The circadian clock temporally coordinates metabolic homeostasis in mammals. Central to this is heme, an iron-containing porphyrin that serves as prosthetic group for enzymes involved in oxidative metabolism as well as transcription factors that regulate circadian rhythmicity. The circadian factor that integrates this dual function of heme is not known. We show that heme binds reversibly to the orphan nuclear receptor Rev-erbalpha, a critical negative component of the circadian core clock, and regulates its interaction with a nuclear receptor corepressor complex. Furthermore, heme suppresses hepatic gluconeogenic gene expression and glucose output through Rev-erbalpha-mediated gene repression. Thus, Rev-erbalpha serves as a heme sensor that coordinates the cellular clock, glucose homeostasis, and energy metabolism.

Microalgal lipids are the oils of future for sustainable biodiesel production. However, relatively high production costs due to low lipid productivity have been one of the major obstacles impeding their commercial production. We studied the effects of nitrogen sources and their concentrations on cell growth and lipid accumulation of Neochloris oleoabundans, one of the most promising oil-rich microalgal species. While the highest lipid cell content of 0.40 g/g was obtained at the lowest sodium nitrate concentration (3 mM), a remarkable lipid productivity of 0.133 g l(-1) day(-1) was achieved at 5 mM with a lipid cell content of 0.34 g/g and a biomass productivity of 0.40 g l(-1) day(-1). The highest biomass productivity was obtained at 10 mM sodium nitrate, with a biomass concentration of 3.2 g/l and a biomass productivity of 0.63 g l(-1) day(-1). It was observed that cell growth continued after the exhaustion of external nitrogen pool, hypothetically supported by the consumption of intracellular nitrogen pools such as chlorophyll molecules. The relationship among nitrate depletion, cell growth, lipid cell content, and cell chlorophyll content are discussed.

Microalgae are a group of unicellular or simple multicellular photosynthetic microorganisms that can fix CO(2) efficiently from different sources, including the atmosphere, industrial exhaust gases, and soluble carbonate salts. Combination of CO(2) fixation, biofuel production, and wastewater treatment may provide a very promising alternative to current CO(2) mitigation strategies.

Microalgae are a diverse group of prokaryotic and eukaryotic photosynthetic microorganisms that grow rapidly due to their simple structure. They can potentially be employed for the production of biofuels in an economically effective and environmentally sustainable manner. Microalgae have been investigated for the production of a number of different biofuels including biodiesel, bio-oil, bio-syngas, and bio-hydrogen. The production of these biofuels can be coupled with flue gas CO 2 mitigation, wastewater treatment, and the production of high-value chemicals. Microalgal farming can also be carried out with seawater using marine microalgal species as the producers. Developments in microalgal cultivation and downstream processing (e.g., harvesting, drying, and thermochemical processing) are expected to further enhance the costeffectiveness of the biofuel from microalgae strategy.

Alpha-ketoglutarate (AKG) is a key molecule in the Krebs cycle determining the overall rate of the citric acid cycle of the organism. It is a nitrogen scavenger and a source of glutamate and glutamine that stimulates protein synthesis and inhibits protein degradation in muscles. AKG as a precursor of glutamate and glutamine is a central metabolic fuel for cells of the gastrointestinal tract as well. AKG can decrease protein catabolism and increase protein synthesis to enhance bone tissue formation in the skeletal muscles and can be used in clinical applications. In addition to these health benefits, a recent study has shown that AKG can extend the lifespan of adult Caenorhabditis elegans by inhibiting ATP synthase and TOR. AKG not only extends lifespan, but also delays age-related disease. In this review, we will summarize the advances in AKG research field, in the content of its physiological functions and applications.

