- Email: [email protected]
GDF15 Pathway
TRMOME 1286 No. of Pages 3
Spotlight
Targeting Obesity and Cachexia: Identification of the GFRAL Receptor–MIC-1/ GDF15 Pathway Samuel N. Breit,1,* Vicky Wang-Wei Tsai,1 and David A. Brown1 Macrophage inhibitory cytokine-1/ growth differentiation factor 15 (MIC-1/GDF15) is a divergent transforming growth factor (TGF[68_TD$IF]b) superfamily cytokine implicated in biological and disease processes including metabolism, cancer, and chronic inflammation, but whose receptor has remained elusive. Four laboratories have recently identified GFRAL, an orphan receptor of [80_TD$IF]the glial-derived neurotrophic factor (GDNF) receptor a family, as the receptor for MIC-1/ GDF15, signaling though the coreceptor Ret. These data identify a new systemic to central nervous system (CNS) circuit that regulates metabolism in response to stress and which could be targeted to treat both severe obesity and anorexia/cachexia syndrome. In [69_TD$IF]the recent September issues of Nature Medicine and Nature, four groups from pharmaceutical companies Novo Nordisk [1], Janssen [2], Eli Lilly [3], and NGM [70_TD$IF]Biopharmaceuticals/Merck [4] have characterized GFRAL (see Glossary), as the receptor for MIC-1/GDF15[71_TD$IF], and the neuronal circuits through which it acts. MIC1/GDF15 is a divergent member of the TGFb superfamily, first described two decades ago, whose serum concentrations rise modestly in many disease
states, but become markedly elevated in others, especially in cancers [5]. These findings have framed MIC-1/GDF15 as a putative causative agent of cancer-associated anorexia/cachexia; a common and currently untreatable syndrome of appetite loss and muscle wasting [6,7]. In addition, because of sometimes markedly elevated concentrations, MIC-1/GDF15 may also be implicated in chronic heart and renal failure-associated cachexia [6,8]. Murine studies have indicated that MIC-1/GDF15 can act on appetite regulation centers in the hypothalamus and hindbrain [6] causing anorexia, and over time, leading to cachexia [6]. [72_TD$IF]Rodent data later emerged, demonstrating that selective surgical lesioning of the area postrema (AP) and nucleus of the solitary tract (NTS), contiguous regions of the hindbrain, could render experimental animals completely unresponsive to the anorexic effects of MIC-1/GDF15 [9]; thus, as a primary site of anorexic central action, the mammalian hindbrain has become an important research focus [9].
Glossary MIC-1/GDF15: distant member of the TGFb cytokine superfamily; most closely related to the GDNFs. TGFb superfamily (classical): large family of cysteine knot proteins divided into subfamilies, members of which act through serine/threonine kinase TBR1 and TBRII receptors and signal using the canonical Smad pathway. TGFb superfamily (nonclassical): consists of GDNFs and their more distant relatives Gas1 and GFRAL. GDNF: first of a four-member subfamily, distantly related to the TGFb superfamily and acting via GPI anchored GFRa1–4 receptors that signal though the tyrosine kinase coreceptor Ret.
