Differential regulation of fibroblast growth factor receptor 1 trafficking and function by extracellular galectins

Fibroblast growth factor receptors (FGFRs) are integral membrane proteins that transmit signals through the plasma membrane. FGFRs signaling needs to be precisely adjusted as aberrant FGFRs function is associated with development of human cancers or severe metabolic diseases. The subcellular localization, trafficking and function of FGFRs rely on the formation of multiprotein complexes. In this study we revealed galectins, lectin family members implicated in cancer development and progression, as novel FGFR1 binding proteins. We demonstrated that galectin-1 and galectin-3 directly bind to the sugar chains of the glycosylated extracellular part of FGFR1. Although both galectins compete for the same binding sites on FGFR1, these proteins elicit different impact on FGFR1 function and cellular trafficking. Galectin-1 mimics fibroblast growth factor as it efficiently activates FGFR1 and receptor-downstream signaling pathways that result in cell proliferation and apoptotic evasion. In contrast, galectin-3 induces extensive clustering of FGFR1 on the cell surface that inhibits constitutive internalization of FGFR1. Our data point on the interplay between extracellular galectins and FGFRs in the regulation of cell fate.

Intracellular partners of fibroblast growth factors 1 and 2 - implications for functions

Fibroblast growth factors 1 and 2 (FGF1 and FGF2) are mainly considered as ligands of surface receptors through which they regulate a broad spectrum of biological processes. They are secreted in non-canonical way and, unlike other growth factors, they are able to translocate from the endosome to the cell interior. These unique features, as well as the role of the intracellular pool of FGF1 and FGF2, are far from being fully understood. An increasing number of reports address this problem, focusing on the intracellular interactions of FGF1 and 2. Here, we summarize the current state of knowledge of the FGF1 and FGF2 binding partners inside the cell and the possible role of these interactions. The partner proteins are grouped according to their function, including proteins involved in secretion, cell signaling, nucleocytoplasmic transport, binding and processing of nucleic acids, ATP binding, and cytoskeleton assembly. An in-depth analysis of the network of these binding partners could indicate novel, non-classical functions of FGF1 and FGF2 and uncover an additional level of a fine control of the well-known FGF-regulated cellular processes.

Nuclear Localization Sequence of FGF1 Is Not Required for Its Intracellular Anti-Apoptotic Activity in Differentiated Cells

Fibroblast growth factor 1 (FGF1) is considered primarily as a ligand for FGF surface receptors (FGFRs) through which it activates a number of cellular responses. In addition to its canonical mode of action, FGF1 can act intracellularly, before secretion or after internalization and translocation from the cell exterior. The role of FGF1 inside the cell is to provide additional protection against apoptosis and promote cell survival. The FGF1 protein contains a specific N-terminal nuclear localization sequence (NLS) that is essential for its efficient transport to the nucleus. Here, we investigated the role of this sequence in the anti-apoptotic response of FGF1. To this end, we produced recombinant FGF1 variants with mutated or deleted NLS and added them to apoptosis-induced cells in which FGFR1 was inactive, either as a result of chemical inhibition or kinase-dead mutation. After internalization, all FGF1 variants were able to protect the differentiated cells from serum starvation-induced apoptosis. To verify the results obtained for NLS mutants, we knocked down LRRC59, a protein that mediates the nuclear transport of FGF1. Upon LRRC59 silencing, we still observed a decrease in caspase 3/7 activity in cells treated exogenously with wild-type FGF1. In the next step, FGF1 variants with mutated or deleted NLS were expressed in U2OS cells, in which apoptosis was then induced by various factors (e.g., starvation, etoposide, staurosporine, anisomycin and actinomycin D). Experiments were performed in the presence of specific FGFR inhibitors to eliminate FGFR-induced signaling, potentially activated by FGF1 proteins released from damaged cells. Again, we found that the presence of NLS in FGF1 is not required for its anti-apoptotic activity. All NLS variants tested were able to act as wild type FGF1, increasing the cell viability and mitochondrial membrane potential and reducing the caspase 3/7 activity and PARP cleavage in cells undergoing apoptosis, both transiently and stably transfected. Our results indicate that the nuclear localization of FGF1 is not required for its intracellular anti-apoptotic activity in differentiated cells and suggest that the mechanism of the stress response differs according to the level of cell differentiation.

