Faculty Bibliography

INTRODUCTION:Epidemiologic studies have demonstrated an association between diabetes and dementia. Insulin signaling within the brain, in particular within the hypothalamus regulates carbohydrate, lipid, and branched chain amino acid (BCAA) metabolism in peripheral organs such as the liver and adipose tissue. We hypothesized that cerebral amyloidosis impairs central nervous system control of metabolism through disruption of insulin signaling in the hypothalamus, which dysregulates glucose and BCAA homeostasis resulting in increased susceptibility to diabetes. METHODS:We examined whether APP/PS1 mice exhibit increased susceptibility to aging or high-fat diet (HFD)-induced metabolic impairment using metabolic phenotyping and insulin-signaling studies. RESULTS:APP/PS1 mice were more susceptible to high-fat feeding and aging-induced metabolic dysregulation including disrupted BCAA homeostasis and exhibited impaired hypothalamic insulin signaling. DISCUSSION:Our data suggest that AD pathology increases susceptibility to diabetes due to impaired hypothalamic insulin signaling, and that plasma BCAA levels could serve as a biomarker of hypothalamic insulin action in patients with AD.

[This corrects the article DOI: 10.1371/journal.pgen.1005625.].

The mechanisms that coordinate and balance a complex network of opposing regulators to control Schwann cell (SC) differentiation remain elusive. Here we demonstrate that zinc-finger E-box-binding homeobox 2 (Zeb2, also called Sip1) transcription factor is a critical intrinsic timer that controls the onset of SC differentiation by recruiting histone deacetylases HDAC 1 and 2 (HDAC1/2) and nucleosome remodeling and deacetylase complex (NuRD) co-repressor complexes in mice. Zeb2 deletion arrests SCs at an undifferentiated state during peripheral nerve development and inhibits remyelination after injury. Zeb2 antagonizes inhibitory effectors including Notch and Sox2. Importantly, genome-wide transcriptome analysis reveals a Zeb2 target gene encoding the Notch effector Hey2 as a potent inhibitor for Schwann cell differentiation. Strikingly, a genetic Zeb2 variant associated with Mowat-Wilson syndrome disrupts the interaction with HDAC1/2-NuRD and abolishes Zeb2 activity for SC differentiation. Therefore, Zeb2 controls SC maturation by recruiting HDAC1/2-NuRD complexes and inhibiting a Notch-Hey2 signaling axis, pointing to the critical role of HDAC1/2-NuRD activity in peripheral neuropathies caused by ZEB2 mutations.

Helical reconstruction represents a convenient and powerful approach for structure determination of macromolecules that assemble into helical arrays. In the case of membrane proteins, formation of tubular crystals with helical symmetry represents an attractive alternative, especially when their small size precludes the use of single-particle analysis. An essential first step for helical reconstruction is to characterize the helical symmetry. This process is often daunting, due to the complexity of helical diffraction and to the low signal-to-noise ratio in images of individual assemblies. Furthermore, the large diameters of the tubular crystals produced by membrane proteins exacerbates the innate ambiguities that, if not resolved, will produce incorrect structures. In this report, we describe a set of tools that can be used to eliminate ambiguities and to validate the choice of symmetry. The first approach increases the signal-to-noise ratio along layer lines by incoherently summing data from multiple helical assemblies, thus producing several candidate indexing schemes. The second approach compares the layer lines from images with those from synthetic models built with the various candidate schemes. The third approach uses unit cell dimensions measured from collapsed tubes to distinguish between these candidate schemes. These approaches are illustrated with tubular crystals from a boron transporter from yeast, Bor1p, and a beta-barrel channel from the outer membrane of E. coli, OmpF.

BACKGROUND:Indications for nipple-sparing mastectomy (NSM) are expanding; however, high-risk patients have more ischemic complications. Surgical devascularization of the nipple-areolar complex (NAC) prior to NSM can reduce complications. This study reports perfusion patterns and complications in high-risk patients undergoing 2-stage NSM. METHODS:Surgical devascularization of the NAC was performed 3-6 weeks prior to NSM in 28 women. Risk factors included ptosis, obesity, smoking, prior breast surgery, and radiation. Using indocyanine green (ICG)-based fluorescence and an infrared camera, blood inflow was visualized intraoperatively. NAC perfusion patterns were classified as: V1, underlying breast; V2, surrounding skin; V3 = V1 + V2, or V4, capillary fill following devascularization. Ischemic complications were analyzed. RESULTS:Baseline perfusion for 54 breasts was 35 % V1, 32 % V2, and 33 % V3. Increasing ptosis was associated with V1 pattern: 86 % for grade 3, 31 % for grade 2, and 18 % for grade 1. Postdevascularization epidermolysis was observed in 63 % of V1 baseline, 41 % of V2, and 22 % of V3 (P = .042) and after NSM in 26 % for V1, 7 % for V2, and 6 % for V3 (P = .131). Ptosis was significantly associated with epidermolysis postdevascularization (P = .002) and NSM (P = .002). Smoking and BMI ≥30 were related to increased ischemic complications. Two or more risk factors were associated with postdevascularization ischemic changes (P = .026), but were not significant after NSM. Nipple loss was not observed, but 2 patients underwent partial areolar resection. CONCLUSION/CONCLUSIONS:Adaptive circulatory changes after devascularization allow tissues to tolerate the additional ischemic challenge of mastectomy. Our findings support extending 2-staged operations to high-risk women previously considered unsuitable for NSM.

