Biology subjects

Lennon-Dumenil, A.-M.

Publications and source records attributed to Lennon-Dumenil, A.-M..

11 recordsLinked to original sources

bioRxiv2025

Macrophages restrict tumor permissiveness to immune infiltration by controlling local collagen topography through a Tcf4-Collagen3 fibrotic axis

During tumorigenesis, the extracellular matrix (ECM), which constitutes the structural scaffold of tissues, is profoundly remodeled. While the impact of such remodeling on tumor growth and invasion has been extensively investigated, much less is known on the consequences of ECM remodeling on tumor infiltration by immune cells. By combining tissue imaging and machine-learning, we here show that the localization of T lymphocytes and neutrophils, which orchestrate antitumor immune responses, can be predicted by defined topographical features of fibrillar collagen networks. We further show that these collagen topographies result from the activation of a fibrotic pathway controlled by the transcription factor Tcf4 upon depletion of tumor-associated macrophages at late tumor stages. This pathway promotes the deposition of collagen 3 by both tumor and stromal cells, resulting in intermingled collagen networks that favor intra-tumoral T cell and neutrophil localization. Importantly, analysis of human colorectal cancer public bulk RNAseq databases showed a strong correlation between Tcf4 and collagen 3, as well as between the expression of these genes and tumor infiltration by T lymphocytes and neutrophils, attesting the clinical relevance of our findings. This study highlights the key structural role of macrophages on the tumor extracellular matrix and identifies collagen network topographies as a major regulator of tumor infiltration by immune cells.

immunology↗

bioRxiv2024

The Arp2/3 complex maintains genome integrity and survival of epidermal Langerhans cells

Myeloid cells use intracellular actin networks for key cellular processes, including cell migration and chemotaxis, phagocytosis or macropinocytosis, as well as immune synapse formation. However, whether actin networks play any role in the development and/or survival of myeloid cells in tissues remains open. Here, we found that the Arp2/3 complex, which is responsible for the nucleation of branched actin networks, is needed for in vivo maintenance of epidermal Langerhans cells (LCs) throughout life. Mice harboring a genetic deletion of the Arpc4 subunit of the complex in myeloid cells form LC networks at birth, but these cells decline in numbers following a process reminiscent of premature cellular aging. By combining in vivo analyses of LCs with in vitro experiments on bone-marrow-derived dendritic cells, we found that Arpc4-deficient cells manage to progress through the cell cycle but accumulate DNA damage associated with aberrant nuclear shapes, lamina reduction and events of nuclear envelope rupture. These results provide the first evidence for a physiological role of Arp2/3 in maintenance of genome integrity and survival of immune cells in tissues.

cell biology↗

bioRxiv2024

Actin polymerization by WASp limits nuclear envelope rupture and inflammation in macrophages

Mutations in the immune-specific actin regulator WASp induce a proinflammatory state in myeloid cells, whose underlying causes remain poorly defined. Here, we applied microfabricated tools that mimic tissue mechanical forces to explore the role of WASp in connecting mechano-sensing to the activation of inflammatory responses in macrophages. We show that WASp-deficient macrophages carry alterations in nuclear structure and undergo increased blebbing and nuclear rupture when exposed to mechanical confinement. High-resolution imaging indicates that WASp drives the formation of protective perinuclear actin structures in response to confinement. Functionally, a proinflammatory gene signature linked to nuclear envelope rupture is preferentially active in confined WASp null macrophages, which partially depends on the cGAS-STING pathway of cytosolic DNA sensing. Analysis of transcriptional datasets of human and mouse tissue macrophages confirmed elevated inflammatory activation in WASp null cells. Together, these data uncover that WASp restricts pro-inflammatory activation of macrophages by preserving nuclear integrity in confined environments, providing novel clues to understand inflammatory activation in Wiskott-Aldrich Syndrome.

immunology↗

bioRxiv2023

Actin-based deformations of the nucleus control multiciliated ependymal cell differentiation.

