A uroguanylin-GUCY2C endocrine axis regulates feeding in mice

Intestinal enteroendocrine cells are critical to central regulation of caloric consumption, since they activate hypothalamic circuits that decrease appetite and thereby restrict meal size by secreting hormones in response to nutrients in the gut. Although guanylyl cyclase and downstream cGMP are essential regulators of centrally regulated feeding behavior in invertebrates, the role of this primordial signaling mechanism in mammalian appetite regulation has eluded definition. In intestinal epithelial cells, guanylyl cyclase 2C (GUCY2C) is a transmembrane receptor that makes cGMP in response to the paracrine hormones guanylin and uroguanylin, which regulate epithelial cell dynamics along the crypt-villus axis. Here, we show that silencing of GUCY2C in mice disrupts satiation, resulting in hyperphagia and subsequent obesity and metabolic syndrome. This defined an appetite-regulating uroguanylin-GUCY2C endocrine axis, which we confirmed by showing that nutrient intake induces intestinal prouroguanylin secretion into the circulation. The prohormone signal is selectively decoded in the hypothalamus by proteolytic liberation of uroguanylin, inducing GUCY2C signaling and consequent activation of downstream anorexigenic pathways. Thus, evolutionary diversification of primitive guanylyl cyclase signaling pathways allows GUCY2C to coordinate endocrine regulation of central food acquisition pathways with paracrine control of intestinal homeostasis. Moreover, the uroguanylin-GUCY2C endocrine axis may provide a therapeutic target to control appetite, obesity, and metabolic syndrome.

Body mass reflects central regulation of caloric consumption by enteroendocrine cells that sense nutrients in the gastrointestinal tract and secrete hormones that activate hypothalamic circuits limiting meal size (1). Although guanylyl cyclase and downstream cGMP signaling are essential regulators of feeding behavior and satiation in invertebrates (2, 3), the role for this primordial signaling mechanism in mammalian appetite regulation remains undefined. Guanylyl cyclase 2C (GUCY2C), principally expressed in intestinal epithelial cells (4–6), is the receptor for diarrheagenic bacterial enterotoxins (STs) (7) and the gut paracrine hormones, guanylin (8), and uroguanylin (9). This hormone-receptor system constitutes a paracrine tumor suppressing circuit whose dysregulation universally characterizes colorectal carcinogenesis (10, 11). Lumenal secretion of the propeptides of uroguanylin (small intestine) and guanylin (colon) stimulates intestinal GUCY2C, regulating fluid and electrolyte balance (12) and epithelial cell homeostatic programs in the gut, organizing the crypt-villus axis (13–15).

Beyond paracrine endolumenal release, these prohormones also undergo endocrine secretion by the gut into the circulation (16, 17). However, in the absence of either cognate receptors mediating extralumenal responses to these peptides (18, 19) or defined homeostatic mechanisms regulating their endocrine secretion from the gut (20), the precise physiological significance of the GUCY2C endocrine axis remains ambiguous. In the context of the central role of the gut-neural axis in controlling nutrient consumption and the importance of guanylyl cyclase activity in central control of invertebrate feeding, we explored the role of GUCY2C signaling in appetite regulation.

The present study reveals that eliminating GUCY2C expression in mice disrupts appetite regulation specifically by impairing satiation, producing hyperphagia associated with comorbidities, including obesity and metabolic syndrome. Corrupted satiation circuits reflect the disruption of a previously unrecognized uroguanylin-GUCY2C endocrine axis regulating appetite. Indeed, food consumption is the first physiological stimulus that induces secretion of prouroguanylin by intestinal epithelial cells into the circulation in mice and humans. This endocrine prohormone signal is selectively decoded centrally by specific proteolytic liberation of uroguanylin, but not guanylin, unexpectedly activating neuronal GUCY2C and downstream anorexigenic pathways. This study suggests that the GUCY2C-hormone axis is at the center of endocrine regulation of central appetite mechanisms and paracrine control of intestinal epithelial cell homeostasis (14, 15). This intersection of mechanisms regulating the acquisition of nutrients centrally and the integrity of cells mediating their processing and absorption in the gut may represent the evolutionary diversification of a more primitive guanylyl cyclase signaling pathway, regulating feeding behavior and energy homeostasis (2, 3). Importantly, the uroguanylin-GUCY2C endocrine axis provides what we believe to be a novel target in the emerging therapeutic armamentarium to address appetite control and the obesity pandemic (21).

