Phospholipid methylation controls Atg32-mediated mitophagy and Atg8 recycling.

Degradation of mitochondria via selective autophagy, termed mitophagy, contributes to mitochondrial quality and quantity control whose defects have been implicated in oxidative phosphorylation deficiency, aberrant cell differentiation, and neurodegeneration. How mitophagy is regulated in response to cellular physiology remains obscure. Here, we show that mitophagy in yeast is linked to the phospholipid biosynthesis pathway for conversion of phosphatidylethanolamine to phosphatidylcholine by the two methyltransferases Cho2 and Opi3. Under mitophagy-inducing conditions, cells lacking Opi3 exhibit retardation of Cho2 repression that causes an anomalous increase in glutathione levels, leading to suppression of Atg32, a mitochondria-anchored protein essential for mitophagy. In addition, loss of Opi3 results in accumulation of phosphatidylmonomethylethanolamine (PMME) and, surprisingly, generation of Atg8-PMME, a mitophagy-incompetent lipid conjugate of the autophagy-related ubiquitin-like modifier. Amelioration of Atg32 expression and attenuation of Atg8-PMME conjugation markedly rescue mitophagy in opi3-null cells. We propose that proper regulation of phospholipid methylation is crucial for Atg32-mediated mitophagy.

Efficacy and safety of linaclotide in treatment-resistant chronic constipation: A multicenter, open-label study.

BACKGROUND: This study aimed to evaluate the efficacy and safety of linaclotide in patients with chronic constipation (CC) or irritable bowel syndrome with constipation (IBS-C) who did not respond to treatment with magnesium oxide (MgO). METHODS: This study was designed as a multicenter, open-label, single-arm, exploratory study. Patients with CC or IBS-C who took MgO and those meeting the medication initiation criteria were administered linaclotide at a daily dosage of 500 µg for 12 weeks. The primary endpoint was a change in the Japanese version of the Patient Assessment of Constipation Quality of Life (JPAC-QOL) score from baseline, which was evaluated by using a paired t-test. KEY RESULTS: The patients' mean age (± standard deviation) was 67.6 ± 13.82 years. The full analysis set included 61 patients. The JPAC-QOL total score was 1.60 at baseline and 0.70 at 12 weeks, with a significant mean change of -0.89 ± 0.721 (p < 0.001). Several secondary endpoints also showed improvement. The frequency of spontaneous bowel movement (SBM) and complete SBM increased by 2.70 ± 7.254 (p < 0.01) and 2.81 ± 5.254 times, respectively (p < 0.001). The Bristol Stool Form Scale, abdominal bloating severity, and straining severity scores improved by 1.33 ± 1.274 (p < 0.001), -0.16 ± 0.563 (p < 0.05), and -0.46 ± 0.795 (p < 0.001) points, respectively. The safety analysis set included 65 patients, 7 of whom had diarrhea, which improved with dose reduction and drug withdrawal. CONCLUSION & INFERENCES: The study was conducted in an older adult population, similar to real clinical practice. Linaclotide may be an option for treating CC that shows an inadequate response to conventional therapy.

The Prevalence and Characteristics of Symptomatic Uncomplicated Diverticular Disease Among Asian Patients With Unexplained Abdominal Symptoms.

Background/Aims: The precise incidence of symptomatic uncomplicated diverticular disease (SUDD) and its effects on the quality of life (QOL) remain unclear, particularly in Asian patients with right-sided SUDD. We assess the prevalence of SUDD and its impact on QOL in a real-world population. Methods: Five institutional cohorts of patients who received outpatient treatment for unexplained abdominal symptoms from January 15, 2020 to March 31, 2022, were included. All patients underwent colonoscopy. SUDD was defined as the presence of recurrent abdominal symptoms, particularly pain in the lower right or left quadrant lasting > 24 hours in patients with diverticulosis at the site of pain. The 36-item short-form health survey was used to assess QOL. Results: Diverticula were identified in 108 of 361 patients. Among these 108 patients, 31% had SUDD, which was right-sided in 39% of cases. Of the 50 patients with right-sided diverticula, 36% had SUDD, as did 15 of 35 patients with left-sided diverticula (43%). Among the 33 patients with SUDD, diverticula were right-sided, left-sided, and bilateral in 39%, 45%, and 15% of patients, respectively. Diarrhea was more frequent in the SUDD group than in the non-SUDD group. Patients with SUDD had significantly lower physical, mental, and role/social component scores than those without SUDD. Conclusions: It is important to recognize that patients with SUDD account for as high as 31% of outpatients with unexplained abdominal symptoms; these patients have diarrhea and a low QOL. The presence of right-sided SUDD was characteristic of Asian patients.

