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.
Highlights
Chemo-resistance is still a major obstacle in efforts to overcome acute myeloid leukemia (AML)
We propose that cancer-associated fibroblasts (CAFs) within the bone marrow (BM) of AML could counter the chemo-sensitivity of leukemia cells by producing growth differentiation factor 15 (GDF15)
We hypothesized that the fibers may not directly affect AML patient prognosis, the reticulin fiber density (RFD) score indicated a poor outcome in AML patients
Summary
Chemo-resistance is still a major obstacle in efforts to overcome acute myeloid leukemia (AML). 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. Their contribution to AML has yet to be fully understood. As an important element of the tumor microenvironment, fibroblasts with an activated phenotype, referred to as ‘activated myofibroblasts’ or ‘cancer-associated fibroblasts’ (CAFs), have been reported to play a critical role in the chemo-resistance of solid tumors [2]. CAFs display phenotypes that are similar to those of myofibroblasts derived from quiescent fibroblasts, which are activated when they interact with carcinoma cells during tumorigenesis [3]. We propose that CAFs within the BM of AML could counter the chemo-sensitivity of leukemia cells by producing GDF15
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