Shear stress stimulated apical endocytosis in renal proximal tubule epithelia

Raghavan, Venkatesan (2015) Shear stress stimulated apical endocytosis in renal proximal tubule epithelia. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Abstract

The proximal tubule (PT) plays a critical role in the reabsorption of ions, solutes and low molecular weight proteins from the glomerular filtrate. Although the PT has been known to acutely modulate ion reabsorption in response to changes in flow rates of the glomerular filtrate, whether apical endocytosis was regulated in response to changes in flow was unknown. I hypothesized that the fluid shear stress (FSS) caused by the flow of glomerular filtrate on the apical surface of the tubules would stimulate apical endocytosis in PT epithelia. I used a cell culture based parallel plate flow chamber system to test my hypothesis, and used PT cells from opossum, mice and humans in this study. I determined that FSS stimulated a rapidly reversible increase in apical endocytosis of both albumin (Megalin ligand) and dextran (fluid phase marker) in OK cells, which starts within 30 min of exposure to a FSS of 1 dyne/cm2 and the response increases linearly for at least three hours so long as FSS is maintained. This FSS-stimulated increase in endocytosis is clathrin and dynamin mediated. Primary cilia act as the principal mechanosensor in this process, and cause an increase in [Ca2+]i through the release of the ryanodine sensitive pool of calcium from the ER. In addition, purinergic signaling, triggered by the bending of cilia, is also important for both the FSS stimulated Ca2+ and endocytic responses.
Lowe syndrome is a rare X linked genetic disease that affects young boys. It is characterized by the loss of OCRL a lipid phosphatase, and causes proteinuria. The FSS stimulated increase in endocytosis is ablated in OCRL depleted human PT cells, and the length of cilia in OCRL depleted cells is also higher. However, the lengthening of cilia is not responsible for the loss of FSS stimulated responses in these cells. This dissertation synthesizes our current understanding of mechanosensitive regulation of endocytic capacity in proximal tubule epithelia, suggests a mechanism that may define the reason for proteinuria in Lowe syndrome patients, and highlights areas of opportunity for future investigations.

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Details

Item Type:	University of Pittsburgh ETD
Status:	Unpublished
Creators/Authors:	Creators Email Pitt Username ORCID Raghavan, Venkatesan ver12@pitt.edu VER12
ETD Committee:	Title Member Email Address Pitt Username ORCID Thesis Advisor Weisz, Ora A weisz@pitt.edu WEISZ Committee Chair Kiselyov, Kirill Committee Member Apodaca, Gerard gla6@pitt.edu GLA6 Committee Member Benos, Panayiotis V. benos@pitt.edu BENOS Committee Member Carattino, Marcelo mdc4@pitt.edu MDC4
Date:	20 October 2015
Date Type:	Publication
Defense Date:	18 September 2015
Approval Date:	20 October 2015
Submission Date:	20 October 2015
Access Restriction:	No restriction; Release the ETD for access worldwide immediately.
Number of Pages:	183
Institution:	University of Pittsburgh
Schools and Programs:	School of Medicine > Integrative Molecular Biology
Degree:	PhD - Doctor of Philosophy
Thesis Type:	Doctoral Dissertation
Refereed:	Yes
Uncontrolled Keywords:	Proximal tubule, Kidney, endocytosis, calcium, flow, shear stress
Date Deposited:	20 Oct 2015 13:56
Last Modified:	15 Nov 2016 14:30
URI:	http://d-scholarship.pitt.edu/id/eprint/26232

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