Decreased outflow facility and Schlemm's canal defects in a mouse model of glaucoma.

Previously we identified B6.EDA+/+ mice as a novel mouse model that presents with elevated IOP and trabecular meshwork damage. Here, we expand on our previous findings by measuring aqueous humor outflow facility and analyzing the integrity of the inner wall of Schlemm's canal. As expected, intraocular pressure (IOP) was increased, and outflow facility was decreased compared to C57BL/6J controls. B6.EDA+/+ mice had significantly increased expression of the adherens junction protein, VE-cadherin by the inner wall endothelium of Schlemm's canal. These data suggest that in addition to trabecular meshwork damage, there are changes in Schlemm's canal in B6.EDA+/+ mice that lead to aqueous outflow dysfunction and ocular hypertension.

Unstructured loop is essential for the activation of mGluR2.

Metabotropic Glutamate Receptors (mGluRs) are Class C G-protein coupled receptors (GPCRs) that are expressed throughout the central nervous system and are involved in several neurological and psychiatric disorders. Although, many studies focused on Glutamate induced activation of mGluR2, however, the role of unstructured loop (or "BC loop") in activation of metabotropic Glutamate receptors is currently unknown. Here, using Förster Resonance Energy Transfer (FRET) based assay in live cells we show that unstructured loop is required for Glutamate induced conformation and hence the activation of the receptor.

Peeking into Sigma-1 Receptor Functions Through the Retina.

This review discusses recent advances towards understanding the sigma-1 receptor (S1R) as an endogenous neuro-protective mechanism in the retina , a favorable experimental model system. The exquisite architecture of the mammalian retina features layered and intricately wired neurons supported by non-neuronal cells. Ganglion neurons, photoreceptors , as well as the retinal pigment epithelium, are susceptible to degeneration that leads to major retinal diseases such as glaucoma , diabetic retinopathy , and age-related macular degeneration (AMD), and ultimately, blindness. The S1R protein is found essentially in every retinal cell type, with high abundance in the ganglion cell layer. Ultrastructural studies of photoreceptors, bipolar cells, and ganglion cells show a predominant localization of S1R in the nuclear envelope. A protective role of S1R for ganglion and photoreceptor cells is supported by in vitro and in vivo experiments. Most recently, studies suggest that S1R may also protect retinal neurons via its activities in Müller glia and microglia. The S1R functions in the retina may be attributed to a reduction of excitotoxicity, oxidative stress , ER stress response, or inflammation. S1R knockout mice are being used to delineate the S1R-specific effects. In summary, while significant progress has been made towards the objective of establishing a S1R-targeted paradigm for retinal neuro-protection , critical questions remain. In particular, context-dependent effects and potential side effects of interventions targeting S1R need to be studied in more diverse and more clinically relevant animal models.

The Sigma-1 Receptor-A Therapeutic Target for the Treatment of ALS?

The membrane bound 223 amino acid Sigma-1 Receptor (S1R) serves as a molecular chaperone and functional regulator of many signaling proteins. Spinal cord motor neuron activation occurs, in part, via large ventral horn cholinergic synapses called C-boutons/C-terminals. Chronic excitation of motor neurons and alterations in C-terminals has been associated with Amyotrophic Lateral Sclerosis (ALS ). The S1R has an important role in regulating motor neuron function. High levels of the S1R are localized in postsynaptic endoplasmic reticulum (ER) subsurface cisternae within 10-20 nm of the plasma membrane that contain muscarinic type 2 acetylcholine receptors (M2AChR), calcium activated potassium channels (Kv2.1) and slow potassium (SK) channels. An increase in action potentials in the S1R KO mouse motor neurons indicates a critical role for the S1R as a "brake" on motor neuron function possibly via calcium dependent hyperpolarization mechanisms involving the aforementioned potassium channels. The longevity of SOD-1/S1R KO ALS mice is significantly reduced compared to SOD-1/WT ALS controls. The S1R colocalizes in C-terminals with Indole(ethyl)amine-N-methyl transferase (INMT ), the enzyme that produces the S1R agonist , N,N'- dimethyltryptamine (DMT). INMT methylation can additionally neutralize endogenous toxic sulfur and selenium derivatives thus providing functional synergism with DMT to reduce oxidative stress in motor neurons . Small molecule activation of the S1R and INMT thus provides a possible therapeutic strategy to treat ALS .

