Distinct subnetworks of the thalamic reticular nucleus.

The thalamic reticular nucleus (TRN), the major source of thalamic inhibition, regulates thalamocortical interactions that are critical for sensory processing, attention and cognition1-5. TRN dysfunction has been linked to sensory abnormality, attention deficit and sleep disturbance across multiple neurodevelopmental disorders6-9. However, little is known about the organizational principles that underlie its divergent functions. Here we performed an integrative study linking single-cell molecular and electrophysiological features of the mouse TRN to connectivity and systems-level function. We found that cellular heterogeneity in the TRN is characterized by a transcriptomic gradient of two negatively correlated gene-expression profiles, each containing hundreds of genes. Neurons in the extremes of this transcriptomic gradient express mutually exclusive markers, exhibit core or shell-like anatomical structure and have distinct electrophysiological properties. The two TRN subpopulations make differential connections with the functionally distinct first-order and higher-order thalamic nuclei to form molecularly defined TRN-thalamus subnetworks. Selective perturbation of the two subnetworks in vivo revealed their differential role in regulating sleep. In sum, our study provides a comprehensive atlas of TRN neurons at single-cell resolution and links molecularly defined subnetworks to the functional organization of thalamocortical circuits.

Postnatal neuronal Bace1 deletion impairs neuroblast and oligodendrocyte maturation.

Beta amyloid cleaving enzyme 1 (BACE1) is largely expressed by neurons and is the sole ß-secretase for initiating the production of neuronal ß-amyloid peptides (Aß). To fully understand the physiological functions of neuronal BACE1, we used mouse genetic approach coupled with unbiased single nucleus RNA sequencing (snRNAseq) to investigate how targeted deletion of Bace1 in neurons, driven by Thy-1-Cre recombinase, would affect functions in the nervous system. Our transcriptome results revealed that BACE1 is essential for maturation of neural precursor cells and oligodendrocytes in mice. RNA velocity analysis confirmed deficit in the trajectory of neuroblasts in reaching the immature granule neuron state in young Bace1fl/fl; Thy1-cre mice. Further analysis of differential gene expression indicated changes in genes important for SNARE signaling, tight junction signaling, synaptogenesis and insulin secretion pathways. Morphological studies revealed a hypomyelination in Bace1fl/fl;Thy1-cre sciatic nerves, but no detectable myelination changes in the corpus callosum, despite clear reduction in myelination proteins in the brain. Functional studies showed reduction in long-term potential, defects in synaptogenesis and learning behavioral. Altogether, our results show that neuronal BACE1 is critical for optimal development of central and peripheral nervous system, and inhibition of neuronal BACE1 will result in deficits in synaptic functions and cognitive behaviors.

Bace1 Deletion in the Adult Reverses Epileptiform Activity and Sleep-wake Disturbances in AD Mice.

Alzheimer's disease (AD) increases the risk for seizures and sleep disorders. We show here that germline deletion of ß-site amyloid precursor protein (APP) cleaving enzyme-1 (BACE1) in neurons, but not in astrocytes, increased epileptiform activity. However, Bace1 deletion at adult ages did not alter the normal EEG waveform, indicating less concern for BACE1 inhibition in patients. Moreover, we showed that deletion of Bace1 in the adult was able to reverse epileptiform activity in 5xFAD mice. Intriguingly, treating 5xFAD and APPNL-G-F/NL-G-F (APP KI) mice of either sex with one BACE1 inhibitor Lanabecestat (AZD3293) dramatically increased epileptiform spiking, likely resulting from an off-target effect. We also monitored sleep-wake pathologies in these mice and showed increased wakefulness, decreased non-rapid eye movement sleep, and rapid eye movement sleep in both 5xFAD and APP KI mice; BACE1 inhibition in the adult 5xFAD mice reversed plaque load and sleep disturbances, but this was not seen in APP KI mice. Further studies with and without BACE1 inhibitor treatment showed different levels of plaque-associated microgliosis and activated microglial proteins in 5xFAD mice compared with APP KI mice. Together, BACE1 inhibition should be developed to avoid off-target effect for achieving benefits in reducing epileptic activity and sleep disturbance in Alzheimer's patients.SIGNIFICANCE STATEMENT BACE1 is widely recognized as a therapeutic target for treating Alzheimer's disease patients. However, BACE1 inhibitors failed in clinical trials because of inability to show cognitive improvement in patients. Here we show that BACE1 inhibition actually reduces sleep disturbances and epileptic seizures; both are seen in AD patients. We further showed that one of clinically tested BACE1 inhibitors does have off-target effects, and development of safer BACE1 inhibitors will be beneficial to AD patients. Results from this study will provide useful guidance for additional drug development.

