Impaired mesenchymal stem cell differentiation and osteoclastogenesis in mice deficient for Igf2-P2 transcripts

Molecular pathological insights into tumorigenesis and progression of giant cell tumor of bone

Giant cell tumor of bone (GCTB) is a primary bone tumor that typically exhibits benign histological appearance and clinical behavior in most cases, with local aggressiveness and rare metastasis. It predominantly affects individuals in the young adult age group. It is characterized by the presence of multinucleated osteoclastic giant cells and a stromal population of neoplastic cells. A key hallmark for GCTB pathogenesis is the G34W genetic mutation in the histone H3.3 gene, which is restricted to the population of cancerous stromal cells and is absent in osteoclasts and their progenitor cells. This review presents a comprehensive overview of the pathology of GCTB, including its histopathological characteristics, cytological features, histopathological variants, and their clinical relevance. We also discuss recent insights into genetic alterations in relation to the molecular pathways implicated in GCTB. A summary of the current understanding of GCTB pathology will update the knowledge base to guide the diagnosis and management of this unique bone tumor.

Roles of DNA methylation in influencing the functions of dental-derived mesenchymal stem cells

OBJECTIVE

DNA methylation as intensively studied epigenetic regulatory mechanism exerts pleiotropic effects on dental-derived mesenchymal stem cells (DMSCs). DMSCs have self-renewal and multidifferentiation potential. Here, this review aims at summarizing the research status about application of DMSCs in tissue engineering and clarifying the roles of DNA methylation in influencing the functions of DMSCs, with expectation of paving the way for its in-depth exploration in tissue engineering.

METHOD

The current research status about influence of DNA methylation in DMSCs was acquired by MEDLINE (through PubMed) and Web of Science using the keywords 'DNA methylation', 'dental-derived mesenchymal stem cells', 'dental pulp stem cells', 'periodontal ligament stem cells', 'dental follicle stem cells', 'stem cells from the apical papilla', 'stem cells from human exfoliated deciduous teeth', and 'gingival-derived mesenchymal stem cells'.

RESULTS

This review indicates DNA methylation affects DMSCs' differentiation and function through inhibiting or enhancing the expression of specific gene resulted by DNA methylation-related genes or relevant inhibitors.

CONCLUSION

DNA methylation can influence DMSCs in aspects of osteogenesis, adipogenesis, immunomodulatory function, and so on. Yet, the present studies about DNA methylation in DMSCs commonly focus on dental pulp stem cells (DPSCs) and periodontal ligament stem cells (PDLSCs). Little has been reported for other DMSCs.

The mechanism of lncRNA MALAT1 targeting the miR-124-3p/IGF2BP1 axis to regulate osteogenic differentiation of periodontal ligament stem cells

OBJECTIVES

This study aimed to investigate the regulatory roles of lncRNA MALAT1, miR-124-3p, and IGF2BP1 in osteogenic differentiation of periodontal ligament stem cells (PDLSCs).

MATERIALS AND METHODS

We characterized PDLSCs by employing quantitative real-time polymerase chain reaction (qRT-PCR) and Western blot analyses to evaluate the expression of key osteogenic markers including ALPL, SPP1, and RUNX2. Manipulation of lncRNA MALAT1 and miR-124-3p expression levels was achieved through transfection techniques. In addition, early osteogenic differentiation was assessed via Alkaline phosphatase (ALP) staining, and mineral deposition was quantified using Alizarin Red S (ARS) staining. Cellular localization of lncRNA MALAT1 was determined through Fluorescence In Situ Hybridization (FISH). To elucidate the intricate regulatory network, we conducted dual-luciferase reporter assays to decipher the binding interactions between lncRNA MALAT1 and miR-124-3P as well as between miR-124-3P and IGF2BP1.

RESULTS

Overexpression of lncRNA MALAT1 robustly promoted osteogenesis in PDLSCs, while its knockdown significantly inhibited the process. We confirmed the direct interaction between miR-124-3p and lncRNA MALAT1, underscoring its role in impeding osteogenic differentiation. Notably, IGF2BP1 was identified as a direct binding partner of lncRNA MALAT1, highlighting its pivotal role within this intricate network. Moreover, we determined the optimal IGF2BP1 concentration (50 ng/ml) as a potent enhancer of osteogenesis, effectively countering the inhibition induced by si-MALAT1. Furthermore, in vivo experiments utilizing rat calvarial defects provided compelling evidence, solidifying lncRNA MALAT1's crucial role in bone formation.

CONCLUSIONS

Our study reveals the regulatory network involving lncRNA MALAT1, miR-124-3p, and IGF2BP1 in PDLSCs' osteogenic differentiation.

CLINICAL RELEVANCE

These findings enhance our understanding of lncRNA-mediated osteogenesis, offering potential therapeutic implications for periodontal tissue regeneration and the treatment of bone defects.

