Glucocorticoids down-regulate the extracellular matrix proteins fibronectin, fibulin-1 and fibulin-2 in bone marrow stroma

TMT-based quantitative proteomic analysis revealed that FBLN2 and NPR3 are involved in the early osteogenic differentiation of mesenchymal stem cells (MSCs)

The delicate equilibrium between osteoblast and adipocyte differentiation of MSCs is highly regulated. We screened for early-stage osteogenesis- or adipogenesis-based MSCs protein expression profiles using TMT-based quantitative proteomic analysis to identify novel participating molecules. Protein annotation, hierarchical clustering, functional stratification, and protein-protein association assessments were performed. Moreover, two upregulated proteins, namely, FBLN2 and NPR3, were validated to participate in the osteogenic differentiation process of MSCs. After that, we independently downregulated FBLN2 and NPR3 over seven days of osteogenic differentiation, and we performed quantitative proteomics analysis to determine how different proteins were regulated in knockdown vs. control cells. Based on gene ontology (GO) and network analyses, FBLN2 deficiency induced functional alterations associated with biological regulation and stimulus-response, whereas NPR3 deficiency induced functional alterations related to cellular and metabolic processes, and so on. These findings suggested that proteomics remains a useful method for an in-depth study of the MSCs differentiation process. This will assist in comprehensively evaluating its role in osteoporosis and provide additional approaches for identifying as-yet-unidentified effector molecules.

The extracellular matrix of hematopoietic stem cell niches

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Comprehensive overview of different classes of ECM molecules in the HSC niche.

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Overview of current knowledge on role of biophysics of the HSC niche.

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Description of approaches to create artificial stem cell niches for several application.

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Importance of considering ECM in drug development and testing.

Hematopoietic stem cells (HSCs) are the life-long source of all types of blood cells. Their function is controlled by their direct microenvironment, the HSC niche in the bone marrow. Although the importance of the extracellular matrix (ECM) in the niche by orchestrating niche architecture and cellular function is widely acknowledged, it is still underexplored. In this review, we provide a comprehensive overview of the ECM in HSC niches. For this purpose, we first briefly outline HSC niche biology and then review the role of the different classes of ECM molecules in the niche one by one and how they are perceived by cells. Matrix remodeling and the emerging importance of biophysics in HSC niche function are discussed. Finally, the application of the current knowledge of ECM in the niche in form of artificial HSC niches for HSC expansion or targeted differentiation as well as drug testing is reviewed.

CRYAB promotes osteogenic differentiation of human bone marrow stem cells via stabilizing β-catenin and promoting the Wnt signalling

Objectives

The osteogenesis differentiation of human bone marrow stem cells (BMSCs) is essential for bone formation and bone homeostasis. In this study, we aim to elucidate novel molecular targets for bone metabolism diseases.

Materials and methods

The dataset GSE80614 which includes mRNA expression profile during BMSCs osteogenic differentiation was obtained from the GEO database (https://www.ncbi.nlm.nih.gov/geo/). The osteogenic differentiation of BMSCs was measured by ALP staining, AR staining and expression of osteogenic markers in vitro. For in vivo assay, we seeded BMSCs onto beta‐tricalcium phosphate (β‐TCP) and transplanted them into muscle pockets of nude mice. Luciferase assay, co‐immunoprecipitation assay and in vitro ubiquitination assay were carried out to investigate the molecular mechanism.

Results

We found that α‐B‐crystallin (CRYAB) expression was elevated during the process of BMSCs osteogenic differentiation. Further studies showed that upregulation of CRYAB significantly enhanced the osteogenic differentiation, while downregulation of CRYAB suppressed it. CRYAB regulated BMSCs osteogenic differentiation mainly through the canonical Wnt/β‐catenin signalling. In addition, we found that CRYAB could physically interact with β‐catenin and protect it from ubiquitination and degradation, which stabilized β‐catenin and promoted the Wnt signalling.

Conclusions

The present study provides evidences that CRYAB is an important regulator of BMSCs osteogenic differentiation by protecting β‐catenin from ubiquitination and degradation and promoting the Wnt signalling. It may serve as a potential therapeutic target for diseases related to bone metabolism.

