title: MARK4 and MARK3 associate with early tau phosphorylation in Alzheimer's disease granulovacuolar degeneration bodies.
abstract: BACKGROUND
  The progression of Alzheimer's disease (AD) is associated with an increase of phosphorylated tau in the brain. One of the earliest phosphorylated sites on tau is Ser262 that is preferentially phosphorylated by microtubule affinity regulating kinase (MARK), of which four isoforms exist. Herein we investigated the expression of MARK1-4 in the hippocampus of non-demented elderly (NDE) and AD cases.
  
  
  RESULTS
  In situ hybridization revealed a uniform, neuronal distribution of all four isoform mRNAs in NDE and AD. Immunohistochemical analyses using isoform-selective antibodies demonstrated that MARK4 in a phosphorylated form colocalizes with p-tau Ser262 in granulovacuolar degeneration bodies (GVDs) that progressively accumulate in AD. In contrast MARK4 is largely absent in the neuronal cytoplasm. MARK3 was localized to a subset of the GVD-containing neurons and also had a weak general cytoplasmic neuronal staining in both NDE and AD. These results suggest that in AD, phosphorylated MARK3 and MARK4 are sequestered and proteolysed in GVDs. MARK1 and MARK2 were absent in GVDs and exhibited relatively uniform neuronal expressions with no apparent differences between NDE and AD.
  
  
  CONCLUSIONS
  We found that the phosphorylated and fragmented forms of MARK4 and to some extent MARK3 are present in GVDs in AD, and that this expression is highly correlated with phosphorylation of tau at Ser262. This may represent a cellular defense mechanism to remove activated MARK and p-tau Ser262 from the cytosol, thereby reducing the phosphorylating effect on tau Ser262 that appears to be a critical step for subsequent neurodegeneration.
authors.forename: Harald
authors.initials: H
authors.lastname: Lund
authors.forename: Elin
authors.initials: E
authors.lastname: Gustafsson
authors.forename: Anne
authors.initials: A
authors.lastname: Svensson
authors.forename: Maria
authors.initials: M
authors.lastname: Nilsson
authors.forename: Margareta
authors.initials: M
authors.lastname: Berg
authors.forename: Dan
authors.initials: D
authors.lastname: Sunnemark
authors.affiliation: Department of Neuroscience, iMed, CNS and Pain Södertälje, AstraZeneca Research and Development, Södertälje, Sweden. gabriel.von.euler@ki.se.
authors.forename: Gabriel
authors.initials: G
authors.lastname: von Euler
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D000544:Alzheimer Disease / Q000378:metabolism / Q000473:pathology*; D048148:Casein Kinase Idelta / Q000378:metabolism; D003594:Cytoplasmic Granules / Q000378:metabolism / Q000473:pathology*; D005260:Female; D057809:HEK293 Cells; D006624:Hippocampus / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D008297:Male; D010766:Phosphorylation; D017346:Protein Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D014162:Transfection; D014617:Vacuoles / Q000378:metabolism / Q000473:pathology*; D016875:tau Proteins / Q000378:metabolism*
chemical_list: D016875:tau Proteins; D012694:Serine; C111833:MARK3 protein, human; C483047:MARK4 protein, human; D048148:Casein Kinase Idelta; D017346:Protein Serine-Threonine Kinases