Type 2 diabetes mellitus as a disorder of galanin resistance

    Type 2 diabetes mellitus as a disorder of galanin resistance Penghua Fang, Mingyi Shi, Yan Zhu, Ping Bo, Zhenwen Zhang PII: DOI: Reference:

S0531-5565(15)30085-1 doi: 10.1016/j.exger.2015.11.007 EXG 9734

To appear in:

Experimental Gerontology

Received date: Revised date: Accepted date:

13 April 2015 10 November 2015 12 November 2015

Please cite this article as: Fang, Penghua, Shi, Mingyi, Zhu, Yan, Bo, Ping, Zhang, Zhenwen, Type 2 diabetes mellitus as a disorder of galanin resistance, Experimental Gerontology (2015), doi: 10.1016/j.exger.2015.11.007

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ACCEPTED MANUSCRIPT Type 2 diabetes mellitus as a disorder of galanin resistance

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Penghua Fanga,b, Mingyi Shib,c, Yan Zhub,c, Ping Bob,c*, Zhenwen Zhangb,c*

Department of Physiology, Nanjing University of Chinese Medicine Hanlin College,

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Taizhou 225300, China b

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Jiangsu Key Laboratory of Integrated Traditional Chinese and Western Medicine for

Prevention and Treatment of Senile Diseases, Yangzhou University, Yangzhou 225001,

c

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China

Department of Endocrinology, Clinical Medical College, Yangzhou University,

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Yangzhou 225001, China

*Corresponding author: Jiangsu Key Laboratory of Integrated Traditional Chinese and Western Medicine for Prevention and Treatment of Senile Diseases, Yangzhou University, Yangzhou 225001, China Tel: +86-0514-87978880; Fax: +86-514-87341733; Email: [email protected] (P. Bo) and [email protected] (Z. Zhang)

Short running title: Galanin resistance and T2DM

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ACCEPTED MANUSCRIPT Abstract The increasing prevalence of type 2 diabetes mellitus with its high morbidity and

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mortality becomes an important health problem. The multifactorial etiology of type 2

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diabetes mellitus is relative to many gene and molecule alterations, and increased insulin resistance. Besides these, however, there are still other predisposing and risk factors

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accounting for type 2 diabetes mellitus not to be identified and recognized. Emerging

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evidence indicated that defects in galanin function played a crucial role in development of type 2 diabetes mellitus. Galanin homeostasis is tightly relative to insulin resistance and

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is regulated by blood glucose. Hyperglycemia, hyperinsulinism, enhanced plasma galanin levels and decreased galanin receptor activities are ones of the characters of type 2

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diabetes mellitus. The discrepancy between high insulin level and low glucose handling is named as insulin resistance. Similarly, the discrepancy between high galanin level and

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low glucose handling may be denominated as galanin resistance too. In this review, the characteristic milestones of type 2 diabetes mellitus were condensed as two analogical conceptual models, obesity-hyper-insulin-insulin resistance-type 2 diabetes mellitus and obesity-hyper-galanin-galanin resistance-type 2 diabetes mellitus. Both galanin resistance and insulin resistance are correlative each other. Conceptualizing the etiology of type 2 diabetes mellitus as a disorder of galanin resistance may inspire a new concept to depth our knowledge about pathogenesis of type 2 diabetes mellitus, eventually leading to novel preventive and therapeutic interventions for type 2 diabetes mellitus. Keywords: Galanin resistance; Insulin resistance; Type 2 diabetes mellitus

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ACCEPTED MANUSCRIPT 1. Introduction The prevalence of type 2 diabetes mellitus is rapidly increasing worldwide and becomes

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an important health problem with its high morbidity and mortality (Malecki, 2004). The

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characters of this disease include an increase in the blood glucose level, a decrease in the blood supply of limbs, damage to blood vessel, heart, retina, beta cell of pancreas,

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neurons with long axons reaching the limbs and other organs (Malecki, 2004).

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Epidemiological investigation demonstrated that there were 371 million people with diabetes in the world, expected to rise to 552 million by 2030 (Guariguata, 2012; Whiting

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et al., 2011). Diabetes mellitus is widespread in the United States according to the report of U.S. Centers for Disease Control and Prevention, with 24 million people diagnosed

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and 5.6 million undiagnosed. The National Institute of Health estimates that over 70 to 80 million people suffer from metabolic syndrome or other "pre-diabetic" conditions. The

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proportion of patients with type 2 diabetes mellitus to total diabetic patients is 90-95%. Blood glucose testing is a base for diagnosis and management of diabetes. Besides, an analysis of volatile organic compounds (VOCs) in the air exhaled from subjects offers a novel diagnostic approach for type 2 diabetes (Dowlaty et al., 2013; Greiter et al., 2010; Mazzatenta et al., 2013).

Despite many factors may result in type 2 diabetes mellitus, the insulin resistance is the core of our understanding of the etiology of type 2 diabetes mellitus. Most likely type 2 diabetes mellitus is caused by modification of the insulin signalling, resulting in reduction in glucose uptake of myocytes, hepatocytes and adipocytes and elevation of blood glucose levels, i.e. development of insulin resistance (Perry et al., 2014; Taylor, 2012). However, besides the insulin resistance other predisposing and risk factors for type 2

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ACCEPTED MANUSCRIPT diabetes mellitus are still scarce to be identified and recognized. Therefore, further exploration of these predisposing and risk factors is urgently needed.

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Recent studies have provided compelling clues that galanin plays an important role in the

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pathogenesis of age-related obesity and type 2 diabetes mellitus, and may be taken as a biomarker to predict these diseases (Fang et al., 2013b, 2014a, 2014b). Galanin, a 29/30

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amino-acid peptide, was isolated in 1983 from porcine intestine by Tatemoto and

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collaborators (Tatemoto et al., 1983). This peptide distributes widely throughout the central and peripheral nervous system as well as other tissues, such as the skeletal muscle,

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heart muscle, adipose tissue, pancreatic islet and carotid body (Fang et al., 2012b; Di Giulio et al., 2015; Lang et al., 2015). Galanin is involved in a multiplicity of

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physiological activities. As a hunger hormone, galanin can regulate energy metabolism and stimulate appetite (Fang et al., 2012a, 2012b). The galanin receptor family is

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currently comprised of three members, GAL1, GAL2 and GAL3 (Webling et al., 2012). All of the subtype receptors are G-protein-coupled receptors and distribute in the hypothalamus, amygdala, hippocampus, paraventricular nucleus (PVN), thalamus, brainstem, spinal cord and dorsal root ganglia (Webling et al., 2012). GAL3 seems to be the important galanin receptor in both the human locus coeruleus and dorsal raphe nucleus versus GAL1 and GAL2 in the rodent brain (Le Maître et al., 2013). GAL1 and GAL3 are known to couple to Gi/Go and inhibit adenylyl cyclase to decrease the cAMP levels (Webling et al., 2012). Excited GAL2, however, may result in hydrolysis of inositol phosphate and activation of phospholipase C through the Gq/G11 pathway to enhance intracellular Ca2+ concentration (Webling et al., 2012). These different signaling pathways may be related to different functions of galanin.

