LDL receptor-related protein 5 (LRP5) affects bone accrual and eye development

Enterococcus faecium Modulates the Gut Microbiota of Broilers and Enhances Phosphorus Absorption and Utilization

Modern broiler chickens have ongoing bone health problems. Phosphorus (P) plays an important role in bone development and increased understanding of P metabolism should improve the skeletal health of broilers. Enterococcus faecium has been widely used as a probiotic in broiler production and is shown to improve skeletal health of rats, but its effect on the bones of broilers remains unclear. This study investigated the effect of E. faecium on P absorption and utilization in broilers and the associated changes in the gut microbiota using 16S rDNA sequencing. Dietary supplementation with E. faecium improved P absorption through upregulation of the expression of intestinal NaP-IIb mRNA and increased the concentration of serum alkaline phosphatase. These actions increased P retention and bone mineralization in E. faecium-treated broilers. The positive effects of E. faecium on P metabolism were associated with changes in the populations of the intestinal microbiota. There was increased relative abundance of the following genera, Alistipes, Eubacterium, Rikenella and Ruminococcaceae and a decrease in the relative abundance of Faecalibacterium and Escherichia-Shigella. Dietary supplementation with E. faecium changed gut microbiota populations of broilers, increased the relative abundance of SCFA (short-chain fatty acid)-producing bacteria, improved intestinal P absorption and bone forming metabolic activities, and decreased P excretion. E. faecium facilitates increased utilisation of P in broilers.

The Function of Wnt Ligands on Osteocyte and Bone Remodeling

Bone homeostasis is continually maintained by the process of bone remodeling throughout life. Recent studies have demonstrated that Wnt signaling pathways play a fundamental role in the process of bone homeostasis and remodeling. Intracellular Wnt signaling cascades are initially triggered by a Wnt ligand-receptor complex formation. In previous studies, the blocking of Wnt ligands from different osteoblastic differentiation stages could cause defective bone development at an early stage. Osteocytes, the most abundant and long-lived type of bone cell, are a crucial orchestrator of bone remodeling. However, the role of Wnt ligands on osteocyte and bone remodeling remains unclear. In our present study, we found that, besides osteoblasts, osteocytes also express multiple Wnt ligands in the bone environment. Then, we used a Dmp1-Cre mouse line, in which there is expression in a subset of osteoblasts but mainly osteocytes, to study the function of Wnt ligands on osteocyte and bone remodeling in vivo. Furthermore, we explored the role of Wnt ligands on osteocytic mineralization ability, as well as the regulatory function of osteocytes on the process of osteoblastic differentiation and osteoclastic migration and maturity in vitro. We concluded that Wnt proteins play an important regulatory role in 1) the process of perilacunar/canalicular remodeling, as mediated by osteocytes, and 2) the balance of osteogenesis and bone resorption at the bone surface, as mediated by osteoblasts and osteoclasts, at least partly through the canonical Wnt/β-catenin signaling pathway and the OPG/RANKL signaling pathway.

USP4 function and multifaceted roles in cancer: a possible and potential therapeutic target

Cancer remains one of the major culprits causing disease-related deaths and leads to a high morbidity and similar mortality. Insidious onset, difficult early detection and a lack of broad-spectrum and effective multi-cancer therapeutic targets have limited the prolongation of cancer patients’ survival for decades. Therefore, a versatile therapeutic target which is involved in various cancer-related signaling pathways and different cancers may be more effective for cancer targeted therapy. USP4, one of the DUBs members which participates in deubiquitination, an inverse process of ubiquitination, can regulate various classical cancer-related signaling pathways, and thereby plays a vital role in some pathological and physiological processes including tumor initiation and progression. Recently, USP4 has been found to exert versatile influences on cells proliferation, migration and invasion, also apoptosis of various tumors. Moreover, USP4 can also act as a prognostic biomarker in several cancers. This review will give a comprehensive introduction of USP4 about its regulatory mechanisms, related signaling pathways, pathophysiological functions and the roles in various cancers which may help us better understand its biological functions and improve future studies to construct suitable USP4-targeted cancer therapy system.

Anti-DKK1 Enhances the Early Osteogenic Differentiation of Human Adipose-Derived Stem/Stromal Cells

Adipose-derived stem/stromal cells (ASCs) have been previously used for bone repair. However, significant cell heterogeneity exists within the ASC population, which has the potential to result in unreliable bone tissue formation and/or low efficacy. Although the use of cell sorting to lower cell heterogeneity is one method to improve bone formation, this is a technically sophisticated and costly process. In this study, we tried to find a simpler and more deployable solution-blocking antiosteogenic molecule Dickkopf-1 (DKK1) to improve osteogenic differentiation. Human adipose-derived stem cells were derived from = 5 samples of human lipoaspirate. In vitro, anti-DKK1 treatment, but not anti-sclerostin (SOST), promoted ASC osteogenic differentiation, assessed by alizarin red staining and real-time polymerase chain reaction (qPCR). Increased canonical Wnt signaling was confirmed after anti-DKK1 treatment. Expression levels of DKK1 peaked during early osteogenic differentiation (day 3). Concordantly, anti-DKK1 supplemented early (day 3 or before), but not later (day 7) during osteogenic differentiation positively regulated osteoblast formation. Finally, anti-DKK1 led to increased transcript abundance of the Wnt inhibitor SOST, potentially representing a compensatory cellular mechanism. In sum, DKK1 represents a targetable "molecular brake" on the osteogenic differentiation of human ASC. Moreover, release of this brake by neutralizing anti-DKK1 antibody treatment at least partially rescues the poor bone-forming efficacy of ASC.

Pten deletion in Dmp1-expressing cells does not rescue the osteopenic effects of Wnt/β-catenin suppression

Skeletal homeostasis is sensitive to perturbations in Wnt signaling. Beyond its role in the bone, Wnt is a major target for pharmaceutical inhibition in a wide range of diseases, most notably cancers. Numerous clinical trials for Wnt-based candidates are currently underway, and Wnt inhibitors will likely soon be approved for clinical use. Given the bone-suppressive effects accompanying Wnt inhibition, there is a need to expose alternate pathways/molecules that can be targeted to counter the deleterious effects of Wnt inhibition on bone properties. Activation of the Pi3k/Akt pathway via Pten deletion is one possible osteoanabolic pathway to exploit. We investigated whether the osteopenic effects of β-catenin deletion from bone cells could be rescued by Pten deletion in the same cells. Mice carrying floxed alleles for Pten and β-catenin were bred to Dmp1-Cre mice to delete Pten alone, β-catenin alone, or both genes from the late-stage osteoblast/osteocyte population. The mice were assessed for bone mass, density, strength, and formation parameters to evaluate the potential rescue effect of Pten deletion in Wnt-impaired mice. Pten deletion resulted in high bone mass and β-catenin deletion resulted in low bone mass. Compound mutants had bone properties similar to β-catenin mutant mice, or surprisingly in some assays, were further compromised beyond β-catenin mutants. Pten inhibition, or one of its downstream nodes, is unlikely to protect against the bone-wasting effects of Wnt/βcat inhibition. Other avenues for preserving bone mass in the presence of Wnt inhibition should be explored to alleviate the skeletal side effects of Wnt inhibitor-based therapies.

Consanguineous-derived homozygous WNT1 mutation results in osteogenesis imperfect with congenital ptosis and exotropia

Background

Wnt signaling pathway plays an important role in promoting ostergenesis. WNT1 mutations have been considered as a major cause of ostergenesis imperfect (OI). We identified an OI patient with pathogenic consanguineous‐derived homozygous WNT1 missense mutation.

Methods

We designed and applied a panel of known 261 genes associated with hereditary bone diseases for targeted next‐generation sequencing to examine clinically diagnosed OI patients. Detected mutations were confirmed by Sanger sequencing.

Results

The female proband presented with severe OI with low bone density, multiple long bone fractures, short stature, and absence of dentinogenesis imperfect and brain malformation. She had congenital ptosis and exotropia with her left eye, and absence of blue sclera. The proband came from a consanguineous family and had a homozygous WNT1 missense mutation (c.677C>T, (p.S226L)). In addition, three other compound heterozygous mutations (c.1729C>T in FKBP10, c.1958A>C in FGFR3, c.760G>C in TRPV4) were also detected in her family members.

Conclusion

We report the first identified case of consanguineous derived homozygous WNT1 mutation leading to severe osteogenesis imperfecta with congenital ptosis and exotropia.

