Publication of the Month | September 2009

Anna C. Balazs and Irving R. Epstein

Emergent or Just Complex?

Efforts toward creating artificial cells are shedding light on how life may have emerged. The concept of emergence in the physical and biological sciences is an elusive one. The term refers to phenomena in which the complexity of structures

SCIENCE; 25 SEPTEMBER 200;  VOL 325; pp 1632-1634

Publication of the Month | August 2009

Wognum S, Lagoa CE, Nagatomi J, Sacks MS, Vodovotz Y.

An Exploratory Pathways Analysis of Temporal Changes Induced by Spinal Cord Injury in the Rat Bladder Wall: Insights on Remodeling and Inflammation.

Background: Spinal cord injuries (SCI) can lead to severe bladder pathologies associated with inflammation, fibrosis, and increased susceptibility to urinary tract infections. We sought to characterize the complex pathways of remodeling,
inflammation, and infection in the urinary bladder at the level of the transcriptome in a rat model of SCI, using pathways analysis bioinformatics.

Methodology/Principal Findings: Experimental data were obtained from the study of Nagatomi et al. (Biochem Biophys Res Commun 334: 1159). In this study, bladders from rats subjected to surgical SCI were obtained at 3, 7 or 25 days post-surgery, and Affymetrix GeneChipH Rat Genome U34A arrays were used for cRNA hybridizations. In the present study, Ingenuity Pathways Analysis (IngenuityH Systems, www.ingenuity.com) of differentially expressed genes was performed. Analysis of focus genes in networks, functional analysis, and canonical pathway analysis reinforced our previous findings related to the
presence of up-regulated genes involved in tissue remodeling, such as lysyl oxidase, tropoelastin, TGF-b1, and IGF-1. This analysis also highlighted a central role for inflammation and infection, evidenced by networks containing genes such as CD74, S100A9, and THY1.

PLoS ONE 4(6): e5852. doi:10.1371/journal.pone.0005852.

Publication of the Month | July 2009

Li J, Olton D, Lee D, Kumta PN, Sfeir C.

Cell derived hierarchical assembly of a novel phosphophoryn-based biomaterial.

Phosphophoryn (PP) is an acidic phosphoprotein belonging to the small integrin-bindingligand N-linked glycoprotein (SIBLING) protein family. PP is highly phosphorylated with approximately 200 phosphates per molecule and has a high affinity for calcium. The aim of this manuscript is to demonstrate that PP has the ability to self-assemble when it is overexpressed in a mammalian cell in the presence of calcium. Our data show that when PP is overexpressed using an adenovirus, the self-assembly occurs in the endoplasmic reticulum (ER) which contains high calcium concentration.

We hypothesize that the physicochemical properties of the highly phosphorylated state and acidic nature of PP are playing an important role in its assembly in the ER. It appears that when a critical concentration of PP is reached, the assembly is then favored and facilitated. This self-assembly could be due to several factors. (1) The ER provides an ideal environment for this phenomenon to occur, since the ER environment usually promotes aggregation [Stevens and Argon: Semin Cell Dev Biol 1999;10:443-454]. (2) In addition to PP's physicochemical properties, the unfolded protein response could also be playing a role in this self-assembly [Schroder and Kaufman: Mutat Res 2005;569:29-63].

Cells Tissues Organs. 2009;189(1-4):252-5.

Publication of the Month | June 2009

Santiago LY, Clavijo-Alvarez J, Brayfield C, Rubin JP, Marra KG

Delivery of adipose-derived precursor cells for peripheral nerve repair

To test the hypothesis that the transplantation of adipose precursor cells (APCs) improves nerve regeneration and functional recovery, human APCs were transplanted into the lumen of a nerve guide in a 6-mm unilateral sciatic nerve defect in athymic rats. The three control groups for the study were biodegradable, polycaprolactone-based nerve conduit without APCs, autograft, and empty defect. Behavioral tests were performed every 3 weeks, and the sciatic functional index (SFI) was calculated based on measurements from the hindlimb prints.

