Glucocorticoid-induced leucine zipper (GILZ) antagonizes TNF-α inhibition of mesenchymal stem cell osteogenic differentiation

Human nonunion tissues display differential gene expression in comparison to physiological fracture callus

The healing of bone fractures can become aberrant and lead to nonunions which in turn have a negative impact on patient health. Understanding why a bone fails to normally heal will enable us to make a positive impact in a patient's life. While we have a wealth of molecular data on rodent models of fracture repair, it is not the same with humans. As such, there is still a lack of information regarding the molecular differences between normal physiological repair and nonunions. This study was designed to address this gap in our molecular knowledge of the human repair process by comparing differentially expressed genes (DEGs) between physiological fracture callus and two different nonunion types, hypertrophic (HNU) and oligotrophic (ONU). RNA sequencing data revealed over ∼18,000 genes in each sample. Using the physiological callus as the control and the nonunion samples as the experimental groups, bioinformatic analyses identified 67 and 81 statistically significant DEGs for HNU and ONU, respectively. Out of the 67 DEGs for the HNU, 34 and 33 were up and down-regulated, respectively. Similarly, out of the 81 DEGs for the ONU, 48 and 33 were up and down-regulated, respectively. Additionally, we also identified common genes between the two nonunion samples; 8 (10.8 %) upregulated and 12 (22.2 %) downregulated. We further identified many biological processes, with several statistically significant ones. Some of these were related to muscle and were common between the two nonunion samples. This study represents the first comprehensive attempt to understand the global molecular events occurring in human nonunion biology. With further research, we can perhaps decipher new molecular pathways involved in aberrant healing of human bone fractures that can be therapeutically targeted.

Synthetic Glucocorticoid-Induced Leucine Zipper Peptide Inhibits Lipopolysaccharide-Induced Ocular Inflammation in Rats

PURPOSE

To demonstrate the anti-inflammatory action of a synthetic glucocorticoid-induced leucine zipper (GILZ98-134) peptide (GILZ-p) in a model of endotoxin-induced uveitis (EIU) in rats.

METHODS

The EIU model was induced in Sprague Dawley rats with an intravitreal injection of lipopolysaccharide (LPS). Synthetic GILZ-p was injected intravitreally 6 h after the LPS injection. To evaluate the anti-inflammatory effects of GILZ-p, the inflammatory response in the anterior chamber and iris of the rat eyes was evaluated with a slitlamp microscope on days 0, 1, 2, 3, and 4 after GILZ-p injection. The retinal expression of inflammatory cytokines was measured on days 0, 1, 2, 3, and 4 after GILZ-p injection. Müller cell gliosis was also detected at planned time points after GILZ-p injection.

RESULTS

Anterior segment inflammation peaked at 24 h after LPS injection in the EIU model. Compared with the controls, intravitreal GILZ-p significantly suppressed LPS-induced anterior segment inflammation in the EIU rats. The levels of retinal inflammatory factors IL-1β, TNF-α, MCP-1, and ICAM-1 were simultaneously reduced by the intravitreal GILZ-p injection. The expression of vimentin in the EIU retina was significantly reduced by GILZ-p, and the downregulated aquaporin 4 in the EIU retina was significantly restored by GILZ-p.

CONCLUSION

The synthetic GILZ-p inhibited the inflammatory reaction in the EIU model and may have utility in the treatment of inflammatory ocular disease.

ELP2 negatively regulates osteoblastic differentiation impaired by tumor necrosis factor α in MC3T3-E1 cells through STAT3 activation

Tumor necrosis factor‐α (TNF‐α) is a pluripotent signaling molecule. The biological effect of TNF‐α includes slowing down osteogenic differentiation, which can lead to bone dysplasia in long‐term inflammatory microenvironments. Signal transducer and activator of transcription 3 (STAT3)‐interacting protein 1 (StIP1, also known as elongator complex protein 2, ELP2) play a role in inhibiting TNF‐α‐induced osteoblast differentiation. In the present study, we investigated whether and how ELP2 activation mediates the effects of TNF‐α on osteoblastic differentiation. Using in vitro cell cultures of preosteoblastic MC3T3‐E1 cells, we found that TNF‐α inhibited osteoblastic differentiation accompanied by an increase in ELP2 expression and STAT3 activation. Forced ELP2 expression inhibited osteogenic differentiation of MC3T3‐E1 cells, with a decrease in the expression of osteoblast marker genes, alkaline phosphatase activity, and matrix mineralization capacity. In contrast, ELP2 silencing ameliorated osteogenic differentiation in MC3T3‐E1 cells, even after TNF‐α stimulation. The TNF‐α‐induced inhibitory effect on osteoblastic differentiation was therefore mediated by ELP2, which was associated with Janus kinase 2 (JAK2)/STAT3 activation. These results suggest that ELP2 is upregulated at the differentiation of MC3T3‐E1 cells into osteoblasts and inhibits osteogenic differentiation in response to TNF‐α through STAT3 activation.