ALX1-transcribed LncRNA AC132217.4 promotes osteogenesis and bone healing via IGF-AKT signaling in mesenchymal stem cells

The osteogenic potential of bone marrow mesenchymal stem cells (BMSCs) is critical for bone formation and regeneration. A high non-/delayed-union rate of fracture healing still occurs in specific populations, implying an urgent need to discover novel targets for promoting osteogenesis and bone regeneration. Long non-coding (lnc)RNAs are emerging regulators of multiple physiological processes, including osteogenesis. Based on differential expression analysis of RNA sequencing data, we found that lncRNA AC132217.4, a 3'UTR-overlapping lncRNA of insulin growth factor 2 (IGF2), was highly induced during osteogenic differentiation of BMSCs. Afterward, both gain-of-function and loss-of-function experiments proved that AC132217.4 promotes osteoblast development from BMSCs. As for its molecular mechanism, we found that AC132217.4 binds with IGF2 mRNA to regulate its expression and downstream AKT activation to control osteoblast maturation and function. Furthermore, we identified two splicing factors, splicing component 35 KDa (SC35) and heterogeneous nuclear ribonucleoprotein A1 (HNRNPA1), which regulate the biogenesis of AC132217.4 at the post-transcriptional level. We also identified a transcription factor, ALX1, which regulates AC132217.7 expression at the transcriptional level to promote osteogenesis. Importantly, in-vivo over-expression of AC132217.4 essentially promotes the bone healing process in a murine tibial drill-hole model. Our study demonstrates that lncRNA AC132217.4 is a novel anabolic regulator of BMSC osteogenesis and could be a plausible therapeutic target for improving bone regeneration.

Cell Biology of Giant Cell Tumour of Bone: Crosstalk between m/wt Nucleosome H3.3, Telomeres and Osteoclastogenesis

Giant cell tumour of bone (GCTB) is a rare and intriguing primary bone neoplasm. Worrisome clinical features are its local destructive behaviour, its high tendency to recur after surgical therapy and its ability to create so-called benign lung metastases (lung 'plugs'). GCTB displays a complex and difficult-to-understand cell biological behaviour because of its heterogenous morphology. Recently, a driver mutation in histone H3.3 was found. This mutation is highly conserved in GCTB but can also be detected in glioblastoma. Denosumab was recently introduced as an extra option of medical treatment next to traditional surgical and in rare cases, radiotherapy. Despite these new insights, many 'old' questions about the key features of GCTB remain unanswered, such as the presence of telomeric associations (TAs), the reactivation of hTERT, and its slight genomic instability. This review summarises the recent relevant literature of histone H3.3 in relation to the GCTB-specific G34W mutation and pays specific attention to the G34W mutation in relation to the development of TAs, genomic instability, and the characteristic morphology of GCTB. As pieces of an etiogenetic puzzle, this review tries fitting all these molecular features and the unique H3.3 G34W mutation together in GCTB.

Paternal systemic inflammation induces offspring programming of growth and liver regeneration in association with Igf2 upregulation

Recent studies suggest that stress can lead to variations in offspring development. However, whether paternal systemic inflammation induces phenotypic changes in the offspring remains unclear. Here, we established an in vivo mouse model of systemic inflammation and investigated the long-term consequences on the offspring. Male, but not female offspring derived from inflammatory fathers (LPS-F1) grew faster than those derived from the control fathers (CON-F1). Moreover, the LPS-F1 males had higher capacity for liver regeneration after injury, as indicated by decreased hepatic fibrosis, apoptosis, and increased hepatocyte proliferation upon carbon tetrachloride challenge. Insulin-like growth factor 2 (Igf2), a key mitogen that drives growth and liver regeneration, was significantly upregulated in the livers of male, but not female offspring from fathers with inflammation. Taken together, paternal inflammation alters the hepatic Igf2 expression and reprograms growth and liver regeneration in male but not female offspring.

Globally altered epigenetic landscape and delayed osteogenic differentiation in H3.3-G34W-mutant giant cell tumor of bone

The neoplastic stromal cells of giant cell tumor of bone (GCTB) carry a mutation in H3F3A, leading to a mutant histone variant, H3.3-G34W, as a sole recurrent genetic alteration. We show that in patient-derived stromal cells H3.3-G34W is incorporated into the chromatin and associates with massive epigenetic alterations on the DNA methylation, chromatin accessibility and histone modification level, that can be partially recapitulated in an orthogonal cell line system by the introduction of H3.3-G34W. These epigenetic alterations affect mainly heterochromatic and bivalent regions and provide possible explanations for the genomic instability, as well as the osteolytic phenotype of GCTB. The mutation occurs in differentiating mesenchymal stem cells and associates with an impaired osteogenic differentiation. We propose that the observed epigenetic alterations reflect distinct differentiation stages of H3.3 WT and H3.3 MUT stromal cells and add to H3.3-G34W-associated changes.

The histone variant mutation H3.3-G34W occurs in the majority of giant cell tumor of bone (GCTB). By profiling patient-derived GCTB tumor cells, the authors show that this mutation associates with epigenetic alterations in heterochromatic and bivalent regions that contribute to an impaired osteogenic differentiation and the osteolytic phenotype of GCTB.

Loss of SRSF2 triggers hepatic progenitor cell activation and tumor development in mice

Splicing factor SRSF2 is frequently mutated or up-regulated in human cancers. Here, we observe that hepatocyte-specific deletion of Srsf2 trigger development of hepatocellular carcinoma (HCC) in mice, which also involves inflammation and fibrosis. Importantly, we find that, when compensatory hepatocyte proliferation is impaired, activation of hepatic progenitor cells (HPCs) play an important role in liver regeneration and tumor formation. Moreover, the cells of HCC- bearing livers display both HPC and hepatocyte markers, with gene expression profiling suggesting HPC origin and embryonic origin. Mechanically, we demonstrate that levels of oncofetal genes insulin-like growth factor 2 (Igf2) and H19 are significantly increased in the tumors, likely due to decreased DNA methylation of the Igf2/H19 locus. Consequently, signaling via the Igf2 pathway is highly activated in the tumors. Thus, our data demonstrate that loss of Srsf2 triggers HPC-mediated regeneration and activation of oncofetal genes, which altogether promote HCC development and progression in mice.

