Nesfatin-1 as a New Potent Regulator in Reproductive System

Nesfatin-1 is a recently discovered anorexigenic peptide which is distributed in several brain areas implicated in the feeding and metabolic regulation. Recently, it has been reported that nesfatin-1 is expressed not only in brain, but also in peripheral organs such as digestive organs, adipose tissues, heart, and reproductive organs. Nesfatin-1 is markedly expressed in the pancreas, stomach and duodenum. Eventually, the nesfatin-1 expression in the digestive organs may be regulated by nutritional status, which suggests a regulatory role of peripheral nesfatin-1 in energy homeostasis. Nesfatin-1 is also detected in the adipose tissues of humans and rodents, indicating that nesfatin-1 expression in the fat may regulate food intake independently, rather than relying on leptin. In addition, nesfatin-1 is expressed in the heart as a cardiac peptide. It suggests that nesfatin-1 may regulate cardiac function and encourage clinical potential in the presence of nutrition-dependent physio-pathologic cardiovascular diseases. Currently, only a few studies demonstrate that nesfatin-1 is expressed in the reproductive system. However, it is not clear yet what function of nesfatin-1 is in the reproductive organs. Here, we summarize the expression of nesfatin-1 and its roles in brain and peripheral organs and discuss the possible roles of nesfatin-1 expressed in reproductive organs, including testis, epididymis, ovary, and uterus. We come to the conclusion that nesfatin-1 as a local regulator in male and female reproductive organs may regulate the steroidogenesis in the testis and ovary and the physiological activity in epididymis and uterus.


INTRODUCTION
Nucleobindin precursor protein, which was identified for the first time in the human and mouse cell lines, is known to have two isotypes, nucleobindin 1 (NUCB1) and nucleobindin 2 (NUCB2) (Miura et al., 1992;Kanai & Tanuma, 1992;Barnikol-Watanabe et al., 1994). This precursor protein contains multiple functional domains including a signal peptide on the N-terminal side, a leucine/isoleucine rich region, a DNA binding domain and a putative nuclear targeting signal, while the second half contains two Ca 2+ -EF-hand motifs and a leucine zipper motif in the C-terminal region (Barnikol-Watanabe et al., 1994). However, NUCB2 only functions physio-logically in humans and rodents (Miura et al., 1992).

Expression of nesfatin-1 in the brain
Nesfatin-1 is initially known to be expressed in the rat hypothalamic nuclei for ingestive behavior regulation

Nesfatin-1 as a New Potent Regulator in Reproductive System
Jinhee Kim and Hyunwon Yang Dept. of Bioenvironmental Technology,College of Natural Sciences,Seoul Women's University,Korea such as the paraventricular nucleus of the hypothalamus (PVN), supraoptic nucleus (SO), arcuate nucleus (ARC), lateral hypothalamic area (LHA), zona incerta and the nucleus of the solitary tract in rats (Oh-I et al., 2006).
2. Roles of nesfatin-1 in the brain

1) Regulation of food intake
The various studies were performed about the central action of nesfatin-1. The initial report showed that the post third ventricular (3v) or fourth ventricle (4v) injection of nesfatin-1 decreases dark phase food intake in freely fed rats (Oh-I et al., 2006). Similarly, injection of nesfatin-1 into the lateral brain ventricle (intracerebroventricular, icv) of ad libitum fed rats reduced the dark phase food intake and controlled the water drinking (Shimizu et al., 2009a;Stengel et al., 2009a;Stengel et al., 2010a;Yosten & Samson, 2009;Yosten et al., 2012). Likewise, microinjection of nesfatin-1 directly into the PVN also suppresses the dark phase food intake in male rats (Maejima et al., 2009;Stengel et al., 2009a).  (Oh-I et al., 2006).

2) Brain activation by stressors
Some studies demonstrated that central nesfatin-1 may play a role in the response to stress, such as abdominal surgery, inflammatory stimulus, intraperitoneal injection of lipopolysaccharide and eating disorder (Bonnet et al., 2009;Dayas et al., 1999;Goebel et al., 2009b;Merali et al., 2008;Okere et al., 2010;Stengel et al., 2010b;Stengel et al., 2011;Xu et al., 2010). These findings are based on the result of that icv nesfatin-1 exerts a CRF receptor-dependent effect in food intake and the central distribution in forebrain, hindbrain and spinal autonomic nuclei, along with the expression of nesfatin-1 in CRF neuron (Foo et al., 2008;Stengel et al., 2009a). In addition, the brain activation by stress is associated with the co-localization of nesfatin-1 immunoreactive neurons and brain transmitters, such as a neurotensin, urocortin and serotonin .

