Spexin Diminishes Atrial Fibrillation Vulnerability by Acting on Galanin Receptor 2.

BACKGROUND: G protein-coupled receptors play a critical role in atrial fibrillation (AF). Spexin is a novel ligand of galanin receptors (GALRs). In this study, we investigated the regulation of spexin and GALRs on AF and the underlying mechanisms. METHODS: Global spexin knockout (SPX-KO) and cardiomyocyte-specific GALRs knockout (GALR-cKO) mice underwent burst pacing electrical stimulation. Optical mapping was used to determine atrial conduction velocity and action potential duration. Atrial myocyte action potential duration and inward rectifying K+ current (IK1) were recorded using whole-cell patch clamps. Isolated cardiomyocytes were stained with Fluo-3/AM dye, and intracellular Ca2+ handling was examined by CCD camera. A mouse model of AF was established by Ang-II (angiotensin II) infusion. RESULTS: Spexin plasma levels in patients with AF were lower than those in subjects without AF, and knockout of spexin increased AF susceptibility in mice. In the atrium of SPX-KO mice, potassium inwardly rectifying channel subfamily J member 2 (KCNJ2) and sarcolipin (SLN) were upregulated; meanwhile, IK1 current was increased and Ca2+ handling was impaired in isolated atrial myocytes of SPX-KO mice. GALR2-cKO mice, but not GALR1-cKO and GALR3-cKO mice, had a higher incidence of AF, which was associated with higher IK1 current and intracellular Ca2+ overload. The phosphorylation level of CREB (cyclic AMP responsive element binding protein 1) was upregulated in atrial tissues of SPX-KO and GALR2-cKO mice. Chromatin immunoprecipitation confirmed the recruitment of p-CREB to the proximal promoter regions of KCNJ2 and SLN. Finally, spexin treatment suppressed CREB signaling, decreased IK1 current and decreased intracellular Ca2+ overload, which thus reduced the inducibility of AF in Ang-II-infused mice. CONCLUSIONS: Spexin reduces atrial fibrillation susceptibility by inhibiting CREB phosphorylation and thus downregulating KCNJ2 and SLN transcription by GALR2 receptor. The spexin/GALR2/CREB signaling pathway represents a novel therapeutic avenue in the development of agents against atrial fibrillation.

Exercise training and spexin ameliorate thyroid changes in obese type 2 diabetic rats: the possible interlaying mechanisms.

Thyroid dysfunction and diabetes mellitus are prevalent endocrine disorders that often coexist and influence each other. The role of spexin (SPX) in diabetes and obesity is well documented, but its connection to thyroid function is less understood. This study investigates the influence of exercise (EX) and SPX on thyroid hypofunction in obese type 2 diabetic rats. Rats were divided into normal control, obese diabetic sedentary, obese diabetic EX, and obese diabetic SPX groups, with subdivisions for M871 and HT-2157 treatment in the latter two groups. High-fat diet together with streptozotocin (STZ) injection induced obesity and diabetes. The EX group underwent swimming, and the SPX group received SPX injections for 8 wk. Results showed significant improvements in thyroid function and metabolic, oxidative, and inflammatory states with EX and SPX treatment. The study also explored the involvement of galanin receptor isoforms (GALR)2/3 in SPX effects on thyroid function. Blocking GALR2/3 receptors partially attenuated the beneficial effects, indicating their interaction. These findings underscore the importance of EX and SPX in modulating thyroid function in obesity and diabetes. Comprehending this interplay could enable the development of new treatment approaches for thyroid disorders associated with obese type 2 diabetes. Additional research is necessary to clarify the exact mechanisms connecting SPX, EX activity, and thyroid function.NEW & NOTEWORTHY This study proves, for the first time, the beneficial effects of SPX on thyroid dysfunction in obese diabetic rats and suggests that SPX mediates the EX effect on thyroid gland and exerts its effect mainly via GALR2.

Spexin acts as a novel glucose-lowering factor in grass carp (Ctenopharyngodon idella).

