Biology subjects

Pozzi, S.

Publications and source records attributed to Pozzi, S..

7 recordsLinked to original sources

bioRxiv2026

NF-κB transcriptionally enhances p53 accumulation dynamics hampering DNA repair

Cells integrate multiple, often concurrent signals through intertwined genetic circuits whose dynamics shape transcriptional programs and cell fate decisions. Among these, the tumor suppressor p53 and the inflammatory transcription factor NF-{kappa}B are central regulators of stress responses in normal and cancer cells, yet their dynamic crosstalk under co-activation remains poorly characterized. Here, we combine genetic approaches, live cell imaging, transcriptomic analysis and mathematical modeling to dissect their dynamic interplay. We find that co-activation of NF-{kappa}B by the inflammatory cytokines TNF- and IL-1{beta} significantly enhance p53 nuclear accumulation upon genotoxic stress or Nutlin3a, and this effect is absent in NF-{kappa}B-deficient cells. Mechanistically, we show that cytokines induce an NF-{kappa}B-mediated increase of TP53 transcription, and mathematical modeling indicates that it is sufficient to account for the observed increased p53 accumulation. Functionally, NF-{kappa}B co-activation rewires p53-dependent transcriptional programs and impairs p53-mediated DNA repair following genotoxic stress, due to a shift of p53 dynamics from oscillatory to more sustained accumulation; p53 oscillatory dynamics and DNA repair remain largely unaltered in absence of NF-{kappa}B. Our results uncover an amplification of p53 response in presence of inflammatory cues that is transcriptionally mediated by NF-{kappa}B and that results, counterintuitively, in functional antagonism. SIGNIFICANCE STATEMENTp53 dynamics have been shown to correlate with the cellular responses of cancer cells to genotoxic insults such as those delivered by chemo- and radiotherapies. However, these dynamics have been mostly studied in settings that do not account for the pro-inflammatory cues that cancer cells might receive from the microenvironment. By addressing this gap, our study uncovers a previously unappreciated mechanism by which inflammatory signals induce an increased p53 accumulation, leading to reduced DNA repair capacity. Our results provide mechanistic understanding on the origin of p53-NF-{kappa}B antagonism and show how dynamically interconnected signalling pathways can produce counterintuitive functional outcomes. Translationally, the contribution of inflammation to the sensitivity of normal and cancer cells to DNA damage might be exploited in the management of chemo- and radiotherapies.

systems biology↗

bioRxiv2025

Astrocytic activation of EMMPRIN contributes to their pathological phenotype in ALS.

Amyotrophic Lateral Sclerosis (ALS) is a fatal disease characterised by the degeneration of upper and lower motoneurons. Onset and progression of the disease are determined by both cell-autonomous neuronal dysfunctions and non-cell-autonomous factors, mainly due to activation of glial cells such as astrocytes and microglia. The Extracellular Matrix Metalloproteinases INducer (EMMPRIN), a glycoprotein expressed by various cell types including neurons, is the major activator of matrix metalloproteinases (MMPs) synthesis and release. EMMPRIN activation can be induced by peptidyl-prolyl isomerase A (PPIA), a chaperone protein with cis/trans isomerase activity, that exhibits cytokine- and chemokine-like behaviour. Previous studies showed that PPIA is highly released in the cerebrospinal fluid (CSF) of ALS patients and animal models where, by activating EMMPRIN on motoneurons, induces neuronal death. Here, we show that EMMPRIN is expressed also by astrocytes, suggesting this cell type as sensitive as motoneurons to PPIA-mediated EMMPRIN activation. We observed that that PPIA-mediated EMMPRIN activation prompt astrocytes toward a pro-inflammatory profile. Interestingly, we found that this pathogenic profile can be reverted by an anti-EMMPRIN antibody. Finally, we provide evidence that the activation of EMMPRIN is relevant for mutant SOD1 and TDP-43 conditions. In conclusion, we demonstrate that EMMPRIN activation in ALS occurs also in astrocytes where it exacerbates their pathological phenotype possibly contributing to the progression of the disease. Furthermore, we suggest the potential use of an anti-EMMPRIN antibody to reduce astrocytic activation during the disease.

