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BACKGROUNDHighly palatable food triggers behavioral alterations reminiscent of those induced by addictive drugs. These effects involve the reward system and dopamine neurons, which modulate neurons in the nucleus accumbens (NAc). The molecular mechanisms underlying the effects of highly palatable food on feeding behavior are poorly understood.METHODSWe studied the effects of 2-week operant conditioning of mice with standard or isocaloric highly palatable food. We investigated the behavioral effects and dendritic spine modifications in the NAc. We compared the translating mRNA in NAc neurons identified by the type of dopamine receptors they express, depending on the type of food and training. We tested the consequences of invalidation of an abundant downregulated gene, Ncdn (Neurochondrin).RESULTSOperant conditioning for highly palatable food increases motivation for food even in well-fed mice. In control mice, free access to regular or highly palatable food results in increased weight as compared to regular food only. Highly palatable food increases spine density in the NAc. In animals trained for highly palatable food, translating mRNAs are modified in NAc dopamine D2-receptor-expressing neurons, mostly corresponding to striatal projection neurons, but not in those expressing D1-receptors. Knock-out of Ncdn, an abundant down-regulated gene, opposes the conditioning-induced changes in satiety-sensitive feeding behavior and apparent motivation for highly palatable food, suggesting down-regulation may be a compensatory mechanism.CONCLUSIONSOur results emphasize the importance of mRNA alterations D2 striatal projection neurons in the NAc in the behavioral consequences of highly palatable food conditioning and suggest a modulatory contribution of Ncdn downregulation.

Forebrain dopaminoceptive neurons play a key role in movement, action selection, motivation, and working memory. Their activity is dysregulated in addiction, Parkinson’s disease and other conditions. To characterize the diverse dopamine target neuronal populations, we compare translating mRNAs in neurons of dorsal striatum and nucleus accumbens expressing D1 or D2 dopamine receptor and prefrontal cortex expressing D1 receptor. We identify D1/D2 and striatal dorso-ventral differences in the translational and splicing landscapes, which establish the characteristics of dopaminoceptive neurons. Expression differences and network analyses identify novel transcription factors with presumptive roles in these differences. Prostaglandin E2 appears as a candidate upstream regulator in the dorsal striatum, a hypothesis supported by converging functional evidence indicating its role in enhancing D2 dopamine receptor action. Our study provides powerful resources for characterizing dopamine target neurons, new information about striatal gene expression patterns, and reveals the unforeseen role of prostaglandin E2 in the dorsal striatum.

The striatum is a critical brain region for locomotor response to cocaine. Although the D1 receptor-expressing neurons are centrally involved in mediating the locomotor effects of cocaine, the molecular pathways controlling this response are not fully understood. Here we studied the role of Pyk2, a non-receptor calcium-dependent protein-tyrosine kinase, in striatum-related functions. We discovered that cocaine injection increases Pyk2 phosphorylation in the striatum of mice in vivo. Pyk2-deficient mice displayed an altered locomotor response to acute cocaine injection. In contrast, they developed normal locomotor sensitization and cocaine-conditioned place preference. Accordingly, a cocaine-activated signaling pathway essential for these late responses, ERK phosphorylation, was not altered. Specific deletion of Pyk2 in the nucleus accumbens or in D1 neurons reproduced this phenotype, whereas deletion of Pyk2 in the dorsal striatum or in A2A receptor-expressing neurons did not. Mice lacking Pyk2 in D1-neurons also displayed lower locomotor response to the D1 receptor agonist SKF-81297 but not to an anticholinergic drug. Our results identify Pyk2 as a regulator of acute locomotor responses to psychostimulants and suggest that changes in Pyk2 expression or activation may alter specific responses to drugs of abuse, or possibly other behavioral responses linked to dopamine action.

