Date of Award

2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Drug Discovery and Biomedical Sciences

College

College of Graduate Studies

First Advisor

Craig C. Beeson

Second Advisor

Rick G. Schnellmann

Third Advisor

James C. Chou

Fourth Advisor

Sherine Chan

Fifth Advisor

Scott T. Eblen

Sixth Advisor

Michael D. Wyatt

Abstract

Acute kidney injury (AKI) is a rapid loss of normal kidney function and is accompanied by a dysregulation of cellular and mitochondrial metabolism, which can be observed before organ dysfunction. A hallmark of AKI is the early and persistent disruption of mitochondrial homeostasis. Mitochondrial biogenesis (MB), the process by which new mitochondria are generated, has been shown to prevent injury and increase the rate of recovery of ischemia-reperfusion injury (IRI)-induced renal dysfunction. However, the molecular mechanisms mediating MB and dysfunction following IRI remain unclear. We elucidated that extracellular signal-regulated kinase 1/2 (ERK1/2) regulates two key mitochondrial and cellular metabolism pathways following AKI. The first is the rapid downregulation of MB through decreased peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) expression, the master regulator of MB. The second is nicotinamide adenine dinucleotide (NAD) loss after IRI, particularly the oxidized form, NAD+. Trametinib, an FDA approved drug, prevents ERK1/2 activation by inhibiting mitogen-activated protein kinase kinase 1/2 (MEK1/2). ERK1/2 inhibition prior to IRI prevents the downregulation of PGC-1α gene expression. In addition, trametinib prevented PGC-1α acetylation, which deactivates PGC-1α, after IRI. This was verified by determining that trametinib inhibited the loss of downstream PGC-1α and MB targets after IRI, including both nuclear- and mitochondrial-encoded genes. NAD+ is a vital coenzyme in cellular metabolism, redox signaling, and contributes to overall cellular health. NAD+ is depleted during injury, and restoration or prevention of this depletion averts worsening injury and often promotes recovery. Inhibition of ERK1/2 activation attenuated NAD+ loss and was mediated through increased nicotinamide phosphoribosyltransferase (NAMPT), the rate-limiting enzyme of the NAD+ biosynthetic salvage pathway. Inhibition of renal ERK1/2 activation decreased miR34a, a known regulator of NAMPT, and led to an increase in NAMPT protein. In conclusion, inhibiting ERK1/2 activation restored PGC-1α protein levels, attenuated the loss of downstream MB targets, increased NAMPT protein, and restored NAD+ after IRI. These cellular alterations ultimately led to restored kidney function following IRI-induced AKI. These studies may help support the identification of potential therapeutic targets for the treatment of AKI.

Rights

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