EMBO Reports最新文献

The lymphocyte immune response begins with antigen recognition on antigen-presenting cells, leading to the formation of the immunological synapse-a specialized interface for biochemical and biophysical exchange. At the synapse, most antigen-engaged receptor microclusters move inward toward the central supramolecular activation cluster (cSMAC) via retrograde F-actin flow, eventually clearing from the cell surface. This retrograde movement and receptor downregulation maintain antigen receptor homeostasis, critical for adaptive immunity, though its regulation remains unclear. Using live T cells, we identify a significant pool of antigen-engaged microclusters moving anterogradely toward the cell periphery, rather than the cSMAC. This movement is driven by actin waves propagating outward and coupling to microclusters through the Wiskott-Aldrich Syndrome Protein. These findings reveal a previously unrecognized mode of actin dynamics-anterograde actin waves-that co-exist with retrograde flow and direct microclusters away from the downregulation zone. This dual actin behavior underscores the complex cytoskeletal mechanisms T cells employ to regulate receptor distribution and maintain signaling homeostasis during immune activation.

Astrocytes, the most abundant glial cell type in the central nervous system, have traditionally been viewed from the perspective of metabolic support, particularly supplying neurons with lactate via glycolysis. This view has focused heavily on glucose metabolism as the primary mode of sustaining neuronal function. However, recent research challenges this paradigm by positioning astrocytes as dynamic metabolic hubs that actively engage in lipid metabolism, especially mitochondrial fatty acid β-oxidation. Far from serving solely as an energy source, fatty acid ß-oxidation in astrocytes orchestrates reactive oxygen species-mediated signaling pathways that modulate neuron-glia communication and cognitive outcomes. This review integrates recent advances on astrocytic fatty acid ß-oxidation and ketogenesis, alongside other metabolic pathways converging on reactive oxygen species dynamics, including cholesterol metabolism and peroxisomal β-oxidation. In reframing astrocytic metabolism from energy provision to signaling, we propose new directions for understanding central nervous system function and dysfunction.

Cell surface glycoproteins Basigin or embigin form heterodimers with monocarboxylate transporters (MCTs), enhancing their membrane trafficking and modulating their transport functions. Cancer cells often reprogram their metabolism and depend on proton-coupled lactate transport mediated by MCTs to sustain their glycolytic state and to maintain intracellular pH. A deeper understanding of MCTs regulation may open avenues for the development of novel inhibitors, potentially applicable in clinical settings. Here, we determine the cryo-EM structures of the human MCT2-embigin complex in both apo and AR-C155858-bound states and observe that embigin engages in extensive interactions with MCT2, facilitating its localization to the plasma membrane and substrate transport. Given the high structural conservation among MCTs, we conduct virtual screening based on MCT1/2 structures and identify Tucatinib as an effective inhibitor of pyruvate transport mediated by both MCT1 and MCT2. We show that Tucatinib potently inhibits the proliferation and migration of cervical tumor cells in vitro and tumor growth in a mouse xenograft model, while exhibiting excellent biological safety. These findings offer molecular insights into the structural and functional mechanism of MCT2 and identify Tucatinib as novel dual inhibitor of both transporters.

The mechanisms regulating gamete fusion and preventing polyspermy in mammalian fertilization remain incompletely understood. This study combines real-time imaging, confocal microscopy and statistical analysis to investigate fertilization and polyspermy prevention dynamics in mice. By tracking the behavior of over one hundred spermatozoa entering the perivitelline space of oocytes, we dissect the respective contributions of oocyte structures (zona pellucida (ZP), perivitelline space (PVS), oolemma) and sperm components (head, flagellum) to fertilization and polyspermy prevention. We find that fertilization requires specific sperm head movements on the oolemma, driven by flagellar beating and facilitated by trapping the flagellum in the ZP, revealing a novel role for this structure. Our kinetic analysis characterizes a slow "penetration block" that gradually limits sperm entry into the PVS and a faster "fusion block" that prevents further fusion events. As the penetration block becomes significant after the fusion block is established, only the latter effectively prevents polyspermy in mice. We propose that it acts through neutralization of excess sperm in the PVS by oocyte-derived proteins CD9 and JUNO coating non-fertilizing spermatozoa.

