Hairy and Enhancer of Split-related with YRPW motif (HEY)2 regulates bone remodeling in mice

Pulsed electromagnetic field-assisted reduced graphene oxide composite 3D printed nerve scaffold promotes sciatic nerve regeneration in rats

Peripheral nerve injuries can lead to sensory or motor deficits that have a serious impact on a patient's mental health and quality of life. Nevertheless, it remains a major clinical challenge to develop functional nerve conduits as an alternative to autologous grafts. We applied reduced graphene oxide (rGO) as a bioactive conductive material to impart electrophysiological properties to a 3D printed scaffold and the application of a pulsed magnetic field to excite the formation of microcurrents and induce nerve regeneration.In vitrostudies showed that the nerve scaffold and the pulsed magnetic field made no effect on cell survival, increased S-100βprotein expression, enhanced cell adhesion, and increased the expression level of nerve regeneration-related mRNAs.In vivoexperiments suggested that the protocol was effective in promoting nerve regeneration, resulting in functional recovery of sciatic nerves in rats, when they were damaged close to that of the autologous nerve graft, and increased expression of S-100β, NF200, and GAP43. These results indicate that rGO composite nerve scaffolds combined with pulsed magnetic field stimulation have great potential for peripheral nerve rehabilitation.

Berberine inhibited the formation of metastasis by intervening the secondary homing of colorectal cancer cells in the blood circulation to the lung and liver through HEY2

BACKGROUND

Metastasis is the leading cause of death in patients with colorectal cancer (CRC). The 5-year survival rate of CRC patients in whom the cancer has spread to distant sites is 13.5%. The most common sites of CRC metastasis are liver and lung. The principal therapies for CRC metastatic disease are surgery, but its benefits are limited.

PURPOSE

This study aimed to reveal the regulatory mechanism of berberine on secondary homing of CRC cells to form metastatic focus. This was more valuable than the previous direct study of the migration and metastasis characteristics of CRC cells.

METHODS

In this study, we used the functional enrichment analysis of differentially expressed genes after berberine treatment and investigated co-expression modules related with CRC metastasis by WGCNA. PPI and survival analyses of significant modules were also conducted. The biological functions of berberine in CRC lung and liver metastasis were investigated by a series of in vitro and in vivo experiments: MTT, colony formation and mouse tail vein injection. And we scanned through the entire extracellular domain of HEY2 protein for autodocking analysis with berberine.

RESULTS

We found the differentially expressed genes (DEGs) after berberine treatment were related with cancer progression and metastasis related pathways. Through WGCNA analysis, four cancer progression and metastasis related modules were detected. After PPI and survival analysis, we identified and validated HEY2 as a hub gene, high expression and poor survival at the metastatic stage. Functionally, berberine inhibited the survival, invasion and migration of CRC cells in vitro and in vivo. Mechanistically, berberine treatment down-regulated the expression of HEY2, metastasis related protein E-cadherin, β-catenin and Cyclin D1 during Mesenchymal epithelial transformation (MET). Berberine and HEY2 showed a significant interaction, and berberine binded to HEY2 protein at the residue HIS-99 interface with a hydrogen-bond distance of 1.9A.

CONCLUSIONS

We revealed that berberine could significantly inhibit the expression of hub gene HEY2 and metastasis related proteins E-cadherin and β-catenin and Cyclin D1 during MET in CRC lung and liver metastases. In total, HEY2 was a promising candidate biomarker for prognosis and molecular characteristics in CRC metastasis.

Transcriptomic alterations underline aging of osteogenic bone marrow stromal cells

BACKGROUND

Multipotent bone marrow stromal cells (BMSCs) are adult stem cells that form functional osteoblasts and play a critical role in bone remodeling. During aging, an increase in bone loss and reduction in structural integrity lead to osteoporosis and result in an increased risk of fracture. We examined age-dependent histological changes in murine vertebrae and uncovered that bone loss begins as early as the age of 1 mo.

AIM

To identify the functional alterations and transcriptomic dynamics of BMSCs during early bone loss.

