HEBP1 - An early trigger for neuronal cell death and circuit dysfunction in Alzheimer's disease.

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that gradually impairs memory, cognition and the ability to perform simple daily tasks. It is the most prevalent form of dementia in the elderly and its incidence increases exponentially with age. Neuronal and synapse loss, key hallmarks of the disorder, are widely regarded to occur early during the onset of AD, and the extent of this loss closely correlates with the progression of cognitive decline and dysfunction of the underlying neuronal circuity. Nevertheless, the mechanisms driving neuronal and synapse loss during early AD remains poorly understood. This review focuses on Heme-binding protein 1 (HEBP1), a mitochondrial-associated protein that has recently emerged as an important mediator of neuronal cell death during early AD pathogenesis. Acting downstream of Aß and heme, HEBP1-mediated apoptosis contributes to neuronal loss and neuronal circuit dysfunction. Deleting HEBP1 expression in neurons protects them from heme- and Aß-induced apoptosis, both of which are mechanisms implicated in neurodegeneration. HEBP1 participates in heme metabolism and binds to heme to modulate mitochondrial dynamics vital to the maintenance of neural circuitry that is affected in AD. HEBP1 elevation is also associated with AGE/RAGE-related neuronal damage, further implicating its involvement in neuronal loss during early AD. Moreover, F2L, a cleavage product of HEBP1 modulates inflammation. Collectively, these findings highlight the importance of HEBP1 in the disruption of neural circuits during early AD.

Loss of FEZ1, a gene deleted in Jacobsen syndrome, causes locomotion defects and early mortality by impairing motor neuron development.

FEZ1-mediated axonal transport plays important roles in central nervous system development but its involvement in the peripheral nervous system is not well-characterized. FEZ1 is deleted in Jacobsen syndrome (JS), an 11q terminal deletion developmental disorder. JS patients display impaired psychomotor skills, including gross and fine motor delay, suggesting that FEZ1 deletion may be responsible for these phenotypes, given its association with the development of motor-related circuits. Supporting this hypothesis, our data show that FEZ1 is selectively expressed in the rat brain and spinal cord. Its levels progressively increase over the developmental course of human motor neurons (MN) derived from embryonic stem cells. Deletion of FEZ1 strongly impaired axon and dendrite development, and significantly delayed the transport of synaptic proteins into developing neurites. Concurring with these observations, Drosophila unc-76 mutants showed severe locomotion impairments, accompanied by a strong reduction of synaptic boutons at neuromuscular junctions. These abnormalities were ameliorated by pharmacological activation of UNC-51/ATG1, a FEZ1-activating kinase, with rapamycin and metformin. Collectively, the results highlight a role for FEZ1 in MN development and implicate its deletion as an underlying cause of motor impairments in JS patients.

Tissue-selective restriction of RNA editing of CaV1.3 by splicing factor SRSF9.

Adenosine DeAminases acting on RNA (ADAR) catalyzes adenosine-to-inosine (A-to-I) conversion within RNA duplex structures. While A-to-I editing is often dynamically regulated in a spatial-temporal manner, the mechanisms underlying its tissue-selective restriction remain elusive. We have previously reported that transcripts of voltage-gated calcium channel CaV1.3 are subject to brain-selective A-to-I RNA editing by ADAR2. Here, we show that editing of CaV1.3 mRNA is dependent on a 40 bp RNA duplex formed between exon 41 and an evolutionarily conserved editing site complementary sequence (ECS) located within the preceding intron. Heterologous expression of a mouse minigene that contained the ECS, intermediate intronic sequence and exon 41 with ADAR2 yielded robust editing. Interestingly, editing of CaV1.3 was potently inhibited by serine/arginine-rich splicing factor 9 (SRSF9). Mechanistically, the inhibitory effect of SRSF9 required direct RNA interaction. Selective down-regulation of SRSF9 in neurons provides a basis for the neuron-specific editing of CaV1.3 transcripts.

S-Nitrosylation of Divalent Metal Transporter 1 Enhances Iron Uptake to Mediate Loss of Dopaminergic Neurons and Motoric Deficit.

