Exacerbated mitochondrial fusion abrogates mitophagy and leads to proinflammatory signalling in Muller glia during diabetic retinopathy

Abstract Purpose: To determine how the dysregulated interplay between mitochondrial dynamics and mitophagy contribute to the progression of diabetic retinopathy [DR]. Methods: 3‐months and 9‐month‐old diabetic mitophagy reporter (MitoQC‐Ins2Akita) mice and their non‐diabetic siblings, were used to evaluate the interplay between mitochondrial dynamics and mitophagy by confocal morphometry. To model the dysregulation of mitochondrial quality control processes in vitro, mitochondrial fission was antagonized in retinal Müller cells (mouse primary and MIO‐M1 cell‐line) using a Drp1 inhibitor peptide (P110), under physiological (5.5 mM) and elevated glucose (30.5 mM) conditions. Mitochondrial fitness was assessed via metabolic flux (Seahorse) along with mitochondrial membrane potential (JC‐1), while the Müller glia inflammatory secretome was determined using Luminex. Results: In contrast to younger ages, 9‐month‐old diabetic mice displayed exacerbated mitochondrial fusion at the outer retina (e.g., increased interconnectivity and mitochondrial aspect ratios), which was strongly associated with impaired mitophagy levels ( r 2 = 0.7, p < 0.001). P110 peptide inhibited mitochondrial fission/exacerbated fusion in retinal Müller cells, and abrogated mitophagy similarly to that found at advanced DR stages. Importantly, exacerbated mitochondrial fusion under hyperglycaemia (but not normoglycaemia) disrupted mitochondrial membrane potential ( p < 0.05) in Müller cell cultures, further compromising mitochondrial fitness, as shown by decreased spare respiratory capacity and bioenergetic health index ( p < 0.001 both). This was accompanied by significantly elevated secretion of key DR pro‐inflammatory factors, particularly CCL2 and VEGF‐A ( p < 0.05 both). Conclusions: Exacerbated mitochondrial fusion contributes to DR pathology by inhibiting mitophagy in Müller glia. Therapies aimed at facilitating mitochondrial fission/mitophagy in a controlled fashion may hold therapeutic potential for managing DR.