METHODS

We collected BMSCs from mice at early to middle ages and compared their self-renewal and differentiation potential. Subsequently, we obtained the transcriptomic profiles of BMSCs at 1 mo, 3 mo, and 7 mo.

RESULTS

The colony-forming and osteogenic commitment capacity showed a comparable finding that decreased at the age of 1 mo. The transcriptomic analysis showed the enrichment of osteoblastic regulation genes at 1 mo and loss of osteogenic features at 3 mo. The BMSCs at 7 mo showed enrichment of adipogenic and DNA repair features. Moreover, we demonstrated that the WNT and MAPK signaling pathways were upregulated at 1 mo, followed by increased pro-inflammatory and apoptotic features.

CONCLUSION

Our study uncovered the cellular and molecular dynamics of bone aging in mice and demonstrated the contribution of BMSCs to the early stage of age-related bone loss.

Notch in skeletal physiology and disease

Notch (Notch1 through 4) are transmembrane receptors that play a fundamental role in cell differentiation and function. Notch receptors are activated following interactions with their ligands in neighboring cells. There are five classic ligands termed Jagged (Jag)1 and Jag2 and Delta-like (Dll)1, Dll3, and Dll4. Recent work has established Notch as a signaling pathway that plays a critical role in the differentiation and function of cells of the osteoblast and osteoclast lineages and in skeletal development and bone remodeling. The effects of Notch are cell-context dependent, and the four Notch receptors carry out specific functions in the skeleton. Gain- and loss-of-function mutations of components of the Notch signaling pathway result in a variety of congenital disorders with significant craniofacial and skeletal manifestations. The Notch ligand Jag1 is a determinant of bone mineral density, and Notch plays a role in the early phases of fracture healing. Alterations in Notch signaling are associated with osteosarcoma and with the metastatic potential of carcinoma of the breast and of the prostate. Controlling Notch signaling could prove useful in diseases of Notch gain-of-function and in selected skeletal disorders. However, clinical data on agents that modify Notch signaling are not available. In conclusion, Notch signaling is a novel pathway that regulates skeletal homeostasis in health and disease.

Glucocorticoids inhibit notch target gene expression in osteoblasts

Glucocorticoids in excess suppress osteoblast function and cause osteoporosis. We demonstrated that cortisol induces the expression of selected Notch receptors in osteoblasts, revealing a potential mechanism for the skeletal effects of glucocorticoids. However, it remains to be determined whether increased expression of Notch receptors results into enhanced signaling. Following activation of Notch, its intracellular domain (NICD) binds to the DNA-associated protein recombination signal binding protein for immunoglobulin kappa-J region (RBPJ) and induces the expression of target genes such as Hey1, Hey2, and HeyL. To determine whether glucocorticoids modulate Notch signaling in the skeleton, 1 month old wild-type mice were administered prednisolone or placebo and sacrificed after 72 h, and gene expression was analyzed in femoral bone. Prednisolone induced Tsc22d3, a glucocorticoid target gene, and suppressed Hey1 and HeyL expression, which is indicative of inhibited Notch receptor activity or direct Hey downregulation. To determine the mechanisms of Hey suppression, wild-type osteoblast-enriched cells were seeded on the Notch cognate ligand Delta-like (DLL)1 or transfected with constructs expressing the NOTCH1 NICD fragment and exposed to either cortisol or vehicle. Cortisol opposed the induction of mRNA and heterogeneous nuclear RNA for Hey1, Hey2, and HeyL by DLL1, but had no effect on mRNA stability, indicating that glucocorticoids inhibit Hey expression by transcriptional mechanisms. Transactivation studies and electrophoretic mobility shift assays revealed that cortisol did not oppose RBPJ-mediated transcription or RBPJ/DNA interactions, respectively. In conclusion, glucocorticoids suppress expression of Hey1, Hey2, and HeyL in osteoblasts by RBPJ-independent transcriptional mechanisms.

