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Brown, D.

Publications and source records attributed to Brown, D..

At least 37 records · Page 2Linked to original sources

Primate-conserved Carbonic Anhydrase IV and murine-restricted Ly6c1 are new targets for crossing the blood-brain barrier

The blood-brain barrier (BBB) presents a major challenge to delivering large molecules to study and treat the central nervous system (CNS). This is due in part to the scarcity of effective targets for BBB crossing, the identification of which is the crucial first step of drug development. Here, we leveraged a panel of adeno-associated viruses (AAVs) previously identified through directed evolution for improved BBB transport to reverse engineer protein targets for enhanced BBB crossing. We identify both murine-restricted Ly6c1 and primate-conserved carbonic anhydrase IV (Car4; CA4) as novel receptors for crossing the BBB. We demonstrate how these receptors can unlock new experimental and computational target-focused engineering strategies by creating the enhanced Ly6c1-binding vector AAV-PHP.eC and by applying AlphaFold2-enabled in silico methods to rank capsids against identified receptors and generate capsid-receptor binding models. Here, with Car4, we add a completely new receptor to the very short list currently available for crossing the BBB in humans and, with Ly6c1, we validate a pipeline for receptor-targeted engineering. The identification of Car4/CA4 and structural insights from computational modeling provide new paths toward human brain-penetrant chemicals (drugs) and biologicals (including gene delivery).

bioengineering↗

Single-cell Genome-and-Transcriptome sequencing without upfront whole-genome amplification reveals cell state plasticity of melanoma subclones

Single-cell multi-omics methods are enabling the study of cell state diversity, which is largely determined by the interplay of the genome, epigenome, and transcriptome. Here, we describe Gtag&T-seq, a genome-and-transcriptome sequencing (G&T-seq) protocol of the same single cells that omits whole-genome amplification (WGA) by using direct genomic tagmentation (Gtag). Gtag drastically decreases the cost and improves coverage uniformity at both the single-cell and pseudo-bulk level when compared to WGA-based G&T-seq. We also show that transcriptome-based DNA copy number inference has limited resolution and accuracy, underlining the importance of affordable multi-omic approaches. Moreover, applying Gtag&T-seq to a melanoma xenograft model before treatment and at minimal residual disease revealed differential cell state plasticity and treatment response between cancer subclones. In summary, Gtag&T-seq is a low-cost and accurate single-cell multi-omics method enabling the exploration of genetic alterations and their functional consequences in single cells at scale.

genomics↗

An Autoinhibited Conformation of the DnaB-Replicative Helicase phage Lambda P Loader Complex

Replicative helicases require loader proteins for assembly at the origins of DNA replication. Multiple copies of the bacteriophage {lambda}P (P) loader bind to and load the E. coli DnaB (B) replicative helicase on replication-origin-derived single-stranded DNA. We find that the E. coli DnaB*{lambda}P complex exists in two forms: B6P5 and B6P6. In the 2.66 [A] cryo-EM model of B6P5, five copies of the {lambda}P loader assemble into a crown-like shape that tightly grips DnaB. In this complex, closed planar DnaB is reconfigured into an open spiral with a sufficiently sized breach to permit ssDNA to enter an internal chamber. The transition to the open spiral involves {lambda}P-mediated changes to the Docking Helix (DH)-Linker Helix (LH) interface. The loader directly stabilizes the open spiral. Unexpectedly, one {lambda}P chain in B6P5 is bound across the breach, precluding entry of replication-origin-derived ssDNA into DnaBs central chamber. We suggest that the B6P6 complex is an early intermediate in the helicase activation pathway wherein neither the DnaB helicase nor the {lambda}P loader has attained its final form. DnaB in this complex adopts a partially open planar configuration, termed ajar planar. The partially ordered {lambda}P loader assembly features a much looser interaction with DnaB. The ssDNA and ATP sites in both complexes are in a configuration ill-suited for binding or hydrolysis. Our work specifies the conformational changes required for the intermediate B6P6 to transition to B6P5 on the pathway to recruitment by the initiator protein complex to the replication origin. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=99 SRC="FIGDIR/small/522210v4_ufig1.gif" ALT="Figure 1"> View larger version (30K): org.highwire.dtl.DTLVardef@1c44809org.highwire.dtl.DTLVardef@1554deeorg.highwire.dtl.DTLVardef@16f6df9org.highwire.dtl.DTLVardef@9d12dd_HPS_FORMAT_FIGEXP M_FIG C_FIG The DnaB helicase loading pathway at the phage {lambda} replication origin populates two intermediate states, distinguished by the number of {lambda}P loaders present. The DnaB ring in the B6P6 complex is planar and partially open. Although it binds six copies of the {lambda}P loader, the ajar planar state of DnaB yields inchoate interactions with the loader. During the maturation of the complex, the planar state of DnaB is reconfigured into an open spiral in the B6P5 complex, which the pentameric {lambda}P ensemble now grips tightly. This transition required the eviction of one copy of the loader. Although the breach in the DnaB open spiral is sufficiently sized for entry of ssDNA into the internal chamber, the disposition of one {lambda}P chain loader across the single breached interface in DnaB effectively blocks the path to physiological replication origin-derived ssDNA. DnaB is depicted in white/gray ribbon format under a transparent surface. The {lambda}P chains are colored orange and shades of blue. The pink cylinder represents the expected path of ssDNA through DnaB.

