Targeting mitochondria in the aged vasculature with SS-31, a proteomic study of brain microvessels.

Functional decline and structural alterations of the brain microvasculature are associated with cognitive impairment and development of dementias such as Alzheimer’s disease during aging. Although mechanisms of leading to microvascular changes during aging are not clear, the loss of mitochondria and reduced efficiency of remaining mitochondria appear to play a major role. While pharmacological agents which target mitochondria such as SS-31 have been shown to be effective in beneficial during aging and diseases, the full extent on mitochondrial- and non-mitochondrial proteins in the brain microvasculature has not been examined. We tested the hypothesis that attenuation of aging-associated changes in the brain microvascular proteome via targeting mitochondria represents a therapeutic option in the aging brain. We used male, aged (>18 months) C57Bl6/J mice treated with a mitochondria-targeted tetrapeptide, SS-31 or vehicle saline. Baseline cerebral blood flow (CBF) was determined using laser speckle imaging during the two-week treatment period. Then, isolated cortical microvessels (MVs), composed of end arterioles, capillaries, and venules, were used for Orbitrap Eclipse Tribrid mass spectrometry. Baseline CBF was similar between the groups, whereas bioinformatic analysis revealed substantial differences in protein abundance of cortical MVs between SS-31 and vehicle groups. Specifically, we identified 6,266 proteins in our data set from which 12% were mitochondrial or mitochondria associated. 107 of these proteins were significantly differentially expressed between the treatment and vehicle groups, and were associated with the oxidative phosphorylation, metabolism, antioxidant defense system, or mitochondrial dynamics. Administration of SS-31 also affected many non-mitochondrial proteins. Our findings suggest that mitochondria in the microvasculature represent a therapeutic target in the aging brain, and widespread changes in the proteome may underlie the mechanisms of rejuvenating actions of SS-31 in the aging phenotype.

脑微血管的功能减退与结构改变，与衰老过程中的认知障碍及阿尔茨海默病（Alzheimer’s disease）等痴呆症的发生密切相关。尽管衰老过程中微血管改变的具体机制尚不明确，但线粒体丢失及残存线粒体功能下降似乎是关键驱动因素。尽管以线粒体为靶点的药理学制剂（如SS-31）已被证实可在衰老及相关疾病中发挥有益作用，但目前尚未系统探究其对脑微血管内线粒体及非线粒体蛋白的整体影响。本研究验证了如下假说：通过靶向线粒体以缓解脑微血管蛋白质组的衰老相关变化，可作为衰老大脑的一种治疗策略。本研究选用18月龄以上的雄性C57Bl6/J小鼠，分别给予线粒体靶向四肽SS-31或生理盐水对照剂处理。在为期两周的给药期间，采用激光散斑成像技术检测小鼠的基线脑血流量（cerebral blood flow, CBF）。随后，分离得到由终末小动脉、毛细血管及微静脉组成的皮层微血管（microvessels, MVs），并采用Orbitrap Eclipse Tribrid质谱仪进行蛋白质组学分析。两组小鼠的基线脑血流量无显著差异，但生物信息学分析显示，SS-31组与对照组的皮层微血管蛋白丰度存在显著差异。具体而言，本数据集共鉴定到6266种蛋白，其中12%为线粒体或线粒体相关蛋白；在这些蛋白中，有107种在给药组与对照组间存在显著差异表达，且这些蛋白主要与氧化磷酸化、代谢过程、抗氧化防御系统及线粒体动态平衡相关。此外，SS-31给药还对大量非线粒体蛋白产生了调控作用。本研究结果表明，微血管内的线粒体可作为衰老大脑的治疗靶点，而蛋白质组的广泛变化或许是SS-31改善衰老表型的潜在机制。