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Lammerding, J.

Publications and source records attributed to Lammerding, J..

At least 19 recordsLinked to original sources

Deep Invaginations of Nuclear Envelope Coordinate Spatial Organization of Chromatin in Epithelium

Cell nuclei are often used to assess cell health, but how their shapes vary in normal tissues and how they respond to mechanical forces is not well understood. Here, we describe deep invaginations of the nuclear envelope (DINEs) as common features of epithelial cell nuclei. After their formation, DINEs exist independently of the cytoskeleton, depend on A-type lamins, and emerge in response to cell crowding, contact inhibition, and tissue maturation. High-resolution imaging shows that, in contrast to the peripheral nuclear lamina, DINEs contain densely packed chromatin with regions of active gene transcription. They also remodel dynamically during confined migration, allowing nuclei to adapt to physical constraints. Mechanistically, DINE formation is linked to suppression of MAPK signaling, while activation of growth-promoting pathways reduces their occurrence. These findings reveal DINEs as intrinsic, mechanosensitive structures that coordinate nuclear shape, chromatin organization, and gene activity, providing new insight into how epithelial cells integrate mechanical and biochemical cues to maintain tissue homeostasis. TeaserDeep nuclear envelope invaginations organize chromatin and gene activity in response to epithelial crowding.

cell biology↗

Antagonistic contributions of A-type and B-type lamins to LBR localization and dynamics

Lamin B receptor (LBR) is an inner nuclear membrane (INM) protein that plays crucial roles in maintaining nuclear architecture and organization of peripheral heterochromatin. Lamins and LBR both contribute to chromatin tethering at the nuclear periphery, and the expression of LBR and A-type lamins is tightly regulated during development to ensure a faithful transition between different chromatin tethering modalities. Despite its well-established association with B-type lamins, the contributions of individual lamin isoforms to LBR localization and anchorage have not been systematically examined. Here, we used mouse embryonic fibroblasts (MEFs) lacking all endogenous lamins (triple lamin knockout: TKO) to assess how specific lamin isoforms and domains regulate LBR subcellular localization and mobility. Whereas ectopic expression of either lamin B1 or lamin B2 was sufficient to tether LBR to the nuclear envelope in TKO cells, expression of lamin A increased the lateral mobility of LBR at the nuclear membrane, resulting in its displacement from the nuclear envelope to the ER. The lamin A-induced displacement of LBR was mediated by phosphorylation of LBR. Overexpression of lamin A in wild-type MEFs similarly increased LBR phosphorylation and promoted its displacement from the nuclear envelope. Collectively, these findings define isoform-specific and antagonistic roles for A-type and B-type lamins in regulating LBR anchorage at the nuclear envelope. In addition, they indicate a lamin A-dependent mechanism that may reflect a broader developmental process, since LBR and lamin A sequentially tether peripheral heterochromatin during development.

cell biology↗

Polarization Increases Nuclear Stiffness in Macrophages Despite Reduction in Lamin A/C Levels

Macrophages are innate immune cells contributing to tissue homeostasis and various pathologies. Signals from their environment can lead macrophages to adapt distinct functional phenotypes, a process called polarization. Because macrophages have been previously shown to degrade the nuclear envelope proteins lamin A/C upon pro-inflammatory polarization, and lamins are considered key determinants of nuclear deformability, we aimed to address the effect of pro-inflammatory stimulation on nuclear mechanics. We present the surprising finding that polarized bone marrow-derived macrophages have less deformable nuclei than unpolarized macrophages, despite their reduced lamin A/C levels. Furthermore, pro-inflammatory macrophages exhibited altered chromatin dynamics relative to unpolarized macrophages, including redistribution of trimethylated histone H3K9 (H3K9me3) from the nuclear periphery to the interior and increased chromatin compaction. Our findings suggest a model in which pro-inflammatory stimulation of macrophages induces chromatin changes that drive nuclear stiffening, and that in these cells, chromatin, rather than the nuclear lamina, is the major driver for resisting nuclear deformation. These findings may have functional relevance for the physiological function of polarized macrophages, as the mechanical properties of the nucleus can influence how these cells adapt and respond to their environments in the context of cell migration or inflammatory disease pathologies.

