Activation of protein kinase C is required for the stable attachment of adherent platelets to collagen but is not needed for the initial rapid adhesion under flow conditions

Identifying the hub genes for Duchenne muscular dystrophy and Becker muscular dystrophy by weighted correlation network analysis

Background

The goal of this study is to identify the hub genes for Duchenne muscular dystrophy (DMD) and Becker muscular dystrophy (BMD) via weighted correlation network analysis (WGCNA).

Methods

The gene expression profile of vastus lateralis biopsy samples obtained in 17 patients with DMD, 11 patients with BMD and 6 healthy individuals was downloaded from the Gene Expression Omnibus (GEO) database (GSE109178). After obtaining different expressed genes (DEGs) via GEO2R, WGCNA was conducted using R package, modules and genes that highly associated with DMD, BMD, and their age or pathology were screened. Gene Ontology (GO) and Kyoto Encyclopaedia of Genes and Genomes (KEGG) enrichment analysis and protein–protein interaction (PPI) network analysis were also conducted. Hub genes and highly correlated clustered genes were identified using Search Tool for the Retrieval of Interacting Genes (STRING) and Cystoscape software.

Results

One thousand four hundred seventy DEGs were identified between DMD and control, with 1281 upregulated and 189 downregulated DEGs. Four hundred and twenty DEGs were found between BMD and control, with 157 upregulated and 263 upregulated DEGs. Fourteen modules with different colors were identified for DMD vs control, and 7 modules with different colors were identified for BMD vs control. Ten hub genes were summarized for DMD and BMD respectively, 5 hub genes were summarized for BMD age, 5 and 3 highly correlated clustered genes were summarized for DMD age and BMD pathology, respectively. In addition, 20 GO enrichments were found to be involved in DMD, 3 GO enrichments were found to be involved in BMD, 3 GO enrichments were found to be involved in BMD age.

Conclusion

In DMD, several hub genes were identified: C3AR1, TLR7, IRF8, FYB and CD33(immune and inflammation associated genes), TYROBP, PLEK, AIF1(actin reorganization associated genes), LAPTM5 and NT5E(cell death and arterial calcification associated genes, respectively). In BMD, a number of hub genes were identified: LOX, ELN, PLEK, IKZF1, CTSK, THBS2, ADAMTS2, COL5A1(extracellular matrix associated genes), BCL2L1 and CDK2(cell cycle associated genes).

Microelectromechanical System Measurement of Platelet Contraction: Direct Interrogation of Myosin Light Chain Phosphorylation

Myosin Light Chain (MLC) regulates platelet contraction through its phosphorylation by Myosin Light Chain Kinase (MLCK) or dephosphorylation by Myosin Light Chain Phosphatase (MLCP). The correlation between platelet contraction force and levels of MLC phosphorylation is unknown. We investigate the relationship between platelet contraction force and MLC phosphorylation using a novel microelectromechanical (MEMS) based clot contraction sensor (CCS). The MLCK and MLCP pair were interrogated by inhibitors and activators of platelet function. The CCS was fabricated from silicon using photolithography techniques and force was validated over a range of deflection for different chip spring constants. The force of platelet contraction measured by the clot contraction sensor (CCS) was compared to the degree of MLC phosphorylation by Western Blotting (WB) and ELISA. Stimulators of MLC phosphorylation produced higher contraction force, higher phosphorylated MLC signal in ELISA and higher intensity bands in WB. Inhibitors of MLC phosphorylation produced the opposite. Contraction force is linearly related to levels of phosphorylated MLC. Direct measurements of clot contractile force are possible using a MEMS sensor platform and correlate linearly with the degree of MLC phosphorylation during coagulation. Measured force represents the mechanical output of the actin/myosin motor in platelets regulated by myosin light chain phosphorylation.

Tumor promoter PMA enhances kindlin-2 and decreases vimentin recruitment into cell adhesion sites

Phorbol diester PMA (phorbol 12-myristate 13-acetate) is a well-known promoter of tumor progression. PMA also regulates cell adhesion by several mechanisms including conformational activation of integrins and integrin clustering. Here, PMA was shown to induce lamellipodia formation and reorganization of the adhesion sites as well as actin and vimentin filaments independently of integrin preactivation. To further analyze the mechanism of PMA action, the protein composition in the α1β1 integrin/collagen IV adhesion sites was analyzed by mass spectrometry and proteomics. In four independent experiments we observed the reduced recruitment of vimentin in relation to integrin α1 subunit. This was in full agreement with the fact that we also detected the retraction of vimentin from cell adhesions by confocal microscopy. Furthermore, the accumulation of kindlin-2 into cell adhesions was significantly increased after PMA treatment. Kindlin-2 siRNA inhibited cell spreading as well as the formation of actin fibrils and cell adhesions, but did not prevent the effect of PMA on lamellipodia formation. Thus, kindlin-2 recruitment was considered to be a consequence rather than the primary cause for the loss of connection between vimentin and the adhesion sites.

