Spatial and temporal translocation of PKCα in single endothelial cell in response to mechanical stimulus

Spatiotemporal distribution of PKCα, Cdc42, and Rac1 before directed cell migration

Cdc42 is a key factor in directed cell migration and accumulates at the leading edge of migrating cells. However, what kind of proteins control Cdc42 and when is unclear. After mechanical wounding, protein kinase C α (PKCα), a conventional PKC isozyme, begins to accumulate at the edges of cells adjacent to the wounded cells (WCs). In this study, we hypothesized that PKCα may be implicated in directed cell migration at an early stage before Cdc42 controls the migration. We focused on the spatiotemporal distribution of PKCα, Cdc42, and Rac1 before cell migration. After wounding, at the edges of cells adjacent to the WCs, PKCα accumulation, Cdc42 accumulation, Rac1 accumulation, and filopodia formation occurred in that order. The PKCα inhibitor suppressed Cdc42 accumulation at the cell edges. These results suggest that inhibition of PKCα activity inhibits cell migration. In addition, it is not Cdc42 but PKCα that may decide the direction of cell migration.

A metabolic reaction-diffusion model for PKCα translocation via PIP2 hydrolysis in an endothelial cell

Hydrolysis of the phospholipid phosphatidylinositol 4,5-bisphosphate (PIP2) at the cell membrane induces the release of inositol 1,4,5-trisphosphate (IP3) into the cytoplasm and diffusion of diacylglycerol (DAG) through the membrane, respectively. Release of IP3 subsequently increases Ca2+ levels in the cytoplasm, which results in activation of protein kinase C α (PKCα) by Ca2+ and DAG, and finally the translocation of PKCα from the cytoplasm to the membrane. In this study, we developed a metabolic reaction-diffusion framework to simulate PKCα translocation via PIP2 hydrolysis in an endothelial cell. A three-dimensional cell model, divided into membrane and cytoplasm domains, was reconstructed from confocal microscopy images. The associated metabolic reactions were divided into their corresponding domain; PIP2 hydrolysis at the membrane domain resulted in DAG diffusion at the membrane domain and IP3 release into the cytoplasm domain. In the cytoplasm domain, Ca2+ was released from the endoplasmic reticulum, and IP3, Ca2+, and PKCα diffused through the cytoplasm. PKCα bound Ca2+ at, and diffused through, the cytoplasm, and was finally activated by binding with DAG at the membrane. Using our model, we analyzed IP3 and DAG dynamics, Ca2+ waves, and PKCα translocation in response to a microscopic stimulus. We found a qualitative agreement between our simulation results and our experimental results obtained by live-cell imaging. Interestingly, our results suggest that PKCα translocation is dominated by DAG dynamics. This three-dimensional reaction-diffusion mathematical framework could be used to investigate the link between PKCα activation in a cell and cell function.

Association of PRKCA expression and polymorphisms with layer duck eggshell quality

1. Eggshell quality is important for the poultry industry. Calcium is deposited during eggshell formation, and protein kinase C alpha (PRKCA) is involved in transmembrane transport of calcium ions in cells. However, the biological function of PRKCA in poultry is still not understood. Therefore, the aim of this study was to explore the association of mRNA expression and single nucleotide polymorphisms (SNPs) of the PRKCA gene with eggshell quality in laying ducks. 2. The mRNA expression and SNPs of the PRKCA gene were detected by real-time fluorescence quantitative PCR (qRT-PCR) and sequencing of PCR products in 45-week-old female Sansui ducks, which is a high production layer duck breed in China. The association of mRNA expression and SNPs in the PRKCA gene with layer duck eggshell traits was analysed using SPSS (v18.0) software. 3. The results demonstrated that PRKCA mRNA was widely expressed in all examined tissues, and expression was highest in kidney and lowest in the gizzard. Furthermore, the PRKCA mRNA level in uterus was significantly positively correlated with eggshell strength and eggshell weight (P < 0.05). Three novel SNPs, the synonymous mutations of g.9571770 T > C in exon 5, g.9583222 C > T and g.9583227 G > A in exon 7, were found in the PRKCA gene, giving four haplotypes and 10 diplotypes, which affected the mRNA secondary structure and free energy. The g.9583222 C > T and g.9583227 G > A mutations were significantly associated with eggshell strength (P < 0.05). Diplotype H1H1 was advantageous for increasing the strength and thickness of an eggshell. 4. In conclusion, the study showed that the mRNA transcription and genetic variation in the PRKCA gene could significantly affect the strength of duck eggshell and that the PRKCA gene is an important candidate gene for improving eggshell quality in poultry.

