Matrix Mechanics Influence Fibroblast–Myofibroblast Transition by Directing the Localization of Histone Deacetylase 4

Bioengineering
Yanfen Li, Claire B. Tang, Kristopher A. Kilian
Cellular and Molecular Bioengineering, Pages 1-11
Publication year: 2017

Introduction—The propagation of mechanochemical signals from the extracellular matrix to the cell nucleus has emerged as a central feature in regulating cellular differentiation and de-differentiation. This process of outside-in signaling and the associated mechanotransduction pathways have been well described in numerous developmental and pathological contexts. However, it remains less clear how mechanotransduction influences the activity of chromatin modifying enzymes that direct gene expression programs.

Objectives—The primary objective of this study was to explore how matrix mechanics and geometric confinement influence histone deacetylase (HDAC) activity in fibroblast culture. Methods—Polyacrylamide hydrogels were formed and functionalized with fibronectin patterns using soft lithography. Primary mouse embryonic fibroblasts (MEFs) were cultured on the islands until confluent, fixed, and immunolabeled for microscopy.

Results—After 24 h MEFs cultured on soft hydrogels (0.5 kPa) show increased expression of class I HDACs relative to MEFs cultured on stiff hydrogels (100 kPa). A member of the class II family, HDAC4 shows a similar trend; however, there is a pronounced cytoplasmic localization on soft hydrogels suggesting a role in outside-in cytoplasmic signaling. Pharmacological inhibitor studies suggest that the opposing activities of extracellular related kinase 1/2 (ERK) and protein phosphatase 2a (PP2a) influence the localization of HDAC4. MEFs cultured on the soft hydrogels show enhanced expression of markers associated with a fibroblast– myofibroblast transition (Paxillin, aSMA).

Conclusions—We show that the phosphorylation state and cellular localization of HDAC4 is influenced by matrix mechanics, with evidence for a role in mechanotransduction and the regulation of gene expression associated with fibroblast–myofibroblast transitions. This work establishes a link between outside-in signaling and epigenetic regulation, which will assist efforts aimed at controlling gene regulation in engineered extracellular matrices.

Cytoskeletal Priming of Mesenchymal Stem Cells to a Medicinal Phenotype

Bioengineering
Amr A Abdeen*, Junmin Lee*, Yanfen Li, Kristopher A Kilian
Regenerative Engineering and Translational Medicine, 2017, 3, 5-14
Publication year: 2017

Mesenchymal stem cell (MSC) therapy is a promising approach for the treatment of cardiovascular disease, demonstrating pronounced trophic, immunomodulatory, and pro-angiogenic activity. However, clinical efficacy has suffered from broad variability, presumably due to cell death upon implantation, and the heterogeneous population of autologous cells. Micropatterning single cells in the same geometry can normalize the phenotype in a population, and variations in subcellular curvature will guide focal adhesion, cytoskeletal organization, and the regulation of distinct epigenetic marks to orchestrate a medicinal secretome. Within 2 days, activated cells show elevated expression of pericyte markers and will recapitulate functional pericyte activity through enhanced association with endothelial cell tubules in co-culture. MSCs are believed to undergo a temporary switch in vivo to an activated state in response to injury; thus, we propose engineering actomyosin contractility after isolation can similarly activate MSCs, which may serve as a general approach to prime a medicinal phenotype for cell-based therapies.

Patterned porous silicon photonic crystals with modular surface chemistry for spatial control of neural stem cell differentiation

Bioengineering
Tiffany H. Huang*, Yi Pei*, Douglas Zhang, Yanfen Li, and Kristopher A. Kilian
Nanoscale, 2016, 8, 10891-10895.
Publication year: 2016

We present a strategy to spatially define regions of gold and nanostructured silicon photonics, each with materials-specific surface chemistry, for azide–alkyne cycloaddition of different bioactive peptides. Neural stem cells are spatially directed to undergo neurogenesis and astrogenesis as a function of both surface properties and peptide identity.

Bridging the gap: from 2D cell culture to 3D microengineered extracellular matrices

Bioengineering
Yanfen Li, Kristopher A Kilian
Advanced Healthcare Materials, 2015, 4 (18), 2780-2796.
Publication year: 2015
Historically the culture of mammalian cells in the laboratory has been
performed on planar substrates with media cocktails that are optimized to
maintain phenotype. However, it is becoming increasingly clear that much of
biology discerned from 2D studies does not translate well to the 3D micro-
environment. Over the last several decades, 2D and 3D microengineering
approaches have been developed that better recapitulate the complex
architecture and properties of in vivo tissue. Inspired by the infrastructure
of the microelectronics industry, lithographic patterning approaches have
taken center stage because of the ease in which cell-sized features can be
engineered on surfaces and within a broad range of biocompatible materials.
Patterning and templating techniques enable precise control over extracel-
lular matrix properties including: composition, mechanics, geometry, cell–
cell contact, and diffusion. In this review article we explore how the fi eld
of engineered extracellular matrices has evolved with the development of
new hydrogel chemistry and the maturation of micro- and nano- fabrication.
Guided by the spatiotemporal regulation of cell state in developing tissues,
techniques for micropatterning in 2D, pseudo-3D systems, and patterning
within 3D hydrogels will be discussed in the context of translating the infor-
mation gained from 2D systems to synthetic engineered 3D tissues.

Cardiorespiratory fitness mediates the effects of aging on cerebral blood flow

Bioengineering
Benjamin Zimmerman, Bradley P Sutton, Kathy A Low, Mark A Fletcher, Chin Hong Tan, Nils Schneider-Garces, Yanfen Li, Cheng Ouyang, Edward L Maclin, Gabriele Gratton, Monica Fabiani
Frontiers in aging neuroscience, 2014, 6, 59
Publication year: 2014

The brain’s vasculature is likely to be subjected to the same age-related physiological and anatomical changes affecting the rest of the cardiovascular system. Since aerobic fitness is known to alleviate both cognitive and volumetric losses in the brain, it is important to investigate some of the possible mechanisms underlying these beneficial changes. Here we investigated the role that estimated cardiorespiratory fitness (eCRF) plays in determining the relationship between aging and cerebral blood flow (CBF) in a group of older adults (ages 55–85). Using arterial spin labeling to quantify CBF, we found that blood flow in the gray matter was positively correlated with eCRF and negatively correlated with age. Subsequent analyses revealed that eCRF fully mediated the effects of age on CBF in the gray matter, but not in the white matter. Additionally, regional measures of CBF were related to regional measures of brain volume. These findings provide evidence that age-related effects on cerebrovascular health and perfusion in older adults are largely influenced by their eCRF levels.