Inhibition of adipocytogenesis by canonical WNT signaling in human mesenchymal stem cells

Stem Cell and Regenerative Therapies for the Treatment of Osteoporotic Vertebral Compression Fractures

Osteoporotic vertebral compression fractures (OVCFs) significantly increase morbidity and mortality, presenting a formidable challenge in healthcare. Traditional interventions such as vertebroplasty and kyphoplasty, despite their widespread use, are limited in addressing the secondary effects of vertebral fractures in adjacent areas and do not facilitate bone regeneration. This review paper explores the emerging domain of regenerative therapies, spotlighting stem cell therapy's transformative potential in OVCF treatment. It thoroughly describes the therapeutic possibilities and mechanisms of action of mesenchymal stem cells against OVCFs, relying on recent clinical trials and preclinical studies for efficacy assessment. Our findings reveal that stem cell therapy, particularly in combination with scaffolding materials, holds substantial promise for bone regeneration, spinal stability improvement, and pain mitigation. This integration of stem cell-based methods with conventional treatments may herald a new era in OVCF management, potentially improving patient outcomes. This review advocates for accelerated research and collaborative efforts to translate laboratory breakthroughs into clinical practice, emphasizing the revolutionary impact of regenerative therapies on OVCF management. In summary, this paper positions stem cell therapy at the forefront of innovation for OVCF treatment, stressing the importance of ongoing research and cross-disciplinary collaboration to unlock its full clinical potential.

CircZNF367 suppresses osteogenic differentiation of human bone marrow mesenchymal stromal/stem cells via reducing HuR-mediated mRNA stability of LRP5

Osteoporosis is a highly prevalent disease characterized by bone mass loss and structural deterioration. There are evidences that altered differentiation of human bone marrow mesenchymal stromal/stem cells (hBMSCs) is a major cause for osteoporosis. Recent studies suggest that circular RNAs (circRNAs) are dysregulated in osteoporosis patients and involved in the pathogenesis of osteoporosis. In the present study, we are aimed to analyze the circRNA expression profiles in osteoporosis patients and identify potential circRNAs that involved in the differentiation of hBMSCs during osteoporosis. Transcriptome RNA-sequencing was conducted to search for differentially expressed circRNAs. Transwell assay, ARS and ALP staining, and ectopic bone formation model were performed to evaluate osteogenic differentiation of hBMSCs. RNA pull-down assay, RNA immunoprecipitation, western blot, and in vitro binding assay were conducted to evaluate the interaction of circRNAs and RNA-binding protein HuR. We found that hsa_circ_0008842 (designated as circZNF367) was upregulated in osteoporosis patients and decreased in hBMSCs during osteogenic differentiation. CircZNF367 overexpression suppressed migration, invasion and osteogenic differentiation of hBMSCs in vitro and in vivo. In comparison, knockdown of circZNF367 promoted migration, invasion and osteogenic differentiation of hBMSCs. CircZNF367 could interact with the RNA-binding protein HuR, thus reduced the mRNA stability of LRP5. Furthermore, HuR overexpression or LRP5 restoration abrogated the effects of circZNF367 overexpression on osteogenic differentiation of hBMSCs. Our results indicated that circZNF367 played a role in osteogenic differentiation of hBMSCs via reducing HuR-mediated mRNA stability of LRP5.

Hydrogel-based delivery system applied in the local anti-osteoporotic bone defects

Osteoporosis is an age-related systemic skeletal disease leading to bone mass loss and microarchitectural deterioration. It affects a large number of patients, thereby economically burdening healthcare systems worldwide. The low bioavailability and complications, associated with systemic drug consumption, limit the efficacy of anti-osteoporosis drugs currently available. Thus, a combination of therapies, including local treatment and systemic intervention, may be more beneficial over a singular pharmacological treatment. Hydrogels are attractive materials as fillers for bone injuries with irregular shapes and as carriers for local therapeutic treatments. They exhibit low cytotoxicity, excellent biocompatibility, and biodegradability, and some with excellent mechanical and swelling properties, and a controlled degradation rate. This review reports the advantages of hydrogels for adjuvants loading, including nature-based, synthetic, and composite hydrogels. In addition, we discuss functional adjuvants loaded with hydrogels, primarily focusing on drugs and cells that inhibit osteoclast and promote osteoblast. Selecting appropriate hydrogels and adjuvants is the key to successful treatment. We hope this review serves as a reference for subsequent research and clinical application of hydrogel-based delivery systems in osteoporosis therapy.

