Zn-regulated GTPase metalloprotein activator 1 modulates vertebrate zinc homeostasis.

Zinc (Zn) is an essential micronutrient and cofactor for up to 10% of proteins in living organisms. During Zn limitation, specialized enzymes called metallochaperones are predicted to allocate Zn to specific metalloproteins. This function has been putatively assigned to G3E GTPase COG0523 proteins, yet no Zn metallochaperone has been experimentally identified in any organism. Here, we functionally characterize a family of COG0523 proteins that is conserved across vertebrates. We identify Zn metalloprotease methionine aminopeptidase 1 (METAP1) as a COG0523 client, leading to the redesignation of this group of COG0523 proteins as the Zn-regulated GTPase metalloprotein activator (ZNG1) family. Using biochemical, structural, genetic, and pharmacological approaches across evolutionarily divergent models, including zebrafish and mice, we demonstrate a critical role for ZNG1 proteins in regulating cellular Zn homeostasis. Collectively, these data reveal the existence of a family of Zn metallochaperones and assign ZNG1 an important role for intracellular Zn trafficking.

Tumor and Microenvironment Evolution during Immunotherapy with Nivolumab.

The mechanisms by which immune checkpoint blockade modulates tumor evolution during therapy are unclear. We assessed genomic changes in tumors from 68 patients with advanced melanoma, who progressed on ipilimumab or were ipilimumab-naive, before and after nivolumab initiation (CA209-038 study). Tumors were analyzed by whole-exome, transcriptome, and/or T cell receptor (TCR) sequencing. In responding patients, mutation and neoantigen load were reduced from baseline, and analysis of intratumoral heterogeneity during therapy demonstrated differential clonal evolution within tumors and putative selection against neoantigenic mutations on-therapy. Transcriptome analyses before and during nivolumab therapy revealed increases in distinct immune cell subsets, activation of specific transcriptional networks, and upregulation of immune checkpoint genes that were more pronounced in patients with response. Temporal changes in intratumoral TCR repertoire revealed expansion of T cell clones in the setting of neoantigen loss. Comprehensive genomic profiling data in this study provide insight into nivolumab's mechanism of action.

Comprehensive Analysis of Hypermutation in Human Cancer.

We present an extensive assessment of mutation burden through sequencing analysis of >81,000 tumors from pediatric and adult patients, including tumors with hypermutation caused by chemotherapy, carcinogens, or germline alterations. Hypermutation was detected in tumor types not previously associated with high mutation burden. Replication repair deficiency was a major contributing factor. We uncovered new driver mutations in the replication-repair-associated DNA polymerases and a distinct impact of microsatellite instability and replication repair deficiency on the scale of mutation load. Unbiased clustering, based on mutational context, revealed clinically relevant subgroups regardless of the tumors' tissue of origin, highlighting similarities in evolutionary dynamics leading to hypermutation. Mutagens, such as UV light, were implicated in unexpected cancers, including sarcomas and lung tumors. The order of mutational signatures identified previous treatment and germline replication repair deficiency, which improved management of patients and families. These data will inform tumor classification, genetic testing, and clinical trial design.

Predicting crystal form stability under real-world conditions.

The physicochemical properties of molecular crystals, such as solubility, stability, compactability, melting behaviour and bioavailability, depend on their crystal form1. In silico crystal form selection has recently come much closer to realization because of the development of accurate and affordable free-energy calculations2-4. Here we redefine the state of the art, primarily by improving the accuracy of free-energy calculations, constructing a reliable experimental benchmark for solid-solid free-energy differences, quantifying statistical errors for the computed free energies and placing both hydrate crystal structures of different stoichiometries and anhydrate crystal structures on the same energy landscape, with defined error bars, as a function of temperature and relative humidity. The calculated free energies have standard errors of 1-2 kJ mol-1 for industrially relevant compounds, and the method to place crystal structures with different hydrate stoichiometries on the same energy landscape can be extended to other multi-component systems, including solvates. These contributions reduce the gap between the needs of the experimentalist and the capabilities of modern computational tools, transforming crystal structure prediction into a more reliable and actionable procedure that can be used in combination with experimental evidence to direct crystal form selection and establish control5.

