Date of Award

December 2022

Document Type


Degree Name

Doctor of Philosophy (PhD)


Biomedical Sciences

First Advisor

Masfique Mehedi


RSV is a negative-sense, single-stranded RNA virus that infects our respiratory tract and can cause severe bronchiolitis and pneumonia worldwide. RSV bronchiolitis causes more fatalities in infants and newborns and leads to severe hospitalization and even death of children. The host-RSV interaction has yet to be explored properly to explain RSV bronchiolitis. This study aimed to elucidate the connection between the modulation of host actin cytoskeletal with viral pathogenesis, including bronchiolitis. As bronchial wall thickening is a common feature of bronchiolitis, the contribution of RSV-infected airway epithelium to bronchial wall thickening was evaluated. RSV infection in the healthy adult bronchial epithelium revealed that RSV infects primarily ciliated cells. RSV substantially induced the actin cytoskeleton's expansion without compromising epithelial membrane integrity and ciliary functions. The actin modulation by RSV infection increased the airway epithelial height. Besides the direct involvement of cytoskeletal factors, the immunological factors, including INF-L1, TNF-α, and IP10, and viral factors, such as nonstructural protein 2 (NS2), could indirectly involve in this process. In addition, whether the morphological change of respiratory epithelial cells during RSV infection has any relationship with epithelial-mesenchymal transition (EMT) was evaluated because persistent RSV infection with chronic lung complications showed a connection with EMT, according to previous reports. In contrast to a potent EMT inducer TGF-β1, RSV did not induce EMT in three different in vitro lung models: A549 cell line, primary normal human bronchial epithelial cells, and pseudostratified airway epithelium. Interestingly, RSV-induced expanded cytoskeleton increased cell surface area and perimeter in the infected airway epithelial cells, distinct from the TGF-β1-driven cell elongation. Indeed, genome-wide transcriptome analysis revealed that both RSV and TGF-β1 have distinct modulatory patterns of the EMT genes. Furthermore, as RSV spreads through cell-to-cell contact by filopodia in addition to shedding, and CDC42 is an upstream regulator of actin polymerization and filopodia formation; therefore, the contribution of CDC42 to filopodia-driven, cell-to-cell transmission of RSV was evaluated. RSV infection in human alveolar basal epithelial cells (A549 cell) increased CDC42 expression. A549 cells transfected with siRNA targeting CDC42 reduced RSV shedding substantially. In line with the previous result, the CDC42 knockdown reduced the quantity and length of the filopodia due to RSV infection. Thus, CDC42 knockdown in A549 cells demonstrated a two-fold effect, including a reduction of virus shedding and a decline in the amount and length of RSV-induced filopodia. Overall, these findings contribute to the upcoming mechanical studies to examine the actin cytoskeletal response of host cells during RSV pathogenesis.

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