Year of Publication

2014

Degree Name

Doctor of Philosophy (PhD)

Document Type

Doctoral Dissertation

College

Pharmacy

Department

Pharmaceutical Sciences

First Advisor

Dr. Gregory Graf

Abstract

ABCD2 (D2) has been proposed as a peroxisomal long-chain acyl-CoA transporter that is essential for very long chain fatty acid metabolism. In the livers of mice, D2 is highly induced by fenofibrate, a PPARα ligand that has been widely used as a lipid lowering agent in the treatment of hypertriglyceridemia. To determine if D2 is a modifier of fibrate responses, wild-type and D2 deficient mice were treated with fenofibrate for 14 days. The absence of D2 altered expression of gene clusters associated with lipid metabolism, including PPARα signaling. Using 3T3-L1 adipocytes, which express high levels of D2, we confirmed that knock-down of D2 modified genomic responses to fibrate treatment. We next evaluated the impact of D2 on effects of fibrates in a mouse model of dietinduced obesity. Fenofibrate treatment opposed the development of obesity, hypertriglyceridemia, and insulin resistance. However, these effects were unaffected by D2 genotype. We concluded that D2 can modulate genomic responses to fibrates, but that these effects are not sufficiently robust to alter the effects of fibrates on diet-induced obesity phenotypes.

Although proposed as a peroxisomal transporter, the intracellular localization of D2, especially in adipose tissue, has not been validated with direct experimental evidence. Sequential centrifugation of mouse adipose homogenates generated a fraction enriched with D2, but lacked well-known peroxisome markers including catalase, PEX19, and ABCD3 (D3). Electron microscopic imaging of this fraction confirmed the presence of D2 protein on an organelle with evidence of a dense matrix and a diameter of ~200 nm, the typical structure and size of a microperoxisome. D2 and PEX19 antibodies recognized distinct structures in mouse adipose. Immunoisolation of the D2-containing compartment from adipose tissue confirmed the scarcity of PEX19. Proteomic profiling of the D2 compartment revealed the presence of proteins associated peroxisome, endoplasmic reticulum (ER), and mitochondria. We conclude that D2 is localized to a distinct subclass of peroxisomes that lack many peroxisome proteins and may physically associate with mitochondria and the ER.

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