superfamily, GDNF, neurturin, artemin, and persephin. All publications demonstrated that germline Gfral gene deleted mice (Gfral / [67_TD$IF]) lost the well-documented anorexic and metabolic effects caused by recombinant MIC-1/GDF15. Furthermore, while Gfral / mice on chow diet did not display altered body weight or food intake, when challenged with a high-fat diet, two of the studies demonstrated increased energy intake, greater weight gain, and worse glucose tolerance relative to controls [2,4]. These data supUntil now, the MIC-1/GDF15 receptor has port a physiological role for the MIC-1/ eluded identification; a major impediment GDF15-GFRAL axis in resisting adiposity to understanding its actions. An important and its consequences (Figure 1). question is why it has taken so long to identify and characterize this receptor. In GFRAL is a transmembrane protein with a short, it seems that highly restricted short cytoplasmic domain lacking any sigGFRAL distribution and contamination naling function. This distinguishes it from of commercial MIC-1/GDF15 reagents GFRa1–4, which are glycophosphatidyliwith TGFb may carry a significant share nositol (GPI)-anchored proteins. These of the blame, with direct evidence indicat- receptors and GFRAL require tyrosine ing that at least some commercial prep- kinase coreceptor Ret for signaling. Thus, arations from a major supplier have been using transfected cell lines lacking contaminated with TGFb [10]. However, expression of endogenous GFRAL, these now, using engineered versions of studies reported that MIC-1/GDF15, [73_TD$IF]GRFAL recombinant MIC-1/GDF15 pro- induced phosphorylation of its coreceptor duced in house, all four landmark publi- Ret, as well as phosphorylation of intracations [1–4] identified the MIC-1/GDF15 cellular signaling molecules extracellular receptor as a previously described signal-regulated kinase (Erk)1/2, Akt, orphan member of the [74_TD$IF]GFRa family: and phospholipase C (PLC)g in a GFRAL [11]. The four classical members GFRAL-dependent manner [1,2]. In the of this family, GFRa1–4, bind the dis- absence of Ret, no signaling via GFRAL tantly-related members of the TGFb was observed [1,2]. Consistent with these
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
1
TRMOME 1286 No. of Pages 3
(A)
Reduced appete and body weight MIC-1/GDF15
MIC-1/GDF15 GFRAL
Ret
Ret
GFRAL
p pErk pAkt pPLCγ (B)
Recombinant MIC-1/GDF15
Recombinant MIC-1/GDF15
GFRAL
MI mAb MIC-1/GDF15 Up in disease
mAb
Ret
C-1 /G D
F15 Appete up
mAb GFRAL
Appete down
Ret Ret
Figure 1. MIC-1/GDF15-GFRAL Axis Reduces Appetite and Body Weight in Mice and may be a Therapeutic Target in Obesity and Anorexia/Cachexia Syndromes. (A) MIC-1/GDF15 binds to GFRAL in the hindbrain area postrema and solitary tract nucleus, which induces activation and phosphorylation of its coreceptor, Ret and phosphorylation of signaling molecules including pErk, pAkt, and pPLCg, ultimately leading to reduction in appetite, food intake and body weight in mouse models. (B) Stimulating this pathway using drugs that target the MIC-1/GDF15-GFRAL pathway might be considered as a putative antiobesity therapeutic strategy. Furthermore, inhibiting this pathway using mAbs to GFRAL or MIC-1/GDF15 might be effective in treating anorexia/cachexia syndromes associated with cancer and other diseases, but this remains to be investigated. Abbreviations: GRFAL, orphan receptor of glial-derived neurotrophic factor receptor a family; mAb, monoclonal antibody; MIC-1/GDF15, macrophage inhibitory cytokine-1/growth differentiation factor 15; pErk, phosphorylated extracellular signal-regulated kinase; pPLCg, phosphorylated phospholipase Cg.
findings, systemic administration of MIC1/GDF15 to mice resulted in rapid phosphorylation of Erk and induction of Fos protein expression in AP/NTS neurons, which was absent in Gfral / mice. These data indicate that MIC-1/GDF15 signaling requires binding to GFRAL followed by further complexing to the Ret coreceptor; from this, a wide variety of signaling events could be potentially triggered, 2
and MIC-1/GDF15-driven effects might ensue.
pleotropic
The primary site of MIC-1/GDF15 anorexic actions is likely to reside in neurons within the AP/NTS. While the reported studies used germline genedeleted, rather than AP/NTS-specific Gfral [75_TD$IF]gene deleted mice, there appears to be limited expression of GFRAL outside
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
