Matrix viscoelasticity regulates dendritic cell migration and immune priming

Background

Tumor development is accompanied by changes in the surrounding tumor microenvironment (TME). Different physical parameters of the TME can sustain tumor progression and restrict immune surveillance. Matrix deposition, for example, is well known to increase local stiffness, impairing immune cell infiltration and tumor killing (Quail and Joyce, 2013). Another physical parameter of the extracellular matrix is viscoelasticity, a time dependent variable measuring relaxation upon deformation (Chaudhuri et al. 2020). While viscoelasticity of the microenvironment has been directly linked to long-lasting chromatin remodeling and phenotype change in fibroblasts and T cells, not much is known about its effect on dendritic cells (DC). In this work, the authors devise a system capable of tuning viscoelasticity of collagen I independently of stiffness to study the DC’ response. They found that viscoelasticity impacts migration and T cell priming, leaving long-lasting changes at mechanosensitive chromatin loci.

Key findings of this preprint

1. Impact of viscoelasticity on DC migration

This study uses type I collagen hydrogels with tunable viscoelasticity to uncouple this parameter from stiffness and microarchitecture. The DC employed were derived from isolation of human blood monocytes and in-vitro differentiation. By observing DC behavior in slow-relaxing gels (elastic), the authors discovered impaired migration and confined trajectories compared to those in fast-relaxing gels (viscoelastic), as measured by mean squared displacement (MSD) analysis. This impairment was consistent across different collagen concentrations; indicating that not only the density of the ECM, but also its time-dependent response to deformation impacts DC migration.

2. Viscoelasticity and transcriptional changes

Slow-relaxing collagens significantly altered transcriptional programs of DC as compared to fast-relaxing gels, with principal component analysis showing viscoelasticity as a primary factor separating gene expression profiles. Gene ontology analysis revealed enrichment in pathways related to cytokine production, T cell proliferation, and extracellular structure organization in DC placed in more elastic gels. Notably, genes associated with AP-1 and NF-κB pathways, including IL-1β and IL-6, were upregulated in DC within slow-relaxing conditions, leading to elevated secretion of these pro-inflammatory cytokines.

3. Elasticity of microenvironment impairs DC priming of T cells

After DC activation, autologous T cells were co-encapsulated in fast and slow-relaxing gels. After 12 days of co-culture, T cell proliferation and activation markers were measured, revealing that in fast-relaxing, more viscous gels T cells are better activated by DC. To exclude the direct effect of viscoelasticity on T cells, the authors also looked at T cells cultivated alone in fast vs slow-relaxing conditions but found no differences. Consistent with reduced DC migration in slow-relaxing gels, time-lapse microscopy showed decreased DC-T cell contacts in that condition.

4. Persistent chromatin changes in DC mediated by viscoelasticity

An interesting observation made by the authors is that the time of pre-incubation of DC in slow-relaxing gels affects their response upon transfer in fast-relaxing gels. Particularly, a single day of priming into slow-relaxing conditions did not affect DC behavior much, whereas 3 days of priming was sufficient to reduce DC migration upon transfer to fast-relaxing gels. This imprinted memory was further investigated by performing ATAC-seq on DC after 1 or 3 days in slow-relaxing gels. It turned out that positive regulators of Arp2/3-mediated actin nucleation, including Wasf1 and Taz, showed reduced chromatin accessibility; indicating persistent changes in loci of genes related to mechanosensing.

5. Persistent chromatin changes in DC mediated by viscoelasticity

Collagen deformation in fast-relaxing gels was observed to depend on actomyosin contractility, which was impaired in DC placed in slow-relaxing gels. This further linked the ability to deform the surrounding substrate to DC migration in the tested conditions. Reduced viscoelasticity led to a less permissive environment for DC to move and consequently prime T cells, indicating viscoelasticity as a critical parameter to DC functioning in tissues.

Why I chose to highlight this preprint

Physical forces acting at biological scales are fascinating and hold much promise to increase our understanding of cellular and organismal function. The authors had the ambitious aim of studying how viscoelastic properties of ECM impact DC behavior and applied advanced chemical modification strategies and cell culture methods to elegantly answer their biological questions.

Questions for the authors

• Besides comparable T cell proliferation in fast vs slow-relaxing gels at steady state, do you have any evidence of T cell activation by DC after single T cell encapsulation in the two different gel conditions?

• DC in slow-relaxing gels are more inflammatory but less capable of activating T cells: do you think that these two phenotypes are linked or rather that migration is the major contributor to T cell priming?

• To your knowledge, do you think response to viscoelasticity shares mainly common traits across cell types or is rather cell-type specific?

References

• Quail, D. F. & Joyce, J. A. Microenvironmental regulation of tumor progression and metastasis. Nat Med 19, 1423–1437 (2013). doi:10.1038/nm.3394

• Chaudhuri O, Cooper-White J, Janmey PA, Mooney DJ, Shenoy VB. Effects of extracellular matrix viscoelasticity on cellular behaviour. Nature. 2020 Aug;584(7822):535-546. doi: 10.1038/s41586-020-2612-2. Epub 2020 Aug 26. PMID: 32848221; PMCID: PMC7676152.

Tags: cancer immunology, dendritic cells, ecm, mechanobiology, viscoelasticity

doi: https://doi.org/10.1242/prelights.41955

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