The secreted beta-amyloid precursor protein ectodomain APPs alpha is sufficient to rescue the anatomical, behavioral, and electrophysiological abnormalities of APP-deficient mice

It is well established that the proteolytic processing of the beta-amyloid precursor protein (APP) generates beta-amyloid (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease (AD). In contrast, the physiological role of APP and of its numerous proteolytic fragments and the question of whether a loss of these functions contributes to AD are still unknown. To address this question, we replaced the endogenous APP locus by gene-targeted alleles and generated two lines of knock-in mice that exclusively express APP deletion variants corresponding either to the secreted APP ectodomain (APPs alpha) or to a C-terminal (CT) truncation lacking the YENPTY interaction motif (APPdeltaCT15). Interestingly, the deltaCT15 deletion resulted in reduced turnover of holoAPP, increased cell surface expression, and strongly reduced Abeta levels in brain, likely because of reduced processing in the endocytic pathway. Most importantly, we demonstrate that in both APP knock-in lines the expression of APP N-terminal domains either grossly attenuated or completely rescued the prominent deficits of APP knock-out mice, such as reductions in brain and body weight, grip strength deficits, alterations in circadian locomotor activity, exploratory activity, and the impairment in spatial learning and long-term potentiation. Together, our data suggest that the APP C terminus is dispensable and that APPs alpha is sufficient to mediate the physiological functions of APP assessed by these tests.

Physiological functions of APP family proteins

Biochemical and genetic evidence establishes a central role of the amyloid precursor protein (APP) in Alzheimer disease (AD) pathogenesis. Biochemically, deposition of the β-amyloid (Aβ) peptides produced from proteolytic processing of APP forms the defining pathological hallmark of AD; genetically, both point mutations and duplications of wild-type APP are linked to a subset of early onset of familial AD (FAD) and cerebral amyloid angiopathy. As such, the biological functions of APP and its processing products have been the subject of intense investigation, and the past 20+ years of research have met with both excitement and challenges. This article will review the current understanding of the physiological functions of APP in the context of APP family members.

APP and APLP2 are essential at PNS and CNS synapses for transmission, spatial learning and LTP

Despite its key role in Alzheimer pathogenesis, the physiological function(s) of the amyloid precursor protein (APP) and its proteolytic fragments are still poorly understood. Previously, we generated APPsα knock-in (KI) mice expressing solely the secreted ectodomain APPsα. Here, we generated double mutants (APPsα-DM) by crossing APPsα-KI mice onto an APLP2-deficient background and show that APPsα rescues the postnatal lethality of the majority of APP/APLP2 double knockout mice. Surviving APPsα-DM mice exhibited impaired neuromuscular transmission, with reductions in quantal content, readily releasable pool, and ability to sustain vesicle release that resulted in muscular weakness. We show that these defects may be due to loss of an APP/Mint2/Munc18 complex. Moreover, APPsα-DM muscle showed fragmented post-synaptic specializations, suggesting impaired postnatal synaptic maturation and/or maintenance. Despite normal CNS morphology and unaltered basal synaptic transmission, young APPsα-DM mice already showed pronounced hippocampal dysfunction, impaired spatial learning and a deficit in LTP that could be rescued by GABA(A) receptor inhibition. Collectively, our data show that APLP2 and APP are synergistically required to mediate neuromuscular transmission, spatial learning and synaptic plasticity.

Acute function of secreted amyloid precursor protein fragment APPsα in synaptic plasticity

