Periodic Reporting for period 1 - LamelliActin (Mechanical Adaptation of Lamellipodial Actin Networks in Migrating Cells)
Période du rapport: 2017-03-01 au 2019-02-28
Many cells need to directionally migrate in response to external stimuli in order to accomplish their versatile functional tasks ranging from embryogenesis to wound healing and immune responses. On the other hand, misguidance of cell migration contributes to the pathogenesis of Europe’s socioeconomic most relevant diseases including cancer, cardiovascular diseases and chronic inflammation and better understanding the fundamental mechanisms of cell migration is of direct clinical relevance.
While directional motion is typically dictated by chemotactic and haptotactic gradients, the actual motility within the organism is restricted by physical constraints, such as the presence of other cells and the extracellular matrix. Correspondingly, the ability to successfully navigate within confined environments in the presence of obstacles is an essential requirement for efficient cell migration within organisms.
Lamellipodia are sheet-like protrusions of dendritic actin networks at the leading edge of migrating cells and inevitably the first cellular structures that encounter obstacles within their path of migration. Despite the well-established role of actin-rich lamellipodia in cell migration, the fundamental question of how lamellipodial actin-networks integrate local mechanical cues, like encountered obstacles into directional decision-making remains poorly understood. In particular, it remains to be determined how network-intrinsic processing of mechanical cues affects cell navigation with complex microenvironments like tissue.
LammeliActin investigated this gap of knowledge by taking advantage of a combination of new experimental approaches. The data generated provides evidence for a yet unknown force generating actin-structure required for cell migration in confined microenvironments and paves the way for the development of novel pharmacological strategies to manipulate cell migration in vivo (Gaertner et al. in preparation).
While directional motion is typically dictated by chemotactic and haptotactic gradients, the actual motility within the organism is restricted by physical constraints, such as the presence of other cells and the extracellular matrix. Correspondingly, the ability to successfully navigate within confined environments in the presence of obstacles is an essential requirement for efficient cell migration within organisms.
Lamellipodia are sheet-like protrusions of dendritic actin networks at the leading edge of migrating cells and inevitably the first cellular structures that encounter obstacles within their path of migration. Despite the well-established role of actin-rich lamellipodia in cell migration, the fundamental question of how lamellipodial actin-networks integrate local mechanical cues, like encountered obstacles into directional decision-making remains poorly understood. In particular, it remains to be determined how network-intrinsic processing of mechanical cues affects cell navigation with complex microenvironments like tissue.
LammeliActin investigated this gap of knowledge by taking advantage of a combination of new experimental approaches. The data generated provides evidence for a yet unknown force generating actin-structure required for cell migration in confined microenvironments and paves the way for the development of novel pharmacological strategies to manipulate cell migration in vivo (Gaertner et al. in preparation).
Dendritic cells (DCs) are antigen presenting immune cells that patrol tissues and constitute efficient immune surveillance. Upon encountering of tissue damage and/or infection DCs mature and rapidly migrate to draining lymph nodes where they present antigens and initiate the adaptive immune response. Consequently, migration is essential to DC function and its misregulation results in severe immunological disorders.
We employed rapid amoeboid crawling dendritic cells (DCs) as a model system for three-dimensional cell migration to analyze actin-dynamics of 3D-confined lamellipodia. Using high resolution light-microscopy and electron microscopy, we discovered that confined DCs form yet undescribed actin-rich microspikes that are connected to the lamellipodial actin network and depend on actin-branching, as well as actin-bundling proteins. Inhibition of microspike-formation by pharmacological and/or genetical manipulation of actin branching and bundling proteins reduced lamellipodial actin-polymerization rates and stalls locomotion under confinement. In contrast, migration of non-confined cells remained unaffected by microspike inhibition. We therefore suggest that actin microspikes of migrating cells may constitute force-generating structures counteracting compressive forces from the surrounding microenvironment, thereby facilitating leading edge protrusion and squeezing through obstacles that block the path of migration. Indeed, partial confinement of cells with nano-structured topographies specifically recruits microspikes to sites of cellular impression. Together, our data suggests an essential role of actin microspikes as force generating actin-structures required for cell migration in confined microenvironments and paves the way for the development of novel pharmacological strategies to manipulate cell migration in vivo (Gaertner et al. in preparation; data was presented at the Gordon research conference “Directed cell migration” 2019 in Galveston, TX).
We employed rapid amoeboid crawling dendritic cells (DCs) as a model system for three-dimensional cell migration to analyze actin-dynamics of 3D-confined lamellipodia. Using high resolution light-microscopy and electron microscopy, we discovered that confined DCs form yet undescribed actin-rich microspikes that are connected to the lamellipodial actin network and depend on actin-branching, as well as actin-bundling proteins. Inhibition of microspike-formation by pharmacological and/or genetical manipulation of actin branching and bundling proteins reduced lamellipodial actin-polymerization rates and stalls locomotion under confinement. In contrast, migration of non-confined cells remained unaffected by microspike inhibition. We therefore suggest that actin microspikes of migrating cells may constitute force-generating structures counteracting compressive forces from the surrounding microenvironment, thereby facilitating leading edge protrusion and squeezing through obstacles that block the path of migration. Indeed, partial confinement of cells with nano-structured topographies specifically recruits microspikes to sites of cellular impression. Together, our data suggests an essential role of actin microspikes as force generating actin-structures required for cell migration in confined microenvironments and paves the way for the development of novel pharmacological strategies to manipulate cell migration in vivo (Gaertner et al. in preparation; data was presented at the Gordon research conference “Directed cell migration” 2019 in Galveston, TX).
LamelliActin made substantial contributions to our general understanding of how cytoskeletal actin-networks perceive, transmit and respond to mechanical signals during cell migration. We achieved our goals by developing novel micro-engineered microfluidic devices allowing us to visualize and quantitatively asses subcellular actin dynamics of single immune cells in response to compression. In addition, we were able to confirm the findings from the reductionist approaches in physiological assays employing living tissues, thus highlighting the in vivo relevance of our results. I therefore envision that LamelliActin will contribute to biological and clinically relevant follow up projects, deciphering the role of mechanical signals in physiologic and disease-related cell migratory events.