Identification and characterization of molecular mechanisms that connect genetic risk factors to initiation and evolution of disease pathophysiology represent major goals and opportunities for improving therapeutic and diagnostic outcomes in Alzheimer's disease (AD). Integrative genomic analysis of the human AD brain transcriptome holds potential for revealing novel mechanisms of dysfunction that underlie the onset and/or progression of the disease. We performed an integrative genomic analysis of brain tissue-derived transcriptomes measured from two lines of mice expressing distinct mutant AD-related proteins. The first line expresses oligomerogenic mutant APP(E693Q) inside neurons, leading to the accumulation of amyloid beta (Abeta) oligomers and behavioral impairment, but never develops parenchymal fibrillar amyloid deposits. The second line expresses APP(KM670/671NL)/PSEN1(Deltaexon9) in neurons and accumulates fibrillar Abeta amyloid and amyloid plaques accompanied by neuritic dystrophy and behavioral impairment. We performed RNA sequencing analyses of the dentate gyrus and entorhinal cortex from each line and from wild-type mice. We then performed an integrative genomic analysis to identify dysregulated molecules and pathways, comparing transgenic mice with wild-type controls as well as to each other. We also compared these results with datasets derived from human AD brain. Differential gene and exon expression analysis revealed pervasive alterations in APP/Abeta metabolism, epigenetic control of neurogenesis, cytoskeletal organization and extracellular matrix (ECM) regulation. Comparative molecular analysis converged on FMR1 (Fragile X Mental Retardation 1), an important negative regulator of APP translation and oligomerogenesis in the post-synaptic space. Integration of these transcriptomic results with human postmortem AD gene networks, differential expression and differential splicing signatures identified significant similarities in pathway dysregulation, including ECM regulation and neurogenesis, as well as strong overlap with AD-associated co-expression network structures. The strong overlap in molecular systems features supports the relevance of these findings from the AD mouse models to human AD.

ECF transporters are a family of active membrane transporters for essential micronutrients, such as vitamins and trace metals. Found exclusively in archaea and bacteria, these transporters are composed of four subunits: an integral membrane substrate-binding subunit (EcfS), a transmembrane coupling subunit (EcfT), and two ATP-binding cassette ATPases (EcfA and EcfA'). We have characterized the structural basis of substrate binding by the EcfS subunit for riboflavin from T. maritima, TmRibU. TmRibU binds riboflavin with high affinity, and the protein-substrate complex is exceptionally stable in solution. The crystal structure of riboflavin-bound TmRibU reveals an electronegative binding pocket at the extracellular surface in which the substrate is completely buried. Analysis of the intermolecular contacts indicates that nearly every available substrate hydrogen bond is satisfied. A conserved aromatic residue at the extracellular end of TM5, Tyr130, caps the binding site to generate a substrate-bound occluded state, and nonconservative mutation of Tyr130 reduces the stability of this conformation. Using a novel fluorescence binding assay, we find that an aromatic residue at this position is essential for high affinity substrate binding. Comparison with other S subunit structures suggests that TM5 and Loop5-6 contain a dynamic conserved motif that plays a key role in gating substrate entry and release by S subunits of ECF transporters.

Multicellular systems develop from single cells through distinct lineages. However, current lineage-tracing approaches scale poorly to whole, complex organisms. Here, we use genome editing to progressively introduce and accumulate diverse mutations in a DNA barcode over multiple rounds of cell division. The barcode, an array of clustered regularly interspaced short palindromic repeats (CRISPR)/Cas9 target sites, marks cells and enables the elucidation of lineage relationships via the patterns of mutations shared between cells. In cell culture and zebrafish, we show that rates and patterns of editing are tunable and that thousands of lineage-informative barcode alleles can be generated. By sampling hundreds of thousands of cells from individual zebrafish, we find that most cells in adult organs derive from relatively few embryonic progenitors. In future analyses, genome editing of synthetic target arrays for lineage tracing (GESTALT) can be used to generate large-scale maps of cell lineage in multicellular systems for normal development and disease.

Lipid accumulation in macrophages has profound effects on macrophage gene expression and contributes to the development of atherosclerosis. Here, we report that angiopoietin-like protein 4 (ANGPTL4) is the most highly upregulated gene in foamy macrophages and it's absence in haematopoietic cells results in larger atherosclerotic plaques, characterized by bigger necrotic core areas and increased macrophage apoptosis. Furthermore, hyperlipidemic mice deficient in haematopoietic ANGPTL4 have higher blood leukocyte counts, which is associated with an increase in the common myeloid progenitor (CMP) population. ANGPTL4-deficient CMPs have higher lipid raft content, are more proliferative and less apoptotic compared with the wild-type (WT) CMPs. Finally, we observe that ANGPTL4 deficiency in macrophages promotes foam cell formation by enhancing CD36 expression and reducing ABCA1 localization in the cell surface. Altogether, these findings demonstrate that haematopoietic ANGPTL4 deficiency increases atherogenesis through regulating myeloid progenitor cell expansion and differentiation, foam cell formation and vascular inflammation.