Androgen receptors and muscle: a key mechanism underlying life history trade-offs

Prioritizing Pesticides of Potential Concern and Identifying Potential Mixture Effects in Great Lakes Tributaries Using Passive Samplers

To help meet the objectives of the Great Lakes Restoration Initiative with regard to increasing knowledge about toxic substances, 223 pesticides and pesticide transformation products were monitored in 15 Great Lakes tributaries using polar organic chemical integrative samplers. A screening-level assessment of their potential for biological effects was conducted by computing toxicity quotients (TQs) for chemicals with available US Environmental Protection Agency (USEPA) Aquatic Life Benchmark values. In addition, exposure activity ratios (EAR) were calculated using information from the USEPA ToxCast database. Between 16 and 81 chemicals were detected per site, with 97 unique compounds detected overall, for which 64 could be assessed using TQs or EARs. Ten chemicals exceeded TQ or EAR levels of concern at two or more sites. Chemicals exceeding thresholds included seven herbicides (2,4-dichlorophenoxyacetic acid, diuron, metolachlor, acetochlor, atrazine, simazine, and sulfentrazone), a transformation product (deisopropylatrazine), and two insecticides (fipronil and imidacloprid). Watersheds draining agricultural and urban areas had more detections and higher concentrations of pesticides compared with other land uses. Chemical mixtures analysis for ToxCast assays associated with common modes of action defined by gene targets and adverse outcome pathways (AOP) indicated potential activity on biological pathways related to a range of cellular processes, including xenobiotic metabolism, extracellular signaling, endocrine function, and protection against oxidative stress. Use of gene ontology databases and the AOP knowledgebase within the R-package ToxMixtures highlighted the utility of ToxCast data for identifying and evaluating potential biological effects and adverse outcomes of chemicals and mixtures. Results have provided a list of high-priority chemicals for future monitoring and potential biological effects warranting further evaluation in laboratory and field environments. Environ Toxicol Chem 2023;42:340-366. Published 2022. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Skeletal Muscle Pathogenesis in Polyglutamine Diseases

Polyglutamine diseases are characterized by selective dysfunction and degeneration of specific types of neurons in the central nervous system. In addition, nonneuronal cells can also be affected as a consequence of primary degeneration or due to neuronal dysfunction. Skeletal muscle is a primary site of toxicity of polyglutamine-expanded androgen receptor, but it is also affected in other polyglutamine diseases, more likely due to neuronal dysfunction and death. Nonetheless, pathological processes occurring in skeletal muscle atrophy impact the entire body metabolism, thus actively contributing to the inexorable progression towards the late and final stages of disease. Skeletal muscle atrophy is well recapitulated in animal models of polyglutamine disease. In this review, we discuss the impact and relevance of skeletal muscle in patients affected by polyglutamine diseases and we review evidence obtained in animal models and patient-derived cells modeling skeletal muscle.

The T850D Phosphomimetic Mutation in the Androgen Receptor Ligand Binding Domain Enhances Recruitment at Activation Function 2

Several key functions of the androgen receptor (AR) such as hormone recognition and co-regulator recruitment converge in the ligand binding domain (LBD). Loss- or gain-of-function of the AR contributes to pathologies such as the androgen insensitivity syndrome and prostate cancer. Here, we describe a gain-of-function mutation of the surface-exposed threonine at position 850, located at the amino-terminus of Helix 10 (H10) in the AR LBD. Since T850 phosphorylation was reported to affect AR function, we created the phosphomimetic mutation T850D. The AR T850D variant has a 1.5- to 2-fold increased transcriptional activity with no effect on ligand affinity. In the androgen responsive LNCaP cell line grown in medium with low androgen levels, we observed a growth advantage for cells in which the endogenous AR was replaced by AR T850D. Despite the distance to the AF2 site, the AR T850D LBD displayed an increased affinity for coactivator peptides as well as the ²³FQNLF²⁷ motif of AR itself. Molecular Dynamics simulations confirm allosteric transmission of the T850D mutation towards the AF2 site via extended hydrogen bond formation between coactivator peptide and AF2 site. This mechanistic study thus confirms the gain-of-function character of T850D and T850 phosphorylation for AR activity and reveals details of the allosteric communications within the LBD.

