title: Decreased BDNF levels are a major contributor to the embryonic phenotype of huntingtin knockdown zebrafish.
abstract: Huntington's disease (HD) is an autosomal dominant, neurodegenerative condition caused by a CAG trinucleotide repeat expansion that is translated into an abnormally long polyglutamine tract in the protein huntingtin. Genetic and transgenic studies suggest that the mutation causes disease predominantly via gain-of-function mechanisms. However, loss of normal huntingtin function resulting from the polyglutamine expansion might also contribute to the pathogenesis of HD. Here, we have studied the effects of huntingtin knockdown in zebrafish using morpholino antisense oligonucleotides, as its huntingtin orthologue has 70% amino acid identity with the human protein. Reduced huntingtin levels did not impact on gastrulation and early development, but caused massive apoptosis of neuronal cells by 24 hpf. This was accompanied by impaired neuronal development, resulting in small eyes and heads and enlargement of brain ventricles. Older huntingtin knockdown fish developed lower jaw abnormalities with most branchial arches missing. Molecular analysis revealed that BDNF expression was reduced by approximately 50%. Reduction of BDNF levels by injection of a BDNF morpholino resulted in phenotypes very similar to those seen in huntingtin knockdown zebrafish. The phenotypes of both huntingtin- and BDNF-knockdown zebrafish showed significant rescue when treated with exogenous BDNF protein. This underscores the physiological importance of huntingtin as a regulator of BDNF production and suggests that loss of BDNF is a major cause of the developmental abnormalities seen with huntingtin knockdown in zebrafish. Increasing BDNF expression may represent a useful strategy for Huntington's disease treatment.
authors.affiliation: Summit (Cambridge) Ltd., Cambridge CB25 9TN, United Kingdom.
authors.forename: Heike
authors.initials: H
authors.lastname: Diekmann
authors.forename: Oleg
authors.initials: O
authors.lastname: Anichtchik
authors.forename: Angeleen
authors.initials: A
authors.lastname: Fleming
authors.forename: Marie
authors.initials: M
authors.lastname: Futter
authors.forename: Paul
authors.initials: P
authors.lastname: Goldsmith
authors.forename: Alan
authors.initials: A
authors.lastname: Roach
authors.forename: David C
authors.initials: DC
authors.lastname: Rubinsztein
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D055785:Gene Knockdown Techniques / Q000379:methods; D006801:Humans; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000235:genetics* / Q000502:physiology; D010641:Phenotype; D015027:Zebrafish / Q000196:embryology* / Q000235:genetics*; D029961:Zebrafish Proteins / Q000172:deficiency / Q000235:genetics* / Q000502:physiology
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D009419:Nerve Tissue Proteins; D029961:Zebrafish Proteins; C524778:htt protein, zebrafish