RADX controls RAD51 filament dynamics to regulate replication fork stability.

The RAD51 recombinase forms nucleoprotein filaments to promote double-strand break repair, replication fork reversal, and fork stabilization. The stability of these filaments is highly regulated, as both too little and too much RAD51 activity can cause genome instability. RADX is a single-strand DNA (ssDNA) binding protein that regulates DNA replication. Here, we define its mechanism of action. We find that RADX inhibits RAD51 strand exchange and D-loop formation activities. RADX directly and selectively interacts with ATP-bound RAD51, stimulates ATP hydrolysis, and destabilizes RAD51 nucleofilaments. The RADX interaction with RAD51, in addition to its ssDNA binding capability, is required to maintain replication fork elongation rates and fork stability. Furthermore, BRCA2 can overcome the RADX-dependent RAD51 inhibition. Thus, RADX functions in opposition to BRCA2 in regulating RAD51 nucleofilament stability to ensure the right level of RAD51 function during DNA replication.

EXO5-DNA structure and BLM interactions direct DNA resection critical for ATR-dependent replication restart.

Stalled DNA replication fork restart after stress as orchestrated by ATR kinase, BLM helicase, and structure-specific nucleases enables replication, cell survival, and genome stability. Here we unveil human exonuclease V (EXO5) as an ATR-regulated DNA structure-specific nuclease and BLM partner for replication fork restart. We find that elevated EXO5 in tumors correlates with increased mutation loads and poor patient survival, suggesting that EXO5 upregulation has oncogenic potential. Structural, mechanistic, and mutational analyses of EXO5 and EXO5-DNA complexes reveal a single-stranded DNA binding channel with an adjacent ATR phosphorylation motif (T88Q89) that regulates EXO5 nuclease activity and BLM binding identified by mass spectrometric analysis. EXO5 phospho-mimetic mutant rescues the restart defect from EXO5 depletion that decreases fork progression, DNA damage repair, and cell survival. EXO5 depletion furthermore rescues survival of FANCA-deficient cells and indicates EXO5 functions epistatically with SMARCAL1 and BLM. Thus, an EXO5 axis connects ATR and BLM in directing replication fork restart.

A human brain vascular atlas reveals diverse mediators of Alzheimer's risk.

The human brain vasculature is of great medical importance: its dysfunction causes disability and death1, and the specialized structure it forms-the blood-brain barrier-impedes the treatment of nearly all brain disorders2,3. Yet so far, we have no molecular map of the human brain vasculature. Here we develop vessel isolation and nuclei extraction for sequencing (VINE-seq) to profile the major vascular and perivascular cell types of the human brain through 143,793 single-nucleus transcriptomes from 25 hippocampus and cortex samples of 9 individuals with Alzheimer's disease and 8 individuals with no cognitive impairment. We identify brain-region- and species-enriched genes and pathways. We reveal molecular principles of human arteriovenous organization, recapitulating a gradual endothelial and punctuated mural cell continuum. We discover two subtypes of human pericytes, marked by solute transport and extracellular matrix (ECM) organization; and define perivascular versus meningeal fibroblast specialization. In Alzheimer's disease, we observe selective vulnerability of ECM-maintaining pericytes and gene expression patterns that implicate dysregulated blood flow. With an expanded survey of brain cell types, we find that 30 of the top 45 genes that have been linked to Alzheimer's disease risk by genome-wide association studies (GWASs) are expressed in the human brain vasculature, and we confirm this by immunostaining. Vascular GWAS genes map to endothelial protein transport, adaptive immune and ECM pathways. Many are microglia-specific in mice, suggesting a partial evolutionary transfer of Alzheimer's disease risk. Our work uncovers the molecular basis of the human brain vasculature, which will inform our understanding of overall brain health, disease and therapy.

