Energy Deficit Phenotype of Cerebral Microvascular Network in the Aged Brains
Authors: Sakamuri Siva Sankara Vara Prasad , Sure Venkata N. , Evans Wesley R. , Kolli Lahari , Albuck Aaron L. , Mostany Ricardo , Busija David W. , Katakam Prasad V.G. 
Published: April 2020

Objective

Aging is associated with an increased risk of neurodegenerative diseases and stroke. Impaired microvascular function was proposed to be the connecting link, but the underlying mechanisms are unclear. Microvasculature is critical for cerebrovascular blood flow, neurovascular coupling, and nutrient transport, and blood‐brain‐barrier. Maintaining these energy‐demanding functions by cerebral microvasculature needs optimal functioning of energy pathways like glycolysis and mitochondrial respiration. Characterization of cellular energy metabolism in the young and aged microvasculature was essential to understand the aging‐induced cerebrovascular pathologies.

Methods

We isolated the microvessels from the brains from young (3 months) and aged mice (24 months). Microvessels were isolated by a combination of filtration (40μm – 300μm) and gradient centrifugation. Microvessels were plated on Seahorse XFe24 culture plates. Basal and compensatory glycolysis, and proton efflux rate (PER) were measured from extracellular acidification rates (ECAR) using glycolysis rate kit. Similarly, mitochondrial respiratory parameters were determined by the measurements from the oxygen consumption rate (OCR), and the fuel dependency of the microvasculature was measured using mitofuel kit.

Results

Aged brain microvasculature showed 26% (73.87±7.6 vs. 100.1±2.9 picomoles of H+/min/μg protein, p<0.01, n=7–9 mice/phenotype) decrease in basal glycolysis when compared with the microvessels from the young mouse brain. Compensatory glycolysis is decreased by 28.3% (121.0±7.0 vs 168.9±13.4 picomoles of H+/min/μg protein, p<0.004, n=7–9 mice/phenotype) in the aged mouse brain microvessels compared to the young mouse brain vessels, whereas the basal proton efflux is decreased by 35.3% (105.2±6.3 vs 162.8±5.9 picomoles of H+/min/μg protein, p<0.0001, n=7–9 mice/phenotype). Microvessels from the aged mouse brain had 36% lower mitochondrial respiration compared to the young mouse brain microvasculature (64.0±10.4 vs 100.0±7.6 picomoles of O2/min/μg protein, p<0.01, n=7–9 mice/phenotype). Glucose (65.6±0.2%, n=4 mice) is the primary fuel preference by the mitochondria in the young mouse brain microvessels followed by glutamine (32.9±0.5%) and fatty acids (27.9±3.0%). Aged microvasculature exhibited unaltered fuel preferences concerning glucose and fatty acids, whereas glutamine utilization is increased by 58% (54.1±2.9% vs 34.3% vs 3.57, n=3 mice) when compared to the young mouse brain microvessels.

Conclusions

We conclude that aged brain microvasculature exhibits compromised energy metabolism including both glycolysis and the mitochondrial respiration. We further conclude that mitochondrial utilization of glutamine as energy fuel is increased in the aged brain microvasculature. The energy deficit phenotype of the brain microcirculatory network may contribute to the aging‐associated cerebrovascular complications.

Support or Funding Information

National Institute of Health: National Institute of General Medical Sciences and National Institute of Neurological Disorders and Stroke (Katakam: R01NS094834) and National Institute on Aging (Mostany: AG047296).