Lysosomal acid lipase is critical for myeloid-derived suppressive cell differentiation, development, and homeostasis

Lysosomal acid lipase （LAL） cleaves cholesteryl esters （CE） and triglycerides （TG） to generate cholesterol and free fatty acid in lysosomes of cells. The down-stream metabolic products of fatty acids are ligands for activation of peroxisome proliferator-activated re-ceptor gamma （PPARγ）. Accumulation of CEs and TGs is resulted from lack of functional LAL in lysosomes of cells, especially in myeloid cells. One characteristic phenotype in LAL knock-out （ lal-/- ） mice is systemic elevation of myeloid-derived suppressive cells （MDSCs）. MDSCs infltrate into multiple distal organs, alter T cell development, and suppress T cell proliferation and lym-phokine production in lal-/- mice, which lead to severe pathogeneses in multiple organs. The gene transcrip-tional profle analysis in MDSCs from the bone marrow has identified multiple defects responsible for MDSCs malformation and malfunction in lal-/- mice, including G protein signaling, cell cycles, glycolysis metabolism, mitochondrial bioenergetics, mTOR pathway etc. In a sep-arate gene transcriptional profle analysis in the lung of lal-/- mice, matrix metalloproteinase 12 （MMP12） and apoptosis inhibitor 6 （Api6） are highly overexpressed due to lack of ligand synthesis for PPARγ. PPARγ nega-tively regulates MMP12 and Api6. Blocking the PPAR signaling by overexpression of a dominant negative PPARγ （dnPPARγ） form, or overexpressing MMP12 or Api6 in myeloid or lung epithelial cells in inducible transgenic mouse models results in elevated MDSCs and infammation-induced tumorigenesis. These stud-ies demonstrate that LAL and its downstream effectors are critical for MDSCs development, differentiation and malfunction.

Contribution of myeloid-derived suppressor cells to tumor-induced immune suppression,angiogenesis,invasion and metastasis

Growing evidence suggests that myeloid-derived suppressor cells （MDSCs）,which have been named ＂immature myeloid cells＂ or ＂myeloid suppressor cells＂ （MSCs）,play a critical role during the progression of cancer in tumor-bearing mice and cancer patients.As their name implies,these cells are derived from bone marrow and have a tremendous potential to suppress immune responses.Recent studies indicated that these cells also have a crucial role in tumor progression.MDSCs can directly incorporate into tumor endothelium.They secret many pro-angiogenic factors as well.In addition,they play an essential role in cancer invasion and metastasis through inducing the production of matrix metalloproteinases （MMPs）,chemoattractants and creating a pre-metastatic environment.Increasing evidence supports the idea that cancer stem cells （CSCs） are responsible for tumorigenesis,resistance to therapies,invasion and metastasis.Here,we hypothesize that CSCs may ＂hijack＂ MDSCs for use as alternative niche cells,leading to the maintenance of stemness and enhanced chemo-and radio-therapy resistance.The countermeasure that directly targets to MDSCs may be useful for against angiogenesis and preventing cancer from invasion and metastasis.Therefore,the study of MDSCs is important to understand tumor progression and to enhance the therapeutic efficacy against cancer.

Effects of Shugan Jianpi Formula(疏肝健脾方)on Myeloid-Derived Suppression Cells-Mediated Depression Breast Cancer Mice

Objective： To observe the intervention effect of Shugan Jianpi Formula （疏肝健脾方,SGJPF） on a breast cancer mouse model with depression and investigate the underlying mechanism of SGJPF in preventing the development of breast cancer. Metkods： The breast cancer model was induced by inoculation of breast cancer cells, the depression model was induced by chronic stress stimuli, and the depression cancer model was established by combining the two factors. The mice were divided into 7 groups： normal control, depression model, tumor model, depression tumor model, SGJPF, chemotherapy, and SGJPF＋chemotherapy groups. The last 3 groups were depression breast cancer mice and treated respectively with SGJPF, chemotherapy drug gemcitabine （GEM）, and SGJPF alongside GEM. The condition of the mice was evaluated by the expression of 5-hydroxytryptamine in hippocampus after the sucrose water test and open field test, weight change, and survival time. Tumor growth was monitored with in vivo imaging. Flow cytometry was used to analyze the level of myeloid-derived suppression cell （MDSC） in the mouse spleen, T cell subsets, and the early apoptosis of CD8~ T cells, Results： The SGJPF＋GEM group had the highest inhibition rate and the longest survival time （P〈0.01）. The MDSC level and the apoptosis rate of CD8＊ T cells was the highest in the SGJPF＋GEM group （P〈0.05）. Conclusions： Depressive disorders and tumor growth could suppress the immune function of mice to different degrees, and the microenvironment in late 4T1 inflammatory breast cancer may play an important role in the pathological process. SGJYF could regulate the immune microenvironment by reducing CD8＊ T lymphocyte apoptosis and tumor cell activity, increasing immune surveillance capability, and inhibiting MDSC proliferation, thus prolonging the survival time of tumor-bearing mice.

Glucocorticoid receptor promotes the function of myeloid-derived suppressor cells by suppressing HIF1α-dependent glycolysis

Immunomodulatory signaling imposes tight regulations on metabolic programs within immune cells and consequentially determines immune response outcomes.Although the glucocorticoid receptor(GR)has been recently implicated in regulating the function of myeloid-derived suppressor cells(MDSCs),whether the dysregulation of GR in MDSCs is involved in immune-mediated hepatic diseases and how GR regulates the function of MDSCs in such a context remains unknown.Here,we revealed the dysregulation of GR expression in MDSCs during innate immunological hepatic injury(IMH)and found that GR regulates the function of MDSCs through modulating HIF1α-dependent glycolysis.Pharmacological modulation of GR by its agonist(dexamethasone,Dex)protects IMH mice against inflammatory injury.Mechanistically,GR signaling suppresses HIF1αand HIF1α-dependent glycolysis in MDSCs and thus promotes the immune suppressive activity of MDSCs.Our studies reveal a role of GR-HIF1αin regulating the metabolism and function of MDSCs and further implicate MDSC GR signaling as a potential therapeutic target in hepatic diseases that are driven by innate immune cell-mediated systemic inflammation.

Myeloid-specific expression of Stat3C results in conversion of bone marrow mesenchymal stem cells into alveolar type Ⅱ epithelial cells in the lung

Bone marrow mesenchymal stem cells (BMSCs) and myeloid lineage cells originate from the bone marrow, and influence each other in vivo. To elucidate the mechanism that controls the interrelationship between these two cell types, the signaling path- way of signal transducer and activator of transcription 3 (Stat3) was activated by overexpressing Stat3C in a newly established c-fms-rtTA/(TetO)7-CMV-Stat3C bitransgenic mouse model, In this system, Stat3C-Flag fusion protein was overexpressed in myeloid lineage cells after doxycycline treatment. Stat3C overexpression induced systematic elevation of macrophages and neutrophils in multiple organs. In the lung, tissue neoplastic pneumocyte proliferation was observed. After in vitro cultured hSP-B 1.5-kb lacZ BMSCs were injected into the bitransgenic mice, BMSCs were able to repopulate in multiple organs, self-renew in the bone marrow and spleen, and convert into alveolar type II epithelial cells. The bone marrow transplantation study indicated that increases of myeloid lineage cells and BMSC-AT II cell conversion were due to malfunction of myeloid progenitor cells as a result of Stat3C overexpression. The study supports the concept that activation of the Stat3 pathway in myeloid cells plays an important role in BMSC function, including homing, repopulating and converting into residential AT II epithelial cells in the lung.