Overcoming mitochondrial hyperfusion as a novel therapeutic target for retinal neuroprotection in diabetes

Abstract

Purpose : Restoration of mitochondrial quality control (MQC) has emerged as a promising strategy for neuroprotection in a plethora of conditions, including diabetic retinopathy (DR). However, the success of potential interventions depends upon our understanding of how MQC mechanisms (dynamics, mitophagy, and biogenesis) are affected during disease progression in specific retinal cells. Our aim was to understand how these processes interplay in the human and murine diabetic retina to develop new mitochondrial-targeted interventions.

Methods : 3-months and 8-month-old diabetic mitophagy reporter (MitoQC-Ins2^Akita) mice were used to evaluate the interplay between mitochondrial dynamics and mitophagy by confocal morphometry. To mimic mitochondrial hyperfusion in vitro, mitochondrial fission in retinal Müller cells (mouse primary and MIO-M1 cell-line) was inhibited using Drp1 inhibitor peptide (P110) under hyperglycaemia (30.5mM). Pharmacological ‘hits’ rescuing mitophagy were assessed for their capability to improve mitochondrial health (membrane potential [ΔΨm]) and bioenergetics (Seahorse metabolic flux). The bio-activity of lead compounds were corroborated in vivo using Mito-QC Ins2^Akita, while therapeutic potential via electroretinography (ERG), retinal thickness (SD-OCT) and immunohistochemical analysis of retinal neurons.

Results : Mitochondria hyperfusion is characteristic of retinal neurodegeneration in human and murine diabetes, inhibiting mitophagy and causing bioenergetic stress. Using our drug screening platform, we identified N6-furfuryladenosine ([N6F] an activator of PINK1 kinase) and three newly identified mitophagy activators capable of rescuing mitochondrial health and bioenergetics under conditions of diabetes-induced hyperfusion. The bio-activity of N6F was further demonstrated in vivo, where oral administration rescued mitophagy in the retina of MitoQC-Ins2^Akita mice. N6F further prevented retinal neurodegeneration, as shown by improved scotopic ERG responses, increased SD-OCT retinal thickness, and neuroprotection to photoreceptors, synaptic terminals and GABAergic amacrine cells.

Conclusions : Exacerbated mitochondrial fusion impairs MQC in the diabetic retina. Overcoming mitochondrial hyperfusion in a controlled fashion may bring innovative interventions for DR.

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