Switching Homes: How Cancer Moves to Bone

Bone metastases (BM) are a very common complication of the most prevalent human cancers. BM are extremely painful and may be life-threatening when associated with hypercalcaemia. BM can lead to kidney failure and cardiac arrhythmias and arrest, but why and how do cancer cells decide to "switch homes" and move to bone? In this review, we will present what answers science has provided so far, with focus on the molecular mechanisms and cellular aspects of well-established findings, such as the concept of "vicious cycle" and "osteolytic" vs. "osteosclerotic" bone metastases; as well as on novel concepts, such as cellular dormancy and extracellular vesicles. At the molecular level, we will focus on hypoxia-associated factors and angiogenesis, the Wnt pathway, parathyroid hormone-related peptide (PTHrP) and chemokines. At the supramolecular/cellular level, we will discuss tumour dormancy, id est the mechanisms through which a small contingent of tumour cells coming from the primary site may be kept dormant in the endosteal niche for many years. Finally, we will present a potential role for the multimolecular mediators known as extracellular vesicles in determining bone-tropism and establishing a premetastatic niche by influencing the bone microenvironment.

Targeted next generation sequencing of nine osteoporosis-related genes in the Wnt signaling pathway among Chinese postmenopausal women

PURPOSE

This study aimed to explore the association between low-frequency and rare variants of Wnt signaling genes and postmenopausal osteoporosis (OP) by the next generation sequencing (NGS) technology.

METHODS

We performed targeted NGS of nine Wnt signaling genes in 400 Chinese postmenopausal women, including 226 cases with decreased bone mineral density (BMD) and 174 controls with normal values. Proxy External Controls Association Test (ProxECAT) and logistic regression analysis were performed by data from internal cases (n = 226) and Genome Aggregation Database (gnomAD) East Asian controls (n = 9435).

RESULTS

The genomic region of interest (ROI) of 94 functional low-frequency and rare variants was associated with OP risk (P < 0.05). The LGR6 gene was associated significantly with OP risk and BMD measurements (BMD, T-score and Z-score) (adjusted-P < 0.05) after adjusting for confounders. The allele A of rs199693693 (K82N) in LRP6 and G of novel variant 1: 202287949 (R840G) in LGR6 were associated with higher BMD, T-score, and Z-score (all adjusted-P < 0.05). ProxECAT showed that LGR4 was significantly different between the internal cases and the external controls (all adjusted-P < 0.05). Logistic regression analysis revealed that the allele G of rs765778410 (T645A) (OR = 26.16, 95% CI: 4.36-156.95, adjusted-P value = 0.026) in LGR6 and A of rs61370283 (L987M) (OR = 15.39, 95% CI: 2.98-79.55, adjusted-P value = 0.037) in LRP5 were associated with increased risk of postmenopausal OP.

CONCLUSION

The LGR4 and LGR6 genes and four potential functional rare variants associate with postmenopausal OP risk. These results highlight the significance of rare functional variants in postmenopausal OP genetics and provide new insights into the potential mutations in this field.

Regulation of Angiogenesis Discriminates Tissue Resident MSCs from Effective and Defective Osteogenic Environments

Background: The biological mechanisms that contribute to atrophic long bone non-union are poorly understood. Multipotential mesenchymal stromal cells (MSCs) are key contributors to bone formation and are recognised as important mediators of blood vessel formation. This study examines the role of MSCs in tissue formation at the site of atrophic non-union. Materials and Methods: Tissue and MSCs from non-union sites (n = 20) and induced periosteal (IP) membrane formed following the Masquelet bone reconstruction technique (n = 15) or bone marrow (n = 8) were compared. MSC content, differentiation, and influence on angiogenesis were measured in vitro. Cell content and vasculature measurements were performed by flow cytometry and histology, and gene expression was measured by quantitative polymerase chain reaction (qPCR). Results: MSCs from non-union sites had comparable differentiation potential to bone marrow MSCs. Compared with induced periosteum, non-union tissue contained similar proportion of colony-forming cells, but a greater proportion of pericytes (p = 0.036), and endothelial cells (p = 0.016) and blood vessels were more numerous (p = 0.001) with smaller luminal diameter (p = 0.046). MSCs showed marked differences in angiogenic transcripts depending on the source, and those from induced periosteum, but not non-union tissue, inhibited early stages of in vitro angiogenesis. Conclusions: In vitro, non-union site derived MSCs have no impairment of differentiation capacity, but they differ from IP-derived MSCs in mediating angiogenesis. Local MSCs may thus be strongly implicated in the formation of the immature vascular network at the non-union site. Attention should be given to their angiogenic support profile when selecting MSCs for regenerative therapy.

Biomarkers in WNT1 and PLS3 Osteoporosis: Altered Concentrations of DKK1 and FGF23

Recent advancements in genetic research have uncovered new forms of monogenic osteoporosis, expanding our understanding of the molecular pathways regulating bone health. Despite active research, knowledge on the pathomechanisms, disease-specific biomarkers, and optimal treatment in these disorders is still limited. Mutations in WNT1, encoding a WNT/β-catenin pathway ligand WNT1, and PLS3, encoding X chromosomally inherited plastin 3 (PLS3), both result in early-onset osteoporosis with prevalent fractures and disrupted bone metabolism. However, despite marked skeletal pathology, conventional bone markers are usually normal in both diseases. Our study aimed to identify novel bone markers in PLS3 and WNT1 osteoporosis that could offer diagnostic potential and shed light on the mechanisms behind these skeletal pathologies. We measured several parameters of bone metabolism, including serum dickkopf-1 (DKK1), sclerostin, and intact and C-terminal fibroblast growth factor 23 (FGF23) concentrations in 17 WNT1 and 14 PLS3 mutation-positive subjects. Findings were compared with 34 healthy mutation-negative subjects from the same families. Results confirmed normal concentrations of conventional metabolic bone markers in both groups. DKK1 concentrations were significantly elevated in PLS3 mutation-positive subjects compared with WNT1 mutation-positive subjects (p < .001) or the mutation-negative subjects (p = .002). Similar differences were not seen in WNT1 subjects. Sclerostin concentrations did not differ between any groups. Both intact and C-terminal FGF23 were significantly elevated in WNT1 mutation-positive subjects (p = .039 and p = .027, respectively) and normal in PLS3 subjects. Our results indicate a link between PLS3 and DKK1 and WNT1 and FGF23 in bone metabolism. The normal sclerostin and DKK1 levels in patients with impaired WNT signaling suggest another parallel regulatory mechanism. These findings provide novel information on the molecular networks in bone. Extended studies are needed to investigate whether these biomarkers offer diagnostic value or potential as treatment targets in osteoporosis. © 2020 American Society for Bone and Mineral Research.

Frizzled 6 disruption suppresses osteoblast differentiation induced by nanotopography through the canonical Wnt signaling pathway

This study aimed to investigate if wingless-related integration site (Wnt) signaling participates in the high osteogenic potential of titanium with nanotopography (Ti-Nano). We showed that among the several components of the Wnt signaling pathway, Frizzled 6 (Fzd6) was the transcript most intensely modulated by nanotopography compared with the untreated Ti surface (Ti-Machined). Then, we investigated whether and how Fzd6 participates in the regulation of osteoblast differentiation caused by nanotopography. The Fzd6 silencing with CRISPR-Cas9 transfection in MC3T3-E1 cells induced a more pronounced inhibition of osteoblast differentiation of cells cultured on nanotopography than those cultured on Ti-Machined. The analysis of the expression of calcium-calmodulin-dependent protein kinase II and β-catenin demonstrated that Fzd6 disruption inhibited the osteoblast differentiation induced by Ti-Nano by preventing the activation of Wnt/β-catenin but not that of Wnt/Ca²⁺ signaling, which is usually triggered by the receptor Fzd6. These findings elucidate the biological function of Fzd6 as a receptor that triggers Wnt/β-catenin signaling and the cellular mechanisms modulated by nanotopography during osteoblast differentiation.

Piezo1/2 mediate mechanotransduction essential for bone formation through concerted activation of NFAT-YAP1-ß-catenin

Mechanical forces are fundamental regulators of cell behaviors. However, molecular regulation of mechanotransduction remain poorly understood. Here, we identified the mechanosensitive channels Piezo1 and Piezo2 as key force sensors required for bone development and osteoblast differentiation. Loss of Piezo1, or more severely Piezo1/2, in mesenchymal or osteoblast progenitor cells, led to multiple spontaneous bone fractures in newborn mice due to inhibition of osteoblast differentiation and increased bone resorption. In addition, loss of Piezo1/2 rendered resistant to further bone loss caused by unloading in both bone development and homeostasis. Mechanistically, Piezo1/2 relayed fluid shear stress and extracellular matrix stiffness signals to activate Ca²⁺ influx to stimulate Calcineurin, which promotes concerted activation of NFATc1, YAP1 and ß-catenin transcription factors by inducing their dephosphorylation as well as NFAT/YAP1/ß-catenin complex formation. Yap1 and ß-catenin activities were reduced in the Piezo1 and Piezo1/2 mutant bones and such defects were partially rescued by enhanced ß-catenin activities.