neuroscience↗

bioRxiv2023

Inactivation of p53 drives breast cancer brain metastasis by altering fatty acid metabolism

Brain metastasis (BM) is a dire prognosis across cancer types. It is largely unknown why some tumors metastasize to the brain whereas others do not. We analyzed genomic and transcriptional data from clinical samples of breast cancer BM (BCBM) and found that nearly all of them carried p53-inactivating genetic alterations through mutations, copy-number loss, or both. Importantly, p53 pathway activity was already perturbed in primary tumors giving rise to BCBM, often by loss of the entire 17p chromosome-arm. This association was recapitulated across other carcinomas. Experimentally, p53 knockout was sufficient to drastically increase BCBM formation and growth in vivo, providing a causal link between p53 inactivation and brain tropism. Mechanistically, p53-deficient BC cells exhibited altered lipid metabolism, particularly increased fatty acid (FA) synthesis and uptake, which are characteristic of brain-metastasizing cancer cells. FA metabolism was further enhanced by astrocytes in a p53-dependent manner, as astrocyte-conditioned medium increased FASN, SCD1, and CD36 expression and activity, and enhanced the survival, proliferation and migration of p53-deficient cancer cells. Consequently, these cells were more sensitive than p53-competent cells to FA synthesis inhibitors, in isogenic cell cultures, in BCBM-derived spheroids, and across dozens of BC cell lines. Lastly, a significant association was observed between p53 inactivation, astrocyte infiltration, and SCD1 expression in clinical human BCBM samples. In summary, our study identifies p53 inactivation as a driver of BCBM and potentially of BM in general; suggests a p53-dependent effect of astrocytes on BC cell behavior; and reveals FA metabolism as an underlying, therapeutically-targetable molecular mechanism.

cancer biology↗

bioRxiv2022

Expansion of Ventral Foregut Primes the Enhancer Landscape for Organ Specific Differentiation

Cell proliferation is fundamental for almost all stages of development and differentiation that require an increase cell number. Although cell cycle phase has been associated with differentiation, the actual process of proliferation is not seen as having a specific role. Here we exploit human embryonic stem cell derived endodermal progenitors that we find are an in vitro model for the ventral foregut. These cells exhibit expansion dependent increases in differentiation efficiency to pancreatic progenitors that are linked to organ-specific enhancer priming at the level of chromatin accessibility and the decommissioning of lineage inappropriate enhancers. Our findings suggest that cell proliferation in embryonic development is about more than tissue expansion, it is required to ensure equilibration of gene regulatory networks allowing cells to become primed for future differentiation. The use of expansion of lineage specific intermediates may therefore be an important step in high fidelity in vitro differentiation.

developmental biology↗

bioRxiv2022

Transcriptional Heterogeneity and Cell Cycle Regulation as Central Determinants of Primitive Endoderm Priming.

