Neurofibromin regulates metabolic rate via neuronal mechanisms in Drosophila

Abstract

Neurofibromatosis type 1 is a chronic multisystemic genetic disorder that results from loss of function in the neurofibromin protein. Neurofibromin may regulate metabolism, though the underlying mechanisms remain largely unknown. Here we show that neurofibromin regulates metabolic homeostasis in Drosophila via a discrete neuronal circuit. Loss of neurofibromin increases metabolic rate via a Ras GAP-related domain-dependent mechanism, increases feeding homeostatically, and alters lipid stores and turnover kinetics. The increase in metabolic rate is independent of locomotor activity, and maps to a sparse subset of neurons. Stimulating these neurons increases metabolic rate, linking their dynamic activity state to metabolism over short time scales. Our results indicate that neurofibromin regulates metabolic rate via neuronal mechanisms, suggest that cellular and systemic metabolic alterations may represent a pathophysiological mechanism in neurofibromatosis type 1, and provide a platform for investigating the cellular role of neurofibromin in metabolic homeostasis.

Loss of NF1 causes tactile hypersensitivity and impaired synaptic transmission in a Drosophila model of autism spectrum disorder

“…Consequently, loss of NF1 leads to excessive Ras and diminished cAMP/PKA signalling (Bergoug et al, 2020). Moreover, levels of phosphorylated MAPK have been shown to be augmented in the NF1 P1 mutant, indicative of excessive Ras activity (Botero et al, 2021; Williams et al, 2001). Therefore, we investigated which of these biochemical functions, if either, might explain the role of NF1 in regulating synaptic transmission and larval mechanoreception.…”

Measuring metabolic rate in single flies during sleep and waking states

“…To measure the whole-body metabolic rate of individual flies during wake and sleeping states, we developed the SAMM system, a stop-flow indirect calorimetry system that simultaneously uses infrared breams to record activity in freely moving flies (Figure 1). In order to increase the sensitivity of the system over a previously published version (Brown et al, 2019;Botero et al, 2021;Stahl et al, 2017;Stahl et al, 2018;Zandawala et al, 2018), we included an advanced analysis of the raw data consisting of smoothing of the flow rate and CO2 data as well as drift correction (Table 1). We also utilized zero-grade air, which contains less than 0.1 ppm total hydrocarbons, to minimize the amount of ambient CO2 entering the respirometry system.…”

“…Indirect calorimetry has been widely used in Drosophila to measure CO2 production (e.g. Botero et al, 2021;Jensen et al, 2014;Nagarajan-Radha et al, 2020;Stahl et al, 2018). In these studies, CO2 release from individuals or groups of flies can be directly measured using a CO2 analyzer, providing a close to real time measurement of CO2 production.…”

“…In these studies, CO2 release from individuals or groups of flies can be directly measured using a CO2 analyzer, providing a close to real time measurement of CO2 production. This approach has been used to test the effects of many different environmental factors including aging (Jensen et al, 2014;Khazaeli et al, 2005;Promislow & Haselkorn, 2002), as well as genetic mutations and backgrounds (Botero et al, 2021;Nagarajan-Radha et al, 2020;Stahl et al, 2017;Stahl et al, 2018;Zandawala et al, 2018).…”

“…Towards this end, we previously developed a Sleep and Activity Metabolic Monitor (SAMM) system that simultaneously measures activity and metabolic rate using indirect calorimetry (Brown et al, 2019;Botero et al, 2021;Stahl et al, 2017;Stahl et al, 2018;Zandawala et al, 2018). This system uses stop-flow respirometry to measure CO2 output from individual flies during sleeping and waking states.…”