Exploring the prevalence of undetected bradyarrhythmia in dementia with Lewy bodies.

PURPOSE: To explore the prevalence of undetected bradyarrhythmia in a cohort of people with dementia with Lewy bodies. METHODS: Thirty participants diagnosed with dementia with Lewy bodies were enrolled from three memory clinics in southern Sweden between May 2021 and November 2022. None had a history of high-grade atrioventricular block or sick sinus syndrome. Each participant underwent orthostatic testing, cardiac [123I]metaiodobenzylguanidine scintigraphy and 24-h ambulatory electrocardiographic monitoring. Concluding bradyarrhythmia diagnosis was obtained until the end of December 2022. RESULTS: Thirteen participants (46.4%) had bradycardia at rest during orthostatic testing and four had an average heart rate < 60 beats per minute during ambulatory electrocardiographic monitoring. Three participants (10.7%) received a diagnosis of sick sinus syndrome, of whom two received pacemaker implants to manage associated symptoms. None received a diagnosis of second- or third-degree atrioventricular block. CONCLUSION: This report showed a high prevalence of sick sinus syndrome in a clinical cohort of people with dementia with Lewy bodies. Further research on the causes and consequences of sick sinus syndrome in dementia with Lewy bodies is thus warranted.

Pacemaker Implants and Their Influence on the Daily Life of Patients with Dementia with Lewy Bodies: A Qualitative Case Study.

INTRODUCTION: Dementia with Lewy bodies (DLB) is an incurable form of dementia associated with detriments to the daily life of patients and carers from their family. Symptoms of orthostatic hypotension, syncope, and falls are supportive of DLB diagnosis. These symptoms may also be present among people with sick sinus syndrome (SSS), and subsequent pacemaker treatment to manage bradyarrhythmia is associated with improved cognitive function. The prevalence of SSS seems to be higher among people with underlying Lewy body pathology compared to the general age-matched population (5.2% vs. 0.17%). To our knowledge, how people with DLB and their family carers may experience pacemaker treatment to manage bradyarrhythmia has not been previously reported. Therefore, the aim of this study was to explore how people with DLB experience daily life following a pacemaker implant to manage associated symptoms of bradyarrhythmia. METHODS: A qualitative case study design was used. Two men with DLB and their spouse carers were repeatedly interviewed as a dyad within 1 year following implant of a dual-chamber rate-adaptive (DDD-CLS) pacemaker to manage SSS in the men. Content analysis was used to assess the qualitative interview data collected. RESULTS: Three categories emerged: (1) gaining control, (2) maintaining a social life, and (3) being influenced by concurrent diseases. Less syncope/falls and remote pacemaker monitoring increased a sense of control in everyday life, while perceived physical and/or cognitive improvements influenced social participation. The men were still affected by concurrent diseases, which continuously influenced each couple's daily life. CONCLUSION: Identifying and managing concurrent bradyarrhythmia through a pacemaker implant could improve well-being for people with DLB.

Thioredoxin-80 protects against amyloid-beta pathology through autophagic-lysosomal pathway regulation.

Aggregation and accumulation of amyloid beta (Aß) are believed to play a key role in the pathogenesis of Alzheimer's disease (AD). We previously reported that Thioredoxin-80 (Trx80), a truncated form of Thioredoxin-1, prevents the toxic effects of Aß and inhibits its aggregation in vitro. Trx80 levels were found to be dramatically reduced both in the human brain and cerebrospinal fluid of AD patients. In this study, we investigated the effect of Trx80 expression using in vivo and in vitro models of Aß pathology. We developed Drosophila melanogaster models overexpressing either human Trx80, human Aß42, or both Aß42/Trx80 in the central nervous system. We found that Trx80 expression prevents Aß42 accumulation in the brain and rescues the reduction in life span and locomotor impairments seen in Aß42 expressing flies. Also, we show that Trx80 induces autophagosome formation and reverses the inhibition of Atg4b-Atg8a/b autophagosome formation pathway caused by Aß42. These effects were also confirmed in human neuroblastoma cells. These results give insight into Trx80 function in vivo, suggesting its role in the autophagosome biogenesis and thus in Aß42 degradation. Our findings put Trx80 on the spotlight as an endogenous agent against Aß42-induced toxicity in the brain suggesting that strategies to enhance Trx80 levels in neurons could potentially be beneficial against AD pathology in humans.

