Recent evidence suggests that endoplasmic reticulum (ER) tubules mark the sites where the GTPase Drp1 promotes mitochondrial fission via a largely unknown mechanism. Here, we show that the SNARE protein syntaxin 17 (Syn17) is present on raft-like structures of ER-mitochondria contact sites and promotes mitochondrial fission by determining Drp1 localization and activity. The hairpin-like C-terminal hydrophobic domain, including Lys-254, but not the SNARE domain, is important for this regulation. Syn17 also regulates ER Ca(2+) homeostasis and interferes with Rab32-mediated regulation of mitochondrial dynamics. Starvation disrupts the Syn17-Drp1 interaction, thus favoring mitochondrial elongation during autophagy. Because we also demonstrate that Syn17 is an ancient SNARE, our findings suggest that Syn17 is one of the original key regulators for ER-mitochondria contact sites present in the last eukaryotic common ancestor. As such, Syn17 acts as a switch that responds to nutrient conditions and integrates functions for the ER and autophagosomes with mitochondrial dynamics.

c NCoR1 (nuclear receptor corepressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptors; NCoR2) are well-recognized coregulators of nuclear receptor (NR) action. However, their unique roles in the regulation of thyroid hormone (TH) signaling in specific cell types have not been determined. To accomplish this we generated mice that lacked function of either NCoR1, SMRT, or both in the liver only and additionally a global SMRT knockout model. Despite both corepressors being present in the liver, deletion of SMRT in either euthyroid or hypothyroid animals had little effect on TH signaling. In contrast, disruption of NCoR1 action confirmed that NCoR1 is the principal mediator of TH sensitivity in vivo. Similarly, global disruption of SMRT, unlike the global disruption of NCoR1, did not affect TH levels. While SMRT played little role in TH-regulated pathways, when disrupted in combination with NCoR1, it greatly accentuated the synthesis and storage of hepatic lipid. Taken together, these data demonstrate that corepressor specificity exists in vivo and that NCoR1 is the principal regulator of TH action. However, both corepressors collaborate to control hepatic lipid content, which likely reflects their cooperative activity in regulating the action of multiple NRs including the TH receptor (TR).T hyroid hormone (TH) is one of the most important metabolic regulators in humans, and its actions in the liver include the regulation of cholesterol and lipid metabolism. Thyroxine (T4) is the major circulating form of thyroid hormone, and it is converted to its active form, triiodothyronine (T3), by a family of deiodinases (1). T3 regulates metabolic processes via thyroid hormone receptor (TR) isoforms that are expressed in all peripheral tissues, including liver. The TRs mediate target gene regulation by recruiting a constellation of coregulators that include corepressors (CoRs) and coactivators depending upon the presence of T3 (2). While classical models suggest that the corepressors are mainly recruited by the unliganded TR, the mechanisms by which T3 coordinates specific signaling in the liver both positively and negatively are still unknown (3). Indeed, recent work by our laboratory and others has demonstrated that the corepressors appear to play a critical role in mediating ligand sensitivity regardless of the concentration of ligand (4-7).The two principal corepressors that are suggested to be involved in mediating TH action are nuclear receptor corepressor 1 (NCoR1) and silencing mediator of retinoid and thyroid hormone receptors (SMRT) (4). They are highly homologous modular proteins and have three similar nuclear receptor (NR) interaction domains (NRIDs) at their C termini (8). Importantly, whole-body gene knockouts (KOs) of NCoR1 or SMRT result in embryonic lethality, but mutation or deletion of only the NRIDs allows for full development (6, 9, 10). In NCoR⌬ID mice, which express an altered NCoR1 allele that lacks the N3 and N2 NRIDs, there is evidence for increased thyroid hormone sensitivity...

on behalf of the J-RHYTHM Registry Investigators* Background--To clarify the influence of hypertension and blood pressure (BP) control on thromboembolism and major hemorrhage in patients with nonvalvular atrial fibrillation, a post hoc analysis of the J-RHYTHM Registry was performed.

