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Emigrated neutrophils regulate ventricular contractility via alpha4 integrin
B Y Poon1, C A Ward, W R Giles
1Department of Physiology and Biophysics and Immunology Research Group, University of Calgary, Calgary, Alberta, Canada.
Insights
Alpha4 integrin, not CD18, significantly reduces neutrophil-induced cardiac myocyte dysfunction and contracture. Targeting alpha4 integrin effectively mitigates myocyte damage caused by emigrated neutrophils.
Area of Science:
- Cardiovascular Biology
- Immunology
- Cellular Physiology
Background:
- Neutrophil adherence to cardiac myocytes involves CD18 and alpha4 integrin.
- The role of these molecules in myocyte dysfunction remains unclear.
Purpose of the Study:
- To investigate the role of CD18 and alpha4 integrin in neutrophil-induced myocyte dysfunction.
- To assess the impact of blocking these integrins on myocyte contractility and function.
Main Methods:
- Myocyte contractility was measured as an index of function.
- Myocytes were exposed to circulating or emigrated neutrophils with or without anti-CD18 or anti-alpha4 antibodies.
- Changes in cell shortening, contraction/relaxation rates, and contracture were analyzed.
Main Results:
- Emigrated neutrophils caused significant myocyte dysfunction, including reduced cell shortening and contracture.
- Anti-alpha4 antibody, but not anti-CD18, significantly protected myocytes from dysfunction induced by emigrated neutrophils.
- Both anti-CD18 and anti-alpha4 antibodies protected against later reductions in contraction and relaxation rates.
Conclusions:
- Alpha4 integrin plays a critical role in mediating cardiac myocyte dysfunction induced by emigrated neutrophils.
- Targeting alpha4 integrin is a promising strategy to mitigate neutrophil-induced cardiac injury.
Abstract:
We have previously shown that CD18 and alpha4 integrin were important in the adherence of emigrated neutrophils to cardiac myocytes. Whether either of these molecules is important in myocyte dysfunction is unclear. In this study, we measured contractility as an index of myocyte function. Control contractility was compared with shortening response in myocytes exposed to neutrophils in the presence and absence of anti-CD18 or anti-alpha4 antibodies. Control unloaded cell shortening, expressed as a percentage of resting cell length, measured 10.06+/-1.16% (n=10) at 5 minutes. Circulating neutrophils caused a 35% reduction in cell shortening, an event prevented by anti-CD18, but not by anti-alpha4 antibody. When emigrated neutrophils were added to the myocytes, a profound reduction (50%) in unloaded cell shortening was noted. A significant increase in CD18 and alpha4 integrin was found on emigrated neutrophils. Addition of anti-CD18 antibody did not protect the myocyte from the emigrated neutrophils, whereas the addition of an anti-alpha4 antibody significantly reduced neutrophil-induced cell shortening, despite some neutrophils still adhering to the myocytes. Furthermore, emigrated neutrophils were able to cause myocytes to go into contracture within 5 minutes in the presence of neutrophils with or without anti-CD18 antibody. In addition to the impairment in unloaded cell shortening, at later times (10 minutes), neutrophils also caused a 40% reduction in the rate of contraction and relaxation. The addition of either anti-CD18 or anti-alpha4 antibody protected the myocytes from these changes. The data suggest that immunosuppression of CD18 on emigrated neutrophils was only partially effective in reducing myocyte dysfunction. In contrast, immunosuppression of the alpha4 integrin alone was sufficient to dramatically reduce all parameters of cell dysfunction measured in this study.