Defining Mitochondrial Cristae Morphology Changes Induced by Aging in Brown Adipose Tissue

Mitochondria are required for energy production and even give brown adipose tissue (BAT) its characteristic color due to their high iron content and abundance The physiological function and bioenergetic capacity of mitochondria are connected to the structure, folding, and organization of its inner-membrane cristae. During the aging process, mitochondrial dysfunction is observed, and the regulatory balance of mitochondrial dynamics is often disrupted, leading to increased mitochondrial fragmentation in aging cells. Therefore, we hypothesized that the morphological changes in BAT mitochondria and cristae observed across aging would reflect alterations to energy dynamics. We developed a quantitative three-dimensional (3D) electron microscopy approach to map cristae network organization in mouse BAT to test this hypothesis. Using this methodology, we investigated the 3D morphology of mitochondrial cristae in adult (3-month) and aged (2-year) murine BAT tissue via serial block face-scanning electron microscopy (SBF-SEM) and3D reconstruction software for manual segmentation, analysis, and quantification. Upon investigation, we found increases in mitochondrial volume, surface area, and complexity and decreased sphericity in aged BAT. Cristae examination revealed decreased cristae volume, perimeter, and complexity, with cristate appearing more heterogeneous. Overall, these data define the nature of the mitochondrial structure in BAT, showing loss of cristae definition across aging, suggesting alterations in functionality and bioactivity.Graphical AbstractWorkflow overview of serial block facing-scanning electron microscopy (SBF-SEM), data segmentation, and 3D analysis of mitochondria using Amira software in murine BAT.