Understanding stem cells and its pivotal role in regenerative medicine

Stem cells (SCs) are clonogenic cells that develop into the specialized cells which later responsible for making up various types of tissue in the human body. SCs are not only the appropriate source of information for cell division, molecular and cellular processes, and tissue homeostasis but also one of the major putative biological aids to diagnose and cure various degenerative diseases. This study emphasises on various research outputs that occurred in the past two decades. This will give brief information on classification, differentiation, detection, and various isolation techniques of SCs. Here, the various signalling pathways which includes WNT, Sonic hedgehog, Notch, BMI1 and C-met pathways and how does it effect on the regeneration of various classes of SCs and factors that regulates the potency of the SCs are also been discussed. We also focused on the application of SCs in the area of regenerative medicine along with the cellular markers that are useful as salient diagnostic or curative tools or in both, by the process of reprogramming, which includes diabetes, cancer, cardiovascular disorders and neurological disorders. The biomarkers that are mentioned in various literatures and experiments include PDX1, FOXA2, HNF6, and NKX6-1 (for diabetes); CD33, CD24, CD133 (for cancer); c-Kit, SCA-1, Wilm's tumor 1 (for cardiovascular disorders); and OCT4, SOX2, c-MYC, EN1, DAT and VMAT2 (for neurological disorders). In this review, we come to know the advancements and scopes of potential SC-based therapies, its diverse applications in clinical fields that can be helpful in the near future.

MiR-1-3p regulates the differentiation of mesenchymal stem cells to prevent osteoporosis by targeting secreted frizzled-related protein 1

Osteoporosis (OP) is a systemic skeletal disorder with the characteristics of bone mass reduction and microarchitecture deterioration, resulting in bone fragility and increased fracture risk. A reduction in the osteoblast-differentiation of bone marrow mesenchymal stem cells (BMSCs) is considered as a basic pathogenesis of osteoporosis. miRNAs play a substantial role in the development and differentiation of BMSCs. In the present study, we found that miR-1-3p was significantly downregulated in the bones of Chinese osteoporotic patients (n = 29). Secreted frizzled-related protein 1 (SFRP1) was predicted as a target gene of miR-1-3p via the TargetScan and PicTar softwares and validated by dual-luciferase reporter assays. The findings revealed that the expression of SFRP1 was inversely correlated with miR-1-3p in osteoporotic patients. We induced mouse MSCs (mMSCs) to osteogenesis or adipogenesis and found that miR-1-3p was upregulated during osteogenesis but downregulated during adipogenesis. The overexpression of miR-1-3p stimulated osteogenesis and inhibited adipogenesis of mMSCs. In addition, ovariectomized (OVX) mice were tested and the function of miR-1-3p in vivo was explored. Immunohistochemistry and histomorphometric assays showed that in vivo inhibition of miR-1-3p increased the expression level of SFRP1 and reduced bone formation and bone mass. Furthermore, tartrate-resistant acid phosphatase (TRAP) staining indicated that the in vivo suppression of miR-1-3p promoted osteoclast activity, suggesting that miR-1-3p may influence bone mass by regulating bone resorption. It can be concluded that miR-1-3p plays a pivotal role in the pathogenesis of osteoporosis via targeting SFRP1 and may be a potential therapeutic target for osteoporosis.

Effect of ELOVL6 on the lipid metabolism of bovine adipocytes

This study investigated the effect of ELOVL6 (elongation of very long chain fatty acids protein 6) and its underlying mechanism on lipid metabolism in bovine adipocytes. The ELOVL6 gene was overexpressed in bovine adipocytes by adenoviruses, and RNA sequencing was performed. Overexpression of ELOVL6 showed reduced proportions of C14:0 (Myristic) and C16:0 (palmitate) fatty acids and increased proportions of C18.0 (stearate) and C20:4n6 (arachidonic) fatty acids in adipocytes. In addition, a total of 2170 differentially expressed genes (DEGs) were found, containing 1802 up-regulated and 368 down-regulated genes. KEGG pathway analysis revealed that the down-regulated genes were linked with the regulation of lipolysis and the Wnt signaling pathway. The up-regulated genes were mainly involved in the FoxO signaling pathway; the PI3K-Akt signaling pathway; and the cAMP signaling pathway. In conclusion, our results suggest that ELOVL6 could affect the fatty acid composition in bovine adipocytes. We identified numerous related DEGs and pathways, which may provide a basis for studying the function and molecular mechanism of the ELOVL6 gene in regulating lipid metabolism.

RNA-seq reveal role of bovine TORC2 in the regulation of adipogenesis

Low intramuscular adipose tissue (marbling) continues to be challenge for improving beef quality in Chinese cattle. Highly marbled meat is very desirable; hence, methods to increase IMF content have become a key aspect of improving meat quality. Therefore, research on the mechanism of adipogenesis provides invaluable information for the improvement of meat quality. This study investigated the effect of TORC2 and its underlying mechanism on lipid metabolism in bovine adipocytes. The TORC2 gene was downregulated in bovine adipocytes by siRNA, and RNA sequencing was performed. Downregulation of TORC2 negatively affected bovine adipocyte differentiation. In addition, a total of 577 DEGs were found, containing 146 up-regulated and 376 down-regulated genes. KEGG pathway analysis revealed that the DEGs were linked with neuroactive ligand-receptor interaction pathway, calcium signaling pathway, cAMP pathway, chemokine signaling pathway and Wnt signaling pathway. Gene Ontology (GO) term analysis of the DEGs showed that down-regulation of TORC2 gene significantly suppressed the genes regulating important GO terms of adipogenesis-related processes in bovine adipocytes, especially regulation of biological activity, regulation of primary metabolic process, regulation of multicellular organismal process, cell adhesion, lipid metabolic process, secretion, chemical homeostasis, regulation of transport, cell-cell signaling, cAMP metabolic process, cellular calcium ion homeostasis, fat cell differentiation, and cell maturation. In conclusion, our results suggest that TORC2 at least in part regulates lipid metabolism in bovine adipocytes. The results of this study provide a basis for studying the function and molecular mechanism of the TORC2 gene in regulating adipogenesis.

