Liyin Zhu

Macrophages Regulate the Angiogenic Switch in a Mouse Model of Breast Cancer

The development of a tumor vasculature or access to the host vasculature is a crucial step for the survival and metastasis of malignant tumors. Although therapeutic strategies attempting to inhibit this step during tumor development are being developed, the biological regulation of this process is still largely unknown. Using a transgenic mouse susceptible to mammary cancer, PyMT mice, we have characterized the development of the vasculature in mammary tumors during their progression to malignancy. We show that the onset of the angiogenic switch, identified as the formation of a high-density vessel network, is closely associated with the transition to malignancy. More importantly, both the angiogenic switch and the progression to malignancy are regulated by infiltrated macrophages in the primary mammary tumors. Inhibition of the macrophage infiltration into the tumor delayed the angiogenic switch and malignant transition whereas genetic restoration of the macrophage population specifically in these tumors rescued the vessel phenotype. Furthermore, premature induction of macrophage infiltration into premalignant lesions promoted an early onset of the angiogenic switch independent of tumor progression. Taken together, this study shows that tumor-associated macrophages play a key role in promoting tumor angiogenesis, an essential step in the tumor progression to malignancy.

Progression to Malignancy in the Polyoma Middle T Oncoprotein Mouse Breast Cancer Model Provides a Reliable Model for Human Diseases

Animal models are powerful tools to analyze the mechanism of the induction of human breast cancer. Here we report a detailed analysis of mammary tumor progression in one mouse model of breast cancer caused by expression of the polyoma middle T oncoprotein (PyMT) in the mammary epithelium, and its comparison to human breast tumors. In PyMT mice, four distinctly identifiable stages of tumor progression from premalignant to malignant stages occur in a single primary tumor focus and this malignant transition is followed by a high frequency of distant metastasis. These stages are comparable to human breast diseases classified as benign or in situ proliferative lesions to invasive carcinomas. In addition to the morphological similarities with human breast cancer, the expression of biomarkers in PyMT-induced tumors is also consistent with those associated with poor outcome in humans. These include a loss of estrogen and progesterone receptors as well as integrin-beta1 expression and the persistent expression of ErbB2/Neu and cyclinD1 in PyMT-induced tumors as they progress to the malignant stage. An increased leukocytic infiltration was also closely associated with the malignant transition. This study demonstrates that the PyMT mouse model is an excellent one to understand the biology of tumor progression in humans.

Absence of Colony Stimulation Factor-1 Receptor Results in Loss of Microglia, Disrupted Brain Development and Olfactory Deficits

The brain contains numerous mononuclear phagocytes called microglia. These cells express the transmembrane tyrosine kinase receptor for the macrophage growth factor colony stimulating factor-1 (CSF-1R). Using a CSF-1R-GFP reporter mouse strain combined with lineage defining antibody staining we show in the postnatal mouse brain that CSF-1R is expressed only in microglia and not neurons, astrocytes or glial cells. To study CSF-1R function we used mice homozygous for a null mutation in the Csflr gene. In these mice microglia are >99% depleted at embryonic day 16 and day 1 post-partum brain. At three weeks of age this microglial depletion continues in most regions of the brain although some contain clusters of rounded microglia. Despite the loss of microglia, embryonic brain development appears normal but during the post-natal period the brain architecture becomes perturbed with enlarged ventricles and regionally compressed parenchyma, phenotypes most prominent in the olfactory bulb and cortex. In the cortex there is increased neuronal density, elevated numbers of astrocytes but reduced numbers of oligodendrocytes. Csf1r nulls rarely survive to adulthood and therefore to study the role of CSF-1R in olfaction we used the viable null mutants in the Csf1 (Csf1op) gene that encodes one of the two known CSF-1R ligands. Food-finding experiments indicate that olfactory capacity is significantly impaired in the absence of CSF-1. CSF-1R is therefore required for the development of microglia, for a fully functional olfactory system and the maintenance of normal brain structure.

