The Neuronal Transcription Factor Creb3l1 Potential Upregulates Ntrk2 in the Hypertensive Microenvironment to Promote Vascular Smooth Muscle Cell-Neuron Interaction and Prevent Neurons from Ferroptosis: A Bioinformatic Research of scRNA-seq Data.

BACKGROUND: There is still a lack of knowledge regarding the association between hypertension and ferroptosis. A single-cell approach was used to study the changes in neuropeptide expression as they might contribute to the mechanisms leading to ferroptosis in a hypertensive microenvironment. METHODS: We analyzed 11798 cells from the SHR group and 12589 cells from the WKY group of mouse arterial cells. CellPhoneDB was used for cell communication analysis, and the SCENIC method was used to identify key transcription factors in neurons. The correlation between Ntrk2 and ferroptosis-related genes was further analyzed and validated via quantitative polymerase chain reaction. RESULTS: The arterial cells were clustered into six cell types. Ligand-receptor analysis suggested that Ngf, Ntf3, Cxcr4, and Ntrk2 were key neuropeptide-related genes involved in the communication between vascular smooth muscle cells and neural cells. In the hypertensive microenvironment, the neuronal transcription factor Creb3l1 appears to play a key role in the upregulation of Ntrk2 to promote the interaction between neurons and vascular smooth muscle cells. An association between Ntrk2 and the ferroptosis death inhibitor Gpx4 was suggested. RT-qPCR experiments confirmed that Ntrk2 downregulation in neural cells was followed by downregulated expression of Gpx4. CONCLUSIONS: Creb3l1, a key transcription factor in vascular neurons, may upregulate Ntrk2 to promote vascular smooth muscle cell-neuron interaction and thereby potentially prevent ferroptosis in neurons.

Adiponectin promotes repair of renal tubular epithelial cells by regulating mitochondrial biogenesis and function.

BACKGROUND: Mitochondrial biogenesis and dysfunction are associated with renal tubular epithelial cell injury and the pathophysiological development of diabetic nephropathy (DN). Adiponectin (APN) is a plasma hormone protein specifically secreted by adipocytes. In the present study, we studied the effects of APN on mitochondrial biogenesis and function in renal tubular epithelial cells and examined the mechanisms underlying its actions. MATERIALS: A rat model of type 2 diabetes mellitus (T2DM) was established using streptozotocin (STZ), and an NRK-52E culture model exposed to high glucose was also used. We found that APN treatment alleviated kidney histopathological injury in T2DM rats, reduced fasting blood glucose (FBG) and postprandial blood glucose (PBG) levels, maintained stable animal weight, promoted cell viability, inhibited apoptosis and the formation of autophagosomes, and also increased mitochondrial mass, mitochondrial DNA (mtDNA) content and mitochondrial membrane potential (MMP) in vivo and in vitro. RESULTS: We found that the expression of AdipoR1/CREB/PGC-1α/TFAM pathway proteins and respiratory chain complex subunits CO1, CO2, CO3, ATP6 and ATP8 were significantly increased after APN treatment. We also found that inhibition of cAMP response element binding protein (CREB) weakened the effects of APN in NRK-52E cells treated with high glucose. Coimmunoprecipitation experiments showed that AdipoR1 interacted with CREB. CONCLUSION: APN promoted mitochondrial biogenesis and function in renal tubular epithelial cells by regulating the AdipoR1/CREB/PGC-1α/TFAM pathway. APN has the potential to serve as an effective drug for the treatment of DN.

Activation of Crtc2/Creb1 in skeletal muscle enhances weight loss during intermittent fasting.

The Creb-Regulated Transcriptional Coactivator (Crtc) family of transcriptional coregulators drive Creb1-mediated transcription effects on metabolism in many tissues, but the in vivo effects of Crtc2/Creb1 transcription on skeletal muscle metabolism are not known. Skeletal muscle-specific overexpression of Crtc2 (Crtc2 mice) induced greater mitochondrial activity, metabolic flux capacity for both carbohydrates and fats, improved glucose tolerance and insulin sensitivity, and increased oxidative capacity, supported by upregulation of key metabolic genes. Crtc2 overexpression led to greater weight loss during alternate day fasting (ADF), selective loss of fat rather than lean mass, maintenance of higher energy expenditure during the fast and reduced binge-eating during the feeding period. ADF downregulated most of the mitochondrial electron transport genes, and other regulators of mitochondrial function, that were substantially reversed by Crtc2-driven transcription. Glucocorticoids acted with AMPK to drive atrophy and mitophagy, which was reversed by Crtc2/Creb1 signaling. Crtc2/Creb1-mediated signaling coordinates metabolic adaptations in skeletal muscle that explain how Crtc2/Creb1 regulates metabolism and weight loss.