cell biology↗

A-type lamins anchor emerin at the inner nuclear membrane via two independent binding sites

Lamins form a dense meshwork at the inner surface of the inner nuclear membrane (INM), where they interact with other nuclear envelope proteins such as emerin. Emerin is an integral membrane protein that is part of the LEM (LAP2/emerin/MAN1) domain family, and mutations in either emerin or lamin A/C can result in Emery-Dreifuss muscular dystrophy (EDMD) and other striated muscle diseases. Emerin is retained at the INM through direct interaction with lamin A/C, and emerins proper subcellular localization is critical for its ability to influence the mechanical properties of the nucleus and participate in various signaling processes. Nonetheless, the requirements for interaction between emerin and lamin A/C at the INM remain incompletely understood. Here, we report that two distinct regions of lamin A/C are each sufficient to properly localize emerin to the INM and prevent emerins lateral diffusion within the INM. In addition to a previously described region of the lamin A/C tail domain able to bind emerin, we identify a novel emerin-interacting domain comprising the linker between the rod and Ig-like fold domains of lamin A/C. We further demonstrate that stably anchoring emerin to the INM requires assembly of A-type lamins into a filamentous network. Collectively, our findings suggest a revised model for emerin retention at the INM, which predicts that two independent lamin A/C domains are required to retain emerin at the nuclear envelope.

cell biology↗

The Deformability of the Mammalian Cell Nucleus is Determined by the Identity of the Lamin Rod Domain

Lamins are nuclear intermediate filament proteins with diverse functions, ranging from organizing chromatin and regulating gene expression to providing structural support to the nucleus. Mammalian cells express two types of lamins, A-type and B-type, which, despite their similar structure and biochemical properties, exhibit distinct differences in expression, interaction partners, and function. One major difference is that A-type lamins have a significantly larger effect on the mechanical properties of the nucleus, which are crucial for protecting the nucleus from cytoskeletal forces, enabling cell migration through confined spaces, and contributing to cellular mechanotransduction. The molecular mechanism underlying this difference has remained unresolved. Here, we applied custom-developed biophysical and proteomic assays to lamin-deficient cell lines engineered to express specific full-length lamin proteins, lamin truncations, or chimeras combining domains from A- and B-type lamins, to systematically determine their contributions to nuclear mechanics. We found that although all expressed lamins contribute to the biophysical properties of the nuclear interior and confer some mechanical stability to the nuclear envelope, which is sufficient to protect the nuclear envelope from small cell-intrinsic forces and ensure proper positioning of nuclear pores, A-type lamins endow cells with a unique ability to resist large forces on the nucleus. Surprisingly, this effect was conferred through the A-type lamin rod domain, rather than the head or tail domains, which diverge more substantially between A- and B-type lamins and play important roles in lamin network formation. Collectively, our work provides an improved understanding of the distinct functions of different lamins in mammalian cells and may also explain why mutations in the A-type lamin rod domain cause more severe muscle defects in mouse models than other mutations.

cell biology↗

Metastatic organotropism in small cell lung cancer

Metastasis is the leading cause of cancer-related deaths, yet its regulatory mechanisms are not fully understood. Small-cell lung cancer (SCLC) is the most metastatic form of lung cancer, with most patients presenting with widespread disease, making it an ideal model for studying metastasis. However, the lack of suitable preclinical models has limited such studies. We utilized rapid autopsy-derived tumors to develop xenograft models that mimic key features of SCLC, including histopathology, rapid and widespread development of metastasis to the liver, brain, adrenal, bone marrow, and kidneys within weeks, and response to chemotherapy. By integrating in vivo lineage selection with comprehensive bulk and single cell multiomic profiling of transcriptomes and chromatin accessibility, we identified critical cellular programs driving metastatic organotropism to the liver and brain, the most common sites of SCLC metastasis. Our findings reveal the key role of nuclear-cytoskeletal interactions in SCLC liver metastasis. Specifically, the loss of the nuclear envelope protein lamin A/C, encoded by the LMNA gene, increased nuclear deformability and significantly increased the incidence of liver metastasis. Human liver metastases exhibited reduced LMNA expression compared to other metastatic sites, correlating with poorer patient outcomes and increased mortality. This study introduces novel preclinical models for SCLC metastasis and highlights pathways critical for organ-specific metastasis, offering new avenues for the development of targeted therapies to prevent or treat metastatic disease.