Developmental exposure to nonylphenol induced rat axonal injury in vivo and in vitro

Increasing evidence indicates that developmental exposure to nonylphenol (NP) causes damage to the central nervous system (CNS). As the most unique and primary component of neuron, axon is an essential structure for the CNS function. Here, we investigated whether developmental exposure to NP affected rat axonal development in vivo and in vitro. Our results showed that developmental exposure to NP 10, 50, and 100 mg/(kg day) caused an obvious decrease in axonal length and density in the hippocampus. Developmental exposure to NP also altered the expression of CRMP-2 and p-CRMP-2, and activated Wnt-Dvl-GSK-3β cascade in the hippocampus, the crucial signaling that regulates axonal development. Even months after the exposure, impairment of axonal growth and alteration of this cascade were not fully restored. In the primary cultured neurons, 30, 50, and 70 μM NP treatment decreased axonal length and impaired axonal function. Similar to in vivo results, it also activated Wnt-Dvl-GSK-3β cascade in cultured neurons. SB-216763, a specific GSK-3β inhibitor, recovered the shortening of axon and the impairment of axonal function induced by NP. Taken together, our results support the idea that exposure to NP induces axonal injury in the developing neurons. Furthermore, the activation of Wnt-Dvl-GSK-3β cascade contributes to the axonal injury induced by NP.

Irisin Exerts Inhibitory Effect on Adipogenesis Through Regulation of Wnt Signaling

Irisin is an exercise-induced myokine known to induce adipocyte browning through induction of uncoupling protein 1. Recent studies have reported that irisin is also an adipokine. However, there is limiting evidence on the role of endogenous irisin from adipocytes. In this study we aim to elucidate the expression and secretion pattern of irisin during adipocyte differentiation and the role of endogenous and exogenous irisin on the adipogenic process. As such, recombinant irisin, plasmid expressing FNDC5 and small interfering RNA were utilized. Our results show that the gene expression of irisin precursor FNDC5 and irisin secretion increases at the early stage of adipogenesis. Both recombinant irisin treated cells and FNDC5-overexpressed cells resulted in inhibition of adipogenesis evidenced by downregulated C/EBPα, PPARγ, and FABP4 expression and reduced lipid accumulation. Further data showed that the inhibitory effect of irisin on adipogenesis is mediated though potentiation of Wnt expression, which is known to determine the fate of mesenchymal stem cells and regulate adipogenesis. Conversely, FNDC5 knockdown cells showed downregulated Wnt expression, but failed to further induce adipogenesis. This study suggests that both exogenous and endogenous irisin is able to inhibit adipogenesis and that activation of Wnt and subsequent repression of transcription factors is partly involved in this process. This provides a novel insight on the local effect of irisin on adipocytes and additional benefit to protect against obesity-related metabolic disorders.

The clinical potential of adipogenesis and obesity-related microRNAs

Obesity is a growing health problem commonly associated with numerous metabolic disorders including type 2 diabetes, hypertension, cardiovascular disease, and some forms of cancer. The burden of obesity and associated cardiometabolic diseases are believed to arise through complex interplay between genetics and epigenetics predisposition, nutrition, environment, and lifestyle. However, the molecular basis and the repertoire of obesity-affecting factors are still unknown. Emerging evidence is connecting microRNAs (miRNAs) dysregulation with adipogenesis and obesity. Alteration in miRNAs expression could result in changes in the pattern of genes controlling a range of biological processes including inflammation, lipid metabolism, insulin resistance and adipogenesis. Hence, understanding exact roles of miRNAs as well as the degree of their contribution to the regulation of adipogenesis and fat cell development in obesity would provide new therapeutic targets for the development of novel and effective anti-obesity drugs. The objective of the current review is to: (i) discuss some of the latest development on relevant miRNAs dysregulation mainly in human adipogenesis and obesity, (ii) emphasize the role of circulating miRNAs as new promising therapeutics and attractive potential biomarkers for treating obesity and associated risk factor diseases, (iii) describe how dietary factors may influence obesity through modulation of miRNAs expression, (iv) highlight some of the actual limitations to the promise of miRNAs as novel therapeutics as well as to their translation for the benefit of patients, and finally (v) provide recommendations for future research on miRNA-based therapeutics that could lead to a breakthrough in the treatment of obesity and its associated pathologies.