Synergistic Effects of Erzhi Pill Combined With Methotrexate on Osteoblasts Mediated via the Wnt1/LRP5/β-Catenin Signaling Pathway in Collagen-Induced Arthritis Rats

Rheumatoid arthritis (RA) is a chronic systemic autoimmune disease characterized by chronic synovitis, bone erosion, and bone loss. Erzhi Pill (EZP), a classic Chinese patent medicine, is often used to treat osteoporosis and shows a capacity for bone metabolism regulation. Methotrexate (MTX), an essential drug for RA treatment, has been reported to inhibit generalized bone loss in RA patients. However, the combined therapeutic effects and mechanism of EZP and MTX in RA have not been fully elucidated. The aim of this study was to investigate the synergistic effect of EZP and MTX on RA and to explore the underlying mechanism through network pharmacological prediction and experimental verification. Chemical compounds of EZP, human target proteins of EZP and MTX, and RA-related human genes were identified in the Encyclopedia of Traditional Chinese Medicine database, PubChem database, and NCBI database, respectively. The molecular network of EZP and MTX in RA was generated and analyzed with Ingenuity Pathway Analysis software according to the datasets. Then, MTX monotherapy, EZP monotherapy, and combined MTX and EZP therapy were administered to collagen-induced arthritis rats, followed by assessment of pathological score, bone damage, bone alkaline phosphatases (BALP), and tartrate-resistant acid phosphatase (TRACP), and of gene levels related to the Wnt1/LRP5/β-catenin pathway according to network pharmacological analysis. Finally, serum samples from MTX-, EZP- and MTX+EZP-treated rats were used to treat the rat osteoblast (OB)-like UMR-106 cell line to evaluate gene levels related to Wnt1/LRP5/β-catenin. Network pharmacological analysis showed that the Wnt/β-catenin signaling pathway was the top signaling pathway shared among MTX, EZP, and RA. The results from in vivo experiments indicated that EZP combined with MTX reduced arthritis severity, alleviated ankle bone damage, increased BALP and decreased TRACP serum levels, and regulated the mRNA expression of Wnt1, LRP5, β-catenin, Runx2, BALP, and BGP in the ankles. In vitro experiments showed that EZP combined with MTX could also improve the expression of genes related to the Wnt1/LRP5/β-catenin pathway. This study demonstrated that EZP in combination with MTX played a synergistic role in regulating OBs in RA, which was connected to the modulatory effect of EZP and MTX on the Wnt1/LRP5/β-catenin signaling pathway.

The physiological role of Wnt pathway in normal development and cancer

Over the decades, many studies have illustrated the critical roles of Wnt signaling pathways in both developmental processes as well as tumorigenesis. Due to the complexity of Wnt signaling regulation, there are still questions to be addressed about ways cells are able to manipulate different types of Wnt pathways in order to fulfill the requirements for normal or cancer development. In this review, we will describe different types of Wnt signaling pathways and their roles in both normal developmental processes and their role in cancer development and progression. Additionally, we will briefly introduce new strategies currently in clinical trials targeting Wnt signaling pathway components for cancer therapy.

Role of thyroid hormones in craniofacial development

The development of the craniofacial skeleton relies on complex temporospatial organization of diverse cell types by key signalling molecules. Even minor disruptions to these processes can result in deleterious consequences for the structure and function of the skull. Thyroid hormone deficiency causes delayed craniofacial and tooth development, dysplastic facial features and delayed development of the ossicles in the middle ear. Thyroid hormone excess, by contrast, accelerates development of the skull and, in severe cases, might lead to craniosynostosis with neurological sequelae and facial hypoplasia. The pathogenesis of these important abnormalities remains poorly understood and underinvestigated. The orchestration of craniofacial development and regulation of suture and synchondrosis growth is dependent on several critical signalling pathways. The underlying mechanisms by which these key pathways regulate craniofacial growth and maturation are largely unclear, but studies of single-gene disorders resulting in craniofacial malformations have identified a number of critical signalling molecules and receptors. The craniofacial consequences resulting from gain-of-function and loss-of-function mutations affecting insulin-like growth factor 1, fibroblast growth factor receptor and WNT signalling are similar to the effects of altered thyroid status and mutations affecting thyroid hormone action, suggesting that these critical pathways interact in the regulation of craniofacial development.

Destroy to Rebuild: The Connection Between Bone Tissue Remodeling and Matrix Metalloproteinases

Bone is a dynamic organ that undergoes constant remodeling, an energetically costly process by which old bone is replaced and localized bone defects are repaired to renew the skeleton over time, thereby maintaining skeletal health. This review provides a general overview of bone’s main players (bone lining cells, osteocytes, osteoclasts, reversal cells, and osteoblasts) that participate in bone remodeling. Placing emphasis on the family of extracellular matrix metalloproteinases (MMPs), we describe how: (i) Convergence of multiple protease families (including MMPs and cysteine proteinases) ensures complexity and robustness of the bone remodeling process, (ii) Enzymatic activity of MMPs affects bone physiology at the molecular and cellular levels and (iii) Either overexpression or deficiency/insufficiency of individual MMPs impairs healthy bone remodeling and systemic metabolism. Today, it is generally accepted that proteolytic activity is required for the degradation of bone tissue in osteoarthritis and osteoporosis. However, it is increasingly evident that inactivating mutations in MMP genes can also lead to bone pathology including osteolysis and metabolic abnormalities such as delayed growth. We argue that there remains a need to rethink the role played by proteases in bone physiology and pathology.

Inducible expression of Wnt7b promotes bone formation in aged mice and enhances fracture healing

There remain unmet clinical needs for safe and effective bone anabolic therapies to treat aging-related osteoporosis and to improve fracture healing in cases of nonunion or delayed union. Wnt signaling has emerged as a promising target pathway for developing novel bone anabolic drugs. Although neutralizing antibodies against the Wnt antagonist sclerostin have been tested, Wnt ligands themselves have not been fully explored as a potential therapy. Previous work has demonstrated Wnt7b as an endogenous ligand upregulated during osteoblast differentiation, and that Wnt7b overexpression potently stimulates bone accrual in the mouse. The earlier studies however did not address whether Wnt7b could promote bone formation when specifically applied to aged or fractured bones. Here we have developed a doxycycline-inducible strategy where Wnt7b is temporally induced in the bones of aged mice or during fracture healing. We report that forced expression of Wnt7b for 1 month starting at 15 months of age greatly stimulated trabecular and endosteal bone formation, resulting in a marked increase in bone mass. We further tested the effect of Wnt7b on bone healing in a murine closed femur fracture model. Induced expression of Wnt7b at the onset of fracture did not affect the initial cartilage formation but promoted mineralization of the subsequent bone callus. Thus, targeted delivery of Wnt7b to aged bones or fracture sites may be explored as a potential therapy.

Enhancing Activity of Pleurotus sajor-caju (Fr.) Sing β-1,3-Glucanoligosaccharide (Ps-GOS) on Proliferation, Differentiation, and Mineralization of MC3T3-E1 Cells through the Involvement of BMP-2/Runx2/MAPK/Wnt/β-Catenin Signaling Pathway

Osteoporosis is a leading world health problem that results from an imbalance between bone formation and bone resorption. β-glucans has been extensively reported to exhibit a wide range of biological activities, including antiosteoporosis both in vitro and in vivo. However, the molecular mechanisms responsible for β-glucan-mediated bone formation in osteoblasts have not yet been investigated. The oyster mushroom Pleurotus sajor-caju produces abundant amounts of an insoluble β-glucan, which is rendered soluble by enzymatic degradation using Hevea glucanase to generate low-molecular-weight glucanoligosaccharide (Ps-GOS). This study aimed to investigate the osteogenic enhancing activity and underlining molecular mechanism of Ps-GOS on osteoblastogenesis of pre-osteoblastic MC3T3-E1 cells. In this study, it was demonstrated for the first time that low concentrations of Ps-GOS could promote cell proliferation and division after 48 h of treatment. In addition, Ps-GOS upregulated the mRNA and protein expression level of bone morphogenetic protein-2 (BMP-2) and runt-related transcription factor-2 (Runx2), which are both involved in BMP signaling pathway, accompanied by increased alkaline phosphatase (ALP) activity and mineralization. Ps-GOS also upregulated the expression of osteogenesis related genes including ALP, collagen type 1 (COL1), and osteocalcin (OCN). Moreover, our novel findings suggest that Ps-GOS may exert its effects through the mitogen-activated protein kinase (MAPK) and wingless-type MMTV integration site (Wnt)/β-catenin signaling pathways.

