title: Small heterodimer partner/neuronal PAS domain protein 2 axis regulates the oscillation of liver lipid metabolism.
abstract: In mammals, circadian rhythms are essential for coordinating the timing of various metabolic processes. The Clock gene regulates diurnal plasma triglyceride fluctuation through nuclear receptor small heterodimer partner (Shp; Nr0b2). Given that SHP is a critical regulator of metabolism in the liver, it is unknown whether SHP is necessary to coordinate metabolism and circadian rhythms. Shp(+/+) and Shp(-/-) mice on a C57BL/6 background (n = 3-5/group) were fed a standard chow diet and water ad libitum. Serum and livers were collected at zeitgeber time 2, 6, 10, 14, 18, and 22. In vivo and in vitro assays included RNA sequencing, quantitative polymerase chain reaction, very-low-density lipoprotein production, adenovirus overexpression and small interfering RNA knockdown, serum parameters, circadian locomotor activity, Oil Red O staining, transient transfection, luciferase reporter assay, chromatin immunoprecipitation assay, gel-shift assay, coimmunoprecipitation, and western blottings. Shp deficiency had a robust global impact on major liver metabolic genes. Several components of the liver clock, including peroxisome proliferator-activated receptor-γ, coactivator 1 (Pgc-1α), neuronal PAS domain-containing protein 2 (Npas2), and retinoic acid-related orphan receptor (Ror)α/γ were sharply induced in Shp(-/-) liver. At the molecular level, SHP inhibited Npas2 gene transcription and promoter activity through interaction with Rorγ to repress Rorγ transactivation and by interacting with Rev-erbα to enhance its inhibition of Rorα activity. Conversely, Npas2 controlled the circadian rhythm of Shp expression by binding rhythmically to the Shp promoter, which was enhanced by nicotinamide adenine dinucleotide, but not nicotinamide adenine dinucleotide phosphate. Phenotypically, Npas2 deficiency induced severe steatosis in Shp(-/-) mice, which was attributed to the dysregulation of lipoprotein metabolism.
  
  
  CONCLUSIONS
  Shp and Npas2 crosstalk is essential to maintain hepatic lipid homeostasis.
authors.affiliation: Department of Physiology and Neurobiology, University of Connecticut, Storrs, CT.
authors.forename: Sang Min
authors.initials: SM
authors.lastname: Lee
authors.forename: Yuxia
authors.initials: Y
authors.lastname: Zhang
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Tsuchiya
authors.forename: Rana
authors.initials: R
authors.lastname: Smalling
authors.forename: Anton M
authors.initials: AM
authors.lastname: Jetten
authors.forename: Li
authors.initials: L
authors.lastname: Wang
mesh_terms: D000818:Animals; D051792:Basic Helix-Loop-Helix Proteins / Q000378:metabolism*; D057906:Circadian Clocks; D025461:Feedback, Physiological; D020869:Gene Expression Profiling; D055785:Gene Knockdown Techniques; D050356:Lipid Metabolism; D008074:Lipoproteins / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D057093:Orphan Nuclear Receptors / Q000378:metabolism; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D020239:Receptor Cross-Talk; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism
chemical_list: D051792:Basic Helix-Loop-Helix Proteins; D008074:Lipoproteins; D009419:Nerve Tissue Proteins; D057093:Orphan Nuclear Receptors; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D018160:Receptors, Cytoplasmic and Nuclear; D014157:Transcription Factors; C491259:Npas2 protein, mouse; C485290:Ppargc1a protein, mouse; C099713:nuclear receptor subfamily 0, group B, member 2