Which way does the Wnt blow? Exploring the duality of canonical Wnt signaling on cellular aging

Genome-Wide Methylation Changes Associated with Replicative Senescence and Differentiation in Endothelial and Bone Marrow Mesenchymal Stromal Cells

Bone marrow mesenchymal stromal cells (BMSCs) are multipotent cells able to self-renew and differentiate, depending on the microenvironment, into adipocytes and osteoblasts. These cells have a limited number of replications and enter replicative senescence during in vitro expansion. The role of DNA methylation (DNAm) assumes importance in cell function and commitment; however, its exact contribution to BMSC differentiation and replicative senescence is still unclear. We performed a genome-wide DNAm analysis on BMSCs cultured in vitro at early passages and induced to differentiate into adipocytes and osteoblasts, and on replicative senescent BMSCs and HUVECs, to identify DNAm patterns of senescence and differentiation. We also compared BMSCs and HUVECs in replicative senescence and found that, in both cellular systems, genome-wide hypomethylation was accompanied by a higher-than-expected overlap of differentially methylated positions (DMPs) and concordance in terms of direction of the change. A Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analysis on lineage-independent senescence-associated DMPs revealed 16 common pathways, including Insulin resistance, Molecule adhesion, and Wnt/β-catenin signaling. In both adipogenesis and osteogenesis, we observed a general demethylation of CpG sites compared with undifferentiated BMSCs with a higher number of DMPs in osteogenesis. KEGG analysis resulted in 30 pathways enriched in osteoblasts and only 2 in adipocytes when compared to undifferentiated cells. When comparing differentiated BMSCs with senescent ones, osteogenesis exhibited a greater overlap with senescence in terms of number of DMPs and direction of methylation change compared to adipogenesis. In conclusion, this study may be useful for future research on general mechanisms that occur in replicative senescence and furthermore to identify trajectories of BMSC differentiation and common aspects of differentiated and senescent cells.

Mesenchymal Stem Cells Could Be Considered as a Candidate for Further Studies in Cell-Based Therapy of Alzheimer's Disease via Targeting the Signaling Pathways

Mesenchymal stem cells (MSCs) are of particular interest because of their potential in regenerative medicine. Stem cell-based therapies cast a new hope for neurodegenerative disease treatment as a regeneration strategy, including treatment for Alzheimer's disease (AD). A multitude of cytokines and factors secreted from MSCs are known to give such multifunctional properties, but associated mechanisms of these factors have yet to be entirely understood. To better understand the in vitro effect of MSCs on a neurodegenerative disorder, we treated primary cortical and hippocampal neural cells with amyloid β (Aβ) as an in vitro cell line model for AD. For this purpose, bone marrow-derived MSCs (BMSCs) were cocultured with Aβ-treated neural cells, collected at day 3, and subjected to absolute telomere length measurement and telomerase activity assay. Next, the gene and protein expression levels of mTOR, p-mTOR, AMPK, p-AMPK, GSK-3β, p-GSK-3β, Wnt3, and β-catenin were investigated. Also, after 3 days of coculture treatment, the supernatant was collected from both groups for cytokine measurement. It was found that telomere length as a biomarker in neurodegenerative disorder as well as telomerase activity had significantly increased in the experimental group, and the presence of IL-6, IL-10, and TGF-β was obviously significant in the cocultured media. Also, BMSCs significantly changed the gene and protein expression of mTOR, AMPK, GSK-3β, and Wnt3/β-catenin signaling pathways components. It was concluded that the mentioned effects of MSCs on neural cells as an in vitro cell line model for AD as a therapeutic agent can be related to the signaling network.

Wnt Glycation Inhibits Canonical Signaling

Glycation occurs as a non-enzymatic reaction between amino and thiol groups of proteins, lipids, and nucleotides with reducing sugars or α-dicarbonyl metabolites. The chemical reaction underlying is the Maillard reaction leading to the formation of a heterogeneous group of compounds named advanced glycation end products (AGEs). Deleterious effects have been observed to accompany glycation such as alterations of protein structure and function resulting in crosslinking and accumulation of insoluble protein aggregates. A substantial body of evidence associates glycation with aging. Wnt signaling plays a fundamental role in stem cell biology as well as in regeneration and repair mechanisms. Emerging evidence implicates that changes in Wnt/β-catenin pathway activity contribute to the aging process. Here, we investigated the effect of glycation of Wnt3a on its signaling activity. Methods: Glycation was induced by treatment of Wnt3a-conditioned medium (CM) with glyoxal (GO). Effects on Wnt3a signaling activity were analyzed by Topflash/Fopflash reporter gene assay, co-immunoprecipitation, and quantitative RT-PCR. Results: Our data show that GO-treatment results in glycation of Wnt3a. Glycated Wnt3a suppresses β-catenin transcriptional activity in reporter gene assays, reduced binding of β-catenin to T-cell factor 4 (TCF-4) and extenuated transcription of Wnt/β-catenin target genes. Conclusions: GO-induced glycation impairs Wnt3a signaling function.

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.

Expression of RON in colorectal cancer and its relationships with tumor cell behavior and prognosis

Aims and background

The aims of the current study were to evaluate whether recepteur d'origine nantais (RON) affects tumor cell behavior and oncogenic signaling pathways in colorectal cancer, and to examine the relationship of its expression with various clinicopathological parameters and patient survival.

Methods

Immunohistochemistry, Western blot and RT-PCR were used to detect the expression of the RON gene in human colorectal cancer tissue. To study the biological role of RON in tumor cell behavior and cellular signaling pathways, we used small interfering RNA (siRNA) to knock down RON gene expression in human colorectal cancer cell lines.

Results

Knockdown of RON inhibited the induction of the invasive growth phenotype and the activation of oncogenic signaling pathways including Akt, MAPK and β-catenin. RON overexpression was associated with tumor size, lymphovascular invasion, depth of invasion, lymph node metastasis, distant metastasis, tumor stage and poor survival.

Conclusions

These results suggest that RON overexpression may help in predicting poor clinical outcomes in colorectal cancer.

