Date of Award
Doctor of Philosophy (PhD)
The bladder urothelium forms a highly specialized watertight barrier to urinary wastes. The urothelium offers an unusual example of tissue regeneration: although urothelial cells do not rapidly turn over under physiological conditions, they have an impressive capacity to regenerate tissue upon injury. Even more remarkable, depending on the modality of injury (sterile, infectious) there appear to be two distinctive modes of urothelial regeneration. We have previously shown that in response to a urinary tract infection (UTI), the urothelial stem cell niche becomes activated and induces rapid restoration of the urothelium, whereas, regeneration following sterile injury does not involve stem cell activity. However, the key driver(s) of mode of regeneration choice has yet to be elucidated.To better understand the regulatory pathways important for tissue regenerative response, we performed large unbiased RNA-Seq and proteomics analyses. We identified interferon-related developmental regulator 1 (IFRD1), a transcriptional co-regulator, as a gene that is rapidly activated upon the induction of a UTI. Ifrd1 has been shown recently to be important for paligenosis, a process differentiated cells use to reenter the cell cycle to regenerate lost tissue. Interestingly, we observe that even in the absence of injury, loss of Ifrd1 results in gross urothelial xi defects: excess vesicular congestion in terminally differentiated cells including aberrant accumulation of mitochondria and abnormal endoplasmic reticulum (ER). Furthermore, we show that Ifrd1 affects localization and trafficking of uroplakins, tetraspanin proteins that constitute organized urothelial plaques, and which dimerize in the ER and assemble into heterotetramer in the Golgi and trans-Golgi network (TGN), where they undergo chain-specific glycosylation and proteolytic processing. Fully formed uroplakin plaques are then expressed along the apical surface of the urothelium where they are eventually endocytosed and undergo recycling. Loss of Ifrd1 results in dysfunctional uroplakin ER-> Golgi translocation and aberrant accumulation in ER. Proteomic analyses revealed a significant increase in the unfolded protein response (UPR) and stress. In agreement with this, we note an increase in the ER chaperone, Bip and the association of IFRD1 with a number of eIF2α subunits, the critical translation initiation factor that quenches global, cellular mRNA translation and can ultimately trigger apoptosis. Indeed, induction of injury in the ifrd1-/- mouse results in massive epithelial exfoliation into the urine and dysregulated recruitment of progenitor cells for regeneration. Ongoing work is elucidating the molecular underpinnings of this response. In sum, we suggest IFRD1 plays a role in the decision-making matrix of urothelial regeneration and that IFRD1 plays a role in urothelial plasticity.
Chair and Committee
Indira U. Mysorekar
Fashemi, Bisiayo Erionmwon, "The Decision Maker: Understanding the role of IFRD1 in urothelial plasticity and regeneration" (2020). Arts & Sciences Electronic Theses and Dissertations. 2584.