Osteogenic differentiation of bone marrow mesenchymal stem cells by adenovirus-mediated expression of leptin

The role of adipokines in osteoporosis management: a mini review

The prevalence of osteoporosis has been on the rise globally. With ageing populations, research has sought therapeutic solutions in novel areas. One such area is that of the adipokines. Current literature points to an important role for these chemical mediators in relation to bone metabolism. Well-established adipokines have been broadly reported upon. These include adiponectin and leptin. However, other novel adipokines such as visfatin, nesfatin-1, meteorin-like protein (Metrnl), apelin and lipocalin-2 are starting to be addressed pre-clinically and clinically. Adipokines hold pro-inflammatory and anti-inflammatory properties that influence the pathophysiology of various bone diseases. Omentin-1 and vaspin, two novel adipokines, share cardioprotective effects and play essential roles in bone metabolism. Studies have reported bone-protective effects of omentin-1, whilst others report negative associations between omentin-1 and bone mineral density. Lipocalin-2 is linked to poor bone microarchitecture in mice and is even suggested to mediate osteoporosis development from prolonged disuse. Nesfatin-1, an anorexigenic adipokine, has been known to preserve bone density. Animal studies have demonstrated that nesfatin-1 treatment limits bone loss and increases bone strength, suggesting exogenous use as a potential treatment for osteopenic disorders. Pre-clinical studies have shown adipokine apelin to have a role in bone metabolism, mediated by the enhancement of osteoblast genesis and the inhibition of programmed cell death. Although many investigations have reported conflicting findings, sufficient literature supports the notion that adipokines have a significant influence on the metabolism of bone. This review aims at highlighting the role of novel adipokines in osteoporosis while also discussing their potential for treating osteoporosis.

Effect of Expansion Media on Functional Characteristics of Bone Marrow-Derived Mesenchymal Stromal Cells

The therapeutic efficacy of mesenchymal stromal cells (MSCs) has been shown to rely on their immunomodulatory and regenerative properties. In order to obtain sufficient numbers of cells for clinical applications, MSCs have to be expanded ex vivo. Expansion media with xenogeneic-free (XF) growth-promoting supplements like human platelet lysate (PL) or serum- and xenogeneic-free (SF/XF) formulations have been established as safe and efficient, and both groups provide different beneficial qualities. In this study, MSCs were expanded in XF or SF/XF media as well as in mixtures thereof. MSCs cultured in these media were analyzed for phenotypic and functional properties. MSC expansion was optimal with SF/XF conditions when PL was present. Metabolic patterns, consumption of growth factors, and secretome of MSCs differed depending on the type and concentration of supplement. The lactate per glucose yield increased along with a higher proportion of PL. Many factors in the supernatant of cultured MSCs showed distinct patterns depending on the supplement (e.g., FGF-2, TGFβ, and insulin only in PL-expanded MSC, and leptin, sCD40L PDGF-AA only in SF/XF-expanded MSC). This also resulted in changes in cell characteristics like migratory potential. These findings support current approaches where growth media may be utilized for priming MSCs for specific therapeutic applications.

Adipokines at the crossroads of obesity and mesenchymal stem cell therapy

Mesenchymal stem cell (MSC) therapy is an emerging treatment strategy to counteract metabolic syndromes, including obesity and its comorbid disorders. However, its effectiveness is challenged by various factors in the obese environment that negatively impact MSC survival and function. The identification of these detrimental factors will provide opportunities to optimize MSC therapy for the treatment of obesity and its comorbidities. Dysregulated production of adipokines, a group of cytokines and hormones derived from adipose tissue, has been postulated to play a pivotal role in the development of obesity-associated complications. Intriguingly, adipokines have also been implicated in the modulation of viability, self-renewal, proliferation, and other properties of MSC. However, the involvement of adipokine imbalance in impaired MSC functionality has not been completely understood. On the other hand, treatment of obese individuals with MSC can restore the serum adipokine profile, suggesting the bidirectionality of the adipokine-MSC relationship. In this review, we aim to discuss the current knowledge on the central role of adipokines in the crosstalk between obesity and MSC dysfunction. We also summarize recent advances in the use of MSC for the treatment of obesity-associated diseases to support the hypothesis that adipokines modulate the benefits of MSC therapy in obese patients.