biochemistry↗

Ribosomal s6 kinase (RSK) is a mediator of aquaporin 2 S256 phosphorylation and membrane accumulation after EGFR inhibition with erlotinib

Vasopressin (VP) activates PKA, resulting in phosphorylation and membrane accumulation of aquaporin-2 (AQP2). Epidermal growth factor receptor (EGFR) inhibition with erlotinib also induces AQP2 membrane trafficking with a phosphorylation pattern similar to VP, but without increasing PKA activity. Here, we identify the ribosomal s6 kinase (RSK) as the final mediator phosphorylating AQP2 in this novel, erlotinib-induced pathway. We found that RSK was expressed in medullary principal cells in rat kidneys. RSK inhibition with BI-D1870 or siRNA blocked erlotinib-induced AQP2 S256 phosphorylation and membrane trafficking. CRISPR-generated RSK knockout cells failed to show increased S256 phosphorylation in response to erlotinib. Like PKA, RSK was able to phosphorylate AQP2 S256 in vitro. Stimulation of PDK1, a known activator of RSK, caused AQP2 S256 phosphorylation and membrane accumulation similar to erlotinib and VP. We conclude that RSK is the terminal kinase phosphorylating AQP2 at S256 upon EGFR inhibition by erlotinib.

physiology↗

Mutated cells mediate distinct inflammatory responses in clonal hematopoiesis

Clonal hematopoiesis (CH) is an age-associated phenomenon that increases risk for hematologic malignancy and cardiovascular disease. CH is thought to enhance disease risk through inflammation in the peripheral blood1. Here, we profile peripheral blood gene expression in 66,968 single cells from a cohort of 17 CH patients and 7 controls. Using a novel mitochondrial DNA barcoding approach, we were able to identify and separately compare mutant TET2 and DNMT3A cells to non-mutant counterparts. We discovered the vast majority of mutated cells were in the myeloid compartment. Additionally, patients harboring DNMT3A and TET2 CH mutations possessed a pro-inflammatory profile in CD14+ monocytes through previously unrecognized pathways such as galectin and macrophage Inhibitory Factor (MIF). We also found that T cells from CH patients, though mostly un-mutated, had decreased expression of GTPase of the immunity associated protein (GIMAP) genes, which are critical to T cell development, suggesting that CH may impair T cell function. Key points- CD14+ monocytes from clonal hematopoiesis patients stimulate inflammation through increased cytokine expression. - T cells from clonal hematopoiesis are deficient in GIMAP expression, suggesting CH may impair T cell differentiation.