StarD7 facilitates phosphatidylcholine (PC) transfer to mitochondria, and is essential for mitochondrial homeostasis. However, the molecular mechanism for PC transfer by protein remains poorly understood. Herein, we describe a putative novel transmembrane (TM) domain C-terminal to the mitochondria-targeting signal (MTS) sequence at the N-terminus of StarD7. The mature form of StarD7 is integrated and/or associated onto the outer leaflet of the outer mitochondrial membrane (OMM) in HEPA-1 and HepG2 cells. A truncated form of StarD7 lacking the TM domain is distributed in the inner space of the mitochondria, and cannot reverse mitochondrial abnormalities, such as complex formation and PC content, when re-expressed in StarD7-KO HEPA-1 cells. Re-expression of wild StarD7 can compensate these mitochondrial functions of StarD7-KO HEPA-1 cells. The precursor form of StarD7 is cleaved between Met76 and Ala77, and Ala77 and Ala78 in the TM domain to produce the mature form. These results suggest that StarD7 is anchored onto the OMM through its N-terminal TM domain, and the C-terminal START domain may extend into the cytoplasm and shuttle PC between the ER and OMM at the ER-mitochondria contact sites.

StarD7 is a phosphatidylcholine (PC)-specific lipid transfer protein essential for the maintenance of mitochondrial PC composition, morphogenesis, and respiration. Here, we studied the role of StarD7 in skeletal myoblast differentiation using mouse myoblast C2C12 cells and human primary myoblasts. Immunofluorescence and immuno-electron microscopy revealed that StarD7 was distributed in the cytosol, inner mitochondria space, and outer leaflet of the outer mitochondrial membrane in C2C12 cells. Unlike human kidney embryonic cell line HEK293 cells, the mitochondrial proteinase PARL was not involved in the processing and maturation of StarD7 in C2C12 cells. StarD7 was constantly expressed during myogenic differentiation of C2C12 cells. The siRNA-mediated knockdown of StarD7 in C2C12 cells and human primary myoblasts significantly impaired myogenic differentiation and reduced the expression of myomaker, myomerger and PGC-1α. The reduction in mitochondrial PC levels and oxygen consumption rates, decreased expression of myomaker, myomerger and PGC-1α, as well as impaired myogenic differentiation, were completely restored when the protein was reintroduced into StarD7-knockout C2C12 cells. These results suggest that StarD7 is important for skeletal myogenesis in mammals. Mitochondrial membranes are composed of two phospholipid bilayers, the inner mitochondrial membrane (IMM) and the outer mitochondrial membrane (OMM). These mitochondrial membranes are essential for compartmentalization of the organelle and for various mitochondrial functions. More than half of the phospholipids in mitochondrial membranes are phosphatidylcholine (PC), followed by phosphatidylethanolamine (PE) (30-40%), cardiolipin (CL) (5-15%), phosphatidylinositol (PI) (2-9%), phosphatidylserine (PS) (1%) and phosphatidylglycerol (PG) (<1%). Mitochondria have enzymes for the biosynthesis of PE, CL and PG but lack the enzymes required for PC, PI and PS synthesis. These lipids are therefore likely supplied from organelles including as the endoplasmic reticulum (ER) which contain the biosynthesis systems for these phospholipids 1,2. Several previous studies have proposed that phospholipids are transferred between the ER and mitochondria via ER-mitochondria contact sites. In yeast, the formation of contact sites is mediated by a protein complex, the ER-mitochondria encounter structure (ERMES) 3. ERMES comprises four core subunits: Mmm1, Mdm10, Mdm34 and Mdm12. Recent studies demonstrated that the Mmm1-Mdm12 complex directly facilitates PS/PE transfer between the ER and mitochondria in vitro and in vivo 4-6. In mammals, ER-mitochondria contact sites are referred to as ER mitochondria-associated membranes (MAM). Several proteins such as mitofusin 2 (MFN2) 7,8 , glucose-regulated protein 75 (GRP75) 9 , mitochondrial fission 1 protein (Fis1) and B-cell receptor-associated protein 31 (Bap31) 10 have been reported to be implicated in the formation of membrane contact sites. A recent study

