Reduction of the expression of the late-onset Alzheimer's disease (AD) risk-factor BIN1 does not affect amyloid pathology in an AD mouse model.

Alzheimer's disease (AD) is pathologically characterized by the deposition of the ß-amyloid (Aß) peptide in senile plaques in the brain, leading to neuronal dysfunction and eventual decline in cognitive function. Genome-wide association studies have identified the bridging integrator 1 (BIN1) gene within the second most significant susceptibility locus for late-onset AD. BIN1 is a member of the amphiphysin family of proteins and has reported roles in the generation of membrane curvature and endocytosis. Endocytic dysfunction is a pathological feature of AD, and endocytosis of the amyloid precursor protein is an important step in its subsequent cleavage by ß-secretase (BACE1). In vitro evidence implicates BIN1 in endosomal sorting of BACE1 and Aß generation in neurons, but a role for BIN1 in this process in vivo is yet to be described. Here, using biochemical and immunohistochemistry analyses we report that a 50% global reduction of BIN1 protein levels resulting from a single Bin1 allele deletion in mice does not change BACE1 levels or localization in vivo, nor does this reduction alter the production of endogenous murine Aß in nontransgenic mice. Furthermore, we found that reduction of BIN1 levels in the 5XFAD mouse model of amyloidosis does not alter Aß deposition nor behavioral deficits associated with cerebral amyloid burden. Finally, a conditional BIN1 knockout in excitatory neurons did not alter BACE1, APP, C-terminal fragments derived from BACE1 cleavage of APP, or endogenous Aß levels. These results indicate that BIN1 function does not regulate Aß generation in vivo.

Lack of BACE1 S-palmitoylation reduces amyloid burden and mitigates memory deficits in transgenic mouse models of Alzheimer's disease.

Alzheimer's disease (AD) is a devastating neurodegenerative disorder characterized by pathological brain lesions and a decline in cognitive function. ß-Amyloid peptides (Aß), derived from proteolytic processing of amyloid precursor protein (APP), play a central role in AD pathogenesis. ß-Site APP cleaving enzyme 1 (BACE1), the transmembrane aspartyl protease which initiates Aß production, is axonally transported in neurons and accumulates in dystrophic neurites near cerebral amyloid deposits in AD. BACE1 is modified by S-palmitoylation at four juxtamembrane cysteine residues. S-palmitoylation is a dynamic posttranslational modification that is important for trafficking and function of several synaptic proteins. Here, we investigated the in vivo significance of BACE1 S-palmitoylation through the analysis of knock-in mice with cysteine-to-alanine substitution at the palmitoylated residues (4CA mice). BACE1 expression, as well as processing of APP and other neuronal substrates, was unaltered in 4CA mice despite the lack of BACE1 S-palmitoylation and reduced lipid raft association. Whereas steady-state Aß levels were similar, synaptic activity-induced endogenous Aß production was not observed in 4CA mice. Furthermore, we report a significant reduction of cerebral amyloid burden and BACE1 accumulation in dystrophic neurites in the absence of BACE1 S-palmitoylation in mouse models of AD amyloidosis. Studies in cultured neurons suggest that S-palmitoylation is required for dendritic spine localization and axonal targeting of BACE1. Finally, the lack of BACE1 S-palmitoylation mitigates cognitive deficits in 5XFAD mice. Using transgenic mouse models, these results demonstrate that intrinsic posttranslational S-palmitoylation of BACE1 has a significant impact on amyloid pathogenesis and the consequent cognitive decline.

Rescue of Learning and Memory Deficits in the Human Nonsyndromic Intellectual Disability Cereblon Knock-Out Mouse Model by Targeting the AMP-Activated Protein Kinase-mTORC1 Translational Pathway.

