The role of sigma 1 receptor in organization of endoplasmic reticulum signaling microdomains

Sigma 1 receptor (S1R) is a 223-amino-acid-long transmembrane endoplasmic reticulum (ER) protein. S1R modulates activity of multiple effector proteins and is a well-established drug target. However, signaling functions of S1R in cells are poorly understood. Here, we test the hypothesis that biological activity of S1R in cells can be explained by its ability to interact with cholesterol and to form cholesterol-enriched microdomains in the ER membrane. By performing experiments in reduced reconstitution systems, we demonstrate direct effects of cholesterol on S1R clustering. We identify a novel cholesterol-binding motif in the transmembrane region of human S1R. Mutations of this motif impair association of recombinant S1R with cholesterol beads, affect S1R clustering in vitro and disrupt S1R subcellular localization. We demonstrate that S1R-induced membrane microdomains have increased local membrane thickness and that increased local cholesterol concentration and/or membrane thickness in these microdomains can modulate signaling of inositol-requiring enzyme 1α in the ER. Further, S1R agonists cause disruption of S1R clusters, suggesting that biological activity of S1R agonists is linked to remodeling of ER membrane microdomains. Our results provide novel insights into S1R-mediated signaling mechanisms in cells.

Sigma-1 Receptor (S1R) Interaction with Cholesterol: Mechanisms of S1R Activation and Its Role in Neurodegenerative Diseases

The sigma-1 receptor (S1R) is a 223 amino acid-long transmembrane endoplasmic reticulum (ER) protein. The S1R modulates the activity of multiple effector proteins, but its signaling functions are poorly understood. S1R is associated with cholesterol, and in our recent studies we demonstrated that S1R association with cholesterol induces the formation of S1R clusters. We propose that these S1R-cholesterol interactions enable the formation of cholesterol-enriched microdomains in the ER membrane. We hypothesize that a number of secreted and signaling proteins are recruited and retained in these microdomains. This hypothesis is consistent with the results of an unbiased screen for S1R-interacting partners, which we performed using the engineered ascorbate peroxidase 2 (APEX2) technology. We further propose that S1R agonists enable the disassembly of these cholesterol-enriched microdomains and the release of accumulated proteins such as ion channels, signaling receptors, and trophic factors from the ER. This hypothesis may explain the pleotropic signaling functions of the S1R, consistent with previously observed effects of S1R agonists in various experimental systems.

Sigma 1 Receptor, Cholesterol and Endoplasmic Reticulum Contact Sites

Recent studies indicated potential importance of membrane contact sites (MCS) between the endoplasmic reticulum (ER) and other cellular organelles. These MCS have unique protein and lipid composition and serve as hubs for inter-organelle communication and signaling. Despite extensive investigation of MCS protein composition and functional roles, little is known about the process of MCS formation. In this perspective, we propose a hypothesis that MCS are formed not as a result of random interactions between membranes of ER and other organelles but on the basis of pre-existing cholesterol-enriched ER microdomains.

Crystal structure of the SH3 domain of growth factor receptor-bound protein 2

This study presents the crystal structure of the N-terminal SH3 (SH3N) domain of growth factor receptor-bound protein 2 (Grb2) at 2.5 Å resolution. Grb2 is a small (215-amino-acid) adaptor protein that is widely expressed and involved in signal transduction/cell communication. The crystal structure of full-length Grb2 has previously been reported (PDB entry 1gri). The structure of the isolated SH3N domain is consistent with the full-length structure. The structure of the isolated SH3N domain was solved at a higher resolution (2.5 Å compared with 3.1 Å for the previously deposited structure) and made it possible to resolve some of the loops that were missing in the full-length structure. In addition, interactions between the carboxy-terminal region of the SH3N domain and the Sos1-binding sites were observed in the structure of the isolated domain. Analysis of these interactions provided new information about the ligand-binding properties of the SH3N domain of Grb2.

