Biochemical analysis of interactions of progranulin and prosaposin in MTG brain samples. (a-b). Co-immunoprecipitation of Progranulin and Prosaposin. a). Western blot control analyses to show interactions of progranulin (PGRN) and prosaposin (PSAP). Immunoprecipitation of PGRN-overexpressing HEK (HEK and HEK1) cells and AD brain sample with protein G- (goat antibody) or protein A- (rabbit antibody) antibody-conjugated magnetic beads. Beads were prepared using non-immune goat IgG, goat anti-PGRN and rabbit anti-PSAP. Immunoprecipitated samples were separated by gel electrophoresis, transferred to membranes, and probed with antibodies to PSAP and PGRN. Samples of total protein (non-immunoprecipitated) from PGRN-overexpressing HEK (HEK) cells and brain sample (AD) were analyzed as specificity controls. Samples immunoprecipitated with PGRN antibody contained PSAP, and samples precipitated with PSAP antibody contained PGRN. b). All of the brain samples from LP, AD and HP cases precipitated with PGRN antibody pulled-down PSAP. A series of cases (n = 5) from each group were analyzed. Western blot images for both antibodies are shown. (c-f) Biochemical analysis of prosaposin in MTG brain protein extracts. c). Western blot analysis of total PSAP protein levels in MTG samples. Representative image of western blot demonstrating PSAP protein in samples from LP, HP and AD cases. The complete images of all samples analyzed for PSAP are shown as Additional file 4: Figure. S4B. D). Scatter plot showing expression levels of PSAP protein in the different groups. Results represent mean ±S.E.M. Significantly increased levels of PSAP protein were present in AD case compared to LP and HP cases but not between LP and HP cases. Significant increased levels of PSAP protein in MTG samples from AD compared to HP (* p < 0.05) and LP (** p < 0.01). e). Positive correlation between PSAP and PGRN protein levels in MTG samples (Pearson r = 0.4674, p = 0.0070). f). Positive correlation between PSAP and Aβ protein levels in MTG samples (Pearson r = 0.4584, p = 0.0083).