MACROPHAGES: IMPORTANT ACCESSORY CELLS FOR REPRODUCTIVE FUNCTION

Macrophages are found throughout reproductive tissues. To determine their role(s), we have studied mice homozygous for a null mutation (Csfmop) in the gene encoding the major macrophage growth factor, colony‐stimulating factor‐1 (CSF‐1). Both male and female Csfmop/Csfmop mice have fertility defects. Males have low sperm number and libido as a consequence of dramatically reduced circulating testosterone. Females have extended estrous cycles and poor ovulation rates. CSF‐1 is the principal growth factor regulating macrophage populations in the testis, male accessory glands, ovary, and uterus. However, analyses of CSF‐1 nullizygous mice suggest that the primary reproductive defect is in the development of feedback regulation of the hypothalamic‐pituitary axis. Although not correlating with deficiencies of microglia populations, electrophysiological investigations indicate an impairment of neuronal responses. This suggests that microglia, under the influence of CSF‐1, act to organize neuronal connectivity during development and that the absence of this function results in a perturbation of the hypothalamicpituitary‐gonadal axis. Macrophages also appear to have functions in the differentiated tissues of the reproductive system, including having a positive influence on steroidogenic cells. These data suggest that macrophages, through their trophic functions, can be considered as essential accessory cells for normal reproductive functioning. J. Leukoc. Biol. 66:765–772; 1999.

Estradiol-17beta regulates mouse uterine epithelial cell proliferation through insulin-like growth factor 1 signaling.

Estradiol-17β (E2) causes cell proliferation in the uterine epithelium of mice and humans by signaling through its transcription factor receptor α (ERα). In this work we show that this signaling is mediated by the insulin-like growth factor 1 receptor (IGF1R) expressed in the epithelium, whose activation leads to the stimulation of the phosphoinositide 3-kinase/protein kinase B pathway leading to cyclin D1 nuclear accumulation and engagement with the canonical cell cycle machinery. This cyclin D1 nuclear accumulation results from the inhibition of glycogen synthase kinase 3β (GSK3β) activity caused by an inhibitory phosphorylation by protein kinase B. Once the IGF1 pathway is activated, inhibition of ER signaling demonstrates that it is independent of ER. Inhibition of GSK3β in the absence of E2 is sufficient to induce uterine epithelial cell proliferation, and GSK3β is epistatic to IGF1 signaling, indicating a linear pathway from E2 to cyclin D1. Exposure to E2 is the major risk factor for endometrial cancer, suggesting that downstream activation of this IGF1-mediated pathway by mutation could be causal in the progression to ER-independent tumors.

The EGF/CSF-1 Paracrine Invasion Loop Can Be Triggered by Heregulin beta 1 and CXCL12

An important step in the process of metastasis from the primary tumor is invasive spread into the surrounding stroma. Using an in vivo invasion assay, we have previously shown that imposed gradients of epidermal growth factor (EGF) or colony-stimulating factor-1 (CSF-1) can induce invasion through an EGF/CSF-1 paracrine loop between cancer cells and macrophages. We now report that invasion induced by other ligands also relies on this EGF/CSF-1 paracrine invasive loop. Using an in vivo invasion assay, we show that MTLn3 breast cancer cells overexpressing ErbB3 exhibit enhanced invasion compared with control MTLn3 cells in response to the ErbB3 ligand HRG-beta1. The invasive response of both MTLn3-ErbB3 and transgenic MMTV-Neu tumors to HRG-beta1 is inhibited by blocking EGF receptor, CSF-1 receptor, or macrophage function, indicating that invasiveness to HRG-beta1 is dependent on the EGF/CSF-1 paracrine loop. Furthermore, we show that CXCL12 also triggers in vivo invasion of transgenic MMTV-PyMT tumors in an EGF/CSF-1-dependent manner. Although the invasion induced by HRG-beta1 or CXCL12 is dependent on the EGF/CSF-1 paracrine loop, invasion induced by EGF is not dependent on HRG-beta1 or CXCL12 signaling, showing an asymmetrical relationship between different ligand/receptor systems in driving invasion. Our results identify a stromal/tumor interaction that acts as an engine underlying invasion induced by multiple ligands.

Colony-stimulating factor 1 receptor (CSF1R) signaling in injured neurons facilitates protection and survival

Colony-stimulating factor 1 and IL-34 protect against and partially reverse neurodegeneration in mice in part via promoting CREB signaling.

Lithium chloride treatment induces epithelial cell proliferation in xenografted human endometrium

BACKGROUND In mouse endometrium, glycogen synthase kinase-3beta (GSK3beta) is a key enzyme controlling nuclear localization of cyclin D1. We developed a functional model of xenografted human endometrium to test whether similar mechanisms are operative in the human by using Lithium chloride (LiCl), an inhibitor of GSK3beta. METHODS Human endometrial samples were obtained from normal volunteers, then implanted under the kidney capsule of nude mice, and treated with estradiol-17beta (E2) or LiCl. Xenografts were assessed for protein expression of MKI-67, mini-chromosome maintenance protein-2, estrogen receptor (ER), progesterone receptor (PR) and cyclin D1. RESULTS Both E2 and LiCl induced a robust proliferative response in the epithelium. Only lithium treatment produced clear nuclear localization of cyclin D1 consistent with the proliferative response observed. Regenerated endometrium had detectable ER and PR expression. CONCLUSION Xenografted human endometrium provides a dynamic model of uterine biology. Administration of LiCl in the absence of E2 induced epithelial proliferation, supporting the hypothesis that human and murine endometrial proliferation may share key regulatory pathways. These data suggest a possible link between the increased menstrual disturbances in women with affective disorders taking lithium and the consequent potential for the development of endometrial proliferative disorder.