GUCY2C-deficient mice exhibit increased body weight, reflecting excess adiposity. Elimination of GUCY2C expression produces mice (Gucy2c^–/– mice) resistant to induction of diarrhea by heat-stable ST (22) but susceptible to carcinogen and genetic induction of intestinal tumorigenesis (13, 14). Interestingly, Gucy2c^–/– mice raised on a standard low calorie diet (LCD) (Supplemental Table 1; supplemental material available online with this article; doi: 10.1172/JCI57925DS1) displayed accelerated growth, with 10.3% ± 0.3% (P < 0.001) increased body mass compared with that of congenic wild-type C57BL/6 mice (Gucy2c^+/+ mice; Figure 1A). Weight differences were also produced by moderate calorie diet (MCD; Supplemental Figure 1A) or high calorie diet (HCD; Figure 1B and Supplemental Figure 1B), primarily composed of carbohydrates or fat, respectively (Supplemental Table 1). The greatest growth differential was observed in female mice raised on a HCD (23), for which Gucy2c^–/– mice were 26.3% ± 1.3% heavier (P < 0.01) than Gucy2c^+/+ mice (Figure 1B).

Figure 1

Gucy2c^–/– mice exhibit increased body weight, reflecting excess adiposity. (A) Growth curves of male Gucy2c^+/+ and Gucy2c^–/– mice raised on LCD (n = 20; P < 0.001). (B) Growth curves of female Gucy2c^+/+ and Gucy2c^–/– mice raised on HCD (n = 20–40; P < 0.01). (C) Adiposity index (percentage body fat) of 12-month-old mice (n = 10–13 per group). (D) Visceral adipose tissue (VAT), subcutaneous adipose tissue (SAT), and total adipose tissue of 12-month-old mice (n = 10–13 per group). (E) Quantification of lean body mass of 12-month-old mice raised on LCD or HCD (n = 10–13 per group). (F) Total body water content of mice determined by 72 hours desiccation at 90°C (n = 6). All data are mean ± SEM. ***P < 0.001.

Excess weight in Gucy2c^–/– mice was associated with greater accumulation of adipose mass and with increases in the percentage of body weight contributed by fat (adiposity index, Figure 1C), reflecting growth in visceral and subcutaneous fat compartments (Figure 1D). In contrast, lean body mass and total body water were equivalent between genotypes (Figure 1, E and F). Hypertrophy of adipose mass in Gucy2c^–/– mice was associated with hepatic steatosis (Figure 2, A and B) and elevated serum leptin (Figure 2C), an adipocyte-derived peptide whose circulating level reflects fat mass. Furthermore, GUCY2C deficiency amplified the metabolic syndrome associated with diet-induced obesity, including cardiac hypertrophy (Figure 2D), hyperleptinemia (Figure 2, E and F), hyperinsulinemia (Figure 2G), and impaired glycemic control (Figure 2H).

Figure 2

GUCY2C deficiency exacerbates metabolic disease. (A) Liver triglyceride content of 12-month-old mice raised on LCD (n = 19). (B) H&E staining of representative left liver lobe sections of 12-month-old mice raised on LCD (scale bar: 200 μM). (C) Mean fasted serum leptin concentrations of mice raised on LCD (n = 6–10 per group). (D) Mean heart size (wet weight) of 12-month-old mice raised on LCD or HCD (n = 10–13 per group). (E) Mean fasted serum leptin concentrations of 12-month-old mice raised on HCD (n = 10). (F) Correlation of fasted serum leptin level and body weight of 12-month-old mice raised on HCD (r² = 0.47, P < 0.01). The diagonal line represents a linear regression model. (G) Mean fasted serum insulin concentrations of 12-month-old mice raised on HCD (n = 10). (H) Glucose tolerance test of fasted 12-month-old mice raised on HCD injected i.p. with glucose (2.5 mg/g) (n = 6). All data are mean ± SEM. NS = P > 0.05. *P < 0.05, **P < 0.01.

GUCY2C-deficient mice exhibit hyperphagia and diminished satiation. Gucy2c^–/– mice were hyperphagic, independent of sex, dietary nutrients, or dietary caloric content (Figure 3A). In that context, body masses of the genotypes were reversibly equalized by pair feeding (Figure 3B), with a direct relationship between calories consumed and weight gained (Figure 3C). Of significance, differential food consumption between genotypes was amplified by fasting, independent of dietary caloric content or nutrient composition (Figure 3D), suggesting impaired satiation. Indeed, fasted and refed Gucy2c^–/– mice displayed deficient postprandial satiation (Figure 3E), regardless of nutrients inducing the satiation response (Figure 3F).

