Stephen Redenti

Engineering retinal progenitor cell and scrollable poly(glycerol-sebacate) composites for expansion and subretinal transplantation.

Retinal degenerations cause permanent visual loss and affect millions world-wide. Presently, a novel treatment highlights the potential of using biodegradable polymer scaffolds to induce differentiation and deliver retinal progenitor cells for cell replacement therapy. In this study, we engineered and analyzed a micro-fabricated polymer, poly(glycerol sebacate) (PGS) scaffold, whose useful properties include biocompatibility, elasticity, porosity, and a microtopology conducive to mouse retinal progenitor cell (mRPC) differentiation. In vitro proliferation assays revealed that PGS held up to 86,610 (+/-9993) mRPCs per square millimeter, which were retained through simulated transplantations. mRPCs adherent to PGS differentiated toward mature phenotypes as evidenced by changes in mRNA, protein levels, and enhanced sensitivity to glutamate. Transplanted composites demonstrated long-term mRPC survival and migrated cells exhibited mature marker expression in host retina. These results suggest that combining mRPCs with PGS scaffolds for subretinal transplantation is a practical strategy for advancing retinal tissue engineering as a restorative therapy.

Survival, migration and differentiation of retinal progenitor cells transplanted on micro-machined poly(methyl methacrylate) scaffolds to the subretinal space.

Stem and progenitor cells can be combined with polymer substrates to generate tissue equivalents in culture. The replacement of retinal tissue lost to disease or trauma using retinal progenitor cells (RPCs) delivered on polymer scaffolds and transplanted into the sub-retinal space of the damaged retina is a promising therapeutic strategy. Micromachining-based, ultra-thin PMMA poly(methyl methacrylate) scaffolds may provide a suitable cytoarchitectural environment for tissue engineering and transplantation to the diseased eye. Here, adhesion of RPCs to polymer, as well as migration and differentiation in the host retina were compared for PMMA scaffolds (6 microm thickness) with either smooth or porous (11 microm diameter) surface topography. RPCs were cultured under identical conditions on smooth or porous laminin-coated polymer scaffolds and transplanted into the subretinal space of C57BL/6 mice. RPCs could be cultured on both scaffolds with similar results, although transplantation with non-porous scaffolds showed limited RPC retention. Porous scaffolds demonstrated enhanced RPC adherence during transplantation and allowed for greater process outgrowth and cell migration into the host retinal layers. Integrated cells expressed the mature neuronal marker neurofilament-200 (nf-200), the glial marker glial fibrillary acidic protein (GFAP) and the retinal-specific marker recoverin. No host foreign body response was seen. In conclusion, ultra-thin film PMMA scaffolds micromachined to contain through pores retain adherent RPCs to a considerably greater extent than unmachined versions during the transplantation process and can serve as a biocompatible substrate for cell delivery in vivo.

The use of progenitor cell/biodegradable MMP2-PLGA polymer constructs to enhance cellular integration and retinal repopulation.

The inability of the adult mammalian retina to regenerate can be partly attributed to the expression of injury-induced inhibitory extracellular matrix (ECM) and cell adhesion molecules. In particular, photoreceptor degeneration stimulates deposition of the inhibitory ECM proteins neurocan and CD44 at the outer limits of the dystrophic retina, where they act as a barrier against cellular migration and axonal extension. We have previously shown that degradation of these molecules, via induction of MMP2, promotes host-donor integration and retinal repopulation following transplantation. Here we present a biodegradable/biocompatible polymer scaffold that has the ability to deliver MMP2, in conjunction with retinal progenitor cells, directly to the site of retinal injury in an attempt to enhance cellular integration and promote retinal repopulation. Pre-activated MMP2, loaded into a PLGA polymer, maintained its activity throughout polymer fabrication and hydrolysis. Following delivery, significant degradation of CD44 and neurocan from the outer limits of the dystrophic retina, without further disruption of retinal architecture, was observed. As a result, the number of retinal progenitor cells that migrated beyond the glial barrier into the degenerating host increased significantly. These cells took up residence in the retinal outer nuclear layer, adopted appropriate photoreceptor morphology and expressed the mature photoreceptor markers recoverin and rhodopsin. Thus, we have created a cell delivery platform that upon transplantation provides controlled release of active-MMP2 directly to the site of retinal injury, stimulating inhibitory ECM barrier removal and enhancement of stem cell integration and retinal repopulation.

