Unique regulation of c-Jun N-terminal kinase by PYK2/CAK-beta in angiotensin II-stimulated vascular smooth muscle cells

Alzheimer risk gene product Pyk2 suppresses tau phosphorylation and phenotypic effects of tauopathy

BACKGROUND

Genetic variation at the PTK2B locus encoding the protein Pyk2 influences Alzheimer's disease risk. Neurons express Pyk2 and the protein is required for Amyloid-β (Aβ) peptide driven deficits of synaptic function and memory in mouse models, but Pyk2 deletion has minimal effect on neuro-inflammation. Previous in vitro data suggested that Pyk2 activity might enhance GSK3β-dependent Tau phosphorylation and be required for tauopathy. Here, we examine the influence of Pyk2 on Tau phosphorylation and associated pathology.

METHODS

The effect of Pyk2 on Tau phosphorylation was examined in cultured Hek cells through protein over-expression and in iPSC-derived human neurons through pharmacological Pyk2 inhibition. PS19 mice overexpressing the P301S mutant of human Tau were employed as an in vivo model of tauopathy. Phenotypes of PS19 mice with a targeted deletion of Pyk2 expression were compared with PS19 mice with intact Pyk2 expression. Phenotypes examined included Tau phosphorylation, Tau accumulation, synapse loss, gliosis, proteomic profiling and behavior.

RESULTS

Over-expression experiments from Hek293T cells indicated that Pyk2 contributed to Tau phosphorylation, while iPSC-derived human neuronal cultures with endogenous protein levels supported the opposite conclusion. In vivo, multiple phenotypes of PS19 were exacerbated by Pyk2 deletion. In Pyk2-null PS19 mice, Tau phosphorylation and accumulation increased, mouse survival decreased, spatial memory was impaired and hippocampal C1q deposition increased relative to PS19 littermate controls. Proteomic profiles of Pyk2-null mouse brain revealed that several protein kinases known to interact with Tau are regulated by Pyk2. Endogenous Pyk2 suppresses LKB1 and p38 MAPK activity, validating one potential pathway contributing to increased Tau pathology.

CONCLUSIONS

The absence of Pyk2 results in greater mutant Tau-dependent phenotypes in PS19 mice, in part via increased LKB1 and MAPK activity. These data suggest that in AD, while Pyk2 activity mediates Aβ-driven deficits, Pyk2 suppresses Tau-related phenotypes.

Does angiotensin II-aldosterone have a role in radiation-induced heart disease?

Radiation-induced heart disease (RIHD) is the potentially lethal side effect of radiation therapy. Clinical trials and epidemiologic studies show the adverse impact of RIHD on the outcome of long-term cancer survivors. However, what factors affect RIHD and how RIHD develop are not yet clear. On the other hand, as we all known, angiotensin II (Ang II) and aldosterone play a vital pathophysiological role in the common cardiovascular disease, including hypertension, atherosclerosis, heart failure, myocardial infarction and cardiac hypertrophy. The pathophysiology of these various syndromes is similar, starting by prior microvascular injury that leads to subsequent myocardium ischemia, all of which cause late fibrous scars. So the pathophysiology of RIHD is similar to the common heart diseases induced by angiotensin-aldosterone. But the effect of angiotensin-aldosterone on RIHD has little been studied. Thus, in the present hypothesis we suggest that angiotensin II-aldosterone plays an important pathophysical role in RIHD, which was confirmed by our pilot study.

Hypoxia affects sex differentiation and development, leading to a male-dominated population in zebrafish (Danio rerio)

Hypoxia is affecting thousands of square kilometers of water and has caused declines in fish populations and major changes in aquatic communities worldwide. For the first time, we report that hypoxia can affect sex differentiation and sex development of zebrafish (Danio rerio), leading to a male-biased population in the F1 generation (74.4% +/- 1.7% males in the hypoxic groups versus 61.9% +/- 1.6% males in the normoxic groups, n = 5; p < 0.05, chi2 test). The increase in males was associated with downregulations of various genes controlling the synthesis of sex hormones (i.e., 3beta-HSD, CYP11A, CYP19A, and CYP19B) as well as an increase in the testosterone/estradiol ratio. The male-dominated populations caused by hypoxia will have reduced reproductive success, thereby threatening the sustainability of natural fish populations.

Redox-dependent protein kinase regulation by angiotensin II: mechanistic insights and its pathophysiology

Reactive oxygen species (ROS) are proposed to induce cardiovascular diseases, such as atherosclerosis, hypertension, restenosis, and fibrosis, through several mechanisms. One such mechanism involves ROS acting as intracellular second messengers, which lead to induction of unique signal transductions. Angiotensin II (AngII), a potent cardiovascular pathogen, stimulates ROS production through the G protein-coupled AngII type 1 receptor expressed in its target organs, such as vascular tissues, heart, and kidney. Recent accumulating evidence indicates that through ROS production, AngII activates downstream ROS-sensitive kinases that are critical in mediating cardiovascular remodeling. Each of these ROS-sensitive kinases could potentially mediate its own specific function. In this review, we will focus our discussion on the current findings that suggest novel mechanisms of how AngII mediates activation of these redox-sensitive kinases in target organs, as well as the pathological significance of their activation.

Aquatic hypoxia is a teratogen and affects fish embryonic development

Hypoxia occurs over large areas in aquatic systems worldwide, and there is growing concern that hypoxia may affect aquatic animals, leading to population decline and changes in community by elimination of sensitive species. For the first time, we report that sublethal levels of hypoxia can significantly increase (+77.4%) malformation in fish embryonic development. Disruption of apoptotic pattern was clearly evident at 24 h post-fertilization, which may be a major cause of malformation. Furthermore, embryonic development was delayed, and balance of sex hormones (testosterone and estradiol) was disturbed during embryonic stages, implicating that subsequent sexual development may also be affected. Overall, our results imply that hypoxia may have a teratogenic effect on fish and delay fish embryonic development, which may subsequently impair species fitness leading to natural population decline.