Light-sheet microscopy of cleared tissues with isotropic, subcellular resolution

We present cleared tissue Axially Swept Light-Sheet Microscopy (ctASLM), which enables isotropic, subcellular resolution, high optical sectioning capability, and large field of view imaging over a broad range of immersion media. ctASLM can image live, expanded, and both aqueous and organic chemically cleared tissue preparations. Depending on the optical configuration, ctASLM provides up to 260 nm axial resolution, an improvement over confocal and other reported cleared tissue light-sheet microscopes by a factor 3–10. We image millimeter-scale tissues with subcellular 3D resolution, which enabled us to automatically detect with computer vision multicellular tissue architectures, individual cells, synaptic spines, and rare cell-cell interactions.

Mutational Analysis of Sigma-1 Receptor's Role in Synaptic Stability

Sigma-1 receptor (S1R) is an endoplasmic reticulum (ER) resident transmembrane protein. In our previous experiments, we demonstrated neuroprotective effects of pridopidine, an agonist of S1R, in cellular and animal models of Huntington’s disease (HD) and Alzheimer’s disease (AD). Consistent with previous observations, deletion of endogenous S1R with CRISPR/Cas9 in cultured hippocampal neurons resulted in fewer mushroom-shaped dendritic spines. Overexpression of human S1R restored mushroom spine density to control levels. In contrast, overexpression of S1R with the Δ31–50 deletion (linked to distal hereditary motor neuropathy) or the E102Q mutation (linked to amyotrophic lateral sclerosis) destabilized mushroom spines. Recently a crystal structure of S1R was determined in lipidic cubic phase. In the present study, we took an advantage of this structural information and performed docking studies with pridopidine and the S1R structural model. We generated a series of S1R point mutations based on residues predicted to be involved in direct association with pridopidine. We discovered that all ligand binding-site mutants were able to compensate for loss of endogenous S1R. However, most of these mutants were not able to support pridopidine-induced rescue of mushroom spines in presenilin-1-mutant cultures. Our mutational analysis was in agreement with in silico docking based on the published S1R crystal structure, with an exception of R119 residue. Our data also suggest that basal S1R activity is required for mature spine stability, whereas agonist-mediated S1R activity is required for stabilization of mushroom spines in the context of disease-causing mutations.

Neuronal Sigma-1 Receptors: Signaling Functions and Protective Roles in Neurodegenerative Diseases

Sigma-1 receptor (S1R) is a multi-functional, ligand-operated protein situated in endoplasmic reticulum (ER) membranes and changes in its function and/or expression have been associated with various neurological disorders including amyotrophic lateral sclerosis/frontotemporal dementia, Alzheimer's (AD) and Huntington's diseases (HD). S1R agonists are broadly neuroprotective and this is achieved through a diversity of S1R-mediated signaling functions that are generally pro-survival and anti-apoptotic; yet, relatively little is known regarding the exact mechanisms of receptor functioning at the molecular level. This review summarizes therapeutically relevant mechanisms by which S1R modulates neurophysiology and implements neuroprotective functions in neurodegenerative diseases. These mechanisms are diverse due to the fact that S1R can bind to and modulate a large range of client proteins, including many ion channels in both ER and plasma membranes. We summarize the effect of S1R on its interaction partners and consider some of the cell type- and disease-specific aspects of these actions. Besides direct protein interactions in the endoplasmic reticulum, S1R is likely to function at the cellular/interorganellar level by altering the activity of several plasmalemmal ion channels through control of trafficking, which may help to reduce excitotoxicity. Moreover, S1R is situated in lipid rafts where it binds cholesterol and regulates lipid and protein trafficking and calcium flux at the mitochondrial-associated membrane (MAM) domain. This may have important implications for MAM stability and function in neurodegenerative diseases as well as cellular bioenergetics. We also summarize the structural and biochemical features of S1R proposed to underlie its activity. In conclusion, S1R is incredibly versatile in its ability to foster neuronal homeostasis in the context of several neurodegenerative disorders.

Molecular genetic analysis of Mycobacterium tuberculosis strains spread in different patient groups in St. Petersburg, Russia

Molecular epidemiological features of Mycobacterium tuberculosis strains among different patient groups in Russia have not been studied well. The aim of our study was to compare the genotypes of M. tuberculosis strains circulating among tuberculosis (TB) patients from different groups: homeless, human immunodeficiency virus (HIV)-infected, prisoners, and the general population of St. Petersburg citizens. One hundred and forty-two M. tuberculosis complex isolates from different TB patient groups were studied using the spacer oligonucleotide typing (spoligotyping) method. The majority of the studied M. tuberculosis isolates in all groups belonged to the Beijing family (55% among homeless; 77% among HIV-infected; 60% among the general population; 81% among prisoners). There were no significant differences in the Beijing family prevalence among homeless patients, HIV/TB co-infected patients, and the general population of TB patients. The lowest genetic diversity of the pathogen was detected among imprisoned patients. The results of our study demonstrate that M. tuberculosis strains circulating among patients from high-risk groups are also spread among the general population of St. Petersburg citizens.