Sustained Notch2 signaling in osteoblasts, but not in osteoclasts, is linked to osteopenia in a mouse model of Hajdu-Cheney syndrome

Individuals with Hajdu-Cheney syndrome (HCS) present with osteoporosis, and HCS is associated with NOTCH2 mutations causing deletions of the proline-, glutamic acid-, serine-, and threonine-rich (PEST) domain that are predicted to enhance NOTCH2 stability and cause gain-of-function. Previously, we demonstrated that mice harboring Notch2 mutations analogous to those in HCS (Notch2HCS) are severely osteopenic because of enhanced bone resorption. We attributed this phenotype to osteoclastic sensitization to the receptor activator of nuclear factor-κB ligand and increased osteoblastic tumor necrosis factor superfamily member 11 (Tnfsf11) expression. Here, to determine the individual contributions of osteoclasts and osteoblasts to HCS osteopenia, we created a conditional-by-inversion (Notch2^COIN ) model in which Cre recombination generates a Notch2^ΔPEST allele expressing a Notch2 mutant lacking the PEST domain. Germ line Notch2^COIN inversion phenocopied the Notch2HCS mutant, validating the model. To activate Notch2 in osteoclasts or osteoblasts, Notch2^COIN mice were bred with mice expressing Cre from the Lyz2 or the BGLAP promoter, respectively. These crosses created experimental mice harboring a Notch2^ΔPEST allele in Cre-expressing cells and control littermates expressing a wild-type Notch2 transcript. Notch2^COIN inversion in Lyz2-expressing cells had no skeletal consequences and did not affect the capacity of bone marrow macrophages to form osteoclasts in vitro In contrast, Notch2^COIN inversion in osteoblasts led to generalized osteopenia associated with enhanced bone resorption in the cancellous bone compartment and with suppressed endocortical mineral apposition rate. Accordingly, Notch2 activation in osteoblast-enriched cultures from Notch2^COIN mice induced Tnfsf11 expression. In conclusion, introduction of the HCS mutation in osteoblasts, but not in osteoclasts, causes osteopenia.

Hairy and Enhancer of Split-Related With YRPW Motif-Like (HeyL) Is Dispensable for Bone Remodeling in Mice

Notch induces Hairy Enhancer of Split (Hes)1 and Hes-related with YRPW motif (Hey) Hey1, Hey2 and Hey-like (HeyL) expression in osteoblasts, but it is not known whether any of these target genes mediates the effect of Notch in the skeleton. We demonstrated that Notch1 activation in osteoblasts/osteocytes induces Hes1, Hey1, Hey2, and HeyL, but HeyL was induced to a greater extent than other target genes. To characterize HeyL null mice for their skeletal phenotype, microcomputed tomography (µCT) and histomorphometric analysis of HeyL null and sex-matched littermate controls was performed. µCT demonstrated modest cancellous bone osteopenia in 1 month old male mice and normal microarchitecture in 3 month old male HeyL null mice. Female HeyL null mice were not different from controls at either 1 or 3 months of age. Bone histomorphometry did not demonstrate differences between HeyL null mice of either sex and littermate controls. In conclusion, HeyL null mice do not exhibit an obvious skeletal phenotype demonstrating that HeyL is dispensable for skeletal homeostasis. J. Cell. Biochem. 118: 1819-1826, 2017. © 2016 Wiley Periodicals, Inc.

Notch Signaling and the Skeleton

Notch 1 to 4 receptors are important determinants of cell fate and function, and Notch signaling plays an important role in skeletal development and bone remodeling. After direct interactions with ligands of the Jagged and Delta-like families, a series of cleavages release the Notch intracellular domain (NICD), which translocates to the nucleus where it induces transcription of Notch target genes. Classic gene targets of Notch are hairy and enhancer of split (Hes) and Hes-related with YRPW motif (Hey). In cells of the osteoblastic lineage, Notch activation inhibits cell differentiation and causes cancellous bone osteopenia because of impaired bone formation. In osteocytes, Notch1 has distinct effects that result in an inhibition of bone resorption secondary to an induction of osteoprotegerin and suppression of sclerostin with a consequent enhancement of Wnt signaling. Notch1 inhibits, whereas Notch2 enhances, osteoclastogenesis and bone resorption. Congenital disorders of loss- and gain-of-Notch function present with severe clinical manifestations, often affecting the skeleton. Enhanced Notch signaling is associated with osteosarcoma, and Notch can influence the invasive potential of carcinoma of the breast and prostate. Notch signaling can be controlled by the use of inhibitors of Notch activation, small peptides that interfere with the formation of a transcriptional complex, or antibodies to the extracellular domain of specific Notch receptors or to Notch ligands. In conclusion, Notch plays a critical role in skeletal development and homeostasis, and serious skeletal disorders can be attributed to alterations in Notch signaling.

