Endurance training increases mitochondrial myoglobin and enhances its interaction with complex IV in rat plantaris muscle.

AIM: Endurance exercise training is known to increase mitochondrial respiration in skeletal muscle. However, the molecular mechanisms behind this are not fully understood. Myoglobin (Mb) is a member of the globin family, which is highly expressed in skeletal and cardiac muscles. We recently found that Mb localizes inside mitochondria in skeletal muscle and interacts with cytochrome c oxidase subunit IV (COXIV), a subunit of mitochondrial complex IV, which regulates respiration by augmenting complex IV activity. In the present study, we investigated the effect of endurance training on Mb-COXIV interaction within mitochondria in rat skeletal muscle. METHODS: Eight-week-old male Wistar rats were subjected to 6-week treadmill running training. Forty-eight hours after the last training session, the plantaris muscle was removed under anesthesia and used for biochemical analysis. RESULTS: The endurance training increased mitochondrial content in the skeletal muscle. It also augmented complex IV-dependent oxygen consumption and complex IV activity in isolated mitochondria from skeletal muscle. Furthermore, endurance training increased Mb expression at the whole muscle level. Importantly, mitochondrial Mb content and Mb-COXIV binding were increased by endurance training. CONCLUSION: These findings suggest that an increase in mitochondrial Mb and the concomitant enhancement of Mb interaction with COXIV may contribute to the endurance training-induced upregulation of mitochondrial respiration by augmenting complex IV activity.

Community-acquired Stenotrophomonas maltophilia bacteremia in liver cirrhosis: A case report.

Stenotrophomonas maltophilia is a Gram-negative bacterium, usually considered a nosocomial pathogen. Its role in community-acquired infections has been reported, but it is still not typically included in differential diagnoses of patients not exposed to the healthcare system. Recently, some reports suggested that liver diseases might also act as a possible risk factor for community-acquired S. maltophilia bloodstream infection. We report a case of a 77-year-old woman with a history of cirrhosis who was diagnosed with community-acquired S. maltophilia bloodstream infection. S. maltophilia not only causes hospital-acquired infections but is also emerging as a pathogen in community settings. Although community-onset infection is still rare and might have lower mortality, this antibiotic-resistant bacterial species should be considered a possible pathogen in patients with liver cirrhosis. Although trimethoprim-sulfamethoxazole is considered the first-line treatment, a study in vitro and a 4-year review of S. maltophilia susceptibility in our institution found that the bacteria were more susceptible to minocycline than to trimethoprim-sulfamethoxazole. Therefore, minocycline might become the first-line treatment in the future.

TOM complex-independent transport pathway of myoglobin into mitochondria in C2C12 myotubes.

Recently, we found that myoglobin (Mb) localizes in both the cytosol and mitochondrial intermembrane space in rodent skeletal muscle. Most proteins of the intermembrane space pass through the outer mitochondrial membrane via the translocase of the outer membrane (TOM) complex. However, whether the TOM complex imports Mb remains unknown. The purpose of this study was to investigate the involvement of the TOM complex in Mb import into the mitochondria. A proteinase K protection assay of mitochondria from C2C12 myotubes confirmed that Mb integrated into the mitochondria. An immunoprecipitation assay verified the interaction of Mb and TOM complex receptors (Tom20, Tom70) in isolated mitochondria. The assay showed a clear interaction of Mb with Tom20 and Tom70. A knockdown experiment using siRNA for TOM complex receptors (Tom20, Tom70) and TOM complex channel (Tom40) did not alter the amount of Mb expression in the mitochondrial fraction. These results suggested that Mb does not necessarily require the TOM complex for mitochondrial import of Mb. Although the physiological role of Mb interactions with TOM complex receptors remains unclear, further studies are needed to clarify how Mb enters the mitochondria independently of the TOM complex.

Evaluating the efficacy of post-operative chemotherapy after curative resection of stage IV gastric cancer with synchronous oligo metastasis: a multicenter retrospective study.

