Abstract P6-12-06: Nonsteroidal, tissue selective androgen receptor modulator (SARM), enobosarm, reduces growth of androgen receptor-positive breast cancer in patient-derived preclinical models

Introduction: In breast cancer the androgen receptor (AR) is the most abundantly expressed steroid receptor with 75-95% of estrogen receptor (ER)-positive and 40-70% of ER-negative breast cancers expressing the AR. Historically, advanced breast cancer has been treated with androgens, resulting in significant clinical response. However, the use of steroidal androgens fell from favor as a result of their virilizing side effects. Nonsteroidal, tissue selective androgen receptor modulators (SARMs) will provide a novel targeted approach to exploit the therapeutic benefits of androgens in breast cancer.

Aims: To test the effects of enobosarm (a first-in-class SARM) and enzalutamide (AR antagonist) on the growth of patient-derived breast cancer xenografts (PDX) and to discern the mechanism of action of AR-targeted therapies in AR-positive breast cancer.

Materials and Methods: AR-positive PDXs with varying receptor expression (ER, progesterone receptor (PR), and HER2) were implanted in immunecompromised mice. Mice carrying PDXs were treated with vehicle, 10 mg/kg/day (mpk) enobosarm (GTx, Inc., Memphis, TN), or 20 mpk enzalutamide (Medivation Inc.), orally. Tumor volume was measured twice or thrice weekly. Tumors that received enobosarm were further analyzed to determine the mechanism of action.

Results: Enobosarm significantly (p<0.01) inhibited the growth of ER-, PR-, and HER2- positive HCI-7 and ER- and PR- negative and HER2-positive HCI-12 PDX. While enobosarm inhibited the growth of HCI-12 by ~80% and HCI-7 by ~60%, enzalutamide failed to inhibit the growth of the HCI-7 PDX. In contrast, neither enobosarm nor enzalutamide inhibited the growth of ER- and PR-negative and HER2-positive HCI-9 PDX, consistent with the heterogeneity of AR-positive breast cancers. Growth of two triple-negative breast cancer (TNBC) PDXs were inhibited by 30-40% by enobosarm, but not by enzalutamide. These results were reproduced in xenografts developed with breast cancer cell lines, MCF-7 and MDA-MB-231 expressing the AR. Gene expression studies conducted with the HCI-12 tumors indicated that enobosarm inhibited the expression of various proliferative genes (MUC2, IL10RA, IGSF1, SLC6A4, and others) and increased the expression of growth inhibitory genes (CYP4F8, MYBPC1, and others). Ingenuity pathway analysis demonstrated that enobosarm inhibited genes that are downstream of HER2 signaling. Interestingly, miR-21-3p, which has been implicated in chemo-resistance, was consistently expressed at approximately 10-50-fold higher than miR-21-5p in PDXs. This imbalance was partially reversed by enobosarm.

Conclusion: These results indicate that AR-positive breast cancers are highly heterogeneous and that enobosarm has promise as novel targeted therapy to treat AR-positive breast cancer. Enobosarm is currently in phase II clinical trial in both ER-positive breast cancer and in TNBC patients.

Citation Format: Narayanan R, Ponnusamy S, Fan M, Yang CH, Grimes BL, Fleming MD, Pritchard EF, Berry MP, Oswaks RM, Fine RE, Loiseau J-C, Schwartzberg LS, Pfeffer LM. Nonsteroidal, tissue selective androgen receptor modulator (SARM), enobosarm, reduces growth of androgen receptor-positive breast cancer in patient-derived preclinical models [abstract]. In: Proceedings of the 2016 San Antonio Breast Cancer Symposium; 2016 Dec 6-10; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2017;77(4 Suppl):Abstract nr P6-12-06.

A cyclic peptide that binds p75(NTR) protects neurones from beta amyloid (1-40)-induced cell death

The current study determined the ability of a p75(NTR) antagonistic cyclic peptide to rescue cells from beta amyloid (Abeta) (1-40)-induced death. p75(NTR)-, p140(trkA)-NIH-3T3 cells or E17 foetal rat cortical neurones were incubated with 125I-NGF or 125I-Abeta (1-40) and increasing concentrations of the cyclic peptide (CATDIKGAEC). Peptide ability to displace 125I-NGF or 125I-Abeta (1-40) binding was determined. Duplicate cultures were preincubated with CATDIKGAEC (250 nM) or diluent and then stimulated with Abeta (1-40). Peptide ability to displace Abeta (1-40) binding, interfere with Abeta (1-40)-induced signalling and rescue cells from Abeta-mediated toxicity was determined by immunoprecipitation and autoradiography, Northern blotting, JNK activation, MTT and trypan blue assays. The peptide inhibited NGF and Abeta (1-40) binding to p75(NTR), but not to p140(trkA). Abeta (1-40) induced c-jun transcription (57.3% +/- 0.07%) in diluent-treated p75(NTR)-cells, but not in cells preincubated with the cyclic peptide. Also, at 250 nM, the peptide reduced Abeta (1-40)-induced phosphorylation of JNK by 71.8% +/- 0.03% and protected neurones against Abeta-induced toxicity as determined by: trypan blue exclusion assay (53% +/- 11% trypan blue-positive cells in diluent pretreated cultures vs. 28% +/- 5% in cyclic peptide-pretreated cultures); MTT assay (0.09 +/-0.03 units in diluent-pretreated cells vs. 0.12 +/- 0.004 units in cyclic peptide-pretreated cells); and visualization of representative microscopic fields. Our data suggest that a cyclic peptide homologous to amino acids 28-36 of NGF known to mediate binding to p75(NTR) can interfere with Abeta (1-40) signalling and rescue neurones from Abeta (1-40)-induced toxicity.

A prospective study of the removal rate of imaged breast lesions by an 11-gauge vacuum-assisted biopsy probe system

BACKGROUND

More than 1,000,000 breast biopsies are performed each year as a result of abnormalities identified by imaging techniques. This prospective study was designed to determine whether complete removal of the imaged evidence of an abnormal mammogram or ultrasonogram could be achieved with percutaneous image-guided procedures using an 11-gauge vacuum-assisted biopsy probe.

METHODS

Forty-five women over the age of 18 years entered the study; 50 breast lesions were identified by ultrasonography or mammography. Biopsies were obtained using an 11-gauge vacuum-assisted probe. At 6 months after biopsy, ultrasonography or mammography examinations of the biopsy site were performed.

RESULTS

Forty-five lesions (90%) were completely removed. At 6 months after biopsy, 82% of the sites were lesion free. The percentage of nonrecurring lesions at 6 months after surgery was inversely related to the size of the original lesion.

CONCLUSION

This device allows biopsies to be successfully combined with complete removal of the imaged lesion in a one-step minimally invasive procedure.

Decreased expression of the NADH:ubiquinone oxidoreductase (complex I) subunit 4 in 1-methyl-4-phenylpyridinium -treated human neuroblastoma SH-SY5Y cells

Oxidative stress and mitochondrial dysfunction have been implicated in Parkinson's disease (PD) pathology. NADH:ubiquinone oxidoreductase (complex I) (EC 1.6.99.3) enzyme activity is aberrant in both PD and 1-methyl-4-phenylpyridinium (MPP(+)) models of PD. Reverse transcription polymerase chain reaction of RNA isolated from MPP(+)-treated human neuroblastoma SH-SY5Y cells identified changes in steady-state mRNA levels of the mitochondrial transcript for subunit 4 of complex I (ND4). Expression of ND4 decreased to nearly 50% after 72 h of MPP(+) (1 mM) exposure. The expression of other mitochondrial transcripts did not change significantly under the same conditions. Pre-incubation of cells with the free-radical spin-trap, N-tert-butyl-alpha-(2-sulfophenyl)-nitrone prior to MPP(+) exposure, prevented decreases in cell viability and ND4 expression. This suggests that functional defects in complex I enzyme activity in PD and MPP(+) toxicity may result from changes in steady-state mRNA levels and that free radicals may be important in this process.

