Increased prothrombin, apolipoprotein A-IV, and haptoglobin in the cerebrospinal fluid of patients with Huntington's disease

Abstract

Huntington's disease (HD) is a progressive neurodegenerative disease caused by an unstable CAG trinucleotide repeat expansion. The need for biomarkers of onset and progression in HD is imperative, since currently reliable outcome measures are lacking. We used two-dimensional electrophoresis and mass spectrometry to analyze the proteome profiles in cerebrospinal fluid (CSF) of 6 pairs of HD patients and controls. Prothrombin, apolipoprotein A-IV (Apo A-IV) and haptoglobin were elevated in CSF of the HD patients in comparison with the controls. We used western blot as a semi-quantified measurement for prothrombin and Apo A-IV, as well as enzyme linked immunosorbent assay (ELISA) for measurement of haptoglobin, in 9 HD patients and 9 controls. The albumin quotient (Qalb), a marker of blood-brain barrier (BBB) function, was not different between the HD patients and the controls. The ratios of CSF prothrombin/albumin (prothrombin/Alb) and Apo A-IV/albumin (Apo A-IV/Alb), and haptoglobin level were significantly elevated in HD. The ratio of CSF prothrombin/Alb significantly correlated with the disease severity assessed by Unified Huntington's Disease Rating Scale (UHDRS). The results implicate that increased CSF prothrombin, Apo A-IV, and haptoglobin may be involved in pathogenesis of HD and may serve as potential biomarkers for HD.

Figure 1. 2-DE maps of CSF proteomes.

Representative 2-DE maps of CSF proteome from a patient with HD (A) and a control (B) are shown. Spots 1–3 indicate proteins with up-regulation in HD. Cropped images containing spots corresponding to prothrombin (spot 1), apolipoprotein A-IV (Apo A-IV, spots 2) and haptoglobin (spot 3) (indicated by arrowheads) derived from 2-DE maps of six CSF samples of patients with HD and paired control samples (C).

Figure 2. Representative Western blots of prothrombin (72 kD) and albumin (64 kD) in CSF and serum of HD patients and their corresponding controls (C).

The resulting data are illustrated in scatter plots with median and interquartile range. The prothrombin/Alb ratio in CSF of HD patients (n = 9) is higher than that in controls (n = 9). *p<0.05, Mann-Whitney U test.

Figure 3. Representative Western blots of Apo A-IV (46 kD) and albumin (64 kD) in CSF and serum, respectively, of HD patients and their corresponding controls (C).

The Apo A-IV/Alb ratios in CSF and serum in comparison with their corresponding control groups are illustrated in scatter plots with median and interquartile rang, respectively. The Apo A-IV/Alb ratio in CSF of HD patients (n = 9) is significantly higher when compared with the controls (n = 9). *p<0.01, Mann-Whitney U test.

Figure 4. Qalb, CSF haptoglobin, and serum haptoglobin concentration in HD patients.

Data are illustrated in scatter plots with median and interquartile rang. Either the Qalb or serum haptoglobin concentration was not different between HD (n = 9) and the controls (n = 9), whereas the CSF haptoglobin was significantly increased in HD. *p<0.05, Mann-Whitney U test.

Figure 5. Linear regression of prothrombin/Alb to motor score, independence scale, and function capacity of UHDRS, respectively.

The ratio of prothrombin/Alb was significantly correlated to subscales of UHDRS, with a positive correlation to motor score (A, r = 0.810, p = 0.008) and a negative correlation to independence scale (B, r = −0.908, p<0.001) and functional capacity (C, r = −0.891, p = 0.001).