Cryo-EM structures of eukaryotic translation termination and ribosome recycling complexes containing eRF1, eRF3 and ABCE1

Translation of an mRNA template into a polypeptide chain is terminated on a stop codon. The stop is recognized in the ribosomal A site by release factors, that subsequently release the polypeptide. This event is followed by ribosome recycling leading to a dissociation of the ribosome into subunits. Eukaryotic eRF1 recognizes all three stop codons and is delivered to the ribosomal A site in a ternary complex with GTP-bound eRF3. ABCE1, a highly conserved ATPase, stimulates peptide release and splits the ribosome in concert with eRF1. The first goal of this work was to study the structural rearrangements of eRF1, eRF3 and ABCE1 on the ribosome during translation termination and ribosome recycling. Two cryo-EM structures were obtained at sub-nanometer resolution: the pre-termination complex containing eRF1 and eRF3, and a termination/pre-recycling complex containing eRF1 and ABCE1. The pre-termination stage showed eRF1 packed against eRF3, unable to catalyze peptide release. In the termination/pre-recycling complex, eRF1 assumed an extended conformation which is further stabilized by ABCE1, with the central domain of eRF1 swung out toward the CCA end of the P-site tRNA. ABCE1 adopted a half-closed conformation of its two nucleotide-binding domains in the termination/pre-recycling complex. According to a model based of these results, splitting the ribosome would require the closing of the two nucleotide-binding domains and a rotation of the iron-sulfur cluster domain of ABCE1, which would in turn push eRF1 into the intersubunit space. Supporting this idea, ABCE1 was shown to remain bound to the small ribosomal subunit after in vitro splitting. 40S-bound ABCE1 adopted a fully closed conformation and in which re-association of the large ribosomal subunit is prevented. As a second goal of this work, native S. cerevisiae ABCE1-bound small ribosomal subunits were purified to complement the in vitro studies and explore the supposed involvement of ABCE1 in translation initiation. Cryo-EM of native 40S-ABCE1 complexes indeed confirmed the closed conformation of ABCE1. Moreover, these complexes were associated with initiator tRNA and eIF1A, an initiation factor which binds the ribosomal A site and is involved in multiple processes in initiation including subunit joining. These results are clearly hinting at an active role of ABCE1 during translation initiation. Yet, the exact role of ABCE1 will be subject of further studies

Amyloid pathology but not APOE ε4 status is permissive for tau-related hippocampal dysfunction

We investigated whether the impact of tau-pathology on memory performance and on hippocampal/medial temporal memory function in non-demented individuals depends on the presence of amyloid pathology, irrespective of diagnostic clinical stage. We conducted a cross-sectional analysis of the observational, multicentric DZNE-Longitudinal Cognitive Impairment and Dementia Study (DELCODE). Two hundred and thirty-five participants completed task functional MRI and provided CSF (92 cognitively unimpaired, 100 experiencing subjective cognitive decline and 43 with mild cognitive impairment). Presence (A+) and absence (A-) of amyloid pathology was defined by CSF amyloid-β42 (Aβ42) levels. Free recall performance in the Free and Cued Selective Reminding Test, scene recognition memory accuracy and hippocampal/medial temporal functional MRI novelty responses to scene images were related to CSF total-tau and phospho-tau levels separately for A+ and A- individuals. We found that total-tau and phospho-tau levels were negatively associated with memory performance in both tasks and with novelty responses in the hippocampus and amygdala, in interaction with Aβ42 levels. Subgroup analyses showed that these relationships were only present in A+ and remained stable when very high levels of tau (>700 pg/ml) and phospho-tau (>100 pg/ml) were excluded. These relationships were significant with diagnosis, age, education, sex, assessment site and Aβ42 levels as covariates. They also remained significant after propensity score based matching of phospho-tau levels across A+ and A- groups. After classifying this matched sample for phospho-tau pathology (T-/T+), individuals with A+/T+ were significantly more memory-impaired than A-/T+ despite the fact that both groups had the same amount of phospho-tau pathology. ApoE status (presence of the E4 allele), a known genetic risk factor for Alzheimer's disease, did not mediate the relationship between tau pathology and hippocampal function and memory performance. Thus, our data show that the presence of amyloid pathology is associated with a linear relationship between tau pathology, hippocampal dysfunction and memory impairment, although the actual severity of amyloid pathology is uncorrelated. Our data therefore indicate that the presence of amyloid pathology provides a permissive state for tau-related hippocampal dysfunction and hippocampus-dependent recognition and recall impairment. This raises the possibility that in the predementia stage of Alzheimer's disease, removing the negative impact of amyloid pathology could improve memory and hippocampal function even if the amount of tau-pathology in CSF is not changed, whereas reducing increased CSF tau-pathology in amyloid-negative individuals may not proportionally improve memory function

