Under homeostatic conditions, animals use well-defined hypothalamic neural circuits to help maintain stable body weight, by integrating metabolic and hormonal signals from the periphery to balance food consumption and energy expenditure. In stressed or disease conditions, however, animals use alternative neuronal pathways to adapt to the metabolic challenges of altered energy demand. Recent studies have identified brain areas outside the hypothalamus that are activated under these 'non-homeostatic' conditions, but the molecular nature of the peripheral signals and brain-localized receptors that activate these circuits remains elusive. Here we identify glial cell-derived neurotrophic factor (GDNF) receptor alpha-like (GFRAL) as a brainstem-restricted receptor for growth and differentiation factor 15 (GDF15). GDF15 regulates food intake, energy expenditure and body weight in response to metabolic and toxin-induced stresses; we show that Gfral knockout mice are hyperphagic under stressed conditions and are resistant to chemotherapy-induced anorexia and body weight loss. GDF15 activates GFRAL-expressing neurons localized exclusively in the area postrema and nucleus tractus solitarius of the mouse brainstem. It then triggers the activation of neurons localized within the parabrachial nucleus and central amygdala, which constitute part of the 'emergency circuit' that shapes feeding responses to stressful conditions. GDF15 levels increase in response to tissue stress and injury, and elevated levels are associated with body weight loss in numerous chronic human diseases. By isolating GFRAL as the receptor for GDF15-induced anorexia and weight loss, we identify a mechanistic basis for the non-homeostatic regulation of neural circuitry by a peripheral signal associated with tissue damage and stress. These findings provide opportunities to develop therapeutic agents for the treatment of disorders with altered energy demand.

Proprotein convertase subtilisin/kexin type 9 (PCSK9) regulates serum LDL cholesterol (LDL-C) by interacting with the LDL receptor (LDLR) and is an attractive therapeutic target for LDL-C lowering. We have generated a neutralizing anti-PCSK9 antibody, mAb1, that binds to an epitope on PCSK9 adjacent to the region required for LDLR interaction. In vitro, mAb1 inhibits PCSK9 binding to the LDLR and attenuates PCSK9-mediated reduction in LDLR protein levels, thereby increasing LDL uptake. A combination of mAb1 with a statin increases LDLR levels in HepG2 cells more than either treatment alone. In wild-type mice, mAb1 increases hepatic LDLR protein levels Ϸ2-fold and lowers total serum cholesterol by up to 36%: this effect is not observed in LDLR ؊/؊ mice. In cynomolgus monkeys, a single injection of mAb1 reduces serum LDL-C by 80%, and a significant decrease is maintained for 10 days. We conclude that anti-PCSK9 antibodies may be effective therapeutics for treating hypercholesterolemia.antibody ͉ LDL-C ͉ LDLR ͉ PCSK9 ͉ hypercholesterolemia P roprotein convertase subtilisin/kexin type 9 (PCSK9) has been implicated as an important regulator of LDL metabolism (1, 2). Human genetic studies provide strong validation for the role of PCSK9 in modulating LDL cholesterol (LDL-C) levels and the incidence of coronary heart disease (CHD) in man. Gain-of-function (GOF) mutations in the PCSK9 gene are associated with elevated serum LDL-C levels (Ͼ300 mg/dL) and premature CHD (3), whereas loss-of-function (LOF) mutations are associated with low serum LDL-C (Յ100 mg/dL) (4). Strikingly, subjects harboring the heterozygous LOF mutations exhibited an 88% reduction in the incidence of CHD over a 15-year period relative to noncarriers of the mutations (5). Moreover, despite a complete loss of PCSK9 and serum LDL-C of Ͻ20 mg/dL, the 2 subjects carrying compound heterozygote LOF mutations appear healthy (6, 7).PCSK9 belongs to the subtilisin family of serine proteases and consists of a prodomain, catalytic domain, and C-terminal V domain (8). Expressed highly in the liver, PCSK9 is secreted after autocatalytic cleavage of its zymogen form (1). The prodomain remains noncovalently associated with the catalytic domain and seems to inhibit further proteolytic enzyme activity (8, 9). Secreted PCSK9 modulates LDL-C levels by posttranslational downregulation of hepatic LDL receptor (LDLR) protein (1). The precise mechanism is unknown, but a direct interaction between repeat A of the LDLR EGF homology domain and the PCSK9 catalytic domain is required (10, 11). Proteolytic cleavage of the LDLR by PCSK9 does not occur (12, 13); rather, the PCSK9:LDLR complex is endocytosed and directed to the endosome/lysosome compartment for degradation (14, 15). Current understanding of the LDLR pathway asserts that apolipoprotein B (apoB) and E (apoE) containing lipoprotein particles endocytosed with the LDLR are transported to the acidic environment of the endosome, where they dissociate from the receptor and are subsequently catabolized in lysosomes, while t...