Protein kinase C ε expression in platelets from patients with acute myocardial infarction

Objective

Platelets play crucial roles in the pathophysiology of thrombosis and myocardial infarction. Protein kinase C ε (PKCε) is virtually absent in human platelets and its expression is precisely regulated during human megakaryocytic differentiation. On the basis of what is known on the role of platelet PKCε in other species, we hypothesized that platelets from myocardial infarction patients might ectopically express PKCε with a pathophysiological role in the disease.

Methods and Results

We therefore studied platelet PKCε expression from 24 patients with myocardial infarction, 24 patients with stable coronary artery disease and 24 healthy subjects. Indeed, platelets from myocardial infarction patients expressed PKCε with a significant frequency as compared to both stable coronary artery disease and healthy subjects. PKCε returned negative during patient follow-up. The forced expression of PKCε in normal donor platelets significantly increased their response to adenosine diphosphate-induced activation and adhesion to subendothelial collagen.

Conclusions

Our data suggest that platelet generations produced before the acute event retain PKCε-mRNA that is not down-regulated during terminal megakaryocyte differentiation. Results are discussed in the perspective of peri-infarctual megakaryocytopoiesis as a critical component of myocardial infarction pathophysiology.

Advanced glycation end products inhibit adhesion ability of differentiated podocytes in a neuropilin-1-dependent manner

Podocyte injury can occur by a number of stimuli. Maintaining of an intact podocyte structure is essential for glomerular filtration; therefore, podocyte damage severely impairs renal function. Recently, we have reported that addition of glycated BSA [advanced glycation end products (AGE)-BSA] to differentiated murine podocytes inhibited neuropilin-1 (NRP1) expression and dramatically influenced podocyte migration ability (Bondeva T, Ruster C, Franke S, Hammerschmid E, Klagsbrun M, Cohen CD, Wolf G. Kidney Int 75: 605-616, 2009; Bondeva T, Wolf G. Am J Nephrol 30: 336-345, 2009). The present study analyzes the influence of AGEs and NRP1 on podocyte adhesion and cytoskeleton reorganization. We show that treatment with AGE-BSA significantly reduced podocyte adhesion to collagen IV, laminin, and fibronectin compared with Co-BSA (nonglycated BSA)-incubated cells, which was further augmented by transient inhibition of NRP1 expression using NRP1 short interference (si) RNA. On the other hand, forced overexpression of NRP1 markedly increased the adhesion ability of podocytes to the ECMs despite the AGE-BSA treatment. No changes were observed when podocyte adhesion to collagen I was assayed. These findings were also manifested with disorganization of podocyte actin stress fibers and decreased lamellipodia formation processes due to AGE-BSA treatment or NRP1 suppression. In addition, AGE-BSA or suppression of NRP1 both reduced the phosphorylation of focal adhesion kinase (FAK) and Erk1/2 in PMA-stimulated differentiated podocytes. Analysis of RhoA family GTPase activity demonstrated that treatment with AGE-BSA or NRP1 depletion inhibited as well the activation of the Rac-1 and Cdc42 but did not affect RhoA activity. All these effects were reversed by forced overexpression of full-length NRP1 cloned into the pcDNA3 vector in differentiated podocytes. Our study demonstrates that AGEs, in part via suppression of NRP1 expression, decreased podocyte adhesion and contribute to reduction of Rac-1 and Cdc42 GTPase activity. These effects may be further responsible for the podocytes damage and loss in diabetic nephropathy. Our findings suggest a role for NRP1 in regulating the podocyte actin cytoskeleton, and therefore reduction of NRP1 expression could be critical for podocyte function.

Differential roles of the PKC novel isoforms, PKCdelta and PKCepsilon, in mouse and human platelets

BACKGROUND

Increasing evidence suggests that individual isoforms of protein kinase C (PKC) play distinct roles in regulating platelet activation.

METHODOLOGY/PRINCIPAL FINDINGS

In this study, we focus on the role of two novel PKC isoforms, PKCdelta and PKCepsilon, in both mouse and human platelets. PKCdelta is robustly expressed in human platelets and undergoes transient tyrosine phosphorylation upon stimulation by thrombin or the collagen receptor, GPVI, which becomes sustained in the presence of the pan-PKC inhibitor, Ro 31-8220. In mouse platelets, however, PKCdelta undergoes sustained tyrosine phosphorylation upon activation. In contrast the related isoform, PKCepsilon, is expressed at high levels in mouse but not human platelets. There is a marked inhibition in aggregation and dense granule secretion to low concentrations of GPVI agonists in mouse platelets lacking PKCepsilon in contrast to a minor inhibition in response to G protein-coupled receptor agonists. This reduction is mediated by inhibition of tyrosine phosphorylation of the FcRgamma-chain and downstream proteins, an effect also observed in wild-type mouse platelets in the presence of a PKC inhibitor.

