Isl1βと膵β細胞に重要な転写因子の過剰発現は、肝臓でのグルコース応答性インスリン産生及び分泌を促進する

筑波大学 (University of Tsukuba)201

Isl1βと膵β細胞に重要な転写因子の過剰発現は、肝臓でのグルコース応答性インスリン産生及び分泌を促進する

筑波大学 (University of Tsukuba)201

Co-chaperone BAG2 Determines the Pro-oncogenic Role of Cathepsin B in Triple-Negative Breast Cancer Cells

Triple-negative breast cancer (TNBC) is considered incurable with currently available treatments, highlighting the need for therapeutic targets and predictive biomarkers. Here, we report a unique role for Bcl-2-associated athanogene 2 (BAG2), which is significantly overexpressed in TNBC, in regulating the dual functions of cathepsin B as either a pro- or anti-oncogenic enzyme. Silencing BAG2 suppresses tumorigenesis and lung metastasis and induces apoptosis by increasing the intracellular mature form of cathepsin B, whereas BAG2 expression induces metastasis by blocking the auto-cleavage processing of pro-cathepsin B via interaction with the propeptide region. BAG2 regulates pro-cathepsin B/annexin II complex formation and facilitates the trafficking of pro-cathespin-B-containing TGN38-positive vesicles toward the cell periphery, leading to the secretion of pro-cathepsin B, which induces metastasis. Collectively, our results uncover BAG2 as a regulator of the oncogenic function of pro-cathepsin B and a potential diagnostic and therapeutic target that may reduce the burden of metastatic breast cancer

A context-specific circadian clock in adipocyte precursor cells modulates adipogenesis

The circadian clock is an intricate molecular network that paces a variety of physiological process to ~ 24 hour day/night cycles. Whereas the central circadian clock in the brain is primarily entrained by light signals, peripheral circadian clocks, which are in most cells in the body, receive cues not only from the central pacemaker but also endocrine and other systemic and tissue-specific signals. Prior studies have connected peripheral circadian clocks to metabolism, primarily with studies focused on the robust clock in the liver that responds to feeding/fasting cycles. Adipose tissue is also critical for metabolism and adipocytes have circadian clocks. Yet, the role of the circadian clock in adipocytes is poorly understood. Here we describe our studies that revealed components of the circadian clock in primary adipocyte precursor cells (APCs) in mice. We made the surprising discovery of a particularly prominent role for the circadian gene Period 3 (Per3) in the APC clock. Furthermore, we elucidated that Per3 directly regulates an output pathway of the APC clock to modulate the expression of the Kruppel-like factor 15 (Klf15) gene. Finally, we discovered that this clock-Klf15 pathway regulates adipogenesis in APCs. These finding have important implications for our understanding of adipose tissue biology and metabolism and, we speculate, will generate opportunities to develop novel therapeutic strategies based on the context-specific features of the circadian clock in APCs

Candesartan, an angiotensin-II receptor blocker, ameliorates insulin resistance and hepatosteatosis by reducing intracellular calcium overload and lipid accumulation

Abstract Insulin resistance is a major contributor to the pathogenesis of several human diseases, including type 2 diabetes, hypertension, and hyperlipidemia. Notably, insulin resistance and hypertension share common abnormalities, including increased oxidative stress, inflammation, and organelle dysfunction. Recently, we showed that excess intracellular Ca2+, a known pathogenic factor in hypertension, acts as a critical negative regulator of insulin signaling by forming Ca2+-phosphoinositides that prevent the membrane localization of AKT, a key serine/threonine kinase signaling molecule. Whether preventing intracellular Ca2+ overload improves insulin sensitivity, however, has not yet been investigated. Here, we show that the antihypertensive agent candesartan, compared with other angiotensin-II receptor blockers, has previously unrecognized beneficial effects on attenuating insulin resistance. We found that candesartan markedly reduced palmitic acid (PA)-induced intracellular Ca2+ overload and lipid accumulation by normalizing dysregulated store-operated channel (SOC)-mediated Ca2+ entry into cells, which alleviated PA-induced insulin resistance by promoting insulin-stimulated AKT membrane localization and increased the phosphorylation of AKT and its downstream substrates. As pharmacological approaches to attenuate intracellular Ca2+ overload in vivo, administering candesartan to obese mice successfully decreased insulin resistance, hepatic steatosis, dyslipidemia, and tissue inflammation by inhibiting dysregulated SOC-mediated Ca2+ entry and ectopic lipid accumulation. The resulting alterations in the phosphorylation of key signaling molecules consequently alleviate impaired insulin signaling by increasing the postprandial membrane localization and phosphorylation of AKT. Thus, our findings provide robust evidence for the pleiotropic contribution of intracellular Ca2+ overload in the pathogenesis of insulin resistance and suggest that there are viable approved drugs that can be repurposed for the treatment of insulin resistance and hypertension

