Disruption of the angiopoietin-like system connects lipid homeostasis and hypothalamic dysfunction in ALS

Alterations in lipid metabolism are manifestations of amyotrophic lateral sclerosis (ALS) that contribute to the risk and rate of progression. Blood levels of triglycerides and cholesterol are altered in ALS patients and pre-symptomatic gene carriers, but mechanistic insights into these changes are lacking.

Serum samples from sporadic ALS patients (n = 118), mutated SOD1 and FUS/TARDBP (n = 20, 40, 17, respectively) with age and gender-matched controls (n = 96) were analysed for alterations in the angiopoietin-like protein (ANGPTL) system using enzyme-linked immunosorbent assays. SOD1^G93A murine model was studied at pre-symptomatic (P50), early symptomatic (P90), and fully symptomatic (P110) stages, along with their wild-type (WT) littermates for ANGPTLs. Untargeted lipidomics on serum was performed using high-resolution liquid chromatography-mass spectrometry. Further, the involvement of the hypothalamus was studied using hypothalamic volumetry in patients and an antibody array spanning 308 proteins in mice.

We show that mutation-specific patterns of systemic lipid abnormalities appear in ALS and that they correlate with reduced levels of angiopoietin-like proteins 3 and 4. ANGPTL-3/4, in turn, correlates with hypothalamic atrophy but not with corticospinal involvement, as determined by MRI volumetry and diffusion tensor imaging. Lipid phenotype and decreased ANGPTL in humans are recapitulated in two SOD1 murine ALS models, in which ANGPTL-3, -4, and -8 expression patterns are consistent with the repartitioning of lipid utilisation from muscles to the brown adipose tissue; systemic levels of ANGPTL-3 correlate with hypothalamic neuroinflammation and vascular permeability and with hypothalamic levels of agouti-related protein and neuropeptide Y.

These data provide a molecular mechanism linking peripheral lipid metabolism to the dysfunction of a specific hypothalamic circuit through the mediation of systemic ANGPTL-3 and -4. This finding constitutes a molecularly defined entry point to manipulate lipid metabolism in ALS.