Control of autophagosome axonal retrograde flux by presynaptic activity unveiled using botulinum neurotoxin type a.

Botulinum neurotoxin type A (BoNT/A) is a highly potent neurotoxin that elicits flaccid paralysis by enzymatic cleavage of the exocytic machinery component SNAP25 in motor nerve terminals. However, recent evidence suggests that the neurotoxic activity of BoNT/A is not restricted to the periphery, but also reaches the CNS after retrograde axonal transport. Because BoNT/A is internalized in recycling synaptic vesicles, it is unclear which compartment facilitates this transport. Using live-cell confocal and single-molecule imaging of rat hippocampal neurons cultured in microfluidic devices, we show that the activity-dependent uptake of the binding domain of the BoNT/A heavy chain (BoNT/A-Hc) is followed by a delayed increase in retrograde axonal transport of BoNT/A-Hc carriers. Consistent with a role of presynaptic activity in initiating transport of the active toxin, activity-dependent uptake of BoNT/A in the terminal led to a significant increase in SNAP25 cleavage detected in the soma chamber compared with nonstimulated neurons. Surprisingly, most endocytosed BoNT/A-Hc was incorporated into LC3-positive autophagosomes generated in the nerve terminals, which then underwent retrograde transport to the cell soma, where they fused with lysosomes both in vitro and in vivo. Blocking autophagosome formation or acidification with wortmannin or bafilomycin A1, respectively, inhibited the activity-dependent retrograde trafficking of BoNT/A-Hc. Our data demonstrate that both the presynaptic formation of autophagosomes and the initiation of their retrograde trafficking are tightly regulated by presynaptic activity.

The sigma-1 receptors are present in monomeric and oligomeric forms in living cells in the presence and absence of ligands.

The sigma-1 receptor (S1R) is a 223-amino-acid membrane protein that resides in the endoplasmic reticulum and the plasma membrane of some mammalian cells. The S1R is regulated by various synthetic molecules including (+)-pentazocine, cocaine and haloperidol and endogenous molecules such as sphingosine, dimethyltryptamine and dehydroepiandrosterone. Ligand-regulated protein chaperone functions linked to oxidative stress and neurodegenerative disorders such as amyotrophic lateral sclerosis (ALS) and neuropathic pain have been attributed to the S1R. Several client proteins that interact with S1R have been identified including various types of ion channels and G-protein coupled receptors (GPCRs). When S1R constructs containing C-terminal monomeric GFP2 and YFP fusions were co-expressed in COS-7 cells and subjected to FRET spectrometry analysis, monomers, dimers and higher oligomeric forms of S1R were identified under non-liganded conditions. In the presence of the prototypic S1R agonist, (+)-pentazocine, however, monomers and dimers were the prevailing forms of S1R. The prototypic antagonist, haloperidol, on the other hand, favoured higher order S1R oligomers. These data, in sum, indicate that heterologously expressed S1Rs occur in vivo in COS-7 cells in multiple oligomeric forms and that S1R ligands alter these oligomeric structures. We suggest that the S1R oligomerization states may regulate its function(s).

Role of the Sigma-1 receptor in Amyotrophic Lateral Sclerosis (ALS).