BACKGROUND: Surgical resection of oligo-metastasis in gastric cancer (GC) is weakly recommended for patients without other incurable factors in the Japanese GC Treatment Guidelines. While post-operative chemotherapy is the standard treatment in patients with stage II or III GC, its efficacy for resected stage IV GC is unclear. This study aimed to evaluate the efficacy of post-operative chemotherapy after curative resection of GC with oligo-metastasis. METHODS: We retrospectively reviewed the medical records of patients with GC who were diagnosed with synchronous oligo-metastasis at 20 institutions in Japan between 2007 and 2012. The selection criteria were: adenocarcinoma, stage IV with oligo-metastasis at liver or lymph node without other distant metastasis, curative resection including synchronous oligo-metastasis, and no prior treatment of GC before surgery. RESULTS: A total of 110 patients were collected. Of the 94 eligible patients, 84 underwent gastrectomy with surgical resection of oligo-metastasis (39 [41%] liver metastasis and 55, [59%] distant lymph node metastasis), followed by post-operative chemotherapy with S-1 (S1: n = 55), S1 plus cisplatin (CS: n = 22), or Others (n = 7). Moreover, 10 patients did not receive post-operative chemotherapy (Non-Cx). The median overall survival (OS) was 35.2 and 11.1 months in the post-operative chemotherapy and Non-Cx groups (hazard ratio, 3.56; 95% confidence interval, 1.74-7.30; p < 0.001), respectively. In multivariable analysis, Non-Cx and age over 70 years were identified as poor prognostic factors for OS (p < 0.05). CONCLUSIONS: Curative resection followed by post-operative chemotherapy in patients with GC with synchronous oligo-metastasis showed favorable survival.

Elucidation of ubiquitin-conjugating enzymes that interact with RBR-type ubiquitin ligases using a liquid-liquid phase separation-based method.

RING-between RING (RBR)-type ubiquitin (Ub) ligases (E3s) such as Parkin receive Ub from Ub-conjugating enzymes (E2s) in response to ligase activation. However, the specific E2s that transfer Ub to each RBR-type ligase are largely unknown because of insufficient methods for monitoring their interaction. To address this problem, we have developed a method that detects intracellular interactions between E2s and activated Parkin. Fluorescent homotetramer Azami-Green fused with E2 and oligomeric Ash (Assembly helper) fused with Parkin form a liquid-liquid phase separation (LLPS) in cells only when E2 and Parkin interact. Using this method, we identified multiple E2s interacting with activated Parkin on damaged mitochondria during mitophagy. Combined with in vitro ubiquitination assays and bioinformatics, these findings revealed an underlying consensus sequence for E2 interactions with activated Parkin. Application of this method to other RBR-type E3s including HOIP, HHARI, and TRIAD1 revealed that HOIP forms an LLPS with its substrate NEMO in response to a proinflammatory cytokine and that HHARI and TRIAD1 form a cytosolic LLPS independent of Ub-like protein NEDD8. Since an E2-E3 interaction is a prerequisite for RBR-type E3 activation and subsequent substrate ubiquitination, the method we have established here can be an in-cell tool to elucidate the potentially novel mechanisms involved in RBR-type E3s.

Heterogeneous expression and role of receptor tyrosine kinase-like orphan receptor 2 (ROR2) in small cell lung cancer.