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ACCEPTED MANUSCRIPT The results from human and animal studies supported that the characters of type 2 diabetes mellitus included obesity, insulin resistance, hyperglycemia, hyperinsulinism,

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enhanced plasma galanin levels and decreased galanin receptor activities. This review

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summarizes our recent studies and relevant papers to provide a new insight into above characters of type 2 diabetes, including insulin resistance, galanin resistance, the

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relationship between galanin and obesity.

2. Insulin resistance

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Numerous studies confirmed that the circulatory insulin level is increased rather than decreased in subjects with high blood glucose and type 2 diabetes mellitus (Malecki,

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2004; Perry et al., 2014; Taylor, 2012). Hyperinsulinaemia precedes the development of type 2 diabetes (Johnson and Olefsky, 2013; Taylor, 2012). Consequently, the concept of

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insulin resistance was emerged. The development of insulin resistance means a progression from normal to impaired glucose tolerance. Molecular biology researches found that the mechanisms and symptoms of insulin resistance were causally linked to gene and molecule alterations, including modification of the insulin receptor substrate (IRS) that triggered insulin signalling pathways (Denley et al., 2007; Khan and Pessin, 2002; Tonks et al., 2013). IRS proteins interact with the regulatory subunit of phosphatidylinositol (PI)-3-kinase (PI3K), which catalyses the formation of the lipid product phosphatidylinositol 3,4,5-trisphosphate (PIP3) to regulate the activity of downstream proteins such as protein kinase B (PKB) and atypical protein kinase C ( PKC) (Denley et al., 2007; Khan and Pessin, 2002; Tonks et al., 2013). Both PKB and PKC play a crucial role in glucose transporter 4 (GLUT4) translocation through activation of

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ACCEPTED MANUSCRIPT Rab GTPase-activating protein (AS160), which is one of the substrates of PKB (Thong et al., 2007). GLUT4 is particularly important for maintaining glucose metabolism

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homeostasis and insulin sensitivity, since it is involved in glucose transport into myocytes

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and adipocytes in response to insulin stimuli (Augustin, 2010; Leto and Saltiel, 2012). In the quiescent condition, the majority of GLUT4 are located in intracellular vesicles at the

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cytosol. As stimulus of insulin, more GLUT4 are translocated to plasma membranes via a

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complex pathway (Bogan et al., 2003; Geiger et al., 2006). Reduced GLUT4 translocation in response to insulin stimuli results in the most prominent defect in glucose

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transport into the cytosol, i,e, development of insulin resistance (Augustin, 2010; Leto and Saltiel, 2012). The important factors in lifestyle for development of lnsulin resistance

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are excessive caloric intake and scanty physical activity, which are easy to result in swell of fat cells in human and animal (Qi et al., 2008; Tuomilehto et al., 2001). Proliferated

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and swelled adipose tissues, as an active endocrine organ, can release bioactive mediators (adipokines), which are closely related to obesity-driven insulin resistance and diabetes mellitus (Zhang et al., 2012). In addition, impaired oxidative rates of fatty acid are also associated with insulin resistance, as fatty acids can interfere with the transmission of insulin signaling (Zhang et al., 2012). Whereas the healthy lifestyle, such as low fat diet, weight reduction and frequent physical activity may prevent and reduce the development of insulin resistance and diabetes (Qi et al., 2008; Tuomilehto et al., 2001). The medical treatment for type 2 diabetes relies reduction in calorie intake and increase in regular physical exercise. Besides, a range of medications that can reduce blood glucose and increase insulin sensitivity should be properly taken, such as Metformin, Thiazolidinediones, Dipeptidyl peptidase-4 inhibitors, Glucagon-like peptide-1 agonist,

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ACCEPTED MANUSCRIPT Alpha-glucosidase inhibitors and Dapagliflozin (Adler et al., 2009).

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3. Galanin and obesity

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The compelling evidence supported that galanin is closely relative to body weight and obesity via regulation of feeding behavior in animals and humans (Fang et al., 2012a). An

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injection of galanin into the hypothalamus, particularly into PVN, stimulates food intake

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in food-sated rats (Kyrkouli et al., 1990). This effect is stronger in the rats as feed with the high-fat diet than with the standard diet (Tempel et al., 1988). The acute increase in

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central galanin content may augment food intake and fat consumption of mammals (Tempel et al., 1988), which may be blocked by the intracerebroventricular (i.c.v.)

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administration of galanin antagonists, M40 and C7, (Corwin et al., 1993) or antisense galanin mRNA (Akabayashi et al., 1994). Besides, repeated PVN injection of galanin

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versus saline during a 7-day test period significantly increased daily caloric intake and body weight of animals (Yun et al., 2005). Furthermore, galanin knockout mice decreased fat-rich diet intake by 48% than controls (Adams et al., 2008), while the obese phenotype of homozygous galanin transgenic C57BL/6J mice reduced energy expenditure and increased body weight (Poritsanos et al., 2009). Last, after chronic administration of galanin by mini-osmotic pumps into the lateral ventricle the galanin knockout mice partially reversed the fat avoidance phenotype (Adams et al., 2008). These results suggest that hypothalamic galanin projection promotes overeating and weight gain when food, particularly dietary fat, is plentiful (Leibowitz et al., 2004). The studies confirm that the central galanin-induced increase in food intake and body weight is mediated by GAL1. An acute or chronic i.c.v. administration of GAL1 agonist

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ACCEPTED MANUSCRIPT M617 markedly stimulated food intake, particularly the consumption of high-fat milk in Sprague-Dawley rats (Saar et al., 2011). Besides, the repeated i.c.v. administration of 20

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μg M617 markedly increased food intake and consumption of cookie mash (14% fat, 79%

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carbohydrate and 7% protein) in Sprague-Dawley male rats (Lundström et al., 2005). However, after the high-fat diet challenge for 2-weeks, GAL1 knockout mice decreased

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their food intake, consuming fewer daily calories than those provided with a lower-fat

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diet and more calories as well as than their heterozygote littermates (Zorrilla et al., 2007). Furthermore, the i.c.v. administration of galanin or M617 may activate c-Fos, a marker of

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cell activation, in central amygdala and dorsomedial hypothalamus, indicating that galanin may upregulate c-Fos expression in hypothalamic nuclei (Blackshear et al.,2007).

