Biology subjects

Galarza, S.

Publications and source records attributed to Galarza, S..

5 recordsLinked to original sources

bioRxiv2019

Control of Astrocyte Quiescence and Activation in a Synthetic Brain Hydrogel

Bioengineers designed numerous instructive brain extracellular matrix (ECM) environments that have tailored and tunable protein composition and biomechanics in vitro to study astrocyte reactivity during trauma and inflammation. However, a major limitation of both protein-based and model microenvironments is that astrocytes within fail to retain their characteristic stellate morphology and quiescent state without becoming activated under \"normal\" culture conditions. Here we introduce a synthetic hydrogel, that for the first time demonstrates maintenance of astrocyte quiescence, and control over activation on demand. With this synthetic brain hydrogel, we show the brain-specific integrin-binding and matrix metalloprotease (MMP)-degradable domains of proteins control astrocyte star-shaped morphologies, and we can achieve an ECM condition that maintains astrocyte quiescence with minimal activation. In addition, we can induce activation in a dose-dependent manner via both defined cytokine cocktails and low molecular weight hyaluronic acid. We envision this synthetic brain hydrogel as a new tool to study the physiological role of astrocytes in health and disease.

bioengineering↗

bioRxiv2019

Tumor cell-organized fibronectin is required to maintain a dormant breast cancer population

Tumors can undergo long periods of dormancy, with cancer cells entering a largely quiescent, non-proliferative state before reactivation and outgrowth. For a patient, these post-remission tumors are often drug resistant and highly aggressive, resulting in poor prognosis. To understand the role of the extracellular matrix (ECM) in regulating tumor dormancy, we created an in vitro cell culture system that combines carefully controlled ECM substrates with nutrient deprivation to observe entrance into and exit from dormancy with live imaging. We saw that cell populations capable of surviving entrance into long-term dormancy were heterogeneous, containing quiescent, cell cycle arrested, and actively proliferating cells. Cell populations that endured extended periods of serum-deprivation-induced dormancy formed an organized, fibrillar fibronectin matrix via v{beta}3 and 5{beta}1 integrin adhesion, ROCK-generated tension, and TGF{beta}2 stimulation. We surmised that the fibronectin matrix was primarily a mediator of cell survival, not proliferation, during the serum-deprivation stress, bacause cancer cell outgrowth after dormancy required MMP-2-mediated fibronectin degradation. Given the difficulty of animal models in observing entrance and exit from dormancy in real-time, we propose this approach as a new, in vitro method to study factors important in regulating dormancy, and we used it here to elucidate a role for fibronectin deposition and MMP activation.

cancer biology↗

bioRxiv2019

2D or 3D? How in vitro cell motility is conserved across dimensions, and predicts in vivo invasion

Cell motility is a critical aspect of wound healing, the immune response, and is deregulated in cancer. Current limitations in imaging tools make it difficult to study cell migration in vivo. To overcome this, and to identify drivers from the microenvironment that regulate cell migration, bioengineers have developed 2D and 3D tissue model systems in which to study cell motility in vitro, with the aim of mimicking the environments in which cells move in vivo. However, there has been no systematic study to explicitly relate and compare cell motility measurements between these geometries/systems. Here, we provide such analysis on our own data, as well as across data in existing literature to understand whether, and which, in vitro models are predictive of in vivo cell motility. To our surprise, many metrics of cell movement on 2D surfaces significantly and positively correlate with cell migration in 3D environments, and cell invasion in 3D is negatively correlated with glioblastoma invasion in vivo. Finally, to best compare across complex model systems, in vivo data, and data from different labs, we suggest that groups report an effect size, a statistical tool that is most translatable across experiments and labs, when conducting experiments that affect cellular motility.

bioengineering↗

bioRxiv2018

Applicability of Drug Response Metrics for Cancer Studies using Biomaterials

Bioengineers have built increasingly sophisticated models of the tumor microenvironment in which to study cell-cell interactions, mechanisms of cancer growth and metastasis, and to test new potential therapies. These models allow researchers to culture cells in conditions that include features of the in vivo tumor microenvironment (TME) implicated in regulating cancer progression, such as ECM stiffness, integrin binding to the ECM, immune and stromal cells, growth factor and cytokine depots, and a 3D geometry more representative of the TME than tissue culture polystyrene (TCPS). These biomaterials could be particularly useful for drug screening applications to make better predictions of efficacy, offering better translation to preclinical in vivo models and clinical trials. However, it can be challenging to compare drug response reports across different platforms and conditions in the current literature. This is, in part, as a result of inconsistent reporting and use of drug response metrics, and vast differences in cell growth rates across a large variety of biomaterial design. This perspective paper attempts to clarify the definitions of drug response measurements used in the field, and presents examples in which these measurements can and cannot be applied. We suggest as best practice to include appropriate controls, always measure the growth rate of cells in the absence of drug, and follow our provided \"decision tree\" matrix when reporting drug response metrics.

bioengineering↗

bioRxiv2017

Control of Thiol-Maleimide Reaction Kinetics in PEG Hydrogel Networks

Michael-type addition reactions are widely used to polymerize biocompatible hydrogels. The thiol-maleimide modality achieves the highest macromer coupling efficiency of the reported Michael-type pairs, but the resulting hydrogel networks are heterogeneous, because polymerization is faster than the individual components can be manually mixed. The reactivity of the thiol dictates the overall reaction speed, which can be slowed in organic solvents and acidic buffers. Since these modifications also reduce the biocompatibility of resulting hydrogels, we investigated a series of biocompatible buffers and crosslinkers to decelerate gelation while maintaining high cell viability. We found that lowering the polymer weight percentage (wt%), buffer concentration, and pH slowed gelation kinetics, but crosslinking with an electronegative peptide was optimal for both kinetics and cell viability. Slowing the speed of polymerization resulted in more uniform hydrogels, both in terms of visual inspection and the diffusion of small molecules through the network. However, reactions that were too slow resulted in non-uniform particle dispersion due to settling, thus there is a trade-off in hydrogel network uniformity versus cell distribution in the hydrogels when using these networks in cell applications.

bioengineering↗