Activation of a novel long-chain free fatty acid generation and export system in mitochondria of diabetic rat hearts

Abstract

A number of reports indicate that a long-chain free fatty acid export system may be operating in mitochondria. In this study, we sought evidence of its existence in rat heart mitochondria. To determine its potential role, we also sought evidence of its activation or inhibition in streptozotocin (STZ)-induced diabetic rat heart mitochondria. If confirmed, it could be a novel mechanism for regulation of long-chain fatty acid oxidation (FAO) in mitochondria. To obtain evidence of its existence, we tested whether heart mitochondria presented with palmitoyl-carnitine can generate and export palmitate. We found that intact mitochondria indeed generate and export palmitate. We have also found that the rates of these processes are markedly higher in STZ-diabetic rat heart mitochondria, in which palmitoyl-carnitine oxidation is also increased. Since mitochondrial thioesterase-1 (MTE-1) hydrolyzes acyl-CoA to CoA-SH + free fatty acid, and uncoupling protein-3 (UCP-3), reconstituted in liposomes, transports free fatty acids, we examined whether these proteins are also increased in STZ-diabetic rat heart mitochondria. We found that both of these proteins are indeed increased. Gene expression profile analysis revealed striking expression of mitochondrial long-chain fatty acid transport and oxidation genes, accompanying overexpression of MTE-1 and UCP-3 in STZ-diabetic rat hearts. Our findings provide the first direct evidence for the existence of a long-chain free fatty acid generation and export system in mitochondria and its activation in STZ-diabetic rat hearts in which FAO is enhanced. We suggest that its activation may facilitate, and inhibition may limit, enhancement of FAO.

An arachidonic acid generation/export system involved in the regulation of cholesterol transport in mitochondria of steroidogenic cells

“…1 panels A and B, antimycin A and oligomycin produce a significant increase in cAMP-induced accumulation of AA into the mitochondria ( . The effect produced by antimycin A and oligomycin on AA accumulation into Leydig cell mitochondria suggested that ATP synthesis is necessary for free fatty acid export as has been shown in rat heart mitochondria [9]. However, this result may also be explained with the theory that, the inhibitors antimycin A and oligomycin increase AA-CoA formation providing more substrate for Acot2 thus, increasing AA accumulation into the mitochondria.…”

“…Mitochondrial AA plays a crucial role mediating the induction of the StAR protein through the conversion to leucotrienes outside the mitochondria. There is a recent report of activation of a novel long-chain free fatty acid generation and export system in mitochondria of diabetic rat heart [9], where Acot2 plays an important role. Disruption of the mitochondrial function with oligomycin, preventing ATP hydrolysis, produced no effect on the rate of generation but it inhibited the rate of export of free fatty acid from the mitochondria [9].…”

Fatty acid oxidation in cardiac and skeletal muscle mitochondria is unaffected by deletion of CD36

“…Isolated mitochondria were incubated with 20 μM [1-14 C]-palmitoyl-carnitine at 37°C for 6 minutes. The reaction was terminated as previously described [7], and the extramitochondrial fluid was separated by centrifugal filtration (0.45μm). Lipids were extracted and fatty acid moieties separated by thin layer chromatography, and the palmitic acid spot visualized and counted [7;8].…”

“…Recent studies on cardiac mitochondria noted the hydrolysis of LCFA-CoA to LCFA by mitochondrial thioesterase I (MTE-I) in the matrix, and these LCFAs are subsequently exported out of the mitochondria by an unidentified protein carrier [7;8]. It has been proposed that uncoupling protein 3 (UCP3) is responsible for LCFA export from the matrix [7], however we recently observed that both MTE-I and fatty acid export are up-regulated ∼5-fold by diabetes without a significant change in UCP3 protein levels [8]. A likely candidate for this process is CD36, however it's role in mitochondrial LCFA export has not been assessed.…”

Type 1 Diabetic Akita Mouse Hearts Are Insulin Sensitive but Manifest Structurally Abnormal Mitochondria That Remain Coupled Despite Increased Uncoupling Protein 3

“…These similarities to type 2 diabetic models prompted us to investigate in this study whether mitochondrial uncoupling also contributes to impaired cardiac efficiency and contractile dysfunction in type 1 diabetic models. To date, measurements of cardiac state 4 respiration rates and ADP-to-O ratios performed in streptozotocin-injected animals have yielded conflicting results, making it difficult to make any conclusions about the presence or absence of mitochondrial uncoupling in this model of type 1 diabetes (8,(13)(14)(15).…”