the CNS and earlier studies have indicated that surgical lesioning of the AP/ NTS abolished the anorexic actions of MIC-1/GDF15 [9]. It would therefore also lend further support to the view that MIC-1/GDF[81_TD$IF]15-induced loss of lean body mass could be a secondary effect to an anorexia-induced energy deficit [6,9]. However, there is still a potential mechanism through which MIC-1/GDF15 might act on cells lacking GFRAL. An alternative transcript of murine GFRAL, lacking a transmembrane and cytoplasmic domain, has been identified [11]. If transcribed, it might act as a soluble receptor, potentially mediating trans signaling and where a soluble MIC-1/GDF15–GFRAL complex could bind to distant cells that express Ret, but not GFRAL. Alternatively, soluble GFRAL could also function as a competitive inhibitor of MIC-1/ GDF15. The AP is a specialized brain region bearing a semipermeable blood[7_TD$IF]-brain barrier allowing systemic signals to readily reach the CNS. While MIC-1/GDF15 is not widely expressed, it circulates in human serum in significant amounts and with a wide normal range of 200–1200 p/ml, as well as being markedly upregulated in pregnancy. Both its gene expression and serum concentrations are upregulated with cell/tissue stress induced by stimuli such as injury, inflammation, or in the context of malignancy. Systemic MIC-1/GDF15 induces activation of AP/ NTS neurons, subsequently initiating a neuronal circuit that also involves brain regions known as the parabrachial region and the central amygdala, which regulate meal termination under physiological as well as stress conditions [4]. Collectively, these findings suggest that MIC-1/GDF15 might play a major role in transmitting both systemic homeostatic and stress signals to GFRAL in the mammalian hindbrain, thus modulating metabolic processes that might play a modest role under physiological conditions, but that
TRMOME 1286 No. of Pages 3
might have a large impact under stress protein and its CNS-restricted receptor conditions, as in the case of anorexia/ GFRAL, is an important new pathway by which stress and nutritional informacachexia syndromes. tion can be transmitted to the nervous In light of all this information, how appro- system to modulate appetite and other priate is the name MIC-1/GDF15 for this metabolic processes. In addition, with furprotein? The original cloning of MIC-1/ ther validation, it may be possible in the GDF15, then named MIC-1, identified it future to therapeutically target this pathas a divergent member of the TGFb way to treat diseases [78_TD$IF]9such as obesity, superfamily with no close relatives [12]. diabetes and anorexia/cachexia. However, it was subsequently termed 1 St Vincent’s Centre for Applied Medical Research, St GDF15, implying that it might act through Vincent’s Hospital and University of New South Wales, the classical TGFb superfamily TBRI and Sydney, New South Wales, 2010, Australia TBRII receptors. We now know this to be *Correspondence: [email protected] (S.N. Breit). incorrect [1,2,4], and the name GDF15 is https://doi.org/10.1016/j.molmed.2017.10.005 thus not really appropriate for its GFRa family relationship, which is functionally References that of a GDNF superfamily cytokine. Per- 1. Yang, L. et al. (2017) GFRAL is the receptor for GDF15 and is required for the anti-obesity effects of the ligand. Nat. haps, following the example set by other Med. 23, 1158–1166 GDNF family cytokines, its name should 2. Mullican, S.E. et al. (2017) GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice be changed to an alternate name such as and nonhuman primates. Nat. Med. 23, 1150–1157 Limosin, after Limos, the Greek God of 3. Emmerson, P.J. et al. (2017) The metabolic effects of GDF15 are mediated by the orphan receptor GFRAL. hunger and starvation. Irrespective of its Nat. Med. 23, 1215–1219 name, the axis formed between this
4. Hsu, J.Y. et al. (2017) Non-homeostatic body weight regulation through a brainstem-restricted receptor for GDF15. Nature 550, 255–259 5. Welsh, J.B. et al. (2003) Large-scale delineation of secreted protein biomarkers overexpressed in cancer tissue and serum. Proc. Natl. Acad. Sci. U. S. A. 100, 3410– 3415 6. Johnen, H. et al. (2007) Tumor-induced anorexia and weight loss are mediated by the TGF-beta superfamily cytokine MIC-1. Nat. Med. 13, 1333–1340 7. Lerner, L. et al. (2015) Plasma growth differentiation factor 15 is associated with weight loss and mortality in cancer patients. J. Cachex. Sarcopenia Muscle 6, 317–324 8. Kempf, T. et al. (2007) Prognostic utility of growth differentiation factor-15 in patients with chronic heart failure. J. Am. Coll. Cardiol. 