The role of microRNAs in the involvement of vascular smooth muscle cells in the development of atherosclerosis

MicroRNAs (miRNAs) are a class of nonprotein-encoding RNAs of ~22 nucleotides in length that bind to or complement each other with a target gene messenger RNA (mRNA) to promote mRNA degradation or inhibit translation of the target mRNA. The protein required [such as Toll-like receptor (TLR) proteins] is controlled at an optimal level. By affecting protein translation, miRNAs have become powerful regulators of biological processes, including development, differentiation, cell proliferation, and apoptosis. MiRNAs are involved in the regulation of proliferation, migration, and apoptosis of vascular smooth muscle cells (VSMCs), thereby affecting the formation of atherosclerosis (AS). In recent years, the role and mechanism of miRNAs involved in AS development in VSMCs have been studied extensively. In the current study, the results and progress in miRNA research are reviewed.

miR-29c induction contributes to downregulation of vascular extracellular matrix proteins by glucocorticoids

Maternal undernutrition increases maternal glucocorticoids (GCs) and alters microRNA expression in offspring. Given that the mechanisms of GC action on vascular development are not clear, this study examined the influence of GCs on microRNA 29c (miR-29c) and its predicted targets in primary rat aorta smooth muscle cells (RAOSMCs). Dexamethasone (Dex) and corticosterone (Cor) time-dependently increased miR-29c expression and reduced collagen type III (Col3A1), collagen type IV (Col4A5), elastin (ELN), and matrix metalloproteinase-2 (MMP2) protein in RAOSMCs. These effects were blocked by mifepristone. These genes were also targeted by miR-29c, as confirmed by a significant decrease in luciferase reporter activity of Col3A1 (34%), Col4A5 (45%), ELN (17%), and MMP2 (28%). In cells transfected with reporter plasmids, including the 3'-untranslated region of genes targeted by miR-29c, treatment with Dex or Cor also resulted in decreases in luciferase activity. Gain or loss of function of miR-29c significantly altered mRNA expression of Col3A1 (26% and 26%, respectively), Col4A5 (28% and 32%, respectively), and MMP2 (24% and 14%, respectively) but did not affect ELN. Gain or loss of function of miR-29c also significantly altered protein levels of Col3A1 (51% and 16%, respectively), Col4A5 (56% and 22%, respectively), ELN (53% and 71%, respectively), and MMP2 (28% and 53%, respectively). Coincubation of anti-miR-29c with Dex or Cor partially attenuated the effects of these steroids on protein expression of Col3A1 (25% and 24%, respectively), Col4A5 (26% and 44%, respectively), ELN (31% and 55%, respectively), and MMP2 (46% and 26%, respectively) in RAOSMCs compared with anti-miR negative controls. Our results demonstrate that GCs regulate the expression of Col3A1, Col4A5, ELN, and MMP2, at least in part, through induction of miR-29c.

Biophysical regulation of hematopoietic stem cells

Blood is renewed throughout the entire life. The stem cells of the blood, called hematopoietic stem cells (HSCs), are responsible for maintaining a supply of all types of fresh blood cells. In contrast to other stem cells, the clinical application of these cells is well established and HSC transplantation is an established life-saving therapy for patients suffering from haematological disorders. Despite their efficient functionality throughout life in vivo, controlling HSC behaviour in vitro (including their proliferation and differentiation) is still a major task that has not been resolved with standard cell culture systems. Targeted HSC multiplication in vitro could be beneficial for many patients, because HSC supply is limited. The biology of these cells and their natural microenvironment - their niche - remain a matter of ongoing research. In recent years, evidence has come to light that HSCs are susceptible to physical stimuli. This makes the regulation of HSCs by engineering physical parameters a promising approach for the targeted manipulation of these cells for clinical applications. Nevertheless, the biophysical regulation of these cells is still poorly understood. This review sheds light on the role of biophysical parameters in HSC biology and outlines which knowledge on biophysical regulation identified in other cell types could be applied to HSCs.

