Monocytic U937 Adhesion, Tumor Necrosis Factor-Alpha and Interleukin-1 Beta Expression in Response to Gelatin-Based Networks Grafted with Arginine-Glycine-Aspartic Acid and Proline-Histidine-Serine-Arginine-Asparagine Oligopeptides

The effects of TGF-alpha, IL-1beta and PDGF on fibroblast adhesion to ECM-derived matrix and KGF gene expression

The goal of this study was to elucidate the control mechanisms by which exogenous proteins regulate keratinocyte growth factor (KGF) expression in fibroblasts adhered to differing substrates and thereby provide insights into both fundamental in vitro cell signaling and cell-biomaterial interaction research. A serum-free culture system in which cells maintained their proliferative capacity was established and employed. The addition of transforming growth factor- alpha (TGF-alpha), interleukin-1beta (IL-1beta) and platelet-derived growth factor-BB (PDGF-BB) individually showed no effect on KGF protein release, however, IL-1beta addition led to increased KGF mRNA transcription, intracellular KGF protein synthesis, and granulocyte-macrophage colony-stimulating factor (GM-CSF) release. Intracellular KGF protein synthesis and extracellular release were enhanced when fibroblasts were treated with a combination of IL-1beta and PDGF-BB which suggests KGF synthesis and release are largely regulated by synergistic mechanisms. Surface-bound fibronectin-derived ligands and individual exogenous proteins promoted fibroblast adhesion to semi-interpenetrating polymer networks (sIPNs) but did not stimulate KGF release despite enhancement of KGF mRNA transcription. Additionally, serum conditioning was found to have a significant impact on KGF synthesis and the subsequent mechanisms controlling KGF release. This study demonstrates that KGF release from fibroblasts is likely regulated by multiple mechanisms involving post-transcriptional and exocytic controls which may be impacted by the presence of serum and how serum is removed from the in vitro cell environment.

Identification of regulatory Hck and PAI-2 proteins in the monocyte response to PEG-containing matrices

Mass spectrometry is a powerful proteomic tool enabling researchers to survey the global proteome of a cell. This technique has only recently been employed to investigate cell-material interactions. We had previously identified material scarcity and limited adherent cells as challenges facing mass spectrometric analysis of cell-material interactions. U937 adherent to tissue culture poly(styrene) was used as a model system for identifying proteins expressed by adherent monocytes and analyzed by HPLC coupled offline to MALDI-ToF/ToF (LC-MALDI). We identified 645 proteins from two cation fractions of crude U937 monocyte cell lysate. Forty three proteins of interest from the 645 were chosen based on literature searches for relevance to monocyte-material inflammation and wound healing. Proteins such as 40S ribosomal protein S19 and tyrosyl tRNA synthetase highlight the ability of LC-MALDI to identify proteins relevant to monocyte-material interactions that are currently unexplored. We used PEG-based semi-interpenetrating polymer networks and PEG-only hydrogels to investigate surface dependent effects on the Src family kinase Hck and plasminogen activator inhibitor-2 (PAI-2) using the pyrazolo pyrimidine small molecule inhibitor PP2 and exogenous urokinase plasminogen activator addition, respectively. Hck is well researched in cell adhesion while PAI-2 is virtually unknown in cell-material interactions. U937 on TCPS and PEG-only hydrogels secreted similar levels of inflammatory cytokines and gelatinase MMP-9. MCP-1 secretion from monocytes on PEG-only hydrogels was Hck independent in contrast to Hck-dependent MCP-1 secretion in U937 on TCPS. Overall, U937 adherent to sIPNs secrete low levels of soluble gelatinase MMP-9, IL-1beta, TNF-alpha, IL-6, and MCP-1 independent of Hck and PAI-2. This work demonstrates significant changes in surface dependent expression of proteins from monocytes adherent to PEG-based materials compared to TCPS.

Modulation of the keratinocyte-fibroblast paracrine relationship with gelatin-based semi-interpenetrating networks containing bioactive factors for wound repair

Gelatin-based semi-interpenetrating networks (sIPNs) containing soluble and covalently-linked bioactive factors have been shown to aid in wound healing; however, the biological responses elicited by the introduction of sIPN biomaterials remain unclear. In the current study, modulation of the re-epithelialization phase of wound healing by sIPNs grafted with PEGylated fibronectin-derived peptides and utilized as platforms for the delivery of exogenous keratinocyte growth factor (KGF) was evaluated. Following wounding, keratinocyte migration, proliferation and protein secretion is largely controlled by diffusible factors, such as KGF, released by the underlying fibroblasts. The impact of sIPNs and exogenous KGF upon the latter keratinocyte-fibroblast paracrine relationship and keratinocyte behavior was explored by monitoring keratinocyte adhesion and cytokine (IL-1alpha, IL-1beta, IL-6, KGF, GM-CSF and TGF-alpha) release. Results were generally similar for keratinocyte monoculture and keratinocyte-fibroblast co-culture systems. Although keratinocyte adhesion increased over time for positive control surfaces, adhesion to the sIPNs remained low throughout the course of the study. Release of IL-1alpha and GM-CSF was increased by exogenous KGF. The effects were more noticeable on the positive control surfaces relative to the sIPN surfaces. Regulation of the release of TGF-alpha was surface dependent, while IL-6 release was dependent upon surface type, the inclusion of exogenous KGF and the presence of fibroblasts. The findings indicate that during re-epithelialization, sIPNs containing soluble bioactive factors aid in wound healing primarily by serving as conduits for KGF, which induces the release of other key cytokines involved in tissue repair.

A study of diffusion in poly(ethyleneglycol)-gelatin based semi-interpenetrating networks for use in wound healing

Semi-interpenetrating networks (sIPNs) designed to mimic extracellular matrix via covalent crosslinking of poly(ethylene glycol) diacrylate in the presence of gelatin have been shown to aid in wound healing, particularly when loaded with soluble factors. Ideal systems for tissue repair permit an effective release of therapeutic agents and flow of nutrients to proliferating cells. Appropriate network characterization can, consequently, be used to convey an understanding of the mass transfer kinetics necessary for materials to aid in the wound healing process. Solute transport from and through sIPNs has not yet been thoroughly evaluated. In the current study, the diffusivity of growth factors and nutrients through the polymeric system was determined. Transport of keratinocyte growth factor was modeled by treating the sIPN as a plane sheet into which the protein was loaded. The diffusion coefficient was determined to be 4.86 × 10^-9 ± 1.86 × 10^-12 cm²/s. Glucose transport was modeled as flow through a semi-permeable membrane. Using lag-time analysis, the diffusion coefficient was calculated to be 2.25 × 10^-6 ± 1.98 × 10^-7 cm²/s. The results were evaluated in conjunction with previous studies on controlled drug release from sIPNs. As expected from Einstein-Stokes equation, diffusivity decreased as molecular size increased. The results offer insight into the structure-function design paradigm and show that release from the polymeric system is diffusion controlled, rather than dissolution controlled.