The key role of APP in the pathogenesis of Alzheimer disease is well established. However, postnatal lethality of double knockout mice has so far precluded the analysis of the physiological functions of APP and the APLPs in the brain. Previously, APP family proteins have been implicated in synaptic adhesion, and analysis of the neuromuscular junction of constitutive APP/APLP2 mutant mice showed deficits in synaptic morphology and neuromuscular transmission. Here, we generated animals with a conditional APP/APLP2 double knockout (cDKO) in excitatory forebrain neurons using NexCre mice. Electrophysiological recordings of adult NexCre cDKOs indicated a strong synaptic phenotype with pronounced deficits in the induction and maintenance of hippocampal LTP and impairments in paired pulse facilitation, indicating a possible presynaptic deficit. These deficits were also reflected in impairments in nesting behavior and hippocampus-dependent learning and memory tasks, including deficits in Morris water maze and radial maze performance. Moreover, while no gross alterations of brain morphology were detectable in NexCre cDKO mice, quantitative analysis of adult hippocampal CA1 neurons revealed prominent reductions in total neurite length, dendritic branching, reduced spine density and reduced spine head volume. Strikingly, the impairment of LTP could be selectively rescued by acute application of exogenous recombinant APPsα, but not APPsβ, indicating a crucial role for APPsα to support synaptic plasticity of mature hippocampal synapses on a rapid time scale. Collectively, our analysis reveals an essential role of APP family proteins in excitatory principal neurons for mediating normal dendritic architecture, spine density and morphology, synaptic plasticity and cognition.

Viral gene transfer of APPsα rescues synaptic failure in an Alzheimer's disease mouse model

Alzheimer's disease (AD) is characterized by synaptic failure, dendritic and axonal atrophy, neuronal death and progressive loss of cognitive functions. It is commonly assumed that these deficits arise due to β-amyloid accumulation and plaque deposition. However, increasing evidence indicates that loss of physiological APP functions mediated predominantly by neurotrophic APPsα produced in the non-amyloidogenic α-secretase pathway may contribute to AD pathogenesis. Upregulation of APPsα production via induction of α-secretase might, however, be problematic as this may also affect substrates implicated in tumorigenesis. Here, we used a gene therapy approach to directly overexpress APPsα in the brain using AAV-mediated gene transfer and explored its potential to rescue structural, electrophysiological and behavioral deficits in APP/PS1∆E9 AD model mice. Sustained APPsα overexpression in aged mice with already preexisting pathology and amyloidosis restored synaptic plasticity and partially rescued spine density deficits. Importantly, AAV-APPsα treatment also resulted in a functional rescue of spatial reference memory in the Morris water maze. Moreover, we demonstrate a significant reduction of soluble Aβ species and plaque load. In addition, APPsα induced the recruitment of microglia with a ramified morphology into the vicinity of plaques and upregulated IDE and TREM2 expression suggesting enhanced plaque clearance. Collectively, these data indicate that APPsα can mitigate synaptic and cognitive deficits, despite established pathology. Increasing APPsα may therefore be of therapeutic relevance for AD.

Specific gene transfer to neurons, endothelial cells and hematopoietic progenitors with lentiviral vectors

We present a flexible and highly specific targeting method for lentiviral vectors based on single-chain antibodies recognizing cell-surface antigens. We generated lentiviral vectors specific for human CD105(+) endothelial cells, human CD133(+) hematopoietic progenitors and mouse GluA-expressing neurons. Lentiviral vectors specific for CD105 or for CD20 transduced their target cells as efficiently as VSV-G pseudotyped vectors but discriminated between endothelial cells and lymphocytes in mixed cultures. CD133-targeted vectors transduced CD133(+) cultured hematopoietic progenitor cells more efficiently than VSV-G pseudotyped vectors, resulting in stable long-term transduction. Lentiviral vectors targeted to the glutamate receptor subunits GluA2 and GluA4 exhibited more than 94% specificity for neurons in cerebellar cultures and when injected into the adult mouse brain. We observed neuron-specific gene modification upon transfer of the Cre recombinase gene into the hippocampus of reporter mice. This approach allowed targeted gene transfer to many cell types of interest with an unprecedented degree of specificity.

Therapeutic Potential of Secreted Amyloid Precursor Protein APPsα

Cleavage of the amyloid precursor protein (APP) by α-secretase generates an extracellularly released fragment termed secreted APP-alpha (APPsα). Not only is this process of interest due to the cleavage of APP within the amyloid-beta sequence, but APPsα itself has many physiological properties that suggest its great potential as a therapeutic target. For example, APPsα is neurotrophic, neuroprotective, neurogenic, a stimulator of protein synthesis and gene expression, and enhances long-term potentiation (LTP) and memory. While most early studies have been conducted in vitro, effectiveness in animal models is now being confirmed. These studies have revealed that either upregulating α-secretase activity, acutely administering APPsα or chronic delivery of APPsα via a gene therapy approach can effectively treat mouse models of Alzheimer's disease (AD) and other disorders such as traumatic head injury. Together these findings suggest the need for intensifying research efforts to harness the therapeutic potential of this multifunctional protein.