Dysregulation of brain and choroid plexus cell types in severe COVID-19.

Although SARS-CoV-2 primarily targets the respiratory system, patients with and survivors of COVID-19 can suffer neurological symptoms1-3. However, an unbiased understanding of the cellular and molecular processes that are affected in the brains of patients with COVID-19 is missing. Here we profile 65,309 single-nucleus transcriptomes from 30 frontal cortex and choroid plexus samples across 14 control individuals (including 1 patient with terminal influenza) and 8 patients with COVID-19. Although our systematic analysis yields no molecular traces of SARS-CoV-2 in the brain, we observe broad cellular perturbations indicating that barrier cells of the choroid plexus sense and relay peripheral inflammation into the brain and show that peripheral T cells infiltrate the parenchyma. We discover microglia and astrocyte subpopulations associated with COVID-19 that share features with pathological cell states that have previously been reported in human neurodegenerative disease4-6. Synaptic signalling of upper-layer excitatory neurons-which are evolutionarily expanded in humans7 and linked to cognitive function8-is preferentially affected in COVID-19. Across cell types, perturbations associated with COVID-19 overlap with those found in chronic brain disorders and reside in genetic variants associated with cognition, schizophrenia and depression. Our findings and public dataset provide a molecular framework to understand current observations of COVID-19-related neurological disease, and any such disease that may emerge at a later date.

Structure of RADX and mechanism for regulation of RAD51 nucleofilaments.

Replication fork reversal is a fundamental process required for resolution of encounters with DNA damage. A key step in the stabilization and eventual resolution of reversed forks is formation of RAD51 nucleoprotein filaments on exposed single strand DNA (ssDNA). To avoid genome instability, RAD51 filaments are tightly controlled by a variety of positive and negative regulators. RADX (RPA-related RAD51-antagonist on the X chromosome) is a recently discovered negative regulator that binds tightly to ssDNA, directly interacts with RAD51, and regulates replication fork reversal and stabilization in a context-dependent manner. Here, we present a structure-based investigation of RADX's mechanism of action. Mass photometry experiments showed that RADX forms multiple oligomeric states in a concentration-dependent manner, with a predominance of trimers in the presence of ssDNA. The structure of RADX, which has no structurally characterized orthologs, was determined ab initio by cryo-electron microscopy (cryo-EM) from maps in the 2 to 4 Å range. The structure reveals the molecular basis for RADX oligomerization and the coupled multi-valent binding of ssDNA binding. The interaction of RADX with RAD51 filaments was imaged by negative stain EM, which showed a RADX oligomer at the end of filaments. Based on these results, we propose a model in which RADX functions by capping and restricting the end of RAD51 filaments.

Platelet Transfusion before CVC Placement in Patients with Thrombocytopenia.

BACKGROUND: Transfusion guidelines regarding platelet-count thresholds before the placement of a central venous catheter (CVC) offer conflicting recommendations because of a lack of good-quality evidence. The routine use of ultrasound guidance has decreased CVC-related bleeding complications. METHODS: In a multicenter, randomized, controlled, noninferiority trial, we randomly assigned patients with severe thrombocytopenia (platelet count, 10,000 to 50,000 per cubic millimeter) who were being treated on the hematology ward or in the intensive care unit to receive either one unit of prophylactic platelet transfusion or no platelet transfusion before ultrasound-guided CVC placement. The primary outcome was catheter-related bleeding of grade 2 to 4; a key secondary outcome was grade 3 or 4 bleeding. The noninferiority margin was an upper boundary of the 90% confidence interval of 3.5 for the relative risk. RESULTS: We included 373 episodes of CVC placement involving 338 patients in the per-protocol primary analysis. Catheter-related bleeding of grade 2 to 4 occurred in 9 of 188 patients (4.8%) in the transfusion group and in 22 of 185 patients (11.9%) in the no-transfusion group (relative risk, 2.45; 90% confidence interval [CI], 1.27 to 4.70). Catheter-related bleeding of grade 3 or 4 occurred in 4 of 188 patients (2.1%) in the transfusion group and in 9 of 185 patients (4.9%) in the no-transfusion group (relative risk, 2.43; 95% CI, 0.75 to 7.93). A total of 15 adverse events were observed; of these events, 13 (all grade 3 catheter-related bleeding [4 in the transfusion group and 9 in the no-transfusion group]) were categorized as serious. The net savings of withholding prophylactic platelet transfusion before CVC placement was $410 per catheter placement. CONCLUSIONS: The withholding of prophylactic platelet transfusion before CVC placement in patients with a platelet count of 10,000 to 50,000 per cubic millimeter did not meet the predefined margin for noninferiority and resulted in more CVC-related bleeding events than prophylactic platelet transfusion. (Funded by ZonMw; PACER Dutch Trial Register number, NL5534.).

