No abstract

BackgroundChemo-resistance is still a major obstacle in efforts to overcome acute myeloid leukemia (AML). An emerging concept has proposed that interactions between the bone marrow (BM) microenvironment and leukemia cells reduce the sensitivity of the leukemia cells to chemotherapy. As an important element of the tumor microenvironment, the cancer-associated fibroblasts (CAFs) are considered to be activated modulators in the chemo-resistance of many solid tumors. But their contribution to AML has yet to be fully understood. Here we report a critical role for CAFs which were thought to be a survival and chemo-protective factor for leukemia cells.MethodsA retrospective study on the BM biopsies from 63 primary AML patients and 59 normal controls was applied to quantitative analysis the fiber stroma in the BM sections. Then immunohistochemistry on the BM biopsies were used to detect the makers of the CAFs. Their effects on drug resistance of leukemia cells were further to be assessed by co-cultured experiments in vitro. Moreover, the possible mechanisms involved in CAF-mediated chemo-protection of AML cells was investigated by antibody neutralization and siRNA knockdown experiments, with particular emphasis on the role of GDF15.ResultsIn our study, excessive reticular fibers in the BM led to higher frequency of relapse and mortality in primary AML patients, bringing the inspiration for us to investigate the functional roles of the fiber-devied cells. We declared that the CAF cells which expressed higher levels of FSP1, α-SMA or FAP protein were widely distributed in the marrow of AML. Then in vitro co-cultured tests showed that these CAFs could protect leukemia cell lines (THP-1/K562) from chemotherapy. Interestingly, this effect could be decreased by either treatment with a neutralizing anti-GDF15 antibody or knockdown GDF15 (with siGDF15) in CAFs. Furthermore, we also confirmed that the GDF15+ cells mainly co-localized with FAP, which was identified as the typical phenotype of CAFs in the BM stroma.ConclusionsWe firstly demonstrate that the functional CAFs are widespread within the BM of AML patients and should be a critical chemo-protective element for AML cells by producing amount of GDF15.Electronic supplementary materialThe online version of this article (doi:10.1186/s13046-016-0405-0) contains supplementary material, which is available to authorized users.

BackgroundThe adipocyte remodeling, including of the morphological change, might indicate special pathological function. Our previous study found that the morphological remodeling of larger marrow adipocytes into small marrow adipocytes correlates with a poor prognosis for acute myeloid leukemia (AML) patients. However, the mechanisms contributed to the marrow adipocyte remodeling are still poorly understood.MethodsGDF15 expression was analyzed by RT-qPCR and western blotting assays in the leukemic cells. The enhancing and antibody neutralization tests in vitro were employed to evaluate the effect of GDF15 on the morphology of mature adipocytes. CCK8 test was used to detect the proliferation of leukemic cells after co-cultivation with small marrow adipocytes. Flow cytometry was used to analysis the proportion of cell cycle of leukemic cells. Immunofluorescence staining and linear analysis were applied to verify the GDF15 expression and the relationship between GDF15 and small marrow adipocytes in AML patients.ResultsIn this study, we found that leukemic cell lines not only expressed significantly higher growth differentiation factor 15 (GDF15) than the other three cytokines associated with adipocyte differentiation in RNA level but also secreted GDF15 factor. Furthermore, the in vitro experiments demonstrated that GDF15 was involved in the conversion of small marrow adipocytes from larger marrow adipocytes. Correspondingly, the leukemic cells proliferated more rapidly through regulating the cell cycle when co-cultured with GDF15-induced small marrow adipocytes. The immunofluorescence staining on the bone marrow sections of AML patients further exhibited that GDF15 was partly produced by leukemic cells. The positive correlation between the concentration of GDF15 in the marrow aspirates and the number and the volume of small marrow adipocytes might suggest the contribution of GDF15 in AML patients (r = 0.72, r = 0.67).ConclusionsGDF15 secreted by leukemic cells was involved in the morphological remodeling of marrow adipocytes, which can in turn promote leukemic cell growth, indicating that GDF15 may be a promising treatment target for AML patients.Electronic supplementary materialThe online version of this article (10.1186/s13046-018-0738-y) contains supplementary material, which is available to authorized users.