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Background and Purpose: A previous study showed that low triglyceride concentration predicts higher mortality after stroke. The aim of our study was to determine whether serum triglyceride level is associated with stroke severity on admission., Methods: 863 consecutive patients with acute ischemic stroke were included. Serum triglyceride level was measured within 36 hours after stroke onset. Stroke severity on admission was assessed using Scandinavian Stroke Scale (SSS). The patients were divided into 2 groups: those with severe stroke (SSS < or =25) and those with mild/moderate stroke (SSS >25)., Results: Patients with severe stroke had significantly lower serum triglyceride level than patients with mild/moderate stroke (1.4+/-0.6 versus 1.7+/-1.3 mmol/L). After adjusting for age, sex, atrial fibrillation, diabetes mellitus, obesity, and ischemic heart disease, patients with triglyceride >2.3 mmol/L had lower risk of severe stroke than those with triglyceride < or =2.3 mmol/L (OR: 0.58; 95% CI: 0.35 to 0.95)., Conclusions: Our results suggest that lower level of triglyceride is associated with the more severe stroke.

TrkA is the receptor tyrosine kinase (RTK) for nerve growth factor (NGF) and stimulates NGF-dependent cell survival and differentiation in primary neurons and also differentiation of neuroblastomas and apoptosis of medulloblastomas. We have previously shown that aspartic acid and glutamic acid substitution (AspGlu and GluAsp) of the activation loop tyrosines in TrkA (Tyr(683) and Tyr(684)) supports NGF-independent neuritogenesis and cell survival in PC12 cell-derived nnr5 cells. In this study, the AspGlu and GluAsp mutant Trks have been analysed for their ability to support NGF-independent and NGF-dependent neuritogenesis, proliferation and cell signalling in the human neuroblastoma cell line, SY5Y. We find that the AspGlu and GluAsp mutant Trks support NGF-dependent, but not NGF-independent, autophosphorylation, neuritogenic responses and/or inhibit cell cycle progression. The NGF-dependent neuritogenic responses are lower for the mutant Trks (approximately 30-60% for AspGlu and 50-60% for GluAsp), relative to wild-type TrkA. While both the AspGlu and GluAsp mutant Trks support NGF-dependent transient phosphorylation of Shc, PLCgamma-1, AKT, FRS2, SH2B as well as prolonged MAP kinase activation, the GluAsp mutant induces stronger NGF-dependent tyrosine phosphorylation of FRS2 and SH2B, as well as a stronger reduction in bromodeoxyuridine (BrdU) incorporation. Collectively, these data suggest that neither absolute levels of receptor autophosphorylation, high levels of TrkA expression nor the activation of a specific signalling pathway is dominant and absolutely essential for neuritogenesis and cell cycle arrest of SY5Y cells.

We demonstrate that the signaling adapter, Grb2, binds directly to the neurotrophin receptor tyrosine kinase, TrkA. Grb2 binding to TrkA is independent of Shc, FRS-2, phospholipase Cgamma-1, rAPS, and SH2B and is observed in in vitro binding assays, yeast two-hybrid assays, and in co-immunoprecipitation assays. Grb2 binding to TrkA is mediated by the central SH2 domain, requires a kinase-active TrkA, and is phosphotyrosine-dependent. By analyzing a series of rat TrkA mutants, we demonstrate that Grb2 binds to the carboxyl-terminal residue, Tyr(794), as well as to the activation loop tyrosines, Tyr(683) and Tyr(684). By using acidic amino acid substitutions of the activation loop tyrosines on TrkA, we can stimulate constitutive kinase activity and TrkA-Shc interactions but, importantly, abolish TrkA/Grb2 binding. Thus, in addition to providing the first evidence of direct Grb2 binding to the neurotrophin receptor, TrkA, these data provide the first direct evidence that the activation loop tyrosines of a receptor tyrosine kinase, in addition to their essential role in kinase activation, also serve a direct role in the recruitment of intracellular signaling molecules.

TrkA is the receptor tyrosine kinase (RTK) for nerve growth factor (NGF) and stimulates NGF-dependent cell survival and differentiation in primary neurons. TrkA expression in neuronal tumors also supports NGF-dependent differentiation of neuroblastomas and apoptosis of medulloblastomas. Phosphorylation of the activation loop tyrosines in RTK's are essential to activation as well as allosteric changes that facilitate substrate interaction and phosphorylation. Acidic amino acid substitution of the activation loop tyrosines in TrkA, Tyr683Tyr684, was performed to mimic the negative charges normally induced by ligand activation and receptor phosphorylation. A total of eight independent mutants containing single or double substitutions were generated for comparison. Herein, we demonstrate that acidic substitution of the activation loop tyrosines is sufficient to induce allosteric changes required for constitutive TrkA kinase activity as well as phosphorylation of TrkA signaling proteins such as Shc, PLCgamma-1, FRS-2 and erk1/2. The strongest constitutively active TrkA mutants, GluAsp and AspGlu, support NGF-independent neuritogenesis and cell survival to levels approximately 65 and 80-100%, respectively, of NGF-activated wild type TrkA. Thus, constitutively active TrkA may provide a useful strategy in future therapeutic approaches to limit the development and progression of neuronal tumors.

We have isolated a human cDNA for the signaling adapter molecule FRS-2/suc1-associated neurotrophic factor target and shown that it is tyrosine-phosphorylated in response to nerve growth factor (NGF) stimulation. Importantly, we demonstrate that the phosphotyrosine binding domain of FRS-2 directly binds the Trk receptors at the same phosphotyrosine residue that binds the signaling adapter Shc, suggesting a model in which competitive binding between FRS-2 and Shc regulates differentiation versus proliferation. Consistent with this model, FRS-2 binds Grb-2, Crk, the SH2 domain containing tyrosine phosphatase SH-PTP-2, the cyclin-dependent kinase substrate p13(suc1), and the Src homology 3 (SH3) domain of Src, providing a functional link between TrkA, cell cycle, and multiple NGF signaling effectors. Importantly, overexpression of FRS-2 in cells expressing an NGF nonresponsive TrkA receptor mutant reconstitutes the ability of NGF to stop cell cycle progression and to stimulate neuronal differentiation.