alpha-chymotrypsin and Cardiomegaly

Hypertensive cardiac remodeling is a major cause of heart failure. The immunoproteasome is an inducible form of the proteasome and its catalytic subunit β5i (also named LMP7) is involved in angiotensin II-induced atrial fibrillation; however, its role in deoxycorticosterone-acetate (DOCA)-salt-induced cardiac remodeling remains unclear. C57BL/6 J wild-type (WT) and β5i knockout (β5i KO) mice were subjected to uninephrectomy (sham) and DOCA-salt treatment for three weeks. Cardiac function, fibrosis, and inflammation were evaluated by echocardiography and histological analysis. Protein and gene expression levels were analyzed by quantitative real-time PCR and immunoblotting. Our results showed that after 21 days of DOCA-salt treatment, β5i expression and chymotrypsin-like activity were the most significantly increased factors in the heart compared with the sham control. Moreover, DOCA-salt-induced elevation of blood pressure, adverse cardiac function, chamber and myocyte hypertrophy, interstitial fibrosis, oxidative stress, and inflammation were markedly attenuated in β5i KO mice. These findings were verified in β5i inhibitor PR-957-treated mice. Moreover, blocking of PTEN (the gene of phosphate and tensin homolog deleted on chromosome ten) markedly attenuated the inhibitory effect of β5i knockout on DOCA-salt-induced cardiac remodeling. Mechanistically, DOCA-salt stress upregulated the expression of β5i, which promoted the degradation of PTEN and the activation of downstream signals (AKT/mTOR, TGF-β1/Smad2/3, NOX, and NF-κB), which ultimately led to cardiac hypertrophic remodeling. This study provides new evidence of the critical role of β5i in DOCA-salt-induced cardiac remodeling through the regulation of PTEN stability, and indicates that the inhibition of β5i may be a promising therapeutic target for the treatment of hypertensive heart diseases.

Topics: Animals; Cardiomegaly; Chymotrypsin; Desoxycorticosterone Acetate; Fibrosis; Hypertension; Inflammation; Male; Mice, Inbred C57BL; Mice, Knockout; Oxidative Stress; Proteasome Endopeptidase Complex; Protein Subunits; PTEN Phosphohydrolase; Signal Transduction; Up-Regulation; Ventricular Remodeling

We have prepared monoclonal antibodies specific for cardiac myosin heavy chain. These antibodies were used for the separation and characterization of the molecular variants of myosin heavy chain present in the rabbit heart. Two molecular forms of myosin heavy chain, HC alpha and HC beta, were isolated from the euthyroid rabbit heart by affinity chromatography. Their reactivity with our antibodies indicated that the primary structures of HC alpha and HC beta differ in at least four and share at least two antigenic determinants. Differences in the primary structure of HC alpha and HC beta were confirmed by analysis of the peptides produced by limited chymotryptic digestion of the two heavy chains. Thirteen peptide differences were consistently found. The HC alpha and HC beta variants are shown by immunologic analysis and in chymotryptic peptide profiles to be identical with the predominant forms of myosin heavy chain synthesized in the hearts of hyperthyroid and adult euthyroid rabbits, respectively. During development and maturation of the euthyroid rabbit heart, HC alpha comprises approximately 50% of the ventricular myosin between birth and 4 weeks of age; it diminishes to 20-30% by 8 weeks and to 10-20% by 12 weeks of age. Cardiac myosin from a 1-year-old rabbit is composed almost entirely of HC beta. Cardiac myosin from embryonic animals at 20 days gestation contained 20% HC alpha. These results show that HC alpha occurs normally in the euthyroid rabbit heart and that the relative proportions of HC alpha and HC beta depend on both the developmental stage and the thyroid state of the animal.

Topics: Aging; Animals; Antibodies, Monoclonal; Antigen-Antibody Complex; Cardiomegaly; Chymotrypsin; Genetic Variation; Heart; Heart Ventricles; Hyperthyroidism; Myocardium; Myosins; Peptide Fragments; Rabbits; Thyroxine