Silencing Mediator of Retinoid and Thyroid Hormone Receptors (SMRT) and the nuclear receptor co-repressor1 (NCoR1) are paralogs and regulate nuclear receptor (NR) function through the recruitment of a multiprotein complex that includes histone deacetylase activity. Previous genetic strategies which deleted SMRT in a specific tissue or which altered the interaction between SMRT and NRs have suggested that it may regulate adiposity and insulin sensitivity. However, the full role of SMRT in adult mice has been difficult to establish because its complete deletion during embryogenesis is lethal. To elucidate the specific roles of SMRT in mouse target tissues especially in the context of thyroid hormone (TH) signaling, we used a tamoxifen-inducible post-natal disruption strategy. We found that global SMRT deletion causes dramatic obesity even though mice were fed a standard chow diet and exhibited normal food intake. This weight gain was associated with a decrease in energy expenditure. Interestingly, the deletion of SMRT had no effect on TH action in any tissue but did regulate retinoic acid receptor (RAR) function in the liver. We also demonstrate that the deletion of SMRT leads to profound hepatic steatosis in the setting of obesity. This is unlike NCoR1 deletion, which results in hepatic steatosis due to the upregulation of lipogenic gene expression. Taken together, our data demonstrate that SMRT plays a unique and CoR specific role in the regulation of body weight and has no role in TH action. This raises the possibility that additional role of CoRs besides NCoR1 and SMRT may exist to regulate TH action.

Nuclear receptor corepressor 1 (NCoR1) is considered to be the major corepressor that mediates ligand-independent actions of the thyroid hormone receptor (TR) during development and in hypothyroidism. We tested this by expressing a hypomorphic NCoR1 allele (NCoR1ΔID), which cannot interact with the TR, in Pax8-KO mice, which make no thyroid hormone. Surprisingly, abrogation of NCoR1 function did not reverse the ligand-independent action of the TR on many gene targets and did not fully rescue the high mortality rate due to congenital hypothyroidism in these mice. To further examine NCoR1's role in repression by the unliganded TR, we deleted NCoR1 in the livers of euthyroid and hypothyroid mice and examined the effects on gene expression and enhancer activity measured by histone 3 lysine 27 (H3K27) acetylation. Even in the absence of NCoR1 function, we observed strong repression of more than 43% of positive T3 (3,3',5-triiodothyronine) targets in hypothyroid mice. Regulation of approximately half of those genes correlated with decreased H3K27 acetylation, and nearly 80% of these regions with affected H3K27 acetylation contained a bona fide TRβ1-binding site. Moreover, using liver-specific TRβ1-KO mice, we demonstrate that hypothyroidism-associated changes in gene expression and histone acetylation require TRβ1. Thus, many of the genomic changes mediated by the TR in hypothyroidism are independent of NCoR1, suggesting a role for additional signaling modulators in hypothyroidism.

Background Blood pressure (BP) variability has reportedly been a risk factor for various clinical events. To clarify the influence of BP visit‐to‐visit variability on adverse events in patients with nonvalvular atrial fibrillation, a post hoc analysis of the J‐RHYTHM Registry was performed. Methods and Results Of 7406 outpatients with nonvalvular atrial fibrillation from 158 institutions, 7226 (age, 69.7±9.9 years; men, 70.7%), in whom BP was measured 4 times or more (14.6±5.0 times) during the 2‐year follow‐up period or until occurrence of an event, constituted the study group. SD and coefficient of variation of BP values were calculated as BP variability. Thromboembolism, major hemorrhage, and all‐cause death occurred in 110 (1.5%), 121 (1.7%), and 168 (2.3%) patients, respectively. When patients were divided into quartiles of systolic BP‐SD (<8.20, 8.20–10.49, 10.50–13.19, and ≥13.20 mm Hg), hazard ratios (HRs) for all adverse events were significantly high in the highest quartile compared with the lowest quartile (HR, 2.00, 95% CI, 1.15–3.49, P =0.015 for thromboembolism; HR, 2.60, 95% CI, 1.36–4.97, P =0.004 for major hemorrhage; and HR, 1.85, 95% CI, 1.11–3.07, P =0.018 for all‐cause death) after adjusting for components of the CHA 2 DS 2 ‐VASc score, warfarin and antiplatelet use, atrial fibrillation type, BP measurement times, and others. These findings were consistent when BP‐coefficient of variation was used instead of BP‐SD. Conclusions Systolic BP visit‐to‐visit variability was significantly associated with all adverse events in patients with nonvalvular atrial fibrillation. Further studies are needed to clarify the causality between BP variability and adverse outcomes in patients with nonvalvular atrial fibrillation. Registration URL: https://www.umin.ac.jp/ctr/ ; Unique Identifier: UMIN000001569.