In Development-A New Paradigm for Understanding Vascular Disease

Under physiological conditions, the arterial endothelium exerts a powerful protective influence to maintain vascular homeostasis. However, during the development of vascular disease, these protective activities are lost, and dysfunctional endothelial cells actually promote disease pathogenesis. Numerous investigations have analyzed the characteristics of dysfunctional endothelium with a view to understanding the processes responsible for the dysfunction and to determining their role in vascular pathology. This review adopts an alternate approach: reviewing the mechanisms that contribute to the initial formation of a healthy protective endothelium and on how those mechanisms may be disrupted, precipitating the appearance of dysfunctional endothelial cells and the progression of vascular disease. This approach, which highlights the role of endothelial adherens junctions and vascular endothelial-cadherin in endothelial maturation and endothelial dysfunction, provides new insight into the remarkable biology of this important cell layer and its role in vascular protection and vascular disease.

The involvement of serum exosomal miR-500-3p and miR-770-3p in aging: modulation by calorie restriction

Recent studies have shown a role for miRNAs in aging and age-related diseases, and the modulation of miRNA expression by diet attracts attention as a new therapeutic strategy. Here, we focused on identifying specific exosomal miRNAs derived from serum of aged rats and the effect of short-term calorie restriction (CR) on their expression.

Exosomes from serum of young (7-month), old (22-month), and old-CR Sprague Dawley rats were isolated and characterized by transmission electron microscopy analyses, dynamic light scattering measurements, and Western blotting. A total of 12 significantly expressed miRNAs in serum exosomes of young and old rats were identified by next generation sequencing. After analysis of qRT-PCR, we found that miR-500-3p and miR-770-3p expression was significantly upregulated by aging and downregulated by CR. Furthermore, receiver operating characteristic (ROC) curve revealed that the selected miRNAs represented high accuracy in discriminating old rats from young rats. Finally, PANTHER analysis predicted selected miRNAs targets genes involved in Wnt/chemokines and cytokines -related inflammatory signaling pathway and function as transcription factor.

In conclusion, our results suggest that the expression of serum exosomal miR-500-3p and miR-770-3p was significantly increased with aging, whereas these were decreased by CR, and age-/CR-modulated exosomal miR-500-3p and miR-770-3p could potentially be used as informative biomarkers candidates for aging.

The emerging role of Wnt signaling dysregulation in the understanding and modification of age-associated diseases

Wnt signaling is a highly conserved pathway that participates in multiple aspects of cellular function during development and in adults. In particular, this pathway has been implicated in cell fate determination, proliferation and cell polarity establishment. In the brain, it contributes to synapse formation, axonal remodeling, dendrite outgrowth, synaptic activity, neurogenesis and behavioral plasticity. The expression and distribution of Wnt components in different organs vary with age, which may have important implications for preserving tissue homeostasis. The dysregulation of Wnt signaling has been implicated in age-associated diseases, such as cancer and some neurodegenerative conditions. This is a relevant research topic, as an important research avenue for therapeutic targeting of the Wnt pathway in regenerative medicine has recently been opened. In this review, we discuss the recent findings on the regulation of Wnt components during aging, particularly in brain functioning, and the implications of Wnt signaling in age-related diseases.

Developmental Drift and the Role of Wnt Signaling in Aging

Population aging is a public health problem affecting the majority of the developed world. As populations age, the incidence of degenerative diseases increases exponentially, leading to large increases in public spending on healthcare. Here we summarize recent findings on the developmental drift theory of aging, and the links that have been established between aging and the Wnt signaling pathways. We focus on insights derived from model organisms connecting the evolutionary basis of aging and the link to developmental programming.

The Role of the Microenvironmental Niche in Declining Stem-Cell Functions Associated with Biological Aging

Aging is strongly correlated with decreases in neurogenesis, the process by which neural stem and progenitor cells proliferate and differentiate into new neurons. In addition to stem-cell-intrinsic factors that change within the aging stem-cell pool, recent evidence emphasizes new roles for systemic and microenvironmental factors in modulating the neurogenic niche. This article focuses on new insights gained through the use of heterochronic parabiosis models, in which an old mouse and a young circulatory system are joined. By studying the brains of both young and old mice, researchers are beginning to uncover circulating proneurogenic "youthful" factors and "aging" factors that decrease stem-cell activity and neurogenesis. Ultimately, the identification of factors that influence stem-cell aging may lead to strategies that slow or even reverse age-related decreases in neural-stem-cell (NSC) function and neurogenesis.

Wnt/β-catenin signaling in bone marrow niche

The bone marrow (BM) niche is a specific physiological environment for hematopoietic and non-hematopoietic stem cells (HSCs). Several signaling pathways (including Wnt/β-catenin) regulate various aspects of stem cell growth, function and death in the BM niche. In addition, the canonical Wnt pathway is crucial for directing self-renewal and differentiation as important mechanisms in many types of stem cells. We review the role of the Wnt/β-catenin pathway in the BM niche and its importance in stem cells. Relevant literature was identified by a PubMed search (1997-2014) of English-language literature by using the following keywords: BM niche, Wnt/β-catenin signaling, osteoblast, osteoclast and bone disease. The Wnt/β-catenin pathway regulates the stability of the β-catenin proto-oncogene. The stabilized β-catenin then translocates to the nucleus, forming a β-catenin-TCF/LEF complex regulating the transcription of specific target genes. Stem cells require β-catenin to mediate their response to Wnt signaling for maintenance and transition from the pluripotent state during embryogenesis. In adult stem cells, Wnt signaling functions at various hierarchical levels to contribute to the specification of the diverse tissues. Aberrant Wnt/β-catenin signaling and its downstream transcriptional regulators are observed in several malignant stem cells and human cancers. Because Wnt signaling can maintain stem cells and cancer cells, the ability to modulate the Wnt pathway either positively or negatively may be of therapeutic relevance. The controlled activation of Wnt signaling might allow us to enhance stem and progenitor cell activity when regeneration is needed.

Dynamic changes of global DNA methylation and hypermethylation of cell adhesion-related genes in rat kidneys in response to ochratoxin A

Ochratoxin A (OTA), which is found in a variety of food products, is associated with the development of nephrotoxicity and carcinogenicity in rats and has raised public health concerns. A previous study in our laboratory indicated that OTA exposure induced cytotoxicity by decreasing global DNA methylation in vitro. However, the relationship between OTA-induced nephrotoxicity and DNA methylation changes in vivo remains unclear. The object of this study was to investigate whether OTA can change global DNA methylation or alter the expression of several critical tumour-related genes by inducing methylation modifications before carcinogenesis. We focused on the mechanism of action of OTA in regard to DNA methylation, including the expression of DNA methyltransferases and the regulation of specific cell signalling pathways. Dynamic and dose-dependent changes of global DNA methylation were observed during OTA-induced nephrotoxicity and probably associated with the expression of DNA methyltransferase 1. 13-week exposure of OTA caused hypermethylation in the promoters of critical cell adhesion-related genes, E-cadherin and N-cadherin, leading to reduction of the corresponding mRNA expression, accompanied by transcriptional activation of the Wnt and PI3K/AKT pathways. These findings suggested that long-term OTA exposure could disrupt DNA methylation profile, which might be one of the possible mechanisms of OTA-induced nephrotoxicity.

