Aberrant induction of type I IFN is a hallmark of the inherited encephalopathy Aicardi-Goutières syndrome (AGS), but the mechanisms triggering disease in the human central nervous system (CNS) remain ...elusive. Here, we generated human models of AGS using genetically modified and patient-derived pluripotent stem cells harboring TREX1 or RNASEH2B loss-of-function alleles. Genome-wide transcriptomic analysis reveals that spontaneous proinflammatory activation in AGS astrocytes initiates signaling cascades impacting multiple CNS cell subsets analyzed at the single-cell level. We identify accumulating DNA damage, with elevated R-loop and micronuclei formation, as a driver of STING- and NLRP3-related inflammatory responses leading to the secretion of neurotoxic mediators. Importantly, pharmacological inhibition of proapoptotic or inflammatory cascades in AGS astrocytes prevents neurotoxicity without apparent impact on their increased type I IFN responses. Together, our work identifies DNA damage as a major driver of neurotoxic inflammation in AGS astrocytes, suggests a role for AGS gene products in R-loop homeostasis, and identifies common denominators of disease that can be targeted to prevent astrocyte-mediated neurotoxicity in AGS.
Precise gene editing in hematopoietic stem and progenitor cells (HSPCs) holds promise for treating genetic diseases. However, responses triggered by programmable nucleases in HSPCs are poorly ...characterized and may negatively impact HSPC engraftment and long-term repopulation capacity. Here, we induced either one or several DNA double-stranded breaks (DSBs) with optimized zinc-finger and CRISPR/Cas9 nucleases and monitored DNA damage response (DDR) foci induction, cell-cycle progression, and transcriptional responses in HSPC subpopulations, with up to single-cell resolution. p53-mediated DDR pathway activation was the predominant response to even single-nuclease-induced DSBs across all HSPC subtypes analyzed. Excess DSB load and/or adeno-associated virus (AAV)-mediated delivery of DNA repair templates induced cumulative p53 pathway activation, constraining proliferation, yield, and engraftment of edited HSPCs. However, functional impairment was reversible when DDR burden was low and could be overcome by transient p53 inhibition. These findings provide molecular and functional evidence for feasible and seamless gene editing in HSPCs.
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•DNA DSBs induced by programmable nucleases transiently activate the DDR in HSPCs•Single-cell transcriptomics show that induced DSBs activate the p53 pathway•AAV6-mediated genome editing aggravates p53 activation and delays HSPC proliferation•Transient p53 inhibition alleviates clonogenic and repopulation defects in edited HSPCs
Precise gene editing has the potential to treat immune and hematological diseases. Genovese, Naldini, Di Micco, and colleagues now show that gene-editing procedures are well tolerated by hematopoietic stem cells and provide molecular evidence of the feasibility of seamless gene editing, strengthening translation of such approaches to humans.
Hematopoietic stem and progenitor cells (HSPC) reside in the bone marrow (BM) niche and serve as a reservoir for mature blood cells throughout life. Aging in the BM is characterized by low‐grade ...chronic inflammation that could contribute to the reduced functionality of aged HSPC. Mesenchymal stromal cells (MSC) in the BM support HSPC self‐renewal. However, changes in MSC function with age and the crosstalk between MSC and HSPC remain understudied. Here, we conducted an extensive characterization of senescence features in BM‐derived MSC from young and aged healthy donors. Aged MSC displayed an enlarged senescent‐like morphology, a delayed clonogenic potential and reduced proliferation ability when compared to younger counterparts. Of note, the observed proliferation delay was associated with increased levels of SA‐β‐galactosidase (SA‐β‐Gal) and lipofuscin in aged MSC at early passages and a modest but consistent accumulation of physical DNA damage and DNA damage response (DDR) activation. Consistent with the establishment of a senescence‐like state in aged MSC, we detected an increase in pro‐inflammatory senescence‐associated secretory phenotype (SASP) factors, both at the transcript and protein levels. Conversely, the immunomodulatory properties of aged MSC were significantly reduced. Importantly, exposure of young HSPC to factors secreted by aged MSC induced pro‐inflammatory genes in HSPC and impaired HSPC clonogenic potential in a SASP‐dependent manner. Altogether, our results reveal that BM‐derived MSC from aged healthy donors display features of senescence and that, during aging, MSC‐associated secretomes contribute to activate an inflammatory transcriptional program in HSPC that may ultimately impair their functionality.
Aged mesenchymal stromal cells (MSC) display early senescence features including SA‐β‐Gal accumulation, DDR, and SASP activation. Through SASP, aged MSC impair the clonogenic potential of hematopoietic stem and progenitor cells (HSPC) and induce the activation of a pro‐inflammatory transcriptional program in young HSPC.