Activation of the adipocyte CREB/CRTC pathway in obesity.

Obesity is a major risk factor for the development of type II diabetes. Increases in adipose tissue mass trigger insulin resistance via the release of pro-inflammatory cytokines from adipocytes and macrophages. CREB and the CRTC coactivators have been found to promote insulin resistance in obesity, although the mechanism is unclear. Here we show that high fat diet feeding activates the CREB/CRTC pathway in adipocytes by decreasing the expression of SIK2, a Ser/Thr kinase that phosphorylates and inhibits CRTCs. SIK2 levels are regulated by the adipogenic factor C/EBPα, whose expression is reduced in obesity. Exposure to PPARγ agonist rescues C/EBPα expression and restores SIK2 levels. CRTC2/3 promote insulin resistance via induction of the chemokines CXCL1/2. Knockout of CRTC2/3 in adipocytes reduces CXCL1/2 expression and improves insulin sensitivity. As administration of CXCL1/2 reverses salutary effects of CRTC2/3 depletion, our results demonstrate the importance of the CREB/CRTC pathway in modulating adipose tissue function.

CREBA and CREBB in two identified neurons gate long-term memory formation in Drosophila.

Episodic events are frequently consolidated into labile memory but are not necessarily transferred to persistent long-term memory (LTM). Regulatory mechanisms leading to LTM formation are poorly understood, however, especially at the resolution of identified neurons. Here, we demonstrate enhanced LTM following aversive olfactory conditioning in Drosophila when the transcription factor cyclic AMP response element binding protein A (CREBA) is induced in just two dorsal-anterior-lateral (DAL) neurons. Our experiments show that this process is regulated by protein-gene interactions in DAL neurons: (1) crebA transcription is induced by training and repressed by crebB overexpression, (2) CREBA bidirectionally modulates LTM formation, (3) crebA overexpression enhances training-induced gene transcription, and (4) increasing membrane excitability enhances LTM formation and gene expression. These findings suggest that activity-dependent gene expression in DAL neurons during LTM formation is regulated by CREB proteins.

CREBH normalizes dyslipidemia and halts atherosclerosis in diabetes by decreasing circulating remnant lipoproteins.

Loss-of-function mutations in the transcription factor CREB3L3 (CREBH) associate with severe hypertriglyceridemia in humans. CREBH is believed to lower plasma triglycerides by augmenting the activity of lipoprotein lipase (LPL). However, by using a mouse model of type 1 diabetes mellitus (T1DM), we found that greater liver expression of active CREBH normalized both elevated plasma triglycerides and cholesterol. Residual triglyceride-rich lipoprotein (TRL) remnants were enriched in apolipoprotein E (APOE) and impoverished in APOC3, an apolipoprotein composition indicative of increased hepatic clearance. The underlying mechanism was independent of LPL, as CREBH reduced both triglycerides and cholesterol in LPL-deficient mice. Instead, APOE was critical for CREBH's ability to lower circulating remnant lipoproteins because it failed to reduce TRL cholesterol in Apoe-/- mice. Importantly, individuals with CREB3L3 loss-of-function mutations exhibited increased levels of remnant lipoproteins that were deprived of APOE. Recent evidence suggests that impaired clearance of TRL remnants promotes cardiovascular disease in patients with T1DM. Consistently, we found that hepatic expression of CREBH prevented the progression of diabetes-accelerated atherosclerosis. Our results support the proposal that CREBH acts through an APOE-dependent pathway to increase hepatic clearance of remnant lipoproteins. They also implicate elevated levels of remnants in the pathogenesis of atherosclerosis in T1DM.

Pectic Oligogalacturonide Facilitates the Synthesis and Activation of Adiponectin to Improve Hepatic Lipid Oxidation.