The autophagy-related protein kinase Atg1 interacts with the ubiquitin-like protein Atg8 via the Atg8 family interacting motif to facilitate autophagosome formation.

In autophagy, a cup-shaped membrane called the isolation membrane is formed, expanded, and sealed to complete a double membrane-bound vesicle called the autophagosome that encapsulates cellular constituents to be transported to and degraded in the lysosome/vacuole. The formation of the autophagosome requires autophagy-related (Atg) proteins. Atg8 is a ubiquitin-like protein that localizes to the isolation membrane; a subpopulation of this protein remains inside the autophagosome and is transported to the lysosome/vacuole. In the budding yeast Saccharomyces cerevisiae, Atg1 is a serine/threonine kinase that functions in the initial step of autophagosome formation and is also efficiently transported to the vacuole via autophagy. Here, we explore the mechanism and significance of this autophagic transport of Atg1. In selective types of autophagy, receptor proteins recognize degradation targets and also interact with Atg8, via the Atg8 family interacting motif (AIM), to link the targets to the isolation membrane. We find that Atg1 contains an AIM and directly interacts with Atg8. Mutations in the AIM disrupt this interaction and abolish vacuolar transport of Atg1. These results suggest that Atg1 associates with the isolation membrane by binding to Atg8, resulting in its incorporation into the autophagosome. We also show that mutations in the Atg1 AIM cause a significant defect in autophagy, without affecting the functions of Atg1 implicated in triggering autophagosome formation. We propose that in addition to its essential function in the initial stage, Atg1 also associates with the isolation membrane to promote its maturation into the autophagosome.

Exploratory, multicenter, open-label study to evaluate the effects of linaclotide in patients with chronic constipation with an insufficient response to magnesium oxide: A study protocol.

Background: Chronic constipation leads to poor quality of life, and treatment remains unsatisfactory for patients. In Japan, magnesium oxide has been commonly used as the first choice of treatment for constipation; however, there are some cases of low satisfaction with magnesium oxide treatment. Linaclotide has recently been used to treat chronic constipation. In this study, we will examine whether linaclotide improves symptoms and quality of life in patients showing insufficient response to magnesium oxide. Methods: This is an exploratory multicenter open-label study. The target number of patients is 64: 32 patients with and 32 without abdominal symptoms. Patients with chronic idiopathic constipation or irritate bowel syndrome with constipation diagnosed according to the Rome-IV criteria are eligible. Patients prescribed 0.99-2 g/day of magnesium oxide for at least 4 weeks will be included. Those who consent to the study will continue taking magnesium oxide for 2-4 weeks, and defecation will be documented. Patients who meet the criteria will be prescribed linaclotide (0.5 mg) daily for 12 weeks. The primary endpoint is a change in the Japanese version of the Patient Assessment of Constipation Quality of Life (JPAC-QOL) score after 12 weeks of treatment. Conclusion: This is the first study to investigate the usefulness of linaclotide as a second-line treatment for chronic constipation. We will test the efficacy of treatment of constipation in patients with inadequate response to magnesium oxide. Trial registration: This study is registered with the Japan Registry of Clinical Trials (jRCT, jRCTs031200048).

Rationale and design of a multicenter, single-group, open-label trial aiming at investigating the effectiveness of elobixibat for loss of defecation desire in patients with chronic constipation.

