poor survival. We mapped the methylation landscape of colon normal tissues, primary tumours and lymph node metastasis, being capable of identified methylation changes throughout the genome. Furthermore, we found five genes with potential for methylation biomarkers of poor prognosis in colorectal cancer patients.

Plasma proteomic profiling of young and old mice reveals cadherin-13 prevents age-related bone loss

The blood exhibits a dynamic flux of proteins that are secreted by the tissues and cells of the body. To identify novel aging-related circulating proteins, we compared the plasma proteomic profiles of young and old mice using tandem mass spectrometry. The expression of 134 proteins differed between young and old mice. We selected seven proteins that were expressed at higher levels in young mice, and confirmed their plasma expression in immunoassays. The plasma levels of anthrax toxin receptor 2 (ANTXR2), cadherin-13 (CDH-13), scavenger receptor cysteine-rich type 1 protein M130 (CD163), cartilage oligomeric matrix protein (COMP), Dickkopf-related protein 3 (DKK3), periostin, and secretogranin-1 were all confirmed to decrease with age. We then investigated whether any of the secreted proteins influenced bone metabolism and found that CDH-13 inhibited osteoclast differentiation. CDH 13 treatment suppressed the receptor activator of NF-κB ligand (RANKL) signaling pathway in bone marrow-derived macrophages, and intraperitoneal administration of CDH-13 delayed age-related bone loss in the femurs of aged mice. These findings suggest that low plasma CDH-13 expression in aged mice promotes aging-associated osteopenia by facilitating excessive osteoclast formation. Thus, CDH-13 could have therapeutic potential as a protein drug for the prevention of osteopenia.

Spi-C positively regulates RANKL-mediated osteoclast differentiation and function

Spi-C is an SPI-group erythroblast transformation-specific domain transcription factor expressed during B-cell development. Here, we report that Spi-C is a novel receptor activator of nuclear factor-κB ligand (RANKL)-inducible protein that positively regulates RANKL-mediated osteoclast differentiation and function. Knockdown of Spi-C decreased the expression of RANKL-induced nuclear factor of activated T-cells, cytoplasmic 1, receptor activator of nuclear factor-κB (RANK), and tartrate-resistant acid phosphatase (TRAP), resulting in a marked decrease in the number of TRAP-positive multinucleated cells. Spi-C-transduced bone marrow-derived monocytes/macrophages (BMMs) displayed a significant increase in osteoclast formation in the presence of RANKL. In addition, Spi-C-depleted cells failed to show actin ring formation or bone resorption owing to a marked reduction in the expression of RANKL-mediated dendritic cell-specific transmembrane protein and the d2 isoform of vacuolar (H+) ATPase V0 domain, which are known osteoclast fusion-related genes. Interestingly, RANKL stimulation induced the translocation of Spi-C from the cytoplasm into the nucleus during osteoclastogenesis, which was specifically blocked by inhibitors of p38 mitogen-activated protein kinase (MAPK) or PI3 kinase. Moreover, Spi-C depletion prevented RANKL-induced MAPK activation and the degradation of inhibitor of κB-α (IκBα) in BMMs. Collectively, these results suggest that Spi-C is a novel positive regulator that promotes both osteoclast differentiation and function.

A gene-controlling protein called Spi-C promotes the development of bone-processing cells called osteoclasts; details of the molecular mechanisms involved will aid understanding of Spi-C’s role in bone health and disease. Osteoclasts degrade bone during the normal process of bone remodeling, balanced by the activity of osteoblast cells that form new bone. Excessive osteoclast activity can cause the bone loss associated with various bone diseases including early-onset osteoporosis. Researchers in South Korea led by Soo Young Lee at Ewha Womans University and Na Kyung Lee at Soonchunhyang University, Asan, found that Spi-C promotes osteoclast development by activating genes that code for key proteins of a signaling pathway known to be crucial for bone health. Drugs that interfere with Spi-C activity may therefore offer a new approach for treating bone disease.

RANKL signaling in bone marrow mesenchymal stem cells negatively regulates osteoblastic bone formation

RANKL signaling is essential for osteoclastogenesis. Its role in osteoblastic differentiation and bone formation is unknown. Here we demonstrate that RANK is expressed at an early stage of bone marrow mesenchymal stem cells (BMSCs) during osteogenic differentiation in both mice and human and decreased rapidly. RANKL signaling inhibits osteogenesis by promoting β-catenin degradation and inhibiting its synthesis. In contrast, RANKL signaling has no significant effects on adipogenesis of BMSCs. Interestingly, conditional knockout of rank in BMSCs with Prx1-Cre mice leads to a higher bone mass and increased trabecular bone formation independent of osteoclasts. In addition, rank^flox/flox: Prx1-Cre mice show resistance to ovariectomy-(OVX) induced bone loss. Thus, our results reveal that RANKL signaling regulates both osteoclasts and osteoblasts by inhibition of osteogenic differentiation of BMSCs and promotion of osteoclastogenesis.