Frizzled-4 is required for normal bone acquisition despite compensation by Frizzled-8

The activation of the Wnt/β-catenin signaling pathway is critical for skeletal development but surprisingly little is known about the requirements for the specific frizzled (Fzd) receptors that recognize Wnt ligands. To define the contributions of individual Fzd proteins to osteoblast function, we profiled the expression of all 10 mammalian receptors during calvarial osteoblast differentiation. Expression of Fzd4 was highly upregulated during in vitro differentiation and therefore targeted for further study. Mice lacking Fzd4 in mature osteoblasts had normal cortical bone structure but reduced cortical tissue mineral density and also exhibited an impairment in the femoral trabecular bone acquisition that was secondary to a defect in the mineralization process. Consistent with this observation, matrix mineralization, markers of osteoblastic differentiation, and the ability of Wnt3a to stimulate the accumulation of β-catenin were reduced in cultures of calvarial osteoblasts deficient for Fzd4. Interestingly, Fzd4-deficient osteoblasts exhibited an increase in the expression of Fzd8 both in vitro and in vivo, which suggests that the two receptors may exhibit overlapping functions. Indeed, ablating a single Fzd8 allele in osteoblast-specific Fzd4 mutants produced a more severe effect on bone acquisition. Taken together, our data indicate that Fzd4 is required for normal bone development and mineralization despite compensation from Fzd8.

Bone Regeneration, Reconstruction and Use of Osteogenic Cells; from Basic Knowledge, Animal Models to Clinical Trials

The deterioration of the human skeleton's capacity for self-renewal occurs naturally with age. Osteoporosis affects millions worldwide, with current treatments including pharmaceutical agents that target bone formation and/or resorption. Nevertheless, these clinical approaches often result in long-term side effects, with better alternatives being constantly researched. Mesenchymal stem cells (MSCs) derived from bone marrow and adipose tissue are known to hold therapeutic value for the treatment of a variety of bone diseases. The following review summarizes the latest studies and clinical trials related to the use of MSCs, both individually and combined with other methods, in the treatment of a variety of conditions related to skeletal health. For example, some of the most recent works noted the advantage of bone grafts based on biomimetic scaffolds combined with MSC and growth factor delivery, with a greatly increased regeneration rate and minimized side effects for patients. This review also highlights the continuing research into the mechanisms underlying bone homeostasis, including the key transcription factors and signalling pathways responsible for regulating the differentiation of osteoblast lineage. Paracrine factors and specific miRNAs are also believed to play a part in MSC differentiation. Furthering the understanding of the specific mechanisms of cellular signalling in skeletal remodelling is key to incorporating new and effective treatment methods for bone disease.

Bruck syndrome 2 variant lacking congenital contractures and involving a novel compound heterozygous PLOD2 mutation

Bruck syndrome (BRKS) is the rare disorder that features congenital joint contractures often with pterygia and subsequent fractures, also known as osteogenesis imperfecta (OI) type XI (OMIM # 610968). Its two forms, BRKS1 (OMIM # 259450) and BRKS2 (OMIM # 609220), reflect autosomal recessive (AR) inheritance of FKBP10 and PLOD2 loss-of-function mutations, respectively. A 10-year-old girl was referred with blue sclera, osteopenia, poorly-healing fragility fractures, Wormian skull bones, cleft soft palate, congenital fusion of cervical vertebrae, progressive scoliosis, bell-shaped thorax, restrictive and reactive pulmonary disease, protrusio acetabuli, short stature, and additional dysmorphic features without joint contractures. Iliac crest biopsy after alendronate treatment that improved her bone density revealed low trabecular connectivity, abundant patchy osteoid, and active bone formation with widely-spaced tetracycline labels. Chromosome 22q11 deletion analysis for velocardiofacial syndrome, COL1A1 and COL1A2 sequencing for prevalent types of OI, and Sanger sequencing of LRP5, PPIB, FKBP10, and IFITM5 for rare pediatric osteoporoses were negative. Copy number microarray excluded a contiguous gene syndrome. Instead, exome sequencing revealed two missense variants in PLOD2 which encodes procollagen-lysine, 2-oxoglutarate 5-dioxygenase 2 (lysyl hydroxylase 2, LH2); exon 8, c.797G>T, p.Gly266Val (paternal), and exon 12, c.1280A>G, p.Asn427Ser (maternal). In the Exome Aggregation Consortium (ExAC) database, low frequency (Gly266Val, 0.0000419) and absence (Asn427Ser) implicated both variants as mutations of PLOD2. The father, mother, and sister (who carried the exon 12 defect) were reportedly well with normal parental DXA findings. BRKS2, characterized by under-hydroxylation of type I collagen telopeptides compromising their crosslinking, has been reported in at least 16 probands/families. Most PLOD2 mutations involve exons 17-19 (of 20 total) encoding the C-terminal domain with LH activity. However, truncating defects (nonsense, frameshift, splice site mutations) are also found throughout PLOD2. In three reports, AR PLOD2 mutations are not associated with congenital contractures. Our patient's missense defects lie within the central domain of unknown function of PLOD2. In our patient, compound heterozygosity with PLOD2 mutations is associated with a clinical phenotype distinctive from classic BRKS2 indicating that when COL1A1 and COL1A2 mutation testing is negative for OI without congenital contractures or pterygia, atypical BRKS should be considered.

WNT Signaling and Bone: Lessons From Skeletal Dysplasias and Disorders

Skeletal dysplasias are a diverse group of heritable diseases affecting bone and cartilage growth. Throughout the years, the molecular defect underlying many of the diseases has been identified. These identifications led to novel insights in the mechanisms regulating bone and cartilage growth and homeostasis. One of the pathways that is clearly important during skeletal development and bone homeostasis is the Wingless and int-1 (WNT) signaling pathway. So far, three different WNT signaling pathways have been described, which are all activated by binding of the WNT ligands to the Frizzled (FZD) receptors. In this review, we discuss the skeletal disorders that are included in the latest nosology of skeletal disorders and that are caused by genetic defects involving the WNT signaling pathway. The number of skeletal disorders caused by defects in WNT signaling genes and the clinical phenotype associated with these disorders illustrate the importance of the WNT signaling pathway during skeletal development as well as later on in life to maintain bone mass. The knowledge gained through the identification of the genes underlying these monogenic conditions is used for the identification of novel therapeutic targets. For example, the genes underlying disorders with altered bone mass are all involved in the canonical WNT signaling pathway. Consequently, targeting this pathway is one of the major strategies to increase bone mass in patients with osteoporosis. In addition to increasing the insights in the pathways regulating skeletal development and bone homeostasis, knowledge of rare skeletal dysplasias can also be used to predict possible adverse effects of these novel drug targets. Therefore, this review gives an overview of the skeletal and extra-skeletal phenotype of the different skeletal disorders linked to the WNT signaling pathway.

Aging aggravates intervertebral disc degeneration by regulating transcription factors toward chondrogenesis

Osterix is a critical transcription factor of mesenchymal stem cell fate, where its loss or loss of Wnt signaling diverts differentiation to a chondrocytic lineage. Intervertebral disc (IVD) degeneration activates the differentiation of prehypertrophic chondrocyte-like cells and inactivates Wnt signaling, but its interactive role with osterix is unclear. First, compared to young-adult (5 mo), mechanical compression of old (18 mo) IVD induced greater IVD degeneration. Aging (5 vs 12 mo) and/or compression reduced the transcription of osterix and notochordal marker T by 40-75%. Compression elevated the transcription of hypertrophic chondrocyte marker MMP13 and pre-osterix transcription factor RUNX2, but less so in 12 mo IVD. Next, using an Ai9/td reporter and immunohistochemical staining, annulus fibrosus and nucleus pulposus cells of young-adult IVD expressed osterix, but aging and compression reduced its expression. Lastly, in vivo LRP5-deficiency in osterix-expressing cells inactivated Wnt signaling in the nucleus pulposus by 95%, degenerated the IVD to levels similar to aging and compression, reduced the biomechanical properties by 45-70%, and reduced the transcription of osterix, notochordal markers and chondrocytic markers by 60-80%. Overall, these data indicate that age-related inactivation of Wnt signaling in osterix-expressing cells may limit regeneration by depleting the progenitors and attenuating the expansion of chondrocyte-like cells.

Targeting fundamental aging mechanisms to treat osteoporosis

Introduction: Osteoporotic fractures represent a growing burden of mortality, morbidity and socioeconomic cost to health-care systems worldwide. Osteoporosis is a disease uniquely associated with aging, therefore, an understanding of the physiological mechanisms underpinning its development as we age may open new avenues for therapeutic exploitation. Novel treatments, as well as refinement of the current approaches, are vital in the effort to sustain healthy, independent patients across the lifespan.Areas covered: This review covers the anabolic and catabolic pathways seen in bone maintenance, highlighting how they are changed with age, leading to osteoporosis. It will also discuss how these changes may be targeted therapeutically, in the development of new therapies, and the refinement of those already in use.Expert opinion: New effective and safe treatments for osteoporosis are still needed. Bone anabolics seem to be the most appropriate therapeutic approach to osteoporosis in older persons. Considering that bone and muscle mass synchronically decline with aging thus predisposing older persons to falls and fractures, combined therapeutic approaches to osteosarcopenia with a dual anabolic effect on muscle and bone will be a major advance in the treatment of these devastating conditions in the future.