Microfabrication of a Three-Dimensional Polycaprolactone Thin-Film Scaffold for Retinal Progenitor Cell Encapsulation

Retinal degenerations are the leading cause of irreversible visual disability among the adult population. Stem-cell-based therapy has the potential to preserve and restore vision in these conditions. In addition to replacing lost or diseased cells, transplanted cells may be able to rescue dying photoreceptors of the host retina. To fully realize the potential of these cells, improved methods for cell delivery are needed. Utilizing microfabrication processes, a novel biodegradeable thin-film cell encapsulation scaffold was developed in polycaprolactone (PCL) as a possible cell transplantation vehicle. Individual thin-film 2–2.5-D PCL layers (<10 μm thin) were structured with varying micro- and nano-geometries (protrusions, cavities, pores, particles) utilizing a modified spin-assisted solvent casting and melt templating technique. Thin-film layers were aligned and thermally bonded to form the 3-D cell encapsulation scaffold (<30 μm thin) and these were found to promote retinal progenitor cell (RPC) retention and provide appropriate permeability. The resulting scaffolds provide a novel platform for the delivery of cells to the outer retina that addresses critical biological constraints related to transplantation to this anatomical location.

Molecular characterization of human retinal progenitor cells.

PURPOSE To examine the molecular profile of fetal human retinal progenitor cells (hRPCs) expanded in vitro and those grown in a co-culture system with mouse retina through the analysis of protein and gene expression and neurotransmitter-stimulated calcium dynamics. METHODS hRPCS were isolated from human retina of 14 to 18 weeks gestational age (GA) and expanded in vitro. Immunoblot, microarray, and immunocytochemistry (ICC) assays were performed on undifferentiated hRPCs and those co-cultured with mouse retinas for 2 weeks. Cell function was assessed by using calcium imaging. RESULTS The ICC results showed a gradual decrease in the percentages of KI67-, SOX2-, and vimentin-positive cells from passages (P) 1 to P6, whereas a sustained expression of nestin and PAX6 was observed through P6. Microarray analysis of P1 hRPCs showed the expression of early retinal developmental genes: VIM (vimentin), KI67, NES (nestin), PAX6, SOX2, HES5, GNL3, OTX2, DACH1, SIX6, and CHX10 (VSX2). At P6, hRPCs continued to express VIM, KI67, NES, PAX6, SOX2, GNL3, and SIX6. On co-culture, there was a significant increase in the expression of MKI67, PAX6, SOX2, GNL3, SIX3, and RHO (rhodopsin). Calcium imaging showed a functional response to excitatory neurotransmitters. CONCLUSIONS Fetal-derived hRPCs show molecular characteristics indicative of a retinal progenitor state up to P6 (latest passage studied). They show a progressive decrease in the expression of immature markers as they reach P6. These cells are functional, respond to excitatory neurotransmitters, and exhibit changes in expression patterns in response to co-culture with mouse retina.

Neuroimaging of zinc released by depolarization of rat retinal cells

Zinc is associated with glutamatergic pathways in brain and retina, yet its role in neuromodulation remains unknown. High concentrations of reactive zinc in vertebrate photoreceptor terminals suggest a neuromodulatory role in the outer plexiform layer but zinc release has not been demonstrated. Using the membrane-impermeable form of the Zn(2+) sensitive fluorescent dye Newport Green, we have demonstrated increased release of Zn(2+) from the rat retina in response to potassium-induced depolarization of retinal cells. This increase was greatest in the outer retina with densest bands observed in the outer plexiform layer and photoreceptor inner segment regions of rat retinal slices.

Localization of zinc transporter-3 (ZnT-3) in mouse retina

Studies of the central nervous system have localized the zinc-transporter-3 (ZnT-3) protein to synaptic vesicles containing glutamate and zinc. We have examined the distribution of the ZnT-3 protein in the light-adapted mouse retina using immunohistochemical techniques. Light microscopic analysis of 15-30-microm retinal sections revealed a rich band of ZnT-3 protein in the region of the outer limiting membrane and photoreceptor inner segments. ZnT-3 reactivity was also present in the outer plexiform, inner nuclear, inner plexiform, and ganglion cell layers. The outer nuclear layer and photoreceptor outer segments did not exhibit ZnT-3 immunoreactivity. In the light-adapted murine retina, ZnT-3 appears localized in regions which have been found reactive for ionic zinc.

Sigma 1 Receptor plays a prominent role in IL-24-induced cancer-specific apoptosis.

