mTORC1 to AMPK switching underlies β-cell metabolic plasticity during maturation and diabetes.

Pancreatic beta cells (β-cells) differentiate during fetal life, but only postnatally acquire the capacity for glucose-stimulated insulin secretion (GSIS). How this happens is not clear. In exploring what molecular mechanisms drive the maturation of β-cell function, we found that the control of cellular signaling in β-cells fundamentally switched from the nutrient sensor target of rapamycin (mTORC1) to the energy sensor 5'-adenosine monophosphate-activated protein kinase (AMPK), and that this was critical for functional maturation. Moreover, AMPK was activated by the dietary transition taking place during weaning, and this in turn inhibited mTORC1 activity to drive the adult β-cell phenotype. While forcing constitutive mTORC1 signaling in adult β-cells relegated them to a functionally immature phenotype with characteristic transcriptional and metabolic profiles, engineering the switch from mTORC1 to AMPK signaling was sufficient to promote β-cell mitochondrial biogenesis, a shift to oxidative metabolism, and functional maturation. We also found that type 2 diabetes, a condition marked by both mitochondrial degeneration and dysregulated GSIS, was associated with a remarkable reversion of the normal AMPK-dependent adult β-cell signature to a more neonatal one characterized by mTORC1 activation. Manipulating the way in which cellular nutrient signaling pathways regulate β-cell metabolism may thus offer new targets to improve β-cell function in diabetes

Loss of Liver Kinase B1 (LKB1) in Beta Cells Enhances Glucose-stimulated Insulin Secretion Despite Profound Mitochondrial Defects

The tumor suppressor liver kinase B1 (LKB1) is an important regulator of pancreatic β cell biology. LKB1-dependent phosphorylation of distinct AMPK (adenosine monophosphate-activated protein kinase) family members determines proper β cell polarity and restricts β cell size, total β cell mass, and glucose-stimulated insulin secretion (GSIS). However, the full spectrum of LKB1 effects and the mechanisms involved in the secretory phenotype remain incompletely understood. We report here that in the absence of LKB1 in β cells, GSIS is dramatically and persistently improved. The enhancement is seen both in vivo and in vitro and cannot be explained by altered cell polarity, increased β cell number, or increased insulin content. Increased secretion does require membrane depolarization and calcium influx but appears to rely mostly on a distal step in the secretion pathway. Surprisingly, enhanced GSIS is seen despite profound defects in mitochondrial structure and function in LKB1-deficient β cells, expected to greatly diminish insulin secretion via the classic triggering pathway. Thus LKB1 is essential for mitochondrial homeostasis in β cells and in parallel is a powerful negative regulator of insulin secretion. This study shows that β cells can be manipulated to enhance GSIS to supra-normal levels even in the face of defective mitochondria and without deterioration over months

LKB1 and AMPK differentially regulate pancreatic β-cell identity.

Fully differentiated pancreatic β cells are essential for normal glucose homeostasis in mammals. Dedifferentiation of these cells has been suggested to occur in type 2 diabetes, impairing insulin production. Since chronic fuel excess ("glucotoxicity") is implicated in this process, we sought here to identify the potential roles in β-cell identity of the tumor suppressor liver kinase B1 (LKB1/STK11) and the downstream fuel-sensitive kinase, AMP-activated protein kinase (AMPK). Highly β-cell-restricted deletion of each kinase in mice, using an Ins1-controlled Cre, was therefore followed by physiological, morphometric, and massive parallel sequencing analysis. Loss of LKB1 strikingly (2.0-12-fold, E<0.01) increased the expression of subsets of hepatic (Alb, Iyd, Elovl2) and neuronal (Nptx2, Dlgap2, Cartpt, Pdyn) genes, enhancing glutamate signaling. These changes were partially recapitulated by the loss of AMPK, which also up-regulated β-cell "disallowed" genes (Slc16a1, Ldha, Mgst1, Pdgfra) 1.8- to 3.4-fold (E<0.01). Correspondingly, targeted promoters were enriched for neuronal (Zfp206; P=1.3×10(-33)) and hypoxia-regulated (HIF1; P=2.5×10(-16)) transcription factors. In summary, LKB1 and AMPK, through only partly overlapping mechanisms, maintain β-cell identity by suppressing alternate pathways leading to neuronal, hepatic, and other characteristics. Selective targeting of these enzymes may provide a new approach to maintaining β-cell function in some forms of diabetes.-Kone, M., Pullen, T. J., Sun, G., Ibberson, M., Martinez-Sanchez, A., Sayers, S., Nguyen-Tu, M.-S., Kantor, C., Swisa, A., Dor, Y., Gorman, T., Ferrer, J., Thorens, B., Reimann, F., Gribble, F., McGinty, J. A., Chen, L., French, P. M., Birzele, F., Hildebrandt, T., Uphues, I., Rutter, G. A. LKB1 and AMPK differentially regulate pancreatic β-cell identity