Figure 3

GUCY2C-deficient mice exhibit hyperphagia and diminished satiation. (A) Daily food consumption of 3-month-old female and male mice fed MCD or HCD. Points represent the mean of 10 daily food intake measurements (n = 10 per group). (B) Growth of female mice pair-fed HCD (2.3 g/mouse/d) (n = 12). (C) Correlation of mean daily food intake and weight gain of 4-month-old mice fed HCD during a 10-day period (r² = 0.72, P < 0.001) (n = 10 per group). The diagonal line represents a linear regression model. (D) Twenty-four–hour food intake of fasted 3- to 4-month-old female and male mice refed MCD or HCD (n = 10–20 per group). (E) Cumulative food intake of 3- to 4-month-old fasted mice refed HCD (n = 10 per group). (F) Two-hour food consumption of fasted mice gavaged with an isovolumetric bolus (300 μl) of water, olive oil, or 35% glucose (n = 5 per group). All data are mean ± SEM. Horizontal bars represent mean values. Scattergram points represent data for individual mice. *P < 0.05, **P < 0.01, ***P < 0.001.

Beyond increased calorie consumption, excess adiposity may also reflect differences in digestion, nutrient absorption, and/or energy mobilization/expenditure. In the context of the central role of dietary fat in obesity (24), lipid digestion was identical between genotypes, and triglycerides were unmeasurable (completely digested), while free fatty acid levels were comparable in stool (Figure 4A). Lipid absorption, distribution, and clearance also were equivalent with genotypes exhibiting identical serum triglyceride kinetics in the absence or presence of tyloxapol (Figure 4, B and C), which inhibits lipoprotein lipase-mediated triglyceride uptake by peripheral tissues (25). Additionally, the transcripts of rate-limiting proteins mediating lipid absorption (Fabp2), glucose absorption (Glut2, Sglt1), fatty acid and triglyceride synthesis (Fasn, Dgat1, Dgat2), and fatty acid oxidation (Acadm, Acadl) were equally expressed in intestines of the genotypes (Figure 4D). Further, energy mobilization and expenditure were equivalent, with genotypes exhibiting identical circadian activity cycles (Figure 4E) and thermoregulatory reflexes to a cold (4°C) environment (ref. 26 and Figure 4F). Thus, differences in these other adipogenic systems were not observed between the genotypes, establishing increased calorie consumption as the cause of the excess adiposity observed in Gucy2c^–/– mice.

Figure 4

GUCY2C-deficient mice do not display increased lipid absorption efficiency or decreased activity/metabolic rate. (A) Free fatty acid content of feces of 3- to 4-month-old mice raised on HCD (n = 16). Scattergram points represent data for individual mice. (B and C) Serum triglyceride concentrations of fasted mice with or without tyloxapol (0.75 mg/g) after olive oil gavage (1.5 mg/g) (n = 5). (D) Levels of expression of metabolic genes in intestine, determined by qRT-PCR, normalized to Vil1 expression (n = 4–5 per group). (E) Daily activity patterns of Gucy2c^+/+ and Gucy2c^–/– mice (n = 6). (F) Core body temperatures of mice exposed to a 4°C environment for 24 hours (n = 6). All data are mean ± SEM. Horizontal bars represent mean values.

Systemic administration of GUCY2C ligands induces satiation. Eliminating GUCY2C expression did not disrupt established gut-neural axes regulating feeding, and enteroendocrine cell number (15) as well as their expression and secretion of intestinal anorexigenic peptides were equivalent in Gucy2c^+/+ and Gucy2c^–/– mice (Supplemental Figure 2, A and B). Similarly, gastric emptying and gastrointestinal transit were identical between genotypes (Supplemental Figure 2C). Surprisingly, activation of intestinal GUCY2C by orally administered ST, a proteolytically resistant receptor superagonist (27, 28), did not alter food consumption in Gucy2c^+/+ mice (Figure 5A), eliminating a role for endolumenal GUCY2C in signaling mechanisms regulating appetite. In contrast, i.v. administration of ST induced satiation in Gucy2c^+/+ mice (Figure 5B), but not Gucy2c^–/– mice (Figure 5C), in a dose-dependent fashion (Figure 5D). Repeated administration of ST to mice with free access to food produced durable reductions in food consumption (Figure 5E). Insensitivity of Gucy2c^–/– mice to the anorexigenic effects of ST was specific, as peptide YY (PYY) (Figure 5F) and cholecystokinin (CCK) (Supplemental Figure 2D) induced satiation comparably in both genotypes. Anorexigenic effects of systemic ST were quantitatively similar to those of PYY (Figure 5G), with a duration of action (2 hours) identical to those of glucagon-like peptide-1 (GLP-1), oxyntomodulin, and PYY (29–31).