Tuberculosis in St. Petersburg and the Baltic Sea region

Tuberculosis (TB) remains a global public health concern and challenges the national structures for infection control and health care, as well as international institutions, to develop and implement new strategies to control and combat this disease. In our report, we investigated the TB epidemiological situation in St. Petersburg and the countries around the Baltic Sea using national epidemiological statistics and epidemiological reports of international organizations, such as the WHO and Euro-TB. After the disintegration of the Soviet Union, a steep increase in tuberculosis was seen in the Russian Federation, St. Petersburg and the Baltic States, after which it stabilized at levels significantly higher compared to the Nordic countries. Moreover, the epidemiological situation in St. Petersburg and the Baltic States was aggravated by the emergence and spread of TB/HIV coinfection, as well as that of drug-resistant M. tuberculosis, which imposed further difficulties in gaining control of TB. During the studied period, the TB burden in neither St. Petersburg nor Baltic States has had a significant impact on the epidemiology in the low TB burden neighbouring countries around the Baltic Sea.

Barriers to completion of tuberculosis treatment among prisoners and former prisoners in St. Petersburg, Russia

SETTING

St. Petersburg, Russian Federation.

OBJECTIVES

To identify barriers to the completion of tuberculosis (TB) treatment among prisoners and former prisoners in St Petersburg, Russia.

DESIGN

Questionnaires were administered to 60 prisoners and 40 former prisoners. Interviews were performed with prison and TB dispensary staff. Treatment follow-up rates were estimated by matching prison release records against attendance records from all 17 St. Petersburg-based TB dispensaries over an 18-month period.

RESULTS

Of 80 released prisoners with active TB in 2002, 21 (26.3%) appeared in dispensary attendance records. Barriers to the completion of TB treatment overall were homelessness, unemployment, alcoholism, drug addiction and difficulty tolerating TB medications with co-morbid illnesses such as human immunodeficiency virus and hepatitis. Prisoners and former prisoners ranked help with obtaining an internal passport and money first, followed closely by food and a job, as the most desirable incentives to completing TB treatment.

CONCLUSIONS

A future program for soon-to-be released and released prisoners in St. Petersburg that offers an array of desirable flexible social welfare services and incentives has the potential to attract and retain patients within TB treatment, but continued efforts must also be made to include drug treatment, job training and keeping former prisoners out of prison.

TB and HIV in St Petersburg, Russia: a looming catastrophe?

BACKGROUND

After decades of improved tuberculosis (TB) control in Russia, notification rates started to rise in 1992. Russia also faces a fast growing human immunodeficiency virus (HIV) epidemic.

OBJECTIVE

To document the extent and characteristics of HIV co-infection in TB patients in St Petersburg, Russia.

DESIGN

A prospective cross-sectional study of HIV coinfected culture-positive TB cases. Between 15 June 2002 and 31 March 2003, TB cases at the St Petersburg City TB hospitals and dispensaries were screened for HIV infection. At the HIV Prevention and Treatment Center, HIV-infected individuals were offered TB screening.

RESULTS

Forty-nine HIV-infected culture-positive TB cases were identified, mainly at TB hospitals and dispensaries. Most were new pulmonary TB cases. The majority were young (69% < or = 30 years of age), male (84%), unemployed (94%) individuals with a history of injection drug use (IDU) (92%), and, in 35% of cases a history of incarceration. Active case finding was high among contacts of cases (9%), but was not successful in HIV-infected IDUs.

CONCLUSION

Although the HIV seroprevalence rate is rising among TB patients, HIV does not yet appear to be driving the St Petersburg TB epidemic. Aggressive collaborative TB-HIV control efforts may still avert adverse effects of HIV on the TB epidemic.