ER-stress response in retinal Müller glia occurs significantly earlier than amyloid pathology in the Alzheimer's mouse brain and retina.

Alzheimer's Disease (AD) pathogenesis is thought to begin up to 20 years before cognitive symptoms appear, suggesting the need for more sensitive diagnostic biomarkers of AD. In this report, we demonstrated pathological changes in retinal Müller glia significantly earlier than amyloid pathology in AD mouse models. By utilizing the knock-in NLGF mouse model, we surprisingly discovered an increase in reticulon 3 (RTN3) protein levels in the NLGF retina as early as postnatal day 30 (P30). Despite RTN3 being a canonically neuronal protein, this increase was noted in the retinal Müller glia, confirmed by immunohistochemical characterization. Further unbiased transcriptomic assays of the P30 NLGF retina revealed that retinal Müller glia were the most sensitive responding cells in this mouse retina, compared with other cell types including photoreceptor cells and ganglion neurons. Pathway analyses of differentially expressed genes in glia cells showed activation of ER stress response via the upregulation of unfolded protein response (UPR) proteins such as ATF4 and CHOP. Early elevation of RTN3 in response to challenges by toxic Aß likely facilitated UPR. Altogether, these findings suggest that Müller glia act as a sentinel for AD pathology in the retina and should aid for both intervention and diagnosis.

BACE1 controls synaptic function through modulating release of synaptic vesicles.

BACE1 initiates production of ß-amyloid peptides (Aß), which is associated with cognitive dysfunction in Alzheimer's disease (AD) due to abnormal oligomerization and aggregation. While BACE1 inhibitors show strong reduction in Aß deposition, they fail to improve cognitive function in patients, largely due to its role in synaptic function. We show that BACE1 is required for optimal release of synaptic vesicles. BACE1 deficiency or inhibition decreases synaptic vesicle docking in the synaptic active zones. Consistently, BACE1-null mice or mice treated with clinically tested BACE1 inhibitors Verubecestat and Lanabecestat exhibit severe reduction in hippocampal LTP and learning behaviors. To counterbalance this synaptic deficit, we discovered that BACE1-null mice treated with positive allosteric modulators (PAMs) of metabotropic glutamate receptor 1 (mGluR1), whose levels were reduced in BACE1-null mice and significantly improved long-term potentiation and cognitive behaviors. Similarly, mice treated with mGluR1 PAM showed significantly mitigated synaptic deficits caused by BACE1 inhibitors. Together, our data suggest that a therapy combining BACE1 inhibitors for reducing amyloid deposition and an mGluR1 PAM for counteracting BACE1-mediated synaptic deficits appears to be an effective approach for treating AD patients.

AAV-expressed eCD4-Ig provides durable protection from multiple SHIV challenges.

Long-term in vivo expression of a broad and potent entry inhibitor could circumvent the need for a conventional vaccine for HIV-1. Adeno-associated virus (AAV) vectors can stably express HIV-1 broadly neutralizing antibodies (bNAbs). However, even the best bNAbs neutralize 10-50% of HIV-1 isolates inefficiently (80% inhibitory concentration (IC80) > 5 µg ml(-1)), suggesting that high concentrations of these antibodies would be necessary to achieve general protection. Here we show that eCD4-Ig, a fusion of CD4-Ig with a small CCR5-mimetic sulfopeptide, binds avidly and cooperatively to the HIV-1 envelope glycoprotein (Env) and is more potent than the best bNAbs (geometric mean half-maximum inhibitory concentration (IC50) < 0.05 µg ml(-1)). Because eCD4-Ig binds only conserved regions of Env, it is also much broader than any bNAb. For example, eCD4-Ig efficiently neutralized 100% of a diverse panel of neutralization-resistant HIV-1, HIV-2 and simian immunodeficiency virus isolates, including a comprehensive set of isolates resistant to the CD4-binding site bNAbs VRC01, NIH45-46 and 3BNC117. Rhesus macaques inoculated with an AAV vector stably expressed 17-77 µg ml(-1) of fully functional rhesus eCD4-Ig for more than 40 weeks, and these macaques were protected from several infectious challenges with SHIV-AD8. Rhesus eCD4-Ig was also markedly less immunogenic than rhesus forms of four well-characterized bNAbs. Our data suggest that AAV-delivered eCD4-Ig can function like an effective HIV-1 vaccine.

