Low Cytochrome Oxidase 1 Links Mitochondrial Dysfunction to Atherosclerosis in Mice and Pigs

Efferocytosis: A new star of atherosclerotic plaques reversal

Efferocytosis is considered the key to eliminate apoptotic cells (ACs) under physiological and pathological conditions in vivo, mainly through different types of macrophages to achieve this process. Especially, tissue-resident macrophages (TRMs) are very significant for inflammation regression and maintenance of homeostasis in vivo. Abnormal efferocytosis will lead to the accumulation of ACs and the release of a variety of pro-inflammatory factors, which mediates the occurrence of many inflammatory diseases, including atherosclerosis (AS). AS is a chronic inflammatory vascular disease with the participation of the immune system. Defective efferocytosis will accelerate the progress of AS to a certain extent. Therefore, it is of great significance to understand the mechanism of efferocytosis and realize the prevention and treatment of AS through efferocytosis. In this review, we will briefly describe the specific process of efferocytosis, deeply discuss the possible molecular mechanism of impaired efferocytosis promoting the development of AS, and summarize the ways to prevent and treat AS through efferocytosis intervention therapy.

A subcellular sampling instrument allows spatial resolution of amyloid deposit-derived organelle-specific effects in microglia

Methodological developments in biomedical research are currently moving towards single-cell approaches. This allows for a much better spatial and functional characterization of, for example, the deterioration of cells within a tissue in response to noxae. However, subcellular resolution is also essential to elucidate whether observed impairments are driven by an explicit organelle. Here, we use the Single Cellome™ System SS2000 (Yokogawa) to investigate the local effects of Aβ plaque-like deposits (characteristic for Alzheimer's disease) on mitochondria in the mouse microglial cell line SIM-A9. First, the specificity of subcellular extraction is demonstrated by detecting subcellular staining and RT-qPCR concerning marker genes by comparing nuclear and mitochondrial samples. Oxygen consumption and gene expression is then assessed in cells near and far from peptide deposits. Mostly, all analyses confirm the high specificity and integrity of the sampled material. In addition, impact of the peptide deposits occur concerning spatial distribution of the cells: e.g., oxygen consumption is only reduced in cells close to Aβ deposits but not in proximity to deposits of biologically inactive Aβ (scrambled) or in far distance. Moreover, a distance-related gene expression pattern occurs, demonstrating the local initiation of mitochondrial changes of microglia when approaching toxic peptide deposits.

Short-term effects of ambient gaseous air pollution on blood platelet mitochondrial DNA methylation and myocardial ischemia

BACKGROUND

The potential effects of short-term exposure to major ambient gaseous pollutants (ozone: O3, carbon monoxide: CO, and sulfur dioxide: SO2) on platelet mitochondrial DNA (mtDNA) methylation have been uncertain and no studies have examined whether platelet mtDNA methylation levels could modify the associations between ambient gaseous pollutants and the risks of ST-segment depression (STDE) and T-wave inversion events (TIE), two indicators of myocardial ischemia.

METHODS

This study used data from a randomized, double-blind, placebo-controlled intervention study with a standardized 24-hour exposure protocol among 110 participants in Beijing. Absolute changes in platelet mtDNA methylation (ACmtDNAm) levels were determined by two repeated measurements on platelet mtDNA methylation levels in blood samples collected before and after the 24-hour exposure period. A multivariable linear regression model and a generalized linear model with a Poisson link function were used to investigate the associations of ambient gaseous pollutants with platelet mtDNA methylation levels, STDE, and TIE, respectively.

RESULTS

Short-term O3 exposure was significantly associated with decreased ACmtDNAm at ATP6_P1 but increased ACmtDNAm at mt12sRNA, MT-COX1, and MT-COX1_P2; short-term CO and SO2 exposures were significantly associated with decreased ACmtDNAm at D-loop, MT-COX3- and ATP-related genes. Moreover, short-term O3 exposure was significantly associated with increased risks of STDE and TIE, and ACmtDNAm at MT-COX1 and MT-COX1_P2 modified the association between short-term O3 exposure and STDE events. L-Arg supplementation attenuated the effects of ambient gaseous pollutants, particularly O3, on ACmtDNAm and STDE.

CONCLUSIONS

Platelet mtDNA methylation levels are promising biomarkers of short-term exposure to ambient gaseous air pollution, and are likely implicated in the mechanism behind the association of ambient O3 pollution with adverse cardiovascular effects. L-Arg supplementation showed the potential to mitigate the adverse effects of ambient O3 pollution.

Porphyromonas gingivalis infection promotes mitochondrial dysfunction through Drp1-dependent mitochondrial fission in endothelial cells

Porphyromonas gingivalis (P. gingivalis), a key pathogen in periodontitis, has been shown to accelerate the progression of atherosclerosis (AS). However, the definite mechanisms remain elusive. Emerging evidence supports an association between mitochondrial dysfunction and AS. In our study, the impact of P. gingivalis on mitochondrial dysfunction and the potential mechanism were investigated. The mitochondrial morphology of EA.hy926 cells infected with P. gingivalis was assessed by transmission electron microscopy, mitochondrial staining, and quantitative analysis of the mitochondrial network. Fluorescence staining and flow cytometry analysis were performed to determine mitochondrial reactive oxygen species (mtROS) and mitochondrial membrane potential (MMP) levels. Cellular ATP production was examined by a luminescence assay kit. The expression of key fusion and fission proteins was evaluated by western blot and immunofluorescence. Mdivi-1, a specific Drp1 inhibitor, was used to elucidate the role of Drp1 in mitochondrial dysfunction. Our findings showed that P. gingivalis infection induced mitochondrial fragmentation, increased the mtROS levels, and decreased the MMP and ATP concentration in vascular endothelial cells. We observed upregulation of Drp1 (Ser616) phosphorylation and translocation of Drp1 to mitochondria. Mdivi-1 blocked the mitochondrial fragmentation and dysfunction induced by P. gingivalis. Collectively, these results revealed that P. gingivalis infection promoted mitochondrial fragmentation and dysfunction, which was dependent on Drp1. Mitochondrial dysfunction may represent the mechanism by which P. gingivalis exacerbates atherosclerotic lesions.

