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Tubular proteinuria and vitamin D deficiency in sickle cell disease

Gliozzi, Megan (2019) Tubular proteinuria and vitamin D deficiency in sickle cell disease. Doctoral Dissertation, University of Pittsburgh. (Unpublished)

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Kidney disease is a significant complication of sickle cell disease (SCD) with great public health concern, causing over 18% of total patient mortality. Proximal tubule (PT) dysfunction, including tubular proteinuria, is a common early symptom of kidney disease in SCD patients and can lead to chronic kidney disease. Although not well understood, PT dysfunction in SCD is thought to be caused by exposure to higher cell-free hemoglobin (Hb) concentrations from increased red blood cell hemolysis. Hb is filtered by the glomerulus to enter the tubule lumen, where it is reabsorbed by PT cells upon binding to multiligand receptors megalin and cubilin. Megalin and cubilin bind to numerous proteins in the kidney filtrate, including albumin, vitamin D binding protein (DBP), and retinol binding protein (RBP), and are important for maintaining vitamin homeostasis and a protein-free urine.

To better understand PT dysfunction at the cellular level, we treated PT cells with physiologic levels of Hb estimated in SCD and measured protein endocytosis and toxicity/oxidative stress. We found that Hb inhibited albumin, DBP, and RBP uptake by PT cells to variable degrees. Hb inhibition occurred in the absence of a cytotoxic response and appeared to be due to direct competition for megalin/cubilin binding. These results suggest that binding competition between Hb and normally filtered proteins may be the primary cause of tubular proteinuria in SCD patients. Additionally, Hb inhibition appeared to be selective for highly alpha helical proteins. Understanding the selectivity of Hb binding competition could help to identify biomarkers and therapeutic compounds to detect and treat tubular proteinuria in SCD patients prior to the onset of kidney disease.

Inhibition of DBP uptake by PT cells could contribute to vitamin D deficiency commonly observed in SCD patients. We also found prolonged Hb exposure created an increased cytotoxic response and alteration of vitamin D hydroxylase expression in PT cells, indicating Hb-induced toxicity may affect vitamin D metabolism. Finally, we observed selective changes in protein reabsorption by PT cells with variation of active vitamin D availability, suggesting further possible complications in protein reabsorption and vitamin D homeostasis in SCD patients with low vitamin D status.


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Item Type: University of Pittsburgh ETD
Status: Unpublished
CreatorsEmailPitt UsernameORCID
Gliozzi, Meganmle24@pitt.edumle240000-0001-7173-4325
ETD Committee:
TitleMemberEmail AddressPitt UsernameORCID
Committee ChairWeisz,
Committee MemberFinegold,
Committee MemberUrban,
Committee MemberJohnston,
Date: 26 September 2019
Date Type: Publication
Defense Date: 30 May 2019
Approval Date: 26 September 2019
Submission Date: 3 June 2019
Access Restriction: 1 year -- Restrict access to University of Pittsburgh for a period of 1 year.
Number of Pages: 114
Institution: University of Pittsburgh
Schools and Programs: School of Public Health > Human Genetics
Degree: PhD - Doctor of Philosophy
Thesis Type: Doctoral Dissertation
Refereed: Yes
Uncontrolled Keywords: Sickle cell disease, tubular proteinuria, proximal tubule, vitamin D, megalin, cubilin
Date Deposited: 26 Sep 2019 16:47
Last Modified: 01 Sep 2020 05:15


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