Wnt signaling regulates the proliferation potential and lineage commitment of human umbilical cord derived mesenchymal stem cells

Relatively less is known about the interactions that tightly regulate the mesenchymal stem cells (MSCs) to maintain their pluripotency. Recent studies reports that Wnt proteins might play an important role in governing the MSC cell fate. In this study, we tested the hypothesis that Wnt proteins differentially regulate in vitro differentiation of human umbilical cord derived MSCs. Stromal cells from human umbilical cord (hUCMSCs) were isolated and treated with Wnt inhibitor/activator. FACS analysis of hUCMSCs for CD29, CD90, CD73, CD44, CD45 marker expression and gene expression of Wnt target genes and lineage specific genes were performed after Lithium Chloride (LiCl) and Quercetin treatment for 6 days. The cultured primary hUCMSCs demonstrated elevated MSC surface marker expression with clonogenic properties and differentiation potentials towards osteogenic, adipogenic and chondrogenic lineages. Downregulation in the expression of Wnt with Quercetin treatment was noted. LiCl treatment increased cellular proliferation but did not influence differentiation suggesting that the cells retain pluripotency whereas Quercetin treatment downregulated stemness markers, Wnt target gene expression and promoted osteogenesis as demonstrated by FACS analysis, calcium estimation and gene expression studies. Shift of differentiation potential after the inhibition of Wnt signaling by Quercetin was evident from the gene expression data and elevated calcium production, driving MSCs towards probable osteogenic lineage. The findings in particular are likely to open an interesting avenue of biomedical research, summarizing the impact of Wnt signaling on lineage commitment of MSCs.

Visual impairment and progressive phthisis bulbi caused by recessive pathogenic variant in MARK3

Developmental eye defects often severely reduce vision. Despite extensive efforts, for a substantial fraction of these cases the molecular causes are unknown. Recessive eye disorders are frequent in consanguineous populations and such large families with multiple affected individuals provide an opportunity to identify recessive causative genes. We studied a Pakistani consanguineous family with three affected individuals with congenital vision loss and progressive eye degeneration. The family was analyzed by exome sequencing of one affected individual and genotyping of all family members. We have identified a non-synonymous homozygous variant (NM_001128918.2: c.1708C > G: p.Arg570Gly) in the MARK3 gene as the likely cause of the phenotype. Given that MARK3 is highly conserved in flies (I: 55%; S: 67%) we knocked down the MARK3 homologue, par-1, in the eye during development. This leads to a significant reduction in eye size, a severe loss of photoreceptors and loss of vision based on electroretinogram (ERG) recordings. Expression of the par-1 p.Arg792Gly mutation (equivalent to the MARK3 variant found in patients) in developing fly eyes also induces loss of eye tissue and reduces the ERG signals. The data in flies and human indicate that the MARK3 variant corresponds to a loss of function. We conclude that the identified mutation in MARK3 establishes a new gene-disease link, since it likely causes structural abnormalities during eye development and visual impairment in humans, and that the function of MARK3/par-1 is evolutionarily conserved in eye development.

Wnt Signaling and Biological Therapy in Rheumatoid Arthritis and Spondyloarthritis

The Wnt signaling pathway plays a key role in several biological processes, such as cellular proliferation and tissue regeneration, and its dysregulation is involved in the pathogenesis of many autoimmune diseases. Several evidences support its role especially in bone complications of rheumatic diseases. In Rheumatoid Arthritis (RA), the Wnt signaling is implicated in systemic and localized bone loss, while available data of its role in Spondyloarthritis (SpA) are conflicting. In the last few decades, the quality of life of rheumatic patients has been dramatically improved by biological therapy, targeting cytokines involved in the pathogenesis of these diseases like tumor necrosis factor (TNF)α, interleukin (IL)-1, IL-6, IL-17. In this review, we reviewed the role of Wnt signaling in RA and SpA, focusing on the effect of biological therapy on this pathway and its possible clinical implications.

The Regulation of Bone Metabolism and Disorders by Wnt Signaling

Wnt, a secreted glycoprotein, has an approximate molecular weight of 40 kDa, and it is a cytokine involved in various biological phenomena including ontogeny, morphogenesis, carcinogenesis, and maintenance of stem cells. The Wnt signaling pathway can be classified into two main pathways: canonical and non-canonical. Of these, the canonical Wnt signaling pathway promotes osteogenesis. Sclerostin produced by osteocytes is an inhibitor of this pathway, thereby inhibiting osteogenesis. Recently, osteoporosis treatment using an anti-sclerostin therapy has been introduced. In this review, the basics of Wnt signaling, its role in bone metabolism and its involvement in skeletal disorders have been covered. Furthermore, the clinical significance and future scopes of Wnt signaling in osteoporosis, osteoarthritis, rheumatoid arthritis and neoplasia are discussed.

Clinical and Molecular Characterization of Familial Exudative Vitreoretinopathy Associated With Microcephaly

PURPOSE

Familial exudative vitreoretinopathy (FEVR) is a rare finding in patients with genetic forms of microcephaly. This study documents the detailed phenotype and expands the range of genetic heterogeneity.

DESIGN

Retrospective case series.

METHODS

Twelve patients (10 families) with a diagnosis of FEVR and microcephaly were ascertained from pediatric genetic eye clinics and underwent full clinical assessment including retinal imaging. Molecular investigations included candidate gene Sanger sequencing, whole-exome sequencing (WES), and whole-genome sequencing (WGS).

RESULTS

All patients had reduced vision and nystagmus. Six were legally blind. Two probands carried bi-allelic LRP5 variants, both presenting with bilateral retinal folds. A novel homozygous splice variant, and 2 missense variants were identified. Subsequent bone density measurement identified osteoporosis in one proband. Four families had heterozygous KIF11 variants. Two probands had a retinal fold in one eye and chorioretinal atrophy in the other; the other 2 had bilateral retinal folds. Four heterozygous variants were found, including 2 large deletions not identified on Sanger sequencing or WES. Finally, a family of 2 children with learning difficulties, abnormal peripheral retinal vasculogenesis, and rod-cone dystrophy were investigated. They were found to have bi-allelic splicing variants in TUBGCP6. Three families remain unsolved following WES and WGS.

CONCLUSIONS

Molecular diagnosis has been achieved in 7 of 10 families investigated, including a previously unrecognized association with LRP5. WGS enabled molecular diagnosis in 3 families after prior negative Sanger sequencing of the causative gene. This has enabled patient-specific care with targeted investigations and accurate family counseling.

LGR6 promotes osteogenesis by activating the Wnt/β-catenin signaling pathway

Leucine-rich repeat containing G-protein-coupled receptor 6 (LGR6) is a member of the rhodopsin-like 7-transmembrane domain receptor superfamily and has high homology to LGR4 and LGR5. LGR6 is highly expressed in osteoblastic progenitors, and LGR6-deficient mice show nail and bone regeneration defect. However, the effect of LGR6 on the osteogenic differentiation of osteoblastic progenitors and its underlying mechanisms are largely unknown. In this study, we overexpressed and knockdown LGR6 with lentivirus in the preosteoblastic cell MC3T3-E1 to observe the effect of LGR6 on osteogenic differentiation and explore its possible molecular mechanism. LGR6 overexpression promoted osteogenic differentiation and mineralization by stabilizing β-catenin to potentiate the Wnt/β-catenin signaling pathway in MC3T3-E1 cells. Conversely, LGR6 knockdown inhibited osteogenic differentiation and mineralization by enhancing β-catenin degradation to inactivate the Wnt/β-catenin signaling pathway. These results reveal that LGR6 is highly expressed in osteoblastic progenitors, and promotes osteogenesis by enhancing β-catenin stability to strengthen the Wnt signaling pathway. This study provides an important reference into the exact mechanisms of osteogenic differentiation.