It has been well documented that neurotrophins, including brain-derived neurotrophic factor (BDNF), are severely affected in Alzheimer's disease (AD), but their administration faces a myriad of technical challenges. Here we took advantage of the early astrogliosis observed in an amyloid mouse model of AD (5xFAD) and used it as an internal sensor to administer BDNF conditionally and locally. We first demonstrate the relevance of BDNF release from astrocytes by evaluating the effects of coculturing WT neurons and BDNF-deficient astrocytes. Next, we crossed 5xFAD mice with pGFAP:BDNF mice (only males were used) to create 5xFAD mice that overexpress BDNF when and where astrogliosis is initiated (5xF:pGB mice). We evaluated the behavioral phenotype of these mice. We first found that BDNF from astrocytes is crucial for dendrite outgrowth and spine number in cultured WT neurons. Double-mutant 5xF:pGB mice displayed improvements in cognitive tasks compared with 5xFAD littermates. In these mice, there was a rescue of BDNF/TrkB downstream signaling activity associated with an improvement of dendritic spine density and morphology. Clusters of synaptic markers, PSD-95 and synaptophysin, were also recovered in 5xF:pGB compared with 5xFAD mice as well as the number of presynaptic vesicles at excitatory synapses. Additionally, experimentally evoked LTP in vivo was increased in 5xF:pGB mice. The beneficial effects of conditional BDNF production and local delivery at the location of active neuropathology highlight the potential to use endogenous biomarkers with early onset, such as astrogliosis, as regulators of neurotrophic therapy in AD. SIGNIFICANCE STATEMENT Recent evidence places astrocytes as pivotal players during synaptic plasticity and memory processes. In the present work, we first provide evidence that astrocytes are essential for neuronal morphology via BDNF release. We then crossed transgenic mice (5xFAD mice) with the transgenic pGFAP-BDNF mice, which express BDNF under the GFAP promoter. The resultant double-mutant mice 5xF:pGB mice displayed a full rescue of hippocampal BDNF loss and related signaling compared with 5xFAD mice and a significant and specific improvement in all the evaluated cognitive tasks. These improvements did not correlate with amelioration of β amyloid load or hippocampal adult neurogenesis rate but were accompanied by a dramatic recovery of structural and functional synaptic plasticity.

Major depressive disorder (MDD) is a common disorder with a variety of symptoms including mood alterations, anhedonia, sleep and appetite disorders, and cognitive disturbances. Stressful life events are among the strongest risk factors for developing MDD. At the cellular level, chronic stress results in the modification of dendritic spine morphology and density. Here, we study the role of Pyk2 in the development of depressive-like symptoms induced by a model of chronic unpredictable mild stress (CUMS). Pyk2 is a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the forebrain principal neurons and involved in spine structure and density regulation. We show that Pyk2 knockout mice are less affected to anxiety-like and anhedonia-like phenotypes induced by the CUMS paradigm. Using region-specific knockout, we demonstrate that this phenotype is fully recapitulated by selective Pyk2 inactivation in the amygdala. We also show that in the absence of Pyk2 the spine alterations, PSD-95 clustering, and NMDA receptors changes induced by the CUMS paradigm are prevented. Our results reveal a possible role for Pyk2 in the response to stress and in synaptic markers expression and spine density regulation in the amygdala. We suggest that Pyk2 contributes to stress-induced responses through micro-structural changes and that its deficit may contribute to the resilience to chronic stress A.G. is a Ramón y Cajal fellow (RYC-2016-19466). This work was supported by the NARSAD foundation (young investigator grant 2016 (Ref. 24803) to A.G.) and Ministerio de Ciencia e Innovació n (SAF2015-67474-R; MINECO/FEDER to S.G.). J.-A.G. lab was supported in part by Inserm, the Université Pierre et Marie Curie (UPMC, Sorbonne Université), the Fondation pour la Recherche Médicale, and the Bio-Psy (Biology for Psychiatry) laboratory of excellence. O.A.-M. was funded by the ISCIII/SERGAS thought a research contract “Sara Borrell” (CD14/ 00091). JA lab was supported by the Spanish Ministry of Economy and Competitiveness (MINECO) (SAF-2014-57160R, SAF-2017-88076-R), Fundació Marató TV3 to J.A. and Instituto Carlos III: Centro de Investigación Biomédica en Red sobre enfermedades neurodegenerativas (CIBERNED), and RETICS RD12/ 0019/0002 to J.A.) SI