Impaired theta-gamma coupling in APP-deficient mice

Amyloid precursor protein (APP) is critically involved in the pathophysiology of Alzheimer's disease, but its physiological functions remain elusive. Importantly, APP knockout (APP-KO) mice exhibit cognitive deficits, suggesting that APP plays a role at the neuronal network level. To investigate this possibility, we recorded local field potentials (LFPs) from the posterior parietal cortex, dorsal hippocampus and lateral prefrontal cortex of freely moving APP-KO mice. Spectral analyses showed that network oscillations within the theta- and gamma-frequency bands were not different between APP-KO and wild-type mice. Surprisingly, however, while gamma amplitude coupled to theta phase in all recorded regions of wild-type animals, in APP-KO mice theta-gamma coupling was strongly diminished in recordings from the parietal cortex and hippocampus, but not in LFPs recorded from the prefrontal cortex. Thus, lack of APP reduces oscillatory coupling in LFP recordings from specific brain regions, despite not affecting the amplitude of the oscillations. Together, our findings reveal reduced cross-frequency coupling as a functional marker of APP deficiency at the network level.

Functions of the APP gene family in the nervous system: insights from mouse models

The amyloid precursor protein (APP) plays a key role in the pathogenesis of Alzheimer's disease (AD), as proteolytical cleavage of APP gives rise to the β-amyloid peptide which is deposited in the brains of Alzheimer patients. During the past years, intense research efforts have been directed at elucidating the physiological function(s) of APP and the question of whether a perturbation of these functions contributes to AD pathogenesis. Indeed, a growing body of evidence has accumulated supporting a role of APP and the two closely related homologues APLP1 and APLP2 in various aspects of nervous system development and function, in particular, for synapse formation and function. This review summarizes recent insights into the in vivo role of the APP gene family from mice lacking individual or combinations of APP family members, with particular emphasis on recently generated knockin mice to examine the in vivo relevance of distinct functional domains.

Comparative analysis of single and combined APP/APLP knockouts reveals reduced spine density in APP-KO mice that is prevented by APPsα expression

Synaptic dysfunction and synapse loss are key features of Alzheimer's pathogenesis. Previously, we showed an essential function of APP and APLP2 for synaptic plasticity, learning and memory. Here, we used organotypic hippocampal cultures to investigate the specific role(s) of APP family members and their fragments for dendritic complexity and spine formation of principal neurons within the hippocampus. Whereas CA1 neurons from APLP1-KO or APLP2-KO mice showed normal neuronal morphology and spine density, APP-KO mice revealed a highly reduced dendritic complexity in mid-apical dendrites. Despite unaltered morphology of APLP2-KO neurons, combined APP/APLP2-DKO mutants showed an additional branching defect in proximal apical dendrites, indicating redundancy and a combined function of APP and APLP2 for dendritic architecture. Remarkably, APP-KO neurons showed a pronounced decrease in spine density and reductions in the number of mushroom spines. No further decrease in spine density, however, was detectable in APP/APLP2-DKO mice. Mechanistically, using APPsα-KI mice lacking transmembrane APP and expressing solely the secreted APPsα fragment we demonstrate that APPsα expression alone is sufficient to prevent the defects in spine density observed in APP-KO mice. Collectively, these studies reveal a combined role of APP and APLP2 for dendritic architecture and a unique function of secreted APPs for spine density.

Familiality of neural preparation and response control in childhood attention deficit-hyperactivity disorder

BACKGROUND

Patients with attention deficit-hyperactivity disorder (ADHD) exhibit difficulties in multiple attentional functions. Although high heritability rates suggest a strong genetic impact, aetiological pathways from genes and environmental factors to the ADHD phenotype are not well understood. Tracking the time course of deviant task processing using event-related electrophysiological brain activity should characterize the impact of familiality on the sequence of cognitive functions from preparation to response control in ADHD. Method Preparation and response control were assessed using behavioural and electrophysiological parameters of two versions of a cued continuous performance test with varying attentional load in boys with ADHD combined type (n = 97), their non-affected siblings (n = 27) and control children without a family history of ADHD (n = 43).

