Peroxisomal changes during hiberation of jerboa (Jaculus orientalis)

Differential regulation of peroxisome proliferator-activated receptor (PPAR)-alpha1 and truncated PPARalpha2 as an adaptive response to fasting in the control of hepatic peroxisomal fatty acid beta-oxidation in the hibernating mammal

Seasonal obesity and fasting-associated hibernation are the two major metabolic events governing hepatic lipid metabolism in hibernating mammals. In this process, however, the role of the nuclear receptor known as peroxisome proliferator-activated receptor (PPAR)-alpha has not been elucidated yet. Here we show, as in human, that jerboa (Jaculus orientalis) liver expresses both active wild-type PPARalpha (PPARalpha1wt) and truncated PPARalpha forms and that the PPARalpha1wt to truncated PPARalpha2 ratio, which indicates the availability of active PPARalpha1wt, is differentially regulated during fasting-associated hibernation. Functional activation of hepatic jerboa PPARalpha, during prehibernating and hibernating states, was demonstrated by the induction of its target genes, which encode peroxisomal proteins such as acyl-CoA oxidase 1, peroxisomal membrane protein 70, and catalase, accompanied by a concomitant induction of PPARalpha thermogenic coactivator PPARgamma coactivator-1alpha. Interestingly, sustained activation of PPARalpha by its hypolipidemic ligand, ciprofibrate, abrogates the adaptive fasting response of PPARalpha during prehibernation and overinduces its target genes, disrupting the prehibernation fattening process. In striking contrast, during fasting-associated hibernation, jerboas exhibit preferential up-regulation of hepatic peroxisomal fatty acid oxidation instead of the mitochondrial pathway, which is down-regulated. Taken together, our results strongly suggest that PPARalpha is subject to a hibernation-dependent splicing regulation in response to feeding-fasting conditions, which defines the activity of PPARalpha and the activation of its target genes during hibernation bouts of jerboas.

Peroxisome proliferator-activated receptors as regulators of lipid metabolism; tissue differential expression in adipose tissues during cold acclimatization and hibernation of jerboa (Jaculus orientalis)

Brown (BAT) and white (WAT) adipose tissues play a key role in the body energy balance orchestrated by the central nervous system. Hibernators have developed a seasonal obesity to respond to inhospitable environment. Jerboa is one of the deep hibernator originated from sub-desert highlands. Thus, this animal represents an excellent model to study cold adaptation mechanism. We report that the adipogenic factor PPARgamma exhibits a differential expression between BAT and WAT at mRNA level. A specific induction was only seen in WAT of pre-hibernating jerboa. Interestingly, PPAR beta/delta is specifically induced in BAT and brain of pre-hibernating jerboa, highlighting for the first time the possible key role of this ubiquitous isoform in the cold adaptation of this true hibernator. Inductions of PPARgamma(2) in WAT and PPAR beta/delta in BAT are blunted by a hypolipemic drug, the ciprofibrate. These changes may be correlated with hibernation arrest and death of treated jerboa. Mitochondrial acyl-CoA dehydrogenase and peroxisomal acyl-CoA oxidase activities in brown and white adipose tissues are decreased up to 85% during cold acclimatization (without food privation). These enzyme activities are subject to a strong induction in BAT and in WAT (3.4-7.5 fold) during the hibernation period. The BAT thermogenesis marker is also largely induced (approximately 4 fold of UCP1 mRNA level) during pre-hibernation period. Unexpectedly, treatment with ciprofibrate deeply affects lipolysis in BAT by increasing acyl-CoA dehydrogenase activity (3.4 fold) and acyl-CoA oxidase at both activity and mRNA levels (2.8 and 3.8 fold, respectively) and enhances strongly UCP1 mRNA level (9.5 fold) during pre-hibernation.

Genetic-dependency of peroxisomal cell functions - emerging aspects

This paper reviews aspects concerning the genetic regulation of the expression of the well studied peroxisomal genes including those of fatty acid beta-oxidation enzymes; acyl-CoA oxidase, multifunctional enzyme and thiolase from different tissues and species. An important statement is PPARalpha, which is now long known to be in rodents the key nuclear receptor orchestrating liver peroxisome proliferation and enhanced peroxisomal beta-oxidation, does not appear to control so strongly in man the expression of genes involved in peroxisomal fatty acid beta-oxidation related enzymes. In this respect, the present review strengthens among others the emerging concept that, in the humans, the main genes whose expression is up-regulated by PPARalpha are mitochondrial and less peroxisomal genes. A special emphasis is also made on the animal cold adaptation and on need for sustained study of peroxisomal enzymes and genes; challenging that some essential roles of peroxisomes in cell function and regulation still remain to be discovered.