Figure 5

Systemic administration of GUCY2C ligand induces satiation. (A) Cumulative food intake of fasted Gucy2c^+/+ mice orally gavaged with 1 μg ST or the inactive alanine-substituted ST analogue, TJU, and refed HCD (n = 10 per group). (B) Cumulative food intake of fasted Gucy2c^+/+ mice injected i.v. with 1 μg ST or TJU and refed HCD (n = 10 per group). (C) Two-hour food intake of fasted Gucy2c^+/+ and Gucy2c^–/– mice injected i.v. with 1 μg TJU or ST and refed HCD (n = 10 per group). (D) Cumulative food intake of fasted Gucy2c^+/+ mice injected with TJU (1 μg) or ST and refed HCD (n = 10 per group). (E) Twelve-hour food intake of nonfasted Gucy2c^+/+ mice fed HCD and injected with 1 μg TJU or ST every 3 hours (n = 10 per group). (F) Two-hour food intake of fasted Gucy2c^+/+ and Gucy2c^–/– mice injected i.v. with TJU (1 μg) or PYY (3 μg) and refed HCD (n = 10 per group). (G) Two-hour food intake of fasted Gucy2c^+/+ mice injected i.v. with TJU (1 μg), ST (1 μg), or PYY (3 μg) and refed HCD (n = 10 per group). All data are mean ± SEM. **P < 0.01, ***P < 0.001.

GUCY2C expression in hypothalamus. Integration of neurohormonal signals regulating appetite occurs in the hypothalamus. Beyond intestine, Gucy2c mRNA was expressed in hypothalamus but not in extrahypothalamic brain segments or extraintestinal tissues (Figure 6A). The full-length coding sequence of Gucy2c, amplified from hypothalamic cDNA (Figure 6B), was identical to the reported sequence (NM_001127318.1; NCBI Reference Sequence). GUCY2C protein was identified in hypothalamus (Figure 6, C and D), and ST stimulated guanylyl cyclase activation and cGMP production in hypothalamic membranes (Figure 6E). Further, central administration of ST directly into the third ventricle reduced feeding, which was quantitatively similar to the anorexigenic effect produced by exendin-4 (Figure 6F), a GLP-1 agonist that decreases feeding after i.c.v. administration (32). Gut hormones regulate appetite, in part, by modulating hypothalamic neuropeptide transcription, balancing the anorexigenic neuropeptide, proopiomelanocortin (Pomc), and the orexigenic neuropeptides, agouti-related peptide (Agrp) and neuropeptide Y (Npy) (33, 34). Hypothalamic expression of these peptides was comparable in fasted Gucy2c^+/+ and Gucy2c^–/– mice (Supplemental Figure 3A). However, i.v. administration of ST selectively induced expression of Pomc mRNA without altering Npy or Agrp transcription (Figure 6G), providing evidence in hypothalamus of GUCY2C activation by ST administration. Moreover, these data suggest that the anorexigenic neuropeptide, POMC, may be one downstream mediator of appetite suppression by GUCY2C.

Figure 6

GUCY2C expression in hypothalamus. (A) Gucy2c expression in tissues of Gucy2c^+/+ mice, normalized to β-actin (Actb) expression (n = 4–6). The inset shows a representative gel image of the Gucy2c qRT-PCR products. (B) PCR products of the coding sequence of Gucy2c from cDNA prepared from Gucy2c^+/+ mouse tissues. Int, intestine; Hyp, hypothalamus; Lu, lung; Kid, kidney; Spl, spleen; NTC, nontemplate control. (C) Representative immunoblot of intestine and hypothalamic GUCY2C. (D) Intestine and hypothalamic GUCY2C protein content determined by immunoblot analyses (n = 3). (E) Guanylyl cyclase activity of membrane preparations with or without 1 μM ST (n = 4). (F) Two-hour food intake of fasted Gucy2c^+/+ mice after administration of TJU (10 μg), ST (10 μg), or exendin-4 (1 μg) into the third ventricle and refed HCD (n = 3 per group). (G) Hypothalamic expression of appetite-regulating neuropeptides, normalized to Actb expression, in fasted Gucy2c^+/+ mice injected i.v. with 1 μg TJU or ST every 2 hours for 8 hours (n = 8). All data are mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.