A dual role for glucocorticoid-induced leucine zipper in glucocorticoid function: tumor growth promotion or suppression?

Glucocorticoids (GCs), important therapeutic tools to treat inflammatory and immunosuppressive diseases, can also be used as part of cancer therapy. In oncology, GCs are used as anticancer drugs for lymphohematopoietic malignancies, while in solid neoplasms primarily to control the side effects of chemo/radiotherapy treatments. The molecular mechanisms underlying the effects of GCs are numerous and often overlapping, but not all have been elucidated. In normal, cancerous, and inflammatory tissues, the response to GCs differs based on the tissue type. The effects of GCs are dependent on several factors: the tumor type, the GC therapy being used, the expression level of the glucocorticoid receptor (GR), and the presence of any other stimuli such as signals from immune cells and the tumor microenvironment. Therefore, GCs may either promote or suppress tumor growth via different molecular mechanisms. Stress exposure results in dysregulation of the hypothalamic-pituitary-adrenal axis with increased levels of endogenous GCs that promote tumorigenesis, confirming the importance of GCs in tumor growth. Most of the effects of GCs are genomic and mediated by the modulation of GR gene transcription. Moreover, among the GR-induced genes, glucocorticoid-induced leucine zipper (GILZ), which was cloned and characterized primarily in our laboratory, mediates many GC anti-inflammatory effects. In this review, we analyzed the possible role for GILZ in the effects GCs have on tumors cells. We also suggest that GILZ, by affecting the immune system, tumor microenvironment, and directly cancer cell biology, has a tumor-promoting function. However, it may also induce apoptosis or decrease the proliferation of cancer cells, thus inhibiting tumor growth. The potential therapeutic implications of GILZ activity on tumor cells are discussed here.

Long non-coding RNA TCONS_00041960 enhances osteogenesis and inhibits adipogenesis of rat bone marrow mesenchymal stem cell by targeting miR-204-5p and miR-125a-3p

A growing number of long non‐coding RNAs (lncRNAs) have been found to be involved in diverse biological processes such as cell cycle regulation, embryonic development, and cell differentiation. However, limited knowledge is available concerning the underlying mechanisms of lncRNA functions. In this study, we found down‐regulation of TCONS_00041960 during adipogenic and osteogenic differentiation of glucocorticoid‐treated bone marrow mesenchymal stem cells (BMSCs). Furthermore, up‐regulation of TCONS_00041960 promoted expression of osteogenic genes Runx2, osterix, and osteocalcin, and anti‐adipogenic gene glucocorticoid‐induced leucine zipper (GILZ). Conversely, expression of adipocyte‐specific markers was decreased in the presence of over‐expressed TCONS_00041960. Mechanistically, we determined that TCONS_00041960 as a competing endogenous RNA interacted with miR‐204‐5p and miR‐125a‐3p to regulate Runx2 and GILZ, respectively. Overall, we identified a new TCONS_00041960‐miR‐204‐5p/miR‐125a‐3p‐Runx2/GILZ axis involved in regulation of adipogenic and osteogenic differentiation of glucocorticoid‐treated BMSCs.

IL-17A Inhibits Osteogenic Differentiation of Bone Mesenchymal Stem Cells via Wnt Signaling Pathway

Background

Interleukin-17A (IL-17A) is not only an important modulator of inflammatory reactions, but also affects bone metabolism, which is involved in osteogenic differentiation of stem cells. However, the role and mechanism of IL-17A in osteogenic differentiation of bone mesenchymal stem cells (BMSCs) are not fully understood. In this study, we investigated the role and mechanism of IL-17A in osteogenic differentiation of BMSCs.

