Lipidomics study of plasma from patients suggest that ALS and PLS are part of a continuum of motor neuron disorders

Abstract

Motor neuron disorders (MND) include a group of pathologies that affect upper and/or lower motor neurons. Among them, amyotrophic lateral sclerosis (ALS) is characterized by progressive muscle weakness, with fatal outcomes only in a few years after diagnosis. On the other hand, primary lateral sclerosis (PLS), a more benign form of MND that only affects upper motor neurons, results in life-long progressive motor dysfunction. Although the outcomes are quite different, ALS and PLS present with similar symptoms at disease onset, to the degree that both disorders could be considered part of a continuum. These similarities and the lack of reliable biomarkers often result in delays in accurate diagnosis and/or treatment. In the nervous system, lipids exert a wide variety of functions, including roles in cell structure, synaptic transmission, and multiple metabolic processes. Thus, the study of the absolute and relative concentrations of a subset of lipids in human pathology can shed light into these cellular processes and unravel alterations in one or more pathways. In here, we report the lipid composition of longitudinal plasma samples from ALS and PLS patients initially, and after 2 years following enrollment in a clinical study. Our analysis revealed common aspects of these pathologies suggesting that, from the lipidomics point of view, PLS and ALS behave as part of a continuum of motor neuron disorders.

Figure 1

oPLS-DA score plots and corresponding loading S-Plots obtained from control and (A) ALS plasma samples at baseline and (B) at follow-up. OPLS-DA loadings S-plots indicate significant lipids species between controls and (C) ALS at baseline and (D) at follow-up times.

Figure 2

oPLS-DA score plots and corresponding loading S-Plots obtained from (A) control and PLS plasma samples at baseline and (B) pooled ALS and PLS plasma samples. OPLS-DA loadings S-plots indicate significant lipids species between (C) controls and PLS at baseline and (D) between all ALS and PLS plasma samples.

Figure 3

Random Forest plot representing the distribution of minimal depth and its mean for the indicated groups of samples. (A) Control versus ALS at baseline, (B) Control versus ALS at follow-up, (C) ALS at baseline versus ALS at follow-up, (D) Control versus PLS at baseline, (E) Control versus PLS at follow-up, (F) PLS at baseline PLS at follow-up, (G) Pooled ALS samples versus pooled PLS samples. Species also identified by oPLS-DA are shown in bold.

Figure 4

Representation of changes in the main categories of lipids in and cholesteryl esters species in plasma from ALS and PLS patients compared to controls. (A) Heat map representation of the most significant fold-changes in the concentration of every class of lipids in plasma from ALS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up). (n = 40 ALS, n = 26 PLS samples and 28 controls analyzed in triplicate. *< 0.05; **< 0.01. T-Test). (B) Graph representations of FC concentrations in ALS and PLS plasma. One-way ANOVA. P values are indicated. (C) Heat map representation of the most significant fold-changes in the concentration of cholesteryl ester (CE) species in plasma from ALS and PLS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up) (D) Graph representations of the average concentration of CE species in ALS and PLS plasma. One-way ANOVA. P values are indicated.

Figure 5

Analysis of TG in plasma from ALS and PLS patients compared to controls (A) Heat map representation of the most significant fold-changes in the concentration of Triradylglycerols (TG) species in plasma from ALS and PLS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up) (n = 40 ALS , n = 26 PLS samples and 28 controls analyzed in triplicate. *< 0.05; **< 0.01. T-Test). (B) Graph representation of DG species average concentration in ALS and PLS plasma compared to controls. One-way ANOVA. P values are indicated (C) Box plot representations of the most significant fold-changes in the concentration of di- and triglyceride species in plasma from PLS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up) (n = 26 PLS samples and 28 controls analyzed in triplicate. *< 0.05; **< 0.01. T-Test).

Figure 6

Analysis of ceramide (Cer) and sphingomyelin (SM) changes in plasma from ALS and PLS patients compared to controls (A) Heat map representation of the most significant fold-changes in the concentration of (A) ceramide and (B) sphingomyelin species in plasma from ALS and PLS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up). Graph representations of the average concentration of (C) ceramide and (D) sphingomyelin species in ALS and PLS plasma. One-way ANOVA. P values are indicated (n = 40 ALS, 26 PLS samples and 28 controls analyzed in triplicate. *< 0.05; **< 0.01).

Figure 7

Analysis of PC and PS in plasma from ALS and PLS patients compared to controls (A) Heat map representation of the most significant fold-changes in the concentration of glycerophosphatidylcholine (PC) species in plasma from ALS and PLS patients compared to controls at the beginning of the study (baseline) and 1 years after (Follow-up). (B) Graph representations of average concentration of specific PC species in ALS and PLS plasma. One-way ANOVA. P values are indicated (C) Heat map representation of the most significant fold-changes in the concentration of glycerophosphatidylserine (PS) species in plasma from ALS and PLS patients compared to controls at the beginning of the study (baseline) and 2 years after (Follow-up). (D) Graph representations of average concentration of specific PS species in ALS and PLS plasma. One-way ANOVA. P values are indicated (n = 40 ALS, 26 PLS samples and 28 controls analyzed in triplicate. *< 0.05; **< 0.01).