Physical Principles of Membrane Shape Regulation by the Glycocalyx.

Cells bend their plasma membranes into highly curved forms to interact with the local environment, but how shape generation is regulated is not fully resolved. Here, we report a synergy between shape-generating processes in the cell interior and the external organization and composition of the cell-surface glycocalyx. Mucin biopolymers and long-chain polysaccharides within the glycocalyx can generate entropic forces that favor or disfavor the projection of spherical and finger-like extensions from the cell surface. A polymer brush model of the glycocalyx successfully predicts the effects of polymer size and cell-surface density on membrane morphologies. Specific glycocalyx compositions can also induce plasma membrane instabilities to generate more exotic undulating and pearled membrane structures and drive secretion of extracellular vesicles. Together, our results suggest a fundamental role for the glycocalyx in regulating curved membrane features that serve in communication between cells and with the extracellular matrix.

Direct comparison of optical and electron microscopy methods for structural characterization of extracellular vesicles.

As interest in the role of extracellular vesicles in cell-to-cell communication has increased, so has the use of microscopy and analytical techniques to assess their formation, release, and morphology. In this study, we evaluate scanning electron microscopy (SEM) and cryo-SEM for characterizing the formation and shedding of vesicles from human breast cell lines, parental and hyaluronan synthase 3-(HAS3)-overexpressing MCF10A cells, grown directly on transmission electron microscopy (TEM) grids. While cells imaged with conventional and cryo-SEM exhibit distinct morphologies due to the sample preparation process for each technique, tubular structures protruding from the cell surfaces were observed with both approaches. For HAS3-MCF10A cells, vesicles were present along the length of membrane protrusions. Once completely shed from the cells, extracellular vesicles were characterized using nanoparticle tracking analysis (NTA) and cryo-TEM. The size distributions obtained by each technique were different not only in the range of vesicles analyzed, but also in the relative proportion of smaller-to-larger vesicles. These differences are attributed to the presence of biological debris in the media, which is difficult to differentiate from vesicles in NTA. Furthermore, we demonstrate that cryo-TEM can be used to distinguish between vesicles based on their respective surface structures, thereby providing a path to differentiating vesicle subpopulations and identifying their size distributions. Our study emphasizes the necessity of pairing several techniques to characterize extracellular vesicles.

Convergent Approaches to Delineate the Metabolic Regulation of Tumor Invasion by Hyaluronic Acid Biosynthesis.

Metastasis is the leading cause of breast cancer-related deaths and is often driven by invasion and cancer-stem like cells (CSCs). Both the CSC phenotype and invasion are associated with increased hyaluronic acid (HA) production. How these independent observations are connected, and which role metabolism plays in this process, remains unclear due to the lack of convergent approaches integrating engineered model systems, computational tools, and cancer biology. Using microfluidic invasion models, metabolomics, computational flux balance analysis, and bioinformatic analysis of patient data, the functional links between the stem-like, invasive, and metabolic phenotype of breast cancer cells as a function of HA biosynthesis are investigated. These results suggest that CSCs are more invasive than non-CSCs and that broad metabolic changes caused by overproduction of HA play a role in this process. Accordingly, overexpression of hyaluronic acid synthases (HAS) 2 or 3 induces a metabolic phenotype that promotes cancer cell stemness and invasion in vitro and upregulates a transcriptomic signature predictive of increased invasion and worse patient survival. This study suggests that HA overproduction leads to metabolic adaptations to satisfy the energy demands for 3D invasion of breast CSCs highlighting the importance of engineered model systems and multidisciplinary approaches in cancer research.

Myeloid Derived Suppressor Cells Migrate in Response to Flow and Lymphatic Endothelial Cell Interaction in the Breast Tumor Microenvironment.

At the site of the tumor, myeloid derived suppressor cells (MDSCs) infiltrate and interact with elements of the tumor microenvironment in complex ways. Within the invading tumor, MDSCs are exposed to interstitial fluid flow (IFF) that exists within the chronic inflammatory tumor microenvironment at the tumor-lymphatic interface. As drivers of cell migration and invasion, the link between interstitial fluid flow, lymphatics, and MDSCs have not been clearly established. Here, we hypothesized that interstitial fluid flow and cells within the breast tumor microenvironment modulate migration of MDSCs. We developed a novel 3D model to mimic the breast tumor microenvironment and incorporated MDSCs harvested from 4T1-tumor bearing mice. Using live imaging, we found that sorted GR1+ splenocytes had reduced chemotactic index compared to the unsorted population, but their speed and displacement were similar. Using our adapted tissue culture insert assay, we show that interstitial fluid flow promotes MDSC invasion, regardless of absence or presence of tumor cells. Coordinating with lymphatic endothelial cells, interstitial fluid flow further enhanced invasion of MDSCs in the presence of 4T1 cells. We also show that VEGFR3 inhibition reduced both MDSC and 4T1 flow response. Together, these findings indicate a key role of interstitial fluid flow in MDSC migration as well as describe a tool to explore the immune microenvironment in breast cancer.