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Last, central GAL2 and GAL3, in contrast, are unlikely to be involved in the stimulating effect of galanin on appetite. A study of genetic mapping in a 17q chromosomal region

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demonstrated that there was no association between GAL2 and obesity phenotypes (Sutton et al., 2006). GAL2/3 agonist AR-M1896 has no impact on c-Fos expression in brain, as well as food intake and body weight of rats or mice (Man et al., 2008). Moreover, the GAL2 agonist M1145 and M1153, or GAL2 antagonist M871 affected neither high-fat milk nor cookie mash intake of animals (Saar et al., 2011). GAL2 knockout mice showed indifferent in feeding behavior and body weight compared with wild mice (Gottsch et al., 2005). There are few data found about the relation berween GAL3 with feeding behavior as yet. The only relative clue is that GAL3 plays a critical role in reducing operant responding to ethanol in alcohol-preferring rats (Ash et al., 2011; Belfer et al., 2007). Collectively, current data support that central galanin is via activation of GAL1 to increase food intake and body weight of animals.

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ACCEPTED MANUSCRIPT In turn, obesity may also affect expression and secretion of galanin in subjects. The circulating galanin levels were elevated in obese women compared to controls, especially

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as body mass index over 31, not in anorexic women (Baranowska et al., 1997, 2000). But

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the levels were decreased in thin women compared to controls. Also, the plasma galanin levels were elevated in obese young women than normally menstruating women

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(Meczekalski and Warenik-Szymankiewicz, 1999), suggesting that the galanin levels

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were respectively or simultaneously related to the severity of obesity and overfeeding (Baranowska et al., 2000). Galanin protein and mRNA levels were also enhanced in PVN

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of obesity-prone rats fed with high-fat diet as compared with the obesity-prone rats fed with high-carbohydrate diet or obesity-resistant rats fed with high-fat diet (Dourmashkin

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et al., 2005). In addition, male Sprague-Dawley rats fed with high-fat diet from birth day to their maturity were divided into obesity-prone or obesity-resistant groups identified by

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weight-gain scores (8-10 g/day vs. 5-7 g/day) (Leibowitz et al., 2007). At day 100 of age the obesity-prone rats had rapider weight gain, 50% greater adiposity and higher galanin levels in PVN than obesity-resistant animals. Intriguingly, there was a age-dependent change in the galanin concentration in PVN and arcuate nuclei of rats. The galanin levels of obese rats were lower in PVN at week 2 of age and in the arcuate nucleus at week 4 of age than that of lean ones (-15% to -25%). However, during the mature stage a significant increase (40%-220%) in galanin concentration was found in the arcuate and dorsomedial nuclei

of

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male

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than

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controls

(Meczekalski

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Warenik-Szymankiewicz, 1999). Taken together, administration of galanin may increase body weight and switch to obesity of subjects. In turn, obesity itself may potentiate galanin secretion. Enhanced galanin

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ACCEPTED MANUSCRIPT levels and obesity are tightly associated together. Noteworthily, galanin is not an early

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player in development of obesity.

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4.Evidence for hyper-galanin and galanin resistance 4.1 Human studies

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A wealth of studies indicated the relevance of galanin concentration to morbidity of type

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2 diabetes mellitus in humans (Fang et al., 2013a; Legakis et al, 2005, 2007; Zhang et al., 2014). The plasma galanin levels were higher in patients with type 1, type 2 and

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gestational diabetes mellitus (Celi et al., 2005; Fang et al., 2013a; Legakis et al, 2005; Nergiz et al., 2014; Zhang et al., 2014). However, intravenous infusion of galanin (80 and

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160 pmol/kg/min) in healthy male volunteers showed that plasma glucose and insulin levels were almost changeless during a glucose tolerance test (Gilbey et al., 1989).

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Besides, during the oral glucose tolerance test galanin infusion did not significantly change plasma glucose levels in both diabetic and non-diabetic patients with acromegaly (Mazziotti et al., 2008). The fasting plasma galanin concentration in healthy volunteers and type 2 diabetic patients was positively correlative with the blood glucose level during the glucose tolerance test (Legakis et al, 2005, 2007). A significant positive correlation was also found between plasma galanin content and body mass index in pregnant women with gestational diabetes mellitus (Fang et al., 2013a; Zhang et al., 2014 ), as well as between plasma galanin level and haemoglobin A1c (HbA1c) content among the type 1 diabetes mellitus (Celi et al., 2005). These results demonstrate that the endogenous plasma galanin contents, not ectogenous, are closely associated with the blood glucose level in humans.

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4.2 Animals studies

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There is growing evidence indicating a suppressive role of galanin in the release of

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insulin from the pancreatic islets (Manabe et al., 2003; Olkowicz et al., 2007; Ruczyński et al., 2002, 2010; Tang et al., 2012). The administration of galanin inhibits basal insulin

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secretion in a dose-dependent manner via inhibiting adenylate cyclase activity through

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activation of petussis-toxin-sensitive inhibitory GTP-binding regulatory protein (Manabe et al., 2003). This inhibitory effect may be blocked by its antagonists (Olkowicz et al.,

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2007; Ruczyński et al., 2002, 2010). However, galanin does not play a major role in the regulation of insulin secretion in humans (Invitti et al., 1995).

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Although galanin may directly inhibit β cell secretion, the inhibitive effect of galanin on

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insulin secretion doesn’t interfere its beneficial impact on insulin sensitivity of subjects,

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which is proved by numerous animal and human studies. Firstly, animals with galanin metabolic disorder are especially prone to developing insulin resistance and type 2 diabetes mellitus (Legakis, 2005). Our and other’s studies demonstrated that diabetic rats have a significant reduction in galanin-immunoreactive cell numbers in pancreatic islets with changed plasma galanin levels (Adeghate and Ponery et al., 2001; He et al., 2011; Liang et al., 2012). The acute injection of galanin into PVN of rats reduced circulating glucose levels (Yun et al., 2005). This study provide convincing evidence that PVN galanin can favor carbohydrate over fat metabolism in muscle and reversing hyperglycemia to counteract the metabolic disturbances induced by a high-fat diet. As a consequence of these actions, galanin may promote the partitioning of lipids away from oxidation in muscle towards storage in adipose tissue

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ACCEPTED MANUSCRIPT (Yun et al., 2005). Secondly, the obese phenotype of the homozygous galanin transgenic C57BL/6J mice

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experienced reduced energy expenditure and increased body weight (Poritsanos et al.,

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2009). In contrast, galanin or GAL1-knockout mice showed a reduction in insulin-mediated glucose uptake and insulin-independent glucose elimination during the

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glucose tolerance tests (Ahrén et al., 2004; Zorrilla et al., 2007).

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Thirdly, the glucose transporter 2 (GLUT2) is predominantly localized in neuronal dendrites and can contribute to insulin signaling transmission and glucose uptake in the

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mammalian brain (Counts et al., 2009). The GLUT2 levels were lower in non-galanin-innervated basalis neurons than in galanin-hyperinnervated neurons (Counts

the former.