Amyotrophic Lateral Sclerosis (ALS) is a neurodegenerative disease affecting spinal cord motoneurons (MN) with an associative connection to Frontotemporal Lobar Dementia (FTLD). The endoplasmic reticulum (ER) bound Sigma-1 Receptor (S1R) chaperone protein localizes to specialized ER cisternae within 10 nm of the plasma membrane in spinal cord ventral horn cholinergic post synaptic C-terminals. Removal of the S1R gene in the Superoxide Dismutase-1 (SOD-1) mouse model of ALS exacerbated the neurodegenerative condition and resulted in a significantly reduced longevity when compared to the SOD-1/S1R wild type (WT) mouse. The proposed amelioration of the ALS phenotype by the S1R is likely due to a "brake" on excitation of the MN as evidenced by a reduction in action potential generation in the MN of the WT when compared to the S1R KO mouse MN. Although the precise signal transduction pathway(s) regulated by the S1R in the MN has/have not been elucidated at present, it is likely that direct or indirect functional interactions occur between the S1R in the ER cisternae with voltage gated potassium channels and/or with muscarinic M2 receptor signaling in the post synaptic plasma membrane. Possible mechanisms for regulation of MN excitability by S1R are discussed.

Noncompetitive inhibition of indolethylamine-N-methyltransferase by N,N-dimethyltryptamine and N,N-dimethylaminopropyltryptamine.

Indolethylamine-N-methyltransferase (INMT) is a Class 1 transmethylation enzyme known for its production of N,N-dimethyltryptamine (DMT), a hallucinogen with affinity for various serotonergic, adrenergic, histaminergic, dopaminergic, and sigma-1 receptors. DMT is produced via the action of INMT on the endogenous substrates tryptamine and S-adenosyl-l-methionine (SAM). The biological, biochemical, and selective small molecule regulation of INMT enzyme activity remain largely unknown. Kinetic mechanisms for inhibition of rabbit lung INMT (rabINMT) by the product, DMT, and by a new novel tryptamine derivative were determined. After Michaelis-Menten and Lineweaver-Burk analyses had been applied to study inhibition, DMT was found to be a mixed competitive and noncompetitive inhibitor when measured against tryptamine. The novel tryptamine derivative, N-[2-(1H-indol-3-yl)ethyl]-N',N'-dimethylpropane-1,3-diamine (propyl dimethyl amino tryptamine or PDAT), was shown to inhibit rabINMT by a pure noncompetitive mechanism when measured against tryptamine with a Ki of 84 µM. No inhibition by PDAT was observed at 2 mM when it was tested against structurally similar Class 1 methyltransferases, such as human phenylethanolamine-N-methyltransferase (hPNMT) and human nicotinamide-N-methyltransferase (hNNMT), indicating selectivity for INMT. The demonstration of noncompetitive mechanisms for INMT inhibition implies the presence of an inhibitory allosteric site. In silico analyses using the computer modeling software Autodock and the rabINMT sequence threaded onto the human INMT (hINMT) structure (Protein Data Bank entry 2A14 ) identified an N-terminal helix-loop-helix non-active site binding region of the enzyme. The energies for binding of DMT and PDAT to this region of rabINMT, as determined by Autodock, were -6.34 and -7.58 kcal/mol, respectively. Assessment of the allosteric control of INMT may illuminate new biochemical pathway(s) underlying the biology of INMT.

Development of benzophenone-alkyne bifunctional sigma receptor ligands.

Sigma (σ) receptors are unique non-opioid binding sites that are associated with a broad range of disease states. Sigma-2 receptors provide a promising target for diagnostic imaging and pharmacological interventions to curb tumor progression. Most recently, the progesterone receptor (PGRMC1, 25 kDa) has been shown to have σ2 receptor-like binding properties, thus highlighting the need to understand the biological function of an 18 kDa protein that exhibits σ2-like photoaffinity labeling (denoted here as σ2-18k) but the amino acid sequence of which is not known. In order to provide new tools for the study of the σ2-18k protein, we have developed bifunctional σ receptor ligands each bearing a benzophenone photo-crosslinking moiety and an alkyne group to which an azide-containing biotin affinity tag can be covalently attached through click chemistry after photo-crosslinking. Although several compounds showed favorable σ2 binding properties, the highest affinity (2 nM) and the greatest potency in blocking photolabeling of σ2-18k by a radioactive photoaffinity ligand was shown by compound 22. These benzophenone-alkyne σ receptor ligands might therefore be amenable for studying the σ2-18k protein through chemical biology approaches. To the best of our knowledge, these compounds represent the first reported benzophenone-containing clickable σ receptor ligands, which might potentially have broad applications based on the "plugging in" of various tags.