Calreticulin functions as a molecular chaperone for the β-amyloid precursor protein 1 1Abbreviations used: Aβ, β-amyloid peptide; AD, Alzheimer’s disease; APP, β-amyloid precursor protein; CHAPS, 3-[(3-Cholamidopropyl)-dimethylammonio]-1-propanesulfonate; Crt, calreticulin; DMEM, Dulbecco’s Modified Eagle Medium; DMJ, deoxymannojirimycin; DTSSP, 3,3′-Dithio bis (sulfosuccinimidylpropionate); ECL, Enhanced Chemiluminescence; ER, endoplasmic reticulum; FBS, fetal bovine serum; HRP, horseradish peroxidase; kDa, kiloDaltons; MES, 2-(N-Morpholino) ethane sulfonic acid; NRS, normal rabbit serum; PBS, PBS; PMSF, phenymethylsulfonyl fluoride; PVDF, polyvinylidene fluoride

Processing of the beta-amyloid precursor protein (APP) in the endoplasmic reticulum and the Golgi apparatus may be critical in generating the beta-amyloid molecules linked to the pathogenesis of Alzheimer's disease. Since chaperone molecules such as calreticulin (Crt) have been shown to be important in the maturation of many glycoproteins, we investigated the interaction between Crt and APP. We show that APP binds transiently to Crt in a manner that is pH, divalent cation, and N-linked glycosylation-dependent. Both immature APP (containing only N-linked sugars) and mature APP (containing both N-linked and O-linked sugars) bind to Crt. Both proteins are part of a complex that appears to be large enough to accommodate other proteins as well. However, while most of the immature form is associated with the complexes, very little of the mature form is. The interaction between APP and Crt is likely to be of physiological significance with respect to APP maturation since Crt is involved in quality control of nascent glycoproteins in the secretory pathway.

Postmastectomy radiotherapy: clinical practice guidelines of the American Society of Clinical Oncology

OBJECTIVE

To determine indications for the use of postmastectomy radiotherapy (PMRT) for patients with invasive breast cancer with involved axillary lymph nodes or locally advanced disease who receive systemic therapy. These guidelines are intended for use in the care of patients outside of clinical trials.

POTENTIAL INTERVENTION

The benefits and risks of PMRT in such patients, as well as subgroups of these patients, were considered. The details of the PMRT technique were also evaluated.

OUTCOMES

The outcomes considered included freedom from local-regional recurrence, survival (disease-free and overall), and long-term toxicity.

EVIDENCE

An expert multidisciplinary panel reviewed pertinent information from the published literature through July 2000; certain investigators were contacted for more recent and, in some cases, unpublished information. A computerized search was performed of MEDLINE data; directed searches based on the bibliographies of primary articles were also performed.

VALUES

Levels of evidence and guideline grades were assigned by the Panel using standard criteria. A "recommendation" was made when level I or II evidence was available and there was consensus as to its meaning. A "suggestion" was made based on level III, IV, or V evidence and there was consensus as to its meaning. Areas of clinical importance were pointed out where guidelines could not be formulated due to insufficient evidence or lack of consensus.

RECOMMENDATIONS

The recommendations, suggestions, and expert opinions of the Panel are described in this article.

VALIDATION

Seven outside reviewers, the American Society of Clinical Oncology (ASCO) Health Services Research Committee members, and the ASCO Board of Directors reviewed this document.

Tumor necrosis factor alpha increases human cerebral endothelial cell Gb3 and sensitivity to Shiga toxin

Hemolytic uremic syndrome (HUS) is associated with intestinal infection by enterohemorrhagic Escherichia coli strains that produce Shiga toxins. Globotriaosylceramide (Gb3) is the functional receptor for Shiga toxin, and tumor necrosis factor alpha (TNF-alpha) upregulates Gb3 in both human macrovascular umbilical vein endothelial cells and human microvascular brain endothelial cells. TNF-alpha treatment enhanced Shiga toxin binding and sensitivity to toxin. This upregulation was specific for Gb3 species containing normal fatty acids (NFA). Central nervous system (CNS) pathology in HUS could involve cytokine-stimulated elevation of endothelial NFA-Gb3 levels. Differential expression of Gb3 species may be a critical determinant of Shiga toxin toxicity and of CNS involvement in HUS.

Isolation and characterization of substance P-containing dense core vesicles from rabbit optic nerve and termini

In neurons, neuropeptides and other synaptic components are transported down the axon to the synapse in vesicles using molecular motors of the kinesin family. In the synapse, these neuropeptides are found in dense core vesicles (DCVs), and, following calcium-mediated exocytosis, they interact with receptors on the target cell. We have developed a rapid, large-scale technique for purifying peptide-containing DCVs from specific nuclei in the central nervous system. By using differential velocity gradient and equilibrium gradient centrifugation, neuropeptide-containing DCVs can be separated by size and density from optic nerve (ON) and its termini, the lateral geniculate nuclei and the superior colliculi. Isolated DCVs contain neuropeptides (substance P and brain-derived neurotrophic factor), synaptic vesicle (SV) membrane proteins (SV2, synaptotagmins, synaptophysin, Rab3 and synaptobrevin), SV-associated proteins (alpha-synuclein), secretory markers for DCVs previously isolated (secretogranin II), and beta-amyloid precursor protein. By using electron microscopic techniques, DCV were also visualized and shown to be immunoreactive for neuropeptides, neurotrophins, and SV membrane proteins. Because of the interesting group of physiological and potentially pathophysiological proteins associated with these vesicles; this isolation procedure, applicable to other CNS nuclei, should represent an important research tool.

Beta amyloid fragments derived from activated platelets deposit in cerebrovascular endothelium: usage of a novel blood brain barrier endothelial cell model system

Amyloid precursor protein (A betaPP) processing results in generation of amyloid beta peptide (A beta) which deposits in the brain parenchyma and cerebrovasculature of patients with Alzheimer's disease (AD). Evidence that the vascular deposits derive in part from A betaPP fragments originating from activated platelets includes findings that individuals who have had multiple small strokes have a higher prevalence of AD compared to individuals who have taken anti-platelet drugs. Thus, determination of whether platelet A betaPP fragments are capable of traversing the blood-brain barrier (BBB) is critical. We have established that activated platelets from patients with AD retain more surface transmembrane-bound A betaPP (mA betaPP) than control platelets. We report here that this mA betaPP can be cleaved to A beta-containing fragments which pass through a novel BBB model system. This model utilizes human BBB endothelial cells (BEC) isolated from brains of patients with AD. These BEC, after exposure to activated platelets which have been surface-labeled with fluorescein and express surface-retained mA betaPP, cleave fluorescein-tagged surface proteins, including mA betaPP, resulting in passage to the BEC layer The data confirm that BEC contribute to processing of platelet-derived mA betaPP and show that the processing yields A beta containing fragments which could potentially contribute to cerebrovascular A beta deposition.