Pyk2 is a Ca2+-activated non-receptor tyrosine kinase enriched in forebrain neurons and involved in synaptic regulation. Human genetic studies associated PTK2B, the gene coding Pyk2, with risk for Alzheimer's disease (AD). We previously showed that Pyk2 is important for hippocampal function, plasticity, and spine structure. However, its potential role in AD is unknown. To address this question we used human brain samples and 5XFAD mice, an amyloid mouse model of AD expressing mutated human amyloid precursor protein and presenilin1. In the hippocampus of 5XFAD mice and in human AD patients' cortex and hippocampus, Pyk2 total levels were normal. However, Pyk2 Tyr-402 phosphorylation levels, reflecting its autophosphorylation-dependent activity, were reduced in 5XFAD mice at 8 months of age but not 3 months. We crossed these mice with Pyk2−/− mice to generate 5XFAD animals devoid of Pyk2. At 8 months the phenotype of 5XFAD x Pyk2−/− double mutant mice was not different from that of 5XFAD. In contrast, overexpression of Pyk2 in the hippocampus of 5XFAD mice, using adeno-associated virus, rescued autophosphorylated Pyk2 levels and improved synaptic markers and performance in several behavioral tasks. Both Pyk2−/− and 5XFAD mice showed an increase of potentially neurotoxic Src cleavage product, which was rescued by Pyk2 overexpression. Manipulating Pyk2 levels had only minor effects on Aβ plaques, which were slightly decreased in hippocampus CA3 region of double mutant mice and increased following overexpression. Our results show that Pyk2 is not essential for the pathogenic effects of human amyloidogenic mutations in the 5XFAD mouse model. However, the slight decrease in plaque number observed in these mice in the absence of Pyk2 and their increase following Pyk2 overexpression suggest a contribution of this kinase in plaque formation. Importantly, a decreased function of Pyk2 was observed in 5XFAD mice, indicated by its decreased autophosphorylation and associated Src alterations. Overcoming this deficit by Pyk2 overexpression improved the behavioral and molecular phenotype of 5XFAD mice. Thus, our results in a mouse model of AD suggest that Pyk2 impairment may play a role in the symptoms of the disease.

The structure and function of spines and excitatory synapses are under the dynamic control of multiple signalling networks. Although tyrosine phosphorylation is involved, its regulation and importance are not well understood. Here we study the role of Pyk2, a non-receptor calcium-dependent protein-tyrosine kinase highly expressed in the hippocampus. Hippocampal-related learning and CA1 long-term potentiation are severely impaired in Pyk2-deficient mice and are associated with alterations in NMDA receptors, PSD-95 and dendritic spines. In cultured hippocampal neurons, Pyk2 has autophosphorylation-dependent and -independent roles in determining PSD-95 enrichment and spines density. Pyk2 levels are decreased in the hippocampus of individuals with Huntington and in the R6/1 mouse model of the disease. Normalizing Pyk2 levels in the hippocampus of R6/1 mice rescues memory deficits, spines pathology and PSD-95 localization. Our results reveal a role for Pyk2 in spine structure and synaptic function, and suggest that its deficit contributes to Huntington’s disease cognitive impairments.

CO 2 is converted into biomass almost solely by the enzyme rubisco. The poor carboxylation properties of plant rubiscos have led to efforts that made it the most kinetically characterized enzyme, yet these studies focused on 100) were active in vitro, with the fastest having a turnover number of 22 ± 1 s−1—sixfold faster than the median plant rubisco and nearly twofold faster than the fastest measured rubisco to date. Unlike rubiscos from plants and cyanobacteria, the fastest variants discovered here are homodimers and exhibit a much simpler folding and activation kinetics. Our pipeline can be utilized to explore the kinetic space of other enzymes of interest, allowing us to get a better view of the biosynthetic potential of the biosphere., Metagenomic and biochemical analysis of previously uncharacterized naturally‐occurring form‐II and II/III rubiscos leads to identification of an enzyme with the fastest CO2 fixation rate described to date.

Forebrain dopamine-sensitive (dopaminoceptive) neurons play a key role in movement, action selection, motivation, and working memory. Their activity is altered in Parkinson’s disease, addiction, schizophrenia, and other conditions, and drugs that stimulate or antagonize dopamine receptors have major therapeutic applications. Yet, similarities and differences between the various neuronal populations sensitive to dopamine have not been systematically explored. To characterize them, we compared translating mRNAs in the dorsal striatum and nucleus accumbens neurons expressing D1 or D2 dopamine receptor and prefrontal cortex neurons expressing D1 receptor. We identified genome-wide cortico-striatal, striatal D1/D2 and dorso-ventral differences in the translating mRNA and isoform landscapes, which characterize dopaminoceptive neuronal populations. Expression patterns and network analyses identified novel transcription factors with presumptive roles in these differences. Prostaglandin E2 was a candidate upstream regulator in the dorsal striatum. We pharmacologically explored this hypothesis and showed that misoprostol, a prostaglandin E2 (PGE2) receptors agonist, decreased the excitability of D2 striatal projection neurons in slices and diminished their activity in vivo during novel environment exploration. We found that it also modulates mouse behavior including by facilitating reversal learning. Our study provides powerful resources for characterizing dopamine target neurons, new information about striatal gene expression patterns and regulation. It also reveals the unforeseen role of PGE2 in the striatum as a potential neuromodulator and an attractive therapeutic target.