Mitochondria exist in dynamic networks that undergo fusion and fission. Mitochondrial fusion and fission are mediated by several GTPases in the outer mitochondrial membrane, notably mitofusin-2 (Mfn-2), which promotes fusion, and dynamin-related protein (Drp-1), which promotes fission. We report that human lung cancer cell lines exhibit an imbalance of Drp-1/Mfn-2 expression, which promotes a state of mitochondrial fission. Lung tumor tissue samples from patients demonstrated a similar increase in Drp-1 and decrease in Mfn-2 when compared to adjacent healthy lung. Complementary approaches to restore mitochondrial network formation in lung cancer cells by overexpression of Mfn-2, Drp-1 inhibition, or Drp-1 knockdown resulted in a marked reduction of cancer cell proliferation and an increase in spontaneous apoptosis. The number of cancer cells in S phase decreased from 32.4 ± 0.6 to 6.4 ± 0.3% with Drp-1 inhibition (P<0.001). In a xenotransplantation model, Mfn-2 gene therapy or Drp-1 inhibition could regress tumor growth. The tumor volume decreased from 205.6 ± 59 to 70.6 ± 15 mm(3) (P<0.05) with Mfn-2 overexpression and from 186.0 ± 19 to 87.0 ± 6 mm(3) (P<0.01) with therapeutic Drp-1 inhibition. Impaired fusion and enhanced fission contribute fundamentally to the proliferation/apoptosis imbalance in cancer and constitute promising novel therapeutic targets.

Rationale Pulmonary arterial hypertension (PAH) is a lethal syndrome characterized by pulmonary vascular obstruction due in part to pulmonary artery smooth muscle cell (PASMC) hyperproliferation. Mitochondrial fragmentation and normoxic activation of hypoxia-inducible factor-1α (HIF-1α) have been observed in PAH PASMCs, however their relationship and relevance to the development of PAH is unknown. Dynamin-related protein-1 (DRP1) is a GTPase that, when activated by kinases that phosphorylate Serine-616, causes mitochondrial fission. It is however unknown whether mitochondrial fission is a prerequisite for proliferation. Objective We hypothesize that DRP1 activation is responsible for increased mitochondrial fission in PAH PASMCs and that DRP1 inhibition may slow proliferation and have therapeutic potential. Methods and Results Experiments were conducted using human control and PAH lungs (n=5) and PASMCs in culture. Parallel experiments were performed in rat lung sections and PASMCs and in rodent PAH models induced by the HIF-1α activator, cobalt, chronic hypoxia, and monocrotaline. HIF-1α activation in human PAH leads to mitochondrial fission by cyclin B1/CDK1-dependent phosphorylation of DRP1 at Serine-616. In normal PASMC, HIF-1α activation by CoCl2 or desferrioxamine causes DRP1-mediated fission. HIF-1α inhibition reduces DRP1 activation, prevents fission and reduces PASMC proliferation. Both the DRP1 inhibitor Mdivi-1 and siDRP1 prevent mitotic fission and arrest PAH PASMCs at the G2/M interphase. Mdivi-1 is antiproliferative in human PAH PASMC and in rodent models. Mdivi-1 improves exercise capacity, right ventricular function and hemodynamics in experimental PAH. Conclusion DRP-1-mediated mitotic fission is a cell cycle checkpoint that can be therapeutically targeted in hyperproliferative disorders such as PAH.