Hematopoietic stem and progenitor cells (HSPCs) emerge from arterial endothelial cells (ECs) through a process termed endothelial-to-hematopoietic-transition (EHT), a process induced by paracrine signals and driven by a transcriptional cascade. Despite inductive signals being broadly received by ECs in the dorsal aorta (DA), only a subset of ECs undergoes EHT, while others maintain their vascular identity. The molecular mechanisms that determine this selective fate decision remain poorly understood. Here, we discover Apelin signaling as a critical regulator of cell fates in the DA, acting as a molecular switch to balance vascular and hematopoietic identities. We show that Apelin receptor (Aplnr)-expressing ECs retain their arterial identity, while Aplnr non-expressing ECs are primed to become hemogenic endothelial cells (HECs) and transition into HSPCs. Loss of Apelin signaling leads to excessive EC-to-HEC conversion and increased HSPC numbers. Conversely, forced Aplnr expression abolishes HSPC formation by maintaining EC identity. These findings reveal that Apelin signaling regulates HSPC formation by preserving endothelial identity. In summary, our findings establish Apelin signaling as a critical regulator for balancing endothelial and hematopoietic fates.

Mouse embryonic stem cells (mESCs), in addition to differentiating into the three germ layers, can reverse typical developmental trajectories, as exemplified by their ability to de-differentiate into 2-cell-like cells (2CLCs) that resemble the mammalian embryo during zygotic genome activation (ZGA). This unique property offers the opportunity to elucidate the molecular principles that govern the pre-implantation stages of mammalian development. Here, we dissect the functions of the chromatin repressor EHMT2, a candidate antagonist of the mESC-to-2CLC transition, by leveraging a multipurpose allele for acute protein depletion and efficient immunoprecipitation. Our experiments revealed distinct principles of EHMT2-mediated gene repression in mESCs based on specific chromatin binding patterns and protein co-factors. Most notably, EHMT2 directly represses large clusters of co-regulated gene loci that comprise a significant fraction of the 2CLC-specific transcriptome by initiating H3K9me2 spreading from distal LINE-1 elements. EHMT2 counteracts the recruitment of the activator DPPA2/4 to promoter-proximal endogenous retroviral elements (ERVs) at 2CLC genes. EHMT2 depletion enhances the expression of ZGA-associated transcripts in 2CLCs and synergizes with spliceosome inhibition and retinoic acid signaling to facilitate the mESC-to-2CLC transition. In contrast to ZGA-associated genes, the repression of germ layer-associated transcripts by EHMT2 occurs outside of gene clusters, in collaboration with ZFP462, and involves binding to non-repetitive candidate enhancers. Our observations provide novel mechanistic insight into how pluripotent cells achieve attenuation of their bidirectional differentiation potential and reveal unique transcriptional features of murine totipotent cells.

Mild rupture of aged erythrocytes occurs in the spleen, resulting in hemoglobin (Hb) release, whereas pathological hemolysis characterizes several diseases. Hb detoxification is attributed to macrophages, but other routes of Hb clearance remain elusive. Here, we uncover that Hb uptake is chiefly executed by liver sinusoidal endothelial cells (LSECs) via macropinocytosis. Consistently, LSECs display proteomic signatures indicative of heme catabolism, ferritin iron storage, antioxidant defense, and macropinocytic capacity, alongside high iron content and expression of the iron exporter ferroportin. Erythrocyte/Hb transfusion assays demonstrate that splenic macrophages excel in erythrophagocytosis, while LSECs and Kupffer cells scavenge the spleen-borne hemolysis products Hb and erythrocyte membranes, respectively. High Hb doses result in transient hepatic iron retention, LSEC-specific induction of heme-catabolizing Hmox1, along with the iron-sensing Bmp6-hepcidin axis culminating in hypoferremia. Transcriptional induction of Bmp6 in LSECs is phenocopied by erythrocyte lysis upon phenylhydrazine and elicits a distinct transcriptional signature compared to iron. Collectively, we identify LSECs as key Hb scavengers, a function that establishes the spleen-to-liver axis for iron recycling and contributes to heme detoxification during hemolysis.