Neurofibromin regulates metabolic rate via neuronal mechanisms in Drosophila
Neurofibromatosis type 1 (NF1) is a genetic disorder predisposing patients to a range of features, the most characteristic of which include areas of abnormal skin pigmentation and benign tumors associated with peripheral nerves, termed neurofibromas. Less common, but more serious symptoms also include malignant peripheral nerve sheath tumors, other malignancies, and learning disabilities. The NF1 gene encodes neurofibromin, a large protein that functions as a negative regulator of Ras signaling and mediates pleiotropic cellular and organismal function. Recent evidence suggests NF1 may regulate metabolism, though the mechanisms are unknown. Here we show that the Drosophila ortholog of NF1, dNf1 regulates metabolic homeostasis in fruit flies by functioning within a discrete brain circuit. Loss of dNf1 increases metabolic rate and feeding, enhances starvation susceptibility, and decreases lipid stores while increasing lipid turnover rate. The increase in metabolic rate is independent of locomotor activity (grooming), and maps to a subset of neurons in the ventral nervous system. The feeding and metabolic rate effects are due to loss of dNf1 in the same set of neurons, suggesting that increased feeding may be a compensatory effect driven by the increase in metabolic rate and lipid turnover. Finally, we show that the Ras GAP-related domain of neurofibromin is required for normal metabolism, demonstrating that Ras signaling downstream of dNf1 mediates the metabolic effects. These data demonstrate that dNf1 regulates metabolic rate via neuronal mechanisms, suggest that cellular and systemic metabolic alterations may represent a pathophysiological mechanism in NF1, and provide a platform for investigating the cellular role of neurofibromin in metabolic homeostasis.