Id transcriptional regulators in adipogenesis and adipose tissue metabolism

Id proteins (Id1-Id4) are helix-loop-helix (HLH) transcriptional regulators that lack a basic DNA binding domain. They act as negative regulators of basic helix-loop-helix (bHLH) transcription factors by forming heterodimers and inhibit their DNA binding and transcriptional activity. Id proteins are implicated in the regulation of various cellular mechanisms such as cell proliferation, cellular differentiation, cell fate determination, angiogenesis and tumorigenesis. A handful of recent studies also disclosed that Id proteins have critical functions in adipocyte differentiation and adipose tissue metabolism. Here, we reviewed the progress made thus far in understanding the specific functions of Id proteins in adipose tissue differentiation and metabolism. In addition to reviewing the known mechanisms of action, we also discuss possible additional mechanisms in which Id proteins might participate in regulating adipogenic and metabolic pathways.

Notch1 and Notch2 expression in osteoblast precursors regulates femoral microarchitecture

Notch receptors regulate cell differentiation and function. Notch1 and Notch2 inactivation in osteoblasts and osteocytes increases cancellous bone volume, but the function of Notch signaling in osteoblast precursors is unknown. To inactivate Notch signaling in immature osteoblastic cells, mice homozygous for conditional Notch1 and Notch2 alleles (Notch1(loxP/loxP);Notch2(loxP/loxP)) were crossed with mice where the osterix (Osx) promoter, regulated by a Tet-Off cassette, governs Cre expression (Osx-Cre). Notch1(loxP/loxP);Notch2(loxP/loxP) control and Osx-Cre(+/-);Notch1(Δ/Δ);Notch2(Δ/Δ) experimental littermate cohorts were obtained. To prevent the effects of embryonic Osx-Cre expression, doxycycline was administered to pregnant dams, but not to newborns. Recombination of conditional alleles was documented in calvarial DNA extracts from 1month old mice. Notch1 and Notch2 inactivation did not affect femoral microarchitecture at 1month of age. Cancellous bone volume was higher and structure model index was lower in 3 and 6 month old Osx-Cre(+/-);Notch1(Δ/Δ);Notch2(Δ/Δ) mice than in control littermates and the effect was more pronounced in female mice. One month old Osx-Cre(+/-);Notch1(Δ/Δ);Notch2(Δ/Δ) male mice transiently exhibited an increase in osteoblast number and a modest suppression in bone resorption. Osx-Cre(+/-);Notch1(Δ/Δ);Notch2(Δ/Δ) female mice displayed a tendency toward increased bone formation at 3months of age, although bone remodeling was suppressed in 6month old Osx-Cre(+/-);Notch1(Δ/Δ);Notch2(Δ/Δ) female mice. Notch1 and Notch2 inactivation increased porosity and reduced thickness of cortical bone. These effects were modest and more evident in 3 and 6 month old female than in male mice of the same age. In conclusion, Notch1 and Notch2 expression in osteoblast precursors regulates cancellous bone volume and microarchitecture.