The histone demethylase Jhdm1a regulates hepatic gluconeogenesis.

Hepatic gluconeogenesis is required for maintaining blood glucose homeostasis; yet, in diabetes mellitus, this process is unrestrained and is a major contributor to fasting hyperglycemia. To date, the impacts of chromatin modifying enzymes and chromatin landscape on gluconeogenesis are poorly understood. Through catalyzing the removal of methyl groups from specific lysine residues in the histone tail, histone demethylases modulate chromatin structure and, hence, gene expression. Here we perform an RNA interference screen against the known histone demethylases and identify a histone H3 lysine 36 (H3K36) demethylase, Jhdm1a, as a key negative regulator of gluconeogenic gene expression. In vivo, silencing of Jhdm1a promotes liver glucose synthesis, while its exogenous expression reduces blood glucose level. Importantly, the regulation of gluconeogenesis by Jhdm1a requires its demethylation activity. Mechanistically, we find that Jhdm1a regulates the expression of a major gluconeogenic regulator, C/EBPα. This is achieved, at least in part, by its USF1-dependent association with the C/EBPα promoter and its subsequent demethylation of dimethylated H3K36 on the C/EBPα locus. Our work provides compelling evidence that links histone demethylation to transcriptional regulation of gluconeogenesis and has important implications for the treatment of diabetes.

Activity of Alzheimer's γ-secretase is linked to changes of interferon-induced transmembrane proteins (IFITM) in innate immunity.

The activity of γ-secretase is critical to the pathogenesis of Alzheimer's disease (AD). How its activity is regulated is intriguing and highly important for any AD therapy that focuses on reduction of toxic amyloid peptides and amyloid deposition in patients. Recently, interferon-induced transmembrane protein 3 (IFITM3) has been identified as a novel regulator of γ-secretase through a specific interaction. This commentary highlights this exciting study and provides an updated link of γ-secretase activity to innate immunity through IFITM3.

Metabotropic Glutamate Receptors in Alzheimer's Disease Synaptic Dysfunction: Therapeutic Opportunities and Hope for the Future.

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by the presence of neuritic plaques and neurofibrillary tangles. The impaired synaptic plasticity and dendritic loss at the synaptic level is an early event associated with the AD pathogenesis. The abnormal accumulation of soluble oligomeric amyloid-ß (Aß), the major toxic component in amyloid plaques, is viewed to trigger synaptic dysfunctions through binding to several presynaptic and postsynaptic partners and thus to disrupt synaptic transmission. Over time, the abnormalities in neural transmission will result in cognitive deficits, which are commonly manifested as memory loss in AD patients. Synaptic plasticity is regulated through glutamate transmission, which is mediated by various glutamate receptors. Here we review recent progresses in the study of metabotropic glutamate receptors (mGluRs) in AD cognition. We will discuss the role of mGluRs in synaptic plasticity and their modulation as a possible strategy for AD cognitive improvement.

Role of the sigma-1 receptor chaperone in rod and cone photoreceptor degenerations in a mouse model of retinitis pigmentosa.

BACKGROUND: Retinitis pigmentosa (RP) is the most common inherited retinal degenerative disease yet with no effective treatment available. The sigma-1 receptor (S1R), a ligand-regulated chaperone, emerges as a potential retina-protective therapeutic target. In particular, pharmacological activation of S1R was recently shown to rescue cones in the rd10 mouse, a rod Pde6b mutant that recapitulates the RP pathology of autonomous rod degeneration followed by secondary death of cones. The mechanisms underlying the S1R protection for cones are not understood in detail. METHODS: By rearing rd10/S1R-/- and rd10/S1R+/+ mice in dim light to decelerate rapid rod/cone degeneration, we were able to compare their retinal biochemistry, histology and functions throughout postnatal 3-6 weeks (3 W-6 W). RESULTS: The receptor-interacting protein kinases (RIP1/RIP3) and their interaction (proximity ligation) dramatically up-regulated after 5 W in rd10/S1R-/- (versus rd10/S1R+/+) retinas, indicative of intensified necroptosis activation, which was accompanied by exacerbated loss of cones. Greater rod loss in rd10/S1R-/- versus rd10/S1R+/+ retinas was evidenced by more cleaved Caspase3 (4 W) and lower rod electro-retinographic a-waves (4 W-6 W), concomitant with reduced LC3-II and CHOP (4 W-6 W), markers of autophagy and endoplasmic reticulum stress response, respectively. However, the opposite occurred at 3 W. CONCLUSION: This study reveals previously uncharacterized S1R-associated mechanisms during rd10 photoreceptor degeneration, including S1R's influences on necroptosis and autophagy as well as its biphasic role in rod degeneration upstream of cone death.

