N Fig. 4B) lowered the frequency of dragged wings (solid line in Fig. 4B).SAP Co-localizes with TTR-A in Drosophila Eye and Prevents Retinal DegenerationTo monitor SAP and TTR-A interaction further, we performed immunohistochemical analysis of fly retinas that co-expressed these two proteins (Fig. 5). TTR-A expressed alone leads to retinal degeneration, as reported previously [32,33]. In Figure 5, we show that in 2-week-old flies, TTR-A secreted by the photoreceptors (Fig. 5A and B, red) accumulated as amyloid aggregates in the retinal compartment around the outer corneal layer (CL), which was confirmed with the amyloid-specific dye p-FTAA [39,40] (Fig. 5E and F, aggregated TTR-A in green). This resulted in damage to the retinal array and MedChemExpress 47931-85-1 leakage of TTR-A outside the CL (individual corneal BIBS39 chemical information lenses shown with arrows are magnified in the insets in Fig. 5). In contrast, SAP expressed alone in the fruit fly retina stayed soluble (Fig. 5C), as no p-FTAA aggregates were detected (Fig. 5G) and no degeneration of the retina was observed compared to control flies (Fig. S2A). Co-expression of SAP and TTR-A (Fig. 5D and H) resulted in complete protection from the degenerative changes induced by TTR-A. Interestingly, SAP colocalized with TTR-A aggregates, as clearly seen in Figure 5 D (additional details in Fig. S2B and C) and by reduced p-FTAA staining of TTR-A (Fig. 5H). Immunoblot analysis of non-reduced head extracts confirmed co-localization of SAP with aggregated TTR-A in fruit flies coexpressing these two proteins (Fig. S3). These flies showed some levels of soluble TTR-A and of unbound monomeric SAP, and had normal wing posture. In contrast, in flies that only expressed TTR-A and that had the dragged-wing phenotype, no soluble TTR-A was detected, as TTR formed large aggregates that did not enter the gel.SAP Prevents TTR-induced ToxicityThe WST-1 assay used above does not provide any information on the type of cytotoxic response induced by mutated TTR. However, we have previously shown that both TTR-A- and TTRD-induced toxicity is associated with apoptotic cell death. In order to study functional effects of SAP binding to pre-fibrillar aggregates, we used TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling) assay to visualize apoptosis. IMR-32 cells were exposed to 20 mM pre-aggregated TTR-A or TTR-D for 3 days, either alone or in the presence of 1.5 mM or 3 mM SAP. In Figure 3A, we present evidence that SAP prevented apoptosis caused by pre-fibrillar aggregates of mutated TTR. Exposure of IMR-32 cells to 20 mM TTR-A (upper row) or 20 mM TTR-D (lower row) induced TUNEL reactivity (green fluorescence), with almost all cells staining positive (left column). Premixing the amyloidogenic mutants of TTR with 1.5 mM SAP reduced the apoptotic cell response (middle column), while 3 mM SAP almost totally extinguished TUNEL-positive reactions (right column). PARP (poly (ADP-ribose) polymerase) cleavage has been used as a marker for downstream effector caspases (Fig. 3B) [38]. The full length PARP (116 kDa) is involved in DNA repair mechanisms and helps cells to maintain their viability. Cleavage of PARP separates its carboxy-terminal catalytic domain (89 kDa) and facilitates cellular disassembly and apoptotic cell death. The IMR32 cells were incubated for 12 h with 20 mM pre-aggregated mutated TTR-A in the presence or absence of SAP, and thereafter the cells were lysed with 0.1 M Tris, pH 6.8, 2 w/v SDS, and 1 v/v b-mercaptoet.N Fig. 4B) lowered the frequency of dragged wings (solid line in Fig. 4B).SAP Co-localizes with TTR-A in Drosophila Eye and Prevents Retinal DegenerationTo monitor SAP and TTR-A interaction further, we performed immunohistochemical analysis of fly retinas that co-expressed these two proteins (Fig. 5). TTR-A expressed alone leads to retinal degeneration, as reported previously [32,33]. In Figure 5, we show that in 2-week-old flies, TTR-A secreted by the photoreceptors (Fig. 5A and B, red) accumulated as amyloid aggregates in the retinal compartment around the outer corneal layer (CL), which was confirmed with the amyloid-specific dye p-FTAA [39,40] (Fig. 5E and F, aggregated TTR-A in green). This resulted in damage to the retinal array and leakage of TTR-A outside the CL (individual corneal lenses shown with arrows are magnified in the insets in Fig. 5). In contrast, SAP expressed alone in the fruit fly retina stayed soluble (Fig. 5C), as no p-FTAA aggregates were detected (Fig. 5G) and no degeneration of the retina was observed compared to control flies (Fig. S2A). Co-expression of SAP and TTR-A (Fig. 5D and H) resulted in complete protection from the degenerative changes induced by TTR-A. Interestingly, SAP colocalized with TTR-A aggregates, as clearly seen in Figure 5 D (additional details in Fig. S2B and C) and by reduced p-FTAA staining of TTR-A (Fig. 5H). Immunoblot analysis of non-reduced head extracts confirmed co-localization of SAP with aggregated TTR-A in fruit flies coexpressing these two proteins (Fig. S3). These flies showed some levels of soluble TTR-A and of unbound monomeric SAP, and had normal wing posture. In contrast, in flies that only expressed TTR-A and that had the dragged-wing phenotype, no soluble TTR-A was detected, as TTR formed large aggregates that did not enter the gel.SAP Prevents TTR-induced ToxicityThe WST-1 assay used above does not provide any information on the type of cytotoxic response induced by mutated TTR. However, we have previously shown that both TTR-A- and TTRD-induced toxicity is associated with apoptotic cell death. In order to study functional effects of SAP binding to pre-fibrillar aggregates, we used TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end-labeling) assay to visualize apoptosis. IMR-32 cells were exposed to 20 mM pre-aggregated TTR-A or TTR-D for 3 days, either alone or in the presence of 1.5 mM or 3 mM SAP. In Figure 3A, we present evidence that SAP prevented apoptosis caused by pre-fibrillar aggregates of mutated TTR. Exposure of IMR-32 cells to 20 mM TTR-A (upper row) or 20 mM TTR-D (lower row) induced TUNEL reactivity (green fluorescence), with almost all cells staining positive (left column). Premixing the amyloidogenic mutants of TTR with 1.5 mM SAP reduced the apoptotic cell response (middle column), while 3 mM SAP almost totally extinguished TUNEL-positive reactions (right column). PARP (poly (ADP-ribose) polymerase) cleavage has been used as a marker for downstream effector caspases (Fig. 3B) [38]. The full length PARP (116 kDa) is involved in DNA repair mechanisms and helps cells to maintain their viability. Cleavage of PARP separates its carboxy-terminal catalytic domain (89 kDa) and facilitates cellular disassembly and apoptotic cell death. The IMR32 cells were incubated for 12 h with 20 mM pre-aggregated mutated TTR-A in the presence or absence of SAP, and thereafter the cells were lysed with 0.1 M Tris, pH 6.8, 2 w/v SDS, and 1 v/v b-mercaptoet.