Risk stratification of perioperative myocardial infarction/injury following noncardiac surgery in high risk patients

Background

Perioperative myocardial infarction/injury (PMI) screening is increasingly recommended by current guidelines. PMI is often caused by type 2 myocardial infarction, and risk stratification tools for these patients are lacking.

Purpose

To derive and internally validate a risk prognostication model for PMI of likely type 2 infarction (lT2MI)

Methods

We included consecutive high-risk patients undergoing noncardiac surgery into this prospective multicenter study. Patients received a systematic routine PMI screening with pre- and postoperative measurement of cardiac troponin (cTn). PMI was prospectively defined as an absolute increase of cTn above the preoperative value. PMI etiology was centrally adjudicated and hierarchically classified by 2 independent physicians based on all clinical information obtained during index hospitalization and selected those with lT2MI for further analyses. To identify risk factors and allow risk stratification in lT2MI, we prespecified that only perioperative variables should be included into the model. We constructed a logistic binary regression model for major adverse cardiac events (MACE) within 120 days, including variables available at time of clinical evaluation: additional symptoms or ECG-criteria required according to the Universal Definition of Myocardial Infarction, absolute increase in cTn (categorized according to level of absolute increase 1–<2 times the 99th percentile, ≥2 to <4 times, and ≥4 times), urgency of procedure, perioperative bleeding (drop in haemoglobin >30g/L or deemed relevant for PMI by adjudicator), and ESC/ESA surgery risk (low, medium, high risk of cardiac events). Variables were omitted from the final model if the p-value was >0.05. Variable levels with similar odds ratios were grouped for simplification of the prognostic model. We constructed a calibration plot and calculated the area under the receiver-operating characteristics curve (AUC) and Brier Score. For internal validation we calculated the predicted probabilities and classified patients into low-risk (predicted event rate <10%), intermediate range (10–20%), and high-risk (>20%), and compared the predicted with the observed event rate.

Results

PMI occurred in 1016/7754 patients (13.1%) of which 750/1016 (73.8%) were adjudicated as lT2MI. MACE within 120 days occurred in 118/750 (15.7%) patients. The initial and final logistic prognostic model for 120-day MACE or death is shown in the table. Internal validation found a good fit of predicted and observed event rate following bootstrapping of 1000 iterations (Figure 1), a good AUC of 0.71 and a Brier score of 0.12.

Conclusion

The derived risk prognostication model for PMI of lT2MI can aid in the stratification of patients and support clinical decision making following noncardiac surgery.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): Swiss National Science FoundationSwiss Heart Foundation

Intracellular FGF1 protects cells from apoptosis through direct interaction with p53

Fibroblast growth factor 1 (FGF1) acts by activating specific tyrosine kinase receptors on the cell surface. In addition to this classical mode of action, FGF1 also exhibits intracellular activity. Recently, we found that FGF1 translocated into the cell interior exhibits anti-apoptotic activity independent of receptor activation and downstream signaling. Here, we show that expression of FGF1 increases the survival of cells treated with various apoptosis inducers, but only when wild-type p53 is present. The p53-negative cells were not protected by either ectopically expressed or translocated FGF1. We also confirmed the requirement of p53 for the anti-apoptotic intracellular activity of FGF1 by silencing p53, resulting in loss of the protective effect of FGF1. In contrast, in p53-negative cells, intracellular FGF1 regained its anti-apoptotic properties after transfection with wild-type p53. We also found that FGF1 directly interacts with p53 in cells and that the binding region is located in the DBD domain of p53. We therefore postulate that intracellular FGF1 protects cells from apoptosis by directly interacting with p53.

P5980Etiology of perioperative myocardial injuries after non-cardiac surgery and associated outcomes

Background

Perioperative myocardial injuries (PMI) are a common complication following non-cardiac surgery associated with significantly increased postoperative mortality. Due to its mostly asymptomatic presentation it is currently often missed in clinical routine. With the advent of routine screening PMI will be an increasingly recognised. Therefore, a more detailed understanding of the different etiologies causing PMI is needed to guide management.