The present study investigated the expression and role of ROR2 in small cell lung cancer (SCLC). To examine the expression of ROR2, 27 surgically resected SCLC tissue samples were immunostained for ROR2. Sixteen tissue samples were positive and some showed intratumor heterogeneity in staining intensity. The heterogeneity of ROR2 expression was also observed in tumor tissues from a PDX model of SCLC, in which there were cells with high ROR2 expression (ROR2high cells) and without its expression (ROR2low cells). These cells were subjected to a RNA sequence analysis. GSEA was performed and the results obtained revealed the enrichment of molecules such as G2M checkpoint, mitotic spindle, and E2F targets in ROR2high cells. The rate of EdU incorporation was significantly higher in ROR2high cells than ROR2low cells from the PDX model and the SCLC cell lines. Cell proliferation was suppressed in ROR2 KO SBC3 cells in vitro and in vivo. Comparisons of down-regulated differentially expressed genes in ROR2 KO SBC3 cells with up-regulated DEG in ROR2high cells from the PDX model revealed 135 common genes. After a Metascape analysis of these genes, we focused on Aurora kinases. In SCLC cell lines, the knockdown of ROR2 suppressed Aurora kinases. Therefore, ROR2 appears to regulate the cell cycle through Aurora kinases. The present results reveal a role for ROR2 in SCLC and afford a candidate system (ROR2-Aurora kinase) accompanying tumor heterogeneity in SCLC.

Prevention and regression of megamitochondria and steatosis by blocking mitochondrial fusion in the liver.

Non-alcoholic steatohepatitis (NASH) is a most common chronic liver disease that is manifested by steatosis, inflammation, fibrosis, and tissue damage. Hepatocytes produce giant mitochondria termed megamitochondria in patients with NASH. It has been shown that gene knockout of OPA1, a mitochondrial dynamin-related GTPase that mediates mitochondrial fusion, prevents megamitochondria formation and liver damage in a NASH mouse model induced by a methionine-choline-deficient (MCD) diet. However, it is unknown whether blocking mitochondrial fusion mitigates NASH pathologies. Here, we acutely depleted OPA1 using antisense oligonucleotides in the NASH mouse model before or after megamitochondria formation. When OPA1 ASOs were applied at the disease onset, they effectively prevented megamitochondria formation and liver pathologies in the MCD model. Notably, even when applied after mice robustly developed NASH pathologies, OPA1 targeting effectively regressed megamitochondria and the disease phenotypes. Thus, our data show the efficacy of mitochondrial dynamics as a unique therapy for megamitochondria-associated liver disease.

Simultaneous presence of the hepato-spleno-mesenteric trunk, a common trunk for both inferior phrenic arteries, the left gastric artery, and a common hepatic artery that ran behind the portal vein in a patient with gastric cancer.

The celiac artery usually trifurcates into the common hepatic artery, splenic artery, and left gastric artery, but it is known to present several anatomical variations. In such cases, detailed knowledge of the variation is needed preoperatively to safely perform surgery. A 77-year-old woman was referred to our hospital for the treatment of gastric cancer. She had a triple anatomical variation: simultaneous presence of the hepato-spleno-mesenteric trunk, a common trunk for both inferior phrenic arteries and the left gastric artery, and a common hepatic artery that ran behind the portal vein. We detected this variation on routine preoperative multidetector computed tomography angiography, and safely and adequately performed laparoscopic distal gastrectomy.

The role of YAP1 in small cell lung cancer.

Yes-associated protein (YAP) and transcriptional coactivator with PDZ-binding motif (TAZ, also known as WWTR1) are core downstream effectors of the Hippo pathway, which is involved in diverse biological processes. The oncogenic effects of YAP and TAZ in non-small cell lung cancer (NSCLC) have recently been reported; however, their roles in SCLC remain unclear. Immunohistochemistry (IHC) on lung cancer tissues and Western blotting (WB) on lung cancer cell lines were performed to examine the expression of YAP1. Genome editing using CRISPR/Cas9 was then used to knockout the YAP1 gene in the H69AR cell line. An RNA-sequence analysis, gene ontology (GO) analysis, WB, cell counting assay, invasion assays, and xenograft studies were conducted on these cells to investigate the biological roles of YAP1. IHC revealed that insulinoma-associated protein 1 was expressed in most cases (28 out of 32 cases), while only four cases expressed YAP1. The knockout of YAP1 in H69AR cells, a chemically induced SCLC-Y subtype, reduced cell proliferation and invasion capacity and restored drug sensitivity. Xenograft assays revealed that the knockout of YAP1 suppressed cell proliferation. Tumor tissues showed the expression of neuroendocrine markers and a low Ki-67 index. In SCLC, YAP1 plays an important role in biological functions, such as cell proliferation, EMT, drug sensitivity, and neuroendocrine differentiation.