After 12 weeks, the nerve as well as right and left gastrocnemius muscles were removed and preserved for histological evaluation. Full regeneration of the sciatic nerve occurred on the rats that received the autograft, the guide, and the guide with APCs; no regeneration was observed on any of the rats in which the defect was left untreated (empty defect). APCs survived transplantation for up to 12 weeks in the injured peripheral nerve. No significant colocalization was observed between the immunostaining for glial fibrillary protein and anti-human lamin A/C, implying that the APCs did not differentiate into Schwann cells at the site of injury. In comparison with the rats with untreated defects, a decrease in muscle atrophy was observed on those rats that received the autograft and the guide with cells as indicated by the gastrocnemius muscle weight ratio and the muscle fiber ratio.

Cell Transplant. 2009;18(2):145-58

Publication of the Month | May 2009

Parekh A, Mantle B, Banks J, Swarts JD, Badylak SF, Dohar JE, Hebda PA.

Repair of the tympanic membrane with urinary bladder matrix.

OBJECTIVES: To test urinary bladder matrix (UBM) as a potential treatment for tympanic membrane (TM) healing and regeneration.

STUDY DESIGN: This prospective pilot study was designed to provide both qualitative and semiquantitative assessment of temporal and spatial healing events in the chinchilla model of chronic TM perforations with and without UBM patching.

METHODS: Bilateral myringotomies were performed and repeated as necessary to create subtotal perforations over an 8-week period. Myringoplasty was then performed, with left TMs serving as controls and right TMs receiving UBM patches. TMs were excised at 4 weeks, 8 weeks, and 12 weeks. Fixed tissue samples were characterized for gross morphology, then processed for microscopic evaluation.

RESULTS: Chronic perforations were maintained with one or more repeated myringotomies. Although both control and patched TMs were thicker than native tissue, patched TMs were transparent and uniform in thickness without any inclusions. UBM patches were readily degraded and replaced by newly deposited and organized host tissue that recapitulated the native TM layers.

Laryngoscope. 2009 Apr 8;119(6):1206-1213.

Publication of the Month | April 2009

Rothstein SN, Federspiel WJ, Little SR.

A unified mathematical model for the prediction of controlled release from surface and bulk eroding polymer matrices.

A unified model has been developed to predict release not only from bulk eroding and surface eroding systems but also from matrices that transition from surface eroding to bulk eroding behavior during the course of degradation. This broad applicability is afforded by fundamental diffusion/reaction equations that can describe a wide variety of scenarios including hydration of and mass loss from a hydrolysable polymer matrix. Together, these equations naturally account for spatial distributions of polymer degradation rate. In this model paradigm, the theoretical minimal size required for a matrix to exhibit degradation under surface eroding conditions was calculated for various polymer types and then verified by empirical data from the literature. An additional set of equations accounts for dissolution- and/or degradation-based release, which are dependent upon hydration of the matrix and erosion of the polymer. To test the model's accuracy, predictions for agent egress were compared to experimental data from polyanhydride and polyorthoester implants that were postulated to undergo either dissolution-limited or degradation-controlled release. Because these predictions are calculated solely from readily attainable design parameters, it seems likely that this model could be used to guide the design controlled release formulations that produce a broad array of custom release profiles.

Biomaterials. 2009 Mar;30(8):1657-64. Epub 2008 Dec 19.

Publication of the Month | March 2009

Scott MJ, Liu S, Shapiro RA, Vodovotz Y, Billiar TR.

Endotoxin uptake in mouse liver is blocked by endotoxin pretreatment through a suppressor of cytokine signaling-1-dependent mechanism.

The liver is the main organ that clears lipopolysaccharide (LPS) and hepatocytes are a major cell-type involved in LPS uptake. LPS tolerance, or desensitization, is important in negative regulation of responses to LPS, but little is known about its mechanisms in hepatocytes. Primary isolated C57BL/6 hepatocytes, and liver in vivo, internalized fluorescent LPS, and this was dependent on Toll-like receptor 4 (TLR4) at the cell surface but not on TLR4-TIR signaling through MyD88. LPS clearance from plasma was also TLR4-dependent. Pretreatment of C57BL/6 hepatocytes with LPS prevented uptake of LPS 24 hours later and this LPS-mediated suppression was dependent on TLR4 signaling through MyD88. Many regulators of TLR4 signaling have been identified and implicated in LPS desensitization, including suppressor of cytokine signaling 1 (SOCS1). SOCS1 mRNA and protein expression increased after LPS stimulation in hepatocytes and in whole liver.