Food stimulates intestinal prouroguanylin secretion, inducing satiation. The hypothalamus is devoid of the endogenous GUCY2C cognate ligands, Guca2a (guanylin) and Guca2b (uroguanylin) (Supplemental Figure 3B), consistent with endocrine, rather than paracrine, regulation of GUCY2C. These hormones are secreted into the circulation by the intestine as inactive propeptides (16, 17), which require proteolytic hydrolysis to liberate C-terminal active peptides. Prouroguanylin, but not proguanylin, induced satiation in mice (Figure 7A), reflecting hypothalamic decoding of these endocrine signals through hormone-specific proteolytic activation (Figure 7B). Hypothalamic activation of prouroguanylin mimicked that produced by pancreas (Supplemental Figure 3C), the principle source of proteolytic liberation of uroguanylin in duodenum (35). Importantly, nutrient consumption induced endocrine secretion of prouroguanylin in mice and humans (Figure 7, C and D), with kinetics precisely corresponding to those of satiation (Figure 7C). Moreover, i.v. administration of prouroguanylin-neutralizing antibodies blocked nutrient-induced satiation (Figure 7E), confirming the role of extraintestinal endocrine GUCY2C signaling in the regulation of appetite.

Figure 7

Food intake stimulates intestinal prouroguanylin secretion inducing central satiation. (A) Cumulative food intake of fasted Gucy2c^+/+ mice injected i.v. with TJU (10 μg), prouroguanylin (10 μg), or proguanylin (10 μg) and refed HCD (n = 10 per group). (B) cGMP production of CT26-GUCY2C cells treated with PBS, prouroguanylin (5 μg), proguanylin (5 μg), hypothalamic protein (350 μg), or combinations for 30 minutes (black bars, pH 5.5; red bars, pH 8.0; dark red bar, combined data of pH 5.5/8.0) (n = 4–10 per group). (C) Food intake and serum prouroguanylin concentrations of fasted Gucy2c^+/+ mice refed HCD (n = 7). (D) Serum prouroguanylin concentrations of human volunteers fasted for 12 hours and fed a standardized test meal (Supplemental Table 2) (P < 0.01, mean postprandial [15–150 minutes] level versus fasting [0 minutes] level) (n = 9). (E) Food intake of fasted Gucy2c^+/+ mice injected with PBS (control) or prouroguanylin antiserum (100 μl, 1:50 dilution) during the 1- to 2-hour interval after refeeding (n = 10 per group). All data are mean ± SEM. *P < 0.05, **P < 0.01, ***P < 0.001.

One essential element contributing to body mass homeostasis is the regulation of appetite orchestrated by endocrine cells sensing nutrient content in the gastrointestinal tract, which activate central anorexigenic circuits. In that context, nutrient-induced intestinal prouroguanylin endocrine secretion stimulating central GUCY2C, downstream anorexigenic pathways, and satiation provides unexpected insight into GUCY2C physiology. GUCY2C, a receptor principally expressed in intestinal epithelial cells (4–6), has been without a definitive role outside the gut. Further, while intestinal GUCY2C prohormones are secreted both paracrinally, regulating lumenal GUCY2C, and endocrinally, the absence of discreet stimuli inducing their secretion and defined extraintestinal receptors mediating their signaling has left the (patho)physiological significance of the GUCY2C endocrine axis ambiguous. Here, for the first time to our knowledge, the essential elements of a GUCY2C endocrine axis have been revealed: (a) a physiological stimulus (nutrient ingestion) inducing secretion of prouroguanylin into the circulation, (b) an extraintestinal GUCY2C target, and (c) a downstream consequence of endocrine hormone-receptor engagement (satiation). Moreover, signal discrimination by one receptor that binds two paracrine hormones in intestine is achieved spatially by compartmentalization, with uroguanylin and guanylin primarily expressed in small intestine and colon, respectively. In contrast, endocrine signals by these hormones are decoded for a single class of receptors outside the intestine by differential proteolytic processing of prohormones at the target organ.