We have previously shown that αB-crystallin (CRYAB), a small heat shock protein (sHsp) that prevents irreversible aggregation of unfolded protein by an ATP-independent chaperone activity, plays a ...pivotal role in the biogenesis of multipass transmembrane proteins (TMPs) assisting their folding from the cytosolic side of the endoplasmic reticulum (ER) (D'Agostino et al., 2013). Here we present evidence, based on phosphomimetic substitutions, that the three phosphorytable serine residues at position 19, 45 and 59 of CRYAB play a different regulatory role in this novel chaperone activity: S19 and S45 have a strong inhibitory effect, either alone or in combination, while S59 has not and counteracts the inhibition caused by single phosphomimetic substitutions at S19 and S45. Interestingly, all phosphomimetic substitutions determine the formation of smaller oligomeric complexes containing CRYAB, indicating that the inhibitory effect seen for S19 and S45 cannot be ascribed to the reduction of oligomerization frequently associated to a decreased chaperone activity. These results indicate that phosphorylation finely regulates the chaperone activity of CRYAB with multipass TMPs and suggest a pivotal role for S59 in this process.
•CRYAB chaperone activity toward ATP7B-H1069Q and Fz4-FEVR.•Phosphomimetic S19D and S45D inhibit CRYAB chaperone activity.•Phosphomimetic S59D protects CRYAB chaperone activity.•Pseudo-phosphorylation decreases CRYAB oligomerization.
The success of Hematopoietic Stem and Progenitor Cell (HSPC) gene therapies critically depends on the capacity to genetically engineer HSPCs without compromising their functional properties. Emerging ...evidence, including our own, indicates that HSPC exposure to currently available gene transfer and gene editing technologies –which require prolonged ex-vivo culture, high viral vector doses and nuclease-induced DNA double strand breaks¬– unexpectedly converge on the DNA damage response (DDR), a signaling cascade leading to cell cycle arrest. Protracted DDR impairs the hematopoietic reconstitution of gene-modified cells upon transplantation; instead, its transient inhibition significantly improves their functionality. This experimental evidence uncovers a previously unappreciated interplay between viral vector sensing and the host cell DDR machinery in human HSPCs. Yet, we have just scratched the surface of a plethora of still unexplored cellular programs potentially hampering the clonal composition and the dynamics of reconstitution upon transplantation of this primitive cell compartment. We build on the innovative concept that current gene engineering protocols may inadvertently trigger the activation of a cellular senescence program in HSPCs with both cell-autonomous and paracrine short- and long-term consequences on engineered human hematopoiesis. By employing quantitative imaging and cutting-edge genomic technologies and taking advantage of uniquely available gene therapy platforms and primary patient samples, we aim to identify the molecular determinants that promote senescence in HSPCs and design innovative hypothesis-driven strategies to mitigate senescence barriers for more effective, safer and clinically broader gene therapy applications. Our findings will unveil a new set of mechanisms controlling the biology of gene-engineered HSPCs and open novel scientific horizons for the development of innovative gene and cell therapies.
Globoid cell leukodystrophy (GLD) is a rare neurodegenerative lysosomal storage disease caused by an inherited deficiency of β-galactocerebrosidase (GALC). GLD pathogenesis and therapeutic correction ...have been poorly studied in patient neural cells. Here, we investigated the impact of GALC deficiency and lentiviral vector-mediated GALC rescue/overexpression in induced pluripotent stem cell (iPSC)-derived neural progenitors and neuronal/glial progeny obtained from two GLD patients. GLD neural progeny displayed progressive psychosine storage, oligodendroglial and neuronal defects, unbalanced lipid composition, and early activation of cellular senescence, depending on the disease-causing mutation. The partial rescue of the neural differentiation program upon GALC reconstitution and psychosine clearance suggests multiple mechanisms contributing to neural pathology in GLD. Also, the pathological phenotype associated to supraphysiological GALC levels highlights the need of regulated GALC expression for proper human neural commitment/differentiation. These data have important implications for establishing safe therapeutic strategies to enhance disease correction of GLD.
•GLD hiPSC-derived neural progenitors show defective neuronal/glial differentiation•GLD neural progeny displays psychosine storage and modest lysosomal impairment•Lipidome unbalance and cellular senescence contribute to the GLD phenotype•Restoring GALC activity partially rescues the GLD phenotypic defects
In this article, Mangiameli et al. study the impact of GALC deficiency and lentiviral vector-mediated GALC rescue/overexpression in GLD hiPSC-derived neural progenitors and their neuronal/glial progeny. The study uncovers unforeseen mutation- and cell type-specific early pathogenic events (i.e. lipid unbalance and activation of a senescence program) that may contribute to GLD neuropathology along with psychosine storage, with important therapeutic implications.
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