CONCLUSIONS

These results demonstrate a reciprocal relationship in levels of the novel PKC isoforms delta and epsilon in human and mouse platelets and a selective role for PKCepsilon in signalling through GPVI.

Two synergistic activation mechanisms of alpha2beta1 integrin-mediated collagen binding

Activation of protein kinase C by 12-O-tetradecanoylphorbol-13-acetate (TPA) induces ligand-independent aggregation of a cell surface collagen receptor, alpha2beta1 integrin. Concomitantly, TPA increases the avidity of alpha2beta1 for collagen and the number of conformationally activated alpha2beta1 integrins. The structural change was shown using a monoclonal antibody 12F1 that recognizes the "open" (active) conformation of the inserted domain in the alpha2 subunit (alpha2I). Amino acid residue Glu-336 in alpha2 subunit is proposed to mediate the interaction between alpha2I domain and beta1 subunit. Glu-336 seems to regulate a switch between open and "closed" conformations, since the mutation alpha2E336A inhibited the TPA-related increase in the number of 12F1 positive integrins. E336A also reduced cell adhesion to collagen. However, E336A did not prevent the TPA-related increase in adhesion to collagen or alpha2beta1 aggregation. Thus, alpha2beta1 integrin avidity is regulated by two synergistic mechanisms, first an alpha2E336-dependent switch to the open alpha2I conformation, and second an alpha2E336-independent mechanism temporally associated with receptor aggregation.

Dual Role of Platelet Protein Kinase C in Thrombus Formation

Protein kinase C (PKC) isoforms regulate many platelet responses in a still incompletely understood manner. Here we investigated the roles of PKC in the platelet reactions implicated in thrombus formation as follows: secretion aggregate formation and coagulation-stimulating activity, using inhibitors with proven activity in plasma. In human and mouse platelets, PKC regulated aggregation by mediating secretion and contributing to alphaIIbbeta3 activation. Strikingly, PKC suppressed Ca(2+) signal generation and Ca(2+)-dependent exposure of procoagulant phosphatidylserine. Furthermore, under coagulant conditions, PKC suppressed the thrombin-generating capacity of platelets. In flowing human and mouse blood, PKC contributed to platelet adhesion and controlled secretion-dependent thrombus formation, whereas it down-regulated Ca(2+) signaling and procoagulant activity. In murine platelets lacking G(q)alpha, where secretion reactions were reduced in comparison with wild type mice, PKC still positively regulated platelet aggregation and down-regulated procoagulant activity. We conclude that platelet PKC isoforms have a dual controlling role in thrombus formation as follows: (i) by mediating secretion and integrin activation required for platelet aggregation under flow, and (ii) by suppressing Ca(2+)-dependent phosphatidylserine exposure, and consequently thrombin generation and coagulation. This platelet signaling protein is the first one identified to balance the pro-aggregatory and procoagulant functions of thrombi.

PKD: a new protein kinase C-dependent pathway in platelets

Protein kinase D (PKD, also known as PKCmu) is closely related to the protein kinase C superfamily but is differentially regulated and has a distinct catalytic domain that shares homology with Ca(2+)-dependent protein kinases. PKD is highly expressed in hematopoietic cells and undergoes rapid and sustained activation upon stimulation of immune receptors. PKD is regulated through phosphorylation by protein kinase C (PKC). In the present study, we show that PKD is expressed in human platelets and that it is rapidly activated by receptors coupled to heterotrimeric G-proteins or tyrosine kinases. Activation of PKD is mediated downstream of PKC. Strong agonists such as convulxin, which acts on GPVI, and thrombin cause sustained activation of PKC and PKD, whereas the thromboxane mimetic U46619 gives rise to transient activation of PKC and PKD. Activation of PKD by submaximal concentrations of phospholipase C-coupled receptor agonists is potentiated by G(i)-coupled receptors (eg, adenosine diphosphate and epinephrine). This study shows that PKD is rapidly activated by a wide variety of platelet agonists through a PKC-dependent pathway. Activation of PKD enables phosphorylation of a distinct set of substrates to those targeted by PKC in platelets.

Vitamin E and omega-3 fatty acids: effectors of platelet responsiveness

This overview focuses on recent evidence in support of vitamin E and omega-3 fatty acids as positive effectors of cardiovascular health through their ability to influence signaling processes in platelets. Special emphasis is placed on vitamin E actions independent of antioxidant activity. The sometimes discordant findings among observational studies, clinical trials, and in vitro cellular studies have been scrutinized for clues to explain possible mechanisms of actions and suggest strategies for future work to define appropriate intakes of these two nutrients.