FGF19 is a unique member of the fibroblast growth factor (FGF) family of secreted proteins that regulates bile acid homeostasis and metabolic state in an endocrine fashion. Here we investigate the cell surface receptors required for signaling by FGF19. We show that ␤Klotho, a single-pass transmembrane protein highly expressed in liver and fat, induced ERK1/2 phosphorylation in response to FGF19 treatment and significantly increased the interactions between FGF19 and FGFR4. Interestingly, our results show that ␣Klotho, another Klotho family protein related to ␤Klotho, also induced ERK1/2 phosphorylation in response to FGF19 treatment and increased FGF19-FGFR4 interactions in vitro, similar to the effects of ␤Klotho. In addition, heparin further enhanced the effects of both ␣Klotho and ␤Klotho in FGF19 signaling and interaction experiments. These results suggest that a functional FGF19 receptor may consist of FGF receptor (FGFR) and heparan sulfate complexed with either ␣Klotho or ␤Klotho.The fibroblast growth factors (FGFs) 2 constitute a structurally related family of 22 proteins (1). This family of secreted proteins has been implicated in a variety of functions including angiogenesis, mitogenesis, vertebrate and invertebrate development, cellular differentiation, wound healing/repair, and metabolic regulations (2, 3). FGFs can be grouped into seven subfamilies based on their sequence similarities and functional properties (4). Four tyrosine kinase receptors have been identified for FGFs (FGFR1-4), each containing an extracellular ligand binding domain, a single transmembrane domain, and an intracellular tyrosine kinase domain (5). Alternative RNA splicing of one of two unique exons in FGFR1-3 results in the two different, b and c, receptor isoforms (2). Because most FGFs only function in an autocrine or paracrine fashion, the tissue distribution of these FGFs determines the tissue specific functions for most of the FGF family members (2, 4).The FGF19 subfamily contains three members, FGF19, FGF21, and FGF23. In contrast to other FGFs, which require heparin or heparan sulfate for high affinity receptor binding and activation, FGF19 subfamily members do not bind heparin with high affinity (6). In addition, FGF19 subfamily members contain intramolecular disulfide bonds, which may function to increase their stability in plasma and allow them to function as hormones (7). Indeed, although FGF19 is not expressed in liver or gallbladder, it can regulate hepatic bile acid metabolism and control gallbladder filling (8 -11). Furthermore, transgenic animals overexpressing FGF19 from skeletal muscle and animals injected with recombinant protein display improved insulin sensitivity, reduced adiposity, and increased metabolic rate (12, 13). In addition, FGF21 has been shown to regulate glucose and lipid metabolism in an endocrine fashion (14), and FGF23 may function as a phosphaturic hormone (15). These unique features of the FGF19 subfamily suggest that they may interact with their receptors differently from the canonical ...

FGF19 subfamily proteins (FGF19, FGF21, and FGF23) are unique members of fibroblast growth factors (FGFs) that regulate energy, bile acid, glucose, lipid, phosphate, and vitamin D homeostasis in an endocrine fashion. Their activities require the presence of ␣ or ␤Klotho, two related single-pass transmembrane proteins, as co-receptors in relevant target tissues. We previously showed that FGF19 can bind to both ␣ and ␤Klotho, whereas FGF21 and FGF23 can bind only to either ␤Klotho or ␣Klotho, respectively in vitro. To determine the mechanism regulating the binding and specificity among FGF19 subfamily members to Klotho family proteins, chimeric proteins between FGF19 subfamily members or chimeric proteins between Klotho family members were constructed to probe the interaction between those two families. Our results showed that a chimera of FGF19 with the FGF21 C-terminal tail interacts only with ␤Klotho and a chimera with the FGF23 C-terminal tail interacts only with ␣Klotho. FGF signaling assays also reflected the change of specificity we observed for the chimeras. These results identified the C-terminal tail of FGF19 as a region necessary for its recognition of Klotho family proteins. In addition, chimeras between ␣ and ␤Klotho were also generated to probe the regions in Klotho proteins that are important for signaling by this FGF subfamily. Both FGF23 and FGF21 require intact ␣ or ␤Klotho for signaling, respectively, whereas FGF19 can signal through a Klotho chimera consisting of the N terminus of ␣Klotho and the C terminus of ␤Klotho. Our results provide the first glimpse of the regions that regulate the binding specificity between this unique family of FGFs and their co-receptors.The FGF19 subfamily of fibroblast growth factors (FGFs), 2 consisting of FGF19, FGF21, and FGF23, has been implicated in the regulation of a variety of metabolic processes (1-4). FGF19 can regulate hepatic bile acid metabolism through repression of the gene encoding cholesterol 7␣-hydroxylase (CYP7A1), the first and rate-limiting step in the biosynthesis of bile acids (5). Elevation of plasma FGF19 levels either by transgenic expression or injection of recombinant protein has been shown to improve insulin sensitivity, reduce adiposity, and increase metabolic rate in rodent diabetes and obesity models (1, 2). FGF21 was found to increase the glucose uptake in mouse 3T3-L1 and primary human adipocytes (3). FGF21 transgenic mice were resistant to diet-induced obesity (3). In addition, injection of recombinant FGF21 reduced plasma glucose and triglycerides to near normal levels in both ob/ob and db/db mice (3, 6). FGF23 reduced serum phosphate levels by suppressing kidney proximal tubular phosphate re-absorption (4). FGF23 also reduced the serum levels of 1,25-dihydroxyvitamin D 3 [1,25(OH) 2 D 3 ] resulting in suppressed intestinal phosphate absorption (4).Unlike other FGFs, which act locally in an autocrine or paracrine manner, FGF19 subfamily members can regulate physiological functions in an endocrine fashion. The fact that this subfa...

Amino-terminal fragments of huntingtin, which contain the expanded polyglutamine repeat, have been proposed to contribute to the pathology of Huntington's disease (HD). Data supporting this claim have been generated from patients with HD in which truncated amino-terminal fragments forming intranuclear inclusions have been observed, and from animal and cell-based models of HD where it has been demonstrated that truncated polyglutamine-containing fragments of htt are more toxic than fulllength huntingtin. We report here the identification of a region within huntingtin, spanning from amino acids 63 to 111, that is cleaved in cultured cells to generate a fragment of similar size to those observed in patients with HD. Importantly, proteolytic cleavage within this region appears dependent upon the length of the polyglutamine repeat within huntingtin, with pathological polyglutamine repeatcontaining huntingtin being more efficiently cleaved than huntingtin containing polyglutamine repeats of nonpathological size.