For what we believe to be the first time, this GUCY2C endocrine axis mediating satiation extends evolutionarily conserved primitive cGMP-dependent circuits regulating feeding behavior across the phylogenetic continuum to mammals (2, 3). Signaling programs mediated by cGMP regulate food acquisition, feeding, and satiation across diverse taxa, including worms, flies, bees, and ants (3). In Drosophila, cGMP signaling inhibits nutrient consumption, particularly following brief periods of starvation, an analog of enhanced satiety (3). Similarly, in Caenorhabditis elegans cGMP is a key mediator of quiescence, the cessation of food intake that is the homolog of satiation in mammals (2). In that context, quiescence in C. elegans is specifically mediated by a membrane-bound guanylyl cyclase expressed in select neurons that control feeding (2). Moreover, elimination of cGMP signaling in C. elegans produces loss of appetite regulation and quiescence, excess consumption of nutrients, and accumulation of fat (2). This phenotype in worms precisely recapitulates excess nutrient consumption, blunting of satiation, and the resultant obesity in mice produced by eliminating GUCY2C, a membrane-bound guanylyl cyclase. Evolutionary conservation of these pathways broadly across the phylogenetic tree highlights the robust solution offered by cGMP signaling to the essential challenge of regulating nutrient acquisition in multicellular organisms (3).

Satiation mediated by the GUCY2C hormone axis establishes what we believe to be the first endocrine role for this receptor in (patho)physiology. Originally isolated as a specific product of intestinal epithelial cells, GUCY2C was first identified as the receptor for bacterial heat-stable STs that induce diarrhea through cGMP-dependent regulation of fluid and electrolyte secretion (7). Identification of endogenous peptides structurally homologous to STs, including uroguanylin and guanylin in the small intestine and colon, respectively, revealed a dichotomous function for components of this system (36). These hormones are secreted lumenally in intestine in a paracrine fashion, regulating intestinal fluid and electrolyte secretion, a function homologous to STs. Moreover, GUCY2C and its paracrine hormone ligands regulate epithelial cell homeostatic processes organizing the crypt-surface axis, including the cell cycle and proliferation, metabolism, DNA damage sensing and repair, and differentiation (13–15, 37).

Beyond these established paracrine functions, guanylin and uroguanylin propeptides are secreted from intestine directly into the circulation (36, 38). However, the precise endocrine physiology mediated by these secreted peptides has remained incompletely defined. This uncertainty is underscored by the absence of established physiological stimuli inducing hormone secretion, receptors outside the intestine mediating downstream signaling by circulating hormones, or discreet responses produced by circulating peptides. An early hypothesis suggested that these peptides formed one link in a gut-renal endocrine axis, coordinating systemic fluid and electrolyte balance (36, 38). However, while oral and i.v. salt challenge increase local paracrine release of these peptides in gut and kidney, respectively, neither increase circulating hormone levels (20, 39). Also, these peptides alter renal fluid and electrolyte secretion in the absence of GUCY2C expression (18). Further, eliminating uroguanylin, but not GUCY2C, expression produces hypertension in mice (40). Moreover, while the evidence base has been ambiguous, recent studies have confirmed the absence of GUCY2C expression in kidney in placental mammals (41). Taken together, these observations demonstrate that renal effects of these peptides are mediated by paracrine signaling that is independent of GUCY2C and cGMP. By contrast, they underscore the role of GUCY2C in endocrine regulation of appetite, in which a discreet physiologic stimulus, food ingestion, induces secretion of hormone into the circulation targeting GUCY2C in hypothalamus, producing satiation.