Mitochondrial fission, regulated by dynamin-related protein-1 (Drp1), is a newly recognized determinant of mitochondrial function, but its contribution to left ventricular (LV) impairment following ischemia-reperfusion (IR) injury is unknown. We report that Drp1 activation during IR results in LV dysfunction and that Drp1 inhibition is beneficial. In both isolated neonatal murine cardiomyocytes and adult rat hearts (Langendorff preparation) mitochondrial fragmentation and swelling occurred within 30 min of IR. Drp1-S637 (serine 637) dephosphorylation resulted in Drp1 mitochondrial translocation and increased mitochondrial fission. The Drp1 inhibitor Mdivi-1 preserved mitochondrial morphology, reduced cytosolic calcium, and prevented cell death. Drp1 siRNA similarly preserved mitochondrial morphology. In Langendorff hearts, Mdivi-1 reduced mitochondrial reactive oxygen species, improved LV developed pressure (92±5 vs. 28±10 mmHg, P<0.001), and lowered LV end diastolic pressure (10±1 vs. 86±13 mmHg, P<0.001) following IR. Mdivi-1 was protective if administered prior to or following ischemia. Because Drp1-S637 dephosphorylation is calcineurin sensitive, we assessed the effects of a calcineurin inhibitor, FK506. FK506 treatment prior to IR prevented Drp1-S637 dephosphorylation and preserved cardiac function. Likewise, therapeutic hypothermia (30°C) inhibited Drp1-S637 dephosphorylation and preserved mitochondrial morphology and myocardial function. Drp1 inhibition is a novel strategy to improve myocardial function following IR.

Acute lung injury is a leading cause of death in bacterial sepsis due to the wholesale destruction of the lung endothelial barrier, which results in protein-rich lung edema, influx of proinflammatory leukocytes, and intractable hypoxemia. Pyroptosis is a form of programmed lytic cell death that is triggered by inflammatory caspases, but little is known about its role in EC death and acute lung injury. Here, we show that systemic exposure to the bacterial endotoxin lipopolysaccharide (LPS) causes severe endothelial pyroptosis that is mediated by the inflammatory caspases, human caspases 4/5 in human ECs, or the murine homolog caspase-11 in mice in vivo. In caspase-11-deficient mice, BM transplantation with WT hematopoietic cells did not abrogate endotoxemia-induced acute lung injury, indicating a central role for nonhematopoietic caspase-11 in endotoxemia. Additionally, conditional deletion of caspase-11 in ECs reduced endotoxemia-induced lung edema, neutrophil accumulation, and death. These results establish the requisite role of endothelial pyroptosis in endotoxemic tissue injury and suggest that endothelial inflammatory caspases are an important therapeutic target for acute lung injury.Caspase-11-mediated endothelial pyroptosis underlies endotoxemia-induced lung injury The Journal of Clinical Investigation R E S E A R C H A R T I C L E4 1 2 5 jci.org Volume 127 Number 11 November 2017the complex process of inflammation involves multiple programmed cell death pathways, depending on the type and magnitude of the inciting stimulus and cell type. From an evolutionary perspective, pyroptosis of cells harboring intracellular bacteria or in which LPS has breached the plasma membrane is an effective means of eliminating an intracellular bacterial niche and activating the host through release of inflammatory mediators such as IL-1β, while sparing uninfected neighboring cells (13,(28)(29)(30). Thus, pyroptosis induced by inflammatory caspases 1/4/5/11 is an innate immune response distinct from the canonical inflammasome activation pathway via cell-surface TLR4 (11,(31)(32)(33)(34). However, caspase-11 can also be immunopathologic in sepsis (35). Caspase-11-deficient mice were protected in endotoxemic shock (10,11), suggesting that in the setting of an overwhelming inflammatory response, the potentially protective pyroptotic mechanism activates an exaggerated pathologic response due to overwhelming cell lysis. The role of the inflammatory caspases 4/5/11 in mediating cytoplasmic LPS signaling and pyroptosis has until now been primarily studied in macrophages or dendritic cells (11,12,14,28,32,36). Their role in destroying the endothelial barrier through widespread endothelial death and pathogenesis of ALI remains unknown. Here, we tested the hypothesis that lung ECs are a primary target for pyroptosis via intracellular sensing of LPS by the inflammatory caspases 4/5/11 and that endothelial pyroptosis is required for the induction of ALI. Results LPS in ECs induces pyroptotic cell death via activation of inflammatory cas...