Cardiovascular Autonomic Dysfunction Is the Most Common Cause of Syncope in Paced Patients.

Introduction: Syncope and orthostatic intolerance in paced patients constitute a common clinical dilemma. We, thus, aimed to determine the etiology of syncope and/or symptoms of orthostatic intolerance in paced patients. Methods: Among 1,705 patients with unexplained syncope and/or orthostatic intolerance that were investigated by cardiovascular autonomic tests, including Valsalva maneuver, active standing, carotid sinus massage, and tilt-testing, 39 patients (2.3%; age 65.6 years; 39% women) had a cardiac implantable electronic device (CIED). We explored past medical history, diagnoses found during cardiovascular autonomic tests, and the further clinical workup, in case of negative initial evaluation. Results: An etiology was identified during cardiovascular autonomic tests in 36 of the 39 patients. Orthostatic hypotension (n = 16; 41%) and vasovagal syncope (n = 12; 31%) were the most common diagnoses. There were no cases of pacemaker dysfunction. The original pacing indications followed guidelines (sick-sinus-syndrome in 16, atrioventricular block in 16, atrial fibrillation with bradycardia in five). Twenty-two of the 39 patients (56%) had experienced syncope prior to the original CIED implantation. Orthostatic hypotension was diagnosed in seven (32%) and vasovagal syncope in nine (41%) of these patients. Of the 17 patients that had not experienced syncope prior to the original CIED implantation, nine patients (53%) were diagnosed with orthostatic hypotension and vasovagal syncope was diagnosed in three (18%). Of the 39 patients, two had implantable cardioverter-defibrillators to treat malignant ventricular arrhythmias diagnosed after syncopal episodes. Conclusion: Cardiovascular autonomic tests reveal the etiology of syncope and/or orthostatic intolerance in the majority of paced patients. The most common diagnosis was orthostatic hypotension (40%) followed by vasovagal syncope (30%), whereas there were no cases of pacemaker dysfunction. Our results emphasize the importance of a complete diagnostic work-up, including cardiovascular autonomic tests, in paced patients that present with syncope and/or orthostatic intolerance.

Pacing therapy in the management of unexplained syncope: a tertiary care centre prospective study.

Objective: Pacemaker (PM) therapy is effective when syncope is associated with bradycardia, but syncope recurrences and fall injuries after PM implantation may occur. We aimed to survey indications and outcomes of PM implantation, following evaluation of unexplained syncope. Methods: Among 1666 consecutive unpaced patients investigated in a tertiary syncope unit by carotid-sinus massage (CSM), head-up tilt test (HUT) and ECG monitoring, 106 (6.4%; age, 65 ± 17 years) received a PM. We assessed bradycardia detection methods, PM implantation indications, and explored incidence of recurrent syncope, fall-related fractures and mortality. Results: Indications for PM therapy were met in 32/106 patients (30%) by CSM, in 41/106 (39%) by HUT, in 14/106 patients (13%) by implantable loop-recorder (ILR) and in 19/106 (18%) by standard ECG. Sinus arrest with asystole was the predominant PM indication during CSM/HUT and external ECG monitoring, whereas ILR detected proportionally the same numbers o f asystole due to sinus arrest and atrioventricular block. During follow-up (median, 4.3 years), 15 patients (14%) had syncope recurrence, 15 suffered fall-related fractures and 9 died. Neither syncope recurrence nor fall-related fractures were dependent on initial PM indication. The composite endpoint of recurrent syncope/fall-related fracture was associated with treated hypertension (OR 2.45; 95% CI 1.00 to 6.0), reduced glomerular filtration rate (OR 1.63 per 10 mL/min↓; 95% CI 1.22 to 2.19) and atrial fibrillation (OR 3.98; 95% CI 1.11 to 14.3). Recurrent syncope predicted increased mortality (OR 9.20; 95% CI 1.89 to 44.8). Conclusions: Cardiovascular autonomic testing and ECG monitoring effectively identify pacing indications in patients with unexplained syncope. After PM implantation, treated hypertension, renal failure and atrial fibrillation predict syncope recurrence and fall-related injury. Recurrent syncope predicts increased mortality.

