Identification of an ATP-sensitive potassium channel in mitochondria.

Mitochondria provide chemical energy for endoergonic reactions in the form of ATP, and their activity must meet cellular energy requirements, but the mechanisms that link organelle performance to ATP levels are poorly understood. Here we confirm the existence of a protein complex localized in mitochondria that mediates ATP-dependent potassium currents (that is, mitoKATP). We show that-similar to their plasma membrane counterparts-mitoKATP channels are composed of pore-forming and ATP-binding subunits, which we term MITOK and MITOSUR, respectively. In vitro reconstitution of MITOK together with MITOSUR recapitulates the main properties of mitoKATP. Overexpression of MITOK triggers marked organelle swelling, whereas the genetic ablation of this subunit causes instability in the mitochondrial membrane potential, widening of the intracristal space and decreased oxidative phosphorylation. In a mouse model, the loss of MITOK suppresses the cardioprotection that is elicited by pharmacological preconditioning induced by diazoxide. Our results indicate that mitoKATP channels respond to the cellular energetic status by regulating organelle volume and function, and thereby have a key role in mitochondrial physiology and potential effects on several pathological processes.

Fetal Doppler Parameters at Term in Pregnancies Affected by Gestational Diabetes: Role in the Prediction of Perinatal Outcomes.

OBJECTIVE: The timing of delivery for women affected by gestational diabetes (GDM) is still controversial. Good clinical practice often suggests offering induction of labor at term in order to reduce the complications associated with this condition, while recent evidence supports expectant management. Fetal Doppler parameters represent a validated tool for testing fetal well-being at term and can select pregnancies that need increased surveillance. The aim of the present study was to evaluate the role of fetal Doppler parameters at term for the prediction of pregnancy outcomes in patients affected by GDM. METHODS: Prospective cohort study in a single center. Evaluation of umbilical artery (UA) PI, middle cerebral artery (MCA) PI, cerebroplacental ratio (CPR) and umbilical-to-cerebral ratio (UCR) at > 37 weeks of gestation in singleton, morphologically normal pregnancies affected by GDM, was performed in order to estimate the association between ultrasound measurements at term and perinatal outcome. Regression linear analysis was used to estimate the association between fetal Doppler parameters and neonatal pH, neonatal Apgar score, neonatal weight and a composite adverse outcome. The receiver operating characteristic (ROC) curve was used to estimate the possible predictive value of the above association. RESULTS: Our results on 130 women showed MCA PI to be the best predictor of perinatal outcomes in terms of low Apgar score at the 1st minute (p = 0.00), pH (p = 0.02) and composite adverse outcome (p = 0.05). UCR showed a significant correlation with neonatal pH (p = 0.02). No significant correlations for UA PI and CPR MoMs have been demonstrated in our population. However, the small sample size is a limitation of the study. CONCLUSION: Evaluation of MCA Doppler and eventually UCR at term can be a useful tool to discriminate pregnancies affected by GDM that can benefit from IOL before 41 weeks in order to reduce complications related to this condition.

The mitochondrial ATP-dependent potassium channel (mitoKATP) controls skeletal muscle structure and function.

MitoKATP is a channel of the inner mitochondrial membrane that controls mitochondrial K+ influx according to ATP availability. Recently, the genes encoding the pore-forming (MITOK) and the regulatory ATP-sensitive (MITOSUR) subunits of mitoKATP were identified, allowing the genetic manipulation of the channel. Here, we analyzed the role of mitoKATP in determining skeletal muscle structure and activity. Mitok-/- muscles were characterized by mitochondrial cristae remodeling and defective oxidative metabolism, with consequent impairment of exercise performance and altered response to damaging muscle contractions. On the other hand, constitutive mitochondrial K+ influx by MITOK overexpression in the skeletal muscle triggered overt mitochondrial dysfunction and energy default, increased protein polyubiquitination, aberrant autophagy flux, and induction of a stress response program. MITOK overexpressing muscles were therefore severely atrophic. Thus, the proper modulation of mitoKATP activity is required for the maintenance of skeletal muscle homeostasis and function.

Multiple Pregnancy and the Risk of Postpartum Hemorrhage: Retrospective Analysis in a Tertiary Level Center of Care.

The aim of our study was to identify characteristics associated with postpartum hemorrhage (PPH defined as blood loss >1000 mL) in twin pregnancies in order to select patients at higher risk to be treated. This retrospective study includes multiple pregnancies between 2015 and 2020. The possible association between pregnancy characteristics and the primary endpoint (occurrence of PPH) was conducted using chi-square or Fisher exact test and Wilcoxon test. Then, univariate logistic models were performed considering as outcome the PPH, and the odds ratios with 95% CI were estimated. Finally, a multivariate logistic model was implemented, including all significant covariates. Seven hundred seven twin pregnancies giving birth beyond 32 weeks were included and of those, 120 (16.97%) had a PPH. The univariate analysis showed that factors significantly associated with PPH were: Preterm delivery, episiotomy, neonatal weight, and mode of delivery. The multivariate analysis showed that the most important factors were episiotomy and neonatal weight. The results show that the performance of episiotomy and the neonatal weight are the factors that most impact the risk of PPH in twin pregnancies. The correct identification of factors associated with PPH in twins could ideally allow to modify the clinical management and positively affect the rate of complications.

