title: Regulation of axonal HCN1 trafficking in perforant path involves expression of specific TRIP8b isoforms.
abstract: The functions of HCN channels in neurons depend critically on their subcellular localization, requiring fine-tuned machinery that regulates subcellular channel trafficking. Here we provide evidence that regulatory mechanisms governing axonal HCN channel trafficking involve association of the channels with specific isoforms of the auxiliary subunit TRIP8b. In the medial perforant path, which normally contains HCN1 channels in axon terminals in immature but not in adult rodents, we found axonal HCN1 significantly increased in adult mice lacking TRIP8b (TRIP8b(-/-)). Interestingly, adult mice harboring a mutation that results in expression of only the two most abundant TRIP8b isoforms (TRIP8b[1b/2](-/-)) exhibited an HCN1 expression pattern similar to wildtype mice, suggesting that presence of one or both of these isoforms (TRIP8b(1a), TRIP8b(1a-4)) prevents HCN1 from being transported to medial perforant path axons in adult mice. Concordantly, expression analyses demonstrated a strong increase of expression of both TRIP8b isoforms in rat entorhinal cortex with age. However, when overexpressed in cultured entorhinal neurons of rats, TRIP8b(1a), but not TRIP8b(1a-4), altered substantially the subcellular distribution of HCN1 by promoting somatodendritic and reducing axonal expression of the channels. Taken together, we conclude that TRIP8b isoforms are important regulators of HCN1 trafficking in entorhinal neurons and that the alternatively-spliced isoform TRIP8b(1a) could be responsible for the age-dependent redistribution of HCN channels out of perforant path axon terminals.
authors.affiliation: Institute of Neuroanatomy, University of Hamburg, Medical Center, Hamburg, Germany.
authors.forename: Wiebke
authors.initials: W
authors.lastname: Wilkars
authors.forename: Zhiqiang
authors.initials: Z
authors.lastname: Liu
authors.forename: Alan S
authors.initials: AS
authors.lastname: Lewis
authors.forename: Travis R
authors.initials: TR
authors.lastname: Stoub
authors.forename: Elena M
authors.initials: EM
authors.lastname: Ramos
authors.forename: Nicola
authors.initials: N
authors.lastname: Brandt
authors.forename: Daniel A
authors.initials: DA
authors.lastname: Nicholson
authors.forename: Dane M
authors.initials: DM
authors.lastname: Chetkovich
authors.forename: Roland A
authors.initials: RA
authors.lastname: Bender
mesh_terms: D000818:Animals; D001369:Axons / Q000378:metabolism*; D002478:Cells, Cultured; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000378:metabolism*; D018891:Dentate Gyrus / Q000166:cytology / Q000378:metabolism / Q000648:ultrastructure; D018728:Entorhinal Cortex / Q000166:cytology / Q000378:metabolism; D005260:Female; D049452:Green Fluorescent Proteins / Q000378:metabolism; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D008565:Membrane Proteins / Q000172:deficiency / Q000378:metabolism*; D051379:Mice; D008810:Mice, Inbred C57BL; D019580:Perforant Pathway / Q000166:cytology / Q000378:metabolism*; D000074401:Peroxins; D015221:Potassium Channels / Q000378:metabolism*; D020033:Protein Isoforms / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D017208:Rats, Wistar; D013347:Subcellular Fractions / Q000378:metabolism; D016610:Tissue Embedding; D014162:Transfection
chemical_list: D054815:Cyclic Nucleotide-Gated Cation Channels; C578666:Hcn1 protein, mouse; C578667:Hcn1 protein, rat; D064428:Hyperpolarization-Activated Cyclic Nucleotide-Gated Channels; D008565:Membrane Proteins; D000074401:Peroxins; C501732:Pex5l protein, mouse; C523657:Pex5l protein, rat; D015221:Potassium Channels; D020033:Protein Isoforms; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins