Biology subjects

Sander, E. A.

Publications and source records attributed to Sander, E. A..

5 recordsLinked to original sources

bioRxiv2022

Native Adiponectin Plays a Role in the Adipocyte Mediated Conversion of Fibroblasts to Myofibroblasts

Adipocytes regulate tissues through production of adipokines that can act both locally and systemically. Adipocytes also have been found to play a critical role in regulating the healing process. To better understand this role, we developed a 3D human adipocyte spheroid system that has an adipokine profile similar to in vivo adipose tissues. Previously, we found that conditioned medium from these spheroids induces human dermal fibroblast conversion into highly contractile, collagen producing myofibroblasts through a transforming growth factor beta-1 (TGF-{beta}1) independent pathway. Here, we sought to identify how mature adipocytes signal to dermal fibroblasts through adipokines to induce myofibroblast conversion. By using molecular weight fractionation, heat inactivation, and lipid depletion, we determined mature adipocytes secrete a factor that is 30-100 kDa, heat labile, and lipid associated that induces myofibroblast conversion. We also show that depletion of the adipokine adiponectin, which fits those physiochemical parameters, eliminates the ability of adipocyte conditioned media to induce fibroblast to myofibroblast conversion. Interestingly, native adiponectin secreted by cultured adipocytes consistently elicited a stronger level of -SMA expression than exogenously added adiponectin. Thus, adiponectin secreted by mature adipocytes induces fibroblast to myofibroblast conversion and may lead to a phenotype of myofibroblasts distinct from TGF-{beta}1 induced myofibroblasts.

bioengineering↗

bioRxiv2020

Magnetic Tweezers with Magnetic Flux Density Feedback Control

In this work, we present a single-pole magnetic tweezers (MT) device designed for integration with substrate deformation tracking microscopy (DTM) and/or traction force microscopy (TFM) experiments intended to explore extracellular matrix rheology and human epidermal keratinocyte mechanobiology. Assembled from commercially available off-the-shelf electronics hardware and software, the MT device is amenable to replication in the basic biology laboratory. In contrast to conventional solenoid current-controlled MT devices, operation of this instrument is based on real-time feedback control of the magnetic flux density emanating from the blunt end of the needle core using a cascade control scheme and a digital proportional-integral-derivative (PID) controller. Algorithms that compensate for an apparent spatially non-uniform remnant magnetization of the needle core that develops during actuation are implemented into the feedback control scheme. Through optimization of PID gain scheduling, the MT device exhibits magnetization and demagnetization response times of less than 100 ms without overshoot over a wide range of magnetic flux density setpoints. Compared to current-based control, magnetic flux density-based control allows for more accurate and precise magnetic actuation forces by compensating for temperature increases within the needle core due to heat generated by the applied solenoid currents. Near field calibrations validate the ability of the MT device to actuate 4.5 m-diameter superparamagnetic beads with forces up to 25 nN with maximum relative uncertainties of {+/-}30% for beads positioned between 2.5 and 40 m from the needle tip.

biophysics↗

bioRxiv2020

Integration of Magnetic Tweezers and Traction Force Microscopy for the Exploration of Matrix Rheology and Keratinocyte Mechanobiology: Model Force- and Displacement-Controlled Experiments

In this work we demonstrate the integration of magnetic tweezers (MT) with substrate deformation tracking microscopy (DTM) and traction force microscopy (TFM) for the investigation of extracellular matrix rheology and human epidermal keratinocyte mechanobiology in the context of human blistering skin diseases. Two model bead-on-gel experiments are described in which an MT device is used to apply a prescribed force or displacement waveform to a fibronectin-coated superparamagnetic bead attached to a type I collagen gel containing a layer of covalently attached red-fluorescent microspheres. Serial fast time-lapse DIC and epifluorescence image acquisitions are used to capture displacements of the bead and microspheres, respectively, in response to the applied force or displacement. Due to the large number of acquired images and the dynamic behavior of substrate microspheres observed during the experiment, new quantitative methods are developed for the tracking and filtering of microsphere displacement data, the selection of L2 regularization parameters used for TFM analysis, and the identification of time intervals within the overall image set that can be approximated as being subject to elastostatic conditions. Two major proof-of-concept applications are described in which integrated MT-DTM/TFM experiments are used to (i) estimate the elastic properties of a fibrillar type I collagen gel substrate and (ii) demonstrate how a force applied to a focal adhesion contact on the apical surface of a living keratinocyte is directly transmitted to basal cell-matrix anchoring junctions as observed by substrate deformations and incremental traction stresses that develop within the collagen subjacent to the cell.

