Mitochondrial membrane models built from native lipid extracts: Interfacial and transport properties

Abstract

The mitochondrion is an essential organelle enclosed by two membranes whose functionalities depend on their very specific protein and lipid compositions. Proteins from the outer mitochondrial membrane (OMM) are specialized in mitochondrial dynamics and mitophagy, whereas proteins of the inner mitochondrial membrane (IMM) have dedicated functions in cellular respiration and apoptosis. As for lipids, the OMM is enriched in glycerophosphatidyl choline but cardiolipin is exclusively found within the IMM. Though the lipid topology and distribution of the OMM and IMM are known since more than four decades, little is known about the interfacial and dynamic properties of the IMM and OMM lipid extracts. Here we build monolayers, supported bilayers and giant unilamellar vesicles (GUVs) of native OMM and IMM lipids extracts from porcine heart. Additionally, we perform a comparative analysis on the interfacial, phase immiscibility and mechanical properties of both types of extract. Our results show that IMM lipids form more expanded and softer membranes than OMM lipids, allowing a better understanding of the physicochemical and biophysical properties of mitochondrial membranes.

Structure and Elasticity of Mitochondrial Membranes: A Molecular Dynamics Simulation Study

“…Recently, Schiaffarino et al measured the bending modulus of the IMM and OMM of giant unilamellar vesicles (GUVs) from the porcine heart using the micropipette aspiration method and obtained K c = 2.32 × 10 −20 J for the IMM and K c = 3.23 × 10 −20 J for the OMM. 18 These values are about 4−5 times smaller than our simulation values. The difference can be attributed to three main reasons: first, the composition and ratio of lipids in the OMM and IMM in the experiment are different from those in our IMM and OMM and IMM models.…”

“…However, there are not many experimental data on the elastic moduli of mitochondrial membranes and especially no experimental results for membranes with lipid compositions like those in our models, so it is difficult to quantify the simulation results. Recently, Schiaffarino et al measured the bending modulus of the IMM and OMM of giant unilamellar vesicles (GUVs) from the porcine heart using the micropipette aspiration method and obtained K c = 2.32 × 10 –20 J for the IMM and K c = 3.23 × 10 –20 J for the OMM . These values are about 4–5 times smaller than our simulation values.…”

“…One might assume that the IMM is stiffer than the OMM due to the high concentration of CL in the IMM compared to the low concentration in the OMM. However, the experimental study by Schiaffarino et al on GUVs of native OMM and IMM extracts from the porcine heart shows that the IMM membrane is softer than the OMM membrane . Although our model of OMM does not contain CL, it contains 5% cholesterol, which increases the bending modulus of O3.…”

“…7 A micropipette aspiration assay was used to study the effects of osmotic pressure or pH on the deformability of the mitochondrial membrane. 15,18 Another method involves using motile bacteria to move throughout the host cells to collide and deform mitochondria, but this method is uncontrollable and unpredictable. 7 Song et al have proposed an optogenetic approach to deform mitochondria via lightinduced recruitment of molecular motors onto mitochondria.…”

Cristae formation is a mechanical buckling event controlled by the inner membrane lipidome

“…For example, the stiffness ( к c ) of saturated PL bilayers is higher than those with unsaturated (Table S1A, B) and polyunsaturated chains 83,84 . Reconstituted membranes from porcine IMM lipids have been observed to be especially soft (low к c ) 85 . Curvature induced by differences in lipid abundance or intrinsic spontaneous curvatures ( c 0 ) of lipids across the two leaflets of the bilayer can be modeled as a net membrane spontaneous curvature C 0 .…”