Although administration of galanin or insulin alone may enhance insulin sensitivity and glucose transporter 4(GLUT4) trafficking, their cooperative effect on insulin sensitivity is still unclear. In the present study, we evaluated the cooperative effect of both reagents compared with solitary treatment with galanin or insulin in type 2 diabetic rats. Galanin and/or insulin were injected singly or together into type 2 diabetic rats once a day for 15 days. The results indicated that coadministration of both reagents compared with treatment with galanin or insulin alone significantly increasedglucose infusion rates in euglycemic-hyperinsulinemic clamp tests, 2-deoxy-[(3)H]d-glucose contents, GLUT4 densities, and pAS160 and protein kinase C activity levels, but reduced blood glucose and insulin levels, as well as retinol-binding protein 4 contents, and did not affect Glut4(Slc2a4) mRNA expression levels in myocytes. The changes in the ratios of GLUT4 immunoreaction in plasma membranes to total cell membranes of myocytes were higher in the coadministrative group compared with either the insulin or the galanin group. These results indicate that cooperation of the two hormones plays a synergic role to improve GLUT4 translocation and insulin sensitivity. This finding indicates the possibility of combining galanin with insulin with the aim of obtaining better antidiabetic efficacy than that of the canonical treatment with insulin alone.

Bu L, Yao Q, Liu Z et al., J Endocrinol. 2014 Mar 17;221(1):157-65. doi: 10.1530/JOE-13-0444. Print 2014 Apr.

Although galanin has been shown to increase glucose transporter 4(GLUT4) expression in skeletal muscle and adipocytes of rats, there is no literature available about the effect of galanin on GLUT4 expression in cardiac muscle of type 2 diabetic rats. In this study, we investigated the relationship between intracerebroventricular administration of M35, a galanin receptor antagonist, and GLUT4 expression in cardiac muscle of type 2 diabetic rats. The rats tested were divided into four groups: rats from healthy and type 2 diabetic drug groups were injected with 2?M M35 for three weeks, while both control groups with 2?l vehicle control. The euglycemic-hyperinsulinemic clamp test was conducted for an index of glucoseinfusion rates. The cardiac muscle was processed for determination of GLUT4 expression levels. The present study showed that the plasma insulin and retinol binding protein 4(RBP4) levels were higher in both drug groups than controls respectively. Moreover, the results showed the inhibitive effect of central M35 treatment on glucose infusion rates in the euglycemic-hyperinsulinemic clamp test and GLUT4 expression levels in the cardiac muscle. These results demonstrate that endogenous galanin, acting through its central receptor, has an important attribute to increase GLUT4 expression, leading to enhance insulin sensitivity and glucose uptake in cardiac muscle of type 2 diabetic rats. Galanin and its fragment can play a significant role in regulation of glucose metabolic homeostasis in cardiac muscle and galanin is an important hormone relative to diabetic heart.

Fang P, Shi M, Guo L3 et al., Peptides. 2014 Oct 18;62C:159-163. doi: 10.1016/j.peptides.2014.10.001. [Epub ahead of print]

This study was to investigate the effect of nicotine on insulin sensitivity and explore the underlying mechanisms. Treatment of Sprague-Dawley rats with nicotine(3 mg/kg/day) for 6 weeks reduced 43% body weight gain and 65% blood insulin level, but had no effect on blood glucose level. Both insulin tolerance test and glucose tolerance test demonstrated that nicotine treatment enhanced insulin sensitivity. Pretreatment of rats with hexamethonium(20 mg/kg/day) to antagonize peripheral nicotinic receptors except for α7 nicotinic acetylcholine receptor(α7-nAChR) had no effect on the insulin sensitizing effect of nicotine. However, the insulin sensitizing effect but not the bodyweight reducing effect of nicotine was abrogated in α7-nAChR knockout mice. Further, chronic treatment with PNU-282987(0.53 mg/kg/day), a selective α7-nAChR agonist, significantly enhanced insulin sensitivity without apparently modifying bodyweight not only in normal mice but also in AMP-activated kinase-α2 knockout mice, an animal model of insulin resistance with no sign of inflammation. Moreover, PNU-282987 treatment enhanced phosphorylation of signal transducer and activator of transcription 3(STAT3) in skeletal muscle, adipose tissue and liver in normal mice. PNU-282987 treatment also increased glucose uptake by 25% in C2C12 myotubes and this effect was total abrogated by STAT3 inhibitor, S3I-201. All together, these findings demonstrated that nicotine enhanced insulin sensitivity in animals with or without insulin resistance, at least in part via stimulating α7-nAChR-STAT3 pathway independent of inflammation. Our results contribute not only to the understanding of the pharmacological effects of nicotine, but also to the identifying of new therapeutic targets against insulin resistance.

