NA,K-ATPASE MESSENGER-RNA LEVELS AND PLAQUE LOAD IN ALZHEIMERS-DISEASE

The expression of Na,K-ATPase alpha 1- and alpha 3-mRNAs was analyzed by in situ hybridization in the superior frontal cortex and cerebellum of brains from five Alzheimer's disease (AD), five nondemented age-ma tched, and three young control subjects. Brains with well-preserved RN A, tested by Northern hybridization of immobilized RNA with [P-32]-lab eled human beta-actin riboprobe, were chosen for analysis. In situ hyb ridization was performed on formalin-fixed, 5 mu m-thick Paraplast sec tions with [S-35]-labeled riboprobes prepared by in vitro transcriptio n of the respective linearized clones: a 537-bp EcoRI-PstI fragment of alpha 1-cDNA and a 342-bp PstI-EcoRI fragment of alpha 3-cDNA. In cor tex, grains related to mRNA were measured by density per unit area in five cortical columns separated by 1.0-1.2 cm in each of two adjacent sections. Each cortical column of 180-mu m width was divided into four depths orthogonal to the pial surface between the pia and the white m atter. Amyloid plaques were counted in the same regions of adjacent se ctions. In addition, alpha 3-mRNA grain clusters over individual pyram idal neurons within depth 4 were analyzed. We found the following sign ificant changes (p < 0.05): 1. Increases in total alpha 1-mRNA by 13-1 9% in AD compared to young and by 7-12% in AD compared to age-matched controls,. 2. Decrease in total alpha 3-mRNA by 31-38% in AD compared to young and age-matched controls. 3. Decrease in alpha 3-mRNA content over individual pyramidal perikarya by 14% in normal aged brains with out plaques compared to young controls, and by 44% in AD relative to y oung controls and by 35% compared to age-matched controls. No signific ant difference (p < 0.2) was found with respect to alpha 1- or alpha 3 -mRNA in cerebellar cortex or individual Purkinje cells among any of t he groups. In addition, there was a trend toward an inverse correlatio n between the levels of alpha 3-mRNA and of diffuse plaques, but not o f neuritic plaques, in AD cases. In conclusion: 1. The increases in al pha 1-mRNA in AD may be related to an increased reactive gliosis. 2. T he declines in alpha 3-mRNA per individual neuron found in normal agin g occur prior to the formation of diffuse plaques and are greatly acce lerated in AD. 3. The declines in alpha 3-mRNA per neuron found in nor mal aging may predispose to or potentiate AD pathogenesis.