cancer biology↗

Ultrack: pushing the limits of cell tracking across biological scales

Tracking live cells across 2D, 3D, and multi-channel time-lapse recordings is crucial for understanding tissue-scale biological processes. Despite advancements in imaging technology, achieving accurate cell tracking remains challenging, particularly in complex and crowded tissues where cell segmentation is often ambiguous. We present Ultrack, a versatile and scalable cell-tracking method that tackles this challenge by considering candidate segmentations derived from multiple algorithms and parameter sets. Ultrack employs temporal consistency to select optimal segments, ensuring robust performance even under segmentation uncertainty. We validate our method on diverse datasets, including terabyte-scale developmental time-lapses of zebrafish, fruit fly, and nematode embryos, as well as multi-color and label-free cellular imaging. We show that Ultrack achieves state-of-the-art performance on the Cell Tracking Challenge and demonstrates superior accuracy in tracking densely packed embryonic cells over extended periods. Moreover, we propose an approach to tracking validation via dual-channel sparse labeling that enables high-fidelity ground truth generation, pushing the boundaries of long-term cell tracking assessment. Our method is freely available as a Python package with Fiji and napari plugins and can be deployed in a high-performance computing environment, facilitating widespread adoption by the research community.

developmental biology↗

Multi-level transcriptomic analysis of LMNA-related dilated cardiomyopathy identifies disease-driving processes

Mutations in the LMNA gene, which encodes the nuclear envelope (NE) proteins lamins A and C, cause dilated cardiomyopathy (LMNA-DCM) and other diseases. The pathogenic mechanisms for LMNA-DCM remain poorly understood, limiting current treatment options and leading to high mortality amongst patients. We developed a mouse model with inducible, cardiomyocyte-specific Lmna deletion (cKO) and performed comprehensive bulk, single-nucleus, and spatial transcriptomic analyses across disease progression. Our analysis identified key disease-driving genes involved in cellular responses to DNA damage, cytosolic pattern recognition receptor signaling, and innate immunity that originated from two disease-specific cardiomyocyte subpopulations. Spatial mapping revealed aberrant interactions between these cardiomyocytes, fibroblasts, and immune cells, contributing to tissue-wide transcriptional changes in cKO hearts. Concurrent cardiomyocyte-specific disruption of the LINC complex, which transmits cytoskeletal forces to the nucleus, substantially reduced NE rupture in cKO cardiomyocytes, normalized expression of more than half of the dysregulated genes, and dramatically improved cardiac function and survival in cKO mice. These findings suggest that NE rupture in cKO cardiomyocytes triggers cytosolic DNA sensing pathways and maladaptive cell-cell communication with fibroblasts and immune cells, leading to fibrosis and inflammation driving LMNA-DCM pathogenesis.

cell biology↗

N-terminal tags impair the ability of Lamin A to provide structural support to the nucleus

Lamins are intermediate filament proteins that contribute to numerous cellular functions, including nuclear morphology and mechanical stability. The N-terminal head domain of lamin is critical for higher order filament assembly and function, yet the effects of commonly used N-terminal tags on lamin function remain largely unexplored. Here, we systematically studied the effect of two differently sized tags on Lamin A (LaA) function in a mammalian cell model engineered to allow for precise control of expression of tagged lamin proteins. Untagged, FLAG-tagged, and GFP-tagged LaA completely rescued nuclear shape defects when expressed at similar levels in lamin A/C-deficient (Lmna-/-) MEFs, and all LaA constructs prevented increased nuclear envelope (NE) ruptures in these cells. N-terminal tags, however, altered the nuclear localization of LaA and impaired the ability of LaA to restore nuclear deformability and to recruit Emerin to the nuclear membrane in Lmna-/- MEFs. Our finding that tags impede some LaA functions but not others may explain the partial loss of function phenotypes when tagged lamins are expressed in model organisms and should caution researchers using tagged lamins to study the nucleus.

