Differential assembly diversifies GABAA receptor structures and signalling.

Type A γ-aminobutyric acid receptors (GABAARs) are pentameric ligand-gated chloride channels that mediate fast inhibitory signalling in neural circuits1,2 and can be modulated by essential medicines including general anaesthetics and benzodiazepines3. Human GABAAR subunits are encoded by 19 paralogous genes that can, in theory, give rise to 495,235 receptor types. However, the principles that govern the formation of pentamers, the permutational landscape of receptors that may emerge from a subunit set and the effect that this has on GABAergic signalling remain largely unknown. Here we use cryogenic electron microscopy to determine the structures of extrasynaptic GABAARs assembled from α4, ß3 and δ subunits, and their counterparts incorporating γ2 instead of δ subunits. In each case, we identified two receptor subtypes with distinct stoichiometries and arrangements, all four differing from those previously observed for synaptic, α1-containing receptors4-7. This, in turn, affects receptor responses to physiological and synthetic modulators by creating or eliminating ligand-binding sites at subunit interfaces. We provide structural and functional evidence that selected GABAAR arrangements can act as coincidence detectors, simultaneously responding to two neurotransmitters: GABA and histamine. Using assembly simulations and single-cell RNA sequencing data8,9, we calculated the upper bounds for receptor diversity in recombinant systems and in vivo. We propose that differential assembly is a pervasive mechanism for regulating the physiology and pharmacology of GABAARs.

Cryo-EM structure of the human α1ß3γ2 GABAA receptor in a lipid bilayer.

Type A γ-aminobutyric acid (GABAA) receptors are pentameric ligand-gated ion channels and the main drivers of fast inhibitory neurotransmission in the vertebrate nervous system1,2. Their dysfunction is implicated in a range of neurological disorders, including depression, epilepsy and schizophrenia3,4. Among the numerous assemblies that are theoretically possible, the most prevalent in the brain are the α1ß2/3γ2 GABAA receptors5. The ß3 subunit has an important role in maintaining inhibitory tone, and the expression of this subunit alone is sufficient to rescue inhibitory synaptic transmission in ß1-ß3 triple knockout neurons6. So far, efforts to generate accurate structural models for heteromeric GABAA receptors have been hampered by the use of engineered receptors and the presence of detergents7-9. Notably, some recent cryo-electron microscopy reconstructions have reported 'collapsed' conformations8,9; however, these disagree with the structure of the prototypical pentameric ligand-gated ion channel the Torpedo nicotinic acetylcholine receptor10,11, the large body of structural work on homologous homopentameric receptor variants12 and the logic of an ion-channel architecture. Here we present a high-resolution cryo-electron microscopy structure of the full-length human α1ß3γ2L-a major synaptic GABAA receptor isoform-that is functionally reconstituted in lipid nanodiscs. The receptor is bound to a positive allosteric modulator 'megabody' and is in a desensitized conformation. Each GABAA receptor pentamer contains two phosphatidylinositol-4,5-bisphosphate molecules, the head groups of which occupy positively charged pockets in the intracellular juxtamembrane regions of α1 subunits. Beyond this level, the intracellular M3-M4 loops are largely disordered, possibly because interacting post-synaptic proteins are not present. This structure illustrates the molecular principles of heteromeric GABAA receptor organization and provides a reference framework for future mechanistic investigations of GABAergic signalling and pharmacology.

GABAA receptor signalling mechanisms revealed by structural pharmacology.

Type-A γ-aminobutyric (GABAA) receptors are ligand-gated chloride channels with a very rich pharmacology. Some of their modulators, including benzodiazepines and general anaesthetics, are among the most successful drugs in clinical use and are common substances of abuse. Without reliable structural data, the mechanistic basis for the pharmacological modulation of GABAA receptors remains largely unknown. Here we report several high-resolution cryo-electron microscopy structures in which the full-length human α1ß3γ2L GABAA receptor in lipid nanodiscs is bound to the channel-blocker picrotoxin, the competitive antagonist bicuculline, the agonist GABA (γ-aminobutyric acid), and the classical benzodiazepines alprazolam and diazepam. We describe the binding modes and mechanistic effects of these ligands, the closed and desensitized states of the GABAA receptor gating cycle, and the basis for allosteric coupling between the extracellular, agonist-binding region and the transmembrane, pore-forming region. This work provides a structural framework in which to integrate previous physiology and pharmacology research and a rational basis for the development of GABAA receptor modulators.

Author Correction: GABAA receptor signalling mechanisms revealed by structural pharmacology.

In Fig. 5b, d, the arrows showing transmembrane domain rotations were inadvertently pointing clockwise instead of anticlockwise. Similarly, 'anticlockwise' should have been 'clockwise' in the sentence 'This conformational change of the ECD triggers a clockwise rotation of the TMD.' In Extended Data Table 1, the units of the column 'Model resolution' should have been Å instead of Å2. These errors have been corrected online.

