Interrogating TGF-ß Function and Regulation in Endothelial Cells.

Transforming growth factor-ß (TGF-ß) is a multifunctional cytokine with important roles in embryogenesis and maintaining tissue homeostasis during adult life. There are three isoforms of TGF-ß, i.e., TGF-ß1, -ß2, and -ß3, which signal by binding to a complex of transmembrane type I and type II serine/threonine kinase receptors and intracellular Smad transcription factors. In most cell types TGF-ß signals via TGF-ß type II receptor (TßRII) and TßRI, also termed activin receptor-like kinase 5 (ALK5). In endothelial cells, TGF-ß signals via ALK5 and ALK1. These two type I receptors mediate opposite cellular response for TGF-ß. The co-receptor endoglin, highly expressed on proliferating endothelial cells, facilitates TGF-ß/ALK1 and inhibits TGF-ß/ALK5 signaling. Knockout of TGF-ß receptors in mice all result in embryonic lethality during midgestation from defects in angiogenesis, illustrating the pivotal role of TGF-ß in this process. This chapter introduces methods for examining the function and regulation of TGF-ß in angiogenesis in in vitro assays using cultured endothelial cells and ex vivo metatarsal explants.

Autotaxin (NPP-2) in the brain: cell type-specific expression and regulation during development and after neurotrauma.

Autotaxin is a secreted cell motility-stimulating exo-phosphodiesterase with lysophospholipase D activity that generates bioactive lysophosphatidic acid. Lysophosphatidic acid has been implicated in various neural cell functions such as neurite remodeling, demyelination, survival and inhibition of axon growth. Here, we report on the in vivo expression of autotaxin in the brain during development and following neurotrauma. We found that autotaxin is expressed in the proliferating subventricular and choroid plexus epithelium during embryonic development. After birth, autotaxin is mainly found in white matter areas in the central nervous system. In the adult brain, autotaxin is solely expressed in leptomeningeal cells and oligodendrocyte precursor cells. Following neurotrauma, autotaxin is strongly up-regulated in reactive astrocytes adjacent to the lesion. The present study revealed the cellular distribution of autotaxin in the developing and lesioned brain and implies a function of autotaxin in oligodendrocyte precursor cells and brain injuries.

Lysophosphatidic acid: mitogen and motility factor.

LPA (lysophosphatidic acid), the simplest of al glycerophospholipids, is a potent inducer of cell proliferation, migration and survival. It does so by activating its cognate G-protein-coupled receptors, four of which have been identified. LPA receptors couple to at least three distinct G-proteins and thereby activate multiple signal transduction pathways, particularly those initiated by the small GTPases Ras, Rho and Rac. Our recent work has shown that LPA signals Rac activation via the Tiam1 GDP/GTP exchange factor and thereby stimulates cell migration. Here we discuss recent progress in our understanding of LPA action.

Hydrogen peroxide inhibits cell cycle progression by inhibition of the spreading of mitotic CHO cells.

Hydrogen peroxide (H(2)O(2)) induces a number of events, which are also induced by mitogens. Since the progression through the G1 phase of the cell cycle is dependent on mitogen stimulation, we were interested to study the effect of H(2)O(2) on the cell cycle progression. This study demonstrates that H(2)O(2) inhibits DNA synthesis in a dose-dependent manner when given to cells in mitosis or at different points in the G1 phase. Interestingly, mitotic cells treated immediately after synchronization are significantly more sensitive to H(2)O(2) than cells treated in the G1, and this is due to the inhibition of the cell spreading after mitosis by H(2)O(2). H(2)O(2) reversibly inhibits focal adhesion activation and stress fiber formation of mitotic cells, but not those of G1 cells. The phosphorylation of MAPK is also reversibly inhibited in both mitotic and G1 cells. Taken together, H(2)O(2) is probably responsible for the inhibition of the expression of cyclin D1 and cyclin A observed in cells in both phases. In conclusion, H(2)O(2) inhibits cell cycle progression by inhibition of the spreading of mitotic CHO cells. This may play a role in pathological processes in which H(2)O(2) is generated.