Validating the RedMIT/GFP-LC3 Mouse Model by Studying Mitophagy in Autosomal Dominant Optic Atrophy Due to the OPA1Q285STOP Mutation

Abstract

Background: Autosomal dominant optic atrophy (ADOA) is usually caused by mutations in the essential gene, OPA1. This encodes a ubiquitous protein involved in mitochondrial dynamics, hence tissue specificity is not understood. Dysregulated mitophagy (mitochondria recycling) is implicated in ADOA, being increased in OPA1 patient fibroblasts. Furthermore, autophagy may be increased in retinal ganglion cells (RGCs) of the OPA1Q285STOP mouse model.Aims: We developed a mouse model for studying mitochondrial dynamics in order to investigate mitophagy in ADOA.Methods: We crossed the OPA1Q285STOP mouse with our RedMIT/GFP-LC3 mouse, harboring red fluorescent mitochondria and green fluorescent autophagosomes. Colocalization between mitochondria and autophagosomes, the hallmark of mitophagy, was quantified in fluorescently labeled organelles in primary cell cultures, using two high throughput imaging methods Imagestream (Amnis) and IN Cell Analyzer 1000 (GE Healthcare Life Sciences). We studied colocalization between mitochondria and autophagosomes in fixed sections using confocal microscopy.Results: We validated our imaging methods for RedMIT/GFP-LC3 mouse cells, showing that colocalization of red fluorescent mitochondria and green fluorescent autophagosomes is a useful indicator of mitophagy. We showed that colocalization increases when lysosomal processing is impaired. Further, colocalization of mitochondrial fragments and autophagosomes is increased in cultures from the OPA1Q285STOP/RedMIT/GFP-LC3 mice compared to RedMIT/GFP-LC3 control mouse cells that were wild type for OPA1. This was apparent in both mouse embryonic fibroblasts (MEFs) using IN Cell 1000 and in splenocytes using ImageStream imaging flow cytometer (Amnis). We confirmed that this represents increased mitophagic flux using lysosomal inhibitors. We also used microscopy to investigate the level of mitophagy in the retina from the OPA1Q285STOP/RedMIT/GFP-LC3 mice and the RedMIT/GFP-LC3 control mice. However, the expression levels of fluorescent proteins and the image signal-to-background ratios precluded the detection of colocalization so we were unable to show any difference in colocalization between these mice.Conclusions: We show that colocalization of fluorescent mitochondria and autophagosomes in cell cultures, but not fixed tissues from the RedMIT/GFP-LC3, can be used to detect mitophagy. We used this model to confirm that mitophagy is increased in a mouse model of ADOA. It will be useful for cell based studies of diseases caused by impaired mitochondrial dynamics.

BNIP3 mediates the different adaptive responses of fibroblast-like synovial cells to hypoxia in patients with osteoarthritis and rheumatoid arthritis

“…LC3 is the most specific and commonly used marker molecule for autophagosomes reported today. EGFP-LC3 labeled autophagy and mitotracker labeled mitochondria were used to locate autophagosomes and mitochondria respectively, and their co-localization was used to determine the occurrence of mitophagy, which is one of the most commonly used methods in the study of mitophagy (Ren et al 2019 ; Diot et al 2018 ). We infected OA-FLSs/RA-FLSs with EGFP-LC3 virus, and then treated the cells with different hypoxia.…”

α6GABAA Receptor Positive Modulators Alleviate Migraine-like Grimaces in Mice via Compensating GABAergic Deficits in Trigeminal Ganglia

“…The signal pixel intensity and colocalization pixels were computationally generated in the form of scatterplot. The weighted colocalization coefficients in percentage were derived from the Pearson correlation coefficient with the scatter-plot threshold set to three times of the standard deviation of the mean value of the background pixels, as reported previously [47,48].…”

Dominant Optic Atrophy (DOA): Modeling the Kaleidoscopic Roles of OPA1 in Mitochondrial Homeostasis

“…Increased autophagy was reported in the RGCs of the B6;C3- Opa1 Q 285 STOP mutant mouse ( 127 ) and in the glycolytic fibers, RGCs, and peripheral neurons of the Opa1 delTTAG mutant mouse ( 124 ), highlighting the autophagic elimination of mitochondria with impaired fusion. More recently, increased mitophagy has been reported in the B6;C3- Opa1 Q 285 STOP mice ( 128 ) and confirmed in mouse RGCs overexpressing a mutated OPA1, showing also that reduced axonal mitochondrial density was linked to increased autophagic mitochondrial degradation in the RGCs soma, in close proximity to axonal hillocks ( 119 ). The B6;C3- Opa1 329−355 del mice were also reported to present an imbalance of redox state possibly increasing mitochondrial ROS, as suggested by the decrease in aconitase activity and induction of antioxidant defenses ( 97 ).…”