The impact of placental anastomoses and umbilical cord insertions' sites on monochorionic twin pregnancy outcomes: Evidence from color-dye injection studies.

INTRODUCTION: Our knowledge of monochorionic pregnancies' complications is largely based on the extensive ongoing research on monochorionic placental structure. Previous studies on the concordance of umbilical cord insertions are limited. This study aimed to evaluate placental anastomoses and cord insertions as independent risk factors for neonatal adverse outcomes. METHODS: This was a prospective study conducted at Fondazione Policlinico Universitario Agostino Gemelli IRCCS, Rome, Italy from April 2021 to December 2022. Seventy-six women with a monochorionic pregnancy were enrolled at their first-trimester scan. After delivery, all placentas that were confirmed to be monochorionic were analyzed according to standard protocols, including those of complicated monochorionic twin pregnancies. The primary outcomes were a Composite Monochorionic Pregnancy Outcome (CMPO) and a Composite Neonatal Adverse Outcome (CNAO). The secondary outcome was the birth weight discordance between the neonates. RESULTS: The CMPO occurred in 15.8 % pregnancies, and the CNAO occurred in 67.1 % pregnancies. The analysis confirmed a significant association between velamentous cord insertions and neonatal adverse events (p = 0.003). Also, a significant positive association (p = 0.0326) between twin birth weight discordance and discordance in twins umbilical cord insertions' sites was found. No significant association between the number and type of the anastomoses and both the CMPO or CNAO was detected. DISCUSSION: Our data suggest that the routine sonographic assessment of umbilical cords' insertion sites during the first trimester could be helpful in predicting fetal and neonatal adverse events. We believe that this sonographic assessment should start to be implemented in our routine care of monochorionic pregnancies.

A High-Throughput Screening Identifies MICU1 Targeting Compounds.

Mitochondrial Ca2+ uptake depends on the mitochondrial calcium uniporter (MCU) complex, a highly selective channel of the inner mitochondrial membrane (IMM). Here, we screen a library of 44,000 non-proprietary compounds for their ability to modulate mitochondrial Ca2+ uptake. Two of them, named MCU-i4 and MCU-i11, are confirmed to reliably decrease mitochondrial Ca2+ influx. Docking simulations reveal that these molecules directly bind a specific cleft in MICU1, a key element of the MCU complex that controls channel gating. Accordingly, in MICU1-silenced or deleted cells, the inhibitory effect of the two compounds is lost. Moreover, MCU-i4 and MCU-i11 fail to inhibit mitochondrial Ca2+ uptake in cells expressing a MICU1 mutated in the critical amino acids that forge the predicted binding cleft. Finally, these compounds are tested ex vivo, revealing a primary role for mitochondrial Ca2+ uptake in muscle growth. Overall, MCU-i4 and MCU-i11 represent leading molecules for the development of MICU1-targeting drugs.

Crosstalk between Mitochondrial Ca2+ Uptake and Autophagy in Skeletal Muscle.

Autophagy is responsible for the maintenance of skeletal muscle homeostasis, thanks to the removal of aberrant and dysfunctional macromolecules and organelles. During fasting, increased autophagy ensures the maintenance of the amino acid pool required for energy production. The activity of the mitochondrial Ca2+ uniporter (MCU), the highly selective channel responsible for mitochondrial Ca2+ uptake, controls skeletal muscle size, force, and nutrient utilization. Thus, both autophagy and mitochondrial Ca2+ accumulation play a pivotal role to maintain muscle homeostasis and to sustain muscle function. Here, we address whether, in skeletal muscle, mitochondrial Ca2+ uptake and autophagy are mutually related. Muscle-restricted MCU silencing partially inhibits the autophagy flux. Moreover, skeletal muscle-specific deletion of the essential autophagy gene Atg7, known to cause the accumulation of dysfunctional mitochondria, drastically reduces mitochondrial Ca2+ accumulation. Thus, a vicious cycle takes place, in which reduced MCU activity hampers the autophagic flux, and loss of autophagy further impairs mitochondrial Ca2+ signaling.

High-Throughput Screening Using Photoluminescence Probe to Measure Intracellular Calcium Levels.

Aequorin, a 22 kDa protein produced by the jellyfish Aequorea victoria, was the first probe used to measure Ca2+ concentrations ([Ca2+]) of specific intracellular organelles in intact cells. After the binding of Ca2+ to three high-affinity binding sites, an irreversible reaction occurs leading to the emission of photons that is proportional to [Ca2+]. While native aequorin is suitable for measuring cytosolic [Ca2+] after cell stimulation in a range from 0.5 to 10 µM, it cannot be used in organelles where [Ca2+] is much higher, such as in the lumen of endoplasmic/sarcoplasmic reticulum (ER/SR) and mitochondria. However, some modifications made on aequorin itself or on coelenterazine, its lipophilic prosthetic luminophore, and the addition of targeting sequences or the fusion with resident proteins allowed the specific organelle localization and the measurements of intra-organelle Ca2+ levels. In the last years, the development of multiwell plate readers has opened the possibility to perform aequorin-based high-throughput screenings and has overcome some limitation of the standard method. Here we present the procedure for expressing, targeting, and reconstituting aequorin in intact cells and for measuring Ca2+ in the bulk cytosol, mitochondria, and ER by a high-throughput screening system.