14-3-3 protein beta isoform is associated with 3-repeat tau neurofibrillary tangles in Alzheimer's disease

14-3-3 proteins play roles in phosphorylation of tau proteins in neurofibrillary tangles (NFT) in Alzheimer's disease (AD). Tau is phosphorylated at serine (pSer) and threonine (pThr) in NFT, and NFT morphology varies according to phosphorylated sites and tau isoform. The roles of 14-3-3 proteins in NFT morphology remain unknown. This study was performed to examine the relationships between 14 and 3-3 proteins and tau phosphorylation of NFT. NFT were labeled with Gallyas impregnation, tau and 14-3-3 immunohistochemistry in paraffin-embedded hippocampal sections from seven AD and three control brains. Anti-tau antisera included monoclonal antisera that recognize pSer262 (pSer262), pSer422 (pSer422), pSer202/pThr205 (AT8), Thr231 (AT180), three-repeat (RD3) and four-repeat (RD4) tau isoform. Anti-14-3-3 protein isoform antisera included polyclonal antisera to beta, gamma, zeta, epsilon, tau, mu and sigma isoforms and monoclonal antiserum to beta antiserum (H8-beta). NFT density was obtained by counting labeled NFT in cornu ammonis (CA) 1-CA4, subiculum and entorhinal cortex. H8-beta and zeta isoforms were strongly expressed in NFT. Regional densities of NFT positive for pSer262, AT8, AT180, and Gallyas impregnation were similar to RD3-positive NFT density with high densities in CA1 and entorhinal cortex. NFT positive for pSer422 showed a similar regional distribution to RD4-positive NFT with high NFT density in CA2-CA4. H8-beta-positive NFT showed a similar regional distribution to RD3-positive NFT. In contrast, zeta isoform-positive NFT showed no specific distribution. In conclusion, H8-beta isoform is associated with development of 3-repeats NFT but a role of 14-3-3 zeta isoform in NFT could not be specified.