Antibody-mediated inhibition of GDF15-GFRAL activity reverses cancer cachexia in mice.

Cancer cachexia is a highly prevalent condition associated with poor quality of life and reduced survival1. Tumor-induced perturbations in the endocrine, immune and nervous systems drive anorexia and catabolic changes in adipose tissue and skeletal muscle, hallmarks of cancer cachexia2-4. However, the molecular mechanisms driving cachexia remain poorly defined, and there are currently no approved drugs for the condition. Elevation in circulating growth differentiation factor 15 (GDF15) correlates with cachexia and reduced survival in patients with cancer5-8, and a GDNF family receptor alpha like (GFRAL)-Ret proto-oncogene (RET) signaling complex in brainstem neurons that mediates GDF15-induced weight loss in mice has recently been described9-12. Here we report a therapeutic antagonistic monoclonal antibody, 3P10, that targets GFRAL and inhibits RET signaling by preventing the GDF15-driven interaction of RET with GFRAL on the cell surface. Treatment with 3P10 reverses excessive lipid oxidation in tumor-bearing mice and prevents cancer cachexia, even under calorie-restricted conditions. Mechanistically, activation of the GFRAL-RET pathway induces expression of genes involved in lipid metabolism in adipose tissues, and both peripheral chemical sympathectomy and loss of adipose triglyceride lipase protect mice from GDF15-induced weight loss. These data uncover a peripheral sympathetic axis by which GDF15 elicits a lipolytic response in adipose tissue independently of anorexia, leading to reduced adipose and muscle mass and function in tumor-bearing mice.

Erratum: Non-homeostatic body weight regulation through a brainstem-restricted receptor for GDF15.

This corrects the article DOI: 10.1038/nature24042.

Non-homeostatic body weight regulation through a brainstem-restricted receptor for GDF15.

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.

Transcriptional control of human antigen R by bone morphogenetic protein.

Human antigen R (HuR) is an RNA-binding protein with protective activities against cellular stress. This study considers the mechanisms by which HuR transcriptional regulation occurs in renal proximal tubule cells. Under basal conditions, HuR mRNA is expressed in two forms: one that contains a approximately 20-base 5'-untranslated region (UTR) sequence and one that contains a approximately 150-base, G+C-rich 5'-UTR that is inhibitory to translation. Recovery from cellular stresses such as thapsigargin and ATP depletion induced increased expression of the shorter, more translatable transcript and decreased expression of the longer form. Analysis of HuR upstream regions revealed sequences necessary for regulation of the shorter mRNA. Within the long, G+C-rich 5'-UTR exist multiple copies of the alternate Smad 1/5/8-binding motif GCCGnCGC. Recovery from ATP depletion induced increases in Smad 1/5/8 levels; further, gel shift and chromatin immunoprecipitation analyses demonstrated the ability of these Smads to bind to the relevant motif in the HuR 5'-UTR. Transfection of exogenous Smad 1 increased HuR mRNA expression. Finally, HuR mRNA expression driven by the Smad-binding sites was responsive to BMP-7, a protein with known protective effects against ischemic injury in kidney. These data suggest that transcriptional induction of a readily translatable HuR mRNA may be driven by a mechanism known to protect the kidney from injury and provides a novel pathway through which administration of BMP-7 may attenuate renal damage.

Expression of the RNA-stabilizing protein HuR in ischemia-reperfusion injury of rat kidney.

The RNA-binding protein human antigen R (HuR) participates in the posttranscriptional regulation of mRNAs bearing 3' AU-rich and U-rich elements, which HuR can stabilize under conditions of cellular stress. Using the LLC-PK(1) proximal tubule cell line model, we recently suggested a role for HuR in protecting kidney epithelia from injury during ischemic stress (Jeyaraj S, Dakhlallah D, Hill SR, Lee BS. J Biol Chem 280: 37957-37964, 2005; Jeyaraj SC, Dakhlallah D, Hill SR, Lee BS. Am J Physiol Renal Physiol 291: F1255-F1263, 2006). Here, we have extended this work to show that small interfering RNA-mediated suppression of HuR in LLC-PK(1) cells increased apoptosis during energy depletion, while overexpression of HuR diminished apoptosis. Suppression of HuR also resulted in diminished levels of key cell survival proteins such as Bcl-2 and Hsp70. Furthermore, rat kidneys were subjected in vivo to transient ischemia followed by varying periods of reperfusion. Ischemia and reperfusion (I/R) affected intensity and distribution of HuR in a nephron segment-specific manner. Cells of the proximal tubule, which are most sensitive to I/R injury, demonstrated a transient shift of HuR to the cytoplasm immediately following ischemia. Over a 14-day period following the onset of reperfusion, nuclear and total HuR protein gradually increased in cortical and medullary proximal tubules, but not in non-proximal tubule cells. HuR mRNA was expressed in two forms with alternate transcriptional start sites that increased over a 14-day I/R period, and in vitro studies suggest selective translatability of these two mRNAs. Baseline and I/R-stimulated levels of HuR mRNA did not parallel those of HuR protein, suggesting translational control of HuR expression, particularly in medullary proximal tubules. These findings suggest that alterations in distribution and expression of the antiaptotic protein HuR specifically in cells of the proximal tubule effect a protective mechanism during and following I/R injury in kidney.