Valproic Acid-Induced Changes of 4D Nuclear Morphology in Astrocyte Cells

Abstract

<jats:title>Abstract</jats:title><jats:p>Histone deacetylase inhibitors, such as valproic acid (VPA), have important clinical implications as human therapeutics and cellular reprogramming agents. They induce chromatin re-organization associated with changes in cell nuclear morphology. Current approaches aiming to quantify these changes so far have been limited to basic 2D measures. Here, we quantified changes in 3D nuclear morphology of primary human astrocyte cells treated with VPA for 7 days (hence, 4D). We compared volumetric and surface-based 3D shape representations of cell nuclei and selected subset of features that jointly discriminated between normal and treated cells with 85% accuracy on day 7. Over time, VPA-treated nuclear morphologies progressed towards larger size and higher shape irregularity. On day 7, all 11 selected size and shape descriptors demonstrated significant difference between treated and untreated nuclear morphologies, including 22.5% increase in volume and 8.3% reduction in extent (shape regularity) for VPA-treated nuclei. Overall, we showed that 4D surface morphometry accurately characterizes the temporal changes in astrocyte nuclear form that are reflective of the underlying valproate-induced chromatin re-organization. These nuclear structural alterations may serve as a biomarker for histone (de-)acetylation events and provide insights into mechanisms of astrocytes-to-neurons reprogramming.</jats:p>

Sodium Valproate-Induced Chromatin Remodeling

“…Recently, a proposal was raised to study VPA-induced imaging changes in the nuclear morphology of astrocyte cells in a temporal context, a process that was named 4D morphometry (Kalinin et al, 2021). The authors reported results that reflected chromatin reorganization not only spatially but also temporally, which allowed them to conclude that their findings provided insights into the mechanisms of astrocyte-to-neuron reprogramming (Kalinin et al, 2021).…”

Unique Astrocyte Cytoskeletal and Nuclear Morphology in a Three-Dimensional Tissue-Engineered Rostral Migratory Stream

“…While we hypothesize that cytoskeletal forces are the predominant mechanism leading to greater nuclear eccentricity, there could be additional factors that are causing these nuclear shape changes. For example, Kalinin and colleagues recently demonstrated that modulation of chromatin compaction with valproic acid treatment leads to changes in astrocyte nuclear shape [ 45 ]. We are currently investigating how these biomaterial conditions that induce TE-RMS formation affect the structure of the astrocyte nuclear lamina and chromatin arrangement to elucidate how they may contribute to astrocyte nuclear elongation.…”

“…It is well known that mechanical changes in nuclear morphology are often accompanied by changes in chromatin organization and gene expression which then lead to downstream alterations in cell activity and signaling [ 41 , 51 – 54 ]. However, there is limited research on how mechanically altering nuclear shape affects gene expression regulation and cell behavior in astrocytes specifically [ 44 , 45 ]. Overall, we performed a thorough structural evaluation of the intermediate filament cytoskeleton and nuclear morphology in TE-RMS astrocytes, revealing a novel astrocyte phenotype that has not previously been described in vitro.…”

3D single-cell shape analysis using geometric deep learning

“…While measuring shape in 2D images has been illuminating, cells exist in 3D environments and their 3D geometry is a rich source of information about the inner workings of cells and tissues. For example, recent pioneering work has demonstrated that shape motifs extracted from 3D images can be linked to lipid membrane signalling and cancer signalling pathways [14], and changes in 3D nuclear morphometry are linked to chromatin organisation [18]. At the scale of developing tissues, the discovery of new 3D geometries has explained how cells pack stably into curved organs [19].…”