cell biology↗

Microtubule forces drive nuclear damage in LMNA cardiomyopathy

Nuclear homeostasis requires a balance of forces between the cytoskeleton and nucleus. Mutations in the LMNA gene, which encodes the nuclear envelope proteins lamin A/C, disrupt this balance by weakening the nuclear lamina. This results in nuclear damage in contractile tissues and ultimately muscle disease. Intriguingly, disrupting the LINC complex that connects the cytoskeleton to the nucleus has emerged as a promising strategy to ameliorate LMNA-associated cardiomyopathy. Yet how LINC complex disruption protects the cardiomyocyte nucleus remains unclear. To address this question, we developed an assay to quantify the coupling of cardiomyocyte contraction to nuclear deformation and interrogated its dependence on the nuclear lamina and LINC complex. We found that, surprisingly, the LINC complex was mostly dispensable for transferring contractile strain to the nucleus, and that increased nuclear strain in lamin A/C-deficient cardiomyocytes was not rescued by LINC complex disruption. Instead, LINC complex disruption eliminated the cage of microtubules encircling the nucleus. Disrupting microtubules was sufficient to prevent nuclear damage and rescue cardiac function induced by lamin A/C deficiency. We computationally simulated the stress fields surrounding cardiomyocyte nuclei and show how microtubule forces generate local vulnerabilities that damage lamin A/C-deficient nuclei. Our work pinpoints localized, microtubule-dependent force transmission to the nucleus as a pathological driver and therapeutic target for LMNA- cardiomyopathy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=131 SRC="FIGDIR/small/579774v5_ufig1.gif" ALT="Figure 1"> View larger version (52K): org.highwire.dtl.DTLVardef@1443daeorg.highwire.dtl.DTLVardef@12d7a8borg.highwire.dtl.DTLVardef@c85900org.highwire.dtl.DTLVardef@14b3c89_HPS_FORMAT_FIGEXP M_FIG C_FIG

cell biology↗

Heterologous expression of Dictyostelium discoideum NE81 in mouse embryo fibroblasts reveals conserved mechanoprotective roles of lamins

Lamins are nuclear intermediate filament proteins that are ubiquitously found in metazoan cells, where they contribute to nuclear morphology, stability, and gene expression. Lamin-like sequences have recently been identified in distantly related eukaryotes, but it remains unclear if these proteins share conserved functions with the lamins found in metazoans. Here, we investigate conserved features between metazoan and amoebozoan lamins using a genetic complementation system to express the Dictyostelium discoideum lamin-like protein NE81 in mammalian cells lacking either specific lamins or all endogenous lamins. We report that NE81 localizes to the nucleus in cells lacking Lamin A/C, and that NE81 expression improves nuclear circularity, reduces nuclear deformability, and prevents nuclear envelope rupture in these cells. However, NE81 did not completely rescue loss of Lamin A/C, and was unable to restore normal distribution of metazoan lamin interactors, such as emerin and nuclear pore complexes, which are frequently displaced in Lamin A/C deficient cells. Collectively, our results indicate that the ability of lamins to modulate the morphology and mechanical properties of nuclei may have been a feature present in the common ancestor of Dictyostelium and animals, whereas other, more specialized interactions may have evolved more recently in metazoan lineages.

cell biology↗

The Lamin A/C Ig-fold undergoes cell density-dependent changes that alter epitope accessibility

Lamins A/C are nuclear intermediate filament proteins that are involved in diverse cellular mechanical and biochemical functions. Here, we report that recognition of Lamins A/C by a commonly used antibody (JOL-2) that binds the Lamin A/C Ig-fold and other antibodies targeting similar epitopes is highly dependent on cell density, even though Lamin A/C protein levels do not change with cell density. The density-dependent Lamin A/C labeling was distinct from previously reported differential apico-basal labeling, which was independent of cell density. Comparison of the density-dependent labeling effects of antibodies recognizing different Lamin A/C epitopes suggests that the effect is caused by partial unfolding or masking of the CE and/or EF loops of the Ig-fold in response to cell spreading. Seeding cells on micropatterned surfaces with different areas confirmed that increased cell spreading resulted in reduced Lamin A/C labeling with the JOL-2 antibody. Surprisingly, JOL-2 antibody labeling was insensitive to depolymerization of cytoskeletal filaments or disruption of the Linker of Nucleoskeleton and Cytoskeleton (LINC) complex. Although the density-dependent changes of the Ig-fold did not alter nuclear stiffness or nucleo-cytoskeletal force transmission, they may nonetheless modulate interaction with lamin binding partners and thereby affect cellular functions. Taken together, our results point to a previously unrecognized change in the Lamin A/C Ig-fold that affects recognition by the JOL-2 antibody. These findings are not only important for the interpretation of immunofluorescence data for Lamin A/C, but also raise the intriguing prospect that the conformational changes may play a role in Lamin A/C mediated cellular function.

