18 April 2019 |       Share
 
 
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CASE STUDIES
Myelotoxicity
Skin Wound Healing
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Endocrine Disruptors
Hepato-Toxicology
Lipid Metabolism
Carcinogenicity
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Lipid Metabolism

Peroxisome Proliferator-Activated Receptors (PPARs) play an important role in the regulation of lipid and carbohydrate metabolism and are involved in the etiopathogenesis of metabolic diseases such as diabetes, arteriosclerosis and other cardiovascular pathologies.


Using repTOP™ PPRE-Luc mice we studied how food consumption is able to modulate PPAR activity.


To better assess the effect of nutrition on PPAR activity, independently of the circadian rhythm, we restricted the access to food to PPRE-Luc mice of both sexes: in particular, an experimental group was fed only during the day and the other only during the night. This was done for 2 consecutive days. We then measured luciferase activity by in vivo imaging and dissected the livers of these animals on the morning of the third day at 09:00 a.m to measure luciferase activity.



(* P < 0.01)

The data obtained in vivo and ex vivo clearly showed that this nutritional schedule affects liver PPAR activity in males, but not in females. In fact, in males fed only during the day, liver PPARs were significantly more activated than in those fed during the night, as shown by stronger bioluminescence. No significant changes were observed in the other parts of the body (such as abdomen). No change was observed in female livers where luciferase activity remained significantly lower than in males.


Secondly, thanks to the sensibility of this reporter mouse model, we verified the extent to which food affects PPAR activity also in relation to sex, we restricted the access to food of PPRE-Luc mice at 9:00 a.m. of day 0 and measured the changes of photon emission in time (at 6h, 24h, and 48 h time points). 



(* P < 0.01 as compared with 0 h; ° P < 0.01 as compared with the 6-h-fasted, untreated aninmals)

In the chest of male mice, we observed a significant increase of photon emission at 6 h (2-fold) which could be blocked by the specific PPAR antagonist MK-886. Interestingly, food deprivation affected also the abdomen, but at longer times and this phenomenon was observed equally well in male and female mice.


Using repTOP™ PPRE-Luc mice we detected a gender difference in the activity of hepatic PPARs.


Several studies have demonstrated that the activity of PPARs in male livers is much higher than in females. Indeed, PPAR alpha is the mediator of the hepatic, gender-specific response to fibrates; this receptor subtype is also important for gender-specific lipid and glucose metabolism, fat storage, and responses to food assumption.
 



(** < P 0.005 as compared with males)

We compare in vivo luciferase expression in female and male mice of the same age and fed ad libitum (left panel on the figure above): in male, repTOP PPRELuc mice photon emission in the chest is quite high, while in females is hardly measurable.
A more extended comparative study (right panel) showed that the gender dimorphism is specific of the liver and PPAR basal activity in the other organs is comparable in the two sexes.


Using repTOP™ PPRE-Luc mice we characterized several agonist and antagonist PPARs ligands.


The possibility to measure the effect of compounds spatio-temporally is of particular interest dealing with ligands of intracellular receptors because it is well known that a given chemical may act as nuclear receptor agonist in one tissue and as antagonist in another.

We performed a study in which the PPRE-luc mice were treated with several ligands each endowed of a selected action of the three PPARs subtypes. With a time course analysis, we could measure the changes of the activity of each compound with time in the different body areas. This rapid and inexpensive study provided the initial profile of each compound in study in terms of potency, tissue targeting and dynamics of action.




The time course of photon emission in repTOP™PPRE-Luc mice after treatment with synthetic PPARs agonists showed the changes of the activity of each compound in time in the different body areas.


These following papers examine in depth the issues discussed above and show the superiority of this transgenic mouse model for the study of PPAR’s physio-patological action and for the profiling of drugs active through this receptor family.

Ciana C, Biserni A, Tatangelo L, Tiveron C, Sciarroni F, Ottobrini L, and Maggi A. A Novel Peroxisome Proliferator-Activated Receptor Responsive Element-Luciferase Reporter Mouse Reveals Gender Specificity of Peroxisome Proliferator-Activated Receptor Activity in Liver. 
Mol Endocrinol. 2007 Feb;21(2):388-400. Epub 2006 Dec 7.

Biserni A, Giannessi F, Sciarroni A F, Milazzo F M, Maggi A and Paolo Ciana. 
In Vivo Imaging Reveals Selective Peroxisome Proliferator Activated Receptor Modulator Activity of the Synthetic Ligand 3-(1-(4-Chlorobenzyl)-3-t-butylthio-5-isopropylindol-2-yl)-2,2-dimethylpropanoic acid (MK-886). Mol Pharmacol. 2008 May;73(5):1434-43.