The obesity pandemic has emerged as one of the greatest global public health threats, affecting more than 300 million adults worldwide (21). Beyond disturbances of body mass, comorbidities directly attributable to obesity, including endocrine, metabolic, and oncologic diseases, decrease patient life expectancy, with an associated economic burden exceeding $100 billion each year in the US (42). Deconvoluting gut-brain endocrine axes regulating appetite and nutrient consumption is one principal focus for developing effective pharmacotherapies that control obesity and metabolic diseases (43). Studies here reveal a GUCY2C endocrine circuit controlling appetite. While the impact of loss of GUCY2C signaling on body weight is smaller than that in other genetic models of obesity, such as leptin-deficient ob/ob mice, this likely reflects the combined effects of this hormone on both appetite and metabolism (44, 45), in contrast to the uroguanylin-GUCY2C system, which appears to exclusively regulate appetite. Also, studies here do not eliminate the possibility of secondary effects of GUCY2C ligands on physiological or behavioral systems that indirectly impact appetite. Nevertheless, the present observations provide a unique opportunity to probe this pathway and its dysregulation as a possible pathophysiologic mechanism contributing to obesity and metabolic disease. Moreover, this mechanism could serve as a previously unrecognized therapeutic target for the management of weight and metabolic disease. Beyond direct GUCY2C ligand supplementation, therapeutic strategies could define mechanisms mediating intestinal release of prouroguanylin and associated oral secretagogues that elevate circulating hormone levels. Also, proteolytic pathways mediating clearance of these peptides from the circulation could be defined and inhibited to enhance effective circulating concentrations of hormone. Furthermore, unique to the uroguanylin-GUCY2C system is the proteolytic activation of the propeptide at the target site. Induction of this proteolytic system may increase the quantity of active uroguanylin at the hypothalamus and thus increase satiation. The potential for developing therapies targeted to this pathway is underscored by the recent advance of GUCY2C ligands into late-stage therapeutic trials for irritable bowel syndrome and chronic constipation (46).

Loss of GUCY2C paracrine hormone expression is a universal early event in colonic neoplasia, disrupting normal epithelial cell homeostasis, which potentiates tumorigenesis (11, 37, 47–49). The present study reveals the coincidence of body mass regulation and tumor suppression by a single hormone receptor system. In that context, it is tempting to speculate that the GUCY2C hormone axis could contribute to the well-established relationship between obesity and colorectal cancer (50). In this model, a deficiency of intestinal GUCY2C hormones lies at the pathophysiologic intersection of these diseases. Thus, a deficiency in intestinal paracrine signaling contributes to tumorigenesis through corruption of epithelial homeostasis, while a deficiency in intestinal endocrine signaling promotes hyperphagia and obesity. The intriguing correlative hypothesis suggests that paracrine and endocrine supplementation of GUCY2C ligands might benefit obese patients at risk for colorectal cancer by coordinately restoring epithelial homeostasis and suppressing appetite, reversing obesity. These considerations underscore the significance of further exploring the pathophysiological role of the GUCY2C hormone axes in mechanisms underlying colorectal cancer and obesity.

Beyond regulating fluid and electrolyte balance and epithelial dynamics in intestine, GUCY2C mediates an extraintestinal endocrine axis controlling satiation. This role for GUCY2C signaling in modulating appetite provides a previously missing evolutionary link between primordial and mammalian signaling programs regulating feeding behavior. In the context of the expanding global obesity pandemic and the associated paucity of effective management options, the GUCY2C endocrine axis offers what we believe to be a novel therapeutic opportunity to regulate appetite, restrict nutrient consumption, and defend against obesity.

View Supplemental data

These studies were supported by grants from NIH (CA75123, CA95026, CA146033) and Targeted Diagnostics and Therapeutics. M.A. Valentino is the recipient of a predoctoral award from the Pharmaceutical Research and Manufactures of America Foundation. P. Li was enrolled in the NIH-supported institutional K30 Training Program In Human Investigation (K30 HL004522) and was supported by NIH institutional award T32 GM08562 for Postdoctoral Training in Clinical Pharmacology. S.A. Waldman is the Samuel M.V. Hamilton Endowed Professor. We thank L. Bennett, D. Merry, S. Croker, B. Leiby, J. Haaf, C. Bonaccorso, A. Bombonati, L. Eisenman, J. Farber, M. Oshinsky, and M. Cooper for their contributions to this research. The prouroguanylin antibody was a gift from M. Goy (University of North Carolina).

Address correspondence to: Scott Waldman, 132 South 10th Street, 1170 Main, Philadelphia, Pennsylvania 19107, USA. Phone: 215.955.6086, Fax: 215.955.7006, E-mail: Scott.Waldman@jefferson.edu.

Conflict of interest: Scott A. Waldman is the Chair of the Data Safety Monitoring Board for the C-Cure Trial sponsored by Cardio3 Biosciences and the Chair (uncompensated) of the Scientific Advisory Board to Targeted Diagnostics and Therapeutics Inc., which provided research funding that, in part, supported this work and has a license to commercialize inventions related to this work.

Reference information: J Clin Invest. 2011;121(9):3578–3588. doi:10.1172/JCI57925.

See the related article at Uroguanylin: how the gut got another satiety hormone.

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