At present, the physiological roles of various hormones in fish glucose metabolism have been elucidated. Spexin, a 14-amino acids polypeptide, is highly conserved in many species and has functions such as reducing body weight and improving insulin resistance. In this paper, the open reading frame (ORF) of spx21 in grass carp (Ctenopharyngodon idella) was cloned, and the tissue distribution of spx1 and spx2, their direct and indirect regulatory effects on glucose metabolism of grass carp were investigated. The ORF of spx2 gene in grass carp was 279 bp in length. Moreover, spx1 was highly expressed in the adipose tissue, while spx2 was highly expressed in the brain. In vitro, SPX1 and SPX2 showed opposite effects on the glycolytic pathway in the primary hepatocytes. In vivo, intraperitoneal injection of SPX1 and SPX2 significantly reduced serum glucose levels and increased hepatopancreas glycogen contents. Meanwhile, SPX1 and SPX2 promoted the expression of key genes of glycolysis (pk) and glycogen synthesis (gys) in the hepatopancreas at 3 h post injection. As for indirect effects, 1000 nM SPX1 and SPX2 significantly increased insulin-mediated liver type phosphofructokinase (pfkla) mRNA expression and enhanced the inhibitory effects of insulin on glucose-6-phosphatase (g6pase), phosphoenolpyruvate carboxykinase (pepck), glycogen phosphorylase L (pygl) mRNA expression. Our results show that SPX1 and SPX2 have similar indirect effects on the regulation of glucose metabolism that enhance insulin activity, but they exhibit opposite roles in terms of direct effects.

Novel hypothalamic pathways for metabolic effects of spexin.

One of the main underlying etiologies of type 2 diabetes (T2DM) is insulin resistance, which is most frequently caused by obesity. Notably, the deregulation of adipokine secretion from visceral adiposity has been identified as a crucial characteristic of type 2 diabetes and obesity. Spexin is an adipokine that is released by many different tissues, including white adipocytes and the glandular stomach, and is negatively connected with the state of energy storage. This peptide acts through GALR2/3 receptors to control a wide range of metabolic processes, including inflammation, browning, lipolysis, energy expenditure, and eating behavior. Specifically, spexin can enter the hypothalamus and regulate the hypothalamic melanocortin system, which in turn balances energy expenditure and food intake. This review examines recent advances and the underlying mechanisms of spexin in obesity and T2DM. In particular, we address a range of topics from basic research to clinical findings, such as an analysis of the possible function of spexin in the hypothalamic melanocortin response, which involves reducing energy intake and increasing energy expenditure while also enhancing insulin sensitivity and glucose tolerance. Gaining more insight into the mechanisms that underlie the spexin system's control over energy metabolism and homeostasis may facilitate the development of innovative treatment approaches that focus on combating obesity and diabetes.

The Checkpoints of Intestinal Fat Absorption in Obesity.

In this chapter, intestinal lipid transport, which plays a central role in fat homeostasis and the development of obesity in addition to the mechanisms of fatty acids and monoacylglycerol absorption in the intestinal lumen and reassembly of these within the enterocyte was described. A part of the resynthesized triglycerides (triacylglycerols; TAG) is repackaged in the intestine to form the hydrophobic core of chylomicrons (CMs). These are delivered as metabolic fuels, essential fatty acids, and other lipid-soluble nutrients, from enterocytes to the peripheral tissues following detachment from the endoplasmic reticulum membrane. Moreover, the attitudes of multiple receptor functions in dietary lipid uptake, synthesis, and transport are highlighted. Additionally, intestinal fatty acid binding proteins (FABPs), which increase the cytosolic flux of fatty acids via intermembrane transfer in enterocytes, and the functions of checkpoints for receptor-mediated fatty acid signaling are debated. The importance of the balance between storage and secretion of dietary fat by enterocytes in determining the physiological fate of dietary fat, including regulation of blood lipid concentrations and energy balance, is mentioned. Consequently, promising checkpoints regarding how intestinal fat processing affects lipid homeostatic mechanisms and lipid stores in the body and the prevention of obesity-lipotoxicity due to excessive intestinal lipid absorption are evaluated. In this context, dietary TAG digestion, pharmacological inhibition of TAG hydrolysis, the regulation of long-chain fatty acid uptake traffic into adipocytes, intracellular TAG resynthesis, the enlargement of cytoplasmic lipid droplets in enterocytes and constitutional alteration of their proteome, CD36-mediated conversion of diet-derived fatty acid into cellular lipid messengers and their functions are discussed.

