Project description:Loss-of-function (LoF) variants in the lipid transporter ABCA7 significantly increase Alzheimer's disease risk (odds ratio circa 2), yet the underlying pathogenic mechanisms and specific neural cell types affected remain unclear. To investigate this, we generated a single-nucleus RNA sequencing atlas of 36 human postmortem prefrontal cortex samples, including 12 carriers of ABCA7 LoF variants and 24 matched non-carriers. ABCA7 LoF variants were associated with transcriptional changes across all major neural cell types. Excitatory neurons, which expressed the highest levels of ABCA7, showed significant alterations in oxidative phosphorylation, lipid metabolism, DNA damage responses, and synaptic signaling pathways. ABCA7 LoF-associated transcriptional changes in neurons were similarly perturbed in carriers of the common AD missense variant ABCA7 p.Ala1527Gly (n = 240 controls, 135 carriers) - predicted by molecular dynamics simulations to disrupt ABCA7 structure -, indicating that findings from our study may extend to large portions of the at-risk population. Human induced pluripotent stem cell (iPSC)-derived neurons carrying ABCA7 LoF variants closely recapitulated the transcriptional changes observed in human postmortem neurons. Biochemical experiments further demonstrated that ABCA7 LoF disrupts mitochondrial membrane potential via regulated uncoupling, increases oxidative stress, and alters phospholipid homeostasis in neurons, notably elevating saturated phosphatidylcholine levels. Supplementation with CDP-choline to enhance de novo phosphatidylcholine synthesis effectively reversed these transcriptional changes, restored mitochondrial uncoupling, and reduced oxidative stress. Additionally, CDP-choline normalized amyloid-beta secretion and alleviated neuronal hyperexcitability in ABCA7 LoF neurons. This study provides a detailed transcriptomic profile of ABCA7 LoF-induced changes and highlights phosphatidylcholine metabolism as a key driver in ABCA7-induced risk. Our findings suggest a promising therapeutic approach that may benefit a large proportion of individuals at increased risk for Alzheimer's disease.

Project description:Rationale: SMAD2 is a co-regulator that binds a variety of transcription factors and modulates activities during human development. Heterozygous SMAD2 loss-of-function (LoF) variants and missense variants are identified in patients with complex congenital heart disease (CHD), and in patients with arterial aneurysms and dissections. Mechanisms that account for distinct cardiovascular phenotypes caused by SMAD2 variants remain unknown. We aimed to define the transcriptional and epigenetic effects of heterozygous SMAD2 loss-of-function (LoF) and missense variants and identify the involvement of transcription factor networks and genes that contribute to CHD. Compared to LoF variants, we assessed the function of rare SMAD2 missense variants of uncertain significance. Methods: We constructed isogenic induced pluripotent stem cells (iPSCs) with heterozygous or homozygous LoF and rare (MAF ≤ 10-5) missense SMAD2 variants identified in CHD probands. Wildtype and mutant iPSCs were studied by bulk RNA sequencing (RNAseq) and chromatin accessibility (ATACseq). Datasets were integrated with published SMAD2/3 chromatin immunoprecipitation (ChIPseq) studies. Cardiomyocyte differentiation and contractility of mutant iPSCs was assessed. Results: SMAD2 haploinsufficiency reduced open chromatin across promoter regions and altered the expression of 385 direct SMAD regulated genes, including ten previously identified as dominant CHD genes. Motif analyses in regions with differential ATAC peaks predicted that SMAD2 haploinsufficiency disrupts interactions with at least five transcription factors, NANOG, ETS, TEAD3/4, CREB1 and AP1. Compared to SMAD2-haploinsufficient cells, iPSCs with heterozygous R114C or W274C variants exhibited shared and distinct patterns of altered chromatin accessibility, transcription factor binding motifs, and dysregulated genes. Conclusions: SMAD2 haploinsufficiency disrupts chromatin interactions and perturbs transcription factor binding, disrupting normal cardiovascular development. Differences in the molecular consequences of LoF and missense variants likely contribute to clinical phenotypic heterogeneity. Additionally, these data indicate opportunities for molecular functional analyses to improve re-classification of SMAD2 variants of uncertain clinical significance.

			Action	DRS
	241106_MP01_PTMs_onTargerProtein.xlsx	Xlsx
	241106_MP_01.raw	Raw
	241106_MP_01_PTM.msf	Msf
	241106_MP_01_allProt.msf	Msf
	241106_MP_02-PTM.msf	Msf

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The EXOSC10S402T allele identified in colon cancer causes early embryonic lethality and suggests EXOSC10 as a biomarker for 5-fluorouracil sensitivity

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