Detection of Concordance between Transcriptional Levels of GPCRs and Receptor-Activity-Modifying Proteins.

A recent phylogenetic analysis showed global co-evolution of G protein-coupled receptors (GPCRs) and receptor-activity-modifying proteins (RAMPs) suggesting global interactions between these two protein families. Experimental validation of these findings is challenging because in humans whereas there are only three genes encoding RAMPs, there are about 800 genes encoding GPCRs. Here, we report an experimental approach to evaluate GPCR-RAMP interactions. As a proof-of-concept experiment, we over-expressed RAMP2 in HEK293T cells and evaluated the effect on the transcriptional levels of 14 representative GPCRs that were selected based on the earlier phylogenetic analysis. We utilized a multiplexed error-correcting fluorescence in situ hybridization (MERFISH) method to detect message levels for individual GPCRs in single cells. The MERFISH results showed changes in GPCR message levels with RAMP2 over-expression in a concordant pattern that was predicted by the earlier phylogenetic analysis. These results provide additional evidence that GPCR-RAMP interactions are more widespread than previously appreciated and that these interactions have functional consequences.

GPCRs globally coevolved with receptor activity-modifying proteins, RAMPs.

Receptor activity-modifying proteins (RAMPs) are widely expressed in human tissues and, in some cases, have been shown to affect surface expression or ligand specificity of G-protein-coupled receptors (GPCRs). However, whether RAMP-GPCR interactions are widespread, and the nature of their functional consequences, remains largely unknown. In humans, there are three RAMPs and over 800 expressed GPCRs, making direct experimental approaches challenging. We analyzed relevant genomic data from all currently available sequenced organisms. We discovered that RAMPs and GPCRs tend to have orthologs in the same species and have correlated phylogenetic trees to the same extent, or higher than other interacting protein pairs that play key roles in cellular signaling. In addition, the resulting RAMP-GPCR interaction map suggests that RAMP1 and RAMP3 interact with the same set of GPCRs, which implies functional redundancy. We next analyzed human transcriptomes and found expression correlation for GPCRs and RAMPs. Our results suggest global coevolution of GPCRs and RAMPS and support the hypothesis that GPCRs interact globally with RAMPs in cellular signaling pathways.

Apolipoprotein E4 Elicits Lysosomal Cathepsin D Release, Decreased Thioredoxin-1 Levels, and Apoptosis.

The major genetic risk factor for Alzheimer's disease (AD), apolipoprotein E4 (ApoE4), has been suggested to have detrimental effects on neurons, including direct toxicity via apoptosis. Thioredoxin-1 (Trx1) is an endogenous antioxidant protein important for redox regulation and participates in the regulation of apoptosis through the inhibition of apoptosis signal-regulating kinase-1 (Ask-1). In this study, we have investigated the effects of ApoE on Trx1 in the brain. Our results showed that the protein levels of Trx1 were reduced in the hippocampus of ApoE4 targeted replacement (TR) mice compared to ApoE3 TR mice. The reduction was also seen in vitro after treatment of both human primary cortical neurons and neuroblastoma cells with human recombinant ApoE4 (rApoE4). Furthermore, ApoE4 caused a disruption of lysosomal integrity and a shift in the localization of Cathepsin D, an enzyme known to degrade Trx1. ApoE4 treatment induced in addition apoptosis through translocation of Death-domain associated protein-6 (Daxx) from the nucleus to the cytosol, suggesting an activation of the Ask-1 pathway. This toxicity was prevented by overexpression of Trx1 and other endogenous Ask-1 inhibitors. Our data suggests that down-regulation of Trx1 is involved in the toxicity caused by ApoE4. An activated ASK-1 pathway might indeed make cells more vulnerable to other insults such as amyloid-ß, which could partially explain the mechanism behind the strongest genetic risk factor for AD.