Rightward hemispheric asymmetries in auditory language cortex in children with autistic disorder: an MRI investigation

Purpose: determine if language disorder in children with autistic disorder (AD) corresponds to abnormalities in hemispheric asymmetries in auditory language cortex. Methods: MRI morphometric study in children with AD (n = 50) to assess hemispheric asymmetries in auditory language cortex. A key region of interest was the planum temporale (PT), which is larger in the left hemisphere in most healthy individuals. Results: (i) Heschl’s gyrus and planum polare showed typical hemisphere asymmetry patterns; (ii) posterior Superior Temporal Gyrus (pSTG) showed significant rightward asymmetry; and (iii) PT showed a trend for rightward asymmetry that was significant when constrained to right-handed boys (n = 30). For right-handed boys, symmetry indices for pSTG were significantly positively correlated with those for PT. PT asymmetry was age dependent, with greater rightward asymmetry with age. Conclusions: results provide evidence for rightward asymmetry in auditory association areas (pSTG and PT) known to subserve language processing. Cumulatively, our data provide evidence for a differing maturational path for PT for lower functioning children with AD, with both pre- and post-natal experience likely playing a role in PT asymmetry

Oxygen-regulated gene expression in murine cumulus cells

Oxygen is an important component of the environment of the cumulus–oocyte complex (COC), both in vivo within the ovarian follicle and during in vitro oocyte maturation (IVM). Cumulus cells have a key role in supporting oocyte development, and cumulus cell function and gene expression are known to be altered when the environment of the COC is perturbed. Oxygen-regulated gene expression is mediated through the actions of the transcription factors, the hypoxia-inducible factors (HIFs). In the present study, the effect of oxygen on cumulus cell gene expression was examined following in vitro maturation of the murine COC at 2%, 5% or 20% oxygen. Increased expression of HIF-responsive genes, including glucose transporter-1, lactate dehydrogenase A and BCL2/adenovirus E1B interacting protein 3, was observed in cumulus cells matured at 2% or 5%, compared with 20% oxygen. Stabilisation of HIF1α protein in cumulus cells exposed to low oxygen was confirmed by western blot and HIF-mediated transcriptional activity was demonstrated using a transgenic mouse expressing green fluorescent protein under the control of a promoter containing hypoxia response elements. These results indicate that oxygen concentration influences cumulus cell gene expression and support a role for HIF1α in mediating the cumulus cell response to varying oxygen.Karen L. Kind, Kimberley K. Y. Tam, Kelly M. Banwell, Ashley D. Gauld, Darryl L. Russell, Anne M. Macpherson, Hannah M. Brown, Laura A. Frank, Daniel J. Peet and Jeremy G. Thompso

Cryoelectron Microscopic Structures of Eukaryotic Translation Termination Complexes Containing eRF1-eRF3 or eRF1-ABCE1

Termination and ribosome recycling are essential processes in translation. In eukaryotes, a stop codon in the ribosomal A site is decoded by a ternary complex consisting of release factors eRF1 and guanosine triphosphate (GTP)-bound eRF3. After GTP hydrolysis, eRF3 dissociates, and ABCE1 can bind to eRF1-loaded ribosomes to stimulate peptide release and ribosomal subunit dissociation. Here, we present cryoelectron microscopic (cryo-EM) structures of a pretermination complex containing eRF1-eRF3 and a termination/prerecycling complex containing eRF1-ABCE1. eRF1 undergoes drastic conformational changes: its central domain harboring the catalytically important GGQ loop is either packed against eRF3 or swung toward the peptidyl transferase center when bound to ABCE1. Additionally, in complex with eRF3, the N-terminal domain of eRF1 positions the conserved NIKS motif proximal to the stop codon, supporting its suggested role in decoding, yet it appears to be delocalized in the presence of ABCE1. These results suggest that stop codon decoding and peptide release can be uncoupled during termination

Development and validation of a brief dementia screening indicator for primary care

