Search

The Keap1–Nrf2 pathway is an evolutionarily conserved mechanism that protects cells from oxidative stress and electrophiles. Keap1 is a repressor of Nrf2 in normal cellular conditions but also a stress sensor for Nrf2 activation. Interestingly, fish and amphibians have two Keap1s (Keap1a and Keap1b), of which Keap1b is the ortholog of mammalian Keap1. Keap1a, on the other hand, is a gene found only in fish and amphibians, having been lost during the evolution to amniotes. We have previously shown that keap1b-knockout zebrafish have increased Nrf2 activity and reduced response to certain Nrf2-activating compounds but that they grow normally to adulthood. This may be because the remaining keap1a suppresses the hyperactivation of Nrf2, which is responsible for the post-natal lethality of Keap1-knockout mice. In this study, we analyzed keap1a;keap1b-double-knockout zebrafish to test this hypothesis. We found that keap1a;keap1b-double-knockout zebrafish, like Keap1-knockout mice, showed eating defects and were lethal within a week of hatching. Genetic introduction of the Nrf2 mutation rescued both the eating defects and the larval lethality, indicating that Nrf2 hyperactivation is the cause. However, unlike Keap1-knockout mice, keap1a;keap1b-double-knockout zebrafish showed no physical blockage of the food pathway; moreover, the cause of death was not directly related to eating defects. RNA-sequencing analysis revealed that keap1a;keap1b-double-knockout larvae showed extraordinarily high expression of known Nrf2-target genes as well as decreased expression of visual cycle genes. Finally, trigonelline or brusatol partially rescued the lethality of keap1a;keap1b-double-knockout larvae, suggesting that they can serve as an in vivo evaluation system for Nrf2-inhibiting compounds.

Necrosis, a form of cell death, occurs not only with the development of various diseases but also with a tumor tissue response to cancer treatment. Therefore, pursuing progress for cancer therapy through induction of necrosis may be one of the most effective approaches for cancer eradication. We herein describe the development of a real-time imaging system to visualize intratumoral necrosis. The system is composed of two types of cells expressing either one of two necrosis imaging reporters that consist of a DnaE intein sequence linking to one of two split-luciferase fragments. When necrosis occurs in a tumor composed of both of the cells, the two types of leaked reporters can reconstitute the enzymatic activity as a result of protein trans-splicing and thereby emit bioluminescence in the presence of the substrate. This system, which was constructed with shrimp-derived luciferase, allowed in vitro imaging of necrosis. We further confirmed real-time imaging of intratumoral necrosis caused by physical or chemical tissue disruption, validating its application in in vivo necrosis imaging. Thus, the constructed imaging system could be a powerful tool for the optimization of the therapeutic condition for cancer therapy and for the evaluation of novel anticancer drugs targeting necrosis.

Summary: Brain development is a highly orchestrated process requiring spatiotemporally regulated mitochondrial dynamics. Drp1, a key molecule in the mitochondrial fission machinery, undergoes various post-translational modifications including conjugation to the small ubiquitin-like modifier (SUMO). However, the functional significance of SUMOylation/deSUMOylation on Drp1 remains controversial. SUMO-specific protease 5 (Senp5L) catalyzes the deSUMOylation of Drp1. We revealed that a splicing variant of Senp5L, Senp5S, which lacks peptidase activity, prevents deSUMOylation of Drp1 by competing against other Senps. The altered SUMOylation level of Drp1 induced by Senp5L/5S affects mitochondrial morphology probably through controlling Drp1 ubiquitination and tubulation of the endoplasmic reticulum. A dynamic SUMOylation/deSUMOylation balance controls neuronal polarization and migration during the development of the cerebral cortex. These findings suggest a novel role of post-translational modification, in which deSUMOylation enzyme isoforms competitively regulate mitochondrial dynamics via Drp1 SUMOylation levels, in a tightly controlled process of neuronal differentiation and corticogenesis.

Summary: Engagement of neural stem/progenitor cells (NSPCs) into proper neuronal differentiation requires the spatiotemporally regulated generation of metabolites. Purines are essential building blocks for many signaling molecules. Enzymes that catalyze de novo purine synthesis are assembled as a huge multienzyme complex called “purinosome.” However, there is no evidence of the formation or physiological function of the purinosome in the brain. Here, we showed that a signal transduction ATPases with numerous domains (STAND) protein, NACHT and WD repeat domain-containing 1 (Nwd1), interacted with Paics, a purine-synthesizing enzyme, to regulate purinosome assembly in NSPCs. Altered Nwd1 expression affected purinosome formation and induced the mitotic exit and premature differentiation of NSPCs, repressing neuronal migration and periventricular heterotopia. Overexpression/knockdown of Paics or Fgams, other purinosome enzymes, in the developing brain resulted in a phenocopy of Nwd1 defects. These findings indicate that strict regulation of purinosome assembly/disassembly is crucial for maintaining NSPCs and corticogenesis.

Background: Kommerell's diverticulum with Stanford type A aortic dissection is a relatively rare condition. There is currently no standard treatment strategy for Kommerell's diverticulum. We herein report our surgical strategy with a review of literature for a case of Kommerell's diverticulum that developed acute aortic dissection. Case presentation: A 54-year-old woman was referred to our hospital after being diagnosed with Stanford type A acute aortic dissection at the hospital where she was admitted for chest and back pain. Contrast-enhanced computed tomography showed a right and left common carotid and left subclavian artery branching from the aortic arch; Kommerell's diverticulum and an aberrant right subclavian artery (RSCA) arising from it were noted in the distal arch. The contralateral aortic wall where Kommerell's diverticulum was located was the entry, resulting in aortic dissection, with retrograde dissection extending into the ascending aorta. Partial thrombosis was detected in the false lumen of the ascending aorta. The dissection extended from the ascending aorta to the common iliac artery. In addition, the thrombosed false lumen in the left common iliac artery was considered to have caused dynamic obstruction due to compression and narrowing of the true lumen. Based on these findings, total arch replacement with reconstruction of the 4-branched vessels in the arch, including an aberrant RSCA, the frozen elephant trunk technique, and femoro-femoral bypass for malperfusion of the left lower extremity were performed with deep hypothermic circulatory arrest. An artificial graft was anastomosed to the right axillary artery, which was used as the blood supply route for cardiopulmonary bypass. After cooling to hypothermia, the central portion of the aberrant right subclavian artery was clipped on the right side of the trachea. Thus, cerebral blood flow was maintained via the right vertebral artery, the aortic arch was opened, and cannulas for selective cerebral perfusion were inserted into the right common carotid artery, the left common carotid artery, and the left subclavian artery. After each vessel was reconstructed, the graft that had been anastomosed to the right axillary artery was anastomosed to the graft used for reconstruction of the right common carotid artery. The patient's postoperative course was generally good. Conclusion: The strategy used by us effectively created transient occlusion of the origin of Kommerell's diverticulum and the primary entry. Our results indicate that this method is feasible and effective for cases in which in situ reconstruction of the branch may be challenging.