The body region specificity in murine models of muscle regeneration and atrophy

AIM

Skeletal muscles are distributed throughout the body, presenting a variety of sizes, shapes and functions. Here, we examined whether muscle regeneration and atrophy occurred homogeneously throughout the body in mouse models.

METHODS

Acute muscle regeneration was induced by a single intramuscular injection of cardiotoxin in adult mice. Chronic muscle regeneration was assessed in mdx mice. Muscle atrophy in different muscles was evaluated by cancer cachexia, ageing and castration mouse models.

RESULTS

We found that, in the cardiotoxin-injected acute muscle injury model, head muscles slowly regenerated, while limb muscles exhibited a rapid regeneration and even overgrowth. This overgrowth was also observed in limb muscles alone (but not in head muscles) in mdx mice as chronic injury models. We described the body region-specific decline in the muscle mass in muscle atrophy models: cancer cachexia-induced, aged and castrated mice. The positional identities, including gene expression profiles and hormone sensitivity, were robustly preserved in the ectopically engrafted satellite cell-derived muscles in the castrated model.

CONCLUSION

Our results indicate that positional identities in muscles should be considered for the development of efficient regenerative therapies for muscle weakness, such as muscular dystrophy and age-related sarcopenia.

Muscle, a conduit to brain for hormonal control of behavior

SBN Elsevier Lecture Investigation into mechanisms whereby hormones control behavior often starts with actions on central nervous system (CNS) motivation and motor systems and is followed by assessment of CNS drive of coordinated striated muscle contractions. Here we turn this perspective on its head by discussing ways in which hormones might first act on muscle that then secondarily drive upstream the evolution and function of the CNS. While there is a lengthy history for consideration of this perspective, newly discovered properties of muscle signaling reveal novel mechanisms that may well be captured by endocrine systems and thus of interest to behavioral endocrinologists.

Evaluating Muscle Mass in Survivors of Acute Respiratory Distress Syndrome: A 1-Year Multicenter Longitudinal Study

OBJECTIVES

Rapid muscle wasting occurs during acute respiratory failure, resulting in muscle weakness and functional impairments. This study examines survivors' body composition in the year after acute respiratory distress syndrome and tests associations of patient characteristics, hospital exposures, and survivors' strength and physical functioning with whole body percent lean mass.

DESIGN

Prospective cohort study with 6- and 12-month follow-up.

SETTING

National study enrolling patients from five study centers.

PATIENTS

Acute respiratory distress syndrome survivors (n = 120).

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

Lean and fat mass from dual energy x-ray absorptiometry. On average, survivors gained whole body total mass (+1.4 kg; 0.1-2.7) and fat mass (+1.2 kg; 0.2-2.2) and maintained lean mass (+0.2 kg; -0.4 to 0.8) between 6 and 12 months. Proportionally, percent fat mass increased and percent lean mass decreased for the whole body, trunk, and legs (p < 0.05). Greater whole body percent lean mass was associated with younger age, male sex, and lower baseline body mass index, but not other patient characteristics or ICU/hospital exposures. Greater percent lean mass was also significantly associated with gait speed and 6-minute walk distance, but not volitional strength or self-reported functional status.

CONCLUSIONS

In the first year after acute respiratory distress syndrome, patients gained fat mass and maintained lean mass. We found no association of whole body percent lean mass with commonly hypothesized hospital risk factors. Direct measurement of body composition and performance-based functional measures may be helpful for understanding functional recovery in ICU survivors.

Targeting the Polyadenylation Signal of Pre-mRNA: A New Gene Silencing Approach for Facioscapulohumeral Dystrophy

Facioscapulohumeral dystrophy (FSHD) is characterized by the contraction of the D4Z4 array located in the sub-telomeric region of the chromosome 4, leading to the aberrant expression of the DUX4 transcription factor and the mis-regulation of hundreds of genes. Several therapeutic strategies have been proposed among which the possibility to target the polyadenylation signal to silence the causative gene of the disease. Indeed, defects in mRNA polyadenylation leads to an alteration of the transcription termination, a disruption of mRNA transport from the nucleus to the cytoplasm decreasing the mRNA stability and translation efficiency. This review discusses the polyadenylation mechanisms, why alternative polyadenylation impacts gene expression, and how targeting polyadenylation signal may be a potential therapeutic approach for FSHD.