Chang Zhang, Lei Shen et al show that conditional deletion of the splicing factor Srsf2 in hepatocytes leads to activation and expansion of hepatic progenitor cells and eventually to hepatocellular carcinoma (HCC) in aged mice. These findings may be relevant to HCC development in humans.

Role of thyroid hormones in craniofacial development

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

IGF2 Mutations

OBJECTIVE

IGF2 is a paternally expressed growth-promoting gene. Here, we report five cases with IGF2 mutations and review IGF2 mutation-positive patients described in the literature. We also compare clinical features between patients with IGF2 mutations and those with H19/IGF2:IG-DMR epimutations.

RESULTS

We recruited five cases with IGF2 mutations: case 1 with a splice site mutation (c.-6-1G>C) leading to skipping of exon 2 and cases 2-5 with different missense mutations (p.(Cys70Tyr), p.(Cys71Arg), p.(Cys33Ser), and p.(Cys45Ser)) affecting cysteine residues involved in the S-S bindings. All the mutations resided on the paternally inherited allele, and the mutation of case 5 was present in a mosaic condition. Clinical assessment revealed Silver-Russell syndrome (SRS) phenotype with Netchine-Harbison scores of ≥5/6 in all the apparently nonmosaic 14 patients with IGF2 mutations (cases 1-4 described in this study and 10 patients reported in the literature). Furthermore, compared with H19/IGF2:IG-DMR epimutations, IGF2 mutations were associated with low frequency of hemihypoplasia, high frequency of feeding difficulty and/or reduced body mass index, and mild degree of relative macrocephaly, together with occasional development of severe limb malformations, high frequency of cardiovascular anomalies and developmental delay, and low serum IGF-II values.

CONCLUSIONS

This study indicates that IGF2 mutations constitute a rare but important cause of SRS. Furthermore, while both IGF2 mutations and H19/IGF2:IG-DMR epimutations lead to SRS, a certain degree of phenotypic difference is observed between the two groups, probably due to the different IGF2 expression pattern in target tissues.

MiRNA-483-5p is involved in the pathogenesis of osteoporosis by promoting osteoclast differentiation

AIMS

The study aimed to investigate the roles of miR-483-5p and IGF2 in osteoclast formation.

METHODS

Blood and bone tissues were collected from osteoporosis and non-osteoporosis patients with hip fractures for gene expression analysis. CD14 + peripheral blood mononuclear cells (PBMCs) were isolated for differentiating osteoclasts. MiR-483-5p mimic and inhibitor was transfected into CD14 + PBMCs, respectively. Predicted by TargetScan and verified by Dual-luciferase reporter assay system, insulin-like growth factor-2 (IGF2) could be targeted by miR-483-5p. IGF2 expression vector was co-transfected with miR-483-5p mimic to study the role of IGF2 in miR-483-5p affecting osteoclast differentiation. Flow cytometry was performed for cell apoptosis analysis.

RESULTS

High-expressed miR-483-5p and low-expressed IGF2 were frequently found in the serums and bone tissues derived from osteoporotic patients. We found that up-regulation of miR-483-5p in CD14 + PBMCs notably increased the number of TRAP-positive cells, at the same time, the expression levels of TRAP, nuclear factor of activated T-cells (NFATc1), cytoplasmic 1 (NFAT2) and Cathepsin K (CTSK) were also up-regulated. However, overexpressed IGF2 effectively reversed such effects produced by up-regulation of miR-483-5p on osteoclastogenesis-related factors in CD14 + PBMCs. Moreover, forced expression of IGF2 could also enhance apoptosis of osteoclasts reduced by miR-483-5p.

CONCLUSIONS

Our study suggests that miRNA-483-5p is involved in the pathogenesis of osteoporosis by promoting osteoclast differentiation.

IGF2 enhanced the osteo-/dentinogenic and neurogenic differentiation potentials of stem cells from apical papilla

OBJECTIVES

In dental tissue engineering, niche is important for maintaining stem cell function and regenerating the dental tissues. However, there is limited knowledge for the growth factors in niche to maintain the function of stem cells. In this study, we investigated the effect of IGF2, a growth factor in stem cells from apical papilla (SCAPs) niche, on differentiation and proliferation potentials of SCAPs.

MATERIALS AND METHODS

Recombinant human IGF2 protein (rhIGF2) was used. Cell counting kit-8 assay, Carboxyfluorescein succinimidyl ester assay, alkaline phosphatase (ALP) activity, Alizarin Red staining, quantitative calcium analysis, immunofluorescence staining and real-time RT-PCR were performed to investigate the cell proliferation and differentiation potentials of SCAPs. And proteomic analysis was used to identify the differential secreted proteins.

RESULTS

By ALP activity assay, we found that 5 ng/mL rhIGF2 might be the optimal concentration for treatment. Then, Alizarin Red staining, quantitative calcium analysis and osteogenesis-related gene expression results showed that 5 ng/mL rhIGF2 could enhance the osteo-/dentinogenic differentiation potentials in SCAPs. Immunofluorescence staining and real-time RT-PCR results showed that neurogenic markers were significantly induced by 5 ng/mL rhIGF2 in SCAPs. Then, CCK-8 assay and CFSE assay results showed that 5 ng/mL rhIGF2 could enhance the cell proliferation in SCAPs. Furthermore, proteomic analysis showed that IGF2 could induce some secreted proteins which function related to the osteogenesis, neurogenesis and cell proliferation.