TLR4 signaling modulates extracellular matrix production in the lamina cribrosa.

The optic nerve head (ONH) is a place of vulnerability during glaucoma progression due to increased intraocular pressure damaging the retinal ganglion cell axons. The molecular signaling pathways involved in generating glaucomatous ONH damage has not been fully elucidated. There is a great deal of evidence that pro-fibrotic TGFß2 signaling is involved in modulating the ECM environment within the lamina cribrosa (LC) region of the ONH. Here we investigated the role of signaling crosstalk between the TGFß2 pathway and the toll-like receptor 4 (TLR4) pathway within the LC. ECM deposition was examined between healthy and glaucomatous human ONH sections, finding increases in fibronectin and fibronectin extra domain A (FN-EDA) an isoform of fibronectin known to be a damage associated molecular pattern (DAMP) that can activate TLR4 signaling. In human LC cell cultures derived from healthy donor eyes, inhibition of TLR4 signaling blocked TGFß2 induced FN and FN-EDA expression. Activation of TLR4 by cellular FN (cFN) containing the EDA isoform increased both total FN production and Collagen-1 production and this effect was dependent on TLR4 signaling. These studies identify TGFß2-TLR4 signaling crosstalk in LC cells of the ONH as a novel pathway regulating ECM and DAMP production.

Fibronectin extra domain A (FN-EDA) causes glaucomatous trabecular meshwork, retina, and optic nerve damage in mice.

BACKGROUND: Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage. Here, we investigate the role of an endogenous Toll-like receptor 4 (TLR4) ligand, FN-EDA, in the development of glaucoma utilizing a transgenic mouse strain (B6.EDA+/+) that constitutively expresses only FN containing the EDA isoform. METHODS: Eyes from C57BL6/J (wild-type), B6.EDA+/+ (constitutively active EDA), B6.EDA-/- (EDA null) mice were processed for electron microscopy and consecutive images of the entire length of the TM and Schlemm's canal (SC) from anterior to posterior were collected and montaged into a single image. ECM accumulation, basement membrane length, and size and number of giant vacuoles were quantified by ImageJ analysis. Tlr4 and Iba1 expression in the TM and ONH cells was conducted using RNAscope in situ hybridization and immunohistochemistry protocols. IOP was measured using a rebound tonometer, ON damage assessed by PPD stain, and RGC loss quantified in RBPMS labeled retina flat mounts. RESULTS: Ultrastructure analyses show the TM of B6.EDA+/+ mice have significantly increased accumulation of ECM between TM beams with few empty spaces compared to C57BL/6 J mice (p < 0.05). SC basement membrane is thicker and more continuous in B6.EDA+/+ mice compared to C57BL/6 J. No significant structural differences are detected in the TM of EDA null mice. Tlr4 and Iba1 expression is increased in the TM of B6.EDA+/+ mice compared to C57BL/6 J eyes (p < 0.05). IOP is significantly higher in B6.EDA+/+ mice compared to C57BL/6 J eyes (p < 0.001), and significant ON damage (p < 0.001) and RGC loss (p < 0.05) detected at 1 year of age. Tlr4 mRNA is expressed in mouse ONH cells, and is present in ganglion cell axons, microglia, and astrocytes. There is a significant increase in the area occupied by Iba-1 positive microglia cells in the ONH of B6.EDA+/+ mice compared to C57BL/6 J control eyes (p < 0.01). CONCLUSIONS: B6.EDA+/+ mice have increased ECM accumulation in the TM, elevated IOP, enhanced proinflammatory changes in the ONH, loss of RGCs, and ONH damage. These data suggest B6.EDA+/+ mice recapitulate many aspects of glaucomatous damage.

Retinal Photoreceptor Protection in an AMD-Related Mouse Model by Selective Sigma-1 or Sigma-2 Receptor Modulation.

