β-Oxidation in hepatocyte cultures from mice with peroxisomal gene knockouts (original) (raw)
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SUBCELLULAR FRACTIONATION STUDIES ON THE ORGANIZATION OF FATTY ACID OXIDATION BY LIVER PEROXISOMES
Annals of the New York Academy of Sciences, 1982
The presence in peroxisomes of the enzymes required for the @-oxidation of fatty acyl-CoA derivatives is now clearly established for a wide variety of tissues and species, including humans.'6 Yet the mechanisms involved in the in vivo regulation of the pathway and its overall rate of activity in intact tissues, are not known. It has been claimed from studies with isolated hepatocytes that only a minor fraction of the peroxisomal activity detected in homogenates, under optimal assay conditions, is expressed in intact ~e 1 l s . l~
Peroxisomal β-oxidation: Insights from comparative biochemistry
Journal of Experimental Zoology, 1991
The activities of fatty acyl-CoA oxidase (FAO) and carnitine palmitoyl transferase (CPT), indices of the capacities of peroxisomal @-oxidation and mitochondrial P-oxidation, respectively, were determined in livers of several vertebrate species notable for differences in dietary fatty acid composition. In suckling rats FA0 activities were half that in adult rats and CPT/FAO ratios twice that of adult rats. As their milk diet is dominated by medium chain fatty acids, this observation is consistent with current ideas about the role of peroxisomal P-oxidation in rat liver in oxidation of long chain unsaturated fatty acids. In nectar-feeding hummingbirds (fatty acids synthesized de novo) FA0 activities were 50% greater than adult rats and CPT/FAO ratios onethird less than adult rats, suggesting that peroxisomal P-oxidation is relatively more important in this species, despite a fatty-acid-poor diet. In marine fish (herring, dogfish shark, hagfish) FA0 activities were all less than 15% that of rats and undetectable in hagfish. CPT/FAO ratios were greater in herring (8.1) and hagfish (> 30) than adult rats (3.11, suggesting that peroxisomal @-oxidation is relatively less important in these species despite a natural diet containing high levels of long chain polyunsaturated fatty acids. These data are discussed in relation to current ideas about the role of peroxisomes in @-oxidation of fatty acids.
Biochemical Journal, 1984
A system was developed in which it is possible to detect in vivo changes in hepatic H202 production, using a combination of the catalase inhibitor, 3-amino-1,2,4-triazole and methanol. In mice, starvation significantly increases hepatic H202 production and plasma non-esterified fatty acid concentrations. Short-term refeeding after a 24h starvation period brings H202 production and plasma non-esterified fatty acid concentration back to normal in 3 h. Administration of insulin 24 h after the onset of starvation normalizes H202 production in less than 2h and decreases non-esterified fatty acid concentration below normal values. The suppression by insulin of H202 production, as well as its coherence with plasma non-esterified fatty acid concentration, indicate that increased H202 production in starved mice reflects peroxisomal ,Boxidation.
Absence of peroxisomes in mouse hepatocytes causes mitochondrial and ER abnormalities
Hepatology, 2005
Peroxisome deficiency in men causes severe pathology in several organs, particularly in the brain and liver, but it is still unknown how metabolic abnormalities trigger these defects. In the present study, a mouse model with hepatocyte-selective elimination of peroxisomes was generated by inbreeding Pex5-loxP and albumin-Cre mice to investigate the consequences of peroxisome deletion on the functioning of hepatocytes. Besides the absence of catalase-positive peroxisomes, multiple ultrastructural alterations were noticed, including hepatocyte hypertrophy and hyperplasia, smooth endoplasmic reticulum proliferation, and accumulation of lipid droplets and lysosomes. Most prominent was the abnormal structure of the inner mitochondrial membrane, which bore some similarities with changes observed in Zellweger patients. This was accompanied by severely reduced activities of complex I, III, and V and a collapse of the mitochondrial inner membrane potential. Surprisingly, these abnormalities provoked no significant disturbances of adenosine triphosphate (ATP) levels and redox state of the liver. However, a compensatory increase of glycolysis as an alternative source of ATP and mitochondrial proliferation were observed. No evidence of oxidative damage to proteins or lipids nor elevation of oxidative stress defence mechanisms were found. Altered expression of peroxisome proliferator-activated receptor alpha (PPAR-␣) regulated genes indicated that PPAR-␣ is activated in the peroxisomedeficient cells. In conclusion, the absence of peroxisomes from mouse hepatocytes has an impact on several other subcellular compartments and metabolic pathways but is not detrimental to the function of the liver parenchyma.
