Structural Analysis Reveals the Deleterious Effects of Telomerase Mutations in Bone Marrow Failure Syndromes

Naturally occurring mutations in the ribonucleoprotein reverse transcriptase, telomerase, are associated with the bone marrow failure syndromes dyskeratosis congenita, aplastic anemia, and idiopathic pulmonary fibrosis. However, the mechanism by which these mutations impact telomerase function remains unknown. Here we present the structure of the human telomerase C-terminal extension (or thumb domain) determined by the method of single-wavelength anomalous diffraction to 2.31 Å resolution. We also used direct telomerase activity and nucleic acid binding assays to explain how naturally occurring mutations within this portion of telomerase contribute to human disease. The single mutations localize within three highly conserved regions of the telomerase thumb domain referred to as motifs E-I (thumb loop and helix), E-II, and E-III (the FVYL pocket, comprising the hydrophobic residues Phe-1012, Val-1025, Tyr-1089, and Leu-1092). Biochemical data show that the mutations associated with dyskeratosis congenita, aplastic anemia, and idiopathic pulmonary fibrosis disrupt the binding between the protein subunit reverse transcriptase of the telomerase and its nucleic acid substrates leading to loss of telomerase activity and processivity. Collectively our data show that although these mutations do not alter the overall stability or expression of telomerase reverse transcriptase, these rare genetic disorders are associated with an impaired telomerase holoenzyme that is unable to correctly assemble with its nucleic acid substrates, leading to incomplete telomere extension and telomere attrition, which are hallmarks of these diseases.

Abstract WP144: Ultrasound Criteria for Assessment of Vertebral Artery Origins

Introduction: We sought to validate ultrasound as a reliable means of assessing vessel stenosis of vertebral artery origins.

Methods: We reviewed 1135 patient charts with ultrasound of the posterior circulation performed 2008-2015 in our Neurovascular Laboratory Imaging Institute. Inclusion criteria consisted of ultrasound and digital subtraction angiography (DSA) performed within three months as well as absence of prior stent placement, resulting in 218 vessels in 133 patients. Using DSA as the gold standard, we determined sensitivity and specificity of ultrasound in detecting occlusion at vertebral artery origin. All patients with non-occluded vertebral artery origins without stent were evaluated for degree of stenosis on DSA, and compared to mean flow velocity (MFV) on ultrasound.

Results: Among 218 vertebral artery origins evaluated, ultrasound showed sensitivity of 85.7% (95% confidence interval (CI) 69.7-95.2%) for occlusion and specificity of 99. 5% (95%CI 96.9-99.9%). Among 126 arteries without occlusion, <50% stenosis had average MFV 39.5 cm/s (SD 19.9), 50-69% stenosis had average MFV 69.2 cm/s (SD 34.7), and severe 70-99% stenosis had average MFV 129 cm/s (SD 30.65), p<0.001 by Kruskal-Wallis test. For detecting ≥70% stenosis, c-statistic of ROC curve was 0.81, and MFV of 70 cm/s has 82% sensitivity and 88% specificity of ≥70% stenosis.

Conclusion: Ultrasound has good sensitivity and excellent specificity for detecting vertebral origin occlusion. Flow velocity can be used to screen for severe stenosis of vertebral artery at origin.

Structure and function of the telomeric CST complex

Telomeres comprise the ends of eukaryotic chromosomes and are essential for cell proliferation and genome maintenance. Telomeres are replicated by telomerase, a ribonucleoprotein (RNP) reverse transcriptase, and are maintained primarily by nucleoprotein complexes such as shelterin (TRF1, TRF2, TIN2, RAP1, POT1, TPP1) and CST (Cdc13/Ctc1, Stn1, Ten1). The focus of this review is on the CST complex and its role in telomere maintenance. Although initially thought to be unique to yeast, it is now evident that the CST complex is present in a diverse range of organisms where it contributes to genome maintenance. The CST accomplishes these tasks via telomere capping and by regulating telomerase and DNA polymerase alpha-primase (polα-primase) access to telomeres, a process closely coordinated with the shelterin complex in most organisms. The goal of this review is to provide a brief but comprehensive account of the diverse, and in some cases organism-dependent, functions of the CST complex and how it contributes to telomere maintenance and cell proliferation.

