Biology subjects

Packirisamy, S.

Publications and source records attributed to Packirisamy, S..

3 recordsLinked to original sources

bioRxiv2025

ECM-stiffness mediated persistent fibroblast activation requires integrin and formin dependent chromatin remodeling

Transient activation of fibroblasts into contractile myofibroblasts is essential for extracellular matrix (ECM) production and remodeling during wound healing and tissue regeneration. While ECM-dependent mechanisms mediating transient activation is well studied, how fibroblasts switch from transient to a persistently activated state and drive fibrosis and aberrant tissue repair in diseases such as cancer is less understood. Here, we show that human cancer-associated fibroblasts (CAFs) switch from transient to persistently activated states upon prolonged exposure to stiff ECMs and stiffness-dependent secreted factors. This switch is accompanied by activation of ECM-stiffness-dependent mechanotransduction pathways and changes in the nuclear architecture and its association with chromatin. Mechanistically, we identify two pathways required for this switch-ECM ligand binding and complete activation of {beta}1 integrins smoothens the nuclear lamina during prolonged exposure, increases nuclear YAP, and reduces lamin-chromatin contacts while in parallel, exposure to the stiff ECM activates the formin mDia2 and independent of alterations in the nuclear architecture alters lamin-chromatin coupling, likely through its role in assembling nuclear actin. Importantly, we find that blocking either pathway prevents persistent myofibroblast activation, which is rescued by inhibition of histone deacetylases, indicating that dynamic chromatin modifications act downstream of these ECM-dependent pathways to maintain the persistently activated state. These findings link integrin-based ECM sensing to chromatin remodeling and fibroblast memory, with implications for stromal plasticity in the tumor microenvironment.

cell biology↗

bioRxiv2024

Extracellular matrix dependent regulation of Septin 7 in focal adhesions promotes mechanosensing and response in fibroblasts.

Fibroblasts are contractile adherent cells that maintain tissue homeostasis by sensing a wide array of changes in the extracellular matrix (ECM) and in response, regulate the physical and compositional properties of the ECM. These diverse cues are sensed by focal adhesions (FAs) that differentially couple changes in the ECM to the actomyosin machinery via modulation of integrin activation and the resultant recruitment of several proteins. One such protein is Septin-7 (Sept-7) that belongs to the septin family and has been found in FA proteomics and interactome studies. Sept-7 however, is not considered an FA protein and is thought to regulate and be regulated by actin outside of FAs. To reconcile these differences, here we used total internal reflection microscopy to image Sept-7 localization and dynamics at the cell-ECM interface and found that that ECM-mediated integrin activation in fibroblasts regulates the formation of spatially distinct higher order Sept-7 structures at FA subpopulations. In and around FAs located in the perinuclear regions of the cell, ECM binding resulted in the formation and stabilization of Sept-7 bundles while ECM binding and complete integrin activation promoted the growth of FA-like elongated Sept-7 structures that dynamically associated with the core of peripheral FAs. Functionally, peripheral Sept-7 structures promoted the elongation of peripheral FAs while perinuclear Sept-7 bundles were critical in regulating the maturation and stabilization of perinuclear FAs. Due to this coupling between the ECM, integrin activation and regulation of Sept-7 structures, we found that Sept-7 is required for a wide range of ECM sensing functions in fibroblasts including modulating sensitivity to changes in ECM stiffness and density and in contributing to the cells ability to remodel the ECM. Collectively, our results show that Sept-7 is an FA protein that gets recruited and assembled in diverse higher order structures in an ECM dependent manner to differentially regulate FA subpopulations and promote mechanosensing and ECM remodelling functions in fibroblasts.

cell biology↗

bioRxiv2022

Extracellular matrix sensing via modulation of orientational order of integrins and F-actin in focal adhesions

Specificity of cellular responses to distinct cues from the extracellular matrix (ECM) requires precise and sensitive decoding of information from the cell surface. However, how known mechanisms of mechanosensing such as force dependent catch bonds and conformational changes in focal adhesion (FA) proteins can confer this sensitivity is not known. Using a combination of polarization microscopy and computational modeling, here we identify regulation of orientational order or molecular co-alignment of FA proteins as a mechanism able to precisely tune cell sensitivity to the ECM. We find that V integrins and F-actin in FAs show changes in orientational order in an ECM-mediated integrin activation dependent manner. This magnitude of orientational order is sensitive to changes in ECM density but independent of myosin-II activity though actomyosin contractility can further fine-tune it. A molecular clutch model for integrin binding ECM ligands demonstrates that orientational order of integrin-ECM binding and catch bonds tune cellular sensitivity to ECM density. This mechanism is also able to decouple ECM density changes from changes in ECM stiffness thus also contributing to specificity. Taken together, our results suggest relative geometric organization of FA components as an important regulator of mechanotransduction.

cell biology↗