RESULTS

Children with ADHD and non-affected siblings showed more variable performance and made more omission errors than controls. The preparatory Cue-P3 and contingent negative variation (CNV) following cues were reduced in both ADHD children and their non-affected siblings compared with controls. The NoGo-P3 was diminished in ADHD compared with controls whilst non-affected siblings were located intermediate but did not differ from both other groups. No clear familiality effects were found for the Go-P3. Better task performance was further associated with higher CNV and P3 amplitudes.

CONCLUSIONS

Impairments in performance and electrophysiological parameters reflecting preparatory processes and to some extend also for inhibitory response control, especially under high attentional load, appeared to be familially driven in ADHD and may thus constitute functionally relevant endophenotypes for the disorder.

Distinct in vivo roles of secreted APP ectodomain variants APPsα and APPsβ in regulation of spine density, synaptic plasticity, and cognition

Increasing evidence suggests that synaptic functions of the amyloid precursor protein (APP), which is key to Alzheimer pathogenesis, may be carried out by its secreted ectodomain (APPs). The specific roles of APPsα and APPsβ fragments, generated by non-amyloidogenic or amyloidogenic APP processing, respectively, remain however unclear. Here, we expressed APPsα or APPsβ in the adult brain of conditional double knockout mice (cDKO) lacking APP and the related APLP2. APPsα efficiently rescued deficits in spine density, synaptic plasticity (LTP and PPF), and spatial reference memory of cDKO mice. In contrast, APPsβ failed to show any detectable effects on synaptic plasticity and spine density. The C-terminal 16 amino acids of APPsα (lacking in APPsβ) proved sufficient to facilitate LTP in a mechanism that depends on functional nicotinic α7-nAChRs. Further, APPsα showed high-affinity, allosteric potentiation of heterologously expressed α7-nAChRs in oocytes. Collectively, we identified α7-nAChRs as a crucial physiological receptor specific for APPsα and show distinct in vivo roles for APPsα versus APPsβ. This implies that reduced levels of APPsα that might occur during Alzheimer pathogenesis cannot be compensated by APPsβ.

sAPPalpha antagonizes dendritic degeneration and neuron death triggered by proteasomal stress

Impaired proteasomal function is a major hallmark in the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD). Here we investigated the biological properties of the secreted cleavage product of APP (sAPPalpha) in antagonizing stress signalling, dendritic degeneration and neuronal cell death induced by the proteasome inhibitor epoxomicin. Analysis of executioner caspase activation demonstrated that sAPPalpha was able to protect PC12 cells from apoptosis triggered by epoxomicin, as well as by genotoxic stress (UV irradiation). This anti-apoptotic effect of sAPPalpha was associated with inhibition of the stress-triggered c-Jun N-terminal kinase (JNK)-signalling pathway. The anti-apoptotic effect of sAPPalpha could also be confirmed in organotypic slice cultures of Thy1-GFP mouse hippocampi. Confocal time-lapse imaging of CA1 pyramidal neurons revealed that preincubation with sAPPalpha preserves the structural integrity of neurons after epoxomicin treatment. Taken together, our data demonstrate that sAPPalpha is neuroprotective under conditions of proteasomal stress.

Co-transmission of conduct problems with attention-deficit/hyperactivity disorder: familial evidence for a distinct disorder