Colony-Stimulating Factor-1-Dependent Macrophage Functions Regulate the Maternal Decidua Immune Responses against Listeria monocytogenes Infections during Early Gestation in Mice

ABSTRACT The association between extreme-prematurity births and intrauterine infection emphasizes the importance of understanding the host immune responses against uterine-invading microbes during early pregnancy to the prevention of preterm births. Listeria monocytogenes, a clinically relevant intracellular bacterium, has a predilection for replication at the maternofetal interface during pregnancy. Here, using mice carrying the recessive null osteopetrotic mutation in the colony-stimulating factor-1 (CSF-1) gene, we show that CSF-1-dependent macrophage functions are required for the maternal decidua immune responses against L. monocytogenes infections during early gestation in mice. In the absence of CSF-1, pregnant mice were more susceptible to uterine infection by L. monocytogenes; their inability to control the expansion of colonized bacteria in the pregnant uterus led to decidual cell death, tissue disintegration, and resorption of the developing embryo. However, CSF-1-deficient mice were able to produce significant levels of both Th1 cytokines and neutrophil chemoattractants and to recruit neutrophils to the decidual tissue in response to Listeria infection. Depletion of macrophages in hormonally induced pseudopregnant mice resulted in higher uterine bacterial levels after L. monocytogenes infection. These data suggest that the anti-Listeria responses in the maternal decidual tissue are dependent on CSF-1-regulated macrophages.

Activation of protein synthesis in mouse uterine epithelial cells by estradiol-17β is mediated by a PKC–ERK1/2–mTOR signaling pathway

Significance Estrogen exposure is the major risk factor for diseases of the endometrium such as endometriosis and endometrial cancer. This is thought to be through its constant stimulation of epithelial cell proliferation. Progesterone blocks the estrogen-induced cell proliferation and exposure to it mitigates the risk for these diseases. However endometriotic tissue and cancer become progesterone resistant. Here we identify an estrogen induced pathway in uterine epithelial cells that activates protein synthesis through mechanistic target of rapamycin (mTOR) in a progesterone independent way. This indicates how protein and DNA synthesis regulation can be differentially controlled in vivo as progesterone blocks only the latter response. Inhibition of mTOR by rapamycin blocked E2-induced protein and DNA synthesis, suggesting that it might be a therapeutic target for these diseases. The uterine epithelium of mice and humans undergoes cyclical waves of cell proliferation and differentiation under the regulation of estradiol-17β (E2) and progesterone (P4). These epithelial cells respond to E2 with increased protein and DNA synthesis, whereas P4 inhibits only the E2-induced DNA synthetic response. Here we show that E2 regulates protein synthesis in these epithelial cells through activating PKC that in turn stimulates ERK1/2 to phosphorylate and thereby activate the central regulator of protein synthesis mechanistic target of rapamycin (mTOR). This mTOR pathway is not inhibited by P4. Inhibitor studies with an estrogen receptor (ESR1) antagonist showed the dependence of this mTOR pathway on ESR1 but that once activated, a phosphorylation cascade independent of ESR1 propagates the pathway. E2 also stimulates an IGF1 receptor (IGF1R) to PI3 kinase to AKT to GSK-3β pathway required for activation of the canonical cell cycle machinery that is inhibited by P4. PKC activation did not stimulate this pathway nor does inhibition of PKC or ERK1/2 affect it. These studies therefore indicate a mechanism whereby DNA and protein synthesis are regulated by two ESR1-activated pathways that run in parallel with only the one responsible for the initiation of DNA synthesis blocked by P4. Inhibition of mTOR by rapamycin in vivo resulted in inhibition of E2-induced protein and DNA synthesis. Proliferative diseases of the endometrium such as endometriosis and cancer are common and E2 dependent. Thus, defining this mTOR pathway suggests that local (intrauterine or peritoneal) rapamycin administration might be a therapeutic option for these diseases.