Abstract
Purpose :
We previously showed that a ketogenic & low protein (KLP) diet slows photoreceptor degeneration in early weaned rd10 mice but the neuroprotective mechanism remains unclear. We performed a proteomics analysis to determine which proteins the KLP diet modulate in the retina as a way to isolate targets that slow retinal degeneration.
Methods :
C57BL6 mice were early weaned and placed on the KLP diet starting at P15. After 30 days of continuous diet administration, ERGs were recorded, serum albumin was measured and retinas were harvested for tandem mass tag (TMT) mass spectrometry to compare differentially expressed proteins. To investigate the effect of dietary protein restriction, a separate group of rd10 mice were early weaned and placed on a low protein diet containing 8% protein. At P23, P30, P40 and P50 weight and blood b-hydroxybutyrate levels were recorded and retinal thickness was measured with optical coherence tomography (OCT). At P30 and P50, serum albumin levels were measured.
Results :
TMT analysis quantified a total of 6247 proteins. Of these, 58 proteins were differentially expressed in the retina due to the KLP diet. Only one of these plays a role in phototransduction (SWOPN1). Of interest was an upregulation of antioxidant (GST, APOA4), lipid metabolism (SCP2) and DNA repair (XRCC4) proteins and a downregulation of markers for neuronal damage (GFAP, NFMP). Mice on the low protein diet weighed an average of 30% less than those on standard chow (SC), but blood albumin concentrations were not significantly different from the SC group (~1300pg/mL). Photoreceptor layer thickness decreased from 60.4uM at P23 to 18.3uM at P50, mimicking the rate of degeneration in the SC group.
Conclusions :
We previously published that the KLP diet reduces phototransduction, which may serve as the protective mechanism of the KLP diet. However, our data show that these changes are not due to a significant change in phototransduction protein expression but rather activation and suppression of key proteins for neuroprotective pathways. The low protein diet results further support the hypothesis that reduced phototransduction and serum albumin are required to elicit photoreceptor protection in the rd10 mice. These data generate novel therapeutic targets for inherited retinal degeneration.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.