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Effects of Stretch on the Bladder Umbrella Cell Apical Junctional Ring

Eaton, Amity (2020) Effects of Stretch on the Bladder Umbrella Cell Apical Junctional Ring. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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A critical component of the epithelial barrier is the apical junctional complex (AJC), a ring- like structure circumscribing polarized epithelial cells, which is composed of the apical-most tight junction, the sub-adjacent adherens junction, and the punctate desmosomes. The AJC is physically associated with both actin and keratin filaments, which also form a belt encircling epithelial cells at the height of the AJC. Together the AJC and its associated cytoskeleton form the apical junctional ring (AJR). Critically, the AJR must maintain its continuity in the face of external mechanical forces that accompany normal physiological functions, such as during breathing, when blood flows through vessels, or when urine accumulates in the bladder; however, it is not well understood how this is accomplished.
To accommodate dramatic changes in urine volume, the AJR of umbrella cells, which line the luminal surface of the bladder, expands during bladder filling and contracts upon voiding; however, the mechanisms that drive these events are unknown. We hypothesize that the active expansion and contraction of the umbrella cell AJR during filling and voiding requires the membrane trafficking of junctional proteins. Using native umbrella cells as a model, we observed that the umbrella cells’ AJR assumed a non-sarcomeric organization in which filamentous actin and α-actinin-4 formed a continuous belt, while non-muscle myosin II A (NMMIIA) formed discontinuous linear tracts along either side of the actin ring. Expansion of the umbrella cell AJR required formin-dependent actin assembly but was independent of NMMII ATPase function. AJR expansion also required membrane traffic, Rab13-dependent exocytosis specifically, but not trafficking events regulated by Rab8a or Rab11a. In contrast, the voiding-induced contraction of the AJR depended on actomyosin dynamics, as well as on RhoA, and dynamin-dependent
endocytosis. Taken together, our studies indicate that an important mechanism by which the urothelium retains continuity in the face of cyclical changes in urine volume is the expansion and contraction of the AJR. Whereas AJR expansion depends on actin polymerization, it also requires exocytosis, presumably of vesicles containing AJR-associated proteins. In contrast, contraction of the AJR is likely driven by actomyosin contraction of the AJR and endocytosis of excess AJR proteins.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Eaton, Amityafe6@pitt.eduafe60000-0003-0791-3411
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairKleyman,
Committee MemberSorkin,
Committee MemberCarattino,
Committee MemberMcClane,
Thesis AdvisorApodaca,
Date: 5 January 2020
Date Type: Publication
Defense Date: 14 October 2019
Approval Date: 5 January 2020
Submission Date: 3 January 2020
Access Restriction: No restriction; Release the ETD for access worldwide immediately.
Number of Pages: 171
Institution: University of Pittsburgh
Schools and Programs: School of Medicine > Cell Biology and Molecular Physiology
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: apical junctional ring, umbrella cell, membrane trafficking
Date Deposited: 06 Jan 2020 02:20
Last Modified: 06 Jan 2020 02:20


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