Epidermal growth factor receptor-dependent maintenance of cardiac contractility

AIMS

Epidermal growth factor receptor (EGFR) is essential to the development of multiple tissues and organs and is a target of cancer therapeutics. Due to the embryonic lethality of global EGFR deletion and conflicting reports of cardiac-overexpressed EGFR mutants, its specific impact on the adult heart, normally or in response to chronic stress, has not been established. Using complimentary genetic strategies to modulate cardiomyocyte-specific EGFR expression, we aim to define its role in the regulation of cardiac function and remodeling.

METHODS AND RESULTS

A floxed EGFR mouse model with α-myosin heavy chain-Cre-mediated cardiomyocyte-specific EGFR downregulation (CM-EGFR-KD mice) developed contractile dysfunction by 9 weeks of age, marked by impaired diastolic relaxation, as monitored via echocardiographic, hemodynamic and isolated cardiomyocyte contractility analyses. This contractile defect was maintained over time without overt cardiac remodeling until 10 months of age, after which the mice ultimately developed severe heart failure and reduced lifespan. Acute downregulation of EGFR in adult floxed EGFR mice with adeno-associated virus 9 (AAV9)-encoded Cre with a cardiac troponin T promoter (AAV9-cTnT-Cre) recapitulated the CM-EGFR-KD phenotype, while AAV9-cTnT-EGFR treatment of adult CM-EGFR-KD mice rescued the phenotype. Notably, chronic administration of the β-adrenergic receptor (βAR) agonist isoproterenol effectively and reversibly compensated for the contractile dysfunction in the absence of cardiomyocyte hypertrophy in CM-EGFR-KD mice. Mechanistically, EGFR downregulation reduced the expression of protein phosphatase 2 A (PP2A) regulatory subunit Ppp2r3a/PR72, which was associated with decreased phosphorylation of phospholamban (PLB) and Ca2+ clearance, and whose re-expression via AAV9-cTnT-PR72 rescued the CM-EGFR-KD phenotype.

CONCLUSIONS

Altogether our study highlights a previously unrecognized role for EGFR in maintaining contractile homeostasis under physiologic conditions in the adult heart via regulation of PR72 expression.

TRANSLATIONAL PERSPECTIVE

Our study highlights a previously unrecognized role for EGFR in maintaining contractile homeostasis under physiologic conditions in the adult heart via regulation of PR72, a PP2A regulatory subunit with an unknown impact on cardiac function. Further, we have shown that cardiomyocyte-expressed EGFR is required for the promotion of cardiac hypertrophy under conditions of chronic catecholamine stress. Altogether, our study provides new insight into the dynamic nature of cardiomyocyte-specific EGFR.

The Effect of Rapid Response System Revision on Standard and Specific Intensive Care Unit Outcomes in a Regional Hospital

Hospital systems for the recognition (afferent limb) and management (efferent limb) of deteriorating patients, or Rapid Response Systems (RRSs), are being mandated worldwide, in spite of conflicting evidence regarding their efficacy. We have evaluated the impact of an Adult Deterioration Detection System (Q–ADDS)–based RRS specifically on illness severity at intensive care unit (ICU) admission and ICU length of stay (LOS), as well as previously studied endpoints. We undertook a retrospective, single-centre observational study comparing equivalent 18-month periods before the Q–ADDS–based RRS, and after implementation. The primary endpoints of the study were illness severity of unplanned ICU admissions from the ward, ICU length of stay, and ICU mortality. Secondary endpoints were RRS call numbers, rate of unplanned ICU admissions, and ward-based cardiorespiratory arrests. Following the introduction of the new RRS, Acute Pain and Chronic Health Evaluation (APACHE) II (17 versus 21, P <0.001), APACHE III (64 versus 68, P=0.011) and Simplified Acute Physiology Score (35 versus 38, P=0.044) scores at ICU admission from the ward were reduced. Fewer patients were in the >50% predicted mortality range of APACHE II (16% versus 32%, P <0.001), APACHE III (18% versus 28%, P=0.012) and Simplified Acute Physiology Score (14% versus 24%, P=0.006). ICU mortality was unchanged (13.7% versus 13.8%, P=0.93). ICU LOS was reduced (3 versus 4 days, P=0.02); prolonged stay (>7 days) was not significantly changed (19% versus 27%, P=0.055). Unplanned ICU admissions, cardiorespiratory arrests and hospital mortality were unchanged. The frequency of RRS activation (48 versus 11 per 1,000 admissions, P <0.001) was markedly increased. This Q–ADDS form–based RRS has resulted in lower illness severity at ICU admission from the ward, and fewer patients with scores associated with a >50% predicted mortality. Overall, ICU length of stay was reduced. These specific outcomes may reliably reflect RRS efficacy, even in smaller centres.