Common disorders of childhood and adolescence are attention-deficit/hyperactivity disorder (ADHD), oppositional defiant disorder (ODD) and conduct disorder (CD). For one to two cases in three diagnosed with ADHD the disorders may be comorbid. However, whether comorbid conduct problems (CP) represents a separate disorder or a severe form of ADHD remains controversial. We investigated familial recurrence patterns of the pure or comorbid condition in families with at least two children and one definite case of DSM-IV ADHDct (combined-type) as part of the International Multicentre ADHD Genetics Study (IMAGE). Using case diagnoses (PACS, parental account) and symptom ratings (Parent/Teacher Strengths and Difficulties [SDQ], and Conners Questionnaires [CPTRS]) we studied 1009 cases (241 with ADHDonly and 768 with ADHD + CP), and their 1591 siblings. CP was defined as > or =4 on the SDQ conduct-subscale, and T > or = 65, on Conners' oppositional-score. Multinomial logistic regression was used to ascertain recurrence risks of the pure and comorbid conditions in the siblings as predicted by the status of the cases. There was a higher relative risk to develop ADHD + CP for siblings of cases with ADHD + CP (RRR = 4.9; 95%CI: 2.59-9.41); p < 0.001) than with ADHDonly. Rates of ADHDonly in siblings of cases with ADHD + CP were lower but significant (RRR = 2.9; 95%CI: 1.6-5.3, p < 0.001). Children with ADHD + CP scored higher on the Conners ADHDct symptom-scales than those with ADHDonly. Our finding that ADHD + CP can represent a familial distinct subtype possibly with a distinct genetic etiology is consistent with a high risk for cosegregation. Further, ADHD + CP can be a more severe disorder than ADHDonly with symptoms stable from childhood through adolescence. The findings provide partial support for the ICD-10 distinction between hyperkinetic disorder (F90.0) and hyperkinetic conduct disorder (F90.1).

Stahlmann C, Slobodskoy Y, Müller UC, Hartmann T, Stein R, Grimm MOW. Upregulation of PGC-1α expression by Alzheimer's disease-associated pathway: presenilin 1/amyloid precursor protein (APP)/intracellular domain of APP

Cleavage of amyloid precursor protein (APP) by β- and γ-secretase generates amyloid-β (Aβ) and APP intracellular domain (AICD) peptides. Presenilin (PS) 1 or 2 is the catalytic component of the γ-secretase complex. Mitochondrial dysfunction is an established phenomenon in Alzheimer’s disease (AD), but the causes and role of PS1, APP, and APP’s cleavage products in this process are largely unknown. We studied the effect of these AD-associated molecules on mitochondrial features. Using cells deficient in PSs expression, expressing human wild-type PS1, or PS1 familial AD (FAD) mutants, we found that PS1 affects mitochondrial energy metabolism (ATP levels and oxygen consumption) and expression of mitochondrial proteins. These effects were associated with enhanced expression of the mitochondrial master transcriptional coactivator PGC-1α and its target genes. Importantly, PS1-FAD mutations decreased PS1’s ability to enhance PGC-1α mRNA levels. Analyzing the effect of APP and its γ-secretase-derived cleavage products Aβ and AICD on PGC-1α expression showed that APP and AICD increase PGC-1α expression. Accordingly, PGC-1α mRNA levels in cells deficient in APP/APLP2 or expressing APP lacking its last 15 amino acids were lower than in control cells, and treatment with AICD, but not with Aβ, enhanced PGC-1α mRNA levels in these and PSs-deficient cells. In addition, knockdown of the AICD-binding partner Fe65 reduced PGC-1α mRNA levels. Importantly, APP/AICD increases PGC-1α expression also in the mice brain. Our results therefore suggest that APP processing regulates mitochondrial function and that impairments in the newly discovered PS1/APP/AICD/PGC-1α pathway may lead to mitochondrial dysfunction and neurodegeneration.

Amyloid precursor protein maintains constitutive and adaptive plasticity of dendritic spines in adult brain by regulating D-serine homeostasis

Dynamic synapses facilitate activity-dependent remodeling of neural circuits, thereby providing the structural substrate for adaptive behaviors. However, the mechanisms governing dynamic synapses in adult brain are still largely unknown. Here, we demonstrate that in the cortex of adult amyloid precursor protein knockout (APP-KO) mice, spine formation and elimination were both reduced while overall spine density remained unaltered. When housed under environmental enrichment, APP-KO mice failed to respond with an increase in spine density. Spine morphology was also altered in the absence of APP The underlying mechanism of these spine abnormalities in APP-KO mice was ascribed to an impairment in D-serine homeostasis. Extracellular D-serine concentration was significantly reduced in APP-KO mice, coupled with an increase of total D-serine. Strikingly, chronic treatment with exogenous D-serine normalized D-serine homeostasis and restored the deficits of spine dynamics, adaptive plasticity, and morphology in APP-KO mice. The cognitive deficit observed in APP-KO mice was also rescued by D-serine treatment. These data suggest that APP regulates homeostasis of D-serine, thereby maintaining the constitutive and adaptive plasticity of dendritic spines in adult brain.