Antisense oligonucleotide sequences targeting the muscarinic type 2 acetylcholine receptor enhance performance in the Morris water maze

Blocking autoinhibitory muscarinic type 2 (m2) acetylcholine receptors in the central nervous system may increase the release of acetylcholine and improve learning and memory. Antisense oligonucleotides (OGNs) complementary to m2 receptor mRNA were synthesized and evaluated for their efficacy at decreasing receptor number and reversing deficits in a cognitive task. Three antisense OGNs, which decreased m2 receptor binding in NG108-15 cells, were continuously infused into the lateral cerebral ventricle of rats for 6 days at a rate of 0.5 micro1/h and a daily dose of 72 microg. Performance in the Morris water maze was compared to groups receiving control OGNs or vehicle alone. Decrements induced by 0.2 mg/kg of scopolamine i.p. were significantly reversed by 2 of the 3 antisense OGNs. Use of antisense OGNs targeting the m2 receptor may be a new strategy to increase cholinergic neurotransmission and improve learning and memory.

Toxicity of various amyloid beta peptide species in cultured human blood-brain barrier endothelial cells: increased toxicity of dutch-type mutant

The amyloid beta peptide (A beta) is the major component of the neuritic and cerebrovascular amyloid plaques that are one of the characteristic features of Alzheimer's disease (AD). This peptide has been shown to be toxic to several relevant cell types, including neurons, cerebrovascular smooth muscle cells, and endothelial cells. We have studied the toxic effects of both soluble and aggregated species of A beta(1-40) and the mutation A beta(1-40)Glu-->Gln(22), which is the major species deposited in the cerebrovascular blood vessels of victims of hereditary cerebral hemorrhage with amyloidosis, Dutch type. We find that aggregates of both peptides, as well as of A beta(1-42) and A beta(25-35), are toxic to cultured human cerebrovascular endothelial cells (hBEC) obtained from the brain of a victim of AD (at doses lower than those that are toxic to CNS neurons or leptomeningeal smooth muscle cells). Soluble A beta(1-40) Gln(22) is equally toxic to hBEC, whereas wild-type A beta(1-40) is toxic only at higher doses. This toxicity is seen at the lowest dose of A beta(1-40) Gln (22) used, 20 nM. The soluble A beta(1-40)Gln(22) aggregates on the surface of the cells, in contrast to A beta(1-40), and its toxicity can be blocked both by an inhibitor of free radical formation and by Congo red, which inhibits amyloid fibril formation. We discuss the possibility that the enhanced toxicity of A beta(1-40)Gln(22) is mediated by a A beta receptor on the endothelial cells.

Serum amyloid A is present in the capillaries and microinfarcts of hypertensive monkey brain: an immunohistochemical study

Serum amyloid A (SAA) is a major inducible acute phase protein characterized as a transient injury specific constituent of high density lipoprotein. We investigated whether the acute phase SAA (A-apoSAA), as a marker of inflammation, is present in the brain of monkeys with surgically induced hypertension of 39 months duration. Sections from brains of normotensive monkeys (systolic blood pressure < 124 mmHg) and hypertensive monkeys (systolic blood pressure > 185 mmHg) were processed for immunohistochemistry with a rabbit polyclonal antiserum to human A-apoSAA. We found that A-apoSAA was present in hypertensive but not in normotensive brain sections. Staining was localized to capillary endothelial cells and occasionally to the entire vessel wall of the prefrontal cortex. Staining was also observed in the capillaries and in medium size vessels of the corona radiata, the head of the caudate and, to a smaller extent, in the putamen. Additionally, the A-apoSAA was present in cells forming a circular configuration within microinfarcts. These findings suggest that high blood pressure in the brain can result in either local production of A-apoSAA in the capillaries and within microinfarcts or uptake of A-apoSAA from the blood

Serum amyloid A in Alzheimer's disease brain is predominantly localized to myelin sheaths and axonal membrane

Immunohistochemical localization of the injury specific apolipoprotein, acute phase serum amyloid A (A-apoSAA), was compared in brains of patients with neuropathologically confirmed Alzheimer's disease (AD), multiple sclerosis (MS), Parkinson's disease (PD); Pick's disease (Pick's), dementia with Lewy bodies (DLB), coronary artery disease (CAD), and schizophrenia. Affected regions of both AD and MS brains showed intense staining for A-apoSAA in comparison to an unaffected region and non-AD/MS brains. The major site of A-apoSAA staining in both diseases was the myelin sheaths of axons in layers V and VI of affected cortex. A-apoSAA contains a cholesterol binding site near its amino terminus and is likely to have a high affinity for cholesterol-rich myelin. These findings, along with our recent evidence that A-apoSAA can inhibit lipid synthesis in vascular smooth muscle cells suggest that A-apoSAA plays a role in the neuronal loss and white matter damage occurring in AD and MS.

Kinesin participates in melanosomal movement along melanocyte dendrites

Movement of melanosomes along melanocyte dendrites is necessary for the transfer of melanin pigment from melanocytes to basal and suprabasal keratinocytes, an event critical to epidermal photoprotection and maintenance of normal skin color. Recent murine data suggest that in melanocyte dendrites the microtubule-associated melanosome movement is bidirectional and that actin-associated myosin V secures the peripheral melanosomes, preparing them to be transferred to surrounding keratinocytes. We now report that human melanocytes express high levels of kinesin, a molecule that participates in microtubule-associated transport of organelles in other cell types, and that ultrastructurally kinesin molecules are closely associated with melanosomes. To determine whether kinesin participates in melanosomal transport, cultured melanocytes were treated with sense or antisense oligonucleotides complementary to kinesin heavy chain sequences. Antisense oligonucleotides decreased kinesin protein levels and inhibited the bidirectional movement of the melanosomes, promoting their backward movement. Furthermore, guinea pigs were exposed to ultraviolet B irradiation, known to enhance transport of melanosomes from melanocytes to epidermal keratinocytes, and then were treated with kinesin sense or antisense oligonucleotides. The areas that were treated with kinesin antisense oligonucleotides showed significantly less pigmentation clinically and histologically than control (sense) oligonucleotide-treated areas. As observed ultrastructurally, in antisense-treated areas melanosomes remained in melanocyte dendrites but over several days were not transferred to the surrounding keratinocytes. Our study supports a major role for kinesin in microtubule-associated anterograde melanosomal transport in human melanocyte dendrites.

Calreticulin is transported to the surface of NG108-15 cells where it forms surface patches and is partially degraded in an acidic compartment

Although calreticulin (Crt) is primarily localized to the endoplasmic reticulum (ER), our results using biotinylation and immunocytochemical methods indicate that a small but significant amount of Crt is present and forms large patches on the surface of NG108-15 cells (a mouse neuroblastoma-rat glioma hybrid cell line). (35)S-labelled Crt molecules begin to reach the cell surface after only 10 min of labelling and disappear slowly from the cell surface. After 4 hr of labelling, approximately half of the newly synthesized Crt molecules are on the cell surface. We believe that some Crt molecules may escape from the KDEL receptor-mediated salvage pathway as they are synthesized and proceed through the secretory pathway to the cell surface. Immunoprecipitation from the culture medium shows that Crt is not released from the cell surface to the medium, suggesting tight binding to surface molecules. NH(4)Cl can block the degradation of Crt; therefore, Crt is presumably degraded in the lysosome pathway. However, blockage of the disappearance of surface Crt is less efficient than that of internal Crt. This suggests that the disappearance of Crt from the cell surface may not be due solely to its degradation, but may reflect transport into another cell compartment such as the ER.

