Insulin-like growth factor-1 overexpression in cardiomyocytes diminishes ex vivo heart functional recovery after acute ischemia

Abstract

BACKGROUND: Acute insulin-like growth factor-1 administration has been shown to have beneficial effects in cardiac pathological conditions. The aim of the present study was to assess the structural and ex vivo functional impacts of long-term cardiomyocyte-specific insulin-like growth factor-1 overexpression in hearts of transgenic aMHC-IGF-1 Ea mice. METHODS: Performance of isolated transgenic aMHC-IGF-1 Ea and littermate wild-type control hearts was compared under baseline conditions and in response to 20-min ischemic insult. Cardiac desmin and laminin expression patterns were determined histologically, and myocardial hydroxyproline was measured to assess collagen content. RESULTS: Overexpression of insulin-like growth factor-1 did not modify expression patterns of desmin or laminin but was associated with a pronounced increase (~30%) in cardiac collagen content (from ~3.7 to 4.8 姯mg). Baseline myocardial contractile function and coronary flow were unaltered by insulin-like growth factor-1 overexpression. In contrast to prior evidence of acute cardiac protection, insulin-like growth factor-1 overexpression was associated with significant impairment of acute functional response to ischemia-reperfusion. Insulin-like growth factor-1 overexpression did not modify ischemic contracture development, but postischemic diastolic dysfunction was aggravated (51ᵠvs. 22ᶠmmHg in nontransgenic littermates). Compared with wild-type control, recovery of pressure development and relaxation indices relative to baseline performance were significantly reduced in transgenic aMHC-IGF-1 Ea after 60-min reperfusion (34ᷥ vs. 62ᷥ recovery of +dP/dt; 35ᱱ% vs. 57ḥ recovery of -dP/dt). CONCLUSIONS: Chronic insulin-like growth factor-1 overexpression is associated with reduced functional recovery after acute ischemic insult. Collagen deposition is elevated in transgenic aMHC-IGF-1 Ea hearts, but there is no change in expression of the myocardial structural proteins desmin and laminin. These findings suggest that sustained cardiac elevation of insulin-like growth factor-1 may not be beneficial in the setting of an acute ischemic insult.