Decitabine in Older Patients with AML: Quality of Life Results of the EORTC-GIMEMA-GMDS-SG Randomized Phase III Trial.

We hypothesized that fit older patients with acute myeloid leukemia (AML) treated with decitabine (DEC) would report better health-related quality of life (HRQoL) outcomes compared to those receiving intensive chemotherapy (IC). We conducted a phase 3 randomized trial to compare DEC (10-day schedule) to IC (3+7) in older fit AML patients. HRQoL was a secondary endpoint, and it was assessed with the EORTC QLQ-C30 and the QLQ-ELD14. The following scales were a priori selected for defining the primary endpoint: physical and role functioning, fatigue, pain, and burden of illness. HRQoL was assessed at baseline, at regeneration from cycle 2, and at 6 and 12 months after randomization, and also prior to allo-HSCT and 100 days after transplantation. Overall, 606 patients underwent randomization. At 2 months, the risk of HRQoL deterioration was lower in the DEC arm than in the 3+7 arm (76% [95% CI, 69 to 82] v 88% [95% CI, 82 to 93]; odds ratio, 0.43 [95% CI, 0.24 to 0.76], P=.003). No statistically significant HRQoL differences were observed between treatment arms at the long-term evaluation combining assessments at 6 and 12 months. HRQoL deteriorations between baseline and post-allo-HSCT were observed in both arms. However, these deteriorations were not clinically meaningful in patients randomized to DEC, while this was the case for those in the 3+7 arm, in four out of the five primary HRQoL scales. Our HRQoL findings suggest that lower-intensity treatment with DEC, may be preferable to current standard IC (3+7), in fit older AML patients. ClinicalTrials.gov (NCT02172872).

Tipifarnib Reduces Extracellular Vesicles and Protects From Heart Failure.

BACKGROUND: Heart failure (HF) is one of the leading causes of mortality worldwide. Extracellular vesicles, including small extracellular vesicles or exosomes, and their molecular cargo are known to modulate cell-to-cell communication during multiple cardiac diseases. However, the role of systemic extracellular vesicle biogenesis inhibition in HF models is not well documented and remains unclear. METHODS: We investigated the role of circulating exosomes during cardiac dysfunction and remodeling in a mouse transverse aortic constriction (TAC) model of HF. Importantly, we investigate the efficacy of tipifarnib, a recently identified exosome biogenesis inhibitor that targets the critical proteins (Rab27a, nSMase2 [neutral sphingomyelinase 2], and Alix [ALG-2-interacting protein X]) involved in exosome biogenesis for this mouse model of HF. In this study, 10-week-old male mice underwent TAC surgery were randomly assigned to groups with and without tipifarnib treatment (10 mg/kg 3 times/wk) and monitored for 8 weeks, and a comprehensive assessment was conducted through performed echocardiographic, histological, and biochemical studies. RESULTS: TAC significantly elevated circulating plasma exosomes and markedly increased cardiac left ventricular dysfunction, cardiac hypertrophy, and fibrosis. Furthermore, injection of plasma exosomes from TAC mice induced left ventricular dysfunction and cardiomyocyte hypertrophy in uninjured mice without TAC. On the contrary, treatment of tipifarnib in TAC mice reduced circulating exosomes to baseline and remarkably improved left ventricular functions, hypertrophy, and fibrosis. Tipifarnib treatment also drastically altered the miRNA profile of circulating post-TAC exosomes, including miR 331-5p, which was highly downregulated both in TAC circulating exosomes and in TAC cardiac tissue. Mechanistically, miR 331-5p is crucial for inhibiting the fibroblast-to-myofibroblast transition by targeting HOXC8, a critical regulator of fibrosis. Tipifarnib treatment in TAC mice upregulated the expression of miR 331-5p that acts as a potent repressor for one of the fibrotic mechanisms mediated by HOXC8. CONCLUSIONS: Our study underscores the pathological role of exosomes in HF and fibrosis in response to pressure overload. Tipifarnib-mediated inhibition of exosome biogenesis and cargo sorting may serve as a viable strategy to prevent progressive cardiac remodeling in HF.