Maturational changes in laminin, fibronectin, collagen IV, and perlecan in germinal matrix, cortex, and white matter and effect of betamethasone

Germinal matrix is selectively vulnerable to hemorrhage in premature infants, and use of prenatal betamethasone is associated with a lower occurrence of germinal matrix hemorrhage. Because the major components of extracellular matrix of the cerebral vasculature-laminin, fibronectin, collagen IV, and perlecan-provide structural stability to blood vessels, we examined whether the expression of these molecules was decreased in the germinal matrix and affected by betamethasone. In both human fetuses and premature infants, fibronectin was significantly lower in the germinal matrix than in the cortical mantle or white matter anlagen. Conversely, laminin alpha1 gene expression was greater in the human germinal matrix compared with the cortical mantle or white matter. Expression of alpha1- and alpha2(IV) collagen chains increased with advancing gestational age. Low-dose prenatal betamethasone treatment enhanced fibronectin level by 1.5-2-fold whereas a high dose reduced fibronectin expression by 2-fold in rabbit pups. Because fibronectin provides structural stability to the blood vessels, its reduced expression in the germinal matrix may contribute to the fragility of germinal matrix vasculature and the propensity to hemorrhage in premature neonates.

Characterization and functional analysis of osteoblast-derived fibulins in the human hematopoietic stem cell niche

OBJECTIVE

In the bone marrow stem cell niche, osteoblasts lining the endosteum are of major importance in supporting hematopoietic stem cell maintenance. Our objective was to analyze expression of the fibulins, highly conserved calcium-binding glycoproteins, which are components of the extracellular matrix of human osteoblasts, and to provide insights into their functional interactions with hematopoietic progenitor cells.

MATERIALS AND METHODS

Expression of the fibulins by human osteoblasts was determined by reverse transcription polymerase chain reaction analysis and by immunofluorescence staining and immunoblotting using fibulin-specific antisera. Recombinant fibulins were used in cell proliferation and differentiation assays with human CD34(+) hematopoietic progenitor cells. Adhesive interactions of CD34(+) cells with fibulins were investigated using cell-adhesion assays.

RESULTS

Human osteoblasts strongly express and secrete fibulin-1 and -2. Whereas fibulin-1 is secreted in its intact form, fibulin-2 synthesized by human osteoblasts undergoes rapid proteolytic degradation. The matrix metalloproteinase-2, which is constitutively expressed by the osteoblasts, seems to be responsible for fibulin-2 degradation. Fibulin-1 showed an inhibitory effect on short-term CD34(+) hematopoietic progenitor cell proliferation. Both fibulin-1 and fibulin-2 were able to diminish erythroid and myeloid colony formation. The CD34(+) cell line KG1a strongly attached to fibulin-2, whereas magnetic-activated cell sorted CD34(+) hematopoietic progenitors did not adhere to either fibulin-1 or fibulin-2. On the other hand, fibulin-1 can strongly interfere with CD34(+) cell adhesion to fibronectin.

CONCLUSION

Fibulins seem to be important components of the extracellular matrix of osteoblasts and are likely to negatively influence the proliferation rate of stem cells and the overall adhesive properties of the endosteal stem cell niche.

Hematopoietic Cells Are a Source of Nidogen-1 and Nidogen-2 during Mouse Liver Development

Nidogen-1 and −2 are key components of basement membranes (BMs). Despite the presence of nidogen molecules in the parenchyma of the developing liver, no BMs are formed therein. This suggests that, in the liver, nidogens may also have functions other than BM formation. As a first step toward the elucidation of the possible cell biological functions of nidogens in the developing liver, we aimed to study their cellular origin. We localized expression of nidogen-1 and nidogen-2 on prenatal days 12, 14, and 16 in the developing mouse liver using in situ hybridization at the light and electron microscopic level and light microscopic immunohistochemistry. Our results show that nidogens are produced both in portal anlagen and in the parenchyma during liver development. In the parenchyma, transcripts can be found in hepatocytes, precursors of stellate cells, endothelial cells and, most interestingly, hematopoietic cells. Using real-time PCR, we found that the gene expression for both proteins shows a decrease from day 14 to day 16 concomitant with a decrease in the hepatic hematopoiesis. We suggest that nidogens may, to some extent, take part in the regulation of hepatic hematopoiesis. (J Histochem Cytochem 54:593-604, 2006)

Specific targeting of gene expression to a subset of human trabecular meshwork cells using the chitinase 3-like 1 promoter

PURPOSE

To compare the gene expression profile of trabecular meshwork (TM) and Schlemm's canal (SC) primary cultures and to identify promoters for targeting gene expression to specific cells in the outflow pathway.

