The Alzheimer's β-secretase enzyme BACE1 is required for accurate axon guidance of olfactory sensory neurons and normal glomerulus formation in the olfactory bulb

Molecular Neurodegeneration

Robert Vassar¹  Thomas C Bozza²  William A Eimer¹  Tharinda W Rajapaksha¹ 

[1] Department of Cell and Molecular Biology, Feinberg School of Medicine, Northwestern University, Chicago, IL 60611, USA;Department of Neurobiology, Northwestern University, Evanston, IL 60208, USA

关键词: olfactory system;    olfactory bulb;    olfactory sensory neuron;    odorant receptor;    glomerulus;    axon targeting;    axon guidance;    Alzheimer's disease;    β-secretase;    β-amyloid;    BACE1;    Aβ;   

Others  :  863974
DOI  :  10.1186/1750-1326-6-88

 received in 2011-12-24, accepted in 2011-12-28,  发布年份 2011

【 摘 要 】

Background

The β-secretase, β-site amyloid precursor protein cleaving enzyme 1 (BACE1), is a prime therapeutic target for lowering cerebral β-amyloid (Aβ) levels in Alzheimer's disease (AD). Clinical development of BACE1 inhibitors is being intensely pursued. However, little is known about the physiological functions of BACE1, and the possibility exists that BACE1 inhibition may cause mechanism-based side effects. Indeed, BACE1^-/- mice exhibit a complex neurological phenotype. Interestingly, BACE1 co-localizes with presynaptic neuronal markers, indicating a role in axons and/or terminals. Moreover, recent studies suggest axon guidance molecules are potential BACE1 substrates. Here, we used a genetic approach to investigate the function of BACE1 in axon guidance of olfactory sensory neurons (OSNs), a well-studied model of axon targeting in vivo.

Results

We bred BACE1^-/- mice with gene-targeted mice in which GFP is expressed from the loci of two odorant-receptors (ORs), MOR23 and M72, and olfactory marker protein (OMP) to produce offspring that were heterozygous for MOR23-GFP, M72-GFP, or OMP-GFP and were either BACE1^+/+ or BACE1^-/-. BACE1^-/- mice had olfactory bulbs (OBs) that were smaller and weighed less than OBs of BACE1^+/+ mice. In wild-type mice, BACE1 was present in OSN axon terminals in OB glomeruli. In whole-mount preparations and tissue sections, many OB glomeruli from OMP-GFP; BACE1^-/- mice were malformed compared to wild-type glomeruli. MOR23-GFP; BACE1^-/- mice had an irregular MOR23 glomerulus that was innervated by randomly oriented, poorly fasciculated OSN axons compared to BACE1^+/+ mice. Most importantly, M72-GFP; BACE1^-/- mice exhibited M72 OSN axons that were mis-targeted to ectopic glomeruli, indicating impaired axon guidance in BACE1^-/- mice.

Conclusions

Our results demonstrate that BACE1 is required for the accurate targeting of OSN axons and the proper formation of glomeruli in the OB, suggesting a role for BACE1 in axon guidance. OSNs continually undergo regeneration and hence require ongoing axon guidance. Neurogenesis and the regeneration of neurons and axons occur in other adult populations of peripheral and central neurons that also require axon guidance throughout life. Therefore, BACE1 inhibitors under development for the treatment of AD may potentially cause axon targeting defects in these neuronal populations as well.