f Mitochondrial morphology is regulated by the balance between two counteracting mitochondrial processes of fusion and fission. There is significant evidence suggesting a stringent association between morphology and bioenergetics of mitochondria. Morphological alterations in mitochondria are linked to several pathological disorders, including cardiovascular diseases. The consequences of stress-induced acetylation of mitochondrial proteins on the organelle morphology remain largely unexplored. Here we report that OPA1, a mitochondrial fusion protein, was hyperacetylated in hearts under pathological stress and this posttranslational modification reduced the GTPase activity of the protein. The mitochondrial deacetylase SIRT3 was capable of deacetylating OPA1 and elevating its GTPase activity. Mass spectrometry and mutagenesis analyses indicated that in SIRT3-deficient cells OPA1 was acetylated at lysine 926 and 931 residues. Overexpression of a deacetylation-mimetic version of OPA1 recovered the mitochondrial functions of OPA1-null cells, thus demonstrating the functional significance of K926/931 acetylation in regulating OPA1 activity. Moreover, SIRT3-dependent activation of OPA1 contributed to the preservation of mitochondrial networking and protection of cardiomyocytes from doxorubicin-mediated cell death. In summary, these data indicated that SIRT3 promotes mitochondrial function not only by regulating activity of metabolic enzymes, as previously reported, but also by regulating mitochondrial dynamics by targeting OPA1.

No abstract

Potassium (K) efflux across the plasma membrane is thought to be an essential mechanism for ATP-induced NLRP3 inflammasome activation, yet the identity of the efflux channel has remained elusive. Here we identified the two-pore domain K channel (K) TWIK2 as the K efflux channel triggering NLRP3 inflammasome activation. Deletion of Kcnk6 (encoding TWIK2) prevented NLRP3 activation in macrophages and suppressed sepsis-induced lung inflammation. Adoptive transfer of Kcnk6 macrophages into mouse airways after macrophage depletion also prevented inflammatory lung injury. The K efflux channel TWIK2 in macrophages has a fundamental role in activating the NLRP3 inflammasome and consequently mediates inflammation, pointing to TWIK2 as a potential target for anti-inflammatory therapies.

Right ventricular hypertrophy (RVH) and RV failure are major determinants of prognosis in pulmonary hypertension and congenital heart disease. In RVH, there is a metabolic shift from glucose oxidation (GO) to glycolysis. Directly increasing GO improves RV function, demonstrating the susceptibility of RVH to metabolic intervention. However, the effects of RVH on fatty acid oxidation (FAO), the main energy source in adult myocardium, are unknown. We hypothesized that partial inhibitors of FAO (pFOXi) would indirectly increase GO and improve RV function by exploiting the reciprocal relationship between FAO and GO (Randle’s cycle). RVH was induced in adult Sprague-Dawley rats by pulmonary artery banding (PAB). pFOXi were administered orally to prevent (trimetazidine, 0.7 g/L for 8 weeks) or regress (ranolazine 20 mg/day or trimetazidine for 1 week, beginning 3 weeks post-PAB) RVH. Metabolic, hemodynamic, molecular, electrophysiologic, and functional comparisons with sham rats were performed 4 or 8 weeks post-PAB. Metabolism was quantified in RV working hearts, using a dual-isotope technique, and in isolated RV myocytes, using a Seahorse Analyzer. PAB-induced RVH did not cause death but reduced cardiac output and treadmill walking distance and elevated plasma epinephrine levels. Increased RV FAO in PAB was accompanied by increased carnitine palmitoyl-transferase expression; conversely, GO and pyruvate dehydrogenase (PDH) activity were decreased. pFOXi decreased FAO and restored PDH activity and GO in PAB, thereby increasing ATP levels. pFOXi reduced the elevated RV glycogen levels in RVH. Trimetazidine and ranolazine increased cardiac output and exercise capacity and attenuated exertional lactic acidemia in PAB. RV monophasic action potential duration and QTc interval prolongation in RVH normalized with trimetazidine. pFOXi also decreased the mild RV fibrosis seen in PAB. Maladaptive increases in FAO reduce RV function in PAB-induced RVH. pFOXi inhibit FAO, which increases GO and enhances RV function. Trimetazidine and ranolazine have therapeutic potential in RVH.