Mesenchymal Stem Cells: Cell Fate Decision to Osteoblast or Adipocyte and Application in Osteoporosis Treatment

Osteoporosis is a progressive skeletal disease characterized by decreased bone mass and degraded bone microstructure, which leads to increased bone fragility and risks of bone fracture. Osteoporosis is generally age related and has become a major disease of the world. Uncovering the molecular mechanisms underlying osteoporosis and developing effective prevention and therapy methods has great significance for human health. Mesenchymal stem cells (MSCs) are multipotent cells capable of differentiating into osteoblasts, adipocytes, or chondrocytes, and have become the favorite source of cell-based therapy. Evidence shows that during osteoporosis, a shift of the cell differentiation of MSCs to adipocytes rather than osteoblasts partly contributes to osteoporosis. Thus, uncovering the molecular mechanisms of the osteoblast or adipocyte differentiation of MSCs will provide more understanding of MSCs and perhaps new methods of osteoporosis treatment. The MSCs have been applied to both preclinical and clinical studies in osteoporosis treatment. Here, we review the recent advances in understanding the molecular mechanisms regulating osteoblast differentiation and adipocyte differentiation of MSCs and highlight the therapeutic application studies of MSCs in osteoporosis treatment. This will provide researchers with new insights into the development and treatment of osteoporosis.

Wnt5a regulates the cell proliferation and adipogenesis via MAPK-independent pathway in early stage of obesity

The early stage of obesity is an important stage in the development of obesity. However, there are few studies which explored the property or changes in obesity at early stage especially involving Wnt5a. The associated gene expression of Wnt5a on cell regeneration and the effect of Wnt5a on rat adipose-derived stem cell (rASC) proliferation and adipogenesis need additional study. Here, we investigated the changes in obesity at early stage and how Wnt5a regulates rASC regeneration, proliferation, and adipogenesis. Our data revealed that obesity at early stage measured by Lee index presented a state with impaired adipogenesis and more infiltrated inflammatory cells but without significant changes in adipocyte sizes and inflammatory factors. The process might be associated with anti-canonical Wnt pathway and a reciprocal Wnt5a/JNK pathway. Besides the gene expression of Wnt5a decreased from cell passage 1 to passage 3. The cell proliferation was regulated by increasing dose of Wnt5a with the maximal effect at 50 ng/mL and 50 ng/mL Wnt5a suppressed adipogenic differentiation at middle-late stage of adipogenesis via anti-β-catenin and a mitogen-activated protein kinase (MAPK) signaling-independent manner. Accordingly, the research helps to gain further insights into the early stage of obesity and its associated changes on a cellular and molecular level.

Effects of WNT3A and WNT16 on the Osteogenic and Adipogenic Differentiation of Perivascular Stem/Stromal Cells

Human perivascular stem/stromal cells (hPSC) are a multipotent mesenchymogenic stromal cell population defined by their perivascular locale. Recent studies have demonstrated the high potential for clinical translation of this fluorescence-activated cell sorting (FACS)-derived cell population for autologous bone tissue engineering. However, the mechanisms underlying the osteogenic differentiation of PSC are incompletely understood. The current study investigates the roles of canonical and noncanonical Wnt signaling in the osteogenic and adipogenic differentiation of PSC. Results showed that both canonical and noncanonical Wnt signaling activity transiently increased during PSC osteogenic differentiation in vitro. Sustained WNT3A treatment significantly decreased PSC osteogenic differentiation. Conversely, sustained treatment with Wnt family member 16 (WNT16), a mixed canonical and noncanonical ligand, increased osteogenic differentiation in a c-Jun N-terminal kinase (JNK) pathway-dependent manner. Conversely, WNT16 knockdown significantly diminished PSC osteogenic differentiation. Finally, WNT16 but not WNT3A increased the adipogenic differentiation of PSC. These results indicate the importance of regulation of canonical and noncanonical Wnt signaling for PSC fate and differentiation. Moreover, these data suggest that WNT16 plays a functional and necessary role in PSC osteogenesis.

Retinoids Regulate Adipogenesis Involving the TGFβ/SMAD and Wnt/β-Catenin Pathways in Human Bone Marrow Mesenchymal Stem Cells

Retinoids may regulate cell differentiation as ligands of retinoic acid receptors (RARs) and/or retinoid X receptors (RXRs). We showed that RAR agonists promoted adipogenesis by upregulating the expression of CCAAT/enhancer-binding protein β (C/EBPβ) in the early stages, but blocked adipogenesis at a later stage in human bone marrow mesenchymal stem cells (hBMSCs). RXR agonists promoted adipogenesis at all time points in hBMSCs. The effect of RAR agonists was mediated mainly by the RARβ subtype. RAR agonists, in contrast to RXR agonists, significantly promoted the expression of RARβ. Knockdown of the RARβ gene via small hairpin RNA (shRNA) attenuated the inhibition of RAR agonists toward adipogenesis. Furthermore, we found that RAR agonists upregulated the transforming growth factor β (TGFβ)/SMAD pathway and Wnt/β-catenin pathway on adipogenesis in hBMSCs, and the stimulating effects were noticeably decreased with the RARβ gene knockdown. Both RAR agonists and RXR agonists inhibited adipogenesis and blocked the promoter activity of C/EBPβ and peroxisome proliferator-activated receptor γ (PPARγ) in SW872 cell. These results indicated the RAR agonists perform dual roles in adipogenesis in hBMSCs, and the TGFβ/SMAD pathway and Wnt/β-catenin pathway may involve the inhibitory effect of RAR agonists. RARβ is the main receptor subtype mediating the effect. The roles of RXR agonists in adipogenesis exhibited cell type-specific differences, and may be based on the integration of signals from different RXR dimers.