【 授权许可】

   
2011 Rajapaksha et al; licensee BioMed Central Ltd.

【 图 表 】

【 参考文献 】

• [1]Vassar R, Bennett BD, Babu-Khan S, Kahn S, Mendiaz EA, Denis P, Teplow DB, Ross S, Amarante P, Loeloff R, et al.: Beta-secretase cleavage of Alzheimer's amyloid precursor protein by the transmembrane aspartic protease BACE. Science 1999, 286:735-741.
• [2]Yan R, Bienkowski MJ, Shuck ME, Miao H, Tory MC, Pauley AM, Brashler JR, Stratman NC, Mathews WR, Buhl AE, et al.: Membrane-anchored aspartyl protease with Alzheimer's disease beta-secretase activity. Nature 1999, 402:533-537.
• [3]Sinha S, Anderson JP, Barbour R, Basi GS, Caccavello R, Davis D, Doan M, Dovey HF, Frigon N, Hong J, et al.: Purification and cloning of amyloid precursor protein beta-secretase from human brain. Nature 1999, 402:537-540.
• [4]Hussain I, Powell D, Howlett DR, Tew DG, Meek TD, Chapman C, Gloger IS, Murphy KE, Southan CD, Ryan DM, et al.: Identification of a novel aspartic protease (Asp 2) as beta-secretase. Mol Cell Neurosci 1999, 14:419-427.
• [5]Lin X, Koelsch G, Wu S, Downs D, Dashti A, Tang J: Human aspartic protease memapsin 2 cleaves the beta-secretase site of beta-amyloid precursor protein. Proc Natl Acad Sci USA 2000, 97:1456-1460.
• [6]Luo Y, Bolon B, Kahn S, Bennett BD, Babu-Khan S, Denis P, Fan W, Kha H, Zhang J, Gong Y, et al.: Mice deficient in BACE1, the Alzheimer's beta-secretase, have normal phenotype and abolished beta-amyloid generation. Nat Neurosci 2001, 4:231-232.
• [7]Roberds SL, Anderson J, Basi G, Bienkowski MJ, Branstetter DG, Chen KS, Freedman SB, Frigon NL, Games D, Hu K, et al.: BACE knockout mice are healthy despite lacking the primary beta-secretase activity in brain: implications for Alzheimer's disease therapeutics. Hum Mol Genet 2001, 10:1317-1324.
• [8]Ohno M, Sametsky EA, Younkin LH, Oakley H, Younkin SG, Citron M, Vassar R, Disterhoft JF: BACE1 deficiency rescues memory deficits and cholinergic dysfunction in a mouse model of Alzheimer's disease. Neuron 2004, 41:27-33.
• [9]Ohno M, Chang L, Tseng W, Oakley H, Citron M, Klein WL, Vassar R, Disterhoft JF: Temporal memory deficits in Alzheimer's mouse models: rescue by genetic deletion of BACE1. Eur J Neurosci 2006, 23:251-260.
• [10]Laird FM, Cai H, Savonenko AV, Farah MH, He K, Melnikova T, Wen H, Chiang HC, Xu G, Koliatsos VE, et al.: BACE1, a major determinant of selective vulnerability of the brain to amyloid-beta amyloidogenesis, is essential for cognitive, emotional, and synaptic functions. J Neurosci 2005, 25:11693-11709.
• [11]Hitt BD, Jaramillo TC, Chetkovich DM, Vassar R: BACE1-/- mice exhibit seizure activity that does not correlate with sodium channel level or axonal localization. Mol Neurodegener 2010, 5:31. BioMed Central Full Text
• [12]Hu X, Zhou X, He W, Yang J, Xiong W, Wong P, Wilson CG, Yan R: BACE1 deficiency causes altered neuronal activity and neurodegeneration. J Neurosci 2010, 30:8819-8829.
• [13]Willem M, Garratt AN, Novak B, Citron M, Kaufmann S, Rittger A, DeStrooper B, Saftig P, Birchmeier C, Haass C: Control of peripheral nerve myelination by the beta-secretase BACE1. Science 2006, 314:664-666.
• [14]Hu X, Hicks CW, He W, Wong P, Macklin WB, Trapp BD, Yan R: Bace1 modulates myelination in the central and peripheral nervous system. Nat Neurosci 2006, 9:1520-1525.
• [15]Kim DY, Carey BW, Wang H, Ingano LA, Binshtok AM, Wertz MH, Pettingell WH, He P, Lee VM, Woolf CJ, Kovacs DM: BACE1 regulates voltage-gated sodium channels and neuronal activity. Nat Cell Biol 2007, 9:755-764.
• [16]Gersbacher MT, Kim DY, Bhattacharyya R, Kovacs DM: Identification of BACE1 cleavage sites in human voltage-gated sodium channel beta 2 subunit. Mol Neurodegener 2010, 5:61. BioMed Central Full Text
