GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of mouse and human pancreatic islet glucagon secretion.

AIMS/HYPOTHESIS: Diabetes mellitus is associated with impaired insulin secretion, often aggravated by oversecretion of glucagon. Therapeutic interventions should ideally correct both defects. Glucagon-like peptide 1 (GLP-1) has this capability but exactly how it exerts its glucagonostatic effect remains obscure. Following its release GLP-1 is rapidly degraded from GLP-1(7-36) to GLP-1(9-36). We hypothesised that the metabolite GLP-1(9-36) (previously believed to be biologically inactive) exerts a direct inhibitory effect on glucagon secretion and that this mechanism becomes impaired in diabetes. METHODS: We used a combination of glucagon secretion measurements in mouse and human islets (including islets from donors with type 2 diabetes), total internal reflection fluorescence microscopy imaging of secretory granule dynamics, recordings of cytoplasmic Ca2+ and measurements of protein kinase A activity, immunocytochemistry, in vivo physiology and GTP-binding protein dissociation studies to explore how GLP-1 exerts its inhibitory effect on glucagon secretion and the role of the metabolite GLP-1(9-36). RESULTS: GLP-1(7-36) inhibited glucagon secretion in isolated islets with an IC50 of 2.5 pmol/l. The effect was particularly strong at low glucose concentrations. The degradation product GLP-1(9-36) shared this capacity. GLP-1(9-36) retained its glucagonostatic effects after genetic/pharmacological inactivation of the GLP-1 receptor. GLP-1(9-36) also potently inhibited glucagon secretion evoked by ß-adrenergic stimulation, amino acids and membrane depolarisation. In islet alpha cells, GLP-1(9-36) led to inhibition of Ca2+ entry via voltage-gated Ca2+ channels sensitive to ω-agatoxin, with consequential pertussis-toxin-sensitive depletion of the docked pool of secretory granules, effects that were prevented by the glucagon receptor antagonists REMD2.59 and L-168049. The capacity of GLP-1(9-36) to inhibit glucagon secretion and reduce the number of docked granules was lost in alpha cells from human donors with type 2 diabetes. In vivo, high exogenous concentrations of GLP-1(9-36) (>100 pmol/l) resulted in a small (30%) lowering of circulating glucagon during insulin-induced hypoglycaemia. This effect was abolished by REMD2.59, which promptly increased circulating glucagon by >225% (adjusted for the change in plasma glucose) without affecting pancreatic glucagon content. CONCLUSIONS/INTERPRETATION: We conclude that the GLP-1 metabolite GLP-1(9-36) is a systemic inhibitor of glucagon secretion. We propose that the increase in circulating glucagon observed following genetic/pharmacological inactivation of glucagon signalling in mice and in people with type 2 diabetes reflects the removal of GLP-1(9-36)'s glucagonostatic action.

Homeostatic control of mitotic arrest.

The spindle assembly checkpoint (SAC) restricts mitotic exit to cells that have completed chromosome-microtubule attachment. Cdc20 is a bifunctional protein. In complex with SAC proteins Mad2, BubR1, and Bub3, Cdc20 forms the mitotic checkpoint complex (MCC), which binds the anaphase-promoting complex (APC/C) and inhibits its mitotic exit-promoting activity. When devoid of SAC proteins, Cdc20 serves as an APC/C coactivator and promotes mitotic exit. During mitotic arrest, Cdc20 is continuously degraded via ubiquitin-dependent proteolysis and resynthesized. It is believed that this cycle keeps the levels of Cdc20 below a threshold above which Cdc20 would promote mitotic exit. We report that p31(comet), a checkpoint antagonist, is necessary for mitotic destabilization of Cdc20. p31(comet) depletion stabilizes the MCC, super-inhibits the APC/C, and delays mitotic exit, indicating that Cdc20 proteolysis in prometaphase opposes the checkpoint. Our studies reveal a homeostatic network in which checkpoint-sustaining and -repressing forces oppose each other during mitotic arrest and suggest ways for enhancing the sensitivity of cancer cells to antitubulin chemotherapeutics.

Sitagliptin and Roux-en-Y gastric bypass modulate insulin secretion via regulation of intra-islet PYY.

