In situ architecture of Opa1-dependent mitochondrial cristae remodeling

Abstract

Cristae membrane state plays a central role in regulating mitochondrial function and cellular metabolism. The protein Optic atrophy 1 (Opa1) is an important crista remodeler that exists as two forms in the mitochondrion, a membrane-anchored long form (l-Opa1) and a processed short form (s-Opa1). The mechanisms for how Opa1 influences cristae shape have remained unclear due to lack of native three-dimensional views of cristae. We perform in situ cryo-electron tomography of cryo-focused ion beam milled mouse embryonic fibroblasts with defined Opa1 states to understand how each form of Opa1 influences cristae architecture. In our tomograms, we observe a variety of cristae shapes with distinct trends dependent on s-Opa1:l-Opa1 balance. Increased l-Opa1 levels promote cristae stacking and elongated mitochondria, while increased s-Opa1 levels correlated with irregular cristae packing and round mitochondria shape. Functional assays indicate a role for l-Opa1 in wild-type apoptotic and calcium handling responses, and show a compromised respiratory function under Opa1 imbalance. In summary, we provide three-dimensional visualization of cristae architecture to reveal relationships between mitochondrial ultrastructure and cellular function dependent on Opa1-mediated membrane remodeling.

Opa1 processing is dispensable in mouse development but is protective in mitochondrial cardiomyopathy

“…We only observed mild changes in cristae density in cardiac mitochondria using TEM. This is in agreement with a recent cryo–electron tomographic analysis of mitochondrial cristae shapes in cells accumulating only l-Opa1 ( 65 ). It should be noted, however, that our in vivo analysis did not distinguish between lamellar and tubular cristae, the ratio of which has been shown to be affected by Opa1 and Opa1 cleavage ( 65 , 66 ).…”

Disruption of the mitochondrial network in a mouse model of Huntington's disease visualized by in-tissue multiscale 3D electron microscopy

“…3DEM combined with sample cryofixation is providing new insights into cellular compartments and their functions [ 5 , 6 , 18 , 20 , 32 ] and is gaining traction in the exploration of neurodegenerative diseases [ 30 , 55 , 67 ]. In HD in particular, these techniques are expanding our understanding of polyQ aggregates and subcellular alterations by working with in vitro samples or cultured cells [ 4 , 19 , 64 , 66 ].…”