Biology subjects

Espinosa, H. D.

Publications and source records attributed to Espinosa, H. D..

3 recordsLinked to original sources

bioRxiv2026

Synaptopodin enables directional mechanoadaptation of integrin-based adhesions

The attachment of cells to their substrate through adhesion complexes is fundamental to tissue architecture and function. These adhesions are inherently optimized to resist shear forces parallel to the substrate, yet certain specialized cells must also withstand substantial perpendicular forces. How cells adapt their adhesion machinery to resist forces in different directions has remained unclear. In the kidney, podocytes experience perpendicular forces from pressurized filtrate flow while maintaining attachment to the glomerular basement membrane through integrin-based adhesions. Here we show that synaptopodin converts adhesions from shear-resistant to perpendicular force-resistant structures through coordinated reorganization of the actin cytoskeleton and adhesion complexes. Using an inertial force application system, we demonstrate that synaptopodin triggers force-dependent redistribution of {beta}1-integrin to the cell periphery specifically in response to perpendicular loading, while synaptopodin-deficient cells lack this directional adaptation and detach. This mechanism operates in multiple cell types and is physiologically essential: synaptopodin-null mice subjected to elevated glomerular pressure develop significant proteinuria and podocyte foot process effacement. These findings reveal a molecular basis for directional mechanoadaptation, whereby a single protein enables cells to reconfigure their adhesion architecture in response to the direction of applied force.

biophysics↗

bioRxiv2024

Ultrastructural viscoelastic behavior of collagen identified by AFM nano-dynamic mechanical analysis

Soft tissues exhibit predominantly time-dependent mechanical behavior critical for their biological function in organs like the lungs and aorta, as they can deform and stretch at varying rates depending on their function. Collagen type I serves as the primary structural component in these tissues. The viscoelastic characteristics of such tissues, stemming from diverse energy dissipation mechanisms across various length scales, remains poorly characterized at the nanoscale. Prior experimental investigations have predominantly centered on analyzing tissue responses largely attributed to interactions between cells and fibers. Despite many studies on tissue viscoelasticity from scaffolds to single collagen fibrils, the time-dependent mechanics of collagen fibrils at the sub-fibrillar level remain poorly understood. This pioneering study employs atomic force microscopy (AFM) nano-rheometry and indentation testing to examine the viscoelastic characteristics of individual collagen type I fibrils at the ultrastructural level within distinct topographical zones, specifically focusing on gap and overlap regions. Our investigation has unveiled that collagen fibrils display a viscoelastic response that replicates the mechanical behavior of the tissue at the macroscale. Further, our findings suggest a distinct viscoelastic behavior between the gap and overlap regions, likely stemming from variances in molecular organization and cross-linking modalities within these specific sites. The results of our investigation provide unequivocal proof of the temporal dependence of mechanical properties and provides unique data to be compared to atomistic models, laying a foundation for refining the precision of macroscale models that strive to capture tissue viscoelasticity across varying length scales.

biophysics↗

bioRxiv2018

A Combined Numerical and Experimental Investigation of Localized Electroporation-based Transfection and Sampling

Localized electroporation has evolved as an effective technology for the delivery of foreign molecules into adherent cells, and more recently, for the sampling of cytosolic content from a small population of cells. Unlike bulk electroporation, where the electric field is poorly controlled, localized electroporation benefits from the spatial localization of the electric field on a small areal fraction of the cell membrane, resulting in efficient molecular transport and high cell-viability. Although there have been numerous experimental reports, a mechanistic understanding of the different parameters involved in localized electroporation is lacking. In this work, we developed a multiphysics model that a) predicts the electro-pore distribution in response to the local transmembrane potential and b) calculates the molecular transport into and out of the cell based on the predicted pore-sizes. Using the model, we identify that cell membrane tension plays a crucial role in enhancing both the amount and the uniformity of molecular transport, particularly for large proteins and plasmids. We qualitatively validate the model predictions by delivering large molecules (fluorescent-tagged bovine serum albumin and mCherry encoding plasmid) and by sampling an exogeneous protein (tdTomato) in an engineered cell line. The findings presented here should inform the future design of microfluidic devices for localized electroporation based sampling, eventually paving the way for temporal, single-cell analysis.

biophysics↗