Modulating microenvironments for treating glioblastoma.

PURPOSE OF REVIEW: This review focuses on the development and progression of glioblastoma through the brain and glioma microenvironment. Specifically we highlight how the tumor microenvironment contributes to the hallmarks of cancer in hopes of offering novel therapeutic options and tools to target this microenvironment. RECENT FINDINGS: The hallmarks of cancer, which represent elements of cancers that contribute to the disease's malignancy, yet elements within the brain tumor microenvironment, such as other cellular types as well as biochemical and biophysical cues that can each uniquely affect tumor cells, have not been well-described in this context and serve as potential targets for modulation. SUMMARY: Here, we highlight how the brain tumor microenvironment contributes to the progression and therapeutic response of tumor cells. Specifically, we examine these contributions through the lens of Hanahan & Weinberg's Hallmarks of Cancer in order to identify potential novel targets within the brain that may offer a means to treat brain cancers, including the deadliest brain cancer, glioblastoma.

Pro-atherogenic shear stress and HIV proteins synergistically upregulate cathepsin K in endothelial cells.

Major advances in highly active antiretroviral therapies (HAART) have extended the lives of people living with HIV, but there still remains an increased risk of death by cardiovascular diseases (CVD). HIV proteins have been shown to contribute to cardiovascular dysfunction with effects on the different cell types that comprise the arterial wall. In particular, HIV-1 transactivating factor (Tat) has been shown to bind to endothelial cells inducing a range of responses that contribute to vascular dysfunction. It is well established that hemodynamics also play an important role in endothelial cell mediated atherosclerotic development. When exposed to low or oscillatory shear stress, such as that found at branches and bifurcations, endothelial cells contribute to proteolytic vascular remodeling by upregulating cathepsins, potent elastases and collagenases that contribute to altered biomechanics and plaque formation. Mechanisms to understand the influence of Tat on shear stress mediated vascular remodeling have not been fully elucidated. Using an in vivo HIV-Tg mouse model and an in vitro cone and plate shear stress bioreactor to actuate physiologically relevant pro-atherogenic or atheroprotective shear stress on human aortic endothelial cells, we have shown synergism between HIV proteins and pro-atherogenic shear stress to increase endothelial cell expression of the powerful protease cathepsin K, and may implicate this protease in accelerated CVD in people living with HIV.

Azidothymidine (AZT) leads to arterial stiffening and intima-media thickening in mice.

HIV positive patients on highly active antiretroviral therapy (HAART) have shown elevated incidence of a number of non-AIDS defining co-morbidities, including cardiovascular disease. Given that HAART regimens contain a combination of at least three drugs, that disease management often requires adjustment of these regimens, and HIV, independent of HAART, also plays a role in development of co-morbidities, determining the role of specific HAART drugs and HIV infection itself from clinical data remains challenging. To characterize specific mediators and underlying mechanisms of disease, in vitro and in vivo animal models are required, in parallel with clinical data. Given its low cost azidothymidine (AZT) contributes to the backbone of a large proportion of HAART treated patients in the developing world where much of the global burden of HIV resides. The goal of this study was to test the hypothesis that AZT can lead to proatherogenic changes including the subclinical markers of arterial stiffening and intima-media thickening in mice. AZT (100mg/kg) or vehicle was administered to wild-type FVB/N mice via oral gavage for 35 days. Cylindrical biaxial biomechanical tests on the common carotid arteries and suprarenal aortas exhibited arterial stiffening in AZT mice compared to controls. Multiphoton microscopy and histology demonstrated that AZT led to increased intima-media thickness. These data correlated with decreased elastin content and increased protease activity as measured by cathepsin zymography; no differences were observed in collagen content or organization, in vivo axial stretch, or opening angle. Thus, this study suggests the drug AZT has significant effects on the development of subclinical markers of atherosclerosis.