CONCLUSIONS

Our results identified that IGF2 might be the potential mediator in niche to promote SCAP function and dental tissue regeneration.

Comprehensive clinical and molecular studies in split-hand/foot malformation: identification of two plausible candidate genes (LRP6 and UBA2)

Split-hand/foot malformation (SHFM) is a clinically and genetically heterogeneous condition. We sequentially performed screening of the previously identified Japanese founder 17p13.3 duplication/triplication involving BHLHA9, array comparative genomic hybridization, and whole exome sequencing (WES) in newly recruited 41 Japanese families with non-syndromic and syndromic SHFM. We also carried out WES in seven families with nonsyndromic and syndromic SHFM in which underlying genetic causes including pathogenic copy-number variants (CNVs) remained undetected in our previous studies of 56 families. Consequently, we identified not only known pathogenic CNVs (17p13.3 duplications/triplications [n = 21], 2q31 deletion [n = 1], and 10q24 duplications [n = 3]) and rare variants in known causative genes (TP63 [n = 3], DLX5 [n = 1], IGF2 [n = 1], WNT10B [n = 3], WNT10B/PORCN [n = 1], and PORCN [n = 1]), but also a de novo 19q13.11 deletion disrupting UBA2 (n = 1) and variants that probably affect function in LRP6 (n = 1) and UBA2 (n = 1). Thus, together with our previous data based on testing of 56 families, molecular studies for a total of 97 families with SHFM revealed underlying genetic causes in 75 families, and clinical studies for the 75 families indicated a certain degree of correlation between genetic causes and phenotypes. The results imply that SHFM primarily occurs as a genetic disorder with genotype-phenotype correlations. Furthermore, the results together with previous data such as the development of SHFM in Lrp6 knockout mice, the presence of SHFM in two subjects with 19q13 deletions involving UBA2, and strong mouse Uba2 expression in the developing limb buds, imply that LRP6 and UBA2 represent plausible candidate genes for SHFM.

Rapamycin-independent IGF2 expression in Tsc2-null mouse embryo fibroblasts and human lymphangioleiomyomatosis cells

Lymphangioleiomyomatosis (LAM) is a rare, almost exclusively female lung disease linked to inactivating mutations in tuberous sclerosis complex 2 (TSC2), a tumor suppressor gene that controls cell metabolic state and growth via regulation of the mechanistic target of rapamycin (mTORC1) signaling. mTORC1 is frequently activated in human cancers and, although the mTORC1 inhibitor rapamycin has a cytostatic effect, it is, in general, unable to elicit a robust curative effect or tumor regression. Using RNA-Seq, we identified (1) Insulin-like Growth Factor (IGF2) as one of the genes with the highest fold-change difference between human TSC2-null and TSC2-expressing angiomyolipoma cells from a patient with LAM, and (2) the mouse IGF2 homolog Igf2, as a top-ranking gene according to fold change between Tsc2^-/- and Tsc2^+/+ mouse embryo fibroblasts (MEFs). We extended transcript-level findings to protein level, observing increased Igf2 protein expression and Igf2 secretion by Tsc2^-/- MEFs. Increased Igf2 expression was not due to epigenetic imprinting, but was partially mediated through the Stat3 pathway and was completely insensitive to rapamycin treatment. An siRNA-mediated decrease of Igf2 resulted in decreased Stat3 phosphorylation, suggesting presence of an autocrine Igf2/Stat3 amplification cycle in Tsc2^-/- MEFs. In human pulmonary LAM lesions and metastatic cell clusters, high levels of IGF2 were associated with mTORC1 activation. In addition, treatment of three primary IGF2-expressing LAM lung cell lines with rapamycin did not result in IGF2 level changes. Thus, targeting of IGF2 signaling may be of therapeutic value to LAM patients, particularly those who are unresponsive to rapamycin.

Histochemical evidence of IGF2 mRNA-binding protein 2-mediated regulation of osteoclast function and adhesive ability

Insulin-like growth factor 2 (IGF2) messenger RNA-binding proteins (IMPs) are a family of oncofetal RNA-binding proteins that play important roles in cell migration, renewal, and metabolism. IMP2 gene expression may be important in determining IGF2 levels and might, thereby, be central to bone metabolism. In our present study, IMP2-deficient mice exhibited more immature bone structures, characterized by abundant residual cartilage cores; growth plates containing more rich cartilage matrix, which was arranged irregularly; and a significantly thicker hypertrophic chondrocyte layer in the femoral metaphysis, compared with wild-type mice. These abnormalities were associated with profound effects on the size and morphology of osteoclasts. Specifically, the osteoclasts exhibited various polymorphisms, failed to form resorption lacunae, and were detached from the bone surface. Consistent with these findings, IMP2 deficiency reduced the expression of two important proteases (cathepsin K and matrix metallopeptidase 9) as well as that of C-SRC, a critical regulator of ruffled border formation in osteoclasts, indicating impaired osteoclastic activity. IMP2-deficient mice also displayed inhibited osteoclast adhesion owing to defects in the CD44-osteopontin signaling pathway. In summary, we used IMP2-deficient mice as a model to determine whether IMP2 plays a role during bone metabolism. Our results indicate that IMP2 deficiency delayed bone remodeling by significantly inhibiting the activity of osteoclasts and impairing their adhesion.