Mesenchymal stem cells-based therapy as a potential treatment in neurodegenerative disorders: is the escape from senescence an answer?

Aging is the most prominent risk factor contributing to the development of neurodegenerative disorders. In the United States, over 35 million of elderly people suffer from age-related diseases. Aging impairs the self-repair ability of neuronal cells, which undergo progressive deterioration. Once initiated, this process hampers the already limited regenerative power of the central nervous system, making the search for new therapeutic strategies particularly difficult in elderly affected patients. So far, mesenchymal stem cells have proven to be a viable option to ameliorate certain aspects of neurodegeneration, as they possess high proliferative rate and differentiate in vitro into multiple lineages. However, accumulating data have demonstrated that during long-term culture, mesenchymal stem cells undergo spontaneous transformation. Transformed mesenchymal stem cells show typical features of senescence, including the progressive shortening of telomers, which results in cell loss and, as a consequence, hampered regenerative potential. These evidences, in line with those observed in mesenchymal stem cells isolated from old donors, suggest that senescence may represent a limit to mesenchymal stem cells exploitation in therapy, prompting scholars to either find alternative sources of pluripotent cells or to arrest the age-related transformation. In the present review, we summarize findings from recent literature, and critically discuss some of the major hurdles encountered in the search of appropriate sources of mesenchymal stem cells, as well as benefits arising from their use in neurodegenerative diseases. Finally, we provide some insights that may aid in the development of strategies to arrest or, at least, delay the aging of mesenchymal stem cells to improve their therapeutic potential.

Overexpression of the Circadian Clock Gene Rev-erbα Affects Murine Bone Mesenchymal Stem Cell Proliferation and Osteogenesis

Bone mesenchymal stem cell (BMSC) age-related changes include decreased osteogenesis and increased adipogenesis. Rev-erbα and the Wnt/β-catenin signaling pathway were known to play important roles in BMSC aging. In this study, we have aimed to elucidate whether Rev-erbα and Wnt/β-catenin signaling interact during BMSC proliferation and osteogenesis. Our results showed that Rev-erbα expression gradually dropped during BMSC osteogenesis, and overexpression of Rev-erbα in BMSCs inhibited cell proliferation and osteogenesis. The inhibition of cell proliferation induced by Rev-erbα overexpression was partially reversed when Wnt/β-catenin signaling was activated. These results suggested that Rev-erbα could promote BMSC aging and may be the negative regulator during the late stage of osteogenesis. The clock gene Rev-erbα and Wnt/β-catenin signaling interact in the regulation of cell proliferation.

Active Wnt/beta-catenin signaling is required for embryonic thymic epithelial development and functionality ex vivo

The Wnt/beta-catenin signaling pathway plays an important role in the commitment and development of thymic epithelial precursors. Here we document similarities of thymic epithelial development during embryogenesis in human and mouse. We stained for thymic epithelial surface markers (EpCAM1, Ly51, K8) and ligand/receptor pair (Wnt4, Fz4). Our results confirm the relevance of using murine test systems to model human embryonic thymic epithelial cell development. We have efficiently transduced murine embryonic epithelial cells using mock (GFP) and Wnt/beta-catenin-inhibiting (ICAT-encoding) recombinant adenoviral vectors. The effect of Wnt4 was assayed in the form of Wnt4-containing supernatant. Gene expressional changes were assessed by Q-PCR and also morphology using conventional and confocal fluorescent microscopy. Functional aberration caused by ICAT was assessed through evaluation of thymocyte maturation. Our results demonstrate that ICAT and Wnt4 have reciprocal effects during embryonic thymic epithelial cell development. While Wnt4 is capable of increasing the expression level of characteristic intracellular (FoxN1), surface (MHCII) and secreted (IL7) molecules, Wnt/beta-catenin inhibition through ICAT can moderately decrease their expression. Morphological changes induced by ICAT resulted in the development of hollow, inflated thymic lobes with reduced epithelial cell numbers. The ICAT-treated thymic lobes also showed significant impairment in supporting thymocyte development and maturation.

Variegated expression of Hsp22 transgenic reporters indicates cell-specific patterns of aging in Drosophila oenocytes

The cytoplasmic chaperone gene Hsp70 and the mitochondrial chaperone gene Hsp22 are upregulated during normal aging in Drosophila in tissue-general patterns. In addition, Hsp22 reporters are dramatically upregulated during aging in a subset of the oenocytes (liver-like cells). Hsp22 reporter expression varied dramatically between individual oenocytes and between groups of oenocytes located in adjacent body segments, and was negatively correlated with accumulation of age pigment, indicating cell-specific and cell-lineage-specific patterns of oenocyte aging. Conditional transgenic systems were used to express 88 transgenes to search for trans-regulators of the Hsp70 and Hsp22 reporters during aging. The wingless gene increased tissue-general upregulation of both Hsp70 and Hsp22 reporters. In contrast, the mitochondrial genes MnSOD and Hsp22 increased expression of Hsp22 reporters in the oenocytes and decreased accumulation of age pigment in these cells. The data suggest that cell-specific and cell lineage-specific patterns of mitochondrial malfunction contribute to oenocyte aging.

Using zebrafish models to explore genetic and epigenetic impacts on evolutionary developmental origins of aging

Can we reset, reprogram, rejuvenate, or reverse the organismal aging process? Certain genetic manipulations could at least reset and reprogram epigenetic dynamics beyond phenotypic plasticity and elasticity in cells, which can be manipulated further into organisms. However, in a whole complex aging organism, how can we rejuvenate intrinsic resources and infrastructures in an intact and noninvasive manner? The incidence of diseases increases exponentially with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but essentially inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these 2 phenomena to rejuvenate over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states based on diverse epigenotypes in response to intrinsic or extrinsic environmental cues and genetic perturbations. We hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds and windows of plasticity and its robustness by molecular genetic and chemical epigenetic approaches, we have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during their embryonic and/or larval stages ("embryonic/larval senescence"). Subsequently, at least some of these mutant animals were found to show a shortened life span, whereas others would be expected to live longer into adulthood. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and its regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes, genotypes, and epigenotypes that can be linked to the senescence phenotype, which facilitates searching for the evolutionary and developmental origins of aging in vertebrates.