Reduced trabecular bone mass and strength in mice overexpressing Gα11 protein in cells of the osteoblast lineage

G protein-coupled receptors (GPCRs) require G proteins for intracellular signaling to regulate a variety of growth and maintenance processes, including osteogenesis and bone turnover. Bone maintenance events may be altered by changes in the activity or level of G proteins, which then modify signaling in bone cells such as osteoblasts. We have previously reported increased levels of Gα11 protein and signaling to phospholipase C/protein kinase C pathways in response to dexamethasone in osteoblastic UMR 106-01 cells. Here we generated pOBCol3.6-GNA11 transgenic mice that overexpress Gα11 protein in cells of the osteoblast lineage (G11-Tg mice). G11-Tg mice exhibit an osteopenic phenotype characterized by significant reductions in trabecular bone mineral density, thickness, number and strength. The numbers of osteoblasts and osteocytes were unchanged in G11-Tg bone, but early markers of osteoblast differentiation, Alp and Bsp, were increased while the late stage differentiation marker Ocn was not changed suggesting reduced osteoblast maturation in G11-Tg trabecular bone which was accompanied by a decreased bone formation rate. Furthermore, in vitro cultures of G11-Tg primary osteoblasts show delayed osteoblast differentiation and mineralization. Histological analyses also revealed increased osteoclast parameters, accompanied by elevated mRNA expression of Trap and Ctsk. mRNA levels of Rankl and M-csf were elevated in vitro in bone marrow stromal cells undergoing osteogenesis and in trabecular bone in vivo. Together, these findings demonstrate that increasing Gα11 protein expression in osteoblasts can alter gene expression and result in a dual mechanism of trabecular bone loss.

Sex and genetic factors determine osteoblastic differentiation potential of murine bone marrow stromal cells

Sex and genetic factors determine skeletal mass, and we tested whether bone histomorphometric parameters were sexually dimorphic in femurs from 1 to 6 month old C57BL/6 mice. Trabecular bone volume declined more rapidly in female mice than in male littermates because of enhanced bone resorption. Although bone formation was not different between sexes, female mice exhibited a higher number of osteoblasts than male littermates, suggesting that osteoblasts from female mice may have a reduced ability to form bone. To determine the impact of sex on osteoblastogenesis, we investigated the potential for osteoblastic differentiation of bone marrow stromal cells from C57BL/6, Friend leukemia virus-B (FVB), C3H/HeJ and BALB/c mice of both sexes. Bone marrow stromal cells from female FVB, C57BL/6 and C3H/HeJ mice exhibited lower Alpl and Osteocalcin expression and alkaline phosphatase activity, and formed fewer mineralized nodules than cells from male littermates. Proliferative capacity was greater in cells from male than female C57BL/6, but not FVB, mice. Sorting of bone marrow stromal cells from mice expressing an α-Smooth muscle actin-green fluorescent protein transgene, revealed a higher yield of mesenchymal stem cells in cultures from male mice than in those from female littermates. Sex had a modest impact on osteoblastic differentiation of mesenchymal stem cells. To determine the influence of sex and genetic factors on osteoblast function, calvarial osteoblasts were harvested from C57BL/6, FVB, C3H/HeJ and BALB/c mice. Alpl expression and activity were lower in osteoblasts from C57BL/6 and C3H/HeJ, but not FVB or BALB/c, female mice than in cells from littermates. Sex had no effect on osteoclastogenesis of bone marrow cultures of C57BL/6 mice, but osteoblasts from female mice exhibited higher Rankl and lower Opg expression than cells from male littermates. In conclusion, osteoblastogenesis is sexually dimorphic and influenced by genetic factors.

Hey bHLH transcription factors

Hey bHLH transcription factors are direct targets of canonical Notch signaling. The three mammalian Hey proteins are closely related to Hes proteins and they primarily repress target genes by either directly binding to core promoters or by inhibiting other transcriptional activators. Individual candidate gene approaches and systematic screens identified a number of Hey target genes, which often encode other transcription factors involved in various developmental processes. Here, we review data on interaction partners and target genes and conclude with a model for Hey target gene regulation. Furthermore, we discuss how expression of Hey proteins affects processes like cell fate decisions and differentiation, e.g., in cardiovascular, skeletal, and neural development or oncogenesis and how this relates to the observed developmental defects and phenotypes observed in various knockout mice.