Altered expression of leptin and leptin receptor in the development of immune-mediated aplastic anemia in mice

The current study aimed to explore the levels of leptin (LEP) and LEP receptor (LEP-R) on the progression of aplastic anemia (AA) with bone marrow fat conversion. An AA model was developed by infusing C57BL/6 lymph node cells into BALB/c mice. At 0, 3, 6, 9, 12, 15 and 18 days after modeling, routine blood counts, bone marrow biopsy slides, lymphocyte subsets (CD4⁺ and CD8⁺ T cells) and cytokine levels [including interleukin (IL)-2, IL-4, IL-5 and interferon-γ] were assessed. LEP and LEP-R levels in peripheral blood serum, mesenchymal stem cells (MSCs) and bone marrow were also analyzed by enzyme-linked immunosorbent assay, polymerase chain reaction and immunohistochemistry. The relevance of LEP, LEP-R and other factors was analyzed by Pearson's correlation analysis. Peripheral pancytopenia (reduced count of white blood cells, red blood cells, hemoglobin and platelets), abnormal immune factor levels and histological changes in bone marrow sections were detected in the AA model mice, suggesting that these mice mimicked the pathological changes commonly observed in AA. In addition, following the establishment of AA, the LEP level was gradually increased and the LEP-R level was reduced in the mice over time (P<0.05). The expression of adipogenic genes, including CCAAT/enhancer-binding protein (C/EBP)α, C/EBPβ and peroxisome proliferator-activated receptor γ, was markedly increased, while the expression of the osteogenic gene runt-related transcription factor 2 was reduced compared with the levels in the control group (P<0.05). Taken together, damage to LEP-R may lead to dysregulation of LEP and the enhancement of MSCs to differentiate into adipocytes, resulting in excessive fat in bone marrow of AA patients.

Microenvironmental factors that regulate mesenchymal stem cells: lessons learned from the study of heterotopic ossification

Bone marrow contains a non-hematopoietic, clonogenic, multipotent population of stromal cells that are later called mesenchymal stem cells (MSC). Similar cells that share many common features with MSC are also found in other organs, which are thought to contribute both to normal tissue regeneration and to pathological processes such as heterotopic ossification (HO), the formation of ectopic bone in soft tissue. Understanding the microenvironmental factors that regulate MSC in vivo is essential both for understanding the biology of the stem cells and for effective translational applications of MSC. Unfortunately, this important aspect has been largely underappreciated. This review tries to raise the attention and highlight this critical issue by updating the relevant literature along with discussions of the key issues in the area.

Leptin Receptor Metabolism Disorder in Primary Chondrocytes from Adolescent Idiopathic Scoliosis Girls

To investigate the underlying mechanisms of low metabolic activity of primary chondrocytes obtained from girls with adolescent idiopathic scoliosis (AIS); AIS is a spine-deforming disease that often occurs in girls. AIS is associated with a lower bone mass than that of healthy individuals and osteopenia. Leptin was shown to play an important role in bone growth. It can also regulate the function of chondrocytes. Changes in leptin and Ob-R levels in AIS patients have been reported in several studies. The underlying mechanisms between the dysfunction of peripheral leptin signaling and abnormal chondrocytes remain unclear; The following parameters were evaluated in AIS patients and the control groups: total serum leptin levels; Ob-R expression in the plasma membrane of primary chondrocytes; JAK2 and STAT3 phosphorylation status. Then, we inhibited the lysosome and proteasome and knocked down clathrin heavy chain (CHC) expression in primary chondrocytes isolated from girls with AIS and evaluated Ob-R expression. We investigated the effects of leptin combined with a lysosome inhibitor or CHC knockdown in primary chondrocytes obtained from AIS patients; Compared with the controls, AIS patients showed similar total serum leptin levels, reduced JAK2 and STAT3 phosphorylation, and decreased cartilage matrix synthesis in the facet joint. Lower metabolic activity and lower membrane expression of Ob-R were observed in primary chondrocytes from the AIS group than in the controls. Lysosome inhibition increased the total Ob-R content but had no effect on the membrane expression of Ob-R or leptin’s effects on AIS primary chondrocytes. CHC knockdown upregulated the membrane Ob-R levels and enhanced leptin’s effects on AIS primary chondrocytes; The underlying mechanism of chondrocytes that are hyposensitive to leptin in some girls with AIS is low plasma membrane Ob-R expression that results from an imbalance between the rate of receptor endocytosis and the insertion of newly synthesized receptors into the membrane.