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et al., 2009). The latter revealed higher glucose metabolism and insulin sensitivity than

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Fourthly, the carotid body as a metabolic sensor is implicated in the regulation of whole body insulin sensitivity (Conde et al., 2014). The deregulation of the carotid body plays an important role in the pathogenesis of insulin resistance (Conde et al., 2014). Recent studies demonstrated that galanin played a modulatory or trophic role in carotid body (Di Giulio et al., 2015; Mazzatenta et al., 2014; Porzionato et al., 2010). Galanin expression is significantly reduced in the carotid body in healthy older man in comparison to healthy young subjects (Mazzatenta et al., 2014). These may be some relation between downregulation of galanin expression in the carotid body and reduction in insulin sensitivity of older man. Fifthly, study results indicated that galanin can cooperate with insulin to play a synergic role in increasing insulin sensitivity (Bu et al., 2014). Co-administration of both galanin

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ACCEPTED MANUSCRIPT and insulin compared with respective treatment with either galanin or insulin significantly increased GLUT4 protein levels and ratios of GLUT4 immunoreaction in plasma

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membranes to total cell membranes in myocytes of type 2 diabetic rats (Bu et al., 2014). Finally, our and other’s studies demonstrated that the administration of M35, a galanin

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antagonist, reduced 2-deoxy-[3H]-D-glucose (2-DG) content in myocytes and adipocytes

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as well as glucose infusion rates in the hyperinsulinemic-euglycemic clamp test, which

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was a direct assessment of insulin sensitivity in healthy and type 2 diabetic rats (Bu et al., 2013; Fang et al., 2014c; Guo et al., 2011; He et al., 2011; Jiang et al., 2009; Liang et al.,

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2012; Zhang et al., 2012). Besides, our recent study demonstrated that the administration of M617, a GAL1 agonist, increased insulin sensitivity in healthy and type 2 diabetic rats

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(Fang et al., 2014d). Quantitative densitometry in skeletal muscle, adipose tissue and cardiac muscle revealed that treatment with M35 significantly decreased GLUT4 protein

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and mRNA expression in plasma membranes of myocytes and adipocytes compared with diabetic controls. The ratios of GLUT4 contents in plasma membrane fractions to total cell membranes were lower in the M35 treatment group compared with diabetic controls, suggesting that endogenous galanin elevated not only GLUT4 protein and mRNA expression level but also the GLUT4 translocation from the intracellular membrane compartments to the plasma membranes in skeletal muscles, adipose tissues and cardiac muscle to sustain insulin sensitivity (Bu et al., 2013; Fang et al., 2014c; Guo et al., 2011; He et al., 2011; Jiang et al., 2009; Liang et al., 2012; Zhang et al., 2012). In addition, quantitative densitometry in cardiac muscle revealed that central treatment with GAL1 agonist M617 significantly increased GLUT4 protein and mRNA expression levels in plasma membranes of cardiac muscle compared with diabetic controls, suggesting that it

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ACCEPTED MANUSCRIPT is through activation of central GAL1, galanin enhanced GLUT4 expression and insulin sensitivity in the cardiac muscle of type 2 diabetic rats (Fang et al., 2014d).

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Altogether, these data indicate that galanin is an important hormone to elevate insulin

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sensitivity and to repress morbidity of type 2 diabetes mellitus in humans and animals.

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4.3 Galanin resistance

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As mentionned above, adminisrarion of galanin can increase insulin sensitivity to reduce blood glucose. But many studies confirmed that galanin levels were increased rather than

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decreased in subjects with pathological hyperglycemia and type 2 diabetes mellitus (Celi et al., 2005; Fang et al., 2013a; Legakis et al, 2005; Nergiz et al., 2014; Zhang et al.,

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2014 ). It appears paradoxical, at first glance, that galanin can increase insulin sensitivity to reduce the blood glucose level, but the high circulating galanin level is observed in

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diabetic subjects. This is similar to the situation of insulin which can decrease the blood glucose level, but patient and animal with type 2 diabetes mellitus frequently present both hyperinsulinism and hyperglycemia. Accordingly, similar to insulin resistance also, a new concept of galanin resistance emerged, which is refered to the discrepancy between high galanin level and low glucose handling. Compelling clues support that the increased galanin resistance is tightly associated with obesity and type 2 diabetes mellitus (see Fig. 1). First, type 2 galanin receptors are mostly expressed in the prefrontal cortex (Abdul-Rahman et al., 2012). GAL2 levels were lower in type 2 diabetic animals than non-diabetic controls, suggesting development of galanin resistance. Next, physical exercise may improve symptom and complication of type 2 diabetes

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ACCEPTED MANUSCRIPT mellitus. Meanwhile, physical activity is an important physiologic stimulation to increase galanin release and galanin receptor activity (He et al., 2011; Murray et al., 2010; Reiss et

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al., 2009; Sciolino et al., 2012; Zhang et al., 2012). After a 20 min acute bout of exercise,

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the plasma galanin concentration in healthy volunteers was significantly higher than each basal value, reaching the peak at 15 min after the exercise (Legakis et al., 2000). Thus, a

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possible explanation is that exercise can promote galanin secretion and galanin receptor

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activity, which is beneficial to ameliorate type 2 diabetes mellitus via reduction of galanin resistance. On the contrary, physical inactivity and obesity are associated with

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development of type 2 diabetes mellitus and reduction in galanin receptor activity to increase galanin resistance.

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Last, both galanin resistance and insulin resistance are correlative each other. The canonical insulin-signaling pathway to trigger GLUT4 translocation is composed of PKC,

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Akt substrate of 160 kDa (AS160) and so on (Sakamoto & Holman 2008). While galanin-induced GLUT4 trafficking is at least via two discrete signaling pathways. The first pathway activates GAL1 and GAL3 to decrease the activity of cAMP response element binding proteins through Gi/o proteins, resulting in activation of AS160. The second pathway activates GAL2 via Gq/11, generating the hydrolysis of inositol phosphate and activation of PKC. Recent study demonstrated that injection of galanin significantly increased pAS160 and PKC activity levels in muscle of type 2 diabetic rats (Bu et al., 2014). Thus, AS160 and PKC are the meeting-points of insulin and galanin signaling pathways to trigger GLUT4 traffic. The intersection and coincidence between both signaling cascades may amplify signaling intensity and enhance signaling transmitting efficacy, inducing much more gains in GLUT4 translocation and glucose

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ACCEPTED MANUSCRIPT uptake than the alone role of either one in myocytes and adipoctyes of type 2 diabetic rats. As there is the synergic role between the two hormones, defects in the effect of galanin

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on amelioration of hyperglycemia may lead to a decline in insulin sensitivity, i.e. galanin

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resistance may result in insulin resistance, vice versa.