Mapping transcriptional heterogeneity and metabolic networks in fatty livers at single-cell resolution

Summary: Non-alcoholic fatty liver disease is a heterogeneous disease with unclear underlying molecular mechanisms. Here, we perform single-cell RNA sequencing of hepatocytes and hepatic non-parenchymal cells to map the lipid signatures in mice with non-alcoholic fatty liver disease (NAFLD). We uncover previously unidentified clusters of hepatocytes characterized by either high or low srebp1 expression. Surprisingly, the canonical lipid synthesis driver Srebp1 is not predictive of hepatic lipid accumulation, suggestive of other drivers of lipid metabolism. By combining transcriptional data at single-cell resolution with computational network analyses, we find that NAFLD is associated with high constitutive androstane receptor (CAR) expression. Mechanistically, CAR interacts with four functional modules: cholesterol homeostasis, bile acid metabolism, fatty acid metabolism, and estrogen response. Nuclear expression of CAR positively correlates with steatohepatitis in human livers. These findings demonstrate significant cellular differences in lipid signatures and identify functional networks linked to hepatic steatosis in mice and humans

Generation of Insulin-Producing Cells from the Mouse Liver Using β Cell-Related Gene Transfer Including <i>Mafa</i> and <i>Mafb</i>

<div><p>Recent studies on the large Maf transcription factors have shown that <i>Mafb</i> and <i>Mafa</i> have respective and distinctive roles in β-cell development and maturation. However, whether this difference in roles is due to the timing of the gene expression (roughly, expression of <i>Mafb</i> before birth and of <i>Mafa</i> after birth) or to the specific function of each gene is unclear. Our aim was to examine the functional differences between these genes that are closely related to β cells by using an <i>in vivo</i> model of β-like cell generation. We monitored insulin gene transcription by measuring bioluminescence emitted from the liver of insulin promoter-luciferase transgenic (MIP-Luc-VU) mice. Adenoviral gene transfers of <i>Pdx1/Neurod/Mafa</i> (PDA) and <i>Pdx1/Neurod/Mafb</i> (PDB) combinations generated intense luminescence from the liver that lasted for more than 1 week and peaked at 3 days after transduction. The peak signal intensities of PDA and PDB were comparable. However, PDA but not PDB transfer resulted in significant bioluminescence on day 10, suggesting that <i>Mafa</i> has a more sustainable role in insulin gene activation than does <i>Mafb</i>. Both PDA and PDB transfers ameliorated the glucose levels in a streptozotocin (STZ)-induced diabetic model for up to 21 days and 7 days, respectively. Furthermore, PDA transfer induced several gene expressions necessary for glucose sensing and insulin secretion in the liver on day 9. However, a glucose tolerance test and liver perfusion experiment did not show glucose-stimulated insulin secretion from intrahepatic β-like cells. These results demonstrate that bioluminescence imaging in MIP-Luc-VU mice provides a noninvasive means of detecting β-like cells in the liver. They also show that <i>Mafa</i> has a markedly intense and sustained role in β-like cell production in comparison with <i>Mafb</i>.</p></div

Bioluminescence emission from the hepatic region of MIP-Luc-VU mice after β cell-related gene transfer.

<p>(A) Diagrammatic representation of bioluminescence monitoring of insulin transcriptional activity. (B) Representative example of dose-dependent bioluminescence emission from the hepatic region. (C) Bioluminescence images of the abdominal section of MIP-Luc-VU mice 3 days after infection. (D) Tissue sections of MIP-Luc-VU liver stained with anti-luciferase antibody with 4′,6-diamidino-2-phenylindole (DAPI) 3 days after gene transfer. Scale bar indicates 100 µm.</p