Differential role of APP and APLPs for neuromuscular synaptic morphology and function

The analysis of mouse models indicated that APP and the related APLPs are important for synapse formation and function. The synaptic role of APP is, however, complex due to partially overlapping functions within the gene family. APP/APLPs are proteolytically cleaved and have both adhesive and signaling properties. Mice lacking individual APP family members are viable, whereas APP/APLP2 and APLP1/APLP2 double knockout (DKO) mice die shortly after birth. Here, we analyzed the morphology of the neuromuscular junction (NMJ) of lethal APLP1/APLP2-DKO mice in comparison to lethal APP/APLP2-DKO mutants and viable single KO mice. We report that, surprisingly, the NMJ phenotype of APLP1/APLP2-DKO mice shows striking differences as compared to APP/APLP2-DKO mice. Unexpectedly, APLP1/APLP2-DKO mice exhibit normal endplate patterning and lack presynaptic nerve terminal sprouting. However, at the level of individual synapses we show that APLP1/APLP2-DKO mice exhibit reduced size of pre- and postsynaptic compartments and reduced colocalization. As APP/APLP2-DKO and APLP1/APLP2-DKO mice show similar penetrance of early postnatal lethality, this suggests that deficits at the level of individual synapses due to impaired synaptic apposition and/or deficits in transmitter release may cause lethality. Using an in vitro cell-adhesion assay, we observed that APP trans-dimerization is considerably less efficient than APLP2 trans-interaction. Thus, differences between APP/APLP2 and APP/APLP1 NMJ formation may be in part explained by differences in APP/APLP2 trans-dimerization properties. Collectively, our study further highlights the distinct and essential role of APLP2 at NMJ synapses that cannot be compensated by APP.

Comparative transcriptome profiling of amyloid precursor protein family members in the adult cortex

BACKGROUND

The β-amyloid precursor protein (APP) and the related β-amyloid precursor-like proteins (APLPs) undergo complex proteolytic processing giving rise to several fragments. Whereas it is well established that Aβ accumulation is a central trigger for Alzheimer's disease, the physiological role of APP family members and their diverse proteolytic products is still largely unknown. The secreted APPsα ectodomain has been shown to be involved in neuroprotection and synaptic plasticity. The γ-secretase-generated APP intracellular domain (AICD) functions as a transcriptional regulator in heterologous reporter assays although its role for endogenous gene regulation has remained controversial.

RESULTS

To gain further insight into the molecular changes associated with knockout phenotypes and to elucidate the physiological functions of APP family members including their proposed role as transcriptional regulators, we performed DNA microarray transcriptome profiling of prefrontal cortex of adult wild-type (WT), APP knockout (APP-/-), APLP2 knockout (APLP2-/-) and APPsα knockin mice (APPα/α) expressing solely the secreted APPsα ectodomain. Biological pathways affected by the lack of APP family members included neurogenesis, transcription, and kinase activity. Comparative analysis of transcriptome changes between mutant and wild-type mice, followed by qPCR validation, identified co-regulated gene sets. Interestingly, these included heat shock proteins and plasticity-related genes that were both down-regulated in knockout cortices. In contrast, we failed to detect significant differences in expression of previously proposed AICD target genes including Bace1, Kai1, Gsk3b, p53, Tip60, and Vglut2. Only Egfr was slightly up-regulated in APLP2-/- mice. Comparison of APP-/- and APPα/α with wild-type mice revealed a high proportion of co-regulated genes indicating an important role of the C-terminus for cellular signaling. Finally, comparison of APLP2-/- on different genetic backgrounds revealed that background-related transcriptome changes may dominate over changes due to the knockout of a single gene.

CONCLUSION

Shared transcriptome profiles corroborated closely related physiological functions of APP family members in the adult central nervous system. As expression of proposed AICD target genes was not altered in adult cortex, this may indicate that these genes are not affected by lack of APP under resting conditions or only in a small subset of cells.

