A PKC that controls polyphosphate levels, pinocytosis and exocytosis, regulates stationary phase onset in Dictyostelium

Many cells can pause their growth cycle, a topic much enriched by studies of the stationary phase (SP) of model microorganisms. While several kinases are implicated in SP onset, a possible role for protein kinase C remains unknown. We show that Dictyostelium discoideum cells lacking pkcA entered SP at a reduced cell density, but only in shaking conditions. Precocious SP entry occurs because extracellular polyphosphate (polyP) levels reach a threshold at the lower cell density; adding exopolyphosphatase to pkcA- cells reverses the effect and mimics wild type growth. PkcA's regulation of polyP depended on inositol hexakisphosphate kinase and phospholipase D. PkcA- mutants also had higher actin levels, higher rates of exocytosis and lower pinocytosis rates. Postlysosomes were smaller and present in fewer pkcA- cells, compared to the wildtype. Overall, the results suggest that a reduced PkcA level triggers SP primarily because cells do not acquire or retain nutrients as efficiently, thus mimicking, or amplifying, the conditions of actual starvation.

Incidence and predictors of postoperative ischaemic stroke after coronary artery bypass grafting in the United States

Background

Postoperative acute ischemic stroke (AIS) is a catastrophic complication of coronary artery bypass grafting (CABG). There is limited data on the incidence and outcomes of AIS complicating CABG in the contemporary era, and whether these have changed over the years.

Purpose

To study the incidence and outcomes of postoperative AIS in a nationally representative cohort of CABG procedures over a 12-year period and examine predictors of AIS in patients undergoing CABG.

Methods

The National Inpatient Sample was used to identify all adult patients (>18 years old) who underwent CABG in the United States between January 2004 and September 2015. Multivariable logistic regression was performed to examine the associations between postoperative AIS and in-hospital mortality and identify predictors of AIS after CABG, expressed as odds ratios (OR) with corresponding 95% confidence intervals (CI).

Results

A total of 2,569,597 CABG operations were analysed. The incidence of postoperative AIS was 1.8% (n=47,279) in the overall cohort increasing from 1.2% in 2004 to 2.3% in 2015 (p<0.001). Significantly higher rates of AIS were observed amongst patients with atrial fibrillation (AF) and those undergoing non-elective or concomitant valve operations over the study period (see Figure). Patient risk profiles increased over time in both AIS and no-AIS cohorts, with higher Charlson comorbidity scores observed amongst AIS patients. AIS was independently associated with increased odds of in-hospital mortality (OR 3.03, 95% CI 2.93, 3.13) and prolonged hospital stay (∼6 more days) and a higher hospitalisation cost (∼$80,000 more) (p<0.001 for all). Several factors were predictors of AIS including age>60 years (61–70 years: OR 1.33, 95% CI 1.29, 1.37; 71–80 years: OR 1.49, 95% CI 1.44, 1.54; >80 years: OR 1.42, 95% CI 1.37, 1.48), female sex (OR 1.33, 95% CI 1.31, 1.36) and AF (OR 1.14 95% CI 1.12, 1.16) (p<0.001 for all). In contrast, on-pump CABG was not an independent predictor of stroke (OR 1.01, 95% CI 0.94, 1.09) (p=0.784).

Conclusion

In this nationally representative study, we have shown that the rates of postoperative stroke following CABG have increased over time in line with complexity of patient risk profiles. The present findings emphasise the need for further work on strategies to reduce the risk of postoperative stroke after CABG.

Trends of postoperative AIS (2004-2015)

Funding Acknowledgement

Type of funding source: None

Functional interaction of PkcA and PldB regulate aggregation and development in Dictyostelium discoideum

Multicellular development in Dictyostelium discoideum involves tightly regulated signaling events controlling the entry into development, initiation of aggregation and chemotaxis, and cellular differentiation. Here we show that PkcA, a Dictyostelium discoideum Protein Kinase C-orthologue, is involved in quorum sensing and the initiation of development, as well as cAMP sensing during chemotaxis. Additionally, by epistasis analysis we provide evidence that PkcA and PldB (a Phospholipase D-orthologue) functionally interact to regulate aggregation, differentiation, and cell-cell adhesion during development. Finally, we show that PkcA acts as a positive regulator of intracellular PLD-activity during development. Taken together, our results suggest that PkcA act through PldB, by regulating PLD-activity, in order to control events during development.