The clinico-pathological spectrum of plaque-type blue naevi and their potential for malignant transformation.

AIMS: Plaque-type blue naevi are rare melanocytic tumours presenting as large, pigmented plaques at birth or during childhood. There is a risk for malignant transformation, but no larger comprehensive studies exist and the diagnosis is challenging, especially on limited biopsy material. The aim is to describe the clinicopathological features and behaviour of the disease more comprehensively. METHODS AND RESULTS: We retrieved eight plaque-type blue naevi, presenting as large, pigmented plaques (median = 7 cm; range = 3-26) most frequently affecting the scalp (four) followed by the cheek, arm, abdominal wall and gluteal cleft (one each), with a slight female predilection. Median age at time of biopsy was 39.5 years (range = 15-90), but three tumours had been present at birth and one since childhood. Histopathologically, the tumours were poorly circumscribed and composed of cellular fascicles of uniform spindle cells in a background of variably prominent pigmented dendritic cells affecting dermis and subcutaneous tissues. The majority had mutations in GNAQ. One tumour showed malignant transformation, characterised by an expansile nodule of pleomorphic epithelioid melanocytes with rhabdoid morphology, high mitotic activity and areas of necrosis. This patient developed metastatic melanoma to lymph nodes. All patients are alive with a median follow-up of 60 months. CONCLUSION: Plaque-type blue naevi are diagnostically challenging tumours with risk for malignant transformation. Awareness and familiarity with the salient clinicopathological features are necessary for reliable diagnosis, and long-term clinical follow-up is required to monitor for malignant transformation.

Navigating the cultural adaptation of a US-based online mental health and social support program for use with young Aboriginal and Torres Strait Islander males in the Northern Territory, Australia: Processes, outcomes, and lessons.

BACKGROUND: Despite disproportionate rates of mental ill-health compared with non-Indigenous populations, few programs have been tailored to the unique health, social, and cultural needs and preferences of young Aboriginal and Torres Strait Islander males. This paper describes the process of culturally adapting the US-based Young Black Men, Masculinities, and Mental Health (YBMen) Project to suit the needs, preferences, culture, and circumstances of Aboriginal and Torres Strait Islander males aged 16-25 years in the Northern Territory, Australia. YBMen is an evidence-based social media-based education and support program designed to promote mental health, expand understandings of gender and cultural identities, and enhance social support in college-aged Black men. METHODS: Our adaptation followed an Extended Stages of Cultural Adaptation model. First, we established a rationale for adaptation that included assessing the appropriateness of YBMen's core components for the target population. We then investigated important and appropriate models to underpin the adapted program and conducted a non-linear, iterative process of gathering information from key sources, including young Aboriginal and Torres Strait Islander males, to inform program curriculum and delivery. RESULTS: To maintain program fidelity, we retained the core curriculum components of mental health, healthy masculinities, and social connection and kept the small cohort, private social media group delivery but developed two models: 'online only' (the original online delivery format) and 'hybrid in-person/online' (combining online delivery with weekly in-person group sessions). Adaptations made included using an overarching Aboriginal and Torres Strait Islander social and emotional wellbeing framework and socio-cultural strengths-based approach; inclusion of modules on health and wellbeing, positive Indigenous masculinities, and respectful relationships; use of Indigenous designs and colours; and prominent placement of images of Aboriginal and Torres Strait Islander male sportspeople, musicians, activists, and local role models. CONCLUSIONS: This process resulted in a culturally responsive mental health, masculinities, and social support health promotion program for young Aboriginal and Torres Strait Islander males. Next steps will involve pilot testing to investigate the adapted program's acceptability and feasibility and inform further refinement.

Applying the antecedent, behaviour, and consequence taxonomy to unintentional firearm injury as determined by a collaborative firearm injury database.

BACKGROUND: Unintentional firearm injury (UFI) remains a significant problem in the USA with respect to preventable injury and death. The antecedent, behaviour and consequence (ABC) taxonomy has been used by law enforcement agencies to evaluate unintentional firearm discharge. Using an adapted ABC taxonomy, we sought to categorise civilian UFI in our community to identify modifiable behaviours. METHODS: Using a collaborative firearm injury database (containing both a university-based level 1 trauma registry and a metropolitan law enforcement database), all UFIs from August 2008 through December 2021 were identified. Perceived threat (antecedent), behaviour and injured party (consequence) were identified for each incident. RESULTS: During the study period, 937 incidents of UFI were identified with 64.2% of incidents occurring during routine firearm tasks. 30.4% of UFI occurred during neglectful firearm behaviour such as inappropriate storage. Most injuries occurred under situations of low perceived threat. UFI involving children was most often due to inappropriate storage of weapons, while cleaning a firearm was the most common behaviour in adults. Overall, 16.5% of UFI involved injury to persons other than the one handling the weapon and approximately 1.3% of UFI resulted in mortality. CONCLUSIONS: The majority of UFI occurred during routine and expected firearm tasks such as firearm cleaning. Prevention programmes should not overlook these modifiable behaviours in an effort to reduce UFIs, complications and deaths.

