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.