Analysis of the process of recovery of the foveolar region after surgery of idiopathic macular ruptures by the «temporal inverted VPM flap» method

Purpose. To analyze the recovery of the foveolar region after successful surgery of idiopathic macular rupture (IMR) using the "temporal inverted VPM flap" method. Material and methods. In 33 patients (34 eyes) aged 65.2±8.1 years, operated on for stage II-IV IMR according to J. Gass (1995), in the postoperative period for up to 1 year, changes in the foveolar region were studied by optical coherence tomography (OCT). Results. Recovery of the foveolar area began from the first days after the operation and lasted for 12 months. In the period from 1 week to 1 month, the recovery and approximation to the U-shaped foveolar contour was noted in all patients. At the final follow-up period: the outer boundary membrane and the ellipsoid zone were completely restored in 26/44 (76%) and 23/34 (68%) eyes, respectively; the average central retinal thickness decreased from 396±62.6 microns to 194±66 microns (p<0.05); the corrected distance visual acuity (CDVA) increased from 0.07±0.04 to 0.35±0.21 (p<0.05). Conclusion The "temporal inverted VPM flap" method is highly effective in the surgery of idiopathic macular ruptures. The process of restoring the microstructures of the foveolar zone begins from the first days after the IMR surgery using the "temporal inverted VPM flap" method, is gradual and lasts up to one year from the start of treatment. The main stages of restoration of the microstructures of the foveolar region are: mechanical overlap of the macular rupture with HPV flaps, filling of the IMR lumen with a "glial plug", restoration of the external photoreceptor layer of the fovea. Key words: foveolar region, outer layers of the retina, idiopathic macular rupture, temporal inverted VPM flap, optical coherence tomography.

High-resolution imaging reveals compartmentalization of mitochondrial protein synthesis in cultured human cells

Human mitochondria contain their own genome, mitochondrial DNA, that is expressed in the mitochondrial matrix. This genome encodes 13 vital polypeptides that are components of the multisubunit complexes that couple oxidative phosphorylation (OXPHOS). The inner mitochondrial membrane that houses these complexes comprises the inner boundary membrane that runs parallel to the outer membrane, infoldings that form the cristae membranes, and the cristae junctions that separate the two. It is in these cristae membranes that the OXPHOS complexes have been shown to reside in various species. The majority of the OXPHOS subunits are nuclear-encoded and must therefore be imported from the cytosol through the outer membrane at contact sites with the inner boundary membrane. As the mitochondrially encoded components are also integral members of these complexes, where does protein synthesis occur? As transcription, mRNA processing, maturation, and at least part of the mitoribosome assembly process occur at the nucleoid and the spatially juxtaposed mitochondrial RNA granules, is protein synthesis also performed at the RNA granules close to these entities, or does it occur distal to these sites? We have adapted a click chemistry-based method coupled with stimulated emission depletion nanoscopy to address these questions. We report that, in human cells in culture, within the limits of our methodology, the majority of mitochondrial protein synthesis is detected at the cristae membranes and is spatially separated from the sites of RNA processing and maturation.

High resolution imaging of nascent mitochondrial protein synthesis in cultured human cells

Human mitochondria contain their own genome, mtDNA, that is expressed in the mitochondrial matrix. This genome encodes thirteen vital polypeptides that are components of the multi-subunit complexes that couple oxidative phosphorylation (OXPHOS). The inner mitochondrial membrane that houses these complexes comprises the inner boundary membrane that runs parallel to the outer membrane, infoldings that form the cristae membranes, and the cristae junctions that separate the two. It is in these cristae membranes that the OXPHOS complexes have been shown to reside in various species. The majority of the OXPHOS subunits are nuclear-encoded and must therefore be imported from the cytosol through the outer membrane at contact sites with the inner boundary membrane. As the mitochondrially-encoded components are also integral members of these complexes, where does nascent protein synthesis occur? Transcription, mRNA processing, maturation and at least part of the mitoribosome assembly process occur at the nucleoid and the spatially juxtaposed mitochondrial RNA granules, is protein synthesis also performed at the RNA granules close to these entities, or does it occur distal to these sites ? We have adapted a click chemistry based method, coupled with STED nanoscopy to address these questions. We report that in human cells in culture, within the limits of our methodology, the majority of mitochondrial protein synthesis occurs at the cristae membranes and is spatially separated from the sites of RNA processing and maturation.

Mitochondrial cristae biogenesis coordinates with ETC complex IV assembly during Drosophila maturation

Mitochondrial cristae contain electron transport chain (ETC) complexes and are distinct from the inner boundary membrane (IBM) in both protein composition and function. While many details of mitochondrial membrane structure are known, the processes governing cristae biogenesis, including the organization of lipid membranes and assembly of proteins encoded by both nuclear and mitochondrial DNA, remain obscure. We followed cristae biogenesis in situ upon Drosophila eclosion using serial-section electron tomography and revealed that the morphogenesis of lamellar cristae coordinates with ETC complex IV assembly. The membrane morphogenesis and gain-of-function were intricately co-evolved during cristae biogenesis. Marf-knockdown flies formed lamellar cristae containing ATP synthase and functional COX. However, OPA1-knockdown flies showed impaired cristae biogenesis. Overall, this study revealed the multilevel coordination of protein-coupled membrane morphogenesis in building functional cristae.