S-Nitrosylation of ß-Arrestins Biases Receptor Signaling and Confers Ligand Independence.

Most G protein-coupled receptors (GPCRs) signal through both heterotrimeric G proteins and ß-arrestins (ßarr1 and ßarr2). Although synthetic ligands can elicit biased signaling by G protein- vis-à-vis ßarr-mediated transduction, endogenous mechanisms for biasing signaling remain elusive. Here we report that S-nitrosylation of a novel site within ßarr1/2 provides a general mechanism to bias ligand-induced signaling through GPCRs by selectively inhibiting ßarr-mediated transduction. Concomitantly, S-nitrosylation endows cytosolic ßarrs with receptor-independent function. Enhanced ßarr S-nitrosylation characterizes inflammation and aging as well as human and murine heart failure. In genetically engineered mice lacking ßarr2-Cys253 S-nitrosylation, heart failure is exacerbated in association with greatly compromised ß-adrenergic chronotropy and inotropy, reflecting ßarr-biased transduction and ß-adrenergic receptor downregulation. Thus, S-nitrosylation regulates ßarr function and, thereby, biases transduction through GPCRs, demonstrating a novel role for nitric oxide in cellular signaling with potentially broad implications for patho/physiological GPCR function, including a previously unrecognized role in heart failure.

Application of a quantitative framework to improve the accuracy of a bacterial infection model.

Laboratory models are critical to basic and translational microbiology research. Models serve multiple purposes, from providing tractable systems to study cell biology to allowing the investigation of inaccessible clinical and environmental ecosystems. Although there is a recognized need for improved model systems, there is a gap in rational approaches to accomplish this goal. We recently developed a framework for assessing the accuracy of microbial models by quantifying how closely each gene is expressed in the natural environment and in various models. The accuracy of the model is defined as the percentage of genes that are similarly expressed in the natural environment and the model. Here, we leverage this framework to develop and validate two generalizable approaches for improving model accuracy, and as proof of concept, we apply these approaches to improve models of Pseudomonas aeruginosa infecting the cystic fibrosis (CF) lung. First, we identify two models, an in vitro synthetic CF sputum medium model (SCFM2) and an epithelial cell model, that accurately recapitulate different gene sets. By combining these models, we developed the epithelial cell-SCFM2 model which improves the accuracy of over 500 genes. Second, to improve the accuracy of specific genes, we mined publicly available transcriptome data, which identified zinc limitation as a cue present in the CF lung and absent in SCFM2. Induction of zinc limitation in SCFM2 resulted in accurate expression of 90% of P. aeruginosa genes. These approaches provide generalizable, quantitative frameworks for microbiological model improvement that can be applied to any system of interest.

Linking vertical movements of large pelagic predators with distribution patterns of biomass in the open ocean.