Activation of tyrosine kinases by reactive oxygen species in vascular smooth muscle cells: significance and involvement of EGF receptor transactivation by angiotensin II

Enhanced production of reactive oxygen species (ROS) such as H(2)O(2) and a failure in ROS removal by scavenging systems are hallmarks of several cardiovascular diseases such as atherosclerosis and hypertension. ROS act as second messengers that play a prominent role in intracellular signaling and cellular function. In vascular smooth muscle cells (VSMCs), a vascular pathogen, angiotensin II, appears to initiate growth-promoting signal transduction through ROS-sensitive tyrosine kinases. However, the precise mechanisms by which tyrosine kinases are activated by ROS remain unclear. In this review, the current knowledge that suggests how certain tyrosine kinases are activated by ROS, along with their functional significance in VSMCs, will be discussed. Recent findings suggest that transactivation of the epidermal growth factor receptor by ROS requires metalloprotease-dependent heparin-binding epidermal growth factor-like growth factor production, whereas other ROS-sensitive tyrosine kinases such as PYK2, JAK2, and platelet-derived growth factor receptor require activation of protein kinase C-delta. Each of these ROS-sensitive kinases could mediate specific signaling critical for pathophysiological responses. Detailed analysis of the mechanism of cross-talk and the downstream function of these various tyrosine kinases will yield new therapeutic interventions for cardiovascular disease.

Distinct mechanisms of receptor and nonreceptor tyrosine kinase activation by reactive oxygen species in vascular smooth muscle cells: role of metalloprotease and protein kinase C-delta

Reactive oxygen species (ROS) are implicated in cardiovascular diseases. ROS, such as H2O2, act as second messengers to activate diverse signaling pathways. Although H2O2 activates several tyrosine kinases, including the epidermal growth factor (EGF) receptor, JAK2, and PYK2, in vascular smooth muscle cells (VSMCs), the intracellular mechanism by which ROS activate these tyrosine kinases remains unclear. Here, we identified two distinct signaling pathways required for receptor and nonreceptor tyrosine kinase activation by H2O2 involving a metalloprotease-dependent generation of heparin-binding EGF-like growth factor (HB-EGF) and protein kinase C (PKC)-delta activation, respectively. H2O2-induced EGF receptor tyrosine phosphorylation was inhibited by a metalloprotease inhibitor, whereas the inhibitor had no effect on H2O2-induced JAK2 tyrosine phosphorylation. HB-EGF neutralizing antibody inhibited H2O2-induced EGF receptor phosphorylation. In COS-7 cells expressing an HB-EGF construct tagged with alkaline phosphatase, H2O2 stimulates HB-EGF production through metalloprotease activation. By contrast, dominant negative PKC-delta transfection inhibited H2O2-induced JAK2 phosphorylation but not EGF receptor phosphorylation. Dominant negative PYK2 inhibited H2O2-induced JAK2 activation but not EGF receptor activation, whereas dominant negative PKC-delta inhibited PYK2 activation by H2O2. These data demonstrate the presence of distinct tyrosine kinase activation pathways (PKC-delta/PYK2/JAK2 and metalloprotease/HB-EGF/EGF receptor) utilized by H2O2 in VSMCs, thus providing unique therapeutic targets for cardiovascular diseases.

A novel hematopoietic adaptor protein, Chat-H, positively regulates T cell receptor-mediated interleukin-2 production by Jurkat cells

Chat (Cas/HEF1-associated signal transducer) is a novel adaptor protein with an N-terminal Src homology-2 domain and C-terminal Cas/HEF1 association domain. We report here the molecular cloning of Chat-H, the hematopoietic isoform of Chat. Chat-H has an extended N-terminal domain besides the known Chat domain structures, suggesting a unique function of Chat-H in hematopoietic cells. Jurkat transfectants overexpressing Chat-H show a marked increase in interleukin-2 production after costimulation of T cell receptor and CD28. The degree of JNK activation is enhanced substantially in the Chat-H transfectants upon costimulation. The Src homology-2 domain mutant of Chat-H loses this signal modulating activity. Expression of the Cas/HEF1 association domain mutant exhibits a dominant negative effect on both JNK activation and interleukin-2 production. We further found that Chat-H forms a complex with Pyk2H and enhances its tyrosine 402 phosphorylation, an up-regulator of the JNK pathway. These results suggest that Chat-H positively controls T cell function via integrating the costimulatory signals.

Cyclosporin A inhibits angiotensin II-induced c-Jun NH(2)-terminal kinase activation but not protein synthesis in vascular smooth muscle cells

Angiotensin II activates three major mitogen-activated protein kinases (MAPK) in vascular smooth muscle cells. Although other angiotensin II-induced MAPKs activation require transactivation of a growth factor receptor, the detailed mechanism by which angiotensin II activates c-Jun NH(2)-terminal kinase (JNK) remains unclear. Here, an immunosuppressant, cyclosporin A but not FK506, selectively inhibited angiotensin II-induced JNK activation in vascular smooth muscle cells. However, cyclosporin A had no inhibitory effect on angiotensin II-induced protein synthesis. Thus, angiotensin II-induced JNK activation but not protein synthesis is mediated by a mechanism sensitive to cyclosporin A, which is independent from calcineurin in vascular smooth muscle cells.