Application of time lags between light and temperature cycles for growth control based on the circadian clock of Lactuca sativa L. seedlings.

The circadian clock plays an important role in agriculture, especially in highly controlled environments, such as plant factories. However, multiple environmental factors have an extremely high degree of freedom, and it is difficult to experimentally search for the optimal design conditions. A recent study demonstrated that the effect of time lags between light and temperature cycles on plant growth could be predicted by the entrainment properties of the circadian clock in Arabidopsis thaliana. Based on this prediction, it was possible to control plant growth by adjusting the time lag. However, for application in plant factories, it is necessary to verify the effectiveness of this method using commercial vegetables, such as leaf lettuce. In this study, we investigated the entrainment properties of the circadian clock and the effect of the time lag between light and temperature cycles on circadian rhythms and plant growth in Lactuca sativa L. seedlings. For evaluation of circadian rhythms, we used transgenic L. sativa L. with a luciferase reporter in the experiment and a phase oscillator model in the simulation. We found that the entrainment properties for the light and temperature stimuli and the effects of time lags on circadian rhythm and growth were similar to those of A. thaliana. Moreover, we demonstrated that changes in growth under different time lags could be predicted by simulation based on the entrainment properties of the circadian clock. These results showed the importance of designing a cultivation environment that considers the circadian clock and demonstrated a series of methods to achieve this.

Peripheral Chorioretinal Imaging Through a Front Prism on Optical Coherence Tomography Angiography.

Purpose: To evaluate the clinical feasibility of peripheral chorioretinal imaging through a front prism on swept-source optical coherence tomography angiography (SS-OCTA). Methods: We prospectively obtained en face OCTA images using SS-OCTA in 10 eyes of 10 healthy volunteers. For the peripheral chorioretinal imaging, the scanning laser passed and refracted through a 45°-90°-45° right-angle prism. We evaluated the qualitative and quantitative characteristics of chorioretinal vessels in the periphery. Results: Using peripheral chorioretinal imaging through a prism, the retinal vasculature was delineated to the equator on the OCTA images, and varices of the vortex vein ampullae were observed on choroidal OCT images. The 3 × 3-mm images revealed three-dimensional morphologies unique to the peripheral vasculature, such as the gap between retinal arterioles and venules in the superficial capillary plexus (SCP) and elliptical and greater lobules in the choriocapillaris layer. Compared with OCTA images obtained without the prism, those obtained through the prism demonstrated an approximately 1.24-fold increase in the lengths in the base apex direction, whereas the lengths in the perpendicular direction showed concordance. The peripheral vessel density (VD) in the inferior quadrant was lower than those in the other quadrants on the SCP and deep capillary plexus, whereas on the SCP images of the macula the lowest VD was observed in the temporal subfield. Conclusions: Peripheral chorioretinal imaging allowed us to generate ultra-widefield panoramic OCTA images and demonstrated morphologic characteristics unique to peripheral chorioretinal vessels. Translational Relevance: OCTA imaging through a front prism can be a technique for acquiring chorioretinal vasculature images in the periphery.

Prevention of Image Quality Degradation in Wider Field Optical Coherence Tomography Angiography Images Via Image Averaging.

