Though discovered over 100 years ago, the molecular foundation of sporadic Alzheimer's disease (AD) remains elusive. To elucidate its complex nature, we constructed multiscale causal network models on a large human AD multi-omics dataset, integrating clinical features of AD, DNA variation, and gene and protein expression into probabilistic causal models that enabled detection and prioritization of high-confidence key drivers of AD, including the top predicted key driver VGF. Overexpression of neuropeptide precursor VGF in 5xFAD mice partially rescued beta-amyloid-mediated memory impairment and neuropathology. Molecular validation of network predictions downstream of VGF was achieved, with significant enrichment for homologous genes identified as differentially expressed in 5xFAD brains overexpressing VGF versus controls. Our findings support a causal and/or protective role for VGF in AD pathogenesis and progression.
One sentence summary: VGF protects against Alzheimer's diseaseAlthough VGF has been reported to regulate fear and spatial memories in mouse models (35,37,38), and to be an AD biomarker, with VGF-derived peptides found to be reduced in the CSF of AD patients compared to healthy controls (39-46), VGF has not previously been causally associated with AD. We determined through our network models that VGF was the only downregulated KD for AD that was conserved across the RNA, protein, and combined RNA and protein networks we constructed. We replicated these findings in other brain regions (47) and in an independent dataset (48,49), and observed evidence of genetic association in the largest AD GWAS to date (10). Given VGF's status as the top KD we identified in our networks, we overexpressed VGF in the 5xFAD mouse model of familial AD and found that it not only lowered overall amyloid plaque and Tau-associated dystrophic neurite levels, but it significantly perturbed gene expression traits that were enriched for genes predicted by our networks to change in response to VGF modulation. Taken together, these results provide molecular and functional validation of our multiscale causal network analysis finding of VGF as a driver of AD pathophysiology. We conclude that the genes and clinical features linked to VGF provide novel insights into the mechanisms underlying AD risk and pathogenesis.Results: Our overall strategy for elucidating the complexity of AD is depicted in Fig. 1 (Fig. S1) and is centered on the objective, data-driven construction of predictive network models of AD that can then be queried to identify network components causally associated with AD. The master regulators that modulate the state of these AD-associated network components can then be readily identified from the network model. We have previously developed and applied the network reconstruction algorithm, RIMBANET, which statistically infers causal relationships between DNA variation, gene expression, protein expression and clinical features that are scored