To investigate why responses of mast cells to antigen-induced IgE receptor (Fc?RI) aggregation depend nonlinearly on antigen dose, we characterized a new artificial ligand, DF3, through complementary modeling and experimentation. This ligand is a stable trimer of peptides derived from bacteriophage T4 fibritin, each conjugated to a hapten (DNP). We found low and high doses of DF3 at which degranulation of mast cells sensitized with DNP-specific IgE is minimal, but ligand-induced receptor aggregation is comparable to aggregation at an intermediate dose, optimal for degranulation. This finding makes DF3 an ideal reagent for studying the balance of negative and positive signaling in the Fc?RI pathway. We find that the lipid phosphatase SHIP and the protein tyrosine phosphatase SHP-1 negatively regulate mast cell degranulation over all doses considered. In contrast, SHP-2 promotes degranulation. With high DF3 doses, relatively rapid recruitment of SHIP to the plasma membrane may explain the reduced degranulation response. Our results demonstrate that optimal secretory responses of mast cells depend on the formation of receptor aggregates that promote sufficient positive signaling by Syk to override phosphatase-mediated negative regulatory signals.
To understand the process of innate immune fungal recognition, we developed computational tools for the rigorous quantification and comparison of receptor recruitment and distribution at cell-cell contact sites. We used these tools to quantify pattern recognition receptor spatiotemporal distributions in contacts between primary human dendritic cells and the fungal pathogens C. albicans, C. parapsilosis and the environmental yeast S. cerevisiae, imaged using 3D multichannel laser scanning confocal microscopy. The detailed quantitative analysis of contact sites shows that, despite considerable biochemical similarity in the composition and structure of these species' cell walls, the receptor spatiotemporal distribution in host-microbe contact sites varies significantly between these yeasts. Our findings suggest a model where innate immune cells discriminate fungal microorganisms based on differential mobilization and coordination of receptor networks. Our analysis methods are also broadly applicable to a range of cell-cell interactions central to many biological problems.
Second-harmonic generation (SHG) imaging can help reveal interactions between collagen fibers and cancer cells. Quantitative analysis of SHG images of collagen fibers is challenged by the heterogeneity of collagen structures and low signal-to-noise ratio often found while imaging collagen in tissue. The role of collagen in breast cancer progression can be assessed post acquisition via enhanced computation. To facilitate this, we have implemented and evaluated four algorithms for extracting fiber information, such as number, length, and curvature, from a variety of SHG images of collagen in breast tissue. The image-processing algorithms included a Gaussian filter, SPIRAL-TV filter, Tubeness filter, and curvelet-denoising filter. Fibers are then extracted using an automated tracking algorithm called fiber extraction (FIRE). We evaluated the algorithm performance by comparing length, angle and position of the automatically extracted fibers with those of manually extracted fibers in twenty-five SHG images of breast cancer. We found that the curvelet-denoising filter followed by FIRE, a process we call CT-FIRE, outperforms the other algorithms under investigation. CT-FIRE was then successfully applied to track collagen fiber shape changes over time in an in vivo mouse model for breast cancer.
The utilization of 3D, physiologically relevant in vitro cancer models to investigate complex interactions between tumor and stroma has been increasing. Prior work has generally focused on the cancer cells and, the role of fibroblast culture conditions on tumor-stromal cell interactions is still largely unknown. Here, we focus on the stroma by comparing functional behaviors of human mammary fibroblasts (HMFs) cultured in 2D and 3D and their effects on the invasive progression of breast cancer cells (MCF10DCIS.com). We identified increased levels of several paracrine factors from HMFs cultured in 3D conditions that drive the invasive transition. Using a microscale co-culture model with improved compartmentalization and sensitivity, we demonstrated that HMFs cultured in 3D intensify the promotion of the invasive progression through the HGF/c-Met interaction. This study highlights the importance of the 3D stromal microenvironment in the development of multiple cell type in vitro cancer models.
Stem cell transplantation holds promise as a therapeutic approach for the repair of damaged myocardial tissue. One challenge of this approach is efficient delivery and long-term retention of the stem cells. Although several synthetic and natural biomaterials have been developed for this purpose, the ideal formulation has yet to be identified.
The increasing interest in studying the interactions between cells and the extracellular matrix (ECM) has created a need for high throughput low-cost three-dimensional (3D) culture systems. The recent development of tubeless microfluidics via passive pumping provides a high throughput microchannel culture platform compatible with existing high throughput infrastructures (e.g., automated liquid handlers). Here, we build on a previously reported high throughput two-dimensional system to create a robust automated system for 3D culture. Operational controls including temperature and sample handling have been characterized and automated. Human mammary fibroblasts (HMFs) suspended in type I collagen are loaded and cultured in microchannel arrays and used to optimize the system operational parameters. A Peltier cooler maintains the collagen as a liquid at 4 °C during cell seeding, followed by polymerization at 37 °C. Optimization of this platform is discussed (e.g., controlling collagen contraction, increasing cell viability, preventing the removal of microchannel contents), and 3D distribution of HMFs is examined by fluorescent microscopy. Finally, we validate the platform by automating a previously developed 3D breast carcinoma coculture assay. The platform allows more efficient 3D culture experiments and lays the foundation for high throughput studies of cell-ECM interactions.
