CD90low glioma-associated mesenchymal stromal/stem cells promote temozolomide resistance by activating FOXS1-mediated epithelial-mesenchymal transition in glioma cells

Background

The tumour microenvironment contributes to chemotherapy resistance in gliomas, and glioma-associated mesenchymal stromal/stem cells (gaMSCs) are important stromal cell components that play multiple roles in tumour progression. However, whether gaMSCs affect chemotherapy resistance to the first-line agent temozolomide (TMZ) remains unclear. Herein, we explored the effect and mechanism of gaMSCs on resistance to TMZ in glioma cells.

Methods

Human glioma cells (cell line U87MG and primary glioblastoma cell line GBM-1) were cultured in conditioned media of gaMSCs and further treated with TMZ. The proliferation, apoptosis and migration of glioma cells were detected by Cell Counting Kit-8 (CCK-8), flow cytometry and wound-healing assays. The expression of FOXS1 in glioma cells was analysed by gene microarray, PCR and Western blotting. Then, FOXS1 expression in glioma cells was up- and downregulated by lentivirus transfection, and markers of the epithelial-mesenchymal transformation (EMT) process were detected. Tumour-bearing nude mice were established with different glioma cells and treated with TMZ to measure tumour size, survival time and Ki-67 expression. Finally, the expression of IL-6 in gaMSC subpopulations and its effects on FOXS1 expression in glioma cells were also investigated.

Results

Conditioned media of gaMSCs promoted the proliferation, migration and chemotherapy resistance of glioma cells. The increased expression of FOXS1 and activation of the EMT process in glioma cells under gaMSC-conditioned media were detected. The relationship of FOXS1, EMT and chemotherapy resistance in glioma cells was demonstrated through the regulation of FOXS1 expression in vitro and in vivo. Moreover, FOXS1 expression in glioma cells was increased by secretion of IL-6 mainly from the CD90^low gaMSC subpopulation.

Conclusions

CD90^low gaMSCs could increase FOXS1 expression in glioma cells by IL-6 secretion, thereby activating epithelial-mesenchymal transition and resistance to TMZ in glioma cells. These results indicate a new role of gaMSCs in chemotherapy resistance and provide novel therapeutic targets.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02458-8.

Cell fusion in cancer hallmarks: Current research status and future indications

Cell fusion is involved in several physiological processes, such as reproduction, development and immunity. Although cell fusion in tumors was reported 130 years ago, it has recently attracted great interest, with recent progress in tumorigenesis research. However, the role of cell fusion in tumor progression remains unclear. The pattern of cell fusion and its role under physiological conditions are the basis for our understanding of the pathological role of cell fusion. However, the role of cell fusion in tumors and its functions are complicated. Cell fusion can directly increase tumor heterogeneity by forming polyploids or aneuploidies. Several studies have reported that cell fusion is associated with tumorigenesis, metastasis, recurrence, drug resistance and the formation of cancer stem cells. Given the diverse roles cell fusion plays in different tumor phenotypes, methods based on targeted cell fusion have been designed to treat tumors. Research on cell fusion in tumors may provide novel ideas for further treatment.

Growth factors contribute to the mediation of angiogenic capacity of glioma-associated mesenchymal stem cells

Mesenchymal stem cells (MSCs) are important components of stromal cell populations and serve a crucial role in tumor growth and progression. Previously, our laboratory successfully isolated and cultured MSCs from human glioma issues and demonstrated that glioma-associated mesenchymal stem cells (gb-MSCs) participate in and maintain tumor angiogenesis. Furthermore, growth factors, such as fibroblast growth factor and vascular endothelial cell growth factor, were demonstrated to be associated with endothelial cell tube formation. However, the effect of transforming growth factor β1 (TGF-β1) and platelet-derived growth factor-BB (PDGF-BB) on the angiogenic activity of gb-MSCs remains unknown. The present study aimed therefore to explore their effects in gb-MSCs angiogenesis. In the present study, gb-MSCs were isolated from patients with glioma and were characterized using flow cytometry and differentiation experiments. Furthermore, the results from tube formation assay revealed that TGF-β1 and PDGF-BB could mediate the angiogenic capacity of gb-MSCs in vitro. In addition, results from immunofluorescence demonstrated that gb-MSCs expressed TGF-β1R and PDGFR, which are the receptors for TGF-β1 and PDGF-BB, respectively. Taken together, these findings indicated that TGF-β1 and PDGF-BB may serve a crucial role in mediating gb-MSC angiogenesis, which might provide a therapeutic strategy for targeting the angiogenic capacity of gb-MSCs in patients with glioma.

Roles of long non-coding RNAs in the hallmarks of glioma

Glioma is one of the most common types of tumor of the central nervous system. Due to the aggressiveness and invasiveness of high-level gliomas, the survival time of patients with these tumors is short, at ~15 months, even after combined treatment with surgery, radiotherapy and/or chemotherapy. Recently, a number of studies have demonstrated that long non-coding RNA (lncRNAs) serve crucial roles in the multistep development of human gliomas. Gliomas acquire numerous biological abilities during multistep development that collectively constitute the hallmarks of glioma. Thus, in this review, the roles of lncRNAs associated with glioma hallmarks and the current and future prospects for their development are summarized.