Background: Approximately 60% of patients with chronic constipation (CC) have a significantly higher rate of loss of defecation desire (LODD). Bile acids are expected to have a restorative effect on defecation desire (DD) because they lower the rectal sensory threshold, which is an objective index of DD. Elobixibat (EXB) specifically inhibits the ileal bile acid transporter/apical sodium-dependent bile acid transporter, which is a transporter involved in the reabsorption of bile acids in the terminal ileum. This study aims to investigate the LODD improvement rate in patients with CC after 4 weeks of EXB treatment. Methods: A total of 40 adult patients with CC who meet the eligibility criteria will be enrolled. Patients will receive oral EXB (10 mg/day) for 4 weeks. A patient diary will be provided daily at 4 weeks after treatment. The primary endpoint will be the percentage LODD improvement at week 4 of the treatment period from week 2 of the observation period using questionnaires. Ethics and dissemination: Ethical approval was obtained from the Yokohama City University Certified Institutional Review Board prior to participant enrolment (approval number: CRB21-008). The results of this study will be submitted for publication in international peer-reviewed journals, and key findings will be presented at international scientific conferences. Participants desiring the results of this study will be directly contacted for data dissemination. Trial registration: This trial was registered at ClinicalTrials.gov (NCT05165199). Protocol version: 1.0, September 21, 2021.

Rationale and design of a multicentre, 12-week, randomised, double-blind, placebo-controlled, parallel-group, investigator-initiated trial to investigate the efficacy and safety of elobixibat for chronic constipation.

INTRODUCTION: Chronic constipation (CC) is a functional disorder that negatively impacts the quality of life of patients. This is a protocol for a multicentre, 12-week, randomised, double-blind, placebo-controlled study to test the efficacy and safety of elobixibat (EXB) versus placebo in patients with CC. METHODS AND ANALYSIS: This will be a multicentre, double-blind, placebo-control, randomised controlled trial. A total of 100 adult patients with CC, diagnosed based on Rome IV criteria, who fulfil the inclusion/exclusion criteria will be enrolled. The patients will be randomly assigned to receive EXB (10 mg) or placebo treatment (n=50 per group). Blood tests and stool sampling will be performed 12 weeks following initiation of treatment and questionnaires will be issued to participants. The primary outcome will be the change in complete spontaneous bowel movements after 12 weeks of administration. The secondary outcomes will include the change in Japanese Patient Assessment of Constipation Quality of Life and absolute serum and faecal bile acid. ETHICS AND DISSEMINATION: Ethics approval has been obtained from Yokohama City University Certified Institutional Review Board before participant enrolment. The results of this study will be submitted for publication in international peer-reviewed journals and the key findings will be presented at international scientific conferences. PROTOCOL VERSION: V.3.0, 15 June 2021. TRIAL REGISTRATION NUMBER: ClinicalTrials.gov (number NCT04784780).

Two distinct mechanisms target the autophagy-related E3 complex to the pre-autophagosomal structure.

In autophagy, Atg proteins organize the pre-autophagosomal structure (PAS) to initiate autophagosome formation. Previous studies in yeast revealed that the autophagy-related E3 complex Atg12-Atg5-Atg16 is recruited to the PAS via Atg16 interaction with Atg21, which binds phosphatidylinositol 3-phosphate (PI3P) produced at the PAS, to stimulate conjugation of the ubiquitin-like protein Atg8 to phosphatidylethanolamine. Here, we discover a novel mechanism for the PAS targeting of Atg12-Atg5-Atg16, which is mediated by the interaction of Atg12 with the Atg1 kinase complex that serves as a scaffold for PAS organization. While autophagy is partially defective without one of these mechanisms, cells lacking both completely lose the PAS localization of Atg12-Atg5-Atg16 and show no autophagic activity. As with the PI3P-dependent mechanism, Atg12-Atg5-Atg16 recruited via the Atg12-dependent mechanism stimulates Atg8 lipidation, but also has the specific function of facilitating PAS scaffold assembly. Thus, this study significantly advances our understanding of the nucleation step in autophagosome formation.

Localization of Atg3 to autophagy-related membranes and its enhancement by the Atg8-family interacting motif to promote expansion of the membranes.

The E2 enzyme Atg3 conjugates the ubiquitin-like protein Atg8 to phosphatidylethanolamine (PE) to drive autophagosome formation in Saccharomyces cerevisiae. In this study, we show that Atg3 localizes to the pre-autophagosomal structure (PAS) and the isolation membrane (IM), providing crucial evidence that Atg8-PE conjugates are produced on these structures. We also find that mutations in the Atg8-family interacting motif (AIM) of Atg3 significantly impairs the PAS/IM localization of Atg3, resulting in inefficient IM expansion. It is suggested that the AIM-mediated PAS/IM localization of Atg3 facilitates membrane expansion in these structures probably by ensuring active production of Atg8-PE on the membranes.

