Dietary serine supplementation reveals a protective effect against ROS in dry AMD

Abstract

Purpose : AMD is the leading cause of blindness among the elderly population with no efficient treatment. Elevated ROS levels in the RPE layer is a hallmark feature of AMD. We have previously shown that loss of Pink1, the master regulator of mitophagy causes glycolytic dysregulation, elevated ROS and reduced PHGDH & serine levels in the RPE. Since serine is directly involved in the management of ROS, here we provide evidence for dietary serine aiding in ROS management in the RPE.

Methods : ARPE-19 cells (in vitro) treated with scramble or Pink1 siRNA and on the RPE from C57 and Pink1^-/- male mice (in vivo) aged 8 months. For dietary serine, mice were fed 0.5% w/v L-serine ad libitum for 6 months (n=3). Fluorometric quantification of (i) ROS, MitoSOX and MtMP levels, (ii) GSH/GSSG and NADP⁺/NADPH ratios (iii) IHC for PHGDH and IBA1 levels (iv) ERG readings in Pink1^-/- mice fed with serine.

Results : Our results showed (i) Dysregulated ROS, MitoSOX and MtMP in siPink1 treated ARPE-19 cells. Serine reduced the ROS load by 60%; MitoSOX by 20% & MtMP by 45% (ii) GSH/GSSG ratio was increased by 2-fold; Total NADPH was increased by 10% (ii) PHGDH was reduced in the RPE of Pink1^-/- mice (iii) IBA1 levels showed an increase in Pink1^-/- mice indicating macrophage infiltration and serine reduced these levels. (iv) TEM of the RPE showed ruffled mitochondrial membranes in Pink1^-/- mice (v) ERG of Pink1^-/- mice show reduced a and b waves and oral serine rescued these responses.

Conclusions : Dietary L-serine supplementation can rescue (i) ROS triggered by Pink1 loss and rescue MitoSOX and membrane potential. (ii) ROS scavengers- GSH/GSSG levels were restored and total NADPH levels were significantly upregulated with serine (iii) Using serine as a dietary supplement in Pink1^-/- mice, ERG readings of both a (RGC layer) and b (PR layer) waves were rescued. These data show that dietary serine can rescue ROS accumulation in the RPE and functional responses of the neural retina thereby making L-serine a viable therapeutic avenue in AMD.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

(i) Loss of Pink1 triggers an altered ROS, MitoSOX, MtMP, GSH/GSSG and Total NADPH levels and was rescued upon serine treatment (ii) PHGDH levels were reduced and (iii) IBA1 levels showed increased macrophage infiltration in Pink1^-/- mice (iv) TEM of RPE mitochondria showed dysregulated membrane ruffles (v) ERG responses in Pink1^-/- mice showed dampened a and b waves which were rescued with oral serine.