Differentiation but not ALS mutations in FUS rewires motor neuron metabolism

Abstract

Energy metabolism has been repeatedly linked to amyotrophic lateral sclerosis (ALS). Yet, motor neuron (MN) metabolism remains poorly studied and it is unknown if ALS MNs differ metabolically from healthy MNs. To address this question, we first performed a metabolic characterization of induced pluripotent stem cells (iPSCs) versus iPSC-derived MNs and subsequently compared MNs from ALS patients carrying FUS mutations to their CRISPR/Cas9-corrected counterparts. We discovered that human iPSCs undergo a lactate oxidation-fuelled prooxidative metabolic switch when they differentiate into functional MNs. Simultaneously, they rewire metabolic routes to import pyruvate into the TCA cycle in an energy substrate specific way. By comparing patient-derived MNs and their isogenic controls, we show that ALS-causing mutations in FUS did not affect glycolytic or mitochondrial energy metabolism of human MNs in vitro. These data show that metabolic dysfunction is not the underlying cause of the ALS-related phenotypes previously observed in these MNs.

Existing and Emerging Metabolomic Tools for ALS Research

“…In addition, fibroblasts from sALS patients showed a different response to ageing compared to controls as an increase in uncoupled mitochondrial respiration, but no decrease in glycolysis, no increase in the oxygen consumption rate or in extracellular acidification rate were observed [80]. Finally, we recently showed that ALS-causing mutations in FUS do not affect cellular respiration in human motor neurons [9]. Altogether, these studies illustrate the value of the Seahorse XF analyzer and its ability to obtain reliable information about mitochondrial respiration and extracellular acidification.…”

“…In our opinion, the latter indicates that mitochondrial dysfunction could represent a general hallmark of ALS rather than being attributed to mutations in SOD1. Yet, we recently showed that mitochondrial dysfunction is absent in FUS-ALS human motor neurons [9]. Thirdly, evidence points to a defective carbohydrate metabolism in ALS.…”

“…The metabolic vulnerability of motor neurons in ALS is further underlined by the initial degeneration of fast-fatigable motor neurons, which require higher peak needs of ATP compared to the slow motor neurons, less prone to neurodegeneration in this context [7]. While glucose is the main energy substrate of the central nervous system [8], it is still unclear to which extent glucose is processed before it is used by neurons to meet their energy demand [9]. In vitro and ex vivo studies have shown that neurons oxidize other non-glucose substrates such as glutamate, a process which has been suggested to protect neurons from excitotoxicity [9][10][11].…”

“…While glucose is the main energy substrate of the central nervous system [8], it is still unclear to which extent glucose is processed before it is used by neurons to meet their energy demand [9]. In vitro and ex vivo studies have shown that neurons oxidize other non-glucose substrates such as glutamate, a process which has been suggested to protect neurons from excitotoxicity [9][10][11]. Additionally, neurons are also able to process ketone bodies to maintain energetic homeostasis [12][13][14].…”

“…Indeed, it remains unclear whether the observed metabolic defects discussed above are a primary event or secondary to other defects such as aberrant epigenetic regulation or a disturbed microbiome. We recently applied state-of-the-art metabolic tools in ALS to investigate the effect of ALS-causing mutations in FUS on the metabolic state of human motor neurons [9]. With the advent of several new technologies and models available to unravel the metabolic differences between healthy and diseased motor neurons and their microenvironment, we here provide an overview of existing and emerging metabolic technologies to guide further investigation on the exact role of metabolism in ALS.…”