Roles of brain and muscle ARNT-like 1 and Wnt antagonist Dkk1 during osteogenesis of bone marrow stromal cells

OBJECTIVES

Many studies have demonstrated that the clock gene, brain and muscle ARNT-like 1 (Bmal1), is directly related to bone ageing by affecting age-related changes to mesenchymal stem cells (MSCs). As a main developmental signal, Wnt may play an important role in this process. Here, we have aimed to elucidate whether Bmal1 positively regulates osteogenesi via Wnt pathways.

MATERIALS AND METHODS

Bone marrow stromal cells were cultured in basic and in osteo-induction medium with Wnt signalling inhibitor Dkk1 and Bmal1 transfection. Proliferation and osteogenesis of MSCs, expression of Bmal1 and activation of Wnt signalling were investigated by flow cytometry, senescence-associated β-galactosidase (SA-β-gal) staining, real-time quantitative PCR and western blot analysis.

RESULTS

Expression of Bmal1 (specially after 7 days osteo-induction), activation of Wnt signalling and osteo-related factors fell significantly during osteo-induction after Dkk1 addition. When cellular Bmal1 was increased by transfection, osteogenesis inhibition by Dkk1 was rescued to a certain extent with activation of Wnt signalling. However, Dkk1 did not significantly affect proliferation or senescence of MSCs during early periods of culture.

CONCLUSION

These findings demonstrated that Bmal1 and Wnt signalling may have a synergistic effect at a particular stage of osteogenesis. Inhibition of Wnt signalling did not greatly affect ageing of MSCs through early passages.

Age-dependent impaired neurogenic differentiation capacity of dental stem cell is associated with Wnt/β-catenin signaling

Two kinds of dental stem cells (DSCs), dental pulp stem cells (DPSCs) and stem cells from human-exfoliated deciduous teeth (SHED), have been identified as novel populations of mesenchymal stem cells that can be induced to differentiate into osteoblasts, chondrocytes, adipocytes, and neuron-like cells in vitro. As we know, both of them originate from the neural crest, but have distinct characteristics and functions in vitro and in vivo. The regeneration potential of DSCs declines with advanced age; however, the mechanism of the impaired potential in DSCs has not been fully explored. In this study, we investigated whether declined neurogenic differentiation capacity is associated with an altered expression of Wnt signaling-related proteins in vitro. We compared stem cells isolated from human dental pulp in two age groups: the exfoliated deciduous teeth (5-12 years), and the third permanent teeth (45-50 years). We found that the expression levels of neuron markers, such as βIII-tubulin, microtubule-associated protein 2(MAP2), tyrosine hydroxylase (TH), and Nestin were lower in the DPSCs group compared with that in the SHED group; however, in supplementation with human recombinant Wnt1 in the medium, the DPSCs were prone to neural differentiation and expressed higher levels of neurogenic markers. In summary, our study demonstrated that Wnt/β-catenin signaling may play a vital role in the age-dependent neural differentiation of DSCs. Therefore, DSCs may provide an ideal source of stem cells that can further extend their therapeutic application in nerve injury and neurodegenerative diseases.

Antidiabetic therapy effects on bone metabolism and fracture risk

Patients with diabetes are at greater risk of fractures mostly due to not only to extraskeletal factors, such as propensity to fall, but also to bone quality alteration, which reduces bone strength. In people with diabetes, insulin deficiency and hyperglycaemia seem to play a role in determining bone formation alteration by advanced glycation end product (AGE) accumulation or AGE/RAGE (receptors for AGE) axis imbalance, which directly influence osteoblast activity. Moreover, hyperglycaemia and oxidative stress are able to negatively influence osteocalcin production and the Wnt signalling pathways with an imbalance of osteoblast/osteoclast activity leading to bone quality reduction as global effect. In addition, other factors such as insulin growth factors and peroxisome proliferator-activated receptor-γ pathways seem to have an important role in the pathophysiology of osteoporosis in diabetes. Although there are conflicting data in literature, adequate glycaemic control with hypoglycaemic treatment may be an important element in preventing bone tissue alterations in both type 1 and type 2 diabetes. Attention should be paid to the use of thiazolidinediones, especially in older women, because the direct negative effect on bone could exceed the positive effect of glycaemic control. Finally, preliminary data on animals and in humans suggest the hypothesis that incretins and dipeptidyl peptidase-4 inhibitors could have a positive effect on bone metabolism by a direct effect on bone cells; however, such issue needs further investigations.

Identification and characterization of microRNAs by high through-put sequencing in mesenchymal stem cells and bone tissue from mice of age-related osteoporosis

The functional deficiencies of bone marrow-derived mesenchymal stem cells (MSCs) may contribute to the aging process and age-related diseases, such as osteoporosis. Although it has been reported that microRNAs (miRNAs) played an important role in mechanisms of gene regulation of aging, and their expression profiles in MSCs osteogenic differentiation were established in recent years, but it is still elusive for the dynamic patterns of miRNAs in aging process. Importantly, the miRNAs in aged bone tissue had not been yet reported so far. Here, we combined high through-put sequencing with computational techniques to detect miRNAs dynamics in MSCs and bone tissue of age-related osteoporosis. Among the detected miRNAs, 59 identified miRNAs in MSCs and 159 in bone showed significantly differential expressions. And more importantly, there existed 8 up-regulated and 30 down-regulated miRNAs in both MSCs and bone during the aging process, with the majority having a trend of down-regulation. Furthermore, after target prediction and KEGG pathway analysis, we found that their targeted genes were significantly enriched in pathways in cancer, which are complex genetic networks, comprise of a number of age-related pathways. These results strongly suggest that these analyzed miRNAs may be negatively involved in age-related osteoporosis, given that most of them showed a decreased expression, which could lay a good foundation for further functional analysis of these miRNAs in age-related osteoporosis.

Increased expression of secreted frizzled-related protein-1 and microtubule-associated protein light chain 3 in keratoconus

PURPOSE

To study the expression of secreted frizzled-related protein-1 (SFRP-1) and microtubule-associated protein light chain 3 (LC3), an autophagy marker, in keratoconus.