The emerging role of AMPK in the regulation of breathing and oxygen supply

Regulation of breathing is critical to our capacity to accommodate deficits in oxygen availability and demand during, for example, sleep and ascent to altitude. It is generally accepted that a fall in arterial oxygen increases afferent discharge from the carotid bodies to the brainstem and thus delivers increased ventilatory drive, which restores oxygen supply and protects against hypoventilation and apnoea. However, the precise molecular mechanisms involved remain unclear. We recently identified as critical to this process the AMP-activated protein kinase (AMPK), which is key to the cell-autonomous regulation of metabolic homoeostasis. This observation is significant for many reasons, not least because recent studies suggest that the gene for the AMPK-α1 catalytic subunit has been subjected to natural selection in high-altitude populations. It would appear, therefore, that evolutionary pressures have led to AMPK being utilized to regulate oxygen delivery and thus energy supply to the body in the short, medium and longer term. Contrary to current consensus, however, our findings suggest that AMPK regulates ventilation at the level of the caudal brainstem, even when afferent input responses from the carotid body are normal. We therefore hypothesize that AMPK integrates local hypoxic stress at defined loci within the brainstem respiratory network with an index of peripheral hypoxic status, namely afferent chemosensory inputs. Allied to this, AMPK is critical to the control of hypoxic pulmonary vasoconstriction and thus ventilation–perfusion matching at the lungs and may also determine oxygen supply to the foetus by, for example, modulating utero-placental blood flow

Pancreatic beta cells express the fetal islet hormone gastrin in rodent and human diabetes

Beta-cell failure in type 2 diabetes (T2D) was recently proposed to involve dedifferentiation of beta-cells and ectopic expression of other islet hormones, including somatostatin and glucagon. Here we show that gastrin, a stomach hormone typically expressed in the pancreas only during embryogenesis, is expressed in islets of diabetic rodents and humans with T2D. While in mice gastrin is expressed insulin+ cells, in humans with T2D gastrin expression occurs in both insulin+ and somatostatin+ cells. Genetic lineage tracing in mice indicates that gastrin expression is turned on in a subset of differentiated beta-cells following exposure to severe hyperglycemia. Gastrin expression in adult beta-cells does not involve the endocrine progenitor cell regulator NeuroG3 but requires membrane depolarization, calcium influx and calcineurin signaling. In vivo and in vitro experiments show that gastrin expression is rapidly eliminated upon exposure of beta cells to normal glucose levels. These results reveal the fetal hormone gastrin as a novel marker for reversible human beta-cell reprogramming in diabetes

Pancreatic beta cells express the fetal islet hormone gastrin in rodent and human diabetes

Beta-cell failure in type 2 diabetes (T2D) was recently proposed to involve dedifferentiation of beta-cells and ectopic expression of other islet hormones, including somatostatin and glucagon. Here we show that gastrin, a stomach hormone typically expressed in the pancreas only during embryogenesis, is expressed in islets of diabetic rodents and humans with T2D. While in mice gastrin is expressed insulin+ cells, in humans with T2D gastrin expression occurs in both insulin+ and somatostatin+ cells. Genetic lineage tracing in mice indicates that gastrin expression is turned on in a subset of differentiated beta-cells following exposure to severe hyperglycemia. Gastrin expression in adult beta-cells does not involve the endocrine progenitor cell regulator NeuroG3 but requires membrane depolarization, calcium influx and calcineurin signaling. In vivo and in vitro experiments show that gastrin expression is rapidly eliminated upon exposure of beta cells to normal glucose levels. These results reveal the fetal hormone gastrin as a novel marker for reversible human beta-cell reprogramming in diabetes