Evidence for the potent influence of stromal organization and function on invasion and metastasis of breast tumors is ever growing. We have performed a rigorous examination of the relationship of a tumor-associated collagen signature-3 (TACS-3) to the long-term survival rate of human patients. TACS-3 is characterized by bundles of straightened and aligned collagen fibers that are oriented perpendicular to the tumor boundary. An evaluation of TACS-3 was performed in biopsied tissue sections from 196 patients by second harmonic generation imaging of the backscattered signal generated by collagen. Univariate analysis of a Cox proportional hazard model demonstrated that the presence of TACS-3 was associated with poor disease-specific and disease-free survival, resulting in hazard ratios between 3.0 and 3.9. Furthermore, TACS-3 was confirmed to be an independent prognostic indicator regardless of tumor grade and size, estrogen or progesterone receptor status, human epidermal growth factor receptor-2 status, node status, and tumor subtype. Interestingly, TACS-3 was positively correlated to expression of stromal syndecan-1, a receptor for several extracellular matrix proteins including collagens. Because of the strong statistical evidence for poor survival in patients with TACS, and because the assessment can be performed in routine histopathological samples imaged via second harmonic generation or using picrosirius, we propose that quantifying collagen alignment is a viable, novel paradigm for the prediction of human breast cancer survival.
The transition of ductal carcinoma in situ (DCIS) to invasive ductal carcinoma (IDC) is a critical step in breast cancer progression. We introduce a simple microfluidic 3D compartmentalized system in which mammary epithelial cells (MCF-DCIS) are co-cultured with human mammary fibroblasts (HMFs), which promotes a transition from DCIS to IDC in vitro. The model enables control of both spatial (distance-dependence) and temporal (transition from larger clusters) aspects within the microenvironment, allowing recapitulation of the in vivo environment in ways not practical with existing experimental models. When HMFs were cultured some distance (0.5-1.5 mm) from the MCF-DCIS cells, we observed an initial morphological change, suggesting soluble factors can begin the transition. However, cell-cell contact with HMFs allowed the MCF-DCIS cells to complete the transition to invasion. Uniquely, the compartmentalized platform enables the analysis of the intrinsic second harmonic generation signal of collagen, providing a label-free quantitative analysis of DCIS-associated collagen remodeling. The arrayed microchannel-based model is compatible with existing infrastructure and, for the first time, provides a cost effective approach to test for inhibitors of pathways involved in DCIS progression to IDC allowing a screening approach to the identification of potential therapeutic targets. Importantly, the model can be easily adapted and generalized to a variety of cell-cell signaling studies.
Interest in constructing a reliable 3-dimensional (3D) collagen culture platform in microfabricated systems is increasing as researchers strive to investigate reciprocal interaction between extracellular matrix (ECM) and cells under various conditions. However, in comparison to conventional 2-dimensional (2D) cell culture research, relatively little work has been reported about the polymerization of collagen type I matrix in microsystems. We, thus, present a study of 3D collagen polymerization to achieve reproducible 3D cell culture in microfluidic devices. Array-based microchannels are employed to efficiently examine various polymerization conditions, providing more replicates with less sample volume than conventional means. Collagen fibers assembled in microchannels were almost two-times thinner than those in conventional gels prepared under similar conditions, and the fiber thickness difference influenced viability and morphology of embedded human mammary fibroblast (HMF) cells. HMF cells contained more actin stress fibers and showed increased viability in 3D collagen matrix composed of thicker collagen fibers. Relatively low pH of the collagen solution within a physiological pH range (6.5-8.5) and pre-incubation at low temperature (approximately 4 degrees C) before polymerization at 37 degrees C allow sufficient time for molecular assembly, generating thicker collagen fibers and enhancing HMF cell viability. The results provide the basis for improved process control and reproducibility of 3D collagen matrix culture in microchannels, allowing predictable modifications to provide optimum conditions for specific cell types. In addition, the presented method lays the foundation for high throughput 3D cellular screening.
Breast epithelial cells sense the stiffness of the extracellular matrix through Rho-mediated contractility. In turn, matrix stiffness regulates RhoA activity. However, the upstream signaling mechanisms are poorly defined. Here we demonstrate that the Rho exchange factor GEF-H1 mediates RhoA activation in response to extracellular matrix stiffness. We demonstrate the novel finding that microtubule stability is diminished by a stiff three-dimensional (3D) extracellular matrix, which leads to the activation of GEF-H1. Surprisingly, activation of the mitogen-activated protein kinase kinase/extracellular signal-regulated kinase pathway did not contribute to stiffness-induced GEF-H1 activation. Loss of GEF-H1 decreases cell contraction of and invasion through 3D matrices. These data support a model in which matrix stiffness regulates RhoA through microtubule destabilization and the subsequent release and activation of GEF-H1.
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