Effects of stanniocalcin hormones on rat brown adipose tissue metabolism under fed and fasted conditions

https://doi.org/10.1016/j.mce.2019.02.004Get rights and content

Highlights

  • BAT expressed Stc1 and Stc2, and fasting increased Stc2 expression.

  • HSTC-1 increased glucose uptake in BAT of fed rats.

  • HSTC-1 increased CO2 formation in BAT of fasting rats.

  • HSTC-2 decreased glycogen levels in BAT of fed rats.

  • HSTC-2 increased glycogen concentration in BAT of fasting rats.

Abstract

In this study we determined the effect of fed and fasting (48 h) states on the expression of stanniocalcin-1 (Stc1) and stanniocalcin-2 (Stc2) in rat brown adipose tissue (BAT), as well as the in vitro effects of human stanniocalcin 1 and 2 (hSTC-1 and hSTC-2) hormones on lipid and glucose metabolism. In addition, lactate, glycogen levels and hexokinase (HK) activity were determined. In fasting Stc2 expression increased markedly. The targets of action of hSTC-1 and hSTC-2 were glucose uptake and oxidation as well as glycogen storage, controlling the energetic metabolism in BAT. The reduction in glycogen concentration induced by hSTC-2 in fed state might have deleterious consequences in BAT, such as decreased thermogenic activity, FA esterification and other adipocyte functions. On the other hand, the increase of glucose uptake caused by hSTC-1 of fed rats could play a role as a plasma glucose-clearing hormone in the postprandial period.

Introduction

Brown adipose tissue (BAT) is a highly specialized tissue involved in non-shivering thermogenesis in mammals (Tapia et al., 2018). It was believed that BAT is active only in small rodents or infants, but recent studies have shown BAT activity in human adults, mainly in the supraclavicular and paravertebral spaces and adjacent to the neck vessels (Cannon and Nedergaard, 2004; Cypess et al., 2009). BAT is densely vascularized, and the brown adipocytes have multilocular depots of triacylglycerols (TG), and a large number of mitochondria (Rosen and Spiegelman, 2014). Thermogenesis in BAT is accomplished via uncoupling protein 1 (UCP-1), which is present in large amounts in mitochondria and is responsible for uncoupling the ATP production and instead produce heat (Rui, 2017). The proton leak via UCP-1 is enhanced by long-chain fatty acid (FA) and inhibited at rest by cytosolic purine nucleotides, mainly ATP (Bouillaud et al., 2016; Thoonen et al., 2016). The central nervous system controls BAT activation via norepinephrine, which binds to β-adrenergic receptors (Cannon and Nedergaard, 2004; Caron et al., 2018; Chen et al., 2017). Other BAT specific activators that increase FA availability to mitochondria have been identified, such as thyroid hormones, retinoids, leptin, natriuretic peptides (Thoonen et al., 2016). Recently, many studies suggest that BAT activation regulates insulin sensitivity (Chondronikola et al., 2014; Lee et al., 2016), lipid homeostasis (Chondronikola et al., 2014), body mass/composition (Yoneshiro et al., 2013) and glucose metabolism (Bartelt et al., 2011). BAT secrete several adipokines, such as neuregulin 4, insulin-like growth factor I (IGF-1), leptin, adiponectin and interleukin-6 that act either on the secreting brown adipocytes (autocrine action) or on other cells types nearby (paracrine action) (Rui, 2017). Also several paracrine, autocrine factors and endocrine (insulin, glucagon, triiodothyronine, glucocorticoids), have been demonstrated to regulate the development, maintenance, and function of BAT (Rosen and Spiegelman, 2014; Villarroya et al., 2017).