BackgroundDetection of “any cognitive impairment” is mandated as part of the Medicare annual wellness visit, but screening all patients may result in excessive false positives.MethodsWe developed and validated a brief Dementia Screening Indicator using data from four large, ongoing cohort studies (the Cardiovascular Health Study [CHS]; the Framingham Heart Study [FHS]; the Health and Retirement Study [HRS]; the Sacramento Area Latino Study on Aging [SALSA]) to help clinicians identify a subgroup of high‐risk patients to target for cognitive screening.ResultsThe final Dementia Screening Indicator included age (1 point/year; ages, 65–79 years), less than 12 years of education (9 points), stroke (6 points), diabetes mellitus (3 points), body mass index less than 18.5 kg/m2 (8 points), requiring assistance with money or medications (10 points), and depressive symptoms (6 points). Accuracy was good across the cohorts (Harrell’s C statistic: CHS, 0.68; FHS, 0.77; HRS, 0.76; SALSA, 0.78).ConclusionsThe Dementia Screening Indicator is a simple tool that may be useful in primary care settings to identify high‐risk patients to target for cognitive screening.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/152503/1/alzjjalz201311006.pd

Arterial hypertension and β-amyloid accumulation have spatially overlapping effects on posterior white matter hyperintensity volume: a cross-sectional study

Abstract Background White matter hyperintensities (WMH) in subjects across the Alzheimer’s disease (AD) spectrum with minimal vascular pathology suggests that amyloid pathology—not just arterial hypertension—impacts WMH, which in turn adversely influences cognition. Here we seek to determine the effect of both hypertension and Aβ positivity on WMH, and their impact on cognition. Methods We analysed data from subjects with a low vascular profile and normal cognition (NC), subjective cognitive decline (SCD), and amnestic mild cognitive impairment (MCI) enrolled in the ongoing observational multicentre DZNE Longitudinal Cognitive Impairment and Dementia Study (n = 375, median age 70.0 [IQR 66.0, 74.4] years; 178 female; NC/SCD/MCI 127/162/86). All subjects underwent a rich neuropsychological assessment. We focused on baseline memory and executive function—derived from multiple neuropsychological tests using confirmatory factor analysis—, baseline preclinical Alzheimer’s cognitive composite 5 (PACC5) scores, and changes in PACC5 scores over the course of three years (ΔPACC5). Results Subjects with hypertension or Aβ positivity presented the largest WMH volumes (p FDR  < 0.05), with spatial overlap in the frontal (hypertension: 0.42 ± 0.17; Aβ: 0.46 ± 0.18), occipital (hypertension: 0.50 ± 0.16; Aβ: 0.50 ± 0.16), parietal lobes (hypertension: 0.57 ± 0.18; Aβ: 0.56 ± 0.20), corona radiata (hypertension: 0.45 ± 0.17; Aβ: 0.40 ± 0.13), optic radiation (hypertension: 0.39 ± 0.18; Aβ: 0.74 ± 0.19), and splenium of the corpus callosum (hypertension: 0.36 ± 0.12; Aβ: 0.28 ± 0.12). Elevated global and regional WMH volumes coincided with worse cognitive performance at baseline and over 3 years (p FDR  < 0.05). Aβ positivity was negatively associated with cognitive performance (direct effect—memory: − 0.33 ± 0.08, p FDR  < 0.001; executive: − 0.21 ± 0.08, p FDR  < 0.001; PACC5: − 0.29 ± 0.09, p FDR  = 0.006; ΔPACC5: − 0.34 ± 0.04, p FDR  < 0.05). Splenial WMH mediated the relationship between hypertension and cognitive performance (indirect-only effect—memory: − 0.05 ± 0.02, p FDR  = 0.029; executive: − 0.04 ± 0.02, p FDR  = 0.067; PACC5: − 0.05 ± 0.02, p FDR  = 0.030; ΔPACC5: − 0.09 ± 0.03, p FDR  = 0.043) and WMH in the optic radiation partially mediated that between Aβ positivity and memory (indirect effect—memory: − 0.05 ± 0.02, p FDR  = 0.029). Conclusions Posterior white matter is susceptible to hypertension and Aβ accumulation. Posterior WMH mediate the association between these pathologies and cognitive dysfunction, making them a promising target to tackle the downstream damage related to the potentially interacting and potentiating effects of the two pathologies. Trial registration German Clinical Trials Register (DRKS00007966, 04/05/2015)