Fate decision of mesenchymal stem cells: adipocytes or osteoblasts?

Mesenchymal stem cells (MSCs), a non-hematopoietic stem cell population first discovered in bone marrow, are multipotent cells capable of differentiating into mature cells of several mesenchymal tissues, such as fat and bone. As common progenitor cells of adipocytes and osteoblasts, MSCs are delicately balanced for their differentiation commitment. Numerous in vitro investigations have demonstrated that fat-induction factors inhibit osteogenesis, and, conversely, bone-induction factors hinder adipogenesis. In fact, a variety of external cues contribute to the delicate balance of adipo-osteogenic differentiation of MSCs, including chemical, physical, and biological factors. These factors trigger different signaling pathways and activate various transcription factors that guide MSCs to commit to either lineage. The dysregulation of the adipo-osteogenic balance has been linked to several pathophysiologic processes, such as aging, obesity, osteopenia, osteopetrosis, and osteoporosis. Thus, the regulation of MSC differentiation has increasingly attracted great attention in recent years. Here, we review external factors and their signaling processes dictating the reciprocal regulation between adipocytes and osteoblasts during MSC differentiation and the ultimate control of the adipo-osteogenic balance.

Genetic Engineering of Mesenchymal Stem Cells for Regenerative Medicine

Mesenchymal stem cells (MSCs), which can be obtained from various organs and easily propagated in vitro, are one of the most extensively used types of stem cells and have been shown to be efficacious in a broad set of diseases. The unique and highly desirable properties of MSCs include high migratory capacities toward injured areas, immunomodulatory features, and the natural ability to differentiate into connective tissue phenotypes. These phenotypes include bone and cartilage, and these properties predispose MSCs to be therapeutically useful. In addition, MSCs elicit their therapeutic effects by paracrine actions, in which the metabolism of target tissues is modulated. Genetic engineering methods can greatly amplify these properties and broaden the therapeutic capabilities of MSCs, including transdifferentiation toward diverse cell lineages. However, cell engineering can also affect safety and increase the cost of therapy based on MSCs; thus, the advantages and disadvantages of these procedures should be discussed. In this review, the latest applications of genetic engineering methods for MSCs with regenerative medicine purposes are presented.

Increased osteogenesis in osteoporotic bone marrow stromal cells by overexpression of leptin

Osteoporosis leads to increased bone fractures and net bone loss, in part because of the dysfunction of bone marrow stromal cells (BMSCs). Leptin is an adipokine that plays important roles in many biological processes, including the regulation of the actions of mesenchymal stem cells. Our aim is to investigate the osteogenic effects of leptin in osteoporotic BMSCs in vitro and in vivo. The leptin gene was transferred into BMSCs isolated from osteoporotic rats by using recombinant adenoviruses. Once the gene and protein expression of leptin had been confirmed, MTT assays were performed; leptin overexpression was confirmed not to affect the viability of osteoporotic BMSCs. However, alkaline phosphatase (ALP) activity measurements, Alizarin red staining and analyses by quantitative real-time reverse transcription with the polymerase chain reaction revealed that leptin upregulated ALP activity, mineral deposition and the mRNA levels of runt-related transcription factor 2, ALP and collagen type І. Lastly, the effects of leptin on osteogenic differentiation were assessed in vivo. Cells transfected with leptin exhibited increased osteogenic differentiation and enhanced formation of bone-like structures. This study thus reveals, for the first time, that the overexpression of leptin in osteoporotic BMSCs (1) enhances their capacity to differentiate into osteoblasts and to form bone-like tissue and (2) might be a useful skeletal regenerative therapy in osteoporotic patients.