Research results support a conjecture that the high level of galanin is in response to the

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development of galanin resistance in type 2 diabetic subjects.. This needs to be addressed

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further with reliable animal models and clinical trials in the future.

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5. Conclusion

The administration of galanin can increase insulin sensitivity to reduce blood glucose.

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The discrepancy between high circulating galanin level observed in diabetic subjects and low glucose handling may be named as galanin resistance, which is a crucial step in the

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pathogenesis of type 2 diabetes mellitus. Both galanin resistance and insulin resistance are correlative each other. The characteristics of type 2 diabetes mellitus may be condensed to both obesity-hyper-insulin-insulin resistance-type 2 diabetes mellitus and obesity-hyper-galanin-galanin resistance-type 2 diabetes mellitus. In depth knowledge of the characteristics and influences of galanin resistance is helpful to better understand the etiology of type 2 diabetes mellitus, and may eventually bring a new strategy for alleviation of type 2 diabetes mellitus.

Acknowledgement This work was supported by the National Health and Family Planning Commission of China (Grant No. W201309) and in part by the Natural Scientific Fund of the Jiangsu

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ACCEPTED MANUSCRIPT Higher Education Institutions of China (Grant No. 14KJB310012) and in part by the Science and Technology Program of Taizhou, China (Grant No. TS201512) and in part by

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the Jiangsu Postgraduate Scientific Research and Innovation Projects (Grant No.

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KYLX15_1387).

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Conflict of interest

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The authors have no conflicts of interest to disclose.

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ACCEPTED MANUSCRIPT References Abdul-Rahman, O., Sasvari-Szekely, M., Ver, A., Rosta, K., Szasz, B.K., Kereszturi,

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E., Keszler, G., 2012. Altered gene expression profiles in the hippocampus and prefrontal

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cortex of type 2 diabetic rats. BMC Genomics. 13, 81.

Adams, A.C., Clapham, J.C., Wynick, D., Speakman, J.R., 2008. Feeding behaviour in

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galanin knockout mice supports a role of galanin in fat intake and preference. J.

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Neuroendocrinol. 20, 199-206.

Adler, A.I., Shaw, E.J., Stokes, T., Ruiz, F., Adler, A., Allerdyce, C., Doherty, T., Farmer,

MA

A., Goenka, N., Hadley-Brown, M., Home, P., Ivory, P., Johns, Y., Lewin, I., McGuire, A., Wood, J., Ayiku, L., Banks, E., Elliott, N., Heath, M., Ruiz, F., Shaw, E., Stokes, T.,

TE

D

2009. Newer agents for blood glucose control in type 2 diabetes: summary of NICE guidance. BMJ. 338, b1668.

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Ahrén, B., Pacini, G., Wynick, D., Wierup, N., Sundler, F., 2004. Loss-of-function mutation of the galanin gene is associated with perturbed islet function in mice. Endocrinology 145, 3190-3196. Akabayashi, A., Koenig, J.I., Watanabe, Y., Alexander, J.T., Leibowitz, S.F., 1994. Galanin-containing neurons in the paraventricular nucleus: a neurochemical marker for fat ingestion and body weight gain. Proc. Natl. Acad. Sci. USA 91, 10375-10379. Ash, B.L., Zanatta, S.D., Williams, S.J., Lawrence, A.J., Djouma, E., 2011. The galanin-3 receptor antagonist, SNAP 37889, reduces operant responding for ethanol in alcohol-preferring rats. Regul. Pept. 166, 59-67. Augustin, R., 2010.The protein family of glucose transport facilitators: It's not only about glucose after all. IUBMB Life 62, 315-333.

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ACCEPTED MANUSCRIPT Bandyopadhyay, G., Standaert, M.L., Galloway, L., Moscat, J., Farese, R.V., 1997. Evidence for involvement of protein kinase C (PKC)-ζ and noninvolvement of

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diacylglycerol-sensitive PKCs in insulin-stimulated glucose transport in L6 myotubes.

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Endocrinology 138, 4721-4731.

Baranowska, B., Radzikowska, M., Wasilewska-Dziubinska, E., Roguski, K., Borowiec,

SC

M., 2000. Disturbed release of gastrointestinal peptides in anorexia nervosa and in obesity.

NU

Diabetes Obes. Metab. 2, 99-103.

Baranowska, B., Wasilewska-Dziubińska, E., Radzikowska, M., Płonowski, A., Roguski,

MA

K., 1997. Neuropeptide Y, galanin, and leptin release in obese women and in women with anorexia nervosa. Metabolism 46, 1384-1389.

TE

D

Belfer, I., Hipp, H., Bollettino, A., McKnight, C., Evans, C., Virkkunen, M., Albaugh, B., Max, M.B., Goldman, D., Enoch, M.A., 2007. Alcoholism is associated with GALR3

AC CE P

but not two other galanin receptor genes. Genes Brain Behav. 6, 473-481. Blackshear, A., Yamamoto, M., Anderson, B.J., Holmes, P.V., Lundström, L., Langel, U., Robinson, JK., 2007. Intracerebroventricular administration of galanin or galanin receptor subtype 1 agonist M617 induces c-Fos activation in central amygdala and dorsomedial hypothalamus. Peptides 2007; 28: 1120-4. Bogan, J.S., Hendon, N., McKee, A.E., Tsao, T.S., Lodish, H.F., 2003. Functional cloning of TUG as a regulator of GLUT4 glucose transporter trafficking. Nature 425, 727-733. Bu, L., Liu, Z., Zou, J., Gao, X., Bao, Y., Qu, S., 2013. Blocking central galanin receptors attenuates insulin sensitivity in myocytes of diabetic trained rats. J. Neurosci. Res. 91, 971-977.

19

ACCEPTED MANUSCRIPT Bu, L., Yao, Q., Liu, Z., Tang, W., Zou, J., Qu, S., 2014. Combined galanin with insulin improves insulin sensitivity of diabetic rat muscles. J. Endocrinol. 221, 157-165.

PT

Celi, F., Bini, V., Papi, F., Santilli, E., Ferretti, A., Mencacci, M., Berioli, M.G., De

RI

Giorgi, G., Falorni, A., 2005. Circulating acylated and total ghrelin and galanin in children with insulin-treated type 1 diabetes: relationship to insulin therapy, metabolic

SC

control and pubertal development. Clin. Endocrinol. (Oxf) 63, 139-145.

NU

Conde, S.V., Sacramento, J.F., Guarino, M.P., Gonzalez, C., Obeso, A., Diogo, L.N., Monteiro, E.C., Ribeiro, M.J., 2014. Carotid body, insulin, and metabolic diseases:

MA

unraveling the links. Front. Physiol. 5, 418.

Corwin, R.L., Robinson, J.K., Crawley, J.N., 1993. Galanin antagonists block galanin

1528-1533.