Researchers in China have shown that a gene known for breaking bones down is also involved in making new bone. Bones are constantly repaired and reshaped by cells which break down bone tissue, osteoclasts, and those which create new bone, osteoblasts. The RANKL gene is known to play an important role in osteoclast development, but Jiacan Su of the Second Military Medical University has shown that it is also important for osteoblasts. Su’s team detected high expression of RANKL and its receptor, RANK, in bone marrow stem cells, and the levels decreased as the stem cells differentiated into osteoblasts. Artificially increasing RANK expression decreased osteoblast differentiation, while reducing its expression increased osteoblast differentiation and bone mass. By showing that RANKL regulates osteoblasts as well as osteoclasts, these findings open new avenues for understanding bones development.

Allosteric regulators selectively prevent Ca2+-feedback of CaV and NaV channels

Calmodulin (CaM) serves as a pervasive regulatory subunit of Ca_V1, Ca_V2, and Na_V1 channels, exploiting a functionally conserved carboxy-tail element to afford dynamic Ca²⁺-feedback of cellular excitability in neurons and cardiomyocytes. Yet this modularity counters functional adaptability, as global changes in ambient CaM indiscriminately alter its targets. Here, we demonstrate that two structurally unrelated proteins, SH3 and cysteine-rich domain (stac) and fibroblast growth factor homologous factors (fhf) selectively diminish Ca²⁺/CaM-regulation of Ca_V1 and Na_V1 families, respectively. The two proteins operate on allosteric sites within upstream portions of respective channel carboxy-tails, distinct from the CaM-binding interface. Generalizing this mechanism, insertion of a short RxxK binding motif into Ca_V1.3 carboxy-tail confers synthetic switching of CaM regulation by Mona SH3 domain. Overall, our findings identify a general class of auxiliary proteins that modify Ca²⁺/CaM signaling to individual targets allowing spatial and temporal orchestration of feedback, and outline strategies for engineering Ca²⁺/CaM signaling to individual targets.

Stac Proteins Suppress Ca2+-Dependent Inactivation of Neuronal l-type Ca2+ Channels

Stac protein (named for its SH3- and cysteine-rich domains) was first identified in brain 20 years ago and is currently known to have three isoforms. Stac2, Stac1, and Stac3 transcripts are found at high, modest, and very low levels, respectively, in the cerebellum and forebrain, but their neuronal functions have been little investigated. Here, we tested the effects of Stac proteins on neuronal, high-voltage-activated Ca²⁺ channels. Overexpression of the three Stac isoforms eliminated Ca²⁺-dependent inactivation (CDI) of l-type current in rat neonatal hippocampal neurons (sex unknown), but not CDI of non-l-type current. Using heterologous expression in tsA201 cells (together with β and α₂-δ₁ auxiliary subunits), we found that CDI for Ca_V1.2 and Ca_V1.3 (the predominant, neuronal l-type Ca²⁺ channels) was suppressed by all three Stac isoforms, whereas CDI for the P/Q channel, Ca_V2.1, was not. For Ca_V1.2, the inhibition of CDI by the Stac proteins appeared to involve their direct interaction with the channel's C terminus. Within the Stac proteins, a weakly conserved segment containing ∼100 residues and linking the structurally conserved PKC C1 and SH3_1 domains was sufficient to fully suppress CDI. The presence of CDI for l-type current in control neonatal neurons raised the possibility that endogenous Stac levels are low in these neurons and Western blotting indicated that the expression of Stac2 was substantially increased in adult forebrain and cerebellum compared with neonate. Together, our results indicate that one likely function of neuronal Stac proteins is to tune Ca²⁺ entry via neuronal l-type channels.SIGNIFICANCE STATEMENT Stac protein, first identified 20 years ago in brain, has recently been found to be essential for proper trafficking and function of the skeletal muscle l-type Ca2+ channel and is the site of mutations causing a severe, inherited human myopathy. In neurons, however, functions for Stac protein have remained unexplored. Here, we report that one likely function of neuronal Stac proteins is tuning Ca2+ entry via l-type, but not that via non-l-type, Ca2+ channels. Moreover, there is a large postnatal increase in protein levels of the major neuronal isoform (Stac2) in forebrain and cerebellum, which could provide developmental regulation of l-type channel Ca2+ signaling in these brain regions.