Stanniocalcin (STC) hormone was first isolated in fish where it was shown to regulate calcium/phosphate homeostasis (Chang et al., 1995; Olsen et al., 1996). In mammals, STC-1 is expressed in a wide range of tissues (De Niu et al., 2000). However, outside of pregnancy and lactation, the mammalian hormone is undetectable in the blood of rats (Juhanson et al., 2016). The data indicate that in mammals, the effect of STC-1 on target cells, such as kidneys, liver, ovary, pancreas, among others, is consistent with paracrine and/or autocrine actions. (De Niu et al., 2000; Yeung et al., 2012). The putative role of STC-1 in intermediary metabolism has been demonstrated in transgenic mice that overexpress this hormone, as these mice exhibit increased food and oxygen consumption in combination with reduced body weight (Filvaroff et al., 2002; Varghese et al., 1998). This energy-wasting phenotype is likely due to the stimulatory effects of STC-1 on mitochondrial electron transport (McCudden et al., 2004), which in excess can result in mitochondrial hypertrophy (Filvaroff et al., 2002). In rats, human STC-1 (hSTC-1) decreased renal gluconeogenic activity when the substrate was 14C-glutamate (Schein et al., 2015). Interestingly, in retroperitoneal white adipose tissue (rWAT) of fed rats, hSTC-1 increases the incorporation of 14C from glucose into total lipids (Cozer et al., 2016). Also, Cozer et al. (2017) showed that hSTC-1 decreases the incorporation of 14C from glucose into total lipids in BAT of fed rats. The authors suggested that the capacity of the glycerol-3-phosphate (G3P)-generating pathway (glycolysis) from glucose is regulated by hSTC-1, decreasing the adequate supply of G3P needed for fatty acid esterification and TG storage in BAT, compromising the tissue thermogenic capacity (Cozer et al., 2017). In addition, the presence of hSTC-1 in the incubation medium did not alter 14C-glucose and 14C-1-palmitic acid oxidation, or uncoupling protein 1 (UCP-1) expression in BAT of fed rats (Cozer et al., 2017).

Stanniocalcin-2 (STC-2) is a paralogue of STC-1 and in mammals it is expressed in nearly all tissues and regulates various biological processes, such as ion transport, cell proliferation, reproduction, and the stress response (Yeung et al., 2012; Zeiger et al., 2011). López et al. (2018) proposed that stanniocalcins, particularly STC-2, are markers of the onset and progression of diabetes mellitus type 2 (DM2) (López et al., 2018). Recently, Jiao et al. (2017) showed that STC-2 acts as an anorexic factor that leads to a significant reduction in body weight (Jiao et al., 2017).

In rats, BAT displays very high rates of glucose uptake per unit weight, and it can constitute a significant glucose-clearing organ especially under sympathetic activation (Cannon and Nedergaard, 2004; Festuccia et al., 2011). In humans, BAT has a great glucose-clearing potential for treating diabetes and other metabolic disorders (Betz and Enerbäck, 2015). Winther et al. (2018) showed that β-adrenergically activated brown adipocytes consume large amounts of glucose, but knockdown of the glycolytic enzymes hexokinase 2 (HK2) and pyruvate kinase M (PKM) in the immortalized brown adipocytes has pronounced negative effects on brown adipocyte glucose and oxygen consumption. Recently, Hjortebjerg et al. (2018) described the presence of STC-2 gene expression in murine BAT. On the other hand, Zhang ete al. (2000) and Zeiger et al. (2011) have suggested that STC-1 and STC-2 play an important role in the cellular response to stress, and 48 h of fasting is a stressful situation for rats. During a stressful situation, the sympathetic nervous system markedly increases glucose uptake in BAT via GLUT-1 (Cannon and Nedergaard, 2004). In BAT, glucose is used for: 1) conversion to glycerol-3-phosphate (G3P) by glycerophosphate dehydrogenase in the glycolytic pathway; 2) de novo lipogenesis; 3) glycogen synthesis; and 4) oxidation (Cannon and Nedergaard, 2004; Carpentier et al., 2018). On the other hand, in BAT the glycerol produced by hydrolysis of stored TG or taken up from plasma is directly converted to G3P by glycerokinase.

On the basis of the above-described literature results, we investigated if the hSTC-1 and hSTC-2 hormones would control the 14C-glucose and 14C-glycerol flux in BAT from fed or fasting rats. Accordingly, Stc1 and Stc2 expression in fed and 48 h fasting states were determined. Moreover, we carried out an in vitro investigation of the role of hSTC-1 and hSTC-2 on [2–14C]-deoxyglucose (2-DG) uptake, 14C-glyceride-glycerol generation from 14C-glucose or direct phosphorylation of 14C-glycerol, de novo lipogenesis from 14C-glucose or 14C-glycerol and 14CO2 production from 14C-glucose in BAT of fed and fasted rats. In addition, lactate and glycogen levels and hexokinase activity (HK) were determined in BAT from fed and fasted rats.

