The Effects of Scaffold Rigidity on Retinal Pigment Epithelial Cells Corina White Symposium on Biomaterials Science 24 October 2016
Background Physiology The retina is the light-responsive tissue layer at the back of the eye where the transduction of light signals to vision begins. Optic Nerve Fiber Bipolar Neuron Photoreceptors Retinal Pigment Epithelium Sclera Cornea Choroid Retina Pupil Lens Iris Cillary Body Optic Nerve Ganglion Cell Cone Cell Rod Cell Bruch s Membrane Choroid 2 Modified from: http://webvision.med.utah.edu/book/part-i-foundations/simple-anatomy-of-the-retina/
Background Physiology The Bruch s Membrane (BM) and Retinal Pigment Epithelium (RPE) are crucial in maintaining a viable and functional neural retina. KEY FUNCTIONS OF BM & RPE Provide Physical Support Phagocytosis of Retinal Waste Regulate Transport Secrete Proteins Absorb Excess Light http://www.sens.org/sites/srf.org/files/anuj_fig_2jpg.jpg 3
Several changes to the retina occur naturally with aging and are characteristically present during age-related macular degeneration. NUMBER OF CASES EXPECTED TO DOUBLE BY 2050 HEALTHY AGED Aged Retina Interrupted Junctions Drusen Changes of BM Thickness of membrane increases Higher level of collagen crosslinking Increased presence of lipids Appearance of drusen Aged/Diseased Phenotype Decreased phagocytic activity Altered regulation of transport Altered protein expression 4
Current Approaches & Challenges There are several hurdles that must be overcome in order for current approaches to be translational. APPROACH Bolus Free Cell Injection CHALLENGES Monolayer does not form Long term efficacy still under investigation Does not address altered transport and mechanical properties In vitro cell studies on aged BM indicate poor attachment, morphology, and viability [1,2] Cell-Scaffold Implants Inflammatory response in vivo De-differentiation of transplanted RPE cells [3,4] [1] Lu, B., et al. Stem Cells, 2009. 27(9): p. 2126-35. [2] Sun, K., et al. Mol Vis, 2007. 13: p. 2310-9. PMID: 18199972 [3] Diniz, B., et al. Invest Ophthalmol Vis Sci, 2013. 54(7): p. 5087-96. PMC3726243 [4] Christiansen, A.T., et al. Stem Cells Int, 2012. 2012: p. 454295. PMC3328168 5
Synthetic polymer scaffolds with varying moduli were fabricated. Aim 1: Modulus - Approach Fabricate and characterize scaffolds of various elastic moduli Culture RPE cells on scaffolds to investigate effects of modulus Pre-polymer solution Glass Mold UV Polymerization Poly(ethylene glycol) diacrylate (PEGDA) Argenine-Glycine-Aspartic Acid-PEG-Acrylate Photoinitiator Buffer Glass Slides Pre-polymer solution Spacer UV LIGHT 6
Young's Modulus (kpa) Results Scaffold modulus is tunable through polymer molecular weight and concentration. 1400 1200 1x 2x 1000 Modulus of Native BM [5] 800 600 400 200 [5] Candiello, Joseph. FEBS Journal 274.11 (2007): 2897-908. 0 20 10 5 3.4 PEGDA Molecular Weight (kda) 7
RPE cells qualitatively show different adhesion patterns on different moduli scaffolds. CONTROL Tissue Culture Polystyrene (TCPS) A Day 7 DEAD (Ethidium Homodimer-1) DAPI Results B High Modulus C Low Modulus SCAFFOLDS B C 1000 kpa 60 kpa DECREASING STIFFNESS 8
METABOLIC ACTIVITY (Normalized to Day 1) Results The metabolic activity of RPE cells significantly decreases on a low modulus scaffold during 14 day culture. 1.2 1 HIGH MODULUS LOW MODULUS TCPS * # 0.8 0.6 0.4 0.2 0 Day 7 Day 14 Day of Culture 9
FOLD CHANGE Cells cultured on substrates with different moduli exhibited significant differences in gene expression compared to control. Results 4 3.5 3 2.5 2 1.5 1 0.5 * * * HIGH MODULUS LOW MODULUS * 0 IL-6 MCP-1 IL-8 SMAD3 CRALBP 10
Summary & Conclusions Scaffold modulus affects cell adhesion, metabolic activity, and expression and can be tuned to optimize post-transplantation survival and function. Growing cells on a viscoelastic surface compared to TCPS affects the cells. Scaffolds with a modulus that mimics native BM stiffness demonstrate: More homogenous cell attachment Higher RPE metabolic activity CONCLUSIONS Scaffold modulus can be tuned to control cell behavior and, with a deeper understanding of the effects, it can be optimized to increase posttransplantation survival and function 11
The Effects of Scaffold Rigidity on Retinal Pigment Epithelial Cells Corina White Symposium on Biomaterials Science 24 October 2016