Self-organized podosomes are dynamic mechanosensors

PtdIns(3,4)P2 instigates focal adhesions to generate podosomes

Cell-to-extracellular matrix (ECM) adhesion plays important roles in various biological events, such as proliferation, differentiation and migration. Distinct from other types of adhesion structures (focal complexes, focal adhesions and so on), podosomes and invadopodia are thought to have additional functions beyond attachment, possibly including invasion into the ECM. for podosomes and invadopodia to invade into the ECM, molecules involved in adhesion, actin polymerization and ECM degradation must be recruited to sites of action. Our recent study demonstrated that podosomes form near newly formed focal adhesions via the minimally expressed phosphoinositide PtdIns(3,4) P2-mediated recruitment of the Tks5-Grb2 scaffold, followed by the accumulation of N-WASP. Although this study demonstrated details of molecular interplay during the transformation of focal adhesion, its regulation in the in vivo invasion process remains to be clarified. Here, we discuss the molecular bases of the transformation of focal adhesions to podosomes/invadopodia based on current understanding.

Biomechanics of the optic nerve head

Biomechanical factors acting at the level of the lamina cribrosa (LC) are postulated to play a role in retinal ganglion cell dysfunction and loss in glaucoma. In support of this postulate, we now know that a number of cell types (including lamina cribrosa cells) are mechanosensitive. Here we briefly review data indicating cellular stretching, rate of stretching and substrate stiffness may be important mechanosensitivity factors in glaucoma. We then describe how experiments and finite element modeling can be used to quantify the biomechanical environment within the LC, and how this environment depends on IOP. Generic and individual-specific models both suggest that peripapillary scleral properties have a strong influence on LC biomechanics, which can be explained by the observation that scleral deformation drives much of the IOP-dependent straining of the LC. Elegant reconstructions of the LC in monkey eyes have shown that local strains experienced by LC cells depend strongly on laminar beam microarchitecture, which can lead to large local strain elevations. Further modeling, suitably informed by experiments, is needed to better understand lamina cribrosa biomechanics and how they may be involved in glaucomatous optic neuropathy.

Cell biology: watching the first steps of podosome formation

Podosomes and invadopodia are actin-rich structures that have come under intense scrutiny over the past several years due to their critical roles in cell migration and invasion. Examination of the initial stages of podosome formation has revealed an important role for the phosphoinositide PI(3,4)P(2) in anchoring the scaffold protein Tks5 to the plasma membrane.