The structurally and genetically distinct sigma-1 receptor (S1R) and sigma-2 receptor (S2R) comprise a unique class of drug binding sites. Their alleles are associated with human diseases involving neuronal systems, such as age-related macular degeneration (AMD) characterized by photoreceptor and retinal pigment epithelium (RPE) atrophy. Previous studies have suggested neuroprotective benefits for the brain and retina from pharmacological modulation of S1R and/or S2R. However, the effect of such modulation on AMD pathology remains underexplored. Here, we evaluated S1R- or S2R-selective modulation in an AMD-related model of Abca4-/-Rdh8-/- mice with a disrupted visual cycle that predisposes RPE and photoreceptors to illumination-induced damage. For S1R modulation, we used (+)-pentazocine, which is a high-affinity S1R-selective drug. For S2R modulation, we chose CM398, a high-affinity and highly S2R-selective ligand with drug-like properties. Abca4-/-Rdh8-/- mice received a single i.p. injection of (+)-pentazocine or CM398 or vehicle 30 min before illumination. Pretreatment with (+)-pentazocine improved electroretinogram a- and b-waves compared to that with vehicle. Consistently, in another AMD-related mouse model induced by tail-vein injected NaIO3, S1R genetic ablation aggravated photoreceptor loss. In Abca4-/-Rdh8-/- mice, pretreatment with CM398 appeared to partially avert illumination-induced photoreceptor loss and autofluorescent granule formation that signals RPE damage, as revealed by optical coherence tomography. Thus, this study using AMD-related models provides evidence of photoreceptor protection afforded by selective modulation of S1R or S2R.

Consensus Recommendation for Mouse Models of Ocular Hypertension to Study Aqueous Humor Outflow and Its Mechanisms.

Due to their similarities in anatomy, physiology, and pharmacology to humans, mice are a valuable model system to study the generation and mechanisms modulating conventional outflow resistance and thus intraocular pressure. In addition, mouse models are critical for understanding the complex nature of conventional outflow homeostasis and dysfunction that results in ocular hypertension. In this review, we describe a set of minimum acceptable standards for developing, characterizing, and utilizing mouse models of open-angle ocular hypertension. We expect that this set of standard practices will increase scientific rigor when using mouse models and will better enable researchers to replicate and build upon previous findings.

Antagonist action of progesterone at σ-receptors in the modulation of voltage-gated sodium channels.

σ-Receptors are integral membrane proteins that have been implicated in a number of biological functions, many of which involve the modulation of ion channels. A wide range of synthetic ligands activate σ-receptors, but endogenous σ-receptor ligands have proven elusive. One endogenous ligand, dimethyltryptamine (DMT), has been shown to act as a σ-receptor agonist. Progesterone and other steroids bind σ-receptors, but the functional consequences of these interactions are unclear. Here we investigated progesterone binding to σ(1)- and σ(2)-receptors and evaluated its effect on σ-receptor-mediated modulation of voltage-gated Na(+) channels. Progesterone binds both σ-receptor subtypes in liver membranes with comparable affinities and blocks photolabeling of both subtypes in human embryonic kidney 293 cells that stably express the human cardiac Na(+) channel Na(v)1.5. Patch-clamp recording in this cell line tested Na(+) current modulation by the σ-receptor ligands ditolylguanidine, PB28, (+)SKF10047, and DMT. Progesterone inhibited the action of these ligands to varying degrees, and some of these actions were reduced by σ(1)-receptor knockdown with small interfering RNA. Progesterone inhibition of channel modulation by drugs was consistent with stronger antagonism of σ(2)-receptors. By contrast, progesterone inhibition of channel modulation by DMT was consistent with stronger antagonism of σ(1)-receptors. Progesterone binding to σ-receptors blocks σ-receptor-mediated modulation of a voltage-gated ion channel, and this novel membrane action of progesterone may be relevant to changes in brain and cardiovascular function during endocrine transitions.

Accelerated retinal ganglion cell death in mice deficient in the Sigma-1 receptor.