Selective glucocorticoid receptor modulator compound A, in contrast to prednisolone, does not induce leptin or the leptin receptor in human osteoarthritis synovial fibroblasts

OBJECTIVE

Glucocorticoids are powerful anti-inflammatory compounds that also induce the expression of leptin and leptin receptor (Ob-R) in synovial fibroblasts through TGF-βsignalling and Smad1/5 phosphorylation. Compound A (CpdA), a selective glucocorticoid receptor agonist, reduces inflammation in murine arthritis models and does not induce diabetes or osteoporosis, thus offering an improved risk:benefit ratio in comparison with glucocorticoids. Due to the detrimental role of leptin in OA pathogenesis, we sought to determine whether CpdA also induced leptin and Ob-R protein expression as observed with prednisolone.

METHODS

Human synovial fibroblasts and chondrocytes were isolated from the synovium and cartilage of OA patients after joint surgery. The cells were treated with prednisolone, TGF-β1, TNF-α and/or CpdA. Levels of leptin, IL-6, IL-8, MMP-1 and MMP-3 were measured by ELISA and expression levels of Ob-R phospho-Smad1/5, phospho-Smad2, α-tubulin and glyceraldehyde 3-phosphate dehydrogenase were analysed by western blotting.

RESULTS

CpdA, unlike prednisolone, did not induce leptin secretion or Ob-R protein expression in OA synovial fibroblasts. Moreover, CpdA decreased endogenous Ob-R expression and down-regulated prednisolone-induced leptin secretion and Ob-R expression. Mechanistically, CpdA, unlike prednisolone, did not induce Smad1/5 phosphorylation. CpdA, similarly to prednisolone, down-regulated endogenous and TNF-α-induced IL-6, IL-8, MMP-1 and MMP-3 protein secretion. The dissociative effect of CpdA was confirmed using chondrocytes with no induction of leptin secretion, but with a significant decrease in IL-6, IL-8, MMP-1 and MMP-3 protein secretion.

CONCLUSION

CpdA, unlike prednisolone, did not induce leptin or Ob-R in human OA synovial fibroblasts, thereby demonstrating an improved risk:benefit ratio.

The effects of PPAR-γ inhibition on gene expression and the progression of induced osteogenic differentiation of human mesenchymal stem cells

Mesenchymal stem cells (MSCs) can differentiate into several cell types, such as osteoblasts and adipocytes, both in vitro and in vivo. Although these two differentiation pathways are distinct from each other, cross-communication between cells of the two lineages exists both systemically and peripherally in the tissue. The transcription factor PPAR-γ, the main switch in adipogenic differentiation of MSCs, has previously been described to have a negative effect on osteogenic differentiation. The aim of this study was to investigate the effect of PPAR-γ inhibition on osteogenic differentiation of human MSCs, in vitro. Extracellular matrix analysis and quantification of osteogenic markers, revealed how these cells respond when the adipogenic differentiation pathway is blocked during induction of osteogenic differentiation. The inhibition leads to a significant increase in mineralization of the extracellular matrix, as well as an increased activity or up-regulated gene expression of alkaline phosphatase, the key enzyme involved in matrix mineralization. Furthermore, it was also demonstrated by microarray analysis, that PPAR-γ inhibition during osteogenic induction leads to a significant up-regulation of a number of genes related to both osteogenesis and adipogenesis such as c10orf10, leptin, GDF5 and KLF15. In conclusion, inhibition of PPAR-γ during induction of osteogenesis leads to increased osteogenic differentiation of human MSCs.

Umbilical cord fibroblasts: Could they be considered as mesenchymal stem cells?

