通过预防或修复线粒体损伤的心脏保护是未满足的治疗需求。了解心肌细胞线粒体在病理生理学中的作用,线粒体形态和区室的可靠表征至关重要.以前的研究大多依赖于二维(2D)常规透射电子显微镜(TEM),从而忽略了真正的三维(3D)线粒体组织。本研究旨在确定心肌细胞超微结构的经典2DTEM分析是否足以全面描述线粒体区室并反映线粒体数量。尺寸,色散,分布,和形态学。
复杂线粒体网络和形态的空间分布,number,使用基于聚焦离子束扫描电子显微镜(FIB-SEM)的比较3D成像系统评估了分离的成年小鼠心肌细胞和成年野生型左心室组织(C57BL/6)中心脏线粒体的大小异质性。用于比较2D与3D数据集,进行了分析策略和数学比较方法。为了确认线粒体变化的3D数据的价值,我们比较了获得的数字值,覆盖区域,大小异质性,和野生型心肌细胞线粒体的复杂性,使用FIB-SEM,来自缺乏细胞溶质和线粒体蛋白BNIP3(BCL-2/腺病毒E1B19-kDa相互作用蛋白3;Bnip3-/-)的小鼠的数据集。使用海马XF分析仪在分离的线粒体上评估线粒体呼吸。心脏活检是从患有心肌炎的男性患者(48岁)获得的。
FIB-SEM纳米图分析显示线粒体数不存在线性关系(r=0.02;P=0.9511),离散度(r=-0.03;P=0.9188),3D和2D结果之间的形状(圆度:r=0.15,P=0.6397;伸长率:r=-0.09,P=0.7804)。累积频率分布分析显示,在3D和2D中线粒体的丰度不同,大小不同。定性,2D数据不能反映3D组织中存在的线粒体分布和动力学。3D分析使发现BNIP3导致更小的缺失,复杂性较低的心肌细胞线粒体(数量:P<0.01;异质性:C.V.野生型89%vs.Bnip3-/-68%;复杂性:P<0.001)形成大的肌原纤维扭曲簇,如在线粒体动力学紊乱的人心肌炎中所见。Bnip3-/-小鼠也显示出更高的呼吸速率(P<0.01)。
这里,我们证明了需要3D分析来表征心脏组织样本中的线粒体特征。因此,我们观察到BNIP3缺失在生理上作为线粒体数量的分子制动,提示在线粒体融合/裂变过程中起作用,从而调节心脏生物能学的稳态。
Cardioprotection by preventing or repairing mitochondrial damage is an unmet therapeutic need. To understand the role of cardiomyocyte mitochondria in physiopathology, the reliable characterization of the mitochondrial morphology and compartment is pivotal. Previous studies mostly relied on two-dimensional (2D) routine transmission electron microscopy (TEM), thereby neglecting the real three-dimensional (3D) mitochondrial organization. This study aimed to determine whether classical 2D TEM analysis of the cardiomyocyte ultrastructure is sufficient to comprehensively describe the mitochondrial compartment and to reflect mitochondrial number, size, dispersion, distribution, and morphology.
Spatial distribution of the complex mitochondrial network and morphology, number, and size heterogeneity of cardiac mitochondria in isolated adult mouse cardiomyocytes and adult wild-type left ventricular tissues (C57BL/6) were assessed using a comparative 3D imaging system based on focused ion beam-scanning electron microscopy (FIB-SEM) nanotomography. For comparison of 2D vs. 3D data sets, analytical strategies and mathematical comparative approaches were performed. To confirm the value of 3D data for mitochondrial changes, we compared the obtained values for number, coverage area, size heterogeneity, and complexity of wild-type cardiomyocyte mitochondria with data sets from mice lacking the cytosolic and mitochondrial protein BNIP3 (BCL-2/adenovirus E1B 19-kDa interacting protein 3; Bnip3-/- ) using FIB-SEM. Mitochondrial respiration was assessed on isolated mitochondria using the Seahorse XF analyser. A cardiac biopsy was obtained from a male patient (48 years) suffering from myocarditis.
The FIB-SEM nanotomographic analysis revealed that no linear relationship exists for mitochondrial number (r = 0.02; P = 0.9511), dispersion (r = -0.03; P = 0.9188), and shape (roundness: r = 0.15, P = 0.6397; elongation: r = -0.09, P = 0.7804) between 3D and 2D results. Cumulative frequency distribution analysis showed a diverse abundance of mitochondria with different sizes in 3D and 2D. Qualitatively, 2D data could not reflect mitochondrial distribution and dynamics existing in 3D tissue. 3D analyses enabled the discovery that BNIP3 deletion resulted in more smaller, less complex cardiomyocyte mitochondria (number: P < 0.01; heterogeneity: C.V. wild-type 89% vs. Bnip3-/- 68%; complexity: P < 0.001) forming large myofibril-distorting clusters, as seen in human myocarditis with disturbed mitochondrial dynamics. Bnip3-/- mice also show a higher respiration rate (P < 0.01).
Here, we demonstrate the need of 3D analyses for the characterization of mitochondrial features in cardiac tissue samples. Hence, we observed that BNIP3 deletion physiologically acts as a molecular brake on mitochondrial number, suggesting a role in mitochondrial fusion/fission processes and thereby regulating the homeostasis of cardiac bioenergetics.