Biophysical Properties of the Basal Lamina: A Highly Selective Extracellular Matrix

In this chapter, we discuss a specialized version of the extracellular matrix, the basal lamina. We focus on biophysical approaches which helped in identifying the mechanistic principles that allow the basal lamina to act as a selective permeability barrier. We discuss the physicochemical interactions that entail binding of molecules or nanoparticles to the basal lamina matrix and outline physiological scenarios where altered selective permeability properties of the basal lamina might contribute to physiological (mal) function

The Biophysical Properties of Basal Lamina Gels Depend on the Biochemical Composition of the Gel

The migration of cells within a three-dimensional extracellular matrix (ECM) depends sensitively on the biochemical and biophysical properties of the matrix. An example for a biological ECM is given by reconstituted basal lamina gels purified from the Engelbreth-HolmSwarm sarcoma of mice. Here, we compare four different commercial variants of this ECM, which have all been purified according to the same protocol. Nevertheless, in those gels, we detect strong differences in the migration behavior of leukocyte cells as well as in the Brownian motion of nanoparticles. We show that these differences correlate with the mechanical properties and the microarchitecture of the gels which in turn arise from small variations in their biochemical composition

Ion-Specific Effects Modulate the Diffusive Mobility of Colloids in an Extracellular Matrix Gel

The diffusion of colloids in complex biological hydrogels is regulated by a broad range of factors including geometric constraints and different types of physical interactions between the particles and the hydrogel constituents. As a consequence, the particle mobility depends not only on the hydrogel microarchitecture but also on the detailed chemical composition of the hydrogel solvent. Here, we employ single particle tracking techniques to quantify the diffusion behavior of submicrometer-sized particles in such a biological hydrogel. We observe three states of colloid mobility: free diffusion, tightly and weakly bound particles, and transitions between those states. Finally, by comparing the efficiency of particle trapping in Matrigel as a function of the ionic strength of the hydrogel buffer, we show that ion-specific effects regulate the efficiency of this trapping process

Lipid Head Group Charge and Fatty Acid Configuration Dictate Liposome Mobility in Neurofilament Networks

Intermediate filaments constitute a class of biopolymers whose function is still poorly understood. One example for such intermediate filaments is given by neurofilaments, large macromolecules that fill the axon of neurons. Here, reconstituted networks of purified porcine neurofilaments are studied and the diffusion behavior of different nanoparticles in the biopolymer network is evaluated. A strong dependence of particle diffusion on the charge state of the particles, and – for liposomes – also on the fatty acid configuration of lipids is observed. The results suggest that both electrostatic and hydrophobic interactions contribute to nanoparticle trapping in neurofilament networks, and that the latter is enabled by lipids with an inverted cone geometry which grant access to the hydrophobic core of the liposome shell

Content of selected ECM proteins in the four different ECM gel variants.

<p>(a) A coomassie staining of the four gel variants shows extra bands in ECM1 at low molecular weight. The star denotes the band which is further investigated by mass spectroscopy (see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118090#pone.0118090.s010" target="_blank">S2 Table</a> for details). (b) The content of fibronectin, laminin, entactin and collagen type IV in the four different ECM gels is analyzed by western blot (for uncropped blots see <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0118090#pone.0118090.s007" target="_blank">S7 Fig</a>.). (c) Densiometric analysis of fibronectin, laminin, entactin and collagen IV signals. The error bars denote the standard deviations as obtained from four independent gel runs.</p

Migration trajectories of dHL-60 cells tracked from hours 4–6 after the cells are embedded into the four different basal lamina matrices.

<p>The starting point of all trajectories is shifted to the origin for clarity, and the end point is marked by a dot. The average start-to-end distance (Euclidean distance) travelled by the cells and the respective standard deviation is denoted by <i>ED</i>. The fraction of cells with an <i>ED</i> greater than <i>ED</i> = 105.5 μm (red circle) is denoted by <i>f</i>. (e) Comparison of the migration velocity of dHL60 cells in different ECM gels. The red line denotes the median of the velocity distribution, the box includes 25% of the observed velocities above and below this median, respectively. The remaining 25% of slower as well as the 25% of faster cells are indicated by the dashed lines. Outliers are denoted by a red cross.</p

Gelation kinetics of the four different gels measured with a macrorheometer.

<p>The temperature is increased from 5°C to 37°C after one minute to induce gelation. The curves shown represent averages of three independent measurements. The inset shows the storage moduli <i>G’</i> of the four gels at 30 min. The error bars denote the error of the mean.</p

Micromorphology of the four gels determined by three different methods.

<p>(a) Exemplary trajectories of PEGylated particles with a diameter of 200 nm in the four different gels. Trajectories are shifted for clarity. (b) Micromorphology of the four different basal lamina gel variants as determined by confocal fluorescence microscopy. Representative staining of the matrix component collagen IV. The scale bar in the upper left image denotes 50 μm and applies to all images. (c) Micromorphology of the whole network of the four gel variants imaged by SEM. The scale bar corresponds to 25 μm and applies to all images.</p