50, 1054–1060 9. Tsai, V.W. et al. (2014) The anorectic actions of the TGFbeta cytokine MIC-1/GDF15 require an intact brainstem area postrema and nucleus of the solitary tract. PLoS One 9, e100370 10. Okamura, H. (2015) Lack of canonical SMAD2 pathway activation by recombinant GDF15 in vitro. J. Cachex. Sarcopenia Muscle 6, 25 11. Li, Z. et al. (2005) Identification, expression and functional characterization of the GRAL gene. J. Neurochem. 95, 361–376 12. Bootcov, M.R. et al. (1997) MIC-1, a novel macrophage inhibitory cytokine, is a divergent member of the TGF-beta superfamily. Proc. Natl. Acad. Sci. U. S. A. 94, 11514– 11519
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
3
Spotlight
Targeting Obesity and Cachexia: Identification of the GFRAL Receptor–MIC-1/ GDF15 Pathway Samuel N. Breit,1,* Vicky Wang-Wei Tsai,1 and David A. Brown1 Macrophage inhibitory cytokine-1/ growth differentiation factor 15 (MIC-1/GDF15) is a divergent transforming growth factor (TGF[68_TD$IF]b) superfamily cytokine implicated in biological and disease processes including metabolism, cancer, and chronic inflammation, but whose receptor has remained elusive. Four laboratories have recently identified GFRAL, an orphan receptor of [80_TD$IF]the glial-derived neurotrophic factor (GDNF) receptor a family, as the receptor for MIC-1/ GDF15, signaling though the coreceptor Ret. These data identify a new systemic to central nervous system (CNS) circuit that regulates metabolism in response to stress and which could be targeted to treat both severe obesity and anorexia/cachexia syndrome. In [69_TD$IF]the recent September issues of Nature Medicine and Nature, four groups from pharmaceutical companies Novo Nordisk [1], Janssen [2], Eli Lilly [3], and NGM [70_TD$IF]Biopharmaceuticals/Merck [4] have characterized GFRAL (see Glossary), as the receptor for MIC-1/GDF15[71_TD$IF], and the neuronal circuits through which it acts. MIC1/GDF15 is a divergent member of the TGFb superfamily, first described two decades ago, whose serum concentrations rise modestly in many disease
states, but become markedly elevated in others, especially in cancers [5]. These findings have framed MIC-1/GDF15 as a putative causative agent of cancer-associated anorexia/cachexia; a common and currently untreatable syndrome of appetite loss and muscle wasting [6,7]. In addition, because of sometimes markedly elevated concentrations, MIC-1/GDF15 may also be implicated in chronic heart and renal failure-associated cachexia [6,8]. Murine studies have indicated that MIC-1/GDF15 can act on appetite regulation centers in the hypothalamus and hindbrain [6] causing anorexia, and over time, leading to cachexia [6]. [72_TD$IF]Rodent data later emerged, demonstrating that selective surgical lesioning of the area postrema (AP) and nucleus of the solitary tract (NTS), contiguous regions of the hindbrain, could render experimental animals completely unresponsive to the anorexic effects of MIC-1/GDF15 [9]; thus, as a primary site of anorexic central action, the mammalian hindbrain has become an important research focus [9].
Glossary MIC-1/GDF15: distant member of the TGFb cytokine superfamily; most closely related to the GDNFs. TGFb superfamily (classical): large family of cysteine knot proteins divided into subfamilies, members of which act through serine/threonine kinase TBR1 and TBRII receptors and signal using the canonical Smad pathway. TGFb superfamily (nonclassical): consists of GDNFs and their more distant relatives Gas1 and GFRAL. GDNF: first of a four-member subfamily, distantly related to the TGFb superfamily and acting via GPI anchored GFRa1–4 receptors that signal though the tyrosine kinase coreceptor Ret.
superfamily, GDNF, neurturin, artemin, and persephin. All publications demonstrated that germline Gfral gene deleted mice (Gfral / [67_TD$IF]) lost the well-documented anorexic and metabolic effects caused by recombinant MIC-1/GDF15. Furthermore, while Gfral / mice on chow diet did not display altered body weight or food intake, when challenged with a high-fat diet, two of the studies demonstrated increased energy intake, greater weight gain, and worse glucose tolerance relative to controls [2,4]. These data supUntil now, the MIC-1/GDF15 receptor has port a physiological role for the MIC-1/ eluded identification; a major impediment GDF15-GFRAL axis in resisting adiposity to understanding its actions. An important and its consequences (Figure 1). question is