Interleukin-24 (IL-24), a member of the IL-10 cytokine family, is an immunomodulatory cytokine that also displays broad cancer-specific suppressor effects. The tumor suppressor activities of IL-24 include inhibition of angiogenesis, sensitization to chemotherapy, and cancer-specific apoptosis. We show that Sigma 1 Receptor (S1R), a ligand-regulated protein chaperone contributes to IL-24 induction of apoptosis. IL-24 generated from an adenovirus expressing IL-24 (Ad.IL-24) induces cancer-specific apoptosis by inducing an endoplasmic reticulum (ER) stress, reactive oxygen species production, and calcium mobilization. The present studies reveals that S1R is required for Ad.IL-24-induced cell death. We provide several lines of evidence to confirm a physical and functional interaction between IL-24 and S1R including: (a) S1R and IL-24 co-localize, as judged by immunocytochemical analysis studies; (b) S1R and IL-24 co-immunoprecipitate using either S1R or IL-24 antibody; (c) S1R agonist (+)-SKF10047 inhibits apoptosis by Ad.IL-24; (d) (+)-SKF10047-mediated inhibition of Ad.IL-24 results in: diminished ER stress protein expression; (e) Calcium mobilization; and (f) ROS production. Collectively, these data demonstrate that S1R interacts with IL-24 and suggest that IL-24:S1R interaction determines apoptosis induction by Ad.IL-24. These studies define Sigma 1 Receptor as a key initial mediator of IL-24 induction of cancer-specific killing. These findings have important implications for our understanding of IL-24 as a tumor suppressor protein as well as an immune modulating cytokine.

Microfluidic Generated EGF-Gradients Induce Chemokinesis of Transplantable Retinal Progenitor Cells via the JAK/STAT and PI3Kinase Signaling Pathways

A growing number of studies are evaluating retinal progenitor cell (RPC) transplantation as an approach to repair retinal degeneration and restore visual function. To advance cell-replacement strategies for a practical retinal therapy, it is important to define the molecular and biochemical mechanisms guiding RPC motility. We have analyzed RPC expression of the epidermal growth factor receptor (EGFR) and evaluated whether exposure to epidermal growth factor (EGF) can coordinate motogenic activity in vitro. Using Boyden chamber analysis as an initial high-throughput screen, we determined that RPC motility was optimally stimulated by EGF concentrations in the range of 20-400ng/ml, with decreased stimulation at higher concentrations, suggesting concentration-dependence of EGF-induced motility. Using bioinformatics analysis of the EGF ligand in a retina-specific gene network pathway, we predicted a chemotactic function for EGF involving the MAPK and JAK-STAT intracellular signaling pathways. Based on targeted inhibition studies, we show that ligand binding, phosphorylation of EGFR and activation of the intracellular STAT3 and PI3kinase signaling pathways are necessary to drive RPC motility. Using engineered microfluidic devices to generate quantifiable steady-state gradients of EGF coupled with live-cell tracking, we analyzed the dynamics of individual RPC motility. Microfluidic analysis, including center of mass and maximum accumulated distance, revealed that EGF induced motility is chemokinetic with optimal activity observed in response to low concentration gradients. Our combined results show that EGFR expressing RPCs exhibit enhanced chemokinetic motility in the presence of low nanomole levels of EGF. These findings may serve to inform further studies evaluating the extent to which EGFR activity, in response to endogenous ligand, drives motility and migration of RPCs in retinal transplantation paradigms.

Actein induces calcium release in human breast cancer cells.

BACKGROUND The triterpene glycoside actein from the herb black cohosh preferentially inhibits the growth of breast cancer cells and activates the ER stress response. The ER IP3 receptor and Na,K-ATPase form a signaling microdomain. Since actein is lipophilic, its action may be limited by bioavailability. PURPOSE To develop actein to prevent and treat cancer, we examined the primary targets and combinations with chemotherapy agents, as well as the ability of nanoparticles to enhance the activity. MATERIALS AND METHODS To reveal signaling pathways, we treated human breast and colon cancer, as well as 293T and 293T (NF-κB), cells with actein, and measured effects using the MTT, luciferase promoter, Western blot and histology assays. To assess effects on calcium release, we preloaded cells with the calcium sensitive dye Fura-2. To enhance bioavailability, we conjugated actein to nanoparticle liposomes. RESULTS Actein strongly inhibited the growth of human breast cancer cells and induced a dose dependent release of calcium into the cytoplasm. The ER IP3 receptor antagonist heparin blocked this release, indicating that the receptor is required for activity. Heparin partially blocked the growth inhibitory effect, while the MEK inhibitor U0126 enhanced it. Consistent with this, actein synergized with the ER mobilizer thapsigargin. Further, actein preferentially inhibited the growth of 293T (NF-κB) cells. Nanoparticle liposomes increased the growth inhibitory activity of actein. CONCLUSIONS Actein alters the activity of the ER IP3 receptor and Na,K-ATPase, induces calcium release and modulates the NF-κB and MEK pathways and may be worthwhile to explore to prevent and treat breast cancer.