Metoprolol represses PGC1α-mediated carnitine palmitoyltransferase-1B expression in the diabetic heart

We have previously shown that metoprolol decreases carnitine palmitoyltransferase-1 (CPT-1) activity, a mechanism which may partly explain its beneficial effects in heart failure. It is possible that this effect occurs as a result of repression of cardiac CPT-1B expression. CPT-1B is induced by the transcription factors peroxisome proliferator activated receptor-alpha (PPAR-alpha) and PPAR-gamma-coactivator 1alpha (PGC1alpha) and repressed by upstream stimulatory factor-2 (USF-2). We therefore hypothesized that metoprolol represses CPT-1B by increasing USF-2-mediated repression of PGC1alpha. Male Wistar Rats were divided into 4 groups: control, control treated with metoprolol for 5 weeks, diabetic and diabetic treated with metoprolol for 5 weeks. After termination, the expression of CPT-1 isoforms, PPAR-alpha, PGC1alpha USF-1 and USF-2, as well as downstream targets were measured. Binding of PPAR-alpha, PGC1alpha and USF-2 to PGC1alpha was measured using coimmunoprecipitation. The occupation of PPAR-alpha and MEF-2A consensus sites in the CPT-1B promoter was measured using chromatin immunoprecipitation assays. Chronic metoprolol treatment decreased the expression of CPT-1B in diabetic hearts. The expression of USF-2 was increased by metoprolol in both control and diabetic hearts, but the association of USF-2 with PGC1alpha was increased by metoprolol only in diabetic hearts. Metoprolol prevented the increase in PGC1alpha occupation of the CPT-1B promoter region observed in the diabetic heart without affecting PPAR-alpha occupation. Metoprolol decreases CPT-1B expression by decreasing PGC1alpha-mediated coactivation of PPAR-alpha and MEF-2A. This is associated with increased PGC1alpha/ USF-2 binding, suggesting that USF-2 mediates the metoprolol-induced repression of PGC1alpha.