Peroxisomal Lipid Degradation via β and β-oxidation in Mammals
Cell Biochemistry and Biophysics, 2000
Peroxisomal β-oxidation is involved in the degradation of long chain and very long chain fatty acyl-(coenzyme A)CoAs, long chain dicarboxylyl-CoAs, the CoA esters of eicosanoids, 2methyl-branched fatty acyl-CoAs (e.g. pristanoyl-CoA), and the CoA esters of the bile acid intermediates di-and trihydroxycoprostanic acids (side chain of cholesterol).
Peroxisome Proliferation and Lipid Peroxidation in Rat Liver1
1986
Male F344 rats were fed a diet containing the peroxisome proliferators 2-(4-(2,2-dichlorocyclopropyl)phenoxy)-2-methyl- propionic acid (ciprofibrate (0.025%)) or (4-chloro-6-(2,3-xyli- dino)-2-pyrimidinylthio)acetic acid (Wy-14643 (0.1%)) for up to 14 months to determine whether hepatic peroxisome prolifera tion caused by these agents results in the induction of membrane lipid peroxidation in the liver. Peroxidative damage of membrane lipids from whole liver, postnuclear, heavy-particle, microsomal,
Journal of Biological Chemistry, 1999
Fatty acid -oxidation occurs in both mitochondria and peroxisomes. Long chain fatty acids are also metabolized by the cytochrome P450 CYP4A-oxidation enzymes to toxic dicarboxylic acids (DCAs) that serve as substrates for peroxisomal -oxidation. Synthetic peroxisome proliferators interact with peroxisome proliferator activated receptor ␣ (PPAR␣) to transcriptionally activate genes that participate in peroxisomal, microsomal, and mitochondrial fatty acid oxidation. Mice lacking PPAR␣ (PPAR␣ ؊/؊) fail to respond to the inductive effects of peroxisome proliferators, whereas those lacking fatty acyl-CoA oxidase (AOX ؊/؊), the first enzyme of the peroxisomal -oxidation system, exhibit extensive microvesicular steatohepatitis, leading to hepatocellular regeneration and massive peroxisome proliferation, implying sustained activation of PPAR␣ by natural ligands. We now report that mice nullizygous for both PPAR␣ and AOX (PPAR␣ ؊/؊ AOX ؊/؊) failed to exhibit spontaneous peroxisome proliferation and induction of PPAR␣-regulated genes by biological ligands unmetabolized in the absence of AOX. In AOX ؊/؊ mice, the hyperactivity of PPAR␣ enhances the severity of steatosis by inducing CYP4A family proteins that generate DCAs and since they are not metabolized in the absence of peroxisomal -oxidation, they damage mitochondria leading to steatosis. Blunting of microvesicular steatosis, which is restricted to few liver cells in periportal regions in PPAR␣ ؊/؊ AOX ؊/؊ mice, suggests a role for PPAR␣-induced genes, especially members of CYP4A family, in determining the severity of steatosis in livers with defective peroxisomal -oxidation. In agematched PPAR␣ ؊/؊ mice, a decrease in constitutive mitochondrial -oxidation with intact constitutive peroxisomal -oxidation system contributes to large droplet fatty change that is restricted to centrilobular hepatocytes. These data define a critical role for both PPAR␣ and AOX in hepatic lipid metabolism and in the pathogenesis of specific fatty liver phenotype.