Leeuw, Diederick Martijn de

AbstractBackgroundLower gray matter connectivity measures are related to faster cognitive decline in prodromal Alzheimer’s Disease (AD). We investigated the biological underpinnings responsible for this loss of brain connections using cerebrospinal fluid (CSF) proteomics.MethodData from ADNI was used to select 82 individuals with MCI and abnormal CSF amyloid (mean age±SD 74±7) and 37 controls with normal amyloid levels (mean age±SD 75±5), for whom repeated MRI‐scans (median of 6 scans over 1.5 follow‐up years) and baseline CSF proteomic data (in total 306 proteins) were available. We used an automated pipeline (Tijms, Series et al. 2012) to construct gray matter networks from 3D‐T1 sequences and calculate connectivity density and gamma – measures previously found to be most strongly related to cognitive decline (Dicks, Vermunt et al. 2020). Linear mixed models were applied to test associations between baseline CSF protein levels and repeated connectivity metrics, controlling for intracranial volume, age and sex. Proteins that demonstrated significant associations (p<0.05) were identified and examined for their biological relevance according to Gene Ontology.ResultConnectivity density declined over time with ‐0.8% per year (pMCI = 0.001; figure 1), which did not differ from controls (pdif = 0.15). Gamma declined faster in MCI than in controls (bMCI = ‐0.016 vs. bCN = ‐0.007, pdif <0.001; figure 1). Higher levels of 99/108 proteins were associated with faster decline in connectivity density (a.o. tau and neuroprentaxins). These proteins were involved in regulation of synapse organization (GO:0050807; pFDR = 7.00E‐07; figure 2). Higher levels of 9/108 proteins associated with less decline and were involved in chemotaxis (GO:0048247; pFDR = 1.40E‐02). Similarly, 25 out 30 proteins (83%) associated with alterations in gamma over time, showed associations of higher levels with less gamma decline and were also involved in chemotaxis (GO:0050926; pFDR = 9.42E‐05; figure 3). There were no protein‐connectivity relationships in controls.ConclusionProteins involved in synapse organization were associated with faster decline in connectivity density over time in patients, while chemotaxis was associated with less decline. This suggests that synaptic degeneration may predict disease progression while immune responses may serve as a resilience mechanism in AD.

AbstractBackgroundIndividuals with prodromal Alzheimer’s Disease (AD) and higher gray matter connectivity measures show slower decline, suggesting resilience to AD. However, the precise biological processes underlying preserved brain connections remains unclear. Here, we studied this question using cerebrospinal fluid (CSF) proteomics.MethodFrom the ADNI we selected 78 individuals with MCI and abnormal CSF amyloid (i.e., prodromal AD) and 34 with normal cognition and normal CSF amyloid levels for whom MRI and CSF proteomic data was available. For each T1 MRI scan we constructed gray matter networks using an automated pipeline (Tijms, Series et al. 2012) and calculated degree, connectivity density, clustering, path length and small‐world measures (i.e. gamma, lambda and small world coefficient). Linear models were used to test associations between each connectivity measure and CSF protein levels while correcting for age and gender. Proteins showing associations of p < 0.1 were selected to find groups of proteins that are associated with biological processes according to Gene Ontology (GO). Proteomic profiles for each connectivity measure were compared to investigate overlap. Finally, we tested for enrichment of potential upstream drivers with the Enrichr tool.ResultIn total, 115 proteins were associated with altered connectivity in prodromal AD subjects (figure 1). The majority of proteins (n = 93, 80%) showed higher levels with stronger (i.e., resilient) brain networks characterized by increased degree, connectivity density, clustering, path length, gamma, lambda or small world coefficient values. In controls, 80 of these 93 proteins showed an opposite relationship, with lower levels relating to higher values for these connectivity measures, which suggests that increased levels in prodromal AD may indicate a compensatory mechanism to maintain strong brain connectivity. According to a pathway analysis in GO, these proteins associated with stronger brain networks were mainly involved in neuroplasticity pathways. A subsequent Enrichr analysis suggested involvement of upstream divers SUZ12 and REST, which are known to regulate neuroplasticity processes.ConclusionWe observed that higher CSF levels of neuroplasticity associated proteins were associated with higher brain connectivity values in prodromal AD, suggesting that plasticity mechanisms may play a role in resilience to AD pathology.