WNT/β-catenin signaling regulates cigarette smoke-induced airway inflammation via the PPARδ/p38 pathway

The mechanisms of WNT/β-catenin signaling involved in airway inflammation of chronic obstructive pulmonary disease (COPD) remain unknown, although recent observations have suggested an important contribution of the pathway in pulmonary parenchymal tissue repair and airway epithelium differentiation. We investigated the role of WNT/β-catenin signaling in cigarette smoke (CS)-related airway inflammation using patient lung tissues, human bronchial epithelial cells (16HBECs), and mouse models. Reduced activity of WNT/β-catenin signaling was observed in the airway epithelium of smokers with or without COPD. The mRNA expression of WNT transcription factor TCF4 negatively correlated with the pack year. The mRNA levels of WNT receptor FZD4 negatively correlated with the mRNA levels of IL-1β. CS exposure decreased the activity of WNT/β-catenin signaling in both 16HBECs and mice. In vitro studies demonstrated the upregulation of inflammatory cytokines TNF-α and IL-1β secretion induced by CS extract (CSE) could be attenuated by β-catenin activator SB216763 and be exacerbated by β-catenin small-interfering RNA (siRNA), respectively. Furthermore, the decrease in the expression of peroxisome proliferator-activated receptor (PPARδ) induced by CSE stimulation could be rescued by SB216763. SB216763 also attenuated the upregulation of phosphorylated p38 mitogen-activated protein kinase (MAPK) stimulated by CSE. Both PPARδ agonist and p38 MAPK inhibitor could suppress the TNF-α and IL-1β release induced by CSE treatment. In addition, PPARδ activation could abolish β-catenin siRNA-mediated aggravation of phosphorylated p38 MAPK in response to CSE. Finally, SB216763 treatment significantly ameliorated peribronchial inflammatory cell infiltration, leukocyte influx, and the release of TNF-α and IL-1β in the bronchoalveolar lavage fluid of CS-exposed mice. Taken together, our findings indicate that the reduced activity of WNT/β-catenin signaling induced by CS may promote inflammatory cytokine production in airway epithelium and have an essential role in airway inflammation in COPD by PPARδ/p38 MAPK pathway.

Transient Canonical Wnt Stimulation Enriches Human Bone Marrow Mononuclear Cell Isolates for Osteoprogenitors

Activation of the canonical Wnt signaling pathway is an attractive anabolic therapeutic strategy for bone. Emerging data suggest that activation of the Wnt signaling pathway promotes bone mineral accrual in osteoporotic patients. The effect of Wnt stimulation in fracture healing is less clear as Wnt signaling has both stimulatory and inhibitory effects on osteogenesis. Here, we tested the hypothesis that transient Wnt stimulation promotes the expansion and osteogenesis of a Wnt‐responsive stem cell population present in human bone marrow. Bone marrow mononuclear cells (BMMNCs) were isolated from patients undergoing hip arthroplasty and exposed to Wnt3A protein. The effect of Wnt pathway stimulation was determined by measuring the frequency of stem cells within the BMMNC populations by fluorescence‐activated cell sorting and colony forming unit fibroblast (CFU‐F) assays, before determining their osteogenic capacity in in vitro differentiation experiments. We found that putative skeletal stem cells in BMMNC isolates exhibited elevated Wnt pathway activity compared with the population as whole. Wnt stimulation resulted in an increase in the frequency of skeletal stem cells marked by the STRO‐1^bright/Glycophorin A⁻ phenotype. Osteogenesis was elevated in stromal cell populations arising from BMMNCs transiently stimulated by Wnt3A protein, but sustained stimulation inhibited osteogenesis in a concentration‐dependent manner. These results demonstrate that Wnt stimulation could be used as a therapeutic approach by transient targeting of stem cell populations during early fracture healing, but that inappropriate stimulation may prevent osteogenesis. Stem Cells2016;34:418–430

MYC is an early response regulator of human adipogenesis in adipose stem cells

Adipose stem cell (ASC) differentiation is necessary for the proper maintenance and function of adipose tissue. The procurement and characterization of multipotent ASCs has enabled investigation into the molecular determinants driving human adipogenesis. Here, the transcription factor MYC was identified as a significant regulator of ASC differentiation. Expression of MYC transcript and protein was found to accumulate during the initial course of differentiation. Loss-of-function analysis using siRNA mediated knockdown of MYC demonstrated inhibition of hormonally stimulated adipogenesis. MYC exhibited an early and sustained expression pattern that preceded down regulation of key suppressor genes, as well as induction of transcriptional and functional effectors. Glucocorticoid stimulation was identified as a necessary component for MYC induction and was found to impact adipogenesis in a concentration-dependent manner. Global gene expression analysis of MYC knockdown in ASC enriched for functional pathways related to cell adhesion, cytoskeletal remodeling, and transcriptional components of adipogenesis. These results identify a functional role for MYC in promotion of multipotent ASC to the adipogenic lineage.