Xu TY, Guo LL, Wang P et al., PLoS One. 2012;7(12):e51217. doi: 10.1371/journal.pone.0051217. Epub 2012 Dec 12.

The di-peptide Trp-His(WH) has vasorelaxant and anti-atherosclerotic functions. We hypothesized that WH has multiple biological functions and may aid AMP-activated protein kinase(AMPK) activation and affect the glucose transport system in skeletal muscle. First, we examined whether WH or His-Trp(HW) can activate AMPKα. Treatment of L6 myotubes with WH or HW significantly increased phosphorylation of AMPKα. WH activatedAMPK independently of insulin and significantly increased glucose uptake into L6 myotubes following translocation of glucose transporter 4(Glut4) to the plasma membrane. This activation was induced by the LKB1 pathway but was independent of changes in intracellular Ca(2+) levels and the Ca(2+)/calmodulin-dependent kinase pathway. L6 myotubes express only one type of oligopeptide transporter, peptide/histidine transporter 1(PHT1, also known as SLC15a4), and WH is incorporated into cells and activates AMPKα following PHT1-mediated cell uptake. These findings indicate that(1) WH activates AMPK and insulin independently enhances glucose uptake following translocation of Glut4 to the plasma membrane,(2) activation of AMPKα by WH is mediated by the LKB1 pathway, without altering the Ca(2+)-dependent pathway, and(3) L6 myotubes express only one type of peptide transporter(PHT1; SLC15a4), which incorporates WH into cells to activate AMPKα.

Soga M, Ohashi A, Taniguchi M et al., FEBS Open Bio. 2014 Oct 22;4:898-904. doi: 10.1016/j.fob.2014.10.008. eCollection 2014.

Insulin resistance(IR) in skeletal muscle is a prerequisite for type 2 diabetes and is often associated with obesity. IR also develops alongside muscle atrophy in older individuals in sarcopenic obesity. The molecular defects that underpin this syndrome are not well characterized, and there is no licensed treatment. Deletion of the transforming growth factor-β family member myostatin, or sequestration of the active peptide by overexpression of the myostatin propeptide/latency-associated peptide(ProMyo) results in both muscle hypertrophy and reduced obesity and IR. We aimed to establish whether local myostatin inhibition would have a paracrine/autocrine effect to enhance glucose disposal beyond that simply generated by increased muscle mass, and the mechanisms involved. We directly injected adeno-associated virus expressing ProMyo in right tibialis cranialis/extensor digitorum longus muscles of rats and saline in left muscles and compared the effects after 17 days. Both test muscles were increased in size(by 7 and 11%) and showed increased radiolabeled 2-deoxyglucose uptake(26 and 47%) and glycogen storage(28 and 41%) per unit mass during an intraperitoneal glucose tolerance test. This was likely mediated through increased membrane protein levels of GLUT1(19% higher) and GLUT4(63% higher). Interestingly, phosphorylation of phosphoinositol 3-kinase signaling intermediates and AMP-activated kinase was slightly decreased, possibly because of reduced expression of insulin-like growth factor-I in these muscles. Thus, myostatin inhibition has direct effects to enhance glucose disposal in muscle beyond that expected of hypertrophy alone, and this approach may offer potential for the therapy of IR syndromes.

Cleasby ME, Jarmin S, Eilers W et al., Am J Physiol Endocrinol Metab. 2014 Apr 1;306(7):E814-23. doi: 10.1152/ajpendo.00586.2013. Epub 2014 Jan 28.