SCOPE: Adiponectin (ADPN), a kind of adipokines, plays an important role in the regulation of lipid metabolism. The objective of this study is focused on the ADPN to investigate the functional mechanisms of pectin oligosaccharide (POS) from hawthorn fruit in the improvement of hepatic fatty acid oxidation. METHOD AND RESULTS: High-fat fed mice are used in this experiment. POS is administrated with the doses of 0.25, 0.75, and 1.5 g kg-1 diet, respectively. The results demonstrate that gene and protein expressions of ADPN synthesis regulators involved in PKA/ERK/CREB and C/EBPα/PPARγ pathways are upregulated by POS administration. POS also activates the AdiopR1/AMPKα/PGC1 and AdipoR2/PPARα signaling pathways to improve the fatty acid oxidation in the liver, which is further accelerated by the enhancement of mitochondrial functions. CONCLUSION: POS can act as an ADPN activator to improve lipid metabolism, leading it to the applications of biomedical and functional foods for ameliorating chronic liver diseases resulted from a high-energy diet.

CREB mediates the C. elegans dauer polyphenism through direct and cell-autonomous regulation of TGF-ß expression.

Animals can adapt to dynamic environmental conditions by modulating their developmental programs. Understanding the genetic architecture and molecular mechanisms underlying developmental plasticity in response to changing environments is an important and emerging area of research. Here, we show a novel role of cAMP response element binding protein (CREB)-encoding crh-1 gene in developmental polyphenism of C. elegans. Under conditions that promote normal development in wild-type animals, crh-1 mutants inappropriately form transient pre-dauer (L2d) larvae and express the L2d marker gene. L2d formation in crh-1 mutants is specifically induced by the ascaroside pheromone ascr#5 (asc-ωC3; C3), and crh-1 functions autonomously in the ascr#5-sensing ASI neurons to inhibit L2d formation. Moreover, we find that CRH-1 directly binds upstream of the daf-7 TGF-ß locus and promotes its expression in the ASI neurons. Taken together, these results provide new insight into how animals alter their developmental programs in response to environmental changes.

Starvation-induced transcription factor CREBH negatively governs body growth by controlling GH signaling.

cAMP responsive element-binding protein H (CREBH) is a hepatic transcription factor to be activated during fasting. We generated CREBH knock-in flox mice, and then generated liver-specific CREBH transgenic (CREBH L-Tg) mice in an active form. CREBH L-Tg mice showed a delay in growth in the postnatal stage. Plasma growth hormone (GH) levels were significantly increased in CREBH L-Tg mice, but plasma insulin-like growth factor 1 (IGF1) levels were significantly decreased, indicating GH resistance. In addition, CREBH overexpression significantly increased hepatic mRNA and plasma levels of FGF21, which is thought to be as one of the causes of growth delay. However, the additional ablation of FGF21 in CREBH L-Tg mice could not correct GH resistance at all. CREBH L-Tg mice sustained GH receptor (GHR) reduction and the increase of IGF binding protein 1 (IGFBP1) in the liver regardless of FGF21. As GHR is a first step in GH signaling, the reduction of GHR leads to impairment of GH signaling. These data suggest that CREBH negatively regulates growth in the postnatal growth stage via various pathways as an abundant energy response by antagonizing GH signaling.

Small leucine zipper protein promotes the metastasis of castration-resistant prostate cancer through transcriptional regulation of matrix metalloproteinase-13.

Matrix metalloproteinases (MMPs) function as central modulators of tissue remodeling. Abnormal expression and altered activity of MMPs result in excessive extracellular matrix degradation and increased tumor metastasis in various cancers. Small leucine zipper protein (sLZIP), belonging to the leucine zipper transcription factor family, functions as a transcriptional regulator of genes involved in various cellular processes. However, its role in MMP expression and castration-resistant prostate cancer (CRPC) metastasis remains unclear. In this study, we investigated the role of sLZIP in MMP-13 expression and its involvement in CRPC metastasis. sLZIP increased MMP-13 transcription by directly binding to its promoter in CRPC cells. We found that the expression levels of glucocorticoid receptor (GR), which represses MMP transcription, were elevated in CRPC cells. However, sLZIP suppressed the inhibitory effect of GR and enhanced the secretion of MMP-13 in CRPC cells. sLZIP promoted cell migration and invasion; however, a specific MMP-13 inhibitor blocked sLZIP-induced cell motility. Depletion of sLZIP using the CRISPR/Cas9 system downregulated MMP-13 messenger RNA expression in PC3 cells. Mice injected with sLZIP-depleted PC3 cells showed significantly reduced metastatic tumor volume in the lung compared with mice injected with control PC3 cells. Our findings suggest that sLZIP plays an important role in MMP-13 induction and CRPC metastasis. Therefore, sLZIP inhibition could be a novel therapeutic strategy for metastatic GR-enriched CRPC.

