No abstract

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.

No abstract

Rationale: Pulmonary arterial hypertension (PAH) is a lethal, femalepredominant, vascular disease. Pathologic changes in PA smooth muscle cells (PASMC) include excessive proliferation, apoptosis-resistance, and mitochondrial fragmentation. Activation of dynamin-related protein increases mitotic fission and promotes this proliferation-apoptosis imbalance. The contribution of decreased fusion and reduced mitofusin-2 (MFN2) expression to PAH is unknown. Objectives: We hypothesize that decreased MFN2 expression promotes mitochondrial fragmentation, increases proliferation, and impairs apoptosis. The role of MFN2's transcriptional coactivator, peroxisome proliferator-activated receptor g coactivator 1-a (PGC1a), was assessed. MFN2 therapy was tested in PAH PASMC and in models of PAH. Methods: Fusion and fission mediators were measured in lungs and PASMC from patients with PAH and female rats with monocrotaline or chronic hypoxia1Sugen-5416 (CH1SU) PAH. The effects of adenoviral mitofusin-2 (Ad-MFN2) overexpression were measured in vitro and in vivo. Measurements and Main Results: In normal PASMC, siMFN2 reduced expression of MFN2 and PGC1a; conversely, siPGC1a reduced PGC1a and MFN2 expression. Both interventions caused mitochondrial fragmentation. siMFN2 increased proliferation. In rodent and human PAH PASMC, MFN2 and PGC1a were decreased and mitochondria were fragmented. Ad-MFN2 increased fusion, reduced proliferation, and increased apoptosis in human PAH and CH1SU. In CH1SU, Ad-MFN2 improved walking distance (381 6 35 vs. 245 6 39 m; P , 0.05); decreased pulmonary vascular resistance (0.18 6 0.02 vs. 0.38 6 0.14 mm Hg/ml/min; P , 0.05); and decreased PA medial thickness (14.5 6 0.8 vs. 19 6 1.7%; P , 0.05). Lung vascularity was increased by MFN2. Conclusions: Decreased expression of MFN2 and PGC1a contribute to mitochondrial fragmentation and a proliferation-apoptosis imbalance in human and experimental PAH. Augmenting MFN2 has therapeutic benefit in human and experimental PAH.Keywords: mitochondrial fission; peroxisome proliferator-activated receptor gamma coactivator-1 a; hypoxia-inducible factor-1 a; optic atrophy 1; female sex Pulmonary arterial hypertension (PAH) is a syndrome characterized by obstructive vascular remodeling, inflammation, and vasoconstriction of small pulmonary arteries. PAH is predominantly a disease of females (1). Recent advances in understanding the mechanism of PAH include the identification of mutations in the bone morphogenetic protein receptor 2 in familial PAH (2-4) and the recognition that increases in proliferation and apoptosisresistance of pulmonary arterial smooth muscle cells (PASMC), that have multifactorial etiology, contribute to vascular obstruction (reviewed in [5]). These discoveries have yet to be translated into approved therapies, and most PAH treatments are vasodilators. Perhaps because of this, the 1-year mortality rates remain high (z15%) (6). Although abnormalities of platelets, the endothelium, fibroblasts, and inflammatory cells contribute critically to the path...

Compared with 7,8-DHF and ANA-12, ketamine is a longer-lasting antidepressant in the social defeat stress model, and synaptogenesis may be required for the mechanisms that promote sustained antidepressant effects of ketamine.