• [17]Vassar R, Kovacs DM, Yan R, Wong PC: The beta-secretase enzyme BACE in health and Alzheimer's disease: regulation, cell biology, function, and therapeutic potential. J Neurosci 2009, 29:12787-12794.
• [18]Hemming ML, Elias JE, Gygi SP, Selkoe DJ: Identification of beta-secretase (BACE1) substrates using quantitative proteomics. PLoS One 2009, 4:e8477.
• [19]Zhao J, Fu Y, Yasvoina M, Shao P, Hitt B, O'Connor T, Logan S, Maus E, Citron M, Berry R, et al.: Beta-site amyloid precursor protein cleaving enzyme 1 levels become elevated in neurons around amyloid plaques: implications for Alzheimer's disease pathogenesis. J Neurosci 2007, 27:3639-3649.
• [20]Yan XX, Xiong K, Luo XG, Struble RG, Clough RW: beta-Secretase expression in normal and functionally deprived rat olfactory bulbs: inverse correlation with oxidative metabolic activity. J Comp Neurol 2007, 501:52-69.
• [21]Sakano H: Neural map formation in the mouse olfactory system. Neuron 2010, 67:530-542.
• [22]Buck L, Axel R: A novel multigene family may encode odorant receptors: a molecular basis for odor recognition. Cell 1991, 65:175-187.
• [23]Ressler KJ, Sullivan SL, Buck LB: A zonal organization of odorant receptor gene expression in the olfactory epithelium. Cell 1993, 73:597-609.
• [24]Vassar R, Ngai J, Axel R: Spatial segregation of odorant receptor expression in the mammalian olfactory epithelium. Cell 1993, 74:309-318.
• [25]Vassar R, Chao SK, Sitcheran R, Nuñez JM, Vosshall LB, Axel R: Topographic organization of sensory projections to the olfactory bulb. Cell 1994, 79:981-991.
• [26]Ressler KJ, Sullivan SL, Buck LB: Information coding in the olfactory system: evidence for a stereotyped and highly organized epitope map in the olfactory bulb. Cell 1994, 79:1245-1255.
• [27]Mombaerts P, Wang F, Dulac C, Chao SK, Nemes A, Mendelsohn M, Edmondson J, Axel R: Visualizing an olfactory sensory map. Cell 1996, 87:675-686.
• [28]Dominguez D, Tournoy J, Hartmann D, Huth T, Cryns K, Deforce S, Serneels L, Camacho IE, Marjaux E, Craessaerts K, et al.: Phenotypic and biochemical analyses of BACE1- and BACE2-deficient mice. J Biol Chem 2005, 280:30797-30806.
• [29]Lin DM, Wang F, Lowe G, Gold GH, Axel R, Ngai J, Brunet L: Formation of precise connections in the olfactory bulb occurs in the absence of odorant-evoked neuronal activity. Neuron 2000, 26:69-80.
• [30]Zheng C, Feinstein P, Bozza T, Rodriguez I, Mombaerts P: Peripheral olfactory projections are differentially affected in mice deficient in a cyclic nucleotide-gated channel subunit. Neuron 2000, 26:81-91.
• [31]Wong ST, Trinh K, Hacker B, Chan GC, Lowe G, Gaggar A, Xia Z, Gold GH, Storm DR: Disruption of the type III adenylyl cyclase gene leads to peripheral and behavioral anosmia in transgenic mice. Neuron 2000, 27:487-497.
• [32]Belluscio L, Gold GH, Nemes A, Axel R: Mice deficient in G(olf) are anosmic. Neuron 1998, 20:69-81.
• [33]Brunjes PC, Borror MJ: Unilateral odor deprivation: differential effects due to time of treatment. Brain Res Bull 1983, 11:501-503.
• [34]Potter SM, Zheng C, Koos DS, Feinstein P, Fraser SE, Mombaerts P: Structure and emergence of specific olfactory glomeruli in the mouse. J Neurosci 2001, 21:9713-9723.
• [35]Vassalli A, Rothman A, Feinstein P, Zapotocky M, Mombaerts P: Minigenes impart odorant receptor-specific axon guidance in the olfactory bulb. Neuron 2002, 35:681-696.
• [36]Cai H, Wang Y, McCarthy D, Wen H, Borchelt DR, Price DL, Wong PC: BACE1 is the major beta-secretase for generation of Abeta peptides by neurons. Nat Neurosci 2001, 4:233-234.