AIMS: The gut hormone peptide tyrosine tyrosine (PYY) is critical for maintaining islet integrity and restoring islet function following Roux-en-Y gastric bypass (RYGB). The expression of PYY and its receptors (NPYRs) in islets has been documented but not fully characterized. Modulation of islet PYY by the proteolytic enzyme dipeptidyl peptidase IV (DPP-IV) has not been investigated and the impact of DPP-IV inhibition on islet PYY function remains unexplored. Here we have addressed these gaps and their effects on glucose-stimulated insulin secretion (GSIS). We have also investigated changes in pancreatic PYY in diabetes and following RYGB. METHODS: Immunohistochemistry and gene expression analysis were used to assess PYY, NPYRs and DPP-IV expression in rodent and human islets. DPP-IV activity inhibition was achieved by sitagliptin. Secretion studies were used to test PYY and the effects of sitagliptin on insulin release, and the involvement of GLP-1. Radioimmunoassays were used to measure hormone content in islets. RESULTS: PYY and DPP-IV localized in different cell types in islets while NPYR expression was confined to the beta-cells. Chronic PYY application enhanced GSIS in rodent and diabetic human islets. DPP-IV inhibition by sitagliptin potentiated GSIS; this was mediated by locally-produced PYY, and not GLP-1. Pancreatic PYY was markedly reduced in diabetes. RYGB strongly increased islet PYY content, but did not lead to full restoration of pancreatic GLP-1 levels. CONCLUSION: Local regulation of pancreatic PYY, rather than GLP-1, by DPP-IV inhibition or RYGB can directly modulate the insulin secretory response to glucose, indicating a novel role of pancreatic PYY in diabetes and weight-loss surgery.

A novel inflammatory pathway mediating rapid hepcidin-independent hypoferremia.

Regulation of iron metabolism and innate immunity are tightly interlinked. The acute phase response to infection and inflammation induces alterations in iron homeostasis that reduce iron supplies to pathogens. The iron hormone hepcidin is activated by such stimuli causing degradation of the iron exporter ferroportin and reduced iron release from macrophages, suggesting that hepcidin is the crucial effector of inflammatory hypoferremia. Here, we report the discovery of an acute inflammatory condition that is mediated by Toll-like receptors 2 and 6 (TLR2 and TLR6) and which induces hypoferremia in mice injected with TLR ligands. Stimulation of TLR2/TLR6 triggers profound decreases in ferroportin messenger RNA and protein expression in bone marrow-derived macrophages, liver, and spleen of mice without changing hepcidin expression. Furthermore, C326S ferroportin mutant mice with a disrupted hepcidin/ferroportin regulatory circuitry respond to injection of the TLR2/6 ligands FSL1 or PAM3CSK4 by ferroportin downregulation and a reduction of serum iron levels. Our findings challenge the prevailing role of hepcidin in hypoferremia and suggest that rapid hepcidin-independent ferroportin downregulation in the major sites of iron recycling may represent a first-line response to restrict iron access for numerous pathogens.

Electroclinical Features of Epilepsy in Mucopolysaccharidosis III: Outcome Description in a Cohort of 15 Italian Patients.

Mucopolysaccharidosis III (Sanfilippo syndromes) types A-D are rare lysosomal storage disorders characterized by heparan sulfate accumulation and neurodegeneration. Patients with MPS III present with developmental stagnation and/or regression, sleep disturbance, and behavioral abnormalities usually in the first years of life. Epilepsy may occur in a proportion of patients during the disease course. However, the progression of epilepsy and EEG changes in MPS III have not been systematically investigated. We report electroclinical features in a cohort of patients with MPS III over a follow-up period ranging from 6.5 to 22 years. Participants include 15 patients (11 females; aged 7-31 years) with MPS III A (n = 7, 47%), MPS III B (n = 5, 34%), MPS III C (n = 2, 13%), and MPS III D (n = 1, 6%). At the time of this study, 8 out of 15 patients (53%) had epilepsy. Epilepsy occurred in patients with advanced disease even in the first decade of life (mean age at onset: 12.1 ± 6.7 years). However, seizure onset may also be associated with abrupt worsening of the neurobehavioral phenotype. The main epilepsy types observed were generalized (four out of eight, 50%), followed by focal (three out of eight, 37%) and combined (two out of eight, 25%) epilepsy and status epilepticus (one out of eight, 12.5%). Seizures were generally controlled by one antiepileptic drug (AED) and most patients (seven out of eight, 87%) were still on therapy after a median follow-up period of 5 years (range: 1-9 years). A total of 66 EEGs were analyzed with a median EEG follow-up duration of 7 years (range: 6 months-14 years). Slowing of the background activity occurred in 7 (46%) patients aged 4-19 years. Epileptiform EEG abnormalities were observed in 10 patients at a mean age of 9.6 ± 2.9 years. EEG epileptiform discharges were not unavoidably linked to epilepsy. Early recognition and careful monitoring of electroclinical features in MPS III is necessary for appropriate care and for the detection of disease progression.