Pharmacological Modulations of the Serotonergic System in a Cell-Model of Familial Alzheimer's Disease.

Serotonin (5-HT) plays a central role in the integrity of different brain functions. The 5-HT homeostasis is regulated by many factors, including serotonin transporter (SERT), monoamine oxidase enzyme (MAO), and several 5-HT receptors, including the 5-HT1B. There is little knowledge how the dynamics of this system is affected by the amyloid-ß (Aß) burden of Alzheimer's disease (AD) pathology. SH-SY5Y neuroblastoma cells transfected with the amyloid precursor protein (APP) gene containing the Swedish mutations causing familial AD (APPswe), were used as a model to explore the effect of Aß pathology on 5-HT1B and related molecules including the receptor adaptor protein (p11), SERT and MAOA gene expression, and MAOA activity after treatment with selective serotonin reuptake inhibitor (SSRI) (sertraline), and a 5-HT1B receptor antagonist. Sertraline led more than 70 fold increase of 5-HT1B gene expression (p < 0.001), an increased serotonin turnover in both APPswe and control cells and reduced intracellular serotonin levels by 75% in APPswe cells but not in controls (p > 0.05). Treatment with the 5-HT1B receptor antagonist increased SERT gene-expression in control cells but not in the APPswe cells. 5-HT and 5-HT1B antagonist treatment resulted in different p11 expression patterns in APPswe cells compared to controls. Although MAOA gene expression was not changed by APPswe overexpression, adding 5-HT lead to a significant increase in MAOA gene expression in APPswe but not control cells. These findings suggest that the sensitivity of the 5-HT1B receptor and related systems is affected by APPswe overexpression, with potential relevance for pharmacologic intervention in AD. This may at least partly explain the lack of effect of SSRIs in patients with AD and depression.

5-HT1B and other related serotonergic proteins are altered in APPswe mutation.

Serotonergic dysfunction is implicated in Alzheimer's disease (AD). In addition, reductions in brain of both monoamine synthesis and release have been reported. Serotonin 1B receptors (5-HT1B), along with serotonin transporter (SERT) are among the regulators of extracellular 5-HT levels. We investigated the effect of the familial AD APP (Amyloid precursor protein) K670N/M671L double mutation, APP Swedish mutation (APPswe), on the expression of 5-HT1B, SERT, MAOA, p11 and 5-HT and its metabolite 5-HIAA in SH-SY5Y human neuroblastoma cell line stably transfected with APPswe mutation. In addition, hippocampal expressions of 5-HT1B and SERT were assessed in wild type and transgenic mice expressing APPswe mutation (Tg2576) at different age groups. We found a reduction of 5-HT1B as well as SERT in both APPswe in vitro and ex vivo. P11 and 5HT were also reduced, whereas 5HT turnover and MAOA were increased. Our results indicate that APPswe induced decreased 5-HT1B expression and 5-HT release, as well as increased MAOA activity and 5-HT breakdown. Further studies to explore the detailed mechanism behind reduced 5-HT1B and SERT in AD and their clinical implications are needed.

Oxidative stress in Alzheimer's disease: why did antioxidant therapy fail?

Alzheimer's disease (AD) is the most common form of dementia in the elderly, with increasing prevalence and no disease-modifying treatment available yet. A remarkable amount of data supports the hypothesis that oxidative stress is an early and important pathogenic operator in AD. However, all clinical studies conducted to date did not prove a clear beneficial effect of antioxidant treatment in AD patients. In the current work, we review the current knowledge about oxidative stress in AD pathogeny and we suggest future paths that are worth to be explored in animal models and clinical studies, in order to get a better approach of oxidative imbalance in this inexorable neurodegenerative disease.

Thioredoxin-80 is a product of alpha-secretase cleavage that inhibits amyloid-beta aggregation and is decreased in Alzheimer's disease brain.

