It has long been hypothesized that abnormalities in lipid biology contribute to degenerative brain diseases. Consistent with this, emerging epidemiologic evidence links lipid alterations with Parkinson disease (PD), and disruption of lipid metabolism has been found to predispose to α-synuclein toxicity. We therefore investigated whether Parkin, an E3 ubiquitin ligase found to be defective in patients with early onset PD, regulates systemic lipid metabolism. We perturbed lipid levels by exposing Parkin +/+ and Parkin -/-mice to a high-fat and -cholesterol diet (HFD). Parkin -/-mice resisted weight gain, steatohepatitis, and insulin resistance. Introduction PARK2 mutations associate with an autosomal recessive juvenileform of Parkinson disease (PD) (1). However, the role of Parkin in the development of PD in mice is surprisingly modest, as the genetic deletion of Parkin (2, 3) and the combined KO of Parkin with additional "candidate Parkinson susceptibility genes" PINK1 and DJ-1 do not substantially replicate the human condition (4). These unexpected findings suggest that the biological function of Parkin may not primarily modulate neurodegeneration but rather that PARK2 mutations increase biological susceptibility to stressors that manifest with substantia nigra neurodegeneration. Thus, the characterization of the functional actions of Parkin could be instrumental in delineating its role in the pathophysiology underpinning the development of PD.Parkin encodes an E3 ubiquitin protein ligase and contains 465 amino acids with multiple distinct domains, including a ubiquitinlike domain, a unique Parkin-specific domain, 2 RING domains, and an in-between-RING domain (5). The structure of this protein with its multiple binding domains is most likely central to the myriad of functions prescribed to Parkin (6). Additionally, the subcellular location of Parkin appears to be dynamic, with a predominant cytosolic localization with redistribution to the nucleus (7) and to the outer mitochondrial membrane (8, 9). Parkin exhibits mono- and multiubiquitination functions (10), and studies show that classical as well as nonclassical ubiquitin linkages facilitate proteosome-dependent and independent Parkin effects (11)(12)(13)(14).

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Perilipin is an adipocyte-specific protein associated with lipid droplets that is crucial for the regulation of storage and mobilization of lipids. We earlier reported that the mouse perilipin gene is regulated by peroxisome proliferator-activated receptor (PPAR) gamma through a peroxisome proliferator-response element (PPRE) positioned upstream of the perilipin promoter. Moreover, we showed that this PPRE also controls expression of the PEX11alpha gene, which is located further upstream. We show here that three elements, A, B, and C, in close proximity downstream of the PPRE, are essential for transactivation of the perilipin gene by PPARgamma. Electrophoretic gel-mobility shift assays demonstrated that nuclear factor (NF)-1 subtypes bind specifically to element B. Furthermore, chromatin immunoprecipitation using 3T3-L1 cells revealed that NF-1A and NF-1B bind to element B in a differentiation-dependent fashion, whereas binding is constitutive with NF-1C and NF-1X. Element C is likely to be a binding motif for nuclear receptors. With PPARalpha, elements A-C do not appear to be required for transactivation of the PEX11alpha gene, so that cooperation with other transcription factors may be differentially involved in selective transactivation of the PEX11alpha and perilipin genes by different PPAR subtypes.

Estrogen receptor-related receptors (ERRs) are orphan members of the nuclear receptor superfamily. A single AGGTCA sequence element preceded by three conserved nucleotides has been identified as a specific recognition motif of ERRs. Here we performed systematic analyses of target sequences on all three ERR subtypes, alpha, beta and gamma. In electrophoretic gel-mobility shift assay and transcriptional reporter assays, they exhibited similar patterns of recognition specificities, showing extremely broad ranges of target sequences. We searched a mouse promoter database for a gene carrying possible ERR-binding sequences. The Rb-1 inducible coiled-coil 1 (Rb1cc1) gene was found to contain two putative ERR binding elements, named response element (RE)-1 and RE-2, in the promoter region. In gene reporter assays, RE-2, but not RE-1, functioned as an effective cis-regulatory element for transactivation by ERRalpha in the presence of a coactivator, peroxisome proliferator-activated receptor gamma coactivator-1alpha. Mutational analyses suggested that RE-2 is recognized by ERRalpha partly as a monovalent element, but also as a direct repeat motif separated by four spacer nucleotides. In vivo binding of ERRalpha to the Rb1cc1 promoter region was confirmed by the chromatin immunoprecipitation assay. Thus, Rb1cc1 is a target gene of ERRalpha, driven by a novel type of recognition sequence.

Many mammalian genes are clustered on the genomes, and hence the genes in the same cluster can be regulated through a common regulatory element. We indeed showed previously that the perilipin/PEX11α gene pair is transactivated tissue-selectively by PPARγ and PPARα, respectively, through a common binding site. In the present study, we identified a gene, named GSPA, neighboring a canonical PPAR target, acyl-CoA oxidase (AOX) gene. GSPA expression was induced by a peroxisome proliferator, Wy14,643, in the liver of wild-type mice, but not PPARα-null mice. GSPA and AOX share the promoter and two peroxisome proliferator-response elements. GSPA mRNA was also found in the heart and skeletal muscle, as well as 3T3-L1 cells. GSPA encodes a protein of 161 amino acids that is enriched in 3T3-L1 cells. Even other gene pairs might be regulated through common sequence elements, and conversely it would be interesting how each gene is aptly regulated in clusters.