Theoretical study of the interactions between peptide tyrosine tyrosine [PYY (1-36)], a newly identified modulator in type 2 diabetes pathophysiology, with receptors NPY1R and NPY4R.

PURPOSE: Diabetes mellitus is a common condition in the clinically obese. Bariatric surgery is one of the ways to put type 2 diabetes in remission. Recent findings propose the appetite-regulator peptide tyrosine tyrosine (PYY) as a therapeutic option for patients with type 2 diabetes. This novel gut hormone restores impaired insulin and glucagon secretion in pancreatic islets and is implicated in type 2 diabetes reversal after bariatric surgery. The current study elucidates the interactions between PYY and the NPY1R and NPY4R receptors using computational methods. METHODS: Protein structure prediction, molecular docking simulation, and molecular dynamics (MD) simulation were performed to elucidate the interactions of PYY with NPY1R and NPY4R. RESULTS: The predicted binding models of PYY-NPY receptors are in agreement with those described in the literature, although different interaction partners are presented for the C-terminal tail of PYY. Non-polar interactions are predicted to drive the formation of the protein complex. The calculated binding energies show that PYY has higher affinity for NPY4R (ΔGGBSA = -65.08 and ΔGPBSA = -87.62 kcal/mol) than for NPY1R (ΔGGBSA = -23.11 and ΔGPBSA = -50.56 kcal/mol). CONCLUSIONS: Based on the constructed models, the binding conformations obtained from docking and MD simulation for both the PYY-NPY1R and PYY-NPY4R complexes provide a detailed map of possible interactions. The calculated binding energies show a higher affinity of PYY for NPY4R. These findings may help to understand the mechanisms behind the improvement of diabetes following bariatric surgery.

PYY, a Therapeutic Option for Type 2 Diabetes?

Metabolic surgery leads to rapid and effective diabetes reversal in humans, by weight-independent mechanisms. The crucial improvement in pancreatic islet function observed after surgery is induced by alteration in several factors, including gut hormones. In addition to glucagon-like peptide 1 (GLP-1), increasing lines of evidence show that peptide tyrosine tyrosine (PYY) plays a key role in the metabolic benefits associated with the surgery, ranging from appetite regulation to amelioration of islet secretory properties and survival. Here, we summarize the current knowledge and the latest advancements in the field, which pitch a strong case for the development of novel PYY-based therapy for the treatment of diabetes.

Gs/Gq signaling switch in ß cells defines incretin effectiveness in diabetes.

By restoring glucose-regulated insulin secretion, glucagon-like peptide-1-based (GLP-1-based) therapies are becoming increasingly important in diabetes care. Normally, the incretins GLP-1 and glucose-dependent insulinotropic polypeptide (GIP) jointly maintain normal blood glucose levels by stimulation of insulin secretion in pancreatic ß cells. However, the reason why only GLP-1-based drugs are effective in improving insulin secretion after presentation of diabetes has not been resolved. ATP-sensitive K+ (KATP) channels play a crucial role in coupling the systemic metabolic status to ß cell electrical activity for insulin secretion. Here, we have shown that persistent membrane depolarization of ß cells due to genetic (ß cell-specific Kcnj11-/- mice) or pharmacological (long-term exposure to sulfonylureas) inhibition of the KATP channel led to a switch from Gs to Gq in a major amplifying pathway of insulin secretion. The switch determined the relative insulinotropic effectiveness of GLP-1 and GIP, as GLP-1 can activate both Gq and Gs, while GIP only activates Gs. The findings were corroborated in other models of persistent depolarization: a spontaneous diabetic KK-Ay mouse and nondiabetic human and mouse ß cells of pancreatic islets chronically treated with high glucose. Thus, a Gs/Gq signaling switch in ß cells exposed to chronic hyperglycemia underlies the differential insulinotropic potential of incretins in diabetes.

