CSF levels of brain-derived proteins correlate with brain ventricular volume in cognitively healthy 70-year-olds

Abstract

Background: The effect of varying brain ventricular volume on the cerebrospinal fluid (CSF) proteome has been discussed as possible confounding factors in comparative protein level analyses. However, the relationship between CSF volume and protein levels remains largely unexplored. Moreover, the few existing studies provide conflicting findings, indicating the need for further research.

Methods: Here, we explored the association between levels of 88 pre-selected CSF proteins and ventricular volume derived from magnetic resonance imaging (MRI) measurements in 157 cognitively healthy 70-year-olds from the H70 Gothenburg Birth Cohort Studies, including individuals with and without pathological levels of Alzheimer's disease (AD) CSF markers (n = 123 and 34, respectively). Both left and right lateral, the inferior horn as well as the third and the fourth ventricular volumes were measured. Different antibody-based methods were employed for the protein measurements, with most being analyzed using a multiplex bead-based microarray technology. Furthermore, the associations between the protein levels and cortical thickness, fractional anisotropy, and mean diffusivity were assessed.

Results: CSF levels of many brain-derived proteins correlated with ventricular volumes in A-T- individuals, with lower levels in individuals with larger ventricles. The strongest negative correlations with total ventricular volume were observed for neurocan (NCAN) and neurosecretory protein VGF (rho = -0.34 for both). Significant negative correlations were observed also for amyloid beta (Ab) 38, Ab40, total tau (t-tau), and phosphorylated tau (p-tau), with correlation ranging between - 0.34 and - 0.28, while no association was observed between ventricular volumes and Ab42 or neurofilament light chain (NfL). Proteins with negative correlations to ventricular volumes further demonstrated negative correlations to mean diffusivity and positive correlation to fractional anisotropy. However, only weak or no correlations were observed between the CSF protein levels and cortical thickness. A + T + individuals demonstrated higher CSF protein levels compared to A-T- individuals with the most significant differences observed for neurogranin (NRGN) and synuclein beta (SNCB).

Conclusions: Our findings suggest that the levels of many brain-derived proteins in CSF may be subjected to dilution effects depending on the size of the brain ventricles in healthy individuals without AD pathology. This phenomenon could potentially contribute to the inter-individual variations observed in CSF proteomic studies.

Keywords: Brain ventricular volume; Brain-enriched proteins; Cerebrospinal fluid; Cortical thickness; Diffusion tensor imaging; Inter-individual variability; Protein profiling.

Fig. 1

Ventricular volumes are similar in individuals with and without early AD pathology. A) Larger intracranial volume (ICV) was observed in males compared to females. B) Total ventricular volume correlates with ICV. C) No differences in ventricular volumes were observed between A-T- and A + T+, based on ICV adjusted volumes

Fig. 2

Association of ventricular volumes and CSF protein levels in A-T- individuals. A) A heatmap based on spearman correlation coefficients between protein levels and ventricular volumes. The heatmap is annotated with correlation per protein with total ventricular volume and correlation to albumin quotient. Two protein clusters were observed, one marked in green, and one marked in yellow. B) Correlation coefficients per protein and ventricular volume. C) Correlation coefficients and p-value for each protein against total ventricular volume. The horizontal dashed line indicates p-value = 0.05. D) Correlation between protein levels and total ventricular volume for the five proteins with strongest negative correlation

Fig. 3

Association between CSF protein levels and grey and white matter status. A) No significant differences were observed for cortical thickness or white matter status measurements between the groups of A-T- and A + T + individuals. B) A heatmap based on spearman correlation coefficients between protein levels and cortical thickness and diffusion tensor imaging (DTI) measurements in healthy individuals. C) Correlation coefficients and p-value for each protein against fractional anisotropy and diffusivity. The horizontal dashed line indicates p-value = 0.05. D) Correlation between protein levels and diffusion tensor imaging measurements

Fig. 4

Comparisons between A-T- (turquoise) and A + T+ (purple). A) Proteins in the yellow ventricular volume associated cluster showed generally higher levels in A + T + individuals compared to the A-T- group. Yellow and green indicates cluster origin from the ventricular volume association analysis. The AD markers were excluded from this visualization. B) The distribution of correlation coefficients between protein levels and ventricular volume in the A-T- group and the A + T + group for the proteins in the ventricle associated (yellow) cluster. C) The five proteins with most significant differences in A + T + compared to A-T-. D) Protein correlations to total ventricular volume per sample group for the same five proteins