INCREASED SYNTHESIS OF p-AMINOBENZOIC ACID ASSOCIATED WITH THE DEVELOPMENT OF SULFONAMIDE RESISTANCE IN STAPHYLOCOCCUS AUREUS

Sulfonamide-resistant strains of Staphylococcus aureus produce greater amounts of p-aminobenzoic acid than do their parent strains. This synthesis occurs both in the absence and in the presence of sulfonamides. The quantity of p-aminobenzoic acid synthesized by resistant strains appears sufficient to account for their resistance to sulfonamide drugs. On the basis of this evidence, it is suggested that the development of ability to synthesize p-aminobenzoic acid in excess of the normal metabolic requirements, as a result of continued exposure to sulfonamides, explains the phenomenon of sulfonamide fastness in Staphylococcus aureus.

Suxamethonium and mivacurium sensitivity from pregnancy-induced plasma cholinesterase deficiency

A fit 36-year-old parturient received a general anaesthetic for manual removal of a retained placenta. She underwent rapid sequence induction of anaesthesia with suxamethonium, shortly followed by 10 mg of mivacurium. One hour later she had failed to establish adequate ventilation despite administration of drugs to reverse neuromuscular blockade. A provisional diagnosis of suxamethonium-related apnoea was made and her lungs were ventilated overnight on the Intensive Care Unit. Plasma cholinesterase levels at the time were reduced to one-third of normal, with normal dibucaine and fluoride numbers. One month later her levels were back within the reference range.

The early diagnosis of acute occlusive mesenteric ischaemia: experimental results and clinical applications

The diagnosis of acute superior mesenteric artery occlusion in the dog has been achieved in every case by isotope scanning of the abdomen using technetium-labelled red cells or technetium-labelled human serum albumin. The white cell count is also significantly elevated, but the changes in the levels of the enzymes CPK, LDH, AST and serum amylase are not specific for actue mesenteric ischaemia. In the human the presence of a normal gut circulation can be demonstrated by isotope scanning provided that the patient is not severely shocked. The presence of a normal gut circulation as shown on the scintigram conclusively eliminates the possibility of acute main trunk occlusion of the superior mesenteric artery. This should be of help in differentiating acute occulusive mesenteric ischaemia from other causes of the acute abdomen. Abdominal scintiscanning is complementary to angiography, which still remains the most precise means of diagnosing acute mesenteric ischaemia. Although the abdominal scintigram is more limited in its application and is not as accurate as angiography, it is quicker to perform, non-invasive, and entirely safe. Abdominal scintiscanning is an excellent screening test to be used in patients suspected of suffering from acute occlusive mesenteric ischaemia.

Humoral and cellular aspects of the immune response to the somatic antigen of Salmonella enteritidis

A study was made of the cellular and humoral aspects of the immune response of the rabbit to the somatic polysaccharide of Salmonella enteritidis. The response to a single intravenous injection was characterized by the appearance of elevated titers of bactericidal antibody between 2 and 3 days later. The maximum titer was dose-dependent and occurred between 5 and 7 days, thereafter declining rapidly during the first month. The significant stabilized levels which then persisted for at least 1 year were also dose-dependent. Most of the antibody produced (>99 per cent) was associated with the macroglobulin fraction of serum. Plaque-forming cells (PFC) elaborating antibody specific for this somatic antigen were detected and enumerated by the technique of localized hemolysis in gel employing polysaccharide-coated sheep erythrocytes. Significant numbers of PFC were encountered in the spleen as early as 14 to 18 hours after a single intravenous injection of antigen; after 36 hours the number of PFC rose rapidly and culminated in a maximum population at 5 days, followed by a rapid decline and plateau similar to that for circulating antibody. The spleen was the principal organ involved in the systemic response, but other lymphoid tissues including bone marrow, peripheral blood leucocytes, and thymus contributed significantly. After an interval of 3 months the effect on humoral antibody titers of a second injection of antigen was dependent on the amount of polysaccharide administered; markedly greater titers were now obtained with 0.02 to 0.002 microg, whereas 0.2 to 20 microg resulted in a duplication of the initial humoral response. The cellular response to a second dose of 5 microg was accelerated; larger numbers of PFC appeared more rapidly, attained a maximum population by day 3, and exceeded the primary response by a factor of two. This acceleration in the attainment of maximum numbers of PFC and the increased bactericidal antibody titers following a second injection of limiting amounts of antigen suggest that these somatic polysaccharides may in fact evoke a "secondary" type of response in the rabbit.