Many predator species make regular excursions from near-surface waters to the twilight (200 to 1,000 m) and midnight (1,000 to 3,000 m) zones of the deep pelagic ocean. While the occurrence of significant vertical movements into the deep ocean has evolved independently across taxonomic groups, the functional role(s) and ecological significance of these movements remain poorly understood. Here, we integrate results from satellite tagging efforts with model predictions of deep prey layers in the North Atlantic Ocean to determine whether prey distributions are correlated with vertical habitat use across 12 species of predators. Using 3D movement data for 344 individuals who traversed nearly 1.5 million km of pelagic ocean in [Formula: see text]42,000 d, we found that nearly every tagged predator frequented the twilight zone and many made regular trips to the midnight zone. Using a predictive model, we found clear alignment of predator depth use with the expected location of deep pelagic prey for at least half of the predator species. We compared high-resolution predator data with shipboard acoustics and selected representative matches that highlight the opportunities and challenges in the analysis and synthesis of these data. While not all observed behavior was consistent with estimated prey availability at depth, our results suggest that deep pelagic biomass likely has high ecological value for a suite of commercially important predators in the open ocean. Careful consideration of the disruption to ecosystem services provided by pelagic food webs is needed before the potential costs and benefits of proceeding with extractive activities in the deep ocean can be evaluated.

The many faces of RNA-based RNase P, an RNA-world relic.

RNase P is an essential enzyme that catalyzes removal of the 5' leader from precursor transfer RNAs. The ribonucleoprotein (RNP) form of RNase P is present in all domains of life and comprises a single catalytic RNA (ribozyme) and a variable number of protein cofactors. Recent cryo-electron microscopy structures of representative archaeal and eukaryotic (nuclear) RNase P holoenzymes bound to tRNA substrate/product provide high-resolution detail on subunit organization, topology, and substrate recognition in these large, multisubunit catalytic RNPs. These structures point to the challenges in understanding how proteins modulate the RNA functional repertoire and how the structure of an ancient RNA-based catalyst was reshaped during evolution by new macromolecular associations that were likely necessitated by functional/regulatory coupling.

Neoantigen T-Cell Receptor Gene Therapy in Pancreatic Cancer.

A patient with progressive metastatic pancreatic cancer was treated with a single infusion of 16.2×109 autologous T cells that had been genetically engineered to clonally express two allogeneic HLA-C*08:02-restricted T-cell receptors (TCRs) targeting mutant KRAS G12D expressed by the tumors. The patient had regression of visceral metastases (overall partial response of 72% according to the Response Evaluation Criteria in Solid Tumors, version 1.1); the response was ongoing at 6 months. The engineered T cells constituted more than 2% of all the circulating peripheral-blood T cells 6 months after the cell transfer. In this patient, TCR gene therapy targeting the KRAS G12D driver mutation mediated the objective regression of metastatic pancreatic cancer. (Funded by the Providence Portland Medical Foundation.).

Hypomorphic RAG deficiency: impact of disease burden on survival and thymic recovery argues for early diagnosis and HSCT.

Patients with hypomorphic mutations in the RAG1 or RAG2 gene present with either Omenn syndrome or atypical combined immunodeficiency with a wide phenotypic range. Hematopoietic stem cell transplantation (HSCT) is potentially curative, but data are scarce. We report on a worldwide cohort of 60 patients with hypomorphic RAG variants who underwent HSCT, 78% of whom experienced infections (29% active at HSCT), 72% had autoimmunity, and 18% had granulomas pretransplant. These complications are frequently associated with organ damage. Eight individuals (13%) were diagnosed by newborn screening or family history. HSCT was performed at a median of 3.4 years (range 0.3-42.9 years) from matched unrelated donors, matched sibling or matched family donors, or mismatched donors in 48%, 22%, and 30% of the patients, respectively. Grafts were T-cell depleted in 15 cases (25%). Overall survival at 1 and 4 years was 77.5% and 67.5% (median follow-up of 39 months). Infection was the main cause of death. In univariable analysis, active infection, organ damage pre-HSCT, T-cell depletion of the graft, and transplant from a mismatched family donor were predictive of worse outcome, whereas organ damage and T-cell depletion remained significant in multivariable analysis (hazard ratio [HR] = 6.01, HR = 8.46, respectively). All patients diagnosed by newborn screening or family history survived. Cumulative incidences of acute and chronic graft-versus-host disease were 35% and 22%, respectively. Cumulative incidences of new-onset autoimmunity was 15%. Immune reconstitution, particularly recovery of naïve CD4+ T cells, was faster and more robust in patients transplanted before 3.5 years of age, and without organ damage. These findings support the indication for early transplantation.