De novo IGF2 mutation on the paternal allele in a patient with Silver-Russell syndrome and ectrodactyly

Although paternally expressed IGF2 is known to play a critical role in placental and body growth, only a single mutation has been found in IGF2. We identified, through whole-exome sequencing, a de novo IGF2 indel mutation leading to frameshift (NM_000612.5:c.110_117delinsAGGTAA, p.(Leu37Glnfs*31)) in a patient with Silver-Russell syndrome, ectrodactyly, undermasculinized genitalia, developmental delay, and placental hypoplasia. Furthermore, we demonstrated that the mutation resided on the paternal allele by sequencing the long PCR product harboring the mutation- and methylation-sensitive SmaI and SalI sites before and after SmaI/SalI digestion. The results, together with the previous findings in four cases from a single family with a paternally inherited IGF2 nonsense mutation and those in patients with variable H19 differentially methylated region epimutations leading to compromised IGF2 expression, suggest that the whole phenotype of this patient is explainable by the IGF2 mutation, and that phenotypic severity is primarily determined by the IGF2 expression level in target tissues.

Paternal Insulin-like Growth Factor 2 (Igf2) Regulates Stem Cell Activity During Adulthood

Insulin-like Growth Factor 2 (IGF2) belongs to the IGF/Insulin pathway, a highly conserved evolutionarily network that regulates growth, aging and lifespan. Igf2 is highly expressed in the embryo and in cancer cells. During mouse development, Igf2 is expressed in all sites where hematopoietic stem cells (HSC) successively expand, then its expression drops at weaning and becomes undetectable when adult HSC have reached their niches in bones and start to self-renew. In the present study, we aim to discover the role of IGF2 during adulthood. We show that Igf2 is specifically expressed in adult HSC and we analyze HSC from adult mice deficient in Igf2 transcripts. We demonstrate that Igf2 deficiency avoids the age-related attrition of the HSC pool and that Igf2 is necessary for tissue homeostasis and regeneration. Our study reveals that the expression level of Igf2 is critical to maintain the balance between stem cell self-renewal and differentiation, presumably by regulating the interaction between HSC and their niche. Our data have major clinical interest for transplantation: understanding the changes in adult stem cells and their environments will improve the efficacy of regenerative medicine and impact health- and life-span.

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The imprinted gene Igf2 is expressed in adult tissue stem cells.

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Igf2 deficiency increases HSC (hematopoietic stem cells) self-renewal and avoids age-related attrition of the HSC pool.

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Igf2 deficiency decreases HSC differentiation and mobilization.

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Igf2 deficiency modifies the interaction between HSC and their environment.

IGF2 belongs to the IGF/Insulin family that regulates growth, aging and lifespan. This role is evolutionarily conserved from worms to mammals. IGF2 favors cell proliferation during embryonic development but its role in adulthood is unknown. To decipher its function we undertook a lifelong analysis of the consequences of Igf2 deficiency on hematopoiesis, in steady-state conditions and during bone marrow transplantation. We demonstrate that lowering Igf2 levels increases the pool of stem cells, without uncontrolled proliferation and migration of immature cells that would lead to cancer. This is a promising way to enhance the stem cells pool during aging that has major interest for transplantation.

Cyclooxygenase-2 deficiency impairs muscle-derived stem cell-mediated bone regeneration via cellular autonomous and non-autonomous mechanisms

This study investigated the role of cyclooxygenase-2 (COX-2) expression by donor and host cells in muscle-derived stem cell (MDSC)-mediated bone regeneration utilizing a critical size calvarial defect model. We found that BMP4/green fluorescent protein (GFP)-transduced MDSCs formed significantly less bone in COX-2 knock-out (Cox-2KO) than in COX-2 wild-type (WT) mice. BMP4/GFP-transduced Cox-2KO MDSCs also formed significantly less bone than transduced WT MDSCs when transplanted into calvarial defects created in CD-1 nude mice. The impaired bone regeneration in the Cox-2KO MDSCBMP4/GFP group is associated with downregulation of BMP4-pSMAD1/5 signaling, decreased osteogenic differentiation and lowered proliferation capacity after transplantation, compared with WT MDSCBMP4/GFP cells. The Cox-2KO MDSCBMP4/GFP group demonstrated a reduction in cell survival and direct osteogenic differentiation in vitro These effects were mediated in part by the downregulation of Igf1 and Igf2. In addition, the Cox-2KO MDSCBMP4/GFP cells recruited fewer macrophages than the WT MDSC/BMP4/GFP cells in the early phase after injury. We concluded that the bone regeneration capacity of Cox-2KO MDSCs was impaired because of a reduction in cell proliferation and survival capacities, reduction in osteogenic differentiation and a decrease in the ability of the cells to recruit host cells to the injury site.

Enoxaparin and rivaroxaban have different effects on human mesenchymal stromal cells in the early stages of bone healing

Objectives

Venous thromboembolism (VTE) is a major potential complication following orthopaedic surgery. Subcutaneously administered enoxaparin has been used as the benchmark to reduce the incidence of VTE. However, concerns have been raised regarding the long-term administration of enoxaparin and its possible negative effects on bone healing and bone density with an increase of the risk of osteoporotic fractures. New oral anticoagulants such as rivaroxaban have recently been introduced, however, there is a lack of information regarding how these drugs affect bone metabolism and post-operative bone healing.

Methods

We measured the migration and proliferation capacity of mesenchymal stem cells (MSCs) under enoxaparin or rivaroxaban treatment for three consecutive weeks, and evaluated effects on MSC mRNA expression of markers for stress and osteogenic differentiation.

