Abstract
<title>Abstract</title> <p> Background Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by progressive motoneuron (MN) degeneration, leading to progressive muscle weakness and paralysis. In the absence of a cure, the diagnosis of ALS remains challenging, often requiring up to one year for confirmation. The skeletal muscle is now recognized as an early pathogenic driver rather than a passive bystander in the disease. Methods We employed lipid imaging mass spectrometry (LIMS) to characterize the spatiotemporal lipid profile of the <italic>Tibialis anterior</italic> (TA) muscle, a vulnerable fast-twitch muscle, in the <italic>hSOD1</italic> <sup> <italic>G93A</italic> </sup> transgenic mouse model of ALS across defined disease stages. Results We identified fiber-type-specific and sex-dependent spatial lipid remodeling. Remarkably, lipid alterations occurred as early as the presymptomatic stage, prior to clinical symptom onset or MN loss. Specifically, LIMS accurately distinguished fast-twitch oxidative-glycolytic (type IIA) from fast-twitch glycolytic fibers (type IIB/IIX) in both wild-type (WT) and mutant mice, confirming the preferential susceptibility of type IIA and IIB fibers. Indeed, muscle lipidome analysis showed that presymptomatic TA muscles lose physiological lipid signatures while acquiring mutation-exclusive alterations. Furthermore, lipid profiles differed between female and male mice, revealing sex-dependent variations while still allowing discrimination of mutant mice at the presymptomatic stage. Finally, disease-associated lipid alterations due to the disease were also detected in serum, enabling accurate classification of presymptomatic mice. Conclusions Together, spatially resolved muscle lipidomics, at the fiber-type level and in a sex-dependent context, established lipid remodeling as an early event in ALS pathogenesis, providing candidate tissue and circulating biomarkers for early diagnosis and disease monitoring. </p>