Oxidative stress alters mitochondrial homeostasis in isolated brain capillaries

Neurovascular deficits and blood-brain barrier (BBB) dysfunction are major hallmarks of brain trauma and neurodegenerative diseases. Oxidative stress is a prominent contributor to neurovascular unit (NVU) dysfunction and can propagate BBB disruption. Oxidative damage results in an imbalance of mitochondrial homeostasis, which can further drive functional impairment of brain capillaries. To this end, we developed a method to track mitochondrial-related changes after oxidative stress in the context of neurovascular pathophysiology as a critical endophenotype of neurodegenerative diseases.

To study brain capillary-specific mitochondrial function and dynamics in response to oxidative stress, we developed an ex vivo model in which we used isolated brain capillaries from transgenic mice that express dendra2 green specifically in mitochondria (mtD2g). Isolated brain capillaries were incubated with 2,2'-azobis-2-methyl-propanimidamide dihydrochloride (AAPH) or hydrogen peroxide (H₂O₂) to induce oxidative stress through lipid peroxidation. Following the oxidative insult, mitochondrial bioenergetics were measured using the Seahorse XFe96 flux analyzer, and mitochondrial dynamics were measured using confocal microscopy with Imaris software.

We optimized brain capillary isolation with intact endothelial cell tight-junction and pericyte integrity. Further, we demonstrate consistency of the capillary isolation process and cellular enrichment of the isolated capillaries. Mitochondrial bioenergetics and morphology assessments were optimized in isolated brain capillaries. Finally, we found that oxidative stress significantly decreased mitochondrial respiration and altered mitochondrial morphology in brain capillaries, including mitochondrial volume and count.

Following ex vivo isolation of brain capillaries, we confirmed the stability of mitochondrial parameters, demonstrating the feasibility of this newly developed platform. We also demonstrated that oxidative stress has profound effects on mitochondrial homeostasis in isolated brain capillaries. This novel method can be used to evaluate pharmacological interventions to target oxidative stress or mitochondrial dysfunction in cerebral small vessel disease and neurovascular pathophysiology as major players in neurodegenerative disease.