METHODS

Under an institutional review board-approved protocol, de-identified and/or surgically discarded normal donor (n = 10) and keratoconus corneas (n = 10) were obtained. The corneal samples were fixed in formalin and embedded in paraffin. Immunohistochemical staining using SFRP-1 and LC3 antibodies was performed.

RESULTS

The majority of expression of SFRP-1 was seen in the epithelium; however, in 3 tissues that showed high expression, staining was also present in the stroma and endothelium. Like SFRP-1, the LC3 expression in keratoconus tissues occurred at 3 different levels: low, medium, and high. Collectively these data suggest that there are differences in the expression levels of SFRP-1 and LC3 in keratoconus tissue compared with the normal tissue. Low expressivity of SFRP-1 seemed to correspond to low expressivity of LC3, whereas medium to high expressivity of SFRP-1 corresponded to medium to high expressivity of LC3.

CONCLUSIONS

Increased expression of SFRP-1 and LC3 was observed in keratoconus corneas. Keratocyte autophagy seen with keratoconus may play a role in the pathogenesis of keratoconus.

FOXOs attenuate bone formation by suppressing Wnt signaling

Wnt/β-catenin/TCF signaling stimulates bone formation and suppresses adipogenesis. The hallmarks of skeletal involution with age, on the other hand, are decreased bone formation and increased bone marrow adiposity. These changes are associated with increased oxidative stress and decreased growth factor production, which activate members of the FOXO family of transcription factors. FOXOs in turn attenuate Wnt/β-catenin signaling by diverting β-catenin from TCF- to FOXO-mediated transcription. We show herein that mice lacking Foxo1, -3, and -4 in bipotential progenitors of osteoblast and adipocytes (expressing Osterix1) exhibited increased osteoblast number and high bone mass that was maintained in old age as well as decreased adiposity in the aged bone marrow. The increased bone mass in the Foxo-deficient mice was accounted for by increased proliferation of osteoprogenitor cells and bone formation resulting from upregulation of Wnt/β-catenin signaling and cyclin D1 expression, but not changes in redox balance. Consistent with this mechanism, β-catenin deletion in Foxo null cells abrogated both the increased cyclin D1 expression and proliferation. The elucidation of a restraining effect of FOXOs on Wnt signaling in bipotential progenitors suggests that FOXO activation by accumulation of age-associated cellular stressors may be a seminal pathogenetic mechanism in the development of involutional osteoporosis.

Basic biology of skeletal aging: role of stress response pathways

Although a decline in bone formation and loss of bone mass are common features of human aging, the molecular mechanisms mediating these effects have remained unclear. Evidence from pharmacological and genetic studies in mice has provided support for a deleterious effect of oxidative stress in bone and has strengthened the idea that an increase in reactive oxygen species (ROS) with advancing age represents a pathophysiological mechanism underlying age-related bone loss. Mesenchymal stem cells and osteocytes are long-lived cells and, therefore, are more susceptible than other types of bone cells to the molecular changes caused by aging, including increased levels of ROS and decreased autophagy. However, short-lived cells like osteoblast progenitors and mature osteoblasts and osteoclasts are also affected by the altered aged environment characterized by lower levels of sex steroids, increased endogenous glucocorticoids, and higher oxidized lipids. This article reviews current knowledge on the effects of the aging process on bone, with particular emphasis on the role of ROS and autophagy in cells of the osteoblast lineage in mice.

Molecular and chemical genetic approaches to developmental origins of aging and disease in zebrafish

The incidence of diseases increases rapidly with age, accompanied by progressive deteriorations of physiological functions in organisms. Aging-associated diseases are sporadic but mostly inevitable complications arising from senescence. Senescence is often considered the antithesis of early development, but yet there may be factors and mechanisms in common between these two phenomena over the dynamic process of aging. The association between early development and late-onset disease with advancing age is thought to come from a consequence of developmental plasticity, the phenomenon by which one genotype can give rise to a range of physiologically and/or morphologically adaptive states in response to different environmental or genetic perturbations. On the one hand, we hypothesized that the future aging process can be predictive based on adaptivity during the early developmental period. Modulating the thresholds of adaptive plasticity by chemical genetic approaches, we have been investigating whether any relationship exists between the regulatory mechanisms that function in early development and in senescence using the zebrafish (Danio rerio), a small freshwater fish and a useful model animal for genetic studies. We have successfully conducted experiments to isolate zebrafish mutants expressing apparently altered senescence phenotypes during embryogenesis ("embryonic senescence"), subsequently showing shortened lifespan in adulthoods. We anticipate that previously uncharacterized developmental genes may mediate the aging process and play a pivotal role in senescence. On the other hand, unexpected senescence-related genes might also be involved in the early developmental process and regulation. The ease of manipulation using the zebrafish system allows us to conduct an exhaustive exploration of novel genes and small molecular compounds that can be linked to the senescence phenotype, and thereby facilitates searching for the evolutionary and developmental origins of aging in vertebrates. This article is part of a Special Issue entitled: Animal Models of Disease.

Over-expression of circadian clock gene Bmal1 affects proliferation and the canonical Wnt pathway in NIH-3T3 cells

Bmal1 is a transcription factor that plays a central role in the regulation of circadian rhythms. Recent study reported that Bmal1-/- mice displayed many known features of premature ageing, such as reduction of bone mass. Our previous study has found that both the proliferation of bone marrow mesenchymal stem cells (BMSCs) and Bmal1 expression decreased with advancing age. It seemed that a positive correlation existed between Bmal1 protein level and the proliferative activity of BMSCs. β-catenin, the core factor of the canonical Wnt pathway, also showed reduced expression in aged mice. In order to further confirm this, we constructed a lentiviral vector to over-express Bmal1 in NIH-3T3 cells; successful transfection was verified. The cell proliferation rate of infected cells was higher than the non-transfected NIH-3T3 cells, suggesting that circadian clock gene Bmal1 can promote proliferation. β-catenin showed an increased expression in NIH-3T3 cells after Bmal1 over-expression, indicating that activation of the canonical Wnt pathway might be the mechanism underlying the effect of circadian clock gene Bmal on promoting cell proliferation.

Identification of biomarkers of human skin ageing in both genders. Wnt signalling - a label of skin ageing?