In cell therapy protocols, many tissues were proposed as a source of mesenchymal stem cells (MSC) isolation. So far, bone marrow (BM) has been presented as the main source of MSC despite the invasive isolation procedure related to this source. During the last years, the umbilical cord (UC) matrix was cited in different studies as a reliable source from which long term ex vivo proliferating fibroblasts were isolated but with contradictory data about their immunophenotype, gene expression profile, and differentiation potential. Hence, an interesting question emerged: Are cells isolated from cord matrix (UC-MSC) different from other MSCs? In this review, we will summarize different studies that isolated and characterized UC-MSC. Considering BM-MSC as gold standard, we will discuss if UC-MSC fulfill different criteria that define MSC, and what remain to be done in this issue.

Cyclic-RGD peptides increase the adenoviral transduction of human mesenchymal stem cells

Human mesenchymal stem cells (hMSCs) have been extensively explored for drug delivery applications due to their safety, immunomodulatory properties, and ability to differentiate into new tissues. The experiments presented in this study were designed to determine peptide-based mechanisms to increase the adenoviral transduction of hMSCs for the purpose of improving their capacity as drug delivery vehicles. Specifically, we demonstrated that cyclic- RGD peptides increased the internalization of adenoviruses into MSCs. MSCs treated with cyclic-RGD peptides had a transduction efficiency of 76.6%±4%, which was significantly greater than the 23.5%±12.2% transduction efficiency of untreated stem cells (P<0.05). Blocking endocytosis with inhibitors of dynamin or actin polymerization decreased the cyclic-RGD-mediated increase in transduction efficiency. MSCs treated with cyclic-RGD and adenoviruses carrying the gene for bone morphogenetic protein-2 produced significantly greater concentrations of this growth factor compared to stem cells treated with only adenoviruses or adenoviruses cocultured with cyclic-RAD peptides. Furthermore, this stem cell-produced bone morphogenetic protein induced alkaline phosphatase expression in C2C12 cells indicating growth factor bioactivity. Taken together, these studies suggest that cyclic-RGD peptides could be used to increase the adenoviral transduction of hMSCs and increase their therapeutic potential.

Differential signalling through ALK-1 and ALK-5 regulates leptin expression in mesenchymal stem cells

Leptin plays a central role in maintaining energy balance, with multiple other systemic effects. Despite leptin importance in peripheral regulation of mesenchymal stem cells (MSC) differentiation, little is known about its expression mechanism. Leptin is often described as adipokine, while it is expressed by other cell types. We have recently shown an in vitro leptin expression, enhanced by glucocorticoids in synovial fibroblasts (SVF). Here, we investigated leptin expression in MSC from bone marrow (BM-MSC) and umbilical cord matrix (UMSC). Results showed that BM-MSC, but not UMSC, expressed leptin that was strongly enhanced by glucocorticoids. Transforming growth factor β1 (TGF-β1) markedly inhibited the endogenous- and glucocorticoid-induced leptin expression in BM-MSC. Since TGF-β1 was shown to signal via ALK-5-Smad2/3 and/or ALK-1-Smad1/5 pathways, we analyzed the expression of proteins from both pathways. In BM-MSC, TGF-β1 increased phosphorylated Smad2 (p-Smad2) expression, while ALK-5 inhibitor (SB431542) induced leptin expression and significantly restored TGF-β1-induced leptin inhibition. In addition, both prednisolone and SB431542 increased p-Smad1/5 expression. These results suggested the ALK-5-Smad2 pathway as an inhibitor of leptin expression, while ALK-1-Smad1/5 as an activator. Indeed, Smad1 expression silencing induced leptin expression inhibition. Furthermore, prednisolone enhanced the expression of TGF-βRII while decreasing p-Smad2 in BM-MSC and SVF but not in UMSC. In vitro differentiation revealed differential osteogenic potential in SVF, BM-MSC, and UMSC that was correlated to their leptin expression potential. Our results suggest that ALK-1/ALK-5 balance regulates leptin expression in MSC. It also underlines UMSC as leptin nonproducer MSC for cell therapy protocols where leptin expression is not suitable.