Abstract
Purpose :
Heat shock proteins (HSPs) are stress-activated molecular chaperones that play a key role in proteostasis. Upregulation of HSPs has been shown to be protective in a variety of neurodegenerative diseases. HSP70 in particular has been reported to play a critical role in photoreceptor stress response and survival. However, the role of HSPs in retinal degeneration (RD) remains unclear. To initiate our investigation of HSP function in photoreceptors, we surveyed RNA and protein expression of HSP70 and other HSPs expressed in the retina.
Methods :
We examined existing laboratory RNA sequencing (RNA-seq) data on flow-sorted photoreceptors (FSPRs) and extracted expression information on HSPs in postnatal wild-type (WT) and three mouse RD models: rd10 (Pde6brd10/rd10), rds (Prph2rd2/rd2), and rd16 (Cep290rd16/rd16). WT and RD rod photoreceptors were compared at postnatal day (P)10. Protein lysates were prepared from whole retina at P10, P14, P18, P28, and two months, and used for detection of HSP70, heat shock cognate 70 (HSC70), and control b-actin by immunoblot. Corresponding histological sections were collected for each time point.
Results :
RNA-seq analysis of WT FSPRs showed postnatal up-regulation with peak at P14 of Hspa1a and Hspa1b, which encode HSP70, and relatively constant expression of Hspa8, which encodes HSC70. At P10, expression of Hspa1a, Hspa1b, and Hspa8 was lower in rd10 and rds photoreceptors compared to WT. Conversely, expression of heat shock factor 1 (Hsf1), a regulator of Hspa1a and Hspa1b, was higher in all RD models than in WT. Immunoblotting showed that HSP70 protein was up-regulated at P14 and remained steadily expressed through P28 in WT retina. However, HSP70 expression declined by P18 in rd16 and rd10, and by P28 in rds. Conversely, HSC70 protein content in the retina appeared unchanged in all RD models compared to WT at P28.
Conclusions :
We report decreased expression of both Hspa1a and Hspa1b RNA in FSPRs and of HSP70 protein in the retina of postnatal RD mouse models, suggestive of an early manifestation of cell dysfunction that may be common to neurodegeneration. We are testing the hypothesis that restoring HSP70 expression to levels observed in WT could slow the progression of RD by bolstering the cell’s adaptive stress response.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.