Elevated iron deposition has been reported in Parkinson's disease (PD). However, the route of iron uptake leading to high deposition in the substantia nigra is unresolved. Here, we show a mechanism in enhanced Fe2+ uptake via S-nitrosylation of divalent metal transporter 1 (DMT1). While DMT1 could be S-nitrosylated by exogenous nitric oxide donors, in human PD brains, endogenously S-nitrosylated DMT1 was detected in postmortem substantia nigra. Patch-clamp electrophysiological recordings and iron uptake assays confirmed increased Mn2+ or Fe2+ uptake through S-nitrosylated DMT1. We identified two major S-nitrosylation sites, C23 and C540, by mass spectrometry, and DMT1 C23A or C540A substitutions abolished nitric oxide (NO)-mediated DMT1 current increase. To evaluate in vivo significance, lipopolysaccharide (LPS) was stereotaxically injected into the substantia nigra of female and male mice to induce inflammation and production of NO. The intranigral LPS injection resulted in corresponding increase in Fe2+ deposition, JNK activation, dopaminergic neuronal loss and deficit in motoric activity, and these were rescued by the NO synthase inhibitor l-NAME or by the DMT1-selective blocker ebselen. Lentiviral knockdown of DMT1 abolished LPS-induced dopaminergic neuron loss.SIGNIFICANCE STATEMENT Neuroinflammation and high cytoplasmic Fe2+ levels have been implicated in the initiation and progression of neurodegenerative diseases. Here, we report the unexpected enhancement of the functional activity of transmembrane divalent metal transporter 1 (DMT1) by S-nitrosylation. We demonstrated that S-nitrosylation increased DMT1-mediated Fe2+ uptake, and two cysteines were identified by mass spectrometry to be the sites for S-nitrosylation and for enhanced iron uptake. One conceptual advance is that while DMT1 activity could be increased by external acidification because the gating of the DMT1 transporter is proton motive, we discovered that DMT1 activity could also be enhanced by S-nitrosylation. Significantly, lipopolysaccharide-induced nitric oxide (NO)-mediated neuronal death in the substantia nigra could be ameliorated by using l-NAME, a NO synthase inhibitor, or by ebselen, a DMT1-selective blocker.

Localisation of Formyl-Peptide Receptor 2 in the Rat Central Nervous System and Its Role in Axonal and Dendritic Outgrowth.

Arachidonic acid and docosahexaenoic acid (DHA) released by the action of phospholipases A2 (PLA2) on membrane phospholipids may be metabolized by lipoxygenases to the anti-inflammatory mediators lipoxin A4 (LXA4) and resolvin D1 (RvD1), and these can bind to a common receptor, formyl-peptide receptor 2 (FPR2). The contribution of this receptor to axonal or dendritic outgrowth is unknown. The present study was carried out to elucidate the distribution of FPR2 in the rat CNS and its role in outgrowth of neuronal processes. FPR2 mRNA expression was greatest in the brainstem, followed by the spinal cord, thalamus/hypothalamus, cerebral neocortex, hippocampus, cerebellum and striatum. The brainstem and spinal cord also contained high levels of FPR2 protein. The cerebral neocortex was moderately immunolabelled for FPR2, with staining mostly present as puncta in the neuropil. Dentate granule neurons and their axons (mossy fibres) in the hippocampus were very densely labelled. The cerebellar cortex was lightly stained, but the deep cerebellar nuclei, inferior olivary nucleus, vestibular nuclei, spinal trigeminal nucleus and dorsal horn of the spinal cord were densely labelled. Electron microscopy of the prefrontal cortex showed FPR2 immunolabel mostly in immature axon terminals or 'pre-terminals', that did not form synapses with dendrites. Treatment of primary hippocampal neurons with the FPR2 inhibitors, PBP10 or WRW4, resulted in reduced lengths of axons and dendrites. The CNS distribution of FPR2 suggests important functions in learning and memory, balance and nociception. This might be due to an effect of FPR2 in mediating arachidonic acid/LXA4 or DHA/RvD1-induced axonal or dendritic outgrowth.

Macromolecular complexes at active zones: integrated nano-machineries for neurotransmitter release.

The release of neurotransmitters from synaptic vesicles exocytosing at presynaptic nerve terminals is a critical event in the initiation of synaptic transmission. This event occurs at specialized sites known as active zones. The task of faithfully executing various steps in the process is undertaken by careful orchestration of overlapping sets of molecular nano-machineries upon a core macromolecular scaffold situated at active zones. However, their composition remains incompletely elucidated. This review provides an overview of the role of the active zone in mediating neurotransmitter release and summarizes the recent progress using neuroproteomic approaches to decipher their composition. Key proteins of these nano-machineries are highlighted.

Phosphorylation-regulated axonal dependent transport of syntaxin 1 is mediated by a Kinesin-1 adapter.