An intraocular drug delivery system using targeted nanocarriers attenuates retinal ganglion cell degeneration.

Glaucoma is a common blinding disease characterized by loss of retinal ganglion cells (RGCs). To date, there is no clinically available treatment directly targeting RGCs. We aim to develop an RGC-targeted intraocular drug delivery system using unimolecular micelle nanoparticles (unimNPs) to prevent RGC loss. The unimNPs were formed by single/individual multi-arm star amphiphilic block copolymer poly(amidoamine)-polyvalerolactone-poly(ethylene glycol) (PAMAM-PVL-PEG). While the hydrophobic PAMAM-PVL core can encapsulate hydrophobic drugs, the hydrophilic PEG shell provides excellent water dispersity. We conjugated unimNPs with the cholera toxin B domain (CTB) for RGC-targeting and with Cy5.5 for unimNP-tracing. To exploit RGC-protective sigma-1 receptor (S1R), we loaded unimNPs with an endogenous S1R agonist dehydroepiandrosterone (DHEA) as an FDA-approved model drug. These unimNPs produced a steady DHEA release in vitro for over two months at pH7.4. We then co-injected (mice, intraocular) unimNPs with the glutamate analog N-methyl-d-aspartate (NMDA), which is excito-toxic and induces RGC death. The CTB-conjugated unimNPs (i.e., targeted NPs) accumulated at the RGC layer and effectively preserved RGCs at least for 14days, whereas the unimNPs without CTB (i.e., non-targeted NPs) showed neither accumulation at nor protection of NMDA-treated RGCs. Consistent with S1R functions, targeted NPs relative to non-targeted NPs showed markedly better inhibitory effects on apoptosis and oxidative/inflammatory stresses in the RGC layer. Hence, the DHEA-loaded, CTB-conjugated unimNPs represent an RGC/S1R dual-targeted nanoplatform that generates an efficacious template for further development of a sustainable intraocular drug delivery system to protect RGCs, which may be applicable to treatments directed at glaucomatous pathology.

Striatopallidal dysfunction underlies repetitive behavior in Shank3-deficient model of autism.

The postsynaptic scaffolding protein SH3 and multiple ankyrin repeat domains 3 (SHANK3) is critical for the development and function of glutamatergic synapses. Disruption of the SHANK3-encoding gene has been strongly implicated as a monogenic cause of autism, and Shank3 mutant mice show repetitive grooming and social interaction deficits. Although basal ganglia dysfunction has been proposed to underlie repetitive behaviors, few studies have provided direct evidence to support this notion and the exact cellular mechanisms remain largely unknown. Here, we utilized the Shank3B mutant mouse model of autism to investigate how Shank3 mutation may differentially affect striatonigral (direct pathway) and striatopallidal (indirect pathway) medium spiny neurons (MSNs) and its relevance to repetitive grooming behavior in Shank3B mutant mice. We found that Shank3 deletion preferentially affects synapses onto striatopallidal MSNs. Striatopallidal MSNs showed profound defects, including alterations in synaptic transmission, synaptic plasticity, and spine density. Importantly, the repetitive grooming behavior was rescued by selectively enhancing the striatopallidal MSN activity via a Gq-coupled human M3 muscarinic receptor (hM3Dq), a type of designer receptors exclusively activated by designer drugs (DREADD). Our findings directly demonstrate the existence of distinct changes between 2 striatal pathways in a mouse model of autism and indicate that the indirect striatal pathway disruption might play a causative role in repetitive behavior of Shank3B mutant mice.