The Investigation of Kisspeptin, Spexin and Galanin in Euthyroid Women with Hashimoto's Thyroiditis.

OBJECTIVE: The hallmarks of Hashimoto's thyroiditis (HT) include the destruction of thyroid cells by leading to insulin resistance (IR), hypothyroidism, and metabolic abnormalities. Kisspeptin, spexin, and galanin control appetite and body weight (BW) to regulate metabolisms. Here, we sought to determine if galanin, kisspeptin, and spexin are linked to the pathophysiology of HT in euthyroid female individuals. METHODS: Forty-five women with HT and 45 healthy control women of the same age participated in the current study. The enzyme-linked immunosorbent assay (ELISA) method was used to measure the serum levels of galanin, spexin, and kisspeptin. RESULTS: In comparison to the controls, HT patients had significantly higher levels of kisspeptin (p < 0.01), galanin (p < 0.01), anti-thyroid peroxidase (anti-TPO) (p < 0.001), anti-thyroglobulin (anti-Tg) (p < 0.001), and body mass index (BMI) (p < 0.05). The two groups were comparable in terms of spexin, free triiodothyronine-3 (fT3), fT4, thyroid-stimulating hormone (TSH) levels, and homeostatic model assessment for insulin resistance (HOMA-IR). Galanin and kisspeptin were seen to have a positive correlation (p < 0.01; r = 0.786). CONCLUSIONS: Euthyroid women with HT were found to have higher levels of kisspeptin and galanin. These results imply that kisspeptin and galanin may be linked to the pathogenesis of hypothyroidism, and as a result, we believe that these markers may be beneficial in the early detection and treatment of HT patients.

Role of Spexin in White Adipose Tissue Thermogenesis under Basal and Cold-Stimulated Conditions.

Spexin (SPX) is a novel adipokine that plays an emerging role in metabolic diseases due to its involvement in carbohydrate homeostasis, weight loss, appetite control, and gastrointestinal movement, among others. In obese patients, SPX plasma levels are reduced. Little is known about the relationship between SPX and white adipose tissue (WAT) thermogenesis. Therefore, the aim of the present study was to evaluate the role of SPX in this process. C57BL/6J male mice were treated or not with SPX for ten days. On day 3, mice were randomly divided into two groups: one kept at room temperature and the other kept at cold temperature (4 °C). Caloric intake and body weight were recorded daily. At the end of the protocol, plasma, abdominal (epididymal), subcutaneous (inguinal), and brown AT (EAT, IAT, and BAT, respectively) depots were collected for measurements. We found that SPX treatment reduced Uncoupling protein 1 levels in WAT under both basal and cold conditions. SPX also reduced cox8b and pgc1α mRNA levels and mitochondrial DNA, principally in IAT. SPX did not modulate the number of beige precursors. SPX decreased spx levels in IAT depots and galr2 in WAT depots. No differences were observed in the BAT depots. In conclusion, we showed, for the first time, that SPX treatment in vivo reduced the thermogenic process in subcutaneous and abdominal AT, being more evident under cold stimulation.

Spexin and its receptors in the yellowtail kingfish (Seriola lalandi): identification, expression profiles and reproductive function.