Apolipoprotein serum amyloid A down-regulates smooth-muscle cell lipid biosynthesis

The addition of acute-phase apolipoprotein serum amyloid A (SAA) to cultured aortic smooth-muscle cells caused a decrease in the incorporation of [(14)C]acetate into lipids. Optimal inhibition of lipid biosynthesis was achieved with 2 microM SAA, and the effect was maintained for up to 1 week when SAA was included in the culture medium. Lipid extracts were subjected to TLC and it was determined that the SAA-induced decrease in [(14)C]acetate incorporation into lipids was attributable to decreases in cholesterol, phospholipid and triglyceride levels. The accumulated mass of cholesterol and phospholipid in SAA-treated cultures was significantly less than that of controls, with no change in the accumulated protein. Moreover, SAA had no effect on either protein synthesis or DNA synthesis, suggesting that SAA specifically alters lipid synthesis. By using a peptide corresponding to the cholesterol-binding domain of acute-phase SAA (amino acids 1-18), it was shown that this region of the molecule was as effective as the full-length protein in decreasing lipid synthesis and the accumulation of cholesterol and phospholipid. The implications of these findings for atherosclerosis and Alzheimer's disease are discussed.

KDEL proteins are found on the surface of NG108-15 cells

Although KDEL proteins are primarily localized to the endoplasmic reticulum (ER), we have employed surface biotinylation method to demonstrate that the KDEL proteins calreticulin (Crt), protein disulfide isomerase (PDI) and the 78-kDa glucose regulated protein (GRP78) are found on the surface of the NG108-15 cell line. In contrast, the 94-kDa glucose regulated protein (GRP94), another KDEL protein, is not found on the cell surface. Calnexin (Cnx), a type-1 integral transmembrane ER protein which is partially homologous to Crt but lacks the KDEL sequence, is not detected on the cell surface either. While only small amounts of the total GRP78, PDI and Crt molecules exist on the cell surface at steady state, a significant fraction of the newly synthesized molecules are transported to the cell surface and transport of these proteins is inhibited by treatment with brefeldin A. The surface GRP78 contains the KDEL sequence. On the cell surface, GRP78, PDI and Crt associate with other proteins and form complexes of different sizes. Surface Crt is found to be essential for the neurite formation when NG108-15 cells are induced to differentiate using dibutyryl cAMP.

Glucose transporter Glut3 is targeted to secretory vesicles in neurons and PC12 cells

In rat brain and cultured neuroendocrine PC12 cells, Glut3 is localized at the cell surface and, also, in a distinct population of homogenous synaptic-like vesicles. Glut3-containing vesicles co-purify with "classical" synaptic vesicles, but can be separated from the latter by sucrose gradient centrifugation. Unlike classical synaptic vesicles, Glut3-containing vesicles possess a high level of aminopeptidase activity, which has been identified as aminopeptidase B. This enzyme has recently been shown to be a marker of the secretory pathway in PC12 cells (Balogh, A., Cadel, S., Foulon, T., Picart, R., Der Garabedian, A., Rousselet, A., Tougard, C., and Cohen, P. (1998) J. Cell Sci. 111, 161-169). We, therefore, conclude that Glut3 is targeted to secretory vesicles in both neurons and PC12 cells.

Platelets and DAMI megakaryocytes possess beta-secretase-like activity

We report here the discovery of two novel human platelet and megakaryocytic DAMI cell enzymes that have beta-secretase-like activity. These activities could potentially effect cleavage of the amyloid precursor protein (APP) at the beta-amyloid peptide N-terminus, by an EC 3.4.24.15-like metalloprotease, and the N terminus-1 position, by a serine protease. Thus both enzymes may generate the amyloidogenic beta-peptide. Studies of intact and Triton X-100-lysed DAMI cells, as well as intact versus subcellular fractions of platelets, demonstrate the presence of these proteolytic activities. The resting platelet has (1) a surface serine protease, demonstrated by its ability to cleave a beta-secretase substrate and by its inhibitor sensitivity; and (2) a metalloprotease, recognized by an antibody to EC 3.4.24.15, which resides intracellularly in the alpha-granule membrane, is translocated to the surface on activation, and shows beta-secretase-like activity by cleaving the same substrate. This metalloprotease can also cleave recombinant APP to a potentially amyloidogenic fragment. Surface metalloprotease was identified in DAMI cells by flow cytometry and Western blotting with a specific anti-EC 3.4.24.15 monoclonal antibody, while activity was identified by using two beta-secretase substrates. This article is the first to document two previously unknown endoproteinases with beta-secretase-like activity in platelets and DAMI cells. These proteases are capable of effecting cleavage of APP and could therefore contribute to Abeta deposition in the cerebrovasculature.

The biochemistry of Alzheimer disease

Biochemical and genetic investigations have identified four key proteins, mutations in which either cause Alzheimer disease (AD) (beta-amyloid precursor protein, presenilin 1 and 2) or confer a higher risk of developing AD (apolipoprotein E). This paper discusses the biochemical evidence that links each protein to AD, various animal and cell models that have been used in these investigations, and the putative interactions between these proteins that lead to AD. Areas that are especially fertile for novel research are noted as are gaps in our present understanding of the etiology of AD.

Brain endothelial cell enzymes cleave platelet-retained amyloid precursor protein

We have previously demonstrated that thrombin-activated platelets from patients with advanced Alzheimer's disease (AD) retain significantly more surface membrane-bound amyloid precursor protein (mAPP) than platelets from non-demented age-matched individuals (AM). We have studied interactions between these platelets and the cerebrovascular endothelium to which activated platelets adhere in a model system, investigating their involvement in the formation of amyloid beta peptide (Abeta) deposits in AD patients. We report here that there appear to be alpha and beta secretase-like activities in primary human blood brain barrier endothelial cell (BEC) cultures from both AD patients and AM control subjects (AD-BEC and AM-BEC, respectively) as well as a gamma secretase-like activity that appears only in AD-BEC. No such activities were observed in human umbilical vein endothelial cells (HUVECs). Furthermore, there is more penetration of the platelet-released products platelet factor 4 and soluble APP through the BEC layer grown from AD patients than that grown from AM individuals, whereas none penetrate through a HUVEC layer. Thus the interaction between platelets, the APP they have retained or released, and cerebral vascular endothelial cells may be at least partially responsible for amyloidogenic deposits around the cerebral vasculature of AD patients.

Blood brain barrier endothelial cells express candidate amyloid precursor protein-cleaving secretases

Proteolytic cleavage of the amyloid precursor protein (A beta PP) results in the generation of the amyloidogenic fragment known as amyloid beta peptide (A beta). Deposition of A beta in the brain parenchyma and cerebrovasculature is a feature of Alzheimer's disease (AD). To date, the process whereby A beta is generated and deposited remains unclear. We have previously established that activated platelets from AD patients retain more A beta PP on their surface than control platelets. We report here that an endothelial cell-derived enzyme can cleave this surface platelet A beta PP. Human blood brain barrier endothelial cells from brains of AD patients were assayed for potential A beta PP-cleaving enzymes using synthetic peptide substrates encompassing the A beta N-terminus cleavage site. A protease activity capable of cleaving A beta PP on the surface of AD platelets was noted. The A beta PP cleavage is partially inhibited by EDTA, by ZincOV, as well as by a specific inhibitor of the Zn metalloprotease E.C.3.4.24.15. Furthermore, the protease is recognized by an antibody directed against it, using immunohistochemistry, Western blot analysis and flow cytometry. The protease is not secreted, but rather resides intracellularly as well as on the surface of the endothelial cells. The data suggest that E.C.3.4.24.15 synthesized by brain endothelial cells may process the platelet-derived A beta PP, yielding fragments which could contribute to cerebrovascular A beta deposits.

