Salvatore Fusco

High-fat diet (HFD) and metabolic diseases cause detrimental effects on hippocampal synaptic plasticity, learning, and memory through molecular mechanisms still poorly understood. Here, we demonstrate that HFD increases palmitic acid deposition in the hippocampus and induces hippocampal insulin resistance leading to FoxO3a-mediated overexpression of the palmitoyltransferase zDHHC3. The excess of palmitic acid along with higher zDHHC3 levels causes hyper-palmitoylation of AMPA glutamate receptor subunit GluA1, hindering its activity-dependent trafficking to the plasma membrane. Accordingly, AMPAR current amplitudes and, more importantly, their potentiation underlying synaptic plasticity were inhibited, as well as hippocampal-dependent memory. Hippocampus-specific silencing of Zdhhc3 and, interestingly enough, intranasal injection of the palmitoyltransferase inhibitor, 2-bromopalmitate, counteract GluA1 hyper-palmitoylation and restore synaptic plasticity and memory in HFD mice. Our d...

Spike timing-dependent plasticity (STDP) is a form of activity-dependent remodeling of synaptic strength that underlies memory formation. Despite its key role in dictating learning rules in the brain circuits, the molecular mechanisms mediating STDP are still poorly understood. Here, we show that spike timing-dependent long-term depression (tLTD) and A-type K+ currents are modulated by pharmacological agents affecting the levels of active glycogen-synthase kinase 3 (GSK3) and by GSK3β knockdown in layer 2/3 of the mouse somatosensory cortex. Moreover, the blockade of A-type K+ currents mimics the effects of GSK3 up-regulation on tLTD and occludes further changes in synaptic strength. Pharmacological, immunohistochemical and biochemical experiments revealed that GSK3β influence over tLTD induction is mediated by direct phosphorylation at Ser-616 of the Kv4.2 subunit, a molecular determinant of A-type K+ currents. Collectively, these results identify the functional interaction between...

Hormones and peptides involved in glucose homeostasis are emerging as important modulators of neural plasticity. In this regard, increasing evidence shows that molecules such as insulin, insulin-like growth factor-I, glucagon-like peptide-1, and ghrelin impact on the function of the hippocampus, which is a key area for learning and memory. Indeed, all these factors affect fundamental hippocampal properties including synaptic plasticity (i.e., synapse potentiation and depression), structural plasticity (i.e., dynamics of dendritic spines), and adult neurogenesis, thus leading to modifications in cognitive performance. Here, we review the main mechanisms underlying the effects of glucose metabolism on hippocampal physiology. In particular, we discuss the role of these signals in the modulation of cognitive functions and their potential implications in dysmetabolism-related cognitive decline.

Deregulated nutrient signaling plays pivotal roles in body ageing and in diabetic complications; biochemical cascades linking energy dysmetabolism to cell damage and loss are still incompletely clarified, and novel molecular paradigms and pharmacological targets critically needed. We provide evidence that in the retrovirus-packaging cell line HEK293-T Phoenix, massive cell death in serum-free medium is remarkably prevented or attenuated by either glucose or aminoacid withdrawal, and by the glycolysis inhibitor 2-deoxy-glucose. A similar protection was also elicited by interference with mitochondrial function, clearly suggesting involvement of energy metabolism in increased cell survival. Oxidative stress did not account for nutrient toxicity on serum-starved cells. Instead, nutrient restriction was associated with reduced activity of the mTOR/S6 Kinase cascade. Moreover, pharmacological and genetic manipulation of the mTOR pathway modulated in an opposite fashion signaling to S6K/S6...

Traditionally linked to an accumulation of cell and tissue oxidative damage, the aging process is currently viewed as the result of a chronic metabolic imbalance and deranged body response to nutrients. This is in keeping with the pivotal role of the insulin/IGF pathway in longevity determination from model organisms to primates, with the association between obesity and age-related disorders, and with the dramatic acceleration of senescence by diabetes. Importantly, metabolic and oxidative damages concomitantly occur in aging as consequences of tissue hyperstimulation by insulin. With its double identity of generator of mitochondrial oxidant species and of signaling adaptor in the insulin receptor cascade, the 66Kd Shc protein (p66Shc) has drawn major attention as a negative determinant of life span and healthy longevity in mammals. We have demonstrated that these effects are related, at least in part, to p66Shc effect on the mTOR/S6K cascade that promotes obesity and insulin resistance and shortens life span.

mRNA localization is an evolutionary conserved mechanism that underlies the establishment of cellular polarity and specialized cell functions. To identify mRNAs localized in subcellular compartments of developing neurons, we took an original approach that combines compartmentalized cultures of rat sympathetic neurons and sequential analysis of gene expression (SAGE). Unexpectedly, the most abundant transcript in axons was mRNA for myo-inositol monophosphatase-1 (Impa1), a key enzyme that regulates the inositol cycle and the main target of lithium in neurons. A novel localization element within the 3' untranslated region of Impa1 mRNA specifically targeted Impa1 transcript to sympathetic neuron axons and regulated local IMPA1 translation in response to nerve growth factor (NGF). Selective silencing of IMPA1 synthesis in axons decreased nuclear CREB activation and induced axonal degeneration. These results provide insights into mRNA transport in axons and reveal a new NGF-responsive localization element that directs the targeting and local translation of an axonal transcript.

Background and objective. Calorie restriction improves memory and learning in rodents through the interplay between the c-AMP responsive Element Binding protein (CREB) and Sirtuin 1 (Sirt-1). Adult neurogenesis is also activated by calorie restriction and may contribute to the beneficial cognitive effects of this dietary regimen, but the underlying molecular interactions are largely unknown. We here investigated whether the CREB-Sirt1 axis is involved in Neural stem cell (NSC) response to nutrient availability in vitro, as a potential mechanism for the metabolic regulation of adult neurogenesis. Methods We used wild-type and CREBloxP/loxP mice as source of NCS. Inhibition of CREB or Sirt-1 expression were achieved by adenoviral transduction of, respectively, the Cre recombinase or a Sirt-1 specific shRNA construct. The Neuropshere assay (NSA) and 5-bromo-2'-deoxyuridine incorporation were used to assess NSC proliferative and self-renewal capacity under conditions of high (4,5 g/L glucose) and restricted (0.9g/L glucose) nutrients, the latter modeling calorie restriction. Gene expression, protein-DNA and protein-protein interactions were evaluated by standard procedures. Results. Proliferation of NSC in low glucose was significantly enhanced (doubled) compared to glucose-rich cultures, indicating an improved self-renewal capacity of stem cells in nutrient-restricted conditions. This behavior was mirrored by a reduced content of intracellular reactive oxygen species and an increased expression of the repressor and Notch target Hairy and Enhancer of Split 1 (Hes1), two biochemical determinants of stemness. Importantly, cell proliferation, neurosphere formation and Hes-1 expression were strongly reduced in CREB-depleted NSC, and were not or marginally affected by glucose availability. In wild type cells, low glucose induced the phosphorylation of CREB and increased its binding with Sirt-1; moreover, CREB was found to directly interact with the Hes-1 promoter in a fashion inducible by low glucose. Interestingly, Sirt-1 depletion, unlike CREB deletion, enhanced NSC proliferation in the NSA assay, but again disrupted responsiveness to low glucose. Conclusions These findings strongly suggest that CREB is activated in NSC in response to limited glucose availability and promotes self-renewal most likely through the induction of Hes-1. Sirt1 participates in this circuitry, presumably by increasing CREB activity and also by limiting NSC proliferation/exhaustion under nutrient restriction. The above results may have important implications for our understanding of how systemic energy metabolism affects adult neurogenesi