biophysics↗

bioRxiv2018

Substrate deformations induce directed keratinocyte migration

Cell migration is an essential part of many (patho)physiological processes in the body, including keratinocyte re-epithelialization of healing wounds. Recent interest in the mechanobiology of tissues suggests that physical forces and mechanical cues from the wound bed (in addition to biochemical signals) may also play an important role in the healing process. Previously, we explored this possibility and found that polyacrylamide (PA) gel stiffness affected primary human keratinocyte behavior and that mechanical deformations in soft (~1.2 kPA) PA gels produced by neighboring cells appeared to influence the process of de novo epithelial sheet formation. In order to clearly demonstrate that keratinocytes do respond to such deformations, we conducted a series of experiments where we observed the response of single keratinocytes to a prescribed local substrate deformation that mimicked a neighboring cell or evolving multicellular aggregate via a servo-controlled microneedle. We also examined the effect of adding either Y27632, a rho kinase inhibitor, or blebbistatin, a non-muscle myosin II inhibitor, on the response of the cells to PA gel deformations. The results of this study indicate that keratinocytes do sense and respond to mechanical signals comparable to those that originate from substrate displacements imposed by neighboring cells, a finding that could have important implications for the process of keratinocyte re-epithelialization that takes place during normal and pathologic wound healing. Furthermore, the Rho/ROCK pathway and the engagement of NM II are both essential to the observed process of substrate deformation-directed keratinocyte migration.

biophysics↗

bioRxiv2017

Collective cell behaviour in mechanosensing of substrate thickness

Extracellular matrix stiffness has a profound effect on the behaviour of many cell types. Adherent cells apply contractile forces to the material on which they adhere, and sense the resistance of the material to deformation - its stiffness. This is dependent on both the elastic modulus and the thickness of the material, with the corollary that single cells are able to sense underlying stiff materials through soft hydrogel materials at low (<10 {micro}m) thicknesses. Here, we hypothesised that cohesive colonies of cells exert more force and create more hydrogel deformation than single cells, therefore enabling them to mechanosense more deeply into underlying materials than single cells. To test this, we modulated the thickness of soft (1 kPa) elastic ECM-functionalised polyacrylamide hydrogels adhered to glass substrates and allowed colonies of MG63 cells to form on their surfaces. Cell morphology and deformations of fluorescent fiducial-marker labelled hydrogels were quantified by time-lapse fluorescence microscopy imaging. Single cell spreading increased with respect to decreasing hydrogel thickness, with data fitting to an exponential model with half-maximal response at a thickness of 3.2 m. By quantifying cell area within colonies of defined area, we similarly found that colony-cell spreading increased with decreasing hydrogel thickness but with a greater halfmaximal response at 54 m. Depth-sensing was dependent on ROCK-mediated cellular contractility. Surface hydrogel deformations were significantly greater on thick hydrogels compared to thin hydrogels. In addition, deformations extended greater distances from the periphery of colonies on thick hydrogels compared to thin hydrogels. Our data suggest that by acting collectively, cells mechanosense rigid materials beneath elastic hydrogels at greater depths than individual cells. This raises the possibility that the collective action of cells in colonies or sheets may allow cells to sense structures of differing material properties at comparatively large distances.

biophysics↗