Section snippets

Animals

Adult male Wistar rats weighing 300 ± 50 g were kept at 22 ± 2 °C with a light/dark cycle of 12 h/12 h. The rats were acclimated to animal facilities for one week and randomly divided into two groups: 1) fed rats consumed a standard diet (20% protein, 55% carbohydrate, and 4.5% lipids; Nutrilab® Brazil) and water ad libitum; and 2) fasted rats were housed in individual cages, with a bed of wood shavings (to improve thermal comfort), and fasted for 48 h with access to water ad libitum. The

Results

Fasting (48 h) did not affect Stc1 expression (Fig. 1). However, Stc2 expression nearly doubled (P < 0.0001) after 48 h fasting when compared with fed state (Fig. 1). Moreover, in fed rats Stc2 gene expression in BAT was fourfold higher when compared to Stc1 gene expression and, in fasting rats, Stc2 gene expression in BAT was twentyfold higher when compared to Stc1 gene expression (P < 0.0001) (Fig. 1).

Fasting (48 h) increased (P < 0.05) the 2-DG uptake in BAT slices (Fig. 2). In fed state,

Discussion

The presence of Stc1 and Stc2 expression in BAT confirms the participation of these hormones in the metabolic regulation of this important thermogenic tissue in mammals. Moreover, in fed rats Stc2 expression in BAT was fourfold higher than Stc1 expression. Hjortebjerg et al. (2018) found that Stc2 expression in BAT of fed mouse had the lowest expression levels compared with epididymal and retroperitoneal white adipose tissues (Hjortebjerg et al., 2018).

Sympathetic innervation is known to

Conclusions

The present study shows that alimentary status controls Stc2 expression, increasing markedly after 48 h of fasting. Stanniocalcins did not alter 14C-glyceride-glycerol and 14C-fatty acid synthesis from 14C-glucose or 14C-glycerol. The targets of action of hSTC-1 and hSTC-2 in BAT were glucose uptake and oxidation as well as glycogen storage, controlling glucose metabolism in BAT. The reduction in glycogen concentration induced by hSTC-2 in fed state might have deleterious consequences in BAT,

References (57)

  • R. Hjortebjerg et al.

    Depot-specific and GH-dependent regulation of IGF binding protein-4, pregnancy-associated plasma protein-A, and stanniocalcin-2 in murine adipose tissue

    Growth Hormone IGF Res.

    (2018)
  • P.B. Jakus et al.

    Cooperation between BAT and WAT of rats in thermogenesis in response to cold, and the mechanism of glycogen accumulation in BAT during reacclimation

    J. Lipid Res.

    (2008)
  • A.V. Kalinovich et al.

    UCP1 in adipose tissues: two steps to full browning

    Biochimie

    (2017)
  • A.Y. Law et al.

    Vasopressin controls stanniocalcin-1 gene expression in rat and mouse kidney

    Mol. Cell. Endocrinol.

    (2012)
  • P. Lee et al.

    Brown adipose tissue exhibits a glucose-responsive thermogenic biorhythm in humans

    Cell Metabol.

    (2016)
  • C.R. McCudden et al.

    Co-localization of stanniocalcin-1 ligand and receptor in human breast carcinomas

    Mol. Cell. Endocrinol.

    (2004)
  • E.D. Rosen et al.

    What we talk about when we talk about fat

    Cell

    (2014)
  • V. Schein et al.

    Stanniocalcin 1 effects on the renal gluconeogenesis pathway in rat and fish

    Mol. Cell. Endocrinol.

    (2015)
  • E. Van Handel

    Estimation of glycogen in small amounts of tissue

    Anal. Biochem.

    (1965)
  • B.H.Y. Yeung et al.

    Evolution and roles of stanniocalcin

    Mol. Cell. Endocrinol.

    (2012)
  • A. Bartelt et al.

    Brown adipose tissue activity controls triglyceride clearance

    Nat. Med.

    (2011)
  • M.J. Betz et al.

    Human brown adipose tissue: what we have learned so far

    Diabetes

    (2015)
  • L. Botion et al.

    Increased adipose tissue glyceroneogenesis in rats adapted to a high protein, carbohydrate-free diet

    Horm. Metab. Res.

    (1995)
  • R.J. Brushia et al.

    Phosphorylase kinase: the complexity of its regulation is reflected in the complexity of its structure

    Front. Biosci.

    (1999)
  • D. Bueno et al.

    Ontogenetic study of glucose and lactate utilisation by rat cerebellum slices

    Med. Sci. Res.

    (1994)
  • B. Cannon et al.

    Brown adipose tissue: function and physiological significance

    Physiol. Rev.

    (2004)
  • A. Caron et al.

    Leptin and brain-adipose crosstalks

    Nat. Rev. Neurosci.

    (2018)
  • A.C. Carpentier et al.

    Brown adipose tissue energy metabolism in humans

    Front. Endocrinol.

    (2018)
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