The circadian clock coordinates physiology and metabolism. mTOR (mammalian/mechanistic target of rapamycin) is a major intracellular sensor that integrates nutrient and energy status to regulate protein synthesis, metabolism, and cell growth. Previous studies have identified a key role for mTOR in regulating photic entrainment and synchrony of the central circadian clock in the suprachiasmatic nucleus (SCN). Given that mTOR activities exhibit robust circadian oscillations in a variety of tissues and cells including the SCN, here we continued to investigate the role of mTOR in orchestrating autonomous clock functions in central and peripheral circadian oscillators. Using a combination of genetic and pharmacological approaches we show that mTOR regulates intrinsic clock properties including period and amplitude. In peripheral clock models of hepatocytes and adipocytes, mTOR inhibition lengthens period and dampens amplitude, whereas mTOR activation shortens period and augments amplitude. Constitutive activation of mTOR in Tsc2^–/–fibroblasts elevates levels of core clock proteins, including CRY1, BMAL1 and CLOCK. Serum stimulation induces CRY1 upregulation in fibroblasts in an mTOR-dependent but Bmal1- and Period-independent manner. Consistent with results from cellular clock models, mTOR perturbation also regulates period and amplitude in the ex vivo SCN and liver clocks. Further, mTOR heterozygous mice show lengthened circadian period of locomotor activity in both constant darkness and constant light. Together, these results support a significant role for mTOR in circadian timekeeping and in linking metabolic states to circadian clock functions. The circadian clock coordinates daily physiology and metabolism in animals. There has been considerable interest in identifying mechanisms that link metabolic signals to circadian time keeping. mTOR (mammalian/mechanistic target of rapamycin) is a major intracellular sensor that integrates nutrient and energy status to fundamental cellular processes. Previous studies have identified a key role for mTOR in regulating photic entrainment and synchrony of the central circadian clock in the suprachiasmatic nucleus (SCN). Given that mTOR activities exhibit robust circadian rhythms in a variety of cells and tissues including the SCN, here we investigated the role of mTOR in orchestrating autonomous functions in central and peripheral circadian clocks. Using a combination of genetic and pharmacological approaches we show that mTOR inhibition slows down the circadian clock and dampens clock oscillations, whereas mTOR activation accelerates the clock and enhances clock oscillations in cells, tissues as well as in mice. Together, these results support a significant role for mTOR in linking metabolic states to circadian time keeping.

Fragile X syndrome (FXS) is the leading genetic cause of autism. Mutations in Fmr1 (fragile X mental retardation 1 gene) engender exaggerated translation resulting in dendritic spine dysmorphogenesis, synaptic plasticity alterations, and behavioral deficits in mice, which are reminiscent of FXS phenotypes. Using postmortem brains from FXS patients and Fmr1 knockout mice (Fmr1(-/y)), we show that phosphorylation of the mRNA 5' cap binding protein, eukaryotic initiation factor 4E (eIF4E), is elevated concomitant with increased expression of matrix metalloproteinase 9 (MMP-9) protein. Genetic or pharmacological reduction of eIF4E phosphorylation rescued core behavioral deficits, synaptic plasticity alterations, and dendritic spine morphology defects via reducing exaggerated translation of Mmp9 mRNA in Fmr1(-/y) mice, whereas MMP-9 overexpression produced several FXS-like phenotypes. These results uncover a mechanism of regulation of synaptic function by translational control of Mmp-9 in FXS, which opens the possibility of new treatment avenues for the diverse neurological and psychiatric aspects of FXS.

Formation of reactive oxygen and nitrogen species is a precipitating event in an array of neuropathological conditions. In response to excessive reactive oxygen species (ROS) levels, transcriptionally dependent mechanisms drive the up‐regulation of ROS scavenging proteins which, in turn, limit the extent of brain damage. Here, we employed a transgenic approach in which cAMP‐response element binding protein (CREB)‐mediated transcription is repressed (via A‐CREB) to examine the contribution of the CREB/cAMP response element pathway to neuroprotection and its potential role in limiting ROS toxicity. Using the pilocarpine‐evoked repetitive seizure model, we detected a marked enhancement of cell death in A‐CREB transgenic mice. Paralleling this, there was a dramatic increase in tyrosine nitration (a marker of reactive species formation) in A‐CREB transgenic mice. In addition, inducible expression of peroxisome proliferator‐activated receptor gamma coactivator‐1α was diminished in A‐CREB transgenic mice, as was activity of complex I of the mitochondrial electron transport chain. Finally, the neuroprotective effect of brain‐derived neurotrophic factor (BDNF) against ROS‐mediated cell death was abrogated by disruption of CREB‐mediated transcription. Together, these data both extend our understanding of CREB functionality and providein vivovalidation for a model in which CREB functions as a pivotal upstream integrator of neuroprotective signaling against ROS‐mediated cell death.

Inducible gene expression appears to be an essential event that couples light to entrainment of the master mammalian circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Recently, we reported that light triggers phase-dependent activation of the mammalian target of rapamycin (mTOR) signaling pathway, a major regulator of protein synthesis, in the SCN, thus raising the possibility that mTOR-evoked mRNA translation contributes to clock entrainment. Here, we used a combination of cellular, molecular, and behavioral assays to address this question. To this end, we show that thein vivoinfusion of the mTOR inhibitor rapamycin led to a significant attenuation of the phase-delaying effect of early-night light. Conversely, disruption of mTOR during the late night augmented the phase-advancing effect of light. To assess the role of mTOR signaling within the context of molecular entrainment, the effects of rapamycin on light-induced expression of PERIOD1 and PERIOD2 were examined. At both the early- and late-night time points, abrogation of mTOR signaling led to a significant attenuation of light-evoked PERIOD protein expression. Our results also reveal that light-induced mTOR activation leads to the translation of mRNAs with a 5′-terminal oligopyrimidine tract such as eukaryotic elongation factor 1A and the immediate early gene JunB. Together, these data indicate that the mTOR pathway functions as potent and selective regulator of light-evoked protein translation and SCN clock entrainment.