Advances in osteoporosis from 1970 to 2018

In 1970, there were no drugs under study for osteoporosis. Estrogen was used, but little was known about the correct dose for preventing bone loss. At that time, fractures were not even recognized as a disease, but regarded as part of normal aging. From 1970 to this year (2018), there have been extensive advances in the osteoporosis field ranging from fracture epidemiology to the remarkable invention of bone density measurements. There have been major advances in therapeutic options available for patients for prevention and treatment of osteoporosis. In parallel, the advances in the laboratory helped elucidate the process of bone remodeling, not only at the macroscopic level but also at the cellular level. This led to rapid advances in translational research from cellular biology to new therapies exemplified by the development of monoclonal antibodies for osteoporosis. Further understanding of the signaling pathways in bone cells will lead to new small molecules made for osteoporosis treatment, perhaps causing less adverse events. University-based research throughout the world has been a leader in most of these advances, and Pharma support for phase 1 to 4 studies helped bring these discoveries to patients. In the osteoporosis field alone, one sees the tremendous value of grant support for university research by National funding agencies such as the National Institute of Health in this country and similar agencies in other countries. There are clinical challenges that have to be solved with long-term compliance with osteoporosis medication if we want to reduce fracture incidence in the long term.

Serum DKK1 is correlated with γ peak of serum electrophoresis in multiple myeloma: a multicenter biomarker study

Aim: DKK1 is reported to be produced at high levels by myeloma cells. Therefore, the applicability of DKK1 as a tumor marker for multiple myeloma (MM) diagnosis was examined. Methods: Serum samples were collected and analyzed by DKK1 concentration kit and capillary zone electrophoresis. Then, the obtained results were statically analyzed. Results: It has been determined that the 10 ng/ml of DKK1 is the optimal level for MM diagnosis. Moreover, there was an ascending linear correlation between the DKK1 concentration and γ peak. Discussion: The observed correlation could be rooted in the positive feedback loop between MM cells and the mesenchymal stem cells. In view of these results, DKK1 could be deemed as diagnostic marker for MM.

The developmental Wnt signaling pathway effector β-catenin/TCF mediates hepatic functions of the sex hormone estradiol in regulating lipid metabolism

The bipartite transcription factor β-catenin (β-cat)/T cell factor (TCF), formed by free β-cat and a given TCF family member, serves as the effector of the developmental Wnt signaling cascade. β-cat/TCFs also serve as effectors of certain peptide hormones or growth factors during adulthood. We reported that liver-specific expression of dominant-negative Transcription factor 7 like 2 (TCF7L2DN) led to impaired glucose disposal. Here we show that, in this LTCFDN transgenic mouse model, serum and hepatic lipid contents were elevated in male but not in female mice. In hepatocytes, TCF7L2DN adenovirus infection led to stimulated expression of genes that encode lipogenic transcription factors and lipogenic enzymes, while estradiol (E2) treatment attenuated the stimulation, associated with Wnt-target gene activation. Mechanistically, this E2-mediated activation can be attributed to elevated β-cat Ser675 phosphorylation and TCF expression. In wild-type female mice, ovariectomy (OVX) plus high-fat diet (HFD) challenge impaired glucose disposal and insulin tolerance, associated with increased hepatic lipogenic transcription factor sterol regulatory element-binding protein 1-c (SREBP-1c) expression. In wild-type mice with OVX, E2 reconstitution attenuated HFD-induced metabolic defects. Some of the attenuation effects, including insulin intolerance, elevated liver-weight gain, and hepatic SREBP-1c expression, were not affected by E2 reconstitution in HFD-fed LTCFDN mice with OVX. Finally, the effects of E2 in hepatocytes on β-cat/TCF activation can be attenuated by the G-protein-coupled estrogen receptor (GPER) antagonist G15. Our study thus expanded the scope of functions of the Wnt pathway effector β-cat/TCF, as it can also mediate hepatic functions of E2 during adulthood. This study also enriches our mechanistic understanding of gender differences in the risk and pathophysiology of metabolic diseases.

Autosomal-Recessive Mutations in MESD Cause Osteogenesis Imperfecta

Osteogenesis imperfecta (OI) comprises a genetically heterogeneous group of skeletal fragility diseases. Here, we report on five independent families with a progressively deforming type of OI, in whom we identified four homozygous truncation or frameshift mutations in MESD. Affected individuals had recurrent fractures and at least one had oligodontia. MESD encodes an endoplasmic reticulum (ER) chaperone protein for the canonical Wingless-related integration site (WNT) signaling receptors LRP5 and LRP6. Because complete absence of MESD causes embryonic lethality in mice, we hypothesized that the OI-associated mutations are hypomorphic alleles since these mutations occur downstream of the chaperone activity domain but upstream of ER-retention domain. This would be consistent with the clinical phenotypes of skeletal fragility and oligodontia in persons deficient for LRP5 and LRP6, respectively. When we expressed wild-type (WT) and mutant MESD in HEK293T cells, we detected WT MESD in cell lysate but not in conditioned medium, whereas the converse was true for mutant MESD. We observed that both WT and mutant MESD retained the ability to chaperone LRP5. Thus, OI-associated MESD mutations produce hypomorphic alleles whose failure to remain within the ER significantly reduces but does not completely eliminate LRP5 and LRP6 trafficking. Since these individuals have no eye abnormalities (which occur in individuals completely lacking LRP5) and have neither limb nor brain patterning defects (both of which occur in mice completely lacking LRP6), we infer that bone mass accrual and dental patterning are more sensitive to reduced canonical WNT signaling than are other developmental processes. Biologic agents that can increase LRP5 and LRP6-mediated WNT signaling could benefit individuals with MESD-associated OI.

New explanation for autosomal dominant high bone mass: Mutation of low-density lipoprotein receptor-related protein 6

LRP5 encodes low-density lipoprotein receptor-related protein 5 (LRP5). When LRP5 with a Frizzled receptor join on the surface of an osteoblast and bind a member of the Wnt family of ligands, canonical Wnt/β-catenin signaling occurs and increases bone formation. Eleven heterozygous gain-of-function missense mutations within LRP5 are known to prevent the LRP5 inhibitory ligands sclerostin and dickkopf1 from attaching to LRP5's first β-propeller, and thereby explain the rare autosomal dominant (AD) skeletal disorder "high bone mass" (HBM). LRP6 is a cognate co-receptor of LRP5 and similarly controls Wnt signaling in osteoblasts, yet the consequences of increased LRP6-mediated signaling remain unknown. We investigated two multi-generational American families manifesting the clinical and routine laboratory features of LRP5 HBM but without an LRP5 defect and instead carrying a heterozygous LRP6 missense mutation that would alter the first β-propeller of LRP6. In Family 1 LRP6 c.602C>T, p.A201V was homologous to LRP5 HBM mutation c.641C>T, p.A214V, and in Family 2 LRP6 c.553A>C, p.N185H was homologous to LRP5 HBM mutation c.593A>G, p.N198S but predicting a different residue at the identical amino acid position. In both families the LRP6 mutation co-segregated with striking generalized osteosclerosis and hyperostosis. Clinical features shared by the seven LRP6 HBM family members and ten LRP5 HBM patients included a broad jaw, torus palatinus, teeth encased in bone and, reportedly, resistance to fracturing and inability to float in water. For both HBM disorders, all affected individuals were taller than average for Americans (Ps < 0.005), but with similar mean height Z-scores (P = 0.7606) and indistinguishable radiographic skeletal features. Absence of adult maxillary lateral incisors was reported by some LRP6 HBM individuals. In contrast, our 16 patients with AD osteopetrosis [i.e., Albers-Schönberg disease (A-SD)] had an unremarkable mean height Z-score (P = 0.9401) lower than for either HBM group (Ps < 0.05). DXA mean BMD Z-scores in LRP6 HBM versus LRP5 HBM were somewhat higher at the lumbar spine (+7.8 vs +6.5, respectively; P = 0.0403), but no different at the total hip (+7.9 vs +7.7, respectively; P = 0.7905). Among the three diagnostic groups, only the LRP6 HBM DXA BMD values at the spine seemed to increase with subject age (R = +0.7183, P = 0.0448). Total hip BMD Z-scores were not significantly different among the three disorders (Ps > 0.05), and showed no age effect (Ps > 0.1). HR-pQCT available only for LRP6 HBM revealed indistinct corticomedullary boundaries, high distal forearm and tibial total volumetric BMD, and finite element analysis predicted marked fracture resistance. Hence, we have discovered mutations of LRP6 that cause a dento-osseous disorder indistinguishable without mutation analysis from LRP5 HBM. LRP6 HBM seems associated with generally good health, providing some reassurance for the development of anabolic treatments aimed to enhance LRP5/LRP6-mediated osteogenesis.

