Our findings indicate that HG-induced downregulation of Cx43 expression and GJIC may contribute to the breakdown of endothelial barrier tight junctions associated with diabetic retinopathy.
PurposeTo investigate whether high glucose (HG) induces mitochondrial dysfunction and promotes apoptosis in retinal Müller cells.MethodsRat retinal Müller cells (rMC-1) grown in normal (N) or HG (30 mM glucose) medium for 7 days were subjected to MitoTracker Red staining to identify the mitochondrial network. Digital images of mitochondria were captured in live cells under confocal microscopy and analyzed for mitochondrial morphology changes based on form factor (FF) and aspect ratio (AR) values. Mitochondrial metabolic function was assessed by measuring oxygen consumption rate (OCR) and extracellular acidification rate (ECAR) using a bioenergetic analyzer. Cells undergoing apoptosis were identified by differential dye staining and TUNEL assay, and cytochrome c levels were assessed by Western blot analysis.ResultsCells grown in HG exhibited significantly increased mitochondrial fragmentation compared to those grown in N medium (FF = 1.7 ± 0.1 vs. 2.3 ± 0.1; AR = 2.1 ± 0.1 vs. 2.5 ± 0.2; P < 0.01). OCR and ECAR were significantly reduced in cells grown in HG medium compared to those grown in N medium (steady state: 75% ± 20% of control, P < 0.02; 64% ± 22% of control, P < 0.02, respectively). These cells also exhibited a significant increase (∼2-fold) in the number of apoptotic cells compared to those grown in N medium (P < 0.01), with a concomitant increase in cytochrome c levels (247% ± 94% of control, P < 0.05).ConclusionsFindings indicate that HG-induced mitochondrial morphology changes and subsequent mitochondrial dysfunction may contribute to retinal Müller cell loss associated with diabetic retinopathy.
Gap junction communication between Müller cells and pericytes is essential for their survival. Downregulation of Cx43 that is HG induced and impairment of GJIC activity in Müller cells contributes to loss of glial and vascular cells associated with the pathogenesis of diabetic retinopathy.
Hyperglycemia, a prominent characteristic of diabetes, has been implicated in the apoptotic death of vascular and neuronal cells in the retina. In diabetic retinopathy, mitochondrial dysfunction, endoplasmic reticulum (ER) stress, and subsequent breakdown of cellular homeostasis play a critical role in retinal cell death. In particular, changes in mitochondrial morphology, mitochondrial membrane potential heterogeneity, oxygen consumption rate and protein misfolding are beginning to be recognized as key players in the demise of retinal vascular cells in diabetes. Some of these key changes contribute to oxidative stress and influence ion transport, impacting overall cellular homeostasis. The primary objective of this review is to provide insight into the mechanisms in which high glucose influences two disparate cellular organelles, mitochondria and ER, in promoting apoptotic demise of retinal vascular and neuronal cells in diabetic retinopathy.
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