Dynamical Mechanisms for Gene Regulation Mediated by Two Noncoding RNAs in Long-Term Memory Formation.

Noncoding RNAs such as miRNAs and piRNAs have long-lasting effects on the regulation of gene expression involved in long-term synaptic changes. To characterize gene regulation mediated by small noncoding RNAs associated with long-term memory in Aplysia, we consider two noncoding RNAs stimulated by 5-HT into a gene regulatory network motif model, including miR-124 that binds to and inhibits the mRNA of CREB1 and piR-F that facilitates serotonin-dependent DNA methylation to lead to repression of CREB2. Codimension-1 and -2 bifurcation analyses of 5-HT regulating both miR-124 and piR-F and a negative feedback strength for oscillation reveal rich dynamical properties of bistability and oscillations robust to variations in all other parameters. More importantly, we verify three stimulus protocols of 5-HT in experiments by our model and find that application of five pulses of 5-HT leads to a transient decrease of miR-124 but increase of piR-F concentrations, which matters sustained high level of CREB1 concentration associated with long-term memory. Furthermore, we perform bifurcation analyses for the concentrations of miR-124 and piR-F as two parameters to explore dynamical mechanisms underlying the epigenetic regulation in long-term memory formation. This study provides insights into revealing regulatory roles of epigenetic changes in gene expression involving noncoding RNAs associated with synaptic plasticity.

Fgf15 Neurons of the Dorsomedial Hypothalamus Control Glucagon Secretion and Hepatic Gluconeogenesis.

The counterregulatory response to hypoglycemia is an essential survival function. It is controlled by an integrated network of glucose-responsive neurons, which trigger endogenous glucose production to restore normoglycemia. The complexity of this glucoregulatory network is, however, only partly characterized. In a genetic screen of a panel of recombinant inbred mice we previously identified Fgf15, expressed in neurons of the dorsomedial hypothalamus (DMH), as a negative regulator of glucagon secretion. Here, we report on the generation of Fgf15CretdTomato mice and their use to further characterize these neurons. We show that they were glutamatergic and comprised glucose-inhibited and glucose-excited neurons. When activated by chemogenetics, Fgf15 neurons prevented the increase in vagal nerve firing and the secretion of glucagon normally triggered by insulin-induced hypoglycemia. On the other hand, they increased the activity of the sympathetic nerve in the basal state and prevented its silencing by glucose overload. Higher sympathetic tone increased hepatic Creb1 phosphorylation, Pck1 mRNA expression, and hepatic glucose production leading to glucose intolerance. Thus, Fgf15 neurons of the DMH participate in the counterregulatory response to hypoglycemia by a direct adrenergic stimulation of hepatic glucose production while suppressing vagally induced glucagon secretion. This study provides new insights into the complex neuronal network that prevents the development of hypoglycemia.

The possible role of CREB-BDNF signaling pathway in neuroprotective effects of minocycline against alcohol-induced neurodegeneration: molecular and behavioral evidences.