Fluid Shear Stress Induces Endothelial Cell Injury via Protein Kinase C Alpha-Mediated Repression of p120-Catenin and Vascular Endothelial Cadherin In Vitro

OBJECTIVE

The present study aimed to characterize the mechanism of fluid shear stress (FSS)-induced endothelial cell (EC) injury via protein kinase C alpha (PKCα)-mediated vascular endothelial cadherin (VE-cadherin) and p120-catenin (p120ctn) expression.

METHODS

We designed a T chamber system that produced stable FSS on ECs in vitro. Human umbilical vein endothelial cells (HUVECs) in which PKCα was knocked down and normal HUVECs were cultured on the coverslips. FSS was impinged on these 2 types of ECs for 0 hours and 6 hours. The morphology and density of HUVECs were evaluated, and expression levels of phosphorylated PKCα, p120-catenin (p120ctn), VE-cadherin, phosphorylated p120ctn at S879 (p-S879p120ctn), and nuclear factor kappa B (NF-κB) were analyzed by Western blot.

RESULTS

HUVECs exposed to FSS were characterized by a polygonal shape and decreased cell density. The phosphorylated PKCα level was increased under FSS at 6 hours (P < 0.05). In normal HUVECs during FSS, p120ctn and VE-cadherin were decreased, whereas p-S879p120ctn and NF-κB were increased, at 6 hours (P < 0.05). In HUVECs after PKCα knockdown, p120ctn and VE-cadherin were not significantly changed (P > 0.05), p-S879p120ctn was undetectable, but NF-κB was decreased (P < 0.05) at 6 hours.

CONCLUSIONS

The possible mechanism of FSS-induced EC injury may be as follows: 1) PKCα induces low expression of p120ctn, which leads to activation of NF-κB and degradation of VE-cadherin; 2) PKCα-mediated phosphorylation of p120ctn at S879 disrupts p120ctn binding to VE-cadherin.

Unloading of intercellular tension induces the directional translocation of PKCα

The migration of endothelial cells (ECs) is closely associated with a Ca²⁺ -dependent protein, protein kinase Cα (PKCα). The disruption of intercellular adhesion by single-cell wounding has been shown to induce the directional translocation of PKCα. We hypothesized that this translocation of PKCα is induced by mechanical stress, such as unloading of intercellular tension, or by intercellular communication, such as gap junction-mediated and paracrine signaling. In the current study, we found that the disruption of intercellular adhesion induced the directional translocation of PKCα even when gap junction-mediated and paracrine signaling were inhibited. Conversely, it did not occur when the mechanosensitive channel was inhibited. In addition, the strain field of substrate attributable to the disruption of intercellular adhesion tended to be larger at the areas corresponding with PKCα translocation. Recently, we found that a direct mechanical stimulus induced the accumulation of PKCα at the stimulus area, involving Ca ²⁺ influx from extracellular space. These results indicated that the unloading of intercellular tension induced directional translocation of PKCα, which required Ca ²⁺ influx from extracellular space. The results of this study indicate the involvement of PKCα in the Ca ²⁺ signaling pathway in response to mechanical stress in ECs.

Three-dimensional model of intracellular and intercellular Ca2+ waves propagation in endothelial cells

Intracellular and intercellular Ca²⁺ waves play key roles in cellular functions, and focal stimulation triggers Ca²⁺ wave propagation from stimulation points to neighboring cells, involving localized metabolism reactions and specific diffusion processes. Among these, inositol 1,4,5-trisphosphate (IP₃) is produced at membranes and diffuses into the cytoplasm to release Ca²⁺ from endoplasmic reticulum (ER). In this study, we developed a three-dimensional (3D) simulation model for intercellular and intracellular Ca²⁺ waves in endothelial cells (ECs). 3D model of 2 cells was reconstructed from confocal microscopic images and was connected via gap junctions. Cells have membrane and cytoplasm domains, and metabolic reactions were divided into each domain. Finally, the intracellular and intercellular Ca²⁺ wave propagations were induced using microscopic stimulation and were compared between numerical simulations and experiments. The experiments showed that initial sharp increases in intracellular Ca²⁺ occurred approximately 0.3 s after application of stimuli. In addition, Ca²⁺ wave speeds remained constant in cells, with intracellular and intercellular speeds of approximately 35 and 15 μm/s, respectively. Simulations indicated initial increases in Ca²⁺ concentrations at points of stimulation, and these were then propagated across stimulated and neighboring cells. In particular, initial rapid increases in intracellular Ca²⁺ were delayed and subsequent intracellular and intercellular Ca²⁺ wave speeds were approximately 25 and 12 μm/s, respectively. Simulation results were in agreement with those from cell culture experiments, indicating the utility of our 3D model for investigations of intracellular and intercellular messaging in ECs.