Results

We demonstrate that enoxaparin, but not rivaroxaban, increases the migration potential of MSCs and increases their cell count in line with elevated mRNA expression of C-X-C chemokine receptor type 4 (CXCR4), tumor necrosis factor alpha (TNFα), and alpha-B-crystallin (CryaB). However, a decrease in early osteogenic markers (insulin-like growth factors 1 and 2 (IGF1, IGF2), bone morphogenetic protein2 (BMP2)) indicated inhibitory effects on MSC differentiation into osteoblasts caused by enoxaparin, but not by rivaroxaban.

Conclusions

Our findings may explain the adverse effects of enoxaparin treatment on bone healing. Rivaroxaban has no significant impact on MSC metabolism or capacity for osteogenic differentiation in vitro.

Cite this article: Dr H. Pilge. Enoxaparin and rivaroxaban have different effects on human mesenchymal stromal cells in the early stages of bone healing. Bone Joint Res 2016;5:95–100. DOI: 10.1302/2046-3758.53.2000595.

PDGFRα signaling drives adipose tissue fibrosis by targeting progenitor cell plasticity

Adipose tissue fibrosis occurs during obesity and is associated with metabolic dysfunction. Iwayama et al. identify perivascular cells as fibro/adipogenic progenitors in white adipose tissue and show that PDGFRα targets progenitor cell plasticity as a profibrotic mechanism.

Fibrosis is a common disease process in which profibrotic cells disturb organ function by secreting disorganized extracellular matrix (ECM). Adipose tissue fibrosis occurs during obesity and is associated with metabolic dysfunction, but how profibrotic cells originate is still being elucidated. Here, we use a developmental model to investigate perivascular cells in white adipose tissue (WAT) and their potential to cause organ fibrosis. We show that a Nestin-Cre transgene targets perivascular cells (adventitial cells and pericyte-like cells) in WAT, and Nestin-GFP specifically labels pericyte-like cells. Activation of PDGFRα signaling in perivascular cells causes them to transition into ECM-synthesizing profibrotic cells. Before this transition occurs, PDGFRα signaling up-regulates mTOR signaling and ribosome biogenesis pathways and perturbs the expression of a network of epigenetically imprinted genes that have been implicated in cell growth and tissue homeostasis. Isolated Nestin-GFP⁺ cells differentiate into adipocytes ex vivo and form WAT when transplanted into recipient mice. However, PDGFRα signaling opposes adipogenesis and generates profibrotic cells instead, which leads to fibrotic WAT in transplant experiments. These results identify perivascular cells as fibro/adipogenic progenitors in WAT and show that PDGFRα targets progenitor cell plasticity as a profibrotic mechanism.

Effect of Metformin on Viability, Morphology, and Ultrastructure of Mouse Bone Marrow-Derived Multipotent Mesenchymal Stromal Cells and Balb/3T3 Embryonic Fibroblast Cell Line

Metformin, a popular drug used to treat diabetes, has recently gained attention as a potentially useful therapeutic agent for treating cancer. In our research metformin was added to in vitro cultures of bone marrow-derived multipotent mesenchymal stromal cells (BMSCs) and Balb/3T3 fibroblast at concentration of 1 mM, 5 mM, and 10 mM. Obtained results indicated that metformin negatively affected proliferation activity of investigated cells. The drug triggered the formation of autophagosomes and apoptotic bodies in all tested cultures. Additionally, we focused on determination of expression of genes involved in insulin-like growth factor 2 (IGF2) signaling pathway. The most striking finding was that the mRNA level of IGF2 was constant in both BMSCs and Balb/3T3. Further, the analysis of IGF2 concentration in cell supernatants showed that it decreased in BMSC cultures after 5 and 10 mM metformin treatments. In case of Balb/3T3 the concentration of IGF2 in culture supernatants decreased after 1 and 5 mM and increased after 10 mM of metformin. Our results suggest that metformin influences the cytophysiology of somatic cells in a dose- and time-dependent manner causing inhibition of proliferation and abnormalities of their morphology and ultrastructure.

miR-30e targets IGF2-regulated osteogenesis in bone marrow-derived mesenchymal stem cells, aortic smooth muscle cells, and ApoE-/- mice

AIMS

Activation of an osteogenic transcriptional program contributes to the initiation of aortic calcification in atherosclerosis. The role of microRNAs in regulating aortic calcification is understudied. We tested the hypothesis that miR-30e regulates an osteogenic program in bone marrow-derived mesenchymal stem cells (MSCs), aortic smooth muscle cells (SMCs), and ApoE(-/-) mice.

METHODS AND RESULTS

In aortas of wild-type mice, we found that miR-30e is highly expressed in medial SMCs. In aortas of old ApoE(-/-) mice, we found that miR-30e transcripts are down-regulated in an inverse relation to the osteogenic markers Runx2, Opn, and Igf2. In vitro, miR-30e over-expression reduced the proliferation of MSCs and SMCs while increasing adipogenic differentiation of MSCs and smooth muscle differentiation of SMCs. In MSCs and SMCs over-expressing miR-30e, microarrays and qPCR showed repression of an osteogenic gene panel including Igf2. Inhibiting miR-30e in MSCs increased Igf2 transcripts. In SMCs, IGF2 recombinant protein rescued miR-30e-repressed osteogenic differentiation. Luciferase and mutagenesis assays showed binding of miR-30e to a novel and essential site at the 3'UTR of Igf2. In ApoE(-/-) mice, injections of antimiR-30e oligos increased Igf2 expression in the aortas and livers and significantly enhanced OPN protein expression and calcium deposition in aortic valves.