cell biology↗

Rear cortex contraction aids in nuclear transit during confined migration by increasing pressure in the cell posterior

As cells migrate through biological tissues, they must frequently squeeze through micron-sized constrictions in the form of interstitial pores between extracellular matrix fibers and/or other cells. Although it is now well recognized that such confined migration is limited by the nucleus, which is the largest and stiffest organelle, it remains incompletely understood how cells apply sufficient force to move their nucleus through small constrictions. Here, we report a mechanism by which contraction of the cell rear cortex pushes the nucleus forward to mediate nuclear transit through constrictions. Laser ablation of the rear cortex reveals that pushing forces behind the nucleus are the result of increased intracellular pressure in the rear compartment of the cell. The pushing forces behind the nucleus depend on accumulation of actomyosin in the rear cortex and require Rho-kinase (ROCK) activity. Collectively, our results suggest a mechanism by which cells generate elevated, intracellular pressure in the posterior compartment to facilitate nuclear transit through 3D constrictions. This mechanism may supplement or even substitute for other mechanisms supporting nuclear transit, ensuring robust cell migrations in confined 3D environments.

cell biology↗

Eliminating elevated p53 signaling in Lmna-mutant mice fails to rescue skeletal muscle defects or extend survival

Lamins A and C, encoded by the LMNA gene, are nuclear intermediate filaments that provide structural support to the nucleus and contribute to chromatin organization and transcriptional regulation. LMNA mutations cause muscular dystrophies, dilated cardiomyopathy, and other diseases. The mechanisms by which many LMNA mutations result in muscle-specific diseases have remained elusive, presenting a major hurdle in the development of effective treatments. Previous studies using striated muscle laminopathy mouse models found that cytoskeletal forces acting on mechanically fragile Lmna-mutant nuclei led to transient nuclear envelope rupture, extensive DNA damage, and activation of DNA damage response (DDR) pathways in skeletal muscle cells in vitro and in vivo. Furthermore, hearts of Lmna mutant mice have elevated activation of the tumor suppressor protein p53, a central regulator of DDR signaling. We hypothesized that elevated p53 activation could present a pathogenic mechanism in striated muscle laminopathies, and that eliminating p53 activation could improve muscle function and survival in laminopathy mouse models. Supporting a pathogenic function of p53 activation in muscle, stabilization of p53 was sufficient to reduce contractility and viability in wild-type muscle cells in vitro. Using three laminopathy models, we found that increased p53 activity in Lmna-mutant muscle cells primarily resulted from mechanically induced damage to the myonuclei, and not from altered transcriptional regulation due to loss of lamin A/C expression. However, global deletion of p53 in a severe muscle laminopathy model did not reduce the disease phenotype or increase survival, indicating that additional drivers of disease must contribute to the disease pathogenesis.

cell biology↗

ATM modulates nuclear mechanics by regulating lamin A levels

Ataxia-telangiectasia mutated (ATM) is one of the three main apical kinases at the crux of DNA damage response and repair in mammalian cells. ATM activates a cascade of downstream effector proteins to regulate DNA repair and cell cycle checkpoints in response to DNA double-strand breaks. While ATM is predominantly known for its role in DNA damage response and repair, new roles of ATM have recently begun to emerge, such as in regulating oxidative stress or metabolic pathways. Here, we report the surprising discovery that ATM inhibition and deletion lead to reduced expression of the nuclear envelope protein lamin A. Lamins are nuclear intermediate filaments that modulate nuclear shape, structure, and stiffness. Accordingly, inhibition or deletion of ATM resulted in increased nuclear deformability and enhanced cell migration through confined spaces, which requires substantial nuclear deformation. These findings point to a novel connection between ATM and lamin A and may have broad implications for cells with ATM mutations--as found in patients suffering from Ataxia Telangiectasia and many human cancers--which could lead to enhanced cell migration and increased metastatic potential.