The goal of our work has been to investigate the mechanisms of gender-independent human skin ageing and examine the hypothesis of skin being an adequate model of global ageing. For this purpose, whole genome gene profiling was employed in sun-protected skin obtained from European Caucasian young and elderly females (mean age 26.7±4 years [n1 = 7] and 70.75±3.3 years [n2 = 4], respectively) and males (mean age 25.8±5.2 years [n3 = 6] and 76±3.8 years [n4 = 7], respectively) using the Illumina array platform. Confirmation of gene regulation was performed by real-time RT-PCR and immunohistochemistry. 523 genes were significantly regulated in female skin and 401 genes in male skin for the chosen criteria. Of these, 183 genes exhibited increased and 340 decreased expression in females whereas 210 genes showed increased and 191 decreased expression in males with age. In total, 39 genes were common in the target lists of significant regulated genes in males and females. 35 of these genes showed increased (16) or decreased (19) expression independent of gender. Only 4 overlapping genes (OR52N2, F6FR1OP2, TUBAL3 and STK40) showed differential regulation with age. Interestingly, Wnt signalling pathway showed to be significantly downregulated in aged skin with decreased gene and protein expression for males and females, accordingly. In addition, several genes involved in central nervous system (CNS) ageing (f.i. APP, TAU) showed to be expressed in human skin and were significanlty regulated with age. In conclusion, our study provides biomarkers of endogenous human skin ageing in both genders and highlight the role of Wnt signalling in this process. Furthermore, our data give evidence that skin could be used as a good alternative to understand ageing of different tissues such as CNS.

Wnt/β-catenin signaling induces the aging of mesenchymal stem cells through promoting the ROS production

Recent studies have demonstrated that the Wnt/β-catenin signaling plays an important role in stem cell aging. However, the mechanisms of cell senescence induced by Wnt/β-catenin signaling are still poorly understood. Our preliminary study has indicated that activated Wnt/β-catenin signaling can induce MSC aging. In this study, we reported that the Wnt/β-catenin signaling was a potent activator of reactive oxygen species (ROS) generation in MSCs. After scavenging ROS with N-acetylcysteine, Wnt/β-catenin signaling-induced MSC aging was significantly attenuated and the DNA damage and the expression of p16(INK4A), p53, and p21 were reduced in MSCs. These results indicated that the Wnt/β-catenin signaling could induce MSC aging through promoting the intracellular production of ROS, and ROS may be the main mediators of MSC aging induced by excessive activation of Wnt/β-catenin signaling.

Wnt/β-catenin and its diverse physiological cell signaling pathways in neurodegenerative and neuropsychiatric disorders

Wnt signaling is a fundamental pathway in embryogenesis which is evolutionary conserved from metazoans to humans. Much of our understanding of Wnt signaling events emerged from key developmental studies in drosophila, zebra fish, xenopus, and mice. Considerable data now exists on the role of Wnt signaling beyond these developmental processes and in particular its role in health and disease. The focus of this special issue is on Wnt/β-catenin and its diverse physiological cell signaling pathways in neurodegenerative and neuropsychiatric disorders. This special issue is composed of six reviews and two original articles selected to highlight recent advances in the role of Wnt signaling in CNS embryonic development, in adult brain function, in neurodegenerative conditions such as Alzheimer's disease, schizophrenia, NeuroAIDS, and in gliomas. The finding that β-catenin can translocate to the nucleus where it binds to TCF/LEF transcription factors to regulate target gene expression was a seminal observation that linked β-catenin/LEF to T cell development and differentiation. We also provide a nostalgic look on recent advances in role of Wnts in T cell development and maturation. These reviews highlight the extensive body of work in these thematic areas as well as identify knowledge gaps, where appropriate. Understanding Wnt function under healthy and diseased conditions may provide a therapeutic resource, albeit it a challenging one, in diseases where dysfunctional and/or diminished Wnt signaling is a prominent player in the disease process.

Interplay between Wnt/β-catenin signaling and HIV: virologic and biologic consequences in the CNS

Considerable studies have evaluated the interaction between Wnt/β-catenin signaling and numerous cellular processes. Emerging findings now demonstrate that Wnt/β-catenin signaling interacts with the life cycle of the Human Immunodeficiency Virus type 1 (HIV-1). Wnt/β-catenin is a restrictive pathway to HIV replication in multiple target cells including peripheral blood mononuclear cells and astrocytes. The molecular interaction between Wnt/β-catenin signaling and HIV has been evaluated in astrocytes because they express robust level of this pathway. The cross talk that occurs between these two components has significant biologic consequences to HIV-mediated neuropathogenesis. This perspective highlights current knowledge regarding the interaction between Wnt/β-catenin signaling and HIV, the interplay between these two pathways as it impacts key features of NeuroAIDS, and provides an assessment of knowledge gaps in the field that could propel our understanding of this interaction to inform novel strategies to exploit Wnt signaling for therapeutic intervention in HIV/NeuroAIDS.

The effect of physiological stimuli on sarcopenia; impact of Notch and Wnt signaling on impaired aged skeletal muscle repair

The age-related loss of skeletal muscle mass and function that is associated with sarcopenia can result in ultimate consequences such as decreased quality of life. The causes of sarcopenia are multifactorial and include environmental and biological factors. The purpose of this review is to synthesize what the literature reveals in regards to the cellular regulation of sarcopenia, including impaired muscle regenerative capacity in the aged, and to discuss if physiological stimuli have the potential to slow the loss of myogenic potential that is associated with sarcopenia. In addition, this review article will discuss the effect of aging on Notch and Wnt signaling, and whether physiological stimuli have the ability to restore Notch and Wnt signaling resulting in rejuvenated aged muscle repair. The intention of this summary is to bring awareness to the benefits of consistent physiological stimulus (exercise) to combating sarcopenia as well as proclaiming the usefulness of contraction-induced injury models to studying the effects of local and systemic influences on aged myogenic capability.

Bone metabolism and fracture risk in type 2 diabetes mellitus

Osteoporosis and type 2 diabetes mellitus (T2DM), both prevalent in aging and westernized societies, adversely affect the health of elderly people by causing fractures and vascular complications, respectively. Recent experimental and clinical studies show that the disorders are etiologically related through the actions of osteocalcin and adiponectin. Meta-analyses of multiple clinical studies show that the hip fracture risk of T2DM patients is increased 1.4-1.7-fold compared with non-DM controls, even though the patients' bone mineral density (BMD) is not diminished. Vertebral fracture risk of the T2DM patients is also increased, and BMD measurement is not sensitive enough to assess this risk. These findings suggest that bone fragility in T2DM patients depends on bone quality deterioration rather than bone mass reduction. Surrogate markers are therefore needed to supplement the partial effectiveness of BMD testing in assessing the fracture risk of the T2DM patients. Markers related to advanced glycation end products may be candidates. These substances modulate bone quality in DM. Until research establishes the usefulness of surrogate markers, physicians should assess fracture risk in T2DM patients not only by measuring the BMD, but also by taking a fracture history and evaluating prior vertebral fractures using spinal X-rays.