Ependymal cells (ECs) are multi-ciliated cells in the brain that contribute to cerebrospinal fluid flow. ECs are specified at embryonic stages but differentiate later in development. Differentiation depends on genes such as GEMC1 and MCIDAS with E2F4/5, but also on cell cycle related factors. In the mouse brain, we observe that nuclear deformation accompanies EC differentiation. Tampering with these deformations either by decreasing F-actin levels or by severing the link between the nucleus and the actin cytoskeleton blocks differentiation. Conversely, increasing F-actin by knocking out the Arp2/3 complex inhibitor Arpin or artificially deforming the nucleus activates differentiation. These data are consistent with actin polymerization triggering nuclear deformation and jump-starting the signaling that produces ECs. A player in this process is the retinoblastoma1 (RB1) protein whose phosphorylation prompts MCIDAS activation. Overall, this study reveals an important role for actin-based mechanical inputs to the nucleus as controlling factors in cell differentiation.

developmental biology↗

bioRxiv2022

Mechanical Stimulation Shapes the Immunoregulatory Properties of Dendritic Cells

Motile cells such as immune and cancer cells experience large deformation events that result from the physical constraints they encounter while migrating within tissues or circulating between organs. It has become increasingly clear that these cells can survive and adapt to these changes in cell shape using dedicated shape sensing pathways. However, how shape sensing impacts their function and fate remains largely unknown. Here we identify a shape sensing mechanism that couples cell motility to expression of CCR7, the chemokine receptor that guides immune cells to lymph nodes. We found that this mechanism is controlled by the lipid metabolism enzyme cPLA2, requires an intact nuclear envelop and exhibits an exquisitely sensitive activation threshold tuned by ARP2/3 and its inhibitor Arpin. We further show that shape sensing through the ARP2/3-cPLA2 axis controls Ikk{beta}-NF{kappa}B-dependent transcriptional reprogramming of dendritic cells, which instructs them to migrate to lymph nodes in an immunoregulatory state compatible with their homeostatic tolerogenic function. These results highlight that the cell shape changes experienced by motile cells evolving within the complex environment of tissues can dictate their behavior and fate.

cell biology↗

bioRxiv2020

Pinching the cortex of live cells reveals thickness instabilities caused by Myosin II motors

The cell cortex is a contractile actin meshwork, which determines cell shape and is essential for cell mechanics, migration and division. Because the cortical thickness is below optical resolution, it has been generally considered as a thin uniform two-dimensional layer. Using two mutually attracted magnetic beads, one inside the cell and the other in the extracellular medium, we pinch the cortex of dendritic cells and provide an accurate and time resolved measure of its thickness. Our observations draw a new picture of the cell cortex as a highly dynamic layer, harboring large fluctuations in its third dimension due to actomyosin contractility. We propose that the cortex dynamics might be responsible for the fast shape changing capacity of highly contractile cells that use amoeboid-like migration.

biophysics↗

bioRxiv2020

Endothelial cell invasiveness is controlled by myosin IIA-dependent inhibition of Arp2/3 activity

Sprouting angiogenesis is fundamental for development and contributes to multiple diseases, including cancer, diabetic retinopathy and cardiovascular diseases. Sprouting angiogenesis depends on the invasive properties of endothelial tip cells. However, there is very limited knowledge on the mechanisms that endothelial tip cells use to invade into tissues. Here, we prove that endothelial tip cells use long lamellipodia projections (LLPs) as the main cellular protrusion for invasion into non-vascular extracellular matrix. We show that LLPs and filopodia protrusions are balanced by myosin-IIA (MIIA) and actin-related protein 2/3 (Arp2/3) activity. Endothelial cell-autonomous ablation of MIIA promotes excessive LLPs formation in detriment of filopodia. Conversely, endothelial cell-autonomous ablation of Arp2/3 prevents LLPs development and leads to excessive filopodia formation. We further show that MIIA inhibits Rac1-dependent activation of Arp2/3, by regulating the maturation state of focal adhesions. Our discoveries establish the first comprehensive model of how endothelial tip cells regulate its protrusive activity and will pave the way towards new strategies to block invasive tip cells during sprouting angiogenesis.

cell biology↗

bioRxiv2020

Developmentally regulated PERK activity renders dendritic cells insensitive to subtilase cytotoxin-induced integrated stress response