ß3AR-Dependent Brain-Derived Neurotrophic Factor (BDNF) Generation Limits Chronic Postischemic Heart Failure.

BACKGROUND: Loss of brain-derived neurotrophic factor (BDNF)/TrkB (tropomyosin kinase receptor B) signaling accounts for brain and cardiac disorders. In neurons, ß-adrenergic receptor stimulation enhances local BDNF expression. It is unclear if this occurs in a pathophysiological relevant manner in the heart, especially in the ß-adrenergic receptor-desensitized postischemic myocardium. Nor is it fully understood whether and how TrkB agonists counter chronic postischemic left ventricle (LV) decompensation, a significant unmet clinical milestone. METHODS: We conducted in vitro studies using neonatal rat and adult murine cardiomyocytes, SH-SY5Y neuronal cells, and umbilical vein endothelial cells. We assessed myocardial ischemia (MI) impact in wild type, ß3AR knockout, or myocyte-selective BDNF knockout (myoBDNF KO) mice in vivo (via coronary ligation [MI]) or in isolated hearts with global ischemia-reperfusion (I/R). RESULTS: In wild type hearts, BDNF levels rose early after MI (<24 hours), plummeting at 4 weeks when LV dysfunction, adrenergic denervation, and impaired angiogenesis ensued. The TrkB agonist, LM22A-4, countered all these adverse effects. Compared with wild type, isolated myoBDNF KO hearts displayed worse infarct size/LV dysfunction after I/R injury and modest benefits from LM22A-4. In vitro, LM22A-4 promoted neurite outgrowth and neovascularization, boosting myocyte function, effects reproduced by 7,8-dihydroxyflavone, a chemically unrelated TrkB agonist. Superfusing myocytes with the ß3AR-agonist, BRL-37344, increased myocyte BDNF content, while ß3AR signaling underscored BDNF generation/protection in post-MI hearts. Accordingly, the ß1AR blocker, metoprolol, via upregulated ß3ARs, improved chronic post-MI LV dysfunction, enriching the myocardium with BDNF. Last, BRL-37344-imparted benefits were nearly abolished in isolated I/R injured myoBDNF KO hearts. CONCLUSIONS: BDNF loss underscores chronic postischemic heart failure. TrkB agonists can improve ischemic LV dysfunction via replenished myocardial BDNF content. Direct cardiac ß3AR stimulation, or ß-blockers (via upregulated ß3AR), is another BDNF-based means to fend off chronic postischemic heart failure.

RADX Promotes Genome Stability and Modulates Chemosensitivity by Regulating RAD51 at Replication Forks.

RAD51 promotes homology-directed repair (HDR), replication fork reversal, and stalled fork protection. Defects in these functions cause genomic instability and tumorigenesis but also generate hypersensitivity to cancer therapeutics. Here we describe the identification of RADX as an RPA-like, single-strand DNA binding protein. RADX is recruited to replication forks, where it prevents fork collapse by regulating RAD51. When RADX is inactivated, excessive RAD51 activity slows replication elongation and causes double-strand breaks. In cancer cells lacking BRCA2, RADX deletion restores fork protection without restoring HDR. Furthermore, RADX inactivation confers chemotherapy and PARP inhibitor resistance to cancer cells with reduced BRCA2/RAD51 pathway function. By antagonizing RAD51 at forks, RADX allows cells to maintain a high capacity for HDR while ensuring that replication functions of RAD51 are properly regulated. Thus, RADX is essential to achieve the proper balance of RAD51 activity to maintain genome stability.