Spexin (SPX1) is a neuropeptide of 14 amino acids (aa), originally identified by bioinformatics, which has been implicated in various physiological functions in vertebrates via galanin receptors 2 and 3 (GALR2/3). To clarify the biological role of SPX1 in the control of reproduction in yellowtail kingfish, which is regarded as a promising species for offshore aquaculture worldwide, cDNA sequences of spx1 and six potential receptors were identified in the current study. The open reading frame of yellowtail kingfish spx1 was 363 nucleotides in size that encoded a 120-aa preprohormone, and its mature peptide was highly conserved among other species. The cDNA sequences of six GALRs (galr1a, galr1b, galr2a, galr2b, galr type 1, and galr type 2) were 1053 base pairs (bp), 1068 bp, 981 bp, 1137 bp, 1038 bp, 924 bp, which encoded G protein-coupled receptors of 350 aa, 355 aa, 326 aa, 378 aa, 345 aa, 307 aa, respectively. Tissue distribution analysis showed that spx1, galr1b, and galr2b transcripts were mainly detected in the brain. The highest mRNA levels of galr1a and galr2a were observed in the pituitary, followed by the brain and ovary. Both galr type 1 and galr type 2 were widely expressed in various tissues, with a peak level in the kidney. Moreover, all spx1 and galr genes significantly fluctuated during early ontogeny, exhibiting different expression patterns. Intraperitoneal injection of SPX1 significantly increased brain gnrh1, gnih, spx1, gal, and tac3 expression, while it inhibited gnrh2, kiss1r, and kiss2r mRNA levels. In the pituitary, SPX1 injection reduced transcript levels of gh, lhß, and fshß. Overall, our results have revealed the involvement of SPX1 in the reproductive functions in yellowtail kingfish.

Spexin role in human granulosa cells physiology and PCOS: expression and negative impact on steroidogenesis and proliferation†.

Spexin (SPX) is a novel neuropeptide and adipokine negatively correlated with obesity and insulin resistance. A recent study investigated expression and regulatory function of SPX in the hypothalamus and pituitary; however, the effect on ovarian function is still unknown. The aim of this study was to characterize the expression of SPX and its receptors, galanin receptors 2 and 3 (GALR2/3), in the human ovary and to study its in vitro effect on granulosa cells (GC) function. Follicular fluid (FF) and GC were obtained from normal weight and obese healthy and diagnosed with polycystic ovarian syndrome (PCOS) women. Expression of SPX and GALR2/3 in the ovary was studied by qPCR, western blot, and immunohistochemistry. The level of SPX in FF was assessed by enzyme-linked immunosorbent assay. The in vitro effect of recombinant human SPX on GC proliferation, steroidogenesis, and signaling pathways (MAP3/1, STAT3, AKT, PKA) was analyzed. Moreover, GC proliferation and estradiol (E2) secretion were measured with and without an siRNA against GALR2/3 and pharmacological inhibition of the above kinases. The results showed that both the SPX concentration in FF and its gene expression were decreased in GC of obese and PCOS women, while the protein expression of GALR2/3 was increased. We noted that SPX reduced GC proliferation and steroidogenesis; these effects were mediated by GALR2/3 and kinases MAP3/1, AKT, and STAT3 for proliferation or kinases MAP3/1 and PKA for E2 secretion. The obtained data clearly documented that SPX is a novel regulator of human ovarian physiology and possibly plays a role in PCOS pathogenesis.

Evaluation of the adipokine levels of pregnant women with preeclampsia.

AIM: The aim of this study was to compare maternal blood and umbilical-cord leptin, spexin and visfatin levels during delivery in severe preeclampsia (PE) with controls, and to evaluate whether any clinical or demographic variables had independent associations with them. METHODS: This is a case-controlled observational study consisting of 45 pregnant women with severe PE and a control group consisting of gestational age-matched 45 healthy pregnant women. We examined the leptin, spexin, and visfatin levels in serum samples taken from maternal blood and umbilical cords during cesarean section in both groups. Leptin, spexin, and visfatin levels were measured by enzyme-linked immunosorbent assay. RESULTS: The maternal leptin and visfatin levels were significantly higher and the maternal spexin levels were significantly lower in the PE group than in the control group (p < 0.001). Similar to the maternal adipokine levels, the umbilical-cord leptin and visfatin levels were significantly higher and the spexin levels were significantly lower in the PE group (p < 0.001). We found a significant positive correlation between maternal body mass index and maternal blood and umbilical-cord serum leptin and visfatin levels in both groups (p < 0.001). CONCLUSION: The leptin, spexin and visfatin levels were significantly altered in the nondiabetic preeclamptic women in our study. We believe that the main reason for these changes may be the hypoxic placenta to protect the fetus and maintain its nutrition.