Two distinct populations of synaptic-like vesicles from rat brain

In nonneuronal cells, several plasma membrane proteins such as exofacial enzymes, receptors, and ion channels recycle between their intracellular compartment(s) and the cell surface via an endosomal pathway. In neurons, however, this pathway has not been extensively characterized. In particular, it remains unclear whether or not it is related to the recycling of small synaptic vesicles, the major pathway of membrane traffic in nerve terminals. To approach this problem, we purified and studied a vesicular fraction from rat brain synaptosomes. Two distinct populations of vesicles with different buoyant densities and sedimentation coefficients were detected in this fraction by sucrose gradient centrifugation and Western blot analysis of the individual proteins. Both populations contain proteins that are markers of synaptic vesicles, namely, SV2, synaptotagmin, synaptophysin, secretory carrier membrane proteins (SCAMPs), synaptobrevin, and rab3a. A striking difference between the two populations is the presence of arginine aminopeptidase activity (a previously suggested marker for the regulated endosomal recycling pathway) exclusively in the lighter less-dense vesicles. The same two vesicular populations were also detected in the preparation of clathrin-coated vesicles isolated from whole rat brain or purified synaptosomes after removal of their clathrin coats by incubation at pH 8.5. We conclude, therefore, that both types of vesicles recycle in synaptosomes via a clathrin-mediated pathway. These data present experimental evidence for biochemical heterogeneity of synaptic-like vesicles in rat brain.

Increased calreticulin stability in differentiated NG-108-15 cells correlates with resistance to apoptosis induced by antisense treatment

Since its first identification as a high-affinity calcium-binding protein over two decades ago [T.J. Ostwald and D.H. MacLennan, Isolation of a high-affinity calcium-binding protein from sarcoplasmic reticulum, J. Biol. Chem., 249 (1974) 974-979], calreticulin has become recognized as a multifunctional protein involved in a wide variety of cellular processes. We have previously shown that it has a protective function in Ca2+-mediated cell death [N. Liu, R.E. Fine, E. Simons and R.J. Johnson, Decreasing calreticulin expression lowers the Ca2+ response to bradykinin and increases sensitivity to ionomycin in NG-108-15 cells, J. Biol. Chem. , 269 (1994) 28635-28639]. We report here that in NG-108-15 neuroblastomaxglioma hybrid cells, calreticulin protein levels increase markedly when these cells are induced to differentiate by treating them with N,N-dibutyryl cAMP (db-cAMP). We demonstrate that the reason for this increase is mostly due to a large increase in the turnover time of calreticulin in differentiated cells. We also show that a calreticulin antisense oligonucleotide, CrtAS1, previously described by Liu and co-workers [N. Liu, R.E. Fine, E. Simons and R.J. Johnson, Decreasing calreticulin expression lowers the Ca2+ response to bradykinin and increases sensitivity to ionomycin in NG-108-15 cells, J. Biol. Chem., 269 (1994) 28635-28639] causes cell death in undifferentiated NG-108-15 cells when antisense treatment is extended for more than 24 h. This effect is not seen in NG-108-15 cells that have been induced to differentiate with db-cAMP until the cells have been treated with antisense for more than 4 days, due to the increased stability of Crt in these cells. Our results indicate that the mechanism by which these cells die is likely to be apoptosis.

Binding of beta-amyloid to the p75 neurotrophin receptor induces apoptosis. A possible mechanism for Alzheimer's disease

Alzheimer's disease is a neurodegenerative disorder characterized by the extracellular deposition in the brain of aggregated beta-amyloid peptide, presumed to play a pathogenic role, and by preferential loss of neurons that express the 75-kD neurotrophin receptor (p75NTR). Using rat cortical neurons and NIH-3T3 cell line engineered to stably express p75NTR, we find that the beta-amyloid peptide specifically binds the p75NTR. Furthermore, 3T3 cells expressing p75NTR, but not wild-type control cells lacking the receptor, undergo apoptosis in the presence of aggregated beta-amyloid. Normal neural crest-derived melanocytes that express physiologic levels of p75NTR undergo apoptosis in the presence of aggregated beta-amyloid, but not in the presence of control peptide synthesized in reverse. These data imply that neuronal death in Alzheimer's disease is mediated, at least in part, by the interaction of beta-amyloid with p75NTR, and suggest new targets for therapeutic intervention.

Retinal Muller glia secrete apolipoproteins E and J which are efficiently assembled into lipoprotein particles

We have shown that apolipoprotein E (ApoE) is synthesized by Muller cells, the major glial cell of the rabbit retina, and secreted into the vitreous after which it is taken up by retinal ganglion cells and rapidly transported into the optic nerve [Amaratunga et al., J. Biol. Chem. 271 (1996) 5628-5632]. In this report we demonstrate that the ApoE secreted by Muller cells in vivo and in culture is efficiently assembled into lipoprotein particles. Apolipoprotein J (ApoJ) is also synthesized by these cells and assembled into lipoprotein particles. The lipoproteins are triglyceride-rich and contain cholesterol esters and free cholesterol. They are heterogeneous, with densities between 1.006 and 1.18 and diameters between 14 and 45 nm. We discuss the possible role of these lipoproteins in supplying the needs of neurons for lipids, especially long axonal projection neurons such as retinal ganglion cells, which are vulnerable to age-related neurodegenerative diseases including Alzheimer's disease.

Evidence for local production of acute phase response apolipoprotein serum amyloid A in Alzheimer's disease brain

Acute phase serum amyloid A (A-apoSAA), but not constitutive apoSAA (C-apoSAA), was identified by Western blotting experiments in brain protein extracts from eight of nine patients with Alzheimer's disease (AD), one with a brain tumor and one with multiple sclerosis. A-apoSAA was not detected in six subjects with Pick's or Lewy Body disease or three other non-AD brain specimens. Apolipoprotein A-I and albumin were not found in any of the brain protein extracts. A-apoSAA mRNA was detected in AD brain by reverse transcription-polymerase chain reaction (RT-PCR). These data suggest that apoSAA is locally produced in AD brain and that investigation of the neuroinflammatory effects of this injury specific apolipoprotein is warranted.

Moderate and advanced Alzheimer's patients exhibit platelet activation differences

We previously reported that platelets from advanced sporadic Alzheimer's disease (AD) patients exhibit two defects: first, an aberrant signal transduction presenting as a thrombin-induced hyperacidification, which is more severe for donors with the apolipoprotein E4 allele (apoE4), and second, an AD-specific Amyloid Precursor Protein (APP) processing defect that presents as retention of APP on the activated platelets' surface and in independent of the apo E allele. This retention of membrane APP correlates with decreased release of soluble APP. To determine at what stage in the disease progression these defects appear, we performed signal transduction and secretion studies on moderate AD patients. Thrombin-activated platelets from these patients do not exhibit either hyperacidification or APP retention; their APP processing and secretion are normal by Western blotting, suggesting that the two platelet defects appear in the advanced stages of AD.