Purpose: To evaluate the mutual effect of widening the field of view and multiple en face image averaging on the quality of optical coherence tomography angiography (OCTA) images. Methods: This prospective, observational, cross-sectional case series included 20 eyes of 20 healthy volunteers with no history of ocular or systemic disease. OCTA imaging of a 3 × 3-mm, 6 × 6-mm, and 12 × 12-mm area centered on the fovea was performed nine times using the PLEX Elite 9000. We acquired averaged OCTA images generated from nine en face OCTA images. The corresponding areas in the three scan sizes were evaluated for the original single-scanned OCTA images and averaged OCTA images both qualitatively and quantitatively. Quantitative measurements included vessel density (VD), vessel length density (VLD), fractal dimension (FD), and contrast-to-noise ratio (CNR). Results: Significant differences in VD, VLD, FD, and CNR (P < 0.001) were observed due to the mutual effect of averaging and differences in scan size. Both qualitative and quantitative evaluations indicated that the quality of 6 × 6-mm averaged images was equal to or better than that of 3 × 3-mm single-scanned images. However, the quality of 12 × 12-mm averaged images did not reach that of 3 × 3-mm single-scanned images. Conclusions: To some extent, multiple en face OCTA image averaging can compensate for the deterioration in image quality caused by widening the field of view. Translational Relevance: Multiple en face OCTA image averaging can be a technique for acquiring wider field OCTA images with good quality.

Brief and Indirect Exposure to Natural Environment Restores the Directed Attention for the Task.

The mental fatigue elicited by working and studying consumed mental resources, thereby eliciting a declined performance and an increased mental stress. The long-term continuous work and study, which is typical for modern workers and students, can increase mental fatigue and health risks. Previous studies reported that the natural environment (i.e., forest and waterside) has a restorative of mental resources (i.e., attention) and reducing stress. However, it is difficult for urban workers and students to take sufficient breaks in real natural environment. We conducted an experiment to examine whether brief and indirect exposure to the natural environment elicits a restorative of attention and reducing stress. Twenty-five undergraduate and graduate students from the university of modern city participated in the experiment. The experiment involved measuring the changes in the task performance of the participants (i.e., sustained attention to response task) and the subjective mental workload (i.e., arousal, valence, and NASA-TLX), while the attention restoration was indexed from physiological response (i.e., skin conductance level, SCL) over time. The participants had two types of resting periods in the middle of the task, i.e., by looking at a blank display (simple break) or by watching a nature video having scenes of, e.g., a forest, small waterfall, and rustling leaves (nature break). The results indicate that the natural environment indirectly depicted through the nature videos does not affect the task performance and the subjective mental workload but decreases the SCL. The results of the physiological response suggest that having rest periods depicting the natural environment, even if indirectly and briefly, can restore the directed attention (i.e., mental resources) for the task. This experiment revealed a useful method of resting for urban workers and students to restore their attention to a task.

Curcumin induces mitochondrial biogenesis by increasing cyclic AMP levels via phosphodiesterase 4A inhibition in skeletal muscle.

BACKGROUND: Previous research has suggested that curcumin potentially induces mitochondrial biogenesis in skeletal muscle via increasing cyclic AMP (cAMP) levels. However, the regulatory mechanisms for this phenomenon remain unknown. The purpose of the present study was to clarify the mechanism by which curcumin activates cAMP-related signalling pathways that upregulate mitochondrial biogenesis and respiration in skeletal muscle. METHODS: The effect of curcumin treatment (i.p., 100 mg/kg-BW/d for 28 d) on mitochondrial biogenesis was determined in rats. The effects of curcumin and exercise (swimming for 2 h/d for 3 d) on the cAMP signalling pathway were determined in the absence and presence of phosphodiesterase (PDE) or protein kinase A (PKA) inhibitors. Mitochondrial respiration, citrate synthase (CS) activity, cAMP content and protein expression of cAMP/PKA signalling molecules were analysed. RESULTS: Curcumin administration increased cytochrome c oxidase subunit (COX-IV) protein expression, and CS and complex I activity, consistent with the induction of mitochondrial biogenesis by curcumin. Mitochondrial respiration was not altered by curcumin treatment. Curcumin and PDE inhibition tended to increase cAMP levels with or without exercise. In addition, exercise increased the phosphorylation of phosphodiesterase 4A (PDE4A), whereas curcumin treatment strongly inhibited PDE4A phosphorylation regardless of exercise. Furthermore, curcumin promoted AMP-activated protein kinase (AMPK) phosphorylation and PPAR gamma coactivator (PGC-1α) deacetylation. Inhibition of PKA abolished the phosphorylation of AMPK. CONCLUSION: The present results suggest that curcumin increases cAMP levels via inhibition of PDE4A phosphorylation, which induces mitochondrial biogenesis through a cAMP/PKA/AMPK signalling pathway. Our data also suggest the possibility that curcumin utilises a regulatory mechanism for mitochondrial biogenesis that is distinct from the exercise-induced mechanism in skeletal muscle.