The occurrence of mental health symptoms in isotretinoin-treated adolescents.

BACKGROUND: Isotretinoin treatment for acne can reduce adverse psychiatric outcomes in adults, but there has been little investigation of the incidence of psychiatric outcomes in treated adolescents. METHODS: This retrospective cohort study using the Rochester Epidemiology Project identified 606 patients aged 12-18 prescribed isotretinoin over a 10-year period between January 1, 2008 and December 31, 2017. Medical records were reviewed to identify psychiatric diagnoses before and during isotretinoin therapy, as well as psychiatric symptoms not captured by formal diagnoses and changes to isotretinoin dosing because of psychiatric diagnoses or symptoms. RESULTS: One hundred seventy-seven (29.2%) had a psychiatric diagnosis prior to isotretinoin initiation, but 98 (16.2%) had a new psychiatric diagnosis or psychiatric symptom while taking isotretinoin. Patients with a psychiatric history were no more likely than those without to receive a new psychiatric diagnosis during treatment (4.5% vs. 3.7%; p = .650), but did experience more psychiatric symptoms, primarily low mood and mood swings (23.7% vs. 7.7%; p < .001). Only 25.5% of the 98 with a new psychiatric diagnosis or psychiatric symptom had a subsequent dose change. A dose change was more likely if patients received a new psychiatric diagnosis (41.7% vs. 20.3%; p = .037) or patients did not have a psychosocial explanation for psychiatric symptoms (34.4% vs. 10.8%; p = .009). CONCLUSIONS: A substantial proportion of adolescent patients prescribed isotretinoin had a prior psychiatric diagnosis. This predicts more psychiatric symptoms during isotretinoin treatment. Adolescents with a psychiatric history who have worsening symptoms and those with new-onset psychiatric symptoms would benefit from close monitoring while taking isotretinoin.

Improving the Therapeutic Index of Smp24, a Venom-Derived Antimicrobial Peptide: Increased Activity against Gram-Negative Bacteria.

Antimicrobial peptides (AMPs) are naturally occurring compounds which possess a rapid killing mechanism and low resistance potential. Consequently, they are being viewed as potential alternatives to traditional antibiotics. One of the major factors limiting further development of AMPs is off-target toxicity. Enhancements to antimicrobial peptides which can maximise antimicrobial activity whilst reducing mammalian cytotoxicity would make these peptides more attractive as future pharmaceuticals. We have previously characterised Smp24, an AMP derived from the venom of the scorpion Scorpio maurus palmatus. This study sought to better understand the relationship between the structure, function and bacterial selectivity of this peptide by performing single amino acid substitutions. The antimicrobial, haemolytic and cytotoxic activity of modified Smp24 peptides was determined. The results of these investigations were compared with the activity of native Smp24 to determine which modifications produced enhanced therapeutic indices. The structure-function relationship of Smp24 was investigated by performing N-terminal, mid-chain and C-terminal amino acid substitutions and determining the effect that they had on the antimicrobial and cytotoxic activity of the peptide. Increased charge at the N-, mid- and C-termini of the peptide resulted in increased antimicrobial activity. Increased hydrophobicity at the N-terminus resulted in reduced haemolysis and cytotoxicity. Reduced antimicrobial, haemolytic and cytotoxic activity was observed by increased hydrophobicity at the mid-chain. Functional improvements have been made to modified peptides when compared with native Smp24, which has produced peptides with enhanced therapeutic indices.

Spray Pattern and Plume Geometry Testing and Methodology: An IPAC-RS Working Group Overview.

Plume characterization for orally inhaled and nasal drug products (OINDP) provides valuable information during OINDP development. Spray pattern and plume geometry techniques, methods, and technology have evolved over the past 20 years since the publication of the original 1998 FDA MDI DPI draft guidance. The International Pharmaceutical Aerosol Consortium on Regulation and Science (IPAC-RS) discusses the historical context and background to plume geometry and spray pattern characterization studies; provides an analysis of the current regulatory context; addresses results from its industry surveys on application and value of such testing; and presents case studies and best practices-seeking to provide insights to regulatory bodies and other stakeholders. Assessment and consideration of published studies and industry experience note the value of plume geometry and spray pattern in development, and that further data is needed regarding their use in assessing formulation characteristics. Continued dialogue between industry and regulatory bodies is needed to establish the optimum use of these techniques.