TE

D

induced feeding in the hypothalamus and amygdala of the rat. Eur. J. Neurosci. 5,

AC CE P

Counts, S.E., He, B., Che, S., Ginsberg, S.D., Mufson, E.J., 2009. Galanin fiber hyperinnervation preserves neuroprotective gene expression in cholinergic basal forebrain neurons in Alzheimer's disease. J. Alzheimers Dis. 18, 885-896. Denley, A., Carroll, J.M., Brierley, G.V., Cosgrove, L., Wallace, J., Forbes, B., Roberts CT, Jr., 2007. Differential activation of insulin receptor substrates 1 and 2 by insulin-like growth factor-activated insulin receptors. Mol. Cell Biol. 27, 3569-3577. Di Giulio, C., Marconi, G.D., Zara, S., Di Tano, A., Porzionato, A., Pokorski, M., Cataldi, A., Mazzatenta, A., 2015. Selective Expression of Galanin in Neuronal-Like Cells of the Human Carotid Body. Adv. Exp. Med. Biol. 860, 315-323. Dos Santos, J.M., Benite-Ribeiro, S.A., Queiroz, G., Duarte, J.A., 2012. The effect of age on glucose uptake and GLUT1 and GLUT4 expression in rat skeletal muscle. Cell

20

ACCEPTED MANUSCRIPT Biochem. Funct. 30, 191-197. Dourmashkin, J.T., Chang, G.Q., Gayles, E.C., Hill, J.O., Fried, S.K., Julien, C.,

PT

Leibowitz, S.F., 2005. Different forms of obesity as a function of diet composition. Int. J.

RI

Obes (Lond). 29, 1368-1378.

SC

Dowlaty, N., Yoon, A., Galassetti, P., 2013. Monitoring states of altered carbohydrate metabolism via breath analysis: are times ripe for transition from potential to reality?

NU

Curr. Opin. Clin. Nutr. Metab. Care 16, 466-472.

MA

Fang, P., Min, W., Sun, Y., Guo, L., Shi, M., Bo, P., Zhang, Z., 2014a. The potential antidepressant and antidiabetic effects of galanin system. Pharmacol. Biochem. Behav.

D

120, 82-87.

TE

Fang, P., Shi, M., Yu, M., Guo, L., Bo, P., Zhang, Z., 2014b. Endogenous peptides as risk markers to assess the development of insulin resistance. Peptides 51, 9-14.

AC CE P

Fang, P., Shi, M., Guo, L., He, B., Wang, Q., Yu, M., Bo, P., Zhang, Z., 2014c. Effect of endogenous galanin on glucose transporter 4 expression in cardiac muscle of type 2 diabetic rats. Peptides 62, 159-163. Fang, P., Shi, M., Zhu, Y., Zhang, Z., Bo P., 2014d. Central injection of GalR1 agonist M617 facilitates GLUT4 expression in cardiac muscle of type 2 diabetic rats. Exp. Gerontol. doi: 10.1016/j.exger.2014.11.009. [Epub ahead of print] Fang, P., Bo, P., Shi, M., Yu, M., Zhang, Z., 2013a. Circulating galanin levels are increased in patients with gestational diabetes mellitus. Clin. Biochem. 46, 831-833. Fang, P., Yu, M., Shi, M., He, B., Zhang, Z., 413 Bo, P., 2013b. The neuropeptide galanin benefits insulin sensitivity in subjects with type 2 diabetes. Curr. Protein Pept. Sci. 14, 669-673.

21

ACCEPTED MANUSCRIPT Fang, P., Yu, M., Guo, L., Bo, P., Zhang, Z., Shi, M., 2012a. Galanin and its receptors: a novel strategy for appetite control and obesity therapy. Peptides 36, 331-339.

PT

Fang, P., Yu, M., Shi, M., Zhang, Z., Sui, Y., Guo, L., Bo, P., 2012b. Galanin peptide

RI

family as a modulating target for contribution to metabolic syndrome. Gen. Comp. Endocrinol. 179, 115-120.

SC

Geiger, P.C., Han, D.H., Wright, D.C., Holloszy, J.O., 2006. How muscle insulin

NU

sensitivity is regulated: testing of a hypothesis. Am. J. Physiol. Endocrinol. Metab. 291, E1258- E1263.

MA

Gilbey, S.G., Stephenson, J., O'Halloran, D.J., Burrin, J.M., Bloom, S.R., 1989. High-dose porcine galanin infusion and effect on intravenous glucose tolerance in

TE

D

humans. Diabetes 38, 1114-1116.

Gottsch, M.L., Zeng, H., Hohmann, J.G., Weinshenker, D., Clifton, D.K., Steiner, R.A.,

AC CE P

2005. Phenotypic analysis of mice deficient in the type 2 galanin receptor (GALR2). Mol. Cell Biol. 25, 4804-4811.

Greiter, M.B., Keck, L., Siegmund, T., Hoeschen, C., Oeh, U., Paretzke, H.G., 2010. Differences in exhaled gas profiles between patients with type 2 diabetes and healthy controls. Diabetes Technol. Ther. 12, 455-463. Guariguata, L., 2012. By the numbers: new estimates from the IDF Diabetes Atlas Update for 2012. Diabetes Res. Clin. Pract. 98, 524-525. Guo, L., Shi, M., Zhang, L., Li, G., Zhang, L., Shao, H., 2011. Galanin antagonist increases insulin resistance by reducing glucose transporter 4 effect in adipocytes of rats. Gen. Comp. Endocrinol. 173, 159-163. He, B., Shi, M., Zhang, L., Li, G., Zhang, L., Shao, H., 2011. Beneficial effect of galanin

22

ACCEPTED MANUSCRIPT on insulin sensitivity in muscle of type 2 diabetic rats. Physiol. Behav. 103, 284-289. Invitti, C., Brunani,

A., Pasqualinotto,

L., Dubini,

A., Bendinelli,

P., Maroni,

PT

P., Cavagnini, F., 1995. Plasma galanin concentrations in obese, normal weight and

RI

anorectic women. Int. J. Obes. Relat. Metab. Disord. 19, 347-349.

Jiang, L., Shi, M., Guo, L., He, B., Li, G., Zhang, L., 2009. Effect of M35, a neuropeptide

NU

skeletal muscle. Neurosci. Lett. 467, 178-81.

SC

galanin antagonist on glucose uptake translated by glucose transporter 4 in trained rat

Johnson, A.M., Olefsky, J.M., 2013. The origins and drivers of insulin resistance.Cell

MA

152, 673-684.