CONCLUSION

miR-30e represses the osteogenic program in MSCs and SMCs by targeting IGF2 and drives their differentiation into adipogenic or smooth muscle lineage, respectively. Our data suggest that down-regulation of miR-30e in aortas with age and atherosclerosis triggers vascular calcification. The miR-30e pathway plays an important regulatory role in vascular diseases.

Upregulation of IGF2 expression during vascular calcification

The process of vascular calcification shares many similarities with that of skeletal mineralisation and involves the deposition of hydroxyapatite crystals in arteries and cardiac valves. However, the cellular mechanisms responsible have yet to be fully elucidated. In this study, we employed microarray analysis to demonstrate the upregulation of more than >9000 genes during the calcification of murine vascular smooth muscle cells (VSMCs), of which the most significantly, differentially expressed gene was Igf2. Following the validation of increased IGF2 expression by RT-qPCR and immunoblotting in calcifying murine VSMCs, IGF2 expression was further demonstrated in the calcified aorta of the Enpp1(-/-) mouse model of medial aortic calcification. Having confirmed that IGF1R and IGF2R were expressed in cultured murine VSMCs, cell-signalling studies in these cells revealed that IGF2 (50 ng/ml) significantly stimulated the phosphorylation of Akt and Erk1/2 (P<0.05). These results potentially indicate that IGF2 may mediate VSMC calcification via the stimulation of Erk1/2 and Akt signalling. This study suggests that the increased IGF2 expression in calcifying VSMCs may reflect the well-established prenatal role of IGF2, particularly as the osteogenic phenotypic transition of VSMCs in a calcified environment recapitulates many of the events occurring during embryonic development. A full understanding of the importance of IGF2 in this pathological process will lead to a better understanding of the aetiology of vascular calcification.

Bone and fat mass in relation to postnatal levels of insulin-like growth factors in prematurely born children at 4 y of age

BACKGROUND

Children born prematurely may be at risk of developing osteopenia. This study investigated whether insulin-like growth factors (IGFs) in the early postnatal period influence bone mass and body composition in prematurely born children.

METHODS

A total of 74 control (gestational age >36 wk; n = 37) and preterm (gestational age <32 wk; n = 37) infants were investigated (mean age ± SD: 4.59 ± 0.31 y). Bone mineral density, body composition, and markers of bone and mineral metabolism were investigated in relation to postnatal IGF levels.

RESULTS

After adjusting for confounders, we found no differences in bone mass, but significantly less lean mass, increased fat mass, and increased osteocalcin levels in ex-preterm infants. Forward stepwise multiple analysis revealed that higher late postnatal IGF-II levels predict lumbar spine bone mineral content (P < 0.05) and lean mass (P < 0.05). When the birth weight standard deviation score was included in the analysis, higher early postnatal IGF-I levels predicted both lumbar spine bone mineral density and bone mineral content (P < 0.05). Higher early postnatal IGF binding protein-3 (P < 0.01) predicted increased fat mass at 4-y follow-up.

CONCLUSION

Ex-preterm children have normal bone mass but different body composition compared with full-term controls. Higher early IGF-I and late postnatal IGF-II concentrations are positive predictors of lumbar spine bone mass.

IGF-1 regulation of key signaling pathways in bone

Insulin-like growth factor 1 (IGF-1) is an unique peptide that functions in an endocrine/paracrine and autocrine manner in most tissues. Although it was postulated initially that liver-derived IGF-1 was the major source of IGF-1 (that is, the somatomedin hypothesis), it is also produced in a wide variety of tissues and can function in numerous ways as both a proliferative and differentiative factor. One such tissue is bone and all cell lineages in the skeleton have been shown to not only require IGF-1 for normal development and function but also to respond to IGF-1 via the IGF-1 receptor. Ligand-receptor activation leads to several distinct downstream signaling cascades, which have significant implications for cell survival, protein synthesis and energy utilization. The novel role of IGF-1 in regulating metabolic demands of the bone remodeling unit is currently under investigation. More studies are likely to shed new light on various aspects of skeletal physiology and potentially may lead to new therapeutics.

Insulin-like growth factor-II is produced by, signals to and is an important survival factor for the mature podocyte in man and mouse

Podocytes are crucial for preventing the passage of albumin into the urine and, when lost, are associated with the development of albuminuria, renal failure and cardiovascular disease. Podocytes have limited capacity to regenerate, therefore pro-survival mechanisms are critically important. Insulin-like growth factor-II (IGF-II) is a potent survival and growth factor; however, its major function is thought to be in prenatal development, when circulating levels are high. IGF-II has only previously been reported to continue to be expressed in discrete regions of the brain into adulthood in rodents, with systemic levels being undetectable. Using conditionally immortalized human and ex vivo adult mouse cells of the glomerulus, we demonstrated the podocyte to be the major glomerular source and target of IGF-II; it signals to this cell via the IGF-I receptor via the PI3 kinase and MAPK pathways. Functionally, a reduction in IGF signalling causes podocyte cell death in vitro and glomerular disease in vivo in an aged IGF-II transgenic mouse that produces approximately 60% of IGF-II due to a lack of the P2 promoter of this gene. Collectively, this work reveals the fundamental importance of IGF-II in the mature podocyte for glomerular health across mammalian species.

Vascular calcifying progenitor cells possess bidirectional differentiation potentials

Calcifying progenitor cells in blood vessels have the potential to differentiate into cells that either promote calcium accumulation or reverse accumulation, and treatment with PPAR? can shift the direction of this differentiation.