A Novel Immunoassay for Malondialdehyde-Conjugated Low-Density Lipoprotein Measures Dynamic Changes in the Blood of Patients Undergoing Coronary Artery Bypass Graft Surgery

Oxidized low-density lipoproteins play an important role in tissue pathology. In this study, we report a sensitive novel enzyme-linked immunosorbent assay for the detection of malondialdehyde-modified low-density lipoprotein (MDA-LDL), a key component of oxidized LDL. The assay is capable of measuring a variable presence of MDA-LDL within human plasma and serum. We demonstrate the robust nature of the assay on samples stored for over 20 months, as well as high inter-operator reproducibility (r = 0.74, p < 0.0001). The assay was capable of detecting dynamic changes in patient blood samples after coronary artery bypass graft surgery, indicating synthesis or release of MDA-LDL with the oxidative stress of surgery, followed by homeostatic clearance. This robust, sensitive and specific assay for circulating MDA-LDL will serve as a valuable translational tool for the improved detection of oxidative forms of LDL in response to a range of physiological or pathological stimuli, with potential clinical applicability.

RNA-sequencing reveals that STRN, ZNF484 and WNK1 add to the value of mitochondrial MT-COI and COX10 as markers of unstable coronary artery disease

Markers in monocytes, precursors of macrophages, which are related to CAD, are largely unknown. Therefore, we aimed to identify genes in monocytes predictive of a new ischemic event in patients with CAD and/or discriminate between stable CAD and acute coronary syndrome. We included 66 patients with stable CAD, of which 24 developed a new ischemic event, and 19 patients with ACS. Circulating CD14+ monocytes were isolated with magnetic beads. RNA sequencing analysis in monocytes of patients with (n = 13) versus without (n = 11) ischemic event at follow-up and in patients with ACS (n = 12) was validated with qPCR (n = 85). MT-COI, STRN and COX10 predicted new ischemic events in CAD patients (power for separation at 1% error rate of 0.97, 0.90 and 0.77 respectively). Low MT-COI and high STRN were also related to shorter time between blood sampling and event. COX10 and ZNF484 together with MT-COI, STRN and WNK1 separated ACS completely from stable CAD patients. RNA expressions in monocytes of MT-COI, COX10, STRN, WNK1 and ZNF484 were independent of cholesterol lowering and antiplatelet treatment. They were independent of troponin T, a marker of myocardial injury. But, COX10 and ZNF484 in human plaques correlated to plaque markers of M1 macrophage polarization, reflecting vascular injury. Expression of MT-COI, COX10, STRN and WNK1, but not that of ZNF484, PBMCs paired with that in monocytes. The prospective study of relation of MT-COI, COX10, STRN, WNK1 and ZNF484 with unstable CAD is warranted.

Oxidative stress, nutritional antioxidants and beyond

Free radical-induced oxidative stress contributes to the development of metabolic syndromes (Mets), including overweight, hyperglycemia, insulin resistance and pro-inflammatory state. Most free radicals are generated from the mitochondrial electron transport chain; under physiological conditions, their levels are maintained by efficient antioxidant systems. A variety of transcription factors have been identified and characterized that control gene expression in response to oxidative stress status. Natural antioxidant compounds have been largely studied for their strong antioxidant capacities. This review discusses the recent progress in oxidative stress and mitochondrial dysfunction in Mets and highlights the anti-Mets, anti-oxidative, and anti-inflammatory effect of polyphenols as potential nutritional therapy.

Cytochrome c oxidase dysfunction enhances phagocytic function and osteoclast formation in macrophages

The mitochondria-to-nucleus retrograde signaling (MtRS) pathway aids in cellular adaptation to stress. We earlier reported that the Ca2+- and calcineurin-dependent MtRS induces macrophage differentiation to bone-resorbing osteoclasts. However, mechanisms through which macrophages sense and respond to cellular stress remain unclear. Here, we induced mitochondrial stress in macrophages by knockdown (KD) of subunits IVi1 or Vb of cytochrome c oxidase (CcO). Whereas both IVi1 and Vb KD impair CcO activity, IVi1 KD cells produced higher levels of cellular and mitochondrial reactive oxygen species with increased glycolysis. Additionally, IVi1 KD induced the activation of MtRS factors NF-κB, NFAT2, and C/EBPδ as well as inflammatory cytokines, NOS 2, increased phagocytic activity, and a greater osteoclast differentiation potential at suboptimal RANK-L concentrations. The osteoclastogenesis in IVi1 KD cells was reversed fully with an IL-6 inhibitor LMT-28, whereas there was minimal rescue of the enhanced phagocytosis in these cells. In agreement with our findings in cultured macrophages, primary bone marrow-derived macrophages from MPV17-/- mice, a model for mitochondrial dysfunction, also showed higher propensity for osteoclast formation. This is the first report showing that CcO dysfunction affects inflammatory pathways, phagocytic function, and osteoclastogenesis.-Angireddy, R., Kazmi, H. R., Srinivasan, S., Sun, L., Iqbal, J., Fuchs, S. Y., Guha, M., Kijima, T., Yuen, T., Zaidi, M., Avadhani, N. G. Cytochrome c oxidase dysfunction enhances phagocytic function and osteoclast formation in macrophages.