Predictability of oppositional defiant disorder and symptom dimensions in children and adolescents with ADHD combined type

BACKGROUND

Oppositional defiant disorder (ODD) is frequently co-occurring with attention deficit hyperactivity disorder (ADHD) in children and adolescents. Because ODD is a precursor of later conduct disorder (CD) and affective disorders, early diagnostic identification is warranted. Furthermore, the predictability of three recently confirmed ODD dimensions (ODD-irritable, ODD-headstrong and ODD-hurtful) may assist clinical decision making.

METHOD

Receiver-operating characteristic (ROC) analysis was used in order to test the diagnostic accuracy of the Conners' Parent Rating Scale revised (CPRS-R) and the parent version of the Strength and Difficulties Questionnaire (PSDQ) in the prediction of ODD in a transnational sample of 1093 subjects aged 5-17 years from the International Multicentre ADHD Genetics study. In a second step, the prediction of three ODD dimensions by the same parent rating scales was assessed by backward linear regression analyses.

RESULTS

ROC analyses showed adequate diagnostic accuracy of the CPRS-R and the PSDQ in predicting ODD in this ADHD sample. Furthermore, the three-dimensional structure of ODD was confirmed by confirmatory factor analysis and the CPRS-R emotional lability scale significantly predicted the ODD irritable dimension.

CONCLUSIONS

The PSDQ and the CPRS-R are both suitable screening instruments in the identification of ODD. The emotional lability scale of the CPRS-R is an adequate predictor of irritability in youth referred for ADHD.

Loss of all three APP family members during development impairs synaptic function and plasticity, disrupts learning, and causes an autism-like phenotype

The key role of APP for Alzheimer pathogenesis is well established. However, perinatal lethality of germline knockout mice lacking the entire APP family has so far precluded the analysis of its physiological functions for the developing and adult brain. Here, we generated conditional APP/APLP1/APLP2 triple KO (cTKO) mice lacking the APP family in excitatory forebrain neurons from embryonic day 11.5 onwards. NexCre cTKO mice showed altered brain morphology with agenesis of the corpus callosum and disrupted hippocampal lamination. Further, NexCre cTKOs revealed reduced basal synaptic transmission and drastically reduced long-term potentiation that was associated with reduced dendritic length and reduced spine density of pyramidal cells. With regard to behavior, lack of the APP family leads not only to severe impairments in a panel of tests for learning and memory, but also to an autism-like phenotype including repetitive rearing and climbing, impaired social communication, and deficits in social interaction. Together, our study identifies essential functions of the APP family during development, for normal hippocampal function and circuits important for learning and social behavior.

A Selective Role for alpha3 Subunit Glycine Receptors in Inflammatory Pain

GlyR α3 has previously been found to play a critical role in pain hypersensitivity following spinal PGE₂ injection, complete Freund's adjuvant (CFA) and zymosan induced peripheral inflammation. In this study, although all models displayed typical phenotypic behaviours, no significant differences were observed when comparing the pain behaviours of Glra3^−/− and wild-type littermates following the injection of capsaicin, carrageenan, kaolin/carrageenan or monosodium iodoacetate, models of rheumatoid and osteoarthritis, respectively. However, clear differences were observed following CFA injection (p < 0.01). No significant differences were observed in the pain behaviours of Glra3^−/− and wild-type littermates following experimentally induced neuropathic pain (partial sciatic nerve ligation). Similarly, Glra3^−/− and wild-type littermates displayed indistinguishable visceromotor responses to colorectal distension (a model of visceral pain) and in vivo spinal cord dorsal horn electrophysiology revealed no differences in responses to multimodal suprathreshold stimuli, intensities which equate to higher pain scores such as those reported in the clinic. These data suggest that apart from its clear role in CFA- and zymosan-induced pain sensitisation, hypersensitivity associated with other models of inflammation, neuropathy and visceral disturbances involves mechanisms other than the EP2 receptor – GlyR α3 pathway.