PURPOSE: The sigma-1 receptor (σR1), a ligand-operated chaperone, has been inferred to be neuroprotective in previous studies using σR1 ligands. The σR1 specificity of the protective function, however, has yet to be firmly established, due to the existence of non-σR1 targets of the ligands. Here, we used the σR1-knockout mouse (Sigmar1(-/-)) to demonstrate unambiguously the role of the σR1 in protecting the retinal ganglion cells against degeneration after acute damage to the optic nerve. METHODS: Retinal σR binding sites were labeled with radioiodinated σR ligands and analyzed by autoradiography. Localization of the σR1 was performed by indirect immunofluorescence on frozen retinal sections. Retinal ganglion cell death was induced by acute optic nerve crush in wild-type and Sigmar1(-/-) mice. Surviving cells in the ganglion cell layer were counted on Nissl-stained retinal whole mounts 7 days after the crush surgery. RESULTS: Photoaffinity labeling indicated the presence of the σR1 in the retina, in concentrations equivalent to those in liver tissue. Immunolabeling detected this receptor in cells of both the ganglion cell layer and the photoreceptor cell layer in wild-type retinas. Quantification of cells remaining after optic nerve crush showed that 86.8±7.9% cells remained in the wild-type ganglion cell layer, but only 68.3±3.4% survived in the Sigmar1(-/-), demonstrating a significant difference between the wild-type and the Sigmar1(-/-) in crush-induced ganglion cell loss. CONCLUSIONS: Our data indicated faster retinal ganglion cell death in Sigmar1(-/-) than in wild-type mice under the stresses caused by optic nerve crush, providing direct evidence for a role of the σR1 in alleviating retinal degeneration. This conclusion is consistent with the previous pharmacological studies using σR1 agonists. Thus, our study supports the idea that the σR1 is a promising therapeutic target for neurodegenerative retinal diseases, such as glaucoma.

Electron-donating para-methoxy converts a benzamide-isoquinoline derivative into a highly Sigma-2 receptor selective ligand.

The sigma-2 (σ2) receptor has been suggested to be a promising target for pharmacological interventions to curb tumor progression. Development of σ2-specific ligands, however, has been hindered by lack of understanding of molecular determinants that underlie selective ligand-σ2 interactions. Here we have explored effects of electron donating and withdrawing groups on ligand selectivity for the σ2 versus σ1 receptor using new benzamide-isoquinoline derivatives. The electron-donating methoxy group increased but the electron-withdrawing nitro group decreased σ2 affinity. In particular, an extra methoxy added to the para-position (5e) of the benzamide phenyl ring of 5f dramatically improved (631 fold) the σ2 selectivity relative to the σ1 receptor. This para-position provided a sensitive site for effective manipulation of the sigma receptor subtype selectivity using either the methoxy or nitro substituent. Our study provides a useful guide for further improving the σ2-over-σ1 selectivity of new ligands.

TMEM97 ablation aggravates oxidant-induced retinal degeneration.

The retinal pigment epithelium (RPE) is critical to the survival of the overlying photoreceptors. Subject to light exposure and active metabolism, the RPE and photoreceptors are particularly susceptible to oxidative damage that plays an important part in age-related macular degeneration (AMD). Recent meta-analyses identified TMEM97 as a new putative AMD risk locus, though it is yet to be functionally verified. The role of TMEM97 in the retina and RPE is not known. Here we investigated TMEM97 function using the sodium iodate model of oxidant-induced retinal degeneration in TMEM97 knockout (KO) mice. We found markedly increased reactive oxygen species (ROS) and loss of photoreceptos in TMEM97 KO mouse retinas relative to wild type (WT) controls. In vitro, sodium iodate treatment of CRISPR-mediated TMEM97 KO RPE cells resulted in diminished abundance of the master antioxidant transcription factor NRF2 and its target gene product SOD2, the mitochondrial superoxide dismutase, as well as elevated ROS and apoptosis markers. Moreover, TMEM97 KO affected proteins key to mitochondrial and lysosomal stability and impeded autophagy flux. These findings suggest that the absence of TMEM97 in RPE cells disturbs redox-balancing systems, thereby heightening oxidative stress. As TMEM97 is a druggable target, this study may inspire interest in basic and translational research in the context of retinal degeneration.