genetics↗

A bi-functional PARP-HDAC inhibitor with activity in Ewing sarcoma

HDAC inhibition has been shown to induce pharmacological BRCAness in cancer cells with proficient DNA repair activity. This provides a rationale for exploring combination treatments with HDAC and PARP inhibition in cancer types that are insensitive to single-agent PARP inhibitors. Here, we report the concept and characterization of a novel bifunctional PARP inhibitor (kt-3283) with dual activity towards PARP1/2 and HDAC enzymes in Ewing sarcoma cells. Compared to the FDA-approved PARP (olaparib) and HDAC (vorinostat) inhibitors, kt-3283 displayed enhanced cytotoxicity in Ewing sarcoma models. The kt-3283-induced cytotoxicity was associated with a strong S and G2/M cell cycle arrest in the nanomolar concentration range and elevated DNA damage as assessed by {gamma}H2AX tracking and comet assays. In three-dimensional spheroid models of Ewing sarcoma, kt-3283 showed efficacy in lower concentrations than olaparib and vorinostat and kt-3283 inhibited colonization of Ewing sarcoma cells in an ex vivo lung metastasis model. In summary, our data demonstrates the preclinical justification for studying the benefit of dual PARP and HDAC inhibition in the treatment of Ewing sarcoma in a clinical trial and provides proof-of-concept for a bi-functional single-molecule therapeutic strategy.

cancer biology↗

ERα-LBD, a novel isoform of estrogen receptor alpha, promotes breast cancer proliferation and endocrine resistance

Estrogen receptor alpha (ER) drives mammary gland development and breast cancer (BC) growth through an evolutionarily conserved linkage of DNA binding and hormone activation functions. Therapeutic targeting of the hormone binding pocket is a widely utilized and successful strategy for breast cancer prevention and treatment. However, resistance to this endocrine therapy is frequently encountered and may occur through bypass or reactivation of ER-regulated transcriptional programs. We now identify the induction of a novel ER isoform, ER-LBD, that is encoded by an alternative ESR1 transcript and lacks the activation function and DNA binding domains. Despite lacking the transcriptional activity, ER-LBD is found to promote breast cancer growth and resistance to the ER antagonist fulvestrant. ER-LBD is predominantly localized to the cytoplasm and mitochondria of BC cells and leads to enhanced glycolysis, respiration and stem-like features. Intriguingly, ER-LBD expression and function does not appear to be restricted to cancers that express full length ER but also promotes growth of triple negative breast cancers and ER-LBD transcript (ESR1-LBD) is also present in BC samples from both ER(+) and ER(-) human tumors. These findings point to ER-LBD as a potential mediator of breast cancer progression and therapy resistance. SIGNIFICANCE STATEMENTEndocrine resistant and metastatic breast cancer (BC) is a clinically significant problem. Our study of fulvestrant resistant cancer cells led to the discovery of a novel ER isoform which we call ER-LBD. Encoded by a truncated transcript variant (ESR1-LBD) and lacking the N-terminal domains (activation of transcription and DNA binding), ER-LBD displays a unique role in BC tumorigenesis and progression by mechanisms that may involve metabolic and cell growth advantages, stemness and therapy resistance. Importantly, ESR1-LBD is preferentially expressed in human breast tumor tissues and may be used as prognostic marker in BC.

cancer biology↗

Assessing microbial growth of six pure cultures grown anaerobically using optical density, ATP measurements, DNA concentrations and 16S rRNA targeted qPCR to compare commonly used techniques in lab and industry settings

This is a paper focusing on the comparison of growth curves using field relevant testing methods and moving away from colony counts. Challenges exist to explore antimicrobial growth of fastidious strains, poorly culturable bacterial and bacterial communities of environmental interest. Thus, various approaches have been explored to follow bacteria growth that can be an efficient surrogate for classical optical density or colony forming unit measurements. Here we tested optical density, ATP assays, DNA concentrations and 16S rRNA qPCR as means to monitor pure culture growth of six different species including Acetobacterium woodii, Bacillus subtilis, Desulfovibrio vulgaris, Geoalkalibacter subterraneus, Pseudomonas putida and Thauera aromatica. Optical density is and excellent, rapid monitoring method of pure culture planktonic cells but cannot be applied to environmental or complex samples. ATP assays provide rapid results but conversions to cell counts may be misleading for different species. DNA concentration is a very reliable technique which can be used for any sample type and provides genetic materials for downstream applications. qPCR of the 16S rRNA gene is a widely applicable technique for monitoring microbial cell concentrations but is susceptible to variation between replicates. DNA concentrations were found to correlate the best with the other three assays and provides the advantages of rapid extraction, consistency between replicates and potential for downstream analysis, DNA concentrations is determined to be the best universal monitoring method for complex environmental samples.

microbiology↗

Cerebrospinal fluid outflow through skull channels instructs cranial hematopoiesis