Absence of catalytic domain in a putative protein kinase C (PkcA) suppresses tip dominance in Dictyostelium discoideum

A number of organisms possess several isoforms of protein kinase C but little is known about the significance of any specific isoform during embryogenesis and development. To address this we characterized a PKC ortholog (PkcA; DDB_G0288147) in Dictyostelium discoideum. pkcA expression switches from prestalk in mound to prespore in slug, indicating a dynamic expression pattern. Mutants lacking the catalytic domain of PkcA (pkcA(-)) did not exhibit tip dominance. A striking phenotype of pkcA- was the formation of an aggregate with a central hollow, and aggregates later fragmented to form small mounds, each becoming a fruiting body. Optical density wave patterns of cAMP in the late aggregates showed several cAMP wave generation centers. We attribute these defects in pkcA(-) to impaired cAMP signaling, altered cell motility and decreased expression of the cell adhesion molecules - CadA and CsaA. pkcA(-) slugs showed ectopic expression of ecmA in the prespore region. Further, the use of a PKC-specific inhibitor, GF109203X that inhibits the activity of catalytic domain phenocopied pkcA(-).

Intracellular proliferation of S. aureus in osteoblasts and effects of rifampicin and gentamicin on S. aureus intracellular proliferation and survival

Staphylococcus aureus is the most clinically relevant pathogen regarding implant-associated bone infection and its capability to invade osteoblasts is well known. The aim of this study was to investigate firstly whether S. aureus is not only able to invade but also to proliferate within osteoblasts, secondly to delineate the mechanism of invasion and thirdly to clarify whether rifampicin or gentamicin can inhibit intracellular proliferation and survival of S. aureus. The SAOS-2 osteoblast-like cell line and human primary osteoblasts were infected with S. aureus EDCC5055 and S. aureus Rosenbach 1884. Both S. aureus strains were able to invade efficiently and to proliferate within human osteoblasts. Immunofluorescence microscopy showed intracellular invasion of S. aureus and transmission electron microscopy images could demonstrate bacterial division as a sign of intracellular proliferation as well as cytosolic bacterial persistence. Cytochalasin D, the major actin depolymerisation agent, was able to significantly reduce S. aureus invasion, suggesting that invasion was enabled by promoting actin rearrangement at the cell surface. 7.5 μg/mL of rifampicin was able to inhibit bacterial survival in SAOS-2 cells with almost complete elimination of bacteria after 4 h. Gentamicin could also kill intracellular S. aureus in a dose-dependent manner, an effect that was significantly lower than that observed using rifampicin. In conclusion, S. aureus is not only able to invade but also to proliferate in osteoblasts. Invasion seems to be associated with actin rearrangement at the cell surface. Rifampicin is effective in intracellular eradication of S. aureus whereas gentamicin only poorly eliminates intracellularly replicating bacteria.

Renal patients' views on generic prescribing and substitution: example from the United Arab Emirates

This survey examined current patient awareness and understanding of generic substitution. We surveyed 188 renal patients using 36 multiple-choice questions in 2 hospitals in the United Arab Emirates. We found that 70% of patients were aware of the availability of generic medicines, 60% understood the terms "generic" and "branded" in relation to medicines and 64% were conscious of generic substitution practice. However, 32% did not know if they were taking generics and 31% felt that generics were not equivalent or only sometimes equivalent to branded medicines. Nearly half (47%) the patients stated they would refuse generic substitution of ciclosporin when it became available if this was just to save the health authority money. In our opinion, random generic substitution should not be implemented because there is still uncertainty and lack of knowledge among patients.