Abuse of alcohol triggers neurodegeneration in human brain. Minocycline has characteristics conferring neuroprotection. Current study evaluates the role of the CREB-BDNF signaling pathway in mediating minocycline's neuroprotective effects against alcohol-induced neurodegeneration. Seventy adult male rats were randomly split into groups 1 and 2 that received saline and alcohol (2 g/kg/day by gavage, once daily), respectively, and groups 3, 4, 5, and 6 were treated simultaneously with alcohol and minocycline (10, 20, 30 and 40 mg/kg I.P, respectively) for 21 days. Group 7 received minocycline alone (40 mg/kg, i.p) for 21 days. Morris water maze (MWM) has been used to assess cognitive activity. Hippocampal neurodegenerative and histological parameters as well as cyclic AMP response element-binding protein (CREB) and brain-derived neurotrophic factor (BDNF) levels were assessed. Alcohol impaired cognition, and concurrent therapy with various minocycline doses attenuated alcohol-induced cognition disturbances. Additionally, alcohol administration boosted lipid peroxidation and levels of glutathione in oxidized form (GSSG), tumor necrosis factor alpha (TNF-α), interleukin 1 beta (IL-1ß), and Bax protein, while decreased reducing type of glutathione (GSH), Bcl-2 protein, phosphorylated CREB, and BDNF levels in rat hippocampus. Alcohol also decreased the activity in the hippocampus of superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR). In comparison, minocycline attenuated alcohol-induced neurodegeneration; elevating expression levels of P-CREB and BDNF and inhibited alcohol induced histopathological changes in both dentate gyrus (DG) and CA1 of hippocampus. Thus, minocycline is likely to provide neuroprotection against alcohol-induced neurodegeneration through mediation of the P-CREB/BDNF signaling pathway.

Enterohepatic Transcription Factor CREB3L3 Protects Atherosclerosis via SREBP Competitive Inhibition.

BACKGROUND & AIMS: cAMP responsive element-binding protein 3 like 3 (CREB3L3) is a membrane-bound transcription factor involved in the maintenance of lipid metabolism in the liver and small intestine. CREB3L3 controls hepatic triglyceride and glucose metabolism by activating plasma fibroblast growth factor 21 (FGF21) and lipoprotein lipase. In this study, we intended to clarify its effect on atherosclerosis. METHODS: CREB3L3-deficifient, liver-specific CREB3L3 knockout, intestine-specific CREB3L3 knockout, both liver- and intestine-specific CREB3L3 knockout, and liver CREB3L3 transgenic mice were crossed with LDLR-/- mice. These mice were fed with a Western diet to develop atherosclerosis. RESULTS: CREB3L3 ablation in LDLR-/- mice exacerbated hyperlipidemia with accumulation of remnant APOB-containing lipoprotein. This led to the development of enhanced aortic atheroma formation, the extent of which was additive between liver- and intestine-specific deletion. Conversely, hepatic nuclear CREB3L3 overexpression markedly suppressed atherosclerosis with amelioration of hyperlipidemia. CREB3L3 directly up-regulates anti-atherogenic FGF21 and APOA4. In contrast, it antagonizes hepatic sterol regulatory element-binding protein (SREBP)-mediated lipogenic and cholesterogenic genes and regulates intestinal liver X receptor-regulated genes involved in the transport of cholesterol. CREB3L3 deficiency results in the accumulation of nuclear SREBP proteins. Because both transcriptional factors share the cleavage system for nuclear transactivation, full-length CREB3L3 and SREBPs in the endoplasmic reticulum (ER) functionally inhibit each other. CREB3L3 promotes the formation of the SREBP-insulin induced gene 1 complex to suppress SREBPs for ER-Golgi transport, resulting in ER retention and inhibition of proteolytic activation at the Golgi and vice versa. CONCLUSIONS: CREB3L3 has multi-potent protective effects against atherosclerosis owing to new mechanistic interaction between CREB3L3 and SREBPs under atherogenic conditions.

The role of CREB and BDNF in neurobiology and treatment of Alzheimer's disease.

Alzheimer's disease (AD) is the most common form of dementia worldwide. ß-amyloid peptide (Aß) is currently assumed to be the main cause of synaptic dysfunction and cognitive impairments in AD, but the molecular signaling pathways underlying its neurotoxic consequences have not yet been completely explored. Additional investigations regarding these pathways will contribute to development of new therapeutic targets. In context, developing evidence suggest that Aß decreases brain-derived neurotrophic factor (BDNF) mostly by lowering phosphorylated cyclic adenosine monophosphate (cAMP) response element binding protein (CREB) protein. In fact, it has been observed that brain or serum levels of BDNF appear to be beneficial markers for cognitive condition. In addition, the participation of transcription mediated by CREB has been widely analyzed in the memory process and AD development. Designing pharmacologic or genetic therapeutic approaches based on the targeting of CREB-BDNF signaling could be a promising treatment potential for AD. In this review, we summarize data demonstrating the role of CREB-BDNF signaling pathway in cognitive status and mediation of Aß toxicity in AD. Finally, we also focus on the developing intervention methods for improvement of cognitive decline in AD based on targeting of CREB-BDNF pathway.