Changes of peroxisomal fatty acid metabolism during cold acclimatization in hibernating jerboa (Jaculus orientalis)

Jerboa (Jaculus orientalis) is a deep hibernator originating from sub-desert highlands and represents an excellent model to help to understand the incidence of seasonal variations of food intake and of body as well as environmental temperatures on lipid metabolism. In jerboa, hibernation processes are characterized by changes in the size of mitochondria, the number of peroxisomes in liver and in the expression of enzymes linked to fatty acid metabolism. In liver and kidney, cold acclimatization shows an opposite effect on the activities of the mitochondrial acyl-CoA dehydrogenase (-50%) and the peroxisomal acyl-CoA oxidase (AOX) (+50%), while in brown and white adipose tissues, both activities are decreased down to 85%. These enzymes activities are subject to a strong induction in brown and in white adipose tissue (3.4- to 7.5-fold, respectively) during the hibernation period which is characterized by a low body temperature (around 10 degrees C) and by starvation. Expression level of AOX mRNA and protein are increased during both pre-hibernation and hibernation periods. Unexpectedly, treatment with ciprofibrate, a hypolipemic agent, deeply affects lipolysis in brown adipose tissue by increasing acyl-CoA dehydrogenase activity (3.4-fold), both AOX activity and mRNA levels (2.8- and 3.8-fold, respectively) during pre-hibernation. Therefore, during pre-hibernation acclimatization, there is a negative regulation of fatty acid degradation allowing to accumulate a lipid stock which is later degraded during the hibernation period (starvation) due to a positive regulation of enzymes providing the required energy for animal survival.

Induction of the expression of the peroxisome proliferator-activated receptor alpha (PPARalpha) by clofibrate in jerboa tissues

Peroxisome proliferator-activated receptor alpha (PPARalpha) is a member of the nuclear hormone receptor superfamily that can be activated by natural fatty acids and various xenobiotics, including clofibrate. This transcription factor primarily regulates genes involved in lipid metabolism and homeostasis. We present the expression pattern of the PPARalpha subtype in the adult jerboa Jaculus orientalis, determined by RT-PCR and Western blotting using specific probes and a polyclonal antibody for PPARalpha, respectively. PPARalpha is highly expressed in liver and kidney, and to a lesser extent in duodenum and colon. PPARalpha expression is increased at the mRNA and protein levels in liver and duodenum of jerboa treated for 2 weeks with the peroxisome proliferator (PP) clofibrate. The induction is tissue-specific as no significant changes are observed in kidney and colon. The present data indicate that the PP-induced PPARalpha gene expression is not dependent on the PPARalpha content in target cells.

Effect of hibernation, thyroid hormones and dexamethasone on cytosolic and mitochondrial glycerol-3-phosphate dehydrogenase from jerboa (Jaculus orientalis)

Tissue distribution of the cytosolic and mitochondrial glycerol-3-phosphate dehydrogenase (cGPDH and mGPDH) activities in jerboa (Jaculus orientalis), a hibernator, shows the highest level of enzyme activity in skeletal muscle and brown adipose tissue, respectively. The effect of hibernation on cGPDH indicates an increase of activity in all tissues examined. In contrast, hibernation decreases mGPDH activity in all tissues, except skeletal muscle. The effect of thyroid hormones on GPDH activity was tissue specific: in kidneys, cGPDH activity doubled in euthermic jerboas treated with T4. In contrast, 6-n-propyl-2-thiouracil treatment provokes an increase of enzyme activity in brown adipose tissue, liver and brain. T4 treatment leads to a 2.7-fold increase in liver mGPDH activity. 6-n-propyl-2-thiouracil treatment decreases mGPDH activity in the skeletal muscle whereas the opposite effect was observed in brain. Dexamethasone stimulates cGPDH in all tissues examined, except skeletal muscle and kidneys. In the case of mGPDH activity, this increase was observed only for brown adipose tissue and brain. Our results suggest that hibernation, thyroid hormones and dexamethasone probably play a role in the regulation of cGPDH and mGPDH activities in jerboa. Our findings confirm that these enzymes are involved in metabolic adaptation to thermal stress in Jaculus orientalis.