Item – Theses Canada

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OCLC number
429724837
Link(s) to full text
LAC copy
LAC copy
Author
Benton, Carley R.(Carley Robin),1975-
Title
The roles of PPAR[alpha], PPAR[gamma] and PGC-1[alpha] on the regulation of the fatty acid transport proteins FATCD36 and FABPpm and effects on skeletal muscle fatty acid transport rate and oxidation.
Degree
Ph. D. -- University of Waterloo, 2006
Publisher
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2007]
Description
2 microfiches
Notes
Includes bibliographical references.
Abstract
The regulation of fatty acid metabolism in skeletal muscle is important as dysregulation can lead to the development of disease states such as insulin resistance and diabetes. The fatty acid transport proteins FAT/CD36 and FABPpm, which reside in the plasma membrane, are integral to this regulation as they function to move fatty acids into skeletal muscle cells. The molecular signals regulating these transport proteins are currently unknown and there is some speculation that the PPAR family of transcription factors, and their co-activator PGC-1[alpha], may play some role in their regulation. Therefore, the purpose of this thesis was to (i) examine whether the PPARs and PGC-1[alpha] play a role in the regulation of FAT/CD36 and FABPpm and (ii) examine the role of PGC-1[alpha] in both sensing and regulating the cellular environment of skeletal muscles and the induction of subsequent alterations of fatty acid metabolism. In the first study we utilized a 1-week contraction protocol to examine the independent and combined effects of chronically increased muscle contraction, and the PPAR[alpha] and [gamma] activators Wy 14,643 and Rosiglitazone, on both the expression and plasmalemmal content of FAT/CD36 and FABPpm and on the rate of fatty acid transport. In resting muscle PPAR[alpha] or [gamma] activation failed to induce the expression of FAT/CD36, while PPAR[gamma] activation only induced FABPpm expression. No subsequent changes in transport were observed. The contraction-induced increases in FAT/CD36 and FABPpm were unaltered by PPAR[alpha] or [gamma] activation and changes in protein expression of FAT/CD36 or FABPpm, induced by either contractions or by Rosiglitazone, were largely attributable to increased transcription. The data of this study shows that in skeletal muscle (i) neither PPAR[alpha] nor [gamma] activation alters FAT/CD36 expression, (ii) PPAR[gamma] activation selectively upregulates FABPpm expression, and (iii) contraction-induced upregulation of LCFA transport does not appear to involve the activation of either PPAR[alpha] or [gamma]. The purpose of the second study was to examine the relationship between PGC-1[alpha] expression and the intramuscular fatty acid accumulation in animal models in which the capacity for fatty acid accumulation in muscle is increased (Zucker obese rat) or reduced (FAT/CD36 null (KO) mice). Rates of palmitate incorporation into triacylglycerols were determined in perfused red (RG) and white gastrocnemius (WG) muscles of lean and obese Zucker rats, and in perfused RG and WG muscles of FAT/CD36 KO mice (KO) and wild type (WT) mice. Palmitate incorporation into triacylglycerol depots was higher in both RG and WG of Zucker obese rats compared with their lean counterparts and was lower in the RG and WG muscles of the FAT/CD36 KO mice vs. wildtype mice. In contrast, PGC-1[alpha] protein content was reduced in both RG and WG in Zucker obese rats relative to leans, while PGC-1[alpha] protein content was upregulated in both RG and WG in FAT/CD36 KO mice compared with wildtype mice. The results of this study indicate that PGC-1[alpha] protein expression is inversely related to components of intramuscular lipid metabolism and may be involved in regulating the cellular responses to alterations in the intramuscular milieu. The purpose of the third study was to (i) measure correlations between PGC-1[alpha] protein expression and both skeletal muscle fiber-type and proteins used as markers of different aspects of fatty acid metabolism, (ii) examine if these correlations, between proteins, are maintained when PGC-1[alpha] is overexpressed, and (iii) examine the effects of PGC-1[alpha] overexpression on mitochondrial palmitate oxidation. To overexpress PGC-1[alpha], 500[mu]g of PGC-1[alpha] DNA was electrotransfected (ET) into red and white tibialis anterior muscles (RTA and WTA). PGC-1[alpha] was shown to be very highly correlated with oxidative fibre type and metabolic and mitochondrial proteins including GLUT4, FABPpm, FAT/CD36, MCT1 and COX4. Following ET for a two-week period, increased protein expression was observed for PGC-1[alpha], FAT/CD36, GLUT4, MCT1, and COX4. In conjunction with the increases in protein expression increases were observed in the palmitate oxidation rate in red and white subsarcolemmal (SS) mitochondria, with no changes observed in either the red or white intermyofibrillar (IMF) mitochondria. The results of this study indicate PGC-1[alpha] co-regulates a co-ordinated metabolic program that results in a more aerobic muscle phenotype, and that this program extends beyond the mitochondrion. In summary, these studies have shown that the PPAR[alpha] and [gamma] isoforms have little to no role as transcription factors governing the contraction-induced increase in expression of FAT/CD36 and FABPpm in skeletal muscle (study 1). In addition, PGC-1[alpha] expression is inversely related to triacylglycerol accumulation in skeletal muscle (study 2), but is highly correlated with both oxidative fiber type and selective markers of oxidative metabolism (study 3). Also, overexpression of PGC-1[alpha] in skeletal muscle increases mitochondrial palmitate oxidation in both red and white fractions of SS mitochondria, with no increase observed in IMF mitochondria (study 3). These findings indicate that while the PPARs and PGC-1[alpha] are implicated in governing aspects of muscle metabolism, it is still unclear whether they are involved in the direct regulation of FAT/CD36 or FABPpm. It is highly probable that other molecular signals are involved and future attention needs to focus on elucidating possible molecular signals, such as specific transcription factors, that function in the regulation of FAT/CD36 and FABPpm.
ISBN
9780494236734
0494236736