During embryonic development cells acquire identity at the same time as they are proliferating, implying that an intrinsic facet of cell fate choice requires coupling lineage decisions to rates of cell division. How is the cell cycle regulated to promote or suppress heterogeneity and differentiation? We explore this question combining time lapse imaging with single cell RNA-seq in the contexts of self-renewal, priming and differentiation of embryonic stem cells (ESCs) towards the Primitive Endoderm lineage (PrE). Since ESCs are derived from the Inner Cell Mass of the mammalian blastocyst, ESCs in standard culture conditions are transcriptionally heterogeneous containing subfractions that are primed for either of the two ICM lineages, Epiblast and PrE. These subfractions represent dynamic states that can readily interconvert in culture, and the PrE subfraction is functionally primed for endoderm differentiation. Here we find that differential regulation of cell cycle can tip the balance between these primed populations, such that naive ESC culture conditions promote Epiblast-like expansion and PrE differentiation stimulates the selective proliferation of PrE-primed cells. In endoderm differentiation, we find that this change is accompanied by a counter-intuitive increase in G1 length that also appears replicated in vivo. While FGF/ERK signalling is a known key regulator of ESCs and PrE differentiation, we find it is not just responsible for ESCs heterogeneity, but also cell cycle synchronisation, required for the inheritance of similar cell cycles between sisters and cousins. Taken together, our results point to a tight relationship between transcriptional heterogeneity and cell cycle regulation in the context of lineage priming, with primed cell populations providing a pool of flexible cell types that can be expanded in a lineage-specific fashion while allowing plasticity during early determination.

developmental biology↗

bioRxiv2020

Tryptophan residues in TDP-43 and SOD1 mediate the cross-seeding and toxicity of SOD1

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease of motor neurons. Neuronal superoxide dismutase-1 (SOD1) inclusion bodies are characteristic of familial ALS with SOD1 mutations, while a hallmark of sporadic ALS is inclusions containing aggregated wild-type TAR DNA-binding protein 43 (TDP-43). Co-expression of mutant or wild-type TDP-43 with SOD1 leads to misfolding of endogenous SOD1 and aggregation of SOD1 reporter protein G85R-GFP in HEK293FT cells, and promotes synergistic axonopathy in zebrafish. This pathological interaction is dependent upon natively solvent-exposed tryptophans in SOD1 (tryptophan-32) and TDP-43 RRM1 (tryptophan-172), in concert with natively sequestered TDP-43 N-terminal domain tryptophan-68. TDP-43 RRM1 intrabodies reduce wild-type SOD1 misfolding in HEK293FT cells, via blocking tryptophan-172. Tryptophan-68 becomes antibody-accessible in aggregated TDP-43 in sporadic ALS motor neurons and cell culture. 5-fluorouridine inhibits TDP-43-induced G85R-GFP SOD1 aggregation in HEK293FT cells, and ameliorates axonopathy in zebrafish, via its interaction with SOD1 tryptophan-32. Collectively, our results establish a novel and potentially druggable tryptophan-mediated mechanism whereby two principal ALS disease effector proteins might directly interact in disease.

cell biology↗

bioRxiv2020

Cyclophilin A knock-out mice develop a pure frontotemporal dementia phenotype with marked TDP-43 pathology

Aggregation and cytoplasmic mislocalization of TDP-43 are pathological hallmarks of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) spectrum. However, the molecular mechanism by which TDP-43 aggregates form and cause neurodegeneration remains poorly understood. Cyclophilin A, also known as peptidyl-prolyl cis-trans isomerase A (PPIA), is a foldase and molecular chaperone. We previously found that PPIA interacts with TDP-43 and governs some of its functions, and its deficiency accelerates disease in a mouse model of ALS. Here we characterized PPIA knock-out mice throughout their lifespan and found that they develop a neurodegenerative disease with key behavioural features of FTD, marked TDP-43 pathology and late-onset motor dysfunction. In the mouse brain, deficient PPIA induces aggregation of the GTP-binding nuclear protein Ran, a PPIA substrate required for TDP-43 nucleocytoplasmic trafficking. Moreover, in absence of PPIA, TDP-43 autoregulation is perturbed and TDP-43 and proteins involved in synaptic function are downregulated, leading to impairment of synaptic plasticity. Finally, we found that PPIA was downregulated in several ALS and ALS-FTD patients and identified a PPIA loss-of-function mutation in a sporadic ALS patient. The mutant PPIA has low stability, altered structure and impaired interaction with TDP-43. These findings strongly implicate that defective PPIA function causes TDP-43 mislocalization and dysfunction and should be considered in future therapeutic approaches.

neuroscience↗