title: Hippocampal synaptic connectivity in phenylketonuria.
abstract: In humans, lack of phenylalanine hydroxylase (Pah) activity results in phenylketonuria (PKU), which is associated with the development of severe mental retardation after birth. The underlying mechanisms, however, are poorly understood. Mutations of the Pah gene in Pah(enu2)/c57bl6 mice result in elevated levels of phenylalanine in serum similar to those in humans suffering from PKU. In our study, long-term potentiation (LTP) and paired-pulse facilitation, measured at CA3-CA1 Schaffer collateral synapses, were impaired in acute hippocampal slices of Pah(enu2)/c57bl6 mice. In addition, we found reduced expression of presynaptic proteins, such as synaptophysin and the synaptosomal-associated protein 25 (SNAP-25), and enhanced expression of postsynaptic marker proteins, such as synaptopodin and spinophilin. Stereological counting of spine synapses at the ultrastructural level revealed higher synaptic density in the hippocampus, commencing at 3 weeks and persisting up to 12 weeks after birth. Consistent effects were seen in response to phenylalanine treatment in cultures of dissociated hippocampal neurones. Most importantly, in the hippocampus of Pah(enu2)/c57bl6 mice, we found a significant reduction in microglia activity. Reorganization of hippocampal circuitry after birth, namely synaptic pruning, relies on elimination of weak synapses by activated microglia in response to neuronal activity. Hence, our data strongly suggest that reduced microglial activity in response to impaired synaptic transmission affects physiological postnatal remodelling of synapses in the hippocampus and may trigger the development of mental retardation in PKU patients after birth.
authors.affiliation: Institute of Neuroanatomy, Institute of Anatomy and Experimental Morphology and.
authors.forename: Katja
authors.initials: K
authors.lastname: Horling
authors.affiliation: Institute of Neuroanatomy.
authors.forename: Gudrun
authors.initials: G
authors.lastname: Schlegel
authors.affiliation: Institute of Neuroanatomy.
authors.forename: Sarah
authors.initials: S
authors.lastname: Schulz
authors.affiliation: Institute of Neuroanatomy.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Vierk
authors.affiliation: Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: Kurt
authors.initials: K
authors.lastname: Ullrich
authors.affiliation: Department of Pediatrics, University Medical Center Hamburg-Eppendorf, Hamburg 20246, Germany.
authors.forename: René
authors.initials: R
authors.lastname: Santer
authors.affiliation: Institute of Neuroanatomy, rune@uke.uni-hamburg.de.
authors.forename: Gabriele M
authors.initials: GM
authors.lastname: Rune
mesh_terms: D000818:Animals; D004195:Disease Models, Animal; D005786:Gene Expression Regulation / Q000187:drug effects; D006624:Hippocampus / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D017774:Long-Term Potentiation; D051379:Mice; D018345:Mice, Knockout; D017628:Microglia / Q000378:metabolism; D009474:Neurons / Q000378:metabolism; D010649:Phenylalanine / Q000494:pharmacology; D010651:Phenylalanine Hydroxylase / Q000235:genetics; D010661:Phenylketonurias / Q000235:genetics / Q000378:metabolism*; D013569:Synapses / Q000378:metabolism; D009435:Synaptic Transmission; D050825:Synaptosomal-Associated Protein 25 / Q000235:genetics / Q000378:metabolism
chemical_list: D050825:Synaptosomal-Associated Protein 25; D010649:Phenylalanine; D010651:Phenylalanine Hydroxylase