Activated Alzheimer disease platelets retain more beta amyloid precursor protein

Upon activation, platelet alpha-granules' soluble contents are secreted and membrane-bound contents are translocated to the plasma membrane. Membrane-bound proteins include the beta-amyloid precursor protein (APP) from which the beta-amyloid (A beta) deposits found surrounding the cerebrovasculature of patients with Alzheimer's Disease (AD) may originate. We show here that activated platelets from AD patients exhibit less APP processing, retain more of the protein on their surface, and secrete less as soluble fragments than do controls. Surface labeling demonstrated that there is little APP or CD62 on the surface of resting platelets. Upon activation, control platelets exhibited more of both proteins on their surface, while advanced AD patients exhibited similar amounts of CD62 as controls, but retained significantly more surface APP. AD platelets secreted similar amounts of most soluble alpha-granule contents as controls, but less APP fragments. Together these results suggest a processing defect that may account for greater deposition of A beta-containing products in the vasculature to which activated platelets adhere.

Transport of GM1 and GM1 inner ester across an in vitro model of the blood-brain barrier

Gangliosides, especially GM1, attenuate the in vivo damage caused by various neurotoxins. The chemically neutral inner ester of GM1 may be a better cytoprotective agent against some neurotoxins than the parent GM1 compound, because it may cross the blood-brain barrier (BBB) more easily than the anionic GM1. Using an in vitro bovine brain endothelial cell model of the BBB, we show the inner ester more readily transverse the tight junction barrier of this model than does GM1. Further, it is demonstrated that the GM1 inner ester is stable for several hours at pH values between 7.0 and 8.2 at 37 degrees C. Finally, the results illustrate that the BBB model may be useful for testing other gangliosides and their various derivatives for increased ability to cross the BBB.

Neurotoxicity of free-radical-mediated serotonin neurotoxin in cultured embryonic chick brain neurons

Exposure of serotonin (5-HT) to oxygen-derived free-radical-generating system, xanthine oxidase-hypoxanthine or to a Fenton reaction results in the formation of the neurotoxin, tryptamine-4,5-dione. In cultured embryonic chick brain neurons, incubation of tryptamine-4,5-dione or its ethyl carbonate derivative resulted in a dose-dependent neurotoxicity (1-100 microM). The addition of sulfhydryl compound, glutathione at 2 or 10 microM significantly enhanced the toxicity induced by 10 microM tryptamine-4,5-dione. On the contrary, glutathione at 10 microM decreased the neurotoxic effect caused by 10 microM 5,6- and 5,7-dihydroxytryptamine in the cultured neurons. The toxicity resulted from 5,6- and 5,7-dihydroxytryptamine could be fully prevented by a 5-HT uptake inhibitor, fluoxetine. However, the toxicity caused by tryptamine-4,5-dione and glutathione conjugate could not be blocked by fluoxetine (10 or 100 microM) or by a glutathione transferase inhibitor, boric acid/serine. The results indicate a different molecular mechanism among 5-HT derived neurotoxins and suggest that tryptamine-4,5-dione and/or its glutathione conjugate would cause neuronal damage, if they are formed in vivo.

Apolipoprotein E is synthesized in the retina by Müller glial cells, secreted into the vitreous, and rapidly transported into the optic nerve by retinal ganglion cells

We have investigated the synthesis and transport of apoE, the major apolipoprotein of the central nervous system, in the retina of the living rabbit. Four hours after the injection of [35S]methionine/cysteine into the vitreous, 44% of [35S]Met/Cys-labeled apoE is in soluble and membrane-enclosed retinal fractions, while 50% is in the vitreous. A significant amount of intact [35S]Met/Cys-labeled apoE is rapidly transported into the optic nerve and its terminals in the lateral geniculate and superior colliculus within 3-6 h in two distinguishable vesicular compartments. Müller glia in cell culture also synthesize and secrete apoE. Taken together, these results suggest that apoE is synthesized by Müller glia and secreted into the vitreous. ApoE is also internalized by retinal ganglion cells and/or synthesized by these cells and rapidly transported into the optic nerve and brain as an intact molecule. We discuss the possible roles of retinal apoE in neuronal dynamics.

The fibril forming region of the beta-amyloid precursor differs from that of the amyloid A precursor in its interaction with lipids

Since the amyloid A (AA) precursoir, serum amyloid A (apoSAA), has been shown to bind cholesterol (C) in the AA fibril forming region, we investigated the interaction of the beta-amyloid precursor protein (AbetaPP) and beta-amyloid (Abeta) peptide with C and phosphatidyl choline (PC) by measuring changes in binding to microtiter wells at physiological pH and ionic strength. While either C or PC inhibited AbetaPP binding to the same extent that C inhibited apoSAA binding, neither C nor PC had any effect on binding of the Abeta peptide, although antibodies to Abeta1-40 did block binding. The binding of (125)I-Abeta1-40 and (125)I-AbetaPP was inhibited by apoE3 and apoE4, but not by either apoSAA or bovine serum albumin. Bound (125)I-AbetaPP was partially released into medium containing C, PC, apoE3, apoE4, or antibodies to AbetaPP. Our results indicate that AbetaPP but not Abeta peptide can be retained in solution in the presence of C and PC and suggest that this failure to interact with lipids may account for the greater insolubility of Abeta fibrils than AA fibrils.

Stereotactic breast biopsy: a practical approach

The continuing increase of women participating in mammographic screening has resulted in a rise in the number of nonpalpable abnormalities identified. The development of minimally invasive and cost-effective methods to achieve accurate histologic diagnosis is needed. Stereotactic needle core biopsy had been used to reduce the number of women requiring needle-directed open surgical biopsies for benign disease. The team approach is essential for implementation of these newer diagnostic and interventional modalities. The surgeon has always taken the responsibility for coordinating the diagnostic and treatment components of appropriate breast care. Therefore, surgeons must continue to integrate new technology into their practices. The extensive experience of more than 3000 stereotactic biopsies performed at The Breast Center has provided the background for discussing the technical aspects of the procedure. The appropriate workup and subsequent indications for patient selection are reviewed. Pre and postprocedural patient considerations are addressed. This should provide an introduction to the basic principles of stereotactic needle core biopsy for implementation into a surgical practice.

Antisense inhibition of protein synthesis and function : rabbit retinal protein

When considering the use of antisense technology for in vivo apphcatron, whether for therapeutic development or for the creation of animal models for human diseases, a major problem is that most extracellular compartments are constantly mixing with the blood, lymph, cerebrospinal fluid (CSF), and so forth, and thus constantly diluting the oligonucleotide. A possibly unique exception to this problem is the vitreous, a gelatinous fluid overlying the inner retinal surface. The vitreous is formed early in development and is in essence a relatively closed compartment with no active transport of fluids or ions. Forensic pathologists make use of this fact in determining the composition of electrolytes at the time of death by sampling the vitreal compartment.