A homozygous nonsense mutation in the cereblon (CRBN) gene results in autosomal recessive, nonsyndromic intellectual disability that is devoid of other phenotypic features, suggesting a critical role of CRBN in mediating learning and memory. In this study, we demonstrate that adult male Crbn knock-out (CrbnKO) mice exhibit deficits in hippocampal-dependent learning and memory tasks that are recapitulated by focal knock-out of Crbn in the adult dorsal hippocampus, with no changes in social or repetitive behavior. Cellular studies identify deficits in long-term potentiation at Schaffer collateral CA1 synapses. We further show that Crbn is robustly expressed in the mouse hippocampus and CrbnKO mice exhibit hyperphosphorylated levels of AMPKα (Thr172). Examination of processes downstream of AMP-activated protein kinase (AMPK) finds that CrbnKO mice have a selective impairment in mediators of the mTORC1 translation initiation pathway in parallel with lower protein levels of postsynaptic density glutamatergic proteins and higher levels of excitatory presynaptic markers in the hippocampus with no change in markers of the unfolded protein response or autophagy pathways. Acute pharmacological inhibition of AMPK activity in adult CrbnKO mice rescues learning and memory deficits and normalizes hippocampal mTORC1 activity and postsynaptic glutamatergic proteins without altering excitatory presynaptic markers. Thus, this study identifies that loss of Crbn results in learning, memory, and synaptic defects as a consequence of exaggerated AMPK activity, inhibition of mTORC1 signaling, and decreased glutamatergic synaptic proteins. Thus, CrbnKO mice serve as an ideal model of intellectual disability to further explore molecular mechanisms of learning and memory.SIGNIFICANCE STATEMENT Intellectual disability (ID) is one of the most common neurodevelopmental disorders. The cereblon (CRBN) gene has been linked to autosomal recessive, nonsyndromic ID, characterized by an intelligence quotient between 50 and 70 but devoid of other phenotypic features, making cereblon an ideal protein for the study of the fundamental aspects of learning and memory. Here, using the cereblon knock-out mouse model, we show that cereblon deficiency disrupts learning, memory, and synaptic function via AMP-activated protein kinase hyperactivity, downregulation of mTORC1, and dysregulation of excitatory synapses, with no changes in social or repetitive behaviors, consistent with findings in the human population. This establishes the cereblon knock-out mouse as a model of pure ID without the confounding behavioral phenotypes associated with other current models of ID.

JC virus infection of meningeal and choroid plexus cells in patients with progressive multifocal leukoencephalopathy.

JC virus (JCV) can cause a lytic infection of oligodendrocytes and astrocytes in the central nervous system (CNS) leading to progressive multifocal leukoencephalopathy (PML). JCV can also infect meningeal and choroid plexus cells causing JCV meningitis (JCVM). Whether JCV also infects meningeal and choroid plexus cells in PML patients and other immunosuppressed individuals with no overt symptoms of meningitis remains unknown. We therefore analyzed archival formalin-fixed, paraffin-embedded brain samples from PML patients, and HIV-seropositive and seronegative control subjects by immunohistochemistry for the presence of JCV early regulatory T Ag and JCV VP1 late capsid protein. In meninges, we detected JCV T Ag in 11/48 (22.9%) and JCV VP1 protein in 8/48 (16.7%) PML patients. In choroid plexi, we detected JCV T Ag in 1/7 (14.2%) and JCV VP1 protein in 1/8 (12.5%) PML patients. Neither JCV T Ag nor VP1 protein could be detected in meninges or choroid plexus of HIV-seropositive and HIV-seronegative control subjects without PML. In addition, examination of underlying cerebellar cortex of PML patients revealed JCV-infected cells in the molecular layer, including GAD 67+ interneurons, but not in HIV-seropositive and HIV-seronegative control subjects without PML. Our findings suggest that productive JCV infection of meningeal cells and choroid plexus cells also occurs in PML patients without signs or symptoms of meningitis. The phenotypic characterization of JCV-infected neurons in the molecular layer deserves further study. This data provides new insight into JCV pathogenesis in the CNS.

Amyloid Precursor Protein (APP) May Act as a Substrate and a Recognition Unit for CRL4CRBN and Stub1 E3 Ligases Facilitating Ubiquitination of Proteins Involved in Presynaptic Functions and Neurodegeneration.

The amyloid precursor protein (APP), whose mutations cause Alzheimer disease, plays an important in vivo role and facilitates transmitter release. Because the APP cytosolic region (ACR) is essential for these functions, we have characterized its brain interactome. We found that the ACR interacts with proteins that regulate the ubiquitin-proteasome system, predominantly with the E3 ubiquitin-protein ligases Stub1, which binds the NH2 terminus of the ACR, and CRL4(CRBN), which is formed by Cul4a/b, Ddb1, and Crbn, and interacts with the COOH terminus of the ACR via Crbn. APP shares essential functions with APP-like protein-2 (APLP2) but not APP-like protein-1 (APLP1). Noteworthy, APLP2, but not APLP1, interacts with Stub1 and CRL4(CRBN), pointing to a functional pathway shared only by APP and APLP2. In vitro ubiquitination/ubiquitome analysis indicates that these E3 ligases are enzymatically active and ubiquitinate the ACR residues Lys(649/650/651/676/688) Deletion of Crbn reduces ubiquitination of Lys(676) suggesting that Lys(676) is physiologically ubiquitinated by CRL4(CRBN) The ACR facilitated in vitro ubiquitination of presynaptic proteins that regulate exocytosis, suggesting a mechanism by which APP tunes transmitter release. Other dementia-related proteins, namely Tau and apoE, interact with and are ubiquitinated via the ACR in vitro This, and the evidence that CRBN and CUL4B are linked to intellectual disability, prompts us to hypothesize a pathogenic mechanism, in which APP acts as a modulator of E3 ubiquitin-protein ligase(s), shared by distinct neuronal disorders. The well described accumulation of ubiquitinated protein inclusions in neurodegenerative diseases and the link between the ubiquitin-proteasome system and neurodegeneration make this concept plausible.