Fibroblast growth factor 21 (FGF21) is a potent antidiabetic and triglyceride-lowering hormone whose hepatic expression is highly responsive to food intake. FGF21 induction in the adaptive response to fasting has been well studied, but the molecular mechanism responsible for feeding-induced repression remains unknown. In this study, we demonstrate a novel link between FGF21 and a key circadian output protein, E4BP4. Expression of Fgf21 displays a circadian rhythm, which peaks during the fasting phase and is anti-phase to E4bp4, which is elevated during feeding periods. E4BP4 strongly suppresses Fgf21 transcription by binding to a D-box element in the distal promoter region. Depletion of E4BP4 in synchronized Hepa1c1c-7 liver cells augments the amplitude of Fgf21 expression, and overexpression of E4BP4 represses FGF21 secretion from primary mouse hepatocytes. Mimicking feeding effects, insulin significantly increases E4BP4 expression and binding to the Fgf21 promoter through AKT activation. Thus, E4BP4 is a novel insulin-responsive repressor of FGF21 expression during circadian cycles and feeding.The mammalian circadian rhythm system plays a fundamental role in coordinating various physiological processes, which are manifested by a precise 24-h cycle and responsiveness to light or food cues (1-4). Recent genetic and biochemical studies of mammals, Drosophila, and bacteria have provided a general model of the circadian clock that is based on a transcriptional-translational feedback loop consisting of both positive and negative circadian clock proteins (1, 4). Besides controlling the core circadian oscillation loop, the clock proteins also actively participate in rhythmic expression of various output genes, which may account for the rhythmic activities in peripheral tissues (1, 3). As demonstrated in various microarray studies, genes important for gluconeogenesis, lipogenesis, and cholesterol synthesis are potential targets of clock proteins (5-8). Therefore, for drug administration and drug design, it becomes critical to understand how the cycling of individual metabolic genes is regulated in a 24-h rhythm (9, 10). E4BP4 (E4-binding protein 4), also called NFIL3, is a b-ZIP (basic leucine zipper) transcription factor initially identified as an IL-3-inducible factor in pro-B lymphocytes (11-13). The biological function of E4BP4 has been largely explored in the immune system, in which E4BP4 knock-out mice are defective in natural killer cell development and IgE class switch (14 -16). E4BP4 was first identified as a clock-controlled gene in mouse liver (17,18). Its mRNA and protein levels oscillate in a circadian fashion, which is anti-phase to DBP (D-site of albumin promoter-binding protein), another clock-controlled output gene (19). The mRNA of E4BP4 peaks at circadian time (CT) 2 0 and troughs at CT 12 (17,20). Although the role of E4BP4 in the mammalian circadian system is unclear, its homologue in Drosophila, vrille, serves as a key component of the core circadian network via a negative feedback loop (21-23). E...

Intracellular heme levels must be tightly regulated to maintain proper mitochondrial respiration while minimizing toxicity, but the homeostatic mechanisms are not well understood. Here we report a novel negative feedback mechanism whereby the nuclear heme receptor Rev-erba tightly controls the level of its own ligand. Heme binding to Rev-erba recruits the NCoR/histone deacetylase 3 (HDAC3) corepressor complex to repress the transcription of the coactivator PGC-1a, a potent inducer of heme synthesis. Depletion of Rev-erba derepresses PGC-1a, resulting in increased heme levels. Conversely, increased Rev-erba reduces intracellular heme, and impairs mitochondrial respiration in a heme-dependent manner. Consistent with this bioenergetic impairment, overexpression of Rev-erba dramatically inhibits cell growth due to a cell cycle arrest. Thus, Rev-erba modulates the synthesis of its own ligand in a negative feedback pathway that maintains heme levels and regulates cellular energy metabolism.[Keywords: Rev-erba; PGC-1a; heme homeostasis; mitochondria; energy] Supplemental material is available at http://www.genesdev.org.

Nuclear receptor Rev-erbα (NR1D1), previously considered to be an orphan nuclear receptor, is a receptor for heme, which promotes transcriptional repression via recruitment of the NCoR-HDAC3 corepressor complex. Rev-erbα gene regulation is circadian, and Rev-erbα comprises a critical negative limb of the core circadian clock by directly repressing the expression of the positive clock component, Bmal1. Rev-erbα also regulates the metabolic gene pathway, thus serving as a heme sensor for coordination of circadian and metabolic pathways.