CD90 determined two subpopulations of glioma-associated mesenchymal stem cells with different roles in tumour progression

Human glioma-associated mesenchymal stem cells (gbMSCs) are the stromal cell components that contribute to the tumourigenesis of malignant gliomas. Recent studies have shown that gbMSCs consist of two distinct subpopulations (CD90⁺ and CD90⁻ gbMSCs). However, the different roles in glioma progression have not been expounded. In this study, we found that the different roles of gbMSCs in glioma progression were associated with CD90 expression. CD90^high gbMSCs significantly drove glioma progression mainly by increasing proliferation, migration and adhesion, where as CD90^low gbMSCs contributed to glioma progression chiefly through the transition to pericytes and stimulation of vascular formation via vascular endothelial cells. Furthermore, discrepancies in long non-coding RNAs and mRNAs expression were verified in these two gbMSC subpopulations, and the potential underlying molecular mechanism was discussed. Our data confirm for the first time that CD90^high and CD90^low gbMSCs play different roles in human glioma progression. These results provide new insights into the possible future use of strategies targeting gbMSC subpopulations in glioma patients.

Current status and potential challenges of mesenchymal stem cell-based therapy for malignant gliomas

Glioma, which accounts for more than 30% of primary central nervous system tumours, is characterised by symptoms such as headaches, epilepsy, and blurred vision. Glioblastoma multiforme is the most aggressive, malignant, and lethal brain tumour in adults. Even with progressive combination treatment with surgery, radiotherapy, and chemotherapy, the prognosis for glioma patients is still extremely poor. Compared with the poor outcome and slowly developing technologies for surgery and radiotherapy, the application of targeted chemotherapy with a new mechanism has become a research focus in this field.

Moreover, targeted therapy is promising for most solid tumours. The tumour-tropic ability of stem cells, including neural stem cells and mesenchymal stem cells, provides an alternative therapeutic approach. Thus, mesenchymal stem cell-based therapy is based on a tumour-selective capacity and has been thought to be an effective anti-tumour option over the past decades. An increasing number of basic studies on mesenchymal stem cell-based therapy for gliomas has yielded complex outcomes.

In this review, we summarise the biological characteristics of human mesenchymal stem cells, and the current status and potential challenges of mesenchymal stem cell-based therapy in patients with malignant gliomas.

Regulation of leptin by agouti

Dominant mutations at the mouse Agouti locus lead to ectopic expression of the Agouti gene and exhibit diabetes, obesity, and yellow coat color. Obese yellow mice are hyperinsulinemic and hyperleptinemic, and we hypothesized that Agouti directly induces leptin secretion. Accordingly, we used transgenic mice expressing agouti in adipocytes (under the control of aP2 promoter, aP212) to examine changes in leptin levels. Agouti expression in adipose tissue did not significantly alter food intake, weight gain, fat pad weight, or insulinemia; however, the transgenic mice were hyperglycemic. We demonstrated that plasma leptin levels are approximately twofold higher in aP212 transgenic mice compared with their respective controls, whereas ubiquitous expression of agouti (under the control of beta-actin promoter, BAP20) led to a sixfold increase in leptin. Insulin treatment of aP212 mice increased adipocyte leptin content without affecting plasma leptin levels. These findings were further confirmed in vitro in 3T3-L1 adipocytes treated with recombinant Agouti protein and/or insulin. Agouti but not insulin significantly increased leptin secretion, indicating that insulin enhances leptin synthesis but not secretion while Agouti increases both leptin synthesis and secretion. This increased leptin synthesis and secretion was due to increased leptin mRNA levels by Agouti. Interestingly, agouti regulation of leptin was not mediated by melanocortin receptor 4, previously implicated in agouti regulation of food intake. These results suggest that increased leptin secretion by agouti may serve to limit agouti-induced obesity, independent of melanocortin receptor antagonism, and indicate that interaction between obesity genes may play a key role in obesity.

The agouti gene product stimulates pancreatic [beta]-cell Ca2+ signaling and insulin release

Ubiquitous expression of the mouse agouti gene results in obesity and hyperinsulinemia. Human agouti is expressed in adipose tissue, and we found recombinant agouti protein to stimulate lipogenesis in adipocytes in a Ca(2+)-dependent fashion. However, adipocyte-specific agouti transgenic mice only became obese in the presence of hyperinsulinemia. Because intracellular Ca(2+) concentration ([Ca(2+)](i)) is a primary signal for insulin release, and we have shown agouti protein to increase [Ca(2+)](i) in several cell types, we examined the effects of agouti on [Ca(2+)](i) and insulin release. We demonstrated the expression of agouti in human pancreas and generated recombinant agouti to study its effects on Ca(2+) signaling and insulin release. Agouti (100 nM) stimulated Ca(2+) influx, [Ca(2+)](i) increase, and a marked stimulation of insulin release in two beta-cell lines (RIN-5F and HIT-T15; P < 0. 05). Agouti exerted comparable effects in isolated human pancreatic islets and beta-cells, with a 5-fold increase in Ca(2+) influx (P < 0.001) and a 2.2-fold increase in insulin release (P < 0.01). These data suggest a potential role for agouti in the development of hyperinsulinemia in humans.