LPS uptake in hepatocytes and liver was significantly reduced following infection with adenoviral vectors overexpressing SOCS1. Similarly, inhibition of SOCS1 using small interfering (si)RNA-mediated knockdown prevented LPS desensitization in hepatocytes. SOCS1 is known to interact with Toll/IL-1 receptor associated protein (TIRAP) and cause TIRAP ubiquitination and degradation, which regulates TLR signaling. We have also shown previously that TIRAP regulates LPS uptake in hepatocytes. SOCS1 coimmunoprecipitated with TIRAP in wild type hepatocyte cell lysates up to 8 hours after LPS stimulation, but not at later times. In the same samples, ubiquitinated TIRAP was detected after 4 hours and up to 8 hours after LPS stimulation, but not at later times.

Conclusion: These data indicate hepatocytes are desensitized by LPS in a TLR4 signaling-dependent manner. LPS-induced SOCS1 upregulation increases degradation of TIRAP and prevents subsequent LPS uptake. The exploitation of these mechanisms of LPS desensitization in the liver may be important in future sepsis therapies.

Hepatology. 2009 Feb. 9 [Epub ahead of print].

Publication of the Month | February 2009

El-Kurdi MS, Hong Y, Stankus JJ, Soletti L, Wagner WR, Vorp DA.

Transient elastic support for vein grafts using a constricting microfibrillar polymer wrap.

Arterial vein grafts (AVGs) often fail due to intimal hyperplasia, thrombosis, or accelerated atherosclerosis. Various approaches have been proposed to address AVG failure, including delivery of temporary mechanical support, many of which could be facilitated by perivascular placement of a biodegradable polymer wrap. The purpose of this work was to demonstrate that a polymer wrap can be applied to vein segments without compromising viability/function, and to demonstrate one potential application, i.e., gradually imposing the mid-wall circumferential wall stress (CWS) in wrapped veins exposed to arterial levels of pressure. Poly(ester urethane)urea, collagen, and elastin were combined in solution, and then electrospun onto freshly-excised porcine internal jugular vein segments. Tissue viability was assessed via Live/Dead staining for necrosis, and vasomotor challenge with epinephrine and sodium nitroprusside for functionality. Wrapped vein segments were also perfused for 24h within an ex vivo vascular perfusion system under arterial conditions (pressure = 120/80 mmHg; flow = 100 mL/min), and CWS was calculated every hour. Our results showed that the electrospinning process had no deleterious effects on tissue viability, and that the mid-wall CWS vs. time profile could be dictated through the composition and degradation of the electrospun wrap. This may have important clinical applications by enabling the engineering of an improved AVG.

Biomaterials. 2008 Aug;29(22):3213-20. Epub 2008 May 2.

Publication of the Month | January 2009

Wescoe KE, Schugar RC, Chu CR, Deasy BM.

The Role of the Biochemical and Biophysical Environment in Chondrogenic Stem Cell Differentiation Assays and Cartilage Tissue Engineering.

The field of regenerative medicine offers hope for the development of a cell-based therapy for the repair of articular cartilage (AC). Yet, the greatest challenge in the use of stem cells for tissue repair, is understanding how the cells respond to stimuli and using that knowledge to direct cell fate. Novel methods that utilize stem cells in cartilage regeneration will require specific spatio-temporal controls of the biochemical and biophysical signaling environments. Current chondrogenic differentiation research focuses on the roles of biochemical stimuli like growth factors, hormones, and small molecules, and the role of the physical environment and mechanical stimuli, such as compression and shear stress, which likely act through mechanical receptors. Numerous signals are associated with chondrogenic-like activity of cells in different systems, however many variables for a controlled method still need to be optimized; e.g., spatial and temporal application of the stimuli, and time of transplantation of an engineered construct. Understanding the necessary microenvironmental signals for cell differentiation will advance cell therapy for cartilage repair.

Cell Biochem Biophys. 2008;52(2):85-102.