Material/Methods

The osteogenic differentiation of BMSCs was induced by osteoblast-induction medium with IL-17A or without IL-17A. The osteogenic differentiation of BMSCs was confirmed by the alkaline phosphatase and alizarin red staining. The lentiviral plasmid was used to construct the sFRP1-shRNA expression vector. The associated osteogenic differentiation marks (RUNX2, ALP, OPN), Wnt signaling pathway inhibitor (sFRP1), and modulators of Wnt signaling pathway (Wnt3, Wnt6) were detected by qRT-PCR and Western blot method.

Results

The results showed that the addition of IL-17A inhibited osteogenic differentiation of BMSCs. IL-17A induced up-regulated expression of sFRP1 and down-regulated expression of Wnt3 and Wnt6 in BMSCs. In addition, sFRP1-shRNA abolished the inhibition effect of IL-17A in osteogenic differentiation of BMSCs and induced up-regulated expression of Wnt3 and Wnt6 in the Wnt signaling pathway in BMSCs.

Conclusions

Our findings show that IL-17A inhibits osteogenic differentiation of bone mesenchymal stem cells via the Wnt signaling pathway.

Role of glucocorticoid-induced leucine zipper (GILZ) in inflammatory bone loss

TNF-α plays a key role in the development of rheumatoid arthritis (RA) and inflammatory bone loss. Unfortunately, treatment of RA with anti-inflammatory glucocorticoids (GCs) also causes bone loss resulting in osteoporosis. Our previous studies showed that overexpression of glucocorticoid-induced leucine zipper (GILZ), a mediator of GC's anti-inflammatory effect, can enhance osteogenic differentiation in vitro and bone acquisition in vivo. To investigate whether GILZ could antagonize TNF-α-induced arthritic inflammation and protect bone in mice, we generated a TNF-α-GILZ double transgenic mouse line (TNF-GILZ Tg) by crossbreeding a TNF-α Tg mouse, which ubiquitously expresses human TNF-α, with a GILZ Tg mouse, which expresses mouse GILZ under the control of a 3.6kb rat type I collagen promoter fragment. Results showed that overexpression of GILZ in bone marrow mesenchymal stem/progenitor cells protected mice from TNF-α-induced inflammatory bone loss and improved bone integrity (TNF-GILZ double Tg vs. TNF-αTg, n = 12-15). However, mesenchymal cell lineage restricted GILZ expression had limited effects on TNF-α-induced arthritic inflammation as indicated by clinical scores and serum levels of inflammatory cytokines and chemokines.

[Tumor necrosis factor-α regulates the osteogenic differentiation of bone marrow mesenchymal stem cells in chronic periodontitis]

Bone marrow mesenchymal stem cells (BMSCs) and ideal adult stem cells for alveolar bone regeneration considerably help restore the structure and function of the periodontium and promote the healing of periodontal disease. Thus, BMSC features, especially the mechanism of osteogenic differentiation, has recently become a research hotspot. Tumor necrosis factor-α (TNF-α), which is the main factor in the periodontal inflammatory microenvironment, is directly related to the osteogenic differentiation of BMSCs. Exploring the TNF-α-regulated differentiation mechanism of BMSCs aids in the search for new treatment targets. Such investigation also promotes the development of stem cell therapy for periodontal diseases. This article aims to describe the potential of TNF-α in regulating the osteogenic differentiation of stem cells.

Pulsed Electromagnetic Field Regulates MicroRNA 21 Expression to Activate TGF-β Signaling in Human Bone Marrow Stromal Cells to Enhance Osteoblast Differentiation

Pulsed electromagnetic fields (PEMFs) have been documented to promote bone fracture healing in nonunions and increase lumbar spinal fusion rates. However, the molecular mechanisms by which PEMF stimulates differentiation of human bone marrow stromal cells (hBMSCs) into osteoblasts are not well understood. In this study the PEMF effects on hBMSCs were studied by microarray analysis. PEMF stimulation of hBMSCs' cell numbers mainly affected genes of cell cycle regulation, cell structure, and growth receptors or kinase pathways. In the differentiation and mineralization stages, PEMF regulated preosteoblast gene expression and notably, the transforming growth factor-beta (TGF-β) signaling pathway and microRNA 21 (miR21) were most highly regulated. PEMF stimulated activation of Smad2 and miR21-5p expression in differentiated osteoblasts, and TGF-β signaling was essential for PEMF stimulation of alkaline phosphatase mRNA expression. Smad7, an antagonist of the TGF-β signaling pathway, was found to be miR21-5p's putative target gene and PEMF caused a decrease in Smad7 expression. Expression of Runx2 was increased by PEMF treatment and the miR21-5p inhibitor prevented the PEMF stimulation of Runx2 expression in differentiating cells. Thus, PEMF could mediate its effects on bone metabolism by activation of the TGF-β signaling pathway and stimulation of expression of miR21-5p in hBMSCs.