Dickkopf 1 mediates glucocorticoid-induced changes in human neural progenitor cell proliferation and differentiation

Glucocorticoids (GC) are critical for normal development of the fetal brain, and alterations in their levels can induce neurotoxicity with detrimental consequences. Still, there is little information available on the effects of GC on human neural stem/progenitor cells (hNPC). In the present study, we have investigated the effects of the synthetic GC dexamethasone (Dex) on hNPC grown as neurospheres, with special focus on their proliferation and differentiation capacity and the underlying molecular mechanisms. Immunocytochemical stainings showed that Dex markedly decreases proliferation and neuronal differentiation while promoting glia cell formation. Analysis of pathway-specific genes revealed that Dex induces an upregulation of the Wnt-signaling antagonist DKK1. Moreover, Dex- or DKK1-treated hNPCs showed reduced transcriptional levels of the two canonical Wnt target genes cyclin D1 and inhibitor of DNA binding 2 (ID2). Chromatin immunoprecipitation showed that Dex, via the glucocorticoid receptor, interacts with the DKK1 promotor. Treatment of hNPC with recombinant DKK1 or neutralizing antibodies indicated that DKK1 has a critical role in the Dex-induced inhibition of proliferation and neuronal differentiation with a concomitant increase in glial cells. Taken together, our findings show that GC reduce proliferation and interfere with differentiation of hNPCs via the canonical Wnt-signaling pathway.

Role of β-catenin/TCF-4 signaling in HIV replication and pathogenesis: insights to informing novel anti-HIV molecular therapeutics

A greater understanding of the interaction between HIV and host signaling pathways that restrict virus production may lead to new methods to purge virus from latent reservoirs and enhance survival/function of cells targeted by HIV. This review highlights the role of the Wnt/β-catenin pathway as a host factor that represses HIV replication in multiple targets, especially those relevant to HIV in the central nervous system.

Bone metabolism and fracture risk in type 2 diabetes mellitus [Review]

Osteoporosis and type 2 diabetes mellitus (T2DM) are now prevalent in aging and westernized societies, and adversely affect the health of the elderly people by causing fractures and vascular complications, respectively. Recent experimental and clinical studies show that both disorders are etiologically related to each other through the actions of osteocalcin and adiponectin. Meta-analyses of multiple clinical studies show that hip fracture risk of T2DM patients is increased to 1.4 to 1.7-folds, although BMD of the patients is not diminished. Vertebral fracture risk of T2DM patients is also increased, and BMD is not useful for assessing its risk. These findings suggest that bone fragility in T2DM depends on bone quality deterioration rather than bone mass reduction. Thus, surrogate markers are needed to replace the insensitivity of BMD in assessing fracture risks of T2DM patients. Markers related to advanced glycation end products as well as insulin-like growth factor-I may be such candidates, because these substances were experimentally shown to modulate bone quality in DM. In practice, it is important for physicians to assess fracture risk in T2DM patients by evaluating prior VFs and fracture histories using spine X-ray and interview, respectively, until the usefulness of surrogate markers is established.

Bone fragility in type 2 diabetes mellitus

The number of patients with osteoporosis or type 2 diabetes mellitus (T2DM) is increasing in aging and westernized societies. Both disorders predispose elderly people to disabling conditions by causing fractures and vascular complications, respectively. It is well documented that bone metabolism and glucose/fat metabolism are etiologically related to each other through osteocalcin action and Wnt signaling. Bone fragility in T2DM, which is not reflected by bone mineral density (BMD), depends on bone quality deterioration rather than bone mass reduction. Thus, surrogate markers are needed to replace the insensitivity of BMD in assessing fracture risks of T2DM patients. Pentosidine, the endogenous secretory receptor for advanced glycation endproducts, and insulin-like growth factor-I seem to be such candidates, although further studies are required to clarify whether or not these markers could predict the occurrence of new fractures of T2DM patients in a prospective fashion.

Aging and bone

Bones provide mechanical and protective function, while also serving as housing for marrow and a site for regulation of calcium ion homeostasis. The properties of bones do not remain constant with age; rather, they change throughout life, in some cases improving in function, but in others, function deteriorates. Here we review the modifications in the mechanical function and shape of bones, the bone cells, the matrix they produce, and the mineral that is deposited on this matrix, while presenting recent theories about the factors leading to these changes.

The Wnt signaling pathway in cellular proliferation and differentiation: A tale of two coactivators

Wnt signaling pathways play divergent roles during development, normal homeostasis and disease. The responses that result from the activation of the pathway control both proliferation and differentiation. Tight regulation and controlled coordination of the Wnt signaling cascade is required to maintain the balance between proliferation and differentiation. The non-redundant roles of the coactivator proteins CBP and p300, within the context of Wnt signaling are discussed. We highlight their roles as integrators of the various inputs that a cell receives to elicit the correct and coordinated response. We propose that essentially all cellular information - i.e. from other signaling pathways, nutrient levels, etc. - is funneled down into a choice of coactivators usage, either CBP or p300, by their interacting partner beta-catenin (or catenin-like molecules in the absence of beta-catenin) to make the critical decision to either remain quiescent, or once entering cycle to proliferate without differentiation or to initiate the differentiation process.

Functional coupling between the extracellular matrix and nuclear lamina by Wnt signaling in progeria

The segmental premature aging disease Hutchinson-Gilford Progeria (HGPS) is caused by a truncated and farnesylated form of Lamin A. In a mouse model for HGPS, a similar Lamin A variant causes the proliferative arrest and death of postnatal, but not embryonic, fibroblasts. Arrest is due to an inability to produce a functional extracellular matrix (ECM), because growth on normal ECM rescues proliferation. The defects are associated with inhibition of canonical Wnt signaling, due to reduced nuclear localization and transcriptional activity of Lef1, but not Tcf4, in both mouse and human progeric cells. Defective Wnt signaling, affecting ECM synthesis, may be critical to the etiology of HGPS because mice exhibit skeletal defects and apoptosis in major blood vessels proximal to the heart. These results establish a functional link between the nuclear envelope/lamina and the cell surface/ECM and may provide insights into the role of Wnt signaling and the ECM in aging.