Insulin resistance(IR) in skeletal muscle is an important component of both type 2 diabetes and the syndrome of sarcopaenic obesity, for which there are no effective therapies. Urocortins(UCNs) are not only well established as neuropeptides but also have their roles in metabolism in peripheral tissues. We have shown recently that global overexpression of UCN3 resulted in muscular hypertrophy and resistance to the adverse metabolic effects of a high-fat diet. Herein, we aimed to establish whether short-term local UCN3 expression could enhance glucose disposal and insulin signalling in skeletal muscle. UCN3 was found to be expressed in right tibialis cranialis and extensor digitorum longus muscles of rats by in vivo electrotransfer and the effects studied vs the contralateral muscles after 1 week. No increase in muscle mass was detected, but test muscles showed 19% larger muscle fibre diameter(P=0.030), associated with increased IGF1 and IGF1 receptor mRNA and increased SER256 phosphorylation of forkhead transcription factor. Glucose clearance into the test muscles after an intraperitoneal glucose load was increased by 23%(P=0.018) per unit mass, associated with increased GLUT1(34% increase; P=0.026) and GLUT4(48% increase; P=0.0009) proteins, and significantly increased phosphorylation of insulin receptor substrate-1, AKT, AKT substrate of 160 kDa, glycogen synthase kinase-3?, AMP-activated protein kinase and its substrate acetyl CoA carboxylase. Thus, UCN3 expression enhances glucose disposal and signalling in muscle by an autocrine/paracrine mechanism that is separate from its pro-hypertrophic effects, implying that such a manipulation may have promised for the treatment of IR syndromes including sarcopaenic obesity

Roustit MM, Vaughan JM, Jamieson PM et al., J Endocrinol. 2014 Nov;223(2):143-54. doi: 10.1530/JOE-14-0181. Epub 2014 Aug 13.

RFamide peptides 43RFa and 26RFa have been shown to promote food intake and to exert different peripheral actions through G-protein-coupled receptor 103(GPR103) binding. Moreover, 26RFa was found to inhibit pancreatic insulin secretion, whereas the role of 43RFa on β-cell function is unknown, as well as the effects of both peptides on β-cell survival. Herein, we investigated the effects of 43RFa and 26RFa on survival and apoptosis of pancreatic β-cells and human pancreatic islets. In addition, we explored the role of these peptides on insulin secretion and the underlying signaling mechanisms. Our results show that in INS-1E β-cells and human pancreatic islets both 43RFa and 26RFa prevented cell death and apoptosis induced by serum starvation, cytokine synergism, and glucolipotoxicity, through phosphatidylinositol 3-kinase/Akt- and extracellular signal-related kinase 1/2-mediated signaling. Moreover, 43RFa promoted, whereas 26RFa inhibited, glucose- and exendin-4-induced insulin secretion, through Gαs and Gαi/o proteins, respectively. Inhibition of GPR103 expression by small interfering RNA blocked 43RFa insulinotropic effect, but not the insulinostatic action of 26RFa. Finally, 43RFa, but not 26RFa, induced cAMP increase and glucose uptake. In conclusion, because of their survival effects along with the effects on insulin secretion, these findings suggest potential for 43RFa and 26RFa as therapeutic targets in the treatment of diabetes.

Granata R, Settanni F, Trovato L et al., Diabetes. 2014 Jul;63(7):2380-93. doi: 10.2337/db13-1522. Epub 2014 Mar 12.

Obestatin was identified in 2005 by Zhang and colleagues as a ghrelin-associated peptide, derived from posttranslational processing of the prepro-ghrelin gene. Initially, obestatin was reported to activate the G-protein-coupled receptor GPR39 and to reduce food intake and gastric emptying. However, obestatin remains a controversial peptide, as these findings have been questioned and its receptor is still a matter of debate, as well as its effects on feeding behavior. Recently, interaction with the glucagon-like peptide 1 receptor has been suggested, in line with obestatin-positive effects on glucose and lipid metabolism. In addition, obestatin displays a variety of cellular effects, by regulating metabolic cell functions, increasing cell survival and proliferation, and inhibiting apoptosis and inflammation in different cell types. Finally, like ghrelin, obestatin is produced in the gastrointestinal tract, including the pancreas and adipose tissue, and exerts both local actions in peripheral tissues, and distant effects at the central level. Therefore, obestatin may indeed be considered a hormone, although additional studies are required to clarify its physiopathological role and to definitely identify its receptor.