Structural Basis of Telomerase Inhibition by the Highly Specific BIBR1532

BIBR1532 is a highly specific telomerase inhibitor, although the molecular basis for inhibition is unknown. Here we present the crystal structure of BIBR1532 bound to Tribolium castaneum catalytic subunit of telomerase (tcTERT). BIBR1532 binds to a conserved hydrophobic pocket (FVYL motif) on the outer surface of the thumb domain. The FVYL motif is near TRBD residues that bind the activation domain (CR4/5) of hTER. RNA binding assays show that the human TERT (hTERT) thumb domain binds the P6.1 stem loop of CR4/5 in vitro. hTERT mutations of the FVYL pocket alter wild-type CR4/5 binding and cause telomere attrition in cells. Furthermore, the hTERT FVYL mutations V1025F, N1028H, and V1090M are implicated in dyskeratosis congenita and aplastic anemia, further supporting the biological and clinical relevance of this novel motif. We propose that CR4/5 contacts with the telomerase thumb domain contribute to telomerase ribonucleoprotein assembly and promote enzymatic activity.

Structure of the Human Telomeric Stn1-Ten1 Complex

The telomeric CST complex plays a central role in chromosome end capping and replication in budding yeast, and homologues of CST were identified recently in higher eukaryotes. The human CST (Ctc1, hStn1, hTen1) has been shown to play a role in telomere maintenance, but the extent of conservation across species has been in question because of low sequence identity (below 10% for Ctc1, the core subunit of the CST complex) and data suggesting subtle differences in function between complexes. We solved the high-resolution crystal structure of the human Stn1-Ten1 complex, which revealed striking structural similarity between the yeast and human CST complexes. We also showed using southern blots and fluorescence in situ hybridization experiments that disruption of the hStn1-Ten1 binding interface in vivo produces elongated telomeres and telomere defects in accordance with what has been previously observed for the yeast CST complex. Our results support structural and functional conservation of telomeric CST across species.

Reduced axonal motor protein expression in non-lesional grey matter in multiple sclerosis

Background:

Multiple sclerosis (MS) is a neurological disease characterised by central nervous system inflammation, demyelination, axonal degeneration and neuronal injury. Preventing neuronal and axon damage is of paramount importance in attempts to prevent disease progression. Intact axonal transport mechanisms are crucial to axonal integrity and evidence suggests these mechanisms are disrupted in MS. Anterograde axonal transport is mediated to a large extent through the kinesin superfamily proteins. Recently, certain kinesin superfamily proteins (KIF5A, KIF1B and KIF21B) were implicated in MS pathology.

Objectives:

To investigate the expression of KIF5A, KIF21B and KIF1B in MS and control post-mortem grey matter.

Methods:

Using both quantitative real-time polymerase chain reaction (PCR) and Immunodot-blots assays, we analysed the expression of kinesin superfamily proteins in 27 MS cases and 13 control cases not linked to neurological disease.

Results:

We have shown significant reductions in KIF5A, KIF21B and KIF1B messenger ribonucleic acid (mRNA) expression and also KIF5A protein expression in MS grey matter, as compared to control grey matter.

Conclusion:

We have shown significant reductions in mRNA and protein levels of axonal motor proteins in the grey matter of MS cases, which may have important implications for the pathogenesis of neuronal/axonal injury in the disease.

Structure of the human telomeric Stn1-Ten1 capping complex

The identification of the human homologue of the yeast CST in 2009 posed a new challenge in our understanding of the mechanism of telomere capping in higher eukaryotes. The high-resolution structure of the human Stn1-Ten1 (hStn1-Ten1) complex presented here reveals that hStn1 consists of an OB domain and tandem C-terminal wHTH motifs, while hTen1 consists of a single OB fold. Contacts between the OB domains facilitate formation of a complex that is strikingly similar to the replication protein A (RPA) and yeast Stn1-Ten1 (Ten1) complexes. The hStn1-Ten1 complex exhibits non-specific single-stranded DNA activity that is primarily dependent on hStn1. Cells expressing hStn1 mutants defective for dimerization with hTen1 display elongated telomeres and telomere defects associated with telomere uncapping, suggesting that the telomeric function of hCST is hTen1 dependent. Taken together the data presented here show that the structure of the hStn1-Ten1 subcomplex is conserved across species. Cell based assays indicate that hTen1 is critical for the telomeric function of hCST, both in telomere protection and downregulation of telomerase function.

