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PhD Discussion: Isabela Fortunato y Marina Martinez
Friday, June 30 @ 10:00 am–11:00 am
Cell migration up and down fibronectin gradients
Isabela Fortunato, Integrative cell and tissue dynamics group
The ability of cells to perform directed migration is essential for biological processes, such as tissue morphogenesis, immune function, and cancer invasion. Directed cell migration is often triggered by spatial gradients in the cellular environment (e.g., chemical gradients, called chemotaxis, substrate stiffness gradients, called durotaxis, or substrate-bound ligand gradients, called haptotaxis). Haptotaxis has been described in vivo as an important phenomenon during physiological and pathological conditions. However, the molecular and mechanical processes that drive this form of directed cell migration remain elusive. Moreover, generating accurate and reliable gradients of immobilized protein in vitro has been challenging and makes it harder to study haptotaxis. Here, we explore how cells sense and respond to gradients of immobilized proteins. We used a photopatterning technique to create well-controlled fibronectin gradients and we studied the migration of single mammary epithelial cells (MCF-10A). This approach allowed us to map cell migration velocity, traction forces, and actin cytoskeleton dynamics as a function of fibronectin density. We observed that cells respond to fibronectin gradients by an initial polarization towards higher protein density in the first hours of migration. Surprisingly, after the initial polarization, cells maintained their directionality even if they were submitted to a negative protein gradient. This suggests that cells adapt their polarity features to maintain the preexisting structures and organelles geometry towards low fibronectin regions until a limitation on creating new adhesions. In this work we find that one key adaptation mechanism is driven by the actin flows, specifically the increase in actin polymerization velocity at the leading edge. Besides haptotaxis, we foresee that these results will shed light on other forms of directed cell migration in which cells integrate several internal and external cues to orient themselves in physiological and pathological processes.
Living myocardial slices as a representative in vitro platform for translational cardiovascular disease
Marina Martínez, Biomaterials for Regenerative Therapies group
Cardiovascular diseases are the leading cause of global mortality, accounting for nearly 45% of all deaths in Europe. Myocardial infarction (MI) is a prevalent condition, where a region of the cardiac muscle undergoes ischemia and up to one billion cardiomyocytes die in just a few hours. The heart has a limited regenerative ability; consequently, cardiomyocytes lost due to MI cannot be replaced. In this scenario, researchers have investigated and developed alternative therapies to promote cardiac repair and regeneration.
Lactate, an important metabolite during cardiogenesis and cardiac development, has been recently described as a potential modulator of the phenotype of cardiac cells in vitro. These findings support a novel use of lactate for endogenous heart regeneration strategies. Nevertheless, effectiveness of ongoing therapeutic approaches is dependent on the level of maturation of cardiac tissue. Hitherto, the regenerative capabilities of lactate in mature cardiac tissue have not been described. In this work, we used living myocardial slices (LMS) as a model of mature cardiac tissue. LMS are 300 μm-thick slices of living myocardium with conserved physiological structure and function. Human and rat adult LMS were treated with lactate to evaluate early cellular, molecular, and functionality changes related to myocardial reprogramming, cardiac structural rearrangements, and fibrosis. Moreover, the effect of lactate was characterized in both healthy and injured adult myocardium.
Functionally, (8 mM) lactate-treated healthy and pathological human LMS displayed an increase in contractility. Expression of fibrotic, pluripotency transcription factors, and cardiomyocyte markers were detected. Exposure of healthy rat LMS to higher concentrations of lactate (20 mM) did not affect LMS viability nor altered LMS contractile force, while promoted LMS stiffening. In cryoinjured rat LMS, lactate drastically increased contractility and altered tissue remodeling in the region bordering the injury.
LMS provide a representative in vitro platform for translational cardiovascular research. By using LMS, characterization of the effect of lactate in mature cardiac tissue has been achieved. Exogenous lactate enhanced cardiac function in both human and injured rat LMS. Upregulation of transcription factors and cardiomyocyte markers may suggest an effect on partial cardiomyocyte reprogramming that would counteract the effects of tissue stiffening. Altogether, this study further supports the prospective use of lactate as a bioactive signal in new endogenous cardiac regeneration strategies.
This PhD Discussion session will be held at Tower I, 11th floor Baobab room, at 10:00am.