Quantitative and qualitative analysis of heart mitochondria for evaluating the degree of myocardial injury utilizing atomic force microscopy

Aberrant mitochondrial dynamics contributes to diaphragmatic weakness induced by mechanical ventilation

In critical care patients, the ""temporary inactivity of the diaphragm caused by mechanical ventilation (MV) triggers a series of events leading to diaphragmatic dysfunction and atrophy, commonly known as ventilator-induced diaphragm dysfunction (VIDD). While mitochondrial dysfunction related to oxidative stress is recognized as a crucial factor in VIDD, the exact molecular mechanism remains poorly understood. In this study, we observe that 6 h of MV triggers aberrant mitochondrial dynamics, resulting in a reduction in mitochondrial size and interaction, associated with increased expression of dynamin-related protein 1 (DRP1). This effect can be prevented by P110, a molecule that inhibits the recruitment of DRP1 to the mitochondrial membrane. Furthermore, isolated mitochondria from the diaphragms of ventilated patients exhibited increased production of reactive oxygen species (ROS). These mitochondrial changes were associated with the rapid oxidation of type 1 ryanodine receptor (RyR1) and a decrease in the stabilizing subunit calstabin 1. Subsequently, we observed that the sarcoplasmic reticulum (SR) in the ventilated diaphragms showed increased calcium leakage and reduced contractile function. Importantly, the mitochondrial fission inhibitor P110 effectively prevented all of these alterations. Taken together, the results of our study illustrate that MV leads, in the diaphragm, to both mitochondrial fragmentation and dysfunction, linked to the up-/down-regulation of 320 proteins, as assessed through global comprehensive quantitative proteomics analysis, primarily associated with mitochondrial function. These outcomes underscore the significance of developing compounds aimed at modulating the balance between mitochondrial fission and fusion as potential interventions to mitigate VIDD in human patients.

Morphological changes of mitochondria-related to apoptosis during postmortem aging of beef muscles

This study aimed to investigate how postmortem muscle cells' mitochondria changed in morphology from three aspects: the outer membrane, cristae, and fission/fusion. Atomic force microscopy (AFM) results showed that mitochondria underwent a morphology transformation from normal to swelling and collapse. Meanwhile, the cleavage of OPA1, upregulation of OMA1, downregulation of Mic60 and transmission electron microscope micrographs revealed that mitochondrial cristae ruptured with an aging time extended. Additionally, the increased expressions of Fis1 and Drp1, and the AFM topographic images mutually confirmed mitochondrial fission. These results further proved from the perspective of mitochondrial morphology that the degree of mitochondrial damage increased with the postmortem aging time extended, which was consistent with the results of the release of cytochrome c caused by the increase of mitochondrial permeability transition pore opening and the decrease of mitochondrial membrane permeability, and further induced the apoptosis of postmortem muscle cells.

Visualization of internal in situ cell structure by atomic force microscopy

Light and electron microscopy have been used to study cell structure for many years, but atomic force microscopy is a more recent technique used to analyze cells, mainly due to the absence of techniques to prepare the samples. Isolated molecules or organelles, whole cells, and to a lesser extent in situ cell structure have been observed by different atomic force microscopy imaging modes. Here, we review efforts intended to analyze in situ the cell structures using approaches involving imaging of the surface of semithin sections of samples embedded in resin and sections prepared with an ultramicrotome. The results of such studies are discussed in relation to their implications to analyze the fine structure of organelles at the nanoscale in situ at enhanced resolution compared to light microscopy.

Morphological analysis of mitochondria for evaluating the toxicity of α-synuclein in transgenic mice and isolated preparations by atomic force microscopy

A key molecular event in the pathogenesis of Parkinson's disease is mitochondrial damage caused by α-synuclein (α-syn). Mitochondria mediates both necrosis and apoptosis, which are associated with morphological changes. However, the mechanism by which α-syn alters mitochondrial morphology remains unclear. To address this issue, we investigated mitochondrial permeability transition pore (mPTP) opening and changes in cardiolipin (CL) levels in mitochondria isolated from the brain of Thy1α-syn mice. Cytoplasmic cytochrome C and cleaved caspase-3 protein levels were upregulated in the brain of transgenic mice. Morphological analysis by atomic force microscopy (AFM) suggested a correlation between mitochondrial morphology and function in these animals. Incubation of isolated mitochondria with recombinant human α-synuclein N terminus (α-syn/N) decreased mitochondrial CL content. An AFM analysis showed that α-syn/N induced mitochondrial swelling and the formation of pore-like structures, which was associated with decreased mitochondrial transmembrane potential and complex I activity. The observed mitochondrial dysfunction was abrogated by treatment with the mPTP inhibitor cyclosporin A, although there was no recovery of CL content. These results provide insight into the mechanism by which α-syn/N directly undermines mitochondrial structure and function via modulation of mPTP opening and CL levels, and suggests that morphological analysis of isolated mitochondria by AFM is a useful approach for evaluating mitochondrial injury.

Effects of sildenafil on nanostructural and nanomechanical changes in mitochondria in an ischaemia-reperfusion rat model

Sildenafil exerts cardioprotective effects by activating the opening of mitochondrial ATP-sensitive potassium channels to attenuate ischaemia-reperfusion (IR) injury. In the present study, we used atomic force microscopy (AFM) to investigate changes in mitochondrial morphology and properties to assess sildenafil-mediated cardioprotection in a rat myocardial infarction model. To investigate the cardioprotective effects of sildenafil, we used an in vivo Sprague-Dawley rat model of IR. Rats were randomly divided into three groups: (i) sham-operated rats (control; n = 5); (ii) IR-injured rats treated with vehicle (normal saline; IR; n = 10); and (iii) IR-injured rats treated with 0.75 mg/kg, i.p., sildenafil (IR + Sil; n = 10). Morphological and mechanical changes to mitochondria were analysed by AFM. Infarct areas were significantly reduced in sildenafil-treated rats (7.8 ± 3.9% vs 20.4 ± 7.0% in the sildenafil-treated and untreated IR groups, respectively; relative reduction 62%; P < 0.001). Analysis of mitochondria by AFM showed that IR injury significantly increased the areas of isolated mitochondria compared with control (24 150 ± 18 289 vs 1495 ± 1139 nm(2) , respectively; P < 0.001), indicative of mitochondrial swelling. Pretreatment with sildenafil before IR injury reduced the mitochondrial areas (7428 ± 3682 nm(2) ; P < 0.001; relative reduction 69.2% compared with the IR group) and ameliorated the adhesion force of mitochondrial surfaces. Together, these results suggest that sildenafil has cardioprotective effects against IR injury in a rat model by improving the morphological and mechanical characteristics of mitochondria.

Atomic force microscopy-based shape analysis of heart mitochondria

Atomic force microscopy (AFM) has become an important medical and biological tool for the noninvasive imaging of cells and biomaterials in medical, biological, and biophysical research. The major advantages of AFM over conventional optical and electron microscopes for bio-imaging include the facts that no special coating is required and that imaging can be done in all environments-air, vacuum, or aqueous conditions. In addition, it can also precisely determine pico-nano Newton force interactions between the probe tip and the sample surface from force-distance curve measurements.It is widely known that mitochondrial swelling is one of the most important indicators of the opening of the mitochondrial permeability transition (MPT) pore. As mitochondrial swelling is an ultrastructural change, quantitative analysis of this change requires high-resolution microscopic methods such as AFM. Here, we describe the use of AFM-based shape analysis for the characterization of nanostructural changes in heart mitochondria resulting from myocardial ischemia-reperfusion injury.