Factors that influence awareness and treatment of atrial fibrillation in older adults

AIM

The aims of this study were to investigate the prevalence of atrial fibrillation (AF), treatment rates of AF and the factors underlying awareness and treatment, in a large nationally representative study.

METHODS

A population sample of people aged 50+, living in the Republic of Ireland, were recruited as part of The Irish longitudinal study on ageing. Ten-minute electrocardiogram recordings were obtained (n = 4890), and analysed to detect AF. Self-reported arrhythmias, subjective and objective health measures (cardiovascular diseases, CHA2DS2-VASc variables and blood pressure) and medications were also recorded. Logistic regressions were used to determine associations with outcomes of presence of AF, lack of awareness and untreated AF.

RESULTS

Overall prevalence of AF was 3% (95% CI: 2.4-3.7%), with a marked age gradient and sex difference [4.8% (men) vs. 1.4% (women); P < 0.0001]. In total, 67.8% were at high risk of stroke (CHA2DS2-VASc ≥ 2), of whom 59.3% were inadequately treated. A high proportion of 38.1% were unaware of having AF. CHA2DS2-VASc nor HAS-BLED score influenced awareness or treatment. Lack of awareness was associated with lower education (P = 0.01), lower cognition (P = 0.04), rural location (OR = 3.67; P = 0.02) and number of general practitioner visits (P = 0.01), whereas untreated AF was influenced by frailty status (P = 0.04).

CONCLUSION

With projected doubling of numbers of persons over 80 in the next 30 years in the British Isles, detection and management of AF is pressing. Two-thirds of adults at high risk of stroke were inadequately treated. More regular screening for AF, application of criteria for stroke and bleeding risk and awareness of factors influencing diagnosis and treatment is recommended.

Soil Nutrients, Bacteria Populations, and Veterinary Pharmaceuticals across a Backgrounding Beef Feedlot

Beef cattle backgrounding operations that grow out weaned calves for feedlot finishing contain several environmentally significant constituents. A better understanding of these constituents and their environmental distribution will aid in the development of effective management guidelines for sustainable beef production. This research investigated soil nutrients, bacterial, and veterinary pharmaceutical concentrations across a small backgrounding beef feedlot on a karst landscape. Results indicated that all contaminants were highly concentrated in the feeder area (FD) and were lower in the other feedlot areas. The FD soils had a pH of 8.2, 59 mg kg soil organic matter (SOM), 2002 mg kg soil test phosphorus (STP), 99.7 mg kg NH-N, and 18.3 mg kg NO-N. The other locations were acidic (5.9-6.9 pH) and contained 39 mg kg SOM, 273 mg kg STP, 21.5 mg kg NH-N, and 2.0 NO-N mg kg. Bacteria populations in the FD averaged 2.7 × 10 total cells, 3.9 × 10 spp., 2.9 × 10 spp, and 4.5 × 10 cells per gram of soil. spp. and spp. concentrations were 1 to 4 orders of magnitude lower at the other locations. showed lower dynamic range and was generally uniformly distributed across the landscape. Antibiotic and parasiticide concentrations in the FD were 86.9 ng g monensin, 25.0 ng g lasalocid, and 10.3 ng g doramectin. Their concentrations were 6- to 27-fold lower in the other feedlot locations. Contaminant management plans for this small feedlot will therefore focus on the feeder and nearby grazing areas where soil nutrients, bacteria populations, and veterinary pharmaceuticals were most concentrated.

Resource utilisation for syncope presenting to an acute hospital Emergency Department

BACKGROUND

Syncope is a common clinical problem accounting for up to 6% of hospital admissions. Little is known about resource utilisation for patients admitted for syncope management in Ireland.

AIM

To determine the utilisation of resources for patients admitted for syncope management.

METHODS

Single centre observational case series of consecutive adult patients presenting to an acute hospital Emergency Department with syncope over a 5-month period.

RESULTS

Two-hundred and fourteen of 18,898 patients (1.1%) had a syncopal episode, 110 (51.4%) of whom were admitted. Mean length of stay was 6.9 days. Sixty-four of these admissions were deemed unnecessary by retrospective review when compared to ESC guidelines. Eighty-five (77.3%) admitted patients had cardiac investigations and 56 (51%) had brain imaging performed.

CONCLUSIONS

Syncope places a large demand on overstretched hospital resources. Most cases can be managed safely as an outpatient and to facilitate this, hospitals should develop outpatient Syncope Management Units.