Publication Date

12-2018

Date of Final Oral Examination (Defense)

10-25-2018

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Biology

Department

Biology

Major Advisor

Allan Albig, Ph.D.

Advisor

Brad E. Morrison, Ph.D.

Advisor

Troy Rohn, Ph.D.

Abstract

The extracellular microenvironment contributes significantly to a cell’s function and behavior. For instance, cell-cell interactions, cell-substrate interactions, and physical forces are all factors of the extracellular environment that can alter cellular behavior. Cells can receive these signals and forces through various membrane channels and receptors that transmit the signals from the extracellular to the intracellular space. Canonical Notch signaling is induced by ligand interactions with neighboring cells, but recent evidence has revealed that Notch signaling can occur through a variety of extracellular stimuli including hyperglycemia, hypoxia, multiple growth factors, fluid shear stress, and extracellular matrix (ECM) composition. Although Notch activation through ligand interactions with adjacent cells have been well established, non-canonical Notch signaling through the microenvironment is poorly understood. Previous evidence suggests a novel activation of Notch signaling through an integrin pathway, proposing Notch as a microenvironmental sensor. Integrins are cell membrane receptors that are mainly recognized for cell-ECM attachment and induction of cellular signaling cascades but have also been shown to respond and transmit signaling through fluid shear stress and ECM stiffness. Since integrins have been shown to regulate Notch signaling and both exhibit a response to fluid shear stress, we hypothesized that Notch signaling responds to fluid shear stress through integrin activation. To test this, we compared Notch activation following exposure to fluid shear stress and Notch activation following shear stress after inhibiting integrin function. Our data confirms that Notch activation is significantly upregulated from fluid shear stress compared to a static control and inhibiting integrin function attenuates this response, suggesting integrins are required for Notch’s upregulation from shear stress. Because integrins also respond and transmit signals from varying ECM stiffness and Notch has been shown to be upregulated during conditions of fibrosis, we hypothesized that Notch signaling will be regulated by varying degrees of ECM stiffness through integrin activation. To investigate this hypothesis, we cultured cells on hydrogels with multiple levels of stiffness and measured Notch signaling. Our results indicate that like shear stress, Notch signaling is influenced by ECM stiffness. Collectively our results indicate that Notch signaling is regulated through microenvironmental forces like fluid shear stress and ECM stiffness and is regulated through integrins. This furthers our understanding of the variations of Notch signaling in response to microenvironmental stimuli and the mechanisms involved. Notch has been implicated in a variety of diseases and our results improve our knowledge of Notch signaling in pathological conditions of the microenvironment including abnormal shear stress (e.g. atherosclerosis) and tissue stiffness (e.g. fibrosis).

DOI

10.18122/td/1469/boisestate

Available for download on Saturday, December 19, 2020

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