Faculty Bibliography

OBJECTIVES: The goal of this study was to develop and validate a noninvasive imaging tool to visualize the in vivo behavior of high-density lipoprotein (HDL) by using positron emission tomography (PET), with an emphasis on its plaque-targeting abilities. BACKGROUND: HDL is a natural nanoparticle that interacts with atherosclerotic plaque macrophages to facilitate reverse cholesterol transport. HDL-cholesterol concentration in blood is inversely associated with risk of coronary heart disease and remains one of the strongest independent predictors of incident cardiovascular events. METHODS: Discoidal HDL nanoparticles were prepared by reconstitution of its components apolipoprotein A-I (apo A-I) and the phospholipid 1,2-dimyristoyl-sn-glycero-3-phosphocholine. For radiolabeling with zirconium-89 (89Zr), the chelator deferoxamine B was introduced by conjugation to apo A-I or as a phospholipid-chelator (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-deferoxamine B). Biodistribution and plaque targeting of radiolabeled HDL were studied in established murine, rabbit, and porcine atherosclerosis models by using PET combined with computed tomography (PET/CT) imaging or PET combined with magnetic resonance imaging. Ex vivo validation was conducted by radioactivity counting, autoradiography, and near-infrared fluorescence imaging. Flow cytometric assessment of cellular specificity in different tissues was performed in the murine model. RESULTS: We observed distinct pharmacokinetic profiles for the two 89Zr-HDL nanoparticles. Both apo A-I- and phospholipid-labeled HDL mainly accumulated in the kidneys, liver, and spleen, with some marked quantitative differences in radioactivity uptake values. Radioactivity concentrations in rabbit atherosclerotic aortas were 3- to 4-fold higher than in control animals at 5 days' post-injection for both 89Zr-HDL nanoparticles. In the porcine model, increased accumulation of radioactivity was observed in lesions by using in vivo PET imaging. Irrespective of the radiolabel's location, HDL nanoparticles were able to preferentially target plaque macrophages and monocytes. CONCLUSIONS: 89Zr labeling of HDL allows study of its in vivo behavior by using noninvasive PET imaging, including visualization of its accumulation in advanced atherosclerotic lesions. The different labeling strategies provide insight on the pharmacokinetics and biodistribution of HDL's main components (i.e., phospholipids, apo A-I).

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.

Aging leads to a proinflammatory state within the vasculature without disease, yet whether this inflammatory state occurs during atherogenesis remains unclear. Here, we examined how aging impacts atherosclerosis using Ldlr(-/-) mice, an established murine model of atherosclerosis. We found that aged atherosclerotic Ldlr(-/-) mice exhibited enhanced atherogenesis within the aorta. Aging also led to increased LDL levels, elevated blood pressure on a low-fat diet, and insulin resistance after a high-fat diet (HFD). On a HFD, aging increased a monocytosis in the peripheral blood and enhanced macrophage accumulation within the aorta. When we conducted bone marrow transplant experiments, we found that stromal factors contributed to age-enhanced atherosclerosis. To delineate these stromal factors, we determined that the vasculature exhibited an age-enhanced inflammatory response consisting of elevated production of CCL-2, osteopontin, and IL-6 during atherogenesis. In addition, in vitro cultures showed that aging enhanced the production of osteopontin by vascular smooth muscle cells. Functionally, aged atherosclerotic aortas displayed higher monocyte chemotaxis than young aortas. Hence, our study has revealed that aging induces metabolic dysfunction and enhances vascular inflammation to promote a peripheral monocytosis and macrophage accumulation within the atherosclerotic aorta.

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.

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.

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.

[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.

BACKGROUND:Nipple reconstruction is the last stage in cosmetic reconstruction of the breast after mastectomy, but no method produces reliable and consistent aesthetic results. This study examined the use of the Biodesign Nipple Reconstruction Cylinder (NRC) during reconstruction of the nipple after mastectomy. METHODS:Patients with a history of breast cancer and mastectomy desiring nipple reconstruction were invited to participate. After obtaining consent, unilateral or bilateral nipple reconstruction was performed. Skin flaps were raised, the NRC was placed beneath the flaps as a stent, and the site was protected for up to 4 weeks with a nipple shield. Nipple projection was measured for 12 months after surgery. Patient satisfaction was measured and adverse events were recorded. Follow-up examinations were performed at 1 week, and then at 1, 3, 6, and 12 months after surgery. RESULTS:Eighty-two nipple reconstructions were performed in 50 patients. Related postoperative adverse events were minor, but reported in 8 reconstructions (9.8%) representing 7 patients (14.0%). Average projection at 6 and 12 months was 4.1 ± 1.6 mm and 3.8 ± 1.5 mm, respectively, compared with 10.5 ± 2.2 mm 1 week after surgery. Of patients completing the satisfaction questionnaire at 12 months, 70/75 (93.3%) of reconstructions were rated "pleased" or "very pleased" with the overall outcome. Overall, 45/46 (97.8%) patients would recommend nipple reconstruction to other women. CONCLUSIONS:The Biodesign NRC offers a safe alternative to nipple reconstruction, resulting in stable projection and a high level of patient satisfaction for 12 months after placement.