Figure 4. Proteasome mRNA and Protein Expression Is Decreased in Heart in Microgravity.

(A) Expression of mRNA encoding many proteasome subunits is dramatically increased by exposure to microgravity in hearts from CS SF flies compared with CS GCs. Hearts from sei/hERG mutant GCs have much lower expression of these same subunits, and the expression is not altered by microgravity. Each box is the average of triplicate samples normalized to the overall averaged expression for all hearts.

(B and C) Images from a single cardiac chamber in GC (B) and SF (C) CS female flies homozygous for Hand-gal4 > UAS polyQ⁴⁶ GFP. Immunohistochemical staining showed proteasome immunoreactivity (red) and PolyQ-GFP (green); scale bar, 10 μm. Merged images show co-localization of some GFP-positive plaques and proteasome aggregates. Myocardial cell nuclei are stained with DAPI (blue).

(D and E) GFP particle count (D) and total area (E) were increased in hearts from females (red symbols) but not males (blue symbols) under microgravity.

(F) Proteasome particle count was significantly higher in females compared with males and was significantly increased in female hearts in response to microgravity.

(G) Proteasome aggregate total area was also significantly increased in females but not in males.

For all graphs, significance was determined by two-way ANOVA and Tukey’s multiple comparisons post hoc test. *p < 0.05, **p < 0.01, ***p < 0.005.