From estrogen-centric to aging and oxidative stress: a revised perspective of the pathogenesis of osteoporosis

Estrogen deficiency has been considered the seminal mechanism of osteoporosis in both women and men, but epidemiological evidence in humans and recent mechanistic studies in rodents indicate that aging and the associated increase in reactive oxygen species (ROS) are the proximal culprits. ROS greatly influence the generation and survival of osteoclasts, osteoblasts, and osteocytes. Moreover, oxidative defense by the FoxO transcription factors is indispensable for skeletal homeostasis at any age. Loss of estrogens or androgens decreases defense against oxidative stress in bone, and this accounts for the increased bone resorption associated with the acute loss of these hormones. ROS-activated FoxOs in early mesenchymal progenitors also divert ss-catenin away from Wnt signaling, leading to decreased osteoblastogenesis. This latter mechanism may be implicated in the pathogenesis of type 1 and 2 diabetes and ROS-mediated adverse effects of diabetes on bone formation. Attenuation of Wnt signaling by the activation of peroxisome proliferator-activated receptor gamma by ligands generated from lipid oxidation also contributes to the age-dependent decrease in bone formation, suggesting a mechanistic explanation for the link between atherosclerosis and osteoporosis. Additionally, increased glucocorticoid production and sensitivity with advancing age decrease skeletal hydration and thereby increase skeletal fragility by attenuating the volume of the bone vasculature and interstitial fluid. This emerging evidence provides a paradigm shift from the "estrogen-centric" account of the pathogenesis of involutional osteoporosis to one in which age-related mechanisms intrinsic to bone and oxidative stress are protagonists and age-related changes in other organs and tissues, such as ovaries, accentuate them.

Effects of age and gender on WNT gene expression in human bone marrow stromal cells

WNT signaling pathways play important roles in the behavior of human bone marrow stromal cells. Although WNT expression has been examined in human bone marrow stromal cells (hMSCs) with limited numbers of subjects or from commercial sources, there are conflicting results on WNT gene expression in hMSCs. Furthermore, the effects of age and gender on WNT expression in hMSCs are largely unknown. In this study, we evaluated RNA expression of all the WNT genes in hMSCs from 19 subjects, 12 women and 7 men, aged from 36 to 85 years. Analysis of WNT gene expression in young and old groups indicated that WNT7B and 14 were expressed significantly higher in the young group. WNT2 and WNT13 showed a trend of higher expression in young group. WNT7B, 13, and 14 were inversely correlated with age. Further analysis for gender-specific difference indicated that WNT16 was expressed significantly higher in men than in women. WNT11 showed a trend of higher expression in hMSCs from women. For the hMSCs from women, WNT13 was inversely correlated with age and WNT4 was positively correlated with age. For the hMSCs from men, WNT7B and WNT14 were inversely correlated with age. These data indicated that most of the age-related WNT genes belong to the canonical WNT signaling pathway. Further, there are gender-specific differences in the expression of WNT4, 7B, 13, 14, and 16 in hMSCs. Age and gender account for many of the sample-to-sample variations in WNT gene expression in human marrow stromal cells.

A screen of apoptosis and senescence regulatory genes for life span effects when over-expressed in Drosophila

Conditional expression of transgenes in Drosophila was produced using the Geneswitch system, wherein feeding the drug RU486/Mifepristone activates the artificial transcription factor Geneswitch. Geneswitch was expressed using the Actin5C promoter and this was found to yield conditional, tissue-general expression of a target transgene (UAS-GFP) in both larvae and adult flies. Nervous system-specific (Elav-GS) and fat body-specific Geneswitch drivers were also characterized using UAS-GFP. Fourteen genes implicated in growth, apoptosis and senescence regulatory pathways were over-expressed in adult flies or during larval development, and assayed for effects on adult fly life span. Over-expression of a dominant p53 allele (p53-259H) in adult flies using the ubiquitous driver produced increased life span in females but not males, consistent with previous studies. Both wingless and Ras activated form transgenes were lethal when expressed in larvae, and reduced life span when expressed in adults, consistent with results from other model systems indicating that the wingless and Ras pathways can promote senescence. Over-expression of the caspase inhibitor baculovirus p35 during larval development reduced the mean life span of male and female adults, and also produced a subset of females with increased life span. These experiments suggest that baculovirus p35 and the wingless and Ras pathways can have sex-specific and developmental stage-specific effects on adult Drosophila life span, and these reagents should be useful for the further analysis of the role of these conserved pathways in aging.

Age-dependent Wnt gene expression in bone and during the course of osteoblast differentiation

Wnt signaling is vital for osteoblast differentiation and recently has been associated with aging. Because impaired osteoblastogenesis is a cellular characteristic of age-induced bone loss, we investigated whether this process is associated with an altered expression of Wnt signaling-related proteins in bone and osteoblasts. Bone marrow cells were isolated from male C57BL/6 mice, aged 6 weeks, 6 months, and 18 months, respectively. Osteogenic differentiation was induced for 3 weeks and assessed using alizarin red staining. Gene expression of Wnt1, 3a, 4, 5a, 5b, 7b, 9b, 10b, lipoprotein receptor-related protein (LRP)-5/6, as well as dickkopf-1 (Dkk-1), sclerostin, and secreted frizzled related protein-1 (sFRP-1) was determined in bone tissue and osteoblasts on days 7, 14, and 21 by real-time RT-PCR. Osteoblast differentiation was significantly reduced in aged mice compared with young and adult mice. In bone tissue, expression levels of all genes assessed were decreased in adult and old mice, respectively, compared with young mice. Mature osteoblasts of aged compared with those of young mice showed enhanced expression of Wnt9b, LRP-6, and Dkk-1, and decreased expression of Wnt5a and 7b. In early osteoblasts, mRNA levels of Wnt1, 5a, 5b, and 7b were increased significantly in aged mice. The expression of Wnt3a, 4, LRP-5, and sclerostin was not altered in aged osteoblasts. In conclusion, osteoblastic expression of each Wnt-related protein is regulated individually by aging. The overall decreased expression of Wnt-related proteins in bone tissue of aged mice underlines the newly discovered association of Wnt signaling with aging.