cell biology↗

Blockage of Lamin-A/C loss diminishes the pro-inflammatory macrophage response

Mutations and defects in nuclear lamins can cause major pathologies in affected tissues. Recent studies have also established potential links between lamins, inflammation, and inflammatory diseases but the underlying molecular mechanisms are unknown. We now report that pro-inflammatory activation of macrophages reduces levels of Lamin-A/C to augment pro-inflammatory gene expression and cytokine secretion. We show that activation of bone-marrow derived macrophages (BMDMs) degrades Lamin-A/C, as preceded by its phosphorylation, which is mediated by Caspase-6 and CDK1, respectively. Inhibiting Lamin-A/C phosphorylation and degradation severely inhibits pro-inflammatory gene expression and cytokine secretion. Using LPS-activated Lamin-A/C Knock Out BMDMs, we confirmed that the activation of the IFN-{beta}-STAT pathway is amplified due to Lamin-A/C reduction, which ultimately augments the pro-inflammatory response. As Lamin-A/C is a previously unappreciated regulator of the pro-inflammatory macrophage response, our findings could provide novel opportunities to treat inflammatory diseases. In first proof-of-concept studies we show that macrophage pro-inflammation, as induced by Lipopolysaccharide or pathogenic E. coli, could be reduced by inhibiting Lamin-A/C phosphorylation and degradation. The inhibition of macrophage pro-inflammation could also be achieved by inhibiting members of the Lamin-A/C regulated IFN-{beta}-STAT pathway, i.e., phospho-STAT1 and phospho-STAT3. This newly found mechanism to suppress the pro-inflammatory response of macrophages will provoke a re-thinking of how inflammation can be addressed therapeutically.

cell biology↗

Mucins form a nanoscale material barrier against immune cell attack

The cancer cell glycocalyx serves as a major line of defense against immune surveillance. However, how specific physical properties of the glycocalyx contribute to immune evasion and how these properties are regulated are not well understood. Here, we uncover how the surface density, glycosylation, and crosslinking of cancer-associated mucins contribute to the nanoscale material thickness of the glycocalyx, and further analyze the effect of the glycocalyx thickness on resistance to effector cell attack. Natural Killer (NK) cell-mediated cytotoxicity exhibits a near perfect inverse correlation with the glycocalyx thickness of target cells regardless of the specific glycan structures present. NK cells expressing a chimeric antigen receptor (CAR) have an enhanced ability to breach the glycocalyx and kill target cells. Equipping the NK cell surface with a mucin-digesting enzyme also improves killing with a performance enhancement that rivals or exceeds CARs in some cases. Together, our results provide new considerations for improving cancer immunotherapies.

biophysics↗

Impaired lamin localization to the nuclear envelope is responsible for nuclear damage in LMNA mutant iPSC-derived cardiomyocytes

The LMNA gene encodes the nuclear envelope proteins Lamins A and C, which comprise a major part of the nuclear lamina, provide mechanical support to the nucleus, and participate in diverse intracellular signaling. LMNA mutations give rise to a collection of diseases called laminopathies, including dilated cardiomyopathy (LMNA-DCM) and muscular dystrophies. Although nuclear deformities are a hallmark of LMNA-DCM, the role of nuclear abnormalities in the pathogenesis of LMNA-DCM remains incompletely understood. Using induced pluripotent stem cell-derived cardiomyocytes (iPSC-CMs) from LMNA mutant patients and healthy controls, we show that LMNA mutant iPSC-CM nuclei have altered shape or increased size compared to healthy control iPSC-CM nuclei. The LMNA mutation exhibiting the most severe nuclear deformities, R249Q, additionally caused reduced nuclear stiffness and increased nuclear fragility. Importantly, for all cell lines, the degree of nuclear abnormalities corresponded to the degree of Lamin A/C and Lamin B1 mislocalization from the nuclear envelope. The mislocalization was likely due to altered assembly of Lamin A/C. Collectively, these results point to the importance of correct lamin assembly at the nuclear envelope in providing mechanical stability to the nucleus and suggest that defects in nuclear lamina organization may contribute to the nuclear and cellular dysfunction in LMNA-DCM.

cell biology↗