In stressed cells, phosphorylation of eukaryotic initiation factor 2 (eIF2) controls transcriptome-wide changes in mRNA translation and gene expression known as the integrated stress response (ISR). We show here that dendritic cells (DCs) display unusually high eIF2 phosphorylation, which is mostly caused by a developmentally regulated activation of the ER kinase PERK (EIF2AK3). Despite high p-eIF2 levels, differentiated DCs display active protein synthesis and no signs of a chronic ISR. eIF2 phosphorylation does not majorly impact DC differentiation nor cytokines production. It is however important to adapt protein homeostasis to the variations imposed on DCs by the immune or physiological contexts. This biochemical specificity prevents translation arrest and expression of the transcription factor ATF4 during ER-stress induction by subtilase cytotoxin or upon DC stimulation with bacterial lipopolysaccharides. This is also exemplified by the influence of the actin cytoskeleton dynamics on eIF2 phosphorylation and the migratory deficit observed in PERK-deficient DCs.

immunology↗

bioRxiv2018

Actomyosin-driven force patterning controls endocytosis at the immune synapse

An important channel of cell-to-cell communication is direct contact. The immune synapse is a paradigmatic example of such type of interaction: it forms upon engagement of antigen receptors in lymphocytes by antigen-presenting cells and allows the local exchange of molecules [1]. Although [2], how forces organize and mechanics has been shown to play an important role in this process impact on synapse function is unknown. We found that mechanical forces are spatio-temporally patterned at the immune synapse: global contractile forces are observed at the synapse periphery and local point-like forces are detected at its centre. The global contractile forces result from a pulsatile centripetal actomyosin flow that leads to formation of F-actin protrusions from which the central point like forces emerge. Noticeably, these force-producing actin protrusions constitute the main site of antigen extraction and endocytosis. Accordingly, deletion of the myosin IIA gene leads to impaired B cell responses. The interplay between global and local forces governed by the actomyosin cytoskeleton therefore controls the endocytic function of the immune synapse and might constitute a more general mechanism in the physical regulation of cell-cell interactions.

cell biology↗

bioRxiv2018

Actin filaments regulate microtubule growth at the centrosome.

The centrosome is the main microtubule-organizing centre. It also organizes a local network of actin filaments. However, the precise function of the actin network at the centrosome is not well understood. Here we show that increasing densities of actin filaments at the centrosome of lymphocytes were correlated with reduced amounts of microtubules. Furthermore, lymphocyte activation resulted in centrosomal-actin disassembly and an increase in microtubule number. To further investigate the direct crosstalk between actin and microtubules at the centrosome, we performed in vitro reconstitution assays based on (i) purified centrosomes and (ii) on the co-micropatterning of microtubule seeds and actin filaments. The two assays demonstrated that actin filaments perturb microtubule growth by steric hindrance. Finally, we showed that cell adhesion and spreading leads to lower densities of centrosomal actin thus resulting in higher microtubule growth. Hence we propose a novel mechanism by which the number of centrosomal microtubules is regulated by cell adhesion and actin-network architecture.

cell biology↗

bioRxiv2018

Macropinocytosis overcomes directional bias due to hydraulic resistance to enhance space exploration by dendritic cells

The migration of immune cells is guided by specific chemical signals, such as chemokine gradients. Their trajectories can also be diverted by physical cues and obstacles imposed by the cellular environment, such as topography, rigidity, adhesion, or hydraulic resistance. On the example of hydraulic resistance, it was shown that neutrophil preferentially follow paths of least resistance, a phenomenon referred to as barotaxis. We here combined quantitative imaging and physical modeling to show that barotaxis results from a force imbalance at the scale of the cell, which is amplified by the acto-myosin intrinsic polarization capacity. Strikingly, we found that macropinocytosis specifically confers to immature dendritic cells a unique capacity to overcome this physical bias by facilitating external fluid transport across the cell, thereby enhancing their space exploration capacity in vivo and promoting their tissue-patrolling function. Conversely, mature dendritic cells, which down-regulate macropinocytosis, were found to be sensitive to hydraulic resistance. Theoretical modeling suggested that barotaxis, which helps them avoid dead-ends, may accelerate their migration to lymph nodes, where they initiate adaptive immune responses. We conclude that the physical properties of the microenvironment of moving cells can introduce biases in their migratory behaviors but that specific active mechanisms such as macropinocytosis have emerged to diminish the influence of these biases, allowing motile cells to reach their final destination and efficiently fulfill their functions.

cell biology↗