A novel role for 12/15-lipoxygenase in regulating autophagy.

12/15-Lipoxygenase (LOX) enzymatically generates oxidized phospholipids in monocytes and macrophages. Herein, we show that cells deficient in 12/15-LOX contain defective mitochondria and numerous cytoplasmic vacuoles containing electron dense material, indicating defects in autophagy or membrane processing, However, both LC3 expression and lipidation were normal both basally and on chloroquine treatment. A LOX-derived oxidized phospholipid, 12-hydroxyeicosatetraenoic acid-phosphatidylethanolamine (12-HETE-PE) was found to be a preferred substrate for yeast Atg8 lipidation, versus native PE, while both native and oxidized PE were effective substrates for LC3 lipidation. Last, phospholipidomics demonstrated altered levels of several phospholipid classes. Thus, we show that oxidized phospholipids generated by 12/15-LOX can act as substrates for key proteins required for effective autophagy and that cells deficient in this enzyme show evidence of autophagic dysfunction. The data functionally link phospholipid oxidation with autophagy for the first time.

Hrr25 triggers selective autophagy-related pathways by phosphorylating receptor proteins.

In selective autophagy, degradation targets are specifically recognized, sequestered by the autophagosome, and transported into the lysosome or vacuole. Previous studies delineated the molecular basis by which the autophagy machinery recognizes those targets, but the regulation of this process is still poorly understood. In this paper, we find that the highly conserved multifunctional kinase Hrr25 regulates two distinct selective autophagy-related pathways in Saccharomyces cerevisiae. Hrr25 is responsible for the phosphorylation of two receptor proteins: Atg19, which recognizes the assembly of vacuolar enzymes in the cytoplasm-to-vacuole targeting pathway, and Atg36, which recognizes superfluous peroxisomes in pexophagy. Hrr25-mediated phosphorylation enhances the interactions of these receptors with the common adaptor Atg11, which recruits the core autophagy-related proteins that mediate the formation of the autophagosomal membrane. Thus, this study introduces regulation of selective autophagy as a new role of Hrr25 and, together with other recent studies, reveals that different selective autophagy-related pathways are regulated by a uniform mechanism: phosphoregulation of the receptor-adaptor interaction.

Atg12-Atg5 conjugate enhances E2 activity of Atg3 by rearranging its catalytic site.

Two autophagy-related ubiquitin-like systems have unique features: the E2 enzyme Atg3 conjugates the ubiquitin-like protein Atg8 to the lipid phosphatidylethanolamine, and the other ubiquitin-like protein conjugate Atg12-Atg5 promotes that conjugase activity of Atg3. Here, we elucidate the mode of this action of Atg12-Atg5 as a new E3 enzyme by using Saccharomyces cerevisiae proteins. Biochemical analyses based on structural information suggest that Atg3 requires a threonine residue to catalyze the conjugation reaction instead of the typical asparagine residue used by other E2 enzymes. Moreover, the catalytic cysteine residue of Atg3 is arranged in the catalytic center such that the conjugase activity is suppressed; Atg12-Atg5 induces a reorientation of the cysteine residue toward the threonine residue, which enhances the conjugase activity of Atg3. Thus, this study reveals the mechanism of the key reaction that drives membrane biogenesis during autophagy.

Roles of protein-disulfide isomerase-mediated disulfide bond formation of yeast Mnl1p in endoplasmic reticulum-associated degradation.

The endoplasmic reticulum (ER) has a strict protein quality control system. Misfolded proteins generated in the ER are degraded by the ER-associated degradation (ERAD). Yeast Mnl1p consists of an N-terminal mannosidase homology domain and a less conserved C-terminal domain and facilitates the ERAD of glycoproteins. We found that Mnl1p is an ER luminal protein with a cleavable signal sequence and stably interacts with a protein-disulfide isomerase (PDI). Analyses of a series of Mnl1p mutants revealed that interactions between the C-terminal domain of Mnl1p and PDI, which include an intermolecular disulfide bond, are essential for subsequent introduction of a disulfide bond into the mannosidase homology domain of Mnl1p by PDI. This disulfide bond is essential for the ERAD activity of Mnl1p and in turn stabilizes the prolonged association of PDI with Mnl1p. Close interdependence between Mnl1p and PDI suggests that these two proteins form a functional unit in the ERAD pathway.