Edaravone Improves Intermittent Hypoxia-Induced Cognitive Impairment and Hippocampal Damage in Rats.

Oxidative stress plays an essential role in obstructive sleep apnea-hypopnea syndrome-induced cognitive dysfunction in children. This study investigated the effects of edaravone, a potent free radical scavenger, on intermittent hypoxia (IH)-induced oxidative damage and cognition impairment in a young rat model of IH. IH rats were treated with edaravone for 4 weeks. Behavioral testing was performed using the Morris water maze, and hippocampal tissues were harvested for further analyses. Edaravone attenuated IH-induced cognitive impairment, reduced morphological and structural abnormalities, and increased the number of mitochondria in the IH rats. Furthermore, edaravone significantly increased the inhibition of hydroxyl free radicals; reduced expressions of superoxide anion, malondialdehyde, and 8-hydroxy-2'-deoxyguanosine; and upregulated the expression of manganese superoxide dismutase, catalase, cAMP, protein kinase A, phosphorylated-cAMP response element-binding (p-CREB), B-cell lymphoma 2, and brain-derived neurotrophic factor in the hippocampal tissue of IH rats. Our findings suggest that edaravone attenuated IH-induced cognitive impairment and hippocampal damage by upregulating p-CREB in young rats.

SIRT1 regulates O-GlcNAcylation of tau through OGT.

Tau is modified with O-GlcNAcylation extensively in human brain. The O-GlcNAcylation levels of tau are decreased in Alzheimer's disease (AD) brain. Sirtuin type 1 (SIRT1) is an enzyme that deacetylates proteins including transcriptional factors and associates with neurodegenerative diseases, such as AD. Aberrant SIRT1 expression levels in AD brain is in parallel with the accumulation of tau. cAMP response element binding protein (CREB), a cellular transcription factor, plays a critical role in learning and memory. In this present study, we found SIRT1 deacetylates CREB and inhibits phosphorylation of CREB at Ser133. The inactivated CREB suppresses OGT expression and therefore decreases the O-GlcNAcylation of tau and thus increases the phosphorylation of tau at specific sites. These findings suggest that SIRT1 may be a potential therapeutic target for treating tauopathies.

Alpinia oxyphylla-Schisandra chinensis Herb Pair Alleviates Amyloid-ß Induced Cognitive Deficits via PI3K/Akt/Gsk-3ß/CREB Pathway.

Alzheimer's disease (AD), one of the most common neurodegenerative diseases, threatens people's health. Based on the theory of traditional Chinese medicine (TCM) efficacy and treatment theory, we first proposed the Alpinia oxyphylla-Schisandra chinensis herb pair (ASHP) for finding a candidate of AD treatment. This study aimed at exploring the effects of ASHP on improving the cognitive function and neurodegeneration, and revealing the possible mechanism. In this study, an amyloid-ß (Aß) induced AD model was established in mice via intracerebroventricular injection. The Y-maze test and Morris water maze test were carried out to observe the behavioral change of mice, which showed that ASHP significantly ameliorated cognitive impairment. In addition, ASHP reduced amyloid-ß deposition and downregulated the hyperphosphorylation of tau via immunofluorescence assay and western blot analysis, respectively. Subsequently we focused on the PI3K/Akt pathway that is a classical pathway related to nervous system diseases. It also noticeably ASHP improved the histopathological changes in the hippocampus and cortex. Moreover, it was found that ASHP could upregulate the PI3K/Akt/Gsk-3ß/CREB signaling pathway in N2a-SwedAPP cells. Taken together, it suggests that ASHP might reverse cognitive deficits and neurodegeneration via PI3K/Akt/Gsk-3ß/CREB pathway.

Environmental Light Is Required for Maintenance of Long-Term Memory in Drosophila.

