Structural, Biophysical, and Functional Studies of TREM2 In Neurodegenerative Disease

Alzheimer\u27s disease (AD) and other neurodegenerative diseases present a large and growing challenge to global health. The immune system, particularly the innate immune system, is increasingly recognized as having a major role in these pathologies. The innate immune system is responsible to contain disease and promote healing. However, immune misregulation exacerbates disease. The innate immunomodulatory receptor Triggering receptor expressed on myeloid cells-2 (TREM2) is expressed on myeloid cells such as dendritic cells, macrophages, and in the brain, on microglia. TREM2 is a single-pass transmembrane receptor with an extracellular Ig domain that mediates ligand binding. This protein regulates inflammation in vitro and is required in vivo to sustain the microglia response during neurodegenerative diseases. Additionally, genetic studies have identified rare coding variants that increase risk for AD and separate variants that cause the severe, early fatal dementia known as Nasu-Hakola Disease (NHD). Combined, these animal and genetic studies have described a crucial role for TREM2 and identified variants that contribute disease risk. However, a full understanding of TREM2 function has been lacking due to a dearth of information regarding its structure and ligands. The goal of this study was to determine the TREM2 structure and understand how the disease variants alter structure and function. The TREM2 Ig domain was expressed, purified, and crystallized using a novel mammalian expression system. The TREM2 crystal structure and subsequent biophysical and functional assays revealed that NHD variants reduce protein stability and cause protein misfolding while the AD variants have minimal structural changes and instead impact ligand binding. TREM2 bound cell-surface sulfated proteoglycans on mammalian cells. AD-risk variants decreased binding while another variant, which is possibly protective, increased binding. These variants mapped a functional ligand-binding surface on the TREM2 protein. Functionally, chemical inhibition of nascent proteoglycan sulfation impaired TREM2 signaling, suggesting a ligand that acts in cis to position TREM2 for signaling. Additionally, TREM2 interacts with the soluble lipoprotein apolipoprotein E (ApoE) and with amyloid beta (Aβ) peptides. Intriguingly, AD-risk variants impair both of these interactions, suggesting a physiological relevance during AD. These experiments offer the first structural and mechanistic studies of TREM2 function and will engender targeted molecular therapies to restore or enhance TREM2 function during neurodegenerative disease

YbtT is a low-specificity type II thioesterase that maintains production of the metallophore yersiniabactin in pathogenic enterobacteria

Clinical isolates of Yersinia, Klebsiella, and Escherichia coli frequently secrete the small molecule metallophore yersiniabactin (Ybt), which passivates and scavenges transition metals during human infections. YbtT is encoded within the Ybt biosynthetic operon and is critical for full Ybt production in bacteria. However, its biosynthetic function has been unclear because it is not essential for Ybt production by the in vitro reconstituted nonribosomal peptide synthetase/polyketide synthase (NRPS/PKS) pathway. Here, we report the structural and biochemical characterization of YbtT. YbtT structures at 1.4-1.9 Å resolution possess a serine hydrolase catalytic triad and an associated substrate chamber with features similar to those previously reported for low-specificity type II thioesterases (TEIIs). We found that YbtT interacts with the two major Ybt biosynthetic proteins, HMWP1 (high-molecular-weight protein 1) and HMWP2 (high-molecular-weight protein 2), and hydrolyzes a variety of aromatic and acyl groups from their phosphopantetheinylated carrier protein domains. In vivo YbtT titration in uropathogenic E. coli revealed a distinct optimum for Ybt production consistent with a tradeoff between clearing both stalled inhibitory intermediates and productive Ybt precursors from HMWP1 and HMWP2. These results are consistent with a model in which YbtT maintains cellular Ybt biosynthesis by removing nonproductive, inhibitory thioesters that form aberrantly at multiple sites on HMWP1 and HMWP2

Biological predictors of chemotherapy-induced peripheral neuropathy (CIPN): MASCC neurological complications working group overview.