Lung tumor cells inhibit bone mineralization and osteoblast activity

Patients with non-small cell lung cancer (NSLC) often develop skeletal complications and fractures. To understand mechanisms of bone loss, we developed a murine model of non-metastatic NSLC. Decreased bone mineral density, trabecular thickness and mineralization, without an increase in bone resorption, were observed in vivo in mice injected with Lewis lung adenocarcinoma (LLC1) cells in the absence of tumor cell metastases. A decrease in trabecular bone mineral density was observed in mice injected with cell-free LLC1 CM. Plasma osteoblast biomarkers and PTH-related peptide (PTHrP) were reduced, and parathyroid hormone (PTH), 1,25-dihydroxyvitamin D, calcium and phosphate concentrations were normal in tumor-bearing mice. LLC1 cell conditioned medium (CM) inhibited alkaline phosphatase activity, osteoblast mineralization, and expression of Alpl and Ocn/Bglap mRNA in MC3T3 osteoblast cultures, whereas non-CM or CM from NIH/3T3 fibroblasts did not induce similar changes. LLC1 CM reduced Wnt3a-stimulated Tcf/Lef reporter plasmid activity and Wnt5A, Tcf1 and Lef1 mRNA expression in MC3T3 cells. Although concentrations of the Wnt inhibitor, DKK2, were increased in LLC1 CM compared to non-CM, depletion of DKK2 from LLC1 CM did not completely restore Wnt3a activity in MC3T3 cultures, and recombinant DKK2 failed to inhibit osteoblast mineralization. The data indicate that in a model of lung adenocarcinoma without bone metastases, tumor cells elaborate a secreted factor(s) that reduces bone mass, bone formation and osteoblast Wnt signaling without increases in bone resorption or calcium-regulating hormone concentrations. The factor(s) mediating this inhibition of osteoblast mineralization require further characterization.

Mendelian bone fragility disorders

Mendelian bone fragility disorders are caused by genetic variants that can be inherited in an autosomal dominant, autosomal recessive or X-linked manner and have a large detrimental effect on bone strength. As a rule, the more damaging the genetic defect is, the earlier the first fracture will occur, typically during bone development. This review focusses on conditions where bone fragility is the most conspicuous characteristic, of which osteogenesis imperfecta (OI) is the best-known disorder. The large majority of individuals with an OI phenotype have disease-causing dominant variants in COL1A1 or COL1A2, the genes coding for collagen type I. Interestingly, large sequencing databases indicate that there are about 10 times more carriers of COL1A1/COL1A2 variants that should lead to OI than there are individuals with a diagnosis of OI. It is possible that at least some of these variants lead to incomplete OI phenotypes and are diagnosed as osteoporosis during adulthood. Apart from mutations affecting collagen type I production, biallelic mutations in LRP5 and WNT1 can cause very rare and severe bone fragility disorders. Heterozygous pathogenic variants in these genes are much more common and can cause the clinical picture of primary osteoporosis. As sequencing studies are more widely performed in adults with bone fragility disorders, evidence is emerging that what appears as primary osteoporosis in fact can be due to mutations in bona fide OI genes. The distinction between OI and primary osteoporosis is therefore likely to blur in future.

Using zebrafish to study skeletal genomics

While genome-wide association studies (GWAS) have revolutionized our understanding of the genetic architecture of skeletal diseases, animal models are required to identify causal mechanisms and to translate underlying biology into new therapies. Despite large-scale knockout mouse phenotyping efforts, the skeletal functions of most genes residing at GWAS-identified loci remain unknown, highlighting a need for complementary model systems to accelerate gene discovery. Over the past several decades, zebrafish (Danio rerio) has emerged as a powerful system for modeling the genetics of human diseases. In this review, our goal is to outline evidence supporting the utility of zebrafish for accelerating our understanding of human skeletal genomics, as well as gaps in knowledge that need to be filled for this purpose. We do this by providing a basic foundation of the zebrafish skeletal morphophysiology and phenotypes, and surveying evidence of skeletal gene homology and the use of zebrafish for post-GWAS analysis in other tissues and organs. We also outline challenges in translating zebrafish mutant phenotypes. Finally, we conclude with recommendations of future directions and how to leverage the large body of tools and knowledge of skeletal genetics in zebrafish for the needs of human skeletal genomic exploration. Due to their amenability to rapid genetic approaches, as well as the large number of conserved genetic and phenotypic features, there is a strong rationale supporting the use of zebrafish for human skeletal genomic studies.

WNT3A accelerates delayed alveolar bone repair in ovariectomized mice

Our goal was to evaluate alveolar bone healing in OVX mice, and to assess the functional utility of a WNT-based treatment to accelerate healing in mice with an osteoporotic-like bony phenotype.

INTRODUCTION

Is osteoporosis a risk factor for dental procedures? This relatively simple question is exceedingly difficult to answer in a clinical setting, for two reasons. First, as an age-related disease, osteoporosis is frequently accompanied by age-related co-morbidities that can contribute to slower tissue repair. Second, the intervals at which alveolar bone repair are assessed in a clinical study are often measured in months to years. This study aimed to evaluate alveolar bone repair in ovariectomized (OVX) mice and provide preclinical evidence to support a WNT-based treatment to accelerate alveolar bone formation.

METHODS

OVX was performed in young mice to produce an osteoporotic-like bone phenotype. Thereafter, the rate of extraction socket healing and osteotomy repair was assessed. A liposomal WNT3A treatment was tested for its ability to promote alveolar bone formation in this OVX-induced model of bone loss.

RESULTS

Bone loss was observed throughout the murine skeleton, including the maxilla, and mirrored the pattern of bone loss observed in aged mice. Injuries to the alveolar bone, including tooth extraction and osteotomy site preparation, both healed significantly slower than the same injuries produced in young controls. Given sufficient time, however, all injuries eventually healed. In OVX mice, osteotomies healed significantly faster if they were treated with L-WNT3A.

CONCLUSIONS

Alveolar bone injuries heal slower in OVX mice that exhibit an osteoporotic-like phenotype. The rate of alveolar bone repair in OVX mice can be significantly promoted with local delivery of L-WNT3A.

The genetic architecture of osteoporosis and fracture risk

Osteoporosis and fracture risk are common complex diseases, caused by an interaction of numerous disease susceptibility genes and environmental factors. With the advances in genomic technologies, large-scale genome-wide association studies (GWAS) have been performed which have broadened our understanding of the genetic architecture and biological mechanisms of complex disease. Currently, more than ~90 loci have been found associated with DXA derived bone mineral density (BMD), over ~500 loci with heel estimated BMD and several others with other less widely available bone parameters such as bone geometry, shape, and microarchitecture. Notably, several of the pathways identified by the GWAS efforts correspond to pathways that are currently targeted for the treatment of osteoporosis. Overall, tremendous progress in the field of the genetics of osteoporosis has been achieved with the discovery of WNT16, EN1, DAAM2, and GPC6 among others. Assessment of the function and biological mechanisms of the remaining genes may further untangle the complex genetic landscape of osteoporosis and fracture risk. With this review we aimed to provide a general overview of the existing GWAS studies on osteoporosis traits and fracture risk.

WNT Signaling in Disease

Developmental signaling pathways control a vast array of biological processes during embryogenesis and in adult life. The WNT pathway was discovered simultaneously in cancer and development. Recent advances have expanded the role of WNT to a wide range of pathologies in humans. Here, we discuss the WNT pathway and its role in human disease and some of the advances in WNT-related treatments.

Castration Determines the Efficacy of ETAR Blockade in a Mouse Model of Prostate Cancer Bone Metastasis

Bone metastasis is a painful complication of advanced prostate cancer. Endothelin-1 is a tumor-secreted factor that plays a central role in osteoblast activation and the osteosclerotic response of prostate cancer metastatic to bone. Antagonists that block the activation of the endothelin A receptor (ETAR), located on osteoblasts, reduce osteoblastic bone lesions in animal models of bone metastasis. However, ETAR antagonists demonstrated limited efficacy in clinical trials of men with advanced prostate cancer who also received standard androgen deprivation therapy (ADT). Previous data from our group suggested that, in a mouse model, ETAR antagonists might only be efficacious when androgen signaling in the osteoblast is lowered beyond the ability of standard ADT. This notion was tested in a mouse model of prostate cancer bone metastasis. Castrated and sham-operated male athymic nude mice underwent intracardiac inoculation of the ARCaPM castration-resistant prostate cancer cell line. The mice were then treated with either the ETAR antagonist zibotentan or a vehicle control to generate four experimental groups: vehicle+sham (Veh+Sham), vehicle+castrate (Veh+Castr), zibotentan+sham (Zibo+Sham), and zibotentan+castrate (Zibo+Castr). The mice were monitored radiographically for the development of skeletal lesions. The Zibo+Castr group had significantly longer survival and a single incidental lesion. Mice in the Zibo+Sham group had the shortest survival and the largest number of skeletal lesions. Survival and skeletal lesions of the Veh+Sham and Veh+Castr groups were intermediate compared with the zibotentan-treated groups. We report a complex interaction between ETAR and androgen signaling, whereby ETAR blockade was most efficacious when combined with complete androgen deprivation.