Trovato L, Gallo D, Settanni F et al., Front Horm Res. 2014;42:175-85. doi: 10.1159/000358346. Epub 2014 Apr 7.

Neuromedin B and neuromedin C are novel decapeptides that have recently been isolated from porcine spinal cord and canine intestinal mucosa. We have studied the effects of neuromedin B and neuromedin C on insulin release from the isolated perfused rat pancreas. The effect of neuromedin B was detectable at a concentration of 10mM, and that of neuromedin C was detectable at a concentration of 1nM. Further increase in the concentration of neuromedin B and neuromedin C resulted in dose-dependent increases in insulin secretion. The effectiveness of neuromedin B and neuromedin C as insulinotropic agents depended on the glucose concentration; both were more effective at a higher concentration of glucose. However, insulinotropic effects of these peptides in the presence of 8.3mM glucose were limited to the first 3 min of a 20-min perfusion. These results, coupled with a recent study demonstrating bombesin-like immunoreactivity in nerves in the pancreas, suggest that neuromedin B and neuromedin C exert a direct local action on insulin secretion in the pancreas.

Nakamura T1, Otsuki M, Okabayashi Y et al., Nihon Naibunpi Gakkai Zasshi. 1989 Aug 20;65(8):695-703.

Xenin-25, a peptide co-secreted with the incretin hormone glucose-dependent insulinotropic polypeptide(GIP), possesses promising therapeutic actions for obesity-diabetes. However, native xenin-25 is rapidly degraded by serum enzymes to yield the truncated metabolites: Xenin 9-25, xenin 11-25, xenin 14-25 and xenin 18-25. This study has examined the biological activites of these fragment peptides. In vitro studies using BRIN-BD11 cells demonstrated that native xenin-25 and xenin 18-25 possessed significant(P<0.05 to P<0.01) Insulin at 5.6 and 16.7 mM glucose, respectively, but not at 1.1 mM glucose. In addition, xenin 18-25 significantly(P<0.05) potentiated the insulin-releasing action of the stable GIP mimetic(D-Ala2) GIP. In contrast, xenin 9-25, xenin 11-25 and xenin 14-25 displayed neither insulinotropic nor GIP-potentiating actions. Moreover, xenin 9-25, xenin 11-25 and xenin 14-25 significantly(P<0.05 to P<0.001) inhibited xenin-25(10-8 M)-induced insulin release in vitro. I.p. administration of xenin-based peptides in combination with glucose to high fat-fed mice did not significantly affect the glycaemic excursion or glucose-induced insulin release compared with controls. However, when combined with(D-Ala2) GIP, all xenin peptides significantly(P<0.01 to P<0.001) reduced the overall glycaemic excursion, albeit to a similar extent as(D-Ala2) GIP alone. Xenin-25 and xenin 18-25 also imparted a potential synergistic effect on(D-Ala2) GIP-induced insulin release in high fat-fed mice. All xenin-based peptides lacked significant satiety effects in normal mice. These data demonstrate that the C-terminally derived fragment peptide of xenin-25, xenin 18-25, exhibits significant biological actions that could have therapeutic utility for obesity-diabetes.

Martin CM, Parthsarathy V, Pathak V et al., J Endocrinol. 2014 Apr 22;221(2):193-200. doi: 10.1530/JOE-13-0617. Print 2014 May.