why it has taken so long to identify and characterize this receptor. In GFRAL is a transmembrane protein with a short, it seems that highly restricted short cytoplasmic domain lacking any sigGFRAL distribution and contamination naling function. This distinguishes it from of commercial MIC-1/GDF15 reagents GFRa1–4, which are glycophosphatidyliwith TGFb may carry a significant share nositol (GPI)-anchored proteins. These of the blame, with direct evidence indicat- receptors and GFRAL require tyrosine ing that at least some commercial prep- kinase coreceptor Ret for signaling. Thus, arations from a major supplier have been using transfected cell lines lacking contaminated with TGFb [10]. However, expression of endogenous GFRAL, these now, using engineered versions of studies reported that MIC-1/GDF15, [73_TD$IF]GRFAL recombinant MIC-1/GDF15 pro- induced phosphorylation of its coreceptor duced in house, all four landmark publi- Ret, as well as phosphorylation of intracations [1–4] identified the MIC-1/GDF15 cellular signaling molecules extracellular receptor as a previously described signal-regulated kinase (Erk)1/2, Akt, orphan member of the [74_TD$IF]GFRa family: and phospholipase C (PLC)g in a GFRAL [11]. The four classical members GFRAL-dependent manner [1,2]. In the of this family, GFRa1–4, bind the dis- absence of Ret, no signaling via GFRAL tantly-related members of the TGFb was observed [1,2]. Consistent with these
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
1
TRMOME 1286 No. of Pages 3
(A)
Reduced appete and body weight MIC-1/GDF15
MIC-1/GDF15 GFRAL
Ret
Ret
GFRAL
p pErk pAkt pPLCγ (B)
Recombinant MIC-1/GDF15
Recombinant MIC-1/GDF15
GFRAL
MI mAb MIC-1/GDF15 Up in disease
mAb
Ret
C-1 /G D
F15 Appete up
mAb GFRAL
Appete down
Ret Ret
Figure 1. MIC-1/GDF15-GFRAL Axis Reduces Appetite and Body Weight in Mice and may be a Therapeutic Target in Obesity and Anorexia/Cachexia Syndromes. (A) MIC-1/GDF15 binds to GFRAL in the hindbrain area postrema and solitary tract nucleus, which induces activation and phosphorylation of its coreceptor, Ret and phosphorylation of signaling molecules including pErk, pAkt, and pPLCg, ultimately leading to reduction in appetite, food intake and body weight in mouse models. (B) Stimulating this pathway using drugs that target the MIC-1/GDF15-GFRAL pathway might be considered as a putative antiobesity therapeutic strategy. Furthermore, inhibiting this pathway using mAbs to GFRAL or MIC-1/GDF15 might be effective in treating anorexia/cachexia syndromes associated with cancer and other diseases, but this remains to be investigated. Abbreviations: GRFAL, orphan receptor of glial-derived neurotrophic factor receptor a family; mAb, monoclonal antibody; MIC-1/GDF15, macrophage inhibitory cytokine-1/growth differentiation factor 15; pErk, phosphorylated extracellular signal-regulated kinase; pPLCg, phosphorylated phospholipase Cg.
findings, systemic administration of MIC1/GDF15 to mice resulted in rapid phosphorylation of Erk and induction of Fos protein expression in AP/NTS neurons, which was absent in Gfral / mice. These data indicate that MIC-1/GDF15 signaling requires binding to GFRAL followed by further complexing to the Ret coreceptor; from this, a wide variety of signaling events could be potentially triggered, 2
and MIC-1/GDF15-driven effects might ensue.
pleotropic
The primary site of MIC-1/GDF15 anorexic actions is likely to reside in neurons within the AP/NTS. While the reported studies used germline genedeleted, rather than AP/NTS-specific Gfral [75_TD$IF]gene deleted mice, there appears to be limited expression of GFRAL outside
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
the CNS and earlier studies have indicated that surgical lesioning of the AP/ NTS abolished the anorexic actions of MIC-1/GDF15 [9]. It would therefore also lend further support to the view that MIC-1/GDF[81_TD$IF]15-induced loss of lean body mass could be a secondary effect to an anorexia-induced energy deficit [6,9]. However, there is still a potential mechanism through which MIC-1/GDF15 might act on cells lacking GFRAL. An alternative transcript of murine GFRAL, lacking a transmembrane and cytoplasmic domain, has been identified [11]. If transcribed, it might act as a soluble receptor, potentially mediating trans signaling and where a soluble MIC-1/GDF15–GFRAL complex could bind to distant cells that express Ret, but not GFRAL. Alternatively, soluble GFRAL could also function as a competitive inhibitor of MIC-1/ GDF15. The AP is a