Specific collagen XVIII isoforms promote adipose tissue accrual via mechanisms determining adipocyte number and affect fat deposition

Collagen XVIII is an evolutionary conserved ubiquitously expressed basement membrane proteoglycan produced in three isoforms via two promoters (P). Here, we assess the function of the N-terminal, domain of unknown function/frizzled-like sequences unique to medium/long collagen XVIII by creating P-specific null mice. P2-null mice, which only produce short collagen XVIII, developed reduced bulk-adiposity, hepatic steatosis, and hypertriglyceridemia. These abnormalities did not develop in P1-null mice, which produce medium/long collagen XVIII. White adipose tissue samples from P2-null mice contain larger reserves of a cell population enriched in early adipocyte progenitors; however, their embryonic fibroblasts had ∼ 50% lower adipocyte differentiation potential. Differentiating 3T3-L1 fibroblasts into mature adipocytes produced striking increases in P2 gene-products and dramatic falls in P1-transcribed mRNA, whereas Wnt3a-induced dedifferentiation of mature adipocytes produced reciprocal changes in P1 and P2 transcript levels. P2-derived gene-products containing frizzled-like sequences bound the potent adipogenic inhibitor, Wnt10b, in vitro. Previously, we have shown that these same sequences bind Wnt3a, inhibiting Wnt3a-mediated signaling. P2-transcript levels in visceral fat were positively correlated with serum free fatty acid levels, suggesting that collagen α1 (XVIII) expression contributes to regulation of adipose tissue metabolism in visceral obesity. Medium/long collagen XVIII is deposited in the Space of Disse, and interaction between hepatic apolipoprotein E and this proteoglycan is lost in P2-null mice. These results describe a previously unidentified extracellular matrix-directed mechanism contributing to the control of the multistep adipogenic program that determines the number of precursors committing to adipocyte differentiation, the maintenance of the differentiated state, and the physiological consequences of its impairment on ectopic fat deposition.

Mutation analysis of WNT10B in obese children, adolescents and adults

Wingless-type MMTV integration site family, member 10B (WNT10B) is an activator of the Wnt pathway. The Wnt pathway is known to play an important role in maintenance and differentiation of stem cells and has been implicated in the origination of obesity. To evaluate the role of genetic variation in WNT10B in obesity further, we performed a mutation analysis on Belgian obese patients and control subjects. A mutation analysis of WNT10B by means of high-resolution melting curve analysis and direct sequencing was performed on 546 obese children and adolescents (mean Z-score of 2.6 ± 0.6 and 2.5 ± 0.4 respectively), 86 morbidly obese adults (mean BMI of 48.0 ± 0.4 kg/m(2)) and 447 lean, healthy controls (mean BMI of 22.1 ± 1.7 kg/m(2)). A total of five novel non-synonymous variants were identified. R228Q was the only coding, non-synonymous variant that was exclusively found in patients, but the variant did not co-segregate with obesity in the three investigated siblings. The remaining four variants were either found both in cases and in control samples (G181D) or only in control samples (A108P, S187R and P315S). The frequency of non-synonymous variants in lean individuals (0.9 %) was higher than in obese individuals (0.3 %) and familial co-segregation of the most promising variant in patients could not be demonstrated. Therefore, we conclude that variations in WNT10B do not contribute to human monogenic obesity in our population.

Vitamin D metabolism in human bone marrow stromal (mesenchymal stem) cells

There are many human extra-renal tissues and cells that biosynthesize 1α,25-dihydroxyvitamin D (1α,25(OH)(2)D) by the action of CYP27B1/1α-hydroxylase. Human marrow stromal cells (hMSCs), also known as mesenchymal stem cells, were isolated from marrow discarded from well-characterized, consented subjects during common orthopedic procedures. Human MSCs can give rise to osteoblasts, chondrocytes, adipocytes, and other lineages. Their in vitro differentiation to osteoblasts is stimulated by 1α,25(OH)(2)D, and recent evidence indicates that they have the capacity to metabolize vitamin D in a regulated manner. Human MSCs express the vitamin D receptor, 25-hydroxylases, 1α-hydroxylase, and 24-hydroxylase; stimulation of in vitro osteoblastogenesis by 25(OH)D depends on the activity of CYP27B1/1α-hydroxylase. The finding that hMSCs are a both a producer and target of 1α,25(OH)(2)D suggests a potential autocrine/paracrine role of vitamin D metabolism in osteoblast differentiation. Expression and enzyme activity of CYP27B1/1α-hydroxylase are upregulated by substrate 25(OH)D and Parathyroid Hormone (PTH) and are downregulated by 1α,25(OH)(2)D. With subject age, there are decreases in basal osteoblast potential and in stimulation of osteoblastogenesis by 1α,25(OH)(2)D, 25(OH)D, and PTH. In vitro treatment with a combination of 25(OH)D and PTH rejuvenated osteoblastogenesis with hMSCs from elders; this was attributable to increases in CYP27B1/1α-hydroxylase and in receptor for each hormone by the reciprocal factor. Other clinical variables beside age, i.e. low serum 25(OH)D or low estimated glomerular filtration rate, are correlated with reduced osteoblastogenesis. These studies suggest that osteoblastogenesis may not be optimal unless there is sufficient serum 25(OH)D substrate for hMSCs to synthesize and respond to local 1α,25(OH)(2)D.