Khan, A.H., Pessin, J.E., 2002. Insulin regulation of glucose uptake: a complex interplay

TE

D

of intracellular signalling pathways. Diabetologia 45, 1475-1483. Kyrkouli, S.E., Stanley, B.G., Seirafi, R.D., Leibowitz, S.F., 1990. Stimulation of feeding

AC CE P

by galanin: anatomical localization and behavioral specificity of this peptide’s effects in the brain. Peptides 11, 995-1001. Lang, R., Gundlach, A.L., Holmes, F.E., Hobson, S.A., Wynick, D., Hökfelt, T., Kofler, B., 2015. Physiology, signaling, and pharmacology of galanin peptides and receptors: three decades of emerging diversity. Pharmacol. Rev. 67, 118-175. Legakis, I.N., 2005a. The role of galanin in metabolic disorders leading to type 2 diabetes mellitus. Drug News Perspect 18, 173-177. Legakis, I., Mantzouridis, T., Mountokalakis, T., 2005b. Positive correlation of galanin with glucose in type 2 diabetes. Diabetes Care 28, 759-60. Legalkis, I.N., Mantzouridis, T., Mountokalakis, T., 2007. Positive correlation of galanin with glucose in healthy volunteers during an oral glucose tolerance test. Horm. Metab.

23

ACCEPTED MANUSCRIPT Res. 39, 53-55. Legakis, I.N., Mantzouridis, T., Saramantis, A., Phenekos, C., Tzioras, C., Mountokalakis,

PT

T., 2000. Human galanin secretion is increased upon normal exercise test in middle-age

RI

individuals. Endocr. Res. 26, 357–364.

Leibowitz, K.L., Chang, G.Q., Pamy, P.S., Hill, J.O., Gayles, E.C., Leibowitz, S.F., 2007.

SC

Weight gain model in prepubertal rats: prediction and phenotyping of obesity-prone

NU

animals at normal body weight. Int. J. Obes (Lond). 31, 1210-1221. Leibowitz, S.F., Dourmashkin, J.T., Chang, G.Q., Hill, J.O., Gayles, E.C., Fried, S.K.,

MA

Wang, J., 2004. Acute high-fat diet paradigms link galanin to triglycerides and their transport and metabolism in muscle. Brain Res. 1008, 168-178.

TE

D

Leto, D., Saltiel, A.R., 2012. Regulation of glucose transport by insulin: traffic control of GLUT4. Nat. Rev. Mol. 459 Cell Biol. 13, 383-396.

AC CE P

Lian, Y., Sheng, S., Fang, P., Ma, Y., Li, J., Shi, Q., 2012. Exercise-induced galanin release facilitated GLUT4 translocation in adipocytes of type 2 diabetic rats. Pharmacol. Biochem. Behav. 100, 554-559. Lundström, L., Sollenberg, U., Brewer, A., Kouya, P.F., Zheng, K., Xu, X., 2005. A galanin receptor subtype 1 specific agonist. Int. J. Peptide Res. Therap. 11, 15-25. Malecki, M.T., 2004. Type 2 diabetes mellitus and its complications: from the molecular biology to the clinical practice. Rev. Diabet. Stud. 1, 5-8. Man, P.S., Lawrence, C.B., 2008. The effects of galanin-like peptide on energy balance, body temperature and brain activity in the mouse and rat are independent of the GALR2/3 receptor. J. Neuroendocrinol. 20, 128-137. Manabe, T., Okada, Y., Sawai, H., Funahashi, H., Yamamoto, M., Hayakawa, T., 2003.

24

ACCEPTED MANUSCRIPT Effect of galanin on plasma glucose, insulin and pancreatic glucagon in dogs. J. Int. Med. Res. 31, 126-132.

PT

Mazzatenta, A., Pokorski, M., Di Giulio, C., 2013. Real-time breath analysis in type 2

RI

diabetes patients during cognitive effort. Adv. Exp. Med. Biol. 788, 247-253. Mazzatenta, A., Marconi, G.D., Zara, S., Cataldi, A., Porzionato, A., Di Giulio C., 2014.

SC

In the carotid body, galanin is a signal for neurogenesis in young, and for

NU

neurodegeneration in the old and in drug-addicted subjects. Front. Physiol. 5, 427. Mazziotti, G., Bonadonna, S., Doga, M., Patelli, I., Gazzaruso, C., Solerte, S.B., De

and

type

2

diabetes

MA

Menis, E., Giustina, A., 2008. Biochemical evaluation of patients with active acromegaly mellitus:

efficacy

and

safety

of

thegalanin test.

TE

D

Neuroendocrinology 88, 299-304.

Meczekalski, B., Warenik-Szymankiewicz, A., 1999. The role of galanin in the etiology

AC CE P

of obesity in young girls. Ginekol. Pol. 70, 328-332. Meex, R.C., Schrauwen-Hinderling, V.B., Moonen-Kornips, E., Schaart, G., Mensink, M., Phielix, E., van de Weijer, T., Sels, J.P., Schrauwen, P., Hesselink, M.K., 2010. Restoration of muscle mitochondrial function and metabolic flexibility in type 2 diabetes by exercise training isparalleled by increased myocellular fat storage and improved insulin sensitivity. Diabetes 59, 572-579. Murray, P.S., Groves, J.L., Pettett, B.J., Britton, S.L., Koch, L.G., Dishman, R.K., Holmes, P.V., 2010. Locus coeruleus galanin expression is enhanced after exercise in rats selectively bred for high capacity for aerobic activity. Peptides 31, 2264-2268.

25

ACCEPTED MANUSCRIPT Nergiz, S., Altınkaya, Ö.S., Küçük, M., Yüksel, H., Sezer, S.D., Kurt Ömürlü, İ., Odabaşı, A.R., 2014. Circulating galanin and IL-6 concentrations in gestational diabetes mellitus.

PT

Gynecol. Endocrinol. 30, 236-240.

RI

Oak, S.A., Tran, C., Pan, G., Thamotharan, M., Devaskar, S.U., 2006. Perturbed skeletal

Physiol. Endocrinol. Metab. 290, E1321-E1330.

SC

muscle insulin signaling in the adult female intrauterine growth-restricted rat. Am. J.

NU

Ozanne, S.E., Olsen, G.S., Hansen, L.L., Tingey, K.J., Nave, B.T., Wang, C.L., 2003. Early growth restriction leads to down regulation of protein kinase C zeta and insulin

MA

resistance in skeletal muscle. J. Endocrinol. 177, 235-241. Olkowicz, M., Ruczyński, J., Cybal, M., Konstański, Z., Petrusewicz, J., Kamińska, B.,

TE

D

2007. New galanin(1-15) analogues modified in positions 9, 10 and 11 act as galanin antagonists on glucose-induced insulin secretion. J. Physiol. Pharmacol. 58, 859-872.

