Constitutive Expression of Peroxisome Proliferator-Activated Receptor α-Regulated Genes in Dwarf Mice

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Abstract
Defects in growth hormone secretion or signaling in mice are associated with decreased body weights (dwarfism), increased longevity, increased resistance to stress, and decreases in factors that contribute to cardiovascular disease and cancer. Peroxisome proliferators (PP) alter a subset of these changes in wild-type mice through activation of the nuclear receptor family member PP-activated receptor α (PPARα). We tested the hypothesis that an overlap in the transcriptional programs between untreated dwarf mice and PP-treated wild-type mice underlies these similarities. Using transcript profiling, we observed a statistically significant overlap in the expression of genes differentially regulated in control Snell dwarf mice (Pit-1dw) compared with phenotypically normal heterozygote (+/dw) control mice and those altered by the PP 4-chloro-6-(2,3-xylidino)-2-pyrimidinyl)thioacetic acid (WY-14,643) in +/dw mice. The genes included those involved in β- and ω-oxidation of fatty acids (Acox1, Cyp4a10, Cyp4a14) and those involved in stress responses (the chaperonin, T-complex protein1ϵ) and cardiovascular disease (fibrinogen). The levels of some of these gene products were also altered in other dwarf mouse models, including Ames, Little, and growth hormone receptor-null mice. The constitutive increases in PPARα-regulated genes may be partly caused by increased expression of PPARα mRNA and protein as observed in the livers of control Snell dwarf mice. These results indicate that some of the beneficial effects associated with the dwarf phenotype may be caused by constitutive activation of PPARα and regulated genes.

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