Circadian clocks are cell autonomous, transcriptionally-based, molecular mechanisms that confer the selective advantage of anticipation, enabling cells/organs to respond to environmental factors in a temporally appropriate manner. Critical to circadian clock function are two transcription factors, CLOCK and BMAL1. The purpose of the present study was to reveal novel physiologic functions of BMAL1 in the heart, as well as determine the pathologic consequences of chronic disruption of this circadian clock component. In order to address this goal, we generated cardiomyocyte-specific Bmal1 knockout (CBK) mice. Following validation of the CBK model, combined microarray and in silico analyses were performed, identifying 19 putative direct BMAL1 target genes, which included a number of metabolic (e.g., β-hydroxybutyrate dehydrogenase 1 [Bdh1]) and signaling (e.g., the p85α regulatory subunit of phosphatidylinositol 3-kinase [Pik3r1]) genes. Results from subsequent validation studies were consistent with regulation of Bdh1 and Pik3r1 by BMAL1, with predicted impairments in ketone body metabolism and signaling observed in CBK hearts. Furthermore, CBK hearts exhibited depressed glucose utilization, as well as a differential response to a physiologic metabolic stress (i.e., fasting). Consistent with BMAL1 influencing critical functions in the heart, echocardiographic, gravimetric, histologic, and molecular analyses revealed age-onset development of dilated cardiomyopathy in CBK mice, which was associated with a severe reduction in lifespan. Collectively, our studies reveal that BMAL1 influences metabolism, signaling, and contractile function of the heart.

Antidepressant mechanisms of action remain shrouded in mystery, greatly hindering our ability to develop therapeutics which can fully treat patients suffering from depressive disorders. In an attempt to shed new light on this topic, we have undertaken a series of studies investigating actions of tricyclic antidepressant drugs (TCAs) at the α2A adrenergic receptor (AR), a centrally important receptor, dysregulation of which has been linked to depression. Our previous work established a particular TCA, desipramine, as an arrestin-biased α2AAR ligand driving receptor endocytosis and downregulation but not canonical heterotrimeric G protein-mediated signaling. The present work is aimed at broadening our understanding of how members of the TCA drug class act at the α2AAR, as we have selected the closely related but subtly different TCAs imipramine and amitriptyline for evaluation. Our data demonstrate that these drugs do also function as direct arrestin-biased α2AAR ligands. However, these data reveal differences in receptor affinity and in the extent/nature of arrestin recruitment to and endocytosis of α2AARs. Specifically, amitriptyline exhibits an approximately 14-fold stronger interaction with the receptor, is a weaker driver of arrestin recruitment, and preferentially recruits a different arrestin subtype. Extent of endocytosis is similar for all TCAs studied so far, and occurs in an arrestin-dependent manner, although imipramine uniquely retains a slight ability to drive α2AAR endocytosis in arrestin-null cells. These findings signify an important expansion of our mechanistic understanding of antidepressant pharmacology, and provide useful insights for future medicinal chemistry efforts.

Circadian rhythms are the daily patterns that occur within an organism, from gene expression to behavior. These rhythms are governed not only externally by environmental cues but also internally, with cell-autonomous molecular clock mechanisms present nearly ubiquitously throughout the cells of organisms. In more complex organisms, it has been suggested that the clock mechanisms serve varied functions depending on the tissue in which they are found. By disrupting core circadian gene function in specific tissues of animal models, the various roles of the circadian clock in differing tissues can begin to be defined. This review provides an overview of the model organisms used to elucidate tissue-specific functions of the molecular circadian clock. V C 2014 IUBMB Life, 66(1):34-41, 2014.

The therapeutic mechanism of action underlying many psychopharmacological agents remains poorly understood, due largely to the extreme molecular promiscuity exhibited by these agents with respect to potential central nervous system targets. Agents of the tricyclic chemical class, including both antidepressants and antipsychotics, exhibit a particularly high degree of molecular promiscuity; therefore, any clarification of how these agents interact with specific central nervous system targets is of great potential significance to the field. Here, we present evidence demonstrating that tricyclic antipsychotics appear to segregate into three distinct groups based upon their molecular interactions with the centrally-important α2A adrenergic receptor (AR). Specifically, while the α2AAR binds all antipsychotics tested with similar affinities, and none of the agents are able to induce classical heterotrimeric G protein-mediated α2AAR signaling, significant differences are observed with respect to arrestin3 recruitment and receptor endocytosis. All antipsychotics tested induce arrestin3 recruitment to the α2AAR, but with differing strengths. Both chlorpromazine and clozapine drive significant α2AAR endocytosis, but via differing clathrin-dependent and lipid raft-dependent pathways, while fluphenazine does not drive a robust response. Intriguingly, in silico molecular modeling suggests that each of the three exhibits unique characteristics in interacting with the α2AAR ligand-binding pocket. In addition to establishing these three antipsychotics as novel arrestin-biased ligands at the α2AAR, our findings provide key insights into the molecular actions of these clinically-important agents.