AC CE P

Perry, R.J., Samuel, V.T., Petersen, K.F., Shulman, G.I., 2014.The role of hepatic lipids in hepatic insulin resistance and type 2 diabetes. Nature 510, 84-91. Poritsanos, N.J., Mizuno, T.M., Lautatzis, M.E., Vrontakis, M., 2009. Chronic increase of circulating galanin levels induces obesity and marked alterations in lipid metabolism similar to metabolic syndrome. Int. J. Obes (Lond). 33, 1381-1389. Porzionato, A., Macchi, V., Barzon, L., Masi, G., Belloni, A., Parenti, A., Palù, G., De Caro, R., 2010. Expression and distribution of galanin receptor subtypes in the rat carotid body. Mol. Med. Rep. 3, 37-41. Qi, L., Hu, F.B., Hu, G., 2008. Genes, environment, and interactions in prevention of type 2 diabetes: a focus on physical activity and lifestyle changes. Curr. Mol. Med. 8, 519-532.

26

ACCEPTED MANUSCRIPT Reiss, J.I., Dishman, R.K., Boyd, H.E., Robinson, J.K., Holmes, P.V., 2009. Chronic activity wheel running reduces the severity of kainic acid-induced seizures in the rat:

PT

possible role of galanin. Brain Res. 1266, 54-63.

RI

Ruczyński, J., Cybal, M., Wójcikowski, C., Rekowski, P., 2002. Effects of porcine galanin, galanin(1-15)NH2 and its new analogues on glucose-induced insulin secretion.

SC

Pol. J. Pharmacol. 54, 133-141.

NU

Ruczyński, J., Konstański, Z., Cybal, M., Kocić, I., Rekowski, P., 2010. Aspartimide modified galanin analogue antagonizes galanin action on insulin secretion. Protein Pept.

MA

Lett. 17, 1182-1188.

Saar, I., Runesson, J., McNamara, I., Järv, J., Robinson, J.K., Langel, U., 2011. Novel

TE

D

galanin receptor subtype specific ligands in feeding regulation. Neurochem. Int. 58, 714-720.

AC CE P

Sakamoto, K., Holman, G.D., 2008. Emerging role for AS160/TBC1D4 and TBC1D1 in the regulation of GLUT4 traffic. Am. J. Physiol. Endocrinol. Metab. 295, E29-E37. Sciolino, N.R., Dishman, R.K., Holmes, P.V., 2012. Voluntary exercise offers anxiolytic potential and amplifies galanin gene expression in the locus coeruleus of the rat. Behav Brain Res. 233, 191-200.

Sutton, B.S., Langefeld, C.D., Campbell, J.K., Haffner, S.M., Norris, J.M., Scherzinger, A.L., Wagenknecht, L,E., Bowden, DW., 2006. Genetic mapping of a 17q chromosomal region linked to obesity phenotypes in the IRAS family study. Int. J. Obes (Lond). 30, 1433-1441. Tang, G., Wang, Y., Park, S., Bajpayee, N.S., Vi, D., Nagaoka, Y., 2012. Go2 G protein mediates galanin inhibitory effects on insulin release from pancreatic β cells. Proc. Natl.

27

ACCEPTED MANUSCRIPT Acad. Sci. U. S. A. 109, 2636-2641. Tatemoto, K., Rökaeus, A., Jörnvall, H., McDonald, T.J., Mutt, V., 1983. Galanin-a novel

PT

biologically active peptide from porcine intestine. FEBS Lett. 164, 124-128.

RI

Taylor, R., 2012. Insulin resistance and type 2 diabetes. Diabetes 61, 778-779.

macronutrient selection. Peptides 9, 309-314.

SC

Tempel, D.L., Leibowitz, K.J., Leibowitz, S.F., 1988. Effects of PVN galanin on

NU

Thong, F.S., Bilan, P.J., Klip, A., 2007. The Rab GTPase-activating protein AS160 integrates Akt, protein kinase C, and AMP-activated protein kinase signals regulating

MA

GLUT4 traffic. Diabetes 56, 414-423.

Tonks, K.T., Ng, Y., Miller, S., Coster, A.C., Samocha-Bonet, D., Iseli, T.J., Xu, A.,

TE

D

Patrick, E., Yang, J.Y., Junutula, J.R., Modrusan, Z., Kolumam, G., Stöckli, J., Chisholm, D.J., James, D.E., Greenfield, J.R., 2013. Impaired Akt phosphorylation in

AC CE P

insulin-resistant human muscle is accompanied by selective and heterogeneous downstream defects. Diabetologia 56, 875-885. Tuomilehto, J., Lindström, J., Eriksson, J.G., Valle, T.T., Hämäläinen, H., Ilanne-Parikka, P., Keinänen-Kiukaanniemi, S., Laakso, M., Louheranta, A., Rastas, M., Salminen, V., Uusitupa, M., 2001. Prevention of type 2 diabetes mellitus by changes in lifestyle amongsubjects with impaired glucose tolerance. N. Engl. J. Med. 344, 1343-1350. Webling, K.E., Runesson, J., Bartfai, T., Langel, U., 2012. Galanin receptors and ligands. Front. Endocrinol (Lausanne). 3, 146. Whiting, D.R., Guariguata, L., Weil, C., Shaw, J., 2011. IDF diabetes atlas: global estimates of the prevalence of diabetes for 2011 and 2030. Diabetes Res. Clin. Pract. 94, 311-321.

28

ACCEPTED MANUSCRIPT Yun, R., Dourmashkin, J.T., Hill, J., Gayles, E.C., Fried, S.K., Leibowitz, S.F., 2005. PVN galanin increases fat storage and promotes obesity by causing muscle to utilize

PT

carbohydrate more than fat. Peptides 26, 2265-2273.

RI

Zhang, Z., Gu, C., Fang, P., Shi, M., Wang, Y., Peng, Y., 2014. Endogenous galanin as a novel biomarker to predict gestational diabetes mellitus. Peptides 54, 186-189.

SC

Zhang, Z., Sheng, S., Guo, L., Li, G., Zhang, L., Zhang, L., 2012. Intracerebroventricular

NU

administration of galanin antagonist sustains insulin resistance in adipocytes of type 2 diabetic trained rats. Mol. Cell Endocrinol. 361, 213-218.

MA

Zorrilla, E.P., Brennan, M., Sabino, V., Lu, X., Bartfai, T., 2007. Galanin type 1 receptor knockout mice show altered responses to high-fat diet and glucose challenge. Physiol.

AC CE P

TE

D

Behav. 91, 479-485.

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Figure 1. A schematic model of the hypothetic cascade of events leading to the development of type 2 diabetes mellitus.

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Obesity

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ACCEPTED MANUSCRIPT Highlights ►Galanin may increase body weight of subjects to switch obesity.

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► Galanin elevates insulin sensitivity in human and rodent models. ► Increased secretion and expression of galanin in type 2 diabetes mellitus.

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►Altered expression levels of galanin receptor in type 2 diabetes mellitus.

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► Type 2 diabetes mellitus as a disorder of galanin resistance.

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