Yes-associated protein 1 localization in response to substrate architecture

Open Access
Author:
Chan, Coreena
Area of Honors:
Biomedical Engineering
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
  • Justin Brown, Thesis Supervisor
  • Timothy Jegla, Honors Advisor
Keywords:
  • YAP
  • YAP1
  • yes-associated protein
  • yes-associated protein 1
  • nanofibers
  • osteogenesis
  • osteogenic differentiation
  • RhoA
  • FAK
  • focal adhesions
  • tissue engineering
  • Hippo signaling pathway
  • cancer
  • tumor suppression
Abstract:
Understanding the interactions between stem cells and their extracellular environment is key to the development of bioscaffolds for tissue regeneration. Yes-associated protein 1 (YAP1) is a transcriptional regulator involved in the Hippo signaling pathway that controls organ size and tumor suppression by regulating cell proliferation and apoptosis. Not much is known about the function of YAP1 in bone homeostasis, but studies have shown evidence that YAP1 promotes osteogenesis and that this mechanism may operate using the FAK/RhoA/YAP1 signaling pathway. In this study, we observed YAP1 nuclear localization in response to unique substrate architectures, including altered cell density and nanofiber surfaces, to reveal the role of YAP1 translocation in specific cell activities, particularly in proliferation and osteogenic differentiation. Culturing mouse mesenchymal stem cells (mMSCs) at greater densities resulted in reduced nuclear localization of YAP1, while lower densities saw increased YAP1 nuclear localization. There was no significant difference in YAP1 nuclear location between mMSCs fixed at similar densities but fixed at different time points, suggesting that YAP1 localization in response to cell density is not temporally controlled. YAP1 nuclear translocation was observed at a specific confluency of mMSCs cultured in increasing stepwise densities, suggesting a possible rapid switch mechanism of YAP1 translocation rather than a gradual translocation process. In altering the surface, human mesenchymal stem cells (hMSCs) cultured on nanofiber surfaces compared to control surfaces demonstrated increased nuclear YAP1 localization. The hMSCs cultured on nanofiber surfaces also demonstrated decreased cell spreading, altered aspect ratios, and larger focal adhesions. Culturing hMSCs on small nanofibers compared to large resulted in greater nuclear YAP1 localization. These data suggest that the formation of larger focal adhesions leads to increased activation of the FAK/RhoA/YAP1 pathway, which results in the translocation of YAP1 to the nucleus to regulate osteogenic differentiation. Understanding the FAK/RhoA/YAP1 pathway through modification of substrate architecture may aid in the development of biomaterials for tissue regeneration.