Influence of extracellular Ca 2+ on cell shape and tensegrity

1. Influence of extracellular Ca2+ on cell shape and tensegrity Background Results In all eukaryotic cells, the extracellular concentration of calcium ions Ca2+ is tightly controlled by hormones like PTH and calcitonin and vitamin-D. Finely, tuned changes in Ca2+modulate a variety of intracellular functions, and disruption of Ca2+ handling leads to cell death (Rosario Rizzuto1 & TullioPozzan, Nature Genetics, 2003). Tensegrity system is a building principle of prestressed structures that stabilize their shape by continuous tension or `tensional integrity' rather than by continuous compression. The “cellular tensegrity model” proposes that the whole cell is a prestressedtensegrity structure. In the model, tensional forces are borne by cytoskeletal microfilaments and intermediate filaments, and these forces are balanced by compression of microtubule struts structural elements , all being interconnected. Most notably, these forces are resisted by internal adhesion proteins and extracellular matrix (ECM) (Donald E. Ingber , Cell Science, 2003). Also recent works show that mechanical distortion of cells and the cytoskeleton through cell surface integrin receptors can profoundly affect cell behavior. Hence, the cytoskeleton also orients much of the cell's metabolic and signal transduction machinery leading to molecular changes. Most important, the binding of integrins to their ligands on ECM and cadherins that link cells to the cytoskeleton, also mediating transmembrane mechanical coupling between neighbor cells, strongly depend on extracellular divalent cations , Ca2+ or Mg2+ (Molecular Biology of the Cell,2002). Ingber proposed that many diseases are the result of abrupt changes in the normal tensile forces of cells influenced by their environment. It is therefore tempting to find a correlation between extracellular Ca2+ and cellular tension (tensegrity). Recently, a mathematical model expressing such relationship between tensegrity and extracellular calcium was established by our group. Students: EyalDekel and Inna Nakhimova, Tel-Aviv University, department of Bio-Medical Engineering Supervisor: Prof. ItzhakBinderman, Tel-Aviv University, department of Bio-Medical Engineering • Table 1: parameters of sub-confluent Human Gingival Fibroblasts (HGF) that were grown in cultures in DMEM medium with serum. • Figure No.1: the graph depicts the relationship between Ca2+ and width/length ratio (HGF that were grown in DMEM medium with serum). • Table 2: parameters of sub-confluent Human Gingival Fibroblasts (HGF) that were grown in cultures in DMEM medium w/0 serum. Objectives • Figure No.2: the graph depicts the relationship between Ca2+and tensegrity force (HGF that were grown in DMEM medium with serum). • Figure No.3: the graph depicts the relationship between Ca2+and strain (HGF that were grown in DMEM medium with serum). • To validate the mathematical model which expresses the relationship between force produced by cell tensegrity and calcium, by collecting large database: • F[pN]=1.86*ln[{597.44-1.19•(θ•x)}/{595.24-1.19•(θ•x)}] • F-force generated, x - concentration of Ca2+, θ – empirically found constant • To examine and analyze the correlation between Ca2+ and the cell’s shape. • In low concentration of calcium (0.25mM) the width/length ratio is high and tensegrityis low. • In 0.75mM concentration of calcium an abrupt increase in cell’s tensegrity and tension occurred, while width/length ratio is low. • In higher concentrations of calcium tensegrity reaches maximum. It seems that such calcium concentration no longer influences tensegrity. Methods • The length and width of 20-25 cells were measured per each concentration. • The cultures w/o serum didn’t show appropriate correlation. Both pictures perform cells in 0.75mM Ca2+ Conclusions • Our results validated the mathematical model which expresses relationship between tensegrity and extracellular calcium. • It seems that extracellular calcium has a profound effect on cell tension and tensegrity and therefore regulates their function.