Chemotherapy-induced peripheral neuropathy (CIPN) is a common and debilitating condition associated with a number of chemotherapeutic agents. Drugs commonly implicated in the development of CIPN include platinum agents, taxanes, vinca alkaloids, bortezomib, and thalidomide analogues. As a drug response can vary between individuals, it is hypothesized that an individual's specific genetic variants could impact the regulation of genes involved in drug pharmacokinetics, ion channel functioning, neurotoxicity, and DNA repair, which in turn affect CIPN development and severity. Variations of other molecular markers may also affect the incidence and severity of CIPN. Hence, the objective of this review was to summarize the known biological (molecular and genomic) predictors of CIPN and discuss the means to facilitate progress in this field

Neurodegenerative disease mutations in TREM2 reveal a functional surface and distinct loss-of-function mechanisms

Genetic variations in the myeloid immune receptor TREM2 are linked to several neurodegenerative diseases. To determine how TREM2 variants contribute to these diseases, we performed structural and functional studies of wild-type and variant proteins. Our 3.1 Å TREM2 crystal structure revealed that mutations found in Nasu-Hakola disease are buried whereas Alzheimer’s disease risk variants are found on the surface, suggesting that these mutations have distinct effects on TREM2 function. Biophysical and cellular methods indicate that Nasu-Hakola mutations impact protein stability and decrease folded TREM2 surface expression, whereas Alzheimer’s risk variants impact binding to a TREM2 ligand. Additionally, the Alzheimer’s risk variants appear to epitope map a functional surface on TREM2 that is unique within the larger TREM family. These findings provide a guide to structural and functional differences among genetic variants of TREM2, indicating that therapies targeting the TREM2 pathway should be tailored to these genetic and functional differences with patient-specific medicine approaches for neurodegenerative disorders. DOI: http://dx.doi.org/10.7554/eLife.20391.00

Effect of Dapagliflozin on Outpatient Worsening of Patients With Heart Failure and Reduced Ejection Fraction A Prespecified Analysis of DAPA-HF

BACKGROUND: In the DAPA-HF trial (Dapagliflozin and Prevention of Adverse Outcomes in Heart Failure), dapagliflozin, added to guideline-recommended therapies, reduced the risk of mortality and heart failure (HF) hospitalization. We examined the frequency and significance of episodes of outpatient HF worsening, requiring the augmentation of oral therapy, and the effects of dapagliflozin on these additional events. METHODS: Patients in New York Heart Association functional class II to IV, with a left ventricular ejection fraction RESULTS: Overall, 36% more patients experienced the expanded, in comparison with the primary, composite outcome. In the placebo group, 684 of 2371 (28.8%) patients and, in the dapagliflozin group, 527 of 2373 (22.2%) participants experienced the expanded outcome (hazard ratio, 0.73 [95% CI, 0.65-0.82]; P CONCLUSION: In DAPA-HF, outpatient episodes of HF worsening were common, were of prognostic importance, and were reduced by dapagliflozin

Dapagliflozin and Diuretic Use in Patients With Heart Failure and Reduced Ejection Fraction in DAPA-HF

Background: In the DAPA-HF trial (Dapagliflozin and Prevention of Adverse-Outcomes in Heart Failure), the sodium-glucose cotransporter 2 inhibitor dapagliflozin reduced the risk of worsening heart failure and death in patients with heart failure and reduced ejection fraction. We examined the efficacy and tolerability of dapagliflozin in relation to background diuretic treatment and change in diuretic therapy after randomization to dapagliflozin or placebo. Methods: We examined the effects of study treatment in the following subgroups: No diuretic and diuretic dose equivalent to furosemide 40 mg daily at baseline. We examined the primary composite end point of cardiovascular death or a worsening heart failure event and its components, all-cause death and symptoms. Results: Of 4616 analyzable patients, 736 (15.9%) were on no diuretic, 1311 (28.4%) were on 40 mg. Compared with placebo, dapagliflozin reduced the risk of the primary end point across each of these subgroups: Hazard ratios were 0.57 (95% CI, 0.36-0.92), 0.83 (95% CI, 0.63-1.10), 0.77 (95% CI, 0.60-0.99), and 0.78 (95% CI, 0.63-0.97), respectively (P for interaction=0.61). The hazard ratio in patients taking any diuretic was 0.78 (95% CI, 0.68-0.90). Improvements in symptoms and treatment toleration were consistent across the diuretic subgroups. Diuretic dose did not change in most patients during follow-up, and mean diuretic dose did not differ between the dapagliflozin and placebo groups after randomization. Conclusions: The efficacy and safety of dapagliflozin were consistent across the diuretic subgroups examined in DAPA-HF