Vascular calcification is an advanced feature of atherosclerosis for which no effective therapy is available. To investigate the modulation or reversal of calcification, we identified calcifying progenitor cells and investigated their calcifying/decalcifying potentials. Cells from the aortas of mice were sorted into four groups using Sca-1 and PDGFRα markers. Sca-1⁺ (Sca-1⁺/PDGFRα⁺ and Sca-1⁺/PDGFRα⁻) progenitor cells exhibited greater osteoblastic differentiation potentials than Sca-1⁻ (Sca-1⁻/PDGFRα⁺ and Sca-1⁻/PDGFRα⁻) progenitor cells. Among Sca-1⁺ progenitor populations, Sca-1⁺/PDGFRα⁻ cells possessed bidirectional differentiation potentials towards both osteoblastic and osteoclastic lineages, whereas Sca-1⁺/PDGFRα⁺ cells differentiated into an osteoblastic lineage unidirectionally. When treated with a peroxisome proliferator activated receptor γ (PPARγ) agonist, Sca-1⁺/PDGFRα⁻ cells preferentially differentiated into osteoclast-like cells. Sca-1⁺ progenitor cells in the artery originated from the bone marrow (BM) and could be clonally expanded. Vessel-resident BM-derived Sca-1⁺ calcifying progenitor cells displayed nonhematopoietic, mesenchymal characteristics. To evaluate the modulation of in vivo calcification, we established models of ectopic and atherosclerotic calcification. Computed tomography indicated that Sca-1⁺ progenitor cells increased the volume and calcium scores of ectopic calcification. However, Sca-1⁺/PDGFRα⁻ cells treated with a PPARγ agonist decreased bone formation 2-fold compared with untreated cells. Systemic infusion of Sca-1⁺/PDGFRα⁻ cells into Apoe^−/− mice increased the severity of calcified atherosclerotic plaques. However, Sca-1⁺/PDGFRα⁻ cells in which PPARγ was activated displayed markedly decreased plaque severity. Immunofluorescent staining indicated that Sca-1⁺/PDGFRα⁻ cells mainly expressed osteocalcin; however, activation of PPARγ triggered receptor activator for nuclear factor-κB (RANK) expression, indicating their bidirectional fate in vivo. These findings suggest that a subtype of BM-derived and vessel-resident progenitor cells offer a therapeutic target for the prevention of vascular calcification and that PPARγ activation may be an option to reverse calcification.

Atherosclerosis involves hardening of the arteries and can lead to heart disease. Calcium accumulation in blood vessels contributes to this process, and this process is regulated by cells that promote calcium accumulation (osteoblasts) and cells that reverse the accumulation (osteoclasts). In this study, we show that vascular calcifying progenitor cells in the blood vessel have the potential to become either osteoblasts or osteoclasts, and that a drug can push these cells towards becoming osteoclasts instead of osteoblasts. Progenitor cells that express both Sca-1 and PDGFRα cell surface proteins were more committed to differentiate into osteoblasts, while cells that only expressed Sca-1 could differentiate into osteoblasts or osteoclasts in a bidirectional manner. Moreover, treatment with a PPARγ agonist could shift the direction of differentiation of Sca-1⁺/PDGFRα⁻ progenitor cells toward osteoclast-like cells, whereas it cannot influence the fates of Sca-1⁺/PDGFRα⁺ progenitors. These results offer new therapeutic targets for reversing calcium accumulation in blood vessels.

Analysis of the role of Igf2 in adrenal tumour development in transgenic mouse models

Adrenal cortical carcinomas (ACC) are rare but aggressive tumours associated with poor prognosis. The two most frequent alterations in ACC in patients are overexpression of the growth factor IGF2 and constitutive activation of Wnt/β-catenin signalling. Using a transgenic mouse model, we have previously shown that constitutive active β-catenin is a bona fide adrenal oncogene. However, although all these mice developed benign adrenal hyperplasia, malignant progression was infrequent, suggesting that secondary genetic events were required for aggressive tumour development. In the present paper, we have tested IGF2 oncogenic properties by developing two distinct transgenic mouse models of Igf2 overexpression in the adrenal cortex. Our analysis shows that despite overexpression levels ranging from 7 (basal) to 87 (ACTH-induced) fold, Igf2 has no tumour initiating potential in the adrenal cortex. However, it induces aberrant accumulation of Gli1 and Pod1-positive progenitor cells, in a hedgehog-independent manner. We have also tested the hypothesis that Igf2 may cooperate with Wnt signalling by mating Igf2 overexpressing lines with mice that express constitutive active β-catenin in the adrenal cortex. We show that the combination of both alterations has no effect on tumour phenotype at stages when β-catenin-induced tumours are benign. However, there is a mild promoting effect at later stages, characterised by increased Weiss score and proliferation. Formation of malignant tumours is nonetheless a rare event, even when Igf2 expression is further increased by ACTH treatment. Altogether these experiments suggest that the growth factor IGF2 is a mild contributor to malignant adrenocortical tumourigenesis.

The adventitia: a progenitor cell niche for the vessel wall

Recent observations suggest that the adventitial layer of blood vessels exhibits properties resembling a stem/progenitor cell niche. Progenitor cells have been isolated from the adventitia of both murine and human blood vessels with the potential to form endothelial cells, mural cells, osteogenic cells, and adipocytes. These progenitors appear to cluster at or near the border zone between the outer media and inner adventitia. In the mouse, this border zone region corresponds to a localized site of sonic hedgehog signaling in the artery wall. This brief review will discuss the emerging evidence that the tunica adventitia may provide a niche-like signaling environment for resident progenitor cells and will address the role of the adventitia in growth, remodeling, and repair of the artery wall.