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EGAS00001003181-sc-2022-07-12T08:26:28Z - samples

ABSTRACT: Clonal tracking of stem cells and their progeny by whole genome sequencing permits exploration of evolutionary genetics in human disease. In this study, we performed phylogenetic reconstruction of haematopoiesis using somatically acquired mutations in 323 single haematopoietic stem and progenitor cell-derived colonies from 10 individuals with an inherited disorder of ribosome assembly, Shwachman-Diamond syndrome. We observed numerous clonal expansions, with recurrent acquisition of mutually exclusive mutations (EIF6, TP53, RPL5, RPL22, PRPF8, chromosomes 7 and 15) in multiple different clones in utero or early childhood converging on the p53-dependent nucleolar surveillance pathway that monitors ribosome integrity. In contrast to clones carrying biallelic TP53 mutations, genomes derived from colonies carrying mono-allelic TP53 mutations displayed no increase in mutation burden or specific mutational signatures. Our study highlights striking loss of clonal diversity with convergent somatic evolution on the p53-dependent nucleolar surveillance pathway from early life to offset the deleterious effects of a germline mutation in a Mendelian haematopoietic disorder.

PROVIDER: EGAD00001009061 | EGA |

REPOSITORIES: EGA

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Project description:Background: Somatic mutations in blood indicative of clonal hematopoiesis of indeterminate potential (CHIP), particularly in DNMT3A, TET2, and JAK2, are associated with an increased risk of hematologic malignancy, coronary artery disease, and all-cause mortality. However, whether CHIP is associated with increased risk of peripheral artery disease (PAD) remains unknown. In addition, chemotherapy frequently causes mutations in DNA Damage Repair (DDR) genes TP53 and PPM1D, and whether CHIP caused by somatic mutations in DDR genes results in increased risk of atherosclerosis is unclear. We sought to test whether CHIP, and CHIP caused by DDR genes, associates with incident peripheral artery disease (PAD) and atherosclerosis. Methods: We identified CHIP among 50,122 exome sequences in individuals from UK and Mass General Brigham Biobanks and tested CHIP status (N=2,851) with incident PAD and atherosclerosis across multiple arterial beds. To mimic the human scenario of clonal hematopoiesis and test whether the expansion of p53-deficient hematopoietic cells contributes to atherosclerosis, a competitive bone marrow transplantation (BMT) strategy was used to generate atherosclerosis-prone Ldlr-/- chimeric mice carrying 20% Trp53-/- hematopoietic cells (20% KO-BMT mice). We then evaluated aortic plaque burden and plaque macrophage accumulation 12 weeks after grafting. Results: CHIP associated with incident PAD (HR 1.7; P=2.2x10-5) and atherosclerosis in multiple beds (HR 1.3; P=9.7x10-5), with increased risk among individuals with DDR CHIP (HR 2.0; P=0.0084). Among atherosclerosis-prone Ldlr null mice, the p53 -/- 20% KO-BMT mice demonstrated increased aortic plaque size (p=0.013) and accumulation of p53-/- plaque macrophages (P<0.001), driven by an abundance of p53-deficient plaque macrophages. The expansion of p53-deficient cells did not affect the expression of the pro-inflammatory cytokines IL-6 and IL-1β in the atherosclerotic aortic wall. Conclusions: Our findings highlight the role of CHIP as a broad driver of atherosclerosis across the entire arterial system, with evidence of increased plaque among p53 -/- 20% KO-BMT mice via expansion of plaque macrophages. These observations provide new insight into the link between CHIP and cardiovascular disease, and lend human genetic support to the concept that post-cytotoxic chemotherapy patients may benefit from surveillance for atherosclerotic conditions in addition to therapy-related myeloid neoplasms.

Project description:Myriad of craniofacial disorders are caused by heterozygous mutations in general regulators of housekeeping cellular functions such as ribosome biogenesis. While it is understood that many of these highly tissue-specific malformations are a consequence of defects in cranial neural crest cells (cNCCs), an embryonic cell group that gives rise to most of the facial structures during embryogenesis, the mechanism underlying cell type-selectivity of these effects remains largely unknown. Here we show that DDX21, a DEAD-box RNA helicase involved in control of both RNA polymerase (Pol) I and Pol II dependent transcriptional arms of ribosome biogenesis, is a key mediator of the nucleolar stress response. Using an in vitro model of Treacher Collins Syndrome (TCS), a craniofacial disorder caused by heterozygous mutations in components of the Pol I transcriptional machinery, we demonstrate that perturbations in ribosomal RNA (rRNA) transcription induce DDX21-mediated surveillance mechanism in cNCCs, leading to DDX21 relocalization from the nucleolus to the nucleoplasm, its eviction from Pol I and Pol II chromatin targets and inhibition of rRNA processing. Importantly, these effects are cell type-selective, cell-autonomous and involve activation of the p53 pathway. We further show that cNCCs are characterized by the inherently high reservoir of p53 mRNA and sensitivity to p53-mediated apoptosis. Remarkably, preventing the loss of DDX21 from nucleolus and chromatin can rescue both the sensitivity to apoptosis and TCS-associated craniofacial phenotypes in vivo. This mechanism is not restricted to TCS, as gene function perturbations linked to other ribosomopathies with craniofacial manifestations also lead to the activation of DDX21 surveillance. Lastly, we provide evidence that inhibition of rRNA synthesis leads to rDNA damage, and furthermore, that rDNA damage is sufficient to activate DDX21 surveillance and elicits tissue-selective and dosage-dependent effects on craniofacial development in vivo.

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EGAS00001003181-sc-2022-07-12T08:26:28Z - samples

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