Effects of Low-dose Triamcinolone Acetonide on Rat Retinal Progenitor Cells under Hypoxia Condition

BACKGROUND

Retinal degenerative diseases are the leading causes of blindness in developed world. Retinal progenitor cells (RPCs) play a key role in retina restoration. Triamcinolone acetonide (TA) is widely used for the treatment of retinal degenerative diseases. In this study, we investigated the role of TA on RPCs in hypoxia condition.

METHODS

RPCs were primary cultured and identified by immunofluorescence staining. Cells were cultured under normoxia, hypoxia 6 h, and hypoxia 6 h with TA treatment conditions. For the TA treatment groups, after being cultured under hypoxia condition for 6 h, RPCs were treated with different concentrations of TA for 48-72 h. Cell viability was measured by cell counting kit-8 (CCK-8) assay. Cell cycle was detected by flow cytometry. Western blotting was employed to examine the expression of cyclin D1, Akt, p-Akt, nuclear factor (NF)-κB p65, and caspase-3.

RESULTS

CCK-8 assays indicated that the viability of RPCs treated with 0.01 mg/ml TA in hypoxia group was improved after 48 h, comparing with control group (P < 0.05). After 72 h, the cell viability was enhanced in both 0.01 mg/ml and 0.02 mg/ml TA groups compared with control group (all P < 0.05). Flow cytometry revealed that there were more cells in S-phase in hypoxia 6 h group than in normoxia control group (P < 0.05). RPCs in S and G2/M phases decreased in groups given TA, comparing with other groups (all P < 0.05). There was no significant difference in the total Akt protein expression among different groups, whereas upregulation of p-Akt and NF-κB p65 protein expression and downregulation of caspase-3 and cyclin D1 protein expression were observed in 0.01 mg/ml TA group, comparing with hypoxia 6 h group and control group (all P < 0.05).

CONCLUSION

Low-dose TA has anti-apoptosis effect on RPCs while it has no stimulatory effect on cell proliferation.

Quantitative tissue-specific dynamics of in vivo GILZ mRNA expression and regulation by endogenous and exogenous glucocorticoids

Glucocorticoids (GC) are steroid hormones, which regulate metabolism and immune function. Synthetic GCs, or corticosteroids (CS), have appreciable clinical utility via their ability to suppress inflammation in immune-mediated diseases like asthma and rheumatoid arthritis. Recent work has provided insight to novel GC-induced genes that mediate their anti-inflammatory effects, including glucocorticoid-induced leucine zipper (GILZ). Since GILZ comprises an important part of GC action, its regulation by both drug and hormone will influence CS therapy. In addition, GILZ expression is often employed as a biomarker of GC action, which requires judicious selection of sampling time. Understanding the in vivo regulation of GILZ mRNA expression over time will provide insight into both the physiological regulation of GILZ by endogenous GC and the dynamics of its enhancement by CS. A highly quantitative qRT-PCR assay was developed for measuring GILZ mRNA expression in tissues obtained from normal and CS-treated rats. This assay was applied to measure GILZ mRNA expression in eight tissues; to determine its endogenous regulation over time; and to characterize its dynamics in adipose tissue, muscle, and liver following treatment with CS. We demonstrate that GILZ mRNA is expressed in several tissues. GILZ mRNA expression in adipose tissue displayed a robust circadian rhythm that was entrained with the circadian oscillation of endogenous corticosterone; and is strongly enhanced by acute and chronic dosing. Single dosing also enhanced GILZ mRNA in muscle and liver, but the dynamics varied. In conclusion, GILZ is widely expressed in the rat and highly regulated by endogenous and exogenous GCs.

