Effect Of Tumor Microenvironment On The Function Of Mast Cells In Tumor Progression

The growth and development of tumors is regulated by a precise balance between pro-and anti-tumorigenic effects, stimulated by the tumor cells themselves, as well as theirs microenvironment. Tumor microenvironment provides an internal milieu in which tumor cell proliferation and survival and tumor growth and development happen. This microenvironment is a complex system, including different cell types, extracellular matrix (ECM), cytokines and other stromal elements. Cellular components of tumor microenvironment is composed of tumor cells, fibroblasts, smooth muscle cells, endothelial cells, adipocytes, glial cells, and resident and recruited immune and inflammatory cells. The molecular composition of the tumor microenvironment is established jointly by tumor cells as well as non-tumor cells. Interaction of tumor cells with other components of tumor microenvironment are crucial factor determining if tumor cells will progress towards metastasis, if they will stay dormant or if they will disappear. The role of the microenvironment during the study of carcinogenesis is now realized to be of critical importance.There is a growing acceptance that bone marrow-derived myeloid cells can play an active role in tumor growth and angiogenesis. Infiltrating myeloid cells populations include mast cells. Mast cells were first described in 1878, which originate from hematopoietic stem cells in the bone marrow, and they mature in the tissues. They are commonly known for their role in allergic and parasites defense reactions, but the function of mast cells in tumor remains to be characterized in detail. Inflammatory stimuli can activate mast cells to release a diverse array of biologically active products, many of which can benefit the tumor including heparin, IL-8, VEGF, PDGF, NGF and SCF. However, mast cells also release molecules that could be considered detrimental to the tumor include IL-1, IL-6, TNF-αand tryptase. Recently, Mast cells are considered as immunoregulatory cells. They can exert positive immunoregulatory effects on immune cells by presenting antigens to T cells and prompting T cells activation. In addition, Mast cells can mediate negative immunomodulatory functions by producing IL-10. Thus, the prognostic significance of mast cells infiltration into tumors is controversial now. The true role of mast cells in tumor remains to be elucidated. Our experiment is aim to reveal whether mast cells have regulatory role on tumor growth. This experiment is subdivided into three parts.PartⅠEffect of mast cells on tumor growth. In this study, we constructed two related tumor models. First, the mice with tumors approximately 1×1cm2 were referred to late stage model. Next, those whose tumors can be only attached were considered as early stage model. It is notable that the meaning of early or late stage tumor was not totally identical to the conception in clinical research. To investigate the regulatory effect of mast cells on tumor growth, two strategies were adopted, i.e, either mast cells degranulation was inhibited or mice were coinoculated with mast cells and H22 cells. We show that mast cells actively inhibit the growth of tumor by attracting CD8+T cells at early stage in our tumor model. However, the growth of tumor is promted by mast cells at late stage in our tumor model by up-regulatting the expression of IL-10 and migrating Treg cells, which is likely concerned with tumor angiogenesis. What factors induce the dual role of mast cells on tumor growth? A lot of endogenous damage-associated molecular pattern (DAMP) molecules are induced release from necrotic tumor cells derived from abnormal stress, inflammation and hypoxia in tumors. Our previous experimental results show that the more tumor diameter is, the more DAMP molecules are induced in tumor tissues. Furthermore, the expression of IL-10 and surface molecules TLR2,4-1BB and B7-H1 in mast cells are markedly up-regulated at late stage tumor in this experiment. Endogenous DAMP molecules seem to play important role in turning the effect of mast cells on tumor growth. Another experiment in our study shows that the growth of tumor was prompted when mice were coinoculated with H22 cells and mast cells stimulated by high concentration NTC-Ms. There is few mast cells presence in tumor tissures, so it is difficult to discuss the role of mast cells on tumor growth in vivo. We have to investigate the biological behaviours of mast cells in vitro.Part II Regulatory effect of the molecules derived from necrotic tumor cells on mast cells biological property. Our previous experimental results show that there are DAMP representative molecules HMGB1 and HSP70 in NTC-Ms which may mimic tumor milieu in vivo. NTC-Ms are used to stimulate BMMCs in vitro in order to mimic the changes of mast cells in tumor tissure. Some genes concernd with angiogenesis (VEGF, PDGF), tissue remodeling (MMP9) and immune-modulation (IL-10, TGF-β) were up-regulated after stimulation with high concentration NTC-Ms. Furthermore, NTC-Ms treatment markedly up-regulated the expression of TLR4, TLR2 and costimulatory molecules CD80, CD86,4-1BB and CTLA-4 in BMMCs. IL-10 production in NTC-Ms-stimulated mast cells are dependent on the TLR4-PI3K-GSK3β-NF-κB signal pathway. The effect of promoting tumor growth of NTC-Ms-stimulated mast cells is concerned with TLR4 or GSK30 activity. The surface receptors and signal molecules of mast cells are changed in favor of the growth of tumor when they are stimulated with NTC-Ms in vitro.PartⅢEffect of tumor on mast cell precursors numbers and phenotype in mice. PartⅠandⅡshow that mast cells have a regulatory effect on tumor growth, vice versa. To investigate whether tumor has an effect of on mast cell precursors numbers and phenotype in mice, partⅢwas carried out. There are significantly higher proportion of mast cell precursors in bone marrow, spleen and peripheral tissures, but no significant changes of the proportion of TLR2 positive cells in BMCP in tumor-bearing mice. It is obviously higher about the proportion of TLR2 positive cells in peripheral tumor tissures in tumor-bearing mice. In tumor-bearing mice, increased mast cell precursors enter peripheral tumor tissures where the expression of Toll-like receptors is up-regulated when they encounter high concentration endogenous DAMP molecules. The inhibitory effect on tumor growth is turned into promotion when mast cells are instructed by endogenous DAMP molecules in tumor microenvironment.This study shows that mast cells actively inhibit the growth of tumor by attracting CD8+T cells at early stage tumor. With tumor growing, mast cells are impacted by high concentration endogenous DAMP molecules in tumor microenvironment and promot the growth of tumor by up-regulatting the expression of IL-10 and attracting Treg cells into tumor tissues. It is important to grasp this property of mast cells in order to know this older as well as younger immune cell. Furthermore, this study could provide scientific data on the applicability of mast cell-based interventions.