Specific techniques for right sleeve lower lobectomy: four case reports.

BACKGROUND: Right sleeve lower lobectomy is rarely performed because pulmonary function of the middle lobe is not spared to the extent of the other lobes and achieving a proper bronchial anastomosis is technically more difficult than other sleeve lobectomies. CASE PRESENTATION: We performed four right sleeve lower lobectomies and had good clinical outcomes using specific technical options, such as telescope anastomosing, pericardiotomy, interlobar dissection between the upper and middle lobes, and angioplasty of the lower pulmonary artery, if needed. CONCLUSIONS: The cases presented herein demonstrated that a right sleeve lower lobectomy is one option by which to preserve the middle lobe using specific techniques and is thus recommended in select patients.

[Three Cases of Solitary Brain Metastasis in Advanced Gastric Cancer].

We have experienced 3 cases of solitary brain metastasis after radical surgery in advanced gastric cancer. All of them have similar characteristics such as, upper third location, solitary metastasis to the cerebellum, and no other organ metastasis. As there is a risk of brain hernia, resection have been underwent first, and radiotherapy administered after surgery. One case has been provided over 2-year survival.

Impact of preoperative chemotherapy as initial treatment for advanced gastric cancer with peritoneal metastasis limited to positive peritoneal lavage cytology (CY1) or localized peritoneal metastasis (P1a): a multi-institutional retrospective study.

BACKGROUND: Gastric cancer (GC) patients with peritoneal metastasis are defined as stage IV in the Japanese classification of GC. For patients with peritoneal metastasis limited to positive peritoneal lavage cytology (CY1) and/or localized peritoneal metastasis (P1a), gastrectomy followed by S1 monotherapy is one of the most widely accepted therapeutic strategy in Japan. This study investigated the efficacy of preoperative chemotherapy as initial treatment in GC patients with CY1 and/or P1a. METHODS: We retrospectively reviewed GC patients diagnosed with CY1 and/or P1a at 34 institutions in Japan between 2008 and 2012. Selection criteria were: adenocarcinoma, no distant metastasis except CY1 or P1a, and no prior treatment. The subjects were divided into an Initial-Chemotherapy group and an Initial-Surgery group, according to the initial treatment. RESULTS: A total of 824 patients were collected and 713 eligible patients were identified for this study. As the initial treatment, 150 patients received chemotherapy (Initial-Cx), and 563 patients underwent surgery (Initial-Sx). Initial-Cx regimens were cisplatin plus S1/docetaxel plus cisplatin plus S1/others (n = 90/37/23). Both overall survival (OS) and progression-free survival (PFS) were similar between the Initial-Cx and Initial-Sx groups (median OS 24.8 and 24.0 months, HR 1.07, 95% CI 0.87-1.3; median PFS 14.9 and 13.9 months, HR 1.04, 95% CI 0.85-1.27). The 5-year OS rates were 22.3% in the Initial-Cx group and 21.5% in the Initial-Sx group. CONCLUSIONS: Although, the preoperative chemotherapy did not show a survival benefit for GC patients with CY1 and/or P1a, initial-Cx showed favorable survival in patients who converted to P0 and CY0.