Crosstalk between bone marrow-derived mesenchymal stem cells and regulatory T cells through a glucocorticoid-induced leucine zipper/developmental endothelial locus-1-dependent mechanism

Bone marrow is a reservoir for regulatory T (T(reg)) cells, but how T(reg) cells are regulated in that environment remains poorly understood. We show that expression of glucocorticoid (GC)-induced leucine zipper (GILZ) in bone marrow mesenchymal lineage cells or bone marrow-derived mesenchymal stem cells (BMSCs) increases the production of T(reg) cells via a mechanism involving the up-regulation of developmental endothelial locus-1 (Del-1), an endogenous leukocyte-endothelial adhesion inhibitor. We found that the expression of Del-1 is increased ∼4-fold in the bone tissues of GILZ transgenic (Tg) mice, and this increase is coupled with a significant increase in the production of IL-10 (2.80 vs. 0.83) and decrease in the production of IL-6 (0.80 vs. 2.33) and IL-12 (0.25 vs. 1.67). We also show that GILZ-expressing BMSCs present antigen in a way that favors T(reg) cells. These results indicate that GILZ plays a critical role mediating the crosstalk between BMSCs and T(reg) in the bone marrow microenvironment. These data, together with our previous findings that overexpression of GILZ in BMSCs antagonizes TNF-α-elicited inflammatory responses, suggest that GILZ plays important roles in bone-immune cell communication and BMSC immune suppressive functions.

Targeting glucocorticoid side effects: selective glucocorticoid receptor modulator or glucocorticoid-induced leucine zipper? A perspective

Glucocorticoids (GCs) are steroid hormones that are necessary for life and important in health and disease. They regulate crucial homeostatic functions, including metabolism, cell growth, and development. Although GCs are regulated by circadian rhythm, increased production is associated with stress. Synthetic GCs are a valuable resource for anti-inflammatory and immunosuppressive therapy. Natural and synthetic GCs transduce signals mainly through GC receptor (GR) activation. Extensive research has explored the downstream targets of the GR, and optimization of GC therapy has required collaborative efforts. One highly promising approach involves new dissociative GR modulators. Because transrepression and transactivation of GR genes induce beneficial and adverse effects, respectively, this approach favors transrepression. Another approach involves the use of GC-dependent genes to generate proteins to mediate therapeutic GC effects. In a third approach, drug discovery is used to identify agents that selectively target GR isoforms to obtain differential gene transcription and effects. In this review, we focus on mechanisms of GR function compatible with the use of dissociative drugs. We highlight GC-induced leucine zipper (GILZ), a gene cloned in our laboratory, as a mediator of GC anti-inflammatory and immunosuppressive effects, to outline our perspective on the future of GC therapy.

Long-term tumor necrosis factor treatment induces NFκB activation and proliferation, but not osteoblastic differentiation of adipose tissue-derived mesenchymal stem cells in vitro

The pro-inflammatory cytokine tumor necrosis factor (TNF) is well known to induce differentiation of bone matrix-resorbing osteoclasts from hematopoietic stem cells. However, the impact of TNF on differentiation of bone matrix-forming osteoblasts from mesenchymal stem cells (MSC) was only fragmentarily studied so far. Therefore, we investigated what impact long-term TNF treatment has on osteoblastic differentiation of MSC isolated from the adipose tissue (ASC) in vitro. In summary, we found continuous TNF exposure to induce the nuclear factor of kappa B pathway in ASC as well as secretion of the pro-inflammatory chemokine interleukin 8, but not the mitogen-activated protein kinase and the apoptosis pathway in ASC. Moreover, TNF neither induced nor inhibited osteoblastic differentiation of ASC, but strongly increased their proliferation rate. In that manner, pro-inflammatory conditions in vivo may generate significantly increased numbers of progenitor cells, and ASC especially, in conjunction with external stimuli, may contribute to the events of ectopic ossification observed in chronic inflammatory diseases. The substantiation of the translation of our in vitro findings to the disease context encourages further in vivo studies.