We have previously demonstrated in human subjects who under euglycemic clamp conditions GLP-1(9-36)amide infusions inhibit endogenous glucose production without substantial insulinotropic effects. An earlier report indicates that GLP-1(9-36)amide is cleaved to a nonapeptide, GLP-1(28-36)amide and a pentapeptide GLP-1(32-36)amide(LVKGR amide). Here we study the effects of the pentapeptide on whole body glucose disposal during hyperglycemic clamp studies. Five dogs underwent indwelling catheterizations. Following recovery, the dogs underwent a 180 min hyperglycemic clamp(basal glucose +98 mg/dl) in a cross-over design. Saline or pentapeptide(30 pmol kg(-1) min(-1)) was infused during the last 120 min after commencement of the hyperglycemic clamp in a primed continuous manner. During the last 30 min of the pentapeptide infusion, glucose utilization(M) significantly increased to 21.4±2.9 mg kg(-1) min(-1)compared to M of 14.3±1.1 mg kg(-1)min(-1) during the saline infusion(P=0.026, paired t-test; P=0.062, Mann-Whitney U test). During this interval, no significant differences in insulin(26.6±3.2 vs. 23.7±2.5 ?U/ml, P=NS) or glucagon secretion(34.0±2.1 vs. 31.7±1.8 pg/ml, P=NS) were observed. These findings demonstrate that under hyperglycemic clamp studies the pentapeptide modulates glucose metabolism by a stimulation of whole-body glucose disposal. Further, the findings suggest that the metabolic benefits previously observed during GLP-1(9-36)amide infusions in humans might be due, at least in part, to the metabolic effects of the pentapeptide that is cleaved from the pro-peptide, GLP-1(9-36)amide in the circulation.

Elahi D, Angeli FS, Vakilipour A et al., Peptides. 2014 Sep;59:20-4. doi: 10.1016/j.peptides.2014.06.004. Epub 2014 Jun 14.

Insulin secretion from pancreatic islet ?-cells is stimulated by glucose. Glucose-induced insulin release is potentiated or suppressed by hormones and neural substances. Ghrelin, an acylated 28-amino acid peptide, was isolated from the stomach in 1999 as the endogenous ligand for the growth hormone(GH) secretagogue-receptor(GHS-R). Circulating ghrelin is produced predominantly in the stomach and to a lesser extent in the intestine, pancreas and brain. Ghrelin, initially identified as a potent stimulator of GH release and feeding, has been shown to suppress glucose-induced insulin release. This insulinostatic action is mediated by G?i2 subtype of GTP-binding proteins and delayed outward K(+)(Kv) channels. Interestingly, ghrelin is produced in pancreatic islets. The ghrelin originating from islets restricts insulin release and thereby upwardly regulates the systemic glucose level. Furthermore, blockade or elimination of ghrelin enhances insulin release, which can ameliorate glucose intolerance in high-fat diet fed mice and ob/ob mice. This review focuses on the insulinostatic action of ghrelin, its signal transduction mechanisms in islet ?-cells, ghrelin"s status as an islet hormone, physiological roles of ghrelin in regulating systemic insulin levels and glycaemia, and therapeutic potential of the ghrelin-GHS-R system as the target to treat type 2 diabetes

Yada T, Damdindorj B, Rita RS et al., Diabetes Obes Metab. 2014 Sep;16 Suppl 1:111-7. doi: 10.1111/dom.12344.

OBJECTIVE: Chemerin is an adipocyte-secreted hormone and has recently been associated with obesity and the metabolic syndrome. Although studies in rodents have outlined the aspects of chemerin"s function and expression, its physiology and expression patterns are still to be elucidated in humans. METHODS: To evaluate for any day/night variation in chemerin secretion, we analyzed hourly serum samples from six females in the fed state. To examine whether energy deprivation affects chemerin levels, and whether this could be mediated through leptin, we analyzed samples from the same subjects in the fasting state while administering either placebo or leptin. To evaluate for any potential dose-effect relationship between leptin andchemerin, we administered increasing metreleptin doses to five females. A tissue array was used to study the expression of chemerin in different human tissues. Ex vivo treatment of human fat explants from three subjects with leptin was carried out to evaluate for any direct effect of leptin on adipocyte chemerin secretion. RESULTS: Chemerin does not display a day/night variation, while acute energy deprivation resulted in a significant drop in circulating chemerinlevels by ~42%. The latter was unaltered by metreleptin administration, and leptin administration did not affect the secretion of chemerin by human adipose tissue studied ex vivo. Chemerin was expressed primarily in the pancreas and liver. Chemerin receptor showed increased expression in the lymph nodes and the spleen. CONCLUSIONS: We outline for the first time chemerin expression and physiology in humans, which are different from those in mice.

Chamberland JP, Berman RL, Aronis KN, et al., Eur J Endocrinol. 2013 Sep 13;169(4):453-62. doi: 10.1530/EJE-13-0098. Print 2013 Oct.