Methods

We included consecutive high-risk patients (defined as known cardiovascular disease or aged ≥65 years) undergoing major non-cardiac surgery at two hospitals into this prospective multicenter observational study. All patients received a systematic screening using cardiac troponin (cTn) in clinical routine for detection of PMI, defined as an absolute cTn-rise from baseline values within 3 days of surgery. Patients were contacted to assess occurrence of major adverse events (MACE) including all-cause death at 30-days. First, we identified preoperative existing comorbidities as well as perioperative factors associated with PMI by multivariable regression analysis. Second, PMI were centrally adjudicated to identify predefined subtypes (“type I myocardial infarction (T1MI)”, “acute heart failure” (AHF), “tachyarrhythmia”, “extra-cardiac” triggers, “unknown”) by two independent reviewers using all clinical information available, and subtypes tested for association with 30-day (MACE).

Results

From 2014 to 2016 we enrolled 4250 patients undergoing 5375 surgeries. PMI occurred after 785 (14,5%) surgeries. Occurrence of PMI was more frequent with older age and cardiovascular comorbidities, especially insulin-dependent diabetes mellitus and chronic kidney disease. Perioperatively multiple known type II triggers (hypotension, bleeding, hypoxemia, tachycardia, length of surgery) were associated with PMI. Only 5,0% of PMI were adjudicated as “T1MI”, 4,3% as “AHF”, 4,3% as “tachyarrhythmia”, 12,0% “extra-cardiac” and the majority of 74,4% as “unknown”. The subtypes were associated increased MACE-rates (24% for T1MI, 40% for “AHF”, 22% for “tachyarrhythmia”, 24% for “extra-cardiac”, 7,1% for “unknown”) compared to non-PMI patients (1,8%, p<0,001 see Figure).

MACE within 30 days following surgery

Conclusion

PMI occurs more likely in patients with preoperative existing comorbidities, PMI are associated with type II triggers in the intra- as well as postoperative period. We identified subtypes allowing a risk-stratification to identify high-risk types and guide clinical management.

Acknowledgement/Funding

Swiss National Science Foundation, Swiss Heart Foundation, Cardiovascular Research Foundation Basel, Roche

Long term outcomes in different aetiologies of perioperative myocardial infarction/injury after noncardiac surgery

Background

Perioperative myocardial infarction/injury (PMI) occurring in the first 48h following noncardiac surgery is a frequent cardiac complication. Better understanding of the underlying aetiologies is urgently needed.

Aim

To explore the association of different aetiologies of PMI with long term outcomes.

Methods

In this prospective multicenter observational study, PMI aetiology was centrally adjudicated and hierarchically classified by two independent physicians based on all information obtained during clinically-indicated PMI work-up including cardiac imaging among consecutive high-risk patients undergoing major noncardiac surgery. PMI aetiology was classified into “extracardiac” if caused by a primarily extracardiac disease such as severe sepsis or pulmonary embolism; and “cardiac”, further subtyped into type 1 myocardial infarction (T1MI), tachyarrhythmia, acute heart failure (AHF), or likely type 2 myocardial infarction (lT2MI). Major adverse cardiac events (MACE) including T1MI, AHF (both only from day 3 to avoid inclusion bias), life-threatening arrhythmia, and cardiovascular death as well as all-cause death were assessed during 365-days follow-up.

Results

PMI occurred in 1016/7754 patients (13.1%). At least one MACE occurred in 684/7754 patients (8.8%) and 818/7754 patients died (10.5%) within 365 days. MACE and all-cause death occurred in 51% (95% CI 31–60) and 38% (95% CI 29–47), 41% (95% CI 28–51) and 27% (95% CI 16–34), 57% (95% CI 41–69) and 40% (95% CI 25–53), 64% (95% CI 45–76) and 49% (95% CI 30–62), as well as 25% (95% CI 22–28%) and 17% (95% CI 14–20) of patients with extracardiac PMI, T1MI, tachyarrhythmia, AHF, and lT2MI, respectively. These associations were confirmed in multivariable analysis.

Conclusion

At 365 days, most PMI aetiologies have unacceptably high rates of MACE and all-cause death, highlighting the urgent need for more intensive treatments.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): Swiss National Science FoundationRoche Diagnostics