BMP9 directly induces rapid GSK3-β phosphorylation in a Wnt-independent manner through class I PI3K-Akt axis in osteoblasts

Bone morphogenetic protein (BMP)9 has been reported to be the most potent BMP to induce bone formation. However, the details of BMP9-transduced intracellular signaling remain ambiguous. Here, we have investigated signal transduction mechanisms of BMP9 in comparison to BMP2, another potent inducer of bone formation, in osteoblasts. In a mouse osteoblast cell line, BMP9 induced higher mRNA levels of alkaline phosphatase (ALP) and runt-related transcription factor 2 (Runx2) than BMP2 within 2 h. Unlike BMP2, BMP9 induced rapid phosphorylation of glycogen synthase kinase 3-β (GSK3-β) and protein kinase B (Akt) and increased the cellular protein content of β-catenin. BMP9 moderately increased mRNA levels of several canonical Wingless-related integration site to lower degrees than BMP2. Furthermore, BMP9-induced GSK3-β phosphorylation was not inhibited by pretreatment with actinomycin D, cycloheximide, or Brefeldin A, indicating it is independent of Wnt protein secretion. BMP9-induced GSK3-β phosphorylation was abrogated by Akt or class I PI3K-specific inhibitors. Moreover, inactivation of GSK3-β by LiCl did not further promote ALP and Runx2 mRNA induction by BMP9 as significantly as that by BMP2. Notably, BMP9-induced GSK3-β phosphorylation was inhibited by small interfering RNA against endoglin and GIPC PDZ domain-containing family, member 1. Taken together, our present findings have indicated that BMP9 directly activates GSK3β-β-catenin signaling pathway through class I PI3K-Akt Axis in osteoblasts, which may be essential for the potent osteoinductive activity of BMP9.-Eiraku, N., Chiba, N., Nakamura, T., Amir, M. S., Seong, C.-H., Ohnishi, T., Kusuyama, J., Noguchi, K., Matsuguchi, T. BMP9 directly induces rapid GSK3-β phosphorylation in a Wnt-independent manner through class I PI3K-Akt axis in osteoblasts.

Review of the Pathways Involved in the Osteogenic Differentiation of Adipose-Derived Stem Cells

Grafts and prosthetic materials used for the repair of bone defects are often accompanied by comorbidity and rejection. Therefore, there is an immense need for novel approaches to combating the issues surrounding such defects. Because of their accessibility, substantial proportion, and osteogenic differentiation potential, adipose-derived stem cells (ASCs) make for an ideal source of bone tissue in regenerative medicine. However, efficient induction of ASCs toward an osteoblastic lineage in vivo is met with challenges, and many signaling pathways must come together to secure osteoblastogenesis. Among them are bone morphogenic protein, wingless-related integration site protein, Notch, Hedgehog, fibroblast growth factor, vascular endothelial growth factor, and extracellular regulated-signal kinase. The goal of this literature review is to conglomerate the present research on these pathways to formulate a better understanding of how ASCs are most effectively transformed into bone in the context of tissue engineering.

Osteoblast-derived NOTUM reduces cortical bone mass in mice and the NOTUM locus is associated with bone mineral density in humans

Osteoporosis is a common skeletal disease, affecting millions of individuals worldwide. Currently used osteoporosis treatments substantially reduce vertebral fracture risk, whereas nonvertebral fracture risk, mainly caused by reduced cortical bone mass, has only moderately been improved by the osteoporosis drugs used, defining an unmet medical need. Because several wingless-type MMTV integration site family members (WNTs) and modulators of WNT activity are major regulators of bone mass, we hypothesized that NOTUM, a secreted WNT lipase, might modulate bone mass via an inhibition of WNT activity. To characterize the possible role of endogenous NOTUM as a physiologic modulator of bone mass, we developed global, cell-specific, and inducible Notum-inactivated mouse models. Notum expression was high in the cortical bone in mice, and conditional Notum inactivation revealed that osteoblast lineage cells are the principal source of NOTUM in the cortical bone. Osteoblast lineage-specific Notum inactivation increased cortical bone thickness via an increased periosteal circumference. Inducible Notum inactivation in adult mice increased cortical bone thickness as a result of increased periosteal bone formation, and silencing of Notum expression in cultured osteoblasts enhanced osteoblast differentiation. Large-scale human genetic analyses identified genetic variants mapping to the NOTUM locus that are strongly associated with bone mineral density (BMD) as estimated with quantitative ultrasound in the heel. Thus, osteoblast-derived NOTUM is an essential local physiologic regulator of cortical bone mass via effects on periosteal bone formation in adult mice, and genetic variants in the NOTUM locus are associated with BMD variation in adult humans. Therapies targeting osteoblast-derived NOTUM may prevent nonvertebral fractures.-Movérare-Skrtic, S., Nilsson, K. H., Henning, P., Funck-Brentano, T., Nethander, M., Rivadeneira, F., Coletto Nunes, G., Koskela, A., Tuukkanen, J., Tuckermann, J., Perret, C., Souza, P. P. C., Lerner, U. H., Ohlsson, C. Osteoblast-derived NOTUM reduces cortical bone mass in mice and the NOTUM locus is associated with bone mineral density in humans.

Wnt signaling in liver disease: emerging trends from a bibliometric perspective

Background

The Wnt signaling pathway, an evolutionarily conserved molecular transduction cascade, has been identified as playing a pivotal role in various physiological and pathological processes of the liver, including homeostasis, regeneration, cirrhosis, and hepatocellular carcinoma (HCC). In this study, we aimed to use a bibliometric method to evaluate the emerging trends on Wnt signaling in liver diseases.

Methods

Articles were retrieved from the Web of Science Core Collection. We used a bibliometric software, CiteSpace V 5.3.R4, to analyze the active countries or institutions in the research field, the landmark manuscripts, important subtopics, and evolution of scientific ideas.

Results

In total, 1,768 manuscripts were published, and each was cited 33.12 times on average. The U.S. published most of the articles, and the most active center was the University of Pittsburgh. The top 5 landmark papers were identified by four bibliometric indexes including citation, burstness, centrality, and usage 2013. The clustering process divided the whole area into nine research subtopics, and the two major important subtopics were "liver zonation" and "HCC." Using the "Part-of-Speech" technique, 1,743 terms representing scientific ideas were identified. After 2008, the bursting phrases were "liver development," "progenitor cells," "hepatic stellate cells," "liver regeneration," "liver fibrosis," "epithelial-mesenchymal transition," and etc.

Conclusion

Using bibliometric methods, we quantitatively summarized the advancements and emerging trends in Wnt signaling in liver diseases. These bibliometric findings may pioneer the future direction of this field in the next few years, and further studies are needed.

TRAF6 function as a novel co-regulator of Wnt3a target genes in prostate cancer

Background

Tumour necrosis factor receptor associated factor 6 (TRAF6) promotes inflammation in response to various cytokines. Aberrant Wnt3a signals promotes cancer progression through accumulation of β-Catenin. Here we investigated a potential role for TRAF6 in Wnt signaling.

Methods

TRAF6 expression was silenced by siRNA in human prostate cancer (PC3U) and human colorectal SW480 cells and by CRISPR/Cas9 in zebrafish. Several biochemical methods and analyses of mutant phenotype in zebrafish were used to analyse the function of TRAF6 in Wnt signaling.

Findings

Wnt3a-treatment promoted binding of TRAF6 to the Wnt co-receptors LRP5/LRP6 in PC3U and LNCaP cells in vitro. TRAF6 positively regulated mRNA expression of β-Catenin and subsequent activation of Wnt target genes in PC3U cells. Wnt3a-induced invasion of PC3U and SW480 cells were significantly reduced when TRAF6 was silenced by siRNA. Database analysis revealed a correlation between TRAF6 mRNA and Wnt target genes in patients with prostate cancer, and high expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis. By using CRISPR/Cas9 to silence TRAF6 in zebrafish, we confirm TRAF6 as a key molecule in Wnt3a signaling for expression of Wnt target genes.

Interpretation

We identify TRAF6 as an important component in Wnt3a signaling to promote activation of Wnt target genes, a finding important for understanding mechanisms driving prostate cancer progression.

Fund

KAW 2012.0090, CAN 2017/544, Swedish Medical Research Council (2016-02513), Prostatacancerförbundet, Konung Gustaf V:s Frimurarestiftelse and Cancerforskningsfonden Norrland. The funders did not play a role in manuscript design, data collection, data analysis, interpretation nor writing of the manuscript.

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TRAF6 positively regulated mRNA expression of b-Catenin and subsequent activation of Wnt target genes in prostate cancer cells in vitro.

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High expression of LRP5, TRAF6 and c-Myc correlated with poor prognosis for patients with prostate cancer.