Short-Term Effects of Different Types of Anti-Glaucoma Eyedrop on the Sclero-Conjunctival Vasculature Assessed Using Anterior Segment OCTA in Normal Human Eyes: A Pilot Study.

BACKGROUND: To investigate the short-term effects of different types of anti-glaucoma eyedrop on sclero-conjunctival vasculatures and their associations with intraocular pressure (IOP) reduction. METHODS: This was a prospective study including 20 healthy subjects. A single instillation of ripasudil or bimatoprost was introduced into the right eyes of the participants. The superficial (conjunctival) and deep (intrascleral) vasculatures of the corneal limbus using anterior-segment optical coherence tomography angiography (OCTA) and IOP were examined in both eyes at baseline and 15 min and 2 h after instillation. RESULTS: In the ripasudil group, the vessel density (VD) (median) at baseline (deep, 13.1%; superficial, 28.5%) significantly increased in both layers at 15 min (deep, 19.9%; superficial, 37.3%) and the deep layer at 2 h (deep, 14.8%; superficial, 31.6%). In the bimatoprost group, the superficial VD significantly changed over time, but the deep VD did not. The greater effect of ripasudil on IOP reduction was significantly associated with a lower baseline VD in the deep layer (at 15 min, p = 0.004; at 2 h, p = 0.018). CONCLUSIONS: Differences in the timing, depth, and extent of the effects on vasculature after instillations, could be detected using OCTA. The IOP-lowering effects of ripasudil might be associated with the deep vasculature.

Mitochondrial Safeguard: a stress response that offsets extreme fusion and protects respiratory function via flickering-induced Oma1 activation.

The connectivity of mitochondria is regulated by a balance between fusion and division. Many human diseases are associated with excessive mitochondrial connectivity due to impaired Drp1, a dynamin-related GTPase that mediates division. Here, we report a mitochondrial stress response, named mitochondrial safeguard, that adjusts the balance of fusion and division in response to increased mitochondrial connectivity. In cells lacking Drp1, mitochondria undergo hyperfusion. However, hyperfusion does not completely connect mitochondria because Opa1 and mitofusin 1, two other dynamin-related GTPases that mediate fusion, become proteolytically inactivated. Pharmacological and genetic experiments show that the activity of Oma1, a metalloprotease that cleaves Opa1, is regulated by short pulses of the membrane depolarization without affecting the overall membrane potential in Drp1-knockout cells. Re-activation of Opa1 and Mitofusin 1 in Drp1-knockout cells further connects mitochondria beyond hyperfusion, termed extreme fusion, leading to bioenergetic deficits. These findings reveal an unforeseen safeguard mechanism that prevents extreme fusion of mitochondria, thereby maintaining mitochondrial function when the balance is shifted to excessive connectivity.

Drp1 Tubulates the ER in a GTPase-Independent Manner.

Mitochondria are highly dynamic organelles that continuously grow, divide, and fuse. The division of mitochondria is crucial for human health. During mitochondrial division, the mechano-guanosine triphosphatase (GTPase) dynamin-related protein (Drp1) severs mitochondria at endoplasmic reticulum (ER)-mitochondria contact sites, where peripheral ER tubules interact with mitochondria. Here, we report that Drp1 directly shapes peripheral ER tubules in human and mouse cells. This ER-shaping activity is independent of GTP hydrolysis and located in a highly conserved peptide of 18 amino acids (termed D-octadecapeptide), which is predicted to form an amphipathic α helix. Synthetic D-octadecapeptide tubulates liposomes in vitro and the ER in cells. ER tubules formed by Drp1 promote mitochondrial division by facilitating ER-mitochondria interactions. Thus, Drp1 functions as a two-in-one protein during mitochondrial division, with ER tubulation and mechano-GTPase activities.