9-(tetrahydro-2-furyl)-adenine and lysophosphatidic-acid

We previously showed that lysophosphatidic acid (LPA) and an adenylyl cyclase inhibitor (ACI) stimulate mitogenic activation of senescent human diploid fibroblasts. Because the modulation of cell proliferation may affect wound healing in aged organisms, we studied the effects of LPA and ACI on in vivo skin wound healing in aged Fisher 344 rats. We found that, in aged rats, wound healing improved in animals treated with LPA and/or ACI (relative to untreated controls), as assessed by histological analysis of reepithelialization and immunostaining for proliferating cell nuclear antigen. The age-dependent activation of mitogenic responses by LPA and ACI was confirmed in other cell types. Taken together, our findings suggest that the activation of mitogenic potential in senescent cells by LPA and/or ACI may translate into enhanced in vivo wound healing and tissue regeneration in aged animals.

Topics: Adenine; Adenylyl Cyclase Inhibitors; Age Factors; Aging; Animals; Cell Movement; Cell Proliferation; Fibroblasts; Humans; Keratinocytes; Lysophospholipids; Male; Mitosis; Proliferating Cell Nuclear Antigen; Rats; Rats, Inbred F344; Receptor Protein-Tyrosine Kinases; Skin; Wound Healing

This study was designed to elucidate the molecular mechanism underlying lysophosphatidic acid (LPA) and adenylyl cyclase inhibitor SQ22536 (ACI)-induced senescent human diploid fibroblast (HDF) proliferation. Because adenosine monophosphate (AMP)-activated protein kinase (AMPK) is known to inhibit cell proliferation, we examined the phosphorylation status of AMPK and p53 and the expression level of p21(waf1/cip1) after treating HDFs with LPA and ACI. Phosphorylation of AMPKalpha on threonine-172 (p-Thr172-AMPKalpha) increases its catalytic activity but phosphorylation on serine-485/491 (p-Ser485/491-AMPKalpha) reduces the accessibility of the Thr172 phosphorylation site thereby inhibiting its catalytic activity. LPA increased p-Ser485/491-AMPKalpha, presumably by activating cAMP-dependent protein kinase (PKA). However, ACI reduced p-Thr172-AMPKalpha by inhibiting the LKB signaling. Our data demonstrated that both LPA and ACI inhibit the catalytic activity of AMPKalpha and p53 by differentially regulating phosphorylation of AMPKalpha, causing increased senescent cell proliferation. These findings suggest that the proliferation potential of senescent HDFs can be modulated through the regulation of the AMPK signaling pathway.

Topics: Adenine; Adenylyl Cyclase Inhibitors; AMP-Activated Protein Kinases; Cell Proliferation; Cells, Cultured; Cellular Senescence; Cyclic AMP-Dependent Protein Kinases; Cyclin D1; Cyclin-Dependent Kinase Inhibitor p21; Diploidy; Enzyme Inhibitors; Fibroblasts; Humans; Lysophospholipids; Models, Biological; Multienzyme Complexes; Phosphorylation; Protein Serine-Threonine Kinases; S Phase; Signal Transduction