Faculty Bibliography

The misfolding and accumulation of the protein fragment beta-amyloid (Abeta) is an early and essential event in the pathogenesis of Alzheimer's disease (AD). Despite close biological similarities among primates, humans appear to be uniquely susceptible to the profound neurodegeneration and dementia that characterize AD, even though nonhuman primates deposit copious Abeta in senile plaques and cerebral amyloid-beta angiopathy as they grow old. Because the amino acid sequence of Abeta is identical in all primates studied to date, we asked whether differences in the properties of aggregated Abeta might underlie the vulnerability of humans and the resistance of other primates to AD. In a comparison of aged squirrel monkeys (Saimiri sciureus) and humans with AD, immunochemical and mass spectrometric analyses indicate that the populations of Abeta fragments are largely similar in the 2 species. In addition, Abeta-rich brain extracts from the brains of aged squirrel monkeys and AD patients similarly seed the deposition of Abeta in a transgenic mouse model. However, the epitope exposure of aggregated Abeta differs in sodium dodecyl sulfate-stable oligomeric Abeta from the 2 species. In addition, the high-affinity binding of 3H Pittsburgh Compound B to Abeta is significantly diminished in tissue extracts from squirrel monkeys compared with AD patients. These findings support the hypothesis that differences in the pathobiology of aggregated Abeta among primates are linked to post-translational attributes of the misfolded protein, such as molecular conformation and/or the involvement of species-specific cofactors.

Almost every aspect of cryo electron microscopy (cryoEM) has been automated over the last few decades. One of the challenges that remains to be addressed is the robust and reliable preparation of vitrified specimens of suitable ice thickness. We present results from a new device for preparing vitrified samples. The successful use of the device is coupled to a new "self-blotting" grid that we have developed to provide a method for spreading a sample to a thin film without the use of externally applied filter paper. This new approach has the advantage of using small amounts of protein material, resulting in large areas of ice of a well defined thickness containing evenly distributed single particles. We believe that these methods will in the future result in a system for vitrifying grids that is completely automated.

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.

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.

The wide range in human skin color results from varying levels of the pigment melanin. Genetic mechanisms underlying coloration differences have been explored, but identified genes do not account for all variation seen in the skin color spectrum. Post-transcriptional and post-translational regulation of factors that determine skin color, including melanin synthesis in epidermal melanocytes, melanosome transfer to keratinocytes and melanosome degradation, is also critical for pigmentation. We therefore investigated proteins that are differentially expressed in melanocytes derived from either White or African American (AA) skin. Two dimensional gel electrophoresis (2-DGE) and mass spectrometry demonstrated that Heat Shock Protein 70-1A (Hsp70-1A) protein levels were significantly higher in AA melanocytes compared to White melanocytes. Hsp70-1A expression significantly correlated with levels of tyrosinase, the rate-limiting melanogenic enzyme, consistent with a proposed role for Hsp70-family members in tyrosinase post-translational modification. Additionally, pharmacologic inhibition and siRNA-mediated down-regulation of Hsp70-1A correlated with pigmentation changes in cultured melanocytes, modified human skin substitutes and ex vivo skin. Furthermore, Hsp70-1A inhibition led to increased autophagy-mediated melanosome degradation in keratinocytes. Our data thus reveal that epidermal Hsp70-1A contributes to the diversity of skin color by regulating the amount of melanin synthesized in melanocytes and modulating autophagic melanosome degradation in keratinocytes.

Cardiolipin is a specific mitochondrial phospholipid that has a high affinity for proteins and that stabilizes the assembly of supercomplexes involved in oxidative phosphorylation. We found that sequestration of cardiolipin in protein complexes is critical to protect it from degradation. The turnover of cardiolipin is slower by almost an order of magnitude than the turnover of other phospholipids. However, in subjects with Barth syndrome, cardiolipin is rapidly degraded via the intermediate monolyso-cardiolipin. Treatments that induce supercomplex assembly decrease the turnover of cardiolipin and the concentration of monolyso-cardiolipin, whereas dissociation of supercomplexes has the opposite effect. Our data suggest that cardiolipin is uniquely protected from normal lipid turnover by its association with proteins, but this association is compromised in subjects with Barth syndrome, leading cardiolipin to become unstable, which in turn causes the accumulation of monolyso-cardiolipin.

In visceral leishmaniasis (VL), it is well-known that a patient in clinical remission of VL remains immune to reinfection, which provides a rationale for the feasibility of a vaccine against this deadly disease. In earlier studies, observation of significant cellular responses in treated Leishmania patients as well as in hamsters against leishmanial antigens from different fractions led to its further proteomic characterization, wherein S-Adenosyl-L-Homocysteine Hydrolase (AdoHcy) was identified as Th1 stimulatory protein. The present study includes immunological characterization of this protein, its cellular responses (lymphoproliferation, NO production and cytokine responses) in treated Leishmania infected hamsters and patients as well as prophylactic efficacy against Leishmania challenge in hamsters and the immune responses generated thereof. Significantly higher cellular responses were noticed against recombinant L. donovani S-Adenosyl-L-Homocysteine Hydrolase (rLdAdoHcy) as compared to soluble L. donovani antigen in treated samples. Moreover, stimulation of peripheral blood mononuclear cells with rLdAdoHcy up-regulated the levels of IFN-gamma, IL-12 and down-regulated IL-10. Furthermore, vaccination with rLdAdoHcy generated perceptible delayed type hypersensitivity response and exerted considerably good prophylactic efficacy ( approximately 70% inhibition) against L. donovani challenge. The efficacy was confirmed by the increased expression levels of inducible NO synthase and Th1-type cytokines, IFN-gamma and IL-12 and down-regulation of IL-4, IL-10 and TGF-beta. The results indicate towards the potentiality of rLdAdoHcy protein as a suitable vaccine candidate against VL

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.