Biological Role And Regulatory Mechanisms Of Tumor-associate Macrophages In Promoting Stemness And Invasiveness Of Glioma Cells

Glioblastoma(GBM,WHO IV)is the most malignant and lethal glioma.Patients with GBM are suffered from dismal prognoses despite treatment with multimodal therapies.The remarkable pathological feature of GBM is aggressiveness and dissemination,leading to high recurrence rates.One of the most important hallmarks of GBM cells is heterogeneity.Evidences have showed that glioma stem-like cells(GSCs)facility tumor initiation,invasion and recurrence,and GSCs are proved to be a potential target for GBM treatment.GSC represents a subpopulation of cancer cells that possess stem-like characteristics such as self-renewing and tumor initiation.Latest evidence has showed that cancer cells with stem-like phenotype exhibit higher invasive capabilities and contribute to poorer outcomes of patients,but the mechanism is still unclear.It has been widely confirmed that the biological behavior of GSCs is mediated by tumor microenvironment.Tumor associated macrophages(TAMs)are abundantly infiltrated in GBM niche to promote the progression of GBM by increasing invasion and suppressing immune response.Recent evidence has also showed that TAMs plays a critical role in GSCs-mediated tumor development,and disturbing TAM-GSC interaction has been proved to have therapeutic potential for glioma patients.However,the multilayered relationship between TAMs and CSCs is intricate,how TAMs promote invasion and stem-like traits of GBM cells has not been fully defined.In this study,we demonstrate IL-22 secreted by TAMs in GBM tissue contributes to the chemotherapy resistance and stemness of GBM cells,IL-22 can also activate macrophage into a M(IL-22)phenotype,and M(IL-22)promotes migration and invasion of GBM cells both in vitro and in vivo.At last,we find that CCL8 is highly expressed by glioma-associated macrophages,and triggers the invasion and stemness of GBM cells through increasing ERK1/2 phosphorylation.The main findings and conclusions of this study are summarized as follows:1.We demonstrate that the main cellular source of IL-22 in glioma tissue is CD14~+/CD16~-/CD163~+/HLA-DR~+TAMs,and the secretion of glioma cells can induce macrophages to secrete IL-22.Il-22 signaling is dramatically activated in recrudescent glioma samples and IL-22R?1 is highly expressed by glioma stem cells.Exogenously adding IL-22increases the stemness and chemotherapy resistance of glioma cells.2.We find that IL-22R?1 is expressed by macrophages from both human and mouse,and IL-22 can activate macrophages into a M(IL-22)phenotype,which is different from“M1”or“M2”phenotype.M(IL-22)is bioinformatically identified as tumor matrisome-associated macrophages,and the secretion of M(IL-22)promotes migration and invasion of glioma cells.In an orthotopic glioma-bearing mice model,M(IL-22)exhibit protumoral behavior.Four M(IL-22)signature factors,IL1?,IL-1Ra,CXCL9 and TNFSF8,are correlated with poor prognosis of GBM patients.3.We uncover that TAMs secrete CCL8 to promote the invasion and stemness of glioma.The presence of CCL8 in tumor microenvironment contributes to more aggressive tumor development and faster tumor growth in vivo.CCL8 can augment the stem-like traits of GBM cells via CCR1 and CCR5.Furthermore,ERK1/2 activation is the downstream mechanism that mediates CCL8-induced invasion and stemness of GBM cells.Our findings provide an insight in understanding the heterogeneous TAMs and CSCs,and lay the basis of developing new glioma therapeutic approaches for specifically targeting TAMs in the future.