Browsing by Author "Fahrenholtz, Monica"

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    Cancer-Associated Fibroblasts Induce a Collagen Cross-link Switch in Tumor Stroma
    (American Association for Cancer Research, 2016) Pankova, Daniela; Chen, Yulong; Terajima, Masahiko; Schliekelman, Mark J.; Baird, Brandi N.; Fahrenholtz, Monica; Sun, Li; Gill, Bartley J.; Vadakkan, Tegy J.; Kim, Min P.; Ahn, Young-Ho; Roybal, Jonathon D.; Liu, Xin; Cuentas, Edwin Roger Parra; Rodriguez, Jaime; Wistuba, Ignacio I.; Creighton, Chad J.; Gibbons, Don L.; Hicks, John M.; Dickinson, Mary E.; West, Jennifer L.; Grande-Allen, K. Jane; Hanash, Samir M.; Yamauchi, Mitsuo; Kurie, Jonathan M.; Bioengineering
    Intratumoral collagen cross-links heighten stromal stiffness and stimulate tumor cell invasion, but it is unclear how collagen cross-linking is regulated in epithelial tumors. To address this question, we used KrasLA1 mice, which develop lung adenocarcinomas from somatic activation of a KrasG12D allele. The lung tumors in KrasLA1 mice were highly fibrotic and contained cancer-associated fibroblasts (CAF) that produced collagen and generated stiffness in collagen gels. In xenograft tumors generated by injection of wild-type mice with lung adenocarcinoma cells alone or in combination with CAFs, the total concentration of collagen cross-links was the same in tumors generated with or without CAFs, but coinjected tumors had higher hydroxylysine aldehyde–derived collagen cross-links (HLCC) and lower lysine-aldehyde–derived collagen cross-links (LCCs). Therefore, we postulated that an LCC-to-HLCC switch induced by CAFs promotes the migratory and invasive properties of lung adenocarcinoma cells. To test this hypothesis, we created coculture models in which CAFs are positioned interstitially or peripherally in tumor cell aggregates, mimicking distinct spatial orientations of CAFs in human lung cancer. In both contexts, CAFs enhanced the invasive properties of tumor cells in three-dimensional (3D) collagen gels. Tumor cell aggregates that attached to CAF networks on a Matrigel surface dissociated and migrated on the networks. Lysyl hydroxylase 2 (PLOD2/LH2), which drives HLCC formation, was expressed in CAFs, and LH2 depletion abrogated the ability of CAFs to promote tumor cell invasion and migration.
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    Investigation of Cell Sources and Surface Modification Strategies for Hybrid and Tissue Engineered Heart Valves
    (2015-11-16) Fahrenholtz, Monica; Grande-Allen, K. Jane
    Bioprosthetic heart valve replacements often calcify and fail, particularly when used to treat pediatric patients. Even recent advances in processing methods have been insufficient to completely address the risk of complications in the pediatric population. Fully synthetic tissue engineered heart valve (TEHV) replacements have been suggested as an ideal replacement, as they can be seeded with autologous cells to form a viable tissue that is capable of somatic growth and hemostasis. However, this technology is still in development, and will not be available to patients within a short (5-10 year) time period. In the interim, some studies have investigated coating methods for current valve replacements to try to improve their biocompatibility in the short term. However, many of these proposed mechanisms face many regulatory issues because of the processing steps involved. In this work, we investigated the characteristics of pediatric valvular interstitial cells (VICs) and their comparability to a potential surrogate cell source, dermal fibroblasts, for long-term TEHV development. We found that these cells behave similarly, particularly when cultured on collagen type I substrates. This study provides additional guidance for the development of TEHVs specifically for pediatric patients and expands current knowledge about pediatric VICs, a previously understudied cell population. The next studies focused on advancing short-term solutions for biocompatibility in bioprosthetic heart valve replacements. Due to the individual variability and difficulty analyzing bioprosthetic tissue, a model surface was developed to aid the optimization of surface coating methods for tissue valves. The bioprosthetic valve surface model (BVSM) was shown to have comparable surface mechanical properties, residual toxicity from glutaraldehyde fixation, and content of reactive groups for surface coating. Additionally, the BVSM was easy to construct, highly reproducible, and allowed for fine-tuning of the surface characteristics which could be altered for future studies of cellular interactions with the surface. In general, the BVSM developed in this work can be applied to optimize and analyze surface coating methods quickly and easily and to answer questions related to cell behavior in response to the surface coatings. Finally, the BVSM was applied in a final study to optimize our proposed two-step surface coating method for bioprosthetic heart valve replacements. This two-step coating method involves non-toxic, mild reactants and conditions which create a thin, polyethylene glycol (PEG)-based hydrogel coating on the surface. This coating can also include other molecules of interest without changes to the reaction protocol. Through the optimization on the BVSM, we demonstrated the formation of a thin, continuous surface coating that successfully repelled protein adsorption and did not significantly affect the BVSM surface mechanical properties. Based on this success, the coating method was translated directly to bioprosthetic tissue samples. Results showed areas of coating formation of the coating on the tissue, confirmed by both SEM and XPS analysis, and that the areal coverage of the coating could be improved with an increase in catalyst concentration. This work demonstrates the feasibility of this proposed coating method for modifying the surface of bioprosthetic heart valve tissue, which could improve the biocompatibility of these devices. In future studies, this coating can be easily modified with molecules to encourage in situ endothelialization for even better hemocompatibility, particularly for pediatric patients. The cell characterization, optimization tools, and coating method developed here could lead to breakthroughs in current device biocompatibility and will support the long-term development of TEHVs as an ideal pediatric valve replacement.
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    Surface coating method to improve implantable device biocompatibility
    (2019-06-18) Fahrenholtz, Monica; Grande-Allen, Kathryn Jane; Rice University; United States Patent and Trademark Office
    Techniques for modifying the surface of implantable devices, such as bioprosthetic valves, to improve the biocompatibility of the implantable devices are provided. In particular, a customizable, non-fouling surface coating may be formed on the surface of implantable devices that improves the biocompatibility of the implantable devices and has the potential to further reduce the occurrence of complications for patients of all ages. Additionally, various molecules of interest to specifically promote endothelialization of the implantable device may be added to the surface coating, which may facilitate the formation of an endothelial layer on the surface of the implantable device that would naturally maintain a non-thrombogenic, non-immunogenic environment in the long-term.