Effects of a Proteasome Inhibitor on Cardiomyocytes in a Pressure-Overload Hypertrophy Rat Model: An Animal Study

Abstract

Background: The ubiquitin-proteasome system (UPS) is an important pathway of proteolysis in pathologic hypertrophic cardiomyocytes. We hypothesize that MG132, a proteasome inhibitor, might prevent hypertrophic cardiomyopathy (CMP) by blocking the UPS. Nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) and androgen receptor (AR) have been reported to be mediators of CMP and heart failure. This study drew upon pathophysiologic studies and the analysis of NF-κB and AR to assess the cardioprotective effects of MG132 in a left ventricular hypertrophy (LVH) rat model.

Methods: We constructed a transverse aortic constriction (TAC)-induced LVH rat model with 3 groups: sham (TAC-sham, n=10), control (TAC-cont, n=10), and MG132 administration (TAC-MG132, n=10). MG-132 (0.1 mg/kg) was injected for 4 weeks in the TAC-MG132 group. Pathophysiologic evaluations were performed and the expression of AR and NF-κB was measured in the left ventricle.

Results: Fibrosis was prevalent in the pathologic examination of the TAC-cont model, and it was reduced in the TAC-MG132 group, although not significantly. Less expression of AR, but not NF-κB, was found in the TAC-MG132 group than in the TAC-cont group (p<0.05).

Conclusion: MG-132 was found to suppress AR in the TAC-CMP model by blocking the UPS, which reduced fibrosis. However, NF-κB expression levels were not related to UPS function.

Keywords: Cardiomyopathy, hypertrophic; MG132; NF-kappa B; Proteasome inhibitors; Receptors, androgen; Ubiquitins.

Fig. 1

Schematic diagram of the experimental design. TAC, transverse aortic constriction.

Fig. 2

Gross appearance of the left ventricular cross sections in each group. The TAC-cont group displayed definitively hypertrophied left ventricles with smaller ventricular cavities than the TAC-sham group. The TAC-MG132 group showed less ventricular thickness than the TAC-cont group. (A) TAC-sham. (B) TAC-cont. The cross-section of the heart showed a nearly obstructed left ventricular cavity with a hypertrophied left ventricular wall (white arrow). (C) TAC-MG132. The left ventricular wall thickness decreased after MG132 administration. The ventricular cavity (white asterisk) was larger than in the TAC-cont group and smaller than in the TAC-sham group. TAC, transverse aortic constriction; cont, control.

Fig. 3

Fibrotic lesions. The ventricular tissue appears blue with Masson trichrome staining because of collagen-rich fibrotic lesions (black asterisk). The TAC-MG132 group showed less fibrosis than the TAC-cont group. (A) TAC-cont (×40). Multiple fibrotic lesions were found in the TAC-cont group. (B) TAC-MG132 (×40). In the TAC-MG132 group, fewer fibrotic lesions (black asterisk) were found than in the TAC-cont group. TAC, transverse aortic constriction; cont, control.

Fig. 4

Expression of AR and NF-κB in the TAC groups. We compared the gene and protein expression of AR and NF-κB between the control and MG132 sub-groups. Both gene and protein expression levels of AR were significantly lower in the MG132 sub-group (p<0.05). However, NF-κB did not show a significant difference between the control and MG132 sub-groups. (A) Gene expression of AR between the TAC-cont and TAC-MG132 groups. The gene expression of AR was reduced by MG132 treatment (p=0.004). (B) Protein expression of AR between the TAC-cont and TAC-MG132 groups. The protein expression of AR was reduced by MG132 treatment (p=0.014). (C) Gene expression of NF-κB between the TAC-cont and TAC-MG132 groups. Gene expression was increased by MG132 treatment (p=0.041). (D) NF-κB activity between the TAC-cont and TAC-MG132 groups. NF-κB activity did not change after MG132 treatment (p=0.481). AR, androgen receptor; NF-κB, nuclear factor kappa-light-chain-enhancer of activated B cells; TAC, transverse aortic constriction; cont, control.