Synaptopodin stress fiber and contractomere at the epithelial junction

Modulation of Piezo1 influences human skin architecture and oxytocin expression

OBJECTIVE

Throughout our existence, the skin senses and analyses the mechanical forces imposed by the environment. In response to these environmental forces, skin can deform itself and achieve a biological response. The subsequent cutaneous plasticity emerges from mechanical properties arising from the collective action of the skin cells, particularly keratinocytes, that govern the tensile strength via cell-to-cell adhesions and via cell-matrix adhesion structures. In addition to serving as force-bearing entities, keratinocytes respond to forces by activating signalling pathways to control their own fate and function. To detect and adapt to mechanical signals, keratinocytes possess a panel of sensory receptors and junctional intercellular structures. Mechanically activated ion channel Piezo1 has been described as a force sensor and as being involved in pleasant touch perception. In this study, relationships between Piezo1 modulation and oxytocin synthesis were investigated.

METHODS

The expression of Piezo1 in the skin was studied and compared with the expression of TRPV1. Dooku1 antagonist and Jedi1 agonist were used to modulate Piezo1. The level of E-cadherin and oxytocin was monitored in ex vivo skin biopsies by immunodetection.

RESULTS

Taken together, our results illustrate the major role of mechanosensitive ion channel Piezo1 in skin barrier integrity, and in peripheral oxytocin synthesis in the skin.

CONCLUSION

In conclusion, this study highlights the relationships between pleasant touch, soft touch and local oxytocin synthesis.

Synaptopodin is necessary for Shigella flexneri intercellular spread

For many intracellular pathogens, their virulence depends on an ability to spread between cells of an epithelial layer. For intercellular spread to occur, these pathogens deform the plasma membrane into a protrusion structure that is engulfed by the neighboring cell. Although the polymerization of actin is essential for spread, how these pathogens manipulate the actin cytoskeleton in a manner that enables protrusion formation is still incompletely understood. Here, we identify the mammalian actin binding protein synaptopodin as required for efficient intercellular spread. Using a model cytosolic pathogen, Shigella flexneri , we show that synaptopodin contributes to organization of actin around bacteria and increases the length of the actin tail at the posterior pole of the bacteria. We show that synaptopodin presence enables protrusions to form and to resolve at a greater rate, indicating that greater stability of the actin tail enables the bacteria to push against the membrane with greater force. We demonstrate that synaptopodin recruitment around bacteria requires the bacterial protein IcsA, and we show that this recruitment is further enhanced in a type 3 secretion system dependent manner. These data establish synaptopodin as required for intracellular bacteria to reprogram the actin cytoskeleton in a manner that enables efficient protrusion formation and enhance our understanding of the cellular function of synaptopodin.

Authors Summary

Intercellular spread is essential for many cytosolic dwelling pathogens during their infectious life cycle. Despite knowing the steps required for intercellular spread, relatively little is known about the host-pathogen interactions that enable these steps to occur. Here, we identify a requirement for the actin binding protein synaptopodin during intercellular spread by cytosolic bacteria. We show synaptopodin is necessary for the stability and recruitment of polymerized actin around bacteria. We also demonstrate synaptopodin is necessary to form plasma membrane structures known as protrusions that are necessary for the movement of these bacteria between cells. Thus, these findings implicate synaptopodin as an important actin-binding protein for the virulence of intracellular pathogens that require the actin cytoskeleton for their spread between cells.

Compression-induced buckling of a semiflexible filament in two and three dimensions

The ability of biomolecules to exert forces on their surroundings or resist compression from the environment is essential in a variety of biologically relevant contexts. For filaments in the low-temperature limit and under a constant compressive force, Euler buckling theory predicts a sudden transition from a compressed to a bent state in these slender rods. In this paper, we use a mean-field theory to show that if a semiflexible chain is compressed at a finite temperature with a fixed end-to-end distance (permitting fluctuations in the compressive forces), it exhibits a continuous phase transition to a buckled state at a critical level of compression. We determine a quantitatively accurate prediction of the transverse position distribution function of the midpoint of the chain that indicates this transition. We find the mean compressive forces are non-monotonic as the extension of the filament varies, consistent with the observation that strongly buckled filaments are less able to bear an external load. We also find that for the fixed extension (isometric) ensemble, the buckling transition does not coincide with the local minimum of the mean force (in contrast to Euler buckling). We also show the theory is highly sensitive to fluctuations in length in two dimensions, and that the buckling transition can still be accurately recovered by accounting for those fluctuations. These predictions may be useful in understanding the behavior of filamentous biomolecules compressed by fluctuating forces, relevant in a variety of biological contexts.