Generation of amyloidogenic C-terminal fragments during rapid axonal transport in vivo of beta-amyloid precursor protein in the optic nerve

The amyloid beta-protein (A beta) is a major component of extracellular deposits that are characteristic features of Alzheimer's disease. A beta is derived from the large transmembrane beta-amyloid precursor protein (beta APP). In the rabbit optic nerve/optic tract (ON), beta APP is synthesized in vivo in retinal ganglion cell perikarya, rapidly transported into the ON axons in small transport vesicles and is subsequently transferred to the axonal plasma membrane as well as to the presynaptic nerve terminals (Morin, P. J., Abraham, C. R., Amaratunga, A., Johnson, R.J., Huber, G., Sandell, J. H., and Fine, R. E. (1993) J. Neurochem. 61, 464-473). Present results indicate that there is rapid processing of beta APP in the ON to generate a 14-kDa C-terminal membrane-associated fragment that contains the A beta sequence. By using equilibrium sucrose density gradient fractionation, this fragment, as well as non-amyloidogenic C-terminal fragments and intact beta APP, are detected in at least two classes of transport vesicles destined for the plasma membrane and the presynaptic nerve terminal. The two classes of transported vesicles are distinguished by labeling kinetics as well as by density. In contrast to the ON, only nonamyloidogenic C-terminal fragments are generated in the retina, which contains the perikarya of retinal ganglion cells and glial (Muller) cells which also produce beta APP.

Inhibition of kinesin synthesis in vivo inhibits the rapid transport of representative proteins for three transport vesicle classes into the axon

We have previously demonstrated that the in vivo vitreal injection of an antisense oligonucleotide directed to the kinesin heavy chain inhibits retinal kinesin synthesis by 82% and concomitantly inhibits rapid transport of total protein into the optic nerve by 70%. These results establish a major role for kinesin in rapid axonal transport in vivo. Recently, the cloning of a family of kinesin-like molecules from the mammalian brain has been reported, and some of these proteins are also expressed in neurons. To assign to specific function to the kinesin heavy chain we inhibited the kinesin synthesis with an antisense kinesin oligonucleotide and assessed the axonal transport into the optic nerve of representative proteins from each of three vesicle classes that contain rapidly transported proteins. Marker proteins used were substance P for peptide-containing synaptic vesicles, the amyloid protein for plasma membrane precursor vesicles, and several integral synaptic vesicle proteins. Our results indicate that the major anterograde motor protein for all three vesicle classes utilizes kinesin heavy chain, although we discuss alternative explanations.

Stereotactic needle biopsy for occult breast lesions: a minimally invasive alternative

Women are being screened with annual mammography in increasing numbers to achieve early diagnosis and improve chances of survival. A minimally invasive and cost-effective biopsy technique is needed to evaluate nonpalpable mammographically detected lesions without decreasing reliability. A technique of core biopsy with a coring needle deployed in a spring loaded gun using stereotactic localization has been developed to fulfill this need. An in-depth study of 500 consecutive stereotactic core biopsies have been analyzed and reported in this article. The study gives statistical evaluation of data and reports the breakdown of the histologic diagnosis of these cases and an analysis of detected malignancies. The study suggests that 75% of the indeterminate mammographic lesions can be judged to be benign and that no further surgery is necessary. The false negative rate is discussed in detail. The indications for stereotactic biopsy, the proper selection of patients, and the suggested follow-up are also addressed. The benign and malignant lesions are characterized in detail.

Decreasing calreticulin expression lowers the Ca2+ response to bradykinin and increases sensitivity to ionomycin in NG-108-15 cells

It has been suggested that the multifunctional protein, calreticulin, is a major calcium sequestering protein in the inositol 1,4,5-trisphosphate receptor-containing endoplasmic reticulum subcompartment. In neuroblastoma X glioma NG-108-15 cells, bradykinin can effectively stimulate the release of inositol 1,4,5-trisphosphate and cause a cytosolic calcium transient. To explore the function of calreticulin as an intracellular calcium sequestering protein, we investigated calcium dynamics in NG-108-15 cells after treatment with an antisense oligonucleotide against calreticulin, CrtAS1. Cells treated with either CrtAS1 or the corresponding sense oligonucleotide CrtPS1 were examined for their calreticulin content by Western blotting, the amplitude of their calcium transient in response to bradykinin, and their sensitivity toward the calcium ionophore, ionomycin. Treatment with CrtAS1 decreased the amount of calreticulin in comparison to CrtPS1-treated and untreated control cells. At the same time, CrtAS1-treated cells had a significantly reduced calcium response to bradykinin and were more sensitive to ionomycin-induced cell death. These data show that the level of calreticulin expression is directly related to the calcium storage capacity of the inositol 1,4,5-trisphosphate-sensitive calcium pool and indicate a direct relationship between the level of calreticulin and the protection against cytotoxic calcium overload.

Ral and Rab3a are major GTP-binding proteins of axonal rapid transport and synaptic vesicles and do not redistribute following depolarization stimulated synaptosomal exocytosis

We have employed high-resolution SDS polyacrylamide gels to demonstrate that there are two major low-molecular-weight GTP-binding proteins associated with axonal membranes including synaptic vesicles, rapid transported membranes and clathrin-coated vesicles. We demonstrate that one of the major proteins is Ral and that the other is Rab3A. Following the depolarization of synaptosomes resulting in increased neurotransmitter release, we see no significant dissociation of either Ral or Rab3a from synaptic vesicle derived membranes in contrast to results reported previously.

Comparison of cDNAs from bovine brain coding for two isoforms of calreticulin

Calreticulin is a major calcium-binding protein of the endoplasmic reticulum of non-muscle cells. In addition to a 1.9-kb calreticulin mRNA, some evidence has suggested the existence of another transcript of 3.75 kb, which is very similar to calreticulin. We report here the isolation and sequencing of cDNA clones from a bovine brain lambda gt11 cDNA library, two of which appear to code for calreticulin and a third for a novel isoform of calreticulin. The deduced amino-acid sequence of the novel clone shares high similarity with mouse calreticulin in the C-terminal 318 amino acids. However, its N-terminal sequence is completely divergent. Northern blot analysis of bovine cerebral cortex RNA indicates that the conserved region of the clone hybridizes to two messages of 1.9 kb and 3.75 kb. The divergent region of this clone hybridizes to the 3.75-kb message, but not to the 1.9-kb message. We believe that this novel clone corresponds to an alternate form of calreticulin which is identical to calreticulin toward the C-terminus, but completely different at the N-terminal region, and that this isoform is encoded by a much larger message.

Inhibition of kinesin synthesis and rapid anterograde axonal transport in vivo by an antisense oligonucleotide

Synthetic antisense oligonucleotides have been used to inhibit specific protein synthesis in vivo. Antisense oligonucleotides directed to kinesin heavy chain were injected into the vitreous of anesthetized rabbits in order to assess the effects on transport in the retinal ganglion cells whose axons form the optic nerve. The antisense oligonucleotide specifically inhibited retinal kinesin synthesis by 82 +/- 7% (n = 4). The rapid axonal transport of the membrane proteins into the optic nerve was concomitantly inhibited by 70 +/- 10% (n = 4). These results provide direct evidence for the specific role of kinesin in rapid anterograde transport in vivo and indicate the utility of antisense oligonucleotides to explore neuronal dynamics in a specific neuronal cell type in a living animal.