Optimal Form for Compliance of Membrane Boundary Shift in Nonlinear Case

In this work, we search the existence shifting compliance optimal form of some boundary membrane, which is not elastic and not isotropic, generating nonlinear PDE. An optimal form of the elastic membrane described by the p-Laplacian is investigated. The boundary perturbation method due to Hadamard is applied in Sobolev spaces.

FIFO ATP synthase responds to glycolysis inhibition by localization into the inner boundary membrane

ABSTRACTMitochondrial F1F0ATP synthase is the key enzyme to fuel the cell with essential ATP. Strong indications exist that the respiratory chain and the ATP synthase are physically separated within cristae. How static this organization is, is largely unknown. Here, we investigated the effect of substrate restriction on mitochondrial respiration and the spatio-temporal organization of ATP synthase. By superresolution microscopy, the localization and mobility of single labelled mitochondrial ATP synthase was determined in live cells. We found, that the ATP synthase under oxidative respiration displayed a clear localization and confined mobility in cristae. Trajectories of individual ATP synthase proteins show a perpendicular course to the longitudinal axis of the respective mitochondrion, exactly following the ultrastructure of cristae. When substrate for TCA cycle and respiration was limited, a significant proportion of ATP synthase localized from cristae to the inner boundary membrane, and only less mobile ATP synthase remained in cristae. These observations showing the plasticity of the spatio-temporal organisation of ATP synthase can explain why ATP synthase show interactions with proteins in distinct mitochondrial subcompartments such as inner boundary membrane, cristae junctions and cristae.

The MICOS component Mic60 displays a conserved membrane-bending activity that is necessary for normal cristae morphology

The inner membrane (IM) of mitochondria displays an intricate, highly folded architecture and can be divided into two domains: the inner boundary membrane adjacent to the outer membrane and invaginations toward the matrix, called cristae. Both domains are connected by narrow, tubular membrane segments called cristae junctions (CJs). The formation and maintenance of CJs is of vital importance for the organization of the mitochondrial IM and for mitochondrial and cellular physiology. The multisubunit mitochondrial contact site and cristae organizing system (MICOS) was found to be a major factor in CJ formation. In this study, we show that the MICOS core component Mic60 actively bends membranes and, when inserted into prokaryotic membranes, induces the formation of cristae-like plasma membrane invaginations. The intermembrane space domain of Mic60 has a lipid-binding capacity and induces membrane curvature even in the absence of the transmembrane helix. Mic60 homologues from α-proteobacteria display the same membrane deforming activity and are able to partially overcome the deletion of Mic60 in eukaryotic cells. Our results show that membrane bending by Mic60 is an ancient mechanism, important for cristae formation, and had already evolved before α-proteobacteria developed into mitochondria.

An evidence based hypothesis on the existence of two pathways of mitochondrial crista formation

Metabolic function and architecture of mitochondria are intimately linked. More than 60 years ago, cristae were discovered as characteristic elements of mitochondria that harbor the protein complexes of oxidative phosphorylation, but how cristae are formed, remained an open question. Here we present experimental results obtained with yeast that support a novel hypothesis on the existence of two molecular pathways that lead to the generation of lamellar and tubular cristae. Formation of lamellar cristae depends on the mitochondrial fusion machinery through a pathway that is required also for homeostasis of mitochondria and mitochondrial DNA. Tubular cristae are formed via invaginations of the inner boundary membrane by a pathway independent of the fusion machinery. Dimerization of the F1FO-ATP synthase and the presence of the MICOS complex are necessary for both pathways. The proposed hypothesis is suggested to apply also to higher eukaryotes, since the key components are conserved in structure and function throughout evolution.

Mitofilin complexes: conserved organizers of mitochondrial membrane architecture

Mitofilin proteins are crucial organizers of mitochondrial architecture. They are located in the inner mitochondrial membrane and interact with several protein complexes of the outer membrane, thereby generating contact sites between the two membrane systems of mitochondria. Within the inner membrane, mitofilins are part of hetero-oligomeric protein complexes that have been termed the mitochondrial inner membrane organizing system (MINOS). MINOS integrity is required for the maintenance of the characteristic morphology of the inner mitochondrial membrane, with an inner boundary region closely apposed to the outer membrane and cristae membranes, which form large tubular invaginations that protrude into the mitochondrial matrix and harbor the enzyme complexes of the oxidative phosphorylation machinery. MINOS deficiency comes along with a loss of crista junction structures and the detachment of cristae from the inner boundary membrane. MINOS has been conserved in evolution from unicellular eukaryotes to humans, where alterations of MINOS subunits are associated with multiple pathological conditions.