Pancreatic Lkb1 Deletion Leads to Acinar Polarity Defects and Cystic Neoplasms▿

LKB1 is a key regulator of energy homeostasis through the activation of AMP-activated protein kinase (AMPK) and is functionally linked to vascular development, cell polarity, and tumor suppression. In humans, germ line LKB1 loss-of-function mutations cause Peutz-Jeghers syndrome (PJS), which is characterized by a predisposition to gastrointestinal neoplasms marked by a high risk of pancreatic cancer. To explore the developmental and physiological functions of Lkb1 in vivo, we examined the impact of conditional Lkb1 deletion in the pancreatic epithelium of the mouse. The Lkb1-deficient pancreas, although grossly normal at birth, demonstrates a defective acinar cell polarity, an abnormal cytoskeletal organization, a loss of tight junctions, and an inactivation of the AMPK/MARK/SAD family kinases. Rapid and progressive postnatal acinar cell degeneration and acinar-to-ductal metaplasia occur, culminating in marked pancreatic insufficiency and the development of pancreatic serous cystadenomas, a tumor type associated with PJS. Lkb1 deficiency also impacts the pancreas endocrine compartment, characterized by smaller and scattered islets and transient alterations in glucose control. These genetic studies provide in vivo evidence of a key role for LKB1 in the establishment of epithelial cell polarity that is vital for pancreatic acinar cell function and viability and for the suppression of neoplasia

mTORC1 to AMPK switching underlies β-cell metabolic plasticity during maturation and diabetes

Pancreatic beta cells (β-cells) differentiate during fetal life, but only postnatally acquire the capacity for glucose-stimulated insulin secretion (GSIS). How this happens is not clear. In exploring what molecular mechanisms drive the maturation of β-cell function, we found that the control of cellular signaling in β-cells fundamentally switched from the nutrient sensor target of rapamycin (mTORC1) to the energy sensor 5'-adenosine monophosphate-activated protein kinase (AMPK), and that this was critical for functional maturation. Moreover, AMPK was activated by the dietary transition taking place during weaning, and this in turn inhibited mTORC1 activity to drive the adult β-cell phenotype. While forcing constitutive mTORC1 signaling in adult β-cells relegated them to a functionally immature phenotype with characteristic transcriptional and metabolic profiles, engineering the switch from mTORC1 to AMPK signaling was sufficient to promote β-cell mitochondrial biogenesis, a shift to oxidative metabolism, and functional maturation. We also found that type 2 diabetes, a condition marked by both mitochondrial degeneration and dysregulated GSIS, was associated with a remarkable reversion of the normal AMPK-dependent adult β-cell signature to a more neonatal one characterized by mTORC1 activation. Manipulating the way in which cellular nutrient signaling pathways regulate β-cell metabolism may thus offer new targets to improve β-cell function in diabetes

Small Extracellular Vesicles Are Key Regulators of Non-cell Autonomous Intercellular Communication in Senescence via the Interferon Protein IFITM3

Senescence is a cellular phenotype present in health and disease, characterized by a stable cell-cycle arrest and an inflammatory response called senescence-associated secretory phenotype (SASP). The SASP is important in influencing the behavior of neighboring cells and altering the microenvironment; yet, this role has been mainly attributed to soluble factors. Here, we show that both the soluble factors and small extracellular vesicles (sEVs) are capable of transmitting paracrine senescence to nearby cells. Analysis of individual cells internalizing sEVs, using a Cre-reporter system, show a positive correlation between sEV uptake and senescence activation. We find an increase in the number of multivesicular bodies during senescence in vivo. sEV protein characterization by mass spectrometry (MS) followed by a functional siRNA screen identify interferon-induced transmembrane protein 3 (IFITM3) as being partially responsible for transmitting senescence to normal cells. We find that sEVs contribute to paracrine senescence.We are grateful to Tom Nightingale and Maria Niklison-Chirou for reading the manuscript. Alissa Weaver provided tagged CD63 constructs; and Jacob Yount and I-Chueh Huang supplied the IFITM3 and shIFITM3 plasmids. We are grateful to Luke Gammon, the Queen Mary University of London (QMUL) Genome Centre, and Gary Warnes for excellent technical support. Mouse hepatic stellate cells were a gift from Scott Lowe. A.O.’s lab is supported by the BBSRC (BB/P000223/1) and The Royal Society(RG170399). M.B. is funded by the MRC (MR/K501372/1) and the Centre for Genomics and Child Health. P.C.-F. (IN606B 2017/014) and J.F.-L.(ED481B 2017/117) are funded by the Xunta de Galicia.S