ABSTRACT
Cognitive deficits after aneurysmal subarachnoid hemorrhage (SAH) are common and disabling. Patients who experience delayed deterioration associated with vasospasm are likely to have cognitive deficits, particularly problems with executive function, verbal and spatial memory. Here, we report neurophysiological and pathological mechanisms underlying behavioral deficits in a murine model of SAH. On tests of spatial memory, animals with SAH performed worse than sham animals in the first week and one month after SAH suggesting a prolonged injury. Between three and six days after experimental hemorrhage, mice demonstrated loss of late long-term potentiation (L-LTP) due to dysfunction of the NMDA receptor. Suppression of innate immune cell activation prevents delayed vasospasm after murine SAH. We therefore explored the role of neutrophil-mediated innate inflammation on memory deficits after SAH. Depletion of neutrophils three days after SAH mitigates tissue inflammation, reverses cerebral vasoconstriction in the middle cerebral artery, and rescues L-LTP dysfunction at day 6. Spatial memory deficits in both the short and long-term are improved and associated with a shift of NMDA receptor subunit composition toward a memory sparing phenotype. This work supports further investigating suppression of innate immunity after SAH as a target for preventative therapies in SAH.
Subject(s)
Memory/physiology , Neutrophils/pathology , Receptors, N-Methyl-D-Aspartate/metabolism , Subarachnoid Hemorrhage/therapy , Animals , Immunity, Innate/immunology , Long-Term Potentiation/physiology , Male , Mice , Mice, Inbred C57BL , Subarachnoid Hemorrhage/blood , Vasospasm, Intracranial/therapyABSTRACT
The mTOR signaling pathway modulates metabolic processes with respect to nutrient availability and other growth-related cues. According to the existing paradigm, mTOR complex 1 (mTORC1) activityin vivo is induced by food and gradually decreases during fasting. We found that mTORC1 activity is controlled by an internal clock mechanism different from the known light-entrainable circadian clock. We observed 24-hr rhythms in phosphorylation of mTORC1 downstream targets, which were entrained by food, persisted during fasting and could be uncoupled from oscillating expression of the canonical circadian clock genes. Furthermore, these rhythms were present in tissues of mice with disrupted light-entrainable circadian clock. We propose tissue-specific rhythms in the expression of tor and its negative regulator deptor as the molecular mechanism of the mTORC1 activity oscillation. Our data demonstrate the existence of at least two independent molecular circadian clocks: one providing metabolic adaptation to periodic light/darkness and the other - to feeding.
Subject(s)
Biological Clocks/physiology , Feeding Behavior/physiology , Signal Transduction/physiology , TOR Serine-Threonine Kinases/metabolism , Animals , Liver/metabolism , Mice , Phosphorylation/physiologyABSTRACT
The circadian clock, an internal time-keeping system, has been linked with control of aging, but molecular mechanisms of regulation are not known. BMAL1 is a transcriptional factor and core component of the circadian clock; BMAL1 deficiency is associated with premature aging and reduced lifespan. Here we report that activity of mammalian Target of Rapamycin Complex 1 (mTORC1) is increased upon BMAL1 deficiency both in vivo and in cell culture. Increased mTOR signaling is associated with accelerated aging; in accordance with that, treatment with the mTORC1 inhibitor rapamycin increased lifespan of Bmal1-/- mice by 50%. Our data suggest that BMAL1 is a negative regulator of mTORC1 signaling. We propose that the circadian clock controls the activity of the mTOR pathway through BMAL1-dependent mechanisms and this regulation is important for control of aging and metabolism.
Subject(s)
ARNTL Transcription Factors/metabolism , Aging/metabolism , Signal Transduction , TOR Serine-Threonine Kinases/metabolism , ARNTL Transcription Factors/deficiency , ARNTL Transcription Factors/genetics , Aging/genetics , Animals , Cell Proliferation , Cells, Cultured , Circadian Rhythm , Enzyme Inhibitors/pharmacology , Fibroblasts/enzymology , Genotype , Intracellular Signaling Peptides and Proteins/genetics , Intracellular Signaling Peptides and Proteins/metabolism , Lung/enzymology , Mechanistic Target of Rapamycin Complex 1 , Mice , Mice, Inbred C57BL , Multiprotein Complexes/metabolism , Phenotype , Phosphorylation , Signal Transduction/drug effects , Sirolimus/pharmacology , TOR Serine-Threonine Kinases/antagonists & inhibitors , TOR Serine-Threonine Kinases/genetics , Time FactorsABSTRACT
Deficiency of the circadian clock transcriptional factor BMAL1 results in the development of premature aging in mice. In agreement with the accelerated aging phenotype, we observed an increase in the number of senescent cells in different tissues (lungs, liver and spleen) of Bmal1(-/-) mice, which suggests the important role of BMAL1 in the control of senescence in vivo. However, no difference in the rate of proliferation and senescence between primary fibroblasts isolated from wild-type and Bmal1(-/-) mice has been detected, suggesting that BMAL1 does not play a significant role in replicative senescence in vitro. BMAL1 deficient fibroblasts had an increased sensitivity to hydrogen peroxide treatment, and reduced sensitivity to DNA damaging anticancer drugs etoposide and daunorubicin. Increased sensitivity of Bmal1(-/-) cells to oxidative stress was p53 independent and correlated with the disrupted regulation of reactive oxygen species (ROS) homeostasis in BMAL1 deficient cells: indeed, circadian oscillations of ROS level can be induced in wild-type but not in Bmal1(-/-) cells. We propose that BMAL1 is important for the regulation of oxidative stress and DNA damage responses, while deregulation of these processes upon BMAL1 deficiency leads to development of stress induced senescence in vivo.
Subject(s)
ARNTL Transcription Factors/metabolism , Cellular Senescence , Circadian Clocks , DNA Damage , Oxidative Stress , ARNTL Transcription Factors/genetics , Animals , Antineoplastic Agents/pharmacology , Cell Death , Culture Media, Serum-Free/metabolism , Daunorubicin/pharmacology , Drug Screening Assays, Antitumor , Etoposide/pharmacology , Fibroblasts/drug effects , Gene Expression Regulation, Neoplastic , Homeostasis , Hydrogen Peroxide/pharmacology , Mice , Mice, Inbred C57BL , Mice, Knockout , Primary Cell Culture , Reactive Oxygen Species , Time FactorsABSTRACT
The circadian clock generates oscillations in physiology and behavior, known as circadian rhythms. Links between the circadian clock genes Periods, Bmal1, and Cryptochromes and aging and cancer are emerging. Circadian clock gene expression is changed in human pathologies, and transgenic mice with mutations in clock genes develop cancer and premature aging. Control of genome integrity and cell proliferation play key roles in the development of age-associated pathologies and carcinogenesis. Here, we review recent data on the connection between the circadian clock and control of the cell cycle. The circadian clock regulates the activity and expression of several critical cell cycle and cell cycle check-point-related proteins, and in turn cell cycle-associated proteins regulate circadian clock proteins. DNA damage can reset the circadian clock, which provides a molecular mechanism for reciprocal regulation between the circadian clock and the cell cycle. This circadian clock-dependent control of cell proliferation, together with other known physiological functions of the circadian clock such as the control of metabolism, oxidative and genotoxic stress response, and DNA repair, opens new horizons for understanding the mechanisms behind aging and carcinogenesis.