Long-term memory (LTM) is stored as functional modifications of relevant neural circuits in the brain. A large body of evidence indicates that the initial establishment of such modifications through the process known as memory consolidation requires learning-dependent transcriptional activation and de novo protein synthesis. However, it remains poorly understood how the consolidated memory is maintained for a long period in the brain, despite constant turnover of molecular substrates. Using the Drosophila courtship conditioning assay of adult males as a memory paradigm, here, we show that in Drosophila, environmental light plays a critical role in LTM maintenance. LTM is impaired when flies are kept in constant darkness (DD) during the memory maintenance phase. Because light activates the brain neurons expressing the neuropeptide pigment-dispersing factor (Pdf), we examined the possible involvement of Pdf neurons in LTM maintenance. Temporal activation of Pdf neurons compensated for the DD-dependent LTM impairment, whereas temporal knockdown of Pdf during the memory maintenance phase impaired LTM in light/dark cycles. Furthermore, we demonstrated that the transcription factor cAMP response element-binding protein (CREB) is required in the memory center, namely, the mushroom bodies (MBs), for LTM maintenance, and Pdf signaling regulates light-dependent transcription via CREB. Our results demonstrate for the first time that universally available environmental light plays a critical role in LTM maintenance by activating the evolutionarily conserved memory modulator CREB in MBs via the Pdf signaling pathway.SIGNIFICANCE STATEMENT Temporary memory can be consolidated into long-term memory (LTM) through de novo protein synthesis and functional modifications of neuronal circuits in the brain. Once established, LTM requires continual maintenance so that it is kept for an extended period against molecular turnover and cellular reorganization that may disrupt memory traces. How is LTM maintained mechanistically? Despite the critical importance of LTM maintenance, its molecular and cellular underpinnings remain elusive. This study using Drosophila is significant because it revealed for the first time in any organism that universally available environmental light plays an essential role in LTM maintenance. Interestingly, light does so by activating the evolutionarily conserved transcription factor cAMP response element-binding protein via peptidergic signaling.

CREB Family Transcription Factors Are Major Mediators of BDNF Transcriptional Autoregulation in Cortical Neurons.

BDNF signaling via its transmembrane receptor TrkB has an important role in neuronal survival, differentiation, and synaptic plasticity. Remarkably, BDNF is capable of modulating its own expression levels in neurons, forming a transcriptional positive feedback loop. In the current study, we have investigated this phenomenon in primary cultures of rat cortical neurons using overexpression of dominant-negative forms of several transcription factors, including CREB, ATF2, C/EBP, USF, and NFAT. We show that CREB family transcription factors, together with the coactivator CBP/p300, but not the CRTC family, are the main regulators of rat BDNF gene expression after TrkB signaling. CREB family transcription factors are required for the early induction of all the major BDNF transcripts, whereas CREB itself directly binds only to BDNF promoter IV, is phosphorylated in response to BDNF-TrkB signaling, and activates transcription from BDNF promoter IV by recruiting CBP. Our complementary reporter assays with BDNF promoter constructs indicate that the regulation of BDNF by CREB family after BDNF-TrkB signaling is generally conserved between rat and human. However, we demonstrate that a nonconserved functional cAMP-responsive element in BDNF promoter IXa in humans renders the human promoter responsive to BDNF-TrkB-CREB signaling, whereas the rat ortholog is unresponsive. Finally, we show that extensive BDNF transcriptional autoregulation, encompassing all major BDNF transcripts, occurs also in vivo in the adult rat hippocampus during BDNF-induced LTP. Collectively, these results improve the understanding of the intricate mechanism of BDNF transcriptional autoregulation.SIGNIFICANCE STATEMENT Deeper understanding of stimulus-specific regulation of BDNF gene expression is essential to precisely adjust BDNF levels that are dysregulated in various neurological disorders. Here, we have elucidated the molecular mechanisms behind TrkB signaling-dependent BDNF mRNA induction and show that CREB family transcription factors are the main regulators of BDNF gene expression after TrkB signaling. Our results suggest that BDNF-TrkB signaling may induce BDNF gene expression in a distinct manner compared with neuronal activity. Moreover, our data suggest the existence of a stimulus-specific distal enhancer modulating BDNF gene expression.