Interactions between the immune and central nervous systems strongly influence brain health. Although the blood-brain barrier restricts this crosstalk, we now know that meningeal gateways through brain border tissues, particularly dural lymphatic vessels that allow cerebrospinal fluid outflow, facilitate intersystem communication. Here we observe that cerebrospinal fluid exits into the skull bone marrow. Fluorescent tracers injected into the cisterna magna of mice travel through hundreds of sub-millimeter skull channels into the calvarial marrow. During meningitis, bacteria usurp this perivascular route to infect the skulls hematopoietic niches and initiate cranial hematopoiesis ahead of remote tibial sites. Because skull channels also directly provide leukocytes to meninges, the privileged sampling of brain-derived danger signals in cerebrospinal fluid by regional marrow has broad implications for neurological disorders. One-Sentence SummarySkull channels transport cerebrospinal fluid from the subarachnoid space to the cranial bone marrow via a perivascular route, which bacteria use during meningitis.

immunology↗

Deep parallel characterization of AAV tropism and AAV-mediated transcriptional changes via single-cell RNA sequencing

Engineered variants of recombinant adeno-associated viruses (rAAVs) are being developed rapidly to meet the need for gene-therapy delivery vehicles with particular cell-type and tissue tropisms. While high-throughput AAV engineering and selection methods have generated numerous variants, subsequent tropism and response characterization have remained low throughput and lack resolution across the many relevant cell and tissue types. To fully leverage the output of these large screening paradigms across multiple targets, we have developed an experimental and computational single-cell RNA sequencing (scRNA-seq) pipeline for in vivo characterization of barcoded rAAV pools at unprecedented resolution. Using our platform, we have corroborated previously reported viral tropisms and discovered unidentified AAV capsid targeting biases. As expected, we observed that the tropism profile of AAV.CAP-B10 in mice was shifted toward neurons and away from astrocytes when compared with AAV-PHP.eB. Our transcriptomic analysis revealed that this neuronal bias is mainly due to increased targeting efficiency for glutamatergic neurons, which we confirmed by RNA fluorescence in situ hybridization. We further uncovered cell subtype tropisms of AAV variants in vascular and glial cells, such as low transduction of pericytes and Myoc+ astrocytes. Additionally, we have observed cell-type-specific responses to systemic AAV-PHP.eB administration, such as upregulation of genes involved in p53 signaling in endothelial cells three days post-injection, which return to control levels by day twenty-five. Such ability to parallelize the characterization of AAV tropism and simultaneously measure the transcriptional response of transduction will facilitate the advancement of safe and precise gene delivery vehicles.

bioengineering↗

The role of migration in mutant evolution in fragmented populations

Mutant evolution in fragmented populations has been studied extensively in evolutionary biology. With an increased focus on evolutionary dynamics in medical research, quantification of mutant load in fragmented populations with varying levels of migration has become especially important. Examples of fragmented populations are hematopoietic stem cell niches in the bone marrow where cells can re-circulate between niches through the blood, or colonic crypts where movement of cells across different crypts is not thought to be common. Here we use a combination of experiments and theory to investigate the role of migration in mutant distribution. In the case of neutral mutants, the experiments confirmed that while the mean number of mutants is not influenced by migration, the probability distribution is, which manifested itself in a change in the skewedness of the distribution of the mutant numbers in the demes. In the case of disadvantageous mutants, we investigated the phenomenon of the increase in the expected number of mutants compared to that of the selection-mutation balance. In a single deme, this increase is observed when the deme size is lower than the critical size, Nc. In a fragmented system that consists of connected demes with a probability of migration, the increase in mutant numbers above the selection-mutation balance can be maintained in small (N < Nc) demes as long as the migration rate is sufficiently small. The migration rate above which the mutants approach the selection-mutation balance decays exponentially with N/Nc. These findings are relevant in the context of the complex and poorly understood processes that may lead to changes in the clonal composition in tissues and tumors.

evolutionary biology↗

The duration of antibiotic treatment is associated with carriage of toxigenic and atoxigenic strains of Clostridioides difficile in dogs.