Loss of Cav1.2 channels impairs hippocampal theta burst stimulation-induced long-term potentiation.

CACNA1 C, which codes for the Cav1.2 isoform of L-type Ca2+ channels (LTCCs), is a prominent risk gene in neuropsychiatric and neurodegenerative conditions. A role forLTCCs, and Cav1.2 in particular, in transcription-dependent late long-term potentiation (LTP) has long been known. Here, we report that elimination of Cav1.2 channels in glutamatergic neurons also impairs theta burst stimulation (TBS)-induced LTP in the hippocampus, known to be transcription-independent and dependent on N-methyl D-aspartate receptors (NMDARs) and local protein synthesis at synapses. Our expansion of the established role of Cav1.2channels in LTP broadens understanding of synaptic plasticity and identifies a new cellular phenotype for exploring treatment strategies for cognitive dysfunction.

Aberrant accrual of BIN1 near Alzheimer's disease amyloid deposits in transgenic models.

Bridging integrator 1 (BIN1) is the most significant late-onset Alzheimer's disease (AD) susceptibility locus identified via genome-wide association studies. BIN1 is an adaptor protein that regulates membrane dynamics in the context of endocytosis and membrane remodeling. An increase in BIN1 expression and changes in the relative levels of alternatively spliced BIN1 isoforms have been reported in the brains of patients with AD. BIN1 can bind to Tau, and an increase in BIN1 expression correlates with Tau pathology. In contrast, the loss of BIN1 expression in cultured cells elevates Aß production and Tau propagation by insfluencing endocytosis and recycling. Here, we show that BIN1 accumulates adjacent to amyloid deposits in vivo. We found an increase in insoluble BIN1 and a striking accrual of BIN1 within and near amyloid deposits in the brains of multiple transgenic models of AD. The peri-deposit aberrant BIN1 localization was conspicuously different from the accumulation of APP and BACE1 within dystrophic neurites. Although BIN1 is highly expressed in mature oligodendrocytes, BIN1 association with amyloid deposits occurred in the absence of the accretion of other oligodendrocyte or myelin proteins. Finally, super-resolution microscopy and immunogold electron microscopy analyses highlight the presence of BIN1 in proximity to amyloid fibrils at the edges of amyloid deposits. These results reveal the aberrant accumulation of BIN1 is a feature associated with AD amyloid pathology. Our findings suggest a potential role for BIN1 in extracellular Aß deposition in vivo that is distinct from its well-characterized function as an adaptor protein in endocytosis and membrane remodeling.

Altered reward sensitivity in female offspring of cocaine-exposed fathers.

Recent rodent studies have demonstrated that parental cocaine exposure can influence offspring behavior, supporting the idea that environmental insults can impact subsequent generations. However, studies on the effects of paternal cocaine exposure are limited and multiple inconsistencies exist. In the current study, we behaviorally characterize the effects of paternal cocaine exposure in a C57BL/6J intergenerational mouse model. Male sires were administered cocaine hydrochloride (20mg/kg) or saline (0.01mL/g) once a day for 75days, and bred with drug naïve females twenty-four hours after the final injection. Offspring, separated by sex, were tested in a battery of behaviors. We found that paternal cocaine exposure altered sensitivity to the rewarding and stimulant effects of psychostimulants and natural reward (sucrose) in female offspring; female cocaine-sired offspring showed blunted cocaine preference using cocaine conditioned place preference (CPP) at a low dose (5mg/kg), but displayed similar preference at a higher dose (10mg/kg) compared to saline-sired controls. Additionally, cocaine-sired female offspring exhibited higher psychomotor sensitivity to cocaine (10mg/kg) and amphetamine (2mg/kg) and consumed more sucrose. Cocaine-sired males exhibited increased psychomotor effects of cocaine and amphetamine. Male offspring also displayed an anxiety-like phenotype. No effect of paternal cocaine exposure was observed on depressive-like, learning and memory or social behavior in male or female offspring. Collectively, our findings show that paternal, chronic cocaine exposure induces intergenerational behavioral effects in male and female offspring with greatest impact on sensitivity to psychostimulants and sucrose in females.

Cacna1c in the Prefrontal Cortex Regulates Depression-Related Behaviors via REDD1.

