HSPA1A and Parkinson disease: Given the increased sequestration of Hsp70, Hsp90, and STI1 to insoluble fractions in the brains of PFF-injected M83+/− mice, and the increased levels of STI1 and other chaperone transcripts in PD (Fig. 1n), we tested whether increased STI1 levels are compensatory and could mitigate for potentially decreased chaperone function in synucleinopathy brains.