Somatostatin secretion by Na+-dependent Ca2+-induced Ca2+ release in pancreatic delta-cells.

Pancreatic islets are complex micro-organs consisting of at least three different cell types: glucagon-secreting α-, insulin-producing ß- and somatostatin-releasing δ-cells1. Somatostatin is a powerful paracrine inhibitor of insulin and glucagon secretion2. In diabetes, increased somatostatinergic signalling leads to defective counter-regulatory glucagon secretion3. This increases the risk of severe hypoglycaemia, a dangerous complication of insulin therapy4. The regulation of somatostatin secretion involves both intrinsic and paracrine mechanisms5 but their relative contributions and whether they interact remains unclear. Here we show that dapagliflozin-sensitive glucose- and insulin-dependent sodium uptake stimulates somatostatin secretion by elevating the cytoplasmic Na+ concentration ([Na+]i) and promoting intracellular Ca2+-induced Ca2+ release (CICR). This mechanism also becomes activated when [Na+]i is elevated following the inhibition of the plasmalemmal Na+-K+ pump by reductions of the extracellular K+ concentration emulating those produced by exogenous insulin in vivo 6. Islets from some donors with type-2 diabetes hypersecrete somatostatin, leading to suppression of glucagon secretion that can be alleviated by a somatostatin receptor antagonist. Our data highlight the role of Na+ as an intracellular second messenger, illustrate the significance of the intraislet paracrine network and provide a mechanistic framework for pharmacological correction of the hormone secretion defects associated with diabetes that selectively target the δ-cells.

PYY plays a key role in the resolution of diabetes following bariatric surgery in humans.

BACKGROUND: Bariatric surgery leads to early and long-lasting remission of type 2 diabetes (T2D). However, the mechanisms behind this phenomenon remain unclear. Among several factors, gut hormones are thought to be crucial mediators of this effect. Unlike GLP-1, the role of the hormone peptide tyrosine tyrosine (PYY) in bariatric surgery in humans has been limited to appetite regulation and its impact on pancreatic islet secretory function and glucose metabolism remains under-studied. METHODS: Changes in PYY concentrations were examined in obese patients after bariatric surgery and compared to healthy controls. Human pancreatic islet function was tested upon treatment with sera from patients before and after the surgery, in presence or absence of PYY. Alterations in intra-islet PYY release and insulin secretion were analysed after stimulation with short chain fatty acids (SCFAs), bile acids and the cytokine IL-22. FINDINGS: We demonstrate that PYY is a key effector of the early recovery of impaired glucose-mediated insulin and glucagon secretion in bariatric surgery. We establish that the short chain fatty acid propionate and bile acids, which are elevated after surgery, can trigger PYY release not only from enteroendocrine cells but also from human pancreatic islets. In addition, we identify IL-22 as a new factor which is modulated by bariatric surgery in humans and which directly regulates PYY expression and release. INTERPRETATION: This study shows that some major metabolic benefits of bariatric surgery can be emulated ex vivo. Our findings are expected to have a direct impact on the development of new non-surgical therapy for T2D correction.

The Role of PYY in Pancreatic Islet Physiology and Surgical Control of Diabetes.

Bariatric surgery in obese individuals leads to rapid and lasting remission of type 2 diabetes (T2D). This phenomenon occurs independently of weight loss possibly via a combination of factors. The incretin hormone GLP-1 has so far been recognised as a critical factor. However, recent data have indicated that elevation in another gut hormone, peptide tyrosine tyrosine (PYY), may drive the beneficial effects of surgery. Here we discuss recent findings on PYY-mediated control of glucose homeostasis and its role in diabetes, in the context of what is known for GLP-1. Identification of factors that increase the expression of PYY following bariatric surgery and elucidation of its role in diabetes reversal may have clinical relevance as a nonsurgical therapy for T2D.