INTRODUCTION: The effects of pancreatic polypeptide (PP) infusion were examined in patients on insulin pump therapy to determine whether PP administration can reduce insulin requirements in patients with type 1 diabetes mellitus (T1DM) or type 3c diabetes mellitus (T3cDM; pancreatogenic). METHODS: Ten subjects with long-standing T1DM (n = 7) or T3cDM (n = 3) on insulin pump treatment received a 72 h subcutaneous infusion of 2 pmol/kg/min bovine PP or saline by portable infusion pump in a single-blinded, randomized, crossover design. RESULTS: Pancreatic polypeptide infusion raised plasma PP levels to 450-700 pmol/liter. Daily insulin infusion requirements (I) fell from 48 ± 6.9 to 40 ± 7.5 U on day 2 (p < .05) and from 46 ± 7.7 to 37 ± 6.6 U on day 3 (p < .05) of PP infusion compared with saline. Corrected for average blood glucose concentration (G), I/G fell in 10/10 subjects during the second 24 h period and in 7/10 subjects during the third 24 h period; sensitivity to insulin, calculated as 1/(I/G), increased 45% ± 12% on day 2 (p < .01) and 34% ± 14% on day 3 (p < .05) of PP infusion. Pancreatic polypeptideresponses to a test meal were compared with the change in insulin infusion requirements in 5 subjects; the reduction in insulin requirements seen during PP infusion correlated with the degree of baseline PP deficiency (p < .002). CONCLUSIONS: A concurrent subcutaneous infusion of PP enhances insulin sensitivity and reduces insulin requirements in patients with long-standing T1DM and T3cDM on insulin pump therapy. The benefit of PP infusion correlated with the degree of PP deficiency.

Rabiee A, Galiatsatos P, Salas-Carrillo R et al., J Diabetes Sci Technol. 2011 Nov 1;5(6):1521-8.

Neural and hormonal mechanisms control pancreatic secretion. The effects of the corticotropin releasing factor(CRF) related neuropeptide urocortin(UCN) on pancreatic exocrine secretion were examined. In anesthetized male rats, pancreatic secretion volume and total protein were assayed. UCN increased pancreatic secretory volume and protein secretion and potentiated cholecytokinin-stimulated protein secretion. Astressin, a non-specific CRF receptor antagonist, inhibited UCN-stimulated protein output while CRF(2) receptor antagonist, antisauvagine-30, was without effect. Atropine, but not subdiaphragmatic vagotomy, inhibited UCN-mediated secretion. In acinar cells, UCN did not stimulate release of amylase nor intracellular cAMP. UCN is a pancreatic exocrine secreatagogue with effects mediated through cholinergic intrapancreatic neurons.

Guzman EA, Zhang W, Lin TR et al., Peptides. 2003 May;24(5):727-34.

Deterioration of functional islet ?-cell mass is the final step in progression to Type 2 diabetes. We previously reported that overexpression of Nkx6.1 in rat islets has the dual effects of enhancing glucose-stimulated insulin secretion(GSIS) and increasing β-cell replication. Here we show that Nkx6.1 strongly upregulates the prohormone VGF in rat islets and that VGF is both necessary and sufficient for Nkx6.1-mediated enhancement of GSIS. Moreover, the VGF-derived peptide TLQP-21 potentiates GSIS in rat and human islets and improves glucose tolerance in vivo. Chronic injection of TLQP-21 in prediabetic ZDF rats preserves islet mass and slows diabetes onset. TLQP-21 prevents islet cell apoptosis by a pathway similar to that used by GLP-1, but independent of the GLP-1, GIP, or VIP receptors. Unlike GLP-1, TLQP-21 does not inhibit gastric emptying or increase heart rate. We conclude that TLQP-21 is a targeted agent for enhancing islet β-cell survival and function

Stephens SB, Schisler JC, Hohmeier HE et al., Cell Metab. 2012 Jul 3;16(1):33-43. doi: 10.1016/j.cmet.2012.05.011.