Activation of canonical wnt pathway promotes differentiation of mouse bone marrow-derived MSCs into type II alveolar epithelial cells, confers resistance to oxidative stress, and promotes their migration to injured lung tissue in vitro

The differentiation of mesenchymal stem cells (MSCs) into type II alveolar epithelial (AT II) cells in vivo and in vitro, is critical for reepithelization and recovery in acute lung injury (ALI), but the mechanisms responsible for differentiation are unclear. In the present study, we investigated the role of the canonical wnt pathway in the differentiation of mouse bone marrow-derived MSCs (mMSCs) into AT II cells. Using a modified co-culture system with murine lung epithelial-12 (MLE-12) cells and small airway growth media (SAGM) to efficiently drive mMSCs differentiation, we found that GSK 3β and β-catenin in the canonical wnt pathway were up-regulated during differentiation. The levels of surfactant protein (SP) C, SPB, and SPD, the specific markers of AT II cells, correspondingly increased in mMSCs when Wnt3a or LiCl was added to the co-culture system to activate wnt/β-catenin signaling. The expression of these factors was depressed to some extent by inhibiting the pathway with the addition of DKK 1. The differentiation rate of mMSCs also depends on their abilities to accumulate and survive in inflammatory tissue. Our results suggested that the activation of wnt/β-catenin signaling promoted mMSCs migration towards ALI mouse-derived lung tissue in a Transwell assay, and ameliorated the cell death and the reduction of Bcl-2/Bax induced by H(2) O(2), which simultaneously caused reduced GSK 3β and β-catenin in mMSCs. These data supports a potential mechanism for the differentiation of mMSCs into AT II cells involving canonical wnt pathway activation, which may be significant to their application in ALI.

Wnt pathway regulation by demineralized bone is approximated by both BMP-2 and TGF-β1 signaling

Allogeneic demineralized bone is used extensively as a clinical graft material because it has osteo/chondroinductive and osteoconductive properties. Demineralized bone powder (DBP) induces chondrogenic differentiation of human dermal fibroblasts (hDFs) in three-dimensional collagen cultures, but the initiating mechanisms have not been fully characterized nor has it been shown that bone morphogenetic proteins (BMPs) recapitulate DBP's effects on target cells. Among the many signaling pathways regulated in hDFs by DBP prior to in vitro chondrogenesis, there are changes in Wnts and their receptors that may contribute to DBP actions. This study tests the hypothesis that DBP modulation of Wnt signaling entails both BMP and TGF-β pathways. We compared the effects of DBP, TGF-β1, or BMP-2 on Wnt signaling components in hDFs by Wnt signaling macroarray, RT-PCR, in situ hybridization, and Western immunoblot analyses. Many effects of DBP on Wnt signaling components were not shared by BMP-2, and likewise DBP effects on Wnt genes and β-catenin only partially required the TGF-β pathway, as shown by selective inhibition of TGF-β/activin receptor-like kinase. The analyses revealed that 64% (16/25) of the Wnt signaling components regulated by DBP were regulated similarly by the sum of effects by BMP-2 and by TGF-β1. In conclusion, signaling mechanisms of inductive DBP in human dermal fibroblasts involve the modulation of multiple Wnt signals through both BMP and TGF-β pathways.

Inactivation of Wnt/β-catenin signaling in human adipose-derived stem cells is necessary for chondrogenic differentiation and maintenance

The Wnt/β-catenin signaling pathway plays critical roles in self-renewal and differentiation of mesenchymal stem cells. However, very little is known about its role in the chondrogenesis of human adipose-derived stem cells (hADSCs). In this study, we analyzed protein expression of several key components of the Wnt/β-catenin signaling pathway using a 21-day in vitro model of hADSC chondrogenesis. Wnt1, β-catenin, and GSK3β levels increased sharply at day 12, peaked at day 18, and then declined. Expression of TCF1, a target gene of Wnt/β-catenin signaling, closely followed that of Wnt1. These results were consistent with changes in endonuclear β-catenin levels. Gene expression of the chondrocyte-specific markers, collagen type II (COL II), SOX9, and aggrecan, increased during hADSC chondrogenesis, peaked at day 12, and then declined. Adding a Wnt inhibitor (days 0-21) resulted in consistently elevated levels of COL II, SOX9, and aggrecan mRNA. In contrast, adding Wnt1 (days 0-21) to cultures led to sustained Wnt/β-catenin signaling over the 21 days and suppressed expression of chondrocyte-specific markers. Moreover, adding Wnt1 at late stages of differentiation (day 18) further diminished chondrocyte-specific marker expression. Together, these results showed that inactivation of Wnt/β-catenin signaling is needed for the progression of chondrogenesis and the maturation and phenotype maintenance of chondroid cells.