The CACNA1C gene that encodes the L-type Ca2+ channel (LTCC) Cav1.2 subunit has emerged as a candidate risk gene for multiple neuropsychiatric disorders including bipolar disorder, major depressive disorder, and schizophrenia, all marked with depression-related symptoms. Although cacna1c heterozygous (HET) mice have been previously reported to exhibit an antidepressant-like phenotype, the molecular and circuit-level dysfunction remains unknown. Here we report that viral vector-mediated deletion of cacna1c in the adult prefrontal cortex (PFC) of mice recapitulates the antidepressant-like effect observed in cacna1c HET mice using the sucrose preference test (SPT), forced swim test (FST), and tail suspension test (TST). Molecular studies identified lower levels of REDD1, a protein previously linked to depression, in the PFC of HET mice, and viral-mediated REDD1 overexpression in the PFC of these HET mice reversed the antidepressant-like effect in SPT and TST. Examination of downstream REDD1 targets found lower levels of active/phosphorylated Akt (S473) with no change in mTORC1 phosphorylation. Examination of the transcription factor FoxO3a, previously linked to depression-related behavior and shown to be regulated in other systems by Akt, revealed higher nuclear levels in the PFC of cacna1c HET mice that was further increased following REDD1-mediated reversal of the antidepressant-like phenotype. Collectively, these findings suggest that REDD1 in cacna1c HET mice may influence depression-related behavior via regulation of the FoxO3a pathway. Cacna1c HET mice thus serve as a useful mouse model to further study cacna1c-associated molecular signaling and depression-related behaviors relevant to human CACNA1C genetic variants.

Alternatively spliced mu opioid receptor C termini impact the diverse actions of morphine.

Extensive 3' alternative splicing of the mu opioid receptor gene OPRM1 creates multiple C-terminal splice variants. However, their behavioral relevance remains unknown. The present study generated 3 mutant mouse models with truncated C termini in 2 different mouse strains, C57BL/6J (B6) and 129/SvEv (129). One mouse truncated all C termini downstream of Oprm1 exon 3 (mE3M mice), while the other two selectively truncated C-terminal tails encoded by either exon 4 (mE4M mice) or exon 7 (mE7M mice). Studies of these mice revealed divergent roles for the C termini in morphine-induced behaviors, highlighting the importance of C-terminal variants in complex morphine actions. In mE7M-B6 mice, the exon 7-associated truncation diminished morphine tolerance and reward without altering physical dependence, whereas the exon 4-associated truncation in mE4M-B6 mice facilitated morphine tolerance and reduced morphine dependence without affecting morphine reward. mE7M-B6 mutant mice lost morphine-induced receptor desensitization in the brain stem and hypothalamus, consistent with exon 7 involvement in morphine tolerance. In cell-based studies, exon 7-associated variants shifted the bias of several mu opioids toward ß-arrestin 2 over G protein activation compared with the exon 4-associated variant, suggesting an interaction of exon 7-associated C-terminal tails with ß-arrestin 2 in morphine-induced desensitization and tolerance. Together, the differential effects of C-terminal truncation illustrate the pharmacological importance of OPRM1 3' alternative splicing.

Predominant expression of Alzheimer's disease-associated BIN1 in mature oligodendrocytes and localization to white matter tracts.

BACKGROUND: Genome-wide association studies have identified BIN1 within the second most significant susceptibility locus in late-onset Alzheimer's disease (AD). BIN1 undergoes complex alternative splicing to generate multiple isoforms with diverse functions in multiple cellular processes including endocytosis and membrane remodeling. An increase in BIN1 expression in AD and an interaction between BIN1 and Tau have been reported. However, disparate descriptions of BIN1 expression and localization in the brain previously reported in the literature and the lack of clarity on brain BIN1 isoforms present formidable challenges to our understanding of how genetic variants in BIN1 increase the risk for AD. METHODS: In this study, we analyzed BIN1 mRNA and protein levels in human brain samples from individuals with or without AD. In addition, we characterized the BIN1 expression and isoform diversity in human and rodent tissue by immunohistochemistry and immunoblotting using a panel of BIN1 antibodies. RESULTS: Here, we report on BIN1 isoform diversity in the human brain and document alterations in the levels of select BIN1 isoforms in individuals with AD. In addition, we report striking BIN1 localization to white matter tracts in rodent and the human brain, and document that the large majority of BIN1 is expressed in mature oligodendrocytes whereas neuronal BIN1 represents a minor fraction. This predominant non-neuronal BIN1 localization contrasts with the strict neuronal expression and presynaptic localization of the BIN1 paralog, Amphiphysin 1. We also observe upregulation of BIN1 at the onset of postnatal myelination in the brain and during differentiation of cultured oligodendrocytes. Finally, we document that the loss of BIN1 significantly correlates with the extent of demyelination in multiple sclerosis lesions. CONCLUSION: Our study provides new insights into the brain distribution and cellular expression of an important risk factor associated with late-onset AD. We propose that efforts to define how genetic variants in BIN1 elevate the risk for AD would behoove to consider BIN1 function in the context of its main expression in mature oligodendrocytes and the potential for a role of BIN1 in the membrane remodeling that accompanies the process of myelination.