AMPK and mTOR play principal roles in governing metabolic programs; however, mechanisms underlying the coordination of the two inversely regulated kinases remain unclear. In this study we found, most surprisingly, that the late endosomal/lysosomal protein complex v-ATPase-Ragulator, essential for activation of mTORC1, is also required for AMPK activation. We also uncovered that AMPK is a residential protein of late endosome/lysosome. Under glucose starvation, the v-ATPase-Ragulator complex is accessible to AXIN/LKB1 for AMPK activation. Concurrently, the guanine nucleotide exchange factor (GEF) activity of Ragulator toward RAG is inhibited by AXIN, causing dissociation from endosome and inactivation of mTORC1. We have thus revealed that the v-ATPase-Ragulator complex is also an initiating sensor for energy stress and meanwhile serves as an endosomal docking site for LKB1-mediated AMPK activation by forming the v-ATPase-Ragulator-AXIN/LKB1-AMPK complex, thereby providing a switch between catabolism and anabolism. Our current study also emphasizes a general role of late endosome/lysosome in controlling metabolic programs.

Galectin-3 is a β-galactoside-binding protein implicated in diverse biological processes. We found that galectin-3 induced human monocyte migration in vitro in a dose-dependent manner, and it was chemotactic at high concentrations (1.0 μM) but chemokinetic at low concentrations (10–100 nM). Galectin-3-induced monocyte migration was inhibited by its specific mAb and was blocked by lactose and a C-terminal domain fragment of the protein, indicating that both the N-terminal and C-terminal domains of galectin-3 are involved in this activity. Pertussis toxin (PTX) almost completely blocked monocyte migration induced by high concentrations of galectin-3. Galectin-3 caused a Ca2+ influx in monocytes at high, but not low, concentrations, and both lactose and PTX inhibited this response. There was no cross-desensitization between galectin-3 and any of the monocyte-reactive chemokines examined, including monocyte chemotactic protein-1, macrophage inflammatory protein-1α, and stromal cell-derived factor-1α. Cultured human macrophages and alveolar macrophages also migrated toward galectin-3, but not monocyte chemotactic protein-1. Finally, galectin-3 was found to cause monocyte accumulation in vivo in mouse air pouches. These results indicate that galectin-3 is a novel chemoattractant for monocytes and macrophages and suggest that the effect is mediated at least in part through a PTX-sensitive (G protein-coupled) pathway.

Galectin-3 is a member of a growing family of beta-galactoside-binding animal lectins. Previous studies have demonstrated a variety of biological activities for this protein in vitro, including activation of cells, modulation of cell adhesion, induction of pre-mRNA splicing, and regulation of apoptosis. To assist in fully elucidating the physiological and pathological functions of this protein, we have generated galectin-3-deficient (gal3(-/-)) mice by targeted interruption of the galectin-3 gene. Gal3(-/-) mice consistently developed fewer inflammatory cell infiltrations in the peritoneal cavities than the wild-type (gal3(+/+)) mice in response to thioglycollate broth treatment, mainly due to lower numbers of macrophages. Also, when compared to cells from gal3(+/+) mice, thioglycollate-elicited inflammatory cells from gal3(-/-) mice exhibited significantly lower levels of NF-kappaB response. In addition, dramatically different cell-spreading phenotypes were observed in cultured macrophages from the two genotypes. Whereas macrophages from gal3(+/+) mice exhibited well spread out morphology, those from gal3(-/-) mice were often spindle-shaped. Finally, we found that peritoneal macrophages from gal3(-/-) mice were more prone to undergo apoptosis than those from gal3(+/+) mice when treated with apoptotic stimuli, suggesting that expression of galectin-3 in inflammatory cells may lead to longer cell survival, thus prolonging inflammation. These results strongly support galectin-3 as a positive regulator of inflammatory responses in the peritoneal cavity.

N6-methyladenosine (m6A) is the most abundant epigenetic modification in eukaryotic mRNAs and is essential for multiple RNA processing events during mammalian development and disease control. Here we show that conditional knockout of the m6A methyltransferase Mettl3 in bone marrow mesenchymal stem cells (MSCs) induces pathological features of osteoporosis in mice. Mettl3 loss-of-function results in impaired bone formation, incompetent osteogenic differentiation potential and increased marrow adiposity. Moreover, Mettl3 overexpression in MSCs protects the mice from estrogen deficiency-induced osteoporosis. Mechanistically, we identify PTH (parathyroid hormone)/Pth1r (parathyroid hormone receptor-1) signaling axis as an important downstream pathway for m6A regulation in MSCs. Knockout of Mettl3 reduces the translation efficiency of MSCs lineage allocator Pth1r, and disrupts the PTH-induced osteogenic and adipogenic responses in vivo. Our results demonstrate the pathological outcomes of m6A mis-regulation in MSCs and unveil novel epitranscriptomic mechanism in skeletal health and diseases.