LRP6 mediates Wnt/β-catenin signaling and regulates adipogenic differentiation in human mesenchymal stem cells

Human mesenchymal stem cells (hMSC) are subjected to the control of several signal transduction pathways during regeneration processes, whereby Wnt/β-catenin signaling is of pivotal importance. Since there exists only fragmentary knowledge concerning the molecular function of the Wnt-coreceptors LRP5 and LRP6 (low-density lipoprotein receptor-related protein) in hMSC, we studied their impact on Wnt/β-catenin signal transduction by RNA interference. For monitoring changes in β-catenin-dependent transcription in a highly sensitive and specific manner, hMSC were stably transfected with a TCF/LEF reporter gene plasmid. In the presence of the activator Wnt3a, knockdown of LRP6 led to a strong decreased Wnt/β-catenin signaling, while RNAi against LRP5 exhibited no effect in this setting. In a reverse approach, ectopic expression of LRP6 resulted in a strong enhancement of Wnt/β-catenin signaling, whereas overexpression of LRP5 exhibited no increased signaling capacity. Furthermore, only the ectopic expression of LRP6--but not that of LRP5--was able to restore Wnt3a-mediated β-catenin signaling after knockdown of endogenously expressed LRP6. These results demonstrate LRP6 as the predominant Wnt3a LRP-receptor in hMSC, which cannot be substituted by LRP5. In addition, we observed enhanced differentiation toward the adipogenic lineage after RNAi against LRP6 which was associated with the induction of PPAR-γ and fat vacuole formation. Thus, LRP6 is not only indispensable for Wnt3a/β-catenin signaling, but also for the suppression of differentiation of hMSC into the adipogenic lineage. Based on these observations, LRP6 may represent an attractive drug target for manipulating hMSC in cell and tissue regeneration approaches.

Single nucleotide polymorphisms in sFRP4 are associated with bone and body composition related parameters in Danish but not in Belgian men

The senescence accelerated mouse P6 (SAMP6) has a low bone mass and has previously shown to be a good model for senile osteoporosis in humans. In addition to a reduced bone mass, SAMP6 mice are obese and have hyperlipidemia. Using positional cloning and expression studies, an increased expression of sfrp4 was found in these mice. SFRP4 is a modulator of the Wnt signalling pathway. This pathway has been previously shown to be involved in regulating bone mass. Additional evidence that sFRP4 has an influence on BMD was delivered by linkage and association studies mostly performed in Asian populations. Based on these data we decided to perform an association study between common variants in sFRP4, BMD, hip geometry parameters and body composition parameters in a population consisting of 1383 Danish men (783 aged 20-29 years; 600 aged 60-74 years). Afterwards we tried to replicate the significant results in a population of 994 Belgian men. In the Danish population we found 6 SNPs associated with BMD at the hip and/or femoral neck. Furthermore, all 6 SNPs were associated with several hip geometry parameters. The homozygous presence of the minor allele resulted for all SNPs (except rs4720265) in a decrease in bone density and bone strength. Finally, we observed in the Danish population age specific associations with height and fat mass. In the Belgian population we tried to replicate the results of three SNPs with BMD and body composition parameters. Unfortunately, we were not able to replicate the results found in the Danish cohort but we found one SNP (rs2598116) associated with height. In conclusion, genetic variation in sFRP4 has an influence on hip fracture risk, percentage body fat and height in a Danish male population. However, we were unable to replicate these results in an independent Belgian population.

Age-related decline in osteoblastogenesis and 1α-hydroxylase/CYP27B1 in human mesenchymal stem cells: stimulation by parathyroid hormone

With aging, there is a decline in bone mass and in osteoblast differentiation of human mesenchymal stem cells (hMSCs) in vitro. Osteoblastogenesis can be stimulated with 1,25-dihydroxyvitamin D(3) [1,25(OH)(2) D(3) ] and, in some hMSCs, by the precursor 25-hydroxyvitamin D(3) (25OHD(3) ). CYP27B1/1α-hydroxylase activates 25OHD(3) and, to a variable degree, hMSCs express CYP27B1. In this study, we tested the hypotheses (i) that age affects responsiveness to 25OHD(3) and expression/activity of CYP27B1 in hMSCs and (ii) that parathyroid hormone (PTH) upregulates CYP27B1 in hMSCs, as it does in renal cells. There were age-related declines in osteoblastogenesis (n=8, P=0.0286) and in CYP27B1 gene expression (n=27, r= -0.498; P=0.008) in hMSCs. Unlike hMSCs from young subjects (≤50 years), hMSCs from older subjects (≥55 years) were resistant to 25OHD(3) stimulation of osteoblastogenesis. PTH1-34 (100 nm) provided hMSCs with responsiveness to 25OHD(3) (P=0.0313, Wilcoxon matched pairs test) and with two episodes of increased 1,25(OH)(2) D(3) synthesis, of cAMP response element binding protein (CREB) activation, and of CYP27B1 upregulation. Both increases in CYP27B1 expression by PTH were obliterated by CREB-siRNA or KG-501 (which specifically inhibits the downstream binding of activated CREB). Only the second period of CREB signaling was diminished by AG1024, an inhibitor of insulin-like growth factor-I receptor kinase. Thus, PTH stimulated hMSCs from elders with responsiveness to 25OHD(3) by upregulating expression/activity of CYP27B1 and did so through CREB and IGF-I pathways.