Hereditary Hemochromatosis (HFE) genotypes in heart failure: Relation to etiology and prognosis

<p>Abstract</p> <p>Background</p> <p>It is believed that hereditary hemochromatosis (HH) might play a role in cardiac disease (heart failure (HF) and ischemia). Mutations within several genes are HH-associated, the most common being the <it>HFE </it>gene. In a large cohort of HF patients, we sought to determine the etiological role and the prognostic significance of <it>HFE </it>genotypes.</p> <p>Methods</p> <p>We studied 667 HF patients (72.7% men) with depressed systolic function, enrolled in a multicentre trial with a follow-up period of up to 5 years. All were genotyped for the known <it>HFE </it>variants C282Y, H63D and S65C.</p> <p>Results</p> <p>The genotype and allele frequencies in the HF group were similar to the frequencies determined in the general Danish population. In multivariable analysis mortality was not predicted by C282Y-carrier status (HR 1.2, 95% CI: 0.8-1.7); H63D-carrier status (HR 1.0, 95% CI: 0.7-1.3); nor S65C-carrier status (HR 1.2, 95% CI: 0.7-2.0). We identified 27 (4.1%) homozygous or compound heterozygous carriers of <it>HFE </it>variants. None of these carriers had a clinical presentation suggesting hemochromatosis, but hemoglobin and ferritin levels were higher than in the rest of the cohort. Furthermore, a trend towards reduced mortality was seen in this group in univariate analyses (HR 0.4, 95% CI: 0.2-0.9, p = 0.03), but not in multivariate (HR 0.5, 95% CI: 0.2-1.2).</p> <p>Conclusion</p> <p><it>HFE </it>genotypes do not seem to be a significant contributor to the etiology of heart failure in Denmark. <it>HFE </it>variants do not affect mortality in HF.</p

Phylogeny of Echinoderm Hemoglobins

Recent genomic information has revealed that neuroglobin and cytoglobin are the two principal lineages of vertebrate hemoglobins, with the latter encompassing the familiar myoglobin and α-globin/β-globin tetramer hemoglobin, and several minor groups. In contrast, very little is known about hemoglobins in echinoderms, a phylum of exclusively marine organisms closely related to vertebrates, beyond the presence of coelomic hemoglobins in sea cucumbers and brittle stars. We identified about 50 hemoglobins in sea urchin, starfish and sea cucumber genomes and transcriptomes, and used Bayesian inference to carry out a molecular phylogenetic analysis of their relationship to vertebrate sequences, specifically, to assess the hypothesis that the neuroglobin and cytoglobin lineages are also present in echinoderms.The genome of the sea urchin Strongylocentrotus purpuratus encodes several hemoglobins, including a unique chimeric 14-domain globin, 2 androglobin isoforms and a unique single androglobin domain protein. Other strongylocentrotid genomes appear to have similar repertoires of globin genes. We carried out molecular phylogenetic analyses of 52 hemoglobins identified in sea urchin, brittle star and sea cucumber genomes and transcriptomes, using different multiple sequence alignment methods coupled with Bayesian and maximum likelihood approaches. The results demonstrate that there are two major globin lineages in echinoderms, which are related to the vertebrate neuroglobin and cytoglobin lineages. Furthermore, the brittle star and sea cucumber coelomic hemoglobins appear to have evolved independently from the cytoglobin lineage, similar to the evolution of erythroid oxygen binding globins in cyclostomes and vertebrates.The presence of echinoderm globins related to the vertebrate neuroglobin and cytoglobin lineages suggests that the split between neuroglobins and cytoglobins occurred in the deuterostome ancestor shared by echinoderms and vertebrates