Clostridioides difficile is a leading cause of human antibiotic-associated diarrhoeal disease globally. Zoonotic reservoirs of infection are increasingly suspected to play a role in the emergence of this disease in the community and dogs are considered as one potential source. Here we use a canine case-control study at a referral veterinary hospital in Scotland to assess: i) the risk factors associated with carriage of C. difficile by dogs, ii) whether carriage of C. difficile is associated with clinical disease in dogs and iii) the similarity of strains isolated from dogs with local human clinical surveillance. The overall prevalence of C. difficile carriage in dogs was 18.7% (95% CI 14.8-23.2%, n=61/327) of which 36% (n=22/61) were toxigenic strains. We found risk factors related to prior antibiotic treatment were significantly associated with C. difficile carriage by dogs. However, the presence of toxigenic strains of C. difficile in a canine faecal sample was not associated with diarrhoeal disease in dogs. Active toxin was infrequently detected in canine faecal samples carrying toxigenic strains (2/11 samples). Both dogs in which active toxin was detected had no clinical evidence of gastrointestinal disease. Among the ten toxigenic ribotypes of C. difficile detected in dogs in this study, six of these (012, 014, 020, 026, 078, 106) were ribotypes commonly associated with human clinical disease in Scotland, while atoxigenic isolates largely belonged to 010 and 039 ribotypes. Whilst C. difficile does not appear commonly associated with diarrhoeal disease in dogs, antibiotic treatment increases carriage of this bacteria including toxigenic strains commonly found in human clinical disease.

microbiology↗

Versatile labeling and detection ofendogenous proteins using tag-assistedsplit enzyme complementation

Recent advances in genome engineering have expanded our capabilities to study proteins in their natural states. In particular, the ease and scalability of knocking-in small peptide tags has enabled high throughput tagging and analysis of endogenous proteins. To improve enrichment capacities and expand the functionality of knock-ins using short tags, we developed the tag-assisted split enzyme complementation (TASEC) approach, which uses two orthogonal small peptide tags and their cognate binders to conditionally drive complementation of a split enzyme upon labeled protein expression. Using this approach, we have engineered and optimized the tag-assisted split HaloTag complementation system (TA-splitHalo) and demonstrated its versatile applications in improving the efficiency of knock-in cell enrichment, detection of protein-protein interaction, and isolation of biallelic gene edited cells through multiplexing.

bioengineering↗

HP1 proteins compact DNA into mechanically and positionally stable phase separated domains

In mammals HP1-mediated heterochromatin forms positionally and mechanically stable genomic domains even though the component HP1 paralogs, HP1, HP1{beta}, and HP1{gamma}, display rapid on-off dynamics. Here we investigate whether phase-separation by HP1 proteins can explain these biological observations. Using bulk and single-molecule methods, we show that, within phase-separated HP1-DNA condensates, HP1 acts as a dynamic liquid, while compacted DNA molecules are constrained in local territories. These condensates are resistant to large forces yet can be readily dissolved by HP1{beta}. Finally, we find that differences in each HP1 paralogs DNA compaction and phase-separation properties arise from their respective disordered regions. Our findings suggest a generalizable model for genome organization in which a pool of weakly bound proteins collectively capitalize on the polymer properties of DNA to produce self-organizing domains that are simultaneously resistant to large forces at the mesoscale and susceptible to competition at the molecular scale.

biochemistry↗

Improved yellow-green split fluorescent proteins for protein labeling and signal amplification

The flexibility and versatility of self-complementing split fluorescent proteins (FPs) have enabled a wide range of applications. In particular, the FP1-10/11 split system contains a small fragment that facilitates efficient generation of endogenous-tagged cell lines and animals as well as signal amplification using tandem FP11 tags. To improve the FP1-10/11 toolbox we previously developed, here we used a combination of directed evolution and rational design approaches, resulting in two mNeonGreen (mNG)-based split FPs (mNG3A1-10/11 and mNG3K1-10/11) and one mClover-based split FP (CloGFP1-10/11). mNG3A1-10/11 and mNG3K1-10/11 not only enhanced the complementation efficiency at low expression levels, but also allowed us to demonstrate signal amplification using tandem mNG211 fragments in mammalian cells.

bioengineering↗

Enabling out-of-clinic human immunity studies via single-cell profiling of capillary blood