3) Effect of anti-inflammatory and anti-apoptosis
Recent two studies reported that effects of nesfatin-1 as an anti-inflammatory and anti-apoptotic peptide in subarachnoid hemorrhage (SAH)-induced rats (O¨zsavci et al., 2011;Tang et al., 2012). These findings suggest that nesfatin-1 exerts neuroprotection in SAH-induced injury in rats by inhibiting neutrophil infiltration and nuclear factor kappa-B-dependent inflammatory responses.
In the pancreas, nesfatin-1 is located in rat islet betacells (Gonzalez et al., 2009) and secreted by high glucose stimulation in vitro Gonzalez et al., 2011a). A certain study has reported that intravenous administration of nesfatin-1 has anti-hyperglycemic effects in hyperglycemic db/db mice (Su et al., 2011). However, this reduction in blood glucose levels was not observed in non-hyperglycemic animals and appears to be insulindependent (Gonzalez et al., 2012a;Su et al., 2011). significantly reduces nesfatin-1 plasma revels in rats . Furthermore, nesfatin-1, which is released from the synaptic endings of the vagus nerve, has an impact on secretory and motor activity of the gastrointestinal tract and regulates the course of digestive functions Stengel et al., 2009b;Xia et al., 2012). Interestingly, a recent paper has been demonstrated that pretreatment with capsaicin (to block autonomic C fibers) abolished the food intake reduction caused by peripheral nesfatin-1 injection. These findings indicate a putative role of vagal afferents in peripheral nesfatin-1 signaling to the brain centers (Shimizu et al., 2009c).
To date, a few studies have focused on nesfatin-1 in the human digestive system. Circulating levels of nesfatin-1 were significantly reduced in fasted type-2-diabetic patients compared to healthy subjects and type-1-diabetic patients.
In addition, intravenous infusion of glucose significantly elevated basal nesfatin-1 levels in healthy adults . However, circulating nesfatin-1 levels were not altered under an oral glucose tolerance test (Tsuchiya et al., 2010). Interestingly, circulating nesfatin-1 levels were significantly lower in patients with restricting-type anorexia nervosa (Ogiso et al., 2011). These results demonstrate that nesfatin-1 expression in the digestive organs is regulated by nutritional status, suggesting a potential role of peripheral nesfatin-1 in energy metabolism.

Expression of nesfatin-1 and its roles in adipose tissues
Nesfatin binding sites were displayed at boundary cells in the tunica albuginea of the testis (Fig. 1B). These results support that paracrine signaling by nesfatin-1 between In addition, we demonstrated that large amounts of nesfatin-1 expression were detected in the mouse epididymis as well as the testis (Kim et al., 2011a). Immunohistochemistry results displayed that nesfatin-1 was expressed at the columnar epithelium ( Fig. 2A). Nesfatin-1 binding sites were also localized at the columnar epithelium  Interestingly, the granulosa and cumulus cells around the oocytes were stained with nesfatin-1, but not the corpus luteum (Fig. 3A). On the other hand, nesfatin-1 binding sites were detected in the theca cells and interstitial cells around follicles (Fig. 3B). These results suggest that nesfatin-1 may play a role as a local regulator via autocrine and paracrine signaling to regulate the steroid- nesfatin-1 was localized on the epithelial cells of endometrium and uterine glands in the uterus (Fig. 4A).
Nesfatin-1 binding sites were displayed in the epithelial cells of uterine glands and neutrophils in the endometrium (Fig. 4B). Neutrophils are known to play an important role in the collapse and recovery of the endometrium (Kaitu'u-Lino et al., 2007). During estrous cycle, neutrophils move from blood into endometrium and the number of them are dramatically increased in the estrous phase (Sonoda et al., 1998;Steffl et al., 2010).
Based on these reports, the finding that nesfatin-1 binding sites were localized on the neutrophils suggests that uterine function may be regulated by nesfatin-1 to attract neutrophils from blood into the endometrium and activate them. In addition, we previously demonstrated that nesfatin-1/NUCB2 expression in the uterus is regulated by estrogen, but not gonadotropin. Its expression levels were significantly increased in the ovariectomized mice treated with 17β-estradiol, whereas the mice treated with PMSG showed no difference compared to non-treated mice (Kim et al., 2011b). These results suggest that nesfatin-1/NUCB2 expression in the uterus may be regulated by estrogen secreted from the ovary, but not gonadotropin released by the pituitary gland.

CONCLUSION
Nesfatin-1 protein produced by neurons in the hypothalamus is known to be secreted into cerebrospinal fluid, be controlling appetite and energy metabolism (Oh-I et al., 2006). Recently, it has been reported that nesfatin-1 is expressed in digestive organs such as the stomach and pancreas (Stengel et al., 2009c) and in adipose tissues (Ramanjaneya et al., 2010  1 reduces darkphase food intake and gastric emptying in rats: differential role of corticotropin-releasing factor 2 receptor. Endocrinology 150:4911-4919.