Amyloid precursor protein is synthesized by retinal ganglion cells, rapidly transported to the optic nerve plasma membrane and nerve terminals, and metabolized

We have investigated the synthesis, axonal transport, and processing of the beta-amyloid precursor protein (APP) in in vivo rabbit retinal ganglion cells. These CNS neurons connect the retina to the brain via axons that comprise the optic nerve. APP is synthesized in retinal ganglion cells and is rapidly transported into the optic nerve in small transport vesicles. It is then transferred to the axonal plasma membrane, as well as to the nerve terminals and metabolized with a t1/2 of less than 5 h. A significant accumulation of C-terminal amyloidogenic or nonamyloidogenic fragments is seen in the optic nerve 5 h after [35S]-methionine, [35S]cysteine injection, which disappears by 24 h. The major molecular mass species of APP in the optic nerve is approximately 110 kDa, and is an APP isoform that does not contain a Kunitz protease inhibitor domain. Higher molecular mass species containing this sequence are seen mostly in the retina. A protease(s) that can potentially cleave APP to generate an amyloidogenic fragment is present in the same optic nerve membrane compartment as APP.

Non-age related differences in thrombin responses by platelets from male patients with advanced Alzheimer's disease

Alzheimer's Disease(AD), characterized by a deposition of beta-amyloid peptide (beta/A4) in the brain and in the cerebral microvasculature of affected individuals, is derived from its precursor protein (beta APP) via proteolytic processing by enzyme(s) which have not yet been characterized or localized. Since platelets carry APP in one of their granules, they have been implicated as a source of the beta/A4 deposits in the microvasculature of AD patients, attributable to either an abnormality in the platelets' stimulus response, in the quantity or nature of the APP they release upon activation and/or in the processing of that protein. We show here that platelets from patients with severe AD have abnormal stimulus responses to alpha-thrombin. Specifically, these cells hyperacidify. While it is not clear why this abnormality occurs, it may contribute to aberrant granule secretion since we have demonstrated earlier that release of platelet granule contents is partially controlled by the cytoplasmic pH.

Kinesin is rapidly transported in the optic nerve as a membrane associated protein

We have investigated the membrane vs. cytosolic distribution of newly synthesized and total kinesin in rabbit retinal ganglion cell axons which comprise the optic nerve. We find that kinesin is rapidly transported into the axon and that this newly synthesized protein is completely membrane-associated while approximately two third of the total kinesin in the optic nerve is membrane associated. Of this membrane associated kinesin about half is resistant to removal by treatment with 100 mM Na2CO3 (pH 11.3) and none can be stripped by 1 M NaCl. The newly synthesized axonal kinesin is completely resistant to removal by Na2CO3 treatment. By these criteria, at least one third of the total and essentially all of the rapidly transported axonal kinesin appears to exist as an integral membrane protein, consistent with it functioning as the anterograde motor for rapid vesicle transport from the cell body through the axon.

Receptor-mediated endocytosis of transferrin at the blood-brain barrier

Rat brains were perfuse with a transferrin-peroxidase conjugate (Tf-HRP) to characterize morphologically the endocytic pathway of transferrin in blood-brain barrier endothelial cells. Electron microscopic evaluation of rat brains perfused with Tf-HRP at 4 degrees C and subsequently warmed to 37 degrees C for brief periods of time (2 minutes) showed sequestration of Tf-HRP in clathrin coated pits and vesicles on the luminal membrane of the brain endothelium. After 5 minutes of warming, diaminobenzidine (DAB) reaction product was present in vesicular structures 250–500 nm in diameter and in associated tubules morphologically identified as large or sorting endosomes. Recycling endosomes were also heavily labelled at this time point. Almost no DAB reaction product remained in the cerebral endothelial cells when the warming period was longer than 15 minutes. Other rat brains were perfused with Tf-HRP at 30 degrees C for 15 minutes prior to fixation and DAB cytochemistry. In these studies, brain endothelial cells contained large amounts of DAB reaction product, mostly localized in 50–100 nm vesicles and tubules, often in the Golgi region of the cells. Coated pits and vesicles and large endosomes were also heavily labelled. Transcytosis of Tf-HRP was not identified in either perfusion protocol. Ultrastructural, indirect immunocytochemical localization of transferrin receptors showed that the transferrin receptor is highly polarized at the blood-brain barrier and is localized only on the apical membrane, in contrast to other polarized epithelial cells, like hepatocytes, in which the receptor is present on the basolateral membrane. The evidence supports an iron transport model in which iron-loaded transferrin is taken up by receptor-mediated endocytosis at the luminal membrane of brain capillaries. The iron then dissociates from transferrin in endosomal compartments and is transcytosed by unknown mechanisms, while the transferrin is retroendocytosed.

Differences in the subcellular localization of calreticulin and organellar Ca(2+)-ATPase in neurons

It has become clear that calcium is an important mediator in the transduction of signals due to ligand binding to cell surface receptors. Cytosolic calcium is typically maintained at low levels in both muscle and non-muscle cells and intracellular sequestering of calcium appears to be important in this process. The identification of intracellular calcium pools has been the subject of much recent study, and it has been proposed that such pools would contain three components: a calcium-activated pump or Ca(2+)-ATPase, a calcium channel such as the inositol trisphosphate receptor or ryanodine receptor, and a high-capacity calcium-binding protein such as calsequestrin or calreticulin. We report here on the localization of two components, the organellar Ca(2+)-ATPase (SERCA) and calreticulin, in neuronal tissues. Using immunofluorescence and subcellular fractionation, we have found that for the most part, these two proteins do not co-localize in neuron cell bodies, dendrites, or axons; but may co-localize at the axon terminal.

Regional distribution of iron and iron-regulatory proteins in the brain in aging and Alzheimer's disease

It is well established that iron, which is of considerable importance for normal neurological function, is highly regulated in all organ systems. However, until recently, iron regulation in the nervous system has received little attention. This study quantitatively compares the levels of the major iron-regulatory proteins, transferrin and ferritin, and iron itself in three cerebral cortical regions of the human brain from material collected at autopsy. Three groups were studied: 1) normal adult (under 65 yr of age), 2) aged (greater than 65), and 3) Alzheimer's disease. Normally, transferrin is more abundant in white matter than in gray matter. Ferritin is approximately 10x more abundant than transferrin throughout the brain regions examined and is evenly distributed, as is iron, in the gray and white matter. In Alzheimer's disease transferrin is consistently decreased particularly in the white matter of the various cerebral cortical regions examined whereas the iron and ferritin changes are inconsistent. The observations in this study are consistent with our general hypothesis that iron homeostasis is disrupted in the aging brain and the alterations in iron-regulatory proteins are exacerbated in Alzheimer's disease. The decrease in transferrin levels could indicate a decreased mobility and subsequent utilization of iron in the brain. Such a decrease in iron availability could play a significant role in neuronal degeneration and increased peroxidative damage known to occur in Alzheimer's disease.

Isolation of a calreticulin-like calcium binding protein from bovine brain

Intracellular calcium levels are stringently regulated in all cells. The nature of this regulation is incompletely understood, but recent evidence indicates that the endoplasmic reticulum plays an important role in sequestering intracellular calcium. Using methods for isolating both calsequestrin and calreticulin, we have isolated a 58 kDa, high capacity calcium binding protein that exists in microsomes that shift their density in an oxalate-mediated density shift assay. This protein which we call CBP-58 bears similarities to the endoplasmic reticulum protein, calreticulin, in that it has a pI of 4.7 containing approximately 30% glutamate and aspartate, has a high capacity for calcium, and stains blue with the carbocyanine dye, 'Stains-all'. Peptide, amino acid, nucleotide and immunochemical analyses reveal further similarities between CBP-58 and calreticulin, but also some marked differences. Its tissue distribution suggests it is highly enriched in brain versus other tissues. We believe that CBP-58 is a calreticulin-like protein and that differences in the amino acid composition and sequences may reflect species diversity in calreticulin.