A positive role of microRNA-15b on regulation of osteoblast differentiation

Osteoblast differentiation is tightly regulated by several factors including microRNAs (miRNAs). In this paper, we report that pre-mir-15b is highly expressed in differentiated osteoblasts. The functional role of miR-15b in osteoblast differentiation was determined using miR-15b mimic/inhibitor and the expression of osteoblast differentiation marker genes such as alkaline phosphatase (ALP), type I collagen genes was decreased by miR-15b inhibitor. Runx2, a bone specific transcription factor is generally required for expression of osteoblast differentiation marker genes and in response to miR-15b inhibitor treatment, Runx2 mRNA expression was not changed; whereas its protein expression was decreased. Even though Smurf1 (SMAD specific E3 ubiquitin protein ligase 1), HDAC4 (histone deacetylase 4), Smad7, and Crim1 were found to be few of miR-15b's putative target genes, there was increased expression of only Smurf1 gene at mRNA and protein levels by miR-15b inhibitor. miR-15b mimic treatment significantly increased and decreased expressions of Runx2 and Smurf1 proteins, respectively. We further identified that the Smurf1 3'UTR is directly targeted by miR-15b using the luciferase reporter gene system. This is well documented that Smurf1 interacts with Runx2 and degrades it by proteasomal pathway. Hence, based on our results we suggest that miR-15b promotes osteoblast differentiation by indirectly protecting Runx2 protein from Smurf1 mediated degradation. Thus, this study identified that miR-15b can act as a positive regulator for osteoblast differentiation.

Role of glucocorticoid-induced leucine zipper (GILZ) in bone acquisition

Glucocorticoids (GCs) have both anabolic and catabolic effects on bone. However, no GC anabolic effect mediator has been identified to date. Here we show that targeted expression of glucocorticoid-induced leucine zipper (GILZ), a GC anti-inflammatory effect mediator, enhances bone acquisition in mice. Transgenic mice, in which the expression of GILZ is under the control of a 3.6-kb rat type I collagen promoter, exhibited a high bone mass phenotype with significantly increased bone formation rate and osteoblast numbers. The increased osteoblast activity correlates with enhanced osteogenic differentiation and decreased adipogenic differentiation of bone marrow stromal cell cultures in vitro. In line with these changes, the mRNA levels of key osteogenic regulators (Runx2 and Osx) increased, and the level of adipogenic regulator peroxisome proliferator-activated receptor (PPAR) γ2 decreased significantly. We also found that GILZ physically interacts with C/EBPs and disrupts C/EBP-mediated PPARγ gene transcription. In conclusion, our results showed that GILZ is capable of increasing bone acquisition in vivo, and this action is mediated via a mechanism involving the inhibition of PPARγ gene transcription and shifting of bone marrow MSC/progenitor cell lineage commitment in favor of the osteoblast pathway.

Choosing the right type of serum for different applications of human adipose tissue-derived stem cells: influence on proliferation and differentiation abilities

BACKGROUND AIMS

Adipose tissue-derived stem cells (ADSCs) are thought to have great potential in regenerative medicine. A xenoprotein-free culture and handling system is desirable. To date, there is only little and contradictory information about the influence of the different types of human serum on ADSC proliferation and differentiation.

METHODS

First, ADSCs were cultured in media containing regular human serum (HS plus) or fetal calf serum (FCS plus) with supplementation of growth factors for three passages. During passage 4, ADSC proliferative activity and adipogenic, osteogenic and chondrogenic differentiation ability was quantified. Second, ADSCs were cultured with three different human sera (regular human serum [HS], human serum from platelet-poor plasma [SPPP] or human serum from platelet-rich plasma [SPRP]) without supplementation of platelet-derived growth factor and assessed accordingly. The growth factor content of the different types of human sera was determined by means of multiplex protein assay and enzyme-linked immunosorbent assay.

RESULTS

The different sera did not affect ADSC doubling time significantly (P < 0.05). Specific glycerol-3-phosphat-dehydrogenase activity was significantly lower in cultures with SPRP (P < 0.01) compared with the other media compositions. Extracellular calcium deposition was significantly higher in cells differentiated in cultures with HS or SPPP compared with those with SPRP, HS plus or FCS (P < 0.01). Glycosaminoglycan content and collagen 2 were highest in cells cultured with SPRP (P < 0.001).

CONCLUSIONS

Culturing ADSCs in human serum appears to be a reasonable and efficient alternative compared with FCS. With respect to the outcome of a sighted clinical application, it appears to be feasible to handle the cells in a serum suitable for the intended later use.