Quality control of mitochondrial protein synthesis is required for membrane integrity and cell fitness.

Mitochondrial ribosomes synthesize a subset of hydrophobic proteins required for assembly of the oxidative phosphorylation complexes. This process requires temporal and spatial coordination and regulation, so quality control of mitochondrial protein synthesis is paramount to maintain proteostasis. We show how impaired turnover of de novo mitochondrial proteins leads to aberrant protein accumulation in the mitochondrial inner membrane. This creates a stress in the inner membrane that progressively dissipates the mitochondrial membrane potential, which in turn stalls mitochondrial protein synthesis and fragments the mitochondrial network. The mitochondrial m-AAA protease subunit AFG3L2 is critical to this surveillance mechanism that we propose acts as a sensor to couple the synthesis of mitochondrial proteins with organelle fitness, thus ensuring coordinated assembly of the oxidative phosphorylation complexes from two sets of ribosomes.

Deletion of capn4 Protects the Heart Against Endotoxemic Injury by Preventing ATP Synthase Disruption and Inhibiting Mitochondrial Superoxide Generation.

BACKGROUND: Our recent study has demonstrated that inhibition of calpain by transgenic overexpression of calpastatin reduces myocardial proinflammatory response and dysfunction in endotoxemia. However, the underlying mechanisms remain to be determined. In this study, we used cardiomyocyte-specific capn4 knockout mice to investigate whether and how calpain disrupts ATP synthase and induces mitochondrial superoxide generation during endotoxemia. METHODS AND RESULTS: Cardiomyocyte-specific capn4 knockout mice and their wild-type littermates were injected with lipopolysaccharides. Four hours later, calpain-1 protein and activity were increased in mitochondria of endotoxemic mouse hearts. Mitochondrial calpain-1 colocalized with and cleaved ATP synthase-α (ATP5A1), leading to ATP synthase disruption and a concomitant increase in mitochondrial reactive oxygen species generation during lipopolysaccharide stimulation. Deletion of capn4 or upregulation of ATP5A1 increased ATP synthase activity, prevented mitochondrial reactive oxygen species generation, and reduced proinflammatory response and myocardial dysfunction in endotoxemic mice. In cultured cardiomyocytes, lipopolysaccharide induced mitochondrial superoxide generation that was prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Upregulation of calpain-1 specifically in mitochondria sufficiently induced superoxide generation and proinflammatory response, both of which were attenuated by ATP5A1 overexpression or mitochondria-targeted superoxide dismutase mimetics. CONCLUSIONS: Cardiomyocyte-specific capn4 knockout protects the heart against lipopolysaccharide-induced injury in endotoxemic mice. Lipopolysaccharides induce calpain-1 accumulation in mitochondria. Mitochondrial calpain-1 disrupts ATP synthase, leading to mitochondrial reactive oxygen species generation, which promotes proinflammatory response and myocardial dysfunction during endotoxemia. These findings uncover a novel mechanism by which calpain mediates myocardial dysfunction in sepsis.

Comparative proteomic analysis of human placenta derived from assisted reproductive technology.

The aim of this study was to use proteomics-based approach to examine differences in protein expression in placenta derived from assisted reproductive technology (ART) and normal pregnancy. Using 2-DE we found that, compared with the control group, 12 spots in standard in vitro fertilization group and 18 spots in intracytoplasmic sperm injection group were identified as significantly differentially expressed proteins. Among them, six spots were differentially expressed in both standard IVF and ICSI groups with the same change tendency. Totally, 20 proteins were successfully identified by MALDI TOF/TOF MS, including proteins involved in the membrane traffic, metabolism, nucleic acid processing, stress response and cytoskeleton. Notably, five proteins detected to be differentially expressed in both ART groups were identified as annexin A3, hnRNP C1/C2, alpha-SNAP, FTL and ATP5A. Some of the proteins were confirmed by Western blot and immunohistochemistry analysis. Our study allowed for the initial identification of these proteins related to various functions in placentation with significantly altered abundance in ART groups. The present results reveal that abnormal protein profiles are involved in ART placenta and these differentially expressed proteins may be valuable for the evaluation of potential association between ART treatment and offspring outcome.

[Effect of rosiglitazone on tumor necrosis factor-alpha-induced nuclear factor-kappaB and coupling factor 6 expressions in human umbilical vein endothelial cells].

OBJECTIVE: To investigate the effect of rosiglitazone on the expression of nuclear factor-kappaB (NF-kappaB) and coupling factor 6 (CF6) induced by tumor necrosis factor-alpha (TNF-alpha) in cultured human umbilical vein endothelial cells (HUVEC). METHODS: Cultured HUVEC of passage 3-5 were stimulated with TNF-alpha and then cultured in the presence of rosiglitazone. The expression of CF6 and NF-kappaB subunit p65 were evaluated by immunocytochemistical method. RESULTS: Pretreatment of HUVECs with rosiglitazone inhibited TNF-alpha-induced expression of CF6 in a dose-dependent manner. The activation of CF6 stimulated by TNF-alpha was suppressed by ROS in a dose-dependent manner. CONCLUSION: TNF-alpha-induced enhancement of the gene expression and release of CF6 is mediated by activation of NF-kappaB signaling pathway. ROS can inhibit the activation of IKK, block NF-kappaB signaling pathway and inhibit the expression of CF6, which may be the mechanism underlying the action of TZDs on hypertension.

High glucose promotes the release and expression of novel vasoactive peptide, coupling factor 6, in human umbilical vein endothelial cells.

As a novel vasoactive peptide, plasma coupling factor 6 (CF6) was shown to be elevated in patients with diabetes mellitus, yet the mechanism involved is unknown. We studied CF6 protein release and its potential mechanism in human umbilical vein endothelial cells (HUVECs) incubated with high glucose levels. High glucose level enhanced CF6 expression and peptide secretion in HUVECs in a time- and concentration-dependent manner, which was independent of increased osmolarity. PKC or p38 MAPK inhibition significantly suppressed high glucose-mediated CF6 release in HUVECs, and the inhibition rate was -45% and -30%, respectively. Also, high glucose-induced CF6 production was antagonized by insulin treatment. Hence, high glucose increases the expression and secretion of CF6 in endothelial cells and appears to be mediated by PKC and p38 MAPK activity.

Synthesis and assembly of adenosinetriphosphatase in synchronous cultures of yeast.

Maximal respiration and expression of mitochondrial enzymes are found at the late-S phase of yeast cells growing synchronously in glucose medium. Adenosinetriphosphatase (ATPase) activity follows a similar pattern. However, the cytosolically synthesized F1-ATPase and also that released from the membrane accumulate in the cytosol during the G1 and early-S phases. After the mid-S phase, when the mitochondrially synthesized membrane factors are available, the enzyme migrates to the membrane and is integrated.