Effects of Chronic Hypertension on Mitochondrial Energy Metabolism in the Cerebral Cortex of Normal and Spontaneously Hypertensive Rats

Background Introduction

Chronic hypertension has destructive structural and functional consequences for cerebral vessels and brain parenchyma. Hypertension impairs cerebrovascular autoregulation (Ferrari & Villa, 2022), not only increasing the risk of acute thrombosis and lacunar ischemic stroke but also leading to chronic cerebral hypoperfusion and neurovascular coupling damage (Cortes-Canteli & Iadecola, 2020). Studies have found that hypertensive rat models, such as spontaneously hypertensive rats (SHR), show significant changes in brain morphology and function, including smaller brain volume, larger ventricles, reduced neuron count (Tajima et al., 1993), and increased susceptibility to cerebral ischemia (Cipolla et al., 2018).

Paper Source

This paper was written by Roberto Federico Villa, Federica Ferrari, and Antonella Gorini, who are from the Laboratory of Pharmacology of the Central Nervous System and Molecular Medicine, Department of Biology and Biotechnology, and the Department of Brain and Behavioral Sciences, University of Pavia, Italy. The paper was published in the second issue of 2024 in the journal “Neuromolecular Medicine”.

Research Process and Methods

Research Subjects and Experimental Groups

The experimental subjects were Wistar Kyoto (WKY) rats and SHR rats, divided into 6, 12, and 18 months old groups, with 6 to 9 rats in each experimental group. The study separated cerebral cortex mitochondria into non-synaptic mitochondria (FM) and intra-synaptic mitochondria, which were further divided into light mitochondria (LM) and heavy mitochondria (HM).

Mitochondrial Extraction and Processing

1. Extraction Steps: Experimental rats were anesthetized with ether at 9 AM and euthanized by injecting a high dose of carbamate (1.4g/kg body weight). Brain tissues were rapidly cooled in a refrigerator and placed in a separation medium containing 0.32 M sucrose, 1.0 mM EDTA-K+, 10 mM Tris-HCl (pH 7.4).
2. Mitochondrial Purification: Non-synaptic and synaptic mitochondria were separated by gradient centrifugation, using sucrose and Ficoll gradient centrifugation to obtain high-purity mitochondrial particles.

Enzyme Activity Detection

Various enzyme catalytic activities were measured in different types of mitochondria: - TCA cycle enzymes: Citrate synthase (CS) and malate dehydrogenase (MDH). - Electron transport chain (ETC) enzymes: Complex I-III (NADH-cytochrome c reductase, CCRT), succinate dehydrogenase (Complex II, SDH), and cytochrome c oxidase (Complex IV, COX). - Glutamate metabolism-related enzymes: Glutamate dehydrogenase (GDH), glutamate-pyruvate transaminase (GPT), and glutamate-oxaloacetate transaminase (GOT).

Data Statistics and Analysis

Experimental data were first analyzed for homogeneity of variance using Bartlett’s test, then two-way ANOVA was used to assess the significance of enzyme activities between different mitochondrial types and rat ages. Tukey and Dunnett post-hoc tests were used for group comparisons. Statistical analysis was performed using StatPlus software.

Research Results

Effects of Physiological Aging

During physiological aging, different types of mitochondria showed varied enzyme activity changes: - TCA enzyme activity: Citrate synthase decreased with age in FM, showed a biphasic trend in LM, and significantly decreased in HM; malate dehydrogenase increased in FM and decreased in HM. - ETC enzyme activity: Complex I-III activity increased in FM and decreased in HM; Complex II decreased in HM. - Glutamate metabolism-related enzymes: Glutamate dehydrogenase remained relatively stable in FM but decreased in LM and HM at 12 and 18 months.

Effects of Chronic Hypertension on Aging

Hypertension affected mitochondrial enzyme activities differently across age groups: - 6 months: - TCA enzyme activity remained largely unchanged. - ETC enzyme activity showed complex metabolic uncoupling, with decreased Complex I-III activity in FM, decreased Complex II activity in HM, and increased Complex IV activity. - Glutamate dehydrogenase activity increased in FM and LM, while glutamate-oxaloacetate transaminase increased in LM. - 12 months: - TCA enzymes and glutamate metabolism-related enzymes generally increased, especially in HM. - ETC enzyme activity tended to stabilize, indicating effective adaptive adjustments at 12 months. - 18 months: - Metabolic activity significantly decreased in all mitochondria, highlighting the critical impact of 18 months age on SHR metabolism, with enzyme activities notably reduced in FM and LM.

Discussion and Conclusion

The study shows that HM is the most susceptible type of mitochondria to aging and hypertension. This method of separating different types of mitochondria reveals specific mechanisms of how hypertension affects brain energy metabolism at different stages, especially the decrease in all metabolic pathway activities at 18 months. This dynamic metabolic adaptation process may provide new insights for further research on pharmacological intervention strategies for coexisting elderly and hypertensive diseases. The study also suggests that regulation of mitochondrial function could be a potential target for treating age-related brain disorders.

Through this in-depth analysis, not only can theoretical support be provided for basic research on hypertension and related geriatric diseases, but it also offers new perspectives and methods for clinical treatment design.