An individuals immune system is driven by both genetic and environmental factors that vary over time. To better understand the temporal and inter-individual variability of gene expression within distinct immune cell types, we developed a platform that leverages multiplexed single-cell sequencing and out-of-clinic capillary blood extraction to enable simplified, cost-effective profiling of the human immune system across people and time at single-cell resolution. Using the platform, we detect widespread differences in cell type-specific gene expression between subjects that are stable over multiple days. SummaryIncreasing evidence implicates the immune system in an overwhelming number of diseases, and distinct cell types play specific roles in their pathogenesis.1,2 Studies of peripheral blood have uncovered a wealth of associations between gene expression, environmental factors, disease risk, and therapeutic efficacy.4 For example, in rheumatoid arthritis, multiple mechanistic paths have been found that lead to disease, and gene expression of specific immune cell types can be used as a predictor of therapeutic non-response.12 Furthermore, vaccines, drugs, and chemotherapy have been shown to yield different efficacy based on time of administration, and such findings have been linked to the time-dependence of gene expression in downstream pathways.21,22,23 However, human immune studies of gene expression between individuals and across time remain limited to a few cell types or time points per subject, constraining our understanding of how networks of heterogeneous cells making up each individuals immune system respond to adverse events and change over time.

bioengineering↗

Active synthesis of collagen (I) homotrimer and matrisomal proteins in Dupuytren's fibrosis

Dupuytrens disease is a common fibroproliferative disease of the palmar fascia of the hand with advanced cases treated surgically. Anti-tumour necrosis factor (TNF) injection has undergone phase 2 trials and may be effective in slowing early-stage disease progression. Here we sought to determine how new synthesis of type I collagen in Dupuytrens differs from normal palmar fascia samples and to analyse the role of TNF in aberrant collagen synthesis. Model non-fibrotic, but fibrous connective tissues, were used to analyse active type I collagen protein synthesis in development, ageing and degenerative disease, where it was restricted to early development and ruptured tissue. Dupuytrens tissue was shown to actively synthesise type I collagen, including abnormal type I collagen homotrimer. TNF- reduced COL1A2 gene expression only in the presence of serum in 2D cell culture and had opposing effects on collagen protein production in the presence or absence of serum. TNF- had only limited effects in 3D tendon-like constructs. Anti-TNF did not reduce type I collagen synthesis in 3D tendon-like constructs or prevent type I collagen homotrimer synthesis in Dupuytrens tissue. Hence, modulation of the TNF- pathway in Dupuytrens disease is unlikely to prevent the pathological collagen accumulation that is characteristic of fibrosis.

cell biology↗

Selective Vulnerability of Senescent Glioblastoma Cells to Bcl-XL Inhibition

Despite decades of research and numerous basic science advances, there have only marginal gains in improving glioblastoma multiforme survival. Therefore, new ideas and approaches for treating this aggressive disease are essential to drive progress forward. Conventional therapies, such as radiation and Temozolomide (TMZ), function to cause oxidative stress and DNA damage yielding a senescent-like state of replicative arrest in susceptible cells. However, increasing evidence demonstrates malignant cells can escape senescence leading to tumor recurrence. Ablation of non-replicating senescent tumor cells after radiation and chemotherapy may be an avenue to reduce the rates of tumor recurrence. Senolytic agents have been developed that selectively target senescent cells, but it remains unknown whether senolytics might be utilized against senescent-like glioma cells. We employed radiation or TMZ to induce a functionally senescent state in human glioblastoma cells. Viable cells that survive these treatments were then utilized to screen candidate senolytic drugs, to identify those selectively effective at ablating senescent-like cells over naive non-tumor and proliferative cells. Among 10 candidate senolytic drugs evaluated, only Bcl-XL inhibitors demonstrated reproducible senolytic activity in radiated or TMZ-treated glioma across the majority of GBM cell lines evaluated. Conversely, Bcl-2 inhibitors and other established senolytic drugs failed to show any consistent senolytic activity. In agreement with these data, Bcl-XL knockdown selectively reduced the viability of senescent-like GBM cells, whereas knockdown of Bcl-2 or Bcl-W yielded no senolytic effect. These findings demonstrate the potential to harness radiation-induced biology to ablate latent surviving cells and highlight Bcl-XL dependency as a potential vulnerability of surviving GBM cells after exposure to radiation or TMZ.

cancer biology↗