Fibronectin extra domain A (FN-EDA) elevates intraocular pressure through Toll-like receptor 4 signaling.

Elevated intraocular pressure (IOP) is a major risk factor for the development and progression of primary open angle glaucoma and is due to trabecular meshwork (TM) damage, which leads to impaired aqueous humor outflow. Here, we explore a novel molecular mechanism involved in glaucomatous TM damage. We investigated the role of an endogenous Toll-like receptor 4 (TLR4) ligand, fibronectin-EDA (FN-EDA), in TGFß2-induced ocular hypertension in mice. We utilized transgenic mouse strains that either constitutively express only FN containing the EDA isoform or contain an EDA-null allele and express only FN lacking EDA, with or without a mutation in Tlr4, in our inducible mouse model of ocular hypertension by injection of Ad5.TGFß2. IOP was measured over time and eyes accessed by immunohistochemistry for total FN and FN-EDA expression. Constitutively active EDA caused elevated IOP starting at 14 weeks of age. Ad5.TGFß2 induced ocular hypertension in wildtype C57BL/6J mice and further amplified the IOP in constitutively active EDA mice. TLR4 null and EDA null mice blocked Ad5.TGFß-induced ocular hypertension. Total FN and FN-EDA isoform expression increased in response to Ad5.TGFß2. These data suggest that both TLR4 and FN-EDA contribute to TGFß2 induced ocular hypertension.

Duplication of clostridial binding domains for enhanced macromolecular delivery into neurons.

Neurological diseases constitute a quarter of global disease burden and are expected to rise worldwide with the ageing of human populations. There is an increasing need to develop new molecular systems which can deliver drugs specifically into neurons, non-dividing cells meant to last a human lifetime. Neuronal drug delivery must rely on agents which can recognise neurons with high specificity and affinity. Here we used a recently introduced 'stapling' system to prepare macromolecules carrying duplicated binding domains from the clostridial family of neurotoxins. We engineered individual parts of clostridial neurotoxins separately and combined them using a strong alpha-helical bundle. We show that combining two identical binding domains of tetanus and botulinum type D neurotoxins, in a sterically defined way by protein stapling, allows enhanced intracellular delivery of molecules into neurons. We also engineered a botulinum neurotoxin type C variant with a duplicated binding domain which increased enzymatic delivery compared to the native type C toxin. We conclude that duplication of the binding parts of tetanus or botulinum neurotoxins will allow production of high avidity agents which could deliver imaging reagents and large therapeutic enzymes into neurons with superior efficiency.

APEX2-enhanced electron microscopy distinguishes sigma-1 receptor localization in the nucleoplasmic reticulum.

The sigma-1 receptor (Sig1R) is an endoplasmic reticulum chaperonin that is attracting tremendous interest as a potential anti-neurodegenerative target. While this membrane protein is known to reside in the inner nuclear envelope (NE) and influences transcription, apparent Sig1R presence in the nucleoplasm is often observed, seemingly contradicting its NE localization. We addressed this confounding issue by applying an antibody-free approach of electron microscopy (EM) to define Sig1R nuclear localization. We expressed APEX2 peroxidase fused to Sig1R-GFP in a Sig1R-null NSC34 neuronal cell line generated with CRISPR-Cas9. APEX2-catalyzed gold/silver precipitation markedly improved EM clarity and confirmed an apparent intra-nuclear presence of Sig1R. However, serial sectioning combined with APEX2-enhanced EM revealed that Sig1R actually resided in the nucleoplasmic reticulum (NR), a specialized nuclear compartment formed via NE invagination into the nucleoplasm. NR cross-sections also indicated Sig1R in ring-shaped NR membranes. Thus, this study distinguishes Sig1R in the NR which could otherwise appear localized in the nucleoplasm if detected with low-resolution methods. Our finding is important for uncovering potential Sig1R regulations in the nucleus.