Abstract
Purpose :
We recently discovered that inflammation of the retinal pigment epithelium (RPE) in MERTK null mice drives photoreceptor degeneration. We also reported that the small GTPase Rab37 is differentially expressed at the transcript level in postnatal day 25 (p25) MERTK null RPE. Here, we aimed to investigate Rab37 in the well characterized Royal College of Surgeons (RCS) rat model of MERTK-associated Retinitis Pigmentosa (RP).
Methods :
Eyeballs from age-matched RCS and wildtype (WT) rats were dissected to yield neural retina and RPE for mRNA and protein extractions.
We measured Rab37 and GAPDH control mRNA levels via RT-PCR.
We analyzed tissue lysates by SDS-PAGE and immunoblotting for Rab37 as well as tissue-specific and housekeeping proteins. mRNA and protein expression were quantified using ImageJ densitometry. Two-tailed Student’s t-tests were performed to assess differences in Rab37 expression between samples.
Results :
At p25 and p35, Rab37 transcript and protein levels were significantly elevated in RCS RPE compared to WT RPE. Normalized Rab37 mRNA levels were ~3-fold greater at p25 (N=4, p<0.0001) and ~2.4-fold greater at p35 (N=4, p<0.001) in RCS RPE when compared to WT RPE. Normalized Rab37 protein levels were ~3.4-fold greater at p25 (N=7, p<0.0001) and ~3.7-fold greater at p35 (N=6, p<0.0001) in RCS RPE when compared to WT RPE. At p10, Rab37 transcript levels were the same in RCS and WT RPE (N=3, p=0.2570), while Rab37protein levels were slightly greater, by 1.6-fold, in p10 WT RPE than in RCS RPE (N=3, p<0.01). There was no difference in Rab37 expression in WT and RCS neural retina tissue at any of the ages tested (p>0.05).
Conclusions :
Rab37 is upregulated in MERTK-deficient RPE of RCS rats at ages that coincide with early disease manifestation and onset of photoreceptor death in MERTK-associated RP. This change was not observed in the RCS neural retina, which contains microglia and Müller cells that express MERTK in wild-type rats, indicating that Rab37 regulation in response to loss of MERTK in the RCS rat may be specific to the RPE. Rab37 and other small GTPases are known to be associated with vesicle dynamics, suggesting possible roles in cell signaling, exocytosis, or phagocytosis. Future efforts aim to identify the effects of Rab37 modulation on RPE functions.
This abstract was presented at the 2023 ARVO Annual Meeting, held in New Orleans, LA, April 23-27, 2023.