No abstract

Proliferation of vascular smooth muscle cells (VSMC) is triggered by two types of growth factors. One activates tyrosine kinase-type receptors and the other activates G-protein-coupled receptors. We found that a conditioned medium of rat VSMC contained a growth-potentiating activity for the latter type of growth factor, and we purified a 70-kDa growth-potentiating factor (GPF) from the conditioned medium. Analyses of GPF and its cDNA revealed GPF to be a gamma-carboxyglutamic acid-containing protein encoded by a growth arrest-specific gene, gas6, which related to protein S. GPF specifically potentiated cell proliferation mediated by Ca(2+)-mobilizing receptors. The presence of a specific binding site suggests that the effect of GPF is mediated by a receptor. Thus, GPF may be a new type of extracellular factor regulating VSMC proliferation.

Traumatic brain injury (TBI) is currently a major cause of morbidity and poor quality of life in Western society, with an estimate of 2.5 million people affected per year in Europe, indicating the need for advances in TBI treatment. Within the first 24 h after TBI, several inflammatory response factors become upregulated, including the lectin galectin-3. In this study, using a controlled cortical impact (CCI) model of head injury, we show a large increase in the expression of galectin-3 in microglia and also an increase in the released form of galectin-3 in the cerebrospinal fluid (CSF) 24 h after head injury. We report that galectin-3 can bind to TLR-4, and that administration of a neutralizing antibody against galectin-3 decreases the expression of IL-1β, IL-6, TNFα and NOS2 and promotes neuroprotection in the cortical and hippocampal cell populations after head injury. Long-term analysis demonstrated a significant neuroprotection in the cortical region in the galectin-3 knockout animals in response to TBI. These results suggest that following head trauma, released galectin-3 may act as an alarmin, binding, among other proteins, to TLR-4 and promoting inflammation and neuronal loss. Taking all together, galectin-3 emerges as a clinically relevant target for TBI therapy.

Gas6 (encoded by growth-arrest-specific gene 6) is a gamma-carboxyglutamic acid (Gla)-containing protein which is released from growth-arrested vascular smooth muscle cells (VSMCs) and potentiates VSMC proliferation induced by Ca2+-mobilizing growth factors, but not that induced by receptor tyrosine kinases. In this study we examined the importance of Gla residues for the biological activities of Gas6 and tried to assess the importance of endogenous Gas6 in VSMC proliferation. We demonstrated that Gla-deficient Gas6 lacked receptor-binding and growth-potentiating activities. Therefore the vitamin K-dependent modification of Gas6 appeared to be essential for its biological activities. Next we used warfarin, an inhibitor of vitamin K-dependent gamma-carboxylation, to estimate the contribution of endogenous Gas6 to VSMC proliferation. Warfarin markedly inhibited the thrombin-induced proliferation of VSMC without affecting the mRNA or protein expression of Gas6. Therefore the inhibition seems to be due to prevention of the vitamin K-dependent modification of Gas6. However, warfarin did not affect epidermal growth factor-induced proliferation. A neutralizing antibody against Gas6 gave a similar result, i.e. it inhibited thrombin-induced VSMC proliferation but not that induced by epidermal growth factor. These results indicate that endogenously produced Gas6 is very important for VSMC proliferation induced by Ca2+-mobilizing growth factors.