Thioredoxin-1 (Trx1) is an endogenous dithiol reductant and antioxidant that was shown to be decreased in Alzheimer's disease (AD) neurons. A truncated form of Trx1, thioredoxin 80 (Trx80), was reported to be secreted from monocytes having cytokine activity. Here, we show that Trx80 is present in human brain in an aggregated form. Trx80 localizes mainly to neurons and is dramatically decreased in AD brains. Trx80 levels in cerebrospinal fluid (CSF) correlate with those of the classical AD biomarkers amyloid-ß (Aß) 1-42 and total tau. Moreover, Trx80 measurements in CSF discriminate between patients with stable mild cognitive impairment, prodomal AD and mild AD. We report that ADAM10 and 17, two α-secretases processing the Aß precursor protein, are responsible for Trx80 generation. In contrast to the periphery, Trx80 has no pro-inflammatory effects in glia, either by itself or in combination with Aß or apolipoprotein E. Instead, Trx80 inhibits Aß(1-42) aggregation and protects against its toxicity. Thus, a reduction in Trx80 production would result in increased Aß polymerization and enhanced neuronal vulnerability. Our data suggest that a deficit in Trx80 could participate in AD pathogenesis.

Estrogen protects against amyloid-ß toxicity by estrogen receptor α-mediated inhibition of Daxx translocation.

Estrogen was shown to promote neuronal survival against several neurotoxic insults including ß-amyloid (Aß). The proposed mechanism includes the activation of the mitogen activated protein kinase/extracellular signal-regulated kinase (Mapk/Erk), phosphatidylinositol 3-kinase/Akt pathways and the upregulation of antiapoptotic proteins. On the other hand, Aß neurotoxicity depends on the activation of apoptosis signal-regulating kinase 1 (Ask1), and both Ask1 activity and Aß toxicity are inhibited by thioredoxin-1 (Trx1). Here, we explored the possibility that estrogen could protect cells against Aß(1-42) toxicity by inhibiting the Ask1 cascade or by modulating Trx1. Cytosolic translocation of death-associated protein Daxx was used as indicator of Ask1 activity. Using human SH-SY5Y neuroblastoma cells, 17ß-estradiol (E2) and specific agonists for estrogen receptor (ER) α or ß we demonstrated that nM concentrations of E2 protected against Aß(1-42) by a mechanism depending upon ERα stimulation, Akt activation and Ask1 inhibition. Moreover, this protection would occur independently of ERß and the induction of Trx1 expression. Our results emphasize the importance of Ask1 cascade in Aß toxicity, and of ERα and Ask1 as targets for developing new neuroprotective drugs.

The SOCS2 ubiquitin ligase complex regulates growth hormone receptor levels.

Growth Hormone is essential for the regulation of growth and the homeostatic control of intermediary metabolism. GH actions are mediated by the Growth Hormone Receptor; a member of the cytokine receptor super family that signals chiefly through the JAK2/STAT5 pathway. Target tissue responsiveness to GH is under regulatory control to avoid excessive and off-target effects upon GHR activation. The suppressor of cytokine signalling 2 (SOCS) is a key regulator of GHR sensitivity. This is clearly shown in mice where the SOCS2 gene has been inactivated, which show 30-40% increase in body length, a phenotype that is dependent on endogenous GH secretion. SOCS2 is a GH-stimulated, STAT5b-regulated gene that acts in a negative feedback loop to downregulate GHR signalling. Since the biochemical basis for these actions is poorly understood, we studied the molecular function of SOCS2. We demonstrated that SOCS2 is part of a multimeric complex with intrinsic ubiquitin ligase activity. Mutational analysis shows that the interaction with Elongin B/C controls SOCS2 protein turnover and affects its molecular activity. Increased GHR levels were observed in livers from SOCS2⁻/⁻ mice and in the absence of SOCS2 in in vitro experiments. We showed that SOCS2 regulates cellular GHR levels through direct ubiquitination and in a proteasomally dependent manner. We also confirmed the importance of the SOCS-box for the proper function of SOCS2. Finally, we identified two phosphotyrosine residues in the GHR to be responsible for the interaction with SOCS2, but only Y487 to account for the effects of SOCS2. The demonstration that SOCS2 is an ubiquitin ligase for the GHR unveils the molecular basis for its physiological actions.