Click Chemistry-mediated Biotinylation Reveals a Function for the Protease BACE1 in Modulating the Neuronal Surface Glycoproteome

The cell surface proteome is dynamic and has fundamental roles in cell signaling. Many surface membrane proteins are proteolytically released into a cell's secretome, where they can have additional functions in cell-cell-communication. Yet, it remains challenging to determine the surface proteome and to compare it to the cell secretome, under serum-containing cell culture conditions. Here, we set up and evaluated the 'surface-spanning protein enrichment with click sugars' (SUSPECS) method for cell surface membrane glycoprotein biotinylation, enrichment and label-free quantitative mass spectrometry. SUSPECS is based on click chemistry-mediated labeling of glycoproteins, is compatible with labeling of living cells and can be combined with secretome analyses in the same experiment. Immunofluorescence-based confocal microscopy demonstrated that SUSPECS selectively labeled cell surface proteins. Nearly 700 transmembrane glycoproteins were consistently identified at the surface of primary neurons. To demonstrate the utility of SUSPECS, we applied it to the protease BACE1, which is a key drug target in Alzheimer's disease. Pharmacological BACE1-inhibition selectively remodeled the neuronal surface glycoproteome, resulting in up to 7-fold increased abundance of the BACE1 substrates APP, APLP1, SEZ6, SEZ6L, CNTN2, and CHL1, whereas other substrates were not or only mildly affected. Interestingly, protein changes at the cell surface only partly correlated with changes in the secretome. Several altered proteins were validated by immunoblots in neurons and mouse brains. Apparent nonsubstrates, such as TSPAN6, were also increased, indicating that BACE1-inhibition may lead to unexpected secondary effects. In summary, SUSPECS is broadly useful for determination of the surface glycoproteome and its correlation with the secretome.

Region-Specific Differences in Amyloid Precursor Protein Expression in the Mouse Hippocampus

The physiological role of amyloid precursor protein (APP) has been extensively investigated in the rodent hippocampus. Evidence suggests that APP plays a role in synaptic plasticity, dendritic and spine morphogenesis, neuroprotection and—at the behavioral level—hippocampus-dependent forms of learning and memory. Intriguingly, however, studies focusing on the role of APP in synaptic plasticity have reported diverging results and considerable differences in effect size between the dentate gyrus (DG) and area CA1 of the mouse hippocampus. We speculated that regional differences in APP expression could underlie these discrepancies and studied the expression of APP in both regions using immunostaining, in situ hybridization (ISH), and laser microdissection (LMD) in combination with quantitative reverse transcription polymerase chain reaction (RT-qPCR) and western blotting. In sum, our results show that APP is approximately 1.7-fold higher expressed in pyramidal cells of Ammon’s horn than in granule cells of the DG. This regional difference in APP expression may explain why loss-of-function approaches using APP-deficient mice revealed a role for APP in Hebbian plasticity in area CA1, whereas this could not be shown in the DG of the same APP mutants.

Contribution of GABAergic interneurons to amyloid-β plaque pathology in an APP knock-in mouse model

The amyloid-β (Aβ) peptide, the primary constituent of amyloid plaques found in Alzheimer's disease (AD) brains, is derived from sequential proteolytic processing of the Amyloid Precursor Protein (APP). However, the contribution of different cell types to Aβ deposition has not yet been examined in an in vivo, non-overexpression system. Here, we show that endogenous APP is highly expressed in a heterogeneous subset of GABAergic interneurons throughout various laminae of the hippocampus, suggesting that these cells may have a profound contribution to AD plaque pathology. We then characterized the laminar distribution of amyloid burden in the hippocampus of an APP knock-in mouse model of AD. To examine the contribution of GABAergic interneurons to plaque pathology, we blocked Aβ production specifically in these cells using a cell type-specific knock-out of BACE1. We found that during early stages of plaque deposition, interneurons contribute to approximately 30% of the total plaque load in the hippocampus. The greatest contribution to plaque load (75%) occurs in the stratum pyramidale of CA1, where plaques in human AD cases are most prevalent and where pyramidal cell bodies and synaptic boutons from perisomatic-targeting interneurons are located. These findings reveal a crucial role of GABAergic interneurons in the pathology of AD. Our study also highlights the necessity of using APP knock-in models to correctly evaluate the cellular contribution to amyloid burden since APP overexpressing transgenic models drive expression in cell types according to the promoter and integration site and not according to physiologically relevant expression mechanisms.