METHODS

The differential gene expression profile of four human TM and three SC primary cultures was analyzed by gene microarrays (Affymetrix, Santa Clara, CA) and confirmed by quantitative real-time PCR. Based on the results, a recombinant adenovirus was constructed with the expression of the reporter gene LacZ driven by the 5' promoter region of the chitinase 3-like 1 (Ch3L1) gene (AdCh3L1-LacZ). The expression of the Ch3L1 promoter was analyzed in human TM and SC cells and in human perfused anterior segments infected with AdCh3L1-LacZ.

RESULTS

gamma-Sarcoglycan, fibulin-2, and collagen XV were identified as the genes more highly expressed in SC than in TM cells. Ch3L1 showed the highest levels of differential expression in TM versus SC cells. Expression analysis of the Ch3L1 promoter demonstrated specific expression in a subset of the TM cells in cell culture and in perfused anterior segments.

CONCLUSIONS

Comparative analysis of gene expression between SC and TM primary cultures identified several genes with promoters potentially capable of targeting gene expression to specific cells within the outflow pathway. Results with the Ch3L1 promoter indicated that two different cell subtypes may be present in the TM. This study provides a new potential tool to investigate the role of these different cell types in both normal and pathophysiological function of the outflow pathway, with implications for possible future glaucoma gene therapy.

Transcriptional and posttranscriptional regulation of fibulin-1 by estrogens leads to differential induction of messenger ribonucleic acid variants in ovarian and breast cancer cells

Fibulin-1 is an extracellular matrix protein overexpressed in epithelial ovarian and breast cancers. In estrogen receptor (ER)-positive ovarian and breast cancer cell lines, fibulin-1 mRNA levels are markedly increased by estrogens. Transfection experiments using fibulin-1 promoter constructs indicate that 17beta-estradiol (E2) increases fibulin-1 gene transcription and that ERalpha is more potent than ERbeta to mediate E2 regulation of the transfected fibulin-1 promoter. Using SL2 cells devoid of specificity protein 1 (Sp1) and site-directed mutagenesis of GC boxes, we evidenced that the E2 regulation occurs through a proximal specificity protein 1 binding site. In addition, we show that fibulin-1C and -1D mRNAs, the two major fibulin-1 splicing variants, are differentially induced by E2. The induction of both mRNAs variants is direct and independent of a newly synthesized protein intermediate. Interestingly, actinomycin D chase experiments demonstrate that E2 treatment selectively shortens the fibulin-1D mRNA half-life. This indicates that estrogens affect differentially the stability of fibulin-1 variants and may explain the lower accumulation of fibulin-1D mRNA on E2 treatment. In conclusion, our data show that estrogens, via ERalpha, are key regulators of fibulin-1 expression at both the transcriptional and posttranscriptional levels. The preferential induction of the fibulin-1C variant, which is overexpressed in ovarian and breast cancer, might play an important role in estrogen-promoted carcinogenesis.

Fibulins: physiological and disease perspectives

The fibulins are a family of proteins that are associated with basement membranes and elastic extracellular matrix fibres. This review summarizes findings from studies of animal models of fibulin deficiency, human fibulin gene mutations, human tumours and injury models that have advanced our understanding of the normal and pathological roles of members of this formerly obscure family.

miRNP:mRNA association in polyribosomes in a human neuronal cell line

MicroRNAs (miRNAs) are small regulatory RNAs that control gene expression by base-pairing with their mRNA targets. miRNAs assemble into ribonucleoprotein complexes termed miRNPs. Animal miRNAs recognize their mRNA targets via partial antisense complementarity and repress mRNA translation at a step after translation initiation. How animal miRNAs recognize their mRNA targets and how they control their translation is unknown. Here we describe that in a human neuronal cell line, the miRNP proteins eIF2C2 (a member of the Argonaute family of proteins), Gemin3, and Gemin4 along with miRNAs cosediment with polyribosomes. Furthermore, we describe a physical association between a let-7b (miRNA)-containing miRNP and its putative human mRNA target in polyribosome-containing fractions. These findings suggest that miRNP proteins may play important roles in target mRNA recognition and translational repression.