Two novel granin-like polypeptides, VGF and pro-SAAS, which are stored in and released from secretory vesicles and are expressed widely in nervous, endocrine, and neuroendocrine tissues, play roles in the regulation of body weight, feeding, and energy expenditure. Both VGF and pro-SAAS are cleaved into peptide fragments, several of which are biologically active. We utilized a highly sensitive and specific radioimmunoassay(RIA) to immunoreactive, pro-SAAS-derived PEN peptides, developed another against immunoreactive, VGF-derived AQEE30 peptides, and quantified these peptides in various mouse tissues and brain regions. Immunoreactive AQEE30 was most abundant in the pituitary, while brain levels were highest in hypothalamus, striatum, and frontal cortex. Immunoreactive PEN levels were highest in the pancreas and spinal cord, and in brain, PEN was most abundant in striatum, hippocampus, pons and medulla, and cortex. Since both peptides were expressed in hypothalamus, a region of the brain that controls feeding and energy expenditure, double label immunofluorescence studies were employed. These demonstrated that 42% of hypothalamic arcuate neurons coexpress VGF and SAAS peptides, and that the intracellular distributions of these peptides in arcuate neurons differed. By RIA, cold stress increased immunoreactive AQEE30 and PEN peptide levels in female but not male hypothalamus, while a high fat diet increased AQEE30 and PEN peptide levels in female but not male hippocampus. VGF and SAAS-derived peptides are therefore widely expressed in endocrine, neuroendocrine, and neural tissues, can be accurately quantified by RIA, and are differentially regulated in the brain by diet and cold stress

Chakraborty TR, Tkalych O, Nanno D et al., Brain Res. 2006 May 17;1089(1):21-32. Epub 2006 May 2.

Here, we demonstrate that the fractalkine(FKN)/CX3CR1 system represents a regulatory mechanism for pancreatic islet β cell function and insulin secretion. CX3CR1 knockout(KO) mice exhibited a marked defect in glucose and GLP1-stimulated insulin secretion, and this defect was also observed in vitro in isolated islets from CX3CR1 KO mice. In vivo administration of FKN improved glucose tolerance with an increase in insulin secretion. In vitro treatment of islets with FKN increased intracellular Ca(2+) and potentiated insulin secretion in both mouse and human islets. The KO islets exhibited reduced expression of a set of genes necessary for the fully functional, differentiated β cell state, whereas treatment of wild-type(WT) islets with FKN led to increased expression of these genes. Lastly, expression of FKN in islets was decreased by aging and high-fat diet/obesity, suggesting that decreased FKN/CX3CR1 signaling could be a mechanism underlying β cell dysfunction in type 2 diabetes.

Lee YS, Morinaga H, Kim JJ et al., Cell. 2013 Apr 11;153(2):413-25. doi: 10.1016/j.cell.2013.03.001.

OBJECTIVE: Pigment epithelium-derived factor(PEDF) is a multifunctional protein with neurotrophic and anti-angiogenic properties. More recently it became evident that PEDF is upregulated in patients with type 2 diabetes and also contributes to insulin resistance in mice. During characterization of the secretome of in vitro differentiated human adipocytes by two-dimensional polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization-MS, we found that PEDF is one of the most abundant proteins released by adipocytes. The aim of this study was to investigate the regulation and autocrine function of PEDF in human adipocytes and to determine its paracrine effects on human skeletal muscle cells(hSkMC) and human smooth muscle cells(hSMC). METHODS AND RESULTS: Human primary adipocytes secrete 130 ng ml(-1) PEDF over 24 h from 1 million cells, which is extremely high as compared with adiponectin, interleukin-6(IL-6) or IL-8. This release of PEDF is significantly higher than from other primary cells, such as adipose-tissue located macrophages(50-times), hSkMC and hSMC(5-times). PEDF protein expression significantly increases during adipogenesis, which is paralleled by increased PEDF secretion. Furthermore, tumor necrosis factor-α and hypoxia significantly downregulate PEDF protein levels. PEDFsecretion was significantly reduced by troglitazone and hypoxia and significantly increased by insulin. Treatment of adipocytes and hSkMC withPEDF induced insulin resistance in adipocytes, skeletal and smooth muscle cells at the level of insulin-stimulated Akt phosphorylation, which was dose dependent and more prominent in adipocytes. Furthermore, inflammatory nuclear factor-αB(NF-κB) signaling was induced by PEDF. In hSMC,PEDF induced proliferation(1.7-fold) and acutely activated proliferative and inflammatory signaling pathways(NF-κB, p38 mitogen-activated protein kinase and mammalian target of rapamycin). CONCLUSION: PEDF is one of the most abundant adipokines and its secretion is inversely regulated by insulin and hypoxia. PEDF induces insulin resistance in adipocytes and hSkMC and leads to inflammatory signaling in hSMC. Because of these diverse actions, PEDF is a key adipokine, which could have an important role in diabetes and obesity-related disorders.