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Galectin-3 is a member of a large family of animal lectins. This protein is expressed abundantly by macrophages, but its function in this cell type is not well understood. We have studied the effect of galectin-3 gene targeting on phagocytosis, a major function of macrophages. Compared with wild-type macrophages, galectin-3-deficient (gal3-/-) cells exhibited reduced phagocytosis of IgG-opsonized erythrocytes and apoptotic thymocytes in vitro. In addition, gal3-/- mice showed attenuated phagocytic clearance of apoptotic thymocytes by peritoneal macrophages in vivo. These mice also exhibited reduced IgG-mediated phagocytosis of erythrocytes by Kupffer cells in a murine model of autoimmune hemolytic anemia. Additional experiments indicate that extracellular galectin-3 does not contribute appreciably to the phagocytosis-promoting function of this protein. Confocal microscopic analysis of macrophages containing phagocytosed erythrocytes revealed localization of galectin-3 in phagocytic cups and phagosomes. Furthermore, gal3-/- macrophages exhibited a lower degree of actin rearrangement upon Fcgamma receptor crosslinkage. These results indicate that galectin-3 contributes to macrophage phagocytosis through an intracellular mechanism. Thus, galectin-3 may play an important role in both innate and adaptive immunity by contributing to phagocytic clearance of microorganisms and apoptotic cells

Galectin-3 is a member of a ␤-galactoside-binding animal lectin family. Previous in vitro studies have demonstrated that galectin-3 is involved in a number of activities; however, the roles of this lectin in physiological and pathological processes in vivo remain to be elucidated. Herein, we show, in a murine model of ovalbumin (OVA)-induced asthma that 1) peribronchial inflammatory cells expressed large amounts of galectin-3; 2) bronchoalveolar lavage fluid from OVAchallenged mice contained significantly higher levels of galectin-3 compared to control mice; and 3) macrophages in bronchoalveolar lavage fluid were the major cell type that contained galectin-3. We investigated the role of galectin-3 in the allergic airway response by comparing galectin-3-deficient (gal3 ؊/؊ ) mice and wild-type (gal3 ؉/؉ ) mice. OVA-sensitized gal3 ؊/؊ mice developed fewer eosinophils and lower goblet cell metaplasia, after airway OVA challenge compared to similarly treated gal3 ؉/؉ mice. In addition, the OVA-sensitized gal3 ؊/؊ mice developed significantly less airway hyperresponsiveness after airway OVA challenge compared to gal3 ؉/؉ mice. Finally, gal3 ؊/؊ mice developed a lower Th2 response, but a higher Th1 response, suggesting that galectin-3 regulates the Th1/Th2 response. We conclude that galectin-3 may play an important role in the pathogenesis of asthma and inhibitors of this lectin may prove useful for treatment of this disease.

Background Breast cancer angiogenesis is key for metastasis and predicts a poor prognosis. Angiotensin-converting enzyme 2 (ACE2), as a member of the renin-angiotensin system (RAS), was reported to restrain the progression of hepatocellular carcinoma (HCC) and non-small cell lung cancer (NSCLC) through inhibiting angiogenesis. However, the relationship between ACE2 and breast cancer angiogenesis remains unclear. Methods The prognosis and relative gene selection were analysed using the GEPIA, GEO, TCGA and STRING databases. ACE2 expression in breast cancer tissue was estimated by reverse transcription-quantitative polymerase chain reaction (qPCR). Breast cancer cell migration, proliferation and angiogenesis were assessed by Transwell migration, proliferation, tube formation, and wound healing assays. The expression of vascular endothelial growth factor A (VEGFa) was detected by qPCR and Western blotting. The phosphorylation of vascular endothelial growth factor receptor 2 (VEGFR2), mitogen-activated protein kinase 1/2 (MEK1/2), and extracellular signal-regulated protein kinase 1/2 (ERK1/2) was examined by Western blotting. Breast cancer metastasis and angiogenesis in vivo were measured using a zebrafish model. Results ACE2 was downregulated in breast cancer patients. Patients with higher ACE2 expression had longer relapse-free survival (RFS). In vitro, ACE2 inhibited breast cancer migration. Meanwhile, ACE2 in breast cancer cells inhibited human umbilical vascular endothelial cell (HUVEC) proliferation, tube formation and migration. In the zebrafish model, ACE2 inhibited breast cancer cell metastasis, as demonstrated by analyses of the number of disseminated foci and the metastatic distance. Neo-angiogenesis was also decreased by ACE2. ACE2 downregulated the expression of VEGFa in breast cancer cells. Furthermore, ACE2 in breast cancer cells inactivated the phosphorylation of VEGFR2, MEK1/2, and ERK1/2 in HUVECs. Conclusions Our findings suggest that ACE2, as a potential resister to breast cancer, might inhibit breast cancer angiogenesis through the VEGFa/VEGFR2/ERK pathway. Trial registration Retrospectively registered. Electronic supplementary material The online version of this article (10.1186/s13046-019-1156-5) contains supplementary material, which is available to authorized users.