AbstractsMedical & Health Science

IkappaB Kinase beta in the Regulation of Cell Migration, Senescence and Fibrosis

by Liang Chen

Institution: University of Cincinnati
Department: Medicine: Toxicology (Environmental Health)
Degree: PhD
Year: 2012
Keywords: Environmental Health; IKK&946; TGF&946; ROS; cornea; wound healing; fibrosis
Record ID: 1983409
Full text PDF: http://rave.ohiolink.edu/etdc/view?acc_num=ucin1329495227


IKKß is a protein kinase critical for the transmission of inflammatory cytokine signals, such as TNFa, to activation of transcription factor NF-¿B and regulation of gene expression. Genetic studies in mice, however, show that IKKß is not only involved in inflammation, but also plays a pivotal role in tissue homeostasis and stress responses. Our previous studies show that IKKß is essential for maintaining redox homeostasis, but the underlying mechanisms and biological consequences have not been understood. The central theme of this thesis is to investigate how IKKß modulates homeostasis and what roles it plays in biological processes. The thesis is composed of three main components. First, mouse fibroblasts were used to investigate the molecular signatures and functions of IKKß. I showed that genetic knockout of Ikkß gene in fibroblasts reduced the expression of anti-oxidants thus increased the intracellular ROS level. The increased ROS in turn activated AP-1, leading to transcriptional activation of the TGFß gene promoter and its expression, while increased TGFß can act through NOX4 to further stimulate ROS production. Removal of IKKß therefore triggered the autocrine amplification of the ROS-TGFß loop that led to progressive ROS accumulation. The IKKß-deficient fibroblasts ultimately displayed SMAD activation, leading to the overproduction of extracellular matrices and remodeling enzymes, accelerated cell motility, and enhanced markers for myofibroblast transformation and cellular senescence. These results suggested that IKKß safeguarded the homeostasis of fibroblasts by repressing a ROS-AP-1-TGFß autocrine regulatory loop. Second, the in vivo roles of IKKß were assessed in keratocytes, the fibroblasts in corneal stoma of the eye. I generated mice with Ikkß ablation specifically in corneal keratocytes. While the knockout mice had normal corneal appearance, suggesting that IKKß was dispensable for corneal keratocytes development and maintenance, they exhibited aggravated infiltration of inflammatory cells, cellular senescence and severe scar formation compared to normal mice in response to alkali burn injury. The wounded corneas of the knockout mice also exhibited enhanced activation of stress response and fibrogenic pathways, including JNK/AP-1 and TGFß/SMAD cascade. Hence, similar to fibroblasts, keratocytes in corneal stroma utilize IKKß for maintaining homeostasis and repressing ROS and TGFß during injury responsesFinally, the roles of IKKß in epithelial cells of the cornea were investigated by generating and using the corneal epithelial-specific Ikkß knockout mice. These mice had normal cornea development and maintenance, but significantly delayed healing of corneal epithelium wounds. Furthermore, delayed wound healing in the knockout cornea was not due to reduced cell proliferation or increased apoptosis, but was correlated to a slower epithelial cell migration. Taken together, results presented in this thesis reveal that IKKß has highly cell type-specific functions apart from its well-recognized roles in…