Famulla S, Lamers D, Hartwig S et al., Int J Obes(Lond). 2011 Jun;35(6):762-72. doi: 10.1038/ijo.2010.212. Epub 2010 Oct 12.

Cellular identity is established by genetic, epigenetic, and environmental factors that regulate organogenesis and tissue homeostasis. Although some flexibility in fate potential is beneficial to overall organ health, dramatic changes in cellular identity can have disastrous consequences. Emerging data within the field of pancreas biology are revising current beliefs about how cellular identity is shaped by developmental and environmental cues under homeostasis and stress conditions. Here, we discuss the changes occurring in cellular states upon fate modulation and address how our understanding of the nature of this fluidity is shaping therapeutic approaches to pancreatic disorders such as diabetes and cancer.

Cell Stem Cell. 2014 Nov 20. pii: S1934-5909(14)00513-X. doi: 10.1016/j.stem.2014.11.001. [Epub ahead of print]

Total or near-total loss of insulin-producing β-cells occurs in type 1 diabetes. Restoration of insulin production in type 1 diabetes is thus a major medical challenge. We previously observed in mice in which β-cells are completely ablated that the pancreas reconstitutes new insulin-producing cells in the absence of autoimmunity. The process involves the contribution of islet non-β-cells; specifically, glucagon-producing α-cells begin producing insulin by a process of reprogramming(transdifferentiation) without proliferation. Here we show the influence of age on β-cell reconstitution from heterologous islet cells after near-total β-cell loss in mice. We found that senescence does not alter α-cell plasticity: α-cells can reprogram to produce insulin from puberty through to adulthood, and also in aged individuals, even a long time after β-cell loss. In contrast, before puberty there is no detectable α-cell conversion, although β-cell reconstitution after injury is more efficient, always leading to diabetes recovery. This process occurs through a newly discovered mechanism: the spontaneous en masse reprogramming of somatostatin-producing δ-cells. The juveniles display "somatostatin-to-insulin" δ-cell conversion, involving dedifferentiation, proliferation and re-expression of islet developmental regulators. This juvenile adaptability relies, at least in part, upon the combined action of FoxO1 and downstream effectors. Restoration of insulin producing-cells from non-β-cell origins is thus enabled throughout life via δ- or α-cell spontaneous reprogramming. A landscape with multiple intra-islet cell interconversion events is emerging, offering new perspectives for therapy

Chera S, Baronnier D1, Ghila L et al., Nature. 514, 503-51-7 2014. October doi: 10.1038/nature13633.

Type I diabetes(T1D) is an autoimmune disease in which an immune response to pancreatic β-cells results in their loss over time. Although the conventional view is that this loss is due to autoimmune destruction, we present evidence of an additional phenomenon in which autoimmunity promotes islet endocrine cell transdifferentiation. The end result is a large excess of δ-cells, resulting from α- to β- to δ-cell transdifferentiation. Intermediates in the process of transdifferentiation were present in murine and human T1D. Here, we report that the peptide caerulein was sufficient in the context of severe β-cell deficiency to induce efficient induction of α- to β- to δ-cell transdifferentiation in a manner very similar to what occurred in T1D. This was demonstrated by genetic lineage tracing and time course analysis. Islet transdifferentiation proceeded in an islet autonomous manner, indicating the existence of a sensing mechanism that controls the transdifferentiation process within each islet. The finding of evidence for islet cell transdifferentiation in rodent and human T1D and its induction by a single peptide in a model of T1D has important implications for the development of β-cell regeneration therapies for diabetes.

Piran R, Lee SH, Li CR et al., Cell Death Dis. 2014 Jul 31;5:e1357. doi: 10.1038/cddis.2014.311.