Presynaptic nerve terminals are formed from preassembled vesicles that are delivered to the prospective synapse by kinesin-mediated axonal transport. However, precisely how the various cargoes are linked to the motor proteins remains unclear. Here, we report a transport complex linking syntaxin 1a (Stx) and Munc18, two proteins functioning in synaptic vesicle exocytosis at the presynaptic plasma membrane, to the motor protein Kinesin-1 via the kinesin adaptor FEZ1. Mutation of the FEZ1 ortholog UNC-76 in Caenorhabditis elegans causes defects in the axonal transport of Stx. We also show that binding of FEZ1 to Kinesin-1 and Munc18 is regulated by phosphorylation, with a conserved site (serine 58) being essential for binding. When expressed in C. elegans, wild-type but not phosphorylation-deficient FEZ1 (S58A) restored axonal transport of Stx. We conclude that FEZ1 operates as a kinesin adaptor for the transport of Stx, with cargo loading and unloading being regulated by protein kinases.

Redox changes and cellular senescence in Alzheimer's disease.

The redox process and cellular senescence are involved in a range of essential physiological functions. However, they are also implicated in pathological processes underlying age-related neurodegenerative disorders, including Alzheimer's disease (AD). Elevated levels of reactive oxygen species (ROS) are generated as a result of abnormal accumulation of beta-amyloid peptide (Aß), tau protein, and heme dyshomeostasis and is further aggravated by mitochondria dysfunction and endoplasmic reticulum (ER) stress. Excessive ROS damages vital cellular components such as proteins, DNA and lipids. Such damage eventually leads to impaired neuronal function and cell death. Heightened oxidative stress can also induce cellular senescence via activation of the senescence-associated secretory phenotype to further exacerbate inflammation and tissue dysfunction. In this review, we focus on how changes in the redox system and cellular senescence contribute to AD and how they are affected by perturbations in heme metabolism and mitochondrial function. While potential therapeutic strategies targeting such changes have received some attention, more research is necessary to bring them into clinical application.

FEZ1 participates in human embryonic brain development by modulating neuronal progenitor subpopulation specification and migrations.

Mutations in the human fasciculation and elongation protein zeta 1 (FEZ1) gene are found in schizophrenia and Jacobsen syndrome patients. Here, using human cerebral organoids (hCOs), we show that FEZ1 expression is turned on early during brain development and is detectable in both neuroprogenitor subtypes and immature neurons. FEZ1 deletion disrupts expression of neuronal and synaptic development genes. Using single-cell RNA sequencing, we detected abnormal expansion of homeodomain-only protein homeobox (HOPX)- outer radial glia (oRG), concurrent with a reduction of HOPX+ oRG, in FEZ1-null hCOs. HOPX- oRGs show higher cell mobility as compared to HOPX+ oRGs. Ectopic localization of neuroprogenitors to the outer layer is seen in FEZ1-null hCOs. Anomalous encroachment of TBR2+ intermediate progenitors into CTIP2+ deep layer neurons further indicated abnormalities in cortical layer formation these hCOs. Collectively, our findings highlight the involvement of FEZ1 in early cortical brain development and how it contributes to neurodevelopmental disorders.

SIRIUS, Ultra-Scintillating Upconversion Breast Implant for Remote Orthotopic Photodynamic Therapy.

Present day strategies for delivery of wireless photodynamic therapy (PDT) to deep-seated targets are limited by the inadequacy of irradiance and insufficient therapeutic depth. Here we report the design and preclinical validation of a flexible wireless upconversion nanoparticle (UCNP) implant (SIRIUS) that is capable of large field, high intensity illumination for PDT of deep-seated tumors. The implant achieves this by incorporating submicrometer core-shell-shell NaYF4 UCNPs into its design, which significantly enhances upconversion efficiency and mitigates light loss from surface quenching. We demonstrate the efficacy of SIRIUS UCNP implant mediated PDT in preclinical breast cancer disease models. In our in vitro experiments, SIRIUS directed 5-Aminolevulinic Acid (5-ALA) based wireless PDT leads to significant reactive oxygen species (ROS) generation and tumor apoptosis in hormonal receptor+/HER2+ (MCF7) and triple-negative (MDA-MB-231) breast cancer cell lines. In our in vivo rodent model, SIRIUS-driven PDT is shown to be significant in regressing tumors when applied to orthotopically inoculated breast tumors. Following successful preclinical validation, we also describe a clinical prototype of UCNP breast implant with potential dual cosmetic and onco-therapeutic functions. SIRIUS is an upconversion breast implant for wireless PDT that fulfils all the design prerequisites necessary for seamless clinical translation.