specialized brain region bearing a semipermeable blood[7_TD$IF]-brain barrier allowing systemic signals to readily reach the CNS. While MIC-1/GDF15 is not widely expressed, it circulates in human serum in significant amounts and with a wide normal range of 200–1200 p/ml, as well as being markedly upregulated in pregnancy. Both its gene expression and serum concentrations are upregulated with cell/tissue stress induced by stimuli such as injury, inflammation, or in the context of malignancy. Systemic MIC-1/GDF15 induces activation of AP/ NTS neurons, subsequently initiating a neuronal circuit that also involves brain regions known as the parabrachial region and the central amygdala, which regulate meal termination under physiological as well as stress conditions [4]. Collectively, these findings suggest that MIC-1/GDF15 might play a major role in transmitting both systemic homeostatic and stress signals to GFRAL in the mammalian hindbrain, thus modulating metabolic processes that might play a modest role under physiological conditions, but that
TRMOME 1286 No. of Pages 3
might have a large impact under stress protein and its CNS-restricted receptor conditions, as in the case of anorexia/ GFRAL, is an important new pathway by which stress and nutritional informacachexia syndromes. tion can be transmitted to the nervous In light of all this information, how appro- system to modulate appetite and other priate is the name MIC-1/GDF15 for this metabolic processes. In addition, with furprotein? The original cloning of MIC-1/ ther validation, it may be possible in the GDF15, then named MIC-1, identified it future to therapeutically target this pathas a divergent member of the TGFb way to treat diseases [78_TD$IF]9such as obesity, superfamily with no close relatives [12]. diabetes and anorexia/cachexia. However, it was subsequently termed 1 St Vincent’s Centre for Applied Medical Research, St GDF15, implying that it might act through Vincent’s Hospital and University of New South Wales, the classical TGFb superfamily TBRI and Sydney, New South Wales, 2010, Australia TBRII receptors. We now know this to be *Correspondence: [email protected] (S.N. Breit). incorrect [1,2,4], and the name GDF15 is https://doi.org/10.1016/j.molmed.2017.10.005 thus not really appropriate for its GFRa family relationship, which is functionally References that of a GDNF superfamily cytokine. Per- 1. Yang, L. et al. (2017) GFRAL is the receptor for GDF15 and is required for the anti-obesity effects of the ligand. Nat. haps, following the example set by other Med. 23, 1158–1166 GDNF family cytokines, its name should 2. Mullican, S.E. et al. (2017) GFRAL is the receptor for GDF15 and the ligand promotes weight loss in mice be changed to an alternate name such as and nonhuman primates. Nat. Med. 23, 1150–1157 Limosin, after Limos, the Greek God of 3. Emmerson, P.J. et al. (2017) The metabolic effects of GDF15 are mediated by the orphan receptor GFRAL. hunger and starvation. Irrespective of its Nat. Med. 23, 1215–1219 name, the axis formed between this
4. Hsu, J.Y. et al. (2017) Non-homeostatic body weight regulation through a brainstem-restricted receptor for GDF15. Nature 550, 255–259 5. Welsh, J.B. et al. (2003) Large-scale delineation of secreted protein biomarkers overexpressed in cancer tissue and serum. Proc. Natl. Acad. Sci. U. S. A. 100, 3410– 3415 6. Johnen, H. et al. (2007) Tumor-induced anorexia and weight loss are mediated by the TGF-beta superfamily cytokine MIC-1. Nat. Med. 13, 1333–1340 7. Lerner, L. et al. (2015) Plasma growth differentiation factor 15 is associated with weight loss and mortality in cancer patients. J. Cachex. Sarcopenia Muscle 6, 317–324 8. Kempf, T. et al. (2007) Prognostic utility of growth differentiation factor-15 in patients with chronic heart failure. J. Am. Coll. Cardiol. 50, 1054–1060 9. Tsai, V.W. et al. (2014) The anorectic actions of the TGFbeta cytokine MIC-1/GDF15 require an intact brainstem area postrema and nucleus of the solitary tract. PLoS One 9, e100370 10. Okamura, H. (2015) Lack of canonical SMAD2 pathway activation by recombinant GDF15 in vitro. J. Cachex. Sarcopenia Muscle 6, 25 11. Li, Z. et al. (2005) Identification, expression and functional characterization of the GRAL gene. J. Neurochem. 95, 361–376 12. Bootcov, M.R. et al. (1997) MIC-1, a novel macrophage inhibitory cytokine, is a divergent member of the TGF-beta superfamily. Proc. Natl. Acad. Sci. U. S. A. 94, 11514– 11519
Trends in Molecular Medicine, Month Year, Vol. xx, No. yy
3